Note: Descriptions are shown in the official language in which they were submitted.
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Cutting Instruments
This invention relates to hard and tough tools and knives capable of
holding an edge and resisting corrosion better than conventional materials used
5 for cutting instruments, and more particularly to processes for making cuttinginstruments of Type 60 Nitinol to produce tools and knives that are hard, tough,and elastic, and which are virtually immune to corrosion.
BACKGROUN~ OF THE INVENTION
The develop",e"l of Damascus steel in the 5th century producecl a hard and
tough material that was, and still is, prized for knives and swords. However, the
,c,rocess of manufacturing Damascus steel is arduous and e.(~ensive, and th
material is susceptible to rusting and other corrosion, so it must be kept oiled and
otherwise protec~ed from corrosive influences. Bec~use of its susceptibility to
corrosion and the need to keep it oiled to prevent such corrosion, Damascus steel
is not suitable for food preparation, skinning game or other meat cutting
applications, so its usefulness in the real world is limited. Its primary applicalion is
for display knives and swords b~c~use of the dislinclive banded appearance of the
material.
2 o Since the develo,c",e"t of Damascus steel, the most im,.,G, lar,t commercial
develG~.i "e"l in the field of cutlery materials in the last century has been corrosion
resistant steel, more cG"""only (although inaccurately) called "stainless steel".
Stainless steel is ~;l ,ara~;teri~ed by the inclusion of chromium and sometimes nickel in
the colnposilion which makes it significantly more corrosion resistant than other types
2 5 of steels, and as a result is now very widely used in most cutlery. However, in order to
obtain the hardness necess~ry for retaining a decent cutting edge, the material must
be well above 400 on the Brinell scale, or 42 on the Rockwell C scale, and preferably
above 500 Brinell. Compositions of corrosion resistant steel having high hardness
have been developed, such as 440C which can be heat treated to a hardness of about
3 o 56 on the Rockwell C scale. That is an adequate hardness for retaining a good
cutting edge, but this material also has a high carbon content of about 1.5% and is
difficult to machine. The high carbon content results in reduced corrosion resistance,
resulting in a ter,dency for the cutting edges of knives made from this material to
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become dull be~use the thin cusp of the cutting edge corrodes away, leaving a
rounded edge. This is particularly true for environments containing the chlorine ion,
such as sea water and chlorine cleaning solutions used in food prepar~tion areas.
The cost of knives made from 440C stainless steel is higher than knives made from
5 other material be~use processing the material and n,aci,i"ing the blade shape is
more difficult than it is for other knife materials. Finally, knives made of 440C
stainless steel have a tendency to lose their luster over a relatively short time bec~l ~se
of tarnishing, stains and corrosion, resulting in a knife blade with an unattractive,
dingy appearance which customers dislike.
FDA requirements for knives used in meat cutting and fish processir,g
operations have very sl, ingent corrosion resistance slandards which limit the
carbon cGnlenl of the stainless steel to no more than 0.10%. Corrosion resistantsteels are available that meet these requirements and knives made from them do
indeed exhibit adequate corrosion resistance for safe use in meat cutting and fish
15 processing facilities. However, these materials are soft, less than 200 on the
Brinell scale, and knives made from these materials dull quickly and must be
sharpened continually. As a conse~uence, these knives last only a short time
before they are shar,uened away and are cl,scarded. This industry has long needed
a knife that is approved for use around meat, poultry and fish by the U.S. FDA and
2 0 would remain sharp for long periods of conslanl use without sl~arpe"ing.
In the field of cutting instruments other than cutlery, the most Si911iriCant
commercially development in the last century has been sintered carbides of silicon,
tUI ,gslen and titanium in a metallic matrix of cobalt or other tou~l)el ling metals
Carbides are very hard and hold a cutting edge better than most other ",dter;als,
25 but they are brittle and tend to shatter when stressed beyond their yield strength.
When designed properly and used within the intended par~n,eters of workpiece
I ,a~(b1ess and cutter feeds and speeds, carbide cutting inserts provide long life to
cutting tools and are very widely used throughout the industry. However, even with
improvements to the matrix material, the bonding interface between the carbides
30 and the matrix material, and the manufacturing processes, no carbide metal matrix
composite materials have been developed that would be suitable for cutlery, and
the material remains so brittle that its use must be carefully controlled to prevent
~ .
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shaller ing of the cutting instrument if the feed speed, cutter speed or the hardness
or toughness of the workpiece excee~s the stress limitations of the carbide cutter.
Chipper and shredder blades, lawn mower blndes, and brush cutter blades are
notorious for their short blade life. These blades have high velocity and often
5 encounter hard materials such as rocks and metal debris in their operation, so they
must be made malleable. If they were made hard to retain a long blade life, theywould be brittle and subject to catastrophic failure in the event of impact with a rock
or the like which could shatter the blade or initiate a crack which could grow through
the blade material and rupture at some unpredictable time in the near future. The
10 malleable material does not crack or sl ~dtler like the harder material would, but it is
also relatively soft and the blade edge quickly becomes rounded in ordinary use.The rounded edge cuts slower, requires more energy to cut, and cuts with a ragged
edge rather than a clean edge, essentially breaking rather than cutting. In large
chipping operations such as slash chipping in logging operations, the conventional
15 chipper blades must be changed frequently, resulting in lengthy and inefflcient
downtime and idling of the operatol s. A blade material for machines of this nature
that is hard and holds an edge, and is tough instead of briHle like conventional hard
materials, would be exl~e,nely ~/el~"le to owners and o,l~erator~ of these machines.
These same considerations also apply to machines such as stump 9l inder.~; and road
2 o scarifying machines that are actually expected to involve conlact with the ground or
with rocks.
Many hand tools such as axes, splitting mauls and picks have the same
malleability requilt:"lenls that blades for chippers and shredders and that sort of
machine have. The cutting or leading edge must be made malleable enough to yield25 or roll over on impact with a hard material so that it does not chip or break and
produce flying metal fragments that would be dangerous to the user or by~landers,
especially to their eyes.
Tools such as pruning shears, clippers, and saws, grdrlin g knives, and chain
saws used on green plants often get gummed up with plant sap that sticks
3 o tel laciously and is very difficult to clean off the tool. The sticky sap inlel reres with
smooth cutting by the tool since it prevents the tool blade from sliding smoothly
through the cut. The sap also promotes corrosion of the tool slJrfaces which makes
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even more difficult the task of cleaning the old sap off the tool. 1 ne corrosion around
the tool cutting edges dulls the cutting edges and also gums up the sharpening tools.
I\Jledical cutting instruments such as chisels files, and s~-lrels currently in use
are made primarily from 300 series stainless steels ~ri~arily bec~use of its corrosion
5 resistance and tendency to bend rather than chip if the instrument encounters bone.
However the 300 series stainless steels are so soft that the instruments quicklybecome dull and must be repl-ced with sharp instruments. Scalpel sha~ ~ .ness is very
important to a surgeon1 and it is co~mo~ ~place in lengthy operaliGns for numerous
scalpels to be used and discarded in the course of the operation.
In the 1 960's the Naval OrJndnce Laboratory in White Oak Maryland invented
an intermetallic compound of nickel and titanium which they named "Nitinol". Oneform of that material which they named "Type 60 Nitinol" has a composition of 57-
63% by weight nickel and the balance titanium. The Navy was interesled in this
material bec~ ~se it was nonmagnetic and potentially useful to the Navy Seal
15 co,nn~andos in knives to defuse mines or cut ancl)ori"y cables on magnetic mines
during the Vietnam war. The Navy had a small quantity of this material-made and an
ex~e~i",ental program was iniliaLed to fashion it into knives for its Seal co",l"a"dos
but the material proved to be so dimcult to machine that the cont, a~;~or was unable to
produce more than a few prototypes and no further knives were made despite the
20 desirable attributes of the knife.
Thus there has long been a need for a cutting instrument that is cor, O5i~1,
proof hard flexible and tough, and can be polished to a high long lasting luster.
This cutting instrument would have the ability to hold an edge for a long period even
in corrosive enviror,r"enls such as salt water and industrial chemicals and it would
25 be FDA approved for use in meat cutting and fish processing facilities as well as in
hospital operating rooms. High production rate processes for making such a knife at
reasonable costs also have been long needed by the industry and once adopted will
militate for the replacement of stainless steel by Type 60 Nitinol for all but the
cheapest cutting instruments.
SUMMARY OF THE INVENTION
Accordingly it is an object of this invention to provide improved processes for
making a cutting instrument from Type 60 Nitinol. Another object of this invention is
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to provide an improved cutting instrument having a monolithic blade with a surface
finish si"oolher than about 20 microinches and an edge hardness exceeding 55 on
the Rockwell C scale. Yet another object of this invention is to provide a cutting
instrument that is immune to corrosion from co"",)on corrosive agents, includingocean saltwater.
These and other objects are attained in a cutting instrument having a
blade made from a blank cut from a plate or strip of Type 60 Nitinol. The plate
or strip, having a thickness of about 0.010"~.500", is first sandblasted to
remove hard oxides that form during hot rolling of the plate. The blade blank iscut out of the plate using a laser cutter, abrasive waterjet or wire electron
discharge machining. The blank is flaLlened to remove any curvature that ma
remain from the rolling operation, and is surface ground to a depth of about .001
to .005 inches top and bottom to remove surface imperfections in the plate. An
edge is ground into the blade blank using a PCBN or dial,lond grinding wheel or
bett and a liberal flooding of coolanl to help capture the Nitinol particles. The
surface of the blade can be polished to a lustrous surface finish, if desired,
smoother than 2 mic, oinches RMS, using a dia"~o, Id grit abrasive polishing
co,npound.
DFSCRIPTION OF THE DRAWINGS
The invention and its many attendant ob~ecls and advantages will become
more clear upon reading the following description of the pre~e(,ed embodiments in
conjunction with the following .II~-.;nys, wherein:
Fig. 1 is a top plan view of a knife made in accordal)ce with this invention;
2 5 Fig. 2 is a side elevation of the knife shown in Fig. 1;
Fig. 3 is a bottom plan view of the knife shown in Fig. 1;
~ Fig. 4 is a sectional side elevation of the knife shown in Fig. 1 along lines
4-4 in Fig. 3;
Fig. 5 is an enlarged sectional side elevation along lines 5-5 in Fig. 1;
Fig. 6 is a plan view of a knife like the one shown in Fig. 1, having a
knurled handle and a latching scabbard;
Fig. 7 is a plan view of the scabbard shown in ~ig. 6;
. .. . . ~
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Fig. 8 is a side elevation along lines 8-8 in Fig. 7;
Fig. 9 is a sectional view along lines 9-9 in Fig. 6;
Fig. 10 is a sectional view along lines 10-10 in Fig. 6;
Fig.11 is a plan view of a second e~bodiment of a knife in accordal)ce
with this invention;
Fig.12 is an exploded plan view of the knife shown in Fig.11, showing the
bolster, handle, butt piece and pin exploded away from the knife body and r~ta~e.l
9oo;
Fig. 13 is a schematic view of a tun~~slen inert gas welding apparatus for
TIG welding the bolster on the knife body shown in Fig.12;
Fig.14 is an enlarged view, partly in section, of the knife body shown in
Fig. 13, showing the bolster welded in place;
Fig. 15 is a view along lines 15-15 in Fig. 14;
Fig.16 is a schematic view of a laser welding appar~lus for welding the
bolster on the knife body shown in Fig.12;
Fig.17 is a schematic view of an electrical resistance welding apparal~s
for welding the bolster on the knife body shown in Fig.12;
Fig.18 is an exploded view of a heat shrinkable handle for the knife shown
in Fig.1;
Fig.19 is a plan view of an assembled knife made from the knife body and
handle shown exploded in Fig. 34;
Fig. 20 is top plan view of a filet knife made in accor~ance with this
invention;
Fig. 21 is a top plan view of the knife body of the filet knife shown in Fig.
24;
Figs. 22 and 23 are side and end elevations of the knife shown in Fig. 20
along lines 22-22 and 23-23, respectively;
Fig. 24 is a top plan view of a hunting knife, with an integral finger bolster,
made in accordance with this invention;
Fig. 25 is a top plan view of the knife body of the knife shown in Fig. 24.
Fig. 26 is a plan view of the knife shown in Fig. 6 in a shipping and storage
box with the cover removed;
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~ig. 27 is an exploded sectional elevation of the knife shown in Fig. 26 and
the shipping and slorage box;
Fig. 28 is a plan view of a folder made in accordance with this invention,
with the top handle slab removed for clarity of illuslrd~ion;
Fig. 29 is a plan view of the folder shown in Fig. 28, with the knife blade
folded into the handle;
Fig. 30 is a schematic view of a waterjet apparatus for cutting knife blanks
from a plate of Type 60 Nitinol;
Fig. 31 is a plan view of a knife blank for the knife shown in Fig. 1;
Fig. 32 is a sectional elevation of a holding jig for holding the knife blank
shown in Fig. 31 for grinding;
Fig. 33 is a schematic view of a belt yl indi"g apparal~s for grinding the
edge of the knife blank shown in Fig. 31;
Fig. 34 is a schematic view of a belt grinder hollow gl il ,d;,~g and edge onto
the knife blank that was edge ground in Fig. 33;
Fig. 35 is a schematic view of a belt grinder hollow 9, indil ,9 an edge
directly without first 9, i, Iding the edge flat as in Fig. 33;
Fig. 36 is a diagra", showing the heating process for forming a hard, slippery
surface material on the Type 60 Nitinol article that is integral with the parent2 0 material;
Fig. 37 is a diagram showing the spectrum of colors that can be obtained
on the surface material of a Type 60 Nitinol article using a heating pr~,cess inaccordance with this invention;
Fig. 38 is an exploded schematic per~pecti~/e view of a razor made in
accordance with this invention;
Fig. 39 is a perspective schematic view of a razor assembled from the parts
exploded in Fig. 38;
Fig. 40 is a plan view of a saw blade made in accordance with this
invention;
Fig. 41 is a cross sectional elevation of a saw blank having teeth set in
accordance with this invention and showing in dotted lines the tooth material that
will be removed for sharpening; and
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Fig. 42 is a per~pe~ti,/e view of the saw blade shown in Fig. 40 and a tool
for setting the teeth of the saw blade.
DESCRIPTION OF THE PREFERRED EMBODIMENT
TuMing now to the drawings, and more particularly to Figs.1-3 thereof, a
knife 30 is shown in the form of what could be termed a "sport knife". The knife 30
has a knife body 32 including a blade 34 and a tang 36. The knife body 32 is made
of a single piece of Type 60 Nitinol, an inter-metallic compound of about 60% nickel
and about 40% titanium by weight that was invented in the 1960's by the Naval
10 O, dn ance Laboratory in White Oak, Maryland. A handle 38 is bonded to the tang
36 by an adhesive such as epoxy which seals the interface between the handle 38
and the tang 36; the handle is also secured to the tang 36 with rivets 40. The
handle 38 of this embodiment is a scale or slab type handle having two slabs 42,one each secured to opposite sides of the full length tang 36. Other handle types
15 are known in the art and can be used insle~d of this full tang scale handle 38, such
as half tang scale handles, such as shown in Fig. 24, and full or partial tang one
piece handles, shown in Fig. MM. The scale type handles are convenient bec~ ~se
of the ease of making the har,dlcs of exotic hardwoods, such as bloodwood, bocote,
zebra wood, or canary wood. S~ I ,etic ",aleridls may be prerer, ed in some
20 applications where wood handles are u"clesirable or not per",illed. Suitable
synthetic materials for handle slabs include Zytel, a reinforced nylon, t)elrin (made
by GE Plastics), or Lexan, a pol~ , L,o"dle also made by GE Plastics. The handlematerials are selected on the basis of function and appearance. For example, theexotic hardwoods are beautiful, durable and hard, but may be s~ ~sceptible to
25 surface abrasion and other influences that could degrade the a~ pearance of the
handle, and governmentai regulations restrict the types of handle materials that can
be used in certain environ",e"~s, such as meat cutting operations. In these
situations, and in situations where the appearance of the knife is of less
i" ~ O~ lal ,ce, a synthetic material handle would be preferable or necess~ry.
3c A series of serrations 44 may be ground along one edge 46 of the blade 34,
producing sharp points 48 which are particularly effective in rapidly sawing through
rope and other tough materials. The opposite edge 50 is hollow ground and
sharpened to a sharp straight edge, and the distal end of the blade is tapered and
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sharpened along both edges 46 and 50 to a sharp point 52. Alternatively, both edges
46 and 50 may be hollow ground to produce two straight sharp edges tapering
symmetrically to a sharp point 52.
Turning now to Figs. 4 and 5, the attachment construction for the handle
slabs 42 uses rivets 40 each having a head 54 that is flat on the top and bottomsurfaces. The rivets are received in rivet holes 55 in the handle slabs 42, and the
rivet heads 54 are received in counterbores 56 in the rivet holes 55, and seat
against the shoulders 58 of the counterbores 56 to hold the slabs 42 against thetang 36. A roll pin 60 fits with an inte~ rerence fit into an axial hole 61 drilled in
10 shanks 62 of the rivets 40. The rivet shanks 62 are received with a sliding fit in a
hole 64 through the tang 36.
Type 60 Nitinol is non-magnetic and is undetectable by may"eto,neters
con""only used in airports and elsewhere to detect concealed weapons. For this
reason, knives made for sale to the civilian market are made with stainless steel
15 rivets 40 and steel roll pins 60, and may also have an iron or steel strip laid in a
shallow recess on the inside surface of the handle slabs to make the knife
detec~ablc by maynetometers. Military knives would have handle slabs fastened
with brass or Nitinol rivets using Nitinol roll pins to make them completely non-
magnetic so that they could be used for probing for magnetic mines and the like.Some knife users have a need for a lanyard by which the knife may be
secured to their wrist or a harness or the like. Underwater divers, workers in
elevated exposed places, fishermen or the like working in locations wherein the
knife would be a I ,~ard or would be lost if it were accidenlally dropped often have a
requirement for such a lanyard. For this purpose, a lanyard bushing 66 with a
25 through bore 68 is driven with an in~e, rerence fit into a hole 70 through the tang 36
and aligned holes 72 through the handle slabs 38. The bushing 66 is flush at its two
ends with the surface of the slabs 42 and the bore 68 is chamfered at its two ends to
prevent cutting the lanyard or ring 74 received in the bushing 66. The lanyard or
ring 74 provides a secure attachment by which the knife 30 may be secured against
30 loss as desired by the users of the knives.
The design of the handle 38 is selected for secure and comfortable gripping,
even in wet or slippery conditions such as skinning and dressing game or gutting fish.
As shown in Figs.1 -3, the handle has a butt end 80 which is sr"o~Jtllly rounded in plan
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profile with a radius of about one half the width of the handle, preferably about 1.2
inches. The length of the handle is about 4.2 inches so that the smooth round butt 80
col"ro, lably engages the heel of the average size hand when the knife is held in a
natural holding manner. Forward of the butt 80, the handle tapers slightly and then
5 flares at the handle midpoint to a bulge 82 which naturally fits the hollow of the palm.
Forward of the bulge 82, the handle again tapers and then flares to the full width of
the handle at a thumb ridge 84 adjace"l the junction line of the handle 38 and the
blade 34. The front edge 85 of each handle slab 42 des~ ibes a convex curve linking
the front edges of the thumb ridges on both edges of the knife 30Several parallel
10 grooves 86 may be cut laterally across the edge of the handle in the concave flaring
surface just to the rear of the thumb ridge 84. The concave suRace in which the
grooves 86 are cut is naturally engaged by the user's thumb when cutting, and
improves the user's grip on the handle. The grooves 86 are also engaged by a latch
88 on one form of sc~hb~rd to hold the knife 30 in the s~b~rd when the knife 30 is
15 fully inserted in the scahb~rd, as described in below conjunction with Figs. 6-10.
The handle slabs 42 can be knurled on their plane surfaces for improved grip
as shown in Fig. 6, especially handle slabs 42 made of Delrin or other synthetic.~,dLerial which tends to be more slippery than wood. The knurling can be applied by
internal ridges on an injection molding die, or for lower volume prorl~lction, can be
2 o cut rapidly with a CNC engraving cutter which can also cut the rounded bevel around the edges of the handle slabs 42.
As shown in Figs. 6-8, a latching scabbard 90 for the knife 30 shown in
Fig. 1 incll ~des top and bottom clan,shell halves g2 and 94 formed by injectionmolding or the like and solvent welded or fused along a waterline junction 96
2 5 shown as a broken line in Fig. 8 since it is not actually visible after joining. The
open end g8 of the sr~hl~,~rd 90 is curved to match the curve of the forward endof the handle slabs 42.
As shown in Figs. 7-10, the latch 88 includes a latch body 100 pivotally
connected to one edge of the scabbard 90 adjacent the open end 98 by a rivet 102.
30 The latch body 100 is channel shaped along its inner edge 104, as shown in Figs. 9
and 10, having space:l legs 106 and 108 that straddle a portion 110 of the scabbard
edge that is reduced in thickness to provide recesses 112 that receive the legs 106
and 108. A leaf spring 113 biases the latch body against the edge of the scZ~bi .fd
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90. The leaf spring 113 is allached at its forward end to the edge of the s~hbArd 90
by fitting into an angled slot in the edge of the sc~hb~rd 90 and then is captured by
fusing the scabbard material through small openings in the end of the spring 113.
The rear end of the latch body 100 is wilened to provide space for a thumb recess
116 by which the user may pivot the latch 100 body about the rivet 102 against the
biasing force of the spring 113 to unlatch the knife 30.
Two depending teeth 118 and 120, shown in Fig. 9 project inwardly from the
inner edges of the channel legs 106 and 108 at the rear end of the latch 100. The
teeth 118 and 120 are shaped with a profile sloping inwardly and forwardly on their
10 rear edges, and perpendicular to the centerline 122 of the sc:~hb:~r(l 90 on their
forward surfaces. This shape facilitates latching of the knife 30 in the scabbard 90
when the knife blade 34 is inserted into the open end 98 of the sc~hb~rd 90 and the
curved front edge 85 of the handle slabs 42 and the thumb ridge 84 cams the sloping
rear surface of the teeth 118 and 120 to pivot the latch body 100 outward about the
15 rivet 102 again~ the biasing force of the leaf spring 113. When the blade 34 is
inserted fully into the scAhb~rd 90 with the curved front edge 85 of the handle slabs
42 enga~ed with the curved open end 98 of the sc~hb~rd, the front one of the
grooves 86 registers with the teeth 118 and 120, and the biasing force of the leaf
spring 113 rotates the latch 100 so the teeth 118 and 120 drop into the groove 86 to
20 hold the knife 30 in the sc~hb~rd 90. The knife 30 may be withdrawn from the
scaL,bard 90 by engaging the recess 116 with the thumb and rotdling the latch 100 to
lift the teeth 118 and 120 out of the groove 86 while sliding the knife 30 out of the
scabbard. Allernali~/ely a molded sheath may be used which is sized to fit the knife
with a tight snug fit to hold it securely in the sheath.
Turning now to Figs.11 and 12, a second embodiment of a knife in
accordance with this invention is shown in the style of what is usually termed a"survival knife" 130. It includes a knife body 132 having a blade 134 and a tang 136,
to which a handle 138 is fastened by rivets 140 through two spaced holes 141 in the
tang 136. rl~ferably, the handle is injection molded in one piece with a re~anyular
30 cross-section axial p~ss~ge therethrough for sliding onto the tang 136 and securing
thereon by a stainless steel butt piece 142. Alternatively, the handle could be made
in two mating slabs 144 with a central axial rectangular recess into which the tang
136 fits snugly. The slabs can be solvent welded, ultrasonically welded, induction
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12
welded or the like to seal the slabs along a junction line 143 where they meet on the
top and bottom sides of the tang 136.
The rear end of the tang 136 fits into a blind mortise 145 in the butt piece 142and a pin 146 extends through a hole 148 in the rear end of the tang 136 and through
a hole 150 in the butt piece 142 to hold the butt piece in place on the tang 136. The
pin 148 could be a stainless steel pin driven with an i"~e, rereoce fit through the
aligned holes 150 and 148 or preferably is a memory metal pin such as 55 Nitinolwhich is a nickel-titanium interl"etallic compound having about 55% nickel and the
balance titanium. The pin is sized slightly larger than the holes 148 and 150 and is
10 pse~ ~loplastically elongated while in its ~la. lensilic state to make it longer and
thinner. The ~l,etohed pin 148 is inse, l~;d into the aligned holes 148 and 150 and
heated above its tl~nsilio(, temperature whereupon the pin reverts to its original
shorter thicker shape which permanently locks it in place in the holes 148 and 150
with an inle, rar~"ce fit. The handle 144 can be made slightly too long so that the
15 hole 148 is positioned slightly forward of the hole 150 so that when the pin 146 is
driven into the holes 148 and 150 or the ",e",ory metal pin recovers its memory
shape it will force the butt piece 142 forward against the handle to create a tight fit of
the handle ~44 between the butt piece 142 and a bolster 154 desc"bed below.
The bolster 154 is attached to the knife body 132 in a groove 156 at the junction
20 of the tang 132 and the blade 134. The bolster 154 shown exploded away from the
knife body 132 in Fig. 12 is a rectany~Jlar plate made of 55 Nitinol having a rectangular
opening 158 sized slightly s",aller than the groove 156. The tang 136 can be flared
slightly from the butt end 160 toward the groove 156 with the width of the butt end 160
sized to be received in the recta,)yular opening 158. The bolster 154 is slid forward on
25 the tang 136 stretching and pseucloplastically d~rol ",ing the portion of the bolster 154
on both sides of the rectangular opening 158 by about 6%. When the bolster is in the
groove 156 it is heated to a temperature above its transition temperature causing it to
spontaneously revert back toward its pre-defor~,ed size. Since the groove width is
slightly greater than the original size of the opening 158 the bolster 154 is slightly
30 strained in tension in the groove 156 causing it to be very tight in the groove 156. If it
is not convenient to grind or cut the tang with a taper toward the butt end 160 the
bolster can be pse~ ~loplastically deformed on a separate fixture and then slipped over
the tang 136 for heating and restoring to its original shape.
... .
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13
Three other methods for alla~;l ,i"g the bolster 154 are shown in Figs.13-15. Inall of these methods, there is no groove 156; instead, the tang 136 is straight its whole
length and has a width equal to the length of the rectangular opening 158 so thebolster slides onto the tang 136 and abuts a shoulder 162 at the junction of the tang
136 and the blade 134. At the position against the shoulder 162, the bolster 154 can
be fusion welded by tungsten-inert gas welding as illusl~ aled in Fig.13, using a filler
rod of Type 60 Nitinol to create a weldment 164 between the knife body 132 and the
bolster around the opening 158 as shown in Figs.14 and 15. The TIG welding uses a
power supply 166 that prod~ ~ces high amperage, high frequency current which is
10 con~ucted through a tungsten rod 168 to produce an electric arc that is blanketed in a
protecti~e curtain of inert gas, such as a mixture of helium and argon supplied through
a sepa, ate tube 170 or, more typically, through a coi ,cent, ic tube around the tu" 3slen
rod 168.
The weldment 164 is ground smooth with a radiused 9, ind;ng wheel (not shown)
15 coated with cubic boron nitride which is an effective abrasive for 9, il Id;ng Type 60
Nitinol. Dia",ond grinding wheels will grind Type 60 Nitinol also, but the diamond
pdtlerl I on the 9~ il ,di"g wheel or belt should be ~ a"do"~ rather than ordered, to prevent
the establishment of fixed grooves cut by aligned rows of diamond particles on the
wheel or belt, which produces peculiar surface finishes.
Two other tecl ,niques for welding the bolster to the knife body 132 are shown
s-,l,en,alically in Figs.16 and 17. A laser, such as a CO2 laser with a 2.5" focal
length focusing optic system 176 and a laser ~~enerator 178 producing about 650
watts continuous wave, prod~ ~ced by Coherent Energy Corp. in Sturbridge, Mass.
produces a s",ooll, solid weldment that needs little touch-up ylindillg in the finished
25 knife.
In Fig.17, an electrical resisla~ ~ce welding technique is illustrated schematically
using a power supply 180 for producing a high amperage current conduGted through a
cable 182 to a clip 184 attached to the bolster 154. The power supply is currentcontrolled to maintain a consta, lt current despite changes to the resistivity of the
30 Nitinol bolster as its temperature changes. In this electrical resistance welding
technique, the central opening 158 in the bolster is slightly undersized so there is
intimate conla~;t under co" ,pression at the interface between the bolster 154 at the
inner edges of the opening 158 and the tang 136 so that a fused joint is created when
.
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14
the material at the inle~ race melts under the influence of the electrical current flowing
from the bolster to the knife body and thence to a ground line 186.
Instead of the handle slabs 42 or the one piece molded handle 144, a dir~re"t
type of handle may be attached to the knife tang, as shown in Figs. 34 and 35 by5 shrinking a handle form 187 molded of a heat-shrinkable material onto the tang 36.
The handle form 187 is sized to slip onto the knife tang 36 of the knife body 32 shown
in Figs. 18 and 19 after grinding and polishing, and to be heat shrunk onto the tang,
locking into the curvilinear indentations in the edge of the tang 36 when it shrinks. A
variety of materials are available for this use, including semirigid and flexible
10 polyolefins, from several suppliers, including Raychem in Menlo Park, CA.
Turning now to Figs. 20-23, a filet knife 200 made in accordance with this
invention is shown having a knife body 202 and a single piece handle 204. The knife
body 202 has a double wedge-cut blade 206 and a half length tang 208. The one
piece handle has a rounded butt end 210 and an opposite inner end 212 into which an
15 axial slot is routed to receivc the tang 208.
The double wedge cut of the blade 206 is ground using the same grinding
equipment ~~isclosed above. The blade is ground to a taper from the root of the blade
~ "t the position of the inner end of the handle 204 to a sharp point at the tip 214,
and is ground to a taper from the back 215 to the cutting edge 216. The blade
20 thickness at the back 215 of the blade at the root is about 0.070" and tapers uniformly
toward the tip 214. This produces a slender blade that has increasing flexibility
toward the tip 214 which facilitates meat cutting close to the bone and is an optimal
size for gutting fish. The tip is very sharp and the blade near the tip is very sharp for
pe"elraling through the hard scales of the fish, and stays sharp.. The slender blade is
25 about at least 5"-7" long to reach deep into the fish. The handle is a textured or
knurled synthetic material such as Delrin, or can be Rosewood which is a close
grained, non-slip wood that stands up well to water, especially if treated occasionally
with linseed oil or food grade mineral oil. A particularly hard, tough and beautiful
variety of rosewood is a West African Rosewood called Bubingia. The butt end of the
30 handle has a lanyard hole 218 by which fishermen in boats can secure the knife
against loss overboard.
The handle 204 is secured to the tang 208 with rivets 220 like the rivets 40
used in the sport knife 30 shown in Fig.1. The same adhesivelsealant is used to seal
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and adhere the tang in the handle slot and to seal the rivet heads in the handlecounterbores, as described previously in connection with Figs. 4 and 5.
A hunting knife 230 made in accordance with this invention is shown in Figs. 24
and 25 having a drop-point blade 232 and a pair of slab handles 234 secured to a5 tang 236 through holes 238 in the tang 236 with adhesive/sealant and rivets 240 like
the rivets 40 shown in Figs. 4 and 5 in the sport knife 30. The hunting knife 230 has a
husky 5" blade 232 about 11/32" thick and one inch wide for most of its length. It is
very strong and can tolerate prying forces and impact from dropping or throwing that
would break most knives at the bolster.
The knife 230 has a knife body 244 shown in Fig. 25 as it looks as laser cut
from the plate 352. An integral finger bolster 242 depends from the knife body 244 at
the junction of the blade 232 and the tang 233. The finger bolster 242 is about 5/32"
wide and as thick as the knife body is, that is, about 11/32". In ordind, y knife material
such as stainless steel or carbon steel, a finger bolster of these dimensions would be
so weak or brittle that it would soon be broken off in the normal rough handling that a
hunting knife normally is subjected to. Type 60 Nitinol that is thermally conditioned as
described above is so strong and tough that it has proven to survive i",pacts and
other forces far in excess of what a knife would normally experience.
A storage and si ,ipping box 250, shown in Figs. 26 and 27 incll ~des a box
frame 252, a top 254 and a bottom 256. The box frame 252 is made from a slab of
wood such as pine or r"ahoga"y that has a central cut-out 258 in the shape of the
knife it is to hold, which is the sport knife 30 in Fig.1. The cut-out 258 is slightly
larger, but similar in shape to the outline of the knife. The cutout may be made with a
simple scroll saw or, in high volume production, may be made with a CNC router.
The top and bottom pieces 254 and 256 are wood slabs about 1/8" thick made
of pine or mahogany. The bottom piece 256 is bonded to the bottom of the box frame
252 with wood glue or epoxy, and the top piece 254 is screwed to the top of the box
frame 252 by small wood screws 260 or is connected by a hinge (not shown) of known
design. The hinge would be used for retail sales in stores where the cuslo,ner would
want to inspect the knife before leaving the store, and in situations where the
customer would want to use the box to display his knife. The screws 260 could beused for catalogue sales. The box may be lined with velvet to convey a suitable
aurora of quality.
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A folder 305 having a blade 310 of Type 60 Nitinol is shown in Figs. 28 and 29.
The folder 305 has two handle slabs 312 (only one of which is shown) riveted to each
other and to a butt piece 314 by rivets 316 and riveted to each other and to a lock bar
320 by a pivot rivet 325. The handle slabs 312 have aligned lunette recesses 327acljacellt the rear of the lock bar 320 which may be pressed to pivot about the pivot
rivet 325 to unlock the blade. The lock bar 320 has a lug 330 on its front end, remote
from the butt end which el ,yages a notch 335 on a rounded surface 336 at the root
end of the blade 305. Engagement of the lug 330 in the notch 335 prevents the knife
blade 310 from inadvel lently folding onto the fingers of the user during use. The
10 blade may be unlocked by pressing on the butt end of the lock bar 320 which pivots
about the pivot rivet 325 to lift the lug 330 out of the notch 335 releasing the blade
310 to fold about a pivot pin 338 to its closed position shown in Fig. 37. A
superelastic Nitinol spring 340 fitted into a slot 342 in the butt piece 314 biases the
lock bar 320 to its locked position. A short screw 344 with a protruding solid screw
15 head is threaded into a ll ,readed hole along the spine of the blade to facilitate one-
handed opening of the blade 310. The screw 344 may be removed and ~h~ eaded intothe hole from the other side of the blade for left-handed users. The hole in the Type
60 Nitinol blade may be lhreaded using the process described in my prior U.S. Patent
A,~",lication No. 08/349 872 entitled '~hreaded Load Transferring Attachment".
The handle slabs 312 are made of titanium alloy such as the widely available 6-
4 alloy and each has a through hole drilled at its front end slightly smaller than the
dia",eter of the pivot pin 338 . A slightly larger hole 346 is drilled through the root end
of the blade 310 for receiving the pivot pin 338 with a snug sliding fit. The pivot pin
338 is made of Type 60 Nitinol and is extremely strong wear resistant and electro-
25 chemically compatible with the blade 310 of the same material. The pivot pin 338 is
pressed with an inte(rerence fit through the holes in the two handle slabs 312 and
slides in the hole 346 in the blade root securing the handle slabs to the blade and
laterally supporting the blade root between the two titanium slabs 312. The tight
sliding fit between the inside surfaces of the titanium handle slabs and the blade root
30 provides long life bearing support for the blade against lateral loads and the high
strength and wear resistance of the pivot pin 338 ensures a long life free of looseness
that conventional folders are often cursed with.
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17
PROCESSES
The processes of ",ahiny the knives in accordance with this invention will now
be described. The processes will be des~;~ ibed with relation to the sport knife 30, but
the same processes are applicable to any other knife design within the scope of this
5 invention.
The knife body 32 is made from a knife blank 350 cut from a plate 352 or sheet
of Type 60 Nitinol hot rolled to about 3/16 inch. Type 60 Nitinol is a very hard material
even before heat treating, and is difficult to cut, drill and grind. Its l ,arduess and
corrosion resistance make it an ideal material for cutting instruments which, when
10 made of ",alerials such as carl,on steel or 440C "stainless" steel conventionally used
for cutting instruments, often rust or cor, ude first at the thin cutting edge and lose their
sharpness in this way. However, the prope, lies that make Type 60 Nitinol ideal for
cutting instruments such as knives, also make it very difficult to cut, drill and grind.
Ingots of Type 60 Nitinol are made by mixing the powered nickel and titanium
15 sponge and melting the composition in a crucible while thoroughly homogenizing the
chemical co",,t~osilion by thermal lreal~enl. The ingot is formed into a s~ab about 2"
thick by hot forging. The forged slab is heated to about 850~C to 900~C and rolled in
a rolling mill. Repealed passes through the rolling mill are necess~y, with reheating
of the slab when it cools below about 700-800~C. Type 60 Nitinol is described in20 Military Specification MIL-N-81191A and is available from Met~ltex Internalional
Corp. in Albany, Oregon.
During rolling, the sheets or plate 352 develop an oxide surface layer that
makes sl ~hse~uent grinding operations slower and less efficient. This surface oxide
layer may be removed by sanr~l~ctin9 the knife blanks, but it is preferable to
25 sandbiast the entire plate 352 with a garnet or other medium before cutting the
blanks 350 out of the plate. Garnet is faster and does a more through job than
sandblasting with sand.
Allel~lpls to machine Type 60 Nitinol have usually proven unsuccessful, but I
have discovered that it can be quickly cut using abrasive waterjet, illustrated
30 schematically in Fig. 30. The sheet 352 is oriented with the direction of rolling parallel
with the long axis 354 of the blank 350 to give the greatest sl~ ~ngll, along the long
axis. Water from a reservoir 356 is pressurized to about 55,000 psi in a pump system
358 and directed through a nozle 360 in a jet about .005-.010 thick, entraining garnet
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18
abrasive pa,licles injected from an abrasive injector 362, will cut Type 60 Nitinol 3/16
inch thick plate at about 18 inches/minute. The waterjet apparatus is available from
Flow Industries in Kent, Washington. rrererably, the cutting is done under water to
ensure capture of the Nitinol dust and to suppress sparking and fumes generated
5 during cutting operations on Nitinol. The waterjet will cut several stacked plates,
preferably with a rolling pressure foot that maintains the plates in contac~ at the cutting
point. However, I prefer to cut the plates in a single thickness since the waterjet tends
to diverge and produce a wider kerf as the distance from the nozle increases. The
nozzle movement a~paratus is digitally controlled by an CNC controller, so the knife
10 blanks 350, shown in Figs. 30 and 31, can be cut automatically out of the Nitinol plate
352 once the ,udtler" is prog,alllrl~e-J into the controller. The cutting operation is labor
efflcient and can be pe,rol",ed at night, so most of the costs of producing the blanks
350 are in the Nitinol ",~lerial costs and cutting machine time. Although subsla"lially
more costly than 440C stainless steel, the superior functional cha, a~;teristics of
15 corrosion resistance, increased hardness and toughness, and 23% lighter weight
provided by Type 60 Nitinol blades more than justify the increased cost.
The rivet holes 64 and the lanyard bushing hole 70 are also cut with the
abrasive water jet. The hole 70 is an inlel rerence hole, so it is rean ,ed after abrasive
waterjet cutting with an abrasive reamer having cubic boron nitride particles adhered
20 to its surface.
Another Illt:lhod for cutting the knife blanks 350 out of the plate 352 of Nitinol
is wire electron discharge machining (EDM). Although this method is slower than
waterjet cutting, it produces a smo~tl ,er edge that reduces or may entirely eliminate
the need for finish edge grinding of the tang 36. Wire EDM machines are available
25 from several sources, including Mitsubishi EDM, MC Machinery Systems, Inc. and
Hansvedt, Inc. col"h,ercially available from Perine Machine Tool Corporation in
Portland, Oregon in various forms.
A third and prere" ed teci)"ique for cutting the knife blanks 350 from the plate352 is laser cutting. Laser cutting has proven to be an ideal technique for cutting
3 0 blanks 350 out of the plate 352 because the laser kerf is very narrow and wastes only
a tiny amount of material. The surface finish of the cut edges of the blank 350 is
remarkably s,nooll, and requires little or no finish grinding around the edge of the
tang 36 before polishing the finished knife. The precision of the guida"ce apparatus
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19
which guides the malerial under the laser cutting head is so accurate that the holes
64 and 70 in the tang 36 can actually be used as coordination features to fixture the
knife blank for edge grinding.
The laser apparatus used to cut the blanks 350 out of the plate 352 delivers a
5 power of 2600 watts at the cutting point. A high pressure inert gas jet is directed at
the cutting point to blow molten material out of the kerf. The laser appardtus is made
by Trumph Manufacturing Company. When cutting Type 60 Nitinol plate about 3/16
thick, a cutting speed of about 100 inches/minute or more can be maintained.
The high speed and excellent surface quality of the laser cutting is unexpected
10 in view of the difficulty encountered using convel ,lional processes to cut Type 60
Nitinol. I believe that the laser cutting works so well ber~use of a combination of four
factors: low ll ,er",al conductivity, low specific heat, low coefficient of thermal
expansion, and the single phase nature of Type 60 Nitinol. The low ~I,er,l,al
conductivity ensures that heat remains concentrated in the cutting zone instead of
15 being conducted rapidly away as in more conductive materials, and the low specific
heat ensure a rapid temperature increase at the cutting point, resulting in rapid
melting of the material under the laser beam. The single phase material does notchange its prope, lies significantly as its temperature increases so it is very stable.
The dimensions of the material are ar~tec~ very little by the heat input by the laser
2 o be~use of the above factors and beca~ Ise of its low coefficient of thermal expansion,
further enhancing its stability during laser cutting. Laser cutting of Type 60 Nitinol that
uniquely co"ll,ines all these factors is fast and produces smooth cuts of unparalleled
speed, accuracy and precision.
The plate 352 as delivered from the rolling mill sometimes has a residu~l curve
2 5 in the direction of the last rolling pass, usually the long direction. This curve must be
removed from the blank 350 before surface yl inding and edge g, indi"g since
othen,Yise the finished knife would have an objectionable curve out of its flat plane. It
is possible to grind the blanks 350 flat, but it is difficult to mount a curved workpiece
on a flat bed of a surface ~, ir~der, and grinding a curved blank 350 to make it flat is
3 o time consuming, costly and wastes material. A preferl ed technique for straightening a
curved knife blank 350 is to heat it to about 800~C - 900~C and then press the hot
blank 350 against a flat surface, holding it there until it cools to room temperature.
After cooling, the blank remains straight, with little or no springback. One simple
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method is to clamp the hot knife blank between the jaws of a vise. Care must be
taken in handling hot knife blanks 350 of Type 60 Nitinol since the very low thermal
conductivity of the material results in a long cool-down time for a hot knife blank. The
knife blank 350 is about 3/16 thick before surface yl inding so it cools much more
5 slowly than a thinner blade such as the filet knife blade shown in Figs. 20-23.
The plate 352 as received from the rolling mill may be somewhat brittle
because the rolling process may involve tapid quenching of the hot Nitinol by cool
rollers. Rapid quenching of the Type 60 Nitinol can greatly increase the hardl ,ess of
the material and reduce its malleability so that it beco",es brittle as well as hard. A
10 heat conditioning step red! ~ces the hardness of the blank 350 to a more easily ground
l ,ardness of about 50-55 RC and increases the toughness of the blank 350 so that it is
unbreakable by any kind of influence that a knife would normally be expected to
encounter. The heat treating step is to heat the plate 352 or the knife blank 350 to a
temperature of 600~C - 900~C and allow it to cool slowly in air to room temperature.
15 This simple process eliminales the intemal stresses in the in~r"al twinning
boundaries that is believed to produce the g(eater llardness when the ,~,aterial is
heated and then quenched quickly.
Since Type 60 Nitinol is non~ aynelic and cannot be ll,agnelically attached to
the bed of a surface grinder an adapter 366 shown in Fig. 32 may be used to grip20 the blank 350. The adapter has a pair of stub pins 368 and 370 that can be moved
toward or away from each other by a screw 372 having right handed lhreads on oneend and left ha"ded ll " ~aJs on the other end. The stub pins fit into the holes 64 in
the knife blank 350 and are moved in opposite directions by rotation of the screw 372
to hold the knife blank 350 securely on the flat upper surface 374 ~darter 366. The
25 adapter 366 has a flat steel base plate 378 that is securely allacl,ed to the bed of a
surface grinder by an electromagnetic holder on the grinder bed.
Surface grinding of the knife blank 350 removes surface blemishes and micro-
cracks that may be created when the plate 352 is hot rolled and red~ ~ces the
thickness of the blade 34 to the desired thickness for that particular style knife.
3 0 Boning knives and filet knives like the knife shown in Figs. 20-23 for example have
thinner blades than ge"eral purpose hunting knives like the knife shown in Fig. 24 or
the blade of the sport knife 30 shown in Fig. 1. Surface grinding can be performed by
conventional grinding equipment but the best abrasive I have found for g~ indi"g Type
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21
60 Nitinol is diamond or polycrystalline cubic boron nitride ~PCBN). The PCBN isprerer,ed bec~ ~se it is much less expensive than the diamond and tends to be
distributed in a random pattern on the 9, inding surface, whereas diamond is often
distributed in an ordered paller~, that produces peculiar patterns on the finished
5 surface. A grinder that enables easy and convenient changing of the grinding surface
for successive stages of increasingly finer mesh grit is the belt grinder. PCBN and
diamond grinding belts are available from the 3M Co"~pally in Minneapolis, Minn.Grinding of Type 60 Nitinol is fundamentally dirrar~nl from 9, i,).Ji"g
conventional materials. Steel may be ground in a relatively soft condition before heat
10 treating to the desired I ,arclness, but Type 60 Nitinol is always hard. Moreover, it is
best to avoid overheating the Type 60 Nitinol at the 9, i"ding face bec~l Ise at high
temperatures, the material galls and the temperature increases rapidly, distol Ling the
blank and shol le";ng the life of the belt. More seriously, high surface temperatures
produced by slow feed rates and deep cutting passes in conjunction with the use of
15 cutting or cooling fluids can product micro-cracks in the ground edge of the knife. The
low thermal conductivity of the Type 60 Nitinol makes it very difficult to remove the
heat once the blank has gotten hot. The surface may be flooded with coolant to
removing heat and lubricate the y, inding face during grinding, but if coolant is used it
is best to ensure that the surface temperalure is not elevated above about 500~C to
2 o prevent rapid quenching and resultant brittleness, which can result in microcracks at
the cutting edge of the knife. The coolant bath also helps to trap the particles of
Nitinol removed by grinding. To reduce the rate of heating and work input into the
material during yl ind;ng, the surface grinding is pel ror",ed with a verv shallow depth
of cut, about 0.001-0.005 inch, prererably 0.001-0.002 inch, and as high a feed rate as
25 the material will tolerate. This cutting schedule prevents heat build-up and enables
removal of heat in a spray of coolant and helps to trap the grinding dust removed from
the parent mdlel ial. The feed speed is slower than the grinding feed speed withconventional ",~lerials, on the order of about 50-120 inches/minute despite the
shallow depth of cut because the material cuts so slowly, but should be as fast as
30 possible to minimize the heat build-up in the knife edge. The coolant spray entrains
the grinding dust, facilitating capture of the dust in the recirculating coolant and
minimizing the health risk presented by Nitinol dust.
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After surface grinding, the edges are ground to a taper of about 5~-10~ as
illusl(aled in Fig. 21. These surfaces are ground by tilting the 9, inder or tilting one
end of the knife blank 350 up about its longitudinal axis on a modified adapter 366'
and passing the knife blank 350 lengthwise with the axis of the blank perpendicular to
5 the rotational axis 380 of the grinding wheel or drum 382 of a belt grinder 384 so the
belt 386 e"gages the surface on a tangent. This produces a flat edge surface 388which can be sharpened directly. The blank can also be hollow ground, as illusll aled
in Fig. 34, by turning the blank 90~ and tilting the axis of the blade slightly away from
the axis 380 of the drum 382 so they are not exactly parallel. The blade is moved
10 along the surface of the drum 382 while the belt or grinding wheel grinds the hollow or
concave surface to produce a hollow ground edge 390 .
The edge can be ground from the blank directly as shown in Fig. 35. The blade
blank 350 is mounted on a modified adapter 366' (shown in Fig. 33) at the desired
blade angle, and the axis 380 of the drum 382 or grinding wheel is tilted slightly away
15 from the direction of elongation of the blade blank 350. The blade blank or the yl inder
384 is moved parallel to the direction of elongation in a series of rapid shallow p~sses
that remove 0.001-0.002 inch of material at each pass. The blank is flipped and
rotated for grinding the other blade edge surfaces. A blade can be completely edge
ground in about ten minutes in this way. The final pass can be with a belt 386 having
20 a finer mesh grit size to produce a finer surface so that less work is needed during the
polishing step.
Edge grinding and surface grinding can momentarily raise the suRace
temperature of the knife edge to a high temperature which is then quenched by the
coolant spray, producing a heat treatment that raises at least a shallow surface layer
25 to a high degree of hardness. The hardness is especially undesirable at the edge of
the blade because, although it is very hard, it can chip if hit hard against an edge of a
hard item such as a rock. Indeed, the Type 60 material in its as-rolled condition is so
brittle that a knife blank can actually be broken by hand and can break if dropped on a
concrete floor from about four feet. In the polishing operation, the knife body can be
30 exposed to severe conditions of bending and is occasionally dropped or thrown by the
buffing wheels. To prevent chipping or breakage caused by hitting or dropping the
knife body while in this state of undesirable hardness/brittleness, it is desirable to heat
treat the entire knife blade after grinding by heating it to about 400~C - 600~C and
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23
allowing it to cool slowly in air to room temperature. An easy and reliable indication of
reaching the proper heat treating tel"peral-lre for this purpose is a change of color of
the Type 60 Nitinol surface from silver to gold. The surface coloring process isrliscl ~ssed in detail below.
Blades with a long tapering tip are easily overheated with a torch and the thin
material at the tip can cool very quickly in air, producing excessive brittleness in the
tip. To prevent such knives from reaching the customer, I drop the knife tip first onto a
co".;rele floor from about 4 feet. If the tip breaks, I merely regrind the tip of the blade
to shape, taking care not to raise the temperature above about 500~C to avoid the
10 same problem from recurring.
The blade is now polished to a finish of about 20-10 micro-inches or finer, downas fine as 5-1 microinches. If the preceding grinding operation produced a bladefinish that is too rough, it may be ground to a finer surface finish using a belt with a
fine aluminum oxide abrasive, although it is preferable that the final pass in the
15 ~l indi"g operation be pe, ror"~ed with a fine grit grinding surface to mini",i~e the
polishing effort. A rough polishing operalion follows, using Turkish emery glued to a
buffng wheel with a suitable adhesive, such as horseshoe cell,6"l. A high power
motor, on the order of 10 hp, removes surface material, including the gold surface
material, producing a luminous plume of sparks. It is necess~ry to protect workers in
20 the vicinity of the polishing operation from the sparks and the dust with capable
exhaust and dust collection equipment. The final polishing is pe, ~or,l,ed with a buffing
wheel i,npregnaled with a fine dia,nond polishing c~mpound. A buffing c~r"pound that
I have found to be particularly effective is Glaz Woch, available from Ralph Maltby in
Newark, Ohio. Contrary to the usage s~lggestions of the distributor, the Glaz Woch is
25 very effective for producing a mirror-like sheen on the polished Type 60 Nitinol blade
using a buffing wheel driven at about 3000 RPM with a 10 HP motor and high buffing
pressure. Other polishing compounds are available from 3M corporation in multiple
mesh grades which, like the series of ever finer grit mesh on the grinding belts, may
be applied in descending mesh size. using a different buffing wheel for each different
30 grit size. Other buffing compounds that also produce a fine finish are E5 Emery
followed by SCR Stainless, produced by Dico Brothers Company in Utica, New York.The finish resulting from these polishing operations has an extremely alllac~i\/e mirror-
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24
smooth appeara~ce that is not degraded over time by stains, corrosion or tarnishing
like the finish on conventional materials.
Ornamentalio", logos, ll ademarks and other indicia can be permanently
engraved into the blade 34 by an electrochemical process that flows direct current
5 through a l, dnsrer medium on which the desired indicia is reproduced. The transfer
medium, which allows the current flow only where the elching action is desired, is
placed directly ag~inst the surface of the blade where the indicia is to be engraved
and an acid soaked pad is laid over the lrans~er medium. A conductor connects the
pad to a l(a,lsrur",er, and a ground conductor grounds the blade back to the
10 lra"srormer. The blade surface and the l~ansrer medium must be very clean and the
ground conductor must be placed as close as possible to the engraving location since
the electrical conductivity of Nitinol is low. The trhnsrG""er is turned on to produce a
DC current of about 5 amps, and the process is allowed to run for about 20 seconds.
The current is then turned off and the pad and transfer medium are removed. The
15 knife blade and l,a"srer medium are rinsed in water to remove traces of acid and the
engraving of that blade is complete. The etching is done before the surface treatment
to be described immediately below becA~ ~se the surface material is non-conductive.
The blade 34 can be processed to have a hard, non-stick, light or dark gray,
chemically inert and electrically non-conductive surface. The process begins after the
20 knife blade has been polished to as smooth a surface as is econo,nically feasible.
The smoother the finish is to start with, the better the finish will be after the sur~ace
conditioning process is done. As shown in Fig. 36 the process begins with I ,ealing
the blade to an elevated temperature, believed to be about 600~C - 900~C in air for
about 2 minutes. I have found that it is r,ecessary to heat the blade outdoors in cold
2 5 air, at an ambient temper~lure of about 0-32~F. I have not determined why these
conditions are necess~ry to produce the gray color, but I believe it may be related to
the cooling rate or the dirrere,lce in air constituents outdoors vs. in~loor~. Minor
dirrere"ces in CO2. ~2, N2 and water vapor co,lcel,l,~lions indoors vs. outdoors may
influence the reaction. I believe that the gray color of the surface material is a
3 0 chemical reaction that produces oxides, nitrides, carbides or other compounds from
the nickel-titanium intermetallic cor"pound of the Type 60 Nitinol. Whatever thereaction is, if indeed it is a reaction, I produce it by heating the knife blade evenly with
a MAPP gas torch until the gray color forms, and then remove the torch and allow the
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blade to cool naturally in air. The cooling occurs slowly bec~use of the low ll ,e""al
conductivity of Type 60 Nitinol, so I allow 30 minutes or more cooling time before the
next step.
When cool, the blade is polished with a fine grit dian~oncl buffing coi"pound
s such as Gl~ Woch mentioned previously, but is not sl ~b,ected to the high power and
high pressure buffing that prod~ ~ced the high gloss following the surface and edge
grinding. A lighter pressure and lower power wheel, on the order of one HP~ is
necess~ry, otherwise the surface ~alerial could be polished off. After buffing, the
blade will be a medium gray color and will have a smooth, shiny surface finish. The
10 heat treatment is repeated to the same temperature and for about the same time
period and conditions, and after cooling, is again polished with the same buffing
steps. The process may be repe~ted several times to produce darker shades of gray
and increasing luster of the surface.
The resulting suRace is a lustrous dark gray and is so hard and slippery that it15 is virtually scratc;l,proof and non- stick. It is chemically inert so it can be used in
enviror,menLs that would be exlr~mely destructive to convenlional knife materials.
The surface is electrically non-conductive so its use around electrical equip",enl
would provide an extra margin of safety to workers. For applications such as pruning
shears, clippers, and saws, yl ~fling knives, and chain saws that are used on green
2 o plants, the plant sap is easy to clean off the tool and the blade is so slippery that it
slides smoothly through the plant being cut. The corrosion resistance ensures that
the blade remains smooth and slippery and the edge remains undrre~ed by the sap
that causes co"osion in prior art blade materials.
For military application in which a shiny knife blade is undesirable because of
2 5 the glint that reflection from the sun or sky produces, a non-reflective matte finish can
be produced by glass-blasting the blade surface before the surface conditioning
process. Glass-blasting uses micron sized glass beads driven against the blade
surface at high velocity to produce a slllooll, but matte or non-shiny finish. The finish
is similar to that produced by sand-blasting with garnet, except that the surface
3 o irregularities on the glass-blasted surface are smaller than the garnet-blasted surface.
A modification of the above surface conditioning process can be used to
produce a similar surface, but with any of a spectrum of colors rather than gray. As
shown in Fig. 37, the colors, gold, red/purple, bluel silver, and green may be obtained
.. . . .
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in the Type 60 Nitinol surface material, depending on the degree to which the Nitinol
is heated. The process is similar to that used to achieve the gray surface material, but
the process is pe,ror",ed indoors at room ten,peralure, between 60~F and 80~F. This
process also starts with polishing the blade to as smooth and shiny a surface finish as
5 is practicable, since a shiny finish is even more important to the appeara"ce of a
colored blade than it is to a black or gray blade. In fact, I have not found it to be
possible to produce any colors other than gray on a glass-bl ~sted blade surface;
some degree of polishing is necess~ry to get the colors shown in Fig. 37. After
polishing, the blade is meticulQ! ~sly cleaned to remove all traces of oil or other residue
10 that could burn onto the blade at high temperature and leave marks in the colored
surface. The blade is heated to a temperature at which the desired color appears on
the surface of the blade. The colors begin to appear at a temperature in the range of
about 400C~ - 650~C. As shown in Fig. 37, the colors al,pear and change as the
temperature increases. Light gold is the first color to appear and, in order, the color
15 changes to darker gold, red/purple, dark blue light blue, and then silver, but a lighter
shade of sliver than the original shade of the polished Type 60 Nitinol material. If the
temperature is raised even higher after the light silver color appears, the blade color
again passes through the gold, red/purple and blue colors as before, but then goes to
green. The ter"perat-lre chan~e required to pass through the second color spectrum
2 0 after the light silver is a narrow t~m~.era~.lre band and can happen so fast that it might
not be noticed. It appears that third and fourth color spectrums with the same colors
follow the second spectrum, and there may be more after the fourth, but the
temperature dirrere"ce becon,es s,~aller between the spectrums so they are diflicult to
discern. After heating, the blade is allowed to air cool and may be bufled with a fine
25 diamond grit such as the Glaz Woch material mentioned above. All of the surface
materials have the same hard, slippery (non-stick), electrically non-conductive
characteristics of the gray surface material discl Issed above.
Curiously, the indicia etched into the sur~ace of the blade as described above
does not take on the color that the blade surface assumes. I believe this may be the
30 result of a rough surface formed by the electrochemical action of the etching process,
but whatever the reason, the result is a remarkable enhancement of the readability of
the indicia on the colored surface.
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If the desired color is say dark blue and the blade is mistakenly heated to a
ten,pelalure at which a subsequent color appears it is possible to proceed through
silver to the second spectrum to recreate the desired color. Doing so is more difficult
bec~use of the narrower temperal.lre band within which color changes occur. In
5 practice it may be preferable to accept the silver color or polish off the suRace
material with a high power buffing wheel impregnated with diamond buffing compound
and repeat the heating process.
The colored blade suRace materials I have produced are with the use of a
hand-held torch applied judiciousiy to obtain the desired color. However l anticipate
10 that mass production of knives to produce these desirable suRace materials would be
done in an electric furnace wherein temperature and al~ospheric conditions could be
precisely controlled. The knife tang could be mounted in a holding fixture which would
be moved through a pass-through furnace in which the necessAry at"~osphere wouldbe maintained and the te",peralure would be raised to that neGess~ry to produce the
15 desired surface ~"aterial. The fixture would then be moved out the other end of the
furnace and the knives would be air cooled in preparation for the final assembly steps
to complete the knife. Aller"alively the heat processing could be a batch operation
which would be slower but would have better control of the cooling rate.
The above coloring prucess could be used to make other Type 60 Nitinol
20 articles such as jewelry. Type 60 Nitinol is body compatible and could be used to
make gold colored ear rings and finger rings in which jewels could be securely
mounted. Gold mountings for jewels in rings are so weak that it is co""~,o"place to
lose the jewels by calch;,lg the mounting pronys on clothing and the like bending the
prongs so the jewel falls out. A Type 60 Nitinol ring heat treated to a gold color would
2 5 have mounting prongs so strong that loss of jewels would become a rare occurrence.
After polishing and heat treating to obtain the desired color tone on the blade
and the edge of the tang 36 the handle slabs 42 are aligned with the tang 36 and the
rivet holes 55 and bushing hole 72 are back drilled in the slabs 42 using the rivet
holes 64 and the bushing hole 70 in the tang 36 as drill guides if the holes are not
30 already drilled during the cutting of the slabs 42. The counter-bores 56 are drilled in
the handle slabs 42 using a pilot counterbore drill guided by the holes 55 and the
rivets 40 are inserted in the holes 64 in the tang 36. An adhesive/sealant is applied to
the inside suRaces and the counterbores 56 of both handle slabs 42 and to the axial
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holes 61 in the rivet shal.hs 62. A roll pin 60 is inserted into the axial holes 61 in the
rivets on one side of the handle and the rivets are inse, led into the rivet holes in the
handle slabs 42. The handle slabs 42 are aligned and applied on the tang 36 and the
rivets 40 are pressed together to seat the roll pin 60 in the axial holes 61 in the rivet
5 shanks 62 and the engage the underside of the rivet heads 54 with the shoulder 58 of
the counterbore 56. A prerer~ ed adhesive/sealant is a modified epoxy composition
called Permabond Grade 309 made by Permabond, Int'l., a division of National Starch
and Chemical Co. in Englewood, N.J. This composition adheres the handle slabs 42to the tang 36 and aJI ,eres the roll pin 60 in the axial holes 61 to provide erlha"ced
10 r etenlion in addilion to that provided by the roll pin 60 by itself. The adhesive/sealant
also seals the interface between the handle slabs 42 and the tang 36, and seals the
rivet head 54 in the Co~ll ILel l,ore 56. After curing, it is inert to the environments
encountered where knives are used, and is a food-grade material, approved by theFDA for use in meat cutting operations.
After the adhesive/sealant is cured, allached handle slabs 42 made of wood
may be saturated with linseed oil or food grade mineral oil to seal the wood pores
against water, and the slabs are polished with a buffing cG",pound, preferably the
Glaz Woch, available from Ralph Maltby in Newark, Ohio. The polished handle is
very sn,ovth and the dtl~d~i~e grain of the exotic hardwood shows clearly and is set
2 o off beautifully by the mirror sheen of the polished blade. Even though the handle is
very smooth, it is not slippery and can be securely gripped by hand, even when wet.
The last step in the process for making the knife is shal ~en;,)g the edge. The
hardness of the Nitinol material makes it possil~le to obtain an ekl,er~)ely sharp and
potentially dangerous edge on the blade which could be injurious to workers
25 manufacturing the knife, so edge sharpening is postponed to the last step. To avoid
prematurely producing a sharp edge on a hollow ground blade that could ~otenlially
be clangerous if the ground blank is not handled carefully, I leave an ~" Isha, ,c,ened
edge of about 0.030 thickness which an be quickly sharpened as the last step. The
final sharpening step produces an edge of about 7.5~ from the cente, lil ,e, or 15~ edge-
3 0 to-edge. This edge is ground onto the cusp of the hollow ground surface 390 or the
wedge cut surfaces to produce a durable, razor-sharp edge on the knife. The sharp
cusp of the edge is virtually immune to corrosion or tarnishing which normally dulls an
edge in knives and other cutting instruments made of conventional materials. Strong
~ ~ .
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chlorine cleaning solutions eat away the edge of conventional stainless steel blades
resulting in dulling of the edge as quickly as overnight1 even if the knife is not used.
Such strong chlorine cleaning solutions have no significant affect on the Type 60
Nitinol knife so the blade edge remains as sharp despite exrosure to these solutions.
5 Moreover the blade is so hard and tough that it retains its sharpness even when
cutting hard materials such as hemp and fiberglass for much longer than
conventional materials1 especially stainless steels that are formulated to resist
corrosion by low percentages of carbon.
The processes desc~ ibed above can also be used for making cutting
10 instruments other than knives. For example a razor blade 400 in a ~lispos~hlecartridge 402 ~er",aneiltly or removably mounted on a handle 404 as shown
schmatically in Figs. 38 and 39 can be made from a roll of thin gauge Type 60
Nitinol strip ",dterial mounted in a plastic base 406 that is held by or integral with a
handle. Such blades are exl~,l,ely sharp and stay sharp for an extended period of
15 use despite their ~Yr~os~ ~re to soap water and high humidity. Their higher cost is
offset by the exl,~:n,ely long life and exlreme sharpness during the long~life. The
primary cause of dulling of razor blades is corrosion of the blade material at the
cusp of the blade edge and to a lesser extent erosion of the cor, oded edge
material by the beard stubble. Even when the razor blade does not appear
20 cor,ocle.l there is a small degree of CGIIOSiO~ concenlldled at the cusp of the edge
which rounds off the cusp and dulls the edge. Type 60 Nitinol resists this corrosion
far better than stainless steel and also has the hardl ,ess and toughness to resist
erosion of the cusp from which softer stainless steel formulations suffer.
The blade 400 has allacl""enl structure by which it is mounted in the base
406. The attacl ,ment structure shown in this embodiment includes a pair of holes
408 which receive plastic pegs 410 that are heat softened and deformed to hold the
blade 400 down against the base 406 as shown in Fig. 39. If the blade 400 is to be
mounted to self align to the profile of the skin to be shaved it can be a much
thinner and narrow strip of Type 60 Nitinol sharpened along one edge and spot
3 o welded by resistal ,ce or laser welding to a titanium support bracket that is spring
loaded in a slot in the cartridge that clips into the handle in conventional razors.
The narrow strip of Type 60 Nitinol is slit from a sheet of type 60 Nitinol hot
rolled to a thickness of about 0.015-0.050 inch. The slitting is preferably done by
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gang roller shears or gang laser cutters and the strips are manipulated by a
vacuum hal Idling system. For razor manufacturers that prefer to use the same
cartridge fa6ricalion ",acl)i,les they currently use, the individual strips are laser
welded end-to-end and rolled in a large coil that can be used in the continuous high
speed automated sharpening and cartridge fabricalion machines now used to make
razor cartridges. The strip of Type 60 Nitinol may be heat treated to a ha, Jness of
about 62 on the Rockwell C scale by heating to about 600~C and rapidly quenched.The edge, hardel~ed in this manner, is fairly brittle, but it is protected in the
mounting handle or cartridge against ii",l~a~ts so the hardlless is not a detriment in
this application. The only detriment, if it could be call that, is the extremely long life
that a razor blade of Type 60 Nitinol has. Its immunity to corrosion in the presence
of environmental influences that commonly degrade the sharpness of convenlional
blades, and its erosion resistance to beard stubble, makes the Type 60 Nitinol razor
last so long that widespread adoption of this technology by the r~or industry will
greatly reduce the total sales volume of razor blades.
Medical instruments such as scalpels, chisels and files made of body
co",palil~le and FDA approved Type 6û Nitinol would be very safe for use in the
operali"g room beca~ ~se of the body compatibility, and would stay sharp for long
periods of use. Scalpel blades are now normally discarded after use, but Type 60Nitinol blades would be so long lasting and corrosion resistant that they could be
sterilized and reused many times, resulting in much less waste of medically
dangerous waste and greatly increased efficiency of hospital o,l~erati"g rooms.
Type 60 Nitinol takes an e,~ mely smootll finish and is very sli~Jpely, so its use as
scalpel blades would be ideal bec~use it would cut through skin and tough collagen
with no tendency to stick in the incision.
Cutter inserts for the blades of stump grinders, brush cutters, lawn mowers,
chipperlshredders, etc. would be sharp and stay sharp because the Nitinol is hard
and tough, not brittle, so there is little danger of the blade ",alerial shattering and
producing dangerous shrapr,el.
3 o Food processor, blender, and coffee grinder blades likewise would be made
with much harder and tougher cutting edges that would stay sharp and never rust or
corrode. The high impact that blender, food processor and coffee grinder blades
experience require that they be made of steel formulations that are not brittle, but
. . . , ~ .
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the non-brittle steels are soft and do not hold an edge. Type 60 Nitinol is hard but
tough; it will not shatter or chip on impact if it is thermally conditioned as desc, ibed
above.
Convenlional camp saws are made of high carbon steel so that the saw teeth
can be tempered to a high degree of hardness1 but the high carbon steel rusts
quickly if it is exposed to moisture and not immediately dried and oiled. That much
care is difficult to provide in the field, so camp saws often become rusty and dull. A
Type 60 Nitinol saw blade 365, shown in Figs. 40 and 41, will not rust and yet it is
naturally hard, on the order of 53 on the Rockwell C scale, and has a cutting edge
o 357 that can be heat treated to a hardness of 62 or higher on the Rockwell "C"
scale.
The saw blade 415 is cut out of a sheet of Type 60 Nitinol hot-rolled from a
hot forged ingot of Type 60 Nitinol by laser cutting at a high cutting rate, on the
order of 100 inches/minute or higher. This produces a flat, elongated blade blank
having two planar faces and a direction of elongation 417. Allacl""enl structure at
one or both ends of the elongated saw blade, in the form of notches or holes 420 as
shown in Fig. 40, and pointed cutting teeth 422 are cut into the profile of the saw
blank at the same time that the saw blank is cut out of the sheet.
As shown in Fig. 42, the teeth of a Type 60 Nitinol saw blade 415 can be set
2 o by heali"g the toothed edge of the saw blade to a high plastic temperature,
preferably red hot, to reduce its yield strength and elasticity. At a temperature of
above 500~C, prt:rer~bly about 650~C, the Type 60 Nitinol can be pl~stiG~Ily
deror",ed and, if held in the d~n~,ed position while it cools to below about 400~C,
will retain its deror",ed position with no springback. The saw teeth 422 are set by
heating to the high plastic temperature and forci,lg a tool steel die 425, having
alternating beveled ramps 427 and recesses 429 machined therein at the saw teethlocdlions, to bend the teeth 422 laterally out from the plane of the blade in
aller"aling dire-,1iQns. The die 425iS held closed while the teeth 422 cool in their
set positions, and is then opened for removal of the saw blade blank 415.
The teeth are ground sharp along one or both inside edges, as indicated in
Fig. 41, by a narrow g, inding wheel or disc, preferably having diamond or PCBN
abrasive particles embedded in its surface. For high volume production, the
grinding discs are ganged on an ap,uaralLJs that grinds the edges on one side of all
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the teeth on one side of the blade at the same time. The g, inding discs do not last
as long as they last when ~ i"cling conventional steel saw blade material which is
hardened after grinding, but the amount of Type 60 Nitinol that must be removed to
sharpen the saw teeth is small, so the discs can be made to last long enough to be
5 economical, especially considering the greater price that a corrosion-proof saw can
com",and in the market place.
After 9~ indlng, the saw blade is heat conditioned as noted above to remove
any brittleness in the teeth resulting from excessive heating during grinding. The
saw blades are cleaned and assembled on a holding fixture and inserted into an
10 oven where they are raised to the temperature at which the gold color appears on
the surface, about 500~C. They are then allowed to cool slowly in the oven to a
temperature below about 400~C and are removed from the oven. The entire blade
is now tough, springy and strong, and is at about 50-53 on the Rockwell C
hardness scale. To increase the hardness of the teeth without creating e~cessive15 brittleness, the tooll ,ed edge 430 is heale~l by induction heating which raises the
temperature of the teeth to a desired high te",,,~erat~lre in the region of 500-600~C.
The heating is done in a controlled te",per~ure environment in which the coolingrate can be controlled to prevent e~.cessively rapid cooling of the teeth that would
cause brittleness. The temperature to which the edge portion of the blade is raised
2 o can be set to produce a difrerent color, say blue, which would give the Type 60
Nitinol saw a very distinctive appearance.
The saw blade 415 may be made as shown in Fig. 41 with a cutting edge
430 made of Type 60 Nitinol welcled to a saw body 435 made of lower cost material
with a higher modulus, such as titanium. This produces a lower cost saw with a
2 5 higher modul~ ~s. The welding may be laser welding or roller resistance welding that
would require little or no touch-up surface grinding.
The same process can be used to make band saw blades, hand saw blades
and circular saw blades. The band saw blade are made in strips of thin Type 60
Nitinol material and cut to length and welded in a loop using laser welding. The3 o teeth are tough and abrasion resistant, so they are good candidates ~or cutting
problem materials such as composites that quickly dull conventional hardened steel
band saw blades.
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Polycrystailine cubic boron nitride tooling may be used for machining the flat
surfaces of the knife blank and the knife edge instead of 91 indil 19. The cutting
depth must be more shallow than for normal machining, and the feed rate is also
slower. Cutting with PCBN tools generate lower cutting forces and removes heat
5 from the workpiece in the chips, so the workpiece remains cool. Although the
PCBN is far more expensive than grinding wheels and belts, the benefits of its use
compared to grinding are better surface finish, reduction of unwanted heating of the
Type 60 Nitinol ground surface, and eli,ll,n~Lion of yl indiny dust.
Obviously, numerous modifications and variations of the ,urefe,,ed
10 embodiments ~iisclosed herein will occur to those skilled in the art in view of this
specification. Accordinyly, it is to be expressly understood that these "lo-liricaliGns
and variations, and the equivalents thereof, are to be embraced within my invention as
defined by the spirit and scope of the following claims, wherein I claim:
