Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to self-locking nuts of the pre-
vailing torque type.
Sauer U. S. Patent No. 2,450,694, granted October S,
1948, discloses a prevailing torque type sel~-loakiny nut Ihere-
inater sometimes "the Sauer nut") comprising a one-piece mekallic
nut body having a threaded bore portion, a first end of which i9
adapted to be entered by a ma~ing externally threaded msmber. At
a second end of the threaded bore portion is an annular recess or
well formed in part by a circumferentially continuous annular
flange portion extending axially away from the first end. The
flange portion includes a cylindrical surface coaxial with and
confronting the axis of the threaded bore portion. The Sauer nut
also includes a pre-formed nylon collar mechanically held in the
recess. The flange portion is crimped to engage the upper surface
of the collar, thus to retain the same in the recess and prevent
the same from turning relative to the body The collar has an in-
- ternal cylindrical surface confronting and coaxial with the thread
axis and having a diameter which is somewhat less than the major
thread diameter, so that continued rotation o~ the externally
threaded member, after it traverses the threaded bore portion, will
cause it to engage the cylindrical surface of the collar to impress
a thread therein and achieve the desired self-lockin~ effect, all
in known fashion.
The pre-formed collar of the Sauer nut has a radial
thicknes which is quite large, thus imposing certain limitations
on the overall dimensions o~ the nut, which limitations are in
certain cases undes.irable, as will be more fully explained here-
inafter.
The Sauer nut has long been, and continues to be, pre-
eminent among prevailing torque type self-locking nuts.
However, for many years it has been evident that it is
highly desirable to develop a new self-locking nut which is capable
of being manufactured at a significantly reduced cost relative to
that o the Sauer nut but which is at least as good as the Sauer
nut as to all significant performance criteria.
The present invention has culminated the search for such
a new nut.
The nut of the present invention can be made at a sub-
stantial reduction in cost relative to the Sauer nut, and is at
least as good as the Sauer nut as to all significant performance
criteria.
In addition, as noted, the manufacture of the Sauer nut
entails crimping of the skirt portion after the collar has been
placed in the recess. This has two disadvantages. One, there is
a limit to the hardness and hence ultimate tensile strength of the
Sauer nut, as any heat treatment to develop that strength must be
accomplished before the collar is placed in the recess and hence
before the crimping operation. Also, the nut body blank of the
Sauer nut cannot be cold formed of high work hardenable material.
Two, in the Sauer nut/ the crimped flange portion overlies and
extends axially beyond the collar, thus contributing to the overall
height of the nut without contributing to its locking ability or
strength.
Ths present invention avoids the crimping operation
and in fact does not involve any metal working operation after
the formation of the nut body. Hence, with the present invention,
--2--
. `' ,
the nut body may be heat treated to any desirable hardness, and
hence strength, thus making it possible to achieve a nut o~
improved strength-to-weight ratio with respect to the Sauer
nut.
Thus, with the present invention, for a given thread
size a smaller and lighter nut can be utilized, or a stronger
nuk can be utilized, all to the benefit of the end user.
By eliminating the crimping operation, the present
in~ention also avoids the necessity for the crimped flange or
more load bearing threads can be built into the nut body for the
same overall nut height.
Rieke U.S. Patent No. 3,316,338, granted April 25,
1967, discloses a prevailing torque type self-locking nut
(hereinafter sometimes "the Rieke nut") in which an internally
threaded metallic nut body is provided with an annular recess
located axially adjacent one end of the nut thread. An annular
grOoVe is pierced in the recess to provide a double undercut-
like configuration. The radial nut surface adjacent the recess
is knurled to provide better adherence of a locking element.
A bolt having a thread and a smooth shank which corresponds to
the core diameter of the nut thread is turned into threaded
engagement with the nut thread, with the smooth shank in
registry with the recess. This assembly is then dipped in
plastic powder, so that the recess is filled with powder which
is also mounded up along the bolt shank. Thereafter the bolt-
nut assembly, with powder, is placed on a heating plate to carry
out a fusing process by h~ating the same to the melting point
of the powder which is thereby fused into a unitary body said
to be firmly bonded to the nut body after cooling and solid-
ification. After coolin~, the bolt is unscrewed from the nut
in the direction such that the shank traverses the nut thread.
The cooled plastic material, which Pxtends over the face of
~;t~ 6J
the nut body, is said to form a unit with the nut.
The nut body of the Rieke nut is complex and therefore
expensive to manufacture, especially due to the necessity for
piercing the double undercut groove in the recess. Also, it is
noted that the radial dimension of the recess is quite larye,
resulting in a locking element which has a ratio of axial length
to radial thickness, apparently not greater than about 1, which
is on the same order of magnitude as the ratio of the axial
length to radial thickness of the pre-formed collar of the
Sauer nut.
With the disclosed method of making the Rieke nut,
it is impossible to prevent the plastic locking element from
extending over ~he adjacent face of the nut body. Furthermore,
such method is not adaptable to mass production techniques.
Newnom U.S. Patent No. 3,975,787, granted August 24,
1976, discloses a prevailing torque type self-locking nut
(hereinafter sometimes "the Newnom nut") having a standard
metallic nut body having a circumferentially uninterrupted
internal screw thread. The self-locking feature is derived
from a ring-like plastic patch having a circumferential extent
of ~reater than 180 adhered to the thread of the nut body.
The Newnom nut is satisfactory for applications which do not
require the performance capabilities of the Sauer nut. The Newnom
nut is made by a method which invol~es seating the nut body, either
end first, on a pin a tapered portion of which cooperates with the
circumferentially uninterrupted thr~ad to define a cavity inko
which powder of the plastic material is inserted. The nut body is
~hen heated to melt the powder.
According to the present invention there is prov~ ded a
prevailing torque type self-locking nut including a metallic nut
body having first and second opposite ends, an internal screw
thread of predetermined nominal major and minor diameters located
between said ends and having a first axial end adjacent said first
end of said body and adapted to be entered by a complementary ex-
ternally threaded member, said body further having a well portion
in open communication with and extending axially from said second
end of said body toward said thread, said well portion having a
- circumferentially continuous internal surface facing the thread
axis and spaced therefrom a distance greater than one-half the
ma~or thread diameter, and a self-Locking bushing of thread im-
pressionable thermoplastics materiall a first portion of said
bushing being within said well portion and a second
poxtion of said bushing being on said nut thread,
said Relf-locking bushing having an external surface secured by
a & esion to the internal surface of said weLl portion and to said
nut thread and an internal surface confront~ng the thread axis
and spaced therefrom a distance less than one-half the ma~or
thread diameter.
9~)
Preferably, the axial end of the self-locking element
remote from the thread is substantially axially coincident with
the s~cond end of the nut body and thu~ the loaking element do~
not overlap the second end o the nut body, or vlce versa.
- Also, in the illustrated embodiments the lnternal sur-
face o the well portion i9 cylindrical and the external and ln-
ternal surfaces of the self-locking element are cylindrical, 80
that the latter is in the form of a thin-walled bushing, tube or
sleeve.
The axial length of ~he self-locking bushing is greater
than twice the pitch of the thread and the ratio of tha axial
length of the self-locking bushing to its radial thickness is at
least 2.5:1. In the illustrated embodiments, this ratio is 3.4:1
or more.
The radial thickness of the self-locking bushing is
quite small, being not greater than the fundamental triangle
height H.
In Paragraph 6.13, H~NDBOOK H28 ~1969~ SCREW-TH~EAD
STANDARDS FOR FEDERAL SERVICES, Issue~ March 1970 by the
20 National Bureau of Standards (SD Catalog N~. C13.11:28~ deflnes
"Fundamental Triangle Height", designated "H", as follows: "The
fundamental triangle height of a thread, ~hat iS, the height of a
sharp-V thread, is the distance, measured radially, between the
sharp major and minor cylinders or cones."
--6--
The invention will be describad with reference to the
accompanying drawing in whiah:
FIG. 1 is an axial sectional view of a prior art sel-
locking nut as tauyht by Sauer U.S, Patent No. 2,450,6g4;
FIG. 2 is a plan view of a first ~ut aompri~ing a nu~
body and a locking bushing;
FIG. 3 i5 a view on line 3-3 of FIG. 2;
FIG. 4 is a plan view o a Recond nut comprising a nut
body and a locking bushing;
FIG. 5 is a view on line 5-5 of FIG. 4;
FIG. 6 i5 an enlarged fragmentary view showing in
axial section, a nut body as in FIGS, 2 and 3, and, in axial
: elevation, a pin, the nut body mounted on the pin, with powder
of thermoplastic material filling a cavity between the nut body
and the pin;
.
FIG~ 7 is a view similar to FIG. 6 but showing the com-
pleted nut of FIGs. 2 and 3 and further showing the d~mensional
rslationqhips among the nut body, the bushiny and the pln;
FIGs~ 8 through ll are views showing in axial ~estlon,
the nut body of FIGs~ 2, 3, 6 and 7 and in fragmentary a~ial
elevation, the pin o~ FIGs~ 6 and 7~ these views depicting in se-
quence a serie~ of steps in the manufacture of the nut of FIGs~
2 and 3;
FIG~ 12 is a Vi9W similar to FIG~ 6 but showing a nut
10 of the invention on a pin utilized in the manufacture of such nut;
FIG~ 13 is a view similar to FIG~ 7 but showing a ~irst
modified completed nut of the invention which ma~r be made from
the nut body of FIG~ 12 with the aid of the pin of FIG~ 12 and
further showing for the first modified completed nut thP dimensional
r~lationships amon.g the bushing, the nut body and the pin; and
FIG~ 14 is a view similar to FIG. 13 but showing a se-
co~d modified completed nut of the invention which may be made from
the nut body of FIG~ 12 with the aid of the pin of FIGo 12 and
fur~her showing for the second modified completed nut the dimen-
sional relationships among the bushing, the nut body and the pin.
FIG~ 1 shows, in axial section, a prior art nut 12, astaught by Sauer U~S. Patent No. 2,450,694 and over which the pre-
~ent invention is an improvement~ Nut 12 is of the prevaillng
tor~ue type and comprises a one-piece matallic nut bo~y 14 having
a ~hreaded bore portion 16. A first end 18 of nut 12 and of bore
portion 16 is adapted to be entered by a mating externally threaded
member (not shown). At a second end 20 of threaded bore portion 16
63
i9 an annular recess or well 22 formed in part by a circumferen-
tially continuous annular flange portion 24 which extends axlall~
away from first end 18 and which includes a c~lindrical ~urfa~e
26 coaxial with and confronting the a~is o~ threaded hore po~tion
16. Nut body 14 further has an annular countersunk shoulder 27
facing away from end 18 and joining surface 26 and second end 20
of threaded portion 16.
Prior art nut 12 also includes a pre-formed (as by
injection molding) nylon locking collar 28 mechanically held in
10 recess 22, Flange portion 24 is crimped so as to be in engagement
with upper surface 30 of collar 28, thus to retain
_g_
the same in recess 22 and prevent the same from turning relakive
to body 14. Resistance of collar 28 to turning may be aided by
staking the portion of flange portion 24 overlying collar 28 at
predetermined locations, as shown at 32. Collar 28 hAs a~ ~n~ernal
cylindrical surface 34 which is ~oaxial with and con~ron~ kh~
axis of threaded bore portion 16 and which has a diameter wh~ch is
somewhat less than the major thread diameter, so that continued
rotation of the externally threaded member, after it traverses
threaded bore portion 16, will cause it to engage cylindrical sur-
10 face 34 of collar 28, ko impress a thread therein and achieve thedesired self~locking effect, all in known fashionO Since collar
28 is pre-formed, it tends to have a sharp corner 35 at the axial
end of surface 34 adjacent threaded bore portion 16.
FIGs. 2, 3, 7 and 11 show a nut 36 comprising a one-
piece metallic nut body 38 having a first end 40 providing nut 36
with a work clamping surface and a second end 42 opposita and
parallel to first end 40. Body 38 is also shown in FIGs. 6, 8, 9,
and 10.
Body 38 also has a circumferentially uninterrupted
20 internal screw thread 44 of predetermined major and minor diameters,
located between ends 40 and 42. The axis of thraad 44 is per-
pendicular to ends 40 and 42 and one axial end of thread 44 is
adjacent end 40 of body 38, so as to be adapted to be ~ntered by
a mating externally threaded member.
Body 38 further has an annulax countersunk shoulder 46
surrounding the axis of thread 44 and facing away from end
--10--
40 at the other end of thread 44 and a well portion 48
extending axially from second end 42 of body 38 toward
thread 44 and in open communication with end 42 and thread
44. Well portion 48 has an internal circumferentially and
axially continuous cylindrical surface 50 coaxial wlth th~ead
44 and spaced from the thread axis a distance greater than
one-half the major thread diameter. Surface 50 is of a pre-
determined axial extent and joins second end 42 of body 38
and shoulder 46.
Nut 36 further includes a thin-walled self-locking
bushing, tube or sleeve 52 of thread impressionable thermoplastic
material, such as nylon, located in well portion 48 and having
an external circumferentially continuous surface 54 secured by
adhesion to surface 50 throughout substantially the entire axial
and circumferential extent thereof. Bushing 52 also has an
internal circumferentially continuous surface 56 confronting
and substantially coaxial with the thread axis and spaced
therefrom a distance less than one-half the major thread
diameter. The axial end of bushing 56 adjacent thread 44 may
be slightly flared outwardly in a bell-mouth like configuration,
as shown at 58, as seen particularly in FIG. 7, to facilitate
entry of a mating externally threaded member into bushing 52.
Nut body 38 is also provided with hexagonal external
wrenching surfaces 60 equidistant from the thread axis and
extending axially throughout a major portion of the axial
length of body 38. Wrenching surfaces 60 define a hexagonal
wrenching configuration of predetermined standard across-the-
flats-dimension.
--11--
~ ~`
Body 38 also has an external conical surface 62 coaxial
with thread 44 and joining end 42 and wrenching surfaces 60 and
providing a visual indication distinguishing end 40 from end 42
and also means whereby the nut can be properly oriented by auto-
matic feeding e~uipment.
Nuts 36 of the 5/8-18 thread size have been made by the
hereinaftçr disclosed method and successfully tested.
The following parameters apply to such nuts 36 of the
5/8-18 thread si2e:
Table 1 - Nut 36 of 5,/8-18 Thread Size
Overall nut height (distance from surface 40 to surface
42) - 0.760 inch;
Nut height (from sur~ace 40 to surface 42) - 0.606 inch;
~eight of surface 50 and axial length of bushing 52 -
0.154 inch;
Diameter of nut body surface 40 - 0.641 to 0.648 inch;
Diameter of bushing surface 56 - 0~557 to 0.569 inch;
Radial thickness of bushing 52 - 0.036 to 0.0~6 inch;
Minor diameter of thread 44 - 0.571 to 0.57~ inch;
Major diameter o thr~ad 44 - 0.625 inch minimum;
Countersunk should~r 46 - 170 included angle;
-12-
Across-the-flats dimension of wrenching surfaces
60 - 0.928 to 0.940 inch; and
Weight per 100 pieces - 9.5 poundsl
By way of comparison, the following parameters
apply to a corresponding hexagonal commercial prior art
nut 12 of the 5/8-18 inch thread size:
Table 2 - Prior Art Nut 12 of 5~8-18 Thread Size
. _ ,
Overall nut height - 0.750 inch;
Nut height (from end 18 to surface 26) - 0.596
10 inch;
Diameter of surface 26 - 0.828 inch;
Diameter o surface 34 - 0.552 inch minimum (and
in most instances about same as minor diameter of thread);
Minor diameter of thread - 0.571 to 0.579 inch;
Major diameter of thread - 0.625 inch minimum;
Countersunk shoulder 27 - 170 included angle;
Across-the-flats dimension of hexagonal wrenching
surfaces - 0.928 to 0.940 inch; and
Weight per 100 pieces - 8.9 pounds.
In the manufacture of prior art nut 12, during the
crimping of flange portion 24 into engagement with the upper
surface 30 of collar 28, the latter is somewhat deformed.
Prior to assembly with body 14, pre-formed collar 28 has inner
and outer coaxial cylindrical surfaces and upper and lower
-13-
plane parallel surfaces perpendicular to the upper and ].ower sur
face~. Initially, the dimensions of collar 2~ for the con~ercial
prior art nut 12 of the 5~8-18 thread si~e are as follow6:
Table 3 - ~ Size
-
Diameter of inner surface (which becomes surface 34) -
0.583 to 0.589 inch;
Diameter of outer surface (which confronts surface 26~ -
0.813 to 0.817 inch;
Radial thickness - 0.112 to 0,117 inch;
Distance from upper surfac~ to lower surface - 0.135 to
0.145 inch;
FIGs. 4 and 5 show a second nut 66, Nut 66 takes ad-
vantage of the fact that there is no deformation of metal af~er
the locking element is in place, as will be explained in greater
detail below.
Nut 66 comprises a one-piece metallic nut body 68
having a first end 70 having an external cylindrical ~lange 71,
providing nut 66 with a work clamping surface and a second end 72
opposite and parallel to first end 70. Flange 71 is qu.ite thin in
20 the axial direction.
Body 68 also has a circumferentially uninterrupted inter-
nal screw thread 74 of predeterminQd major and minor diameters,
located between ends 70 and 72. The axis of thread 74 is perpend~-
cular to ends 70 and 72 and one axial end of thread 74 is
adjacent-end 70 of body 68, so as to be adapted to be
-14-
entered by a mating externally threaded member.
Body 68 further has an annular countersunk shoulder
76 surrounding the axis of thread 74 and facing away from end
70 at the other end of thread 74 and a well portion 78 extending
axially from second end 72 of body 6~ toward thread 74 and in
open communication with end ~2 and thread 74. Well portion 78
has an internal circumferentially and axially continuous
cylindrical surface 80 coaxial with thread 74 and spaced from
the thread axis a distance greater than one-half the major
thread diameter. Surface 80 is of a predetermined axial
extent and joins second end 72 of body 68 and shoulder 76.
Nut 66 further includes a thin-walled self-locking
bushing, tube or sleeve 82 of thread impressionable thermo-
plastic material, such as nylon, located in well portion 78
and having an external circumferentially continuous surface 84
secured by adhesion to surface 80 throu~hout substantially the
entire axial and circumferential extent ther~of. Bushing 82
also has an internal circumferentially continuous surface 86
confronting and substantially coaxial with the thread axis
and spaced therefrom a distance less than one-half the major
thread diameter. The axial end of bushing surface 86 adjacent
thread 74 may be slightly flared outwardly in a bell-mouth like
configuration (in the manner shown at 58 in FIG. 7 for bushing
52), to facilitate entry of a mating externally threaded member.
Nut body 68 is also provided with hexagonal external
wrenching surfaces 90 equidistant from the thread axis and
extending axially throughout a major portion of the axial length
of body 68. Wrenching surfaces 50 to 90 define a hexagonal
wrenching configuration of predetermined standard across-the-
flats dimension, but smaller than that of nut body 38.
Body 68 also has an external conical surface 92
coaxial with thread 74 and joining end 72 and wrenching
~ J~
surfaces 90 and providing a visual indication distinguishing
end 70 ~rom end 72 and also m~ans whereby the nut can be
properly oriented by automatic feeding equipment.
Nuts 66 of the 5/8-18 thread size have b~en made
by the hereinafter disclosed method and succe~sfully t~sted.
The following parameters apply to such nuts 66 of
the 5/8-18 thread size:
Table 4 - Nut 66 of 5/8-18 Thread size
Overall nut height ~distance from surface 70 to
surface 72) - 0.685 inch;
Nut height (from surface 70 to surface 80) - 0.531
inch;
Height of surface 80 and axial length of bushing
82 - 0.154 inch;
Diameter of nut body surface 80 - 0.641 to 0.648
inch;
Diameter of bushing surface 86 - 0.557 to 0.569
inch;
Radial thickness of bushing 82 - 0.036 to 0.046
inch;
Minor diameter of thread 74 - 0.571 to 0.579 inch;
Major diameter of thread 74 - O.625 inch minimum;
-16-
Countersunk shoulder 76 - 170 included angle;
Across-the-flats dimension of wrenching surfaces 90
0.865 to 0.877 inch;
Outside diameter of ~lange 71 ~ 1.047 inches; and
Weight per 100 pieces - 7.1 pounds.
It will be seen that ~he 5/8-18 nu~ 66 achieves a weight
saving of about 20~ with respect to the 5/8-18 prior art nut 12
This weight saving is made possible by the fact that the present
invention involves no metal deformation after the locking element
lO is in place in the nut body, thus permitting heat treatment of the
nut body to increase its strength and reduce its size, primarily
by utilizing a smaller, but still a standard size hexagonal wrench-
ing configuration.
Even without the strength consideration, it is possible
to achieve significant weight saving (reduction of size of hexag-
onal wrenching configuration). In the 5/8-18 prior art nut 12,
the 0.828 inch diameter of surface 26 requires that the outar dia-
meter of flange portion 24 be 0.892 inch, which latter dimension
must be less ~han the across-the~flats dimension of the hexagonal
20 wrenching configuration~ Thus, it would be impossible to utilize
in the 5/8-18 prior art nut 12 the 0.865 to 0.877 inch across-the-
flats dimension of the 5/8-18 nut 66, which is possible in the
latter nut due to the radial thinness of bushing 52.
Thus~ a geometric limitation on the size of the hexagonal
wren hing configuration is overcome. So far as geometry is conce~
,S3{~,~
it i~ merely necessary that the across-the-flats dimension
of the hexagonal wrenching configuration be greater than
the diameter of ~urface 50 or 80.
Prior art nuts 12 of the 5/8-18 thread size and
nuts 36 of the same thread size, and made hy the hereina~ex
described method, have been subjected to torque reuse tests
in accordance with Military Specification MIL-N-25027. Both
passed with the following substantially equivalent results,
all of which are in inch-pounds:
10 Table 6 - Torque Reuse Tests
Prior Art Nut 12 of 5/8-18 Thread Size
. _ . _
Torque _ _ _ _ _
_ample 1st O_ 1st Off7th On 7th Off15th On15th Off
1 100 110 100 120 100 120
2 95 100 120 130 95 95
3 120 100 60 60 60 60
4 150 140 140 135 100 100
120 140 150 145 115 110
Nut 36 of 5/8-18 Thread Size
. _ _
Torque _ _ __
Sample 1st On 1st Off 7th On 7th Off 15th On 15th Off
1140 160 120 140 60 75
2100 140 100 140 90 110
~150 150 110 120 50 60
4135 115 95 100 45 44
5120 120 110 130 110 90
6120 140 100 115 70 70
7120 120 140 140 75 75
-18-
-
~ ~J~ ~ ~ 9 ~
The MIL-N-25027 requirement for each "On" torque is 300 inch-
pounds maximum and for each '7Off" tor~ue is 32 inch~pounds minimum.
The method of khe production o~ nut 36 will now be de-
scribed. In broad terms, the method utillxes powder of thermo-
plastic material, such as nylon, which powder is placed within sur-
face 50 of nut body 38 which is then heated to melt the powder.
Upon cooling, the molten thermoplastic material solidifies to form
the desired bushing 52 strongly adhered to surface 50.
More particularly, the steps of the method are illus~rated
in FIGs. 6 through 11. The method is carried out with the aid of a
pin or mandrel 100. Pin 100 is of a material to which the melted
thermoplastic material will not adhere. Examples of suitable man-
drel material are fluoroplastic resins, such as Teflon, as is well
known.
Pin 100 has a bottom cylindrical portion 102 o predeter-
mined diameter, an intermediate or sealing cylindrical portion 106
of smaller diameter than bottom portion 102 and a top or cavity-de-
fining cylindrical portion 110 of smaller diameter than intermediate
portion 106. Top c~lindrical portion 110 has a rounded tip 112 at
the axial end thereof remote from portion 102.
Portions 102, 106 and 110 are coaxial and portions 102
and 106 are joined by a plane annular shoulder or nut body support
surface 104 perpendicular to the axis of pin 100, while portions 106
and 110 are joined by a plane annular shoulder or sealing surface
108, also perpendicular to the axis of pin 100.
--19--
The intersection of portion 106 and sealing surface 108 is
abrupt, to provide a sharp corner therebetween.
Pertinent dimensions of the pin lO0 which was used
in manufacturing nuts 36 of the 5/8-18 thread size are as
follows:
Table 7 - Pin 100 for Nut 36 of 5/8~13 Thread Size
Diameter of bottom portion 102 and outer diameter
of nut support surface 104 - 0.812 inchi
Diameter of intermediate portion 106 and outer
diameter of sealing surface 108 - 0.562 inch;
Diameter of top portion llO - O.477 to 0.483 inch;
Axial length of intermediate portion 106 - 0.596
inch;
Axial length of top portion llO - 0.194 inch;
Combined axial length of portions 106 and llO -
0.790 inch; and
Radius of rounded tip 112 - 0.060 inch.
Nut body 38 is placed on pin lO0, with the axis
of pin lO0 vertical, until end 40 rests on nut body support
surface 104, and the axis of thread 44 is substantially
coincident with the axis of pin lO0. With body 38 and pin
lO0 thus assembled, the following relationships appear:
intermediate por~ion 106 is within thread 44 with a radial
clearance of about 0.004 to about 0.008 inch therebetween;
sealing surface 108 lies in a plane which is about 0.01 inch
below the plane of the end of surface 50 adjacent thread 44;
-20-
and the axial end of pin 100 remote from portion 102 lies in a plane
which is about 0.030 inch above surface 42.
Nut body 38 and pin 100 cooperate to provide an annula~
cavity 114 which is open at end 42 of nut body 38. Mor~ partiaularly,
cavity 114 is defined by surface 50, the upper end of thrs~d 44 and
shoulder 46 of nut body 38 and by top cylindrical portion 110 and
sealing surface 108 of pin 100. Cavity 114 has a radial dimension
of about 0.080 to 0.084 inch.
With body 38 assambled with pin 100 as aforesaid, these
parts are passed under a powder supply tube 116 (FI~. 8) which pro-
vides a constantly flowing stream 118 of powder of the thermoplastic
material, thus to deposit powder in cavity 114 until it is completely
filled~ During such depositing an excess amount of powder may be
deposited on surface 42 of body 38 and on the end of pin 100 remote
from portion 102. Sealing surface 108 prevents any substantial
amount of powder from falling out the bottom of cavity 11~
Any such excess powder is removed by passing the body
38-pin 100 assembly beneath a hood 124 in the form of an inverted
funnel and which subjects the cavity end of the assembly to a puff
of air 122, all as shown in FIG. 9.
Removal of excess powder may also be aided by brushin~
upper end of the body 38-pin 100 assembly with a felt wiper (not
shown) after powder deposition (FIG. 8) and prior to subjecting
tha assembly to the puff of air 122.
After removal of excess powder, the situation is as
best shown in FIG. 6, with powder completely filling cavity 114
as shown at 120 and possibly slightly running up onto rounded
tip 112 of pin 100.
-21-
Next, the bod~ 38-pin 100 assembly is passed between a
pair of parallel induction heating elements 126 which are located
close to body 38 in the axial vicinity of top portion 110 of pin
100, as shown in FIG. 10. Heating elements 126 heat body 38 to
a temperature suEficiently high to melt powder 120. The ~irst
powder to melt is that in contact with surface 50 The melting
proceeds thence inwardly until all of powder 120 has been melted.
When powder of thermoplastic material is melted and then solidified,
the volume of solidified thermoplastic material is substantially
less than that previously occupied by the powder. For rough purposes,
it may be deemed that the solidified material occupies about one-half
the volume previously occupied by the powder. Because the melting of
powder 120 proceeds from the outside in, the surface tension of the
molten thermoplastic material adjacent surface S0 draws additional
thermoplastic material which is located immediately inwardly of the
already m~lten thermoplastic material into the molten mass, and so on
until all of powder 120 has become molten, and the molten material is
a unitary mass in wetting contact with surface 50 but spaced radially
outwardly of the location occupied by portion 110 of pin 1004
Upon subsequent cooling, the thermoplastic material within
surface S0 solidifies, thus to provide the desired self-locking
bushing 52 strongly adhered to surface 50. FIG. 7 shows the dimen-
sional relationships between bushing 52 and pin 100. It is also
noted that, due to the surface tension of the molten thermoplastic
powder, the axial ends of bushing surface 56 may become slightly
flared outwardly, providing a meniscus-like contour.
At an appropriate time aft~r powder 120 starts to melt,
nut 36 is removed from pin 100, as indicated in FIG. 11.
-22-
The axial end of bushing 52 remote from thread 44 is
axially coincident with end 42 of nut body 38, thus overcoming
the dimensional restrictions which are inherent in prior art
nut 12 due to the crimped flange portion of the latter.
Adherence of the bushing to the nut body may be enhanced
by grit blasting surface 50 to provide up to 3-l/2 times the
original surface area, by applyiny a chromate or an iron phosphate
conversion coating (40 to 90 mg/square foot) to provide protection
against infusion of water along the bond line bekween nut body 38
and bushing 52, applying a primer ~such as an epoxy) to surface
50, and/or by utilizing a type of nylon powder in which a primer is
incorporated. An example of the latter is available from Thermoclad
Company, 4688 Ircquois Avenue, Erie, Pennsylvania 15511, under the
designation "DURALON JM". DURALON JM is a nylon powder which in-
corporates a primer. The paxticle size is approximately as follows:
5% coarser than 80 mesh;
45% 80 to 200 mesh; and
50~ finer than 200 mesh.
An important consideration is the tendency of the molten
thermoplastic material to sag, i~eO, to become concentrated at
! the bottom of cavity 114 before it has had an opportunity to solidify.
If sagging is severe enough, the result is an unsatisfactory product.
It has been found that the sagging problem can be avoided
if the ratio of the axial length of bushing 52 or 82 to its radial
thickness is quite large. More particularly, if that ratio is at
least about 2.5, sagging is generally not a problem. For the 5/8-18
nuts 36 and 66, dimensioned as above, the ratio can vary between
about 3.4 and 4.3.
-23
From the foregoing dimensions of collar 28 of the 5/8-16
prior art nut 12, it can be seen that the maximum value of the
ratio of the axial length of collar 28 to i~s radial thickness is
about 1.3, a fiyure which is typical for prior art nuts 12 of
all thread sizes.
The diameter of bushing surface 56 or 86 is largely
predetermined by the desired locking action of the nut, as is the
axial length of bushing 52 or 82, that axial length being on the
order of magnitude of several thread pitches. To maximize the
ratio of the axial length of bushing 52 or 82 to its radial thickness,
the diameter of surface 50 or 80 is chosen to be as small as possible,
just large enough so that the integrity of the bond of bushing surface
54 or 84 to nut body surface 50 or 80 is not destroyed when the
external thread of a complementary member traverses and impresses a
thread in bushing 52 or 82.
For the 5/8-18 nuts 36 and 66, dimensioned as above, the
diameter of surfaces 50 and 80 is 103% of the nominal major thread
diameter. In other nuts 36 and 66, the diameter of surfacPs 50
and 80 may be up to 105% of the nominal major thread diameter.
Other techniques for alleviating the sagging problem
include the incorporation of a thixotropic agent (such as silica
or mica particles) in the thermoplastic powder, inverting the nut
while it is cooling and/or accelerating cooling by ~uenching in an
oil bath.
It is to be understood ~hat the use herein of the term
"thermoplastic material" is broad enough to include such material
containing additives, such as primers and thixotropic agen~s.
Other modifications which might be used to enhance
retention of the bushing include making surface 50 or 80 ellip-
-24-
, .
soidal (to provide partial thread engagement along the minor axis of
the ellipse or not); interrupting surface 50 or 80 with thr~ad
segments extending to nut body end 42 or 72; roughening surface
50 or 80 by providing the same with shallow corrugations, flukes
or splines; or providing surface 50 or 80 with a reverse ~aper,
as by staking nut body end 42 or 72 while nut body 38 or 68 is
being formed.
To revert to the hereinabove disclosed method, several
seconds are required for powder 120 to become completely molten
after body 38-pin 100 assembly passes heating elements 126. It
has been found that it is possible to remove body 38 from pin 100
at any time after melting is substantially underway but before it
is complete, with no adverse effect on the finished product. It
is even more unnecessary for body 38 to remain on pin 100 until
the thermoplastic material completely solidifiesO ~ence, the parts
may never be physically related as shown in FIGo 7~
Some users of prevailing torque type self-locking nuts
have specifications tharefor, which specifications include maximum
dimensional limitations for axial nut length, often making no
dimensional provision for the inclusion of a self-locking element
surmounting the nut thread.
Substantial reductions in the axial length of nuts
embodying the invention can be achieved by utilizing the techni~ues
illustrated in FIGs. 12, 13 and 14~
FIGs. 13 and 14 show first and second modified nuts 128
and 130, respectively, embodying the lnvention. Each of nuts 128
and 130 includes a modified one-piece metallic nut body 132
(FIGs. 12, 13 and 14). Nut 128 further includes a thin-wall~d
self-locking bushing, tube or sleeve 134 of thread impressionable
thermoplastic material, such as nylon, and nut 130 further includes
a ~hin-walled self-locking bushing, tube or sleeve 136. Bushings
134 and 136 differ only as to th~ir internal configurations, as
described hereinafter
-25-
. .
" ~
~ 3
Modified nut body 132 has a flrst end ~not shown) pro-
vidîng a work clamping surface, a seco.nd end 138 and a circumfer-
entially uninterrupted int..ernal screw thread 140 of prede~ermined
major and minor diame~.ers and p~edetermined pitch locat~d be~ween the
work clamping surface and end 138. The axls of thread 140 ls
perpendicular to the work clamping surface and end 138 and one axial
end of thread 140 is adjacent the work clamping surface, so as to
be adapted to be entered by a mating externally threaded member.
Nut body 132 further has a well portlon 142 extending axially fxom
second end 138 toward thread 140 and in open communication with end
138 and thread 140~ Well portion 142 has an internal circumferentially
and axially continuous cylindrical surface 144 coaxial with thread
140 and spaced from the ~hread axis a distance greater than one-half
the major thread diameter Surface 144 joins second end 138 and
extends therefrom a predetermined axial distance toward thread 140.
The last-mentioned axial distance may be on the order of magnitude
of one thread pi~cho
The axial end of cylindrical surface 144 remote from end
138 intersects a countersunk surface 146 coaxial with surface 144
and having a predetermined conical angle, which for nut body 132 is
about 60. Thread 140 runs out on countersunk surface 146.
The diameter of surface 144 and the magnitude of the
conical angle of surface 146 are such that surface 146 interrupts
thread 140 over an axial distance which may be on the order of
magnitude of one thread pitch, or slightly greaterO
The diameter of surface 144 may be between about 101%
and about 105% of the major thread dlameterO
-26-
FIGs. 12, 13 and 14 show nut hody 132 mounted on a pin
148, which is of a material to which the melted thermoplastic
material used for locklng elements 134 and 136 will not adhere.
Pin 148 has a bottom cylindrical portlon ~not shown) of predeter-
mined diameter and providing a nut body support surface, an
intermediate or sealing cylindrical portion 150 of smaller
diameter than the bottom portion and a cavity-defining portion
152 which has a rounded tip 154 at the axial end thereof remote
from portion 150.
Cavity-defining portion 152 is defined in part by a
frusto-conical element 156 coaxial with and axially joinin~ and
extending from cylindrical portion 150. Blement 156 is of
maximum diameter at its circle of juncture with portion 150.
Cavity-forming portion 152 is further defined by a cylindrical
element 158 coaxial with element 156 and axially extending from
the end of element 156 to rounded tip 154.
The diameter of cylindrical portion 150 is slightly
less than the minor thread diameter, and is such that portion
150 can be freely recelved, but just barely so, within
20 thread 140.
The conical angle of frusto-conical elemen-t 156 may
be about 30 and its axial len~th, between its circle oE
juncture with cylindrical portion 150 and its circle of juncture
with cylindrical element 158, may be between one and one-half
and two thread pitches.
Nut body 132 is placed on pin 148, with the axis of
pin 148 vertical, until the work clamping surface rests on the
nut body support surface of pin 148, and the axis of thread 140
is substantially coincident with the axis of pin 148 With nut-
body 132 and pin 148 thus assembled, it should be noted that theplane of the circle of juncture of frusto-conical element 156
and cylindrical element 158 may coinclde or nearly coincide with
the plane of the circle of juncture of countersunk surface 146
and the cylinder of the minor thread diameter. Ths axial length
of cylindrical element 158 is such that the axlal end of element
158 remote from element 156 lies in a plane slightly above
second end 138 of nut body 1320
Nut body 132 and pin 148 cooperate to provide an
annular cavity 160 (FIG. 12) which is open at end 138 of nut
body 132. More particularly, cavity 160 is defined by surface
144, surface 146, the portion of ~hread 140 confronting frusto-
conical element 156, frusto-conical element 156 and cylindrical
element 158
With body 132 assembled with pin 148, cavity 160 is
filled with powder of the thermoplastic material as shown at
162 in FIG. 12, in previously described fashion. Next, the
body 13~-pin 158 assembly is passed between a pair of induction
heating elements which heat bod~ 132 to a temperature sufi-
ciently high to melt powder 162, thus to become a unitary massin wetting contact with surface 144, surface 146 and the
adjacent portion of thread 140.
Upon subsequent coolin~, the thermoplastic material
within the body 132 solidifies, thus to pro~ide bushing 134
~FIG. 13) or 136 (FIG. 14), ha~ing an external surface secured
by adhesion to surface 144, surface 146 and the full thread 140
axially adjacent surface 146, as indicated at 140a. The axial
extent of bushing 134 or 136 on the full thread 140 is, as shown,
somewhat greater than one thread pitch. The portion of the
bushing adhered to thread 140 may be circumferentially continu-
ous, as is the case with nuts 128 or 130, or it may be circum-
ferentially limited. In the latter event, the portion of the
-~8-
.,
, ~
bushing on thread 140 may be in the Eorm of at least one axiallyextendiny finger.
Nut 128 or 130 may be plated, as with cadmium, after
formation of bushin~ 134 or 136. Such plating should be carried
out in an acidic plating bath, since it has been found that iE
an alkaline bath, such as cyanide, is used the adhesion of the
self-locking element to the nut body is adversely affected.
Surprisingly, with an acid plating bath, such adhesion is not
afected
It is to be noted that bushing 134 ~FTG. 13) has an
inner surface 164 confronting the nut axis and spaced therefrom
a distance less than one-half the major diameter of thread 140.
More particularly, inner surface 164 is spaced from the nut axis
a distance which is less than sne-half the minor diametex oE
thread 140. It is also to be noted that the portion of inner
surface 164 axially adjacent end 138 is somewhat convex, due
to slight sagging during cooling of the thermoplastic material.
The portion of inner surface 164 axially remote from end 138
in general follows tha contour of thread 140 and i9 slightly
outwardly flared at the axial end of bushing 134 which is
entered by a mating externally threaded member~
It is to be noted that bushing 136 (FIG. 14) has an
inner surface 166 confronting the nut axis and spaced therefrom
a di8tanca less than one-halE the major diameter of thread 140.
_~9_
_ _
t ,
More particularly, inner surface 166 is spaced from the ~ut axis
a distance which is le~s ~han one-half the minor diameter of
thread 140. It is also to be noted that the portion of inner
surface 166 axially adjacent end 138 is substantially cylindrical.
The portion of inner surface 166 axially remote from end 138 in
general follows the contour of thread 140 and is slightly out-
wardly flared at the axial end of bushing 136 which is entered
by a mating externally threaded member.
~oth nut 128 and nut 130 were made using a thermoplastic
powder which was a mixture of DURALON JM nylon 11 powder and
epoxy, the latter being introduced to enhance adhesion of the
bushing to the nut body~ Various ratios of epoxy to total
weight of the mixture have been tried~ It has been found that
if the ratio is 15~ or greater, the bushing will exhibit un-
desirable fissuring, which leaves something to be desired from
the standpoint of appearance.
-30-
_
For nuts 128 and 130, the ratio of the ~xial length of
that portion of the self-locking element which is within well por-
tion 142 to the radial thickness of that portion is substantially
less than 2.5. For that condition, it has been found that if
DURALON JM nylon 11 powder alone is used for the self-loc~ing
element, sagging is a problem. However, it has been discovered
that if the ratio of apoxy to total weight of the mixture is greater
than about 3-1/2~, the results are surprising as to the sagging
problem. Epoxy alone sags significantly, but when said ratio is
greater than 3-1/2~, sagging is much less ~han when either is used
alone.
Accordingly, the preferred range for said ratio is be-
tween 3-1/2~ and 15~ and a particularly preferred ratio is about
7-1/2~.
In any event, the mixture which was used to make nuts
128 and 130 was about 10% epoxy and 90~ DURALON JM nylon 11 powder.
In the fabrication of nut 128, nut body 132 was main-
tained in an upright position during cooling, whereas in the fabri-
cation of nut 130, nut body 132 was inverted during cooling. This
difference in proce~sing accounts for the differance between the
contours o bushing surfaces 164 and 166, that o~ the latter being
~l~ghtly preerable to that of the ormer.
By following the techniques of FIGs. 12, 13 and 14, it
has been possible to reduce axial nut length by about 1-1/2 to 2
pitches.
The parts may never be physically related as shown in
FIGs. 13 and 14, for the same reason given in the foregoing dis-
cussion of FIG. 7.
-31-
