Note: Descriptions are shown in the official language in which they were submitted.
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Multibond Hardfaced Composites
Field of the Invention
The field of the invention is hardfacing and
providing wear resistance to industrial equipment.
Background of the Invention
A principal cost to the industrial
establishment each year is in metal structure and
equipment destroyed by abrasion from loose materials
such as sand, rock and other silicious compounds.
Various means are employed to combat this
abrasion, and nearly all of these means are with metal
as other materials do not have the strength to
withstand the heavy abuse experienced in these uses.
Depending on the nature of the service, the
protecting material is usually a compromise between a
metal or metal composite of high hardness with
accompanying brittleness and lower hardness with
accompanying toughness, the highest abrasion resistance
being obtained from a composite of very high hardness
carbides in a semihard metal matrix. This material can
only be used on a large area basis as a welded-on layer
no greater than about 3/8" thick and only for pure
scratch abrasion such as sand flowing by gravity down a
chute.
When the service involves absorption of
higher energies such as high velocity particle
impingement or from impacts such as from falling rocks,
the carbide-matrix combination must be of a softer and
hence tougher type to avoid spalling and breakout of
the facing. Use of these softer material results in
greater erosion of the component and hence shorter
life.
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~The usual types of metal protection are heat
- treated steel, case hardened steel and hardfaced steel
bar or plates, with a unit of thickness of high
performance hardfacing being equivalent to 5 to 20
S units of thickness of hardened steel in equivalent wear
life in pure scratch abrasion. As the need for energy
absorption increases, the hardfacing must be dropped
back to lower hardness carbides in a softer and tougher
matrix to avoid spalling and breakage; so the advantage
over steel becomes less.
As the need for energy absorption continues
to rise, it reaches an area where the entire part can
be made from a lower hardness carbide containing alloy
that is produced as a "hard metal casting" of which
thousands of tons are produced and used yearly. For
still higher energy absorption needs, the hard metal
casting will not resist breakage, and a heat treated
steel must be used. Here we are at a level where there
is extreme toughness but such low hardness that very
thick and heavy sections are required to give anything
acceptable in wear life. So hard metals used in
current forms have reciprocal limitations.
Both of the hard metals weld applied coatings
and the hard metal castings have their limitations.
The weld applied coating is limited in depth to about
3/8" of high performance hard metal. The hard metal
casting must be lowered in hardness and type of carbide
contained to avoid brittleness and breakage.
The most cost effective hardfacing used in
industry is called a high chromium iron. It consists
of a main body of iron with up to about 30 percent
-chromium and up to about 4 1/2 percent carbon and is
low in cost because it is made directly from
ferrochromium and plain low carbon steel. This general
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class of material can have varied properties, depending
upon its analysis. One version of it is as a cast
alloy used for a variety of different types of
industrial equipment subject to abrasion. One name for
this alloy is HC-250, originally developed by American
Brake Shoe Company. It has about 27 percent chromium
and about 2 1/2 percent carbon and the balance iron.
This alloy has a content of about 20 percent chromium
carbides of a type which have about 1,000 Bhn and would
be of one or more of the analyses Cr23C6 or Cr3C. In the
annealed state it can be machined and has good
toughness. However, its composite hardness is such
that it is below the level of silica (SiO2), which is
the component that gives hardness to most loose
materials found on the earth. It therefore tends to
have limited life when subject to the abrasion of
silicious materials.
On the other hand, another form of this class
of alloy has up to 30 percent chromium and 4 to 4 1/2
percent carbon. This alloy forms carbides of the
analysis of Cr7C3 in combination with iron, generally
termed M~C3, which have a hardness of about 1700 Bhn,
which is well above the hardness of the silicious
materials usually handled. Its performance in abrasion
with such materials is outstanding and its cost is
still low since it is also made directly from
ferrochromium and iron. This alloy is used as a
hardfacing applied by welding up to the depths of about
3/8". It cannot be made other than as a very small
casting because of its brittleness characteristic.
This alloy was used first on a large area basis in
facing large diameter pipe for use in handling
catalysts in the refining industry. It was early
recognized that the Cr7 or M7C3 carbide was necessary to
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give it good performance and long life and this was
specified as early as 1954 for the production of lift
pipe for use in TCC cracking units in the refining
industry.
S Fully faced plates, for example 4' by 9'
dimensions, were developed and introduced in 1965.
Here again the need for the M7C3 carbide was evident in
the variety of services to which these plates were put.
To obtain that carbide, of course, required an analysis
containing in excess of 4 percent carbon.
Examples of such hardfacing plates are
- illustrated in U.S. Patent Nos. 3,402,459; 3,407,478
and 3,494,749, but the thickness of their hardfacing
cannot exceed about 3/8".
Other facings containing carbides such as of
columbium, vanadium, molybdenum, and titanium would
provide such performance, but their cost is so much
greater that they are not cost effective for large area
coverage.
Considering the hard metal facing, each bit
of hard metal has less support as distance between it
and the point where it is welded to its steel backing
increases. Hence the limitations on the depth of high
performance facing which can be used.
Since the hard metal is welded to steel at
only one of its dimensions, its usual effective depth
is limited to about 3/8".
Hard metal castings can be produced in heavy
thickness, but their matrix hardness and their type of
carbides must be of low enough hardness that they will
not break in service. The result is more rapid wear.
Resistance to abrasion in the metals field
has been accomplished historically by the use of
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hardened plate and bar, by case hardening of the same
or by hardfacing these forms.
Through hardened forms are of lowest cost but
also of lowest hardness and length of life,
experiencing the greatest unit metal loss in a given
abrasions situations. Through hardening must be kept
to a relatively low value as higher hardness in a
through hardened piece will cause brittleness and
breakage.
Case hardened forms present a harder surface
- and will outwear the through hardened forms per unit of
weight loss, but the cases are so thin that the total
life will still be relatively short as compared to
through hardened material where a few times the total
thickness of piece is allowable.
Hardfaced forms will give the greatest life
and least loss of material in a given abrasion
situation, but a really effective facing of hardfaced
forms cannot be applied at a depth great enough to give
long life in heavy abrasion situations. Also in such
situations the facing will chip and be prematurely lost
by flexing of the base and/or impact by high energy
particles.
Summary of the Invention
In the present invention instead of being
welded only in a plane parallel to the surface of the
base plate, the hardfacing is also welded to steel
members in different planes, such as planes transverse
to the plane of the base and can be welded,
mechanically secured or not to the base plate. The
base plate may be formed of any mild steels and the
like which are relatively ductile, malleable and
weldable and which may be cut, bent, shaped, welded or
bolted to a surface to be ade abrasion resistant. The
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base plate can also be the surface to be hardfaced.
The hardfacing or abrasion resistant material comprises
a brittle weldable alloy containing carbide having a
hardness above that of silica. The transverse steel
elements have a thickness and are spaced apart a
distance which reduces fracturing of the hardfacing or
abrasion resistant alloy.
It is an object of the present invention to
provide a multibond hardfaced composite which provides
high performance hardfacing to any practical thickness
desired.
A further object of the present invention is
the provision of a multibond hardfaced composite having
a mild steel base plate and steel members in planes
different from that of the base plate and a brittle
weldable alloy containing carbide of a hardness above
that of silica welded to one or both of the base plate
and the steel members, the steel members being spaced
apart a distance which reduces fracturing of the alloy.
~ further object of the present invention is
the provision of multibond hardfaced composites of any
desired practical thickness having the strength
required for heavy abusive services.
Other and further objects and features appear
throughout the specification and claims.
Brief Description of the Drawinqs
Figure l is a vertical sectional view of a
multibond hardfaced composite in the form of a
hardfaced bar according to the invention.
Figure 2 is a vertical section of multibond
hardfaced composites in the form of a hardfaced slab
according to the invention.
Figure 3 illustrates the hardfaced slab of
i Figure 2 tacked or fillet welded to a substrate.
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Figure 4 is a vertical section of the
multibond hardfaced composites in the form of a grate.
Figures 5 and 6a illustrate the multibond
hardfaced composites in the form of tiles secured
together and to a surface.
Figure 6B is a side view of the multibond
hardfaced composites in the form of tiles mechanically `
interlocked.
Figure 7 illustrates a plurality of the
10 multibond hardfaced composites secured to a roll.
Figures 8-13 illustrate various forms, uses
- and applications of the multibond hardfaced composites
according to the invention.
Figure 14 is a graph showing the relative
15 distance between supports satisfactory for low and high
hardness metals for parallel supports and tube filled
supports.
Figure 15 is a perspective view of a lamina
: bar or sandwich of hardfaced composites according to
20 the invention.
Presently Preferred Embodiments of the Invention
As previously mentioned, the multibond
hardfaced composite of the present invention comprises
a hardfacing brittle, weldable alloy containing carbide
` 25 of a hardness above that of silica welded to steel
members in different planes, such as transverse to the
plane of the surface to which they are to be secured by
welding or mechanical means.
This provides heavy support to each elemental
30 mass of facing on two sides, as well as on the bottom,
which allows the facing to absorb high energy inputs as
impact or shock in compression in which the material is
strong without being subjected to tension or shear in
which it is weak. This allows the use of much harder
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facing materials (massed primary carbides) in a given
service. It also allows employment of hardfaced plate
metal to almost any depth to greatly extend service
life.
The distance needed between the transverse
supports will depend on the brittleness (composite
hardness) of the hard metal. The higher the composite
hardness, the closer together must be the transverse
steel supports to which it is welded. The actual
dimensions are determined by trials in service in a
given application.
Hardfacing metal will vary from low hardness
such as 800 Bhn carbide in a 200 Bhn matrix all the way
to 1700 Bhn carbides in a 450-500 Bhn matrix. The
preferred facing to be used in this invention because
of most abrasion resistance for the cost is the AWS
classification Fe Cr A-1 high carbon. This is
principally an alloy of 15 to 30 percent Cr with 2-5
percent carbon. The bonding of the high hardness
carbide facing in different planes gives it the
strength required for use in heavy abuse services and
provides longer life in all services. It allows the
use of high performance hardfacing to any practical
thickness desired.
The amount of distance required between an
elemental mass of high carbide metal and the point
i, where it is welded to a steel transverse member will
also vary with the form of the structure. The
enveloping forms such as pipe tube or hex and square
structures will allow the largest unsupported distance
to a transverse steel element, for example up to about
3 1/2". In the case of nonenveloping forms, the
transverse or cross members can be spaced up to about
3" apart.
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Referring to Figure 14, the graph illustrates
satisfactory spacing between parallel supports and
tube-shaped supports for AWS Fe Cr A-1 type facings.
For example, in the case of transverse numbers, the
thickness is up to 1/2" and is spaced apart a maximum
of about 3.0". In the case of tubes of any geometric
cross-sectional shape, the tubes have a thickness up to
1/2" and a maximum internal diameter of about 3.5".
The spacing of the steel support elements
required to accomplish the purposes of the composite
varies according to the brittleness and hence lack of
ductility of the facing. For abrasion purposes the
most brittle facings have the highest hardness and
abrasion resistance as explained previously, and will
require weld bonding at the shortest distance from a
steel support.
Compression tests were run on samples
comparing a faced piece of 1.76" diameter with 3/8"
thick hardfacing on 1" plate with a 3/16" tube of mild
steel the same diameter filled with the same material
4.5 C. Fe Cr A-l (nugget). The faced piece failed at
83,000 lbs./sq. in. when a piece broke out. The nugget
cracked internally at 129,000 lbs./sq. in. but was left
intact (and hence usable for abrasion protection). So
even after it had withstood 5S percent more load, it
was still available for abrasion service as before.
The first field test on the all-face slab
installed in a 3 ft. by 10 ft. long area of a bucket in
a copper mine showed the slab standing up 1/8" higher
than the competing protection next to it, which was a
section of bar with hardfacing applied in the
conventional manner.
- In the present invention, the mass of hard
metal to be used is bonded in different planes so that
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no particle of hard metal is an extended distance from
its bonding point. The actual longest distance to be
allowed depends on the construction and the service. A
filled and bonded tube can use a longer distance
because the mass at center is surrounded by bonded
metal. Lighter impact protection requirement will
allow a longer distance of a mass to its point of
welded support.
It its preferred form the multibond composite
comprises a mass of hard metal bonded on three sides to
a steel support which is in close proximity as
described above.
The base plate may be the surface to be
hardfaced or formed of any mild steel which is
relatively ductile, malleable and weldable, and which
may be cut, bent, shaped and welded or bolted to a
surface. Similarly, the cross or transverse members
can be of a mild steel.
The following are examples of carbide
containing alloy materials or weldable brittle
materials which form the hardfacing surface of the
multibond hardfaced compositions.
Example 1.
Percent
Chromium------------------------------------- 27
Carbon--------------------------------------- 3.5
Balance-------------------------------------- Iron
Example 2.
Percent
Chromium-~------------------------------------ 33
Carbon----------------~-~-~~~~~~~~~~~~~~~~~~~~ 3 5~4 5
Balance--------------------------------------- Iron
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Example 3.
Percent
Chromium-------------------------------------- 25-33
Manganese------------------------------------- 0-8
Carbon--------------------------------------- 2.S-5
Molybdenum----------------------------------- 0-2
Boron----------------------------------------- ~0-5
Iron------------------------------------------ Balance
Example 4.
Percent
Carbon-----------------------------------~--~~ 4
Silicon--------------------------------------0.8
Iron------------------------------------------~Balance
Exam~le 5.
lS Percent
Chromium-------------------------------------- S
Carbon---------------------------------------- 2
Boron----------------------------------------- S
Iron------------------------------------------ 8alance
Example 6.
Percent
Carbon-----------------~--~~~~~~~~~~~~~~~~~~~ 3-5
Chromium------------------------------------- 18
Boron---------------------------------------- 4
25 Nickel--------------------------------------- Balance
: Example 7.
Percent
Chromium------------------------------------- 20
Carbon--------------------------------------- 2
Iron-------------------------------~--------- Balance
The following are examples of various uses of
the multibond hardfaced composites.
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Example 8.
:Referring to Figure 1, a channel form 10 of
mild steel is filled with high performance brittla
weldable alloy 12. The brittle weldable alloy containing
carbide 12 is welded and supported on three sides against
energy inputs of the service which would otherwise
shatter unprotected facing of this width and depth. The
channel form 10 can be made of any length to form a bar
or can be made in short lengths for convenience in
shipping and secured together without decreasing its
usefulness. It is attached by fillet welding 14 to a
surface 16 to be protected, although it can be attached
by bolting or steel welding.
Example 9.
15Referring to Figure 2 in which the reference
letter "a" has been added to like numerals of Figure 1,
illustrated is an all-face slab made by filling floor
grating with high performance metal 12a against a bottom
; plate or assembled side by side. The slab is made in
various sizes, for example, up to about 1 foot square.
These are attached by fillet welding (not shown) to
produce large area assemblies as required. This
configuration allows flexing of a large area of substrate
without causing breakout of the facing. Each slab
functions as a small unit of a large area.
Exam~le 10.
Referring to Figure 10 which illustrates
assembly of the all-face slab of Figure 2, slab 1 is
tacked or fillet welded to substrate all around, slabs 2-
3-4 are tacked or fillet welded on right, top and bottom,
slab 5 is tacked or fillet welded left, right and bottom,
slab 6 is tacked or fillet welded right and bottom, and
so on.
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Example 11.
Referring to Figure 4, a floor grating of
multibond hardfaced composites lOb, 12b is illustrated
with the reference numeral "b" applied to reference like
numerals of the preceding figure, shown secured to the
plate.
Example 12.
Referring to Figures 5 and 6, multibond
hardfaced components are illustrated in the form of tiles
1, 2, 3, also called nuggets, which may be provided in
various geometric shapes, for example, hex, square and
round. Individual tiles consist of a tube of the chosen
geometric shape of a length equal to the depth of face
desired filled with high carbide metal alloy which is
welded to the sides of the tubes.
Example 13.
The methods of attachment will depend on the
service requirement and the skills available to the end
user for installation. For example in Figure 5 the tiles
1, 2, and 3 are welded as installed. A row of tiles is
set out against a side plate which is tacked or fillet
welded in place against a base plate. A second row of
tiles, not shown, is lined up against the first row and
tacked or welded in place until the desired area is
covered. This area will have whatever thickness is
desired but will be able to flex with the base plate and
absorb high energy inputs without damage.
Exam~le 14
Referring to Figure 6, round tiles la, 2a and
3a are assembled by placing two tiles together (as la and
2a) and welding them together and to the base as at "A."
Tile 3a is positioned contacting both tiles la and 2a and
similarly welded as at B and C.
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Other forms of filled tubing can be used and
attached to a base plate by tack or fillet welding or
mechanical means.
An example of a mechanical interlock method of
attachment which does not require welding is illustrated
in Figure 6b.
The above are some examples of the use of high
performance (and brittleness) hard metal in deep deposits
with proximity bonding to give 3-way support. The bottom
need not be welded to the surface to be hard surfaced,
but can be secured thereto by mechanical means.
Various further applications and uses of the
multibonded hardfacing composites are illustrated in
Figures 7-13.
Figure 7 illustrates a wear bar having
multibond hardfaced composites according to the invention
attached to a mill roll.
Figure 8 illustrates intermeshing crossbars
having multibond hardfaced composites applied according
to the invention.
Figure 9a illustrates multibond hardfaced
composites applied to bucket teeth according to the
invention.
Figure 9b is a cross-sectional view taken along
the line A-A of Figure 9b. Grooves are provided in the
tooth to form the transverse supports 10, and the
hardfacing alloy 12 is cast into the grooves in the tooth
and are supported by the supports 10.
Figures 10a, b illustrate a hammer mill hammer
having multibond hardfaced composites applied to it
according to the invention.
Figures lla, b illustrate a faced bar of
multibond hardfaced composites applied to a grader blade
according to the invention.
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Figures 12a, b, c, and d illustrate multibond
hardfaced composites as removable shoes according to the
invention applied to coal pulverizing rolls.
Figure 13 illustrates flexible hardfacing of
multibond hardfaced composites which flex independently
of each other for securing to a surface to be hardfaced.
Figure 14 is a graph illustrating satisfactory
spacing between supports of parallel bars and filled
tubes.
Figure 15 illustrates a lamibar in which the
mild steel plates 10 serve as the transverse support
members for the hardfacing particles 12 welded to the
sides of the support members 10. This "sandwich" or
composite bar can be as wide as desired and the
hardfacing alloy 12 as deep as desired, and it can be
welded or bolted to a surface to be hardfaced.
Other types of uses, not shown, are hardfacing
of blades for graders, dozers, snow plows, grizzly bars,
chutes, linings such as for buckets, target plates, and
other applications.
The hardest and most brittle facings can be
used as they are protected by the steel plates by which
they form a sandwich. A heat resisting or abrasion
resisting plate may also be used so that the composite
presents the maximum form of abrasion resistance
; available in the metals field for heavy abrasion.
The present invention has the following
advantages over conventional hardfacing and hard metal
castings of the prior art:
1. It allows the use of high performance
facing in energy absorbing uses where
softer materials were formerly needed.
2. It allows the use of effective
thicknesses ~any times that possible for
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the same type of hardfacing used in the
usual mode.
3. It permits a very thick deposit of
hardfacing material to a surface to be
hardfaced, such as by bolting or plug
welding. As to effective depth, almost
any depth may be employed by bonding the
facing to suitably placed transverse
steel elements.
4. The depth can be any producible by the
arc weld casting process, preferably
bulkwelding.
5. Because of the greatly enhanced support,
harder,- higher performance but more-
brittle metal can be used which
outperforms hard metal castings.
The uses of the multibond hardfaced composite
include the areas now served by hardfacing or hard metal
castings plus areas which they are not able to serve.
While presently preferred embodiments have
been given for purposes of disclosure, various changes in
and applications and uses may be made which are within
the spirit of the invention as defined by the appended
claims.
What is claimed is:
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