In a hammer mill, such as used for pulverizing coal, or breaking
and grinding scrap metal, rock, masonry, refuse and the like, the
hammers are exposed to wear. In time, a part of the wearing surface
of the hammer is worn away and the hammer becomes less effective.
A worn hammer is returned to its original weight and dimensions
by depositing a molten exothermic material on the worn surface.
The worn hammer is supported and enclosed by a mold so that the
worn surface faces upwardly. The exothermic material is ignited
and flows into the mold chamber into contact with the worn surface
until the desired hammer dimensions and weight are achieved. Excess
exothermic material overflows from the mold chamber into a sump.
The exothermic material deposits a weld on the worn surface of the
hammer which is similar to Ni-Hard, a known wear resistant metal.
1. Method of rebuilding worn hammers used in hammer mills where
the hammer is elongated with a pair of opposite ends in the elongated
direction with a head at one end, with the one end forming a wearing
surface, extending transversely of the elongated direction and an
eye at the opposite end, and the wearing surface on the head becomes
worn away during use, whereby the dimension between the wearing
surface and the opposite end decreases from a starting dimension,
the method comprising the steps of supporting the worn hammer with
the elongated dimension thereof being substantially vertical and
with the wearing surface located upwardly above the eye, at least
laterally enclosing the worn head within a mold forming a mold chamber
extending upwardly from the worn surface, providing a seal between
the head and the mold below the worn surface, igniting an exothermic
material in a space separate from the mold chamber, when the ignited
exothermic material forms a molten metal, flowing the molten metal
into the mold chamber over the worn surface of the head and filling
the mold chamber with the molten metal until the surface of the
molten metal reaches the desired dimension between the wearing surface
and the opposite end of the hammer.
2. Method, as set forth in claim 1 including the steps of forming
a completely enclosed mold chamber containing the worn surface of
the head with the mold chamber having an upper surface extending
transversely of the elongated direction of the hammer and defining
the rebuilt wearing surface.
3. Method, as set forth in claim 2 providing a crucible cavity
connected to the mold chamber and located above the mold chamber,
forming a closure between the crucible cavity and the mold chamber,
melting the closure between the crucible cavity and the mold chamber
by means of the molten metal formed by the ignited exothermic material
so that the molten metal can flow into the mold chamber.
4. Method, as set forth in claim 3 forming a sump cavity in flow
communication with the mold chamber with the sump cavity extending
downwardly below and upwardly from the upper surface of the molding
5. Method, as set forth in claim 4 flowing the molten metal from
the crucible cavity through the mold chamber into the sump cavity
for preheating the worn surface of the hammer head to a desired
welding temperature and filling the mold chamber with the molten
exothermic material for rebuilding the wearing surface of the head.
6. Method, as set forth in claim 1 forming the mold chamber with
an overflow at the level of the rebuilt wearing surface and filling
the molten metal into the mold chamber until the level of the molten
metal reaches the overflow, and collecting the molten metal flowing
over the overflow.
7. Method, as set forth in claim 1 permitting the molten metal
within the mold chamber to cool and become welded to the worn head,
and after a predetermined cooling period, removing the mold and
any excess material from the rebuilt head.
BACKGROUND OF THE INVENTION
The present invention is directed to rebuilding hammers used in
hammer mills for pulverizing coal and for breaking and grinding
metal scrap, rock, masonry, refuse and the like. A worn hammer is
rebuilt and returned to its original dimensions and weight by depositing
a molten exothermic material on the worn surface. The exothermic
material is selected so that the resultant weld is similar to Ni-Hard,
a known wear-resistant metal.
In modern steel-making operations, coal is ground to a specific
mesh size before coking so that coke of a proper quality for use
in modern, high-throughput blast furnaces is available. Coal is
pulverized in a hammer mill device, such as the Coalpactor, supplied
by the Pennsylvania Crusher Corporation. In such a hammer mill,
a large number of hammers, mounted on shafts, are rotated at high
speed within a housing for grinding the coal to the desired size.
The head of the hammer grinds the coal and, in turn, the grinding
or wearing surface becomes worn and loses its effectiveness. When
such a hammer loses about one-half inch of its length and about
10 per cent of its weight, the hammer is considered worn out and
must be replaced.
In the past, worn hammers have been scrapped. Attempts to increase
the life of hammers by conventional hardfacing techniques have not
In other types of hammer mills, with the hammers providing a crushing
or grinding action, the wearing surface of the hammer becomes worn
and less efficient, until finally it must be replaced.
In rebuilding worn-out hammers, the rebuilt hammer must closely
match the weight and over-all length of a new hammer. Moreover,
the cost of rebuilding must be less than the cost of a new hammer
or it should provide a significantly longer effective lifetime.
SUMMARY OF THE INVENTION
Therefore, the primary object of the present invention is to provide
a method of, and apparatus for, rebuilding worn hammers used in
a hammer mill. Further, the invention includes the exothermic material
used for rebuilding the hammer and the makeup of the metal layer
deposited on the worn wearing surface.
When at least some of the hammers in a coal pulverizer or hammer
mill become worn, all of the hammers are removed and replaced. In
a typical coal pulverizer, 156 hammers are removed and replaced.
The hammers have an elongated shape, with a head at one end and
an eye at the other, with the eye mounted on a shaft for rotating
the hammers. The hammers are positioned side by side along the shaft.
The head has a generally flat wearing surface which provides the
grinding or crushing action. During use, the wearing surface is
gradually worn away, until the amount of wear requires removal and
replacement of the hammers. As mentioned above, the hammers are
removed and replaced as a group. In a typical coal pulverizer hammer,
when half an inch is worn off the wearing surface, the hammer must
be replaced. Depending on the type of operation being carried out
by the hammer mill, the size and weight of the hammer may vary greatly.
As an example, forged steel paddle hammers are available from the
Pennsylvania Crusher Corporation in the range of 12.5 to 53.5 pound
sizes. Other hammers, of at least a 200-pound size, are also used
in hammer mills.
In rebuilding hammers, the hammer is supported on a frame so that
the wearing surface of the head faces upwardly. A mold member is
positioned on the support enclosing the head and the wearing surface
to be rebuilt. A seal is provided between the mold and the support
frame. An amount of a thermite or exothermic material sufficient
to rebuild the worn hammer is introduced into a crucible cavity
at a location above the molding chamber. Initially, a steel tapping
disk blocks flow from the crucible cavity into the molding chamber.
After the exothermic mixture is ignited and becomes molten, the
steel tapping disc melts and the molten mixture flows into the molding
cavity, filling the cavity up to the finished wearing surface of
the hammer. Excess molten material flows into a sump. When the molten
material freezes within the molding cavity and is welded to the
existing hammer surface, and following a predetermined cooling period,
the part of the mold remaining around the hammer head is removed,
the gate and sump are broken off and, if necessary, any excess weld
material is ground away. The weight and the length of the rebuilt
hammer is then checked against the hammer specifications.
It is significant in rebuilding smaller hammers, such as hammers
weighing 10 to 60 pounds that the dimension between the eye of the
hammer and the wearing surface at the end of the hammer head is
maintained within very limited tolerances, such as +/- one-sixteenth
of an inch in the over-all length of the hammer. Larger hammers,
over 60 pounds, have only maximum length requirements.
The apparatus used for rebuilding a worn hammer depends on the
over-all size and weight of the hammer. In the smaller range, the
hammers can be rebuilt on a support frame. Preferably, the frame
is mounted on rollers or wheels so that it can be moved between
Larger hammers, which cannot be handled manually, require a stationary
apparatus for the rebuilding operation.
For smaller-sized hammers an upwardly extending support frame is
constructed from angle members. An upwardly facing support surface
is provided with shaped recesses to receive the underside of the
head, that is the surface of the head opposite the wearing surface.
With the precise formation of such a recess, the hammer to be rebuilt
can be positioned exactly so that the rebuilt wearing surface is
at a predetermined dimension from the opposite end of the hammer.
A graphite plate is mounted on the support surface so that it laterally
encloses the lower part of the hammer head. A sealing paste is provided
between the graphite plate and the worn hammer head, and also on
the upwardly-facing surface of the graphite plate. A mold is placed
on the upper surface of the graphite plate with the paste forming
a seal between the graphite plate and the lower end of the mold
and the lower part of the head. The mold forms a mold chamber which
laterally encloses the worn hammer head in closely-fitting relation.
In one arrangement of the mold chamber, an upper limiting surface
is formed which defines the finished wearing surface of the hammer
head, after it is welded.
The mold includes a crucible cavity spaced above the mold chamber
with a passageway extending from the lower end of the crucible cavity
into the upper end of the mold chamber. A steel tapping disc is
seated within a recess in the lower end of the crucible cavity,
and forms a closure for the passageway from the cavity into the
In addition, a sump cavity is located within the mold and is connected
by an opening with the upper end of the mold chamber.
It is important in forming the support frame that the support surface,
on which the hammer head rests within the recess, is flat, smooth
and normal to the shank of the hammer. Otherwise, the resulting
weld formed by the molten exothermic material will not extend properly
from the worn surface on the head. If the weld formed on the head
is not normal, but oblique, the rebuilt hammer must be rejected.
For ease in performing the rebuilding operation, it is important
that the hammer can be inserted into the support frame downwardly
into the recess. The support frame must have a cut-out of adequate
size to receive the hammer eye and shank. The graphite plate in
combination with the sealing paste affords a seal around the hammer
head and prevents leakage of the molten exothermic material, or
weld metal, downwardly along the sides of the hammer. The sealing
material is a refractory paste applied as a bead around the entire
periphery of the hammer head in the region of the graphite plate
and as a coating on the graphite plate surface on which the mold
In the rebuilding operation, the thermite or exothermic material
within the crucible cavity is ignited, and after the exothermic
reaction is complete, in about 30 seconds, tapping of the molten
metal is delayed until the steel tapping disc melts. This delay,
about ten seconds, allows time for the molten slag and metal to
separate into two layers with the slag floating on top. When the
steel tapping disc melts, the superheated molten metal flows downwardly
from the crucible cavity into the mold chamber, across the top of
the worn hammer head and into the sump cavity. Initially, the molten
metal preheats the cold hammer head, which is at ambient temperature,
to the welding temperature, and since the opening to the sump cavity
is located below the top of the mold chamber, the initial flow passes
into the sump cavity. When the sump and the mold chamber are full,
flow out of the crucible cavity is stopped, and the metal within
the molding chamber freezes on the worn surface of the hammer head,
forming a weld. Normally, some weld metal remains in the base of
the crucible cavity with the slag collecting on top of the metal.
After permitting the molten metal to cool for about 30 minutes,
the mold is broken away and the rebuilt hammers can be removed from
the stand. After further cooling to near ambient temperature, the
gate and sump are fractured off and any remaining excess metal is
removed. The rebuilt hammer is then checked to determine if it meets
the required specification.
In the apparatus just described, the mold chamber is formed with
a closed upper end for defining the finished wearing surface of
the rebuilt hammer head. When the size of the hammer is such that
a completely enclosed mold chamber is not feasible, an open-top
mold chamber is provided. A crucible cavity is provided for flowing
the molten exothermic material into the mold chamber over the worn
wearing surface of the hammer head. The mold chamber is provided
with an overflow outlet, having an invert located at the level in
the molding chamber corresponding to the finished rebuilt wearing
surface of the hammer. Accordingly, since the initial flow of the
molten exothermic material cannot be used to preheat the worn surface
of the hammer head, a preheating operation must be performed. With
the worn wearing surface preheated, the ignited exothermic material
in the molten stage is then passed from the crucible cavity into
the molding chamber. When the molten material reaches the level
of the invert, it flows into a sump providing a level finished wearing
surface on the hammer head.
Based on the weld required to rebuild the hammer head so that it
is returned to its original dimensions, the amount of the exothermic
mixture to be used is determined. An amount of the exothermic material
in excess of the amount required for welding the worn wearing surface
of the hammer is provided to assure that the wearing surface is
returned to its original dimensions.
An example of an effective exothermic mixture for smaller hammers
contains the following components:
______________________________________ Material Percent ______________________________________
atomized aluminum powder 21.5 millscale (18% FeO) 70.2 graphite
powder 2.9 high carbon ferromanganese 1.0 Nickel Oxide Sinter 75
2.9 low carbon ferrochromium 1.5 100.0% ______________________________________
An example of an effective exothermic material for larger hammers
contains the following components:
______________________________________ Material Percent ______________________________________
atomized aluminum powder 21.4 millscale (18% FeO) 69.9 graphite
powder 3.4 high carbon ferromanganese 1.0 Nickel Oxide Sinter 75
2.8 low carbon ferrochromium 1.5 100.0% ______________________________________
It has been found that the weld metal produced using these exothermic
mixtures has basically the same composition as a well-established
wear resistant material known as Ni-Hard. In addition to an as-deposited
hardness of 50-55 Rc, the microstructure contains a high volume
of carbides providing better resistance to abrasive wear than the
original steel hammers which have been heat treated to the same
degree of hardness. In tests conducted to date, it has been found
that hammers rebuilt in accordance with this method have about twice
the effective lifetime of new hammers. The deposited weld in accordance
with the present invention includes:
______________________________________ Material Percent ______________________________________
carbon 3.0 manganese 0.6 silicon 1.0 nickel 4.5 chromium, 1.5 ______________________________________
and the remainder iron.
Since smaller hammers are rebuilt in a different procedure then
larger hammers, two different exothermic mixtures are required,
however, the resultant weld metal composition is essentially the
A significant feature of the applicant's invention involves the
support of the hammer and the arrangement of the mold on the support
so that the rebuilt wearing surface is located at a specific dimension
above the hammer eye. Unless this dimension is maintained within
close tolerances, the rebuilt hammer does not operate effectively.
In a hammer mill, a plurality of the hammers are mounted in side-by-side
relation on a shaft. Accordingly, the wearing surface of the hammer
heads have a dimension extending in the direction of rotation of
the hammers and another dimension extending perpendicularly of the
rotational dimension. The perpendicular dimension is significant,
since if this dimension is not maintained within accurate limits
there may be interference between the movement of adjacent hammers
on the shaft. Accordingly, the dimension extending transversely
of the rotational dimension must be kept within close tolerances,
however, the dimension in the rotational direction is not as critical.
The over-all dimensions, however, must be retained to assure that
the weight of the rebuilt hammer does not fall outside the required
The various features of novelty which characterize the invention
are pointed out with particularity in the claims annexed to and
forming a part of this disclosure. For a better understanding of
the invention, its operating advantages and specific objects attained
by its use, reference should be had to the accompanying drawings
and descriptive matter in which there are illustrated and described
preferred embodiments of the invention .
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a hammer for use in a hammer mill;
FIG. 2 is a perspective view of the hammer shown in FIG. 1 however,
with the hammer turned approximately 90 degrees about the vertical
FIG. 3 is a perspective view of another embodiment of a hammer
head, however, with a slightly different configuration of the head;
FIG. 4 is an elevational view of a support frame for use in rebuilding
a worn hammer;
FIG. 5 is a top view of the support frame shown in FIG. 4;
FIG. 6 is an end view of the support frame shown in FIG. 4;
FIG. 7 is an enlarged perspective view of a mold for use on the
support frame shown in FIG. 4;
FIG. 8 is a sectional view of the mold shown in FIG. 7;
FIG. 9 is an elevational view of another hammer, larger as compared
to the hammers in FIGS. 1-3;
FIG. 10 is a side elevational view of the hammer displayed in FIG.
FIG. 11 is a perspective view of the hammer in FIGS. 9 and 10 mounted
on a support frame;
FIG. 12 is a schematic showing of the molding apparatus for rebuilding
the hammer of FIGS. 9 and 10; and
FIG. 13 is a schematic view of the molding apparatus and the means
for flowing the thermite mixture in the molding apparatus.
DETAILED DESCRIPTION OF THE INVENTION
In FIGS. 1 and 2 perspective views are shown of a hammer 1 characterized
above as a smaller hammer, used in a coal pulverizer. The hammer
1 is elongated in the vertical direction, as viewed in FIGS. 1 and
2 with a head 2 at the upper end, an eye 3 at the lower end, and
a shank 4 extending between the eye and the head. The upper surface
5 of the head is its wearing surface and cooperates with a stationery
housing surface, not illustrated, for pulverizing coal. The lower
end of the head 2 has a V-shaped section 6 with a pair of opposite
sides converging inwardly in the downward direction and terminating
in an apex 7. The V-shaped section 6 with the apex 7 is not significant
with regard to the pulverizing operation, however, it is significant
concerning the support of the hammer during the rebuilding operation.
During use, the wearing surface 5 is gradually worn away until
it is worn down to the dashed line 5a, whereby the hatched section
between the original wearing surface 5 and the worn surface 5',
is worn away. Due to the wear experienced by the hammer, its over-all
length has been reduced, its weight decreased, and the hammer can
no longer properly crush coal. At this point in the operation of
the coal pulverizer, the hammers must be replaced and replacement
involves a significant cost. In the past, though the worn hammers
have lost only about half an inch in their over-all length, that
is between the bottom of the eye 3 and the original wearing surface
5 and about 10% of its weight, the hammer is normally scrapped.
Attempts have been made in the past to rebuild the hammers by conventional
hardfacing techniques, however, such rebuilding has not been successful.
In FIGS. 1 and 2 the wearing surface 5 is shown as a flat planar
surface, however, the wearing surface of conventional hammers, as
originally forged, may have a slightly rounded shape, extending
in the direction of a rotation due to forging procedure. It is not
necessary to provide this slight rounding-off when the hammer is
In FIG. 3 another embodiment of a smaller hammer is shown, where
the same reference numerals are used as in FIGS. 1 and 2 however,
with the addition of the suffix a. The hammer 1a has a head 2a at
its upper end, and eye 3a at its lower end, with a shank 4a interconnecting
the head and the eye.
The upper surface 5a of the head 2a is the original wearing surface
before it is exposed to wear. The significant difference from the
embodiment shown in FIGS. 1 and 2 is that the shaped section 6
a is rounded, rather than wedge or arrowhead shaped.
As can be noted in FIGS. 1 and 2 and in FIG. 3 the eye 3a has
a maximum diameter greater than the corresponding dimension of the
head 2 for effecting adequate structural strength. This dimensional
difference is significant regarding the manner in which the hammer
is supported during the rebuilding operation.
When it is determined that a hammer mill is no longer operating
effectively, due to wear of the individual hammers, all of the hammers
are removed, though the extent of wear varies. Further, the size
of the hammer has a bearing on the type of apparatus needed to rebuild
the wearing surface. If the hammers are in the range of 10 to 60
pounds, it is possible to carry out the rebuilding operation with
a relatively lightweight structure, however, as the hammer size
increases, particularly to the point where the hammers cannot be
handled manually by a single individual, the type of apparatus for
rebuilding the wearing surface is significantly different from the
support structure for lighter weight or smaller hammers.
In FIGS. 4 5 and 6 a support frame 10 is illustrated for rebuilding
relatively small coal pulverizer hammers. For example, the hammers,
such as illustrated in FIGS. 1 and 2 have an over-all hammer length,
as viewed in FIGS. 1 and 2 from the original or rebuilt wearing
surface 5 to the lowest point of the eye 3 of 125/8 inches with
an allowable tolerance of a +/- one-sixteenth of an inch. The weight
of such hammers is in the range of 7495 to 7595 grams, or slightly
under 17 pounds. Such a hammer size is easily handled by a single
The support frame 10 shown in FIGS. 4 5 and 6 can be constructed
to support a number of hammers. In practice, it has been found that
the support frame can handle five separate hammers effectively.
However, a support frame can be used for any number of hammers and,
as shown in the drawing, only a single worn hammer 1 is mounted
on the support.
The support 10 is formed of angles or similar structural members
based o the over-all size of the support frame.
The support frame 10 includes vertically extending legs 12 with
an upper horizontally extending support member 14 mounted on the
legs. The support member 14 has an upper planar horizontal support
surface 16. A V-shaped recess 18 is cut in the surface 14 to receive
the V-shaped section 6 of the hammer 2. This recess must be very
accurately formed so that the hammer is held in a rigid position
and is exactly located relative to the finished wearing surface
5 of the head 2 of the hammer 1. As can be seen in FIG. 4 the V-shaped
section 6 fits exactly within the recess 18 so that the remainder
of the head 2 projects upwardly from the recess.
The surface 14 of the support frame 10 as seen in FIG. 5 has
the recess 18 located on opposite sides of a rectangular cut out
20 larger in the long direction of the support frame so that the
eye 3 of the hammer 1 can be inserted downwardly through the support
surface whereby the V-shaped section 6 fits into the recess 18.
Accordingly, if the hammer 1a, with the different shaped section
6a is used, as in FIG. 3 the recess is shaped accordingly.
As can be seen in FIGS. 4 and 6 steel straps or similar structural
sections are provided along the lower part of the support frame
on each of the opposite sides of the eye 3 of the hammer head to
maintain the hammer steady during the rebuilding operation. A thin
steel base plate 24 is provided on the support surface 16 and has
cutouts in register with the recesses 18 and forms the opening 20
for the passage of the hammer eye 3 downwardly through the support
surface 16 between the straps 22. A graphite plate 26 is mounted
on top of the steel plate and is shaped to closely accept the cross-sectional
shape of the head 2 of the hammer 1 at a location above the V-shaped
section 6. In one embodiment, the base plate 24 is a 1/4" thick
and the graphite plate 1" thick. A sealing paste 28 is applied
to the opening formed in the graphite plate to receive the head.
For ease in assembly, the graphite plate can be split in half.
In FIG. 4 a mold 30 is shown schematically, resting on the top
surface of the graphite plate 26. The thickness dimension of the
steel base plate 24 and of the graphite plate 26 along with the
mold, are selected so that the wearing surface 5 of the hammer head
2 can be returned to its original dimension relative to the opposite
end of the hammer. The mold 30 is described subsequently in more
detail and includes a mold chamber 32 which receives the worn head
2 and has a horizontal upper surface 34 defining the upper limit
of the chamber and arranged to form the finished wearing surface
5 of the head 2. It can be seen in FIG. 4 that the worn surface
5' is spaced downwardly from the upper surface 34 of the mold chamber
In FIG. 7 an exterior view of the mold 30 is shown. In FIG. 8
a cross-section of the mold is illustrated resting on the graphite
plate 26 with the sealing paste 28 positioned between the opening
formed within the graphite plate 26 and the worn hammer head 2 and
between the upper surface of the graphite plate and the bottom surface
of the mold 30. The worn surface 5' of the hammer head 2 is spaced
downwardly from the upper surface 34 of the mold cavity 32. The
surface 34 is located at the selected over-all length dimension
of the hammer 1 from the lower end of the eye 3.
A crucible cavity 36 is formed within the mold 30 with the lower
end of the cavity located above the upper surface 34 of the mold
chamber 32. A passageway 38 connects the lower end of the crucible
cavity 36 with the upper end of the mold chamber 32. A steel tapping
disc 40 is seated within a recess 42 at the upper end of the passageway
38 and forms a closure for the passageway. On the opposite side
of the mold a sump cavity 44 communicates with the upper end of
the mold chamber 32 through an opening 46. The sump cavity 44 extends
downwardly below the upper surface 34 and also upwardly above the
upper surface 34 within the mold chamber 32.
The mold has a planar lower surface 48 which rests on the graphite
plate 26. The mold 30 is a sand-resin mold and is formed exactly
to the dimensions of the hammer head extending normally of the vertical.
The mold is formed of two mating parts which can be secured together
after the hammer head 2 is enclosed by the graphite plate.
In rebuilding the wearing surface 5 on the head 2 initially an
amount of exothermic material in excess of the amount required to
rebuild the wearing surface of the hammer is filled into the crucible
cavity 36. If necessary, a graphite pipe, not shown, can be placed
on top of the mold aligned above the crucible cavity for increasing
the volume of the cavity for the exothermic mixture.
The exothermic material is formed of 21.5% aluminum powder, 70.2%
millscale (18% FeO), 2.9% graphite powder, 1.0% high carbon ferromanganese,
2.9% Nickel Oxide Sinter 75 and 1.5% low carbon ferrochromium.
The exothermic mixture is ignited by conventional means and the
exothermic reaction is completed in about 30 seconds, with molten
slag and metal forming two layers, the slag floating on top of the
metal. After another ten seconds, the steel tapping disc 40 melts
and the molten metal flows downwardly from the crucible cavity 36
through the passage 38 into the mold chamber 32. As the molten metal
flows over the top or worn surface 5' of the hammer head 2 it preheats
the worn surface of the head to the desired welding temperature
and then flows into the sump cavity. The following molten metal
fills the mold chamber 32 up to the level of the upper surface 34
with a portion of the molten metal remaining in the passageway 38
and possibly in the bottom of the crucible cavity 36. The slag formed
in the exothermic reaction collects on top of the metal within the
bottom of the crucible cavity 36.
After the metal has ceased to flow, it freezes and becomes welded
to the worn surface 5' of the hammer head 2 returning the wearing
surface 5 to its original shape and dimension from the bottom of
the hammer eye 3. The molten metal is allowed to cool for about
30 minutes and during this period some of the mold drops off. After
30 minutes, the mold is broken away and the hammer can be removed
from the stand. After further cooling to near ambient temperature,
the gate, extending from the crucible cavity to the mold chamber,
and the sump are fractured off and any remaining excess weld material
can be removed, such as by grinding. The rebuilt hammers are then
checked to assure that the hammers meet the established specifications.
The support frame 10 can be mounted on casters or wheels for ease
in transporting hammers to various work stations.
By using the above exothermic mixture, the weld deposited on the
head 2 for reconstituting the original wearing surface 5 is made
up of about 3% carbon, 0.6% manganese, 1% silicon, 4.5% nickel,
1.5% chromium and the remainder iron. As a result, a hardened wear
resistant material is formed similar to Ni-Hard. The original hammer
which is forged, is heat treated after the forging operation. The
wearing surface rebuilt in accordance with the present invention,
does not require any further heat treatment and provides a wearing
surface with improved resistance to abrasive wear as compared to
the original forged hammers. To date, hammers rebuilt in accordance
with the present invention have been found to have an effective
lifetime of about twice that of the original forged hammers which
In FIGS. 9 and 10 a larger sized hammer 101 is illustrated which
cannot be rebuilt conveniently in the support frame 10 shown in
FIGS. 4-6. The hammer 101 has a starting weight of approximately
230 pounds. Further, it does not have a configuration similar to
the head illustrated in FIGS. 1-3 which would permit the support
of the hammer by the shaped section 6 6a, as shown in FIGS. 1 and
The hammer, elongated in the vertical direction, as viewed in FIGS.
9 and 10 has a head 102 at the upper end, an eye 103 at the lower
end and a shank 104 extending between the eye and the head. The
upper surface 105 of the head is its wearing surface and cooperates
with a housing surface, not shown, for pulverizing different materials.
The upper surface 105 is flat or planar, on both sides of the vertical
center line and then is beveled outwardly and downwardly to the
opposite ends of the surface. From the beveled ends of the surface
105 the sides of the head taper inwardly toward one another and,
closely above the eye 103 the sides extend generally parallel down
to the eye. The eye has a central opening 103a arranged to be mounted
on a shaft, so that a plurality of the hammers can be rotated about
the shaft axis for effecting a breaking or pulverizing action.
As can be seen in FIG. 10 one vertical face of the head 102 and
shank 104 is stepped inwardly as compared to the opposite face.
This inset arrangement is provided to prevent any interference between
adjacent hammers as they are rotated on the shaft.
During use, the wearing surface 105 of the head 102 wears down
as the hammer is rotated. The leading edge of the hammer becomes
worn. The typical wear of the hammer head is shown by the hatched
sections in FIGS. 9 and 10. During operation, as the leading edges
of the hammers become worn to the extent shown by the hatching,
the hammers are reversed on the shaft so that the leading end becomes
the trailing end and gradually the reversed leading end wears down.
When both edges of the hammer have become worn as shown by the hatching
in FIG. 9 the hammers must be replaced.
Because of its weight, the hammer shown in FIGS. 9 and 10 cannot
be handled manually, instead a lifting mechanism must be used to
position the hammer for rebuilding the worn surface 105'.
In FIG. 11 a support frame 110 is shown including horizontal support
members 111 of an inverted channel shape. A vertical support member
113 shown in dashed lines, extends upwardly from the horizontal
support members 111. The vertical support member 113 has a horizontally
arranged pin 115 projecting outwardly from it, with the pin having
a diameter corresponding generally to the diameter of the opening
103a in the eye so that the opening in the eye can be fitted onto
the pin for supporting the hammer in the vertical direction.
Above the pin 115 an adjustment frame 117 is supported on the
vertical support 113 and is of a sufficient size so that it fits
around and is spaced from the shank 104 of the hammer 101. To permit
the placement of the hammer on the support frame 110 within the
adjustment frame 117 one leg 117a, of the adjustment frame is movable
about a pivot axis 117b, so that it can be opened and closed. A
lock pin 118 attached to the opposite end of the leg 117a from the
pivot axis 117b permits the frame to be closed after the hammer
is placed on the pin 115. The frame includes four screws 119 arranged
in pairs on opposite sides of the frame, so that by manipulating
the screws the hammer can be held in a vertical position.
After the hammer 101 is mounted and plumbed on the support frame
110 the mold is ready to be assembled. Initially, as shown in FIG.
12 a graphite plate 126 is supported on the adjustment frame 117
so that it extends around the worn head 110 at a location spaced
vertically below the worn portions 105'. Sealing paste 128 is deposited
on the surface of the graphite plate to form a seal. A two-part
or two-half sand mold 130 is supported on the graphite plate and
completely encloses the sides of the head 102 of the hammer 101.
The interior of the sand mold 130 is shaped to correspond to the
dimensions of the head.
Due to the precise dimensioning of the pin 115 supporting the eye
103 of the hammer, the location of the adjustment frame 117 and
the proper selection of the thickness dimension of the graphite
plate 126 the mold 130 is shaped and dimensioned for returning
the worn surfaces on the head to its original shape and dimensions.
The mold 130 as can be seen in FIG. 12 has inwardly projecting
top surfaces 130a for forming the bevels on the top surface 105
of the hammer. The upper edges of the surfaces 130a define the finished
top surface 105 of the hammer. The mold has an over-flow 131 at
the center between the bevels with the invert of the over-flow located
at the finished top surface of the head 102.
The hammer 101 and the various parts forming the mold are enclosed
by a light gauge steel shell 133 with the upper edge of the shell
spaced slightly below the upper surface of the mold 130. The space
between the inside of the shell 133 the hammer, and the mold, is
filled with loose sand 134 to guard against leakage of weld metal
and to insulate the hammer.
After the arrangement shown in FIG. 12 is completed, the worn hammer
is ready to be rebuilt. In FIG. 13 the hammer and mold are shown
turned 90.degree. as compared to FIG. 12. As distinguished from
the mold arrangement shown in FIGS. 7 and 8 for molding the worn
surfaces of the smaller hammer 1 a separate thermic crucible 137
is spaced above the mold 131 with an outlet 137a closed by a automatic
tapping thimble 137b.
A ceramic pouring cup 139 is located below the outlet 137a and
forms a 90.degree. bend so that the molten mixture can flow out
of the crucible 137 and into the mold 130. The ceramic pouring cup
139 prevents the flow of molten metal from the crucible 137 directly
into the mold, because such direct flow would tend to erode the
worn surface of the hammer.
In the first part of the specification, an example of an effective
exothermic mixture or thermite mixture for larger hammers is set
forth. Such mixture would be filled into the crucible 137 with the
automatic tapping thimble 137b blocking flow through the outlet
137a. After the mixture is ignited it takes about 50 seconds for
it to become molten and erode the tapping thimble and then flow
downwardly through the pouring cup 139 into the mold. The molten
metal fills the upper part of the mold 130 up to the invert of the
over-flow 131. After sufficient molten metal flows into the mold,
any excess will flow out through the over-flow 131 into a catch
basin, not shown.
As with the smaller hammer repair described above, the repaired
larger hammer is allowed to cool and after a given period of time,
the mold is stripped from the hammer, the adjustment frame is opened,
and the hammer is lifted, by means of a lifting device, off the
pin 115. The rebuilt or repaired hammer is then checked to assure
that it meets the established specifications.
While specific embodiments of the invention have been shown and
described in detail to illustrate the application of the inventive
principles, it will be understood that the invention may be embodied
otherwise without departing from such principles.