Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to hammers of the
type used in fiberising mills for the production of asbestos
fibers.
Hammers of such type generally have an elongated
shaft provided at a free end thereof with a head adapted
to crush asbestos rocks. The shaft must have sufficient
tensile strength to withstand the revolutionary force to
which it is normally subjected (for example, an average
of 1 000 rpm on a 4 feet radius) while having sufficient
elongation to withstand the shock it receives from the
continuous barrage of rocks being crushed. A minimum
elongation is required in order to overcome the shock and
thus prevent breakage of the shaft. On the other hand,
the head itself must be of sufficient hardness to withstand
the continuous abrasion to which it is subjected. One
therefore, requires a wear-resistant material for the head
so as to provide maximum working life.
In existing hammers, the shaft and head are cast
as a one-piece tool made of only one materialO To ensure
the shaft does not fracture in operation, a material having
sufficient elongation and tensile strength is selected.
This material has a low hardness and wear resistance because
of the properties it was selected for, resulting in the
rapid wear of the head. As a result of such rapid wear,
the hammers have to be changed at short intervals resulting
in high stoppage time and manhours.
It is the object of this invention to obviate
to the above problem and to provide a hammer which has a
much greater working life and thus saves stoppage time and
manhours. The hammer must therefore overcome the clash
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between the requirements of tensile strength and elongation
and those of hardness and wear resistance.
In accordance with the present invention, there is
thus provided a hammer for use in fiberising mills for the
production of asbestos fibers, comprising an elongated
shaft having a coupling end and a free end opposite the
coupling end, and a wear resistant head adjacent the free
end of the shaft and extending along a major portion thereof
towards the coupling end.
A hammer in accordance with the invention is
therefore a two-piece construction in which the wear
resistant head extends along a major portion of the shaft.
This two-piece construction enables one to use on the one
hand any material which provides the necessary tensile
strength and elongation to the shaft and, on the other hand,
any material which provides the necessary hardness and wear
resistance to the wear resistant head.
A preferred embodiment of the invention will now
be described in greater detail with reference to an example
thereof as illustrated in the accompanying drawings, in
which:
Figure 1 is a side elevation view of a hammer for
use in the production of asbestos fibers, according to the
prior art;
Figure lA is an end elevation view of the hammer
illustrated in Figure 1:
Figure 2 is a part sectional side elevation view
of a hammer according to a preferred embodiment of the
invention,
Figure 2A is an end elevation view of the hammer
illustrated in Figure ~;
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Figure 3 is a side elevation showing the shaft
used in the embodiment represented in Figure 2, and
Figure 3A is an end elevation view of the shaft
illustrated in Figure 3.
Referring first to Figure 1, there is shown a
prior art hammer which consists of a one-piece cast tool
comprising an elongated shaft 10 and a head 12. The other
end 16 of the shaft serves as a coupling end and is provided
with an eyelet 18 for coupling the shaft 10 to drive means
(not shown) adapted to rotate the hammer. As best shown
in Figure lA, the head 12 is rectangular in cross-section
and is provided with two longitudinally extending grooves
20 and 20', one on each of the opposed surfaces 22 and 22'.
The grooves 20 and 20' are located on the surfaces 22 and 22'
so as to provide two working impact surfaces 20,24 and
20~,24~ Since the shaft 10 and the head 12 are one-piece
cast and are thus made of the same cast material which
cannot meet at the same time the necessary requirements of
tensile strength and elongation for the shaft and those of
hardness and wear resistance for the head, the head wears
rapidly resulting in frequent stoppage and high manhours.
In order to overcome this problem, the wear
resistant head is made secured over the shaft, thereby
enabling one to select for the wear resistant head a material
providing the necessary hardness and wear resistance inde-
pendently of the material used for the shaft to provide the
necessary tensile strength and elongation. ~hus, in the
preferred embodiment of the invention illustrated in Figure 2,
a wear resistant head 112 is provided which is secured over
a major portion of the shaft 102. The shaft 102 has a
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coupling end 104 provided with an eyelet 106, an inwardly
tapering ~ead section 108 adjacent its free end and a straight
support section 110 contiguous to the head section 108, as
best shown in Figure 3, the head section 108 gradually
tapers towards the coupling end 104 so as to assist the
wear resistant head 112 to remain attached to the shaft.
me wear resistant head 112 which extends entirely over the
head section 108 of the shaft defines the hammer head.
As shown in Figure 2A, the wear resistant head
112 has substantially the same cross-sectional con~iguration
as the prior art head 12 illustrated in Figure lA, and is
thus rectangular in cross-section and is similarly provided
with two longitudinally extending grooves 116 and 116' one
on each of the opposed outer surfaces 118 and 118', The
grooves 116 and 116' are disposed on the surfaces 118 and
118' so as to also provide two working impact surfaces
116,120 and 116',120'. The head section 108 of the shaft
has a cross-section of substantially the same configuration
as the wear resistant head 112 and is provided with two
longitudinally extending grooves 122 and 122', as best
shown in Figure 3A. The head section 108 is symmetrically
disposed within the wear resistant head 112, the ~aper of
the head secti~n 108 of the shaft assisting in the anchorage
of the wear resistant head 112 onto the shaft 102.
As already mentioned, the shaft may be made of any
material which provides the necessary tensile strength and
elongation and the head of any material which provides the
necessary hardness and wear resistance. With respect to
the known required properties, the shaft 102 should have a
tensile strength of at least 20 tons per square inch and an
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elongation of at least 8%.
On the other hand, the wear resitant head 112
should have a hardness of at least 350 Brinnell. As examples
of suitable materials, one may use for the shaft spheroidal
graphite cast iron having a tensile strength of 27 tons per
square inch and an elongation of 12% and, for thé wear
resistant head, Ni-hard cast iron type 2-hi strength
(ASTM specification A532 1 - 13) with a Brinell hardness
of 550.
Using the above materials, a hammer as illustrated
in Figure 2 was made by first casting the shaft 102 and then
casting thereonto the wear resistant head 112, according
to the conventional casting procedures for the materials
utilized. The resulting hammer was thereafter stress
relieved at 450C for 8 hours. This treatment overcomes
the stresses that were induced in the shaft when the wear
resistant head was cast onto the shaft. The hammer so
manufactured has proven to be very successful in that it has
a life tirne of up to five times longer that any known or
existing hammer, while marketed at a competitive price.
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