Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present in~ention relates to a process for the
production of hard metallic cast molded parts with areas of
increased wear resistance that are created by including in the
mold mold bodies tha* cause a local alloying effect with the
castinc~ materials in the casting mold. The present invention
also relates to the use c)f hard cast molded parts of this type
as bueket teeth and/or bucket lips for exeavators.
When ores, rocks or other natural or artifieial
material are moved or reduced, a large number of technical
problems are ereated with regard to the material that is used
for the wearing parts of the tools used in these proeesses.
Partieular problems occur when the material that is to be
reduced, in addition to being very hard, is also very tough.
With regard to materials of this kind, for the reduction of
which tools used up to now made of hard manganese steel lasts
only a short while, the additional reduetion used for further
proeessing is then only economically feasible if the value of
the produet is far greater than the resultlng wear costs
ineurred for any given quantity. The difficulties that are eaused
for the redueing machinery or those of its parts that are
subjeet to wear result, in particular, because of the ~aet that
in addit~on to the frictional loads that occur the material that
is to be broken down also eauses impaet and eoneussion loads on
the wearing parts.
In order to improve the resistanee of heavily loaded
cast parts, it has been proposed that a surface hardening effeet
on those areas that are subjected to large wearing loads ean
be improved by the application of alloying pastes on certain
areas of the mold prior to east~ncJ. This measure, used during
easting, has considerable disadvantages, namely, it is
ineonvenient to use, and uneertain or impreeise with regard
to the extent o~ teehnological improvement, and is slight with
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regard to the depth of the alloy~ ef~ect since only thin la~ers
of paste can be used.
Another measure which is usea with the same purpose,
consists in embeddiny hard portlons in the hollow volume of the
càsting mold, these being surrounded in the filled mold portion
by the matrix of the molding material and then bringing about
a reduction in wear. Even thou~h the effective de~th is I -
considerably greater than that achieved by the use of alloying
pastes, this measure still cannot be regarded as completely
satisfactory since additional steps must be taken, such as the
use of wire netting or suctlon, in order to fix the individual
hardening material grains or pieces in-the hollow portion of the
mold form in order that even distribution is ensured throughout -.
the cast part.
Thus, the present invention reduces or desirably
eliminates these disadvantages and provides a process which
makes it possible to produce wear resistant cast parts with
the necessary combination of hardness and toughness such as to
meet the partlcular demands and thus to produce them in the best
possible manner in the most cost effective way.
According to the present invention there is provided
a process for the production of hard metallic cast molded parts
with.areas of increased wear resistance created by the incorpor-
ation of mold bodies in the casting mold whlch produces a local
alloying effect with a smelt material, characterized in that a
basic metal smelt of hard manganese steel and porous mold bodies
are used, these bodies being formed by the foaming of fine
particle.ferroboron with an aqueous solution of an alkali silicate.
Thus, according to the process of the present invention,
a basic metal smelt consistin~ of hard manganese steel and
a porous mold body is used, this being pr~duced by foaming a fine
grain ferroboron with an aqueous alkall-silicate soluti~n,
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desirably with additional hardening materials mixed in, preferably
in core boxes.
The fact that powdered ferroboron reacts with an
aqueous alkali-silicate solution during foaming thus forming a
porous ~old body is most surpris~ng and has no counterpart in
the behaviour of other iron alloys, e.g., iron manganese, under
similar conditions. The reaction ts accelerated by heating, so
that it appears appropri~te for the production of a mold body
that the foaming takes place at a temperature of at least
approximately 80C. Even though it is preferred that the form
reyuired for the porous mold body is achieved by the use of
suitàble mold boxes during the hardening of the foamed ~ass, the
shaping can also be carried out after the foam has hardened.
It is, of course, understood that the resulting pore volume is
effected primarily by the degree to which the mold is filled
as well as by the concentration of the silicate solution. Even
though the reaction mechanism for the foaming has not been
completely explained, it can be stated that this does not
involve a pyrolitic decomposition.
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The present invention will be further illustrated by
way of the following Examples.
Exam~
A fine grain ferroboron (grain size 0.02 - 0.075 mm)
was mixed with a 30~ solution of sodium silicate to form a viscous
paste. This paste was then used as a filling for approximately
one half of the volume of the core boxes which were used to shape
the bucket teeth. The core boxes were then heated to 120C for
a peri~d of two hours,thus forming the porous mold bodies, in
which the pore size was, on average, 0.7 mm with the pore
volume amounting to approximately 50%. These four mold bodies
were then usea in a so-called "green" casting mold made of silicate
sand for the production of the bucket teeth and secured by means
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of mold nails in such a manner th~t approximately 50% was exposed
relative to the surface area of the tooth sides. Casting was
carried out with a smelt of hard manganese steel at a pouring
temperature of 153C. When used, the bucket teeth produced in
this manner exhibited outstanding stength.
Exam~le 2.,
Mold bodies having a pore volume of approximately 50%,
and measuring 100 x 100 x 15 mm, were produced in a core box
as in Example 1 from a paste-like mixture of an intimate mix
consisting of 80% by weight of the ferroboron described in Example
1, and 20~ by weight ca~borundum (grain size 0.05 - 0.1 mm) with a
30% solution of sodium silicate. These mold bodies were
incorporated in the edge areas of the lips of buckets at equal
distances of approximately 20 mm in the casting mold and secured
thereto with moldnails. Castlng was carried out with a smelt
of hard manyanese steel at a temperature of 1540C. The
excavator buckets that were used-in tin mines and thus exposed
to particularly high rates of wear could be improved several
fold in this manner.
The present invention will be further illustrated by
way of the accompanying drawings in which:
Figs. 1 through 4 are photo micrographs of edge zone
structures (Figs. l to 3) and basic metal matrix (Fig. 4) at
250 x magnification of cast metal parts in accordance with the
present invention.
In order to dem~nstrate the hardness characteristics
of the cast parts produced according to the invention, determined
primarily by the pore volume of the porous ferroboron mold
bodies, the edge alloy zones were examined by means of etching
using a 2~ solution of HNO3 and these were related to the edge
zone structures ~Figs. l - 3) of the structure of the basic metal
matriX of hard mang~nese steel (Fig. 4) shown at a 250 x
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magnification.
Figure 1 shows such a structure obtained by using a
ferroboron mold body having a pore volume of 20% with borideute-
ktikum, in which connection 90% of the ground surface displays
a hardness of 820 - 860 HV. I.n the structure shown in Figure 2
the pore volume of the mold body amounted to 40%; the surface
proportion had 800 ~ 860 HV has been reduced by approximately
50~ whereas the basic mass (Mn-austenite containing boron) was
at 300 HV.. Figure 3 shows a structure in which the pore
~olume amounted to 60~. ~he proportion of the surface at 800 -
860 HV amounted to 30% and the hardness of the basic mass was
also 300 HV. Finally, Fig~ 4 shows the structure of the basic
metal matrix, that is to say hard manganese steel, at the
same magnification; its hardness amounted to 240 HV.`
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