Impact crushing machine

An impact crushing machine provided with easily repairable strikers fixedly arranged along the circumference of a rotor at regular angular intervals so as to extend radially of the rotor. A plurality of seats fixedly mounted respectively with striking chips formed of a durable hard material such as a hard metal are arranged in lines and rows on and detachably fixed to the radially outer end of the striker for individual replacement. When the striking chip is abraded to an unusable extent, the seat mounted with the worn striking chip and a seat fixedly mounted with an unworn striking chip can be interchanged for the further use of the striker, so that the frequency of replacing the heavy striker with a new one is reduced and the operating cost of the impact crushing machine is reduced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates generally to an impact crushing machine for 
crushing rocklike materials, such as rocks, ores and clinker, and, more 
particularly, to an impactor for such an impact crushing machine, having 
strikers resistant to wear and capable of being replaced by new ones when 
worn out. 
2. Description of the Prior Art: 
FIG. 21 illustrates a conventional impact crushing machine 1. A rocklike 
material fed through a feed opening 2 formed in one side of the upper part 
of the impact crushing machine 1 into a crushing chamber 3 is struck and 
crushed by strikers 6 fixedly attached to the periphery of a rotor 5 
rotatively supported on a main shaft 4. Pieces of the rocklike material 
sent flying by the rotor 5 collide against and are crushed into smaller 
pieces by a liner 7a attached to a first inpact plate liner 7 provided in 
the upper section of the crushing chamber 3. The pieces of the rocklike 
material repulsed by the first inpact plate liner 7 are struck further by 
the strikers 6. Then, some of the pieces of the rocklike material repulsed 
by the first inpact plate liner 7 and struck further by the strikers 6 are 
sent flying again against a liner 8a of a second inpact plate liner 8 
provided in the upper section of the crushing chamber, whereby the pieces 
of the rocklike material are crushed further into finer pieces. 
The conventional impact crushing machine employs solid strikers 6 formed of 
a hard metal such as a high chromium cast iron, a high manganese steel or 
a chromium-molybdenum steel. However, since the rocklike material 
subjected to crushing includes hard mineral pieces, the strikers 6 are 
worn gradually as shown in FIGS. 22(a), 22(b), 22(c) and 22(d) by the 
frequent impact of the hard mineral pieces on the strikers 6. That is, the 
striking end 6a of the striker 6 originally having an angular shape as 
indicated by solid lines in FIG. 22(a) is worn and rounded gradually as 
indicated by broken lines in FIG. 22(b). 
Since it is economically disadvantageous to throw away the striker 6 worn 
in a shape as shown in FIG. 22(b), Japanese Patent Provisional Publication 
(Kokai) No. 58-174245 discloses an impact crushing machine in which the 
worn striker as shown in FIG. 22(b) is turned over for reuse in a position 
as shown in FIG. 22(c) and is used until the same is worn in shapes 
indicated by broken lines in FIG. 22(d) or a worn striker is inverted 
upside down for reuse. 
Japanese Patent Provisional Publication (Kokai) No. 58-15079 discloses an 
impact crushing machine employing strikers each coated with an 
abrasion-resistant ceramic material to improve the abrasion resistance of 
the striker. 
However, since the striker employed in the conventional impact crushing 
machine is not sufficiently abrasion-resistant, the striking end of the 
striker is worn round in a short period of use to strike rocklike pieces 
obliquely deteriorating the crushing ability of the impact crushing 
machine. Moreover, since the striker employed in the conventional impact 
crushing machine is a solid member, the worn striker must be replaced 
wholly by a new one, which requires an increased operating cost. 
Furthermore, the worn striker is replaced by a new one, or is turned over 
or inverted for reuse, for example, every one and half or three months 
when used for crushing rocks to produce aggregate. However, since the 
striker weighs about 100 kg, the replacement of the worn striker with a 
new one, or turning over or inverting the worn striker requires hard work. 
The striker employed in the impact crushing machine disclosed in Japanese 
Patent Provisional Publication No. 58-15079 is provided with a 
abrasion-resistant chip, such as a hard ceramic chip or a hard metal chip. 
However, this striker has problems in that the striker must wholly be 
replaced with a new one when the abrasion-resistant chip is broken and 
that the hard metal chip is expensive and uneconomical. Accordingly, this 
striker is not applied practically to a heavy impact crushing machine. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an impact 
crushing machine provided with strikers which are durable, sufficiently 
abrasion-resistant and can easily be replaced with new ones when worn out. 
In one aspect of the present invention, an impact crushing machine 
comprises a rotor mounted for rotation on a main shaft extended within a 
casing, a plurality of strikers for impinging rocklike pieces, fixedly 
attached to the circumference of the rotor to crush rocklike pieces and to 
send rocklike pieces flying, and a inpact plate liner for repulsing and 
crushing rocklike pieces, extended around the rotor at an appropriate 
distance from the circumference of the rotor. This impact crushing machine 
is characterized in that a plurality of seats are arranged in the axial 
direction of the rotor and are detachably fixed to the extremity of each 
striker, and striking chips formed of a hard material are fixed 
respectively to the seats. 
In another aspect of the present invention, an impact crushing machine 
comprises a rotor mounted for rotation on a main shaft extended within a 
casing, a plurality of strikers for impinging rocklike pieces, fixedly 
attached to the circumference of the rotor to crush rocklike pieces and to 
send rocklike pieces flying, and an inpact plate liner for repulsing and 
crushing rocklike pieces, extended around the rotor at an appropriate 
distance from the circumference of the rotor. This impact crushing machine 
is characterized in that a plurality of seats are detachably fixed to the 
extremity of each striker, the plurality of striking chips formed of a 
hard material are fixed respectively to the seats, and the plurality of 
seats and/or the plurality of striking chips are arranged axially and 
radially of the rotor. 
Since the striking end of the striker which is subjected to the highest 
impact is formed of a hard material, the sectional shape of the striker 
does not change significantly during crushing operation for an extended 
period of time and hence the opening 9 (FIG. 21) between the extremity of 
the striker and the inner end of a chute remains constant. Therefore, the 
dropping of rocklike pieces through the opening 9 is limited to the least 
extent, the crushing ability of the striker can always be maintained 
constant, the positional adjustment of the inpact plate liner, which has 
been necessary every seven to ten days, is not necessary, and abrasion of 
the liner of the impact crushing machine is reduced significantly because 
the rocklike pieces are crushed mainly by the strikers. 
Since the plurality of striking chips formed of an expensive hard material 
are attached to the seat attached to the striking end of the striker 
respectively in the plurality of sections arranged radially and/or axially 
of the rotor, the worn striking chips can be changed individually or can 
be turned over or inverted individually for reuse, which enables the 
economical use of the expensive striking chips. In relacing the worn 
striking chip with a new one or in changing the position of the worn 
striking chips, each set of the striking chip and the seat can be removed 
individually from the rotor and hence the heavy striker need not be 
removed from the rotor, which facilitates replacing the worn striking chip 
with a new one and changing the position of the worn striking chip. 
Accordingly, the positional interchange between the striking chips 
disposed respectively at different specific positions and abraded 
partially with respect to the width due to their positional condition can 
readily be achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1(a) and 1(b), a striker 10, in a first embodiment, 
according to the present invention comprises a body 11 having a recessed 
part 12 having inlet parts 13, a plurality of seats 14, arranged in a row 
respectively fitting the recesses and fixed to the recessed part 12 of the 
body 11, and hard metal chips 15 respectively brazed to the seats 14. The 
seats 14 are detachably fixed to the body 11 respectively with bolts 17. A 
brazing sheet (i.e., a clad sheet formed by cladding both sides of a 
copper plate, respectively, with two layers of silver solder) is used for 
brazing the hard metal chip 15 to the seat 14. The hard metal chip 15 may 
be fixed to the seat 14 by welding, such as pressure welding by HIP, 
electron beam welding or laser welding, or by mechanical means. The inlet 
parts 13 are provided to prevent the seats 14 from being loosened by 
shocks and to prevent the action of a high centrifugal force on the bolts 
17. The bottom surface of the seat 14 is engraved in a shape as shown in 
FIGS. 14(a), 14(b) or 14(c) so that the bottom surface and the inlet part 
13 complement each other. 
The seats 14 respectively holding the hard metal chips 15 are arranged 
axially and radially of a rotor 5. The hard metal chips 15 are classified 
into hard metal chips 15a having a smaller thickness and hard metal chips 
15b having a larger thickness. The hard metal chips 15a are arranged along 
a radially inner line or row and the hard metal chips 15b are arranged 
along a radially outer line or row with respect to the rotor 5. The outer 
corner of each hard metal chip 15b tends to be abraded in a shape 
indicated by a broken line X. When one corner of the hard metal chip 15b 
is abraded to a maximum extent, the seat 14 holding the abraded hard metal 
chip 15b is inverted upside down to use the same hard metal chip 15b until 
the other corner thereof is abraded to an extent as indicated by a broken 
line Y. 
To use both the opposite corners of the hard metal chip 15 by turning over 
or inverting the seat 14 holding the hard metal chip 15, it is desirable 
to form the hard metal chip 15 in a symmetrical shape with respect to the 
vertical or horizontal center line thereof, such as a square shape as 
shown in FIG. 1(b), or a circular shape. It is also desirable to chamfer 
the edges of the hard metal chip 15 in a radius of 4 mm to avoid the 
concentration of stress on the edges of the hard metal chip 15 in crushing 
rocks. Chamfering the edges of the hard metal chip 15 also is effective 
for relieving the residual strain of the corners of the contact surface. 
The hard metal chip 15 may be formed of any suitable hard metal, for 
example, a WC (tungsten carbide) base hard metal containing appropriate 
amount of TiC (titanium carbide, TaC (tantalum carbide), NbC (niobium 
carbide), VC (vanadium carbide), Mo.sub.2 C (molybdenum carbide) and/or 
TiN (titanium nitride). In most cases, Co (cobalt) is used as a bonding 
material. The (life ratio)/(cost ratio) of the hard metal chip formed of 
K20 (JIS B 4104) was greater than one. 
It was found through experimental rock crushing operation that the life of 
the striker 10 employed in the first embodiment was six times that of a 
conventional striker formed of 27Cr cast steel or greater. Since the hard 
metal chip 15 is brittle, the hard metal chip 15 is not absolutely 
unbreakable. Therefore, the number of hard metal chips 15 which would be 
broken was estimated in relation to the amount of crushed rock through 
stochastic calculation using the respective Weibull distributions of the 
strength of rock and that of the hard metal chip, and hard metal chips 
which would be broken were eliminated beforehand through proof tests such 
as load tests. However, only a few hard metal chips were rejected. Thus, 
the accidental breakage of the hard metal chips during the rock crushing 
operation was avoided. 
It was also found through the experimental rock crushing operation that 
crushed rocks produced in the initial stage of the rock crushing operation 
and crushed rocks produced in the final stage of the rock crushing 
operation in which abraded hard metal chips were used were the same in 
particle size distribution, which proved that the crushing ability of the 
striker of the present invention was not deteriorated through the rock 
crushing operation. 
FIGS. 2(a) and 2(b) show modifications of the hard metal chip 15. In the 
modification shown in FIG. 2(a), the thickness of the hard metal chip 15b' 
is varied along the radial direction to reduce the quantity of the hard 
metal forming the hard metal chip, to extend the life of the striker and 
to use only one side of the hard metal chip so that the hard metal chip is 
economized. In such a tapered hard metal chip tapered toward the radially 
inner end thereof, the minimum thickness t is on the order of 3 mm and the 
inclination .theta. of the back surface to the front surface is in the 
range of 3.degree. to 25.degree.. Tensile stress exerted by the impact of 
a rocklike piece on the surface of the hard metal chip having a thickness 
of t can be analyzed by a finite element method and is expressed by 
EQU .sigma.=k(P/t.sup.2) 
where .sigma. is the tensile stress, k is a proportinal constant, and P is 
an impact applied to the hard metal chip by a rocklike piece. Therefore, 
the reduction of the minimum thickness t (FIG. 15) of the hard metal chip 
entails frequent cracking of hard metal chips. From such a point of view, 
various trial hard metal chips varying in the minimum thickness t in the 
range of 2 to 10 mm and in the inclination .theta. of the back surface in 
the range of 0.degree. to 30.degree. were subjected to cracking tests in 
which the circumferential speed of the rotor was 28 m/sec, the size of the 
rocklike pieces was in the range of 0 to 50 mm and crushing rate was 140 
t/hr. 
The results of the cracking test are shown in FIG. 15, in which black 
circles indicate hard metal chips which were cracked to an unusable 
degree, blank triangles indicate those which were partly chipped at the 
edges to a degree which will not interfere with the practical crushing 
operation of the impact crushing machine, and blank circles indicate those 
which were neither cracked nor chipped. As is obvious from FIG. 15, the 
hard metal chips are sufficiently durable when the inclination .theta. is 
in the range of 3.degree. to 25.degree. and the minimum thickness t is on 
the order of 3 mm. More explicitly, all the hard metal chips having the 
minimum thickness of 3 mm and the inclination .theta. in the range of 3 
.degree. to 25.degree. were cracked somewhat on the working surfaces 
thereof. This is due to the reduction of the minimum thickness t to the 
lower limit of the desirable range. All the hard metal chips having the 
inclination .theta. of 25.degree. and the minimum thickness in the range 
of 3 to 7 mm were chipped somewhat. In those hard metal chips, the angle 
.phi. between a tangent f and the joining surface is an acute angle and 
thereby stress is concentrated on the contact point between the upper 
contact surface 23 of the hard metal chip and the body of the striker to 
chip a portion of the hard metal chip in the vicinity of the contact 
point. 
A large inclination .theta. is advantageous in preventing cracking and 
chipping when the minimum thickness t is sufficiently large, because the 
greater the inclination .theta., the greater the thickness of the outer 
end of the hard metal chip. When the inclination .theta. was 3.degree., 
the hard metal chips respectively having a minimum thicknesses of 3 mm and 
5 mm were chipped, while those having a minimum thickness of 7 mm or 
greater were not chipped. When the inclination .theta. was 5.degree., the 
hard metal chips having a minimum thickness t of 3 mm were chipped, while 
those having a minimum thickness t of 5 mm or above were not chipped. 
Thus, it was found that hard metal chips having a minimum thickness t of 5 
mm or above and the inclination .theta. in the range of 5.degree. to 
20.degree. will not be chipped at all. The material forming the trial hard 
metal chips was K20 (JIS B 4104). 
In the striker 10' shown in FIG. 2(a), the radially inner hard metal chip 
15a' is inverted for successive use even if the worn radially outer hard 
metal chip 15b' is replaced with a new one. In the striker 10" shown in 
FIG. 2(b), the radially outer hard metal chip 15b" has a large inclination 
.theta. so that the thickness of the outer end which is subjected to the 
highest abrasive force is increased. However, the acute angle between the 
abraded surface and the joining surface of this chip is liable to be 
decreased rapidly, as compared with those of the hard metal chips of FIG. 
1(a), 1(b) and 2(a), with the progress of abrasion of the hard metal chip, 
which is possible to entail the chipping of that portion. Therefore, in 
the striker 10" of FIG. 2(b), the outer end of the hard metal chip 15b" is 
protruded from the outer end of the seat 14" to prevent the rapid decrease 
of the acute angle. Chamfering the outer edge of the seat contiguous with 
the hard metal chip in a suitable radius also is effective for preventing 
cracking. 
In embodiments of the present invention shown in FIGS. 16(a), 16(b) and 
16(c), the contact surface of a seat 14 also is inclined at an inclination 
.theta.. In this arrangement, the angle of the upper edge of a hard metal 
chip on the side of the seat remains in an obtuse angle even if the hard 
metal chip is abraded progressively, and hence the edge of the hard metal 
chip will not be chipped and the life of the hard metal chip will be 
extended. 
FIG. 17 shows the results of experimental rock crushing operation for the 
rock crushing tests of various hard metal chips 15c varying in a minimum 
thickness t using strikers as shown in FIG. 16(c) varying in the 
inclination .theta. of the contact surface 18c of the seat. In this 
experimental rock crushing operation, the circumferential speed of the 
rotor was 28 m/sec, the size of the rocks was in the range of 0 to 50 mm, 
the crushing rate was 140 t/hr, and the material of the hard metal chips 
15c was K20 (JIS B 40104). 
In FIG 17, blank circles indicate hard metal chips which were neither 
cracked nor chipped, blank triangles indicate those chipped somewhat to a 
degree which will not interfere with the crushing operation of the impact 
crushing machine, and black circles indicate those damaged seriously to an 
unusable degree. 
As is obvious from FIG. 17, an inclination greater than an angle of 
3.degree. limited damages in the hard metal chips to an acceptable extent, 
and a minimum thickness t of 5 mm or above is sufficient when the 
inclination is an angle of 3.degree. or above. However, when the minimum 
thickness is 3 mm, all the hard metal chips were chipped somewhat even if 
the inclination .theta. was greater than an angle of 3.degree., and all 
the hard metal chips were damaged to an unusable extent when the minimum 
thickness was 2 mm. Although the hard metal chips were neither cracked not 
chipped when the inclination .theta. was greater than an angle of 
25.degree., rocks sent flying by the crushing surface 20c impinged against 
the backside of the body of the adjacent striker abrading the backside of 
the body when the inclination .theta. was greater than the angle of 
25.degree.. Therefore, it is not desirable to form the contact surface of 
the seat with an inclination greater than an angle of 25.degree.. 
Referring again to FIGS. 2(a) and 2(b), the respective upper ends of the 
bodies 11' and 11" of the strikers 10' and 10" are abraded in a shape as 
indicated by broken lines while the bodies 11' and 11" are used for an 
extended period of operation, and thereby the bolts 17 respectively 
fastening the seats 14' and 14" to the bodies 11' and 11" are liable to be 
loosened. Therefore, it is desirable, if necessary, to position the bolt 
17 fastening the seat 14' to the body 11' radially inside with respect to 
the center of the seat 14' as shown in FIG. 2(a) or to screw the bolt 17 
fastening the seat 14" to the body 11" in the seat 14" obliquely as shown 
in FIG. 2(b) depending on the kind of the rocklike material to be crushed. 
When all the hard metal chips are the same in shape, all the seats are the 
same in shape and the seats holding the hard metal chips are arranged in 
two lines on the striker as mentioned above, the seats holding the hard 
metal chips and arranged on the radially outer line and those arranged on 
the radially inner line can be replaced with each other, when the hard 
metal chips on the radially outer line have been abraded to an unusable 
degree, to extend the life of the striker. Thus, the hard metal chips 
arranged on the radially inner line serve as spare parts. 
Such an arrangement is possible in the striker 10 of FIG. 1(a) when the 
hard chips 15a and 15b are of the same thickness and the seats 14 are of 
the same thickness. Such an arrangement is possible also in strikers shown 
in FIGS. 3(a), 3(b), 4(a), 4(b), 4(c), 5(a) and 5(b), in which a single 
seat is divided into a plurality of sections arranged symmetrically in two 
or three lines and hard metal chips having the same shape or symmetrical 
shapes are brazed respectively to the plurality of sections of the seat. 
In the striker in a second embodiment according to the present invention 
shown in FIGS. 3(a) and 3(b), a plurality of hard metal chips 21a having 
the same shape are brazed to a rectangular seat 20a in two lines, namely, 
a radially outer line and a radially inner line. Bolts 23a fastening the 
seat 20a to the body 22a of the striker are removed, and then the seat 20a 
is inverted upside down to extend the life of the striker. In this 
striker, the bolts 23a are screwed in the seat 20a in the middle portion 
of the same with respect to the radial width as best shown in FIG. 3(b ). 
Therefore, the distance between the top 24a of the body 22a and the center 
axis of each bolt 23a is sufficiently long. Accordingly, even if the top 
24a of the body 22a is abraded greatly as indicated by a broken line 25a, 
the bolts 23a are not exposed to the impact of rocklike pieces and hence 
the bolts 23a are not caused to be loosened. 
In the striker shown in FIG. 4(a) (FIG. 4(b)), hard metal chips 21b (21c) 
are arranged symmetrically in two lines with the thinner end of each hard 
metal chip 21b (21c) positioned on the side of the line of symmetry so 
that the hard metal chips 21b (21c) are abraded evenly as indicated by a 
broken line. 
In the striker shown in FIG. 4(c), hard metal chips 21d are arranged in 
three lines, and dead stocks 28d indicated by broken lines are formed in 
the gaps 27d between the radially adjacent hard metal chips 21d to 
suppress the abrasion of a seat 20d. 
In the strikers shown in FIGS. 4(a), 4(b) and 4(c), the distance between 
the top of the body of each striker and the center axis of each bolt 23b, 
23c or 23d, similarly to the in the striker shown in FIG. 3(b), is 
sufficiently large, and hence the heads of the bolts 23b, 23c and 23d are 
not exposed to the abrasive action of rocklike pieces. 
FIGS. 5(a) and 5(b) show a striker, in a third embodiment, according to the 
present invention. In this striker, each bolt 23e is inserted through a 
through hole formed in a seat 20e and is screwed in the body 22e of the 
striker. Counterbores 29e are formed in the impact surface of the seat 20e 
to receive the heads of the bolts 23e, respectively. During the crushing 
operation, dead stock 30e is formed in the counterbores 29e to prevent 
abrasion of the heads of the bolts 23e. 
FIGS. 6(a), 6(b) and 6(c) show a striker in a fourth embodiment according 
to the present invention and FIGS. 7(a), 7(b) and 7(c) show a modification 
of the same striker. In this striker, hard metal chips 21f having a 
relatively small width with respect to the axial direction are arranged on 
a radially inner line and hard metal chips 21g having a relatively large 
width with respect to the axial direction are arranged on a radially outer 
line so that the hard metal chips 21f and 21g are arranged in a zigzag 
arrangement. Therefore, dead stocks 30f are formed respectively in gaps 
27f between the adjacent hard metal chips 21f as shown in FIG. 6(c). Thus, 
the quantity of the expensive hard metal chips used in this embodiment is 
less than that of the hard metal chips used in the first embodiment shown 
in FIG. 1(a) by about 15% of the quantity of the hard metal chips used in 
the first embodiment. The life of the striker in the fourth embodiment 
provided with the hard metal chips 21g formed of a hard metal K20 (JIS B 
4104) or a thickness of 15 mm was about ten times that of a conventional 
solid striker formed of a chromium-rich cast steel. 
A striker in a fifth embodiment according to the present invention shown in 
FIGS. 7(a), 7(b) and 7(c) is a modification of the striker in the fourth 
embodiment. In this striker, hard metal chips 21h arranged on a radially 
outer line have a relatively small height, namely, a small vertical size 
as viewed in FIG. 7(a), as compared with that of the hard metal chips 21g 
of the fourth embodiment, and hard metal chips 21i arranged on a radially 
inner line have a relatively small height as compared with that of the 
hard metal chips 21f of the fourth embodiment. Therefore, a relatively 
large gap as compared with that of the fourth embodiment is formed between 
the hard metal chips 21h on the radially outer line and the hard metal 
chips 21i arranged on the radially inner line. As shown in FIG. 7(c), dead 
stocks 30h and 30i are formed over exposed parts not covered with the hard 
metal chips 21h and 21i, so that the abrasion of the exposed parts is 
prevented. In this embodiment, the quantity of the hard metal chips is 
further reduced as compared with that of the hard metal chips of the 
fourth embodiment. The life of the striker in the fifth embodiment was 
substantially the same as that of the striker in the fourth embodiment. 
The quantity of the hard metal used for forming the hard metal chips of 
the fifth embodiment was less than that of the hard metal used for forming 
the hard metal chips of the first embodiment (FIG. 1(a)) by about 30% of 
the latter. 
In each of the foregoing embodiments, the radial size of the gap between 
the hard metal chips arranged on the radially outer line and those 
arranged on the radially inner line is smaller than the radial size of the 
hard metal chips. 
FIGS. 8(a) and 8(b) show a striker in a sixth embodiment according to the 
present invention. In this striker, laterally elongate hard metal chips 
21j are brazed to the radially outermost portion of a seat 20j in three 
lines. Dead stocks 28j are formed as indicated by broken lines in gaps 27j 
between the radially adjacent hard metal chips 21j. The hard metal chips 
21j arranged on the radially outer and middle lines are subjected to the 
abrasive action of rocklike pieces, while the hard metal chips 21j 
arranged on the radially inner line protect a portion of the seat 20j in 
which bolts 23j are screwed. Although the radially inner portion of the 
seat 20j is abraded finally to a surface indicated by an alternate long 
and short dash line in FIG. 8(b), threaded holes for receiving the bolts 
23j are protected by the hard metal chips 21j arranged on the radially 
inner line. 
FIG. 9 shows a modification of the striker in the sixth embodiment. In this 
striker, hard metal chips 21k are arranged in two lines and are attached 
obliquely to a seat 20k relative to the surface of the seat 20k. 
Therefore, the angle .theta. of the upper corner of the abraded hard metal 
chip 21k, namely, the angle between the abraded surface 26k of the hard 
metal chip 21k and the back of the same seated on the recess in the seat 
20k, is large when the hard metal chip 21k is abraded to the maximum 
degree, and hence the upper corner of the hard metal chip 21k is hardly 
chipped. 
In the foregoing embodiments, the hard metal chips are arranged on the body 
of the striker in lines and rows. In practical crushing operation, only 
the hard metal chips arranged on the radially outer line among the hard 
metal chips are abraded intensely while the rest of the hard metal chips 
are scarcely abraded. Accordingly, the hard metal chips need not be 
arranged in a plurality of axial lines if only a crushing function 
matters; a plurality of hard metal chips may be attached to a plurality of 
seats arranged in a single axial line along the outer end of the body of 
the striker or to a single seat having a plurality of sections and 
extended in an axial direction along the outer end of the body of the 
striker as illustrated in FIGS. 10(a), 10(b), 11(a) to 11(c), 12(a), 
12(b), 13(a) and 13(b). 
In a striker in a seventh embodiment according to the present invention 
shown in FIG. 10, a plurality of hard metal chips 21l are arranged in a 
single axial line. Each hard metal chip 21l and each seat 20l are square 
in shape. Therefore, when one edge of the hard metal chip 21l is abraded 
to a maximum extent, the seat 20l can be turned through an angle of 
90.degree. to use a new edge of the hard metal chip 21l. The life of the 
striker in the seventh embodiment was 10 times that of the conventional 
striker formed of high chromium cast iron. As mentioned above, the seat 
and the body of the striker are abraded in shapes indicated by broken 
lines 25b, 25c and 25d in FIGS. 4(a), 4(b) and 4(c). It was found that the 
angles respectively between the abraded surface indicated by the broken 
line 25b and the top 24b, between the abraded surface indicated by the 
broken line 25c and the top 24c, and between the abraded surface indicated 
by the broken line 25d and the top 24d is approximately an angle of 
15.degree.. That is, these broken lines correspond to a falling curve of 
rocklike pieces. FIG. 18 shows the results of experimental examination of 
the falling mode of rocklike pieces. 
FIG. 18 is a graph showing the variation of the depth of abrasion at the 
top of the striker with the quantity of crushed rocklike pieces, hence, 
the duration of crushing operation. As is obvious from FIG. 18, the depth 
of abrasion increases to a value on the order of 27 mm and the angle 
.theta. between the top and the abraded surface increases to an angle of 
15.degree. and the depth of abrasion and the angle .theta. remain constant 
thereafter. Therefore, when the fastening members such as bolts are 
provided on radially inner side relative to the broken line indicating the 
limit of abrasion, the fastening member will not be abraded. Furthermore, 
a bolt fastening the axially outermost seat 14 to the body of the striker 
is positioned axially inside relative to a plane inclined at an angle of 
15.degree. to the surface of a side casing liner 9 and passing the axially 
outer end 20 of the contact surface 19 between the hard metal chip 15 and 
the seat 14 as shown in FIG. 19. 
FIG. 20 is a graph showing the variation of the measured depth h of 
abrasion of the side surface of the striker and that of the measured angle 
.theta. between the abraded surface 21 and the side surface of the striker 
with the quantity of crushed rocklike pieces, hence, with the duration of 
crushing operation when the rotor 5 was rotated at a circumferential speed 
of 28 m/sec for experimental crushing operation. As is obvious from FIG. 
20, the depth h increased to a value on the order of 25 mm and the angle 
.theta. increased to an angle of 15.degree. and remained constant 
thereafter regardless of the material of the body of the striker. 
Accordingly, the bolt will not be abraded when the same is provided at a 
position axially inside the abraded surface 21 inclined at an angle of 
15.degree. to the original side surface of the striker. 
The strikers shown in FIGS. 11(a), 11(b) and 11(c) are designed on the 
basis of such experimental results. A top surface 24m (24n, 24p) including 
those of a seat 20m (20n, 20p) and the body 22m (22n, 22p) of the striker 
(strikers) is inclined radially inward at an angle of 15.degree. to a 
tangent 32m (32n, 32p) to a hard metal chip 21m (21n, 21p) at the upper 
end of the same. Accordingly, the seat 20m (20n, 20p) and the body 22m 
(22n, 22p) are not subject to abrasion, and hence the head of a bolt 23m 
(23n, 23p) fastening the seat 20m (20n, 20p) to the body 22m (22n, 22p) is 
not abraded. Furthermore, since a portion of the seat 20m (20n, 20p) near 
the contact surface between the hard metal chip (21m (21n, 21p) and the 
seat 20m (20n, 20p) is not abraded in a groove, the hard metal chip is 
hardly chipped even if the upper edge of the hard metal chip is abraded 
with a sharp edge, which further reduces the consumption of the hard metal 
chips. 
FIGS. 12(a) and 12(b) show a striker in a eighth embodiment according to 
the present invention. In this embodiment, hard metal chips 21q each have 
the shape of a isosceles trapezoid in a front elevational view and 
disposed with the longer one of the parallel sides flush with the top of 
the body of the striker. Dead stocks 30q are formed in substantially 
triangular gaps between the adjacent hard metal chips 21q. The quantity of 
the hard metal chips 21q used in this embodiment is smaller than that of 
the hard metal chips 21l used in the seventh embodiment shown in FIGS. 
10(a) and 10(b), and is smaller than that of the hard metal chips 15 used 
in the first embodiment shown in FIG. 1(a) by more than 50% of the 
quantity of the hard metal chips 15. Thus, the eight embodiment is very 
economical. Since the exposed surface of a seat holding the hard metal 
chips 21q and fastened to the body of the striker with bolts 23q is 
protected by the head stocks 30q, the seat is not subject to abrasion. 
Thus, in the strikers shown in FIGS. 4(c), 5(b), 6(c), 7(c), 8(b), 11(a) to 
11(c), and 12(b), dead stocks are formed over corners between the radially 
inner surfaces of the hard metal chips and the seats, and the front 
surfaces of the body and the seats to protect the corners from abrasion. 
In a striker shown in FIG. 13(a), as compared with the striker shown in 
FIG. 10(b), the front surface of the upper end of a body 22r is recessed 
in a wider area so as to extend in flush with the contact surface between 
a seat 20r and the body 22r and to extend radially inward from the 
radially inner side of the seat 20r, and dead stock 30r is formed over the 
exposed portion of the front surface of the recessed part to suppress the 
abrasion of the body 22r to the least extent. 
In the foregoing embodiments, each hard metal chip is joined to each seat 
by fusion such as brazing, and the seat is detachably fixed to the body of 
the striker. Accordingly, the worn or chipped hard metal chips can 
individually be changed for new ones by removing the seats from the body 
of the striker without requiring heavy work such as for replacing a 
conventional worn striker by a new one. 
The foregoing embodiments are the application of the present invention to 
an impact crushing machine provided with strikers which are fixedly 
mounted on a rotor. Naturally, the present invention is applicable also to 
an impact crushing machine provided with strikers capable of swinging back 
and forth with respect to the rotating direction of the rotor. 
Furthermore, the hard metal chips may be provided on the front surface of 
both the opposite ends of the body of a striker or on the front and back 
surfaces of one end of the body of a striker in order to use the striker 
in an inverted position. 
As is apparent from the foregoing description, an impact crushing machine 
according to the present invention comprises a rotor mounted for rotation 
on a main shaft extended within a casing, a plurality of strikers for 
striking rocklike pieces fixedly attached to the circumference of the 
rotor, and a repulsing plate extended around the rotor at an appropriate 
distance from the rotor, crushes rocklike pieces by applying an impact to 
rocklike pieces with the extremities of the strikers and the repulsing 
plate, and is characterized in that a plurality of seats are removably 
attached to the extremity of the body of each striker and that a hard 
metal chip is joined to each seat by fusion such as brazing. Therefore, 
only the hard metal chips which are far more abrasion-resistant than the 
conventional strikers formed of a high chromium cast iron are exposed to 
the impact of rocklike pieces, and hence the strikers of the present 
invention can be used for an extended period of operation and thereby the 
period of maintenance is extended remarkably. Since the hard metal chips 
and the seats are arranged individually in lines and rows or in a line, 
each seat can individually be removed from the body of the striker to 
change a worn hard metal chip for a new one, or the seat can be turned 
over or inverted to use an unworn portion of the hard metal chip held 
thereon when the previously working portion of the same hard metal chip is 
worn to a maximum extent, so that the expensive hard metal chips are 
economized. Furthermore, in replacing a worn hard metal chip with a new 
one, only a member having a weight of two to three kilograms including the 
weight of the seat needs to be removed from the striker instead of wholly 
removing, for example, the conventional striker having a weight greater 
than 100 kg from the rotor. Thus, the worn hard metal chip can be replaced 
with a new one through a simple technique without requiring a heavy work. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.