US3398801A - Pneumatic impact hammer for rock crushing and pile driving - Google Patents

Description

Aug. 27, 1968 ElMA-rsu KoToNE 3,398,801

PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING Filed Aug. 22, 1966 '7 Sheets-'Sheet 1 ATTORNEY f ISC /IBB INVENTOR EIMATSU KOTONE IZA EIMATSU KOTONE Aug. 27, 1968 PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING '7 SheetsySheet 2 Aug. 27, 1968 3,398,801

PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING Filed Aug. 22. 1966 EIMATSU K OTONE '7 Sheets-'Sheet 5 /w /Zwf //f//W//Z Zwf//////M/// 7%/ Aug. 27, 1968 I-:lMATsu KOTONE PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING 7 Sheets- Sheet 4 v Filed Aug. 22, 1966 FIG. I4B

FIG. I2

FIG, 9

FIG. ISA

FIG. I6

INVENTOR. ElMm-su Komme FIG. IGB

ug 27, 1968 EIMATsu Ko'roNE PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING Filed Aug. 22, 196e '7 Sheets- 'Sheet 5 4 INVENTOR. EnMATsu KoToNE -MW FIG. ISC

Aug 27, 1968 EIMA-rsu KoToNE 3,398,801

PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING Filed Aug. 22, 1966 7 Sheets-Sheet 6 INVENTOR.

EIM ATSU KOTONE Aug. 27, 1968 EIMA-rsu Ko'roNE .3,398,801

PNEUMATIC IMPACT HAMMER FOR ROCK CRUSHING AND PILE DRIVING Filed Aug. 22, 1966 7 Sheets-'Sheet '7 FIG. 2O

INVENTOR. EIMATSU KOTON E Wagga United States Patentl O ice ABSTRACT OF THE DISCLOSURE A pneumatic impact hammer in which the piston is reciprocated in a cylinder which carries an impact tool for limited vibration in one end with pneumatic control means to prevent the impact piston from reciprocating when the tool is in its extended position and this is accomplished by suitable valve means which prevents all except one reciprocation of the impact piston when the impact tool is at the limit of its extended work position to prevent damage to the impact hammer and to the mechanism and also prevents loss of pneumatic pressure.

The present invention relates to pneumatic impact hammers and particularly to an automatic impact hammer -for crushing rough pieces of ores, rocks and the like in mining or excavation works and for driving piles in building construction.

Heretofore, separate mechanisms have been used for pneumatic hammers and for pile driving and such mechanisms have had objectionable features such as being damaged under no-load conditions.

An object of the present invention is to provide a single mechanism suitable as an impact hammer for drilling, rock crushing and the like and also suitable for driving piles.

A further object is to provide an impact hammer which automatically avoids the strains on the hammer construe tion as soon as a no-load condition occurs.

A further object is to provide a cushioning structure which prevents damage tothe hammer on the rst no-load stroke and completely avoids damaging impact after the rst no-load stroke.

A further object is to provide a support for the hammer whereby remote operation can be obtained by the operator of a modified earth-moving machine known as a bulldozer.

A further object is to provide the means for interchanging chisel-type bits and pile-driver-type bits.

Other and further objects will be apparent as the demription proceeds and upon reference to the accompanying drawings wherein:

FIGURE 1 is a vertical section through the cylinder, the tool retainer, the Valve receiving cap and the valve mechanism and the impact absorbing cushion arrangement showing the piston in raised position ready to be driven into impact relation with the bit shown in raised position and in Contact with a stone to be broken.

FIGURE 2 is a horizontal section taken substantially on line 2 2 of FIGURE 1 showing the axial passages completely through the valve box and showing other passages opening inwardly ofthe annular valve box.

FIGURE 3 is a section taken on line 3-3 of FIGURE 1 through the hollow cylinder showing the axial passages for alignment and communication with some of the axially extending passages of the annular valve box.

FIGURE 4 is a fragmentary elevation of the noise-reducing muffler or damper from an outlet in the Wall of the cylinder.

The FIGURES 5 to 8, inclusive, are vertical sectional views similar to FIGURE 1 showing the piston in different positions of operation and showing the inverted cup- 3,398,801 Patented Aug. 27, 1968 shaped piston-type valve in its different operating positions.

FIGURE 9 is an enlarged fragmentary vertical section 'showing the inverted cup-shaped valve in raised position of FIGURE 8 with the piston moving downwardly for the impact stroke.

FIGURE 10 is a bottom plan view of the valve seat guide disc which is positioned on the annular valve box to 'complete the valve casing and showing axially extending apertures for registry with the axially extending passages in the annular valve box.

FIGURE 11 is a section taken substantially on line 11-11 of FIGURE 10 showing the slot and indentation in a circular rib thereof for the axial passage of pneumatic duid. v v

FIGURE 12 is a plan view of the annular valve box showing axial passages for registry with the axially extending apertures of the valve disc of FIGURE 10 which axial passages of the valve box open inwardly and showing a radial opening and axial passage for cooperation with the slot of valve disc of FIGURE l0 and a diametrically opposed slot for registry with the indentation of FIG- URE 10.

FIGURE 13 is a bottom plan view of the valve box.

FIGURE 14 is a section taken on line 14-14 of FIG- URE 12 showing one of the axial passages of the valve box which registers with an axial passage of the valve disc and which opens to the interior of the valve box adjacent the bottom thereof for communication with the lower grooves of the inverted cup-shaped valve.

FIGURE 14A is a fragmentary elevation taken along line 14A-14A of FIGURE 12 showing the radial passages extending completely through the valve box.

FIGURE 14B is a section taken on line 14B-14B of FIGURE l2 showing the axial passage completely through the valve box and which has a radial passage which regiters with the slot in the cover valve disc.

FIGURE 15 is a fragmentary section taken substantially on line 15-15 of FIGURE 13 showing a downwardly opening axial passage with a radial passage for cooperation with a groove of the inverted cup-shaped valve.

FIGURE 15A is a fragmentary elevation of the interior of the valve box showing the axial passages for register with the axially extending apertures in the valve disc and showing the opening to the inner surface of the valve box adjacent the bottom thereof.

FIGURE 15B is a section taken substantially on line 15B-15B of FIGURE 13 showing the radial passages completely through the valve box and showing a di'erent axial passage to the bottom edge of the valve box with a radially extending opening for registry with a diiferent axial passage in the cylinder.

FIGURES 16, 16A, and 16B, are fragmentary sections taken substantially on line 16-16 of FIGURE 15 and lines 16A-16A and 16B-16B of FIGURE 15B, respectively.

FIGURE 16 C is a diagrammatic development of the interior of the cylinder, the interior lof the annular valve 4box and a circumferential section of the valve seat guide disc showing the axial alignment of the axially extending passages and the cooperation of the radial passage of the valve box with the inverted cup shaped valve with external annular grooves and the cooperation of the power piston with radial passages in the cylinder.

FIGURE 17 is a front elevation of the hammer positioned between guiding pillars for driving a pile.

FIGURE 18 is a side elevation with parts in section of the hammer used as a pile driver with the guide pillars omitted.

FIGURE 19 is a top plan View of the hammer used as a v pile driver.

FIGURE 20 is a side elevation of the hammer mounted on a vehicle of the bulldozer type showing how remote control is obtained for the rock crushing or rock drilling tool.

FIGURE 21 is a plan view of the bracket for supporting the hammer from a bulldozer.

FIGURE 22 is a fragmentary rear elevation of one-half of the bracket of FIGURE 21.

FIGURE 23 is a fragmentary side elevation showing one inclined position of the hammer in full lines and another inclined position of the hammer in phantom outline which positions can be obtained by suitable manipulation of the controls of the bulldozer through the brackets which support the hammer.

Brieliy the present invention includes a pneumatic impact hammer mounted on the supporting linkage of a bulldozer as a substitute for the usual earth-engaging blade and the hammer includes a cylinder having a freely slidable impact piston therein for impact abutment against the shank end of a rock-crushing bit or a pile-driving bit, which bit is retained for limited sliding movement in one end of the hammer cylinder and valve means are provided on the other end of the cylinder to provide pneumatic pressure for moving the impact piston in both directions of movement with the valve means cooperating With axial and radial passages in the cylinder and in a cylindrically shaped valve box in axial alignment with the cylinder and the passages therein with a movable inverted cup-like valve element slidable in the valve box to cause the source of pneumatic pressure to be connected with the selected sections of the hammer cylinder to obtain the necessary movement of the impact piston to produce the impact force on the bit used therewith.

Referring more particularly to the drawings a hammer cylinder 1 slidably supports an impact piston 2 having a tapered impact end which is adapted to strike a rockcrushing tool 3 having a circumferential rib 3A spaced from the impact receiving and of the bit and engageable with an inwardly extending lip 4 of a tool retainer 4A whereby the bit may have limited axial movement between engagement of the rib 3A by contacting the lip 4 of the retainer 4A and engagement of the rib 3A with a bushing 5 received in an annular rabbet in the retainer end of the cylinder.

A hollow cap 6 closed at one end and communicating with and mounted on the other end of the hammer cylinder 1 is provided with a passage 6A for pneumatic pressure which communicates with a series of cylindrical shaped chambers 6B, 6C, 6D, and 6F with the chamber 6F communicating with exhaust passages 6G and the inlet 6A having a supply bushing 6H for supplying pneumatic pressure to the chambers.

Between a pair of plates 7, 7 a plurality of rubber-like cushion elements 7A are mounted being held against displacement by plates 7B, 7B secured by screws 7C to one of the plates. Longitudinally extending bolts 8 pass through aligned bolt receiving apertures in the plates 7, cushion sheets 7B, cap 6, hollow cylinder 1, and bit retainer 4A with lock-type nuts 8A being secured to the other end of the bolts 8 and being received in rabbet-like recesses in the bit retainer 4A to maintain the parts in assembled relation and to provide for taking the impact shock of the piston 2 against the lbit 3 when the bit 3 has its rib 3A in abutment with the lip 4 of the bit retainer.

A valve seat guide disc 9 is received in the upper end of the cylindrical chamber 6D and has its lower circumferential surface abutting an annular valve box 10 which is maintained in indexed relation by a pin 10A which assures that axially extending passages 11 in the circumferential portion of the valve guide disc 9 will be aligned with axially extending passages 11A which extend downwardly through the 4valve box and communicate with inwardly extending passages 11B to the interior of the annular valve box 10 where such axial passage 11B is `adapted to cooperate with van inverted cup-shaped valve having a narrow annular groove 12A communicating with an intermediate annular groove 12B and a noncommunieating annular groove 12C. A stem 12D of the inverted cup-shaped valve passes through the valve seat guide disc 9 and into the pressure chamber 6C. A triangular crosssection rib 9A telescopes within the valve box 10 and the disc has a slot 9B on its undersurface and opposed thereto is an indentation 9C for a purpose hereinafter described. The bottom end of the valve box 10 and the bottom end of the cap 6 are received in an externally opening rabbet in the upper end of the cylinder 1 leaving an abutment for preventing the valve 12 which is of greater diameter than the bore lof the cylinder 1 from passing into the cylinder 1 thereby limiting the axial movement of the valve 12.

An upper exhaust port 13 is provided in the wall of the cylinder 1 which is covered exteriorly by a damper or muler 13A which includes a hollow casing having a peripheral ange 13B which is secured to the cylinder by screws 13C. A plurality of batlies 13D, 13D are provided on the interior of the damper in staggered relation so that the gases passing through the exhaust opening 13 will move through a zigzag path to outlet openings 13E. The baffle plates 13D are made of a synthetic resin which is perforated by the addition of a foaming agent when plasticized thereby providing an effective zigzag air passage which bafes the noises emitted from the port 13 and such gases then pass outwardly through openings 13E to the atmosphere with a minimum of noise.

In the operation of the hammer, the piston 2 is initially in the position shown in FIGURE 5 in contact with the bit 3 which is in turn in contact with the objects such as rough pieces of ore, rock or concrete (not shown). In this condition the `weight of the cylinder 1 causes the bushing S to have its lower edge in engagement with the rib 3A and air is delivered to the inlet bushing 6H to a section Z of the cylinder bore by way of an air passage from chamber 6A, 6B, 6C through axial passages 11 in disc 9 and registering axial passages 11A in the valve box 10, the lower ends of such passages 11A being closed by the bottom wall of the valve box 10 with the radially extending port 11B communicating with the narrow circumferential bottom groove 12A since the cup-shaped valve 12 is in its lower position as shown in FIGURE 5 due to the pressure against the center hub 12D. The land 12A separating narrow groove 12A and intermediate groove 12B provides for passage of the compressed -air around the circumferential grooves 12A and 12B to a radial port 14 communicating with an axial port 14A in the valve box which in turn communicates with an axial passage 14B in the cylinder 1 which communicates with an inwardly extending port 14C which communicates `with the space Z beneath the piston 2 thereby causing a relatively high pressure urging the piston 2 upwardly into the region Y of the cylindrical bore which region Y has low atmospheric pressure through the port 13. As the piston moves upwardly the port 13 is closed by the piston but air is released from the section Y through passages including radial opening 15 communicating with axial passage 15A communicating with passage 15B in the valve box which communicates with a radial passage 15C and around the circumferential groove 12C to radially extending passages 15D to the annular chamber 6F and to the atmosphere through passages 6G as shown in FIGURE 6 until the volume above the piston 2 is reduced to that shown at X in FIGURE 6 permitting the piston to be raised above the passage 15.

As the piston moves from the position in FIGURE 5 to that shown in FIGURE 6 air is permitted to pass outwardly through another port 16 communicating with an axially extending passage 16A which communicates with a passage 16B in the valve box 10 to the upper end of the valve box and into communication with a slot 9B in the valve disc through radial opening 16C between the valve disc seat 9 and the top of the inverted cup-shaped valve 12 and through a clearance radial groove 16D which registers with indentation 9C interrupting the rib 9A of the valve seat disc and thence outwardly through the groove 16D to the annular space in chamber 6F surrounding the valve box and thence to the atmosphere through opening 6G.

As the head of the piston 2 is lifted higher than the opening a corresponding reduction in the volume of section X of the cylinder causes an increase of the pressure in section X thereby moving the cup-shaped valve 12 upwardly to the position shown in FIGURE 7 which position of the valve is also shown in FIGURES 8 and 9. The raised position of the valve 12 results in raising the circumferential -groove 12A out of communication with apertures 11B and at the same time brings the lower edge of the skirt portion of the valve 12 above the bottom edges of the apertures 11B and therefore air is not supplied to the narrow circumferential groove 12A but is supplied directly into the bore of the cylinder by Way of the apertures 11 in the disc 9, axial passage 11A in the valve box and radially inwardly extending passages 11B thereby connecting the pressure from inlet 6A directly to the space above the piston thereby causing the piston to move downwardly which is readily permitted since the section W in FIGURE 7 is open to the atmosphere through upper port 13 thereby decreasing the pressure below the piston to atmospheric and the piston is thereby moved downwardly due to its lweight and the pressure in the valve end of the cylinder.

As the piston moves downwardly past the openings 15 down to the opening 16 as shown in FIGURE 8, the air is not released from a section V of the bore to the outlet 6G by way of passage 15, 15A and circumferential groove 12C of the valve since the groove 12C is raised above radial aperture 15C so that the radial aperture 15C is closed with the portion of the cup-shaped valve providing the land between groove 12B and 12C.

When the head of the piston is lowered from opening 16 down to the exhaust port 13 as from the level T down to the level U as shown in FIGURE 8, the air is-released from section V to the outlets by way of an air passage made up with the opening 16, passage 16A, passage 16B in the valve box and the passage formed by slot 9B and passage 16C to the tine clearance between the upper surface of the cup-shaped valve 12 and the valve seat disc 9 and through the clearance between radial channel 16D and the annular space in chamber 6F and thence to the outlet passages 6G whereby preparing the cup-shaped valve for movement to its lower position.

Instantly when the top of piston 2 passes the upper exhause port 13 in its downward movement the air is discharged from section V into the atmosphere through port 13, thereby decreasing the pressure in section V although the piston moves due to its inertia and the remaining pressure in section V until the piston strikes the bit 3.

The discharge of air out of section V into the atmosphere decreases the pressure below the inverted cupshaped valve 12 to substantially atmospheric and because pressure is applied to the upper surface of valve 12 through ports 16, axial passages 16A, 16B and 16C in addition to the pressure applied to the valve stem or boss 12D in the pressure chamber, thereby causing the valve 12 to return to its position shown in FIGURES 5 and 6 so that a new cycle may be started.

As the piston is brought lower than the exhaust port 13 the air is released from a section S in FIGURE 8 to the'outlets 6G by way of passages 14C, 14B, 14A, and 14 to circumferential groove 12B which provides communication between passage 14 and radially extending apertures 14D in the valve box which radially extending apertures 14D communicate with the annular space in charnber 6F and thereby to the outlets 6G and the atmosphere thereby maintaining atmospheric pressure in section S even though the piston is moving downwardly, thereby permitting the piston to continue its high velocity movelll ment until it strikes the bit 3 to crush the object in engagement with the bit and the impact hammer is now in the position for repeating the cycle with the valve 12 moved to its lowered position.

An index pin 10P is received in aligned recesses in the adjacent ends of the cylinder 1 and the valve box 10 to assure proper alignment of the cooperating passages in the cylinder and in the valve box as described above.

As long as compressed gas is fed to the inlet bushing 6H and the bit 3 is in engagement with the work to -receive the impact, the impact piston 2 is driven back and forth in a continuous manner and the expansion lof pressure air through the exhaust port 13 is dampened by the baies 13D so that the noises are kept to a minimum as the gases pass through the baffles which are perforated by the foaming -agent in the formation of the baffles and as the expanding air is deflected and retarded as it moves through the damper 13A and through the outlet holesl 6G whereby the noise is effectively absorbed to keep any noise within tolerable limits.

There is no danger of the hammer being injured during any no-load operation of the hammer. When the bit 3 is in engagement with the work, the bit assumes the position shown in FIGURES l and 5 to ,8, inclusive, and therefore the impact of the piston 2 on the bit 3 results in movement of the bit. However, if the bit is not in engagement with the work, and the piston 2 strikes the bit, the bit is moved to its extended position Where the rib 3A engages the inwardly extending lip 4 of the tool retainer 4A, thereby resulting in a substantial impact force against such lip and the retainer 4A which impact force is transferred by the bolts 8 to the upper plate 7 and the force is cushioned against the cushioning rubber-like sheets 7A and since the bit is not against the work, the bit remains in this extended position with the rib 3A against the lip 4.

The section Z is then opened to the atmosphere through the aligned ports 17 and 17A in the bushing 5 and in the cylinder 1, thereby decreasing the pressure in the area Z to atmospheric and cancelling any pressure difference between the region Z and the region Y in cylinder 1 as shown in FIGURE 5 and therefore the piston 49 is prevented from being lifted upwardly and therefore there is no possibility of a repetition of the no-load stroke.

Upon reference to the diagram shown in FIGURE 16C, the various passages, ports and the cooperating posi.

tions of the grooves of the inverted cup-shaped valve 12 are shown to bring out the cooperation of the various radially extending ports of the valve box with the grooves of the inverted cup-shaped valve thereby more clearly bringing out the relative cooperation of the parts, it being understood that the diagram indicates 4a surface development of the interior surface of the cylinder 1 and of the annular valve box as well as a surface development of the circumferential section of the valve seat disc 9 shown in section. The surface development has been extended beyond the 360 degrees with the intermediate angles shown for the purpose of illustration and to bring out the cooperative relation with respect to the sectional views.

For remote control or operation, the pneumatic impact hammer in accordance with the invention is to be equipped on arms 72, 73 of a shovel loader, power shovel, bulldozer or a similar machine as shown in FIG. 20. The impact hammer 36 is held by the arms-72, 73 by the intermediary of a bracket means in place of a shovel, blade or similar means. As best shown in FIGS. 2l to 24, the bracket means in accordance with the invention comprises a pair of side forks 77, 77 rotatably connected' with the arm 73, a central fork 75 rotatably connected with the arm 72, a lateral bar 76 to fix both the side forks 77, 77 and the central fork 75 on it, a pair of channel holders 74, 74 fixed to the lateral bar 76 and the central fork 75. The channel holders 74 are fastened with the bolts 78, 78 on the flat contacts 64 provided on the wall of cylinder 37. The impact hammer 36 is ready to work on the 4arms 72, 73 of a machine when the channel holders 74, 74 are fastened rmly on the flat contacts 64, 64'. The impact hammer 36 is lifted up and down by the arm 73, tilted ahead and back by the arm 72 as shown in FIG. 22, in a remote control by an operator comfortably sitting on the machine for safe, easy, etlicient crushing operations. The remote control of impact hammer is especially recommendable for crushing rough pieces of rocks or ores following the initial explosion in mining.

The pneumatic impact hammer in accordance with the invention serves quite well as a pile-driver when it is provided with a driving head 68 in place of the chisel 50 which is compatible with it, as shown in FIG. 18. The driving head 68 has a hole 67 to guide the head of a pile 66 shown in dotted line in FIG. 18. Brackets 69, 69 are iixed on the flat contacts 64, 64' of cylinder wall 3S in a manner to embrace a pair of guide pillars 70, 70' at the both sides of cylinder 37 in a freely slidable relation, as best shown in FIGS. 17 and 19. The eyebolt 65 is engaged with a suitable hanger means of an apparatus (not shown) usually employed in building and construction work. In this state, the pneumatic impact hammer 36 is ready for pile-driving in much more eicient and economical way than steam hammers of known practice.

It will thus be seen that the impact hammer in accordance with the present invention is light and compact, safe and economical, yet powerful and eiiicient, in crushing rough pieces of ores or rocks in mining or excavation works while it is tolerably noiseless in discharge of pneu matic pressure, sufficiently protected from damages due to a no-load stroke of hammer, reliably avoiding repetition of such a no-load stroke, and remotely controllable for special operations. Moreover, the impact hammer in accordance with the invention serves quite well as -a piledriver in building and construction work while it is featured with all the above-mentioned advantages.

While a preferred embodiment of the invention has been illustrated by way of example in the drawings and particularly described, it will be understood that modifications may be made in the shown embodiment.

It will be apparent that changes may be made within the scope of the invention as set forth in the valid scope of the appended claims.

What is claimed is:

1. A pneumatic impact hammer for rock crushing and pile driving comprising a hollow cylinder, an impact piston slidably mounted in said cylinder, a tool `mounted in one end of said cylinder, a cap on the other end of said cylinder having a passage for the entrance of pneumatic pressure, passage means for the exhaust of pneumatic pressure, means to maintain the hammer in assembled relation, and valve means pneumatically responsive to the position of the impact piston and the position of the tool to forceably move said impact piston repeatedly against said tool; wherein said cap is a separate member having a plurality of chambers therein with one chamber in communication with the pneumatic pressure entrance and another chamber in communication with the exhaust passage means, a valve guide disc mounted in said cap, a cylindrical valve box abutting said valve disc and said hollow cylinder, a cup-shaped valve slidably mounted in said valve box, said cup-shaped Ivalve having a plurality of annular grooves therein, said valve box having a plurality of axial and radial passages for communication with the grooves of said valve, said valve disc and said cylinder having passages cooperating with the passages in said valve box for conducting pneumatic fluid to opposite ends of said impact piston in timed relation with the motion of the impact piston to produce the hammering action on said tool.

2. A pneumatic impact hammer for rock crushing and pile driving comprising a hollow cylinder, an impact piston slidably mounted in said cylinder, a tool mounted in one end of said cylinder, a cap on the other end of said cylinder having a passage for the entrance of pneumatic pressure, passage means for the exhaust of pneumatic pressure,

means to maintain the hammer in assembled relation, and valve means pneumatically responsive to the position of the impact piston and the position of the tool to forceably move said impact piston repeatedly against said tool; wherein said tool is provided with a rib spaced from the piston impacting end thereof, and a tool retainer having an inwardly extending lip is mounted on the one end of said cylinder to retain the tool in position and prevent the tool from removal, resilient cushion means mounted on the other end of the piston abutting said cap, bolt means extending through said resilient cushion and along said cap, said cylinder and said tool retainer securing said parts in assembled relation whereby when the tool is extended and the piston impacts said tool the reaction of the rib of said tool against the lip of said retainer is absorbed by said resilient cushion.

3. A pneumatic impact hammer according to claim 2, in which an exhaust passage is provided in said cylinder adjacent said one end where the mounted end of the tool is positioned with the tool closing said exhaust passage when the tool is in retracted position, said exhaust passage adjacent said one end of said cylinder being uncovered when the tool is in extended position thereby preventing pneumatic pressure from building up to return the piston to the other end of said cylinder.

4. A pneumatic impact hammer for rock crushing and pile driving comprising a hollow cylinder, an impact piston slidably mounted in said cylinder, a tool mounted in one end of said cylinder, a cap on the other end of said cylinder -having a passage for the entrance of pneumatic pressure, passage means for the exhaust of pneumatic pressure, means to maintain the hammer in assembled relation, and valve means pneumatically responsive to the position of the impact piston and the position of the tool to orceably move said impact piston repeatedly against said tool; wherein said cap is a separate member having a plurality of concentric cylindrical chambers therein, a valve guide disc mounted in one of said chambers and having a central opening therethrough and a plurality of pneumatic pressure passages along the periphery thereof, a hollow cylindrical Valve box mounted in one of said chambers and having axially extending passages with some of said axially extending passages in communication with the passages through said valve guide disc and with others of said axially extending passages opening axially towards said cylinder, said cylinder having axial passages in communication with some of the axial passages in said valve box, said valve box having radial passages extending inwardly from said axially extending passages therein, said cylinder having radial passages extending inwardly from said axial passages therein, said cylinder and said valve box having some passages extending radially completely therethrough, a cup-shaped valve mounted in said valve box and having a plurality of circumferential grooves in selective communication with some of the radial passages of said valve box, pneumatic pressure supply means to said cylindrical chambers, and exhaust passage means extending outwardly from the outer periphery of said valve box, the relation between said passages being such that pneumatic pressure supplied will cause reciprocation of said impact piston against said tool when the tool is in operating position and a single stroke only of the impact piston will occur when the tool is out of its operative position.

5. A pneumatic impact hammer for rock crushing and pile driving comprising a hollow cylinder, an impact piston slidably mounted in said cylinder, a tool mounted in one end of said cylinder, a cap on the other end of said cylinder having a passage for the entrance of pneumatic pressure, passage means for the exhaust of pneumatic pressure, means to maintain the hammer in assembled relation, and valve means pneumatically responsive to the position of the impact piston and the position of the tool to forceably move said impact piston repeatedly against said tool; wherein said passage means for the exhaust of pressure includes a radially extending passage intermediate the ends of said cylinder, and a muler damper is mounted on the cylinder in communication with said radially extending exhaust passage, said y'muiiler having a plurality of small outlet openings distant from said radial passage in said cylinder whereby the exhaust gas noise is kept to a minimum.

6. A pneumatic impact hammer according to claim 2, in which the edge of said valve box abutting said valve guide disc has relieved portions to provide for pneumatic pressure to be applied between the -valve guide disc and the cup-shaped valve, and a stem is provided in said cupshaped 4valve extending through a central opening in said valve guide disc into the pressure chamber whereby pneumatic pressure is applied to said valve stem.

References Cited UNITED STATES PATENTS 747,752 12/1903 Murphy 173-15 1,582,614 4/1926 Kusunoki et al 91-299 2,312,367 3/ 1943 Gartin 91--299 2,773,481 12/1956 Blale 173-135 2,975,846 3/1961 Bodine 173-22 3,032,013 5/1962 Vincent 173-137 3,045,768 7/1962 Huffman 173-137 3,216,511 11/1965 Ladd et al. 173-22 JAMES A. LEPPINK, Primary Examiner.

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