US2773481A - Percussion tools - Google Patents

Description

ecu 11, 1956 A. BLAKE 9 9 PERCUSSION TOOLS Filed Jan. 14, 1954 IN V EN TOR.

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United States Patent PERCUSSION TOOLS,

Archie Blake, Buffalo, N. Y., assignor to Mechanical Research Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application January 14, 1954, Serial No. 404,115

6 Claims. (Cl. 121-12) This invention relates to percussion tools and more particularly to improvements in percussion tools of the class including pressure fluid operated paving breakers, riveters, air hammers and the like.

' Pressure fluid operated percussion tools are generally powered by a reciprocating piston or hammer slidably mounted in an actuating cylinder provided in the casing.

of the tool. A manually operated valve controls the supply of pressure fluid to the tool and when the valve is opened an automatically operable internal valve structure alternately feeds the pressure fluid for brief periods to the upper and lower portions of the actuating cylinder -to reciprocate the hammer therein. When the hammer has'reached the extreme limits of its movement on the power stroke, it strikes or impacts an anvil, commonly called the tappet, and the impact drives a work member arranged with the anvil for receiving work blows therefrom.

The actuating cylinder of such pressure fluid operated tools has a predetermined capacity or volume and the reciprocating hammer moves within the limits of the cylinder under the influence of the pressure fluid. Where I the pressure of the fluid supply is relatively constant the range of the hammer reciprocations remains relatively constant regardless of the particular material having work performed thereon by the tool. There is then no way to 'vary the stroke length of the hammer and thereby alter slow, heavy blows to the work member, for this impact action is more eflective for breaking such material. On the other hand, if the material is easily fracturable (as for example, thin concrete), it is more desirable to have relatively rapid and lighter impact blows delivered to the work member of the paving breaker by the reciprocating hammer. The rapidity and magnitude of the impact delivered by the hammer to the work member may be varied by altering the stroke length of the hammer. It is apparent then that it is very advantageous to provide control of the hammer stroke length.

There has long been a need in pressure fluid operated percussion tools for means to selectively vary the stroke length of the actuating hammer to meet the individual characteristics of the material having work performed thereon and it is accordingly an object of this invention .to provide in tools of this class means for accomplishing this result. Still another object is to provide means for ,varying thevolume of the actuating cylinder in pressure fluid operated tools so that the stroke length of the actuating hammer reciprocating within, the cylinder can be varied to render the tool more efficient in operation. A further object is that of providing'valve controlled expansion tanks communicating with the actuating cylinder of pneumatic tools so that the eflective volume of the actuating cylinder may be selectively varied to alter the stroke length of the actuating hammer. Further objects and advantages will appear as the specification proceeds.

In the accompanying drawing a longitudinal sectional view of a conventional paving breaker incorporating my invention is illustrated in Figure 1.

The paving breaker illustrated in the drawing is conventional and well-known in the art. However, a brief description of the structure and operation thereof believed necessary for a complete understanding of this invention will be set out.

The drawing shows a pneumatic paving breaker A having a casing 10, a pair of laterally-extending handles 11 in the top thereof, an actuating valve handle 12 adjacent one of the handles 11, a valve assembly 13, a cylinder 14, an actuating hammer or piston 15 mounted for reciprocating movement within the cylinder 14, an anvil or tappet 16 having a portion thereof extending upwardly and into the cylinder 14 for receiving blows from the hammer 15, a spike orv work member 17 equipped with the usual work point (not shown), and a supply fitting 18 for connecting a suitable supply of pressure fluid to the cylinder 14 through the valve assembly 13 and suitable passages in the casing 10.

Customarily the work member 17 is hexangular in shape and is slidably mounted within an appropriate passage-19 provided in the casing 10. The passage is enlarged at 20 to provide clearance for an annular flange 21 with which the work member is equipped. A pivotallymounted, spring biased key or retainer 22 having a protuberance or ear 23 extending into the enlarged passage 20 prevents the work member 17 from accidentally falling from the casing 10, while pivoting of the retainer in a clockwise direction withdraws the car 23 from the pas sage 20, permitting free removal and replacement of the work member 17. For the purposes of this invention,

,7 the work member 17 and tappet 16 may be a unitary structure, but a damaged spike is economically replaced when the parts are separate since the Work member need only be finished roughly, While the tappet for proper operation must have a finished surface.

The tappet 16 has a head 24 integrally formed with an enlarged body portion 25. A downwardlyand outwardly-sloping shoulder 26 connects the head 24 and body 25 and this shoulder is adapted to mate with a corresponding shoulder 27 provided at the upper end of an enlarged passage 28 formed in the casing 10 as an upward extension of the work member passage 19. The upper end of the passage 28 is restricted, and the head portion 24 of the tappet is slidably and snugly received therein, while the body portion.25 is snugly received within the passage 28. In the illustration, the casing 10 is shown in four partsan upper casing or cylinder portion 10a and a lower casing portion or front head 10b, a connector member or tappet seat member 10c located between and joining these parts, and a back head 10d.

The valve assembly 13 is of usual construction and is automatically operable on the pressing of the valve handle 12 to automatically supply the pressure fluid to the upper and lower portions of the cylinder v14 for reciprocating the piston or hammer 15. In one position the valve incorporated at the assembly 13 connects the supply fitting 18 and the lower end of the cylinder 14 through a longitudinally-extending passage 29. Thus, the pressure fluid discharges through the orifice 30 adjacent the lower end of the cylinder 14 and pushes against the bottom of the hammer 15 to force it upwardly in the cylinder 14. Then .thevalve automatically reverses when the rising of. ,the

lower edge of the hammer 15 above the exhaust port 31 which communicates with the exterior by a passage 32 through the side wall of the casing permits the pressure fluid in the lower portion, of, the cylinder 14 to escape. to atmosphere, thus reversiiigthe flow of, pressure. fluidinto the cylinder 14 to deliver. it adjacent the upper end. of the cylinder through an annular inlet 33. Conversely, when the hammer 15 is moved, downwardly until its upper edge haspassed the exhaust; port 31, the valve in the assembly 13' reverses itself again and delivers the pressure fluid through the passage 29 and orifice 30 to the lower end of the, cylinder, while. the pressure fluid in the upper portion of the cylinder is exhausted through the port. 31 and passage32.v

So far the structure described is conventional and well-known in the art and a further description thereof. in.detail is believed unnecessary.

In the operation of this structure a workman grasps the handles 11 and positions the working end of the work member 17 in proper position with respect to. the material to be broken. The workman then depresses the valve handle 12 and because of the described automatic reversing action of the valve pressure fluid is delivered alternately and for brief periods to the upper and lower ends of the cylinder 14 to actuate the hammer or piston 15 in reciprocating motion. Atthe end of each downstroke of the hammer 15 in this reciprocating motion it strikes the tappet 16, and the resulting impact. force. is operative to drive the work member 17 a very small distance into the material being broken. The, reciprocatory cycle is repeated about 1200 times per minute in a typical tool. The rapid blows imparted into the work member 17 are effective to break the material upon which the work is being done.

It may be noted that the hammer 15 never rises on the upstroke to the top of the cylinder 14, but always stops and, reverses its direction of movement at some point spaced below the upper end of the cylinder. The reason for this is that as the hammer 15 rises in the cylinder 14, the volume of the upper portion of the cylinder progressively decreases and the progressively decreasing volume of course provides a progressively increasing pressure, which is sufiicient to stop the hammer at some point below the upper end of the cylinder. The hammer then never strikes the upper end of the cylinder during normal operation of the paving breaker.

It is evident that the hammer 15 reciprocates within determined limits provided by the cylinder 14, and there is no way in which the workman can vary the stroke length of the hammer for the purpose of adjusting the paving breaker action to the characteristics of a specific work material by providing either relatively light or heavy blows as may be most eflicient for the work to be done thereon.

Combined with a conventional paving breaker, as heretofore described, I provide a pair of expansion tanks, 34 and 35 secured to the casing 10. The tanks 34 and, 35 communicate respectively withpassages 36 and, 37,. both of-which are in open communication with a valve chamber 38 provided in an enlargement 39 formed integrally with the side wall of the casing 10. A passage 40 is in open'communication at one end with the valve chamber 38 and at its other end with the upper portion, of the cylinder 14. Preferably, the passage 40 communicates with the cylinder 14 at a point as near the upper end thereof as is physically practical.

Mounted for rotary movement within the valve chamber 38 is a valve 41 that is adapted to block communication between the passages 36 and 37 and the valve chamber 38 when in closed position, and to be selectively moved to open the passage 36 and establish communicationbe tween the tank, 34 and cylinder 14 while still blocking herpassage 37, andalso to. be moved to a seoond. operating: position wherein both of the passages-36 and 37 are unblocked so that both of the tanks are in open communication with the cylinder 14 through the passage 40.

The valve 41 is secured to a link 42 pivotally secured by a pin and slot connection to a lever 43. The lever 43 is pivoted about the pin 43a carried in the casing 10. The lever 43 is pivotally connected at its other end to a strap 44 pivotally joined with an actuating trigger 45. The trigger 45 is equipped at its upper end with a finger grip 46 to facilitate movement thereof. Trigger 45 is biased in the down position by a coil spring 47 coaxially mounted upon a pin 48 extending at one end into a handle 11 and slidably received at its other end within a suitable passage provided in the trigger 45 to permit upward movement thereof. The trigger 45 is provided with laterally-extended flanges 49 slidably received within channel members 50 carried by the casing 10. It is clear that movement of the trigger 50 toward the handle 11 rotates the valve41 to connect: selectively either, the tank 34 or the tanks 34 and 35 with the cylinder 14.

In operation the workman manipulates the paving breaker in the usual manner to accomplish the breaking of concrete slabs or other material. Normally, the trigger 45 will be in the down position illustrated and the valve 41 will be in closed position. In the. event that it becomes desirable to lengthen the stroke of the hammer 15' so that it rises Within the: cylinder 14 to an uppermost position near the top closure of the cylinder for the purpose of increasing the power of the impact between the hammer 15 and the tappet 16, as for example, where the material having work performed thereon is particularly hard, the workman raises the trigger 45 one position so that the valve 41 is rotated to establish communication between the tank 34 and the cylinder 14. The volume of the upper portion of the cylinder 14 is thereby effectively increased, so that the hammer 15 will rise much higher in the cylinder before its movement is stopped by the less; rapidly increasing fluid pressure corresponding to this greater effective volume. The stroke length is thereby increased. Furthermore, if the material is extremely hard or thick, the workman raises the trigger 45 to its uppermost position and thereby rotates the valve 41. to establish. communication between both of the tanks 34- and 35 and the cylinder 14. The, effective volume of the, cylinder is thereby increased by, the amount equal to the two volumes of the expansion tanks, and the hammer 15 will b driven upwardly by the action of the pressure fluid entering the lower portion. of the cylinder through the passage 29 and port 30 to a still higherpoint within the cylinder 14, so, that the stroke length of the hammer 15 is increased toan even, greater extent, andmuch heavier though slower blows are imparted to the work member.

The sizev of thetanks 34 and 35. is small in comparison to the size of the paving breaker and will not add measurably to its overall size. The. capacity of the. tanks may be varied to accommodate them to particular paving breaker designs, andany desiredvariation in the stroke length of the hammer, within the limits defined by the respective locationsof the top and bottom closures of the cylinder,.may be provided by a suitable tank volume. Moreover, any number ofqtanks and combinations of sizes may be provided.

It is seen that Ihave provided a means for selectively varying the volume of the actuating cylinder in pressure fluid operated tools whereby the stroke length of the actuating hammer may be changed as desired to vary the power of the impact between the hammer: and the tappet, so that the operating characteristics of thepaving breaker may be adjusted in relation to the characteristics of each material having work performedupon While in the foregoing specificationI have set forth an embodiment of my invention in considerable detail for purposes, of illustration, it will be apparent: that changes may readily be made by those skilled in the art without departing from the spirit of the invention.

I claim:

1. In combination with a pressure fluid percussion tool having a cylinder and a hammer actuated by the pressure fluid and mounted for reciprocation in the cylinder for actuating a work member, at least one expansion tank communicating through a manually operable valve with said cylinder adjacent the upper end thereof, whereby the stroke length of said hammer is increased when the valve is open and said tank is in open communica tion with said cylinder.

2. In a conventional paving breaker, a casing, said casing providing a cylinder, a hammer mounted for reciprocation in said cylinder and adapted to impart work blows to the work member movably carried in said casing, means for alternately supplying a fluid under pressure to opposite ends of said cylinder to reciprocate said hammer, at least one expansion tank connected to said cylinder at the end thereof most removed from said work member and having a volume sufficient to increase the efiective volume of said cylinder so that the stroke ength of said hammer is increased to increase the magnitude of the blow imparted thereby to said work memher, and a manually operable valve controlling communication between said tank and cylinder.

3. In a conventional paving breaker, a casing, said casing providing a cylinder, a hammer mounted for reciprocation in said cylinder and adapted to impart work blows to a work member movably carried in said casing, means for alternately supplying a fluid under pressure to opposite ends of said cylinder to reciprocate said hammer, at least one expansion tank connected to said cylinder at the end thereof most removed from said work member and having a volume suflicient to increase the effective volume of said cylinder when in communication therewith so that the stroke length of said hammer is increased but not to the point of hammer impact with the upper end of the cylinder, and a manually operable valve for controlling communication of said tank with said cylinder.

4. In a paving breaker having a casing providing a cylinder, and a hammer mounted for reciprocation in the cylinder for impacting a work member carried by the casing, said hammer being reciprocated by the alternate automatic connection of a pressure fluid supply for brief periods to opposite ends of the cylinder, the combination comprising a pair of expansion tanks each connected to said cylinder adjacent the upper end thereof, and a control valve for controlling communication of said tanks with said cylinder, the first of said tanks having a volume such that when in communication with said cylinder the stroke length of said hammer is increased but not to the extent that it impacts the upper end of the cylinder, the second of said tanks having a volume relative to the first of said tanks such that when both are in communication with said cylinder said hammer has an even greater stroke length, said valve being selectively operable to establish communication with said cylinder and the first of said tanks or both of said tanks or to block communication with both of said tanks.

5. In a percussive tool having a cylinder, a hammer reciprocable therein and being adapted at one end of its stroke to impart blows to a work member, means for alternately supplying fluid under pressure to opposite end portions of said cylinder to cause reciprocation of said hammer, tank means adapted to communicate with said cylinder adjacent the end thereof remote from the blow imparting end, and means for selectively establishing communication of said tank means with said cylinder to increase the stroke length of said hammer.

6. The percussive tool of claim 5 in which said tank means are of sufficient volume to cause impact of said hammer with the remote end of said cylinder when the tank means are in communication with said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 1,083,369 LeGendre Jan. 6, 1914 1,804,216 Gustafson May 5, 1931 2,100,541 Gartin Nov. 30, 1937

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