US2660153A - Percussive tool - Google Patents

Description

F. ABT

PERCUSSIVE TOOL Nov. 24, 1953 2 Sheets-Sheet l Filed oct. 25, 195ol l l w,

ig M l/l/lIlI/ll ATTOR N EY F. ABT

PERcUssIvE Toor.

2 Sheets-Sheet 2 Filed OCT.. 25, 1950 Eng EL INVENTOR Ill/ IIIIIIIIIII/II Franz Abt 77 ATTORNEY Patented Nov. 24, 1953 PERCUS SIV E TOOL Franz Abt, Essen-Margarethenhoehe, Germany,

assignor of one-half to Karl Adler, Washington, D. C.

Application October 25, 1950, Serial No. 195,257

Claims priority, application Germany October 28, 1949 4 Claims.

The present invention relates to an arrangement for reducing the recoil of percussive tools such as hammers that are operated by compressed air and especially hammers wherein the lower edge of a multi-stepped tubular valve is used for opening and closing the exhaust ports through which the operating air escapes after the working stroke.

In such hammers the exhaustports extend substantially to the top due to the fact that the relatively short tubular valve is located near the top of the hammer so that only a small compression chamber is available for the returning piston. Such a compression chamber, however, is necessary for absorbing the kinetic energy of the mass represented by the returning piston. If the compression chamber is small, the energy exerted by the returning piston must also be of small magnitude. if the latter were oi great magnitude the compression produced would be excessive and the recoil would be excessive. Therefore, in order to be able to absorb a large amount of piston recoil energy despite the diiiiculties interposed by the nature of the control valve system mentioned above, the control means must be disposed at a deeper point in the cylinder, or, what amounts to the same thing, the compression chamber must be lengthened. lncreasing the compression chamber however reduires the provision of an increased and harmful space, or, what amounts to the same thing, the non-utilized piston stroke will be increased in length because the compression pressure must not be permitted to become excessive.

In order to produce satisfactory hammers despite the presence of compression chambers oi short constructional height, the energy of the returning piston is absorbed, in accordance with the present invention, by causing the returning piston to slide into a cap, hereinafter called a recoil cap, the piston tting in sealing relation in said recoil cap and serving to form a compression chamber therein. The recoil cap is buffered by the pressure medium so that said cap acts as a resilient buffer as soon as the pressure rises excessively or when sudden short pressure surges are produced by the piston in its return travel into the compression chamber of the recoil cap. On the other hand, the recoil cap should be able to travel back along with the piston in order thus to take up any residual kinetic energy still present in the piston which could not be absorbed in the compression chamber of the recoil cap.

Attempts have been made heretofore to absorb the recoil by means of an air dashpot, but the arrangements proposed therefor were not successful nor were they based on the method underlying the present invention.

This divided absorption of the kinetic energy of the returning piston, effected by the incorporation of a recoil cap, serves to reduce the constructional length of the entire controlling mechanism to a substantially greater extent than would be possible if no recoil cap is used, because the greater portion of the energy of the returning piston is used up in moving the recoil cap, so that the compression stroke of said cap can be reduced. It is obvious that the power absorbing capacity of the recoil cap depends on the size of the surface thereof subjected to the pressure medium.

The invention oiiers the following advantages: a. The possibility of absorbing a large amount of piston recoil energy by means of a short effective compression space, thus increasing both the speed of the returning piston and the number of blows struck by the piston without, hcwever, thereby producing more violent recoils.

b. Insuring full use of the piston stroke, thus attaining the most powerful piston blows possible.

c. Achieving the greatest possible economy in air consumption inasmuch as the harmful space needed for compression and disposed ahead of the recoil cap can be kept as small as possible.

d. If the recoil energy of the piston is reduced, that is, due to being expended on softer material, smaller or even no recoil movements will be required of the recoil cap. Consequently the piston stroke will be reduced, the number of blows will increase and the piston blows will become weaker, that is, a hammer having an incorporated recoil cap will automatically increase its stroke and hence its percussive force as the piston return energy increases, that is, as the rebounds become stronger, such as are engendered when harder material is operated on.

Tests made in actual practice have demonstrated the correctness and significance oi the present invention. Thus, in the case of a hammer having a piston diameter1 ci 35 mm. (1% inches) and a piston stroke ci 14o mm. (5l/2 inches), the piston was able to slide rapidly into the recoil cap, the latter being set in motion thereby.

The subject matter of the invention will be illustrated by Way of a number of embodiments.

The invention is shown in the form of several embodiments in Figures l to 8.

In Figs. 1 and 6 no recoil caps are shown in order to facilitate comparison with hammers that are provided with recoil caps. In Figs. 1 to 8, i and 2 represent the tubular valve that closes and opens the exhaust ports 3; the valve is shown in its lower limit position.

In Figs. 2, 3 and 7, li represents the recoil cap of which the area of the at surface 5 acted on by the compressed. air is equal to the pressure affected area of the oppositely facing counteracting surface of the cap. in Figs. 4, 5 and 8, the recoil cap is indicated by '5, the area of the surface 8 thereof acted on by the compressed air being greater than the area of the opposite counteracting surface of the cap since in this case the annular surface i is relieved of air pressure load. The recoil caps li and 'i are continuously acted on by compressed air, entering through passageways il, but in the compression chambers I2 and it, theheight of which is indicated by i6, the reversal of the tubular valves i, 2 is effected at the expense of the kinetic energy of the piston lli. rThe compression-induced pressure in the compression chambers I2 and i3 should not exceed the operating pressure at all or at most only to ight extent. Such excess occurs however in the of ha -ers not preided with recoil caps, such as those shown in Figs. 1 and 6 if the height i5 of the compression chamber is very low and if a great deal of energy is provided by the returning piston. Compression values amounting' to more 15 atmos. atmospheric (214 lbs. per inch) have been observed where the actual operating pressure amounted merely to 6 atmos, above J (85 lbs. per sq. inch). This indicates the tud'e of the recoil.

In the case of the hammers shown in Figs. 2, 3, 4, 5, .7 and 8 any excess compression in the compression chambers i2 and ifi would nieve the recoil caps l and i along with piston iii upwardly at the expense of any residual kinetic energy possessed by the returning piston I4. Although the pressure engendered by compression in the recoil cap s3 is the same as the operating pressure to start with, the compression*induced pressure in the recoil caps 'i increases in accordance with the size ratio prevailing between the area of the pressure-loaded surface 8 and the reduced area of the opposite counteracting surface. Any airengendered blows that vnay occur in the cornpression spaces l2 and it are absorbed by the cushion formed by air entering through the passageways i i. The recoil caps :i and 'l have therefore been shown incorporated in a number of the figures in order to indicate the nature of structure required for keeping the height i@ of the compression chamber as small as possible and to keep the terminal compressional height as harm less as possible. The latter in the case oi an adiabatic compression assumed to taire place in a perfectly cylindrical compression chamber amounts, theoretically, at an operating pressure of 6 atmos. above atmospheric, to about 25% of the aforesaid height, and at an operating presn sure of 4 atmos. in excess of atmospheric, it amounts to about 32% of the heights represented by the numerals i5 and i5 if it is desired that the compression-engendered pressure should be equal to the operating pressure of 6 and 4 atmospheres above atmospheric (85 lbs. per sq. in. and 5'? lbs. per sq. in.) respectively.

Figs. 1 to 5 show a three-step tubular valve l of usual construction and of the reciprocally actuated type; this serves to open and close the operating air exhaust ports 3.

Figs. 6, 7 and 8 show tubular valves of the twostep type wherein the function of the unloading step Va' of the three-step tubular valve I shown in Figs. 1 to 5 is performed by the unloading step it (in Figs. 6, 7 and 8) by having the recoil cap i extend into the two-step tubular valve 2 in air-sealed but sliding relation, a guide bushing is therefor being shown in Figs. 6 and '7, and the recoil cap 'I serving as a control bushing in Fig. ES. The two types of tubular Valves l and 2 operate in similar fashion.

The recoil cap shown herein for preventing recoil and for making it possible to absorb large amounts of the energy of the returning piston is also applicable to all other types of percussive tools including those using control means other than those herein shown.

I claim:

1. In a pneumatic percussive tool having a cyln inder, a piston hammer reciproeabie therein, pressure-actuated reciprocable valve means controlled by the movements of the for controlling the admission of operating pressure to the cylinder on opposite sides of hammer, the combination of a cup-shaped irnperforate recoil cap separate from the valve slideably mounted at the rearward of the cylinder' for compression of air between d can and the returning piston hammer, the n nmer being sealingly tele-scopable within said cap for entrapment of air therebetween in the bowl of said cap, means defining a closed buffer chamber at the rear of said cap, and passageway means constantly providing communication between chamber and the operating pressure to thereby constantly subject the rear of cap to the operating pressure.

2. The structure deiined in claim 1, in which the effective pressure area of the cap exposed. to the operating pressure is greater than the tive pressure area thereof exposed to the air coinpressed between the piston and said cap.

3. The structure deiined in claim 1, in which the valve means is of multi-stepped tubular form with the piston slideable therein, and the recoil cap is telescopingly and sealingly engageabie with the rearward end of the tubular valve mea- 4, rlhe structure deiined in claim 1, in wl the valve means is of two-Step tubul r forin the piston slideable therein, and the c i telescopingly and sealingly engagea'ole within the rearward end of the tubular valve means.

FRANZ References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 727,431 Peck May 5, 1903 996,880 Oldham July 4, 197.1

1,071,263 Robertson Aug. 1913 1,352,191 Henig Sept. '7, 1920 1,460,272 Rehfeld June 1923 1,582,614 Kusunoki et al Apr. 2?, 1926 1,739,338 Wadsworth "Dec, 10,

Images