US2067886A - Free piston power hammer - Google Patents

Description

Jan. 19, 1937. BYFQRD 2,067,886

FREE PISTON POWER HAMMER Fil ed Sept. 13, 1935 2 Sheets-Sheet l 9 /,'I6 l la E J- fiforcgbz g g fofd fli Jan. 19, 1937. H. BYFORD FREE PISTON POWER HAMMER F iled Sept. 13, 1935 2 Sheets-Sheet 2 [lg/ENTOR ,Jforqgv By ford ry ATTORN EYS UNITED STATES Patented Jan. 19, 1937 FREE PISTON Power. 11

Application September 13, 1935, Serial No. 40,505

2 Claims.

r lE My present invention relates to the art of power hammers and more particularly to a free piston power hammer.

Many types of electrically driven power hammers have been created each claiming certain advantages. My present type of hammer is that having a reciprocating piston which at the moment of impact is moving freely along its guiding cylinder and which is free to rebound after it has delivered its blow without in any way placing any shock on the mechanism driving it. The general design of my present hammer is such that it is possible to employ a cylindrical striking member so that an even heat treatment can be given the same, something not true of many types of electric hammers. Most electric hammers rely upon a plurality of rapidly delivered light blows to accomplish their purpose. This form of energy delivery is sufiiciently effective for certain types of work, where it is necessary to deliver a heavy blow, as in riveting and demolition work, it is necessary to have in a single striking element enough mass so that a real blow can be delivered as is required in upsetting rivets and in shattering masonry and the like. It follows the general principles that in upsetting metal a heavy hammer is used and in breaking rock a heavy hammer is used. In both of these fields it has been found that even if the same amount of energy is delivered a succession of rapidly delivered, light blows, it is not effective. With my present construction I believe I have overcome the deficiency of this general class of hammers which have been offered in the past.

Another feature that has been widely sought is to provide a percussion tool of this general character which is so constructed that the shock incidental to its operation will not destroy the tool. I have provided in my present design an air cushioning arrangement similar in part to that shown in Patent No. 1,191,948 and an improvement on said patent issued as No. 1,489,312. Each of these patents show a type of hammer similar in certain respects to this present disclosure. It is believed, however, that in my present construction I have provided a tool which can be closely coupled so that it will not be unwieldy for use; which will use the crank shaft in the nature of a cam as distinguished from the type employing a connecting rod arrangement as do the patents listed. With my present arrangement I provide for a considerable reduction in speed between the relatively high speed electric motors which are most efficient in this kind of work and the sleeve cylinder which actuates my piston striker. In this way I am able to employ a relatively heavy striker that gives the striking blow which is so necessary in certain kinds of work.

Figure 1 is an elevation of a tool made after the teachings of my invention, certain parts of which are broken away to better illustrate the construction.

Figure 2 is a vertical, sectional View of the form of tool shown in Figure 1, with the cutting plane revolved 90 degrees.

Figure 3 is a vertical, sectional view through a hammer of a smaller size than that shown in Figures l and 2 and showing a slightly modified connection between the crank shaft and the striker piston.

Figure 4 is a fragmentary, sectional view showing the lower portion of Figure 3 with the cutting plane revolved 90 degrees.

Referring to the drawings, throughout which like reference characters indicate like parts, 6 designates the striker employed in my tool. This, I prefer to form as a cylindrical block of steel to the end that it may be machined and heat treated after the best teachings of air hammer constructions in which a relatively heavy striking piston is employed. By forming the striker as a cylinder the heat treating problem is greatly simplified and a striker of long and useful life can be expected. Striker ii is mounted for limited reciprocation within the striker cylinder 8. This cylinder is preferably closed at its upper end and open at its lower end except for the collar member 9 which is secured in its lower end. This may be secured by screwing the same in place as indicated in the drawings, or in any other suitable manner. This collar is made necessary in my present structure to assure that the piston will be carried upwardly by cylinder 8. For certain uses it may be desirable to insert a renewable striking face as is indicated at iii.

Cylinder 8 is in turn mounted for limited reciprocation within the sleeve housing ll. Housing II is closed at its lower end by an end closure member ii; which in turn is provided with a tool bushing it adapted to accommodate the shank of a suitable tool at it. Cylinder 8 is reciprocated within housing M by the crank shaft 58 which is suitablyconnected to an upward extension of cylinder 8. In Figures 1 and 2, which structure is intended for heavy demolition work or rock drilling, I have shown the connecting means between the crankshaft i8 and the cylinders. Extending upwardly from the top, closed end of the cylinder 3, I provide a central, rigid extension forming a cross head 8' having the rectangular opening 29. Slidabiy disposed within this opening I provide a bearing block having a rectangular exterior surface and a cylindrical interior surface, and comprising two sections 2i and 22, which surround, and coact with, the crank-pin of the crankshaft 58. It will be apparent that the rotating motion of the crank shaft will cause the bearings 2i and 22 to reciprocate transversely of the longitudinal axis of the cylinder along the guideway 20 thus obviating the necessity of a pivot pin or wrist pin of the cylinder. This compact arrangement of parts provides a rugged, string and durable construction adapted for heavy-duty work.

Suitable bearings and gearings are provided to operatively connect the crank shaft 18 with the electric motor 24. In Figures 1 and 2, in order to get a relatively slow acting striker 6, I provided first a worm gear reduction consisting of the worm 26 secured to motor 24, the worm gear 26 which, in turn, drives the pinion 30 which meshes with a gear 3| secured to crank shaft l8.

Suitable, preferably rubber faced, handles 32 and 33 are provided. These are secured to the motor housing at a convenient height for operation and one of the handles 33 is preferably provided with a cam member 34 adapted to operatively engage the operating lever 35 of the electrical switch 36. This serves as a convenient means for connecting motor 34 with the power line 38.

In the modified form of my invention shown in Figures 3 and 4, the same striker mechanism is employed and the piston and housing arrangement in which the cylinder reciprocates is very similar to the heavy type. In this form, however, it is permissible in the smaller forms, as shown, to use a higher striking speed. Consequently the gearing can be simplified and I have indicated a pinion 48 secured to the electric motor W. This gear is, in turn, operatively disposed in engagement with gear 44 which is secured to crank shaft 46.

The cylinder assembly is slightly modified at its upper end. In this modified form I find it desirable to use a built up crank shaft 46 having two end members with crank webs as 4! and 48 and to secure the same together by a stud member 59 which should be suitably keyed within both the web members to prevent either of the webs being angularly displaced with respect to the other. As in the previous forms the cylinder proper has an upward, central, transverse, extension forming an arched yoke as 5| which is machined on a radius struck from the pivot point 52 to form an interior bearing surface 53 and a relatively wide connecting link 54 is provided connecting stud 50 with the pivot or wrist pin 52. Pivot 52 should be provided with ample clearance so that the bearing load for the retraction of the cylinder and piston will occur or be imposed on the bearing surface 53 by head 54 thus relieving some of the strain from the wrist pin 52. This action equalizes the tendency for wear, relieving pivot or wrist pin 52 of the retraction of the load which, with this tool, may be rather heavy where the striker or hammer 6 does not have a tool to rebound from. Suitable switching means is provided at 55 so that the tool will be under easy control of the operator at all times.

Method of operation In operating my tool, after the motor is started, the crank shaft as I8 or 46 is driven at a uniform speed in one direction. As it is driven around each revolution of the crank shaft moves cylinder 8 down to the lower limit of its stroke and then up to its upper limit. Assuming that the piston is at its lower limit when the motor is started; the first action is to carry up the piston or striker member 6, which will be engaged by flange or collar 9. As soon as the cylinder 8 has reached the limit of its travel it will, of course, stop and start downwardly. The striker, however, having considerable inertia will tend to carry on up toward the crank shaft. In so doing it will be checked by an air cushion at the upper end of the piston and the acting as a spring not only stops the striker in its upward movement without jar to the mechanism, but enables it to store up within the compressed air the energy which would otherwise be wasted in destructive force on the device itself. As soon as the striker comes to rest it will be carried down toward the tool bit i6 by cylinder 8 and the energy which has been stored up in the trapped air will also be added to the force imparted to the striker by cylinder 8 and a very effective blow delivered to the tool bit l6. Normally, as soon as the striker hits the bit there is a rebound action which starts striker 6 upwardly. This rebound may not carry the striker up far but it will tend to start it backward and it will then be picked up by collar 9 with the least possible shock to the mechanism. Machine tolerance does not permit of having too close a fit between the striker piston 6 and cylinder 8. Consequently, each time the air is trapped in the upper part of cylinder 8 there is a tendency for part of the air to pass by the striker. To provide against any appreciable loss of air, I have provided the small spring loaded valves 59 and 59 which open on the downward stroke. A resupply of air is provided. by ports 50 which are, in turn, provided with elongated opening 62 to the end that air will be supplied to the crank case proper through a considerable portion of the stroke of the cylinder to the end that sumping will not be affected; it normally being arranged that the piston covers the ports during the major portion of its movement.

The foregoing description and the accompanying drawings are believed to clearly disclose a preferred embodiment of my invention, but it will be understood that this disclosure is merely illustrative and that such changes in the invention may be made as are fairly within the scope and spirit of the following claims:

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a power operated hammer, the combination with a barrel having a crank shaft journaled therein, a cylinder in said barrel having a valve seat in its upper end, an inwardly opening spring pressed air valve in said seat, a freestriking piston in said cylinder, a spring interposed between the piston and the upper end of I I the cylinder, a cross head on the cylinder, and means forming a transversely reciprocating bearing between said cross head and said crank shaft.

2. In a power operated hammer, the combination with a barrel having a crank shaft journaled therein, a cylinder in said barrel having a valve seat in its upper end and an inwardly opening spring-pressed valve in said seat, an annular collar threaded in the lower end of the cylinder, a free striking piston in said cylinder, a slotted cross head on the exterior of the cylinder, a rectangular bearing block reciprocable transversely in said slot, and a spring interposed between the piston and the cylinder.

HORACE BYFORD.

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