GB2318755A - Hydraulic hammer - Google Patents

Abstract

A hydraulic hammer for driving a pile 1 or other structural element into the soil, has a ram 3 mounted for reciprocating motion in relation to a casing 2. A hydraulic cylinder 4 mounted on the casing 2 has a piston connected with the ram 3. A pump 5 of the hydraulic drive for the hammer has a pressure line 12 and a drain line 13 connected via a hydraulic distributor 6 with the chambers of the hydraulic cylinder 4. The ram 3 has a cavity 8, filled with an elastic fluid medium, which accommodates two (or more) plungers 9,10 projecting from the ram 3 outwards towards the pile cap 7 and pile 1. The plungers 9,10 are concentrically arranged, one or more ring-shaped plungers 10 surrounding a central rod-shaped plunger 9 (and each other), each plunger 9 projecting towards the pile 1 in relation to the adjacent surrounding plunger 10. The cavity 8 of the ram 3 can be communicated with the pressure line 12 of the hydraulic drive via a duct 20. The latter may accommodate a throttle valve 21 or a non-return valve 22, or both arranged in parallel.

Description

2318755 HYDRAULIC HAMMER Percussive-action mechanisms are used for driving

into the soil reinforced concrete piles, steel sheet piles, steel pipes, as well as piles of any other type during construction of piled foundations of buildings and structures.

The problem of preserving piles, particularly reinforced concrete ones, from fracture constitutes one of the most acute problems in pile driving practice. One of the approaches to solving this problem resides in using shock absorbing elements interposed between the impact weight (ram) of a hammer and the axial end of a pile. Normally, shock absorbing elements are manufactured from materials which are milder than steel, e.g. from hard and strong species of wood, asbestos, felt, plastics, etc. (Lubnin V. V., Zaikina VZ- "Machines and Equipment for Driving Piles", Moscow, 1988). However, shock absorbing elements are not durable., they quickly fail. Their failure is quickened due to overheating in the process of their operation because of poor heat conduction of the material of the shock absorbing elements. Moreover, overheating deteriorates elastic properties of the material, thereby making it impossible to achieve stable shock absorbing properties. Short service life of shock absorbing elements affects the overall output of pile driving works.

Also known in the art is a hammer for driving piles (Japanese Patent No. 6147932) using a different more technically up-to-date method for absorbing shocks. This hammer comprises a casing, an impact weight (ram) arranged for reciprocating movement in relation to the casing and having a cavity filled with an elastic medium, and a piston disposed in the cavity and projecting from the ram towards pile. The hammer further comprises a hydraulic cylinder intended to move the ram with a piston rod, and a pump with a pressure line, a drain line, and a hydraulic distributor.

Owing to this structural arrangement, the impact of a blow is significantly reduced, since the energy of a blow is transmitted to a pile over a long span of time because of conversion of the kinetic energy of the rarr. into potential energy of the 2 elastic medium compressed within the cavity of the ram and then into work for driving a pile.

The main disadvantage of the above-cited apparatus resides in the fact that its piston is exposed to considerable impact loads due to "recoil", i.e. in the course of performing work of plunging a pile into the soil owing to the energy of the elastic medium compressed in the cavity of the ram, when the elastic medium compressed by the process of administering a blow in the ram cavity acts upon the piston, brings it (and a pile) up to speed, and strikes it against the lower end of a chamber enclosing the elastic medium.

Another disadvantage of the prior-art hammer resides in leakage of its elastic medium through seals of its piston. Besides, wear and heating of piston seals as a result of friction also represent a certain problem.

It would be desirable to be able to improve reliability and to extend the service life of a hammer by minimizing arising impact stresses, by reducing friction, and by compensating for fluid medium leaks.

The present invention provides a hydraulic hammer for driving structural elements, such as, e.g., piles, the hydraulic hammer comprising a casing, a ram arranged for reciprocating motion in relation to the casing, and a hydraulic cylinder mounted on the casing, the piston rod of which is connected with the ram, the ram comprising a cavity filled with elastic medium. The cavity of the ram accommodates two or more plungers protruding from the ram (towards a pile) said plungers being made in the form of, concentrically arranged, a central rod-like plunger, and one or more plungers surrounding the central plunger (and each other) in such a manner that each plunger projects (towards a pile) in relation to its adjacent surrounding plunger.

It is preferable that the side surfaces of the plungers and the two side of that portion of the ram which envelopes the outer plunger be made cylindrically shaped. Preferably, all the plungers have outward circular projections at the cavity end, while each annular plunger and the ram portion enveloping the outer plunger have circular inward projections at the other end (facing a pile). Optionally, it is possible to place tubular metal sleeves between adjacent plungers and between the outer plunger and the 3 ram, between the outward projection of a male component and the inward projection of a female component.

It is convenient if a pump of a hydraulic drive of the hammer comprises a pressure line and a drain line connected, both of them via a hydraulic distributor, with the cavities of a hydraulic cylinder.

The ram cavity filled with elastic medium can be permanently connected with the pressure line of the hydraulic drive of the hammer. The connection can include a throttle valve, or a check valve arranged so as to direct the fluid flow towards the ram cavity, or a throttle valve and a check valve arranged in parallel.

Surfaces of conjugation of one plunger to another, and those of conjugation of the outer plunger with the ram portion enveloping it can be packed with seals. Equally possible is an alternative embodiment, in which such seals are not used, but, instead, the plungers are separated from the rain cavity by an elastic hermetical diaphragm.

These structural arrangements reduce the energy of a blow administered by each plunger on adjacent enveloping plunger and that of a blow administered by the outer plunger on the inward projection of the ram during recoil, i.e. as the plungers advance from the ram under the effect of pressure of the fluid medium in the ram cavity, as compared with the prior art. This advantageous effect takes place, in the first place, due to a reduction in the weight of each of the plungers as against the weight of a single one-piece piston, and, in the second place, due to a reduced collision speed as a result of a shorter stroke for acceleration of each of the plungers as compared with the length of the distance for acceleration of the one-piece piston. Moreover, tubular metal sleeves interposed between the outward projections of male components and the inward projections of female components absorb shocks, thereby reducing stresses arising.

Provision for a communication passage between the ram cavity and the pressure line offers an extremely important advantage, since owing to this feature the fluid medium in the cavity at an initial moment of a blow is already found under a working pressure, thus permitting an increase of the energy-intensity of the fluid medium. In other words, with equal volumes, compressibility of fluid media used, and energies taken up, the plunger stroke becomes shorter. Besides, the presence of this 4 communication passage makes it possible to compensate possible leakage of the fluid elastic medium from the rwn cavity.

Provision for several plungers produces another beneficial effect, namely: conditions for heat liberation and heat removal are improved for sealing elements provided between the plungers and between the outer plunger and the ram, since the amount of heat liberated during a blow is distributed between two or more seals. Wear of the latter also becomes less intensive. In the alternative embodiment, use of the elastic hermetical diaphragm, adapted to separate the plungers from the ram cavity, permits a drastic reduction in friction and heat liberation.

The present invention will be better understood with the help of the accompanying drawings illustrating specific embodiments thereof, in which:

Figure 1 shows a hydraulic hammer in a longitudinal sectional view; Figure 2 shows a longitudinal sectional view of the lower end of the hydraulic hammer, in a first alternative embodiment thereof, Figure 3 shows a longitudinal sectional view of the lower end of the hydraulic hammer in its initial position, in another embodiment; Figure 4 is a view similar to Figure 3, in the process of administrating a blow., and Figure 5 is a graph showing pile driving force, F, versus movement, S, of the plungers from the initial position of a hammer in accordance with the invention (a solid line) and of the cited prior-art hammer (a dotted line).

Referring to Figure 1, there is shown one embodiment of a hydraulic hammer in accordance with the invention, it is intended for driving into the soil a structural element, such as, e.g., a pile 1, and comprises a casing 2, a ram 3, a hydraulic cylinder 4 for moving the rain 3, a pump 5 with a hydraulic distributor 6, a cap 7 for driving a pile 1, a ram cavity 8 filled with a fluid elastic medium, such as, e.g., liquid, or gas, or a liquid/gas mixture, a central rod-shaped plunger 9, and a ring- shaped plunger 10. The central plunger 9 projects axially (towards the pile) to a valve A in relation to the ringshaped plunger 10 that envelopes the plunger 9, while the ring-shaped plunger 10 projects axially (toward the pile) to a value B in relation to the ram portion enveloping it. A shock-absorber 11 is interposed between the casing 2 and the cap 7, while the hydraulic drive of the hammer comprises a pressure line 12 and a drain line 13.

Figure 2 represents an alternative embodiment of the ram 3 with two plungers, viz. a central plunger 9 and a ring-shaped plunger 10. Both plungers 9 and 10 have circular outward projections 14 and 15, respectively, while the ring-shaped plunger 10 and the enveloping ram portion are provided with circular inward projections 16 and 17, respectively, on the side facing the pile 1. A tubular metallic sleeve 13 is interposed between the outward projection 14 of the central piston 9 and the inward projection 16 of the ring-shaped plunger 10, while a tubular metallic sleeve 19 is interposed between the outward projection 15 of the ring-shaped plunger 10 and the inward projection 17 of the ram 3.

The cavity 8 (Figure 1) of the ram 3 can be communicated with the pressure line 12 of the hydraulic drive via a duct 20. The latter may accommodate a throttle valve 21, or a check (non-return) valve 22, or, arranged in parallel, a throttle valve 21 and a check valve 22, as shown in Figure 1. The plungers 9, 10 are packed with seals 23,24, respectively.

Figure 3 represents an alternative embodiment, in which an elastic hermetical diaphragm 25 is used (instead of the seals 23,24). This embodiment is shown in its initial position in which no blow is administered.

Figure 4 represents the same embodiment as in Figure 3, at the moment of a blow, when the kinetic energy of the ram 3 has become converted, as a result of the blow, into potential energy of the fluid elastic medium compressed within the ram cavity 8. With this, the movement of the plunger 10 in relation to the ram 3 is equal to B, and the movement of the plunger 9 in relation to the plunger 10 is equal to A and in relation to the ram 13 is equal to A + B. In Figure 5, the solid line in the graph shows a hammer according to the invention the dependence of a pressure force F exerted by the fluid medium filling the cavity 8 onto plungers 9 and 10, transmitted onto the cap 7 and, further on,, onto the pile 1, as a function of a distance S to which the plungers are plunged into the cavity 8. The distance S is taken from its initial position, at which there is no impact action onto these plungers. Here the value S corresponds to the stroke of the central plunger 9 to the 6 value A (see Figure 1) and the pressure force onto the central plunger 9 from the fluid medium in the cavity 8 varies from a value F,, up to a value F I, respectively. The value S2 = A + B (see Figures 1, 3, 4) corresponds to a position in which both plungers 9 and 10 are fully retracted into the cavity 8, i.e. they are both flush with the ram 3. In this position, the pressure force exerted by the fluid medium in the cavity 8 onto the plungers increases from F2 up to F3.

For the sake of comparison, Figure 5 shows on the same scale (in chain dotted line) the dependence F = f(S) for the prior-art hammer, with the proviso that for both hammers starting data are equal, i.e. a complete identity of the total surface areas of the axial ends of the plungers 9, 10 and of the piston in the prior-art hammer, identical volumes and properties of the fluid medium in the cavity 8, values of energy compressed by a blow of the fluid medium in the cavity 8 (in Figure 3 this value, taken in the adopted scale, is equal to the area between the axis S and the corresponding graph line). In this case, S2 is the value of movement of the piston into the cavity 8 in the prior-art hammer.

The hammer is operated in the following manner:

At the end of its working stroke, at an initial moment of a blow, the central piston 9 strikes the cap 7, the force F. (Figure 5) on the plunger 9 and on the pile 1 being equal to the product of the working surface area of the upper axial end of the plunger 9 by the initial pressure in the cavity 8 (i.e. the pressure in the pressure line 12). The central plunger 9 plunges into the cavity 8 (Figure 1) to be retracted into the ringshaped plunger 10 to a value A. With this, the pressure force onto the plunger increases up to a value F, because of a pressure rise inside the cavity 8. Further on, both plungers 9 and 10 move as a single whole and slide into the cavity 8 by a value S2 - S, = B until a moment at which the cap 7 abuts against the lower plane of the ram 3. With this, the force at the plungers 9 and 10 will increase from F2 to F3 to become equal to the product of the total axial-end surface area of the plungers 9 and 10 times the corresponding pressure of the fluid medium in the cavity 8, while the rise of the force F will take place along the line C (Figure 5) whose angle of ascent will increase as compared with the preceding stage of the blow.

7 The next stage of this cycle is a "recoil", i.e. a damped unloading process when the velocity of the pile 1 is greater than that of the ram 3. First the plungers 9 and 10 are moved out of the cavity 8 as a single whole (i.e. a reverse movement is effected along the line C by a value B = S2 - SJ up to a moment at which the outward projection 15 of the plunger 10 will come to abut against the sleeve 19 and - through it - against the inward projection 17 of the ram 3. Thereupon, the plunger 9 is drawn out of the plunger 10 until a moment at which the outward projection 14 of the plunger 9 will abut against the sleeve 18. At that moment the pile 1 detaches itself from the plungers and continues to move by inertia, so that its kinetic energy is converted into work of overcoming the soil resistance.

In the case of the prior art hammer, the pile driving process takes place in a similar manner and, obviously, the line C (Figure 5) must be parallel to the line C.

As seen in Figure 5, with a hammer according to the present invention, the energy-intensity of the fluid medium in the cavity 8 is greater since complete movement displacement of both plunger S2 is smaller than the displacement of the one-piece portion S2 of the prior art. Moreover, wear and heating of each of the seals 23 and 24 (Figure 1) of the plungers 9 and 10 are also less than wear and heating of the piston seals in the prior art, since the values of these parameters are proportional to displacement of a seal in the process of administering a blow. In case of A = B, this means, for instance, that S1 = S2 - S1 = 0AS and S2 = 0.8S2.

In the event of using an elastic hermetical diaphragm 25 instead of the seals 23,24 of the plungers 9 and 10 (i.e. using the embodiment of the rain 3 shown in Figures 3, 4), there is a drastic drop in friction during movement of the plungers 9 and 10. The use of the diaphragm 25 is rendered possible due to the fact that, practically, displacements of the plungers 9 and 10 in relation to one another, and those of the outer ring- shaped plunger 9 in relation to enveloping it ram portion are very small. For instance, an embodiment of the hydraulic hammer developed by the ROPAT Design Bureau has a percussive weight of 6 t and three plungers; displacement of each plunger in relation to an adjacent enveloping component is equal to 3 mm, thus providing a sufficient service life for a 12 mm thick rubberized cloth diaphragm.

8 The above-described hydraulic hammer offers an extremely important advantage as regards reduced impact loads onto plungers during "recoil". As is known, kinetic energy is expressed by the formula mv2 12, wherein m is the mass and v is the velocity of a moving object. Then, even if only two plungers are used, the weight of each plunger drops two-fold as compared to the prototype. Besides, the value of v2 for each plunger is proportional to the displacement. Thus, the value Of V2 for the central plunger is equal to 0.8, and for the ring-shaped plunger 0.4, of the corresponding value of the square of the piston velocity in the prior art. In other words, energy of the plungers during recoil is 2.5 times less for the central plunger and 5 times less for the ring-shaped plunger. The fact of using the sleeves 18 and 19 (Figures 2, 3, 4) makes it possible to dampen the recoil energies of the plungers in a smooth way by converting the kinetic energy of the plunger into the energy of an elastically compressed sleeve, thereby drastically relieving impact- induced stresses in the plungers. In practice the desired qualitative characteristics of plunger strength, longevity, and wear resistance, an thermal conditions are achieved with two and more plungers in the first alternative embodiment (i.e. with seals used to pack conjugated surfaces of the plungers), and with three and more plungers in the second embodiment with an elastic hermetical diaphragm.

Consequently, it is possible to achieve the following advantages:

- a drastic reduction of impact-induced stresses arising in plungers during cc remil" by minimizing the recoil energy of plungers and absorbing these shocks; - lower wear and heating caused by friction of seals of pistons; - automatic compensation for leaks from the shock-absorbing cavity of the ram.

9

Claims (9)

CLAIMS:

1. A hydraulic hammer comprising a casing, a ram arranged for reciprocating motion in relation to the casing, and a hydraulic piston and cylinder device mounted on the casing and having a piston rod connected with the rain, an interior cavity of the ram being filled with an elastic fluid medium amd housing two or more plungers projecting axially from the rain, the plungers being concentrically arranged, each plunger projecting axially in relation to an adjacent surrounding plunger.

2. A hydraulic hammer as claimed in claim 1, wherein each plunger has an outward projection at the end adjacent the ram cavity, and wherein each plunger, except the central one, as well as the ram portion surrounding the plungers, has an inward projection at the end remote from the ram cavity.

3. A hydraulic hammer as claimed in claim 2, wherein in each conjugation of adjacent plungers and in the conjugation of the outer plunger with the surrounding rain portion, a metallic sleeve is interposed between the outward projection and the inward projection.

4. A hydraulic hammer as claimed in any preceding claim, further comprising a hydraulic drive pump and a drain line connected with the hydraulic piston and cylinder device via a hydraulic distributor.

5. A hydraulic hammer as claimed in claim 4, wherein the ram cavity is communicated with the pressure line of the pump.

6. A hydraulic hammer as claimed in claim 5, including duct means for connecting the rain cavity with the pressure line, the duct means including a throttle valve, or a cheek valve arranged in such a manner as to direct the fluid flow towards the ram cavity, or both the throttle valve and the check valve arranged in parallel.

7. A hydraulic hammer as claimed in any preceding claim, including sealing elements between conjugated surfaces of adjacent plungers and between conjugated surfaces of the outer plunger and the surrounding ram portion.

8. A hydraulic hammer as claimed in any preceding claim, wherein the plungers are separated from the rain cavity by an elastic hermetical diaphragm.

9. A hydraulic hammer substantially as described with reference to, and as shown in, Figure 1, Figure 2, or Figures 3 and 4 of the accompanying drawings.