GB2472665A - A hydraulic pile driver with cushions to reduce impact noise - Google Patents

Abstract

A pile driver includes an anvil 26, a reciprocating mass 11, a cushion 28 and a casing 1. The mass is lifted by hydraulic means 15, 17 and released to impact the anvil via the cushion. The casing is open ended and maintains the alignment of the various components. The anvil and/or the mass may be provided with an annular bearing ring 27 which presses against the casing throughout the motion of the mass to reduce vibration and noise.

Description

I

Noise Reduction in Hydraulic Piling Hammers The present invention has been divided out of application number GBO9 14052.6 filed on 12 August 2009.

Hydraulic piling hammers use a reciprocating mass to repeatedly strike an anvil, located on the head of an elongate pile, for the purpose of driving said pile into the ground to form part of a foundation. The reciprocating mass is lifted by hydraulic means and dropped predominantly under the influence of gravity. The vertical distance through which the mass is lifted may be varied by a control means in order that the energy imparted to the pile can be varied, within limits, to suit the pile type, the ground conditions and the intended working load of the pile. The reciprocating mass and the anvil are both slidably located in an appropriate axial relationship by a casing that is itself slidably located on a mast, or leader, in order that the whole assembly may follow the movement of the pile as it is driven into the ground.

There is a large and growing market for light-duty driven piles for the support of industrial sheds, domestic property, retail premises, health centres, etc. on brown-field sites. Piles of this type are frequently required to be driven adjacent to existing domestic and commercial property, so there is considerable interest in reducing noise levels and ground quake to a practical minimum. Piles may be formed from thin-wall hollow steel sections, filled with concrete after being driven to depth, or may be of pre-cast concrete construction with minimal embedded steel reinforcement.

Such piles are easily damaged by an excessively high driving force or by a driving force that rises too steeply at impact. In recognition of that fragility and the need to reduce quake it is common practice to fit a relatively soft resilient driving cushion to the impacting face of the anvil, and to use a relatively large reciprocating mass falling through a relatively short distance; the energy at each impact is maintained, but the lower velocity at impact is kinder to the pile. Further, the reduced movement of the reciprocating mass results in a useful increase in the number of impacts achievable in a given period of time. However, if the size of the machine supporting the piling hammer is not to be increased, then any increase in the weight of the reciprocating mass must be offset by an equivalent reduction in the weight of the remainder of the hammer components, principally the hammer casing. Unless preventative measures are taken, simply removing metal from the casing is likely to increase the operating noise level.

The object of the present invention is to provide a piling hammer, employing a relatively heavy reciprocating mass operating within a light-weight casing, with an improved means of damping any vibration of the hammer casing that may occur as a result of normal working impacts and impacts with the casing itself resulting from lateral movement of the internal sliding members within their normal working clearances. Although the invention relates primarily to piling hammers having an energy rating of between 6 kJ and 70 kJ and which are used for driving light-duty piles (as defined hereinbefore) the principles involved may be applied more generally.

A detailed description of one embodiment of the invention now follows, by way of example only, with reference to the accompanying figures of which: Figure 1 is an external front view of a 56 kJ piling hammer according to the present invention.

Figure 2 is a cross-sectional elevation of the piling hammer shown in figure 1, but rotated 45 degrees about a vertical axis, in which the internal components are positioned appropriately to represent the hammer being suspended and out of use.

Figure 3 is an enlarged cross-sectional elevation of the upper half of the piling hammer shown in figure 1, in which the internal components are positioned appropriately to represent the hammer being located on the head of a pile with the reciprocating mass resting on the driving cushion.

Figure 4 is a cross-sectional elevation of the lower half of the piling hammer shown in figure 3.

Figure 5 is an enlarged view of part of figure 4, showing the striking face of the reciprocating mass, the driving cushion, and the head of the anvil.

With reference to figures 3 and 4, the upper housing of the piling hammer consists of a cylindrical steel shell 1 fitted with flanges 2 and 3 at the top and bottom respectively to provide for bolted connections to the lid 4 and to the lower housing assembly. Below the upper flange 2 are four equally spaced openings 5 through which air is drawn into, or discharged from, the space above the reciprocating mass.

The vertical position of the openings 5 is such that as the reciprocating mass reaches the limit of its nominal maximum upward movement, the openings are closed off. The volume of air trapped above the reciprocating mass then acts as a cushion to reduce or prevent direct impact with the lid 4 in the event of maladjustment of the control system. Each opening communicates with a vertical duct that serves to transfer air between the spaces above and below the reciprocating mass.

The thickness of the steel shell need only be sufficient to allow its internal diameter to be machined to an appropriate geometrical tolerance and surface finish. The air ducts provide significant stiffening, allowing the shell material to be thinner than would otherwise be the case. It is perfectly acceptab!e to manufacture the shell by rolling and seam welding, and the internal machining operations need only achieve about 80% cleanup. It may further simplify and cheapen manufacture to divide the housing into two parts joined by bolted flanges 9 and 10. The design of the reciprocating mass is such that, as will become apparent later, the two parts of the housing may be held in acceptable alignment by commercial quality bolts passing through drilled holes in the flanges; there is no need for fitted bolts or a machined spigot.

A number of ancillary items need to be attached to the upper housing: guides (not shown) to allow the housing to be slidably restrained by the mast or leader; a lifting point or rope pulley (not shown) to allow the piling hammer to be bodily raised and lowered relative to the mast or leader; and pile-handling equipment (not shown) typically consisting of a small winch and rope management rollers or pulleys. All of these items will subject the upper housing to high concentrated loads that necessitate the use of appropriate reinforcement to avoid local distortion and over-stress. To save weight the two rear duct structures may be adapted to provide the reinforcement necessary to attach the guides, and the two front ducts may form part of the reinforcing structure necessary to support the winch system.

To minimise the physical size of the reciprocating mass it is constructed from a fabricated steel shell 11 filled with lead 12 poured-in in a molten state. The periphery of the reciprocating mass is for the most part left as fabricated with a nominal radial clearance in the upper housing of about 5 mm, but is accurately grooved in two places to allow the fitting of annular rings 13 of a proprietary self-lubricating hard-wearing non-conductive bearing material of low coefficient of friction. Minimising friction is particularly important if the hammer is to be used for driving inclined piles.

The annular rings 13 also serve to provide a measure of pneumatic sealing between the reciprocating mass and the upper housing assembly to ensure that movement of the reciprocating mass is able to effectively displace the air in the spaces above it and below it. If the upper housing assembly is manufactured in two parts (joined by flanges 9 and 10) then the joint is positioned such that neither of the annular rings 13 have to pass over it; a small miss-alignment at said joint is then of no consequence.

Rebound of the reciprocating mass from the driving cushion is unlikely to be perfectly true, ordinarily causing the reciprocating mass to rattle against the inner wall of the upper housing within the limits imposed by its normal working clearance, That has been overcome by urging the annular rings 13 outwards into continuous contact with the inner wall of the casing by the use of partially compressed resilient 0' rings 67 fitted into annular grooves in the reciprocating mass as shown in detail in figure 5. In that way the reciprocating mass is positively centralised within the housing, and any tendency to rattle is greatly reduced.

To reduce the height of the hammer the centre of the weight is provided with an upper recess 14 to accommodate the body 15 of the hydraulic lifting cylinder. The hydraulic lifting cylinder rod 17 is attached to an intermediate plate 16, and a lower recess 18 provides access. The cylinder rod 17 is attached by a castellated nut 19 via steel disks 20. In accordance with common engineering practice, misalignment caused by a build-up of manufacturing tolerances and operating clearances is accommodated by resilient disks 21.

The upper housing assembly is closed by lid 4 of shallow conical form, to resist deflection under load, and to which is attached the body of the hydraulic lifting cylinder 15 via steel disks 24, resilient disks 23 and castellated nut 25. The resilient disks serve the same purpose as those fitted to the cylinder rod attachment.

Preferably the hydraulic lifting cylinder is of the double-acting type and is fitted with a secondary outer tube, both to provide a low resistance annular path for oil entering and leaving the cylinder's lower chamber, and to avoid the possibility of distortion of the primary cylinder tube by loads transmitted through the cylinder mounting. The hydraulic circuit and its control mechanism follow established practice.

With reference to figures 4 and 5, the lower end of the upper housing assembly guides the head 26 of the anvil via a combined annular bearing and damping ring 27, pressed into contact with the internal surface of the upper housing by partially compressed resilient 0' rings 67 best seen in figure 5. The driving cushion 28 rests on top of the anvil head 26, held in position by a flanged retaining tube 29 secured to the anvil head by bolts 30. The outer edge of the anvil head 26 supports an upstanding annular ring 31 of height greater than the thickness of the driving cushion. The lower outer edge of the reciprocating mass is machined back to provide a shoulder 32 dimensioned such that in normal use the reciprocating mass does not under any circumstances compress the driving cushion sufficiently for the shoulder 32 to make contact with the upper face of the annular ring 31. As the cushion deteriorates with prolonged use it is subject to a measure of permanent set, so the minimum separation between the ring 31 and the shoulder 32 will gradually reduce. Since the reciprocating mass is electrically isolated from the upper housing, any significant reduction in the separation can be detected by suitable electronic n-ieans and used to operate a service indicator.

The driving cushion 28 and the anvil head 26 are perforated with a plurality of passages 33a, 33b and 33c to allow the through-flow of air displaced by the movement of the reciprocating mass. (The passages are shown aligned along a common diameter for illustrative purposes only.) The anvil head 26 is fitted with a number of locating pins 34 that engage with slots 35 in the driving cushion 28 to ensure that the cushion and the anvil head remain in proper angular alignment. The back and forth passage of air as the reciprocating mass lifts and falls provides for the forced removal of heat generated within the driving cushion material as a result of its repeated vertical compression. Any excess of air not required for cooling is passed through a central orifice in plate 36. In the preferred arrangement shown, the upper surface of the anvil head 26 is slightly concave. The method of attachment of the driving cushion 28 ensures that said cushion follows that contour.

Preferably the anvil assembly is of two-piece construction. The anvil proper, shown best in figure 4, comprises anvil head 26 connected to a substantial flange 48 by a simple tubular member 68. It operates in conjunction with a driving dolly comprising outer and inner tubes 46 and 47, closed at the top and shaped to fit loosely within the recess in the underside of the anvil proper. The anvil and driving dolly are bonded together via a layer of suitable resilient material cast-in-situ during manufacture. To simplify manufacture the various air passages that have to pass through the resilient layer may be drilled after curing rather than prior to casting. The lower end of the driving dolly is machined with a wide groove into which is fitted a substantial annular bearing 49, which may preferably take the form of two semi-circular shells. The axis of the pile being driven is unlikely to be perfectly aligned with the axis of the driving dolly, resulting in the dolly being urged to move laterally, within its working clearance in the lower housing, at each impact, generating noise.

That problem has been significantly reduced by the use of partially compressed resilient 0' rings, fitted into annular grooves in the dolly, in order to urge the bearing shells 49 outwards into continuous sliding contact with the housing. Both the outer and the inner tubes of the driving dolly are perforated in order that cooling air passing through the various passages in the anvil head 26 can be re-combined in, or be drawn from, a common annular chamber below the anvil flange 48. The bottom end of the anvil stem is closed by a substantial plate fitted with suitable means to readily attach a variety of locating sockets 50 dimensioned to suit the different sizes and types of pile to be driven. Suitable attachment means may include bolts 51 in combination with locating pins 52.

The lower end of the upper housing assembly is partially closed by a pair of substantial semi-circular plates 37 which, when fitted in their working positions, provide a central opening through which the driving dolly descends with a generous working clearance to allow for the passage of a proportion of the air displaced by the reciprocating mass. The semi-circular plates support two four-component curved cushions 38 and 40 located between curved shoulders 39 on the plates' upper and lower surfaces. The cushions are held in place by top-hat bushes 41, through-bolts 42 and self-locking nuts 43. The outer curved shoulders 39 of the semi-circular plates 37 also serve to accurately align the upper and lower housings. The cushions, positioned as they are between the underside of the head of the anvil and the anvil flange 48, serve to limit the downward and upward movement of the anvil within the hammer casing.

A lower housing assembly, provided with flange 53, is attached to the lower flange 3 of the upper housing by bolts that also pass through the semi-circular plates 37. The lower housing comprises an outer tube 54 surrounding the anvil flange 48, and an inner coaxial tube 55 which guides the lower end of the driving dolly via bearing 49.

The two tubes are rigidly connected together by a number of equally spaced vertical panels 56. Further stiffening is provided by the horizontal plates 57 and 59, the upper plates 57 being pierced by a series of openings 58. The lower end of the inner tube 55 is reinforced by the ring 61. The vertical panels 56 are provided with openings 62 to allow air to flow freely round the annular chamber (the lower collection manifold) bounded by the lower housing tubes 54 and 55 and the horizontal plates 57 and 59. The lower end of the outer tube 54 is pierced by four equally spaced openings 63 (shown only in figure 2) vertically aligned with the openings 5 in the upper housing. As already mentioned, four vertical ducts connect the upper vent openings with the lower vent openings.

The upper housing, and to a lesser extent the lower housing, are thin enough, in isolation, to resonate within the audible spectrum if stimulated to do so. The bearing ring 27 fitted to the head of the anvil, together with the bearing rings 13 fitted to the reciprocating mass and the bearing ring 49 fitted to the driving dolly, serve to dampen any such tendency to vibrate by physical contact, such contact being maintained and enhanced by the partially compressed resilient 0' rings 67. Further, the rapid vertical movement of bearing rings 27, 13 and 49 as the pile is actually driven serves to continuously re-define the physical dimensions (and hence the resonant frequencies) of those regions of the hammer casing that are positioned above, between and below the bearing rings. As a result the short burst of energy emanating from each impact with the driving cushion is unable to promote or maintain resonant vibration of the hammer casing.

It is preferable that the casing flanges be fitted with appropriate sealing means (not shown) and that a shielded and filtered breather valve (not shown), of the type commonly fitted to hydraulic system reservoirs on mobile plant, be fitted to the hammer lid 4. As the internal air warms as a result of operation of the hammer the increase in air pressure is limited by the breather relief valve, excess pressure being vented to atmosphere. While cooling after use, the lost air is replaced by air drawn back into the hammer through the breather fitter and through a suction check valve that opens with minimal pressure.

The piling hammer may be manufactured, for example, in three distinct housing diameters, there being, for each diameter, a standard' reciprocating mass with light' and heavy' variants offering around 20% less mass and 20% more mass respectively. With this manufacturing philosophy a comprehensive range of piling hammer energy ratings may easily be produced, for example 8 kJ, 11 kJ, 14 kJ, 18 kJ, 25 kJ, 32 kJ, 42 kJ, 56 kJ and 70 kJ. Further, such a manufacturing philosophy allows a purchaser, should their requirement change over time, to make many advantageous changes to the energy rating of their hammer(s) at a relatively low cost.

Many variations in the sizes, proportions, materials of construction and constructional details of the piling hammer described above can be made without departing from the scope of the present invention.

Claims (7)

1. Claims 1. A piling hammer comprising an anvil assembly which may include an integral driving dolly and which, during operation, is located on the head of the pile to be driven, a reciprocating mass alternately lifted and released by hydraulic means, said mass, when released, falling predominantly under gravity and impacting said anvil assembly, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil assembly and reciprocating mass in an appropriate axial relationship, and in which any annular bearing that may be fitted to said anvil assembly, including said driving dolly if present, and said reciprocating mass, is urged outwards into continuous sliding contact with the inner surface of said casing by resilient means.
2. 2. A piling hammer according to claim 1, in which the resilient means used to urge any annular bearing into continuous sliding contact with the inner surface of the hammer casing comprises one or more partially compressed resilient 0' rings.
3. 3. A piling hammer according to claim 2, in which any partially compressed resilient 0' ring is located in an annular groove in its supporting member.Amendments to the claims have been made as follows: Claims 1. A piling hammer comprising an anvil member which, during operation, is located on the head of the pile to be driven, a reciprocating mass alternately lifted and released by hydraulic means, said reciprocating mass, when released, falling predominantly under gravity and impacting said anvil member, via a resilient driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil member and said reciprocating mass in an appropriate axial relationship, sliding bearing members being provided to reduce the wear of, and friction between, said open-ended casing and said anvil member, and said open-ended casing and said reciprocating mass, and in which any of said sliding bearing members has associated with it a resilient means that serves to urge said sliding bearing member into continuous sliding contact and, as a direct consequence of that action, also serves to urge the sliding component, be it said anvil member or said reciprocating mass, into a central position within its lateral working clearance within said open-ended casing in order to reduce the noise that would otherwise be generated as a result of the unrestrained lateral rattle of said anvil member and/or said reciprocating mass within said working clearance during operation.2. A piling hammer according to claim 1, in which the range of action of the resilient means associated with any sliding bearing is sufficient to ensure that it remains effective throughout the wearing life of said sliding bearing.3. A piling hammer according to claim 2, in which any sliding cylindrical bearing, that has associated with it a resilient means and has a diameter significantly greater than its length, is of the split-ring type in order that its diameter may automatically adjust under the influence of said resilient means.
4. 4. A piling hammer according to claim 2, in which any sliding cylindrical bearing, *:*" that has associated with it a resilient means and has a length that is approximately equal to or significantly greater than its diameter, is comprised of two or more : sectors of a cylinder in order that its diameter may automatically adjust under the * influence of said resilient means.** ** ** *
5. 5. A piling hammer according to any preceding claim, in which the resilient * . means is comprised of one or more partially compressed resilient 0' rings. *.. -** **: * *
6. 6. A piling hammer according to claim 5, in which any partially compressed resilient 0' ring is located in an annular groove.
7. 7. Noise reduction measures applied to a piling hammer substantially as described hereinbefore, with reference to the accompanying drawings.