GB2472606A

GB2472606A - A hydraulic pile driver with cushions to reduce impact noise

Info

Publication number: GB2472606A
Application number: GB0914052A
Authority: GB
Inventors: David Frederick Spriggs
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-08-12
Filing date: 2009-08-12
Publication date: 2011-02-16
Anticipated expiration: 2029-08-12
Also published as: GB2472666A; GB2472665B; GB201006271D0; GB201006263D0; GB0914052D0; GB2472665A; GB2472666B; GB2472606B

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 mass, anvil and cushion should be shaped so the impact initially occurs at the outer edge. There may be a sound barrier separate from the casing to reduce noise. The anvil and/or the mass may be provided with an annular bearing ring 27 which presses against the casing to reduce vibration and noise. Impacts may be transmitted to the pile via a further cushion and a driving dolly located below the anvil. There may be ducts allowing airflow between the space above and the space below the mass to cool the apparatus, and in particular the cushions.

Description

Noise Reduction in Hydraulic Piling Hammers 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.

Upward movement of the reciprocating mass and both upward and downward movement of the anvil, within the casing, are of necessity limited by mechanical stops. Such stops may be cushioned to prevent physical damage caused by energetic impact and, for reasons that will become apparent later, the cushion limiting upward movement of the anvil may conveniently be referred to as a secondary driving cushion while the cushion limiting downward movement of the anvil may conveniently be referred to as an over-travel cushion.

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, containing a relatively large reciprocating mass operating within a light-weight casing, with a number of novel sound reduction measures concentrated in the immediate locality of those components that constitute the major sources of noise. 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 4a is a cross-sectional elevation of the lower half of the piling hammer shown in figure 3 but with an alternative anvil design.

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

Figure 5a shows an alternative design for the components shown in figure 5.

Figure 6 is a plan view of the driving cushion and the head of the anvil (of the design shown in figure 5) showing a preferred pattern of air passages.

Figure 7 is a horizontal cross-section of a piling hammer according to the present invention, showing two alternative constructions for the air transfer ducts, and also showing the preferred arrangement of the secondary driving and over-travel cushions and associated air passages.

Figure 8 is a series of five cross-sectional elevations of a piling hammer according to the present invention, showing how the positions of the major components change during a complete operating cycle.

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 construction of these ducts is described later.

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 acceptable 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.

In the present invention the annular rings 13 are urged outwards into continuous contact with the inner wall of the casing by the use of partially compressed synthetic 0' rings 67 fitted into narrow annular grooves in said reciprocating mass as shown in detail in figure 5. In that way the reciprocating mass is positively centralised within the housing, and rattle is eliminated.

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.

Preferably the cylinder rod is extended upwards through the piston and out through the top of the cylinder.

At rest the upper and lower chambers of the hydraulic lifting cylinder are inter-connected via hydraulic valves (not shown), preferably of the poppet type to provide a rapid response to control signals, and preferably mounted in a housing directly attached to the head of the hydraulic cylinder. When the piling hammer is powered-up ready to operate the lower chamber of the lifting cylinder is supplied with oil under pressure from a suitable power source. At the same time the upper chamber is supplied with oil via the poppet valves, equalising the pressure on the upper and lower faces of the cylinder piston so that there is little or no net force applied to the reciprocating mass. To raise the reciprocating mass the poppet valves are re-configured by the control system to disconnect the upper chamber from the lower, and instead connect it to the system reservoir. The imbalance of pressure across the cylinder's piston then produces sufficient force to lift the reciprocating mass at the required rate. After a suitable interval, determined either by a timer or by a position sensor connected to the reciprocating mass, the poppet valves are returned to their starting configuration. Pressure balance across the cylinder's piston is then restored and the motion of the reciprocating mass is thereafter predominantly under the influence of gravity, oil simply being transferred from one chamber of the cylinder to the other. Cavitation of the oil is suppressed as a result of the transfer taking place at full system pressure, but friction at the various pressurised sliding seals interferes in a small way with the free-fall of the reciprocating mass. That effect, together with any friction generated between the reciprocating mass and the casing, may be offset by making the diameter of the upper rod of the lifting cylinder slightly smaller than that of the lower rod, generating a small compensatory downward force.

With reference to figures 4, 5 and 6, 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 synthetic 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 means 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 (best seen in figure 6) to allow the through-flow of air displaced by the movement of the reciprocating mass. 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. The arrangement shown is suitable for hammer energy ratings in the range of 42 kJ to 70 kJ; smaller versions of the hammer may use proportionately fewer air passages.

In the preferred arrangement as 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. The intention is to ensure that contact between the flat horizontal lower face of the reciprocating mass and the driving cushion initially occurs at or near the outer edge and progressively extends inwards as compression of the cushion increases. The same effect could also be produced by dishing the impacting face of the reciprocating mass, or by profiling one face or both faces of the driving cushion, or by any combination of similar measures. Although technically more demanding, the driving cushion may be attached to the lower face of the reciprocating mass instead of to the upper face of the anvil. The essential feature in all cases is that the gap between the opposed closing faces of the reciprocating mass and the anvil head 26, after subtracting the thickness of the un-compressed driving cushion 28 at the point of measurement, reduces towards the outer edge of said cushion in a controlled manner.

The purpose of the physical arrangement described is to ensure that air trapped between the reciprocating mass and the driving cushion 28 is progressively directed inwards and then downwards through the air passages in the driving cushion and in the head of the anvil. The division of the air-stream through a number of passages and the subsequent turbulent re-mixing provides a significant muffling effect, greatly reducing the noise generated at impact in comparison to hammers in which trapped air is of necessity squished violently outwards at the moment of impact.

Although it is preferable that the driving cushion be manufactured in one piece, it may also be assembled from a number of layers of material, or from a series of nested annular rings, or from a number of discrete components of arbitrary shape, the design of the air passages and the retaining means of necessity being modified appropriately in each case.

The vertical compression of the driving cushion 28 does not reduce its material volume to any significant extent but instead causes it to deform, such deformation taking the form of outward bulging at all unrestrained vertical surfaces, which include, in the present invention, the surfaces of the air passages and the outer edge adjacent to the upstanding annular ring 31. At the moment of impact the reciprocating mass may be falling at a velocity of 4 metres per second or more. The resulting rapid outward deformation of the outer edge of the cushion produces a significant sound pressure front. That pressure front initially radiates outwards, but is reflected back by a sound barrier comprising the annular ring 31 to prevent it impinging directly onto the inner surface of the upper housing, further attenuating noise generated by the impact. The partially compressed synthetic rings 67 ensure that the annular ring 31 is itself prevented from ringing. Alternatively, the annular ring 31 may be attached to the lower surface of the reciprocating mass instead of to the anvil, or rings of different diameters may be attached to both the anvil and the reciprocating mass, their diameters and lengths being such that they overlap, one within the other, at the moment of impact. Such an arrangement is shown in figure 5a.

The upper housing is thin enough to resonate within the audible spectrum if stimulated to do so, although the measures already described serve to greatly reduce such stimulation. The bearing/damping ring 27 serves to dampen any such tendency to vibrate by physical contact, such contact being maintained and enhanced by the partially compressed synthetic 0' rings 67. Further, the rapid vertical movement of the anvil and bearing/damping ring 27, resulting from impact by the reciprocating mass, serves to continuously re-define the physical proportions, and hence the resonant frequencies, of the upper housing both above and below said bearing/damping ring. As a result the greatly attenuated short burst of energy emanating from each impact with the driving cushion is unable to promote or maintain resonant vibration of the upper housing.

With reference to figures 4 and 7, 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 hole through which the stem of the anvil 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 a four-component curved over-travel cushion 38 located between curved shoulders 39 on the plates' upper surface, and a four-component curved secondary driving cushion 40 located between similar curved shoulders on the plates' lower surface. The cushions are held in place by top-hat bushes 41, through-bolts 42 and self-locking nuts 43. The abutting ends of the semi-circular plates 37 are shaped to form the air passages 44, and the plates are drilled to provide additional air passages 45. These details are best seen in figure 7. The outer curved shoulders 39 of the semi-circular plates 37 also serve to accurately align the upper and lower housings.

The stem of the anvil comprises the outer tube 46 combined with a concentric inner tube 47. At an appropriate distance below the anvil head 26 the outer tube 46 is provided with a substantial flange 48. The anvil stem then extends further downwards and 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 anvil, resulting in the anvil being urged to move laterally within its working clearance in the lower housing at each impact, generating noise. In the present invention that problem has been significantly reduced by using partially compressed synthetic 0' rings fitted in grooves, machined in the anvil stem, to urge the bearing shells 49 outwards into continuous sliding contact with the housing, as shown in figure 4.

Both the outer tube 46 and the inner tube 47 of the anvil are perforated in order that cooling air passing through the various passages in the anvil head 26 can be re-combined in, or drawn from, a common annular chamber below the anvil flange 48.

(The various paths taken by the cooling air-streams are described in more detail in due course.) 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 by the piling hammer. Suitable attachment means may include bolts 51 in combination with locating pins 52.

Figure 4a shows an alternative anvil, mechanically interchangeable with the version already described, and designed to further reduce the noise emitted by the hammer during operation. The anvil is reduced to its bare essentials, the head 26 being connected to the flange 48 by a simple tubular member 68. The stem of the previous design, now separated from the anvil head and flange, and consisting primarily of the outer and inner tubes 46 and 47, is extended upwards, closed at the top and re-shaped so that it can fit loosely within the recess in the underside of the new anvil. In this new form the old anvil stem may conveniently be referred to as a driving dolly. The anvil head 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 pass through the resilient layer may be drilled after curing rather than prior to casting. This alternative two-part arrangement offers two advantages over the single-part anvil. Firstly, any tendency for the anvil flange 48 to ring as a result of impact is greatly reduced by the damping effect of the immediately adjacent resilient layer. Secondly, noise generated at the impacting faces of the anvil no longer have a direct metallic path to the lower attachment face for the pile socket 50, noise now being attenuated by having to pass through the resilient layer.

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.

These semi-circular plates, clamped as they are between the lower flange of the upper housing and the upper flange of the lower housing, create a localised structure of great rigidity that, in combination with the effect of the bearing/damping ring 27 located in the head of the anvil, ensures that impacts with either the secondary driving cushion 38 or the over-travel cushion 40 are unable to excite vibration in either the upper or lower housings.

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 anvil stem 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.

Four vertical ducts connect the upper vent openings 5 with the lower vent openings 63. In this way a substantially fixed volume of air is continuously driven, by the motion of the reciprocating mass, back and forth through the ducts, which serve as air-to-air heat exchangers. To improve heat transfer the duct walls are provided with fins both on the outside surface and on the inside surface. Figure 7 shows two different duct arrangements in horizontal cross-section, the larger ducts shown at the left of the figure being more suitable for higher energy versions of the piling hammer while those shown at the right are more suitable for lower energy versions.

The ducts are formed by attaching plates 64, together with combined external and internal cooling fins 65, at each of the four quarter points of the casing, so that the effective width and depth of the hammer remains unchanged. External fins 66 are also added. The number of cooling fins and their dimensions may need to be adjusted to cater for differences in intended duty cycle and ambient temperature.

It is preferable that the casing flanges be fitted with appropriate gaskets 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 filter and through a suction check valve that opens with minimal pressure.

The following paragraphs describe the movement of the internal parts of the piling hammer during one complete operating cycle, and the paths taken by the internal air-stream.

While the hammer is being hoisted to its working position, guided by its associated mast or leader, the anvil drops to a position in which the underside of the anvil head 26 is resting on the over-travel cushion 38, as shown in figure 2. The reciprocating mass rests on the driving cushion 28, but compression of the cushion is at this time very low because the dead weight of the reciprocating mass is only a small fraction of its effective dynamic weight during impact.

When the hammer is lowered onto a pile, as shown in figure 8a, the anvil and reciprocating mass remain in mutual contact but the housing assembly drops until the secondary driving cushion 40 contacts the upper surface of the anvil flange 48.

Operating the hammer then causes the reciprocating mass to be lifted up to the required drop height as shown in figure 8b, and then to be released to fall predominantly under the influence of gravity.

As the reciprocating mass falls, cooling air, driven downwards through the outer ring of passages 33a in the driving cushion 28 and the anvil head 26, passes predominantly through the openings 44 and 45 in the semi-circular plates 37, where it circulates around the rear of the secondary driving cushion 40 and continues downwards through the annular gap between the outer edge of the anvil flange 48 and the inside of the lower housing outer tube 54. This flow of air cools both the over-travel cushion 38 and the secondary driving cushion 40. Air driven downwards through the central orifice in the plate 36 passes through radial passages in the anvil stem inner tube 47 and into the annular space between said inner tube and the anvil stem outer tube 46, where it combines with cooling air driven downwards through the intermediate and inner rings of passages 33b and 33c in the driving cushion 28.

This combined air-stream then passes through the lower radial passages in the anvil stem outer tube 46 and into the annular space below the anvil flange 48, where it combines with the cooling air from the secondary driving cushion 40, and passes into the lower collection manifold. The upper radial passages in the anvil stem outer tube 46 have a pressure balancing function. They ensure that the flow of air through each of the cooling passages in the driving cushion 28 is for the most part proportional to the size of the passage and is not unduly effected by the position of the passage within said cushion.

As soon as the reciprocating mass falls into contact with the driving cushion 28, as shown in figure 8c, said cushion starts to compress and apply a downward force to the anvil and thence to the pile. The downward acceleration of the pile increases rapidly, momentarily leaving the hammer housing assembly behind to fall relatively slowly predominantly under the influence of gravity. Once downward movement of the pile ceases (said downward movement shown in figure 8d being 100 mm) the housing is able to catch up and again makes contact with the anvil flange 48 via the secondary driving cushion 40 as shown in figure 8e. If the drop height is large and the ground is soft then the anvil and the pile may be driven downwards so far that the underside of the anvil head 26 makes contact with the over-travel cushion 38, the compressive load generated in said cushion then urging the hammer housing assembly downwards at a greater rate.

If the housing assembly has not made contact with the secondary driving cushion 40 by the time that the hydraulic operating cylinder is again attempting to lift the reciprocating mass, said operating cylinder preferentially drives the housing assembly downwards, at first, as a result of its lower mass (in comparison to that of the reciprocating mass) and as a result of its existing downward movement under the influence of gravity. In these circumstances the impact between the anvil flange 48 and the secondary driving cushion 40 is quite energetic, and in the appropriate conditions may usefully drive the pile further. The secondary driving cushion is sufficiently robust and sufficiently well ventilated by the cooling air-stream that such impacts can be withstood on a repetitive basis.

Impacts with any of the cushion members causes them to deform by bulging outwards at their unrestrained vertical surfaces. Deformation is rapid and generates sound pressure waves in the surrounding air that could be transmitted to the outer casing. However, the cooling air-stream previously described is specifically designed to maintain close contact with the cushion members in order to extract the maximum amount of heat, and in the process that moving body of air also absorbs sound energy during impacts. The complex and rapid movement of the cooling air-stream, frequently splitting and re-combining as it does through the cooling circuit, attenuates the entrained sound energy by destructive interference and disrupts the direct transmission of energy from the cushion members to the hammer casing. In that way the cooling air flow contributes to the overall attenuation of noise.

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. In particular the number, position, size, shape and construction of the various air ducts, vents and passages forming the totality of the cooling air path may be subject to wide variation.

Claims

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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which the topology of the closing surfaces of said reciprocating mass and said anvil, in combination with any variation in thickness of said driving cushion, combine to ensure that compression of said driving cushion initially occurs at or near its outside edge in plan.
2. A piling hammer according to claim 1, in which the driving cushion consists of a number of separate resilient components of arbitrary shape that, taken together, perform the function of a driving cushion and may be regarded as a driving cushion.
3. A piling hammer according to claims 1 and 2, in which, during impact, an imaginary line drawn on the surface of the driving cushion to represent at any instant the outer limit of uncompressed cushion material, moves towards the central axis of the piling hammer, either progressively or intermittently, as compression of said driving cushion increases.
4. A piling hammer according to claim 3, in which, during impact, air displaced towards the central axis of the hammer from between the closing faces of the reciprocating mass and the anvil is directed through a number of openings, slots or passages whereby turbulent splitting and mixing serves to attenuate sound pressure waves, present in the air-stream, by a process of destructive interference.
5. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which, during impact, said driving cushion is surrounded, in plan, by a sound barrier, entirely separate from said casing, for the purpose of reflecting and containing sound pressure waves emanating from the outer unrestrained surface of said driving cushion as a result of its outward deformation during impact.
6. A piling hammer according to claim 5, in which the sound barrier is attached to the anvil member.
7. A piling hammer according to claim 5, in which the sound barrier is attached to the reciprocating mass.
8. A piling hammer according to claim 5, in which sound barriers are attached to both the anvil member and to the reciprocating mass.
9. A piling hammer according to claim 8, in which, during impact, the two sound barriers are arranged to overlap in the direction of the longitudinal axis of the hammer.
10. A piling hammer according to claims 6 and 7, in which the sound barrier is damped to reduce the amplitude and duration of any vibration that may be induced in said sound barrier.
11. A piling hammer according to claims 8 and 9, in which either or both of the sound barriers is or are damped to reduce the amplitude and duration of any vibration that may be induced in said sound barrier(s).
12. A piling hammer according to claims 10 and 11, in which the damping of any sound barrier is achieved by the use of partially compressed synthetic 0' rings.
13. A piling hammer according to claim 12, in which the partially compressed synthetic 0' rings are located in circumferential grooves in the sound barrier.
14. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which the head of said anvil is provided with a bearing ring that is urged outwards into continuous contact with the inner surface of said casing by a resilient means for the purpose of damping vibration in said casing.
15. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which the head of said anvil is provided with a bearing ring that is urged outwards into continuous contact with the inner surface of said casing by a resilient means for the purpose of preventing any noise inducing impact with said casing as a result of unrestrained lateral shake of the head of said anvil within its normal working clearance within said casing.
16. A piling hammer according to claims 14 and 15, in which the resilient means used to urge the anvil head bearing into continuous contact with the inner surface of the hammer casing comprises a number of partially compressed synthetic 0' rings.
17. A piling hammer according to claim 16, in which any noise barrier attached to the head of the anvil, and the hammer casing adjacent to the head of the anvil, are simultaneously damped by the use of a common assembly of partially compressed synthetic 0' rings.
18. A piling hammer according to claims 16 and 17, in which the partially compressed synthetic 0' rings are located in circumferential grooves in the head of the anvil.
19. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which said reciprocating mass is fitted with a number of bearing rings that are urged outwards into continuous contact with the inner surface of said casing by a resilient means for the purpose of damping vibration in said casing.
20. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which said reciprocating mass is fitted with a number of bearing rings that are urged outwards into continuous contact with the inner surface of said casing for the purpose of preventing any noise inducing impact with said casing as a result of unrestrained lateral shake of said reciprocating mass within its normal working clearance within said casing.
21. A piling hammer according to claims 19 and 20, in which the annular bearings fitted to the reciprocating mass are urged outwards into continuous contact with the hammer casing by a number of partially compressed synthetic 0' rings.
22. A piling hammer according to claim 21, in which any noise barrier attached to the impacting face of the reciprocating mass, and the hammer casing adjacent to the impacting face of said reciprocating mass, are simultaneously damped by the use of a common assembly of partially compressed 0' rings.
23. A piling hammer according to claims 21 and 22, in which the partially compressed synthetic 0' rings are located in circumferential grooves in the reciprocating mass.
24. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which an annular bearing, fitted to the stem of said anvil, is urged outwards into continuous contact with said casing for the purpose of damping vibration in said casing.
25. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which an annular bearing, fitted to the stem of said anvil, is urged outwards into continuous contact with said casing for the purpose of preventing any noise inducing impact with said casing as a result of unrestrained lateral shake of the stem of said anvil within its normal working clearance within said casing.
26. A piling hammer according to claims 24 and 25, in which the annular bearing, fitted to the stem of the anvil, is urged outwards into continuous contact with the hammer casing by a number of partially compressed synthetic 0' rings.
27. A piling hammer according to claim 26, in which the partially compressed synthetic 0' rings are located in circumferential grooves in the stem of the anvil.
28. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which excessive downward movement of said anvil relative to said casing is restrained by a resilient member, referred to as an over-travel cushion, which is wholly contained within said casing for the purpose of attenuating noise generated as a result of impacts with said over-travel cushion.
29. A piling hammer according to claim 28, in which the over-travel cushion consists of a number of discrete resilient components of arbitrary shape that, taken together, perform the function of an over-travel cushion.
30. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which excessive upward movement of said anvil relative to said casing is restrained by a resilient member, referred to as a secondary driving cushion, which is wholly contained within said casing for the purpose of attenuating noise generated as a result of impacts with said secondary driving cushion.
31. A piling hammer according to claim 30, in which the secondary driving cushion is constructed from a number of resilient components of arbitrary shape that, taken together, perform the function of a secondary driving cushion.
32. A piling hammer according to claims 28 to 31, in which the over-travel cushion and the secondary driving cushion are both attached to a common supporting means designed to provide the hammer casing with a localised region of exceptional rigidity to reduce or eliminate vibration of said casing resulting from impacts with said over-travel cushion and secondary driving cushion.
33. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, the upward and downward limits of anvil movement within said casing being separately controlled by cushions of elastic material, and in which all three of said cushions (the driving cushion and the cushions limiting upward and downward movement of the anvil) are positioned as closely together within the hammer casing as is practicable in order that noise reduction measures applied at each point of impact have a beneficial influence at adiacent Doints of imoact. thereby to imDrove the overall effectiveness 36. A piling hammer according to claims 34 and 35, in which an annular bearing fitted to the driving dolly is urged outwards into continuous contact with the casing for the purpose of damping vibration in said casing.37. A piling hammer according to claims 34 and 35, in which an annular bearing fitted to the driving dolly is urged outwards into continuous contact with the casing for the purpose of preventing any noise inducing impact with said casing as a result of unrestrained lateral shake of said driving dolly within its normal working clearance within said casing.38. A piling hammer according to claims 36 and 37, in which the annular bearing fitted to the driving dolly is urged outwards into continuous contact with the hammer casing by a number of partially compressed synthetic 0' rings.39. A piling hammer according to claim 38, in which the partially compressed synthetic 0' rings are located in circumferential grooves in the driving dolly.40. 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which a forced current of air passing over or around or through slots or passages contained within said driving cushion, primarily for cooling purposes, is also used to carry away from said driving cushion a proportion of the sound energy resulting from impacts, said sound energy carried away from said impacts subsequently being attenuated by a process of destructive interference resulting from the repeated splitting and re-combination of said air stream.41. 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 mass, when released, fafling predominantly under gravity and impacting said anvil for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, the limits of upward and downward movement of said anvil within said casing being mediated by cushions, and in which a forced current of air passing over and around said cushions, primarily for cooling purposes, is also used to carry away from said cushions a proportion of the sound energy resulting from impacts, said sound energy carried away from said impacts subsequently being attenuated by a process of destructive interference resulting from the repeated splitting and re-combination of said air stream.42. Noise reduction measures applied to a piling hammer substantially as described hereinbefore, with reference to the accompanying drawings.Amendments to the Claims have been filed 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 mass, when released, falling predominantly under gravity and impacting said anvil, via a resilient driving cushion, for the purposes of driving said pile, an open-ended casing surrounding and slidably locating said anvil and reciprocating mass in an appropriate axial relationship, and in which the topology of the closing surfaces of said reciprocating mass and said anvil, in combination with any variation in thickness of said driving cushion, combine to ensure that compression of said driving cushion initially occurs at or near its outside edge in plan.2. A piling hammer according to claim 1, in which the driving cushion consists of a number of separate resilient components of arbitrary shape that, taken together, perform the function of a driving cushion and may be regarded as a driving cushion.3. A piling hammer according to claims 1 and 2, in which, during impact, an imaginary line drawn on the surface of the driving cushion to represent at any instant the outer limit of uncompressed cushion material, moves towards the central axis of the piling hammer, either progressively or intermittently, as compression of said driving cushion increases.4. A piling hammer according to any preceding claim, in which, during impact, air displaced from between the closing faces of the reciprocating mass and the anvil is directed through a number of openings, slots or passages whereby turbulent splitting and mixing serves to attenuate sound pressure waves, present in the air- * stream, by a process of destructive interference.