GB1602281A

GB1602281A - Load transmitting structure

Info

Publication number: GB1602281A
Application number: GB1584877A
Authority: GB
Original assignee: Delta Materials Research Ltd
Current assignee: Delta Materials Research Ltd
Priority date: 1977-04-15
Filing date: 1977-04-15
Publication date: 1981-11-11
Also published as: FR2387488A1; DE2815827A1

Description

(54) LOAD TRANSMITTING STRUCTURE (71) We, DELTA MATERIALS RESEARCH LIMITED, a British Company, of P.O. Box 22, Hadleigh Road, Ipswich, Suffolk, IP2 OEG, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to structures which are subject to impact and/or vibration and is particularly concerned with such structures designed to minimise the noise radiated therefrom.

Impact-generated noises such as those occurring in metal-to-metal impacts, in for example automatic feed stop mechanisms which use a steel stud striking a metal plate, stamping presses, swaging hammers, forging hammers and meshing high force or high torque gear teeth, constitute some of the most difficult noise problems encountered in industry.

When an impact occurs involving a machine structure, noise is produced at the actual point of impact. An energy wave then flows back from the impact area to the remainder of the machine structure and is translated into vibration and then noise radiation. The noise radiation would be greatly reduced if the energy wave could be isolated from the machine structure.

The amount of impact energy transmitted from, for example, a steel stud hammer or gear to its surrounding structure depends upon the so-called specific acoustic impedance of the surrounding structure. Generally the greater the difference between the specific acoustic impedance of the part subject to impact and that of the surrounding structure the greater the energy loss.

It is known that certain materials, such as rubber, when inserted into the path of the energy wave are effective substantially to reduce the impact energy transmitted to the machine structure. This is the general principle of vibration isolation of machinery. As a practical matter, however, rubber nads of the like inserted between the faces of metal parts which strike each other have a very short life. Furthermore, the amount of displacement of the rubber is such as to restrict its use severely, and in the case of hammers, would preclude its use if meaningful work is to be carried out.

In the present invention, we provide a load-transmitting structure comprising a metal member; at least one other metal part having no metal-to-metal contact with the member; and a load-transmitting and acoustically isolating solid insert, which is arrange between the member and the part or parts to transmit load from one to the other in a given direction, which is made predominantly of a material or materials having a specific acoustic impedance differing substantially from that or those of the metal member and part, or parts and which is so constrained and closely confined over substantially its entire surface or surfaces by the member and part or parts that deformation of the insert due to loading in the said direction is substantially entirely hydrostatically compressive and is consequently limited in extent.

The specific acoustic impedance of the insert or each insert so constrained is so different from that of the member and the remainder of the structure that it provides substantial vibration isolation; generated and radiated noise is thus largely confined to the member when subject to impact. At the same time the constraining of the insert, which ensures that the insert is always in surface-to-surface contact with the adjacent faces of the member and the part or parts and that substantially no deformation of the insert occurs save hydrostatic compression, results in a relatively high life for the insert and a minimum relative displacement between the member and the part or parts.

Examples of the use to which the invention may be put are as follows: 1. to isolate the work areas of stamping and punch presses by insertion of constrained inserts in the press ram and underneath the work piece; 2. to produce a low noise mechanical feed stop with a controlled amount of de flection. In accordance with the procedures normally followed heretofore in such devices a metal stud is allowed to strike a metal plate and there being no measurable deflection large impulses are generated as a result of such impact.The use of constrained inserts serves to reduce the amplitude of the impulses generated and this is accomplished without large deflections which would render the feed stop imprecise and unacceptable; 3. to reduce the impact noise on engagement of a key in key clutch operation of e.g. a fly-wheel; 4. to reduce the flow of vibrational energy to the machine structure originating from the out of balance forces generated by the mismatch of meshing gear forces, particularly those used to transmit substantial forces or torques either of a cyclical type e.g. stamping presses or continuously e.g. rod or wire drawing machines.

5. to support a vibration generating element from a supporting structure in order to minimise the transmission of vibration to that structure and hence the noise generated by that structure. Thus a bearing house may be supported in a machinery structure by an annular constrained insert as described. The constrained insert has an acoustic impedance greatly different from the surrounding metal structure and ensures that very little vibrational energy is transmitted outwards from the bearing.

The deflection of the insert may be controlled by varying the amount of resilient material it contains as, for example, by varying the size and the geometry of the insert, or by using an inert bulk extender, for example, sand or vermiculite. Whilst an elastomer without a filler or extender is effective in reducing noise generated, for example, by the feed stops on a chain making machine, the use of an extender is thus preferred. To have maximum effect the resilient insert should extend across as large a cross section of the member as possible.

Heretofore, difficulties have been encountered in devising means to reduce the impact noise of hammers without destroying their capability to work. By increasing the momentum of a drop hammer with constant energy, a reduction in noise can be obtained and the same amount of work carried out. The noise generating mechanism from hammers is similar to that from feed stops. The energy not transmitted directly as impact noise by the hammer itself travels back into the machine structure to be transformed and radiated as noise. By providing an insert made of rubber, plastics or other resilient material of suitable bulk modulus the progress of this energy wave may be impeded and the energy to be radiated as noise reduced.

However, the reduction in mass of the hammer due to lower specific gravity of the resilient material relative to metal it may replace greatly reduces the work capability of the hammer. To avoid that problem, the resilient material may include particles of dense solids such as lead and, preferably, tungsten and uranium. That results in a reduction in the deflection and an increase in mass. It is possible by proper selection of the filler employed and its amount to have the mass of the insert greater than the mass of the metal of the hammer it replaces; in that case the momentum of the hammer is increased and, if the kinetic energy is kept constant, a reduction in impact noise generated by the hammer head itself is obtainable.

As before mentioned, the invention is applicable to a gear wheel, when the member subject to impact and/or vibration carries gear teeth and the remainder of the structure is a hub carrying, or adapted to carry, a shaft. In a preferred form of the invention, the member is a teeth-carrying rim having a plurality of integral, inwardly directed, sector-shaped parts, and the hub has a similar number of integral, outwardlydirected, sector-shaped parts disposed between the sector-shaped parts of the rim, the insert being a layer of resilient material on all faces of the hub which are contiguous with faces of the rim. To avoid the occurrence of large deflections between the rim and hub, which might affect the ability of the gears to carry out useful work, the insert material may include as before an inert bulk extender, such as sand and vermiculite.

The invention will be more readily understood by way of example from the following description of impact-sustaining structures in accordance therewith, reference being made to the accompanying drawings, in which Figure 1 is a cross-section through the striking part of a hammer; Figure 2 is a plan view of a gear wheel with its cover plates removed; Figures 3 and 4 are sections on the lines III-III and IV-IV of Figure 2, both cover plates being shown; and Figures 5 and 6 are plan views of respectively the rim and hub of the gear wheel.

In Figure 1, an impact-subject member is illustrated as a hammer head 12 which is hollowed out to have an annular wall 13 and a frusto-conical internal surface 14.

The hammer head is carried by a body 15 having a reduced cylindrical face 16 on which wall 13 can slide and an internal frusto-conical surface 17. The space between the surfaces 14 and 17 is completely filled by an insert 18 of resilient material which extends laterally to the wall 13. The insert 18 is bonded to head 12 and body 15 over all the surfaces of the latter and is preferably an elastomer, such as rubber, filled with particles of heavy metal as described above.

The insert is closely constrained between the head 12 and body 15 and cannot deform, except in the direction of relative movement between the head and body. The clearance between the head and body is such that no extrusion of the insert into the clearance takes place. When the hammer strikes a work piece the insert is hydrostatically compressed, in the manner of a confined liquid subject to a compressive force; the impact energy is then transmitted from the head to the body only through the insert 18, the head and body being nowhere in metal-to-metal contact.Because of the abrupt changes in specific acoustic impedance from the hammer head 12 to the insert 18 and from the insert 18 to the body 15, the impact energy, and particularly the noise-generating vibratory components, are impeded so that little noise is transmitted to the body 15 and hence from the body 15 and its associated structure to the air, the impact noise being then largely limited to that transmitted to the air by the head 12.

Because of the constrained nature of the insert 18, and the absence of transverse deformation, the wear of the insert is small and the insert has an appreciable life. At the same time, the deformation of the insert in the direction of relative movement is maintained at a relatively low level, particularly when the insert is made of a filled elastomer.

An insert having a cross-section similar to that of Figure 1 but of annular form may be employed to isolate a bearing acoustically from its machine structure. In that case, the bearing has a bearing house which is attached to a ring having a cross section similar to the member 12, and the machine structure has an opening which receives the annular insert and has a grooved periphery similar to that shown at 17.

A hammer head constructed as shown in Figure 1 has been found to reduce peak impact noise by 9dB (A) and to be capable of withstanding impulsive loads of 50 tons and several hundred repetitive loads from a 5 ton fly press.

The low-noise gear wheel illustrated in Figures 2 to 5 consists of two major parts a a rim 20 carrying integral gear teeth 21 and a hub 22 which is in torque-transmitting relation with the rim 20 and which has a bore 24 by which the hub can be keyed to a shaft.

As best shown in Figures 3 and 5, the rim has two integral, inwardly-directed, sector-shaped parts 30, each subtending 90" at the centre. The axial width of each part 30 is less than that of the rim 20 and the inner face of each part is arcuate.

The hub 22 has similarly two, integral, outwardly-directed, sector-shaped parts 31 (Figures 4 and 6), each of which subtends 90" at a point slightly off the centre so that parallel faces exist between parts 30 and 31, and each of which has an axial width rather less than that of the parts 30. The hub 22 can thus be fitted within the rim 20 with the parts 31 lying between the parts 30 (Figure 2). In that position there are gaps between the hub 20 and the arcuate faces of parts 30; between the adjacent radial faces of parts 30 and 31; and between the outer arcuate faces of parts 31 and the rim 20. Further, the end faces 32 of parts 31 are below the levels of the corresponding end faces 33 of parts 30.

The resilient insert is in the form of a filled rubber layer 35 which covers all the surfaces of the hub 22 and its parts 31 except the end faces of the hub adjacent the bore 24. When the gear wheel is completed, the layer thus fills all the gaps between the hub and rim and brings the end faces of the parts 31 to the same level as the end faces 33 of parts 30.

The gear wheel further has two annular cover plates 36 and 37 which overlie the end faces of the parts 30 and 31 and which are held in place by bolts 38 which pass into holes 40 in the parts 30. While the insert layer 35 may encase the hub 22 prior to entry of the latter in the rim, the layer 35 may alternatively be formed in situ by assembling the metal parts and then injecting resilient material into the various gaps formed between the parts.

It will be observed that the rim .nd hub are nowhere in metal-to-metal contact and that there is no vibration transmitting connection between the rim and hub through the cover plates 36 and 37. Further, the insert 35 is fully constrained in that it is entirely confined between the various surfaces of the hub, rim and cover plates. The torque is transmitted between the gear teeth and the hub only through those parts of the insert 35 lying between the radial faces of the parts 30 and 31 seen in Figures 5 and 6. The torque transmission is again accompanied by the hydrostatic compression of the insert.

Accordingly, noise generating components at the gear teeth are isolated by the insert and are either prevented from reaching the hub or reach the hub only in attenuated form. At the same time, relative angular movement between the rim and hub is limited, particularly when a filled rubber is employed, because that relative movement is limited to the hydrostatic compression of the insert. A suitable elastomer for the insert is polyurethane rubber of 40 Shore A scale hardness.

The inserts may be given desired properties to render them suitable for specific applications by suitable choice of the elastomer and the filler used. Thus, for example, for applications involving higher temperatures silicone rubber could be used; in applications where high damping vibration is desired a polysulphide rubber could be used; whilst for low noise hammers a highly filled plastics material would be useful to minimise the displacement, for example, lead, tungsten, or uranium in polyethylene, polypropylene, P.V.C. or nylon.

WHAT WE CLAIM IS: - 1. A load-transmitting structure comprising a metal chamber; at least one other metal part having no metal-to-metal contact with the member; and a load-transmitting and acoustically isolating solid insert, which is arranged between the member and the part or parts to transmit load from one to the other in a given direction, which is made predominantly of a material or materials having a specific acoustic impedance differing substantially from that or those of the metal member and part, or parts and which is so constrained and closely confined over substantially its entire surface or surfaces by the member and part or parts that deformation of the insert due to loading in the said direction is substantially entirely hydrostatically compressive and is consequently limited in extent.

2. A structure according to claim 1, in which the insert comprises an elastomer which includes a bulk extender.

3. A structure according to claim 2, in which the bulk extender is sand or vermiculite.

4. An impact-sustaining structure according to claim 2 and in the form of a movable impact applying device, such as a drop hammer, in which structure the extender comprises particles having a density sufficiently great to give the insert a density higher than that of the metal of the member.

5. An impact-sustaining structure according to claim 4, in which the particles are selected from lead, tungsten and uranium.

6. A structure according to any one of the preceding claims, in which the member is in use intended to be subject to impact and that member and the part or parts closely confine one another and permit relative sliding movement, and the insert is constrained between surfaces of the member and the part or parts, being constrained against deformation laterally of the said direction.

7. A structure according to any one of claims 1 to 3 in the form of a gear wheel, in which structure the member carries gear teeth and the part or parts includes a hub carrying, or adapted to carry, a shaft.

8. A structure according to claim 7, in which the member and the hub have cooperating torque-transmitting parts which are separated by the insert.

9. A structure according to claim 8, in which the member is a teeth-carrying rim having a plurality of integral, inwardly directed, sector-shaped parts, and the hub has a similar number of integral, outwardlydirected, sector-shaped parts disposed between the sector-shaped parts of the rim, the insert being a layer of resilient material on all faces of hub which are contiguous with faces of the rim.

10. A structure according to any one of claims 1 to 3, in which the member is subject to vibration and is supported by the insert from the part or parts.

11. A structure according to claim 10, in which the insert is of annular form.

12. A structure according to claim 11, in which the member is an annular bearing housing, the insert being constrained between faces of the bearing housing and annular faces of the part or parts.

13. A structure subject to impact and/or vibration, substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. compression of the insert. A suitable elastomer for the insert is polyurethane rubber of 40 Shore A scale hardness. The inserts may be given desired properties to render them suitable for specific applications by suitable choice of the elastomer and the filler used. Thus, for example, for applications involving higher temperatures silicone rubber could be used; in applications where high damping vibration is desired a polysulphide rubber could be used; whilst for low noise hammers a highly filled plastics material would be useful to minimise the displacement, for example, lead, tungsten, or uranium in polyethylene, polypropylene, P.V.C. or nylon. WHAT WE CLAIM IS: -

1. A load-transmitting structure comprising a metal chamber; at least one other metal part having no metal-to-metal contact with the member; and a load-transmitting and acoustically isolating solid insert, which is arranged between the member and the part or parts to transmit load from one to the other in a given direction, which is made predominantly of a material or materials having a specific acoustic impedance differing substantially from that or those of the metal member and part, or parts and which is so constrained and closely confined over substantially its entire surface or surfaces by the member and part or parts that deformation of the insert due to loading in the said direction is substantially entirely hydrostatically compressive and is consequently limited in extent.

11. A structure according to claim 10, in which the insert is of annular form.