GB2084694A - A shock and vibration isolation mat - Google Patents

Abstract

A shock and vibration isolation mat comprising a resilient mat formed in two or more parts 1, 2 in which one part or parts alternate with a second part or parts, the one part or parts 1 having protruding spigots 3 to slide in holes 4 in one or both surfaces of the second part or parts 2, the length of the spigots 3 being less than the depth of the holes 4 in the second part or parts to produce trapped air pockets 5 between the two parts. <IMAGE>

Description

SPECIFICATION A shock and vibration isolation mat This invention relates to an improvement in shock and vibration isolation materials and mountings.

Vibration isolation materials and mountings have up to date been constructed from various combinations of cork, cork and rubber, rubber, natural and synethetic cork, plastics and fibre laminations, rubber and plastics, felt and rubberised felt combinations, foam rubbers and rubber bonded to metal combinations. Vibration isolation or damping can only be achieved when the vibration isolation medium deflects under both static and dynamic loads. This deflection may be almost fully elastic i.e.

with little damping or energy absorption, e.g. natural rubber or steel springs, or with a combination of elasticity and damping. Damping or energy absorption is usually achieved through internal friction converting a proportion of the kinetic energy of the vibration into heat. This friction damping is usually achieved by either relative molecular movements of a material, e.g. in the case of rubber, or relative mechanical movement in the case of materials based on fibres or cork.

An isolator with no damping will achieve a high degree of vibration isolation but a low degree of stability for the equipment being isolated. Therefore, damping is usually necessary for reasons of stability, although the effect is to reduce the percentage isolation.

In order to isolate low frequency vibrations, such as those experienced in buildings, the isolator must possess a relatively low spring constant, so that large deflections are achieved under relatively low loading conditions.

Anti-vibration materials made from cork, plastics, fibre or combinations thereof have the disadvantage that they are relatively stiff, possessing a relatively high spring constant, and therefore are not able to isolate low frequency vibration. Steei springs are ideal for isolating low frequency vibration because they can be designed to suit any required spring constant. However, they suffer from the disadvantage of low damping and must generally be supplemented with some form of damping arrangement. Rubber either in the natural form or in a synthetic form is a better material for isolating vibrations. Natural rubber is generally more elastic than synthetic, but does not possess the same degree of damping. However, rubber is almost incompressible and can only deflect under load when it can change shape.Hence, anti-vibration pads made from rubber generally have either a tread pattern or a series of grooves or recesses in one or both load-bearing surfaces, in order to allow space for the rubber to deform. These spaces are generally not enclosed spaces and the air can readily escape when the rubber isolator is subjected to a static or dynamic loading.

According to the invention a vibration isolation mat comprises a rubber mat having two or more parts, in which one part or parts alternates with a second part or parts the one part or parts having a series of rubber spigots protruding from one or both sides to locate with corresponding recesses in the surface or surfaces of the other part or parts, the length of the spigots being less than the depth of the corresponding recesses and the diameter of the spigots being such as to allow a sliding or interference fit in the recesses to produce trapped air pockets between the parts.

The invention will be described with reference to the accompanying drawings: Figure 1 is a perspective view of a machine foundation the sides being lined with expanded polystyrene, and the base being supported by vibration isolation mats.

Figure 2 is a section of a two part vibration isolation mat.

Figure 3 is a section of a multi layered mat.

A vibration isolation mat A is used to absorb vertical machine vibrations and is shown in Figure 1 as a support for a machine foundation a2 at the base of a pit for receiving said foundation a2. Said pit comprises concrete floor and side walls a'. The walls of the pit may be lined with expanded polystyrene a4, as shown, to create an air gap, or further isolation mats A if horizontal vibration has also to be absorbed. A sealant a3 closes the gap between the top of the concrete walls and the top of the machine foundation a2.

Vibration isolation mats may also be mounted on top of the machine foundation a2, between it and the base of the machine.

In one embodiment of the present invention, as shown in Figure 2, an isolation mat A is formed as a two-part rubber mat 1,2, each part being made from natural or synthetic rubber, depending on the application and environment. One part 1, has a series of spigots 3 of rubber protruding from one side which locate in corresponding recesses 4 moulded into one side of the other part 2. The height of the spigots 3 in part 1 is less than the depth of the corresponding recesses 4 in the other part 2.

When the two parts 1,2 are pressed together the spigots 3 on part 1 locate in the corresponding recesses 4 in the other part 2. The diameter of the spigots 3 is such as to produce a sliding or interference fit in the corresponding recesses 4. The height of the spigots 3 is less than the depth of the recesses 4 so that trapped air pockets 5 are produced inside each recess 4. When the two parts 1,2 are fitted together and placed underneath a machine base, or a concrete foundation, they form a highly effective low frequency isolator. The reason for this is that the air pockets create both a space into which the rubber can deform to achieve the necessary deflection under static and dynamic loadings and, in addition, during the dynamic loading, the trapped air is alternately compressed and then allowed to expand and in so doing acts as an air damping suspension system.

In the embodiment illustrated in Figure 2, the surfaces 6 of the mat parts 1 and 2 which are remote from the spigots and recesses respectively are substantially plain or smooth.

An alternative isolation mat arrangement (not illustrated), which increases both the static deflec tion and the air damping, consists of one mat part 1, with spigots 3 protruding from both sides and two mat parts 2 one on top and bottom faces respectively of the spigotted part 1 to form a sandwich with the spigotted part 1 in the centre.

Alternatively, the recesses 4 may be formed in both surfaces of the mat 2 with a spigot mat 1 engaging each side forming a sandwich or a plurality of both mats 1,2 may be assembled to form a double sandwich.

Moreover, the mats 1,2 need not be plain on their surfaces 6 remote from the spigots and recesses.

These surfaces 6 may be serrated or moulded with raised patterns to increase their grip on the concrete.

Different degrees of deflection or spring constant and damping characteristics can be achieved by varying the hardness and type of rubbers used, the dimensions of the spigots and recesses and also by using multiple thicknesses of the embodiments already described to increase deflection of the mat.

For example, Figure 3 shows a mat comprising two thicknesses of the embodiment shown in Figure 2.

The mats may be moulded from nitrile rubber (N BR), neoprene rubber (CR), natural rubber (NR), butyl rubber(BR) silicon rubber (Si), polyurethane (UR) or other elastic polymers or combinations thereof.

The resultant vibration isolator comprised of a two or more part rubber mat, as described, is a very effective substitute for a steel spring suspension system for isolating low frequency vibrations. The energy absorption capacity of the material is also enhanced by the effect of air damping.

Claims (6)

1. A shock and vibration isolation mat comprising a rubber mat having two or more parts, in which one part or parts alternates with a second part or parts, the one part or parts having a series of rubber spigots protruding from one or both sides to locate with corresponding recesses in the surface or surfaces of the other part or parts, the length of the spigots being less than the depth of the corresponding recesses and the diameter of the spigots being such as to allow a sliding or interference fit in the recesses to produce trapped air pockets between the parts.

2. A shock and vibration isolation mat as claimed in claim 1 in which the mat is applied between the floor of a foundation pit and a machine foundation located therein.

3. A shock and vibration isolation mat as claimed in claims 1 or 2 in which the mat is applied between the side walls of the foundation pit and the sides of the machine foundation located therein.

4. A shock and vibration isolation mat as claimed in claim 1, in which the mat is applied between the machine and the foundation.

5. A shock and vibration isolation mat as claimed in any preceding claims in which the spigots on one part of the mat locate with a sliding or interference fit in the recesses in another part and when assembled enclose air pockets between the two parts.

6. A shock and vibration isolation mat substantially as described hereinbefore with reference to and as illustrated by the accompanying drawing.