GB2083864A

GB2083864A - Gas flow silencer

Info

Publication number: GB2083864A
Application number: GB8128501A
Authority: GB
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1980-09-24
Filing date: 1981-09-21
Publication date: 1982-03-31
Also published as: DE8127607U1; SE8006664L; FR2490855B1; FR2490855A1

Abstract

A porous plastics foam body 122 in a string net tube 125 is clamped over substantially its entire length between a resilient member 123 and the wall of the air passage 121. The member 23 may be a helical or zig-zag, Figs. 2A and 2B (not shown), wire spring or a further foam body or a rubber body. A pair of foam bodies (152, 154), Fig. 4 (not shown) may be clamped by a single helical spring (153). <IMAGE>

Description

SPECIFICATION Silencer device The present invention relates to a silencer device for use in the absorption of sound waves in a gas flow, which device comprises an elongate passage for the conduction of a said gas flow in use of the device and at least one elongate sound absorbing means disposed in said passage and comprising a body of a resilient and porous material having a transverse cross sectional diameter which is smaller than the transverse cross sectional diameter of the passage.

Previously known devices of this type use a sound absorbing core which is freely movable inside the passage transversely thereof. A characteristic feature of such previously known devices is that the cross section of the sound absorbing core is substantially smaller than that of the passage to facilitate easy introduction and mounting of the core inside the passage. Since the core of such known devices is completely free to move between the walls of the passage it is longitudinally supported only at one end which means that the core is exposed to a considerable longitudinal tension during passage of a gas flow.

It is also of vital importance that the absorption core should be securely supported relative to the passage, because otherwise it might be pulled along with the gas flow and fold up on itself thereby choking the passage. Furthermore, the freely movable absorption core may in some cases itself act as a secondary noise source as it vibrates and wobbles between the walls of the passage which is clearly undesirable in a silencer device.

It is an object of the present invention to avoid or minimize one or more of the abovementioned disadvantages and to provide a silencer device of the abovementioned type in which the sound absorbing core is substantially immovably fixed in the passage against transverse movement so that secondary noise generation is avoided and a safer and more secure attachment of the absorption core within the passage is achieved.

The present invention provides a silencer device for use in the absorption of sound waves in a gas flow, which device comprises an elongate passage for the conduction of a said gas flow in use of the device and at least one elongate sound absorbing means disposed in said passage and comprising a body of a resilient and porous material having a transverse cross sectional diameter which is smaller than the transverse cross sectional diameter of the passage, said sound absorbing means being resiliently held in a transverse direction relative to the passage by a resilient biasing means extending alongside said sound absorbing means.

In silencer devices of the type to which the invention pertains, the sound absorbing core or body may be made of a resiliently deformable polymeric foam material. Preferably it is made of a plastics foam material which is porous and has very good sound absorbing properties. The use of such a material for the sound absorbing means is advantageous also in that it is highly resilient and easy to bend which means that when the air flow passage is in the form of a rubber hose the sound absorbing body very easily adapts to the actual shape of the passage. However, the use of a plastics foam material by itself as the sound absorbing body is to some extent less preferred in that it has a relatively low resistance to the mechanical forces generated by the passing gas flow and may be subject to mechanical wear.

Indeed the use of such a material without any kind of reinforcement could result in the sound absorbing body being torn apart when exposed to a violent gas flow. Accordingly sound absorbing body is preferably enclosed within a section of tubular reinforcing net e.g. a string net hose which protects the plastics foam material against mechanical wear and damage and acts as a reinforcement for the plastics foam sound absorbing body.

Further preferred features and advantages of the invention will appear from the following description given by way of example of some preferred embodiments illustrated with reference to the accompanying drawings in which: Figs. 1 A and 1 13 are transverse and longitudinal cross-sections respectively of a first silencer comprising a cylindrical absorption core resiliently clamped between a coil spring and the interior walls of the silencer passage; Figs. 2A, 3 and 4 are corresponding views similar to Fig. 1 A of second, third, and fourth embodiments; and Fig. 213 is a partially cut-away perspective view of the second embodiment of Fig. 2.

In Figs. 1A and 1B there is shown a silencer comprising a cylindrical passage 121 defined by a conduit 120. A sound absorbing core in the form of a cylindrical body is clamped within the passage 121 against a side wall of the conduit 120 by means of a resilient biasing means in the form of a coil spring 123. The latter extends in parallel with and alongside the sound absorbing body 122 and is of substantially the same length as the latter.

The silencer device according to this embodiment of the invention is assembled by feeding the sound absorbing body 122 into the conduit 120. At the same time or subsequently the coil spring 123 is introduced into the passage in a stretched-out state i.e. under the longitudinal tension so that its effective transverse diameter is reduced to such a size that the spring may pass through the passage alongside the sound absorbing body 122 more or less freely. When the absorption body 122 and the coil spring 123 are correctly located in the passage 121 the coil spring 123 is allowed to contract longitudinally back towards its normal state and its transverse diameter or cross section increases back towards its normal size which is such that the absorption core 122 is clamped by the spring 123 against the wall of the passage 121.The contact pressure between the core 122 and the wall of passage 121 gives rise to a frictional force between the body 122 and the wall strong enough to substantially prevent the body 122 from being displaced by the air flow. It is to be noted that the resilient clamping force between the body 122 and the wall of the conduit 120 is due to the contraction force of the coil spring 123, but that once this is mounted in the passage the major part of the transverse resilient deformation resulting from the transverse biasing forces exerted by the spring 123 does in fact take place in the resiliently deformable sound absorbing body which in this case is of a resiliently deformable porous plastics foam material i.e. the coil spring portions in contact with the body 122 press into the sides of the body displacing the adjacent portions of the body generally radially inwardly of the outer circumference of the body to a greater or lesser extent as shown in Fig. 1 A. The absorption core 122 is protected against mechanical wear by a surrounding string net hose 125.

In Figs. 2A and 2B there is shown a second embodiment of the invention. According to this embodiment, a sound absorbing body 132 of cylindrical shape is clamped within a cylindrical passage 131 defined by a conduit 130. The clamping force acting on the sound absorbing body is exerted by a zig-zag shaped wire spring 133. The silencer device is assembled in a manner similar to that described above which means that the body 132 and the wire spring 133 are introduced into passage 131 whilst the spring 133 is in a longitudinally extended state. Once the body 132 and the spring 133 are properly longitudinally located within the passage 131 the spring 133 is allowed to contract longitudinally and, thereby, exert a transverse clamping force upon the body 132 as the spring expands transversely.In order to protect the sound absorption body 132 against mechanical wear and damage it is surrounded by a tubular net 135 in the form of a string net hose 135.

In Fig. 3, there is a third silencer device according to the invention in which two resilient elongate body means 142, 143 are mounted in parallel alongside one another in a flow passage 131 defined by a conduit 140. Both of them may be made of a resiliently deformable porous plastics foam material having sound absorbing properties. Alternatively, one of these body means 142, 143 may be made of a non-porous but resiliently deformable material e.g. rubber and act as a spring means alone like the spring means of the previously described embodiments. This silencer is assembled by simultaneous introduction of the two cores during elongation of both of them allowing both of them to expand radially once they are properly located longitudinally in the passage 141 and allowed to contract axially.

In Fig. 4 there is shown a fourth embodiment of the invention in which two sound absorbing bodies 152,154 are located in parallel alongside one another with a clamping spring 153 in a cylindrical passage 151 defined by a conduit 150.

The spring 153 is a cylindrical coil spring which during assembly of the device is stretched longitudinally to assume a reduced cross-sectional extent. A clamping force acting on the bodies 152, 154 is obtained by longitudinal contraction of the spring means 153 with transverse expansion as in the above described embodiments.

The above described examples are given for the purposes of illustration only of some embodiments which are covered by the claims. It is to be understood that the embodiments of the invention are not limited to the described examples but may be freely varied within the scope of the claims.

Claims

1. A silencer device for use in the absorption of sound waves in a gas flow, which device comprises an elongate passage for the conduction of a said gas flow in use of the device and at least one elongate sound absorbing means disposed in said passage and comprising a body of a resilient and porous material having a transverse cross sectional diameter which is smaller than the transverse cross sectional diameter of the passage, said sound absorbing means being resiliently held in a transverse direction relative to the passage by a resilient biasing means extending alongside said sound absorbing means.

2. A silencer device according to Claim 1 wherein said resilient biasing means is of substantially the same length as the sound absorbing means.

3. A silencer device according to Claim 1 or Claim 2, wherein the resilient biasing means comprises a cylindrical coil spring.

4. A silencer device according to Claim 1 or Claim 2, wherein said spring means comprises a zig-zag shaped wire spring.

5. A silencer device according to Claim 1 or Claim 2, wherein the resiliently biasing means comprises a substantially homogeneous body of a resiliently deformable material.

7. A silencer device according to any one of Claims 1 to 6 wherein the sound absorbing means is of a resiliently deformable polymeric foam material.

8. A silencer device according to Claim 7 wherein the sound absorbing means is of a plastics foam material.

9. A silencer device according to Claim 8 wherein the plastics foam material is enclosed in a tubular reinforcing net.

10. A silencer device according to Claim 1 substantially as described hereinbefore with particular reference to Figs. 1A and 1 B, Figs. 2A and 2B, Fig. 3 or Fig. 4 of the accompanying drawings.