GB1603874A

GB1603874A - Silencers

Info

Publication number: GB1603874A
Application number: GB4578077A
Authority: GB
Original assignee: National Research Development Corp UK; National Research Development Corp of India
Current assignee: National Research Development Corp UK; National Research Development Corp of India
Priority date: 1978-04-26
Filing date: 1978-04-26
Publication date: 1981-12-02

Description

(54) IMPROVEMENTS IN AND RELATING TO SILENCERS (71) We, NATIONAL RESEARCH DEVELOPMENT CORPORATION, a British Corporation established by Statute, of Kingsgate House, 66-74 Victoria Street, London, S.W.1, 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:- The present invention relates to silencers for hand-held, power-driven apparatus and in particular, but not exclusively, to silencers for hand-held concrete breakers.

During the last decade a lot of work has been carried out on silencing hand-held breakers. Silencers and damped-steel tools are now available to fit every breaker; even so it has been found that a silenced breaker will cause annoyance when working outside an occupied building. For example in a typical case investigated it was found that the noise from a conventionally silenced pneumatic breaker measured at the first floor level of a building outside which the breaker was being used was 68 dBA against a background level of 55 dBA and although 68 dBA is not very loud, due to the nature of the noise it tended to be annoying, the rattle and ringing of the steel and the pulsating exhaust air being the main causes.

According to the invention there is provided a silencer for a hand-holdable power-driven breaker apparatus comprising a flexible shield of matenal adapted to fit to the breaker to surround the breaker and a fitted breaker tool and with a bottom end providing a breaker-tool aperture, the shield or at least one part of the shield being of transparent or translucent material so that an operator can see from outside the shield what is happening inside the shield.

Conveniently the bottom end of the shield is weighted to encourage contact with material acted on by the breaker-tool.

In preferred embodiments, however, the silencer may be provided with a flexible brush carried at the bottom end of the shield.

The shield is preferably able to flex to adjust to dimensional changes as the breaker steel penetrates the material being operated on.

For use with a hand-held breaker, the shield may be open at the top i.e. of a generally annular configuration and, in use, it is secured e.g. by a clip or the like, around some part of the apparatus with which the shield is to be used. The shield may be of dome-like configuration at the top so as substantially completely to enclose the apparatus with which it is to be used.

When the shield is weighted at its bottom edge, this may be by any convenient means, for example by ballast. Sand, gravel or other particulate material might be used for this purpose but a liquid, especially a colourless liquid like water, is thought usually to be preferable.

Where instead a flexible brush is used, the brush is preferably detachably secured to the rest of the shield to allow a replacement brush to be fitted when desired. For example the brush may include a base member attached to the rest of the shield by one or more clips.

The flexible nature of the shield may be achieved in a number of ways but a preferred method is to have the shield or at least a portion of the shield formed as a concertina-like structure.

In particular embodiments of the invention where only the top portion of the shield is so formed the bottom portion of the shield is made of transparent or translucent material or includes at least a part of transparent or translucent material. Conveniently in such cases the bottom portion of the shield is of cylindrical shape.

Alternatively, or additionally, the shield, or a section of the shield, may be doublewalled in which case the shield, or the double-walled section of the shield, includes means enabling the space between the double walls to be internally pressurised by a supply of compressed air fed to this space.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings of which Figures 1 and 3 show vertical sections of three silencers according to the present invention fitted on a handheld 36 Kg Compair breaker. Figure 4 is a cross section taken on the line -IVin Figure 3. Figure 5 shows a vertical section of another embodiment of the invention. Figures 6 and 7 are cross sections of the shield taken on the lines VI-VI and VII-VII in Figure 5 but omitting the breaker. Figure 8 shows a brush seal for use with the embodiments of Figures 1 to 7 in place of the brush seal illustrated in Figures 1, 2 and 3 or Figure 5.

The same reference numerals have been used in the Figures to indicate like parts in the Figures. In particular, reference number 12 has been used throughout for the breaker, reference number 13 for the breaker tool, and reference numeral 14 for the shield.

Referring now to Figure 1, in the embodiment illustrated there the shield 14 is a concertina-like structure formed from a single skin bag of approximately 3 mm thickness. The material of the bag may be opaque (e.g. synthetic rubber) or transparent e.g. p.v.c.). When an opaque material is used then a transparent or translucent part is provided, which may be windows as indicated at 15, 16, so that the operator can see from outside the shield what is happening inside the shield.

At its top end the shield is secured to the breaker by a clip 17. At its bottom end the shield is secured by a clip 21 to a circular brush 19 providing an acoustic seal with the material 22 on which the breaker is operating.

The embodiment of Figure 2 is identical to that of Figure 1 except that the lower portion (23) of the shield is cylindrical and may be formed of a different material to the top portion 24. If desired, this lower portion may be provided with reinforcement.

In the embodiment shown in Figure 3, the top portion of the shield is formed as a single-skinned bellows 25 and the bottom portion of the shield is formed as a doublewalled cylindrical portion 27.

As with the second embodiment, the choice of materials for each of the two portions is the same as in the first embodiment and once again windows are provided if the cylindrical portion 27 is made of opaque material.

To ensure that the cylindrical portion 27 is fairly rigid, there is provided within the volume surrounded by Portion 27 a rigid reinforcement member 29 which is secured at its bottom end (by cli 21 to the brush 19 and at its top end &commat;y (by ciip 30) to the bottom of the bellows 25.

The reinforcement member 29 comprises a ring 31 (of approximately 200 mm diameter) at its top end and four equally spaced longitudinal ties 33 (see also Figure 4) which abut with the top surface of the brush.

In operation, compressed air can be bled off from the breaker supply line (35) to inflate portion 27 into the bell shape shown in Figures 3 and 4. The maximum thickness t of the double wall cavity is approximately 65 mm. Numeral 37 indicates a tap for con tolling or stopping the bleed.

With a breaker fitted with a standard steel, noise readings, taken for the system illustrated in Figures 3 and 4 showed the shield 14 to be responsible for an overall sound reduction of about 8 dBA (at 7 metres from the source) in addition to the reduction attributable to the conventional muffler now provided as a matter of course around the exhaust ports of the top end of the breaker. With a breaker fitted with a muffled steel, the reduction attributable to the shield was 5.5 dBA.

The shield was shown to be particularly advantageous in suppressing noise at higher frequencies e.g. from about one kHZ upwards.

Although Figure 3 and 4 show one example of a multi-walled shield, it will be appreciated that more than two walls can be used if desired. For example a three walled version could be produced so as to provide two layers of compressed air around the machine to be silenced. Such shields might have the advantage of providing even better sound insulation and toughness than the two-walled version.

Figures 5 to 7 show an embodiment in which the shield 14 is a concertina-like structure made from flexible plastic of approximately 3 mm thickness. The material should be translucent or transparent in order to transmit light into the shield. The upper part of the shield is smaller in section than the lower part. A window 40 is placed in the shield where the sectional change occurs. The window material is preferably glass-clear plastic. It is mechanically fastened on to the shield.

In the embodiments so far described in this Specification, the use of a brush at the bottom edge of the shield to provide an acustic seal is of course an important practical feature. The brushes 19 shown in Figure 1 to 3 and Figure 8 have been shown to operate satisfactorily in this respect. In each case, the bristles of the brush are secured in a plywood ring 30, 220 mm outside diameter, 100 mm inside diameter and 25 mm in thickness, using bundles of nylon bristles 4 mm diameter, each bundle being 9 mm diameter and 75 mm long. The bundles are fixed to the plywood bases in 4 concentric circles to form a circular curtain, which while allowing exhaust air to escape acts as an acoustic barrier.

The nylon strip brush 42 shown in Figure 5 is an alternative to the brush 19 shown in the eariler Figures. Manufactured by Kleeneze Ltd., the brush 42 is housed in a metal channel 44 made into a ring of 220 mm diameter to form a circular curtain 60 mm tall and 9 mm deep.

When the breakers of Figures 1 to 7 are to be used near a vertical obstruction such as a kerb, or in a trench, the circular brushes so far illustrated may be interchanged with a D-shaped brush. With the straight edge of the brush placed along the kerb or the trench wall the breaker may then be used normally with minimum hindrance from the silencer.

When it is desired to operate the breaker at a slant to the vertical then the brush conveniently takes the form shown in Figure 8, where the bristles of the brush are cut at an angle to achieve the desired seal with material 22.

In variations of the above embodiments, means are provided to lift the brush and hence the bag, up to a height of 200 mm from ground level, in order to reveal the tool point. This may be desirable when the tool needs to be positioned accurately. The lifting means could be either foot or hand operated. Means may also be provided to adjust the height of the bag, in order that it may be easily fitted to different makes of concrete breakers.

WHAT WE CLAIM IS: 1. A silencer for a hand-holdable power-driven breaker apparatus comprising a flexible shield of matenal adapted to fit to the breaker to surround the breaker and a fitted breaker tool and with a bottom end providing a breaker-tool aperture, the shield or at least one part of the shield being of transparent or translucent material so that an operator can see from outside the shield what is happening inside the shield.

2. A silencer as claimed in Claim 1 in which the bottom end aperture has an edge provided by a flexible brush to engage material acted on by the breaker-tool and form a sound-reducing enclosure.

3. A silencer as claimed in any preceding Claim in which the shield is able to flex to adjust to dimensional changes as the breaker steel penetrates the material being operated on.

4. A silencer as claimed in Claim 3 in which the shield is able to flex by having the shield or at least a portion of the shield formed as a concertina-like structure.

5. A silencer as claimed in any preceding claim in which the shield, or a section of the shield, is double-walled and the shield, or the double-walled section of the shield, includes means enabling the space between the double walls to be internally Pressurised by a supply of compressed air fed to this space.

6. A silencer as claimed in any preceding claim in which the cross-section of the shield changes at a point in its length and at least there provides a viewing window into the shield body.

7. A shield as claimed in any preceding claims in which a viewing window is provided lying in a plane substantially transverse to the shield body.

8. A shield as claimed in any preceding claim having an open top end to receive and clip around a breaker body.

9. A silencer as claimed in any preced- ing claim in which the shield has a dome-like configuration to close it at the top so as substantially completely to enclose the apparatus with which it is to be used.

10. A silencer as claimed in any of Claims 1 to 8 in which the shield is open at the top being of a generally annular configuration so that, in use, it may be secured around some part of the apparatus with which the shield is to be used.

11. A silencer as claimed in any preceding Claim including means for lifting the bottom end of the shield to reveal the point of a tool in use on the apparatus.

12. A silencer substantially as hereinbefore described with reference to and as illustrated in Figure 1, or Figure 2, or Figures 3 and 4, or Figures 5, 6 and 7 of the accompanying drawings or any of these Figures including the brush seal of Figure 8.

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

Claims

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

5 is an alternative to the brush 19 shown in the eariler Figures. Manufactured by Kleeneze Ltd., the brush 42 is housed in a metal channel 44 made into a ring of 220 mm diameter to form a circular curtain 60 mm tall and 9 mm deep.

When the breakers of Figures 1 to 7 are to be used near a vertical obstruction such as a kerb, or in a trench, the circular brushes so far illustrated may be interchanged with a D-shaped brush. With the straight edge of the brush placed along the kerb or the trench wall the breaker may then be used normally with minimum hindrance from the silencer.

When it is desired to operate the breaker at a slant to the vertical then the brush conveniently takes the form shown in Figure 8, where the bristles of the brush are cut at an angle to achieve the desired seal with material 22.

In variations of the above embodiments, means are provided to lift the brush and hence the bag, up to a height of 200 mm from ground level, in order to reveal the tool point. This may be desirable when the tool needs to be positioned accurately. The lifting means could be either foot or hand operated. Means may also be provided to adjust the height of the bag, in order that it may be easily fitted to different makes of concrete breakers.

WHAT WE CLAIM IS: 1. A silencer for a hand-holdable power-driven breaker apparatus comprising a flexible shield of matenal adapted to fit to the breaker to surround the breaker and a fitted breaker tool and with a bottom end providing a breaker-tool aperture, the shield or at least one part of the shield being of transparent or translucent material so that an operator can see from outside the shield what is happening inside the shield.
2. A silencer as claimed in Claim 1 in which the bottom end aperture has an edge provided by a flexible brush to engage material acted on by the breaker-tool and form a sound-reducing enclosure.
3. A silencer as claimed in any preceding Claim in which the shield is able to flex to adjust to dimensional changes as the breaker steel penetrates the material being operated on.
4. A silencer as claimed in Claim 3 in which the shield is able to flex by having the shield or at least a portion of the shield formed as a concertina-like structure.
5. A silencer as claimed in any preceding claim in which the shield, or a section of the shield, is double-walled and the shield, or the double-walled section of the shield, includes means enabling the space between the double walls to be internally Pressurised by a supply of compressed air fed to this space.
6. A silencer as claimed in any preceding claim in which the cross-section of the shield changes at a point in its length and at least there provides a viewing window into the shield body.
7. A shield as claimed in any preceding claims in which a viewing window is provided lying in a plane substantially transverse to the shield body.
8. A shield as claimed in any preceding claim having an open top end to receive and clip around a breaker body.
9. A silencer as claimed in any preced- ing claim in which the shield has a dome-like configuration to close it at the top so as substantially completely to enclose the apparatus with which it is to be used.
10. A silencer as claimed in any of Claims 1 to 8 in which the shield is open at the top being of a generally annular configuration so that, in use, it may be secured around some part of the apparatus with which the shield is to be used.
11. A silencer as claimed in any preceding Claim including means for lifting the bottom end of the shield to reveal the point of a tool in use on the apparatus.
12. A silencer substantially as hereinbefore described with reference to and as illustrated in Figure 1, or Figure 2, or Figures 3 and 4, or Figures 5, 6 and 7 of the accompanying drawings or any of these Figures including the brush seal of Figure 8.