METHOD OF AND APPARATUS FOR PACKING EXHAUST SILENCER CASINGS

Abstract: A strand of fibres of a suitable silencing material, e.g. basalt, is chopped into discrete lengths by passing it between two rollers (12, 15) one (15) of which carries a cutter (14). The chopped roving is carried in an air flow, established by an air blast, air jet or a vacuum, into a silencer casing (1) via a restrict­ ed opening (10). The fibres «fluff-up» to a wool-like consisten­ cy as they pass into the silencer casing (1). The strand may comprise continuous or relatively short fibres and these may be twisted, plaited or laid parallel.

Description: METHOD OF AND APPARATUS FOR PACKING EXHAUST SILENCER CASINGS This invention relates to a metnoa of an apparatus for packing exhaust silencer casings. Such silencer casings contain packing in order to assist in silencing exhaust gases from an engine by virtue of conversion of kinetic energy of the exhaust gases into mechanical displacements of the pacKing and thus heating thereof. The packing may be fibre "fluffed-up" into a wool-like consistency. This material can be produced by chopping continuous strands of glass fibre. In the past such silencer casings have been packed manually and, to assist in this process, it has been proposed to apply a vacuum to one end of the silencer casing. In order to adapt the process for automatic operation, glass fibre material in wool-like form has been fed into a hopper, from which it passes along ducts before being metered into individual quantities, each suitable for packing one silencer casing. However the material has been prone to clog in the ducts and this has made the accurate meterinq of the material difficult, if the expense of weigh pans is to be avoided. According to a first aspect of this invention there is provided a method of packing an exhaust silencer casing, which comprises establishing gas flow through the casing, chopping into discrete lengths a strand consisting of fibres other than continuous glass fibres, and allowing the chopped fibres to be carried into the casing in the gas flow. It should be noted that the term "strand" used in this specification refers to a plurality of fibres which may be twisted, plaited or laid parallel. A strand typically comprises 200 - 1600 fibres. The term "roving" refers to a bundle of strands. A roving typically comprises eight or more strands and may comprise over 500 fibres. The term "fibre" refers to an elongate object, such as a filament, from which a wool-li'ce material can be mace. It has been found that the individual fibres of each discrete length of chopped strand separate as they are carried inbo the silencer casing in the gas flow so that the fibres "fluff-up" in the desired manner in the silencer casing itself or as they enter the casing. According to a second aspect of this invention there is provided apparatus for packing an exhaust silencer casing comprising: means for establishing gas flow into the casing, and means for chopping into discrete lengths a strand consisting of fibres other than continuous glass fibres, the arrangement being such that the chopped fibres are carriea into the casing in the gas flow. Preferred features of the invention will be apparent from the subsidiary claims of this'specification. This invention will now be illustrated, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is part sectional view of a first embodiment of apparatus according to this invention; Figure 2 is a side view of a gun of the apparatus shown in Figure L; Figure 3 1S a front view of che gun flown in Figure 2; Figure 4 is a plan view of the gun shown in Figure 2; and Figure 5 is a schematic view of a second embodiment of apparatus according to this invention. The apparatus for packing a silencer casing 1 shown in Figure 1 comprises vacuum producing apparatus 2, sealing apparatus 3 and a gun 4. The silencer casing l is circular in cross-section, and One end thereof is closed by an end piece 5 which supports a perforated tube 6 extending through the silencer casing 1. The end piece 5 also supporrs a stub pipe 7 which, in use, connects the silencer to the rest of the exhaust assembly. A similar end piece (not shown) bearing a stub pipe ts welded to the other end of the silencer casing 1 after it has been packed. The vacuum producing apparatus 2 has a rubber sealing memoer 8 whiten fits tightly around the stub pipe 7. A vacuum is producea in the apparatus by means of a centrifugal compressor (not hown) driven by a forty horse power (29.8 K) motor (not shown). This produces a vacuum of around ten inches of mercury (33.9 KNm'2) in the apparatus 2. The sealing apparatus 3 likewise has a sealing member 9 and this seals against the open end of the casing 1 and also blocks off the open end of the perforated tube 6, as the tube 6 should not be filled with any packing material. The sealing member 9 includes a circular aperture 10 whose diameter is 3/4 inch (19mm) which provides communication between the interior of the sealing apparatus 3 and the interior of the casing 1. The aperture 10 forms a restriction in the pathway from the gun 4 to the interior of the casing 1. Figure 2 shows roving being fed into the gun 4 and discrete lengths of this being emitted from the gun 4. The roving consists of a bundle of strands each of which consists of a plurality of fibres, eg at least 100 or at least 1000 fibres, of a mineral such as basalt, ie the material from which rockwool is made. Other types of fibres which when "fluffed-up" form a wool-like material may be used, for instance ceramic fibres. The fibres typically have a diameter in the range of 6-12 microns. Attention is arawn to the co-pending British Patent Application No. 82/25865 (Serial No. ) which relates specifically to the use 0:' continuous glass fibres in similar apparatus. The fibres in each strand may be twisted , plaited or laid parallel and the fibres may be continuous,ie extend the length of the strand, or may be relatively short in which case they may be spun to form a strand in much the same manner as cotton or wool is spun to form threads. Preferably, the roving fed into the gun 4 comprises eight or more strands so that each discrete chopped length thereof consists of a large number of fibres, eg over 2000 fibres. However, it is possible to operate the apparatus with only a single strand being fed into the gun 4. Preferably, the fibres have a diameter of less than 30 microns or less than 15 microns. The roving is fed into the gun 4 from a spool (not shown) containing a length of about two hundred meters of roving. The gun 4 has an air-powered motor, contained in a housing 11, to which a rubber roller 12 is coaxially attached. The roving is driven through the gun 4 by means of the rubber roller 12 and a steel roller 13 which is hard in contact with the rubber roller 12. The roving is cut into discrete lengths by means of a cutter 14 mounted diametrically through a further roller 15 so that the cutter 14 extends along a generator of the roller 15. Every haif revolution of roller 15, the roving is severed at the point of contact between the rollers 12 and 15. The rollers 12, 13 and 15 are contained in a housing 16 (see Figures 3 and 4) having an inlet 17 and an outlet 18. Exhaust air from the air powered motor is fed into the housing 16 and, since the area of the outlet 18 is much greater than that of the inlet 17, the chopped lengths of roving are projected out of the gun 4 with the aid of a blast of this exhaust air. In operation a silencer casing 1 to be filled with packing is fitted onto the vacuum producing apparatus 2 and the sealing apparatus 3 is brought up to the open end of the casing 1. The centrifugal compressor is started. The gun 4 is then run and left running for a pre-determined period of time. This pre-determined period corresponds to the desired weight of fibre it is desired to pack into the particular silencer casing I and this can be calculated simply from the weight per unit length of the roving and the velocity at which the roving is fed through the gun 4. The chopped lengths of roving projected from the gun 4 are all sucked through the aperture 10 in the sealing member 9 by the vacuum applied at the other end of the silencer nosing 1, and the casing 1 is gradually filled with fibres. It has been found that the fibres in each chopped length of roving separate either before they enter the silencer casing 1 or while they are in the silencer casing I (probably the separation mainly takes place within the silencer), and this results in the production of the desired wool-like form of the fibres in the casing 1. The air flow within the casing 1 will of course be turbulent since it is being sucked through the perforated tube 6. The fibres do not pass into the tube 6 themselves. One advantage of the apparatus and method described is that it is possible to accurately meter the quantity of fibres with which each casing is packed Also, the ducting require for handling wool-like glass fibre is not required. The described method and apparatus may be used to pack any form of silencer casing including those in which exhaust gases make multiple passes of the whole or part of the length of the silencer casing. Various modifications of the method or apparatus are of course possible. For example, tests have been carried out with an arcuate aperture 10 in the sealing member 9, the aperture 10 having length of about four times its breadth. Although the roving "fluffed-up" in a satisfactory manner, it was nevertheless found that it "fluffed-up" better with the 3/4 inch (19 mm) diameter aperture referred to earlier. A second embodiment of the apparatus according to this invention is shown in Figure 5. This apparatus differs from that shown in the previous figures in that no vacuum is required to draw the chopped roving into the silencer casing. Instead, the chopped roving is carried into the casing by an air flow. A silencer casing 20 to be filled with packing is closed a the lower end as seen in Figure 5 by a closing plate 21 which has an aperture through which a perforated tube 22 of the silencer extends. The silencer casing 20 is mounted on a platform 23 through which air can pass. At the upper end of the silencer casing 20 as seen in the Figure is a closing plate 24 which carries a plug 25 for closing the upper end of the perforated tube 22. Chopped strands of roving are fed into the silencer casing 20 via a tube 26 and a conical member 27, the tube 26 being sealed in an aperture in the closing plate 24. The tube 26 thus forms a restriction in the pathway from a gun 28 to the interior of the casing 20. The gun 28 supplies chopped roving to the wide end of the conical member 27. The gun 28 is similar to the gun 4 described except that the exhaust. air thereof does not assist in projecting the chopped strands of roving from the gun 28, the chopped roving being projected from he gun 28 solely by the rotation of the rollers 12, 13 and 15. A narrow tube 29 opens into the tube 26, and compressed air is ?supplied through the narrow tube 29 into the tube 26. it has Seen found that the compressed air fed into the tube 26 draws large quantities of air into the conical member 27, through the wide end thereof and hence through the tube 26 into the silencer casing 20. The chopped roving is therefore carried by this air flow into the silencer casing 20. The air flow leaves the silencer casing 20 via the perforated tube 22. It has been found that the fibres of the chopped roving are "fluffed-up" in this process, and that the silencer casing 20 is filled in a very satisfactory manner. Examples of suitable dimensions and pressures for the apparatus shown in Figure 5 will now be given. Length of tube 26 3 inches (76.2 mm) Diameter of tube 26 1/2 inch (12.7 mm) Semi-angle of conical member 27 300 Diameter of wide end of conical member 27 3 inches (76.2 mm) Angie between tubes 29 and 26 35 Pressure of compressed air in 100 Ibs ins -2 tube 29 (689.5 KNm ) It is believed that the narrow diameter of the tube 26 is important in "fluffing-up" the chopped roving, since only with a narrow diameter is sufficient turbulence created in the tube 26 to acnieve this. Similarly, it is believed that the narrow aperture 10 in the apparatus shown in Figure 1 is responsible for creating the necessary turbulence to cause "fluffing-up". The narrower the diameter of the tube 26 or aperture 10, the smaller the compressed air pressure or vacuum needed to "fluff-up" the chopped roving. However, if the diameter is too small, the restriction is prone to clogging. It will be apparent that any means of establishing an air flow or us flow through the silencer casing to be packed may be used to carry the chopped roving nto the casing. This invention also relates to an exhaust silencer casing packed in accordance with the method described above and to an exhaust system comprising such a silencer casing.

Claims: CLAIMS 1 A method of packing an exhaust silencer casing, which comprises establishing gas flow through the casing, chopping into discrete lengths a strand consisting of fibres other than continuous glass fibres, and allowing the chopped fibres to be carried into the casing in the gas flow. 2 A method as claimed in claim 1, in which the strand consists of at least one hundred fibres. 3 A method as claimed in claim 2, in which the strand consists of at least a thousand fibres. 4 A method as claimed in any one of claims 1 to 3, in which the diameter of the fibres is less than thirty microns. 5 A method as claimed in claim 4, in which the diameter of the fibres is less than fifteen microns. 6 A method as claimed in anyone of claims 1 to 5, in which the strand comprises mineral fibres , eg basalt fibres, or ceramic fibres. 7 A method as claimed in any one of claims 1 to 6, in which the strand is fed between two rollers engaging one another, one of which is driven. 8 A method as claimed in claim 7, in which the strand passes between a pair of rollers, one of which has a cutter extending along a generator thereof. 9 A method as claimed in claim 7 or claim 8, in which the chopped fibres are projected into the casing with the assistance of a gas blast. 10 A method as claimed in any one of claims 1 to 9, in which the gas flow leaves the casing via a perforated tube which extends therethrough. 11 A method as claimed in any preceding claim, in wnich the gas flow carries the chopped fibres or filaments through a restriction, the breadth of which is less than one inch (25.4 mm), before they enter the casing. 12 A method as claimed in claim 11, in which the gas flow carries the chopped fibres through a tapering tube, the narrow end of which forms the restriction. 13 A method as claimed in any one of claims 1 to 12, in which the gas flow is established by reducing the pressure where the gas flow leaves the casing. 14 A method as claimed in any one of claims 1 to 12, in which the air flow is established by means of a jet of compressed air directed into the casing. 15 A method as claimed in claims 12 and 14, in which the jet is fed into the restriction. 16 A method as claimed in claim 15, in which the jet is inclined to the gas flow through the restriction. 17 An exhaust silencer casing packed according to a method as claimed in any preceding claim. 18 An exhaust system comprising a silencer casing as claimed in claim 17. 19 Apparatus for packing an exhaust silencer casing comprising: means for establishing gas flow into the casing, and means for chopping into discrete lengths a strand consisting of fibres other than continuous glass fibres, the arrangement being such that the chopped fibres or filaments are carried into the casing in the gas flow.

Inventors: ROBINSON, NORMAN
Applicants: UNIPART GROUP LIMITED
Application year: 1985
Main classification: F01N7
IPC codes: F01N1, B01D39, F01N13