GB2187133A

GB2187133A - Spinning die for production of blown fibre

Info

Publication number: GB2187133A
Application number: GB08605093A
Authority: GB
Inventors: Ian David Slack
Original assignee: Extrusion Systems Ltd
Current assignee: Extrusion Systems Ltd
Priority date: 1986-02-28
Filing date: 1986-02-28
Publication date: 1987-09-03
Also published as: GB8605093D0; GB2187133B

Abstract

The die comprises a body member (1) having a passage (3) extending therethrough, part of the passage (3) being reduced in diameter to form a venturi (9). A polymer pressure feed duct (11) extends through the body member and opens into the passage in the venturi where the velocity of the gas flow is maximised and the gas flow is mainly laminar. At the downstream side (7) of the venturi the gas flow rapidly expands and creates turbulence which breaks up the polymer into minute fibres. To enhance turbulence a secondary gas passage (17) may be provided opening into the passage downstream of the venturi. Usually blown fibre is produced by injecting a stream of molten polymer from a die coaxially into a turbulent stream of hot gas moving at a high velocity. The known process has a large consumption of compressed gas required to carry and break up the polymer flow into fibres whilst discharging to the atmosphere. Further due to the polymer entering a turbulent gas stream, the conversion of the polymer to fibre is not always completed. <IMAGE>

Description

SPECIFICATION Spinning die for use in the production of blown fibre The present invention relates to a spinning die for use in the production of blown fibre.

Polymeric substances such as nylon, polyester and polypropylene can be formed intoveryfine fibres for use in textile type products by the 'blown fibre' process. Essentially, this process involves the injection of a stream of molten polymerfromadie coaxially into a turbulent stream of hot gas moving at a high velocity. The hot gas is usually hot air and in the process a stream of polymer is broken up to form very fine fibres as low as 0.2 denier perfilament. For the process to work, the gas must be at a temperature at least equal to the temperature of the die through which the polymer is injected, and high enough to prevent premature solidification of the molten polymer.

Whilst this blown fibre process has been in usefor several yearsforthe production of non-woven textilesforfilter cloths and wipers, it has a couple of disadvantages. One is that the process has a large consumption of compressed air, and the other is that the conversion of the polymer to fibre is not always completed, and globules of polymer can befound dispersed over the fibre. The large consumption of compressed air results from the large volume of compressed air required to carry and break up the polymer flow into fibres whilst discharging into the atmosphere. The second problem is caused by the stream of elastic polymer entering a turbulent air stream causing uneven and spasmodic draw-down into fibre.

The aim ofthe present invention isto provide a spinning diefor use in blowing fibre,the die overcoming the above prior art problems.

According to the present invention there is provided a spinning die for use in the production of blown fibre, said die comprising a body member having a passage extending therethrough, part of said passage being reduced in diametertoform a venturi, a polymer pressurefeed ductextending through the body member and opening into said passage in said venturi.

In a preferred embodiment ofthe present invention said passage is of circular transverse crosssection and the venturi is formed by gradually reducing and then increasing the diameter of the said passage. Preferably, on the inlet side of the venturi the reduction in diameter is parabolic to minimise turbulence in the gas flow through the said passage.

Arranged preferably at right angles to said passage, is the polymer pressure feed duct which preferably has a conically shaped end nearest to said passage, a capillary connecting the conicaliy shaped end with said venturi.

In operation ofthe preferred embodiment, a stream of heated gas, preferably air, is pressure fed into the said passage, the gas flow accelerating through the venturi and subsequently discharging to atmosphere. Molten polymer supplied underpres- sure into the said feed duct is forced through the capillary and into the accelerated gas stream in theventuri. The flow of gas through the venturi is mainly laminarand is at maximum velocity causing the polymer entering the gas flow to be carried away by the gas flow at a constant rate. At the downstream end of the venturi, the gas flow rapidly expands imparting turbulence which breaks up the polymercarried with it into minute fibres which are ejected from the outlet end of said passage.

In a modified embodiment of the present invention a secondary gas passage extends through said main body and opens into said passage on the downstream side of the venturi. Gas flowthrough said venturi induces a current of gas to enter said passage via said secondary gas passage. The effect of this induced secondary gas is to increase the turbulence which breaks the polymer into fibres, and to also cool the gas stream preventing fusing together of the fibres.

Due to the polymer being introduced into the venturi where gas flow is at maximum velocity, a much lowervolume of air is required compared with the known coaxial flow system. Further, by maximising turbulence, efficient fibre production is ensured.

The present invention will now befurtherdescri- bed, by way of exampie, with reference to the ac companying drawing, in which a preferred embodiment of the present invention is shown in schematic axial cross-section.

The preferred embodiment of spinning die constructed according to the present invention and illustrated in the accompanying drawing comprises a main body 1 through which a main passage 3 extends. The main passage 3 is circular in transverse cross-section and has an inlet end 5 and an outlet end 7, a reduced diameter portion of said main passage 3forming a venturi 9.

A polymer pressure feed duct 11 extends at right angles to the main passage 3 and has a conicallyshaped end region 13 nearest to the main passage 3, the conically shaped end region 13 connecting with the centre ofthe venturi 9via a capillary duct 15.

Downstream ofthe venturi 9 a secondary passage 17 opens into the main passage 3.

In use, a stream of heated air is pressure fed into the inlet end 5 of the main passage 3, the airflow accelerating through the venturi 9 and discharging to the atmospherethrough outlet end 7. Molten polymer is supplied under pressure into the feed duct 11 and is forced through capillary duct 15 and into the accelerated air stream in the venturi 9.

The flow of airthrough the venturi 9 is mainly lam- inarand is at maximum velocity, causing the polymer entering the airflow to be carried away at a constant rate. At the downstream end of the venturi 9 the airflow rapidly expands importing turbulence which breaksupthe polymercarriedwith itinto minute fibres which are ejected from the outlet end 7 ofthemain passage 3.

Turbulence is increased by the provision of the secondary passage 17,thevacuum created bythe venturi 9 in the main passage 3, drawing airthrough the secondary passage 17. The effect of this sec ondary induced air is to both increase theturbulence to break down the polymer flow into fibres, and to also cool the air stream to prevent fusing together of the fibres.

The present invention thus provides a simple spinning die for use in the production of blown fibre, the spinning die overcoming certain problems and disadvantages inherent in the prior art apparatus used in the blown fibre process.

Claims

1. A spinning die for use in the production of blown fibre, said die comprising a body member having a passage extending therethrough, part of said passage having a reduced transverse dimension to form a venturi, a polymer pressure feed duct extending through the body member and opening into said passage in said venturi.

2. A die as claimed in claim 1, in which the passage has a circulartransverse cross-section.

3. A die as claimed in claim 2, in which the venturi is formed bythe passage having a graduallyreducing and increasing diameter along partof its length.

4. Adie as claimed in claim 2 orclaim 3, in which the passage on what is, in use, the inlet side of the venture, is reduced in diameter parabolically.

5. A die as claimed in any one of claims 1 to4, in which the polymer pressure feed duct is arranged to open into the passage at right angles to the passage.

6. Adie as claimed in anyone of claims 1 to 5, in which the polymer pressure feed duct has a conically shaped region nearto said passage, a capillary connecting the conically shaped end with said venturi.

7. A die as claimed in anyone of claims 1 to 6, in which a secondary passage extendsthroughthe body member and opens into said passage on what is, in user the downstream side oftheventuri.

8. A method of producing blown fibre, compris ing the steps offeeding a stream of heated gas under pressurethrough through a passage in a body member of a spinning die, part ofthe passage having a reduced dimension to thus form aventuri, and feeding molten polymer under pressure through a pressure feed duct which extends through said body member and opens into said passage in said venturi.

9. A method as claimed in claim 8, in which sec ondarygas is drawn into the polymer and gas stream in the passage downstream oftheventuri.

10. A method of producing blown fibre substantially as hereinbefore described with reference to the accompanying drawings.

11. A spinning die for use in the production of blown fibre, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.