GB2036122A

GB2036122A - Making Fibrous Webs

Info

Publication number: GB2036122A
Application number: GB7939448A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1978-11-24
Filing date: 1979-11-14
Publication date: 1980-06-25
Also published as: DE2850833A1; DE2850833C3; ATA678479A; CH630425A5; AT372121B; FR2442288A2; DE2850833B2; IT7927416A0; FR2442288B2; GB2036122B; IT1165375B

Abstract

A process for producing fleeces comprising substantially unidirectional short fibres on a support (for use as reinforcements in composite materials), in which a suspension of fibres in a fluid medium is conveyed down a channel to the surface of a rotating drum where the fibres are deposited on the support with the suspension liquid being drawn into the interior of the drum by a pressure gradient. The alignment of the fibres being improved by including, in the channel 2, a number of longitudinally aligned partitions 5 which subdivide the channel before the suspension 10 is fed to the drum 6. <IMAGE>

Description

SPECIFICATION Process for Producing Fleeces or Mats from Short Fibres on a Support The invention relates to a process for production of fleeces or mats with orientated short-fibres on a support which form reinforcements for composite materials. A process for producing such mats is described in GB 1419392.

In this specification the process is carried out with a greater speed for the peripheral surface of drum than the speed at which the suspension is fed thereto. In this process a first orientation of the short fibres is effected during the flow in the channel (3). The main alignment effect, however, is obtained in transition from the channel to the drum surface, as a result of acceleration of the fibre suspension due to the speed difference between the drum and suspension flow.

The precision of the alignment of the short fibres exerts a considerable influence on the strength properties of the material produced.

This invention seeks to provide, in a process as aforesaid, for better alignment of the fibres, whilst still in the channel.

According to this invention there is provided a process for the production of fleeces comprising substantially unidirectional short-fibres on a support wherein the fibres are suspended in a fluid medium and conveyed to the surface of a rotating drum where the fibres are deposited on the support with the suspension fluid being sucked into the interior of the drum using a pressure gradient, in which process the suspension of fibres is fed to the drum through a channel having subdivisions formed by longitudinal partitions. In such an arrangement and with a sufficiently small distance between the divisions between individual channels alignment and compaction of the fibres is achieved due to frictional effects and different flow velocities which result in velocity components which are directed transverse to the flow.

According to a further development of the invention the passage provided for the feed of the fibre suspension in the channel is narrowed before it flows up onto the drum.

The narrowing of the channel accelerates the fibre suspension, as a result of which the short fibres are considerably compacted in addition to being aligned to the maximum. Tests have shown that in the final pressing and hardening of components made of non-woven fibrous fabrics produced in accordance with the invention far less pressure is required for the purpose of obtaining the desired density and strength. It has thus become possible, by means of these nonwoven fabrics, to press and harden even largearea components in autoclaves, in which, as is known, the pressures must not exceed about 10 bar, without strength and rigidity losses from inadequate proportions of fibre. Despite this moderate pressure it has proved possible to increase the bending strength by about 50% and the bending modulus by about 20% by comparison with the process of patent 141 9392.

This means that the strength properties of components of short-fibre non-woven fabrics almost reach the same levels as in corresponding components of endless fibres.

Embodiments according to the invention are illustrated in the accompanying drawings by way of examples only. In the drawings: Figure 1 shows the gradient of flow velocity in non-subdivided channel, Figure 2 shows the gradient in a divided channel, Figure 3 shows in perspective and schematically the feeding of the fibre suspension to the drum through a channel with divisions, Figure 4 shows in plan a channel with divisions and a converging feed passage also containing the division, and Figure 5 shows a further channel in accordance with Figure 4 but with divisions in the parallel part only of the channel.

Referring to the drawings in Figure 1 the velocity gradient in a channel 2 in which the flow of the suspension is not divided is shown and this has zero speed at the sides 3, increasing parabolically to a maximum at 4 and remaining constant over the remaining central part of the channel. In this arrangement and by vectorial action it is only within the portions between the sides 3 and the point 4 that the speed exerts a directional aligning force on the fibres. This force is obtained as a result of the fact that the flow ofthe suspension in this portion has a lateral speed component.If the channel 2 is divided by partitions 5 as shown in Figure 2 it is possible to arrange, by positioning the divisions 5 at suitable spacing, for the maximum speed 4 to be reached mid-way between the divisions so that a horizontal component acts on all the short fibres in the suspension between the sides 3.

An apparatus 1 shown in simplified configuration for the production of short-fibre fleeces or mats is shown in Figure 3 and comprises a channel 2 with divisions 5, and a drum 6 with collecting vessel 7. The drum 6 rotates in the direction shown by the arrow 8. By means of a device with a stirring mechanism (not shown) a suspension 10 of, for example glycerine and short fibres, is fed to the channel 2 and distributed thereover by means of a flow divider 1 The suspension 10 passes through divisions 5, which exert the aforementioned alignment effect on the fibres, so that they emerge over a lip 1 2 on which they are aligned longitudinally of the flow.The fibres flow onto the surface 1 3 of the drum 6 and as this is rotating at a peripheral speed equal to or greater than the feed speed of the suspension 10 the short fibres undergo a further directional alignment. The production of the fleece material and further processing is effected in a manner described in GB 141 9392.

To densify and compact the fibres in the suspension 10 flowing over the lip 12 onto the drum 6 the feed passage may be made convergent by baffles 1 5 mounted at an angle to the flow. In this arrangement the divisions 5 may diverge also to the lower edge of the channel 2 (as shown in Figure 4) or may terminate at the start of the diverging part (as in Figure 5) as the fibres retain their alignment between the baffles 1 5. It is also possible to construct the channel 2 without divisions and to use a convergent part only.

Claims

1. A process for the production of fleeces comprising substantially unidirectionai short fibres on a support wherein the fibres are suspended in a fluid medium and conveyed to the surface of a rotating drum where the fibres are deposited on the support with the suspension fluid being sucked into the interior of the drum using a pressure gradient, in which process the suspension of fibres is fed to the drum through a channel having subdivisions formed by longitudinal partitions.

2. A process in accordance with Claim 1, wherein the part of the channel feeding the fibre suspension to the drum is made convergent.

3. A process in accordance with Claim 2, wherein the partitions extend into the convergent part of the channel.

4. A process in accordance with Claim 3, wherein the suspension is fed between converging sides of the channel.

5. A process in accordance with Claim 2, wherein the partitions terminate at the commencement of the converging part of the channel.

6. A process for the protection of fleeces carried out substantially as herein described with reference to Figures 2 to 5 of the accompanying drawings.

7. Apparatus for producing fleeces in accordance with Claim 1 substantially as herein described with reference to and as shown in Figures 2 to 5 of the accompanying drawings.