GB2062617A - Method of manufacturing glass fibres - Google Patents

Abstract

A method of manufacturing glass fibres in which molten glass is drawn through a plurality of nipples 6 in the wall of a vessel 2 in which is maintained a reservoir of molten glass, the upper surface of which is indicated by the chain line 21. The method comprises the steps of allowing particulate glass material, fed to an opening 4 in the cover 3 of the vessel 2, to fall freely through a distance x onto a region of a horizontal or substantially horizontal shelf 12, melting the particulate glass material on the shelf 12 and allowing it to flow over an edge 13 of the shelf into the reservoir of molten glass. The minimum distance y between the edge 13 and the boundary of said region is 0.3x, and a hydrostatic head of molten glass is maintained in said reservoir, above the nipples, which is not less than 150 mm but is less than the height of the edge 13 above the nipples. <IMAGE>

Description

SPECIFICATION Method of manufacturing glass fibres This invention relates to a method of manufacturing glass fibres.

It is customary to produce glass fibres in a continuous manner by drawing molten glass through a plurality of nipples located in the wall of a vessel, for example a crucible. A reservoir of molten glass is maintained in the vessel by supplying particulate glass material, for example glass scrap or cullets, to the vessel and melting this material by means of heating devices, for example radiant electric heating elements, within the vessel.

One apparatus for producing glass fibres in the above-mentioned way is disclosed in U.S. Patent No. 3,918,946. In operating the apparatus described in this U.S. Patent, it has been found that some of the solid glass material supplied via the conduits 12, 1 2a tends to carry over into the clarifying section 1 6 of the crucible 2 and reach the nipples or perforations of the bottom plate 5 in an unmelted state, resulting in breakage of the fibres issuing from the bottom plate.

The present invention aims to provide a method of manufacturing glass fibres which avoids the disadvantage mentioned above.

According to the invention, a method of manufacturing glass fibres by drawing molten glass through a plurality of nipples in the wall of a vessel in which a reservoir of molten glass is maintained, comprises the steps of allowing particulate glass material to fall freely through a distance x onto a region of a horizontal or substantially horizontal shelf, melting the particulate glass material on said shelf and allowing it to flow over an edge of the shelf into the reservoir of molten glass, the minimum distance between said edge and the boundary of said region being 0.3x, and maintaining a hydrostatic head of molten glass in said reservoir, above the nipples, which is not less than 150 mm but is less than the height of said edge above the nipples.

When using the method of the invention, many of the glass particles falling onto said region of the shelf will come to rest within the boundary of the region and those particles that rebound out of the region will come to rest on the shelf.

Consequently, the risk of unmelted glass material passing into the reservoir of molten glass is virtually eliminated.

Of course, the greater the minimum distance between said edge of the shelf and the boundary of the region onto which the particulate glass material falls, the smaller the chance of solid particles of glass passing into the reservoir of molten glass. However, if this distance is made too great, the apparatus becomes too large and the economic viability of the method decreases.

Generally speaking, it is preferred that this minimum distance should not greatly exceed 0.5x.

It is preferred that the particulate glass material should commence its free fall onto said region of the shelf with a vertical component of velocity substantially equal to zero. This can be achieved by feeding the particulate glass material substantially horizontally to its point of free fall, for example using a screw conveyor or a vibratory feeder.

When carrying out the method according to the invention, I have found that a very economical production of glass fibres results if the particulate glass material is fed onto the shelf at a rate not exceeding 20 g per hour per cm2 of the area of the entire shelf.

The preferred particulate glass material for use in the method according to the invention is broken glass scrap which has been sieved through a No. 3 mesh (ASTM) screen. It is preferred to avoid the use of prepared glass material, such as marbles.

Preferably, the melted glass, in flowing to said edge of the shelf, passes through a trough in the shelf and/or over a barrier on the shelf. Any foreign matter in the glass becomes trapped by the trough and/or barrier and is not carried over into the reservoir of molten glass.

Preferably, the method according to the invention is performed in apparatus in which said shelf forms an integral part of the wall of the vessel in which said reservoir of molten glass is maintained. Preferably, the nipples are provided in a nipple plate forming the bottom of the vessel.

The nipples may be of a conventional design, but preferably steps are taken to maintain the outlet end faces of the nipples as cool as possible, in order to minimise the risk of these end faces being "wetted" by the issuing molten glass. For example, the cross-sectional area of the material of the nipples may be greater at the outlet end of a nipple compared with a region of the nipple upstream of the outlet end, and this region of the nipple may be surrounded by a ring of thermally insulating material, for example ceramic material.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a sectional elevation, taken on the line I--) of Figure 2, of part of an apparatus for manufacturing glass fibres by the method according to the invention, Figure 2 is a plan of the crucible of the apparatus of Figure 1, with the cover partly broken away, and Figure 3 is a sectional view, on a greatly enlarged scale, through partgf the nipple plate of the apparatus of Figures 1 and 2.

The drawings show a glass-spinning apparatus comprising a vessel in the form of a crucible 2 constructed from refractory material, the crucible being open at its bottom. The crucible is provided with a cover 3 having two openings 4 therein.

The bottom of the crucible is closed by a substantially horizontally disposed, rectangular nipple plate 5 in which a plurality of glass fibre drawing nipples 6 are mounted. Flanges 7 and 8 secured to each of the two opposed long edges of the plate 5 incline downwardly from the plate 5 and are embedded in refractory, thermally insulating material 9 surrounding the crucible 2.

The nipple plate 5, its flanges 7, 8, and at least that part of the insulating material 9 surrounding the lower part of the crucible 2 may be arranged in substantially the same way as the correspondingly numbered items in the apparatus shown in the drawings of U.S. Patent No. 3,918,946. Further refractory, thermally-insulating material 11 overlies the cover 3, this insulating material being arranged in a readily removable manner to allow easy access to the cover 3.

The openings 4 in the cover 3 overlie a shelf 12 formed in the wall of the crucible 2, this shelf terminating in an edge 13 which also defines the upper limit of a lower portion 14 of the crucible 2 in which, during use of the apparatus, a reservoir of molten glass is maintained. The shelf 12 may be horizontally disposed or, as shown, it may incline downwardly at an angle of a few degrees to the horizontal in the direction towards the edge 13. A trough 15 is formed in the shelf adjacent to the edge 13.

Five radiant electric heating elements 17, supported in the end walls of the crucible 2, extend through the upper part 16 of the crucible and serve to melt glass delivered onto the shelf 12 and to maintain the glass in the lower portion 14 of the crucible in a molten state. These heating elements have not been shown in Figure 2.

The numeral 18 designates any conventional feeding device, such as a vibratory feeder or a screw conveyor, for delivering broken glass scrap in a substantially horizontal direction to the openings 4 in the cover 3. The glass material fed to the openings 4 in this way preferably has a maximum grain size of about 5 mm, such that it will pass through a No. 3 sieve (ASTM).

In use of the above described apparatus, the particulate glass material fed to the two openings 4 falls freely onto the shelf 12 in two regions 19 of the latter directly below the openings 4, the boundary of one of these regions being shown in chain lines in Figure 2 where it is designated by the numeral 20. The minimum distance of the boundary 20 from the edge 14 of the shelf 12 is y, and in the example shown, y is equal to 0.45x, where x is the maximum height through which glass particles, fed to the openings 4, fall freely onto the regions 19 of the shelf 12. Many of the glass particles fed to the shelf 12 will remain in or very close to the regions 19, but some particles will rebound out of the regions 19 and come to rest in other regions of the shelf 12, possibly as far away as the trough 1 5.

The particles of glass material delivered to the shelf 12 are melted by the heating elements 17 and the molten glass flows across the shelf 12, through the trough 1 5 arid over the edge 13 into the lower portion 14 of the crucible 2. Any foreign matter carried along by the molten glass is deposited in the trough 1 5.

During spinning of glass fibres from the nipples 6, molten glass is maintained in the portion 14 of the crucible 2 approximately to the level indicated by the chain line 21 in Figure 1. The height of the level 21 above the upper surface of the bottom plate 5 should be at least 150 mm, but must not be as great as z, which is the height of the edge 13 above the upper surface of the plate 5. In the example shown, the edge 13 is somewhat rounded and in order to remove all doubt this edge is considered to be located along a line where the curved portion 22 of the wall of the crucible 2 is tangential to the plane of the shelf 1 2.

Figure 3 shows a preferred construction of part of the nipple plate 5. From this Figure it will be seen that each nipple 6 has a converging frustoconical inlet 23, an intermediate cylindrical orifice 24 and a diverging frusto-conical outlet 25. The outer surface 26 of the nipple is cylindrical and there is a circular flange 27 at the lower end of the nipple. A ring 28 of ceramic insulating material surrounds the nipple intermediate the flange 27 and the lower surface of the nipple plate 5. In one example of nipples of this design, the main body of the nipple had a length of 9.5 mm and a diameter of 6.5 mm. The orifice 24 had a diameter of 3 mm.

the inlet 23 had a cone angle of 900 and the outlet 25 a cone angle of 15 . The flange 27 had a diameter of 7.5 mm and a depth of 1 mm. The flange 27 has a cross-sectional area which is greater than that of the portion of the nipple immediately upstream of the flange 27.

Consequently, the end face 29 of the nipple is substantially cooler than the portion of the nipple which is surrounded by the ceramic ring 28. This aids in preventing "wetting" of the end face 29 by the glass drawn from the nipple. The spaces between the lower ends of the nipples 6 may be filled with fibrous refractory insulating material (not shown).

In one example of apparatus of the kind described above, there were 214 nipples 6 in the bottom plate 5, each of these nipples having the dimensions set out in the preceding paragraph.

The heightxwas 215 mm and the distance ywas 97 mm (corresponding to 0.45x). The entire shelf 12 had an area of 920 cm2 and the particulate glass material was fed through the openings 4 at a uniform rate of 12 kg per hour, corresponding to a rate of 1 3 g per hour per cm2 of the area of the shelf 12.

In a modified form of the above described apparatus, a barrier 30 (shown in chain lines in Figures 1 and 2) is secured to, or formed integrally with, the shelf 12 adjacent to, and substantially parallel with, the edge 13. The barrier 30, which may have a height of from 2 to 5 cm, can extend the whole width of the shelf 12 or may terminate short of the end walls of the crucible 2. The barrier 30, which may replace, or be provided in addition to, the trough 15, prevents foreign matter carried along by the molten glass from passing over the edge 13 into the lower portion 14 of the crucible.

Claims (10)

1. A method of manufacturing glass fibres by drawing molten glass through a plurality of nipples in the wall of a vessel in which a reservoir of molten glass is maintained, comprising the steps of allowing particulate glass material to fall freely through a distance x onto a region of a horizontal or substantially horizontal shelf, melting the particulate glass material on said shelf and allowing it to flow over an edge of the shelf into the reservoir of molten glass, the minimum distance between said edge and the boundary of said region being 0.3x, and maintaining a hydrostatic head of molten glass in said reservoir, above the nipples, which is not less than 1 50 mm but is less than the height of said edge above the nipples.

2. The method claimed in claim 1, in which the particulate glass material commences its free fall onto said region of the shelf with a vertical component of velocity substantially equal to zero.

3. The method claimed in claim 1 or 2, in which the particulate glass material is fed onto the shelf at a rate not exceeding 20 g per hour per cm2 of the area of the entire shelf.

4. The method claimed in any of the preceding claims, in which the particulate glass material used is broken glass scrap which has been sieved through a No. 3 mesh (ASTM) screen.

5. The method claimed in any of the preceding claims, in which the melted glass, in flowing to said edge of the shelf, passes through a trough in the shelf and/or over a barrier on the shelf.

6. The method claimed in any of the preceding claims, in which the molten glass in said reservoir is drawn through a nipple plate, in which said nipples are mounted, which forms the bottom of said vessel.

7. The method claimed in claim 6, in which the cross-sectional area of the material of each nipple is greater at the outlet end of a nipple compared with a region of the nipple upstream of the outlet end.

8. The method claimed in claim 6 or 7, in which the outlet ends of the nipples project below said nipple plate, and the spaces between the projecting portions of adjacent nipples are filled with thermally-insulating material.

9. A method of manufacturing glass fibres substantially as hereinbefore described with reference to the accompanying drawings.

10. Glass fibres when made by the method claimed in any of the preceding claims.