GB2065096A - Nozzle plate for drawing glass fibres - Google Patents

Abstract

In the spinning of glass fibre from molten glass the high temperature of the molten glass has necessitated the use of platinum for the plate and nipples of the draw bar. According to the invention the nipples (5) are largely embedded in the plate (1) so as to delay the onset of cooling as the glass passes through the nipples. This reduces the required temperature of entry to the nipples and enables the use of lower grade materials, such as alloy steels or nickel chromium alloy, for the plate (1) and nipples (5). Thermocouple holder (4) and cooling pipe (6) may be provided. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the production of glass fibres This invention relates to the production of glass fibres.

Glass fibre is normally manufactured by the direct melt process in which a glass melt is formed in a melting bath and molten glass is fed from there by appropriate ducts to a plurality of drawbars each of which consists of a number of nipples set in a precious metal plate. The glass is spun into fibres as it passes through the nipples and cools to plastic state and is then drawn to the required gauge while still warm.

One form of small scale plant which has been proposed is a romelting plant, formed wholly of platinium, and therefore very expensive, to which glass beads are fed and from which glass fibre is spun.

In an alternative approach, which has not yet had much commercial application, the glass if fed to and remelted in a small crucible having a base formed by a draw bar or other arrangement of nipples. Such plant is suitable for comparatively small scale production.

In all cases, it is customary, in order to get the necessary mechanical strength and wear resistance at the temperatures involved, to use draw bars and nipples of platinum. This material is of course extremely expensive and its use raises very considerably the overall cost of a glass fibre production complex.

For the proper spinning of glass fibre, the nipples have to have a considerable length, e.g.

8.5 mm, so that they extend for a large proportion of their length beyond the plate in which they are set.

Accordingly, cooling of the glass starts fairly high in the nipple, even if the plate is heated, as is usual, e.g. by having an electric current passed through it.

It has previously been proposed to use a plate of alloy sheathed with a noble metal or alloy, and nipples of noble metal or alloy, protruding below the sheet. This particular proposal has not been commercial used, apparently due to the difficulty of maintaining the integrity of the sheathing at an economic cost.

It has now been discovered, and this forms the basis of the present invention, that by ensuring that a substantial proportion of the length of the nipple is embedded in the plate, the onset of cooling can be delayed so that the temperature of the glass entering the nipple can be at a lower level, e.g. 1 000C rather than say 12200 C, and this low temperature enables the use of temperature resistant alloys in place of platinum to be acceptable.

Accordingly, the present invention consists in a draw bar for spinning glass fibre, comprising a plate having a plurality of nipples set therein, in which the plate and the nipples are formed of a temperature resistant alloy and the thickness of the plate is such that a substantial proportion of the length of each nipple projects is embedded in the plate.

The use of alloys rather than platinum makes the use of a thick plate economic and the lower temperature thus made feasible makes the use of alloy practicable. It is envisaged that up to about one half of the overall length the nipple may protrude from the plate.

Such a draw bar may be used in direct melt plant or in a crucible using remelted glass.

The plate and nipples may be of alloy steel or other temperature resistant alloy, such as a nickel chromium alloy.

The invention further consists in a method of producing glass fibre comprising spinning molten glass through a draw bar according to the invention as set forth above.

Preferably, the temperature of the glass in the region of entry to the nipple is maintained at or below 11000C.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a plan view of a draw bar according to a preferred form of the invention; Figure 2 is a section on an enlarged scale illustrating some details of Figure 1; Figure 3 is a scrap side elevation showing a modification of a detail; and Figure 4 is a scrap bottom plan view showing another modification.

Figure 1 shows a draw bar in the form of a plate 1 of an appropriate heat resistant base metal alloy, such as an alloy steel or a nickel/chromium alloy, suitable for operating with molten glass at temperatures up to about 11 00 C. The plate 1 is surrounded by a somewhat thinner flange 2 integrally formed therewith. The plate is formed with a pattern of staggered rows of holes, as generally indicated in Figure 1 at 3, and in the particular example shown, there are a total of 405 holes arranged in seven rows. Two of the holes, indicated at 3a, will be occupied by thermocouples mounted in holders 4 as illustrated in Figure 2, and the other 403 holes will be used for mounting of glass spinning nipples 5, also as illustrated in Figure 2.

Figure 2 shows the nipples 5 and holders 4 in the "as inserted" state in which they protrude somewhat above the plate. Before use they are plasma welded so that the protruding parts fill cavities shown at 1 a as indicated by the broken lines.

In order to prevent any excessive cooling as the glass passes through the nipples, the plate 1 has heavy electrical current passed therethrough by means of terminals 10, 11, 12 and 13, each of which is formed by a pair of plates welded together, and the plate pairs being then welded to the plate 1.

As indicated in Figure 2, the thermo-couple holder has a cavity 14 to receive a thermo-couple by which the temperature of the plate 1 can be regularly monitored.

A modified terminal arrangement for the plate heating is shown in Figure 3. Each pair of terminals 12, 13 and 10, 11 is replaced by a single terminal 17 made up of four plates, of which only two extend as far as the plate 1 and are welded to it. The extra current loading on these two plates provides localised heating near the ends of the plate 1, which is useful in maintaining an even temperature along the whole length of the plate 1.

Each of the nipples 5 shown comprises a leadin section 5a, a throat Sb and a lead-out section 5c, part of which protrudes beyond the plate 1. A major proportion of the length of the nipples 5 is within the confines of the plate 1 and only a minor proportion extends below the plate 1 into the ambient atmosphere.

In the particular example, each nipple 5 may have an overall length of 8.5 mm of which 3 mm projects below the plate 1 for the onset of cooling so that the glass is sufficiently solidified to leave the nipple.

The flange 2 may have a thickness of 1.5 mm.

The diameter of the holes for the nipples 5 may be 6 mm and the holes may be arranged at 9 mm centres within the rows, with the rows being 9 mm apart.

The dimensions are chosen such that the temperature of the molten glass in contact with the plate and entering the nipples can be at a minimum, whereby the use of alloys steels, or other high temperature resistant alloys, rather than platinum for the plate 1 and nipples 5 becomes permissible. The nipples have to be sufficiently long for the glass to form into filaments as it passes therethrough and to start to cool in the latter part of the nipple. By ensuring that the filament is properly formed in the part of the nipple which is actually embedded in the plate 1, and therefore prevented from premature cooling, the temperature of the glass being fed in can be kept down. This effect is further enhanced by the use of an electric current to heat the plate.

Also, cooling by means of water circulating through pipes 6 may be used to provide rapid cooling of the glass at the very end of the nipple and on emergence therefrom. Figure 4 shows a suitable arrangement of such cooling pipes 6 in a modified form of plate 1. It will be seen that a pipe 6 is arranged at each side of the rows of holes 3 and that a further pipe 6 is arranged between two groups of three rows of holes 3.

Various modifications may be made within the scope of the invention.

Claims (7)

1. A draw bar for spinning glass fibre, comprising a plate having a plurality of nipples set therein, in which the plate and the nipples are formed of a temperature resistant alloy and the thickness of the plate is such that a substantial proportion of the length of each nipple is embedded in the plate.

2. A draw bar as claimed in claim 1, in which the plate and nipples are formed of alloy steel.

3. A draw bar as claimed in claim 1, in which the plate and nipples are formed of a nickel chromium alloy.

4. A draw bar as claimed in claim 1, 2 or 3, in which the plate has terminals attached thereto for passage of a heating electric current through the plate.

5. A draw bar for spinning glass fibres, substantially as hereinbefore described with reference to the accompanying drawing.

6. A method of producing glass fibre comprising spinning molten glass through a draw bar as claimed in any of the preceding claims.

7. A method as claimed in claim 6, in which the temperature of the glass in the region of entry to the nipples is maintained at or below 1 000C.