JPS59111932A - Jig for pulling molten quartz - Google Patents

Abstract

PURPOSE:To provide the titled jig having long life, at a low cost, by covering the surface of a molybdenum substrate closely with a tungsten film. CONSTITUTION:A tungsten film having a thickness of about 0.005-0.5mm. is formed closely to the surface of a jig for the pulling of molten quartz and consisting of sintered molybdenum prepared by powder metallurgy, etc. The application of the film is carried out by vacuum evaporation, sputtering, CVD process, flame coating, etc. When the above tungsten-coated jig is heat-treated before use in an inert atmosphere at about 1,600-2,200 deg.C for a definite time interval, the molybdenum and the tungsten are mutually diffused at the junction interface between the substrate and the film, and the bond strength of the substrate and the film can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a jig useful for drawing fused quartz out of a molten tank and molding it.

[Technical background of the invention and its problems]

A quartz pipe is formed by drawing quartz melted in a melting tank through a jig (nozzle) consisting of an outer tube with a constant diameter of Mi and a core coaxially disposed inside the outer tube.

The jig used at this time is usually made of sintered molybdenum manufactured by powder metallurgy.

This molybdenum has an extremely high melting point (2620±10℃
), it has excellent properties such as high mechanical strength and resistance to thermal shock, but on the other hand, it has low resistance to fused silica and is easily eroded. Therefore, there is a problem in the service life that the shape gradually thins out during use and the product becomes unusable.

[Purpose of the invention]

The present invention aims to eliminate the above-mentioned drawbacks of molybdenum jigs and provide a long-life and inexpensive fused silica drawing jig.

[Summary of the invention]

The present inventors focused on the fact that tungsten has a higher melting point than molybdenum, is a material that is less likely to be corroded by fused silica, and the coefficients of thermal expansion of both are close to each other, and adopted molybdenum as the base material. The present invention was completed based on the idea that if the surface of this base material was coated with tungsten, the entire jig could be made resistant to the corrosion of fused silica.

That is, the fused silica drawing jig of the present invention is characterized by comprising a molybdenum base material and a tungsten film closely covering the surface of the base material.

The thickness of the tungsten film covering the base material surface is 0.0
The thickness is preferably in the range of 0.05 to 0.5 mm.

If the thickness is less than 0.005 mm, the resistance to the corrosive action of fused silica is insufficient;
Exceeding this value will not improve the effect significantly until it reaches a saturation state, which is not only uneconomical, but also causes peeling and cracking due to thermal stress caused by the difference in thermal expansion between the base material and the coating. The tendency for such phenomena to occur increases.

The tungsten film needs to be formed in close contact with the surface of the molybdenum base material. This is because if there is a gap between the two, it will induce phenomena such as cracking and peeling of the film.

Therefore, in the present invention, the formation of the tungsten film is carried out by vacuum evaporation method, sputtering method, CVD method (Chemical
It is preferable to apply a vacuum thin film forming method such as al vapor denomination; a thermal spraying method such as a flame spraying method or a plasma spraying method.

Among these film forming methods, the vacuum thin film forming method is superior to the thermal spraying method in that it can form a film of uniform thickness with good adhesion to the base material, but on the other hand, However, there is a problem that a film having a thickness of only several tens of micrometers can be formed at most, and that the film formation speed is slow and productivity is poor.

The thermal spraying method can form a thick film in a short time even if the base material is somewhat porous, so it is much more efficient than the vacuum thin film forming method in terms of productivity and cost.

Furthermore, if the jig manufactured as described above is further heat-treated in an inert atmosphere at 1,600 to 2,200 degrees Celsius for a predetermined period of time before use, molybdenum and tungsten will be released at the bonding interface between the base material and the film. This is effective because they mutually diffuse, increasing the bonding strength at the bonding interface.

[Embodiments of the invention]

Two molybdenum rods (density 9.7'10ttt) with a diameter of 20m7n and a length of 50mm were manufactured using a conventional powder metallurgy method.

The surface of one of them was coated with a tungsten film having a thickness of Q, 1 mm by flame spraying, and was used as a sample of the present invention.

The two rods were immersed in fused silica at about 1500° C., removed after 10 hours, and their weight loss was measured.

The amount reduction rate of the sample of the present invention was 2%, and the reduction rate of the molybdenum rod was 10%.

〔Effect of the invention〕

As is clear from the above description, the material of the present invention is hardly corroded by fused silica, and is therefore suitable as a drawer jig material. Furthermore, since the base material is molybdenum, which is easier to manufacture than tungsten, the overall cost is also lower.

Furthermore, it can be used not only as a fused quartz but also as a jig for drawing out ordinary molten glass, glass fiber, ceramic fiber, etc., and has a wide range of applications.

Claims (1)

[Claims] 1. A fused silica drawing jig comprising a molybdenum base material and a tungsten film that closely covers the surface of the base material. 2. The fused silica drawer jig according to claim 1, wherein the coating has a thickness of 0.005 to 0.5 mm.