JPS6031050Y2 - quartz glass crucible - Google Patents

Description

[Detailed description of the invention] This invention relates to an improvement of a quartz glass crucible for melting optical glass and the like.

In this type of quartz glass crucible, oxides of heavy metals such as lead tend to settle at the bottom during glass melting, and this has a strong effect of corroding the quartz glass crucible, so it is difficult to make the entire crucible have a uniform wall thickness. , or the bottom wall was thicker than the side wall.

However, if the entire quartz glass crucible is made to have the same wall thickness, or if the bottom part in particular is increased in thickness, cracks are likely to occur when the temperature rises and the crucible cools down.

For this reason, there is a drawback that the life span is shortened even though the bottom wall thickness is increased.

Furthermore, as the temperature at the bottom of the crucible rises, highly corrosive oxides such as lead tend to accumulate at the bottom, so an increase in wall thickness actually has a negative effect on life in this respect as well.

In view of these circumstances, this invention was developed after repeated experiments.
This is a reversal of the conventional idea, and by making the wall thickness of the bottom of the crucible relatively thin, the cooling efficiency of the bottom is improved, increasing the life of the crucible and improving the quality of processed materials such as molten glass. .

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a longitudinal section of a quartz glass crucible for melting optical glass as an example of the present invention.

When the inner diameter of the crucible 1 is D1 and the height is H, the part IA from the open end of the crucible 1 to 172H is set to the same wall thickness as before, and the lower part, that is, 172H from the open end of the crucible 1. From this point, gradually thicken the lower middle portion 1B.

Furthermore, the wall thickness within 1/3D of the bottom is thinner than that of the intermediate portion IB.

Table 1 shows the 4 pieces actually manufactured with different wall thicknesses.
The different types of fused silica crucibles are listed below.

Note that the values shown in Table 1 are the average values of the wall thickness of each part of the crucible, and the wall thickness of each part changes continuously little by little, and the wall thickness changes suddenly at the boundaries of each part. Not that I'm doing it.

When the four types of crucibles listed in Table 1 were manufactured for each purpose and used to actually melt optical glass, the results shown in Table 2 were obtained.

As was found from the experimental results shown in Table 2, the crucible has a longer life when the wall thickness at the bottom of the crucible is made relatively thinner.

Furthermore, when measuring the homogeneity of the glass in terms of lead content, the crucible according to the present invention was superior to conventional products in all cases.

Furthermore, in the practical test, the above-mentioned test fall, 1 and NO,
4 at 300°C/Hr, test example 1, 2 and No. 3 at 200
When the temperature was raised at a rate of °C/Hr, cracks were observed in 2 to 3 of 0 pieces, 1, 2, and 2, but 3, 3, 4, and 4 were cracked. There were no outbreaks.

When the bottom of the crucible is made thin as in the present invention, the cooling efficiency of the bottom is improved, promoting convection of the molten glass to make the glass uniform, and heavy oxides such as lead are not concentrated at the bottom.

However, if the wall thickness of the bottom of the crucible becomes extremely thin, the mechanical strength will be weakened, so it is desirable that the ratio of the IC portion to the IB portion be approximately 0.65 to 0.75.

Furthermore, the intermediate portion is thicker than the opening portion to increase mechanical strength.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of a quartz glass crucible according to the present invention. 1... Quartz glass crucible, H... Its height, D... Its inner diameter.

Claims (4)

[Scope of utility model registration request] (1) The thickness of the middle part from the side to the bottom should be thicker than the thickness near the opening, and the thickness of the bottom should be increased to the extent that it improves the cooling efficiency of the bottom and promotes convection of the melt. A quartz glass crucible characterized in that the wall thickness of the intermediate portion is thinner. (2) When the inner diameter of the quartz glass crucible is D1 and the height is H, the intermediate portion exists from about 172H from the open end of the quartz glass crucible, and the thinner part at the bottom is about 173D. The quartz glass crucible according to claim 1 of the utility model registration claim, characterized in that the quartz glass crucible lies within the range. (3) The quartz glass crucible according to claim 1 or 2 of the utility model registration claim, wherein the crucible is configured to be used for melting optical glass. (4) The wall thickness ratio of the bottom portion and the middle portion is approximately 0.6.
5 to 0.75, the quartz glass crucible according to claim 1.2 or 3 of the utility model registration claim.