The types and causes of glass stones
Stone is the most dangerous of vitreous body defect, it can destroy the appearance of the products and optical homogeneity. At the same time because it has the different thermal expansion coefficient and glass, so will cause additional stress, greatly reduce the mechanical strength and thermal stability of the products, and often result in difficulties of annealing process.
in the vitreous, stone is sometimes tiny crystals, also sometimes bulky crystal, stone is a decentralized sometimes sometimes is gathered, sometimes gather a large number of tiny crystals in the whole piece of fog.
all these phenomena that stones have different type, its chemical composition and mineral composition also each are not identical, according to the reasons of the stones, generally can be divided into the batch of stones, kiln self-closed, refractory stones and stone crystallization.
( 1)
with material stones is the batch no melt components in the batch or impurity particles, in most cases, the stone is the batch of quartz grain, technological factors related to the stone of the batch is as follows:
(1) material composition not appropriate;
(2) the component particles of the batch of heterogeneity;
3. Bad batch mixing;
4. Improper feeding method;
5) melting conditions are destroyed.
( 2)
the self-closed kiln and kiln kiln self-closed calculi of cantilever often eroded by alkaline gas and alkali powder, kiln self-closed and cliffs of the kiln refractory effect with a base to form a glass drops, reach a certain weight and viscosity after falling by kiln self-closed or along the kiln wall into the vitreous generated in the stone, silica brick and alkali reaction generated fusible silicate, formed in the drip into the glass melt kiln, self-closed calculi usually contains coarse grain of mud carp quartz and white silica crystals, this is because the silicate crystal drops of long generated by high temperature in the furnace, usually have the darker color, self-closed will produce kiln refractory is the cause of low quality, kiln self-closed with higher temperature material particles were carefully and improper methods.
( 3) Refractory stones
in direct contact with vitreous melted refractory material is a product of the glass melt erosion and damage form refractory stones. Refractory materials such as crucible, direct contact with the glass tank furnace bricks are made of refractory clay, as a result, this kind is often called refractory clay stones, stone cliffs and crucible on the kiln, though the causes are different, but also into the refractory clay stone to study.
refractory clay is similar to the batch of some stones, but the stone circle is usually the batch is much better than stone of refractory clay, refractory clay stone almost always is a polygon.
refractory stones produced is mainly due to the refractory material of low quality and contribute to, such as high porosity, mechanical damage, the fuse burned and masonry is not close, etc. , other such as high melting temperature, glass melt too alkaline, and the quality of glass furnace in fluctuation is too strong, will greatly promote the erosion of refractory materials.
( 4) Analysis crystal
vitreous crystallization of stones is not due to the heterogeneous material formed by the addition of, but by the crystallization of glass itself. The appearance of the crystallization calculi is varied, stone size often between percent a few millimeters to several centimeters, shape, and is often a variety of color, but the crystal has the correct geometry is its characteristic, general industrial use glass crystallization often encountered for scale white quartz, silica, wollastonite, grey stone, sodium silicate wollastonite, diopside, also in the special glass with silver, lead and aluminum compounds.
crystallization stone is one of the factors of glass melt crystallization performance, the performance depends on the chemical composition of glass, at the same time, there are many factors promote the generation of crystallization calculi; The destruction of the melting temperature and mold temperature to reinforce glass melt crystallization orientation, in addition to the chemical composition of modified glass makes it has smaller crystallization ability, we must formulate and strictly abide by the reasonable fusion system and the system of mold temperature.