[China Glass Network] 1. Overview
In the vitreous body, inclusions such as bubbles, nodules, crystallization, stones, and the like, defects of these vitreous bodies, greatly degrade the quality of the glass. For borosilicate glass, the stone is a dangerous defect in the vitreous, which is a crystalline solid inclusion appearing in the vitreous, which has a serious influence on the glass, and is more likely to be caused when the borosilicate glass fiber precursor is drawn. Brushed broken ends and flying silk. Even if these stones do not cause breakage, they will greatly reduce the strength of the glass fiber.
2. Types of stones in high borosilicate glass electric melting furnace
The stones of the borosilicate glass electric melting furnace can be classified into raw material stones, stones introduced by clinker, refractory stones and some stones produced by foreign pollutants.
(1) Raw material stones are some of the coarser materials in the batch which have not been allowed to melt completely and remain in the glass, or the raw materials contain some heavy minerals. Among the borosilicate glasses, mainly sand stones.
(2) The stone introduced by clinker is derived from the ball of clams, the clinker produced by the ball, and the glass block of the kiln.
(3) Refractory stones, domes and chest walls are exposed to the fly materials of the batch materials and the volatiles from the glass at high temperatures, and gradually fall or flow down into the glass to cause stones; pool walls and glass Direct contact can also flaking due to erosion or reacting with certain components of the glass to form a refractory mineral phase. These are collectively referred to as refractory stones.
(4) crystallization stones, borosilicate glass at 1000 ° C, has a clear tendency to crystallization, when in the four corners of the glass furnace, due to slow flow, heat dissipation, low temperature, it is difficult to heat, forming a so-called " In the dead zone, the crystal can grow sufficiently, and if it is wrapped in flowing glass, it will produce harmful crystallization stones.
(5) The foreign pollutants are mainly caused by the fracture and erosion of molybdenum electrodes and silicon carbon rods.
3. Analysis of the causes of stones
The reasons for the formation of high borosilicate glass electric melting furnace kiln are as follows:
(1) Raw material stones are mainly caused by uneven mixing of the batch materials, so that the mineral raw materials are too concentrated and cannot be fully contacted. The glass liquid is not completely melted, and the incompletely melted particle clusters flow out with the glass liquid to form granular or flocculent stones.
(2) The stone introduced by the clinker, the clinker of the borosilicate glass electric melting furnace is derived from the chopping ball, the clinker produced by the ball, and the glass block of the kiln. The glass blocks of the ball and the kiln are generally clean and will not cause stones. The clinker produced by the ball will inevitably be mixed with other impurities, so some stones will be produced.
(3) Refractory stones, refractories have long-term interaction with high borosilicate glass liquid or volatile products, are eroded, and enter high borosilicate glass liquid to produce stones. In the borosilicate glass electric melting kiln, mainly caused by the erosion of quartz bricks, when the quartz bricks are eroded by high-temperature borosilicate glass liquid, the quartz bricks become quartz and become metastable cristobalite, and a large number of scaly cracks appear. When the metastable quartz is eroded by the glass, the large particles gradually decompose into small particles, thereby entering the glass, causing stones, and the stones are mostly opaque white.
(4) The crystallization stone is mainly caused by the “dead angle†of the kiln, and the dead angle temperature is in the crystallization temperature growing area for a long time.
(5) Foreign pollutant stones, the heating of the high borosilicate electric melting furnace is heated by carbon rods. When the carbon rods are broken due to arcing, the carbon rod slag generated enters the glass liquid, causing black stones in the products. In addition, the high borosilicate glass electric melting furnace adopts a molybdenum electrode. When the liquid level of the glass is low, the molybdenum is oxidized at a high temperature, and black stones may also appear. These two phenomena lead to a small amount of stones, but if an abnormality occurs, a large number of stones will continue to be produced continuously.
4, the inspection of stones
Although the causes of various stones are different, the same method can be used for their inspection. The purpose of the test is to ascertain the chemical composition and mineral composition of the stone to determine the cause of the stone, and further take measures to prevent and eliminate it. The test methods for borosilicate glass stones generally use the following methods:
(1) Macroscopic or magnifying glass observation method, which is a relatively simple and simple method, because the compound stones and devitrified stones formed by quartz are white; the stones formed by the refractory material are yellow or gray; inclusions such as molybdenum electrodes It has a distinct metallic color, so it can be clearly identified as a stone.
(2) Lithofacies analysis method, the stone samples are sliced ​​under a polarizing microscope, and the mineral optical properties of the minerals are examined by a polarizing microscope, and the mineral type of the stones can be accurately determined.
(3) Scanning electron microscopy, which is an apparatus for imaging and analyzing secondary electrons, backscattered electrons, and electrons absorbed by electron beam interaction with matter. The basic working principle is that after the cathode emits electrons and accelerates into a fine electron beam by anodizing, the grid surface scanning is performed on the surface of the sample in a sequence of time and space under the driving of the scanning coil. The focused electron beam interacts with the surface of the sample to generate secondary electrons, backscattered electrons and absorbed electrons, which are received by the detector and converted into electrical signals, which are amplified by video and output to the screen of the picture tube to obtain an image of the surface topography of the sample.
This method can better obtain the morphological features of the stone, and at the same time, the chemical composition of the stone micro-region and the local part can be analyzed by using the matched spectrometer and the energy spectrometer. According to the obtained crystal morphology and chemical composition, the type of stone can be accurately judged.
5, the method of reducing stones
(1) For the stones produced by the batch materials, the agitation should be strengthened, and the sampling inspection should be carried out frequently to prevent the incorporation of uneven batch materials.
(2) The stone solution introduced by clinker is mainly to strengthen the clinker management and timely select the debris in the clinker.
(3) The stones caused by refractory materials should be said to be difficult to avoid, but as long as the control is strengthened, the amount of the stones should be controlled. When the kiln is built, the masonry process is improved. During the heating process, the temperature rises in strict accordance with the temperature rise curve. , to avoid extreme cold and heat daily.
(4) The solution of the crystallization stone is mainly to prevent the occurrence of the "dead angle" of the kiln, and secondly to prevent the temperature of the molten glass from being in the crystallization temperature growing region for a long time.
(5) The external pollution mainly comes from carbon rods and molybdenum electrodes. In this process, during the heating process, the operation of the carbon rods should be checked frequently, and abnormalities should be treated in time. The carbon rods for arcing and breaking should be docked and estimated. Enter the length of the carbon rod in the glass and clean the glass. For the oxidation of the molybdenum electrode, the daily liquid level control should be strengthened, and the low-level and timely adjustment should be made.
Through the above measures, the amount of stones can be further reduced, and the quality of the electric kiln borosilicate glass can be improved.
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