In practice, the causes of waste products are analyzed from the aspects of raw materials, formulation, molding, firing, and glazing, and some corresponding improvement measures are proposed.
The ceramic vacuum tube shell has been widely used in the current power electronics industry, such as high-frequency high-power electron tubes, electric vacuum tube switches, X-ray tubes and other shells. Glass is the earliest material used for the tube shell, but the loss of the glass is large, and the dielectric loss increases rapidly with the increase of temperature, so use the glass as the shell of the tube, even if the power of the tube is low, if the operating frequency There is danger of softening or bursting beyond 2000 MHZ. At present, all kinds of electronic tubes with high power are made of 95Al2 ceramics.
95Al2 ceramics have high mechanical strength, good insulation properties, low high-frequency loss, high electric strength, high temperature resistance and thermal shock resistance; the degassing temperature of an electron tube made of it can be much higher than the electron tube of a glass tube shell The degassing is more thorough and is particularly suitable for the production of high power electronic tube shells used at higher frequencies and higher temperatures.
Ceramic vacuum tube shell molding methods are mainly isostatic pressing, hot die casting and cold casting molding, hot die casting method in China is the earliest molding process. In the early 1980s, the isostatic pressing method was applied in China. The ceramic vacuum tube shell produced by this method has the advantages of high density, no porosity, etc. At present, more and more domestic manufacturers adopt this method.
Because the use conditions of ceramic vacuum tube shells are rather special and require high technical performance of the products, the state has set specific standards for the inspection of such products. If the waste products are categorized and the causes are analyzed to improve the original production process, the product yield and economic benefits will be improved.
2 ceramic vacuum tube shell waste ceramic vacuum tube shell from the raw material to the finished product through the ingredients, ball milling, granulation, molding, green processing, firing, glazing, glaze and other processes, it is easy due to poor control of the processes or improper operation And cause waste. Common causes of waste products are raw fire, inconsistent dimensions, cracking, yellowing of color, spots, defects, scratches, sticky powder, and glazed defects.
3 Common waste product causes and improvement measures 3.1 Burning According to the national standard, the ceramic vacuum tube should be subjected to a liquid permeability test after firing to determine if the product is completely sintered. If the product absorbs the redness in whole or in part, the product is burned. There are two main causes of raw fire: First, improper formulation or mistakes in ingredients; Second, the firing temperature of the blank is too low, the holding time is insufficient, and the temperature difference in the kiln is large. In addition, the large particle size of the alumina raw material and the short milling time also lead to raw burn. The improvement measures are to design a reasonable formula and firing temperature curve, and choose the alumina material with a suitable particle size.
3.2 Dimensional Non-conformity Ceramic vacuum bulbs require strict dimensional requirements during assembly, so dimensional inspection is an important part. The size does not match the following two conditions.
3.2.1 The reason that the overall size is too large or too small is that the shrinkage ratio of raw materials during molding is not well controlled, resulting in the overall size of the green body being too large or too small, and the product size after firing is generally large or small.
3.2.2 The deformation of the product is mostly flat, out of round, and skewed. The causes of deformation are: inappropriate raw material formulation improper raw material formulation Main reasons: First, the alumina raw material is too fine, the firing shrinkage is too large; second, the plastic binder content in the raw material is too much, and the green body is easily deformed in the forming process; Third, the flux content in the blank is too high, and the tendency of self-weight deformation after sintering increases.
Improper loading method When the billet and the gasket are inconsistently sintered, the blank and the gasket interfere with each other during sintering, resulting in irregular deformation of the product during firing.
The improper firing system does not control the heating rate, the temperature difference in each zone of the kiln, and the high fire point, resulting in excessive deformation of the product due to overheating.
The improvement measure is to accurately determine the shrinkage rate of the raw materials before molding, and to select suitable raw materials, formulas and firing systems.
3.3 Cracking Cracking is mainly caused by the formation of fine dark cracks in the process of forming and handling of the green body, stress release at high temperatures, cracks exposed; In addition high temperature stage heating too fast, shrinkage is too fast, high temperature quenching, high temperature water cooling, etc. Cause cracking factors.
The improvement measure is to adjust the firing curve of the product.
3.4 Color Yellow ceramic vacuum bulbs generally require the same color as white, and yellow color is one of the reasons for the waste. The cause of partial or overall yellowing of the porcelain body is many, and the main reason is that the raw material is mainly impure. For example, Fe2., Ti2, ZrQ and other components in the raw material are too high, such as Fe2.>0.44, which can affect the color of the porcelain body). In addition, burning or overcooking and cooling too slowly before 800" causes the reoxidation of FeO to also cause yellowing of the color.
3.5 Speckled spots are heterogeneous speckles that are distributed on the surface or in the interior of the sintered body and in the glaze layer. This is due to the fact that mineral impurities are burned into the body or glaze. Impurities are mainly generated from alumina raw materials, impure auxiliary materials, or impure glaze raw materials; iron or stainless steel impurities are mixed in the process of ball grinding and spray granulation; and the top of the high-temperature kiln is burnt during firing.
Improvement measures: First, we must strictly select materials, use pure alumina raw materials, auxiliary raw materials, and glaze raw materials; secondly, strengthen process hygiene; spray-granulated materials should be iron-removed.
3.6 Defects Defects are exfoliation along the edges or corners of ceramic vacuum envelopes. It is mainly caused by bumping of the blank due to improper operation of workers in each process.
There are collisions between the raw material during processing and during loading and unloading; the loading and unloading force is not properly applied when clearing the floating powder on the surface of the greenware and loading the kiln; the grinding machine, grinding wheel, jig, etc. impact the blank during grinding; the blank is stacked improperly and is handled. Collide with each other when cleaning.
Improvement measures: Strengthen the management of the production process. Workers should be particularly careful when handling products. Products must be handled with care and light to avoid collisions. When stacking blanks, they should be separated from each other and avoid direct contact with each other. jobs.
3.7 Scratches Scratches are shallow grooves or scribed lines on the surface of porcelain pieces, which are mainly caused by the tool being scratched or improperly selected by the tool during processing.
Improvements: Care should be taken when machining the greenware to avoid the tool being drawn onto the surface of the blank and the proper tool selection.
3.8 Sticky powder Sticky powder refers to powder that is sintered on the surface of a ceramic vacuum envelope. Since the powder produced during the green processing is not completely cleaned before the green body is fired, the green body is sintered on the surface of the ceramic tube shell when it is fired, and it is difficult to dispose of the green body, resulting in waste products.
Improvement measures: Clean the float powder on the surface of the greenware thoroughly before firing.
3.9 Glazed Defect Glaze is a continuous glass layer that fused on the surface of the porcelain body. In general, the glaze layer is very thin, but it plays a significant role in improving the electrical properties, mechanical properties and chemical stability of the ceramic part. At the same time, the glaze layer can also make the porcelain surface clean, beautiful and untainted. , playing a decorative and protective role. Therefore, ceramic vacuum tube shells are generally required to be glazed. The glaze on the porcelain surface should have a uniform, smooth, glossy surface.
Due to the process of glaze formulation and other reasons, there are often defects in the glaze, and the common defects are as follows.
1 lack of glaze and pile glaze lack of glaze refers to the lack of glaze ceramic glazed shell part of the blank body; heap glaze refers to the ceramic shell on the surface of the glaze layer local thickening. One cause of the lack of glaze and pile glaze is due to improper glaze operation, uneven glaze on the surface of the green body; second, the proportion of glaze is too large or too small, and the glaze is too thick or too thin and not Uniform.
Improvement measures: Improve the glaze technique and prepare a suitable glaze slurry.
3.9.2 glaze no light caused by glazed matt mainly due to: glaze temperature control is not appropriate, the choice of glaze formulations are unreasonable, resulting in the glaze layer during the glaze process is absorbed by the body, resulting in poor glaze layer melting; Glazes containing high levels of calcium oxide affect glaze gloss due to the tendency to crystallize on cooling. In addition, too thin a glaze on the surface of the green body when glazed can also cause the glaze to be dull.
Improvement measures: adjust the glaze formulation; control the glaze firing temperature curve; the glaze containing high calcium oxide is rapidly cooled from the sintering temperature to about 750†in the initial stage of cooling; master the glaze layer thickness of the blank to avoid the glaze layer Too thin.
3 The bubbles in the bubble glaze are not evenly distributed in the glaze. Generally, the common air bubbles exist either at the interface between the porcelain and the glaze, or at the place directly adjacent to the glaze surface. The most common size of bubbles is 0.04-0.05mm. Bubbles are generated for the following two reasons: The bubbles that the glaze itself discharges. This is mainly due to the lower maturation temperature of the glaze; the narrower maturation zone or the high glaze temperature; the carbon or decomposition products deposited in the glaze do not burn out before the glaze melts, and the carbon burns after the glaze melts. The gas is difficult to run out and is wrapped on the surface of the glaze. It may also be caused by too much soluble salts in the glaze. In addition, improper glazing process, resulting in local glaze too thin or too thick will also produce bubbles.
Improvement measures: Choose a reasonable glaze formulation, pure glaze raw materials, a suitable glaze firing system, and improve the glaze technology.
From the deeper part of the porcelain body into the glaze bubbles. This is because the air filled when the porcelain body is still porous is discharged from the porcelain body with the degree of sintering upon heating.
4 Conclusions From the above analysis of the common waste products of ceramic vacuum tubes, some waste products are related to raw materials, formulas, glazes, and firing systems. Some waste products are entirely caused by human factors. In order to reduce the appearance of waste products, the development of low-temperature fast-burning ultra-white permeating tiles is taken into consideration. Shuihua Huang Wenzhong (Guangzhou Conghua Astra Building Material Co., Ltd. 510925) In recent years, the production technology of vitrified tiles has been continuously improved and people are polishing. The quality and variety requirements of bricks are also getting higher and higher. In order to meet the needs of market customers, our factory has developed ultra-white infiltration glass tiles. Due to its high whiteness, rich colors, wear resistance and strong anti-fouling power, it is an ideal decorative material and has a wide market prospect and economic benefits.
2 Determination of product formulation 2.1 Determination of the formula of the blank 2.1.1 Principle of selection The material of the blank must enable the permeation liquid to penetrate into the blank, and the whiteness of the fired blank must meet certain standards. Our factory mainly considers the following aspects when adopting blank formulation materials: 1) The blank should adapt to the firing system of vitrified tiles, and the burnt whiteness should be up to the standard; 2) The blank should be easy to shape and shape After having a high strength, can adapt to printing; 8) The body has a good water permeability, so that the liquid penetrates easily; 4) The slurry should have good thixotropy, so that the body is not easy to produce cracks in the drying process.
2.1.29 Selection of raw materials used Conghua ultra-white sand, Yichun feldspar and washed ball clay, Conghua white mud, Guangfeng black talc, raw material formulations than the ratio of raw materials shown in Table 1; raw material appearance and burnt whiteness as shown in Table 2 The raw material chemical composition is shown in Table 3; the formula chemical composition is shown in Table 4.
Table 1 Formulation Material Ratio Tt% > Name Conghua Ultra-white sand Yichun feldspar Washing ball Conghua Baimu Guangfeng Black talc content Table 2 Raw material raw material Natural appearance and burnt whiteness Raw material name Appearance quality in natural state Burned white Degree Conghua Super White Sand White Sand Unsintered Whiteness: 5 Degrees Washable Ball Soil Black Soft Block Unsintered Whiteness: 86 Degree Yichun feldspar White Pan-Green Light Green Granules Fully Porcelain Whiteness: 78 Degree Conghua White Mud White With a point of light gray soft unsintered whiteness: 6 degrees Guangfeng black talc black sheet unsintered whiteness higher hand: First, the use of pure alumina raw materials, auxiliary materials and glaze raw materials, greatly reducing the appearance of waste products, Increase economic efficiency.
Strengthen process hygiene in the process of spray granulation; second, develop a reasonable firing system; third, strengthen the control of molding and glazing processes; and fourth, strengthen the
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