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When the temperature in the kiln is raised to the critical softening point of the ceramic glaze and the glass, the pigment begins to infiltrate into the glaze from the surface of the glaze layer under the double action of its solvent corrosion and self-weight, thereby forming the glaze effect. In order to ensure that the colorant can penetrate into the glaze at high temperature without losing color, it is very important to select the colorant according to the softening temperature of the glaze. Under normal circumstances, the baking temperature is about 25Â°C lower than the glaze softening temperature. Under such temperature matching, the color material can penetrate into the glaze without causing the glaze layer to melt excessively and cause the picture to be deformed.
The calcination temperature has a great influence on the coloration of ceramics and glass pigments. Excessively high or low firing temperatures can cause aging and unfading of the pigments. Most of the colored silicates are stable only at a certain temperature. If they exceed a certain temperature, they must be discolored or decomposed, and only a few silicates remain in their original colors after cooling. For example, brown iron silicate will decompose into oxygen and ferrous silicate when heated above 1200Â°C. If it is cooled slowly, it will have a reverse reaction and regenerate the original iron silicate. Many silicates are colored at 900-1000Â°C. It is very bright, but when the temperature rises again, it becomes dark; when the copper silicate is heated to 1200Â°C it shows a dark red color, and at 1300Â°C the color turns to a grayish yellow.
Such as selenium, cadmium with red, red / orange / orange series of colors available, other pigments can also be mixed in proportion to produce numerous transition colors. During production, it is necessary to avoid superimposing high-viscosity high-viscosity colorants on the high-temperature-viscosity colorants, and also to avoid the high-temperature series of color materials being laminated on the low-temperature series of colorants, which would otherwise be explosive. Such as blue, purple can be stacked on the top of the green, and selenium red can not be laminated on the milk yellow above, or prone to eating phenomenon (ie fade). Jinhong series pigments have high temperature resistance, and generally have a firing temperature of 830Â°C. Selenium red series pigments have lower temperature resistance, and the firing temperature is generally 750Â°C. The temperature of the kiln is too high, and some of the pigments will not penetrate into the glaze, and they will not be cooked and baked, and the glaze will be dull. Therefore, controlling the roasting temperature enables the coloring ability of the coloring material to be high, the glossiness is high, the color reproduction is perfect, and the viewing quality is strong.
The composition of the glass colorant and the ceramic colorant is basically the same, but since the glass is an inorganic amorphous solid that is cooled and solidified by the melt, the baking temperature of the glassware decals should not be too high, otherwise it would Causes the glassware to deform, resulting in waste products. The melting temperature of the glass is usually 1200 to 1600Â°C. Glass can also be decorated with dyeing techniques, such as adding iron oxide and chromium oxide to make the glass brown and green.
The glass products need to be decorated with decal paper. The surface of the glass products must be smooth, free from pockmarks, the glass is transparent and free from turbid substances, and there are no bubbles. Therefore, the glass raw materials must be added with a clarifier, such as sodium sulfate, to accelerate the release of gases from the molten system. Sulfur oxides.
The quality screen printing ceramics and glass decals not only need to faithfully reproduce the tone and color at all levels of the original, but also check whether the color rendering effect of the pigments after high-temperature baking is satisfactory, and whether the amount of lead and cadmium dissolved meets the national standards. Standard or international FDA standards. Only at the same time meet the above three elements, it can be regarded as a qualified decal.
In mass production, if the tone of the pattern on the decal is reproduced well, the hue of the screen after high-temperature firing is far from that provided by the customer, or pinholes, cracks, bursts, and wrinkles appear on the surface of the pattern after firing. Pleat, fading and matt dull surfaces, or lead and cadmium dissolution exceeding national standards and other undesirable phenomena, are all unqualified products. At this time, remedial measures can be taken. If the individual color material fades, it may be that the firing temperature is high, so let's cool it down. If it still fades, there may be too much solvent in the pigment. Pinholes may be caused by blisters caused by residual bubbles or pigments in the printed area, or the printed decals may not enter the high-temperature furnace without being completely dried. If the color glaze layer cracks, popping or there is the phenomenon of peeling off, is due to overprinting at the overprinting thickening of the pigment, burning temperature is too high or high temperature viscosity of the pigment stacked on the high temperature viscosity of the pigment above. The color is not bright and sharp, appears to be dry because the printing of the pigment is too thin or the glaze layer of the product is not dense, and the pigment is too thin and the solvent is not suitable for printing. Therefore, the prepared ink is preferably left for a day or two, so that it has good rheological properties. The amount of lead and cadmium dissolved exceeds the standard. Finally, a layer of the same series of varnish can be printed on the surface of the flower paper, which can not only improve the gloss of the picture, but also reduce the amount of lead and cadmium elution, in order to meet the safety standards and export requirements.
Source: Luoyang Printing Industry Co., Ltd. Feng Zhishu
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