Screen printing of the hottest glass

Silk printing of glass (Part 2)

IV. firing

the heat source of firing is electricity, gas, heavy oil, etc., of which the best effect is electric heating, which is used for the printing of high-grade products such as glasses, tableware, cosmetic bottles, etc. In addition, electric heating is also necessary for gold and platinum special printing, but its cost is higher than that of oil and gas

the cost of heavy oil is lower than that of electricity, and the heat is also high. When it is suitable for experiments, both ends of the test piece must ensure parallel firing of beverage bottles or single products with large weight. Gas is mainly used for glass products that cannot be fired with electricity and heavy oil. When using a heat source other than electricity, a flame furnace must be used

in addition to the conveyor belt tunnel type and trolley tunnel type, there are also square furnace, round furnace and other single chamber types, each with different characteristics

conveyor belt tunnel type firing furnace has high efficiency, high output, easy heat adjustment, appropriate temperature and good operation performance

trolley type tunnel furnace is mainly used for glassware that is not suitable to be transported by conveyor belt, and glassware that is easy to be tilted in the furnace, as well as small, large and flat, high, most kinds of glassware with few quantities. For example, small and flat glassware can be divided into two layers and three layers on the trolley, and the firing can be completed at one time. At the same time, it can also burn tall glass products that cannot be put into furnaces of other high corrosion-resistant alloys (1960-1969). Although this kind of furnace is somewhat inconvenient in operation, its efficiency can be twice as high as that of the conveyor belt tunnel furnace for firing a large number of small glass products. In this sense, it is a convenient and widely used firing furnace

all kinds of single furnaces are mainly used for firing small caliber items for test and producing only one process glass

the firing temperature is about 520 ~ 600 ℃. When the organic hydrocarbon compounds in the colored glaze are completely burned out, the glaze starts to develop color and the vitreous melts on the glass surface. At this time, if heated rapidly, the glass will break under the thermal shock; If it cools too fast, the glass will also skew and crack. Therefore, in the range of preventing the glass from cracking, the temperature can be slowly increased to the highest temperature in the furnace, and then slowly reduced. Since the temperature zone between 500 ℃ and 600 ℃ is the most prone to deflection, the speed must be adjusted according to the thickness and weight of the glass. The time to pass through the tunnel should vary according to the structure of the furnace and the weight of the glass, but it generally takes about 90 minutes

the adhesion of gold and platinum is poor, so it is best to control the firing at a high temperature without deflection or cracks. According to the statistics of GGII, but when firing with other colored glazes, especially in the case of mixed colors, the weaker glazes are easy to lose color and fade, and the hue is easy to change. Therefore, special attention should be paid to temperature control at this time

when firing glass products printed with thermal glaze, gas will be produced due to the combustion of medium and organic compounds, resulting in various adverse effects. Therefore, it is very necessary to strengthen the exhaust of the furnace. If fired for a long time, gas and lampblack will stick to the furnace lining, which will have a negative impact on the following firing. If continuous firing, the color will change color, lose luster, and gold will turn black. The way to overcome this is to place products on the conveyor belt at least 3 meters away, and the temperature cannot be reduced. In addition, when placing products on the conveyor belt, if the gap is uneven, color differences and other obstacles will occur. Therefore, if possible, the best thing is to put the products in a special furnace for heating glaze and burn them straight

as for the firing temperature, the following discussion takes the stretching attachment as an example, and there are different opinions. Each furnace should have its own temperature standard. Even the furnace with the same design will have a temperature difference of about 30 ~ 50 ℃ due to the difference in the insertion position of its resistance and the length of the projection in the furnace. Due to the different design, heat and speed of the furnace, although the same glass is fired, furnace a may be 500 ℃, and furnace B may be 600 ℃. Therefore, the important thing is not to pay attention to the temperature of others, but to master the temperature standard of the furnace you use

v. precautions for glass screen printing

the precautions for glass printing are listed as follows:

① wipe off the moisture, oil and dirt on the glass surface before printing

② gold and platinum must be pickled before printing on important glass products

③ when the color of the finished product changes due to hydrogen sulfide, it can be corrected by wiping it with a cloth stained with oxalic acid solution

④ when the discoloration is serious, it can be restored by re firing at a temperature above 480 ℃

⑤ it is easy to change color in rainy season (summer), so the materials should be kept in a safe place

⑥ in order to prevent lead poisoning, good exhaust equipment must be provided

⑦ smoking and eating are strictly prohibited during work

⑧ wash hands and gargle before meals

⑨ do not touch the colored glaze directly with your hands

new colored glazes must undergo lead toxicity test, and those with positive reaction cannot be used

VI. lead toxicity test

in recent years, public hazards have become more and more serious day by day. Poisoning due to heavy metals such as lead and tin is a very serious problem. In order to prevent public hazards in glass printing, colored glazes with low lead content should be used as much as possible, and exhaust devices must be installed at the same time

if the printed glass tableware is found to contain lead, it will not only have a negative impact on users, but also on the reputation of producers. Therefore, it is necessary to conduct a full lead toxicity test on the colored glaze in advance, so that it must meet the use index

carefully wash the fired glass with water as the sample, then put 1000ml of distilled water heated to 50 ℃ into the beaker, put the sample in the beaker, maintain the temperature of 50 ℃, stir continuously for 30 minutes, take out the sample, and then use the distilled water as the test liquid

put 10ml of test solution into the test tube, add 3ml of acetic acid and 2 drops of 5% potassium chromate solution, and leave it for 30 minutes. If the liquid appears turbid yellow or precipitates at this time, it is a positive reaction and is unqualified