Common forming defects and solutions of ultra white calendered photovoltaic glass



There are many factors that affect rolling forming, such as the material properties of glass, the quality of molten glass liquid, the structure of overflow port, rolling roller diameter, annealing kiln, and even external temperature changes. Generally speaking, the factors that affect rolling forming refer to the kiln pressure at the overflow port in front of the rolling roller, the temperature and transverse temperature of the glass liquid, the speed of the rolling roller, and the surface temperature of the rolling roller. If the above five factors change, the production situation will have corresponding changes, resulting in different forming defects. Common forming defects include white spots, black spots, scratches, roller marks, pattern deformation, inclusions, orange peel, watermarks, bubble scars, microcracks, bright and hidden lines, thickness deviations, etc,  Glass product  .


1 White spot



Also known as gray spots, it is due to the oxide generated during the use of the rolling roller leaving a unique milky white spot on the patterned surface, which sometimes needs to be cleaned and observed at a specific angle and under specific light. It can be solved by brushing and washing rolls.





2 black dots



A black dot like defect caused by the embossing roller shedding patterns. Due to the rotational friction between the copper collar of the shaft head and the roller, metal powder flies into the glass liquid, and high-temperature carbonization is pressed out with the glass, mixed in the board surface. Oil can be added to the shaft head to ensure lubrication and reduce friction.





3 Scratches



After being washed with water, there are white lines on the surface of the glass plate under the light. Due to sharp foreign objects rubbing and scratching the surface of the glass, the shape of the scars is different and the position is not fixed, usually in a linear shape. This also includes other scratches that cause the glass surface to lose its luster.



(1) Scratches on the upper surface



The scratch on the upper surface may be caused by the friction of broken glass hidden under the cold end mold proof liquid curtain on the glass plate after explosion, or by the detachment of the thermocouple in the annealing furnace and the top of the glass strip, which is irregular. Usually, its position on the glass strip needs to be measured, and then an illuminated flashlight is used to inspect the glass plate at the exit of the annealing furnace. If there are scratches, the observation hole of the annealing furnace can be opened for further investigation. If there are no scratches on the outlet, it indicates that it is caused by the cold end. Then, gradually investigate backwards according to the corresponding position and quickly identify the cause.



(2) Scratches on the lower surface



The scratches on the lower surface may be caused by the friction between the metal part of the cold end conveyor roller and the glass plate, and the spacing of these scratches is uniform and regular. Similarly, measure its position on the glass plate and confirm if there is a pattern. Then, check the glass strip at the exit of the annealing kiln to determine if it comes from the hot end. If so, open the slag removal hole under the annealing kiln according to the corresponding position and find the cause. If there are no scratches on the outlet, it can be confirmed that it comes from the cold end. Based on its regular spacing, identify the roller that caused the scratches to further solve the problem. In addition, the presence of broken glass on the cold end wafer taking table or improper wafer taking operation can also cause scratches. So it is necessary to regularly clean the tablet taking table to ensure its cleanliness and tidiness.


4 roller printing
The first type is the horizontal or long or short imprints on the surface of the glass plate, which may feel uneven when touched in severe cases. Generally, there is no unevenness or curved roller imprint. The possible reasons for this may be unstable transmission of the calender or transition roller, improper air flow ratio between the calender blade and nozzle, or excessive temperature of the formed glass liquid or rapid drawing speed. So it is necessary to ensure smooth lubrication and transmission of the calender or transition roller, appropriately reduce the temperature of the glass liquid in front of the roller, or reduce the pulling speed, and adjust the air flow rate of the air knife or nozzle.
There is also a roller stamp with a width of about 20 mm that is perpendicular to the rolling roller and fixed in a longitudinal pattern on the glass plate. The main reason is that the speed ratio is not suitable, or there is a gap between the transition roller and the auxiliary roller of the rolling machine, or it may be due to poor processing of the rolling roller itself. Usually, it is necessary to adjust the pulling speed ratio or the speed ratio of the upper and lower rollers, the air flow rate of the air knife, the height difference between the transition roller and the auxiliary roller of the rolling machine appropriately, and also adopt effective and minimally influential methods. Replace the rolling roller in severe cases. At the same time, machine operators should regularly observe whether there are any debris flowing out of the overflow port. If there are any, they should use a spoon to remove them in a timely manner to prevent pressure marks on the glass surface.


5 Pattern deformation
When the forming temperature is too high, the rolling machine speed does not match the annealing kiln, or the annealing kiln speed is too fast, pattern deformation often occurs. Under normal circumstances, the speed of the annealing kiln machine is only 1-2% higher than that of the rolling machine. The lateral deformation of the pattern is caused by the lateral temperature difference of the glass liquid at the discharge port. So it is necessary to align the discharge port with the middle of the gate brick and blow air to reduce the lateral temperature difference of the glass liquid at the discharge port. Longitudinal deformation is caused by the surface temperature of the lower roller being too high, the pulling amount being too large, the contact area between the glass liquid and the lower roller being too large, the temperature of the glass liquid being too high, and the cooling water volume of the lower roller being too small. According to the degree of deformation, effective measures with minimal impact can be taken to solve it.


6 Inclusions
Unmelted mixture particles and other impurities embedded on the surface of glass or wrapped in glass panels. So it is still required that the operator should have a sense of responsibility, pay attention to observation, and quickly use tools to remove any debris at the exit.


7 Toad skin and orange skin
Due to temperature and speed ratio, the glass surface appears to be uneven and uneven. Alternatively, due to the oxidation of the roller surface, the presence of sulfate attachments, the surface smoothness is damaged, and the glass plate surface is uneven, presenting toad or orange peel. Only by washing the roller can it be eliminated, or by re grinding on the grinder during roller replacement to improve the quality of the roller surface, can it be completely resolved.


8 Watermarks
From the front, the glass panel appears in a sheet shape, with a noticeable difference in color from other parts, usually turning white. It is usually caused by local water pollution of the lower roller or incomplete cleaning during the cleaning of the lower roller. So it is necessary to try to avoid water pollution on the lower roller, and the lower roller must be cleaned thoroughly.


9 Bubble scars
From the front of the glass panel, there are dark scars on a vertical straight line with different colors compared to other parts. Generally, after a machine change, a large number of bubbles must be discharged, and some will gather into a large bubble that cannot be discharged, rotating back and forth in front of the roller. Generally, the method of using a heavy iron hook is used: one person observes the specific position of the bubble scar, and the other person takes it

10 microcracks
A very small, unobservable thin stripe in glass that can be touched with a finger and reduces the strength of the glass. Most fractures originate from microcracks and usually occur at the edges of the glass surface, with double velvet glass being the majority. It is generally caused by the low temperature of the glass strip or the low temperature of the rolling roller, auxiliary roller, and transition roller themselves. It is possible to increase the temperature appropriately, such as burning the edge, turning down the rolling roller, auxiliary roller, transition roller, etc.


11 Bright and Hidden Lines
There are traces on the glass plate in the direction of pulling, showing white or dark stripes that can be observed at specific angles and under specific light, and are more obvious when viewed from the side.
The reason for this is that the lower edge of the lip brick has excessive pollution due to frequent machine changes or repeated shaking of scallions. If the scallions are not large enough during normal production, they are easily affected by thin glass and form black and white bright lines on the board surface. By lowering the body of the calender and increasing the scallions, or gently pushing along the lip brick surface with a shovel, the problem can be solved by allowing the calender to remove debris from the glass liquid, but do not damage the lip brick.


12 Thickness deviation
The deviation between the thickest or thinnest value of the same piece of glass and the nominal thickness is the thickness deviation, and glass with thickness exceeding the standard becomes scrap. Usually, it is due to the low temperature of the glass liquid on both sides before the roller and the large difference in temperature between the middle, causing the glass plate to be thick on both sides and thin in the middle. At the same time, the bending of the rolling roller can also cause longitudinal thickness deviation of the glass plate. Adjust the temperature of the glass liquid on both sides before the roller, add insulation layer or burn edge fire to reduce the lateral temperature difference. At the same time, an infrared thermometer is used to display the longitudinal fluctuation of the glass plate temperature, find a point with the smallest fluctuation, turn on the synchronization switch, lock the contact surface of the upper and lower rollers, and the longitudinal thickness deviation can be improved.