Our factory plywood hot press is a second-hand equipment purchased during the technical transformation in 1988. The specification is 3 X 7 feet and the total pressure is 600t. The manufacturer is Qiqihar Light Industry Machinery Forging Factory. After 5 years of use, the plywood products produced gradually become defective. After the plywood is hot pressed, it needs to be stacked for a period of time according to the process requirements. At this time, the plate pile has a high end and a low end. After the product is sawed, one end is severe. Degumming, cracking, first-class, second-class product rate is reduced to 20%, and the repair rate sometimes reaches 70%.
1 Causes of hot plate corrosion
In response to the above situation, our factory's technical and maintenance personnel have carried out a large number of inspection, measurement and analysis work. According to the three elements of hot pressing: pressure, temperature and time, the first is suspected that the cylinder pressure is uneven, or the pressure oil is unevenly distributed in the six cylinders, so the inlet valve, the oil separation valve and the oil pipe are cleaned and inspected. The hydraulic oil was replaced. Then install the pressure gauge test in the spare vent hole of the cylinder, which is unsuccessful. The steam passage inside the hot platen was inspected again, and the hot pressing temperature was measured, and no problem was found.
Later, the operator found that each time the heating was started in the cold state, the right end of the pressing surface of the pressure plate, that is, the cracked end of the plywood, dropped. Upon inspection, it was found that there was a corrosion zone with a width of 80-100 mm on the pressing surface of the pressure plate, and the depth ranged from 0.5 to 1.5 mm. The water leakage is where the weld of the steam through hole plug inside the pressure plate is eroded, causing the steam water to be extravasated. In the hot state, the water droplets are evaporated and therefore cannot be seen.
After analysis, the reasons are as follows: the platen size is 3x7 feet, and the plywood format produced by our factory is 3X6 feet. The plate is replaced with one end and the other end is 1 foot; and the pressure plate on the pressure plate has a pad. The loading and unloading plate has no padding on the pressing surface. During the work, a large amount of formaldehyde vapor and water vapor are not discharged in time, and the surface is directly fumigation, and sometimes the excess glue adheres to the surface, so that the platen is corroded for a long time. Produce defects.
2 Repair of corrosion surface of hot plate
Due to the high cost of replacing the press hot plate, our factory has adopted the following repair methods.
1 After removing the hot plate, brush off the rust with a steel brush, and then remove the rust with dilute hydrochloric acid (concentration of 15% to 20%) to expose the plate to metallic color.
2 Surfacing welding in the corrosion zone with φ5mm 422 electrode. Since the single-sided surfacing will cause the platen to bend, double-sided surfacing should be used to offset the stress of the welding pile.
3 On the gantry planer, the surfacing welded plate is double-sided planed, and the amount of planing is 0.5mm.
4 If the plug weld is cracked due to planing, it needs to be dug. That is, after double-sided planing, each of the pressure plates is subjected to steam pressure test one by one, and it is found that there are water drops, and the mark is made. After the test steam is turned off, a long groove or a round groove is ground at the weld of the water ball by an angle grinder, and then welded, and then ground with a sander.
3 Measures to prevent corrosion of hot plate
The pressed surface of the pressure plate is padded with a 1.5 mm thick polished stainless steel plate as follows:
1 The size of the steel plate pressing plate is processed, and a part of the fixing piece is left at the long and wide ends (two fixing pieces are left on both sides in the width direction; 8 fixed pieces are left on both sides in the longitudinal direction), and φ6 is drilled on each fixing piece. 2 mm hole.
2 Drill the M6 ​​xl5mm internal thread hole at the corresponding position in the thickness direction of the platen.
3 Bend the tab upwards and secure it to the platen with a M6 x 10mm screw.
The above repairs have saved a lot of money for our factory. Moreover, after taking the above precautionary measures, it has been 7 years since the platen has not been abnormally damaged and is used well.
1 Causes of hot plate corrosion
In response to the above situation, our factory's technical and maintenance personnel have carried out a large number of inspection, measurement and analysis work. According to the three elements of hot pressing: pressure, temperature and time, the first is suspected that the cylinder pressure is uneven, or the pressure oil is unevenly distributed in the six cylinders, so the inlet valve, the oil separation valve and the oil pipe are cleaned and inspected. The hydraulic oil was replaced. Then install the pressure gauge test in the spare vent hole of the cylinder, which is unsuccessful. The steam passage inside the hot platen was inspected again, and the hot pressing temperature was measured, and no problem was found.
Later, the operator found that each time the heating was started in the cold state, the right end of the pressing surface of the pressure plate, that is, the cracked end of the plywood, dropped. Upon inspection, it was found that there was a corrosion zone with a width of 80-100 mm on the pressing surface of the pressure plate, and the depth ranged from 0.5 to 1.5 mm. The water leakage is where the weld of the steam through hole plug inside the pressure plate is eroded, causing the steam water to be extravasated. In the hot state, the water droplets are evaporated and therefore cannot be seen.
After analysis, the reasons are as follows: the platen size is 3x7 feet, and the plywood format produced by our factory is 3X6 feet. The plate is replaced with one end and the other end is 1 foot; and the pressure plate on the pressure plate has a pad. The loading and unloading plate has no padding on the pressing surface. During the work, a large amount of formaldehyde vapor and water vapor are not discharged in time, and the surface is directly fumigation, and sometimes the excess glue adheres to the surface, so that the platen is corroded for a long time. Produce defects.
2 Repair of corrosion surface of hot plate
Due to the high cost of replacing the press hot plate, our factory has adopted the following repair methods.
1 After removing the hot plate, brush off the rust with a steel brush, and then remove the rust with dilute hydrochloric acid (concentration of 15% to 20%) to expose the plate to metallic color.
2 Surfacing welding in the corrosion zone with φ5mm 422 electrode. Since the single-sided surfacing will cause the platen to bend, double-sided surfacing should be used to offset the stress of the welding pile.
3 On the gantry planer, the surfacing welded plate is double-sided planed, and the amount of planing is 0.5mm.
4 If the plug weld is cracked due to planing, it needs to be dug. That is, after double-sided planing, each of the pressure plates is subjected to steam pressure test one by one, and it is found that there are water drops, and the mark is made. After the test steam is turned off, a long groove or a round groove is ground at the weld of the water ball by an angle grinder, and then welded, and then ground with a sander.
3 Measures to prevent corrosion of hot plate
The pressed surface of the pressure plate is padded with a 1.5 mm thick polished stainless steel plate as follows:
1 The size of the steel plate pressing plate is processed, and a part of the fixing piece is left at the long and wide ends (two fixing pieces are left on both sides in the width direction; 8 fixed pieces are left on both sides in the longitudinal direction), and φ6 is drilled on each fixing piece. 2 mm hole.
2 Drill the M6 ​​xl5mm internal thread hole at the corresponding position in the thickness direction of the platen.
3 Bend the tab upwards and secure it to the platen with a M6 x 10mm screw.
The above repairs have saved a lot of money for our factory. Moreover, after taking the above precautionary measures, it has been 7 years since the platen has not been abnormally damaged and is used well.
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