When blowing air after mold closing on a blow molding machine, if the mold loosens to both sides (in the mold closing direction), it indicates mold bulging. Possible causes include:
First, insufficient mold closing pressure. The solution is to increase the mold closing pressure.
Second, a damaged oil seal in the mold closing cylinder is causing oil leakage, preventing the actual mold opening pressure from reaching the required level. Checking the pressure gauge is useless in this case. It could be due to oil leakage from the piston in the mold closing cylinder (or, if there's only one cylinder, check the mold closing cylinder) or a damaged oil seal on the piston. The testing method is to disconnect the oil pipe in the piston rod direction after mold closing to drain the oil until it stops flowing. Then, continue the mold closing action and observe if a large amount of oil flows out from the area where the oil pipe was disconnected. There shouldn't be a large amount of oil flowing out without the mold closing action. The only solution is to replace the piston or oil seal.
Third, improper adjustment of the mechanical origin and tilt angle of the mold closing mechanism during factory manufacturing can cause mold bulging. If mold bulging occurs frequently, this should be suspected, and the manufacturer should be contacted for adjustment.
Fourth, it could be a problem with the blow molding machine's mold mechanism. For older machines where this isn't the first time this has happened, this possibility should be considered. Ultimately, this problem stems from the technician's machine setup habits and parameter issues. It's complicated to resolve, requiring step-by-step troubleshooting to pinpoint which part is loose.
Fifth, a malfunction in the solenoid valve controlling the mold's opening and closing. The solution is to disassemble and inspect it or replace it with a spare part.
