Injection molding is considered one of the most common plastic part manufacturing processes. The process usually begins with taking the thermoplastic/thermoset polymers in the form of pellets or granules and heating them to the molten state. The melt is then injected into a chamber formed by a split-die mold. The melt remains in the mold and is either chilled down to solidify (thermoplastics) or heated up to cure (thermosets). The mold is then opened and the part is ejected.
For the injection molding cycle to begin, four criteria must be met: mold open, ejector pins retracted, shot built, and carriage forward. When these criteria are met, the cycle begins with the mold closing. This is typically done as fast as possible with a slow down near the end of travel. Moulders cannot afford slow cycles particularly in adverse and tough economic environment. One unnecessary drag on productivity is gas and air entrapment in the mould, which is not always cured by conventional venting approaches.
Mold-Vac�s air/gas evacuation system is a self-contained, stand-alone system that pulls a vacuum on the vents during injection, and its patented air blowback function assists in ejection and helps clean and purge the vents and ejector pins after every cycle. The microprocessor controlling both the vacuum and blowback functions receives a signal from the injection press then applies a vacuum that can be adjusted from 0 to 24 mm Hg. The system purges air at a rate of 0.02 cu in/sec, said to be the fastest in the industry. Vacuum and blowback operate on a timer setting programmed by the molder. Users mount the portable unit beside the press, position two limit switches, and connect vacuum tubing from the unit to the mold. The mold requires an air-tight seal. Time between maintenance shutdowns for the mould was lengthened by a factor of at least two or three along with lower rejects. The unit eliminates part burns, voids, and associated molding problems caused by gas and air entrapment. The unit cleans and purges vent pins thus eliminating residue build up, while reducing mold maintenance. Both thermoplastic and thermoset can be used with Mold Vac -- ABS, Acetyl, Nylon, Ultem, PPO, PP to Phenolics. The operation of the unit is not dependent on material type, but when quality problems are the result of gas or air entrapment. The unit is self-contained, i.e., all controls, gauges, etc. are mounted in a common panel for immediate installation and operation. Simply mount the unit beside the press, position the limit switches (2 supplied) and lastly, connect vacuum type tubing from the Mold-Vac to the mold. To assist in part ejection, the Mold-Vac provides a burst of compressed air just prior to mold open. Simply by setting the blowback timer to the desired setting (same as total cycle time). Opening the mold under vacuum can cause part distortion, the Mold-Vac's blowback feature eliminates this possibility. The second phase is controlled by the blowback limit switch. To eliminate residue buildup in vented pins, or tool steel erosion, position the blowback limit switch to activate upon mold open. Upon activation, compressed air will purge vented pins (with proper mold modifications) which will reduce mold maintenance.
How this system compare to a conventional vacuum pump: