1 – An injection mold should have a minimum of 6 parting line vents, more for larger molds. There should be a vent at each inch interval around the perimeter of the molding cavity and each vent should extend to the outer edge of the mold into the atmosphere. These should be cleaned out at least once every 24 hours, and more if needed. There cannot be too many vents or too much venting. As long as the vents are of the proper thickness and length, they can be any width, and they can be any number. A good rule of thumb is to allow at least 30% of the parting line perimeter for venting. The following drawing demonstrates this.   2 – If you believe a mold needs a vent somewhere that is not vented, you can create a temporary vent by placing two pieces of  ½” wide masking tape on the shutoff land in the area in question, leaving a ½” gap between them. That will act like a vent and allow you to mold 1 or 2 cycles to see what difference it makes in the molded part.  3 – Never use a single mold temperature control unit to maintain water temperature between 2 mold halves. Each mold half should have its own temperature control unit for complete effectiveness. If only one unit is used for both halves, the water leaving the first half may not be at the right temperature for the second half. Each half should be maintained separately to accommodate specific needs of each half. And both halves should never be at the same temperature or you will not be able to ensure that the molded part stays on the half with an ejection system in place.  4 – Waterlines should be hooked to the mold, after it is mounted in the press, so that water enters the mold near the bottom and exits the mold near the top. That ensures that any air in the mold lines will be purged out immediately and never cause hot spots in the mold during the production run. 5 – Mold temperatures should be checked periodically by using a flat probed pyrometer. Each mold half should be checked separately and the probe should be touched to 5 or 6 points on each mold half. There should not be more than a 10 degree (F) difference between any 2 of those points or between the two mold halves themselves.  If greater differences occur it indicates improper cooling conditions and this should be rectified by cleaning lines, adding cooling channels, inserting baffles to the cooling lines, etc. 6 – A molded part will always try to stay on the hottest half of a mold. In most cases we want that to be the Clamp Unit side of the mold because that is where the ejection unit is to push the final part out of the mold. Warpage and sticking might be controlled by keeping this thought in mind. 7 – The ejection half of the mold should be 5 to 10 degrees (F) hotter than the injection half to ensure the molded part will stay on the ejection half. Be careful though because too much heat difference will cause a “lockup” of the 2 mold halves, or galling of some metal components. 8 – A hot mold will produce a part with a finish that has more gloss than a part molded on a cold mold. A hot mold will also produce a darker part than a cold mold. 9 – Use of commercial insulation sheets placed between the mold and the platens of the machine will result in less energy used for maintaining mold temperatures and create greater consistency of temperature throughout the mold. These are available in ¼” or ½” thick sheets and can be permanently mounted directly on the clamping faces of the injection mold halves.


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