An Analysis of Operational Conditions for Plastic Mold Injection Molding

Under what circumstances should a mold temperature machine be used to heat the mold? And when should a plastic mold be cooled with a chiller? Below are some conditions for injection molding.

The installation and commissioning specifications of household plastic molds

Pre-inspection of the mold

Before the mold is installed on the injection molding machine, an inspection should be carried out in order to discover quality problems in a timely manner, so as to avoid dismantling after installation. When inspecting the fixed template and the moving template of the mold separately, pay attention to the directional markings to avoid mistakes during mold clamping.

Installation of the inclined guide mold

During installation, two people should cooperate closely and pay attention to safety. If there is a lateral parting mechanism on the mold, the sliding block should be installed in a horizontal position, that is, the movable block should move left and right.

Mold fastening

When the positioning ring of the mold is loaded into the positioning ring seat on the fixed template of the injection molding machine, the mold should be closed at an extremely slow speed, so that the movable template can gently press the mold, and then the pressure plate should be installed. The pressure plate must be installed with 4 pieces of gaskets on both upper and lower sides. When the upper-pressure plate is installed, the height of the adjusting screw should be adjusted to be level with the mold foot, that is, the pressure plate should be flat. If the pressure plate is slanted, the mold foot cannot be pressed tightly. The side of the pressure plate should not be close to the mold to avoid friction damage to the mold.

Correction of the top rod ejection distance

After the household plastic mould is fastened, slowly open the mold until the movable template stops retracting. At this time, adjust the position of the top rod to leave a gap of not less than 5 mm between the ejection plate on the mold and the bottom plate of the movable template in order to eject the product and prevent damage to the mold.

Adjustment of mold clamping tightness

In order to prevent flash and ensure proper exhaust, when adjusting the hydraulic plunger-elbow lock mechanism, take mainly visual inspection and experience. When closing the mold, the elbow should extend naturally and not be too stiff or too weak, so that the mold clamping tightness is just right. For molds that require mold temperature, the mold clamping tightness should be checked after the household plastic mold is heated.

Turn on the cooling water

After the cooling water is turned on, check whether it is unobstructed and whether there is any leakage.

The molding conditions of household plastic molds

Mold clamping pressure: It should be greater than the total pressure of plastic injected into the mold and should not produce flash.

The pressure and speed have a certain relationship in the mold. The purpose is to evenly fill all corners with the appropriate amount of material. Too low pressure may cause short shots, shrinkage, while too high pressure may cause flash, overpacking, sticking to the mold, burning, and damage to the mold and high internal stress.

Speed: The speed determines the condition of the material in the mold gating system and the product. Fast speeds can cause flash, overpacking, and burning, while slow speeds can cause short shots, shrinkage, poor bonding, and easy breakage.

Temperature: Different materials have different temperatures. If the temperature is too low, the color of the melted plastic will be uneven, and the internal stress of the product will increase. If the temperature is too low and the pressure is too high, the screw may break. If the temperature is too high, the product will have flash, and due to cooling, shrinkage will occur. The material will decompose, turn yellow, change color, and break easily. If the cooling time is too long, it will be difficult to exhaust, and gas will remain.

Back pressure: The resistance when the screw rotates and moves backward to feed is called back pressure. Its role is to make the material more compressed during conveying and to remove the air and moisture from the screw. This will make the melted plastic free of gas components that affect the surface of the product. Low back pressure can lead to bubbles and silver streaks on the surface. High back pressure can cause overheating, caking, overflowing, long cycles and screw non-retreat. It is also important to use a loosening device when the back pressure is high: for some materials, the loosening is necessary, while others do not require it. When the back pressure is high, attention should be paid to the distance from the air and overflow.

The mold temperatures and the length of cooling time will affect the products of household plastic injection molds for sale, including shrinkage, tolerance of dimensions, surface brightness, cycle times. So we should adjust thses factors as needed. For thicker acrylic or PC products, mold temperature is necessary to avoid bubbles and high internal stress.

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