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Annealing,Cushion,Degradation,Flash,Fountain Flow

ABIS Mold Technology Co.,Ltd Updated: Apr 21, 2017

Annealing: A molded plastic part is heated enough to permit sufficient movement of the polymer molecules which allows relaxation. This can reduce stress within the part and when combined with fixturing, can also be used to reduce/eliminate excessive warpage.

Cushion:The material remaining in the barrel, in front of the screw, after the mold filling and pack stages of the injection process is called the cushion.  Having a cushion ensures that the screw does not bottom out against the front of the barrel, thereby preventing control of packing. Cushion is critical for most parts to assure they can be properly packed out.

Degradation: Degradation of a plastic material can occur as a result of reduction in molecular weight, separation of the polymer and its additives, damage to the additives, or a chemical reaction. Conditions leading to material degradation during injection molding can include: too high of a melt temperature, long residence times, excessive shear rates and frictional heating in a runner, poor venting, and dead or low flow areas in the injection barrel or hot runner system. Additionally, some materials can degrade as a result of improper drying. For example, drying a material at too high of a temperature for too long can create oxidation. Additionally, injection molding certain materials with too much moisture, such as Nylon, PC and polyurethanes can cause the material to undergo hydrolysis.

Molding Flash: A thin film of plastic showing at the parting line of the mold or between mold inserts. This can be caused by an excessive gap between any mating steel halves that are forming the molded part; clamp tonnage may be too low; poorly controlled process resulting in the entire cavity being filled under velocity control (transfer position incorrectly set). If the mold is older, it may be caused by tooling wear or damage. If it is a multi-cavity tool the balance should be checked as cavities can fill at very different conditions. This could be discovered using the 5-step processMolding simulation could also be used to troubleshoot.

Fountain Flow:The plastic in the flow channel’s center is flowing faster than the material along its perimeter. The flow in a runner is considered to be laminar and flow along the channel wall is considered to be zero. The material at the flow front is pushed forward and “fountains” to the channel wall. The result is that during mold filling, the first material injected into an empty melt flow channel fountains to the channel walls. As additional material is added, this newer material advances to the flow front and continually fountains to the wall.

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