Burrs are a type of molding defects in which molten resin flows through gaps in the parting line of the mold and solidifies as it does. A familiar example would be the thin skin that adheres around a Thai pancake.
In the case of tie-roasting, the more thin skin you have, the more you feel like you are getting something out of it.
However, when it comes to resin-molded products, the appearance is not good, and even if you remove the burrs, the process increases and the cost goes up. In particular, there is no good thing about having burrs, as they can cause injury, especially when glass fibers are mixed in with the resin.
There are three main factors that can cause burrs. 1.
(1) A defective die fitting causes a gap, through which the resin flows and burrs (A).
2. Insufficient rigidity of the mold causes the mold to deform during injection, creating a gap that allows resin to flow into the mold.
3. Insufficient clamping force of the molding machine causes the mold to open, resulting in burrs (B)
In addition to this, it can also occur when excessive injection pressure is applied, or when the runner and molded product are close together in the mold layout.
Examples of countermeasures are
(1) Lower injection pressure
(2) Lower injection speed
(3) Lower mold temperature
(4) Lower resin temperature
The presence or absence of gas venting also affects the degree of burr generation.
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