Injection Molding Trouble Shooting--01 - Ningbo Jinyi Precision Machinery Co., Ltd.

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Injection Molding Trouble Shooting--01

Injection Molding Trouble Shooting

1) Short Shot

As the name suggests, "short shot" means that not enough resin has flowed into the mold to fill it adequately. The main causes for short shot are the mold condition or flowability problems with the resin. The problem is alleviated when a greater volume of resin flows more easily.

This is done by raising temperature and pressure as well as enlarging the gate to reduce resin resistance.

Cause	Solution
Injection pressure is too low	Increase injection pressure
Resin flows too slowly	Increase temperature in the cylinder. Increase injection speed
Mold temperature is too low and resin viscosity is too high	Increase the mold temperature
Resin supply is insufficient	Increase the resin volume
Too much flow resistance is at the sprue, runner and gate	Increase the sectional area of the gate, sprue and runner, and shorten the length. Make the sprue, runner and gate surfaces more slippery
Too much flow resistance is in the cavity	Change the gate position; increase the thickness of the mold cavity; modify design to improve flow

2) Mold Release Defects

Cause	Solution
Resin is not cooled sufficiently	Lower the mold temperature; increase the cooling time
The resin overflows	Reduce the injection pressure Lower the resin temperature Lower the mold temperature Reduce the packing pressure
The surface of the cavity, sprue, runner or gate is not good	Improve the surface
releasing slope is insufficient	Increase the releasing slope Reduce resistance to mold release
Other steps.	Core: lengthen the ejector pin, increase the ejector pin size Undercut: Decrease the undercut discharge angle Cavity: Use a parting agent

Should the resin not drain from the sprue, take the following measures

Cause		Solution
The sprue is not cooled sufficiently.	Reinforce the cooling channel in the sprue. Lengthen the cooling time.
Mold nozzle rounding and injection molding machine nozzle rounding do not fit properly.	Make the diameter of the sprue front larger than that for the injection molding machine nozzle. Improve the nozzle rounding.
The sprue is not clean enough.	Clean the sprue thoroughly.

If the sprue is discharging hard, inspect for blockage : Sometimes the plate-shaped plastic pieces causes the problem.

3) Weld Line

the weld line is the place where the resin flow contacts the two halves of the mold.

The line appears when the resin temperature is not high enough for the molted polyme to completely blend together. Eliminating the weld line altogether is difficult, so molds are designed to position the weld line where it will not show on the finished product and where it will not weaken the product.

Cause		Solution
Molten resin flows too slowly.	Raise the temperature of the cylinder.
Injection pressure is low.	Increase injection pressure.
Mold temperature is too low.	Mold temperature is too low. Increase the mold temperature.
Cavity on air discharge port is insufficient.	Increase the size of the air discharge port.
The shape of the gate and cavity are improper.	Increase the thickness of the part where the weld line appears . Install an overflow tap. Change the gate location.
Too much lubricant and releasing agent are used	Reduce the amount.

4) Flow Mark

"flow mark" is a trace of the resin flow through the gate center. When the resin to flow into the mold cools too quickly, it will form a border with the resin that flows in subsequently, leaving the flow mark. The problem occurs when the resin viscosity is too high, the resin and(or) mold temperature are not uniform or when thickness variations are severe.

Cause		Solution
The resin viscosity is too high.	Increase the temperature of the cylinder and mold. Accelerate injection speed.
The resin temperature not uniform.	Enlarge the cold slug well. Raise the nozzle temperature. Minimize variations in thickness to prevent part to cool too quickly.
The mold temperature is not high enough.	Raise the mold temperature.

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