how to avoid weld line defect

When the molten plastics meet with inserts, holes, areas with discontinuous flow velocity and areas with interrupted filling material flow in the mold cavity in the form of multiple strands, and when gate jet filling occurs, linear weld marks are generated due to incomplete fusion. The existence of weld lines greatly weakens the mechanical strength of the products. The method to overcome the weld mark is basically the same as that to reduce the depression of the product.

1、 Equipment

Poor plasticization and uneven melt temperature can prolong the molding cycle and make the plasticization more complete. If necessary, replace the machine with large plasticization capacity.

Two, mold aspects

(1) If the mold temperature is too low, the mold temperature shall be appropriately increased or the local temperature at the fusion joint shall be purposefully increased.

(2) The flow channel is small, too narrow or too shallow, and the cold charging well is small. The size of the flow channel should be increased to improve the efficiency of the flow channel and increase the volume of the cold charging well.

(3) Expand or reduce the gate section and change the gate position. The gate shall be opened to avoid the melt flowing around the inserts and holes. The gate with injection mold filling shall be corrected, relocated or buffered with a stop. Try not to use or use less multiple gates.

(4) Poor exhaust or no exhaust hole. Exhaust channels shall be opened, expanded or dredged, including the use of inserts and thimble gaps.

3、 Process aspect

(1) Increase the injection pressure and prolong the injection time.

(2) Adjust the injection speed: high speed can make the molten material reach the confluence without cooling, and low speed can make the air in the mold cavity have time to discharge.

(3) Adjust the temperature of the barrel and nozzle: the temperature is high, the viscosity of the plastic is small, the flow pattern is unobstructed, and the welding mark becomes thinner; Low temperature reduces the decomposition of gaseous substances.

(4) The release agent shall be used as little as possible, especially the silicon containing release agent, otherwise the material flow will not be fused.

(5) Reduce clamping force to facilitate exhaust.

(6) Increase the screw speed to reduce the plastic viscosity; Increase the back pressure to increase the density of plastic.

4、 Raw materials

(1) Raw materials should be dried and liquid additives in the formula should be minimized.

(2) Properly add lubricants and stabilizers to plastics with poor fluidity or high heat sensitivity. If necessary, use plastics with good fluidity or high heat resistance.

5、 Product design

(1) If the wall thickness is small, the parts shall be thickened to avoid premature curing.

(2) If the position of the insert is improper, it shall be adjusted in order.