Analyze the silver wire problem of injection molding defects in four aspects

Posted by jj on November 12th, 2020

Silver streaks are mainly caused by incomplete drying of the raw materials and caused by moisture or volatile components (mainly interference from water vapor, decomposition gas, solvent gas, and air). When silver filaments are produced, firstly use thoroughly dried pellets for forming experiments. If this cannot be eliminated, check for other reasons. Next, we will analyze the plastic injection molding defect silver wire problem from four aspects.

The specific reasons for silver wire are as follows:

1. Injection molding machine:

(1) The barrel and screw are worn out, or there are dead ends of material flow in the rubber head and rubber ring, which will be decomposed by long-term heating.

(2) The heating system is out of control, causing the temperature to be too high and decomposing. Check whether there are problems with the heating elements such as thermocouples and heating coils. Improper screw design can cause improper exhaust or easily bring in air.

2. Mold:

(1) Poor exhaust;

(2) The friction resistance of the runner, gate, and cavity in the mold is large, causing local overheating and decomposition; (3) Unbalanced distribution of the gate and cavity, and unreasonable cooling system will cause unbalanced heating and local overheating or Block the passage of air;

(4) The cooling passage leaks into the cavity;

(5) There is some unplasticized plastic cold material on the injection molded part, increasing the size of the cold material cavity; expanding the tail of the runner to form an additional plastic cold material cavity; using electric heating nozzle and nozzle sleeve;

(6) The runner and gate are too small or the length is too long, causing plastic to condense during transportation. If necessary, increase the runner diameter and gate depth.

  3. Process:

(1) Set temperature, pressure, speed, back pressure, melt glue motor speed is too high to cause decomposition, or pressure, speed is too low, injection time, pressure holding is insufficient, back pressure is too low, the density is due to failure to obtain high pressure If it is insufficient to melt the gas and the silver streak appears, appropriate temperature, pressure, speed and time should be set and multi-stage injection speed should be used.

 (2) Low back pressure and fast speed make it easy for air to enter the barrel and enter the mold with the molten material. When the cycle is too long, the molten material is heated in the barrel for too long and decomposes. The plastic stays in the injection cylinder for too long, reducing Total cycle time; the injection volume is too small for the injection requirements (it is recommended to use 20% to 80% of the injection volume of the machine).

(3) Insufficient amount of material, too large buffer pad, too low material temperature or too low mold temperature will affect the material flow and molding pressure, and promote the formation of bubbles.

(4) The surface temperature of the melt is too high, reduce the temperature of the injection cylinder; the temperature of the melt is too low to make the mold filling time unstable, increase the temperature of the injection cylinder; increase the nozzle temperature; increase the mold filling speed

(5) There is too much mold release agent on the surface of the mold, so thoroughly clean the surface of the mold with white spray

4. Plastics:

(1) The plastic has high humidity, the proportion of added recycled materials is too large or contains harmful scraps (the scraps are easily decomposed), and the plastics should be fully dried and eliminated.

(2) To absorb moisture from the atmosphere or from the colorant, the colorant should also be dried. It is best to install a dryer on the machine.

(3) The amount of lubricant, stabilizer, etc. added to the plastic is too much or the mixing is uneven, or the plastic itself contains volatile solvents. The mixed plastic will also decompose when the degree of heating is difficult to balance.

 (4) The plastic is contaminated and mixed with other plastics.