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Cause Analysis of Silver Grain in Plastic Injection Products

Cause Analysis of Silver Grain in Plastic Injection Products

Plastic injection molding products with silver grain, including surface air bubbles and internal pores. The main reason for the defects is the interference of gases (mainly water vapor, decomposition gas, solvent gas and air).

Ⅰ. Analysis of the specific causes of silver grain in plastic injection molding products

1. Machine aspect

(1) cylinder, screw wear or rubber head, rubber ring there is a dead Angle of material flow, long-term heat and decomposition.

(2) The heating system is out of control, resulting in high temperature and decomposition, should check whether there is a problem with the thermocouple, heating ring and other heating components. Improper screw design, resulting in a solution or easy to bring in air.

2. Mould

(1) Poor exhaust.

(2) The friction resistance of the runner, gate and cavity in the mold is large, resulting in local overheating and decomposition.

(3) Unbalanced distribution of gate and cavity and unreasonable cooling system will cause heat imbalance and local overheating or blocking of air channels.

(4) The cooling channel leaks into the cavity.

3. Plastic

(1) The plastic humidity is high, the proportion of recycled material is too much or contains harmful debris (debris is easy to decompose), should fully dry the plastic and eliminate debris.

(2) Moisture absorption from the atmosphere or moisture absorption from the colorant, colorant should also be dried, it is best to install a dryer in the machine.

(3) The amount of lubricant and stabilizer added in the plastic is too much or mixed unevenly, or the plastic itself has volatile solvent. Mixed plastic heat degree is difficult to take into account when the decomposition will occur.

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

4. Processing

(1) set up the temperature, pressure, speed, back pressure, melt cause decomposition motor speed is too high, or low pressure, speed, injection time, holding insufficient, low back pressure, inadequate due to failed to get high density to melt with silver lines, with the gas should be set up the appropriate temperature, pressure, speed and time and adopt the multistage injection speed.

(2) Low back pressure and fast speed easily make the air enter the cartridge. With the molten material entering the mold, too long cycle will make the molten material in the cartridge heated for too long and decompose.

(3) the amount of material is insufficient, the feeding cushion is too large, the material temperature is too low or the mold temperature is too low, all affect the flow of the material and forming pressure, and promote the formation of bubbles.

Ⅱ. Plastic injection molding products have the reason of fusion joint analysis

The fused plastic in the cavity due to encounter insert holes, flow rate incoherent area, filling material flow interrupted area and in the form of multi-strand confluence, due to not complete fusion and linear fusion joint.

In addition, the weld joint will also be generated when the gate injection molding occurs, and the strength and other properties of the weld joint are very poor. The main reasons are as follows:

1. Processing

(1) The injection pressure and speed are too low, the barrel temperature and the mold temperature are too low, resulting in the premature cooling of the molten material into the mold and the appearance of melting joints.

(2) When the injection pressure and speed are too high, there will be spraying and melting joints.

(3) The rotational speed should be increased, and the back pressure pressure should be increased to reduce the viscosity and increase the density of the plastic.

(4) the plastic should be dry, recycled material should be used less, the amount of release agent is too much or the quality is not good will also appear melting joint.

(5) Reduce the clamping force, convenient exhaust.

2. Mould

(1) The same cavity gate is too many, should reduce the gate or symmetric setting, or as close as possible to the melting joint setting.

(2) the exhaust at the fusion joint is poor, and the exhaust system should be set up.

(3) The runner is too large, the size of the pouring system is improper, and the gate should be opened to avoid the melt flowing around the insert hole as much as possible, or the insert should be used as little as possible.

(4) If the wall thickness changes too much or the wall thickness is too thin, the wall thickness of the product should be uniform.

(5) If necessary, a fusion well should be set up at the fusion joint to make the fusion joint separate from the workpiece.

3. Plastic

(1) Lubricants and stabilizers should be added appropriately to plastics with poor fluidity or heat sensitivity.

(2) Plastic contains many impurities, if necessary, to change the quality of plastic.

Ⅲ. Injection molding products vibration grain cause analysis

PS and other rigid plastic parts on the surface near its gate, with the gate as the center to form a dense ripple, sometimes called vibration grain.

The reason is that the melt viscosity is too large and in the form of stagnant filling mold, the front of the material a contact with the cavity surface will soon condense and shrink up, and later the melt and expand, has shrunk the cold material to continue to advance the process of continuous alternating so that the material flow in advance formed surface vibration grain.

The solution:

(1) Increase the barrel temperature, especially the nozzle temperature, but also increase the mold temperature.

(2) Increase the injection pressure and speed, so that it can quickly fill the model cavity.

(3) Improve the size of runner and gate to prevent excessive resistance.

(4) The die exhaust should be good, and a large enough cold well should be set up.

(5) Plastic injection molding products should not be designed too thin.

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