This article will tell you some common problems in the injection molding process and also the corresponding solutions.
The reason and solution of the product lacking glue after a period of production.
When the machine starts to work, the melt glue in the material tube of the injection molding machine has a long heated time, low viscosity and good fluidity. So the product is easy to run off the edge.
After a period of production, the melt glue constantly takes away the heat. Then, that results in insufficient melt glue, high viscosity and poor fluidity, which makes the product lacks glue. Therefore, you should gradually increase the temperature of the feed pipe to solve this problem.
After a period of production, the melted glue continuously takes away the heat. And that results in insufficient melt glue, high viscosity and poor fluidity, which makes the product lacks glue. Now, you should increase the material tube temperature.
The ellipse shape of the product is due to the uneven glue input, resulting in uneven pressure around the product, making the product become ellipse shape. You can inject the glue from three point to make the injected glue even.
It is required that the mold material has good rigidity, small elastic deformation and small thermal expansion coefficient.
The acid resistance test of the product is to detect its internal stress and the location of the internal stress focus point to eliminate the internal stress of the product.
When inserts are placed in the product, internal stress will be formed due to hot melt meets cold inserts during injection, which reduces the strength of the product and make it easy to crack. During production, you can preheat the inserts.
If the exhaust point of the mold is unreasonable. Not only does it fail to exhaust, but it will cause deformation or dimensional changes of product. So the exhaust point of the mold should be reasonable.
You can set the exhaust point at the place where the product is injected with glue and burnt in the trapped gas.
If the exhaust point of the mold is unreasonable. Not only does it fail to exhaust, but it will cause deformation or dimensional changes of product. So the exhaust point of the mold should be reasonable.
You can set the exhaust point at the place where the product is injected with glue and burnt in the trapped gas.
The low melt temperature or low mold temperature, and insufficient injection pressure can’t help to make a good combination of glass fiber and plastic in the glue, causing revealed fiber.
You can increase the temperature of melt and mold to increase the injection pressure.
If the temperature of the inlet is too high or too low, it will cause unstable back feeding of the machine, make the amount of feed unstable, and affect the size and appearance of the product.
Cause: the cold glue in the product or the dust in the material.
You can raise the temperature of the nozzle, add a cold feed well and keep the raw materials well to prevent dust from entering.
Injection ability PW = injection pressure ( kg / cm2 ) × injection volume ( cm3 ) / 1000
Injection horsepower PW ( KW ) = injection pressure ( kg / cm2 ) × injection rate ( cm3 / sec ) × 9.8 × 100%
Injection rate V ( cc / sec ) = л / 4 × d2 × rd2: diameter of material tube r: density of material
Injection thrust F ( kgf ) = л / 4 ( D12-D22 ) × P × 2D1: cylinder inner diameter D2: piston rod outer diameter P: system pressure
Injection pressure P（ kg / cm2 ） = [ л / 4 × ( D12-D22 ) × P × 2 ] / ( л / 4 × d2 )
Plasticizing capacity W ( g / sec ) = 2.5 × ( d / 2.54 ) 2 × ( h / 2.54 ) × N × S × 1000 / 3600 / 2h = screw front tooth depth (cm) S = raw material density
System pressure ( kg / cm2 ) = the highest working pressure set in the hydraulic circuit. The injection pressure refers to the actual pressure of the injection molding machine. The two are not equal.
(1) Appropriate viscosity and good viscosity performance
(2) Good lubricity and rust resistance
(3) Good chemical stability, not easy to gasify into colloid
(4) Good foaming
(5) Low corrosion to machine parts and sealing devices
(6) Low ignition point (flash point) and freezing point requirements
When the working environment temperature of the system is high, oil with higher viscosity should be used. Conversely, use oil with lower viscosity.
The oil with higher viscosity should be used. Because at high pressure under the high working pressure, sealing is difficult and leakage Is the main problem. Conversely, when the working pressure is low, oil with a lower viscosity should be used. When the working speed of the working parts of the hydraulic system is high, the flow rate of the oil is also high. At this time, the pressure loss will also increase, and the leakage will be relatively reduced. You should use oil with lower viscosity. Conversely, use oil with higher viscosity according to the low moving speed of working parts.
If the setting of the release position is too large, it will cause the return material to absorb oxygen, oxidize the rubber material and generate bubbles. If the position is set too small, the pressure in the barrel is high. The shear force is so high that the rubber will be decomposed and the nozzle will flood. So the position error cannot exceed 0.4 mm.
Melt position = product weight / ( maximum stroke / maximum melt amount )
The core of thick material can be evacuated to make hollow pipe fittings, which can save materials and shorten the cycle time.
The use of gas in injection molding can evenly distribute the pressure. When the plastic cools and solidifies, the gas can compensate for the volume shrinkage of the plastic through expansion.
Reduce the internal stress of molded products, thereby improving the stability of the shape and eliminating deformation and warpage.
It’s caused by the overheated middle hole needle and the uneven shrinkage of product. The middle hole needle can be made of phosphor copper material with fast heat dissipation and the mold is exhausted in the middle of the product.
Due to the stress on the surface of product, it causes cracking after screen printing. You can increase the mold temperature and reduce the stress. And annealing can be used to eliminate the stress.
The large injection pressure and holding pressure, and the residual internal stress at the nozzle make the product easily broken.
Solution: Try to reduce the injection pressure and holding pressure as much as possible, and increase the mold temperature appropriately.
Because of the weld line of column, the assembly column is prone to bursting.
Solution: increase the exhaust of mold, appropriately increase the mold temperature and speed up the injection rate to reduce the weld line.
It mainly results from the imbalance of heat shrinkage, or the internal stress of the product itself.
Raw materials that are not dry enough, uneven thickness of the glue, poor exhaust of the mold, and easy decomposition of the raw materials may make the product bubbles.
Solution: Fully dry the raw materials, increase the mold exhaust, minimize the uneven thickness of the glue.
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