Solutions To Common Plastic Mold Problems

Plastic products processing--methods to prevent mold cracks

1. Reasons for cracks in the mold: 1. Insufficient rigidity of the mold 2. Stress concentration at the corners of the cavity

2. Associated knowledge

1. The wall thickness design of the mold is an important parameter of the mold design, and the strength calculation (simple tension calculation) is performed to ensure the necessary thickness of the mold. Also, additional grooves are used to utilize the overall rigidity of the mold.

2. Stress concentration is easy to occur when processing the corners of the mold cavity, and cracks are also prone to occur here, so the corners must be processed into a shape with a round corner R.

3. Solutions

1. Process the edges and corners of the mold cavity into a shape with a round corner R, and process it into a grooved shape on the parting surface of the mold to strengthen and enhance the rigidity of the mold

4. Due to the difference of materials;

Plastic products processing--methods to prevent sticky bending of molds

1. Reasons for viscous bending of the mold: 1. Insufficient rigidity of the mold 2. Bulging of the mold due to injection pressure

2. Associated knowledge

1. The cavity will expand a little due to the injection pressure. If the mold is restored to its original shape, but the pressure in the mold is still high, the product is cooled and solidified, and the mold reacts with a large force when it returns to its original shape. Because of the mold, the mold has to be opened a little.

3. Solution:

1. Immediately: manage the injection pressure, do not rise above the set value.

2. Long-term: set the groove and force adjustment.

4. Due to the difference in materials: it is difficult to deal with materials with high rigidity.

5. Reference matters;

1. Because it is easy to happen when the mold is tested, it is better to attach a dial gauge to the mold and slowly increase the injection pressure while monitoring.

2. The mold that produces viscous expansion is removed from the injection machine and decomposed, and the product is softened by heating and removed. 3. It is due to the lack of rigidity of the mold, which is strengthened and clamped from the outside with a splint.

Knowledge of plastic molds - the reason why the mold is out of stock and broken:

1. The toughness of the molding pin is insufficient. 2. The root angle R of the molding pin is incomplete.

2. Related Knowledge

1. The hole of the molding pin is related to the position of the locking mold screw on the mold, so the molding pin is thin and long, because of the molding pressure, it is easy to bend and break, so this kind of pin must be heat treated to have both very toughness and a certain hardness.

2. Since the stress concentration of the pin is mostly concentrated at the corner R of the root, if there is damage to this part during processing, it is common for the stress concentration to break the molding pin here.

3. Solution: Heat treatment on the molding pin.

Four due to differences in materials;

5. Reference items: Usually the mold should have spare parts for de-molding pins.

Plastic mold knowledge--the method of taking out the products remaining in the mold cavity

1. Squeeze the brass sheet into the gap between the product and the mold, and pry the product out of the mold cavity, but use this method carefully for non-ferrous alloy molds.

2. In order to achieve this purpose, a brass sheet should be prepared on the injection molding machine (for example, a brass sheet with a thickness of 3MM, a width of 300MM, and a knife-shaped front end)

3. Substituting a screwdriver will cause major damage to the mold.

4. For products that cannot be cut or cracked, use the above-mentioned brass sheet to tap the product directly with a hammer. However, this may cause the surface of the mold cavity to be recessed, so it can only be used on the surface of the product and the surface of the model. Crack, do not scratch the surface of the cavity.

5. In order to cut off the product, there is also a method of directly heating with a blowtorch, which is only effective for large-scale occasions. But be careful to stay away from combustibles. For small-scale occasions, you can use the method "35 to remove the remaining material head in the nozzle, the fourth point" method to take it out.

6. If there is a small part of the product residue that cannot be removed no matter how you do it, use the solvent of this material (such as acetone, etc.) to coat it, and knock it out with a brass rod after it is dissolved, but pay attention to the solvent not being close to the fire.

7. Remove the residual product on the surface of the mold cavity, wipe it clean with a cloth and spray a release agent. However, it should be noted that the release agent will affect the secondary processing (coating, welding, etc.) of the product, so be careful when using it

Plastic mold knowledge--methods to prevent mold from rusting

1. Reasons for mold rusting; 1. Decomposition of products of molding materials. 2 mold resurgence. 3 sweaty hands.

2. Associated knowledge;

1. The most common corrosion of the mold is the product (gas, residue) of the decomposition of the molding material. In order to prevent the mold from rusting, the most widely used method is to chrome-plate the mold cavity, but the chrome-plating cannot fully solve the problem, because the decomposition product also corrodes the deep part of the pinhole. And these places are exactly the places that cannot be plated.

2. When the mold is cooled below the moisture regain point, the moisture in the air will regenerate on the surface of the mold to produce water droplets, and rust will occur.

3. Solve problems;

1. Short-term countermeasures: gently wipe the surface of the cavity with a cloth. Fully dry the molding material and lower the temperature of the barrel to prevent the material from decomposing.

2. Long-term: Turn the product material into a material that does not corrode the mold by the decomposition product.

4. Due to the difference in plastic materials

1. Materials that are easy to decompose, such as PVC, POM, EVA, PC, and foaming materials. Because the decomposition product has a corrosive effect on the mold, the mold should be chrome-plated.

5. References

1. When the molding is temporarily stopped, spray the anti-rust agent on the mold cavity, and then close the mold.

2. When the mold is out of use for a long time, apply a layer of butter to the outside and active parts of the mold.

How to take out the remaining chip in the nozzle

1. On the side of the nozzle, use the tip of a thick copper rod to align with the mold sprue material and tap lightly. After a little movement, use a thin copper rod to poke it out.

2. In order to achieve this purpose, the injection molding machine should be equipped with a number of thin copper rods (such as a diameter of 4MM, a length of 300MM, a brass rod with a sharpened front) and a thicker brass rod ( Diameter 12MM front sharpened)

3. If a screwdriver is used instead, the mold will be seriously damaged.

4. When it is impossible to poke out from the side of the nozzle, use an iron wire (about 4MM in diameter and sharpen the front end) to heat it with a heater such as an alcohol lamp until it turns red and poke the nozzle material from the side of the mold cavity to fully replace it. After cooling, clamp it with pliers and take it out. At this time, the lower part of the pliers must be placed in a brass plate (or cloth strip) to prevent damage to the mold and take out the sprue material.

5. When the sprue material cannot be taken out by using the above methods, use the solvent of this material (such as acetone, etc.) near.

6. After taking it out, blow it off with gas in the sprue hole, spray the release agent, and carry out normal production.