Blog
Injection molded parts sticky mold, mold failure analysis and troubleshooting skills
Date:2018-02-28

Mold failure

 

There are many reasons for sticky mold and poor mold release, and mold failure is one of the main reasons. The causes and treatment methods are as follows:

 

1.The mold cavity rough surface, if the mold cavity and the flow path left with chipping, scoring, scars, pits and other surface defects, plastic parts will be very easy to adhere to the mold, resulting in demoulding difficulties. Therefore, should try to improve the mold cavity and runner surface finish, the best cavity surface chrome, polishing process, the direction of action of the polishing tool should be consistent with the melt filling direction.

 

2.Wear and tear mold or insert the gap at the block is too large. When the melt in the mold scratched parts or inserts within the flash gap, it will also cause demoulding difficulties. In this regard, should repair the damaged area and reduce the insert gap.

 

3. The lack of rigid mold. If the mold can not be opened at the beginning of injection, it indicates that the mold is deformed under the effect of injection pressure due to insufficient rigidity. If the deformation exceeds the elastic limit, the mold can not be restored to its original state, can not continue to use. Even if the deformation does not exceed the elastic limit of the mold, the melt cools and solidifies in the cavity under very high conditions to remove the injection pressure. After the mold is restored and deformed, the plastic part is clamped by the resilience and the mold still can not be opened.

 

Therefore, in the design of the mold, you must design enough rigidity and strength. Test mode, it is best to install the dial indicator on the mold, check the mold cavity and the mold in the mold filling process is not deformed, the initial injection when the test injection pressure should not be too high starting point, should be observed while the mold deformation , While slowly raising the injection pressure, the deformation control in a certain range.

 

When the rebound force is too large to cause clamping failure, only by increasing the mold opening force is not enough, the mold should be disassembled and decomposed, and plastic parts heated softened and removed. For the lack of rigidity of the mold, in the mold inlaid frame, improve rigidity.

 

4.Stripping off the slope or moving, set the parallelism between the poor. In the design and production of mold, should ensure adequate demoulding draft, or plastic mold is difficult demoulding, forced ejection, often resulting in plastic parts warp, the top of the site whitish or cracked. Mold movement, set the template to be relatively parallel, otherwise it will lead to the cavity offset, resulting in poor demolding.

 

5.Pouring system design is unreasonable. If the runner is too long, too small, the main runner and sub-runner part of the connection strength is not enough, the main runner without cold material hole, poor balance of the gate, the main runner diameter and nozzle hole diameter with improper or sprue sleeve and nozzle The spherical surface does not match, will lead to sticky mold and mold release bad. Therefore, the length of the runner should be shortened and its cross-sectional area should be appropriately increased to increase the strength of the connecting part between the main runner and the runner. Cold material holes should be arranged on the main runner.

 

Determine the gate position, you can increase the auxiliary gate and other methods to balance multi-cavity mold filling rate of each cavity and reduce the pressure within the cavity. Under normal circumstances, the mainstream end of the small diameter of the nozzle should be larger than the nozzle aperture 0.5 ~ 1mm, the radius of the concave circle of the sprue sleeve should be larger than the nozzle spherical radius of 1 ~ 2mm.

 

6. The top of the body design is not reasonable or improper operation. If the ejector is out of range, the ejector is out of balance or the top plate is not moving well, it will result in the mold being unable to release the mold.

 

In the circumstances permit, should try to increase the ejector effective ejecting area, to ensure adequate ejection stroke, plastic ejection speed should be controlled in the appropriate range, not too fast or too slow. The main reason for the poor action of the roof is due to the stickiness between the sliders.

 

For example, when the roof pushes the slide core to move, the temperature of the slide core is higher than that of other cores because of no cooling device at the slide core. During the continuous operation, the gap between the pillar body and the slide core is extremely small, Bad, another example, when the pin holes and the top of the guide pin parallel to the poor or top pin bending, the roof will be bad action.

 

If there is no pin in the pushing mechanism, when there is a foreign matter between the top plate and the mounting plate, the top plate is inclined, and then the top plate is not operated properly. In the large mold, if only a mandrel role, the roof can not be balanced thrust, will also have a poor action.

 

7.Poor mold exhaust or mold core without air inlet can also cause sticky mold and mold release bad. Should improve the mold exhaust conditions, mold core should be set into the air inlet.

 

8. Improper mold temperature control or cooling time is not appropriate. If the parting surface is difficult to mold release, the mold temperature can be increased and shorten the cooling time. If the cavity surface is difficult to mold release, may be appropriate to reduce the mold temperature or increase the cooling time. In addition, the fixed mold temperature is too high, can lead to poor demoulding. Mold cavity material is porous soft material will cause sticky mold. In this regard, should be replaced by hard steel or surface plating.

 

Poor runner out of the poor, no pull fishing gate institutions, the sub-surface below the concave cavity line more than mold lines and other mold defects will affect the degree of mold release. In this regard, should pay attention and be trimmed.

 

Improper control of process conditions

 

If the injection molding machine specifications larger, screw speed is too high, the injection pressure is too large, injection dwell time is too long, it will form an overfill, making the molding shrinkage than expected, demoulding this is difficult.

 

If the barrel and the melt temperature is too high, the injection pressure is too large, the hot melt easily into the gap between the mold inserts to produce flash, leading to poor demoulding.

 

In addition, the nozzle temperature is too low, the cooling time is too short and the injection cut off, will cause demoulding bad. Therefore, in the exclusion sticky mold and mold failure, should appropriately reduce the injection pressure, shorten the injection time, reduce the barrel and melt temperature, extend the cooling time, and to prevent the melt cut off.

 

Raw materials do not meet the requirements

 

Mixing of raw materials with impurities during packaging and shipping, or mixing of different grades of raw materials during pre-drying and preheating, as well as foreign matter in the barrel and hopper, can lead to mold sticking. In addition, the particle size of the raw material is too large or too sticky mold to a certain extent. Therefore, the molding material should be well cleaned and screened.

 

Improper use of mold release agent

 

The purpose of using the release agent is to reduce the adhesion between the surface of the plastic part and the surface of the mold cavity and prevent the two parts from sticking to each other in order to shorten the molding cycle and improve the surface quality of the plastic part.

 

However, since the mold release effect of the mold release agent is affected not only by the chemical reaction but also by the physical conditions, and the molding raw material and the processing conditions are different, the optimum type and amount of the selected mold release agent must be determined according to the specific situation to make sure. If used improperly, often can not produce a good mold release effect.

 

The molding temperature, the effective operating temperature of the oil-free mold release agent generally not more than 150 degrees, should not be used at high temperature molding; silicone oil and metal soap mold release agent operating temperature is generally 150 degrees to 250 degrees; poly four Fluoroethylene release agent working temperature can reach more than 260 degrees, is the best mold release agent under high temperature conditions.

 

In terms of raw materials, soft plastic parts are more difficult to demold than hard plastic parts. In terms of method of application, the pasty release agent is to be applied with a brush, and the sprayable release agent is sprayed using a spray device. Because the paste release agent in the brushing is difficult to form a regular uniform mold layer after mold release surface will have a wave marks or stripes, it should be possible to use a sprayable mold release agent.

Previous:Chinaplas 2018
Blog
Top
Product Catalog
Products