Injection Molding Disposable Aviation Cup PS Hard Transparent Plastic Cup Injection Molding Plastic Cup Mold
Injection mold failure
There are many reasons for mold sticking and poor demolding, and mold failure is one of the main reasons. The causes and treatment methods are as follows:
1. The surface of the injection mold cavity is rough. If there are surface defects such as gouges, nicks, scars, dents, etc. in the mold cavity and runner, the plastic parts will easily adhere to the mold, resulting in difficulty in demolding. Therefore, the surface finish of the mold cavity and runner should be improved as much as possible. The inner surface of the cavity should be well plated with chrome. When polishing, the movement direction of the polishing tool should be consistent with the filling direction of the melt.
2. The injection mold is worn and scratched or the gap at the insert is too large. When the molten material produces flash in the scratched part of the mold or in the gap of the insert, it will also cause difficulty in demolding. In this regard, the damaged part should be repaired and the gap between the inserts should be reduced.
3. Insufficient rigidity of the injection mold. If the mold cannot be opened at the beginning of the injection, it indicates that the mold is deformed under the action of the injection pressure due to insufficient rigidity. If the deformation exceeds the elastic limit, the mold cannot be restored to its original shape and cannot be used continuously. Even if the deformation does not exceed the elastic limit of the mold, the melt is cooled and solidified under high conditions in the mold cavity, and the injection pressure is removed. After the mold is deformed, the plastic part is clamped by the resilience force, and the mold still cannot be opened.
Therefore, when designing a mold, sufficient rigidity and strength must be designed. When trying out the mold, it is recommended to install a dial indicator on the mold to check whether the cavity and mold base are deformed during the filling process. The initial injection pressure during mold test should not be too high, and the deformation of the mold should be observed. , While slowly increasing the injection pressure, control the amount of deformation within a certain range.
When the clamping force is too large and the clamping mold fails, it is not enough to increase the mold opening force. The mold should be disassembled immediately, and the plastic part should be heated and softened before being taken out. For molds with insufficient rigidity, a frame can be inlaid on the outside of the mold to increase the rigidity.
4. Insufficient or dynamic demolding angle, poor parallelism between fixed templates. When designing and making the mold, ensure sufficient demolding angle, otherwise the plastic part will be difficult to demold. When the plastic part is forced out, it will often cause the plastic part to warp, and the ejected part becomes white or cracked. When the mold moves, the fixed template should be relatively parallel, otherwise it will cause the cavity to shift and cause poor demolding.
5. The design of the pouring system is unreasonable. If the runner is too long or too small, the strength of the connecting part between the main runner and the sub-runner is not enough, the main runner has no cold slug, the gate balance is poor, the diameter of the main runner and the nozzle hole are not properly matched, or the sprue sleeve and nozzle If the spherical surfaces of the spheres do not match, it will lead to poor mold sticking and demolding. Therefore, the length of the runner should be appropriately shortened and its cross-sectional area should be increased, and the strength of the connecting part of the main runner and the runner should be improved, and a cold slug hole should be set on the main runner.
When determining the gate position, you can balance the filling rate of each cavity in the multi-cavity mold and reduce the pressure in the cavity by adding auxiliary gates and other methods. In general, the diameter of the small end of the main runner should be 0.5~1mm larger than the nozzle aperture, and the radius of the concavity of the sprue sleeve should be 1~2mm larger than the spherical radius of the nozzle.
6. Unreasonable design or improper operation of ejector mechanism. If the ejection device stroke is insufficient, the ejection is uneven or the top plate does not move well, the plastic part cannot be demolded.
When conditions permit, the effective ejection area of the ejector rod should be increased as much as possible to ensure sufficient ejection stroke. The ejection speed of the plastic part should be controlled in an appropriate range, not too fast or too slow. The main cause of poor top plate movement is the sticking between the sliding parts.
For example, when the top plate pushes the sliding core, because there is no cooling device at the sliding core, its temperature is higher than other cores. During continuous operation, the gap between the column body and the sliding core is extremely small, which often produces stickiness and leads to the core pulling action. Poor, for example, when the ejector pin hole and the top plate guide pin are in poor parallelism or the ejector pin is bent, the top plate will malfunction.
If there is no stop pin in the jacking mechanism, if there is a foreign object between the top plate and the mounting plate, the top plate will tilt and the rear top plate will not operate properly. In medium and large molds, if there is only one ejector pin, the top plate cannot be pushed evenly, and malfunctions will also occur.
7. Poor mold exhaust or mold core without air inlet will also cause mold sticking and poor demolding. The exhaust conditions of the mold should be improved, and air inlets should be provided at the mold core.
8. Improper mold temperature control or inappropriate cooling time. If it is difficult to release the mold at the parting surface, the mold temperature can be appropriately increased and the cooling time can be shortened. If it is difficult to release the mold at the cavity surface, the mold temperature can be appropriately reduced or the cooling time can be increased. In addition, if the temperature of the fixed mold is too high, it will also lead to poor demolding. When the mold cavity is made of porous soft material, it will cause mold sticking. In this regard, it should be replaced with hard steel or surface electroplating treatment.
Mold defects such as poor sprue pullout, no pull-and-fishing mechanism for the gate, low depression below the parting surface, and mold defects such as the cavity edge line exceeding the parting line will affect the demolding of the plastic part to varying degrees. In this regard, attention should be paid and repaired.
Improper control of process conditions
If the size of the injection molding machine is large, the screw speed is too high, the injection pressure is too high, and the injection holding time is too long, overfilling will be formed, making the molding shrinkage rate smaller than expected, and demolding will be difficult.
If the temperature of the barrel and the melt is too high, the injection pressure is too high, the hot melt will easily enter the gap between the mold inserts to produce flash, resulting in poor demolding.
In addition, the nozzle temperature is too low, the cooling time is too short, and the injection is interrupted, which will cause poor demolding. Therefore, when troubleshooting the mold sticking and demolding failures, the injection pressure should be appropriately reduced, the injection time should be shortened, the barrel and the molten material temperature, the cooling time should be extended, and the molten material should be prevented from breaking.
Raw materials do not meet the requirements for use
If the raw materials are mixed with impurities during the packaging and transportation, or the raw materials of different grades are mixed during the pre-drying and pre-heating process, and foreign objects are mixed in the barrel and hopper, it will cause the plastic parts to stick to the mold. In addition, the uneven or too large particle size of the raw materials also has a certain degree of influence on the mold sticking. Therefore, the purification and screening work should be done for the molding raw materials.
Improper use of 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, prevent the two from sticking to each other, so as to shorten the molding cycle and improve the surface quality of the plastic part.
However, because the mold release effect of the mold release agent is affected by both chemical action and physical conditions, and the molding materials and processing conditions are different, the quality and dosage of the mold release agent must be selected according to the specific Circumstances to determine. If used improperly, it will often fail to produce a good demoulding effect.
As far as the molding temperature is concerned, the effective working temperature of fatty oil release agents should generally not exceed 150 degrees, and should not be used during high-temperature molding; the working temperature of silicone oil and metal soap release agents is generally 150 degrees ~ 250 degrees; poly four The working temperature of vinyl fluoride mold release agent can reach above 260 degrees, which is a good mold release agent under high temperature conditions.
In terms of raw material varieties, soft polymer plastic parts are more difficult to demold than hard polymer plastic parts. As far as the method of use is concerned, the paste release agent should be applied with a brush, and the sprayable release agent should be sprayed with a spraying device. Since it is difficult to form a regular and uniform mold layer when the paste-like mold release agent is applied, there will be wavy marks or stripes on the surface of the plastic part after mold release, so it should be possible to use a sprayable mold release agent.