Mold failure
There are many reasons for sticky mold and poor mold release, mold failure is one of the main reasons for its production and processing methods are as follows:
one, Mold cavity surface roughness, if the mold cavity and the flow path left with chisel, nicks, scars, pits and other surface defects, plastic parts will be very easy to adhere to the mold, resulting in demoulding difficulties.Therefore, we should try to improve Mold cavity and runner surface finish, the inner surface of the cavity is best chrome plating, polishing process, the direction of action of the polishing tool should be consistent with the melt filling direction.
two, Die wear or tear at the insert or the gap at the insert is too large.When the melt in the mold scratched parts or insert the gap within the flash when it will cause demoulding difficulties.To this, should repair the lesion and reduce the insert Slot.
three, If the mold is not open at the beginning of the injection, it indicates that the mold is deformed under the injection pressure due to insufficient rigidity, and if the deformation exceeds the elastic limit, the mold can not be restored to the original shape and can not be used any more. Not exceed the elastic limit of the mold, the melt in the mold cavity under high cooling and solidification to remove the injection pressure, the mold recovery after deformation, the role of plastic parts by the resilience is caught, the mold still can not open.
Therefore, the design of the mold, we must design sufficient rigidity and strength test mode, it is best to install a dial indicator on the mold to check the cavity and the mold in the mold filling process is not deformed during the initial test injection Initial injection pressure should not be too high, should be observed while the mold deformation, while slowly raising the injection pressure, the deformation control in a certain range.
When there is too much rebound caused clamping failure, only by increasing the mold opening force is not enough, should immediately remove the mold to disassemble, and plastic parts heated softened and removed for lack of rigidity of the mold, mold outside Inlaid frame, improve rigidity.
four, Mold release gradient is insufficient or moving, set the parallelism between the poor template.In the design and production of mold, should ensure adequate stripping slope, or plastic mold is difficult demoulding, forced ejection, often resulting in plastic parts warp , The top of the site whitish or cracked etc. Mold movement, set the template to be relatively parallel, otherwise it will lead to the cavity offset, resulting in poor demolding.
Fives, Gating system design 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 cold material hole, poor balance of the gate, the main runner diameter and nozzle hole diameter with improper Or the sprue sleeve does not match the spherical surface of the nozzle, will lead to poor adhesion and demoulding.Therefore, should shorten the runner length and increase its cross-sectional area, improve the main runner and shunt connection parts of the intensity, should be set in the mainstream Cold material hole.
When determining the position of the gate, the filling rate of each cavity in the multi-cavity mold can be balanced and the pressure in the cavity can be reduced by adding auxiliary gates etc. In general, the diameter of the small end of the main channel should be larger than the nozzle aperture by 0.5 ~ 1mm, the radius of the concave circle of the sprue sleeve should be 1 ~ 2mm larger than the spherical radius of the nozzle.
six, Improper design of the ejector mechanism or improper operation can result in the mold being unable to release if the ejector is out of range, unbalanced or unbalanced.
In the circumstances permit, should try to increase the ejector effective ejecting area, to ensure a sufficient ejection stroke, plastic ejection speed should be controlled in the appropriate range, not too fast or too slow. The reason is due to the slider between the sticky.
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, and the top plate can not be balanced in a large mold if only one ejector rod is used Thrust, will also have a bad action.
Seven, Poor mold exhaust or mold core without air inlet will also lead to sticky mold and mold release bad.It should improve the mold exhaust conditions, mold core should be set at the inlet.
Eight, Improper mold temperature control or the length of cooling time is not appropriate.If hard to mold release at the parting surface, may be appropriate to increase the mold temperature and shorten the cooling time.If the cavity surface difficult to mold release, the mold may be appropriate to reduce the temperature or increase Cooling time.In addition, the fixed mold temperature is too high, can lead to poor demoulding.When the mold cavity material is porous and soft material will cause sticky mold.For this, should be replaced by hard steel or surface plating.
Runner pull out poor, no pull fishing gate mechanism, sub-surface below the concave, the cavity line beyond the mold line and other mold defects will affect the degree of mold release. In this regard, attention should be given and to 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 poor demoulding.Therefore, in the exclusion sticky mold and mold failure, should reduce the injection pressure, shorten the injection time and reduce the barrel and Melt temperature, extended cooling time, and to prevent the melt off flow.
Raw materials do not meet the requirements
If the raw materials are mixed in the packaging and transportation impurities, or pre-drying and preheating process mixed with different grades of raw materials, as well as the barrel and hopper mixed with foreign matter, will lead to plastic parts sticking mold.In addition, the raw material of the particle size unevenness or Too large adhesive mold also have a certain degree of impact.Therefore, the molding material should be good purification screening.
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 determine if not used properly, 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 the case of raw materials, the soft polymer part is more difficult to demold than the rigid polymer part, and in terms of the method of application, the pasty release agent is applied with a brush and the sprayable release agent is applied using a spraying device Spraying.As the paste release agent in the brushing is difficult to form a regular and uniform mold layer after mold release plastic parts will have a wave mark or stripes, so it should be possible to use a sprayable mold release agent.