Reason Analysis of Medical Mold Shrinkage Depression

During the injection molding process, product shrinkage and depression are relatively common phenomena. The main reasons for this are:

1. Machine aspect

(1) The nozzle hole is too large to cause the molten material to flow back and shrink, and if it is too small, the resistance is large and the amount of material is insufficient to shrink.

(2) Flash will also shrink due to insufficient clamping force. Check whether there is any problem with the clamping system.

(3) If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be selected to check whether the screw and barrel are worn.

2. Mold

(1) The part design should make the wall thickness uniform and ensure consistent shrinkage.

(2) The cooling and heating system of the mold should ensure that the temperature of each part is consistent.

(3) The gating system must be smooth and the resistance should not be too large. For example, the size of the main channel, runner, and gate must be appropriate, the finish must be sufficient, and the transition area must have a circular arc transition.

(4) For thin parts, the temperature should be increased to ensure smooth material flow, and for thick-walled parts, the mold temperature should be lowered.

(5) The gate should be opened symmetrically, and it should be opened in the thick-walled part of the part as far as possible, and the volume of the cold slug well should be increased.

3. Plastic

The shrinkage of crystalline plastics is worse than that of non-crystalline plastics. During processing, the amount of material should be increased appropriately, or an agent should be added to the plastics to speed up crystallization and reduce shrinkage depressions.

4. Processing

(1) The temperature of the barrel is too high and the volume changes greatly, especially the temperature of the forehearth. For plastics with poor fluidity, the temperature should be raised appropriately to ensure smoothness.

(2) The injection pressure, speed, and back pressure are too low, and the injection time is too short, so that the material volume or density is insufficient and the shrinkage pressure, speed, and back pressure are too large, and the time is too long, resulting in flash and shrinkage.

(3) The feeding amount means that when the cushion pad is too large, the injection pressure is consumed, and if it is too small, the feeding amount is insufficient.

(4) For parts that do not require precision, after the injection and pressure holding are completed, the outer layer is basically condensed and hardened, and the sandwich part is still soft and can be ejected. Release the mold early and let it cool slowly in air or hot water , can make the shrinkage sag gentle and not so conspicuous without affecting the use.

Cause Analysis of Medical Mold Shockmarks

Rigid plastic parts such as PS form dense corrugations on the surface near the gate with the gate as the center, sometimes called vibration lines. The reason is that when the viscosity of the melt is too high and the mold is filled in stagnation, the material at the front end will condense and shrink as soon as it touches the surface of the cavity, and the later melt will expand and the cold material that has shrunk will continue to advance. The continuous alternation makes the material flow form the surface vibration pattern in the progress.

Solution

(1) Increase the barrel temperature, especially the nozzle temperature, and the mold temperature should also be increased.

(2) Increase the injection pressure and speed to quickly fill the mold cavity.

(3) Improve the size of runners and gates to prevent excessive resistance.

(4) The exhaust of the mold should be good, and a sufficiently large cold slug well should be set.

(5) The parts should not be designed too thin.

Cause analysis of medical mold swelling and bubbling

Some plastic parts swell or bubble quickly on the back of the metal insert or in particularly thick areas after molding and demolding. This is because the plastic that has not completely cooled and hardened releases gas and expands under the action of internal pressure penalties.

Solution:

1. Effective cooling. Reduce the mold temperature, prolong the mold opening time, and reduce the drying and processing temperature of the material.

2. Reduce the mold filling speed, reduce the forming cycle, and reduce the flow resistance.

3. Increase the holding pressure and time.

4. Improve the situation that the wall surface of the workpiece is too thick or the thickness changes greatly.

Medical mold Manufacturer

Looking for plastic injection mold suppliers, Dragon Mold will be your good choice, we are a leading manufacturer of high quality cavity preforming molds. With rich experience, we have provided molds to customers in various industries, including food and beverage, cosmetics, pharmaceuticals, etc.

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