Mold Crack - Causes and Measures
Molded plastic parts are produced in a wide range of products for a variety of applications, and cracking is one of the common issues that occur during production. Mold cracking can cause a range of problems, such as reject parts, undesired surface textures, and cosmetic defects. The severity of the cracks and the amount of material affected by them will vary depending on the molding process and material used. This article provides an overview of some of the common causes of mold cracking and measures that can be taken to reduce the occurrences of cracks.
1.Temperature Imbalance
A temperature imbalance in the mold is one of the most common causes of mold cracking. If the temperature of the mold is too cool, the plastic material shrinks faster than it should, causing the plastic part to distort and the mold to crack. If the temperature of the mold is too hot, the plastic material can expand and then contract back too quickly, again causing the plastic part to distort and the mold to crack. To reduce the chances of a temperature imbalance, it is important that the mold is regularly maintained and that the temperature of the material and the mold are monitored continually.
2. Contamination
Contamination of the mold or material can also lead to mold cracking. Foreign material introduced into the mold can result in temperature imbalance, inadequate fill, and inaccurate shrinkage of the plastic parts. It is important to ensure the mold and material are cleaned regularly and that any potential sources of contamination are minimized.
3. Pressure Imbalance
A pressure imbalance in the mold is another potential cause of mold cracking. If the pressure of the plastic material is too high, the mold can be overfilled and cause the plastic material to distort and the mold to crack. Conversely, if the pressure of the plastic material is too low, the plastic material can shrink and the mold can crack. To reduce the chances of a pressure imbalance, it is important that the pressure of the plastic material and the mold are monitored continually.
4. Insufficient Mold Design
If the design of the mold is insufficient, the plastic parts can distort, leading to cracking of the mold. Common design inadequacies include insufficient venting to relieve pressure buildup, inadequate releasing of the plastic material, and lack of proper cooling channels. It is important to ensure that mold design is done properly to reduce the chances of mold cracking.
5. Improper Mold Clearance
Improper mold clearance can also lead to cracking of the mold. If the clearance between the two halves of the mold is too small, the plastic material may not have enough room to flow and fill the mold, leading to cracking. Conversely, if the clearance between two halves of the mold is too large, the plastic material may expand and contract too quickly, leading to cracking. It is important to ensure that the mold has the correct clearance for the plastic material being used.
6. Improper Venting
Venting is a key factor in the prevention of mold cracking. If there is inadequate venting, the pressure within the mold can build up and cause the plastic parts to distort, leading to cracking. It is important to ensure that the mold is properly vented and that the vent size is appropriate for the plastic material being used.
7. Material Selection
The material being used can also have an impact on the likelihood of mold cracking. If the material used is too hard or too brittle, it can be more likely to crack than a softer, more flexible material. It is important to select the proper material for the application to reduce the chances of mold cracking.
In conclusion, mold cracking is a common issue that can occur during production of molded plastic parts. The causes of mold cracking are varied and can include temperature imbalance, contamination, pressure imbalance, insufficient mold design, improper mold clearance, improper venting, and material selection. To reduce the occurrence of cracking, it is important to ensure that the mold is regularly maintained and monitored, that any potential sources of contamination are minimized, and that proper design, clearance, venting, and material selection are followed.
