How to extend the service life of preform molds
一. Correct use of molds
1. Reasonable injection molding process parameter settings
2. Correct mold opening and closing operation
3. Avoid overload operation
二．Daily maintenance of the mold
1. Cleaning work
2. Lubrication and maintenance
3. Inspection and tightening work
三. Regular maintenance of the mold
1. Appearance inspection and repair
2. Dimensional accuracy detection and adjustment
3. Inspection and replacement of internal parts
四．Storage management of molds
1. Dry storage environment
2. Reasonable placement method
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一. Correct use of molds
1. Reasonable injection molding process parameter settings
Injection pressure and speed: During the preform injection molding process, the appropriate injection pressure and speed should be set according to the characteristics of the plastic raw materials and the structure of the preform. Excessive injection pressure will cause excessive impact on the mold cavity and core, resulting in increased wear. For example, for PET preforms, it is generally more appropriate to control the injection pressure at 80-150MPa. The injection speed should not be too fast, especially when filling thin-walled parts. Too fast injection speed may cause melt fracture, scour the mold surface, and affect the mold life.
Holding pressure and time: Holding pressure is to compensate for the shrinkage of plastic during cooling. Reasonable holding pressure and time can ensure the dimensional accuracy of the preform while reducing the internal stress of the mold. If the holding pressure is too high or the time is too long, the mold cavity will be under greater pressure, which is easy to cause mold deformation. Generally speaking, the holding pressure is determined according to the plastic material and the wall thickness of the preform, and the holding time usually accounts for 10-30% of the entire molding cycle.
Cooling time: Adequate and reasonable cooling time is one of the key factors to extend the life of the mold. If the cooling time is too short, the preform is easy to deform after demolding, and the mold temperature will be too high, reducing the mechanical properties of the mold. For preform molds, the cooling time usually accounts for 40-60% of the molding cycle. The cooling time should be determined according to factors such as the thickness of the preform and the thermal properties of the plastic to ensure that the preform can be fully cooled and the mold is prevented from being in a high temperature state for a long time.
2. Correct mold opening and closing operation
The mold opening and closing speed of the injection molding machine should be adjusted appropriately. Too fast mold opening speed may generate a large impact force, resulting in damage to the guide mechanism, demolding mechanism and other components of the mold. Generally speaking, the initial speed of mold opening can be set slightly slower, then gradually speed up, and then slow down when approaching the maximum mold opening stroke. The same is true when closing the mold to avoid damage between mold parts due to collision.
Open and close the mold strictly in accordance with the design requirements of the mold. For example, some complex preform molds may have special clamping and demolding sequences, which must be carried out in accordance with the prescribed operating procedures to prevent mold damage. At the same time, ensure that the clamping force of the injection molding machine is within the allowable range of the mold design to avoid damage to the mold due to excessive clamping force.
3. Avoid overload operation
Do not produce beyond the design capacity of the mold. For example, if the maximum number of injections designed for the mold is 30 times per minute, do not try to exceed this capacity by increasing the injection molding machine's shooting rate. Because excessively frequent injection molding will cause excessive pressure and friction on the various parts of the mold, accelerating the wear of the mold.
Note that the injection volume of the injection molding machine cannot exceed the maximum capacity of the mold. If the injection volume is too large, the cavity may swell due to overfilling, causing damage to the clamping mechanism and cavity wall of the mold.
二．Daily maintenance of the mold
1. Cleaning work
After each use, clean up plastic residues, oil stains and other impurities on the mold surface in time. If these impurities accumulate on the mold surface, they will affect the heat dissipation performance of the mold, and may also enter the preform during the next injection molding, affecting the quality of the preform. You can use a special mold cleaning agent and a soft brush for cleaning. For some difficult-to-clean parts, such as near the gate, you can use a small tool to clean them.
Clean the cooling system of the mold regularly. If scale or impurities are blocked in the cooling channel, it will affect the cooling efficiency and cause uneven cooling of the preform. You can use a descaling agent and a high-pressure water gun to clean the cooling channel. It is generally recommended to clean it every 3-6 months. The specific frequency depends on the water quality and production environment.
2. Lubrication and maintenance
Regularly lubricate the moving parts of the mold, such as guide columns, push rods, sliders, etc. It is very important to choose a suitable lubricant. Generally, a high-temperature and wear-resistant lubricant such as molybdenum disulfide grease is used. The frequency of lubrication depends on the production situation, and lubrication operations are usually performed once a week or every two weeks.
During the lubrication process, ensure that the lubricant is evenly applied to the surface of the moving parts to avoid too much or too little lubricant. Too much lubricant may contaminate the plastic raw materials and affect the quality of the preform; too little lubricant cannot achieve a good lubrication effect, resulting in increased wear of the parts.
3. Inspection and tightening work
Regularly check whether the various parts of the mold are loose or damaged. Focus on checking the fixing screws of the mold, the connection between the core and the cavity, the demolding mechanism, etc. If the screws are found to be loose, tighten them in time to prevent the mold from having problems such as part displacement during the injection molding process.
Check whether the seals of the mold are intact. For example, if the sealing gasket of the cooling system is damaged, it will cause water leakage and affect the normal use of the mold. The damaged seals should be replaced in time to ensure that the mold is well sealed.
三. Regular maintenance of the mold
1. Appearance inspection and repair
Periodically (usually every 3-6 months) conduct a comprehensive inspection of the appearance of the mold. Check whether there are cracks, wear, corrosion, etc. on the surface of the mold. For slight wear on the surface, polishing and other methods can be used to repair it to restore the smoothness of the mold surface. If cracks are found, analyze the cause, such as whether it is caused by fatigue, stress concentration, etc., and take corresponding repair measures, such as welding repair or replacement of damaged parts.
Check the wear of the gate and runner. The gate part is prone to wear and deformation due to the frequent flushing of the plastic melt. If the gate size changes, it will affect the molding quality of the bottle embryo, and the gate parts need to be repaired or replaced in time. The wear of the runner will also affect the flow of the plastic melt. For severely worn runners, it can be repaired by replacing inserts or reprocessing.
2. Dimensional accuracy detection and adjustment
Use measuring tools (such as calipers, micrometers, three-coordinate measuring instruments, etc.) to regularly detect the key dimensions of the mold (such as cavity size, core size, positioning size, etc.). If it is found that the dimensional deviation exceeds the allowable range, the cause should be analyzed. It may be caused by wear, deformation, etc. Depending on the specific situation, the dimensional accuracy can be restored by adjusting the compensation device of the mold (if any) or reprocessing the mold parts.
For multi-cavity molds, the dimensional consistency between each cavity should also be checked. If the size difference between the cavities is too large, the quality of the bottle embryo will be inconsistent. The mold needs to be adjusted, such as adjusting the flow channel balance, correcting the cavity size, etc., to ensure that the quality of the bottle embryo produced by each cavity is the same.
3. Inspection and replacement of internal parts
Check whether the internal parts of the mold, such as springs and ejectors, are fatigued, deformed or damaged. If the spring loses its elasticity, it will affect the normal operation of the demolding mechanism; wear or bending of the ejector will make it difficult to demold the preform. For damaged internal parts, they should be replaced in time, and when replacing, ensure that the specifications and quality of the new parts meet the requirements.
Perform a comprehensive inspection of the cooling system of the mold, including cooling pipes, joints, valves, etc. Check whether the cooling pipes have leaks, blockages, etc., whether the joints are loose, and whether the valves can work properly. For problematic parts, repair or replace them in time to ensure that the performance of the cooling system is good.
四．Storage management of molds
1. Dry storage environment
When the mold is not in use temporarily, store it in a dry and well-ventilated environment. A humid environment can cause the mold to rust, especially for mold parts containing steel materials. Desiccant, such as silica gel desiccant, can be placed in the mold storage area to absorb moisture in the air and keep the environment dry.
Avoid storing molds in an environment with corrosive gases. For example, do not place the mold near a chemical raw material warehouse to prevent the mold from being corroded. If the mold surface has been treated with anti-rust treatment, make sure that the storage environment will not damage the anti-rust coating.
2. Reasonable placement method
The mold should be placed in the correct way during storage to avoid deformation of the mold due to its own weight or external factors. For large preform molds, special mold racks can be used for storage, and the molds can be placed horizontally on the racks, and all parts of the molds must be well supported.
For mold parts that cooperate with each other, such as cores and cavities, some soft materials (such as foam plastics) can be placed between them to prevent collision and wear between parts. At the same time, the mold should be marked, indicating the model, specifications, usage and other information of the mold to facilitate next use and management.
Foshan Heyan Precision Mold Technology Co., Ltd.'s main business is preform molds, blow molds, bottle cap molds and other products. It has a strong engineering, R&D, technology, and sales team, advanced processing equipment and rich project experience. If you want to know more or have special needs, please call 13318345050, WeChat at the same number.pet bottle mold
