Preparation before injection molding in Wuhan Handern
DATE：2020/12/23 8:44:43 / READ： / SOURCE：This station
Preparation before injection molding
The injection molding process includes three stages: preparation before molding, injection molding process and modification and post-treatment after molding. Hollow plate equipment www.handern.com
In the preparation process before molding, due to the different forms and properties of plastic supply, the structure and use requirements of products, the preparation work before molding of various products is also different. The general preparatory work includes:
(1) In general, the particle resin has a certain water absorption (see table 11-4). When the amount of permanent absorption is higher than the allowable value of forming process, drying treatment must be carried out before molding. The existence of moisture is one of the reasons for the crosslinking reaction and degradation of plastics at high temperature, which often results in the degradation of product performance and appearance quality. Such as PA, PSU, PC and other hygroscopic materials are very sensitive to moisture at the molding temperature. A small amount of moisture will cause product defects (silver, streaks, bubbles, etc.) and even performance degradation. The AB5. PMA cellulose plastics should also be dried. But for PE, PP, POM and other plastics storage is better, generally can not need to dry.
There are many drying methods, such as hot air circulation drying, infrared drying, vacuum drying and new negative pressure boiling drying. The first two equipments are simple and suitable for small batch production. Vacuum drying is most suitable for drying niyou plastics which are easy to be oxidized and discolored at high temperature. However, the negative pressure boiling drying method is most suitable for the rapid drying of large quantities of plastics due to its boiling state, large heating area and short drying time.
(2) Due to the requirements of assembly and strength, it is often necessary to make metal parts in the products when the inserts are preheated. The joint must be preheated before being put into the mold, especially for the larger waiting parts. In order to reduce the difference of cooling shrinkage between metal and plastic, and reduce the shrinkage stress around 64 pieces due to the difference of thermal expansion coefficient between them.
The selection of meteoric heat temperature should not damage the surface of metal insert, such as plating front and antirust layer. Generally, the preheating temperature is 100 ~ 130c, and the copper insert made of aluminum can be preheated to 150C.
(3) In the process of injection molding, when changing the product, changing the raw materials and colors, we can clean the material sheet. In order to save time and raw materials, pay attention to the following when cleaning the barrel:
① If the residual plastic in the material sheet has good thermal stability, new material can be directly added to replace the residual material in the material sheet. Hollow plate equipment www.handern.com
② If there are heat sensitive plastics (such as PVC, POM, PCTFE) in the material sheet, in order to prevent overheating and decomposition, plastics with good thermal stability (such as PE and PS) can be used for transitional refueling. First, heat sensitive plastics are replaced by new materials to replace PE and PS materials.
③ If the molding temperature of the new material is higher than the residual plastic in the material sheet, the temperature of the material sheet and nozzle should be raised to the minimum molding temperature of the new material, and then the feed back of the new material should be added, and the new material should be added until the injection melt is completely recycled.
④ If the new material is low in dry material and plastic remains, cut off the heating, add the return material of new material while cooling down, and carry out "air injection", and add new material when the injection material is completely returned.
The injection molding process includes three stages: preparation before molding, injection molding process and modification and post-treatment after molding. Hollow plate equipment www.handern.com
In the preparation process before molding, due to the different forms and properties of plastic supply, the structure and use requirements of products, the preparation work before molding of various products is also different. The general preparatory work includes:
(1) In general, the particle resin has a certain water absorption (see table 11-4). When the amount of permanent absorption is higher than the allowable value of forming process, drying treatment must be carried out before molding. The existence of moisture is one of the reasons for the crosslinking reaction and degradation of plastics at high temperature, which often results in the degradation of product performance and appearance quality. Such as PA, PSU, PC and other hygroscopic materials are very sensitive to moisture at the molding temperature. A small amount of moisture will cause product defects (silver, streaks, bubbles, etc.) and even performance degradation. The AB5. PMA cellulose plastics should also be dried. But for PE, PP, POM and other plastics storage is better, generally can not need to dry.
There are many drying methods, such as hot air circulation drying, infrared drying, vacuum drying and new negative pressure boiling drying. The first two equipments are simple and suitable for small batch production. Vacuum drying is most suitable for drying niyou plastics which are easy to be oxidized and discolored at high temperature. However, the negative pressure boiling drying method is most suitable for the rapid drying of large quantities of plastics due to its boiling state, large heating area and short drying time.
(2) Due to the requirements of assembly and strength, it is often necessary to make metal parts in the products when the inserts are preheated. The joint must be preheated before being put into the mold, especially for the larger waiting parts. In order to reduce the difference of cooling shrinkage between metal and plastic, and reduce the shrinkage stress around 64 pieces due to the difference of thermal expansion coefficient between them.
The selection of meteoric heat temperature should not damage the surface of metal insert, such as plating front and antirust layer. Generally, the preheating temperature is 100 ~ 130c, and the copper insert made of aluminum can be preheated to 150C.
(3) In the process of injection molding, when changing the product, changing the raw materials and colors, we can clean the material sheet. In order to save time and raw materials, pay attention to the following when cleaning the barrel:
① If the residual plastic in the material sheet has good thermal stability, new material can be directly added to replace the residual material in the material sheet. Hollow plate equipment www.handern.com
② If there are heat sensitive plastics (such as PVC, POM, PCTFE) in the material sheet, in order to prevent overheating and decomposition, plastics with good thermal stability (such as PE and PS) can be used for transitional refueling. First, heat sensitive plastics are replaced by new materials to replace PE and PS materials.
③ If the molding temperature of the new material is higher than the residual plastic in the material sheet, the temperature of the material sheet and nozzle should be raised to the minimum molding temperature of the new material, and then the feed back of the new material should be added, and the new material should be added until the injection melt is completely recycled.
④ If the new material is low in dry material and plastic remains, cut off the heating, add the return material of new material while cooling down, and carry out "air injection", and add new material when the injection material is completely returned.
Author：admin