1. What are the main performance requirements of plastic molds?
The main functional requirements of plastic molds In plastic molding processing, the quality of the molds has an obvious role in ensuring product quality. Different types of plastic products and different product molding processes have different requirements for the material, function, and shape of the mold. Heat-resistant performance With the emergence of high-speed molding machinery, the production speed of plastic products has accelerated. Since the molding temperature is generally between 160 and 350°C, some have poor fluidity and fast molding speed, which will cause the mold surface temperature to exceed 400°C in a very short time. When the working temperature of the mold is high, the hardness and strength of the mold will decrease, leading to early wear or plastic deformation of the mold and failure. In order to ensure the accuracy and minimal deformation of the mold during use, the mold steel should have high heat resistance. In order to reduce temperature rise, mold steel should have good thermal conductivity and low thermal expansion coefficient.
Most of the working conditions of molds with sufficient temperature at the working temperature are very harsh, and some often bear large loads, which then lead to brittle fracture. The extrusion molding pressure is relatively high, generally 10~35MPa. Therefore, in order to avoid sudden brittle fracture of mold parts during operation, the mold must have high strength and toughness. Wear resistance With the expansion of the use of plastic products, it is often necessary to add inorganic materials such as glass fiber to enhance plasticity. Due to the addition of additives, the fluidity of the plastic is greatly reduced, resulting in wear of the mold, so the mold is required Has outstanding wear resistance. Corrosion resistance: Adding flame retardants and polyvinyl chloride to ABS resin may release corrosive gases during the molding process. Sometimes the mold will be corroded and damaged at the air runner opening, so the mold steel is required to have excellent corrosion resistance.
Excellent cutting performance As plastic products become larger, more complex and precise in shape, mold steel is required to have excellent cutting performance and less work hardening during the cutting process. In order to avoid mold deformation and affect accuracy, it is hoped that the residual stress during processing can be controlled to a minimum. Mirror polishing processability: The inner and outer surfaces of the mold cavity are smooth, and the molding surface is required to be polished to a mirror surface with a surface roughness lower than Ra0.4μm to ensure the appearance of the plastic pressed parts and facilitate demolding. Dimensional precision mold inserts have high machining accuracy and high matching accuracy. The cavity dimensional accuracy is generally level 3~5. The joint surfaces of the splicing cavity must be tightly sealed to prevent molten material from entering the gap and causing material leakage. Pattern pattern photoetchability properties: Many plastic products have pattern patterns added to their surfaces in order to beautify them. In the leather industry, large leather pattern embossed plates are used, which requires mold steel to have good pattern photoetchability.
The injection molding machine of the injection molding process needs to work quickly in a strong, high-speed, high-temperature, and high-pressure environment. Its injection mechanism is a high-pressure, high-speed, and local high-temperature machine.
The main danger areas of injection molding machines are as follows:
(1) Feeding area: Due to the rotation of the screw in this area, do not place iron rods or other foreign objects;
(2) Material pipe protection zone: This area is the raw material heating area, the temperature is extremely high, and there is a risk of electric shock;
(3) Nozzle area: This area is where high-pressure raw materials are sprayed, and there is a risk of splashing;
(4) Mold area: This area is the high-speed and high-voltage switch action area of the mold, which is very dangerous. In addition, raw materials may also be discharged from the closed surface of the mold, so special attention is required;
(5) Pallet area: The mechanical effect is strong and requires special attention;
(6) Clamping mechanism: high speed and strong mechanical effect, requiring special attention.
1. Use more pure resin in the injection molding process
In the injection molding process of many plastics, especially those such as polyvinyl chloride, styrene, polyethyl acetate, and acrylics, trace amounts of residual monomers can produce unpleasant odors. It is enough to use resins with very difficult monomer residues to eliminate these odors. If you use an inherently odorless resin, the results will be poor.
2. Change additives in injection molding processing
The tertiary amine catalysts used in the production of polyurethane foam often produce a very weak odor and, in addition, can form fog on the interior windows of cars. One way to solve this problem is to find alternatives to these amines. One measure is to use polyols. The remaining hydroxyl compounds are not only part of the polyurethane molecular chain, so they are also catalytically active. Some polyols can also replace half of the tertiary amine catalyst, so the resulting product emits less odor than that.
Phenol stabilizers used in PVC extrusion or calendering are often replaced by high-odor zinc stabilizers. The heat stabilizer tin octoate is also common in automotive PVC due to its high odor and low fogging properties. In products, plant-derived oils (such as erucic acid and oleic acid) have a much higher odor than amine lubricants (used in polyolefin and styrene food packaging materials) made from animal-derived oils.
3. Injection molding processing adsorbent
If the polymer is filled with a small amount of zeolite (an aluminosilicate adsorbent), it will act to eliminate the odor of the material. Zeolite has a large number of discs that can capture small gas molecules that carry odor. This molecular adsorbent has been successfully used in polyolefin extruded tubing, injection molding processing and extrusion blow molded containers, isolation packaging materials, extruded packaging materials and seals. Molecular adsorption powder can also be added to plastics as a hygroscopic agent. In addition to removing water vapor, this water vapor will also contribute to the odor of plastic products.