Type Of Cooling In Plastic Extrusion
There are two main purposes for polishing precision stamping dies. One is to increase the brightness and precision of precision molds. The second is to make the mold easy to demould.
In the polishing process, the coarse oil stone is generally used first, and the surface of the machined mold cavity is roughly polished, and the tool marks of the machine and the tool are polished. Then use a fine oil stone to polish the polishing marks of the rough stone. Then use a fine sandpaper to polish the polished surface of the fine stone. Finally, using a polishing paste or a polishing paste, the final surface of the cavity of the mold is polished and polished to achieve a bright, mirror-like effect.
Precision stamping die mechanical polishing is a polishing method that removes the polished convex portion and obtains a smooth surface by cutting, plastic deformation of the material surface, and the like. Generally, oil stone strips, wool wheels, sandpaper, etc. are used, which are mainly operated by hand. For special parts such as the surface of the rotary body, auxiliary tools such as a turntable can be used, and the method of super-fine polishing can be used for high surface quality requirements.
Ultra-fine grinding and polishing is a special-purpose grinding tool. In the polishing liquid containing abrasive, it is pressed against the machined surface to perform high-speed rotary motion. With this technology, the surface roughness of Ra0.008μm can be achieved, which is the most efficient among various polishing methods. This method is often used in optical lens molds.
3. Cooling of the product
Product cooling is an important measure to ensure the geometry and internal structure of the product. After the plastic extrusion coating leaves the machine head, it should be cooled immediately, otherwise it will be deformed under the action of gravity.
The problem of crystallization can be ignored for amorphous materials such as polyvinyl chloride. The plastic product can be quenched by direct cooling with water, so that it is cold-permeable in the cooling water tank and no longer deformed. For the cooling of crystalline polymers such as polyethylene and polypropylene, the problem of crystallization should be considered. If the quenching method is adopted, it will adversely affect the structure of the plastic product and generate internal stress. This is one of the reasons for the cracking of the product in the future, and it must be taken seriously in the extrusion process.
The extrusion layer of a crystalline plastic such as polyethylene or polypropylene is preferably carried out by a stepwise cooling method using a warm water cooling method. Generally, depending on the auxiliary equipment of the equipment, the cooling water tank should be segmented and divided. The water temperature can be started from the plastic extrusion layer into the first stage of the water tank at a temperature of 75 ° C ~ 85 ° C, the water temperature is reduced step by step, until the room temperature, the smaller the temperature difference of each section of water temperature is more reasonable.