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.