Today, the application field of PA pipes is further expanded. At present, the proportion of applications in drinking water transformation, municipal sewage, solar water pipelines, ground source heat pump pipelines, communications, medical, power, heating, gas medical and other industries has increased significantly. As a professional PA hose manufacturer, let us understand the basic principles of extrusion molding of PA pipe production line from these aspects.
(1) Pressure. During the extrusion process, due to the viscosity of the melt, the change in the depth of the screw groove, and the obstacles caused by the filter plate and the die, a certain pressure was established inside the melt along the axis of the barrel. The establishment of this pressure makes the material uniform and dense, which is one of the important conditions for obtaining qualified plastic parts. Unlike temperature, changes in pressure over time also produce periodic fluctuations. Such fluctuations also have an adverse effect on plastic parts, resulting in defects such as local looseness, uneven surfaces, and bending. The reasons for the pressure fluctuations are the unreasonable design of the screw and the barrel, the change in the speed of the screw, and the unstable heating and cooling system. In order to reduce pressure fluctuations, plastic machinery should reasonably control the screw speed to ensure high temperature accuracy during heating and cooling.
(2) Temperature, temperature is one of the important conditions to ensure the smooth progress of the extrusion process. The plastic needs to undergo a very complicated temperature change process from the feeding hopper to the final molding. Strictly speaking, the extrusion molding temperature should refer to the temperature of the plastic melt, but this temperature depends largely on the barrel and screw. temperature. This is because most of the heat of the plastic melt is provided by the heater outside the barrel except for a part of the frictional heat generated when mixing in the barrel. Therefore, in actual production, for convenience, the barrel temperature is often used to approximate the molding temperature.
(3) Traction speed. Extrusion molding mainly produces products of continuous length, so traction devices must be provided. The plastic products extruded from the die and die will be stretch oriented under the action of traction. The higher the degree of stretch orientation, the greater the tensile strength of the product in the orientation direction, but the greater the length shrinkage after cooling. Generally, the traction speed should match the extrusion speed. The ratio of traction speed to extrusion speed is called the traction ratio, and usually its value is greater than 1.
(4) Extrusion speed. Extrusion speed refers to the amount of plasticized material or length of plastic parts extruded from the extruder head and die in a unit time, and it represents the level of the extruder’s production capacity. There are many factors that affect the extrusion speed: such as the structure of the head, screw and barrel, the speed of the screw, the performance of the heating and cooling system and the plastic. When the structure of the extruder and the type of plastic and product type have been determined, the extrusion speed is only related to the screw speed. Therefore, adjusting the screw speed is the main measure to control the extrusion speed. The extrusion speed also fluctuates during the production process, which has a significant adverse effect on the shape and dimensional accuracy of the product. In order to ensure uniform extrusion speed, a screw that responds to the product should be selected, and the screw rotation speed and temperature should be strictly controlled to prevent changes in extrusion pressure and melt speed caused by temperature changes, resulting in changes in extrusion speed.