Views:6 Author:Site Editor Publish Time: 2019-04-20 Origin:Site
When the krah pipes are produced, we find that not all of them are perfect. Some of them will have different levels of defects. It’s no doubt that the manufactured krah pipes will be checked and the unqualified krah pipes will be eliminated at last, but do you know what factors cause their defects. This passage introduces four factors will cause the defective, if you are interested in this, please read this.
To ensure continuous production, a traction device must be installed. The Krah tube stretches under traction. The higher the degree of stretching, the greater the tensile strength and the longer the shrinkage after cooling. The traction speed should generally be greater than the extrusion speed.
The extrusion speed is the mass or length of the plastic extruded from the extruder die per unit time. The faster the extrusion speed, the higher the production capacity, and the more krah tubes are produced.
The extrusion speed also fluctuates during the production process, which affects the geometry and dimensional accuracy of the krah tube. Therefore, the screw speed and extrusion temperature should be strictly controlled to prevent fluctuations in the extrusion speed due to changes in temperature and pressure.
Although it has been proved that the extrusion speed is related to the screw diameter, the depth of the spiral groove, the length of the homogenization section, and the screw rotation speed. However, in the case of the structure of the extrusion machine, the type of plastic and the type of plastic part have been determined, the extrusion rate is only related to the screw speed. Therefore, adjusting the screw speed is the main measure to control the extrusion rate.
Temperature is one of the important conditions for the krah tube to be extruded. In the krah tube processing, a complex temperature change process is required. The change process starts from a powdery or granular solid material, and after heating, the high temperature product is extruded from the handpiece. The temperature of the extruded pipe, ie the temperature of the plastic melt, depends to a large extent on the temperature of the barrel and the screw. But in addition to this, a small part of the temperature comes from the frictional heat generated during the mixing process.
The temperature of the barrel and the plastic are different in each section of the screw, and the temperature of each section of the barrel must be controlled in order to smoothly carry out the production process of the krah tube and efficiently produce high-quality parts. The adjustment of the barrel temperature is achieved by the extruder's heating and cooling system and temperature control system.
The thermal decomposition temperature of the plastic should be higher than the temperature of the head, and the temperature at the die can be slightly lower than the temperature of the head. However, this temperature difference should not affect the fluidity of the plastic melt. Once a temperature-related problem occurs during the krah tube forming process, it will cause a series of defects such as uneven strength and dull surface. There are many factors that cause this problem, such as spiral design, heating, unstable cooling system, and changes in screw speed.
During the extrusion of the krah tube, the resistance of the material, the change in the depth of the screw groove, and the obstruction of the filter screen, filter plate and die will create a certain pressure inside the plastic. This pressure is one of the important conditions for a plastic to become a homogeneous melt. Increasing the head pressure can increase the mixing uniformity and stability of the extruded melt, but excessive head pressure will affect the yield of the krah tube.
As with temperature, changes in pressure over time can also cause periodic fluctuations. Changes in screw speed, instability in heating and cooling systems are the causes of pressure fluctuations. In order to ensure the quality of the krah tube, the screw speed should be reasonably controlled to ensure the stability of the pressure as much as possible.
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