Does the Clearance between the Screw and Barrel Affect the Performance?

The radial expansion of the extruder screw barrel caused by the pressure load, and the occurrence of the gap change is quite small, which can be ignored. On the contrary, the temperature difference of the extruder screw barrel in the feeding section of the extruder needs special attention.


Ⅰ. The influence of the temperature difference between the extruder screw and barrel on the gap


The extruder barrel in the feeding section is generally cooled by water, but the extruder screw has a higher temperature due to the high heat conduction in other areas. Therefore, there is a temperature difference between the extruder screw and the barrel. This temperature difference causes the expansion of the two to be different, which in turn changes the gap between the two.


If the gap is too small to exceed the original assembly gap, the extruder screw will lock up. In order to avoid the occurrence of the extruder screw lock, when designing the extruder, the gap of the extruder screw barrel in the feeding section is increased, that is, the diameter of the extruder screw in the feeding section is reduced to at least 0.002 mm per millimeter.


In this way, after increasing the gap between the screw and barrel of the extruder in the feeding section, the working performance of the extruder will not be basically affected, and the possibility of the screw of the extruder will be greatly reduced.


Ⅱ. The influence of the gap between the screw and barrel of the extruder on the performance


Since the gap between the screw and the barrel is related to the output of the extruder and the processing and assembly accuracy, when designing the extruder, it is necessary to consider the gap between the screw and the barrel from various factors. If the gap is too small, the extrusion output will increase the output, but the wear of the screw and barrel will increase. If the gap is too large, on the one hand, the leakage flow will increase and the output will decrease; on the other hand, it will cause the melt film to thicken, which is not conducive to heat conduction and reduces the shear rate, which is not conducive to the melting of the material.


In addition, in the design of the extruder, different gap values must be selected according to the nature of the processed material. For example, for temperature-sensitive materials, the gap value can be larger to reduce thermal decomposition due to shear. For low-viscosity non-thermal-sensitive materials, such as high-density polyethylene, the gap can be smaller to increase its shear.


With the development of the plastic industry and the continuous expansion of extruder applications, the requirements for screw elements and kneading blocks are no longer limited to traditional styles. With our rich experience in the field of screw element manufacturing, we intend to base on the characteristics of our customers' own products, such as nitrided steel, chrome vanadium steel, stainless steel and SKD11, K110, 1.2379, W6Mo5Cr4V2, SuS18, HS35, HS45, HS10V wear-resistant powder metallurgy. In fact, suitable accessories can effectively extend the uptime of the basic machine and reduce production costs for customers.


Regarding production specifications, in addition to providing standard twin-screw extruder accessories produced by general domestic manufacturers, we can also design and manufacture special-purpose parts according to your requirements. At the same time, we also provide surveying and mapping business and parts processing business of major foreign extruder companies. If you have any needs, please feel free to consult us.

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