First of all, mechanical seals are used to cool the polymer to a semi-molten state through the non-contact surface of the shaft and then form self-sealing. In fact, this sealing method is relatively simple, but it will be affected by the melt temperature, easily lead to spring and wedge ring deformation, as well as impurities in the easy to appear, affecting the service life of the melt pump. Secondly, packing seal, this method wears very fast, because often need to compact packing, replacement is more frequent, which will bring a certain amount of maintenance workload to enterprises, but also increase the cost of maintenance, if maintenance is not in place, it will affect the normal use of later, even leakage phenomenon, so this kind of sealing method is generally used in small. Among the laboratory devices of Type I. Finally, the spiral seal, which is based on the two previous sealing methods, has been improved and optimized. Nowadays, most of the melt pumps adopt spiral seal. The reverse spiral groove is machined on the inner surface of the shaft seal, which can make the polymer back pressed to the inlet, and the effect is obvious.