The key technique of using plunger method to extrude PE-XE pipes is converting into plunger intermittence about reciprocal motion from crank continual rotary motion by crank-link mechanism. The plunger punched raw material intermittently into the runner, and the optimal structure runner will turn the solid state raw material which entered intermittently into continuously extrusion viscoelastic state PE-XE tubing parison. This process is quite different from the operating principle of screw extruder.

Firstly, the screw in the screw extruder makes the continual rotary motion, while, the plunger in the plunger-type extrusion makes the reciprocal motion. The continuous rotation can work smoothly with high speed. However, the higher speed of reciprocal motion moves, the bigger vibration of it turns

Secondly, the PE-XE melt viscosity is very high, this is the reason of must use the reciprocal motion extrusion, so the flowing speed will be limited for this high viscosity melt. .

Thirdly, the PE-XE melt must stay enough time in die to endure the oxygen decomposition and complete the cross-linkage reaction with PE.

An Analyst of Conditions Affecting Production Rate

The first item among above three requires optimization design to the RAM main engine to achieve the best working condition. The speed of plunger pushes the material is proportional to the plunger activity frequency and the distance. General speaking, the higher of frequency, the longer of distance, and bigger amount of pushing materials will be. These two enhancements will also cause equipment's vibration to increase. Its optimized value after the optimization design and the test of production practice turns to be frequency 4-8 /s, distance 30-40 millimeters. The PE-XE melt viscosity only could offer few parameters for change, may make certain improvement through adjustment of raw material formula. Well, it can increase the production rate by improve friction between melt and mold surface.

The third item is the most valuable subject for study. The above two items can’t raise the production rate efficiency unless the third item has been solved. There are three requirements need to be satisfied if you want the PE-XE pipe leaving the die after finished the cross-linkage reaction completely. First, need to stay enough time in the die. Second, must have enough temperature level. Third, number of cross linking machine needs to be appropriate. The mold temperature has the limit, is impossible to rise to decomposes the above temperature.