Why is there uneven discharge of die head during extrusion?

The main reasons for the uneven discharge of die head are: 

(1) Unreasonable design of die head flow channel, including insufficient local feed, the length design of the die head straight section or the compression ratio design mismatch and many other factors; 

(2) The die gap is not uniform, and the flow channel system of the profile extrusion die is complex, and a significant feature of it is that there are many slits and grooves. Because the formation of the slit involves many parts, such as core, core support plate, shape plate, etc., the machining accuracy and matching accuracy of the above parts have a significant influence on the uniformity of the slit. In addition, the die often needs to be disassembled in the process of debugging or maintenance, and after repeated disassembly, the positioning accuracy of the die positioning element may be reduced due to wear, which leads to the change of the die clearance; 

(3) The surface of the die head is not evenly heated, and the uneven heating of the surface of the die head often causes uneven discharge of the die head. The main reasons for this phenomenon are as follows: first, the heating plate deformation or the surface of the die head is uneven, resulting in bad contact between the heating plate and the die head; Second, the thermoelectric coupling does not achieve good contact with the die head; Third, the heating power of the heating plate is not uniform. For the currently widely used cast aluminum heating plate or multi-layer stainless steel heating plate, if the power of each piece of a set of heating plates is different or the power distribution on the same piece is not uniform, it will cause heating differences during use; Fourth, if a heater is burned out or the heating power line is burned off, the heating unevenness will be further aggravated, and the unheated side of the material will be slow, dull and even burned; 

(4) Fluctuation or uneven discharge of extruder will also cause uneven discharge of die head. The fluctuation or uneven discharge of extruder is mainly due to uneven clearance between screw and barrel, and excessive extrusion back pressure or extruder heating unequal cause.