The production process of soft PVC plastic pipe is divided into four parts: raw material pretreatment, kneading, granulation and extrusion.
1. The PVC resin, plasticizer, stabilizer, lubricant, filler and pigments used in raw material pretreatment are screened and ground.
2. Kneading will use inefficient kneading machine to knead the treated raw materials for a long time, so that all kinds of ingredients are evenly dispersed and the effect of swelling absorption is good.
3. Extrusion or calendering mixing can be used to granulate kneading materials.
4. Extruders for extruding pipes can be divided into flat extrusion and vertical drawing [see figure (a)] and flat extrusion and horizontal drawing [see figure (b)] according to their way of discharging.
The abnormal phenomena in the forming process of soft PVC plastic pipes, their causes and solutions:
First, the surface is not lustrous: causes: poor plasticization, too low temperature of the nose; solutions: increase the temperature of the fuselage, increase the temperature of the nose
2. There are particles on the surface of the hose: the causes are improper resin screening or fish eye of the resin itself; the solutions are to screen the resin more carefully or replace the resin.
3. Non-circular pipe wall: causes: high extrusion temperature, inappropriate cooling conditions; solutions: reducing processing temperature, adjusting water volume and cooling tank length
4. Clouds, patches and rough surfaces on the surface
Reasons: too high temperature of machine head, decomposition of die adhesive, too high temperature at start-up to solve; Measures: reduce the temperature of machine head, clean die, adjust start-up temperature, first coat the machine head with lubricant before start-up
5. Bubbling of surface pipes: Causes: Host temperature is too high and semi-finished products contain moisture; Solutions: Reducing temperature and drying semi-finished products
6. Material marks on the pipe wall: Causes: impurities in the die, scratches at the outlet of the die and the core die; Solutions: cleaning the die, polishing the die and the core die
7. Welding marks
Reasons: unreasonable structure of mandrel shunt channel, too low temperature of die, too small compression ratio of die, too short setting length and too high temperature; solving measures: improving shunt channel structure, increasing temperature of die and improving design parameters of die
8. Excessive soft discharging and pipe sagging: Causes: too high temperature control; Solutions: lowering temperature
9. Non-uniform Thickness of Pipes
Causes: large gap between barrel and screw, extrusion pulse, too small head compression ratio, uneven feeding, abnormal traction speed
Solutions: Mainframe should be repaired, head design improved, feeding system repaired, traction speed corrected and traction roller adjusted.
10. Coke grains or decomposed yellow lines appear on the wall of the pipe
Reasons: die angle, material partial decomposition, internal material partial decomposition, high temperature of main engine or machine head, poor material stability
Solutions: Mould removal, cleaning or improvement of machine head design, cleaning main engine, adjusting temperature, checking heating ring, improving formula design, improving material stability
11. There are pits or impurities on the surface of the pipe:
Causes: There is decomposition stock in the die; Solutions: Increase the speed, use the material to bring out impurities or decomposition materials, if ineffective, clean the die.
12. Inconsistent Diameter Size and Specification
Causes: large diameter: die temperature is too low, drawing ratio is small, pipe diameter is small: die temperature is too high, drawing ratio is large
Solutions: adjusting die temperature, adjusting drawing ratio, adjusting die temperature, adjusting drawing ratio