Hard tube should be chosen in the production of resin with low polymerization degree of SG - 5 resin, the higher the degree of polymerization, the better the physical mechanical properties and heat resistance, but resin illiquid, bring certain difficulty to processing, so generally selected viscosity is (1.7 ~ 1.8) x 10-3 pa • s SG - 5 resin is advisable.
The hard tube generally adopts lead stabilizer, its thermal stability is good, commonly used tribasic lead, but its own lubrication is poor, usually and lubricity good lead, barium soap class.
Hard tube processing, selection and use of lubricant is very important, should not only consider the lubrication lower molecular inter-atomic forces, make the melt viscosity drops favorable forming, and will consider the lubrication, prevent melt with hot metal adhesion, make the products surface brightness.
Inner lubrication is generally used in metal soap, with external lubrication with low melting wax
Mainly use calcium carbonate filler and barium (barite powder), calcium carbonate surface of tube performance is good, but the dosage too much will affect tube performance, pressure pipe and the corrosion resistance is best without or with less filling agent.
RPVC pipe molding with SG - 5 type of PVC resin, and adding stabilizer, lubricant, filler, pigment, etc., these materials after appropriate treatment according to the formula of kneading, if squeeze tube adopts single screw extruder, also should cause grain powder, after kneading extrusion molding again;If double screw extruder can be used directly in powder forming.
C. Process conditions and control
In the process of production, due to the PVC is heat-sensitive material, even adding heat stabilizer can only is to improve the decomposition temperature and prolonged stability and decomposition of impossible not to appear, which requires the PVC processing temperature should be strictly controlled.In particular, RPVC, because its processing temperature and decomposition temperature are very close, often because of temperature control improper decomposition phenomenon.