Can molding machines for PVC be used for CPVC molding?

The molding processes for CPVC and PVC are very similar.

CPVC molding processes such as extrusion and injection molding can generally use equipment and tools for PVC molding. However, appropriate temperature settings, screws and other molding machine settings are required.

What Is the Main Difference Between CPVC and PVC Processing?

The main differences between PVC and CPVC are thermal stability and viscosity.

CPVC will not melt without the application of moderate heat and will not exhibit excellent physical properties. On the other hand, it will decompose if exposed to excessively high temperatures. Below is a reference document illustrating the crystalline melting points of PVC and CPVC.

Can molding machines for PVC be used for CPVC molding?

Key Points

PVC and CPVC materials have different thermal stabilities:

• The residence time of CPVC in the molding machine must be as short as possible.
• Temperature setting is important to ensure melting and gelling of the material.

Viscosity (Fluidity)）

In general, the viscosity of CPVC is higher than that of PVC. In the case of PVC, the viscosity (=K-value) is set simply by the degree of polymerisation. In the case of CPVC, on the other hand, the viscosity (=K-value) is set by a combination of degree of polymerisation and chlorination.

Key Points

• Loads on motors, back pressure.

PVC and CPVC materials have different thermal stabilities:

• Screw / Mold shape

The structure of the screw and mould tools is an important factor. Molding equipment must be suitable for CPVC molding.

• Attention to shear heating

The screw undergoes shear heating. Temperature control is therefore required to keep the material at the correct temperature.

Differences in molding processes (CPVC vs. PVC)

Extrusion molding

	PVC	CPVC
Twin-screw extruder	Screw motor：High torque Screw：Parallel　φ60-170 　　　 Conical　φ50-85	Screw mortar：High torque Screw：Parallel　φ60-135 　　　 Conical　φ50-70
Screw rotation	ー	Lower than PVC
Condition (Barrel Temp.)	300 – 340℉	340 – 410℉
Mold type	Stainless steel	Stainless steel Small quantity (flow channel section) Mold angle: acute angle

Injection molding

	PVC	CPVC
Injection machine	Screw mortar: High torque Barrel cooling: Blower	Screw mortar: High torque Barrel cooling: Blower Barrel zone: 4-5 zone Nozzle: Short nozzle、φ：Larger than PVC
Screw rotation	9-14 m/sec	8-13 m/sec (lower than PVC)
Condition (Barrel Temp.)	320 – 365℉	320 – 392℉
Condition (holding pressure)	100 – 170 MPa	100 – 170 MPa
Mold type	Stainless steel Gate: Direct gate	Stainless steel Gate: Direct gate

Deformed extrusion molding

	PVC	CPVC
Single screw extruder	Single screw machine Screw: Dulmage, Fullfight	Single screw machine Screw: Fullfight recommended (Dulmage) L/D = 22 – 25 Compression ratio: 2.5 – 3.2
Screw rotation	15~ rpm (65 mm single)	15–25 rpm (65 mm single)
Condition (Barrel Temp.)	284 – 338℉	300 – 370℉
Mold type	Stainless steel	Stainless steel