Brief introduction of PVC-DWV foam core pipes-4

3.2 Reference formula based on Ca Zn stabilizer:

‌A. Inner/outer layer formula (SG-5 resin)

 - PVC resin: 100PHR

 - Ca zn stabilizer: 6.5PHR

 - Stearic acid: 1.2PHR

 - Paraffin: 0.6PHR

 - CPE: 7PHR

 - heavy calcium 180PHR

‌B. Foam core layer formula (SG-7 resin)‌

 - PVC resin: 100PHR

 - Ca zn stabilizer: 5.5PHR

 - Stearic acid: 1.5PHR

 - Paraffin: 1.0

 - CPE: 5PHR

 - Heavy calcium: 120PHR 

 - Light calcium: 30PHR

 - AC foaming agent/blowing agent: 0.8PHR

4.Formula optimization direction

‌-Filler adjustment‌: Light calcium and heavy calcium can be mixed (such as 50PHR of light calcium + 100 parts of heavy calcium in the core layer ) to reduce density while maintaining strength

-‌Lubrication balance‌: If melt fracture occurs during processing, PE wax (0.2-0.5PHR) can be added to improve melt fluidity

‌-Cost reduction strategy‌: Under the premise of meeting performance requirements, the dodage of heavy calcium in core layer can be increased to 200PHR, but the amount of lubricant needs to be increased simultaneously.

5.Equipment selection

The extrusion of PVC core foam pipes can be done with a single screw extruder or a twin screw extruder.

During production, two extruders can be used to feed the material, or three extruders can be used to feed the material. Generally, two extruders are used to extrude and supply more molding materials. 

The center lines of the two extruders are arranged at a 45° angle at the molding die. One extruder extrude the material for the inner and outer skin molding of the core foam pipes, and the other extruder extrude the material for the foam core layer molding. 

Since the material used for the foam core layer molding is greater than the material used for the inner and outer skin layers, the two extruders selected have different specifications. For example, if the extruder for the foam core layer is Ф65mm, the extruder for the inner and outer skin layers should be Ф45mm.

The composite molding mold structure of the PVC core foam pipes is relatively complex, and it is a mold structure for producing the core foam pipes with two extruders.

The extruder is the inlet for the inner and outer skin layers of the extrusion pipe; the inlet "Ⅱ" is the inlet for the foam core layer of the extrusion tube. 

The melt streams extruded by the two extruders enter from two feed ports respectively, and the inner and outer skin layers and the core layer are formed in the mold respectively, and then merged and compounded into a core layer foam pipe. While running forward, the raw materials in the core layer foam under the most suitable temperature conditions between the die and the sizing sleeve to form a PVC core layer foam pipe.

To be continued...