Silane cross-linked polyethylene pipe INTERSOL ... - Watts Industries

SILANE CROSS-LINKED POLYETHYLENE PIPE
3 - MANUFACTURING PROCESSES INVOLVING SILANE CROSS-LINKING
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The use of silanes as cross-linking agents is based mainly on two industrial methods:
1) A TWO-STEP PROCESS (SIOPLAS)
2) A ONE-STEP PROCESS (MONOSIL)
3.1 - Two-step Sioplas method
The Sioplas method was developed in 1968 and consists of two steps (see figure 2):
-) step 1
Polyethylene, silane and a small quantity of peroxide plus further additives (anti-oxidants) are processed in a
single or twin-screw extruder. They are blended at temperatures such as to “graft” the polyethylene with the
silane. Such cross-linkable product is granulated and stored in air-tight containers.
-) step 2
The cross-linkable polyethylene with the addition of a catalyst masterbatch is melted and reblended in a second
extruder, then converted into the final product (pipe).
These two steps are followed by cross-linking in hot water (normally 80 to 85°C) for a time depending on the pipe
wall thickness.
Diagram of the two-step Sioplas method
Grafting step
Polyethylene+
pellets
Silane+
peroxide
Liquid of
the pump
Step 1
Grafting extrusion
(typically L/D=25)
Pelletizing unit
Shaping step
Ppackaging and
storage in dry
conditions of the
grafted polymer
Grafted pellets
Additives
Anti-oxidant +
Catalyst
Step 2
Shaping
extrusion
Finished product
Cross-linking in water
Fig.2