Technical data

Electrofusion Fitting Cooling
One of the most misunderstood and often ignored components of the entire electrofusion
process is the cooling phase. It is often assumed that if the fitting is cool enough to
touch it must be cool enough to remove the restraint device or even pressure test the
connections. The cooling phase is critical to the success of the electrofusion pro-
cess and careful attention should be given to insure that the stated cooling times are
properly adhered to.
The importance of the cooling phase can be illustrated in the actions of the melt pool.
Using the following Figure we will look closer at the melt pool stages created during
the electrofusion process.
Electrofusion Fitting Fusion Cycle
Interface Temperature vs Time Curve
Time [s]
Temperature [C]
Polymer Solidifies
Polymer Melts
1
2
3
A)
B)
C)
D)
End of Specified Fusion
Time or end of heat cycle
Acceptable Temperature/Time to remove
restraint devices
Acceptable Temperature/Time to perform
pressure testing
Point of Current Termination & Optimum
Bonding Temperature
The complete
FUSION CYCLE
consists of:
A) The Melt Generation Phase
B) The Melt Containment Phase
C) The Melt Co-Crystallization Phase
D) The Melt Cooling Phase
(see Concept of Electrofusion Theory statement for more details)
Beginning of Fusion
Cycle
&
1
3
2
MELT POOL STAGES
UnFused Joint Liquefied Melt Pool Solidified Melt Pool
When current is applied to the fitting, the plastic in the fitting and on the pipe surface
begins to melt and form a melt pool (A & B). With continued application of current, the
melt pool deepens at the pipe and fitting interface which in turn forces internal pres-
sures to build up. This process is known as co-crystallization between the melted
pipe and fitting material (C). The cooling phase (D) (combined with the design of the
fitting) provides a controlled environment between the pipe and the fitting where re-
solidification can effectively take place. This cooling phase begins immediately fol-
lowing the termination of current being supplied to the fitting and continues for a
period of time beyond the point where the PE polymer resolidifies (also known as
clamping time). This allows ample time for the fusion area to regain the strength and
flexibility it exhibited prior to fusion. Any movement or external stresses (binding,
pulling, etc.) applied to the fused area during this cooling phase may result in a com-
promised fusion joint.
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