McElroy A714201, Operator'S Manual

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Overview
2 - 1
Theory of Heat Fusion
The principle of heat fusion is to heat two pipe surfaces to
a designated temperature, and then fuse them together by
application of force. This develops pressure which causes flow of
the melted materials, which causes mixing and thus fusion. When
the thermoplastic material is heated, the molecular structure is
transformed into an amorphous condition. When fusion pressure
is applied, the molecules from each thermoplastic part mix. As
the joint cools, the molecules return to their form, the original
interfaces are gone, and the fitting and pipe have become one
monolithic unit. A strong, fully leak tight connection is the result.
The principal operations include:
Clamping The pipe pieces are held axially and radially to allow
all subsequent operations to take place.
Facing The pipe ends are faced to establish clean, parallel
mating surfaces perpendicular to the centerline of the
pipes.
Aligning The pipe ends are aligned with each other to
minimize mismatch of the pipe walls.
Heating
A melt pattern that penetrates into the pipe is formed
around both pipe ends.
Fusing The melt patterns are joined with a specified force,
which is constant around the pipe interfacial area.
Cooling The fusion joint is held immobile with a specified force
until adequately cooled.
Inspecting Visually examine the entire circumference of the joint
for compliance with the standard or fusion procedure
used.
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