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H Ü R N E R S c h w e i s s t e c h n i k G m b H
Nieder-Ohmener Str. 26
35325 Mücke, Germany
ing them repeatedly or by holding them down. The settable
temperatures range from 190°C through 250°C. When this
setting was changed, the screen starts flashing again, until
the heating element has reached the new nominal temper-
ature. The new value is saved to memory, for use after the
machine is switched off and on again. To see the current ac-
tual temperature of the heating element, hold down both
temperature keys. A dot in the lower right-hand corner of
the screen indicates that the actual temperature is showing.
4.2
Understanding the Stages of the Welding Process
The welding process proper, after pipe butt facing and pipe
alignment check, has the following four stages, or phases,
also illustrated by the time-and-pressure diagram below.
• Bead Build-up Stage – In this stage, t
the pipes are pressed against the heating element and
heated to the temperature of it; to ensure consistent
bead formation, do this at drag pressure (P
given in the welding value tables in the Appendix.
• Heating Stage – In this stage, t
pipes remain in contact with the heating element, soak-
ing heat from it; the pressure is reduced to drag pres-
sure (P
) plus P
t
2
the Appendix.
• Change-over Stage – In this stage, t
pressure is shut off from the pipes, the carriage is moved
apart to the far end to allow taking the heating ele-
ment out from in-between the pipes.
• Joining and Cooling Stage – This stage is character-
ized by a succession of events. First, after change-over,
the pipe butts are put together and pressure increases
as a linear ramp to drag pressure (P
the welding value tablss in the Appendix (t
gram). Then, the joint cools down at P
pressure is completely removed from the the pipes (t
the diagram) or until pressure is reduced to one-third
of P
(10 seconds into t
5
case, cooling is completed at the reduced pressure.
Pipe and fitting manufacturers may include data on
how long the new joint should not be exposed to ex-
P
P
+ P
+ P
P
P
1
1
t
t
t
t
1
1
Version October 2021
2
as given in the welding value tables in
in the diagram); in the second
5
P
P
5
5
P
P
+ P
+ P
2
2
t
t
t
t
t
t
t
t
2
2
3
3
4
4
HÜRNER Manual Hydr. 355 2.0 User's Manual
in the diagram,
1
) plus P
as
t
1
in the diagram, the
in the diagram,
3
) plus P
as given in
t
5
in the dia-
4
+ P
, either until
t
5
in
5
+ P
+ P
t
t
t
t
t
t
5
5
6
6
t
t
13
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