17
4.8.3.
Flame and heating
4.9
LOKRING® connections
(VULKAN Lokring
Rohrverbindungen GmbH
& Co. KG)
Flame
• The neutral flame should be used for copper-copper and copper – steel tubes.
When the oxygen addition reaches the ratio for the fuel gas to be completely combust, the feather that ex
-
tended out from the bright inner cone disappears. This flame is used when the arc access of carbon in the
reducing flame is detrimental to the base metals or when maximum flame temperature is required.
Heating:
When brazing tubes type joints follow these steps for best results.
• First, heat the inside tube. Copper is a very excellent heat conductor and will draw the heat down inside
the joint.
• Then bring the torch to the fitting. Move the torch between the tube and fitting to ensure even heat, and
apply the filler metal. The phosphorus – copper brazing material will flow toward the heat into capillary
for a sound joint. Filler metal through the length of the capillary is desired.
• When copper is heated to the brazing temperature, surface oxides will flake off as the part cools. This
flaking can be detrimental inside the tube. In this application an inert gas such as nitrogen is bled through
the tube during and after brazing.
Systems containing the flammable refrigerants R600a or R290 must not be brazed. In such cases, a
LOKRING® connection as shown can be used.
Newly made systems can be brazed as usual, as long as they have not been charged with a flammable
refrigerant. Charged systems are never to be opened by using a flame. Compressors from systems with a
flammable refrigerant must be evacuated to remove the refrigerant residues from the oil.
Furthermore, those refrigeration systems must be opened with a pipe cutter. The brazing on HC-cooling
circuits is only allowed if the existing refrigerant has been disposed according to regulations and if the high
and low-pressure circuits are subsequently flushed separately with nitrogen. Even if the compressor is not
to be replaced, the brazing is only allowed under flowing nitrogen as a protective gas. On all other occasions,
the brazing close to flammable refrigerants is strictly forbidden.
When working on a system, the connections have to be established with pressure fitted connections. With
a solderless connection, this can be established for aluminum, copper, or steel pipes. The connection con-
sists of two rings and a connection piece to receive the two pipes, which is to be connected. Because of the
conical internal contour of the rings and the special external contour of the connection piece, the radius
of the connection piece will be reduced to the diameter of the pipes to generate a hermetic metal to metal
compound.
Torch
Inner cone
bluish white
Bluish
Bluish to orange
Neutral flame - No acetylene feather
Illustrations by kind permission of
VULKAN Lokring Rohrverbindungen GmbH & Co. KG
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