【材料热加工】电渣焊

The consumable guide variant of the process uses a much simpler set-up and equipment arrangement
which does not require the wire feed mechanism to climb. In this case, the wire is delivered
to the weld pool down a consumable, thick-walled tube which extends from the top of the joint
to the weldpool. Support for the molten bath is provided by two pairs of copper shoes which
are moved upwards, leapfrogging each other as welding progresses. The tubular guides can be
further supplemented by additional consumable plates attached to the tube. Generally, as the
thickness of plate increases, the number of wires/guides increases, approximately in the ratio
of one wire per 50mm of thickness, see figure 2.

Fig.2. Consumable guide welding


Current status
---------------
In the fabrication industry, the process continues to be used for thick walled pressure vessels
which are post-weld normalised and for structures such as blast furnace shells and steel ladles
which are used at above ambient temperatures. The process is also extensively used for the welding
of railway points.
Important current issues
------------------------
Considerable interest was shown in electro slag welding during the 1970s when ideas for increasing
welding speed were investigated. This was seen as an important parameter for increasing productivity
and as a way of reducing heat input to improve HAZ and weld metal impact properties.
However, since that time little has been done by way of development. Those developments that have
taken place have been limited to the tuning of parameters and tailoring techniques for specific applications.
Benefits
--------
The principal benefits of the process are:
speed of joint completion; typically 1 hour per metre of seam, irrespective of thickness
lack of angular distortion
lateral angular distortion limited to 3mm per metre of weld
high quality welds produced
simple joint preparation, i.e. flame-cut square edge
major repairs can be made simply by cutting out total weld and re-welding
Risks
-----
Electro slag welding is not one of the major welding processes because the high heat input generates large,
coarse grained weld metal and HAZs which lead to poor fracture toughness properties in these areas.
Toughness improvements can only be achieved by post-weld normalising treatment. Additionally,
the near parallel-sided geometry of the weld, combined with the coarse grains, can make it difficult
to identify defects at the fusion boundary by standard ultrasonic NDT techniques.
The process has considerable potential for increasing productivity. However, its use has been limited
because of relatively poor understanding of the process and, for specific applications, the significance
of the fracture toughness values. As a result, use of the process has been restricted to a few niche applications.


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