Welders
Chamber welding method vs. butt welding with automatic deburring - Strecker's study
Joining the ends of strands and stranded conductors in front of the extruder is an important issue in cable production. Which is the best method to ensure continuous production?
Basically, there are two different ways. These are the chamber welding method and the dual upset butt welding process with automatic deburring.
Chamber Welding Method
With the chamber welding method, the joint is produced by resistance pressure welding in a tube (chamber), which is
made of glass, ceramic or graphite. The choice of tube material is made depending on the strand or stranded conductor cross-section as well as the welder’s capacity, respectively.
For welding the two stranded conductor ends, i.e., the end of the already running cable drum and the beginning of the new drum, the two stranded conductors are inserted into the tube (see Figure 1) in such a way that the point of
contact is in the middle. This assembly is then inserted into the formed grooves inside the welder’s clamping jaws and
firmly clamped.
In the image, a ceramic tube (right) and a stranded aluminum conductor within a ceramic tube (left).
The point of contact of the two stranded conductor ends is brought to melting temperature via ohmic resistance when
switching in welding current, then the ends are pushed together and welded in the tube by the prevailing upset pressure.
The material having become liquid is diffused evenly between the single wires forming the stranded conductor.
After completion of the welding process, the welded strand is unclamped and the tube is smashed.
On butt welding machines designed for smaller strand sizes, the material is upset via spring pressure as a rule, with
the clamping devices opened or closed via pedal for ease of operation—so the operator has both hands free to handle the strand ends as well as the tube (see the Type SE 1 butt welder below). For bigger stranded conductors, clamping as well as upsetting is done pneumatically (see the Type SE 130 buttwelder below).
Once the welding process is completed, the surface of the welded joint is free of any burrs, clean, smooth and hardly
bigger in cross-section than the original material (see below).
In the image above, a copper stranded conductor of 1200 mm² welded with ceramic tubes.
Generally, welds made by tubes require a little refinishing (i.e., by filing), because of the slightly increased cross-section that result from the process itself. This facilitates their passing through the in-let die of the extruder without problems.
The chamber welding method is suitable for regular strand constructions as well as for fine-stranded, flexible stranded
conductors.
Dual Upset Butt welding Process with Automatic Deburring
This welding method has been applied most successfully for decades to butt weld solid wires as well as for joining stranded conductors without any tubes. It is a proven and welltried process, even preferred by quite a number of reputable cable manufacturers.
Contemporary extruders (XLPE) are fitted with inlet dies, which allow no significant tolerances in outer diameter of the stranded conductor. At the same time, these lines work with short processing time. As a result, there is the necessity to produce within the shortest delay possible welded joints of identical outer diameter compared to the original stranded conductor. Furthermore, the welds must be safe and reliable, i.e., the first weld must already succeed optimally so the extruder’s storage won’t run empty.
These requirements can be conditionally fulfilled by butt welding machines working according to the chamber welding method only. And all the more as the individual operator’s correct handling of the complete process has an important impact on the success of the weld.
When releasing a dual upset butt welding process with automatic deburring, first the point of contact of the stranded conductor ends is brought to the required welding temperature with low pressure (welding pressure) only. Once the material has become liquid, high pressure (upset pressure) is switched in and presses out of the welding zone all heat-influenced material, leaving just very few tenths of a millimeter in the welded joint. The stranded conductor’s flexibility is influenced negatively in this rather short area only. Welding electrodes are fitted with knife-shaped inserts that immediately after the process shear off the welding burr produced during the process. The still-closed burr ring is torn apart when opening the clamping device and falls off. All motions, e.g., clamping as well as upsetting and deburring are fully hydraulically activated.
The weld is identical in diameter when compared to the unwelded original material (see figure below), with a welding zone that is much shorter than on welds made according to the chamber welding method.
In the figure, a stranded aluminum conductor welded on a dual upset butt welder with automatic deburring (without tubes).
The welding time is also very short. A weld on stranded copper conductors 1200 mm² will only take up to maximum of 30 seconds when using a dual upset butt welding machine with automatic deburring type MK 300 (see figure below).
Another, positive side effect on dual upset butt welding machines with automatic deburring is no running costs for purchasing tubes as so-called consumable items, and no need to keep them in storage.
Dual upset butt welding machines with automatic deburring are the optimum solution for joining regular stranded conductors. However, they cannot be used for fine-stranded flexible conductors.
Lately, both welding methods as mentioned before can also be used for welding different kinds of stranded conductors to ensure continuous production also when changing the crosssection or material. This is necessary for extruders designed for medium-frequency cables, which allow a type change without stopping the line. This means that stranded conductors made of the same material, but with different cross-sections can be joined both with the chamber welding method (with tubes) as well as with the dual upset welding method with automatic deburring (without tubes).
However, certain limitations must be respected in this context. On principle, a stranded conductor running in the extruder can be welded to a smaller cross-section only to allow trouble-free passing through the extruder die. The difference in cross-section may be up to two steps, for example, 95 mm² to 120 mm² or maybe 95 mm² to 150 mm².
On dual upset butt welding machines with automatic deburring, it is possible not only to join different cross-sections, but also stranded conductors made of different materials as well (see figures below).
Left: Dual upset butt welding principle: Stranded copper conductors of different cross-sections.
Right: Stranded copper to aluminum conductor of identical cross-section.
The chamber welding method does not allow the welding of different cross-sections made of different materials though.
As a result of recent developments, it is possible to offer butt welding by medium-frequency working at about 1000 Hz,
with 3-phase current supply. So there will no longer be a single phase load of the mains supply. The amperage absorbed during a welding cycle is reduced substantially, e.g., divided by two approximately. As a result, fuse protection is facilitated in particular for bigger butt welding machines having a capacity of 100 kVA or more (mains fuses, often a transformer is installed exclusively for the butt welding machine).
Medium-frequency technology is not limited to new machines only, but it is also possible to modify existing machines.
For more information or consultation, contact the AUGUST STRECKER sales team or visit the website www.strecker-limburg.de
