The first high frequency tube & pipe welders were developed nearly 60 years ago and used sliding copper contacts rather than induction coils. The contact welding process is still widely used to produce certain tubular products, particularly large diameter pipe & structural tubing. Contact welding offers some benefit in terms of efficiency on large diameter tubing since the contacts can be placed closer to the weld point than a coil. This results in a shorter "vee" and are duction in the amount of weld power required. The need for impeders is also reduced in some cases with contact welding.
Early contact welders used hard drawn bus bar copper for the contact tips but abrasion against the moving strip required that the be replaced frequently. An ideal contact material should have high electrical conductivity combined with the ability to with stand hot abrasion. No single metal meets both requirements. Silver, copper & aluminium are all good electrical conductors but they are also soft & have poor wear resistance. Modern contact welding materials use a mixture of copper or silver with tungsten or tungsten carbide. These are not alloys but sintered mixtures of metals. During sintering the copper or silver melts & coats the grains of tungsten or tungsten carbide, resulting in a material with very high conductivity combined with the wearing properties of tungsten.
Contact welding is not suitable for all types of tube or pipe and it generally produces a less consistent weld due to the inherent variations in electrical resistance caused by the sliding contacts. Contact marking & possible contamination of the weld due to copper or silver may limit the applications of this process in some types of tubing & pipe..
EHE contacts & bus assemblies
EHE has over 30 years of experience in high frequency welding & we have applied this to our range of contact welding accessories. All EHE contact shoes are CNC machined from pure high conductivity carbon deoxidized copper (Alloy 10200).
Contact tips are silver soldered in place using precision fixtures to ensure that each assembly maintains close tolerances. All parts receive a thin plating of electroless tin to resist oxidation of the electrical mating surfaces. This minimises any heating due to poor electrical connections. With modern solid state contact welders,currents in excess of 1000 amps may flow through the contacts & into the tube. Any resistance causes severe localized overheating & variations in weld temperature.
All contact shoes, flexible adapters & down leads must be water cooled at the high currents & frequencies used for tube welding.Our experience at working with HF welders over 30 years enables us to design & manufacture the most efficient and cost effective accessories for this process.
The use of precision fabricated contacts, contact shoes, flexible adapters & down leads with minimize variations in weld temperature, resulting in fewer defects and less mill down time.
Contact tip materials
Many of our customers prefer to replace the contact tips them selves as they wear out. We stock a variety of contact materials for this purpose & can supply it either machined to final contact shape, or in the form of 8" long bars in various widths & thicknesses. The following materials are available from stock:-
1 TC-5 (TC50) comprises 50% copper & 50% tungsten carbide. This material is commonly used for welding hot rolled steel. It has good wear properties but is more likely to cause contact marking on the product.
2 20S contains 20% silver with 80% tungsten metal. Other ratios are also available.20S is frequently used to weld cold rolled or P&O steel and reduces contact marking at the expense of reduced operating life. It is also considerably more expensive than TC-5.
3 Pure copper is rarely used these days but results in very little marking of the tube.Because it is soft, it wears far more quickly than materials containing tungsten but it has the advantage of being inexpensive & readily available from many sources.
We offer re-tipping of all our contact shoes at competitive prices, using the same precision fixtures & silver brazing technique as our new contact assemblies. Recent variations inthe prices of copper, silver & most other metals require that we price each quotation to the market. Please call, fax or email your requirements for a fast & up to date quotation.