Monday, July 25, 2016

Demand Pulse Welding: A Brief History

Demand Pulse Welder
Demand Pulse Welder
One of the oldest welding technologies still in use today is resistor controlled arc welding. The technology is old, but when combined with more modern controls, provides exceptionally high quality performance. Resistor controlled arc welding incorporates edge-wound resistors using a special current-controlling alloy.

From the 1930’s until 1990, nearly all Multiple Operator Systems were the same general layout – a big bulk power supply, with “grids” connected by means of cable to form a system of distributed power. Originally designed for use in shipyards, this system minimized the use of high voltage primary power, distributing 75-80 volts of secondary voltage instead.

Historically, the most common application of resistor controls has been in Multiple Operator Welding Systems, widely used in shipyards and heavy construction. Nearly all the Nuclear Electric Power Plants were built using Multiple Operator Systems.

Big Four Manufacturing Company of Saint Louis, Missouri, pioneered the concept of connecting Multiple Operator systems in a complete loop configuration. This LOOP concept greatly improved the voltage stability of  Multiple Operator systems, because with all the power connected to a single circuit, voltage drops were reduced or eliminated due to the nature of a DC circuit. In 1977, Big 4 Manufacturing introduced their innovative and very successful Series 77 Control.

After the Three Mile Island incident and the subsequent slowing of the Nuclear Power Industry, Big 4 decided it was in their best interest to expand into the general fabricating, refinery and petro-chemical markets. Their popular soft arc was great for most welding, but was inadequate on pipe root passes with 5P, then the most common method use for oil related pipe. To provide an arc better suited for pipeline, Big 4 devised a circuit to make their resistor grid “think” it was a Lincoln generator. They called this new system “Arc Ram”. Arc Ram worked beautifully with 5P and similar electrodes and led to the design of a MIG system which they called  Demand Pulse.

Not to be confused with ...

"Short-circuiting Metal Transfer" (Short Arc) welding was introduced by Linde in the late fifties for welding sheet metal. During the 1960s, short-arc became widely used, sometimes for the wrong applications. When using short-arc the wire can contact the molten weld pool resulting many times with the weld not fusing to the base metal. This is called a "cold lap". Cold lap associated with Short Arc became a reason why many welding shops won’t use “wire” welding processes on pressure welds. Unfortunately, mis-used Short Arc welding gave ALL GMAW welding on pressure welds a bad name.

Demand Pulse to the Rescue

Demand Pulse rarely extinguishes the arc. Metal transfers through the arc, and the arc’s are much shorter than those from Pulse Spray. The transfer occurs above the molten pool, so spatter doesn't explode from the puddle. It is a "constant current" process. The operator selects a base current, similar to some GMAW Pulse Spray applications, adjusts the wire feed speed to give the correct voltage, and begins to weld. Lower voltage will cause the puddle to freeze faster, higher voltage will cause the puddle to be more fluid.

In short arc, a current pulse is triggered by the short-circuit condition caused by the wire driving into the work piece. Demand Pulse forces the transfer to occur before short-circuit, at a voltage selected by the operator, above the weld pool. This has two important effects: the arc does not extinguish and the spatter level is greatly reduced because the molten tip of the wire does not contact the weld pool. Because the arc is not extinguished, cold laps are virtually eliminated.

Many reference books describe short arc as a "random pulse" method of welding. Random in the sense that the pulse is triggered as a function of wire feed speed. The faster the wire feed speed, the faster the short circuits (pulses). Demand Pulse is exactly the same, except it does not short!

This blog post was abstracted from a 2004 press release from Aftek Welders, the only remaining company providing resistor controlled welding machines, and parts supplier for all Multiple Operating Systems. You can read the full version of  "AFTEK – the Best Welders you never heard of…” here.

Thursday, July 21, 2016

New Video Highlighting Custom Heat Treating Power Console Examples

This new video illustrates the variations in design and custom capabilities Hotfoil-EHS has for building specialized power consoles.  Special power requirements, corrosion-resistance, weather-proofing, custom paint or coatings, special control options and custom cable sets are all available from Hotfoil-EHS. Challenge them with your toughest heat treating requirement. You'll be pleasantly surprised with the response.

Tuesday, July 19, 2016

Hotfoil EHS Provides "The Heat" for Strong, New Tappan Zee Bridge

welding heat treating
The Tappan Zee Bridge stretches over the Hudson River and connects South Nyack, NY with Tarrytown, NY. The original bridge, completed in 1955, was only intended to last 50 years. Construction on a new, $3.9 billion replacement bridge started in 2013 and is scheduled for completion in 2018.

Hotfoil EHS is working closely with the bridge contractors supplying welding heat treating equipment. Large metal structures, such as bridge supports, pilings, and girders need careful pre-heating and post heating to ensure strong, lasting welds. Contractors on the Tappan Zee Bridge specified Hotfoil EHS power consoles, electric heaters, and thermocouples for their welding heat treating requirements.

welding heat treating
Clam shell heater.
Here are photos from the pre-heating of piling welds. The applications uses "clam shell" heaters with magnetic thermocouples. The clam shell heaters are named that because of their hinged design, making it easy to place them around large, round workpieces. The magnetic thermocouples are very convenient because the magnets keep them firmly in place and are quick to remove.

welding heat treating
Close-up of heater fastener.
A Hotfoil 6-way (six zones) power console is used to control the temperature of the workpiece by controlling the power provided to the clam shell heaters.

For more information, visit http://www.hotfoilehs.com.








welding heat treating
Piling with clam shell heater and
thermocouples installed.
   

welding heat treating
6 Way Power Console




Thursday, July 14, 2016

Custom Heat Treating Power Consoles Solve Many Potential Field Problems

Weather-proof, Stainless Steel Power Console
Weather-proof, Stainless Steel
Power Console
Standard heat treating power consoles available from a variety of manufacturers pretty much cover the same set of basic welding requirements. In many field situations however, there can be unusual circumstances such as difficult locations, available power sources, and environmental concerns. In these situations custom manufactured power consoles will provide welding outcomes with fewer operational problems, higher quality output, and greater safety.

Standard power consoles are available 3, 6, 9, 12, 18, 24 and 36 zone configuration (zones are many times referred to as "way" such as 3 way console, 6 way console, 9 way console, etc.) Each zone provides a point of control. The type of control can vary depending on the requirement of the weld. Some zones only need simple on-off or proportional control. Some welding jobs require more sophisticated temperature control profiles, thus requiring tight control with temperature vs. time ramping. Additionally, these more sophisticated control requirements may also need data logging or recording for quality compliance. In many situations custom cable sets are required to deliver the heater power and thermocouples to the workpiece. A power console manufacturer should have the experience and knowledge to consult, recommend, and install whatever zone control and cabling requirements your job needs.

Power console and custom cable sets
Power console and
custom cable sets
The operating environment is another important consideration for power console customization. Standard power console cabinets are usually made from a medium gage sheet metal and painted with an industrial grade rust-resistant paint. While fine for relatively dry and non-corrosive atmospheres, these are subject to quick deterioration when moved into areas where higher than normal concentrations of salt, chlorine, or other corrosive gasses exist. In these situations, careful consideration of exposed materials needs to be applied. Perhaps an all stainless steel design is needed? Or maybe special corrosion resistant paints or epoxy resins should be specified? Or maybe you only need a special color paint? Working with a power console manufacturer who has the flexibility in their manufacturing process and experience on the floor to provide these options is preferred.

Custom painted power console
Custom painted
power console
Finally, look for a power console manufacturer who can handle unusual power system requirements. A manufacturer who can adapt their systems to unique voltages and current requirements is a big plus. Look for an equipment company that has experience and production capabilities for a wide variety of transformers - single or dual- and can even supply custom built transformers.

And of course, always try and find equipment built right here in the USA.

For more information on ANY welding power console, contact:

Hotfoil-EHS
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
www.hotfoilehs.com
Email: dap@hotfoilehs.com