Seam Welding
Questions and Answers
A seam welder has the same components as any other resistance welder. They require the same water cooling as all resistance welders. Water or other similar fluid is a must to perform the cooling of these critical machine components. These components are:
• Transformer
• Conductors
• Control
• Electrodes
In the case of the seam welder the electrode is a seam welding wheel water cooled at the central hub. Some applications generate excessive heat at the weld area and demand the use of external flood cooling directly at the weld joint.
ARROWS INDICATE EXTERNAL FLOOD COOLING TUBES
The question raised is: Can compressed air be substituted for water?
Water as compared to air at a minimum is fifty times more heat conductive than air. For the machine components it is doubtful that a machine manufacturer would warrant a machine cooled with air. Water must be used for the machine.
If a part producer chooses to externally cool the wheel weld face and part with air, that is up to the producer and his customer and the quality specifications required. Many parts are not externally cooled. It depends upon the amount of heat generated. Air may work?
Water flood cooling is messy but it works.
FOR ADDITIONAL INFORMATION REFER TO OTHER ARTICLES IN THIS BLOG:
“WHAT IS THE PROPER AMOUNT OF WATER COOLING FOR SEAM WELDING?”
“IS THE WATER USED FOR SEAM WELDING HARMFUL AFTER BEING USED FOR COOLING?”
References: RWMA- RWMA Resistance Welding Manual 4th Edition
AWS- AWS Standard J1.2 Guide to the Installation and Maintenance of Resistance Welding Machines
Seam welding can generate large amounts of heat. Especially when making a liquid tight continuous weld. This heat is very visible at the actual weld joint. You stated that you are using cooling water as specified by the machine manufacturer at 20 l per minute. This may be adequate for the machine under normal operation. It does not mean that at the weld area the cooling is adequate.
Heat can be a suspect to address. The machine produces good welds for 300 meters. Then cracks appear. After stopping for a period of time the machine is cooled down. A restart produces good product for another 300 meters. If the hub cooling of the wheel cannot adequately cool the wheel to keep the wheel rim face at a steady heat condition, the rim face heat will build up and gradually get hotter. The part will not cool as quickly and the process will change. Apparently, CRACKING results.
Cooling of the part/wheel weld area with external direct water flood cooling as shown below is one option. This is messy but functional. The general rule of thumb is a flow rate of 4-6 l per minute.
ARROWS INDICATE FLOOD WATER TUBES
The other option is to attach a water cooling chamber on one face of the wheel. Use “O” rings to seal the water in and flood the chamber with water to near the weld face.
Is the Wheel rim face condition an issue?
• Is the wheel being faced/dressed during use?
• Does it build up and get rough and cause the cracks due to no dressing?
• When the machine stops do the wheels get dressed and produce good product until they get rough again?
Since heat is an issue one has to address the issue of the machine duty cycle. Is the machine operating safely at less than the normally rated 50% maximum duty cycle?
Several articles in this blog address Duty Cycle including:
HOW DO YOU CALCULATE DUTY CYCLE?
If the machine is nearing the 50% value then additional water cooling may be required. Cooling towers or Chillers may be needed.
Reference: RWMA – Resistance Welding Manual Section 4
Weld schedules are available the Resistance Welding Manual and AWS Standard C1.1 for many of the most frequently used materials. The information commonly provided is the proper electrode design, size and material. The weld force, weld time and weld current are also published. The minimum distance between welds if usually listed and the expected nugget or button size is shown. Tensile properties frequently are also published.
All of this is good information to use as a starting point. Each application will dictate some variation from these settings. These numbers will act as a good guide or goal for your application.
I suggest a purchase of a copy of AWS Standard C1.1. It has a complete set of data that you can use for initial set up. Then fine tune for your machine, product being welded and desired results.
References: AWS C1.1 Recommended Practices for Resistance Welding
RWMA – RWMA Resistance Welding Manual 4th Edition
All seam welders are designed and built with precision bearings, a moving shaft that extends to the seam welding wheel, and conductive shoes that rotate on the shaft to pick up the current from the stationary conductors in the housing. The entire housing is sealed and contains a conductive grease or lubricant to insure long life and good electrical conduction.
This housing and shaft assembly is a very precise piece of machinery designed to last for many years with proper maintenance. Maintenance of lubrication would be one of those items.
An article on Seam Shaft maintenance is available:
CAN WORN SEAM WELDING SHAFTS BE REWORKED?
KNURL DRIVEN SEAM WELDER
Should one permit a seam welder head to run low on lubricant is an obvious answer, NO.
It would be similar to running your vehicle engine or transmission low on oil or transmission fluid. Eventually the engine freezes up or the transmission fails to shift.
No one wants to reach that point. Follow the manufacturers maintenance instructions.
The other alternative is to establish an in-house preventive maintenance procedure.
American Welding society has a standard available to serve as a guide for and in house preventative maintenance program.
AWS Standard J1.2- “Guide to Installation and Maintenance of Resistance Welding Machines”
References: RWMA Resistance Welding Manual 4th Edition
AWS J1.2 Guide to Installation and Maintenance of Resistance Welding Machines
The seam weld wheels perform two functions. One is to function as an electrode and deliver the force and current into the part at the desired weld interface. This is a moving location as the wheels roll.
ROLL SPOT SEAM WELDS
The second function is to move the part into position for each new weld. One or both wheels may be driven to perform this function. In some cases, the part is driven and the wheels float and follow the part movement.
In all circumstances the direction of the wheel motion at the part surface is always the same direction as the part motion.
If the part is moving into the throat of the machine. The upper and lower wheels will both turn with a motion into the throat of the machine. At the surface they are both moving in the same direction. If one wants to talk clockwise vs counterclockwise, if the upper is turning clockwise the lower is counterclockwise. If you look from the other side of the machine the opposite is true.
SEAM WELD WHEEL ROTATION
Always both wheel surface motions are in the direction of the material motion.
Reference: RWMA – Resistance Welding Manual 4th Edition
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