Controls & Transformers
Questions and Answers
Constant current is a very useful feature of today’s controls. If this feature is present and you ask for 10,000 amps. The control will deliver that amperage each weld. It won’t matter if you are near the edge of the part or putting half of the file cabinet into the throat of the AC machine as you move across the part. The control with constant current will deliver 10,000 amps to the weld. It has a feedback coil that tells it the amperage that is flowing and it makes corrections to deliver the proper amount during the weld.
To convert incoming air pressure to the force at the electrodes is a very simple calculation. To do so you must know the line pressure and the diameter of the air cylinder.
SCR contactors are subject to heating due to the high currents that they sometimes have to carry. They are normally air or water cooled but can still over heat if driven too hard or not cooled correctly. Heat is one of SCR’s main failure modes. SCR’s fail in the “ON” shorted mode. This makes caution very important. Over temp monitors on the contactors is recommended by the SCR manufacturers.
SCR’s carry a large amount of current and generate a lot of heat. The larger units are water cooled. There are some definite recommendations that must be followed for plumbing the SCR contactor. Always use nonconductive low carbon hose.
Controls have a function available that is called retraction. This describes an action of the pneumatic cylinder or servo. Retraction can speed up the weld operation when repeating like welds near each other. We don’t want the cylinder to open fully just enough to allow part or gun movement to the next weld location. Then the weld repeats. Another example is to open enough to load the next part but not full open to reduce cylinder travel time.
Page 29 of 39
Have a Question?
Do you have a question that is not covered in our knowledgebase? Do you have questions regarding the above article? Click here to ask the professor.