Page 91 - MetalForming-Oct-2018-issue

Welding Well
Fig. 3—Condensation can cause problems inside of welder controls.
forging action, called fast follow-up, must be present whether the force is applied with a pneumatic cylinder, air-over-oil cylinder or electric servo.
To minimize moisture in the air sup- ply, a common problem seen with air- operated resistance welders, compres- sors should be equipped with an air dryer, and each machine should have its own air filter and regulator.
If not permanently lubricated, make sure that the cylinder’s lubricator (oiler) is set properly, with approximately one drop of lightweight oil per 20 machine strokes. Most lubricators are set too high, resulting in the machine’s air- exhaust mufflers, if installed, becoming clogged with oil. In addition to making a mess, this restricts air from exiting the cylinder and can reduce weld qual- ity due to inadequate forging force.
Yearly preventive maintenance of an air-operated resistance welder should include a look inside of the air cylinder. If moisture is in the air supply and if the machine sits idle, cylinder walls and shafts may become pitted and need polishing or replacement.
Keep Your Cool
Water-cooled machines require at least 1.5 gal./min. of water per circuit when the welder runs production.
Heavy-duty single-phase AC welder transformers, the industry standard for decades, tolerated overheating due to lower water flow, but that is not the case with newer-technology three- phase, mid-frequency direct-current (MFDC) power supplies in wide use today.
MFDC units will not withstand abuse and out-
put diodes will short out
quickly if operated without
proper cooling. MFDC power supplies need at least 2 gal./min. and possibly more
if noted on the data tag. Water quality also is important, with
the American Welding Society’s C1 document providing good infor- mation on cooling-water chemistry.
Long-term machine perform-
ance relies on proper maintenance
of the water-cooling system. If connected to city or well water,
we often see “gunk” accumulate inside of the hoses and other water passages, which are often small-diameter copper tubes. Contaminants such as mud, slime, algae and scale can partially or totally block the flow of cooling water, causing the welder to overheat. (Fig. 2)
Various commercially available cleaning solutions can help remove deposits from a welder’s internal water- cooling lines. Choose a cleaning system that does not attack copper and brass and be sure to install a water filter to catch what is flushed out.
Avoid the problem altogether by con- necting the welder to a self-contained recirculating refrigeration-type water chiller that can provide coolant at a con- sistent temperature and flow rate. How- ever, a chiller also can cause problems if it is set to operate below the prevailing dew-point temperature, which creates condensation. In addition to causing the welder’s electrodes and electrode holders to sweat and drip on the floor at the operator’s feet, the machine’s water-cooled transformer could short out when internal insulation breaks down due to water saturation.
Another common victim of conden- sation: the water-cooled silicon-con- trolled rectifier (SCR) contactor inside of the welder’s control cabinet (Fig. 3). A chiller that includes an optional dew- point-compensation feature helps avoid condensation by automatically adjusting water temperature based on prevailing conditions.
Fig. 4—Rebuilds transform decades-old quality resistance welders into machines that look and work like new. Shown here: before and after images of a com- pletely stripped and remanufactured machine, and a new welder control with programmable functions.
Control Your Future
If the control on your resistance welder is more than 10 years old, con- sider an upgrade. Like all electronics, welder controls become obsolete quickly and manufacturers no longer support many models. Therefore, it pays to be proactive and avoid a crisis. Even if your older controls work well, new models, with various monitoring and feedback features for enhanced weld quality and worker safety, deserve consideration.
Your machine may be an ideal can- didate for a makeover or upgrade. Rebuilds transform decades-old quality resistance welders into machines that look and work like new, with some retrofitted with new MFDC power sup- plies and controls (Fig. 4).
It comes down to this: Show your resistance-welding machines some respect via preventive maintenance, makeovers and upgrades and you will avoid production delays. Your efforts will be worth the time and money. MF
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