Page 45 - MetalForming-Aug-2018-issue
P. 45

   This illustration shows proper use of a water-cooling tube inside of a spot-welding elec- trode holder and tip. With one end cut on a 45-deg. angle, the tube forces water flow as close as possible to the end of the internal water-cooling cavity in a typical spot-weld- ing tip.
Water, Water, Everywhere
Although a recirculating chiller can be filled with city water, it’s better to use a mixture of distilled water and glycol, especially for outdoor chillers. Never acceptable: the use of automo- tive antifreeze in a chiller.
In addition, many of our customers assume that using deionized water is fine, but doing so will quickly destroy a chiller due to leaching of minerals from the chiller’s internal components.
Condensation Kills Resistance Welders
Although common sense would indicate that water to cool RW machines should be as cold as possible, condensation quickly becomes a prob- lem during the summer, when the pre- vailing dew point (the temperature at which water vapor condenses), sur- passes the process-water temperature.
Since dew-point temperatures greater than 70 F are common during the muggy summer months, it’s best to set chillers at temperatures exceeding the dew point to avoid internal sweating of the machine’s transformer and sili- con-controlled rectifier (SCR), which could cause an electrical short.
Also, avoid puddles of water inside of the control cabinet and condensa- tion dripping off of the electrodes and holders. A water-saver relay and sole- noid valve used to turn off water to the welding transformer about 1 min. after the last welding cycle will prevent con- densation damage to the welding trans- former from condensation.
In addition, some chillers now include a highly recommended feature, automatic dew-point compensation, which removes the need to adjust man- ually the chiller’s water-temperature setpoint during humid weather.
Caution: If your RW machine has a direct water-cooled SCR assembly, never leave the machine sitting idle with the power on and the water turned off. Doing so can cause the stagnant water in the hose to generate heat and steam, causing the hose to burst and
water-cooling cavity in a typical spot- welding tip.
Common Water-Cooling Problems
Large roof-mounted water towers long represented the most common method to supply cooling water to spot welders, but they present a unique set of problems, including inconsistent process water temperatures due to varying ambient air temperatures throughout the year.
In addition, dirt and other contam- inates in the tower can cause problems. I remember visiting a Japanese-owned automotive-parts manufacturer with cherry trees planted around its build- ing. Although beautiful, their blossoms clogged the system each spring.
Additional problems resulted from this plant’s use of black-iron water lines throughout the facility, which corroded internally after a couple of years and introduced flakes of rust into the system, clogging the small- diameter internal water-cooling cir- cuits in their transgun-type portable spot welders.
Another reason for not recommend- ing a cooling tower for use with spot welders: A plant’s water-flow capacity often doesn’t increase upon installation of additional water-cooled machinery.
Sometimes, plants cool RW machines with well water. Often viewed as a free cooling method, the minerals present eventually clog a machine’s water-cool-
ing circuits. In addition, well water may be too cold and cause condensation.
Some plants use large recirculating reservoir tanks cooled by truck radia- tors. I’ve also seen welders cooled by water pumped from 55-gal. drums into which bags of ice are poured. Due to inconsistent water temperatures, nei- ther option is recommended.
The Big Chill
Finally, small radiator-type water recirculators for use with arc-welding machines are usually inadequate for cooling a production RW machine.
Steve Derrick, manufacturing engi- neering manager at Innovative Hearth Products in Russellville, AL, recalls inheriting a group of 30 RW machines cooled by those little recirculators. Dra- matic improvements resulted from replacing those units with self-con- tained refrigeration-type water chillers properly sized for his welders.
“It was obvious that the little radia- tor-type recirculators were not doing the job because our spot-welding tips were too hot to handle,” says Derrick. “Sometimes we had to stop production to let the welders cool down. In addi- tion, our weld quality varied through- out the day.
“A water chiller solved that problem, and I will be buying more in the future,” he adds. “And we order our chillers with optional castors so that we can move them easily from welder to welder.”
MetalForming/August 2018 43
Welding Well

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