Maintaining a resistance welder water system
How to keep the water circuit in peak operating condition

By Michael J. DeFalco

This article addresses these and other questions about the water circuit in resistance welders:

1. Why is water cooling necessary?
2. Does the water system ever required maintenance?
3. How important is the water cooling system on a resistance welder?
4. Should the water system be part of a preventive maintenance program?
5. What are the effects of poor water cooling or poor water flow?
6. What are the best methods for optimizing flow?
7. Can the water flow be increased?
8. How critical is water temperature?
9. How do the water flow rate and temperature affect the copper and electrodes?

Effects of Ineffective Water Cooling

Consider the operation of your water system. Do any of the following occur?
1. Do you have to continually adjust your welder because weld quality is deteriorating?
2. Do you have to change welding tips more often than usual?
3. Do you blow fuses on your welder?
4. Do you occasionally lose a silicon controlled rectifier (SCR), ignitron tubes?
5. Does your welder go through a warm-up cycle?

Any of these occurrences can be caused by ineffective water cooling of your welding machine.Your welder system layout should be similar to the one shown in Figure 1. There should be separate water-in, and a separate water-out circuits for the secondary circuit (upper and lower), the upper electrode, the lower electrode, the welding transformer, and the weld control. All of these should go directly to a common manifold.

Keeping Components Cool

Following are some guidelines for keeping resistance welding machine components cool.

Welding Transformer.
Always follow the manufacturer's recommendations. In lieu of specifications, use the following guidelines.

Plumb the transformer with fittings the same size as the water inlet and outlet. Make sure water hoses are not bundled together with power connections. Minimum flow rate is two gallons per minute (GPM) for 100KVA or less. For each additional 100KVA, increase the flow by 0.5 GPM.

Welding Control.
Follow the manufacturer's directions. The only components to be cooled in a welding control are the SCRs or ignitron tubes.

Typically, the recommendation is 1.2 GPM for a single set of SCRs or a set of size "B+C" ignitron tubes. Consult the device manufacturer for larger sizes.

Follow the specifications for hose length minimum requirements (see Bulletin #5 from the Resistance Welder Manufacturers'Association [RWMA]). Many weld controls incorporate a flow switch that ensures a minimum amount of cooling (GPM) flow before the unit is allowed to pass current. RWMA Bulletin #5 states that when the power is on, the water must be flowing.

Weldng Electrodes.
Welding electrodes do the work of welding and are the generators of heat and force. They are, therefore, consumed in the process.

Each electrode/holder combination requires a minimum of 1.5 GPM. Water comes into the electrode through the center tube and goes out around this tube (make sure tubes are cut at a 45-degree angle and go to the bottom of the tip). Most holders are of the ejector type, with a pin at the top that ejects the electrode.

Secondary Circuit
The secondary circuit of the welder is composed of everything from the welding transformer's secondary terminals to the electrodes. Since this article has already discussed the transformer and the electrodes, let's now look at the copper in between. Sometimes, flexible laminated shunts are used; other times, flexible air, or water,cooled cables are used. Regardless, the job is the same: to pass current from the welding transformer to the welding tips.

When laminated shunts are used, be sure the shunt has at least the same area as the copper conductor bar to which it is connected (thickness and width). Make sure there is water cooling near the ends of these flexible shunts, as it will extend their life.

When using water-cooled weld cables, be sure water flow is at least 2 GPM per cable. When cooling all other copper connections, regardless of size, the rule of thumb is that the copper should be comfortable to the touch. Keep in mind that the actual flow rate will be based on actual duty cycle of the welder. Recommendations are for 1 to 2 GPM. Remember, copper is less conductive when it gets hot.

As shown in these component descriptions, resistance welders commonly require 5 to 10 GPM or more of water cooling.

Plumbing the Water

In assessing the flow required to run a welder, you must understand how flow is lost. In Schedule 40 pipe (one of the most common types), for every 100 feet the water has to travel in a 1/2-inch pipe at 5 GPM, flow is reduced by about 5-1/2 feet per second, or 11.2 pounds per square inch (PSI) water pressure.

When water travels through a 90 degree pipe elbow, the reduction in flow is roughly equal to 50 diameters of pipe, or 25 inches of straight pipe. This is equal to a 2 percent decrease in water pressure for each 90-degree bend encountered. Additionally, if a standard 1/2-inch ball valve is used to turn water on and off to the welder, the loss is about 6.25 percent PSI per valve, or a net decrease of 0.5 GPM.

For example, if your machine has four 90-degree elbows and two ball valves, net PSI loss would be 20 percent with a flow loss of 21 percent, or equivalent to a 1.5 GPM loss in water flow. This does not take into consideration the flow losses incurred simply by the water moving through the pipes.

Keeping the flow at the same rate (5 GPM) and increasing the pipe size from 1/2 inch to 3/4 inch would decrease pressure and friction losses by 75 percent and have the same effect as doubling the flow rate to 10 GPM.

The Effect of Poor Water Flow

When electrodes do not receive enough water flow, the result is accelerated deterioration of the welding surfaces, which is caused by putting heat in faster than it can be removed.

In Figure 2, the electrode on the left was cooled at l-1/2 GPM, the electrode in the center was cooled at 1 GPM, and the electrode on the right was cooled at 1/2 GPM. All other variables-weld settings, number of welds, welding machine, and material-were the same for each electrode.

The electrode on the right shows the greatest amount of welding surface deterioration, which demonstrates what a major difference a small amount of change in water flow can cause.

The copper should be comfortable to the touch or it is too hot. Copper is rated at its full conductivity at 68 degrees Fahrenheit. Class 2 copper is 85 percent conductive at 68 degrees F. When copper turns dark, it has gotten too hot and oxidized. When it oxidizes, it loses its ability to conduct electricity.

Water Components and Concepts

Hose and Tubing Connectors.
Connectors can be made of brass, plastic, stainless steel, or polyvinyl chloride (PVC). A variety of push-on fittings are available for atl types of hosing. These quick-connect fittings help make the maintenance person's job easier. Some types of push-on fittings have a Teflon ring on the unit, so Teflon tape is not needed.

Hoses.
Rubber, plastic, and potyethylene hoses are recommended for all external connections. When plumbing or replacing hoses on ignitron tubes or SCRs, be sure to follow the manufacturer's recommendations.

Note that SCRs or ignitron tubes in the weld control have line voltage potential, so use only nonconductive rubber, plastic, polyethylene, or Teflon hose (see hose (see RWMA Bulletin #14).

Reducing Water Turns. Wherever possible, use flexible hosing with a minimum number of 90-degree fittings. This maximizes the water flow rate, which is the critical parameter.

Preventive Maintenance
To avoid major problems and equipment breakdowns, establish a preventive maintenance program for your resistance welder water system. Here are suggested maintenance schedules for various parts of the equipment.

Secondary Circuit Connections
Once a year (or more frequently if the equipment runs two or three shifts) tear down the secondary circuit and resurface the connections. This will reduce heat generation, minimize the built-up resistance (oxidation) in the copper connections (which generate unnecessary heat), and maximize the conductivity of the secondary circuit.

Note that when the connections oxidize, resistance builds up and a voltage drop results. This voltage drop decrease the amount of voltage applied to the electrodes and decreases the ability of the voltage to break through coatings on the materials at the weld interface.

When cleaning copper connections it is a good idea to silver-plate the resurfaced connections, which can be done quickly and cost-effectively. Although not immediately apparent on alternating current (AC) welders, silver plating makes the connection interfaces more conductive and durable It also allows you to double your intervals between preventive maintenance on the secondary circuit.

Remember, the highest resistances in the secondary or any circuit are in the connections. If you use a copper paste and the cooling is not at recommended specs the paste will melt and drip out of the joint. This paste is made of fine granules of copper suspended in oil. When was the last time you oiled an electrical connection to make it more conductive?

Electrode Holders (see Figure 3)
Electrode holders are easy to disassemble and clean. Perform the following checks and adjustments twice a year:
1. Check for worn "O" rings and good fit of the cooling/ejector tube in the cap.
2. Clean up the electrode shank end with a Morse taper reamer. The shank end wears as electrodes are changed.
3. Make sure spring and tip knock out (button on top) are free to advance and return.
4. Make sure the water tube that contacts the electrode can slide freely in the upper tube. This tube should be cut at a 45-degree angle and be long enough to reach the end of the electrode without falling out of the up-per tube (see Detail 10 in Figure 3). Never use pliers when setting a tube to fit electrodes.

Water-Cooled Welding Cable
(see Figure 4). Check the following as prescribed:
1. Are the cable sleeve or cable ends warm to the touch? If so, and water elsewhere in the circuit appears to be flowing, the cable is plugged. This is usually caused by broken wire strands. This plug is difficult to clear, so the cable should be replaced.
2. Does the cable jacket leak? If the cable has gotten too hot, water may leak out of the ends. The cable jacket can be replaced by the manufacturer if needed.

A preventive maintenance program can be instituted for checking cables and forecasting life that includes:
1. A micro-ohm quality check for resistance of cables as .they come in to ensure they meet the manufacturer's specifications.
2. On-line periodic checks of cables and welding parameters (such as welding current).
3. A monthly check of machine cables. The frequency of checks can be decreased based on data collected. When cable resistance doubles, it is time to change the cable.

Welding Transformer.
Perform the following as prescribed:
1. Check the case of the transformer. If it is warmer than room temperature, water flow is insufficient or a passage in the transformer is blocked.
2. Using a micro-ohm meter, check the resistance at the transformer lugs and record it. Include this in a maintenance log and check it monthly to determine preventive maintenance schedules.
3. Clean poor flowing copper lines by pumping a solution of muriatic acid and water through the system for several minutes, followed by several minutes of fresh water. Be sure to dispose of the waste properly.

Welding Control.
SCRs or ignitron tubes are the only components in the welding control that require water cooling. Perform the following maintenance once a year:
1. Measure flow through the SCRs or ignitron tubes with an in-line water flow meter. The flow should be at least 1.2 GPM.
2. Flush the cooling lines by reversing the in and out connections. Do not flush back into the water system.
3. Make sure the connections on the SCR or ignitron tube thermostats are not bypassed. The best way to test the thermostats is to remove them from the SCR or ignitron tube and apply heat with a soldering iron. After the thermostat clicks on, measure the contact resistance with an ohm meter. Resistance should be near infinity.
4. Measure water flow switch contacts, looking for a near zero reading. The switches should tum on with 1.2 GPM.
5. Check the resistivity of the water hose (refer to RWMA Bulletin #14).

Conclusion
As explained in this article, water system maintenance is very important to keep resistance welders running. Hopefully, you are now aware of the necessity for water cooling, the effects of poor water cooling, water cooling requirements for each component in the welding system, and how a tittle preventive maintenance can alleviate other costly problems occurring as a result of poor water cooling.

Michael J. DeFalco is Vice President and Training Director with
Spectrum U.S.A. Inc., Chicago, Illinois

For copies of Bulletins #5 and #14 discussed in this article, contact the RWMA, 1900 Arch Street, Philadelphia, PA 19103-1404, Tel: (215) 564-3484, Fax: (215) 564-2175.

Questions or comments may be emailed to jeff@bannerweld.com