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I received an e-mail from a reader who has spent the last three years researching this subject. He brought up a very good point. Refractometers are not as accurate when the coolant has been contaminated with way lube-type oils. He states that coolant test strips are more accurate and I agree. I have checked with a number of coolant distributors, and they do stock test strips for minimal cost. Oil, like any contaminant, can give you a false reading when testing coolant part levels. If at any time you have any questions, suggestions, or alternatives to what we discuss here, please send me an email at mbreen@ellisonwi.com. In this field, it is all about learning and getting better at what we do. Without outside input, improvement is virtually impossible. Now, back to this month’s topic: inspecting the electrical cabinet. Air Cooling System and Fans Inspecting the electrical cabinet entails more than you might expect. The good news is that it is normally a clean area to work. The first thing to do is open the doors. Take note of the temperature of air that comes out of the enclosure. It should not be hot. Electronics do not like heat; heat can cause everything from intermittent, unexplainable faults to complete component failure. As we all know, most drives and PCBs (printed circuit boards) can be very costly. (Note: some older DC-type drives will generate quite a bit of heat.) Excessive heat is probably a sign that the air-cooling system is not functioning correctly. Most machine tools have some type of air-cooling system in the cabinet that uses small axial-type fans to push the air. Your axis and spindle drives normally also will have a fan mounted to them as well. The card rack or control module will have fans on them as well. Most machines will have some type of heat exchanger mounted to the door or cabinet. The reason for the heat exchanger is it keeps the outside air out and inside air in. Fans push outside air through one side, while fans inside the cabinet will push air through the other side. The two sides are separated by metal fins. The two bodies of air do not mix because the air quality in many shops is poor. Coolant and oil mist, if allowed to get into the electrical cabinet, will coat and insulate everything, causing heat to stay in the components. Over time, this will cause premature failure to the components. The best way to inspect the fans is to make sure they are maintaining good airflow. If not, replace them. The fans that are exposed to outside air should be inspected for cleanliness. If dirty, turn the power off, remove the fan, wipe off the dirt with some cleaning solution on a rag, and remount the fan. Turn the power on and check for airflow. I do not advise dipping fans in cleaning solution; it could ruin the motor when you power up the fan. Some propellant-type motor cleaners also work, but the fan blades will still require wiping by hand. Voltage, Connectors, and Memory Batteries You also will need to check voltages. Check the incoming power, the power supplies, and the transformer secondaries. Most power companies will only guarantee their power to be within 10% of their rated values. High or low voltage can cause damage to everything in the cabinet. Inspect all connectors for tightness. Machines vibrate and components will loosen. Do not forget to turn the power off for this step. You also should inspect the door gasket. If this gasket is bad, contaminants can enter the cabinet. Check your records to find out when the memory batteries were last replaced. If you have ever had to re-establish your parameters from scratch, you will understand the significance of this step! The parameters are the brains and limitations of the machine. The machine probably will not be able to boot up without them. We are talking about significant downtime. When replacing the batteries, be very careful to follow the machine tool builder’s instructions to the smallest detail. Most replacements are done with the power on; otherwise, you may have a time limit to replace the batteries. Next month we will discuss the accuracy of your machine’s axes, and how to check it. Talk to you then. Mike Breen started as an aircraft electrician in the U.S. Army’s 101st Airborne and later became a Certified Electronic Engineer, with 14 years’ experience in machine tool repair. Recently, he has been a Field Service Engineer with Ellison Machinery Company of Wisconsin, holding this position for more than six years. Mike has designed and implemented complete preventive maintenance programs for many successful companies resulting in significant increases in their machines’ performance. For comments and inquiries about these articles, his e-mail address is mbreen@ellisonwi.com - October 2000 |
Coolant Update: Last month we discussed the cleaning of your machine tools. Before we get into this month’s subject, I would like to go back to the article that addressed coolants.