Basic Electric Motor Maintenance Regional Service Manger Ed Robinson Regional Service Manger erobinson@weg.net

Misalignment of sheaves and couplings Eli Lilly Study Primary causes of failure: Misalignment of sheaves and couplings Over/under lubrication of bearings Improper tension in belted systems Temperature: Readings taken on the drive-end bell housing within 1 in. of the drive shaft closely approximate the internal winding and bearing temperatures

Basic Maintenance Bearing & Lubrication Maintenance Coupling Maintenance Electrical Inspection

Bearing Failures Bearing Failures are the #1 cause of motor failures. Over 60% of all motor failures are attributed to the bearings. However, many external factors contribute to the actual failure of the bearings. The bearing itself is not usually the culprit. So, let’s start by talking about the original design and what affect that has on the life.

Bearing Design Shape Ball Bearings Roller Bearings Cylindrical Roller Bearings are used for heavy radial loaded applications, like a V-belt drive. There is NO axial loading. Deep Groove Radial Ball Bearings are used for “general purpose” applications. They work with both radial and axial type loading.

Bearing Design Size Same Bore Size 200 Series Ball Bearing 300 Series The 300 Series has larger diameter balls or rollers and a larger outside diameter which results in the heavier load carrying capacity And…… Given the same load, the 300 Series will last twice as long as the 200 Series.

Bearing Design Size It’s very easy to see the difference in the 300 series bearing on the left, and the 200 series on the right.

Bearing Design Factors in the life of a bearing Load and Speed. Those are the two determining factors in designing a bearing for a particular application and the life expected from that bearing in that application. The size of the bearing will help determine how much load, and for how long the bearing can handle that load. The size and type of the rolling element also plays an important part in the load rating. Since you can’t change the design characteristics or the size of the bearings in your motors, it is a good idea to include these things in your analysis for selecting a new motor, in the beginning.

Bearing Design Life L10 Life Of 100 bearings tested, under the same load and speed conditions, the L10 life is where 10% of the bearings will fail (or 90% will survive).

Bearing Design Life L50 Life Of 100 bearings tested, under the same load and speed conditions, the L50 life is where 50% of the bearings will fail (and only 50% will survive).

Bearing Design Life L10 Life Some Manufacturers use L10 life in engineering their motors. And some use L50 life in engineering their motors. L50 allows them to downsize the bearing and save money. But who really pays?

Bearing Maintenance Basic Inspection Shaft “Feel”, without the motor running Turn the shaft by hand … Before 1st use to distribute grease. Does it turn easily ? Feel for flat spots, rubbing, stiffness, etc … Bearing Noise while running (unloaded) Listen to the motor bearings … Listen for abnormal sounds, squealing, squeaking, grinding, etc … Unloaded roller bearings will definitely make a “rattling” noise..

Bearing Maintenance Hi Tech Inspection Vibration Analysis Infrared Thermography RTD Thermal Analysis

Bearing Failure Factors Leading causes of bearing failure Lack of lubrication Too much lubrication Incompatibility of greases Contamination of lubrication Internal Winding Temperatures

Bearing Lubrication Re-lubrication Intervals Believe it or not, too much lubrication in a ball bearing can have the same result as not enough lubrication

Nameplate Information The nameplate tells you exactly what type, how much, and how often to add lubrication.

Bearing Lubrication Grease Did you know you can’t mix just any grease with any other grease? It’s true - doing so can cause catastrophic damage to equipment. And it’s true even if the grease types are the same. Why is this? Grease consists of two parts - the actual lubricant (normally oil) and a carrier, or base. Each has it’s own function. It’s the carriers that are not compatible. Always know the base of the grease you are adding and the base of the grease you are adding to. Once you know those things, you can use the chart on the next page to determine if you can add one grease to the other. The grease compatibility chart will help ----

Bearing Lubrication

Bearing Lubrication How does the grease get into the rolling element? Positive Pressure Lubrication System

Bearing & Lubrication Maintenance Coupling Maintenance Basic Maintenance Bearing & Lubrication Maintenance Coupling Maintenance Electrical Inspection

Example D - Large Sheave = 18” d - Small Sheave = 12” Belt Drives Belt Over-Tension is a Primary Source of Bearing, Belt and Motor Shaft Failure. Example D - Large Sheave = 18” d - Small Sheave = 12” C - Ctr Dist = 36” C2 = 1296” 18 - 12 = 6” - - 6/2 =3” 32 = 9” 1296 - 9 = 1287” t 1287” Span = 35.8” 35.8 / 64 = .5” 1/2” Belt Deflection

Belt Drives If you have a V-belt tension gauge and want to tension by force, you can use a chart like this. This is a much more accurate method of tensioning.

Belt Drives Life Expectancy The load has a great deal of effect on the life of the belt. A 25% overload on the belt drive, will result in only 50% of the design belt life.

Belt Drives Life Expectancy The tension also has a great deal of effect on the life of the belt. A 18% over-tension on the belt drive, will also result 50% of the design belt life.

Belt Drives Life Expectancy Heat is also a major factor. Designing good ventilation for the V-Drive can make a big difference. A 20o temperature increase above ambient, will also result 40% loss in the design life of the belt.

Installation Belt Drives Most of the belt problems begin with the original installation of the belts. Prying the belts on (as pictured below) can break the cords in the belt, not to mention external groove damage along the sides of the belts where they ride in the groove of the sheave.

Belt Drives Alignment Another problem that is often overlooked is the sheave alignment. This type of misalignment can result is belt overheating, shortened life, as well as bearing overloading.

Belt Drives Maintenance Another much looked over issue is the sheave groove wear. When the sheave grooves wear, and dish out, as shown below, you lose belt contact on the sides of those grooves. Then, you have to over tension the belt to try and make it work. That puts excess overhung load on the bearing and shaft.

Critical Factors Original Design Alignment Tension Clean Cool Belt Drives Maintenance As you can see, a great deal of cost effective maintenance can be done on a simple V-belt drive. Critical Factors Original Design Alignment Tension Clean Cool

Direct Coupling Shaft Alignment Laser Alignment * University of Tennessee, College of Engineering Laser Alignment

Bearing & Lubrication Maintenance Coupling Maintenance Basic Maintenance Bearing & Lubrication Maintenance Coupling Maintenance Electrical Inspection

Electrical Inspection There are a lot of items included in this area, but it starts with good wiring practices, including good clean connections, and good grounding procedures. Many electrical failures involving motors happen during the initial connections. If your electrician doesn’t understand the wiring diagram, get some outside help. Don’t use the trial and error method. Most electrical failures that happen because of miss-connection, will do so quickly. This is an expensive mistake.

Preventative Electrical Maintenance Checking the initial wiring procedures, before starting the motor the first time.

Thermocouple / Thermostat Motor Protection Protecting the motor from overloads Thermocouple / Thermostat Bi-metal construction (dual expansion rate) Alarm (or) Overheat Inexpensive Thermistor: Solid State Switch Increase in temperature causes additional resistance in sensor , energizing the external relay. Thermocouple Thermistor Relay

Motor Protection Protecting the motor from overloads RTD’s: Resistance Temperature Detectors Resistance change fed to external instruments allow for : Alarm Signal Temperature Readout Automatic Shutdown Continuous trend chart recording

Motor Protection Change in resistance proportional to temperature Protecting the motor from overloads RTD’s: Resistance Temperature Detectors Change in resistance proportional to temperature Linear signal allows for exact temperature report More expensive than Thermistors or Thermostats

Preventative Electrical Maintenance

Preventative Electrical Maintenance Effects of voltage variation Periodic checks of Voltage and Current measurements might save some real problems down the road.

Preventative Electrical Maintenance Unbalanced Voltage supply lines are responsible for a lot more failures than are usually thought of A motor with a good service factor and low temperature rise might cover for the 3% unbalance, but not for 5%.

Manufacturers Control Application vs. Design Issues Customers Control (Preventable) Correct Electrical Connections Bearing Lubrication V- Drive Maintenance Shaft Alignment Thermal Overload Prot Connections – loose bolts, nuts, and screws Manufacturers Control (Warranty) Short Circuit Between Turns Short Circuit in Stator Slot Phase to Ground Short Rotor Failures Rotor Bar Breakage Excessive Rotor Heating

Preventative Maintenance Preventative Maintenance compares to Reactive Maintenance as a checkup or physical compares to emergency room treatment.

Cost of Failure Cost Time or Life Equipment Life/Cost Curve Corrective Maintenance Time or Life Cost Preventative Maintenance Predictive Maintenance

Predictive Maintenance Differs from Preventative Maintenance by using scheduled analysis of: Shaft Misalignment Relubrication Balancing Vibration And then using that analysis to predict the longest period of life you can get from your equipment, BEFORE it fails.

Predictive Technologies Vibration Analysis: Couplings Bearings Gears Infrared Thermography: Electrical Connections Insulation Deterioration Mechanical Considerations

Infrared Thermography Motor Starter Overload

Heat pattern caused by an improperly aligned motor Infrared Thermography Heat pattern caused by an improperly aligned motor

Conclusions You can get more for your maintenance dollars with Preventive and Predictive maintenance routines. The old days of “Don’t fix it if it ain’t broke” are going by the way. Downtime and lost production is simply too expensive to let it run ‘til it quits. Identifying the critical applications, and starting a routine to log the failures, their causes and repairs is the first step.

Conclusions Also, identifying the right motor in the first place is a great place to start. Some of the most important features to look for are: Motor Insulation and Temperature Rise Service Factor Bearing Sizes and Load Capacities Construction Materials Efficiency ( Not only does the efficiency of the motor save you operating costs, but it helps to ensure the quality of materials the motor is built with )