Though clutches and brakes differ in purpose and application, for troubleshooting and problem-solving purposes their operating principles are similar. We focus here on positive-action units that are either electrically or mechanically actuated (“spring-set”), which includes brakes with On-Off action and Start-Stop clutches.

Most problems in the field show up as overheating, torque loss, or coil failure. Unless you dig until you find the culprit, you’ll probably keep replacing failed parts that result from the problem, without resolving the problem. Here are some tongue-in-cheek guidelines to help you.

Fail to read instructions

It has become a cliché: “When all else fails, read the instructions.” The fact: Clutches and brakes are precision devices with close tolerances. For troublefree service, they may have special assembly, installation, or adjustment requirements you must not overlook. When replacing a unit, even with one that looks the same, don’t just pull the old unit and slap in the new one. Instead, “before all else fails, read the instructions!”

Likewise, some sizes or designs have procedures for adjusting the air gap as it increases because of wear, or procedures for replacing components as they exceed wear limits. If you fail to follow all the maintenance and adjustment procedures in the instructions, you may not ruin your clutch or brake immediately, but you can be sure you’ve shortened its life.

Misalign it

Most electric brakes and clutches are installed in a direct-drive configuration, and alignment is just as important as it is with a motor. If bearings and shafts are not aligned, extra stresses and vibrations that develop can turn into major problems. Most industrial clutches and brakes are similar in design and have a small air gap between armature and magnet body. The effect of any misalignment is magnified, particularly on clutches, and can cause vibration and torque loss.

When you install or replace clutches or brakes, be aware that there are NEMA specifications on how they fit to motors or gearboxes, governing tolerance ranges for things such as register and bolt circles. Brake and clutch manufacturers set their design criteria to be compatible with this “window,” and proper alignment is normally the equipment manufacturer’s responsibility. You can incurtrouble when mounting a new brake or clutch on used equipment if you don’t assure that motors or drives remain within NEMA tolerances. If the motor end bearings are worn, any shaft wobble will be exaggerated farther from the motor where the clutch or brake may be mounted — and what is really a motor problem may first show up as clutch or brake failure.

To avoid trouble, measure shaft runout both axially and radially, and check it against NEMA tolerances. These are usually around 0.004 in. radially and 0.002 in. axially, but they vary some by motor size. Also, check motor-shaft end float. Most equipment can tolerate float up to about 0.020 in. Most manufacturers’ instruction sheets include allowable indicator runouts for mating equipment.

Overhung loads can cause trouble. Particularly on clutch applications with a sprocket or sheave, there is a limit to the side force or tension you can apply without overloading the bearing and deflecting the output shaft.

If a unit has a retaining bracket, don’t bolt it down tightly or weld it in place unless you want premature failure. The retaining tab is mainly to prevent rotation when the clutch is applied, and it is necessary only to pin it in place so it is somewhat free-floating. Bolting it tightly can create hub-and-shaft misalignment and bearing prestress. This can lead to quick clutch failure and even drive damage.

Misassemble it

Electromagnetic clutch with integral roller chain sprocket in typically tough duty. “Roto- Sprocket” mounts in underpart of ice-cream-bar wrapping machine. It positions product.

We’re back at “read the instructions,” but repair or replacement of a clutch or brake presents many opportunities for misassembly.

Setscrews are a simple but often-overlooked example, if calls from the field are an indication. You’ll find them on driven hubs of components that mount to motor shafts. Depending on component size, components may be keyed only or keyed and secured by setscrews, especially on larger units. Fail to read about them on the instruction sheet if you want failure in the future.

A related problem can occur when improper installation or maintenance contradicts a desired rating, such as a NEMA class, API standard, or FDA regulation. This is more often the case for a special product tailored to an application, rather than for off-theshelf units. Most industrial clutches are unenclosed, similar to drip-proof motors, and should be shrouded against direct water spray.

Some brakes and clutches come with features such as special sealing and plated components for washdown applications, such as those in the food industry. Replacing plated fasteners or other components with unplated items will accelerate rust and cause early failure. Finally, replacing components such as friction discs with nonoriginal parts may drastically change operating characteristics. Use components not designed and tested with your specific brake or clutch and you may compromise performance. A replacement friction disc may look like and fit like the original, but it could have a much different friction coefficient and shorter life, for example.

Shake and break

Two types of vibration can trouble your clutch or brake. Operating vibrations from uneven loads, poor alignment, or misassembly will obviously destroy a unit if left unchecked. These phenomena are often cumulative, growing larger as they cause wear or loosen mountings. More subtle are environmental vibrations, caused by other adjacent or mobile equipment. Particularly when machinery having clutches or brakes with ball or roller bearings is stored or inactive for a long time, these vibrations and the bearings’ static loads may cause “false brinelling.” Result: Tiny dents in the bearing raceway. They will cause vibration and wear as rolling elements pass over them when the clutch goes back in service. The easy solution: Periodically turn the shafts on which the units mount — maybe once a month. It can improve the health of motor and line-shaft bearings, too.

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