FAQs
What features should I look for in a ball bearing?
How can I get the longest life out of my bearings?
What shaft and housing fit do my bearings require?
How often should I grease my bearings, and how much grease do they need?
What features should I look for in a mounted bearing?
What is the best method for installing mounted bearings?
What features should I look for in roller chain?
What features should I look for in a sprocket?
What are some guidelines for good chain performance?
When should I replace my chain or sprockets?
How can I get the longest life out of my V-belt drive?
What’s the best tension for my drive?
When should I replace my sheave?
How should I select a gear reducer?
BEARINGS
What features should I look for in a ball bearing?
- HIGH DIMENSIONAL ACCURACY – There are various sets of tolerances for the boundary dimensions (ID, OD, width) of bearings, as well as the characteristics of the balls. Most standard bearings meet ABEC 1, the lowest set of tolerances. Higher-precision bearings hold to ABEC 3 or better.
- HONED RACEWAYS – Ball paths should not just be ground, but honed to a smoother finish. Smoother ball paths mean smoother, quieter, longer life.
- PRECISION BALLS – Standard bearing balls are Grade 25, or up to 0.000025” from perfect roundness. Precision bearings use Grade 10 balls, or within 0.000010” from perfect roundness.
- QUIET AND SMOOTH RUNNING – At high speeds and loads, even minor noise and vibration can be greatly magnified. Ball bearings should be tested for vibration and noise, both before and after lubrication.
- GREASE – Grease is the lifeblood of a bearing; it needs to be able to handle high temperatures and high loads without breaking down.
- STEEL RETAINER – An all-steel retainer will be stronger, more heat-resistant, and more rigid than a plastic retainer.
How can I get the longest life out of my bearings?
- CHECK YOUR FITS FIRST. A loose shaft or housing fit will let the bearing wobble or creep and cause uneven wear. A tight shaft or housing fit will reduce internal clearance and prevent grease or oil from lubricating the bearing properly.
- CHECK YOUR LOAD. Overloading will greatly accelerate metal fatigue and shorten the bearing life. Underloading will cause rolling elements to skid rather than roll, damaging the running surfaces.
- INSTALL WITH CARE. To press into a housing, make sure you press on the outer race; to press onto a shaft, press on the inner race. If installing by hand, avoid sharp blows; use a block of wood or a piece of pipe between the hammer and bearing, and tap it in at various points around the bearing.
- FOLLOW A LUBRICATION SCHEDULE. Overlubrication can blow out bearing seals and let in contaminants. It also churns and generates resistance (rather than reducing it), and can lead to dramatic heat build-up.
- KEEP THEM CLEAN. Contaminants can get embedded in the running surfaces and do irreparable damage to the rolling elements. Even tiny amounts of water can get trapped in the grease and lead to internal rust.
- KEEP THEM ALIGNED. Misalignment between the shaft and housing forces the rolling elements into an oval path, rather than circular, leading to uneven wear and possibly destroying the retainer.
- DAMPEN VIBRATION. Vibration from elsewhere in the machine causes the bearing to chatter and damages the running surfaces. Vibration may be caused by misalignment of a drive component, or a component being out-of-balance.
What shaft fit do my bearings require?
- SHAFT FIT varies by bearing type and by specific application. The tolerances indicated below are general guidelines, and assume the following: solid rotating shaft, stationary housing, normal load conditions. For more specific info, feel free to contact our sales personnel.
SHAFT FITS
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
How often should I grease my bearings, and how much grease do they need?
- FOR STARTERS, note that most sealed bearings come pre-greased from the factory with a 25%-35% grease fill. This is all the grease the bearings will ever need, because the relubrication interval (explained below) is longer than the expected life of the bearing.
- DON’T JUST GUESS. It can be tempting to give the bearings a pump of grease each day, or to pump until grease comes out from under the seals. However, this effectively destroys the seal’s ability to keep contaminants out of the grease; and too much grease “churns” inside the bearing, generating resistance and leading to rapid heat build-up.
- FREQUENCY: The accompanying chart shows approximate relubrication intervals. Start at the bottom by choosing your speed; follow the line straight up until you meet the curve that matches your bearing O.D., then go straight left to see the relubrication interval for your bearing type.
- AMOUNT: To find ounces, [(OD in inches) x (width in inches) x 0.114]. To find grams, [(OD in mm) x (width in mm) x 0.005].
- FOR EXAMPLE, suppose your application has a 6209 ball bearing, running at 1,750 RPM in a clean, smooth machine for 24 hours a day, 7 days a week. A 6209 bearing has a shaft diameter of 45mm, an OD of 85mm, and a width of 19mm. Using the chart and the formula, the bearing only needs 8 grams of grease every 10,000 hours. If your grease gun delivers around 1.35 grams per stroke, that means the bearing needs 6 strokes every 13 months; you could average it out to a stroke every 8 weeks or so.
- When greasing a bearing by means of a zerk, make sure the zerk and the grease gun nozzle are clean, and if possible, make sure the zerk is always covered between greasings. Otherwise, you could be pumping dirt and contaminants straight into your bearings.
MOUNTED BEARINGS
What features should I look for in a mounted bearing?
- EXTENDED INNER RING – Since shafting is almost always undersized, it can “cock” in the inner ring, which can reduce bearing life by up to 66%. Longer inner rings reduce the cocking angle, and extend bearing life.
- ANTI-ROTATION DEVICE – The bearing’s outer ring needs to be able to self-align in the housing, without spinning and wearing out. An anti-rotation pin gives you the best of both worlds.
- TRUE BEARING STEEL – Some mounted bearings have carbon steel inner rings, based on the reasoning that the inner ring wears more evenly than the outer ring. But 52100 bearing steel has a yield strength of 325,000 lbs; carbon steel has a yield strength of only 53,000 lbs. Both rings should be true bearing steel.
- STEEL FLINGER – Protects the seal from damage, and provides a labyrinth to keep contaminants away from your grease.
- STEEL RETAINER – An all-steel retainer will be stronger, more heat-resistant, and more rigid than a plastic retainer.
- ANNEALED SETSCREW PORTS – When the race hardening process also hardens the setscrew ports, these can become distorted and brittle, leading to cracking or reduced holding power. Annealing the ports relieves the distortion and makes the threads more ductile.
What is the best method for installing mounted bearings?
- SHAFT PREPARATION: Wipe the shaft clean and remove any burrs that could cause the bearing’s inner race to deform when the setscrews are tightened down. Proper shaft diameter is CRITICAL. Check the shaft diameter against the specifications in the “Shaft Fit” table; if it’s not within those tolerances, its use may lead to premature bearing failure.
- MOUNTING: Slide the bearing (and collar, if applicable) onto the shaft in the desired position. DO NOT use anti-seize lubricant on the shaft or bearing. Leave the setscrews (and collar, if applicable) loose.
- BASE PREPARATION: Make sure the base of the mounted bearing and the support surface are clean and flat. Any unevenness in the surface can deform proper bearing fits and lead to premature failure. Securely fasten the mounted bearing to the support surface using the machinery manufacturer’s recommendations.
- TIGHTENING:
- Setscrew lock: Begin tightening both setscrews down alternately with the proper torque, until both setscrews are locked to the shaft at the proper torque.
- Eccentric collar lock: Place the eccentric collar on the bearing’s inner race and turn rapidly in the direction of rotation, until the eccentric grooves engage the collar to the bearing. Use a drift or punch in the hole of the collar and drive it sharply with a hammer in the direction of the shaft’s rotation. This will help to ensure the lock on the shaft. Tighten the collar’s setscrew using the proper torque.
How often should I grease my mounted bearings, and how much grease do they need?
CHAIN DRIVES
What features should I look for in roller chain?
- SOLID ROLLER – A split roller can deform under load. Solid rollers can take higher speeds and are more shock-resistant.
- WIDE WAIST PLATES – Thicker waists on the side plates are 30% more resistant to fatigue, and help resist elongation.
- PRECISION HEAT TREATMENT – A chain is only as strong as its weakest link. Computer-controlled heat treatment results in uniform chain strength.
- SHOT PEENING, BALL DRIFTING, FACTORY PRELOADING – Processes that relieve stress and deformities and increase strength and holding power.
What features should I look for in a sprocket?
- HARDENED TEETH – Chain rollers are hardened steel; if they run on an unhardened sprocket, the teeth will wear and deform very quickly. Bringing sprocket teeth near the hardness of the chain rollers will increase the life of the sprocket, without shortening chain life.
What are some guidelines for good chain performance?
- FREQUENT LUBRICATION. Bare metal-to-metal contact leads to wear and metal fatigue; therefore, good lubrication is essential to chain performance and life. Manual lubrication (brush or spout can every 8 hours) provides the lowest performance. An oil bath increases the speed limit by 7 to 10 times.
FEET PER MINUTE
|
- THE RIGHT OIL. Oil has to get between the moving parts of the chain to be effective. Smaller chain needs lighter oil; however, increasing temperatures require heavier oil. See the accompanying table.
OIL VISCOSITY
|
When should I replace my chain or sprockets?
- CHAIN wears internally. The pins, bushings, and rollers are in constant contact, and as they wear they lose small amounts of material. Although you cannot see the parts themselves, wear and corrosion may be indicated by reddish-brown material coming out when the chain is oiled. Chain also stretches as it wears. A chain should be replaced when it has stretched by 2.5% to 3%.
- A SPROCKET wears at the points where the chain contacts the teeth. As chain stretches and the rollers get further apart, they don’t drop into the gullets, but ride higher on the teeth. As the teeth wear at those higher points, they deform and “hook”, or start to bend to one side. By this point, the sprocket and the chain both need to be replaced.
V-BELT DRIVES
How can I get the longest life out of my V-belt drive?
- PROPER TENSION is often overlooked. All belts need to be tensioned when first installed, but they stretch dramatically during the first 24 hours of operation and lose their tension. This can cause them to squeal and can rapidly lead to sheave wear. Proper maintenance includes tensioning the belts at regular intervals throughout their life. New belts are available for high-power and HVAC applications that are more stretch-resistant; contact our sales personnel for more information.
- WORN SHEAVES can be a source of rapid belt wear. When tension forces a V belt to conform to a worn sheave wall, the belt runs hotter and its life will be shorter.
- MISALIGNMENT will lead to uneven wear. The belt should enter and leave the sheave groove in a straight line, or else the sides of the belt will wear out very quickly as they scrape against the sheave edges. Eventually, this can cause the belt to flip over in the groove, which will destroy it. Usually, sheaves can be aligned by using a straight-edge against the outer faces; for long-center drives, there are laser-alignment tools available.
What’s the best tension for my drive?
- A general rule of thumb is that tension can be estimated by measuring the deflection of the belt at the middle of the span. Under proper tension, the deflection should be about 1/64th the center distance.
- A closer estimate can be obtained from the table below.
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
- The exact tension depends on specific drive information: the diameters of the sheaves, the center distance, the speed and horsepower, etc. Contact our sales personnel for a drive calculation tailored to your specific drive.
When should I replace my sheave?
- Belt-drive efficiency depends on full contact between the belt and the sheave walls. As a sheave wears, the walls where the belt should ride go from being flat to being “dished” or concave. Therefore, worn sheaves dramatically reduce the efficiency of the drive. Some symptoms of worn sheaves are…
- NOISY DRIVE. As the walls of the sheave wear, the belt does more slipping than gripping, and tends to squeal. Belt dressing may reduce the noise for a while, but it does not restore lost metal to the sheave wall. A squealing drive may just need to be properly tensioned, but if the noise persists or returns shortly, check your sheaves.
- ABNORMAL BELT WEAR. When tension forces a V belt to conform to a worn sheave wall, it runs hotter and its life will be shorter. A misaligned drive will wear more quickly on one side than the other, and can even cause the belt to flip over. If you keep burning through sets of new belts, you should inspect your sheaves.
- VISUAL CUES. The worst sheave wear will be a highly-polished track in the sheave wall, deep enough that you can feel it with your finger. Lesser (but no less important) wear may be harder to spot with just your eyes. A sheave gauge, usually consisting of plastic wedges shaped like a new belt, can be inserted into the groove. If the gauge doesn’t fit squarely into the groove and you can see daylight around the edges, your sheave is worn and must be replaced.
GEAR REDUCERS
How should I select a gear reducer?
- The kind of reducer you need will depend on your application. The first information you should have handy is your input horsepower and speed, the output speed you need, and the method of mounting to the motor or equipment. From there, we can help you determine the style that best suits your needs.
- WORM GEAR reducers usually have the lowest up-front price tag. The input is at a right-angle to the output. However, since horsepower is transmitted by the wiping action of the worm across the face of the wormwheel, worm gears are high-friction and very inefficient. In a 50:1 reduction, less than 70% of the input horsepower is converted to output horsepower, and the rest is converted to heat. Depending on your reduction, then, you might want to consider whether the initial cost savings is worth the higher energy costs down the road.
- McGuire has an in-house assembly center for building modular worm gear reducers for drives from 1/3 HP to 20 HP and from 30 to 350 RPM (at 1750 input RPM).
- HELICAL GEAR reducers are more expensive, but are far more efficient than worm gear reducers, up to 96%. Input is parallel to the output. They can also handle greater horsepower in a smaller box, because multiple gear sets can achieve cumulative reduction in the same space. (Helical gears are used in car transmissions, for example.) Therefore, you may decide that the higher up-front price is worth the energy savings.
- McGuire has an in-house assembly center for building modular inline helical gear reducers for drives from 1/6 HP to 30 HP and from 7 to 630 RPM (at 1750 input RPM).