A gearbox is used to control the operating speed of industrial equipment. Proper selection, gearbox care and maintenance of gearboxes is critical. Failure of the gearbox causes the equipment and associated plant to stop.
A gearbox is selected for the duty it must perform. It converts a high input speed to a lower output speed and so permits one driver element, such as an electric motor, to do numerous duties. Each selection must take consideration of the following points.
For example, in the selection of a gearbox to be direct coupled to an agitator for a stirred tank, consideration must be given to the distance the output shaft bearings are apart. Bearings positioned further apart cope better with the bending forces generated by the paddles located at the end of the agitator shaft.
The load type will affect the selection of the gear type. Steady, continuous loads can be accommodated by spur gears, but impact loads can break spur gear teeth. A more robust gear to use in impact load situations would be a helical gear. This gear shape offers more tooth cross-sectional area and because of the helix dissipates impact forces axially and tangentially.
Another style of gearing often seen on slow moving, high load applications is the worm and worm wheel. Planetary gearboxes are available where space is limited for standard design gearboxes.
Gearbox Care
A well-selected gearbox will have a long service life. Long term gearbox care and maintenance will involve checking oil levels and for critical or expensive gearboxes checking oil quality. Oil quality ought to be tested at least every two years for stationary plant and every year for mobile plant. More often if the loading or service duty is arduous. A simple site test for gearbox oil is to take a sample and look at the color, note the smell, look and feel for presence of grit and feel the slipperiness compared to fresh oil. If you are concerned, then send a sample to a lubrication test lab.
An oil analysis should include tests for the oil’s lubricity, changes in the oil’s condition, condition of additives, solids particle counts for larger than 2-, 5- and 15-micron particles, moisture pick-up, dust/dirt contamination and the metals in the oil.
The choice of lubricant is critical. The oil must retain its properties at the operating temperature. The gearbox manufacturer is best able to advise the oil to use. Where the manufacturer cannot be contacted, one of the major oil companies can offer practical suggestions on the oil to use.
Mixing of different oils in the same gearbox is poor gearbox care practice. Unless you can tell the oil supplier with certainty what oil is already in the gearbox so a match can be specified, do not cross mix oils. Mineral and synthetic oils are not compatible. It is better to drain the old oil out, flush the gearbox through with the new oil, put in the new oil to the required level and run the gearbox for two to three hours and finally dump, flush and refill the gearbox again.
Breathers are fitted to prevent shaft seals blowing out as the internal pressure rises when the gearbox is warming up to operating temperature. A breather allows moisture in the air and dirt from the surroundings to enter the gearbox.
Locate and protect the breather to reduce the risk of contamination. Check with the gearbox manufacturer to see if a breather is needed and if not then do without it.
Breathers in dusty locations require an air filter to clean dust particles 2 micron and smaller. Where they are exposed to hosing down, they must be protected from water ingress by shrouding or by locating the air intake at the end of a hose extended to outside the wash down region. Ensure that the hose is well clamped at the gearbox and breather intake.
Unexpected high working loads can occur that will destroy gearboxes. For overload conditions shear pins can be installed in the drive train or motor overload protection can be fitted to the power supply. For those services where impact loading is normal such protection is mandatory.
A belt or chain drive gearbox should be oriented so the forces in the drive pull the gearbox down onto its feet. Where the orientation of the gearbox causes the gearbox to be pulled off its feet there is a risk the feet will break from fatigue caused by fluctuating loads. In this case additional clamping of the body to the support frame may be necessary.
Gearbox Maintenance
When a gearbox is open cleanliness is critical. Dirt and dust entering bearings and gear teeth spaces will cause wear and rapid failure. If gears with chipped teeth are reused, chamfer the chipped edges to remove loose metal.
Gearbox bearings may require pre-loading to a minimum bearing load to prevent excessive noise and wear. Preloading bearings ensure that the rolling elements are properly bedded onto the races and prevent the rolling elements skipping and sliding around the tracks.
Mike Sondalini
Mike Sondalini is a Senior Consultant at PWWEAM System-of-Reliability. BEng(Hons), MBA, CPEng. As a consultant and trainer, Mike was able to present his insights to his clients, suggesting innovative approaches to plant and equipment reliability. Their feedback was resoundingly positive. Efforts which earned him an international reputation for articulate, out-of-the-box articles on plant and equipment reliability, life-cycle EAM, maintenance management, work quality assurance, and team building. After decades of dedicated research, Mike authored “Industrial Manufacturing Wellness: The Complete Guide to Successful Enterprise Asset Management” a revolutionary approach on how maintenance and physical asset management systems should be run, the book detailed who, what, where, when, why, and how outstanding reliability could be achieved. Each step based in scientific and mathematical understanding to ensure repeatability of results and optimal outcomes.
Oh "Overall Equipment Effectiveness", I've heard about that before! Unfortunately, in many facilities, that's all OEE (Overall Equipment Effectiveness) is to the personnel. Something they heard of, talked about or read about. Many maintenance departments today still do not effectively utilize the OEE tool even though it's widely used among the world class companies.
Oh "Overall Equipment Effectiveness", I've heard about that before! Unfortunately, in many facilities, that's all OEE (Overall Equipment Effectiveness) is to the personnel. Something they heard of, talked about or read about. Many maintenance departments today still do not effectively utilize the OEE tool even though it's widely used among the world class companies.
Contrary to popular opinion, a centrifugal pump is not designed to develop one head at a single capacity as requested by the pump purchaser. In fact a pump is designed and produced to supply a whole range of head-capacity conditions as identified on it’s performance curve. The pump will operate on that curve if it is driven at the particular speed for which the curve is drawn.
Contrary to popular opinion, a centrifugal pump is not designed to develop one head at a single capacity as requested by the pump purchaser. In fact a pump is designed and produced to supply a whole range of head-capacity conditions as identified on it’s performance curve. The pump will operate on that curve if it is driven at the particular speed for which the curve is drawn.
Ask for a modern centrifugal pump recommendation from your favorite supplier and chances are he will recommend one of the standard pump designs that conform to either the A.N.S.I., I.S.O. or D.I.N. specifications. On the surface that might seem like a good recommendation, but the fact is that all of these designs will cause you maintenance problems. Refer to the illustration prior to diving into the details of the obvious problems found within these designs.
Ask for a modern centrifugal pump recommendation from your favorite supplier and chances are he will recommend one of the standard pump designs that conform to either the A.N.S.I., I.S.O. or D.I.N. specifications. On the surface that might seem like a good recommendation, but the fact is that all of these designs will cause you maintenance problems. Refer to the illustration prior to diving into the details of the obvious problems found within these designs.
It's important to find out if material flows are present or not throughout a bulk-processing facility; material cost savings and increased plant efficiency can offset an investment in monitoring. Most bulk solids processors can do this using low-cost acoustic emission-monitoring technology.
It's important to find out if material flows are present or not throughout a bulk-processing facility; material cost savings and increased plant efficiency can offset an investment in monitoring. Most bulk solids processors can do this using low-cost acoustic emission-monitoring technology.
The most common question asked by seal salesmen is "what are you sealing?" This is usually followed by asking about shaft size, product, temperature, speed, stuffing box pressure and any other operating conditions they can think of. The problem with this simplistic approach is that you would have to have a very large data bank of information to reference a particular problem so as to be able to make a sensible seal recommendation. There is a much more logical approach to the problem that we will be discussing in the following paragraphs.
The most common question asked by seal salesmen is "what are you sealing?" This is usually followed by asking about shaft size, product, temperature, speed, stuffing box pressure and any other operating conditions they can think of. The problem with this simplistic approach is that you would have to have a very large data bank of information to reference a particular problem so as to be able to make a sensible seal recommendation. There is a much more logical approach to the problem that we will be discussing in the following paragraphs.
Sizing electric motors correctly for hydraulic power units can save a sizable amount of money over the life of the equipment. If system pressure and flow are constant, motor sizing simply boils down to the standard equation: hp = QP / 1714EM
Sizing electric motors correctly for hydraulic power units can save a sizable amount of money over the life of the equipment. If system pressure and flow are constant, motor sizing simply boils down to the standard equation: hp = QP / 1714EM
