Tech Tip: Lubrication

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How often should I replenish the grease in my speed reducer?

Many speed reducers are “maintenance-free” and do not require periodic replenishment. These reducers will not have a fitting for adding grease. Higher ambient temperatures and more hours per day will shorten maintenance intervals so consult the manufacturers literature.

Do not forget to purge excess grease after replenishment – otherwise the excess grease may cause the reducer to overheat or the seals to fail. 

How do you ensure proper oil level for a gearbox?

Oil lubricated gearboxes have different ways to ensure an oil level for proper lubrication. The oil level can be determined by an overflow plug, bullseye gauge, oil sight gauge or dip stick.      

When filling a gearbox with oil, the unit should not be in operation, and the oil should be poured until it reaches the oil level required by the gearbox manufacturer. During operation, the oil either splashes and is pumped if the gearbox counts with a forced lubrication system. As the oil circulates in the unit, the oil level gauge is likely to display a different level from the initial fill. This is completely normal.

Filling a unit during operation may overfill the unit. This usually results in overheat, which later results in premature failure. If there is a need to check if the oil level meets the manufacturer’s requirements, or if there are signs of leakage, it is recommended to stop the gearbox from operation, let the unit cool at room temperature and re-check oil level.

 

What should I consider when my application's ambient temperature is above the standard clutch temperature limit?

The standard temperature limit on a clutch is usually dependent on the lubricant being used. A rotating clutch will generate its own heat as well, so a high ambient temperature plus temperature rise caused by rotation can reach a temperature where many standard oil and grease lubricants start to experience thermal breakdown. High temperature greases are available that can operate at ambient temperatures above the common 100°F limit most clutches have.

What are the effects of ambient temperature on oil lubrication?

In the market, there is a variety of applications that work under extreme ambient temperatures. There are applications where gearboxes drive conveyors on freezers, as there are applications where gearboxes drvie rollers forming molten metal on steel mills. 

On cold ambient temperature applications, the oil viscosity increases, causing possible issues during the start-up of the gearbox. And on hot ambient temperature applications, the oil viscosity is reduced which leads to metal-to-metal contact, resulting on wear and failure of the gearbox.

It's important to lay out what the ambient temperature range of the application is (minimum and maximum ambient temperature) and compare to the standard operating conditions of the gearbox. This way, a solution can be developed to suit the application. 

Solutions can be as simple as selecting the right oil viscosity for the application and/or a more rigorous maintenance schedule. As the ambinet temperature widens, the use of accessories such as oil heaters and coolers can be selected to optimize the life of the lubricant, and, as a consequence, the life of the gearbox.

How do I use oil analysis for determining gearbox condition?

Oil analysis is a great tool for determining gear box condition. It's important to have a base line for comparison so always sent at least one clean sample analysis.

For consistency, the oil should be pulled from the gearbox from the same point or port every time. Only if it is safe to do so, oil should be pulled while the reducer is running at operating temperature. Otherwise, sample as soon as possible after shutdown. Ideally the sampling point should be where the oil turbulence is greatest. If pulling the sample from a port, the port should be caped when not in use to prevent contamination. Oil should drain directly into a clean container and the container sealed as soon as possible to prevent contamination.

What do we need to check when changing sheaves?

Changing sheave diameter is an easy way to change the output speed of a reducer. When changing from a larger sheave to a smaller one it necessary to calculate the overhung load to make sure the input bearings will not be overloaded. If calculation information is not available, follow the rule of thumb that the new sheave diameter is at least three times larger than the shaft diameter.

Grease Storage

Grease should be stored in a cool, dry clean environment.  Do not stack multiple boxes and always stack tubes and cartridges in a vertical position.   Oil tends to separate out from tubes and cartridges left on their side for extended periods of time.

Why is Proper Motor Lubrication Critical?

Lubricant compatibility with the factory-installed material is critical. Mixing incompatible lubricants may cause the mixture to lose all of its lubricating abilities very quickly causing premature bearing failure. Also, it is important to never over grease. Over greasing can cause excessive bearing temperatures, premature lubrication breakdown and bearing failure. You should re-lubricate based on the motor instruction guide.

What are the three (3) Cs of lubricant storage?

Avoiding Contamination of product.
Preventing Confusion of what the product is (and its usage).
Providing Containment to prevent environmental pollution.

Determining the Proper Amount of Bearing Lubrication

It is very important to select the right amount grease when lubricating a bearing.  Under lubrication can cause too much friction and, therefore, increased wear and heat.  But, over lubrication is just as bad.  It can cause increased fluid friction which leads to increased heat, increased torque and shorter operational.  As a general rule of thumb, the grease fill for low speed applications should be 75-90% of the free volume; medium speed applications 35-50% of the free volume; and high speed applications 10-30% of the free volume.

What is the Most important Property of a Lubricant?

The most important property of a lubricant is viscosity. In general terms, viscosity is a fluid’s ability to resist motion. A high viscosity means the fluid is thicker (ex. molasses) and does not flow as easily as a low viscosity fluid (ex. water). A higher viscosity fluid will typically make a thicker film between the moving surfaces and support greater loads.

The information provided in Tech Tips is not meant to be all-encompassing, but rather to draw attention to and provide information about the particular subjects covered. All suggestions and recommendations contained in Tech Tips are based upon information that is believed to be accurate to the best of the experience and knowledge of PTDA’s contributing members, but are made without guarantee or representation as to results. PTDA and Tech Tip contributors expressly disclaim any warranties or guaranties, express or implied, as to the accuracy or completeness of any information published in Tech Tips, and disclaims and makes no warranty that the information in Tech Tips will fulfill any of your particular purposes or needs. PTDA and Tech Tip contributors disclaim liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on Tech Tips.