In This Issue:

• Up Front: Particle Counter Reveals Filtration Problem

• Book Bits: Influence of Contaminants on Bearing Life

• Today's Tip: Implementing an Oil Loss Control Program

• Q & A: How Much Grease Is Enough?
  

Up Front

Particle Counter Reveals Filtration Problem

We recently got a particle counter to use onsite. We took a sample from the hydraulic system on the secondary arm of our No.3 paper machine. The filter on this system is 3 microns, so we expected to find that the ISO cleanliness level to be at least 15/13.

We were shocked that this system was operating at an ISO 22/20 - incredibly dirty for system using a servo-valve. We started by changing the filter, checking that it wasn't in by-pass and looking for areas of ingression. Everything checked-out all right.

After further investigation, we noticed on the schematic of the system that almost all of the flow was circulating between the pump through the tank by the relief valve. The flow needed to feed the cylinder was so low that only a small amount of oil was circulating through the filter.

We installed the filter where all of the flow had to circulate through the filter and instantly the particle count went down to 14/13. Having a particle counter onsite was instrumental in discovering this problem. (Submitted by Richard Marois, Mechanical Supervisor, Kruger, Inc. Thanks Richard!)

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Book Bits

Influence of Contaminants on Bearing Life

From "The Practical Handbook of Machinery Lubrication":

In general, the important parameters influencing bearing wear are contaminant particle size, concentration, hardness and lubricant film thickness. Increases in all of these parameters except film thickness, will increase bearing wear.

Increasing lubricant viscosity will reduce bearing wear for a given contamination level.

Bearings operating in a contaminated lubricant exhibit a higher initial rate of wear than those not running in a contaminated lubricant. But, with no further contaminant ingress, this wear rate quickly diminishes as the contamination particles are reduced in size as they pass through the bearing contact area during normal operation.

More information about "The Practical Handbook of Machinery Lubrication".

Today's Tip

• If you decide to implement a program to control oil losses, one of the first steps you can take is to check records of the amount purchased compared with the amount sent for disposal. Try to account for the difference by looking for leaks, products consumed in the process, evaporative losses and products wasted due to contamination or misapplication.

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Q & A

How Much Grease Is Enough?

"All of the formal training I've had on the application of lubricants suggests that on greasable bearings, one should never pump in so much grease as to push out the external seals.

However, the instruction manual that comes with Dodge Type-E bearings states: "Operation in presence of dust, water or corrosive vapors--Under these conditions the bearing should contain as much grease as speed will permit, because a full bearing with consequent slight leakage is the best protection against entrance of foreign material".

Won't this just ruin the seal and allow for easier entrance of foreign material? I currently teach my technicians to add the amount of grease as determined by the SKF formula G = DB/10, where G is grease in ounces, D is bearing OD, and B is bearing width; or as I've read in Lube-Tips, one shot per inch of shaft diameter. Is this not enough in dusty environments? "

Several factors influence the quantity of grease that would go into a bearing at the selected interval. Critical factors include:

1. Design of the bearing (plain, roller, ball or spherical roller).

2. Type of shield used in the bearing.

3. Size and speed from which to calculate dN values.

4. Viscosity of the lubricant in the grease.

The Dodge Type-E bearing has a shield and lip seal configuration, with an option for an additional two-stage lip seal. This type of seal, by design, will allow for discharge of grease without damage at the outer perimeter of the seal. You could consider this a type of shielded bearing configuration.

A SEALED bearing is not designed to be purged. If you apply too much grease too quickly, you can rupture the seal and compromise the life of the bearing.

If you look closely at the manufacturer's guidelines you should see both general and specific directions for relubrication, including frequency and quantity for a given speed and load. The OEM (Original Equipment Manufacturer) parameters are typically the best starting point for relubrication practices. The OEM will also suggest that if you have a highly aggressive environment that it may be necessary to adjust the interval or volume to increase the amount of grease to the bearing. The SKF formula also provides a good starting point. Again, the calculated value must be adjusted to accommodate the environment.

The decision to flood or purge a bearing should be taken within the context of bearing construction, production environment and OEM guidelines. This is rarely a simple question.

Mike Johnson, Senior Technical Consultant, Noria Corporation

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