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!)

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.

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.

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

Up Front

Worth Another Look
Just relying on the oil analysis lab technician to give the right diagnosis is not always enough! While reviewing oil sample reports for a Cummins 855 big cam, we noticed that fuel content of the oil had been reported at 2.4 percent on the last sample. This was well within the trigger point for the lab, but when viewed against the average of 1.2 percent in the previous reports, we were concerned.

We checked the maintenance records and found that an injector change-out had been performed 150 hours before this sample was taken.

On investigation, we found one of the fuel-sealing O-rings had been nicked. This could have escalated into a fully blown seal with consequent severe fuel dilution. If this problem had not been found, it could have easily cost more than $50,000 in downtime and repair costs.

This is a perfect example that secondary diagnosis by house personnel is a good idea. (Submitted by Jack Denz, Aggreko International. Thanks Jack!)

Book Bits

The Basics of Multigrades
From "The Practical Handbook of Machinery Lubrication":

Multigrade oils are made by blending a low-viscosity oil with special additives called Viscosity Index Improvers. For example, when these polymer additives are blended in the correct proportion with an SAE 15W oil, the oil flows like an SAE 15W oil at low temperatures and like an SAE 40 oil at high temperatures. The result is an SAE 15W/40 oil that will provide wide protection over an extended temperature range.

Multigrade oils have five main advantages over single grade oils. These oils offer:

(a) One oil for year-round use.

(b) Improved low-temperature starting.

(c) Excellent high-temperature performance.

(d) Improved overall fuel economy by providing less battery drain on cold starts, less idling time and faster warm up.

(e) Faster, full-pressure lubrication over a wider temperature range. That is, an SAE 15W/40 oil provides full flow lubrication in approximately 1 minute, and 45 seconds at -25°C compared to an SAE 30 oil which requires approximately 3 minutes and 15 seconds to achieve full flow lubrication.

Today's Tip

During the cold start (wintertime) of a hydraulic system the pop-up indicators on the filters can alarm (turn red). When the system is operated by a skilled technician who understands the reason, there is no problem.

However, when an operator mistakenly thinks that the indicator popped up during a cold startup (nuisance alarm) when actually the filter is plugged with dirt, the filter goes into by-pass and the system can be contaminated.

To solve this problem, most of our systems also have pressure differential and temperature sensors. An alarm will sound only if the pressure differential setting is exceeded at 40°C. We have found this to be more reliable. (Submitted by Remco Bolderink, Project Coordinator, KENZ offshore Service. Thanks Remco!)

Q & A

Getting the Dirt on Dirt
"What are the elements I should look for in elemental analysis to detect dust and dirt contamination of my lubricants?"

Solid particles are one of the most destructive contaminants. Dust and dirt getting into the reservoirs from the environment and poor lubrication practices are the most common source of surface damage and wear. Maintaining lubricants free of dirt is a smart proactive action that can significantly increase the life of your machinery.

Consider this: silicon (Si) is an indicator of dirt in our lubricants. The earth's outer layer, is 4 to 60 kilometers thick. The crust, as this layer is known, is rich in oxygen and silica with lesser amounts of aluminum, iron, calcium, potassium, sodium and magnesium.

Average composition of the earth's crust:

SiO2 - 58.09%

AlO3 - 15.35%

FeO3 - 7.29%

Ca - 3.6%

Na - 2.97%

K - 2.57%

Mg - 2.11%

This indicates that the predominant elements are silicon (Si) and aluminum (Al). Keep in mind, however, that not all the places in the world will have the same metals in the same proportion. For example, the presence and proportion of metals in mining environments differ from those in coastal or industrial environments.

Dust and dirt composition in the working environment are also affected by process materials. If you want to know their exact composition, place an open container with new lubricant next to your equipment for several days. Shake the sample, send it to your lab, and compare the analysis results with your new oil base line for elemental analysis elements increase.

Use a ratio of elements present to identify dirt ingression (for example, Al:Si:Ca = 1:4:2).

Note that emission spectroscopy can not detect 100 percent of the elements because of particle size bias.

Gerardo Trujillo, Senior Technical Consultant, Noria Latin America