Grease sampling – how it should be done
The sampling of a representative specimen is the basis for a qualified analysis and diagnostically conclusive statement. This is particularly the case with taking grease samples.
Extracting a grease sample with the syringe:
If the grease sample is taken with the syringe, the grease is only sucked into the tube, which has an approximate length of 20cm. The syringe is not supposed to come in direct contact with the grease:
- Plug the tube onto the syringe cone;
- Clean the surroundings of the extraction site with the cleaning cloth; and
- Suck the grease into the plastic tube, watch the flow of the grease.
Depending on the scope of analyses, an analysis is possible starting from approximately 1gm of grease, which is the equivalent of 2cm of grease in the tube. If the tube is filled completely (8-10gm), all tests in the respective kit (1-4) can be done.
After sampling, pull the tube off the syringe. Bend the tube in the middle and put it into the sample bottle with the kink at the top.
Please note: Do not duct-tape the tube or the tube’s endings.
Taking a grease sample with the spatula:
If extraction of the grease with the syringe is not possible, you can use one of the three spatulas. This may be the case if you have to deal with hard to reach bearings and inoperative components or if the sample has to be taken at the sealing lip or from pressure relief holes:
- Clean the surroundings of the extraction site with the cleaning cloth provided in the kit;
- Scrape the grease off at the representative spots with the spatula;
- Collect the grease; which may escape due to re-lubrication directly at the sealing;
- Wipe off the grease sticking to the spatula at the lid or at the mouth of the sample bottle.
The spatulas provided in different versions and widths allow for a representative sampling.
Please note: If the grease is mixed in track at a slow rotation of the bearing before sampling you will obtain a diagnostically conclusive reference sample. Make sure via visual control that you only draw up used grease.
Taking a sample using the grease sampler kit:
- Ensure the tools are clean and tidy;
- Wear gloves;
- Take a sample container or grease sampler kit and install the grease sampler on the drain line of bearing housing or gear housing, see figure 1. The grease quantity in the image is 0.5gm, or 0.02oz;
- Using the pen provided, mark it with date of sampling and machine number/bearing position or with a unique identification referring to the report template; and
- Mark both the lid and container to avoid mismatch
If the bearing is accessible, use the stainless steel spatulas provided. The best sampling areas are on the cage bars, on the raceways or beside the roller set. Put the grease sample directly in the marked sample container but do not fill it completely with 0.5 grams being sufficient for one analysis. If the sample is also to be used later, for trend analysis for instance, take a bigger sample.
If the bearing is not accessible, use the tube (cut 10-15cm, or 4-6in) and syringe to suck grease through the housing by removing the grease nipples. In the case of sampling through grease escape holes, remove hardened and dirty grease before operation. On slewing bearings the inspection screw can be removed and tube inserted to collect sample:
- Pump grease;
- Fill 4-5cm (1.5-2in) of the tube with grease; and
- Place in the sample container waiting for analysis.
Be sure to keep half a centimetre (1/4 inch) of the tube clean to pump it back in the container. Grease should not reach the syringe.
These samples are less representative than those taken directly from the bearing, but can still help identify some issues.
Sampling set for taking samples on the slew ring bearing:
Grease samples are taken at the same time as the inspection measurements. Analysis of the used grease provides additional information about the raceway condition.
Bearings with grease sampling ports:
The grease sampling set comprises a plastic tube, various cap plugs, a suction device, a sample box for up to five samples and an information sheet, which describes the procedure in detail.
Take samples from the main loading zone.
Remove the screw plug selected for taking the sample - item 1 and if necessary item 2 opposite (figures 3 and 4).
Before taking the grease sample, cut the supplied tube at an angle of 45° so that it is slightly longer than the grease sampling port. Then insert the tube into the raceway area of the port (figure 5).
Make sure that the surface cut at 45° faces in the opposite direction to the direction of rotation (figure 6).
The sampling ports must be closed again with the screw plugs.
When the sample has been taken, close both tube ends with the plastic caps.
Number the grease sample and place it in the labelled sample box.
Add the necessary information (see grease sampling set in figure 2) to the top of the sample box.
Bearings without grease sampling ports:
If there are no grease sampling ports on the bearing, one or more grease samples should be taken at the seal. This area near a grease nipple must be cleaned and the sample should preferably be taken in the main working area.
During re-greasing at the prepared grease nipple (without rotation of the bearing), the first grease escaping from the sealing lip is taken as the sample (figure 7) and 3cm is sufficient.
Please note: Be careful when taking the sample or the result may be falsified by contamination.
Fe limit values: A limit value for iron (Fe) contamination in the lubricant depends greatly on the operating parameters and the lubrication intervals. Depending on the application, the value can be as high as 20,000ppm.
Sampling using the Grease Thief (T):
Tear open the Grease Thief bag and attach the relief-hole end of the Grease T piston-handle to the T-handle tool by inserting into the slotted rod. You may have to release the locking knob to expose the slot.
Pull back the slotted rod and thread the base of the Grease T into the female threads of the pusher tube, then insert the locking knob into the proper hole to set the depth of the sample.
Position 1 places the end of the Grease T 7cm from the opening of the bearing when fully extended. Each position increase adds 1cm to that depth. When changing position, measure and confirm that the proper depth has been set.
Position the pusher rod so that the red piston is flush with the end of the Grease T. The stinger on the Grease T will be sticking out.
Open the access plug, and fully insert the grease T and T handle into the drain until the stinger probe contacts the desired location.
Slide the pusher rod forward to core a grease sample.
When the pusher rod has been slid completely forward, hold it in that position as the T handle and Grease Thief are withdrawn from the housing and access hole.
Using a clean rag, wipe the excess grease from the T handle parts and the outside of the Grease T body, being careful not to contact the grease inside.
Remove the locking knob from the positioning hole and the slotted rod. Unthread the Grease T from the pusher rod, while allowing the slotted rod to spin with the Grease T body.
Before placing the yellow cap onto the Grease T for shipment, purge a small portion of the grease from the Grease T into the yellow cap to relieve any pressure build up from placing the cap on the full Grease T.
Once a small amount of the grease is in the yellow cap, slide the yellow cap on the Grease T just far enough to engage the thread as a friction fit. This will ensure the Grease T is full and no sample is lost through the purge holes.
Place the filled and capped Grease T into the shipping tube provided and thread on the cap to the shipping tube.
Affix the sample label on the tube, filling out all necessary information.
Place the shipping tube inside the shipping envelope and affix the proper postage. Send to the laboratory for analysis.