Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/847153
access was drastically restricted. When this was the case, I would look up the bearing dimensions online. Once we had our measurements and figured out the calculation, we were in the ballpark for how much grease to put in the bearing. For example, let's say a bearing requires 1 ounce of grease. What is an ounce of grease? One pump? Ten pumps? Who knows? Even if the grease gun is rated for a certain amount, it is not always accurate. Therefore, it is imperative to calibrate all grease-dispensing equipment at your facility. Use a kitchen or postal scale to determine the weight in ounces per stroke of each grease gun. You can find quality scales for less than $15. At our facility, one of our maintenance coordinators borrowed his wife's kitchen scale for us to use. I highly recommend you refrain from stealing your wife's scale and instead buy one specifically for this purpose. At our plant, we line the scale with a rag, zero it out, then squirt 20 pumps of grease onto the scale and divide the total weight by 20 to get an average. We then label each gun with the average volume per stroke. That way the delivery means our technicians use doesn't matter. We can still ensure the bearing is receiving the proper volume of grease. Knowing the quantity of grease the bearing needs, we can calculate how many pumps it will take based on the gun's average output per pump. We also utilize battery-powered grease guns with a digital readout. These are calibrated with the same method. DETERMINING RELUBRICATION FREQUENCIES Our next obstacle was determining how often to apply this amount of grease. There are multiple tables, charts and calculators for establishing the proper frequency. The major factors in determining relubrication frequency are load, operation time, type of bearing, speed, temperature and environment. Keeping these factors in mind, the formula we use is: T = K x [(14,000,000/n x (d0.5)) – 4 x d], where T = the time (in hours) until the next relubrication, K = the product of all the correction factors, n = speed (revolu- tions per minute), and d = the bore diameter (in millimeters). The correction factors account for temperature, moisture, contamination, vibration, position and bearing design. Fortunately, most of our equipment runs at about the same speed, temperature and vibration. We also use very similar bearing designs. This leaves us accounting for mois- ture, contamination and position. It is astonishing to see how small changes can affect the time between regreasing. For instance, mounting a bearing at a 45-degree angle or with temperatures of more than 150 degrees F will cut the interval in half. At our mill, contamination and mois- ture are the greatest challenges after installation. We use the same style of bearing in a variety of applications. One is indoors but contends with some light COVER STORY