Smart Methods: Part 3
by Christer Idhammar
Note: This column is a continuation of the December and February P&P maintenance columns by Christer Idhammar. In those columns, Mr. Idhammar reviewed smart corrective maintenance methods that are valuable for both new and experienced maintenance personnel.
Before discussing smart corrective maintenance methods, I would like to say that I appreciate feedback from readers. If you have any new or old tricks of the trade that would fall under the category of “smart methods,” please send them to me so I can share your ideas with other readers. And many thanks to the author of the following method!
How to dry a wet electric motor. Apply a DC current, from, for example, a welding machine, to two of the three motor T leads of a three-phase motor. Apply about half of the loading rate for about thirty minutes. This procedure has saved many motors located in pits in our mill.
—Mark Humphrey, Alliance Forest
The following sections discuss products and techniques that help avoid over-greasing, provide better sealing, and keep belt tensions consistent.
OVER-GREASING. It is a well-known fact that over-greasing of bearings is just as big of a problem as under-greasing. Knowing how much grease to put in a bearing is still a big problem that lubricators must deal with. There are formulas that can be used, and suppliers can recommend the volume of grease to put in the bearing. The volume is often given in the number of strokes from a grease gun. However, depending on the type of grease gun, the volume using this method can vary over 100%!
Many products are available to help mills apply the correct amount of bearing grease. SPM Instruments of Marlborough, Conn., has a device called the Lubchecker that mills can put on the grease gun. It will measure and tell you when the grease reaches the bearing. UVLM Inc. of Centralia, Wash., has an instrument that listens for a change in sound, which indicates that the bearing has the right amount of grease. A new product from ASSALUB of Atvidaberg, Sweden, is an electronic grease volume meter that measures and displays the exact amount of grease delivered to the bearing.
When a bearing is running hot because it was over-greased and needs to be cooled, it is still very common for mills to apply water or air to the bearing housing. Is this what you do? Well, if so, it is the wrong thing to do, because you will only worsen the condition inside the bearing. The outer ring shrinks and the pressure inside the bearing increases. You should cool the shaft and possibly, at the same time, the bearing housing.
COMPOUND SEALING MATERIAL. It can be expensive to keep a store full of all different types and sizes of braided sealing material needed in a mill for pumps, refiners, and valve glands. Braided seals also have to be repacked while equipment is down and they require quite a lot of costly seal and cooling water. In fact, a refiner or a pump can typically use 11,000,000 gal/yr of water, costing about $5,500/year.
Manufacturers of compound sealing materials claim to provide seals that avoid most of the costs mentioned in the preceding paragraph. The compound can be injected in seal and valve glands and no seal water is required for pumps. If a leak occurs, the leak can be sealed while a pump or refiner is in operation. Tom-Pac Inc. of Montreal, Que., and UTEX in the U.S., are suppliers of this type of product.
HYDRAULIC MOTOR SHELF. A hydraulic motor shelf was officially recognized as one of the best maintenance products in Scandinavia last year. The advantage with this kind of hydraulic motor shelf is that V-Belts can be set at, and kept at, exactly the right tension. Belts are also very quick to change because the shelf can easily be moved and the motor does not require realignment. Energy savings are substantial and belt life is prolonged.