Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/468007
4 | January - February 2015 | www.machinerylubrication.com FROM THE FIELD JEREM Y WRIGH T | NORI A CORPOR AT ION s winter weather settles in across much of the United States with cold fronts creeping in from the north, have you ever thought about the effects these tempera- ture changes can have on your equipment's reliability? All machines and lubricants have practical limits when it comes to operating temperatures. Often the focus is only on the upper limit, since high temperatures can wreak havoc on the health of the lubricant and the machine, as well as cause safety concerns in some cases. However, rarely do you hear someone discussing the lower limits. At extremely low temperatures, such as those experienced during the startup of equipment found outside on a cold winter morning, the fl uid within the housing can reach a point where it actually congeals and will no longer fl ow. This limit is called the pour point. In circulating systems, the viscosity becomes so high at this point that the oil fl ow is restricted. Components will then starve of lubrication, which leads to an early metal-on-metal death. Of course, circulating systems aren't the only ones that rely on oil fl ow. Imagine how a splash-lubricated gearbox handles a cool, thick fl uid. When these gearboxes are designed properly and using the correct fl uid viscosity, oil is brought up to the gear tooth interface and even to the shaft bear- ings and other reduction stages higher in the sump as the gearset runs through the oil sump level. When the oil viscosity is increased to the point where it will no longer fl ow, the submerged gear will push congealed "chunks" of lubricant out of the way and will not lift it to the other compo- nents within the housing that desperately need to be lubricated. Another side effect of the increased viscosity is a higher startup torque. This increased load may be enough to cause a catastrophic failure or at least consume a massive amount of energy because of the excessive friction. The effects on viscosity are not the only attacks the lubricant must endure from the cold. In extreme cases, blended base oils can begin to separate into different phases. This separation process is called stratifi cation. The additives are also susceptible to becoming insoluble at colder temperatures. When they become insoluble, additives tend to gravitationally separate from the base oil and form deposits at the bottom of the sump. If the equipment requires these addi- tives and they are in the form of a sludge or deposit at the bottom of the sump, the lubri- cant's performance will be hindered and the machine could be damaged. What is considered cold? Most base oils and greases are able to withstand moderate temperature dips to 0 degrees C and many to minus 10 degrees C without much decrease in performance. However, at minus 20 degrees C and beyond, some lubricants become unsuitable and begin to reach their pour point. The pour point is dictated by the base oil quality as well as the presence of certain additives. A good rule of thumb is to always select a lubri- cant with a pour point that is at least 10 degrees C lower than your lowest expected startup temperature. V i s c o s i t y HOW COLD Temperatures Affect Your LUBRICANTS A 56% of Lube-Tips subscribers say cold temperatures have caused problems for the lubricants at their plant