Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1336798
4 | January - February 2021 | www . machinerylubrication.com COVER STORY • Breathers: Restricted view of color-indicating desiccant from hydration never makes sense. • Guards: Mesh guards on belts, chains and couplings must be clean to inspect tension and alignment of moving parts. Impaired Heat Transfer Heat is a fundamental enemy of machine reliability, both the cause and effect of so many failures. Dust cakes form a thermal insu- lating blanket around the machine surface that impedes the ability for internal heat to escape and to be known. is causes the heat to build within the machine which can lead to an assortment of runaway problems. Many relate to the infamous Arrhenius Rate Rule (for every 10C increase in temperature, life is cut in half ). • Reduced Oil and Grease Life: Arrhenius Rate Rule (ARR) related to base oil and additive life. • Short Seal Life: Heat degrades seals more rapidly, causing them to harden, glaze, crack, crumble and loose elasticity. • Higher Rate of Corrosion: Most forms of corrosion are tempera- ture sensitive. • Shorter Filter Life (thermal fatigue): Many types of filters experi- ence thermal fatigue leading to cracks and rupture. • Shorter Motor Life: A 10C increase in temperature cuts electric motor life in half. • Viscosity Starvation: Abnor- m a l l y h i g h l u b r i c a n t temperature thins the oil (less viscous) which can cause higher rubbing, galling and abrasive wear. • Inhibited Film Strength: Heat c a n prematurely deplete important additives such as antiwear and antiscuff additives. Contaminant Ingestion e closer contamination (dirt and water) get to ingression points, the bigger the problem. Dust cakes hold particles near critical interfaces at seals, joints, hatches, ports and other high-risk ingression zones. • Grease Fittings: In many cases, caked-on dirt is so thick that grease nipples cannot be seen. e activity of cleaning the region prior to relubrication can cause particles to get pressed into the grease nipple port. Regreasing can then drive these particles into the core of the bearing where harm is waiting to be done. • Fill Ports: Oil mist cakes around fill ports and hatches place particles in close proximity to the opening during routine servicing (top-ups, oil changes, sampling and inspections). • Dirty Breather Media: Dust cakes packed around breathers interfere with air flow, in and out. Inhaled air across or through dirt can cause surge ingression of particles and lead to frequent need for breather replacement. • Sump Sediment: Over time dust cakes that draw particles into the machine result in sedi- ment buildup on the bottom of sumps, reservoirs and gear cases. Over time there can be more sediment in the sump than oil. e oil level gauge may show a full charge, but that is often not the case. Half the oil means half the oil's service life. • Short Filter Life: e job of the filter is to remove particles from oil. e more particles are permitted to ingress the harder the filter has to work to keep up with ingression. e result is shorter filter service life plus the added cost of labor to replace them. Dust Cakes Extract Oil from Grease A lesser-known problem asso- ciated with dust cakes is grease dry-out. Oil can be extracted from grease if there is either an absorbent path or a gravitational path. is is easily observed by placing a dollop of grease on absorbent cloth or paper. A portion of the base oil from the grease will be wicked out of the thickener. is hardens the grease, impairs mobility and reduces the oil content needed for lubrication. Dust cakes around exposed grease zones on bearings, gearing, hinge-pins etc. will have a similar effect. It's not much different than applying Oil-Dri (calcium bentonite) on an oily workshop floor or driveway. Fine dust cake parti- cles that build up have high surface area. ey slowly draw oil out of the grease in the machine. e more oil that is extracted, the more dust particles will collect, forming an increasingly thick cake. Resulting drier and harder grease inside the bearings, etc. will potentially have impaired lubricant flow, lubricant