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2014SumShotcreteEMag

Nozzleman Knowledge Because greases’ protective properties in wet- mix pump applications are temporary, to be effec- tive, grease must be continuously replenished before mixing actions alter the grease layers’ beneficial properties. To accomplish this, grease intervals must occur far more frequently than most operators realize. Because unintentional mixing of concrete slurries and grease does not occur with typical construction equipment, most mechanics and operators are unaware of the required timing of grease replenishment for wet- mix pumps. Even veteran operators may not be able to accurately pinpoint the optimum interval Fig. 3: Properly lubricated shaft bearing at to replenish grease. 3000 hours Wet-Mix Grease Requirements permit valve rotation between material cylinders during pumping. Are Unique Additionally, swing-tube-type pumps use Experience proves, despite a rigorous greasing large, sealed outlet bearings that are directly regimen, abrasive concrete slurries will still exposed to and vulnerable to damage from pres- manage to enter, contaminate, and damage critical surized abrasive slurries. Insufficient or con- seal and bearing surfaces. taminated grease within any of these critical Once past the seal, concrete slurries tend to points can cause immediate, severe damage. harden, and will quickly plug the small grease When grease is properly applied at seal and replenishment grooves within the bearing surface, bearing surfaces, it lubricates and protects, but effectively ending the component’s ability to also acts to fill available space between the accept future grease. Without sufficient grease, bearing, shaft, and sealing surface, thus denying abrasion and corrosion will permanently damage access to incoming abrasive slurries. To accom- the affected bearing surfaces. plish this, a greasing device must be connected At this point, complete breakdown and disas- to a permanently affixed grease fitting. Applied sembly is the only viable option to prevent a major under pressure, grease must flow through a series bearing failure. of small drilled passageways that direct grease to This is why wet-mix pump grease require- completely fill and coat the bearing surfaces. ments are unique. In addition to normal replenish- Because functioning grease fittings act as one-way ment, greasing during the washout process is valves, greases cannot be pushed backward and required to flush accumulated slurry residue from out of the way by pressurized slurries attempting bearing surfaces before it can harden. to flow into the bearing surfaces. During each washout, concrete slurries and contaminated grease must be flushed from seal Why Grease Doesn’t Work and bearing surfaces by vigorously adding addi- Applying grease does not provide permanent tional grease until a clean flow of grease is visible lubrication. When grease is used in wet-mix pump outside the seal surface. If this critical step is applications, its benefits are temporary at best. omitted even once, slurry residue can remain and Grease within a bearing area does not break down harden within the sealed bearing assembly. Count- or disappear from use. Rather, as the bearing less major failures can be directly attributed to surfaces are rotated, grease is slowly pushed improper on-the-job wet-mix pump greasing/ aside. With continued movement, contamination flushing procedures. in the form of concrete slurry can enter the bearing To provide optimum bearing service life, lubri- area and mix with the remaining grease to form cation of the greaseable components of a wet-mix a corrosive, abrasive paste. Even though grease pump requires two distinct steps. The first step is is present, the protective properties of the grease rigorous grease replenishment during use. Manu- are lost. Contaminated grease has the abrasive facturers may recommend specific intervals; properties of sandpaper, so continued movement however, veteran operators replenish grease far causes severe wear and permanent damage to the more often. Because excess greasing cannot affected bearing and seal surfaces. damage wet-mix equipment, it is best to be safe. 34 Shotcrete • Summer 2014


2014SumShotcreteEMag
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