Extending the life of throw-away gearboxes

Worm gearboxes are typically used as an inexpensive way to provide high, single-reduction gear ratios for machine drives and conveyors. These gearboxes are tolerant of start-and-stop operations and load variations, and are used with many types of food processing equipment.

In mixers or packaging machinery, worm gearboxes are often buried inside the processing machinery. In conveyor drives, they are mounted overhead. Their inaccessibility makes it difficult to maintain and service them. The result is that often, they are not well-maintained, resulting in potential drive component damage and wear, and faulty motion control.

The main drive component of a worm gearbox is constructed of bronze. Extreme pressure (EP) lubricant additives that would normally enhance the sliding friction properties of the gearbox can be corrosive to bronze. This bars the use of these helpful additives in the worm gear oil formulation. The result is worm gear oil with minimal additives, having to provide all lubrication properties through high-viscosity film strength.

Disposable gearbox

Working in partnership with a lubricant manufacturer, gearbox manufacturers identified a synthetic polyalphaolefin (PAO) lubricant that has become a standard oil for worm gears. However, the inaccessibility of the gearboxes still deterred proper maintenance of the systems.

To simplify maintenance requirements, one gearbox manufacturer designed a disposable gearbox filled with the standard PAO oil. The design offered maintenance personnel at food processing plants the opportunity to forego oil changes or repairs. Designed for 2,000 hours of operation, the gearbox is simply thrown away after 12 weeks.

Long-life food-grade lubricant

At a pizza-crust manufacturing plant, the standard oil change interval on its mixers, packaging machinery and conveyors was 2,000 hours. To improve gear lubrication and simplify maintenance, it switched to Molykote L-1146FG Synthetic Gear Oil, a Dow Corning product.

Unlike oils made in conventional fractionation processes, synthetic oil is made by combining smaller molecular building blocks to meet targeted performance specifications and to minimize impurities. The new oil contains a new-generation phosphorus anti-wear (AW) additive to reduce friction between the gears and extend service lifetime.

The formulation is non-corrosive to the bronze drive components. What is more, it is a food-grade lubricant. Plant management at this facility had adopted a policy of using only food-grade synthetic PAO products for MRO needs. Although in many cases these products exceed the unit cost of the conventional mineral oils they replace, their superior performance more than makes up for the difference. Standardizing on food-grade products also eliminated the possibility that plant workers would confuse one type of oil with another.

Using the new synthetic oil formulation, the standard oil change interval has now been extended to 9,000 hours in the disposable gearboxes, over four times the design life of either the conventional lubricant products or the synthetic lubricant used as OEM fill for the throwaway gearbox design.

As a result, the pizza-crust manufacturer can count on its machinery and conveyors to run for over a year before scheduling replacement of the throw-away worm gearbox.

In addition, friction within the gearbox was prevented to such an extent that the operating temperature during production dropped 11°C (20°F).

Maintenance savings in time and equipment are high, since machine uptime has increased dramatically. The PAO synthetic oil gives excellent lubrication at high and low temperatures, reduced volatility and compatibility with equipment designed for use with mineral oils. It conforms to USDA listing requirements applicable to meat and poultry plants, and is qualified for direct food contact under FDA regulations.

Instead of throwing out a gearbox every three months, the plant now sees a 350% increase in the equipment life because of the new worm gear oil. IL

For more information, visit www.dowcorning.com.

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