From a glass-half-full perspective, the relatively short life of electric motors in food manufacturing environments is a blessing in disguise, giving companies the opportunity to reassess their power transmission system when it's time to order a replacement motor.
Ten-plus years is the rule-of-thumb for induction motors in general industry, notes Mark Gmitro, business development engineer-food and beverage at Baldor Electric Co., Greenville, S.C. In sectors such as grain-foods production, 6-10 years is more likely, and in harsh environments like poultry plants, 2-3 years of useful life is not unheard of. Standard NEMA motors manufactured in recent years boast electrical efficiencies that rival premium motors, discouraging many organizations from upgrading.
As specified by the Energy Independence and Security Act of 2007, a 25 hp four-pole motor must attain a nominal full-load efficiency of 91.7 percent. Upgrading to a NEMA premium motor only improves energy efficiency to 93.6 percent. The difference becomes greater as motor size decreases, but even at 1 hp, a premium motor only boosts efficiency 3 percentage points.
Gearing upgrades, on the other hand, can result in substantial efficiency gains. Converting from worm to helical gearing can improve efficiency 10-30 percent, Gmitro says. Another 5-7 percent gain can be realized with a synchronous belt instead of V-belt drives. Better still, some components can be eliminated completely if a holistic review of the power transmission system is done. "It's an opportunity to increase efficiencies and reduce costs," he adds.
"In almost any factory, there will be a mix of worm gearing and spur gearing that is only 65-80 percent efficient but very inexpensive," suggests Peter Feil, vice president and general manager of Stober Drives Inc., Maysville, Ky. "They do the job, but they're very energy inefficient." Most of the loss is caused by friction in the worm set.
Minimal friction occurs in a helical bevel gear, regardless of the speed ratio. Because the teeth are angled, more than one tooth is engaged at any given time. Cost is the downside: A right-angle helical bevel gear can cost twice as much as a comparable worm gear, which also is more compact and can be used in space-constrained applications where the precision gear won't fit.
Prices for helical bevel gears have declined as their use in industry has increased, although the grinding, honing and hardening required ensure that they will command a premium over conventional gears, says Feil. The tradeoff is greater durability and less likelihood a production-halting breakdown.
Tight seals are a must when placing motors and gears into service in high-pressure washdown conditions, which is why Stober engineered a reducer with IP69K certification. The company recently released a stainless steel version. A stainless steel helical bevel from Baldor will be available in January, according to Doug McCallum, industry account manager, complementing a stainless-steel worm box already in distribution.
More efficient gearing can produce savings energy, McCallum points out. For example, a 2 hp motor coupled with a 70 percent efficient gear will deliver 1.4 hp to the application, the same output as a 1.5 hp motor paired with a 95 percent efficient gearbox.
Some manufactures are leapfrogging gear upgrades and adding variable speed drives (VSD) to their power systems, Gmitro says, particularly for the pumps and fans that account for two-fifths of the electricity consumed by industry. Large motors that are subjected to multiple starts are ideal VSD candidates, and as the cost of those drives falls, their use in food and beverage manufacturing increases.
Gmitro recalls a project involving a 50 hp starch pump that was controlled by a ball valve that was closed about 30 percent of the time. Upgrading to a VSD produced $12,800 a year in energy savings alone, for a simple payback of six months.
Unfortunately, the savings from small motors is considerably less dramatic, and food plants usually are populated with many of those. In an audit of a poultry plant's drives, Gmitro determined only 36 of its 180 drives were powered by motors of 5 hp or larger.
That's an argument for less advanced motor controls. Similarly, a gear that is engaged only sporadically might be better served by a worm gear and its no-slip advantage. Many factors must be weighed to determine optimal power transmission, and they require a systems approach, not piecemeal replacement.