Machinedesign 1295 1011 Stainless Steel Gearbox 0 0

Design by Objective: Withstanding washdown

Oct. 1, 2011
High pressure. Hot water. Caustic chemicals. Combine these challenges and you'll understand what machinery must resist in harsh environments such as food

High pressure. Hot water. Caustic chemicals. Combine these challenges and you'll understand what machinery must resist in harsh environments such as food processing plants. To help your next design stay dry, we're showcasing a few washdown-ready products along with an inside look at specialized bearings suited for corrosive settings.

Stainless steel gearbox meets sanitation rules

The stainless steel K series speed reducer (KSS) is IP69K certified to withstand extreme dust, contaminants, high-pressure washing and steam cleaning, and caustic solutions. The KSS can accept up to a 3 hp input and outputs up to 3,400 in.-lb. What's more, the totally enclosed unit keeps contaminants out and food-grade lubricating oil in, offering maintenance-free operation. Three sizes come with a choice of keyed or keyless hollow shafts and single or double-sided solid shafts.

STOBER Drives Inc.
(606) 759-5090

Linear shaft motor handles harsh settings

The Linear Shaft Motor features a stainless steel magnetic shaft, suiting it for use in harsh and washdown environments. This non-cogging motor uses all-magnetic flux, enabling it to complete moves with submicron resolution. Its noncritical air gap allows material buildup on the shaft (such as dust) without a loss in linear force. A fiberglass sleeve on the inside of the forcer (coils) completely protects windings from water and debris; coils are further sheltered by epoxy resin that fills the forcer's interior.

Nippon Pulse America Inc.
(540) 633-1677

Medical-grade epoxy stands up to sterilization

EP42HT-2ND2MED (Black) two-component epoxy fully complies with the testing requirements of USP Class VI plastics. This medical-grade epoxy resists recurrent autoclaving and sterilizations including radiation, steam, ethylene oxide, and chemical sterilants. It also insulates electrically with a volume resistivity of more than 1,012 ohm-cm, a dielectric constant of 3.8, and a tensile strength exceeding 12,000 psi at ambient temperatures. Heat resistant to 450° F, it withstands inorganic and organic acids, alkalis, organic solvents, and aromatic hydrocarbons.

Master Bond Inc.
(201) 343-8983

IP69K gearmotor withstands washdown

The IP69K-rated stainless steel SANIMotor encapsulates all electrical components in thermally conductive epoxy resin, allowing use in ambient temperatures to 104° F. The motor is enclosed in 304 stainless steel tubing, sealed with rubber o-rings, and secured with hex bolts to prevent leaking. Two frame sizes are available — 34F and 49F — for the three-phase, 230-V SANIMotor. Each size is mated to seven standard gearing ratios, which output 345 to 8 rpm and rated torques from 7 to 500 in.-lb.

Bison Gear & Engineering Corp.
(800) 282-4766

Actuators sport stainless body, rugged seals

All-stainless-steel ERD electric rod-style actuators are designed for stringent food and beverage applications. A smooth, 304 stainless steel body and Viton seals equip the IP67-rated ERD for caustic cleaning environments. The actuator is available in stroke lengths to 12 in. Depending on the choice of ball nut or solid nut, it delivers up to 200 lb of thrust or speeds to 40 in./sec. Solid nuts made of engineered resins offer quiet performance at lower cost. Ball nuts offer positioning accuracy and repeatability with longer life.

Tolomatic Inc.
(800) 328-2174

Battling corrosion, one bearing at a time

The battle against corrosion in food processing applications is challenging, but it's a war that food and beverage manufacturers must wage because the impact of corrosive invasion is notorious: It weakens base materials, limits machine longevity, affects human health, and is unsightly to boot. In one tactic to win this war, washdown-duty ball bearings are being incorporated into machine designs.

Ball bearing products have changed considerably over the last 15 years. Manufacturers listened to end users' corrosion concerns and developed bearings that offer high load capacity and longevity in tough environments. Some have focused particular effort on improving housings, raceways, seals, and the bearing cage itself.

Material tradeoffs, special coatings
A major challenge for manufacturers is to create bearings that maximize corrosion protection while maintaining material strength and load capacity. Typically, materials with superior corrosion resistance lack sufficient mechanical properties, such as strength and hardness required for suitable bearing operation. Conversely, steels with the best characteristics for bearing operation offer unsatisfactory performance when exposed to harsh environments and reactive chemicals. That's changing, though.

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Bearing housings
Bearing housings are now available with specialized coatings, platings, 304 and 316 series stainless steels, as well as nonmetallic polymers such as PBT, polypropylene, and polyamide resins. Many of these nonmetallic polymers are enriched with antimicrobial agents that help kill microorganisms. Common coatings used on cast iron or steel bearing housings include powder epoxy paint, nickel, and nylon. Some offerings are more effective than others against certain chemicals, loads, and general environmental hazards. For example, stainless steel housings withstand acetone exposure quite well, unlike nonmetallic PBT housings. The key is to select the right housing material based on the application.

Bearing races and rollers
In addition to housing protection, the bearing itself also must be considered. Stainless steels are offered as inner rings, rollers, and outer rings in material grades such as 420, 410, 303, 304, and the most widely used, 440C. However, many stainless steels do not maintain the same load-carrying capacities of their ferrous steel counterparts. As a result, bearing capacity may drop as much as 20% below standard steel offerings. Another caveat: Stainless steels are not inert with many chemicals and environments. Therefore, many common ball bearing products include a plated option, with platings applied to the inner and outer ring raceways in the form of zinc chromate, low phosphorous nickel, nickel composites, or variations of chrome. Much like housings, the bearing itself should be selected based on the application and with performance expectations balanced against cost and functionality.

Outer geometry
Most corrosion-resistant products are designed and intended for use within the food and beverage industries. In these applications, it's important to avoid choosing a bearing with pockets or voids in and around the housing where food, moisture, and contamination can become entrapped. These areas facilitate bacteria growth and corrosion. Instead, choose a bearing with solid feet, solid underbodies, and a flat and smooth surface. This style is more effective at repelling contamination and hindering particle accumulation.

Lubrication and sealing
Many applications in the food, beverage, and pharmaceutical industries use washdown processes with a variety of chemicals to kill bacteria and microorganisms. These harsh processes can be lethal to bearings that are not adequately protected. The two most critical factors for successful antifriction bearing operation are effective lubrication and contamination prevention, yet high-pressure wash threatens both of these.

Moisture ingress into the sealed bearing cavity deteriorates lubrication, corrodes raceways and rollers, degrades contact surfaces, and leads to premature bearing failure. Therefore, the best means to prevent bearing failure is to protect lubricant stability and prevent contamination from entering the bearing cavity by using a premium sealing system.

Many sealing systems are available for washdown components. The most effective seals are 304 or 316 stainless steel shields that include a rotating flinger and at least three elastomeric contact lips on each side of the bearing. Rotating flingers help propel contaminants away from the bearing entryway. Furthermore, the larger the flinger's diameter, the more centrifugal acceleration is utilized, resulting in a more effective seal. These flingers may have elastomeric contact extensions as well. The three contacting lips of the main, non-rotating shield are shaped to allow excess grease to flow past, yet prevent moisture and contaminant ingress. The contact pressure of each seal lip is adapted to maximize seal effectiveness, while minimizing drag to allow for a wide operating speed range for the bearing. When the bearing is lubricated, the area between each contact lip forms a grease dam, which acts as a supplemental barrier to prevent foreign particle entry.

Additional sealing is often accomplished with end closures that completely seal the insert on one side of the housing. Closures typically snap into place and are held rigid to the bearing housing. If the shaft ends at the bearing, the bearing can be completely closed and protected; if the shaft continues beyond the bearing, end closures are available that allow the shaft to extend through them. These open-end closures often employ an additional rotating labyrinth for greater protection and reliability.

Another effective tactic to protect mounted ball bearings in washdown environments is to fill the sealed bearing cavity 100% with grease. This allows for a larger grease reservoir, builds a bigger grease dam in and around the seal area, decreases the impact of moisture invasion into the bearing cavity, and adds greater reliability for extended relubrication intervals. Most of these washdown-ready bearings are offered with H1-rated food-grade grease, making them suitable in food, beverage, and pharmaceutical processing machines.

Creative cage designs
Some of the latest developments in ball bearing technology include revolutionary cage designs, which help channel and protect lubrication near the rolling elements. If washdown procedures allow moisture to compromise the sealed bearing cavity, grease can become contaminated and depleted. The new cages prevent these problems by creating compartments that safeguard the lubricant near the balls, which allows them to be in constant contact with effective lubrication. The result is reduced wear, minimized friction, and less heat. In turn, the bearing does not require the aggressive relubrication intervals that bearings with standard cages need.

This month's handy tips courtesy of Galen Burdeshaw, Baldor's CO engineering manager for Dodge bearings. For more information, or call (864) 297-4800.

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