Safe lubricants may limit the performance of components in food processing and packaging machines. So machine builders have come up with ways to minimize these limitations.
Lubricants used in machines that handle food and beverages must be nontoxic. To achieve this result, they’re prohibited from containing ingredients used in other lubricants to enhance performance characteristics such as wear resistance and corrosion resistance. This restriction applies especially to H1 lubricants, which are used where they may contact the food or beverage (see box, “Primer on food-grade lubricants”). H2 lubricants have fewer limitations because they don’t contact the food.
These ingredient restrictions limit the effectiveness of lubricants used on bearings, gears, chain, and other machine components, especially in severe operating environments that are common to food processing and packaging. In canning operations, for example, the principle environmental factors are water washdown and high temperatures.
As a result, those who manufacture food packaging machines must find ways to either compensate for the lubricant shortcomings or boost lubricant performance. Here are some of the ways in which they handle this performance issue.
Machines in food and beverage plants are frequently cleaned with water or steam, which washes away or dilutes the lubricant in machine components. You can do two things to prevent this problem, according to Ricardo Hein, area manager for international business, Castrol Industrial North America, Downers Grove, Ill:
• Install protective guards around the machine components or seal them to prevent the lubricant from washing away.
Or, you can teach maintenance personnel to avoid washing the lubricated areas when cleaning.
• Select either a mineral-based (petroleum) or synthetic lubricant with good water resistance. Synthetics are required for extreme temperatures (over 180 F, and under O F).
Be sure that the lubricant also has good wear resistance, shear stability, corrosion resistance, and oxidation stability (for long life) by consulting the manufacturer’s selection guide. These guides generally list the main performance attributes of each lubricant. They may also include pertinent data from ASTM or other tests used to evaluate lubricant characteristics.
Hot and dusty ride
The conveyors that transport food from processing to packaging operations contain drive components such as bearings, geared speed reducers, conveyor chain and sprockets, and belt sheaves. In most cases, H2 lubricants suffice for these components. But if the food is exposed to the lubricant, H1 is required.
A differential motion conveyor, for example, moves food products to the packaging area by cycling slowly forward and quickly backward. The X-Force conveyor, manufactured by the Food Engineering Corp. (FEC), Minneapolis, uses grease-lubricated spherical roller bearings to support the conveyor drive shafts. The bearings operate at 200 to 800 rpm, which generates enough heat to soften some greases and cause them to drip. Because the conveyor is typically in an exposed food area, H1 lubricant must be used.
“Some of the H1 greases that we tried in these bearings overheated,” says FEC project leader Tim Batman, “causing the bearings to fail.” Eventually, the company found an H1 grease that inhibits heat buildup, and it has prevented further bearing failures.
“Dusty environments are also a problem,” continues Tim Batman. “For example, dust from sugar gets into conventional bearings and prevents the lubricant from maintaining sufficient film thickness.” This causes overheating, which breaks down the lubricant, in turn causing more overheating, until the bearings become pitted and eventually seize.
FEC tried to find bearings with seals that keep the lubricant in and dust out, but these were unavailable. Therefore, for dusty applications, the company seals the bearings inhouse, applying a labyrinth seal inside and a lip seal outside, with a cap and O-ring over the entire assembly.
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Putting a lid on it
Seaming machines that seal beverage cans have bearings, gears, conveyor chain, and cams that must be lubricated. “Some food grade lubricants allow excessive heat buildup in these machine components,” says Jim Crush, director of customer service, Angelus Sanitary Can Machine Co., Los Angeles. Also, if the amount of lubricant is low, bearings corrode. To compensate for these shortcomings, the company recommends relubricating these components more frequently — about twice as often as with conventional lubricants.
“A year ago, we switched to ceramic ball bearings to support the seaming rolls in our high-speed (over 700 cans/min) machines,” according to Richard Cabori, marketing manager at Angelus. Slower machines use tapered roller bearings. “The ceramic bearings cost more, but they require less lubrication and they last up to three times longer, thereby reducing downtime. In one case, reducing downtime with ceramic bearings enabled a company to increase production by 11.7 million cans per year.”
Sterilizers dish out heat
Machines that sterilize cans of food to prevent spoilage include two basic types. One is a rotary pressure sterilizer, consisting of parallel cooking and cooling cylinders. In these cookers, large open gears drive rotating reels that carry the cans through the cooking steam. These gears and associated bearings are grease lubricated.
Another type is a hydrostatic version, in the form of a tower that extends up to 80-ft high. Large gearboxes drive conveyor chains to transport the filled cans vertically through the heated sterilizer. Both gearboxes and chain are grease lubricated.
Because the food is sealed in cans, these machines require only H2 lubricants. However, some food plants equip all of their machines with H1 lubricants to ensure maximum safety and simplify inventory requirements.
“To get around the shortcomings of H1 lubricants,” says Joost Veltman, sr project engineer at The FMC Corp., Madera, Calif., “we design equipment so the lubricated components are below the product line, or they have guards to prevent dripping.” Such designs enable using H2 lubricants. For example, gearboxes are usually located outside of the food contact area or they are guarded.
To reduce the need for lubrication, the sterilizers also incorporate self-lubricating bearings made of plastic composite materials. Because the sterilizers operate at high temperatures, up to 275 F, they require bearings made of high-temperature composites such as PEEK, Ultem, or PPA. These composite materials contain lubricants such as graphite and silicone. For strength, the materials are typically reinforced with carbon or glass fiber.
These composites must be carefully selected to fit the required PV rating (pressure and velocity) for the load conditions.
Primer on food-grade lubricants
Companies that process food or beverages must use lubricants that perform a dual role. First, the oil or grease must protect high-speed machine components from wear, corrosion, heat, and contaminants. Second, it must be safe for contact with edible products.
These lubricants are required to meet one of two ratings of the U.S. Dept. of Agriculture (USDA): H1 or H2. The H1 rating applies to lubricants with incidental contact — those that are used where they may contact edible products. For example, an H1 lubricant is used on open gears or chain, or in machinery located above the food product, where the lubricant can splash or drip onto the food.
H2 covers lubricants with no food contact. These lubricants can be used where there is no possible contact with edible products, such as in enclosed gearboxes or chain cases, in machinery located below the product, or where the product is sealed in a container.
Food packaging machines may require either H1 or H2 lubricants, depending on the type of machine and its function. For example, a can filling and sealing machine that allows contact between the lubricant and the food needs an H1 lubricant. But a machine that subsequently packs these filled cans into a cardboard carton does not expose the food, therefore an H2 lubricant can be used.
The specific type of lubricant (oil or grease) required depends on the type of component to be lubricated (gears, chain, bearings, or seals), the operating loads and speeds, and the environmental conditions. In any case, the machine manufacturer usually recommends a specific lubricant type.
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Typically, the lubricant must provide resistance to water, steam, and cleaning agents; and in some cases, compatibility with plastics. Certain food industries require lubricants to operate in the presence of other elements: ice and extreme temperature changes (dairy); disinfectants and blood (meat and poultry); flour dust and high temperature (baking); fruit acids and acetic acid (canning); or dust, wide temperature differences, and sugar crystals (sugar).
Lubricants get better
In many applications, food grade lubricants perform as well as conventional lubricants according to Tim Stanford, brand manager, Product & Brand Management Group, Chevron Global Lubricants, San Francisco. For highly loaded gears, however, H1 lubricants provide less wear resistance because they don’t contain extreme pressure (EP) additives, Also H1 lubricants may offer less corrosion resistance, depending on the application.
For H2 lubricants, very few ingredients or additives are prohibited. Therefore, these lubricants exhibit little or no drop in performance compared to conventional types. There may be a few exceptions, such as lubricants tailored for very special applications.
In recent years, manufacturers have developed improved formulations that reduce the gap in performance between H1 and conventional lubricants. These new lubricants offer extended wear life and higher temperature ranges according to Steve Mazzola, sr. technical marketing engineer, Kluber Lubrication North America L.P., Londonderry, N.H.
The degree of improvement of these new lubricants is difficult to quantify, because it depends on the application and how well the lubricant matches the application. However, test results give some clues about how well the new lubricants may perform. For example, tests for highly loaded worm gears indicate that previous H1 lubricants produced wear life about 20% of that for a conventional hydrocarbon gear oil, whereas newer H1 versions increase the wear life up to about 80%. In another case, ASTM tests of an industrial oil indicate that a newer H1 version increases wear life about two to four times compared to the previous version.