9 selection tips for food processing bushings

Health and hygiene are of utmost concern in these sensitive applications

The production of a thermoplastic hollow bar. All images courtesy of Vesconite Bearings
The production of a thermoplastic hollow bar. All images courtesy of Vesconite Bearings

Extracting, filtering, milling, purifying, mincing, liquefying, emulsifying, cooking, pickling, pasteurizing, canning, slicing, dicing and drying are some of the many physical and chemical ways raw ingredients are transformed into other processed foods. As with any equipment in a food processing plant, instruments and apparatuses need to be assessed based on their longevity, cost and whether they are fit-for-purpose. It is also important in a hygiene-critical environment for the equipment to be safe and hygienic for use. The health toll on consumers can be high if this is not considered, and the impact on a food company can be devastating if hygiene-related issues result in costly food recalls and significant reputational damage.

Like all equipment, bushings must be assessed for their suitability for an application. Like other apparatuses connected in the industry, health and hygiene are important considerations. After all, often-inconspicuous bushings play a part in many food-related processes. They are intimately involved in many types of equipment – including blenders and mixers, ice machinery, picking and weighing equipment, and conveyors. Food processing bushings perform many millions of cycles and are an essential, although often unacknowledged, part of food processing. As a result, end users may want to look at these nine health and hygiene considerations before they choose a bushing for their production lines.

1. Swell index

Fortune Magazine reports that microbiological contamination is responsible for 47 percent of food recalls. Microorganisms such as bacteria, yeast and fungi and their buildup should be avoided. When selecting bushings, materials such as non-food-grade nylon should be avoided because it absorbs water and harvests bacteria. Other bushing materials should be carefully investigated. Only those thermoplastics that do not swell should be considered because microbes thrive in an environment of trapped stagnant water.

2. The right color

Unsurprisingly, white is the preferred color for food processing bushings. Many thermoplastics are this color and should be considered for food applications in which direct contact with food occurs. The color allows quality controllers to quickly ensure that nothing foreign has entered the system that led to a color change in the bearing. It also ensures that no color is transferred from the bushing to the food product and that no visible foreign material can be detected in the final product.

3. Lubrication

Food-grade lubricants can be used safely in food processing plants, without the concern that the lubricants may contain toxins that will be harmful in the food that they contact. Bushings, including thermoplastic ones, often operate better with lubricants.

However, many thermoplastic bushings offer the advantage of no lubrication in the food processing plant if required. This eliminates food particulates being trapped in lubricant and later contaminating the production chain.

4. Chemical resistance

Cleaning is of extreme importance in a food processing environment, and the bushings that are chosen should not degrade when they contact food chemicals or cleaning chemicals that are used to ensure hygiene in the processing environment. Many thermoplastic bushings have demonstrated chemical resistance over a range of acids and alkalis, and these may be preferred to untested bushings.

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5. Optimal operating range

For many food processing lines, steam cleaning is the advised cleaning method. Numerous thermoplastics can operate in high-temperature ranges, and these should be chosen instead of plastics that cannot withstand high temperatures. The temperature of the steam used should be verified, though, since some plastic bushings will melt if they are exposed to high temperatures for sustained periods.

6. Certification for food-grade applications

Different certifications are available for plastic bushings and the polymer materials that they are made of. Among them are the U.S. Food and Drug Administration certification and the National Test Laboratory certification of France. These apply different aqueous tests (including distilled water, acetic acid and ethanol tests) and a fat test that might include testing using sunflower oil. These are designed to ascertain the inertness of the polymers and the likelihood of a compound in the polymer being transferred to the food.

7. Toxic component avoidance

Thermoplastics are often preferred to metallic components, including bronzes, which often contain lead and tin. Avoiding tin and lead has become important to food processing companies as consumers become increasingly aware of the dangers of heavy metals to tissues and organs.

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8. Optimal bushing fit

Other buying considerations besides the physical properties of a bushing may be used for purchasing decisions including the optimal bushing fit, because food that remains in the running clearance of an ill-fit bushing is likely to lead to contamination of the entire production chain. Optimal bushing fit requires that operating temperatures be included in the selection process since some bushings expand when heated.

9. Smoothness

During the production process, food and beverages also tend to fall into any crack or hole on any equipment’s surface. Some bushings are designed to have these features since they are necessary for smooth operation. Others have fewer moving parts and are constructed into a single unit. Depending on the bushing required, thermoplastic bushings may offer advantages because they tend to have smooth surfaces in which food particles are unlikely to accumulate. If they have been chosen for their smoothness and their lack of cavities, they must remain dent- and damage-free. To achieve this, improper, forceful mounting – which might cause denting, wearing or cracking – should be avoided. Similarly, the bushing should not be roughly handled during maintenance. Care should always be taken when any contamination concern exists.

Foodborne contamination

Fortune Magazine noted that the yearly cost of food-related medical treatment, lost production and mortality caused by illness related to foodborne pathogens totals $55 million in the U.S. Because of this, food processors are looking carefully at all parts of their production chain in which equipment contacts food.

No study that we are aware of has identified bushings as a high risk for foodborne pathogens, but bushing manufacturers are keen to ensure that the risk of food-related illness or diseases associated with their components remains low. Bushings, as with other types of equipment, must be investigated to determine whether incidental food contact is possible. Once this is determined, bushings can be specified based on the hygiene concerns appropriate for each application.

Today’s rapidly urbanizing and increasingly wealthier global population spends less time on food preparation because of increasing time demands, so processed food demand is growing each year. This would not be a major concern, except that food-related outbreaks and recalls are also increasing. Foodborne illnesses and their risk to food consumers and food processing companies cannot be underestimated, and any opportunity to be more vigilant about hygiene should be taken.

Case study: Sugar mill converts to high-temperature hanger bushings

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A sugar mill in Kwazulu Natal, South Africa, converted to Hitemp 150 screw hanger bushings for its conveyor that transports massecuite, a dense mass of sugar crystals with mother liquor obtained by evaporation during the sugar production process. The polymer that makes up the hanger bushing is brown, and this is regarded as suitable for the application since it is not the final sugar that it is exposed to but the earlierstage raw materials.

The 11 double-flanged bushings support the screw conveyor and ensure that it does not collapse or touch the housing as it transports the hot, gritty, viscous mixture of liquefied sugar granules.

The sugar mill initially tested two high-temperature bushings alongside bronze bushings.

The polymer bushings performed well and showed limited wear, while the bronze bushings were worn and became a deformed elliptical shape. The polymer bushings were made from a polymer with a high temperature tolerance, low frictional qualities and wear resistance. They are also preferred over brass components because brass contains lead and tin and presents health challenges.

While more expensive than the bronze product, the polymer bushings offered the advantage of not having to be checked weekly, as is the case with the bronze bushings. They were also less likely to be stolen, unlike bronze bushings, which are made of a material soughtafter among scrap metal recyclers.

After the successful comparative test of the two polymer bushings, the mill replaced its bronze screw conveyor bushings entirely and ordered 11 high-temperature polymer bushings.

The mill has used the polymer bushings for four years, including the two-year testing phase. The full complement of polymer screw conveyor hanger bushings have been in use for two years.

Cost savings are particularly important for South African sugar producers that have recently experienced a severe drought that had limited sugar production. Because of this, different properties, including color, were regarded as relatively unimportant next to the maintenance savings and good wear characteristics of the polymer.

Eddie Swanepoel is a technical consultant for Vesconite Bearings. He may be reached at eddie@vesconite.com or +27 11 616 1111. Swanepoel will also be at the American Society of Sugar Cane Technologists Joint Meeting June 14 – 16, 2017,  in New Orleans; the Kwa-Zulu Natal Industrial Technology Exhibition July 26 – 28 in Durban, South Africa; and the South African Sugar Technologists Association Congress Aug. 15 – 17 in Durban, South Africa.

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