Heart of steel

To overcome the problem of food products being contaminated by the chain lubricant used in conveyor systems, the use of steel belts is on the increase.

When designing any mechanical conveyor system for the food, beverage, packaging or pharmaceutical industries, the big dangers to be considered are the potential breeding and the spreading of pathogenic micro-organisms. The pre-requisites, therefore, are easy-to-clean, non-corrosive materials free from potential dirt-collecting crevices. Another problem area is the lubricant; clean applications require either use of an expensive food-grade lubricant or lubrication-free chain.

There are a number of ways to achieve non-lube performance of drive chains which vary with the load capacity and life requirements of the transmission medium. Today engineering plastics, especially self-lubricating acetyl types, play a part but, in the main, such chains suit applications where corrosion resistance and weight saving are more important than load capacity. Where conventional externally lubricated steel roller chains are normally used, power transmission capacity and wear life are the main criteria for selection and an all-steel lube-free chain is required.

There are two main methods of achieving lubrication-free steel roller chain and both involve internal lubrication between the load bearing surfaces, between the chain pin, internal bushing and the roller. As the chain passes over a sprocket, particularly a driven one, it is these internal bearing surfaces that have to articulate under load. Given inadequate lubrication, these are the main areas of wear and the resulting chain elongation.

The first method for lubrication is to pack the rollers with a high-viscosity grease lubricant that maintains internal lubrication. Externally the chain is virtually dry to the touch and additional external lubrication is virtually impossible due to the inability to penetrate through the existing lubricant. This type of lubrication limits the temperature range of the chain and has a limited effective life span.

The second method is oil impregnation of the components during their manufacture. This is known as sintering. The steel bushings are forged with lubricant that is included within the material structure of the steel. During operation, the lubricant forms an extremely thin layer between the pin and internal roller surfaces. Meanwhile, the exterior of the chain is totally dry to the touch, a condition that stops it acting as a surface receptor for harmful contaminant particles.

An additional benefit of this process is that the motion of the lubricant within the rollers under load is from the centre outwards, the opposite direction to conventionally lubricated chains that draw lubricant in from the exterior.

As a result of this, any debris from the atmosphere that does settle on the surface of the chain is mostly excluded from the load bearing surfaces of the rollers and deters the acceleration of wear. The overall performance of a good lube-free chain is also enhanced by specially hardened pins and rollers treated with an extra durable coating.

The durable rollers facilitate super smooth engagement on the sprocket for longer periods of time, reducing sprocket wear significantly. Moreover, the smooth articulation of chain and sprocket reduces power transmission losses by a high order. There are some obvious initial benefits to using lube-free or (internally lubricated) chain.

Food production environments that have traditionally used expensive food grade lubricants can now operate lines without the need for chain lubrication, even in some arduous wash-down environments. Although only sintered chain is recommended in these environments.

A recent scare in Germany in which a number of food products had to be recalled as they had become contaminated by the chain lubricant in the manufacturer’s machinery highlighted the problem. Germs and potentially harmful bacteria are attracted to the dust gathered by the lubricant grease and this can be transported and fall in the food during the manufacturing process.

To overcome this problem, the use of steel belts in such applications is increasing as they are easy to clean and can be made from a number of stainless steel grades— such as 304 FH and 316 FH — that possess very high anti-corrosion properties.

The wash-down with corrosive fluids is commonplace in applications such as the transportation of dairy products and similar conveying lines as the prevention of harmful bacterial infection is critical. Steel belts do not need lubrication to transmit power and, unlike other types of belting, are totally free from particulate. Due to their high temperature resistance and good heat transfer properties, steel belts can even be cooked on, thus saving processing time during food manufacture.

They present design engineers with opportunities not available in other drive components, such as the benefits of using narrow steel belts and drive tapes in diverse applications and their use in precision indexing systems is now being increasingly realised by design engineers from many industries.

However, belts are not limited to steel; other materials are being used such as carbon for magnetic applications, inconel for very high temperature applications, and titanium for high-bend stress applications.

Important characteristics of steel belts include the fact that they are essentially unstretchable, accurate and repeatable. They possess extremely high strength-to-weight ratios, require no lubrication, are intrinsically clean, as well as being thermally and electrically conductive. They can operate in hostile environments and are also quiet, generating no cordal vibration.

‘The combination of its high strength, ‘non-stretch’ characteristic and the fact that it is manufactured to machining specifications means that the synchronous steel belt is a very powerful tool in automation systems requiring precision indexing and high repeatability,’ said David Huntley, managing director of Belt Technologies.

‘Other applications include simple conveying, high-temperature (oven) conveyors, clean room conveyors, imaging belts, heat-sealing bands, casting belts, vacuum conveyors, carriage positioning systems, X/Y positioning systems, robotic arms and zero-backlash drives.’