Engineering thermoplastic gear, guidance and conveyor component systems have become disruptor technologies in production engineering as Industry 4.0 produces smarter factories and processing plants that are more efficient, hygienic, productive and less wasteful.
Materials such as Wearlon nylon gears, Wearace acetal gears, and Wearex UHMWPE drive components – material types originally introduced to the market to fill niche applications – are more often becoming materials of first choice, according to Cut To Size Plastics. This is happening as machine builders and production engineers seek out materials that will enable their digitally communicating Industry 4.0 systems to function faster, with closer tolerances, less maintenance and down-time, easier washdown and less need for constant lubrication, attracting grit and wear.
“Thermoplastic technology is advancing quickly to fill many needs and these materials are extremely tough,” says Laurie Green, Managing Director of Cut To Size Plastics and an Australasian engineering thermoplastics pioneer. “Ultra-high molecular weight (UHMW) gear racks in use internationally, for example, have shown part lives multiple times longer – sometimes ten or more times longer – than their metal predecessors.
“While most gears were traditionally made from various metals, plastic gear technology is pushing the previous limits of load bearing, torque handling, and gear drive capabilities. As well as being highly suitable for new machinery, these plastic gears and gear racks can be identical in design to their existing metal predecessors, making them directly interchangeable with steel and other OEM and custom metal gears and racks.”
Different plastics benefits
Self-lubrication is a key benefit of Wearlon nylon gears, because a constant issue with many metal drive gears is the need for external lubrication. This is a major problem when gears are hard to access or where lubricant will only exacerbate a problem – for example gears that operate in high-dust or gritty environments.
“Wearace acetal is a great choice for plastic gears, for example, because the typical objective in such a device is to minimise the friction resulting from contact,” says Green. “Acetal is very slippery (i.e. it has a very low coefficient of friction) and therefore minimal energy is lost in the internal contact interaction between gears.
“Wearex ultra-high molecular weight polyethylene (UHMWPE) and other high-performance plastic gears and gear racks offer wear and noise reduction advantages over comparable metal products. UHMWPE is generally looked to when impact resistance is key.”
Green’s company has more than 40 years’ experience as a provider of OEM and custom parts that replace metals to increase productivity, decrease down-time and lead to greater revenue for customers while maintaining the specifications required by the equipment, project and application. Cut To Size has worked with industries, extending from food & beverage and primary livestock and crop processing, through to machine building, resources, materials handling, construction and manufacturing to develop hard-wearing OEM and easily retrofitted gear components for multiple applications.
“Major advances in engineering thermoplastics formulation technologies – and a growing realisation of their unique benefits – mean industry no longer is as firmly rusted on to metals drives as it once was,” Green adds. “Today, the options are far more plentiful and attractive.
“While there is no one ideal answer to all applications – whether you are considering metals or thermoplastics – it is important to consider all the options and not automatically revert to old choices that may no longer be optimum for new needs. It could be that old choices are best, but it could be more likely that a cheaper, more durable and better performing alternative has evolved in response to Industry 4.0.”
Critical properties
When selecting a plastic material for a specific application, Green says it is important to base the choice on critical properties associated with the task, such as thermal expansion, or the plastic’s ability to change in shape, area and volume in response to temperature changes. The coefficient of thermal expansion is the degree of expansion divided by the change in temperature. The higher the coefficient number, the more change in size. Several major thermoplastic compounds exhibit acceptable thermal expansion performance. Three of the most commonly used are Wearlon nylons, Wearace polyacetal, and UHMWPE.
Wearlon nylons are well-suited for use in food contact applications, such as food processing and packaging conveyor systems. The Wearlon family shares major advantages such as high mechanical strength, hardness and stiffness, as well as high mechanical damping capacity. They offer good fatigue and very high wear resistance, with good sliding and emergency running properties.
They are suitable for machinery subject to constant moisture and washdown. These properties, along with good machinability, lend them to typical applications such as bearings, guides, chain wheels and guides, bushings and slide and guide plates, toothed racks, mixer rollers, guide rails, rope pulleys, bearings, tappets, cam discs, gear wheels, transport stars, mixer blades, pump wheels, pinions, curved guides, crane supports and idler and guide rollers.
Wearace polyacetal is a cost-efficient material that offers excellent strength, stiffness and dimensional stability as well as wear resistance and easy machining. Acetal has an 80-120 coefficient of thermal expansion, and, as a polyoxymethylene (POM) homopolymer, a high-end temperature of 120 degrees Celsius while the POM copolymer has a temperature range of -40 to 120 degrees Celsius.
While typically specified for handling lesser loads than nylons, Wearace polyacetal is eminently suitable and highly cost-efficient for sliding, guiding and roller elements of materials handling machinery. Typical uses that benefit from Wearace’s properties include gear wheels with small moduli, cams, heavily loaded bearings and rollers, bearings and gears with small clearances, valve seats, snap fit assemblies, and insulating components for electrical engineering and parts which operate continuously in water of 60-80 degrees Celsius.
“The most popular property of POM is its ease of machining,” adds Green. “It is also very hard and abrasion-resistant, and it is more resistant to creep, which is the tendency for material to stay bent if left under a stress for too long. POM is also resistant to chemicals. It is generally unaffected by solvents, fuels and lubricants found in industrial environments.”
Industry-specific examples of Wearace applications range from scraper blades on gelatine extruders, buffer blocks on electromagnetic bogie brakes and ratchet wheels on stapling machines. Being physiologically inert, Wearace is highly suitable for food contact applications in natural form.
UHMWPE is a thermoplastic polyethylene featuring extremely high molecular density. It is highly durable, with the highest impact resistance of all thermoplastics with great abrasion and heat resistance. It’s another plastic well-suited for food and beverage industry applications. It has a 130-200 coefficient of thermal expansion and a high-end temperature of 95 degrees Celsius.
“UHMW and other high-performance plastic gears and gear racks offer wear and noise reduction advantages over comparable metal products,” says Green. “UHMW materials are generally looked to when impact resistance is key.”
Cut To Size Plastics offers high-strength, custom-designed and OEM replacement parts for gears and other power transmission components used in industrial and commercial applications. The company works with customers to find the most cost-effective solutions for their specific project demands, drawing on extensive local experience complemented by global supplier expertise for companies considering thermoplastic components.