Compression set can become an insidious and chronic problem with metal coil springs supporting and isolating food and beverage vibratory applications. These can include dairy applications, powdered products, liquid-solid separation, and primary processing applications involving vibratory screening process in production, conveying, and packaging.
The technical term "compression set" simply means that some springs get tired over their lifetime of hard work and can settle, or set, suffering permanent compression by up to 27 per cent below their original design height. This means they don't perform to their original specifications.
Compression set can occur in dairy and beverage applications including dewatering and liquid/solid separation, a field where vibrating screens are often utilised to dewater liquids from solids, including animal wastes and production byproducts. Vibrating screens are also used in dairy industries to separate solids from milk particles while curds from whey remain separate. Reliable vibratory processes also help where Industry 4.0 automation programmes increase production speeds and productivity while placing an additional premium on reliability.
Whatever the application, spring wear can make the vibrating equipment the springs support potentially unstable and prone to breakages. One reason is because spring set doesn't always happen evenly, and can affect different springs under different parts of machinery to a different extent, says Simon Agar, General Manager of actuation, isolation, and suspension specialists, Air Springs Supply.
One side of a bank of springs may become more worn than another, for example, affecting dynamic stability, imposing uneven loads, and even leading to breakages and production interruptions. The problem is compounded by the springs often being in the most inaccessible parts of machinery where workers have to crawl around in confined spaces, leading to delays and OH&S issues," he says.
One way to alleviate excessive spring set and breakages in a number of applications is by using proven rubber-and-fabric Marsh Mellow™ isolators from Firestone, distributed throughout Australia by Air Springs Supply, which has been a leading Australia-wide isolation, actuation, and suspension specialist for more than 40 years.
Marsh Mellows are in use worldwide in applications such as shaker screens, crushing equipment, vibrating bins, conveyor and other vibrating equipment used in manufacturing, materials handling, and processing, food and beverage, and primary product processing.
Cylindrical Marsh Mellow springs are constructed of a solid rubber core with a hollow centre and several plies of fabric-reinforced rubber as an outer cover. The plies provide the springs with stability as well as a consistent cylindrical shape.
The springs' components (rubber, bias plies, size of centre) can be combined in different ways to meet specific load and performance requirements).
This gives them great flexibility and precision, says Simon Agar, whose company's experience spans applications of both solid and hollow (bellows-type) air springs throughout Australia over more than 40 years.
Marsh Mellows operate silently with greater load capacities than conventional coil springs, while typically outperforming all-rubber alternatives in many areas, by having greater load capacity and more compact size for comparable tasks.
They can't break, splinter, or fragment like a metal spring. One of their big advantages is that they suffer only a maximum of 7 per cent compression set over the life of the part. This means they can be changed in and out of different sets of springs without upsetting the dynamic balance of the whole set, says Simon.
High overload capabilities
Marsh Mellow springs' flexibility also helps eliminate downtime and potential damage to machinery. When a coil spring fails, it will often crack, allowing fragments of the coil to damage equipment and interfere with production flow. This problem is eliminated with the rubber construction of the Marsh Mellows, which exhibit exceptionally high overload characteristics and usually do not fail catastrophically, offering some support even during failure in exceptional circumstances.
Marsh Mellows:
- Protect systems from the effects of structurally transmitted vibration, without needing air inflation.
- Are an effective passive isolator with superior characteristics to steel springs. Their rubber and fabric spring structure's isolation performance surpasses both steel and rubber-only springs.
- Offer the engineering advantage of constant vibration isolation under changing production loads. Their variable spring rate allows for a nearly constant natural frequency, which is the rate at which a body vibrates when disturbed, without being subject to a driving or damping force.
- Offer greater deflection capabilities. This advantage – along with the load-carrying influences of the fabric reinforcement – mean Marsh Mellows can carry a greater load when compared with a solid rubber part of the same modulus and dimensions.
- Cost-efficiently support OH&S programmes aimed at reducing industrial deafness by reducing structurally transmitted noise caused by vibration. Their operation is quiet, unlike steel springs, which often suffer coil chatter and readily transit high frequency structural noise.
- Offer reliability, corrosion resistance, low cost, compactness, and basic simplicity – characteristics that are important in a wide spectrum of applications, including particularly damp environments, washdown and production automation applications.
- No maintenance or lubrication is required to maintain their performance. This delivers both hygiene benefits, resulting from the lack of lubricants to attract grime, as well as OHS and productivity benefits from curtailed upkeep of the machinery in which they are used.
More compact and less costly
Marsh Mellows' ability to maintain a cylindrical shape while supporting greater loads means a smaller overall size can be used compared with an all-rubber spring of identical load capacity. This is important when considering an application with a small design envelope. Marsh Mellow springs' high load capability also means fewer springs may be needed in an application, resulting in less overall cost.
Also, the lateral spring rate of a Marsh Mellow spring can be less than the vertical spring rate, resulting in a lower lateral natural frequency. The low natural frequencies of Marsh Mellow springs mean they provide excellent isolation of forced frequencies in the range of 800-1200 cycles per minute (13-20 Hz).
"Because rubber is an incompressible fluid, it will flow to the path of least resistance. This means that, as a Marsh Mellow's height compresses, the fabric-reinforced rubber plies pantograph and the diameter grows. This supports the rubber core laterally, even at 30-40 per cent compression," says Simon Agar.
Naturally different types of springs have different performance characteristics suited to particular tasks. Different spring types and construction offer different benefits in different applications. These should always be discussed with suppliers having wide experience in the particular area of application being considered.
About us:
Air Springs Supply offers cost-efficient and reliable solutions for actuation and isolation systems employed in industries extending from construction, conveying and food and beverage and primary product processing through to mining and energy, metalworking, manufacturing, materials handling, NVH removal, production automation, safety and testing applications.
From rugged actuators that make heavy lifting easier, isolators that keep vibration from moving to unwanted areas and pick & place solutions that move delicate items safely, we work hard to find an effective solution from our wide array of products and experience.
