Mineral processing and bulk handling machinery operators face issues as OEM actuators and isolators wear
As OEM comminution equipment components inevitably wear out over the years ahead, many mine, quarry and bulk materials handlers will be looking for ways to replace isolators used in their crushers, grinders, conveyors and vibrating screens.
Without good isolators, machinery can literally shake itself to pieces – and damage the workplace environment with NVH hazards (noise, harshness, vibration).
The search for reliable isolator replacements is expected to ramp up over the years from now as operators focus on maintaining the wave of OEM equipment that was imported to Australia fully built up when companies rushed to satisfy demand during the mining and economic booms of a decade ago.
“Companies using this OEM equipment will be driven by the twin imperatives of having to work equipment harder than ever to maintain production volumes, while simultaneously ensuring that nothing breaks down to interrupt cash flow,” says actuation and isolation specialist James Maslin.
This means that many of the old metal coil springs that came with OEM machinery will need to be replaced, preferably with isolators that are easy to fit, don’t break, tolerate aggressive environments and are simple to replace while production continues.
Air Springs Supply Pty Ltd is offering a maintenance-free alternative to metal springs that doesn’t require lubrication or upkeep and won’t set (suffer permanent compression) like metal springs to reduce efficiency. These proven robustly engineered rubber-and-fabric Marsh Mellow® springs are manufactured by Firestone and in use worldwide in applications such as shaker screens, crushing equipment, vibrating bins, conveyors and other equipment subject to vibration.
“While no one spring design is ideal for all applications, Marsh Mellows offer considerable advantages over both conventional coils and solid rubber springs for many tasks, says Mr Maslin, who is Sales and Marketing Manager for Air Springs Supply Pty ltd, which is the national distributor of Firestone Industrial actuation, isolation and suspension products.
Firestone Marsh Mellow® spring, left, and Airmount™ and Airstroke™ isolators and actuators, right. They have advantages over traditional cylinders in that they are durable, operate well in corrosive and abrasive environments, easily accept misalignment and have a high ratio of stroke to collapsed height
These include both Marsh Mellows and Firestone’s inflatable Airmount™ isolators and Airstroke™ actuators, which are also used worldwide in vibrating equipment and can easily cross over from Goodyear, Conti, Rexroth, Norgren and similar components incorporated globally by OEM manufacturers. Both types of rubber spring offer the OHS advantage of silent operation, while also providing very high isolation efficiencies, says Mr Maslin.
Marsh Mellows operate silently with more spring travel and greater load capacities than conventional coil springs, while outperforming all-rubber alternatives in many areas, such as greater load capacity and more compact size for comparable tasks.
The 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 spring’s components (rubber, bias plies, size of centre) are combined in different ways to meet specific load and performance requirements (such as those of crushing and screening equipment).
This gives them great flexibility and precision, says Mr Maslin, whose experience spans applications of both solid and hollow (bellows-type) air springs throughout Australia over more than 10 years. (Details of applications can be researched on Air Springs’ website, www.airsprings.com.au.)
One of the big advantages of Marsh Mellows is that they offer constant vibration isolation with changing loads. Their variable spring rate allows for a nearly constant natural frequency under the impact of such loads, says Mr Maslin.
And because of the Marsh Mellows’ greater deflection capabilities – and the load-carrying influences of the fabric reinforcement – it can carry a greater load when compared to a solid rubber part of the same modulus and dimensions.
Their ability to maintain a cylindrical shape while supporting greater loads means a smaller overall size can be used compared with an all-rubber springs 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).
Increased stability, reduced downtime
Rubber is an incompressible fluid which 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.
Marsh Mellow springs’ flexibility also helps eliminate downtime and potential damage to machinery. When a coil springs fails, it will often crack, allowing fragments of the coil to damage equipment. This problem is eliminated with the rubber construction of the Marsh Mellows.
Additionally, Marsh Mellow springs exhibit exceptionally high overload characteristics and usually do not fail catastrophically, offering some support even during failure.
Marsh Mellow springs reduce 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.
Marsh mellows have no moving parts. No maintenance or lubrication is required to maintain their performance.
“Existing coil springs supporting crushing and screening equipment have to put up with a lot in life,” says Mr Maslin. “Not only are they expected to function reliably in often wet and corrosive environments, but also they have to cope with rapidly changing loads and sudden severe impacts.
“Not surprisingly, many suffer trauma as a result. One problem is noisy coil chatter as loads change. Under constant battering, coils may also suffer spring set, or permanent compression below their original design height. This means they do not perform to their original specifications.
In the worst cases, they break. Then there is not only downtime to consider, but also maintenance workers have to get right into some of the most inaccessible entrails of industrial equipment.
“And even when they are functioning perfectly, the row produced by conventional coils can be a hazard to hearing – not to mention sanity,” says Mr Maslin.
“In many cases, Marsh Mellows are the ideal substitute for OEM actuators and isolators that have outlined their usefulness. Naturally different types of springs have different performance characteristics suited to particular tasks. These should always be discussed with suppliers having wide experience in the particular area of application being considered.” said Mr Maslin,