Vibration and noise are old enemies at mine, quarry and mineral processing sites, hazards that have been pushed into the spotlight in recent years by concerns both about worker safety and about plant efficiency and reliability.
Vibration occurs in all rotating or reciprocating machinery as a result of forces generated within it. Sometimes the vibration is intended – as in vibrating screens and vibrating conveyor sections, for example – and sometimes it is caused by imbalances in rotors, bearings, springs and gears as vibration migrates from the source to surrounding structures and wear-prone components.
If vibration is left unchecked, the consequences can include:
- Breakdowns and downtime including Bearing failures, metal spring cracking and collapse, metal structure cracking and weaknesses potentially leading to unexpected plant shutdowns.
- Operator fatigue and noise nuisance (NVH - noise, harshness and vibration is increasingly a factor in workers compensation issues)
- Energy waste due to kinetic energy required for vibration
- Interference with nearby computer, electrical and electro-magnetic equipment, potentially leading to production disruption.
A simple, robust and effective means of solving vibration and isolation problems created by such equipment is provided by Marsh Mellow® springs, which are fabric-reinforced solid rubber isolators used for quiet isolation of machinery vibration and for general shock absorption throughout industry.
The cylindrical springs, developed by Firestone - the world's biggest producer of air springs for isolation and actuation - are used world-wide as an alternative to metal coil springs for applications involving quarries and mineral processing as well as building, construction, computer, electrical and electronic equipment including motors, gearboxes, compressors, conveyors, materials handling machinery and shock absorbers.
Marsh Mellows give consistent performance regardless of changing loads, while offering high lateral stability and compact size, says James Maslin, National Sales and Marketing Manager for Marsh Mellows' Australian distributor, Air Springs Supply Pty Ltd, which has a nation-wide sales and service network, established for more than 30 years.
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, says Maslin, whose experience spans applications of both solid and hollow, bellows-type, Airmount® air springs throughout Australia "Marsh Mellow springs are quiet in operation, unlike steel springs which readily transmit high frequency structural noise and often suffer from coil chatter. A failing coil spring may crack, causing fragments of the coil to damage equipment, resulting in expensive downtime. This problem is eliminated with Marsh Mellow springs, which are tolerant of overload and, if they ever do fail, do not fail catastrophically.
"The quiet performance of Marsh Mellows – and the fact that they resist water and grit – means they are ideal for applications where high levels of workplace safety and hygiene are essential. Such applications can range from metals and minerals plants through to primary processing, timber and paper and food and beverage.
"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)," he says.
"Their high load capability means fewer springs may be needed in an application, resulting in less overall cost," said Maslin, adding that Marsh Mellow spring elements may be modified to meet customers' specific load and performance requirements.
Marsh Mellow's fabric-reinforced spring has more lateral stability than an all-rubber spring of the same size, so it can support greater loads while maintaining its cylindrical shape.
A spring with a smaller overall size than an all-rubber spring of identical load capacity can be chosen, which is an important factor where space is restricted, says Mr Maslin
Marsh Mellow springs are maintenance-free. They have no moving parts and require no lubrication. Their rubber and fabric-reinforced construction is corrosion resistant for a durable, long life. The spring has been proven in the worst damp and corrosive environments of mines and mills where a standard coil spring will fail.
The springs available from the Marsh Mellow catalogue range in size from the 0216 model with an unloaded height of 44 mm and outside diameter of 41 mm, through to models such as the 0243 with an unloaded height of 203 mm and an outside diameter of 279 mm. The new Marsh Mellow manual and Marsh Mellow isolation springs can obtained from Air Springs Supply of Meadowbank, NSW, or by inquiry to their agents in all States.