Eliminate metal fatigue and noise challenges to vibratory mineral processing equipment

Noise and fine control of vibratory processes are twin challenges facing mining, bulk handling, quarry and construction materials processes.
Noise and fine control of vibratory processes are twin challenges facing mining, bulk handling, quarry and construction materials processes.

Large-scale vibrating equipment used in minerals, bulk materials and construction materials processing can contain built-in hazards that may not become apparent until they fail.

This is because the banks of metal springs typically found in vibratory equipment are subjected to constant cyclic loading – and ultimately fatigue – that can produce spring settling over time, giving reduced performance compared with the original specifications, which are important for optimum performance of the task in hand.

“The resultant changing of stiffness and efficiency – and ultimately failures – are difficult to measure and even harder to predict. But they become all too obvious when difficult-to-access springs may finally break, bringing processes to a complete halt,” says pneumatic actuation and isolation specialist Vinh Lam.

Then, the plant affected has to send in maintenance teams to undertake the heavy and hazardous task of disassembling and returning to service the vibratory equipment vital to production continuity of coal, iron ore and other minerals as well as construction materials processed using vibrating screens, classifiers, feeders, shakers and sieves. Losses due to broken links in the production chain can in the worst cases be measured in millions, says Vinh Lam, of Air Springs Supply Pty Ltd, which through its Australian network provides engineered rubber-and-fabric pneumatic actuator and isolator solutions precision manufactured by Firestone Industrial Products to overcome both metal fatigue and noise issues endemic to vibrating machinery.

Firestone Airstroke and Airmount actuators and isolators offer virtually silent, reliable performances over a range from just a few dozen kilograms in the case of palm sized Ministroke Polyactuators to more than 40,000 kg per units in the case of convoluted types
Firestone Airstroke and Airmount actuators and isolators offer virtually silent, reliable performances over a range from just a few dozen kilograms in the case of palm sized Ministroke Polyactuators to more than 40,000 kg per units in the case of convoluted types

Firestone Airmount® Isolators and complementary Airstroke® pneumatic actuators are, in effect, heavy-duty balloons that both contain no internal moving parts to break or wear. Their resulting lack of internal friction and inherent rapid cycling capability makes them very suitable for tasks such as conveying equipment and vibrating machinery.

They are essentially identical in construction and toughness to Firestone Airide suspension air springs used in their thousands throughout Australia beneath heavy trucks and semi-trailers plying rough outback roads and the same challenging conditions encountered by static machinery on remote and grimy mine sites where reliability is paramount.

Airstrokes and Airmounts offer 40-40,000 kg of suspending, lifting or pushing power and strokes (extensions) of up to 350 mm, powered by simple, basic compressor equipment found on every substantial mine site, quarry, or bulk materials site.

They do not require periodic maintenance or lubrication, and are available in a broad range of sizes, meaning they can be used for tasks ranging from delicate shaker tasks (gold separation, for example) through to conveyors, heavy shakers, screens, and crushers used on bulkier commodities too, including coal, iron ore and battery materials.

Vibration is both an OH&S hazard and a metal fatigue risk to the machines, screens, motors and conventional springs used to suspend vital plant.
Vibration is both an OH&S hazard and a metal fatigue risk to the machines, screens, motors and conventional springs used to suspend vital plant.

By reducing structurally transmitted noise, vibration, and harshness (NVH) they help reduce fatigue and damage in processing structures.

Any given Airmount, for example, can also easily handle a substantial change in load (a common occurrence in mineral processing) simply by adjusting the air pressure, whereas coil springs are designed for a very narrow operating range.

Also, because of their nearly constant natural frequency, Airmounts react in a much less violent manner than coil springs during start-up and shut-down conditions, as the input frequency changes. Because they do not exhibit the chatter that conventional coil springs do, they are better suited for handling changing loads or overload conditions than coil springs.

Operators can adjust the kPa/PSI input based on the speed they’re running the actuator or isolator motor for specific applications, such as grinding. Plus, the operator can implement a burst cycle, which gives a burst of power that dislodges items stuck in the screen.

Airmount® isolators can also help take the harmonics out of vibrating bars employed on some screening equipment. Laying a vibrating bar on air takes out any whipping motion and allows the bar to move uniformly.

“There are clearly advantages in different applications to using the Firestone Airmount isolators over hydraulics or coil springs,” says Vinh Lam. “Any type of hydraulic device can come with headaches due to their high psi, shafts, and leakage, etc.”

Coil springs – in addition to being sometimes too rigid and un-accommodating for the speed variations required – may be affected by corrosives and grit in ways that the air springs are not.
Coil springs – in addition to being sometimes too rigid and un-accommodating for the speed variations required – may be affected by corrosives and grit in ways that the air springs are not.

In addition to overcoming problems of vibration and noise transmission, Airmounts inflated to different pressures (and occasionally filled with different mediums, such as water or solutions instead of air) can be used to change the nature of the vibratory effect being produced by the vibrator motor.

Because friction is reduced, and there are no internal moving parts to break or wear, Airmounts and Airstrokes are very suitable for high-repetition tasks involving either isolation or actuation. The flexible air springs’ ability to arc without a clevis – to bend and to tolerate uneven and fluctuating loads – also means they are suitable for materials handling tasks such as tensioning webs, belt take-up on conveyors, or powering scissors lifts.

“Air Springs are outstanding isolators, in which role Airmounts reliably achieve isolation efficiencies often well exceeding 99%,” says Vinh. “Their outstanding performance suits them to applications such as suspending vibrating screens or motors and compressors commonly found throughout heavy industrial plants, where they are generally used where weights exceed 100 kg per mounting point.”

Replacement actuators and isolators

In considering their options for replacement actuators and isolators, engineers, operations staff, and OH&S managers also increasingly have to take close account of a more recent challenge of eliminating noise generated in the comminution process.

Loud noise can create physical and psychological stress and reduce productivity, according to globally respected authorities such as the US Occupational Health and Safety Administration and Work Safe Australia. Noise can also interfere with communication and concentration, raise heart rates and hypertension, and contribute to workplace accidents and injuries by making it difficult to hear warning signals.

“Over the last 20 years or so, the issue of NVH and industrial deafness has become far more prominent than in the past,” says Vinh Lam. In addition to their outstanding actuator and isolator performance, near-silent running Airstrokes and Airmounts solve this emerging issue before it becomes an OH&S liability.

Depend on experience

Naturally, different types of springs and isolators 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. Air Springs Supply has been a leader in the fields of actuation, isolation, and suspension for more than 40 years.