Tag Archives: chutes

Botswana diamond mine feels the impact of Weba Chute Systems custom solution

Comminution of minerals, Diamond mining, Mineral processing, Mining equipment, , , , , ,

Faced with a challenge of large rocks in the run-of-mine (ROM) feed regularly damaging main support structures, chutes and a grizzly feeder, a diamond mine in Botswana reached out to Weba Chute Systems to design a solution to overcome this costly challenge, which included major safety hazards.

According to Hilton Buys, Regional Manager at Weba Chute Systems, the mine’s existing chutes at the ROM section were cracking and breaking under the barrage of heavy kimberlite rocks measuring up to 1 m in diameter.

“Even the robust grizzly feeder could not withstand the impact of these rocks, which were free-falling about two metres from an apron feeder before contact,” Buys said. “Apart from the costs incurred by this damage, the transfer points were posing a significant safety hazard to mine employees.”

The solution – designed and manufactured at Weba Chute Systems’ Wadeville facility – was a special four-tonne swing door in a discharge chute, feeding from the apron feeder to the grizzly. The heavy, fabricated door is strong enough to withstand the impact while absorbing the energy of the falling rocks before allowing them to drop onto the loading section of the grizzly. The feed can then move in a more controlled manner over the grizzly into the crusher below.

“The key principle was for the door not to give way easily, thereby reducing the velocity and momentum of the large chunks,” Buys said.

There was also a design requirement to accommodate the movement of smaller rocks. This was dealt with through the addition of a second door, to also ease these rocks onto the grizzly to ensure a more gradual feed into the crusher feed chute. The success of the design, which is based on the Weba Chute Systems principle of controlled flow, has been demonstrated in the chute’s ability to operate with very little maintenance, he says. The only components needing regular attention are chute lips and swing door rails.

“We also included some specific design elements in the crusher feed chute, by installing impact rubbers,” Buys said. “Any rocks that may diverge from the main flow stream will then strike this rubber, minimising the vibration and impact on the body of the chute and are still able to drop gently into the crusher.”

Following on the success of this design, the solution was repeated at other customers’ sites, including mines in the Northern Cape which experienced similar challenges.

Martin Engineering on resolving bulk material handling issues with flow aids

Bulk handling, Comminution of minerals, Equipment maintenance, Mining equipment, Mining maintenance, Mining services, , , , , ,

In order to achieve controlled and consistent flow on conveyors handling large volumes of bulk material, transfer chutes and vessels must be designed not just to accommodate – but to actually facilitate – the flow of the cargo they will be handling.

Unfortunately, because so many conditions can hamper effective cargo flow, engineering a conveyor and chutework that would handle every material situation is virtually impossible.

Even modest changes in moisture content can cause adhesion to chute or vessel walls or agglomeration at low temperatures, especially if the belt is stagnant for any period of time. Even during continuous operation, a bulk material can become compressed, and physical properties often change due to natural variations in the source deposits, suppliers or specifications, or if the material has been in storage. If left to build up, material can encapsulate belt cleaners and deposit harmful carry-back onto the return side, fouling idlers and pulleys, according to Martin Engineering. At worst, systems can become completely blocked by relatively small (and common) changes. To overcome these issues, a variety of devices collectively known as flow aids can be employed.

What Are Flow Aids?

As the term implies, flow aids are components or systems installed to promote the transport of materials through a chute or vessel, controlling dust and spillage. Flow aids come in a variety of forms, including rotary and linear vibrators, high- and low-pressure air cannons and aeration devices, as well as low-friction linings and special chute designs to promote the efficient flow of bulk materials. These modular systems can be combined in any number of ways to complement one another and improve performance. The components can be used for virtually any bulk material or environment, including hazardous duty and temperature extremes. One of the primary advantages is that an operation can obtain a level of control over the material flow that is not possible any other way.

When employing flow aids, it is critical that the chute and support components are sound and the flow aid be properly sized and mounted, because the operation of these devices can create potentially damaging stress on the structure, the company says. A properly designed and maintained chute will not be damaged by the addition of correctly sized and mounted flow aids.

It is also important that any flow aid device be used only when discharges are open and material can flow as intended. The best practice is to use flow aids as a preventive solution to be controlled by timers or sensors to avoid material build-up, rather than waiting until material accumulates and restricts the flow. Using flow aid devices in a preventive mode improves safety and saves energy, since flow aids can be programmed to run only as needed to control buildup and clogging.

Air cannons

One solution for managing material accumulation in chutes and vessels is the low-pressure air cannon, originally developed and patented by Martin Engineering in 1974. Also known as an “air blaster”, it uses a plant’s compressed air to deliver an abrupt discharge to dislodge the buildup. Cannons can be mounted on metallic, concrete, wood or rubber surfaces. The basic components include an air reservoir, fast-acting valve with trigger mechanism and a nozzle to distribute the air in the desired pattern to most effectively clear the accumulation.

The device performs work when compressed air (or some other inert gas) in the tank is suddenly released by the valve and directed through an engineered nozzle, which is strategically positioned in the chute, tower, duct, cyclone or other location. Often installed in a series and precisely sequenced for maximum effect, the network can be timed to best suit individual process conditions or material characteristics. The air blasts help break down material accumulations and clear blocked pathways, allowing solids and/or gases to resume normal flow. In order to customize the air cannon installation to the service environment, specific air blast characteristics can be achieved by manipulating the operating pressure, tank volume, valve design and nozzle shape.

In the past, when material accumulation problems became an issue, processors would have to either limp along until the next scheduled shutdown or endure expensive downtime to install an air cannon network. That could cost a business hundreds of thousands of dollars per day in lost production. Many designers proactively include the mountings in new designs so that future retrofit can be done without hot work permits or extended downtime. A new technology has even been developed for installing air cannons in high-temperature applications without a processing shutdown, allowing specially-trained technicians to mount the units on furnaces, preheaters, clinker coolers and in other high-temperature locations while production continues uninterrupted.

Engineered vibration

The age-old solution for breaking loose blockages and removing accumulations from chutes and storage vessels was to pound the outside of the walls with a hammer or other heavy object. However, the more the walls are pounded, the worse the situation becomes, as the bumps and ridges left in the wall from the hammer strikes will form ledges that provide a place for additional material accumulations to start.

A better solution is the use of engineered vibration, which supplies energy precisely where needed to reduce friction and break up a bulk material to keep it moving to the discharge opening, without damaging the chute or vessel. The technology is often found on conveyor loading and discharge chutes, but can also be applied to other process and storage vessels, including silos, bins, hoppers, bunkers, screens, feeders, cyclones and heat exchangers.

There is another innovative solution that prevents carry-back from sticking to the rear slope of a discharge chute. The live bottom dribble chute uses material disruption to reduce friction and cause tacky sludge and fines to slide down the chute wall and back into the main discharge flow. By addressing these issues, operators can experience a reduction in maintenance hours, equipment replacement and downtime, lowering the overall cost of operation.

Flow aid devices deliver force through the chute or vessel and into the bulk material. Over time, components will wear, or even break, under normal conditions. Most of these devices can be rebuilt to extend their useful life. Because clearances and fits are critical to proper operation, it’s recommended that flow aid devices be rebuilt and repaired by the manufacturer, or that the manufacturer specifically train plant maintenance personnel to properly refurbish the equipment.

This article was provided to International Mining by Martin Engineering

Martin Engineering on confined safe entry for chutes, silos and hoppers

Bulk handling, Equipment maintenance, Mining equipment, Mining maintenance, Mining safety, , , , , ,

Martin Engineering, a global innovator in the bulk material handling industry, is urging operators to locate safe access points before attempting to unblock chutes, silos and hoppers in order to prevent potential accidents on site.

As the company says, many factors can cause bulk materials to adhere to the sides of chutes, silos and hoppers – including humidity, moisture content, size/texture of the raw material or increased production volume – resulting in lost capacity or clogging.

Ongoing accumulation reduces flow and eventually stops production in order to address the issue, causing expensive downtime and requiring extra labour to clear the obstruction.

Martin Engineering Product Engineer, Daniel Marshall, said: “Clearing extensive build up often involves confined space entry, but the consequences of untrained staff entering a chute, silo or hopper can be disastrous, including physical injury, burial and asphyxiation.

“Without proper testing, ventilation and safety measures, entering vessels containing combustible dust could even result in a deadly explosion.”

What is confined space entry?

The US Occupational Safety and Health Administration (OSHA) defines “confined space” as an area not designed for continuous employee occupancy and large enough for an employee to enter and perform assigned work, but with limited or restricted means for entry or exit. “Permit-required confined space” means a confined space that has one or more of the following characteristics:

  • The vessel contains or has the potential of containing a hazardous atmosphere such as exposure to explosive dust, flammable gas, vapour, or mist in excess of 10% of its lower flammable limit;
  • Atmospheric oxygen concentration below 19.5%, or above 23.5%;
  • There is the potential for material to engulf, entrap or asphyxiate an entrant by inwardly converging walls or by a door which slopes downward and tapers to a smaller cross-section; or
  • Contains any other recognised serious safety or health hazards.

Entering a confined space

Working in confined spaces typically requires special personnel training, safety harness and rigging, extensive preparation and added personnel for a ‘buddy system’.

Marshall continued: “Systems designed to minimise permit-required confined spaces can provide a significant return on investment and the best time to reduce the amount of confined-space entry for component maintenance and replacement is during the specification and design stages of a project.”

Many manufacturers offer systems and products that can reduce the need for confined space entry.

Examples would include:

  • Modular chute designs with abrasion-resistant liners;
  • Chutes that hinge open and lay down for liner replacement;
  • Skirtboards with external liners;
  • Belt cleaners that can be serviced without confined space entry;
  • Flow aids such as air cannons and vibrators to reduce build up; and
  • Modular air cleaners for specific locations rather than centralised dust collection.

Global regulations, standards and best practices

Rules regarding confined space entry vary greatly depending on the country, even down to the state, province or prefecture level. As always, regional and local codes should be identified and followed, but general rules can be drawn from regulations established in major industrial markets such as Australia/New Zealand, Canada and the United States. Commonalities between governmental regulations provide employers with a measured approach to safety.

Prior to starting the job, these procedures include:

  • Review the permit and the job-specific work procedures;
  • Gather and inspect all necessary PPE;
  • Test and/or calibrate any safety gear, test instrumentation or communication tools;
  • If a current Job Safety Analysis or safety check list does not exist, perform a risk assessment;
  • Hold a pre-job meeting making sure all workers are aware of the hazards and safe work practices;
  • Conduct proper tests for toxins, vapour, dust levels, oxygen levels and material-specific hazards;
  • Perform as much cleaning and maintenance as possible outside of the vessel;
  • Post completed confined space entry permit outside of the vessel;
  • Isolate contaminants and moving parts to prevent the accidental introduction of materials; and
  • Proper lock-out/tag-out/block-out/test-out procedures must be completed and documented prior to entry.

During the procedure, they include:

  • Perform maintenance/cleaning using non-toxic substances such as water and avoid using heat/fire in the confined space. Never use oxygen to purge a confined space, as this can create a fire and explosion hazard;
  • Provide ventilation if possible;
  • Select personal protective/safety equipment such as safety helmet, gloves, hearing protectors, safety harness and lifeline and breathing apparatus;
  • Assign a trained observer to monitor the procedure and internal conditions, and provide escape assistance if needed; and
  • Practice fast evacuation of the confined space.

“Over time, well-designed access improves safety and saves money,” Marshall said. “Safe access that is carefully located and adequately sized will increase dependability and also reduce the downtime and associated labour required for maintenance.”

He advises that companies consider equipment designs which minimise the need for confined space entry, including improved access doors, vibrators, air cannons or silo cleaning services.

“Conveyor systems that are properly outfitted with appropriate cleaning and material discharge equipment create a safer workplace, while experiencing longer life and less downtime,” he concluded.

Belzona 1814 to protect chutes, hoppers and screw conveyors

Equipment maintenance, Mining equipment, Mining maintenance, , , , , ,

Belzona has released a new epoxy-based material to, it says, resist the harshest abrasive environments typically found in the mining, cement, pulp & paper, biomass and other industries.

Belzona 1814 can be applied with a brush or a float to protect assets preventing metal loss and subsequent downtime, either on its own or as part of a system with alumina tiles, the company says.

Supplied in 30 kg units, compatible with mechanical mixers and boasting a long working life, Belzona 1814 is most suited for application to large assets, including chutes, hoppers and screw conveyors, according to Belzona.

Belzona R&D Manager, Jason Horn, said: “There was a need for a lasting abrasion protection system, which can be easily mixed in large volumes and applied over sizeable areas.

“Our second objective was to create a formulation with performance equal to our existent abrasion resistant materials, while keeping the costs down – the benefit of which could then be passed onto our end users.

“We believe, with Belzona 1814, we have produced a high performance and cost-effective system.”