The key distribution system of any mineral processing plant is its conveyor network. Thomas Greaves, managing director of DYNA Engineering, explains how cleanliness keeps it running.
Unscheduled stoppages and shutdowns of a conveying system will cause major losses of productivity and income. If it remains undetected, or is caused by a serious problem, it can mean a shutdown of the entire plant operation in a matter of moments.
It’s definitely better to be safer than sorry when dealing with conveyor belt cleaning and maintenance procedures.
The head culprit is carry-back
Material being transported on a conveyor belt is discharged at the head pulley. However, a small percentage of the material won’t be discharged – it will stick to the belt surface. Carry-back is the term used for this residual material. It causes spillage along the return strand of the conveyor which, if left unchecked, will quickly build up and drop off causing a variety of increasingly expensive and extremely serious problems.
The amount of carry-back on a return conveyor belt can be affected by:
- The consistency of the material – whether it is dry or wet
- The characteristics of the material – whether its large lumps or fine dust
- The mechanical design of the conveyor – e.g. the belt speed and pulley diameter
Cleaning equipment to remove
carry-back
Most belt cleaning equipment is aimed at removing the greatest possible percentage of carry-back at the head/discharge pulley. This is broadly broken down into contact cleaners and non-contact cleaners. The most common types of contact cleaners are:
- Primary, secondary and tertiary scrapers
- Brush cleaners
- V-Plows or Return Ploughs
Non-contact cleaners used most often are:
- Air knives
- Spray bars
A spray bar is a pipe arrangement with several evenly spaced spray nozzles fitted. The spray nozzles are used to disperse a liquid, usually water, in a desired pattern over an area, to increase the liquid’s surface area, or to create an impact force on a surface. Water is distributed across the belt surface to clump materials together within the water, creating a mud or sludge, so it can be more effectively scraped from the surface. Or the water is used to impact the surface to dislodge particles from the belt surface and flow away with the water during the scraping process.
Depending on the characteristics of the materials being conveyed and the intended application, spray pressure and pattern play an important role to achieve your best outcome.
Usual location of the spray bar
Normally located between the primary and secondary scraper, a spray bar is designed to position the spray nozzles in the most effective position in relation to the conveyor belt surface. Both distance and angle to the belt surface need to be optimised for the highest cleaning efficiency.
After the primary scraper has performed its initial cleaning function, some material may still be present. To further decrease carry-back, water is sprayed onto the belt surface. The water is used to soften the carry back and wash away particles into the chute to be re-combined with the material flow. In this configuration, the secondary scraper, located after the spray bar, finishes the cleaning of the conveyor belt, and also removes any remaining water from the conveyor belt.
Spray bars can be configured in many ways depending on the application, space, and surrounding structure. Some common examples include using the secondary scraper shaft as the spray bar as shown in the photo or mounting a separate spray bar between the scrapers.
Another common configuration is to install spray bars between the secondary and tertiary scraper.
This adds an additional level of cleaning which will result in the best possible clean for the conveyor belt.
Dust suppression assistance
Spray bars can also be used in dust suppression applications. When dust forming materials are aerated or exposed to moving air streams, particles can be separated and carried away in the air. In the case of the material being conveyed, the belt velocity or even a gust of wind can result in dust generation. In these cases, simply wetting the surface material can be an effective counter measure.
Another main dust generating location is where the material is disturbed. Well known locations can include loading points, chutes, crushers, and screens.
Spray bars can be effective in many of these locations to reduce the amount of dust that is allowed to escape into the surrounding environment. In this case, the liquid is atomised into the air as mist, forming water droplets that are used to capture dust particles. The droplets are either sprayed toward the source of the dust or redirected with a fan towards the dust generating location. Dust will be captured by the droplets and carried towards the ground by gravity.
Benefits of DYNA Engineering’s FastFit spray bars
DYNA FastFit spray bars are a unique design that employs a fully retractable spray bar mounted in a stationary shaft to form a two-part assembly. With the stationary shaft remaining in its location, the spray bar can simply and safely be removed by disconnecting from the water supply and removing two clips.
Then the spray bar can be retracted from the stationary shaft in a matter of seconds. No need for stoppages. No need for highly skilled labour.
There are no tools required to remove the spray bar, no need to remove guards, and the opening left when the spray bar is removed complies with AS 4024 Safety of Machinery.
DYNA FastFit Spray Bars can be designed for a vast range of applications, flow rates and supply pressures. Configured to suit almost any application, they are made from stainless steel for a long-lasting solution. They will not rust or corrode and are suitable for non-potable water sources including high salinity water and recycled process water.
Safer maintenance
When the spray bar is removed from the stationary shaft, maintenance can be performed in a safe and ergonomic location. This allows maintenance personnel to quickly remove any sediment build up from the pipe and unblock any clogged nozzles from outside of the chute.
Blockages are a common point of failure when using water sourced from recycled process water or dam water. The spray bar can then be simply returned to its original position, water supply connected and returned to operation.
Because this can be done safely while the conveyor is running, there is no need to wait for the next shutdown. This ensures cleaning efficiency is maintained and carry-back is kept to a minimum throughout the production cycle.