There is an increasing need for owners and operators of conveyor belt systems to have a clear understanding of the different types of cleaning equipment available, the features and benefits of different cleaning techniques, as well as where the cleaners should be located for optimum results.
The head culprit – carryback
Material transported on a conveyor belt is discharged at the head pulley. However, a small percentage of this conveyed material will not be discharged with the bulk of the load stream – it will stick to the belt surface. Carryback (or carryover) 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.
This is why you need up to date and efficient belt cleaning equipment properly fitted and constantly operating on all of your conveyor systems.
The amount of carryback on a return conveyor can be affected by:
• The consistency of the material – whether it is dry or wet
• The characteristics of the material – whether the product comprises large lumps or fine dust
• The mechanical design of the conveyor – e.g. the belt speed and pulley diameter
Range of cleaning equipment
Most belt cleaning techniques are aimed at removing the greatest possible percentage of carryback at the source, that is at the head/discharge pulley. A very comprehensive range of conveyor belt cleaning equipment is available, broadly broken down into contact cleaners and non-contact cleaners. The most common 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.
Focus on 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 carryback, water is sprayed onto the belt surface. The water is used to soften the carryback 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 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 that 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 materials 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.