Let's start with the fundamentals … what is carryback?
Carryback is the product that makes its way past the drop off point and runs back along the underside of the conveyor belt. The amount of carryback on the belt can depend on a number of factors including the type of product, whether it be iron ore, coal, or aggregate; the way the belt is oriented; or even the climate or environment surrounding the application. No matter what the cause, the goal is always consistent - to recover the carryback product before it creates hazards and results in a loss of productivity.
When carryback leaves the belt, it has to go somewhere; that somewhere is typically the ground, creating mountains of product. This isn't only a significant on-site hazard, but it creates a clean-up job that can create unscheduled downtime for the site.
Carryback on a conveyor is inevitable no matter what the product, however avoiding this is typically no problem if you've got the right equipment installed. With some sites losing close to a tonne of product every day just because of carryback, recovering the lost product seems like the obvious solution to an increase in productivity and revenue. However picking the right equipment to solve the issue of carryback isn't always as straight forward as a "one product fits all" type of purchase. Below we've outlined the best methods for combatting carryback.
The First Step: Selecting a Belt Cleaner
Picking equipment to combat carryback can vary depending on the application. Whilst some options are more financially viable, they may not achieve the desired result in heavy-duty settings. Belt cleaning tools include primary cleaners, secondary cleaners, spray bars, and wash boxes. Each of these work effectively for different purposes; however on their own they don't always eliminate carryback as a whole and can leave a gap in your defence.
Primary Belt Cleaners & Secondary Belt Cleaners
Primary belt cleaners with tungsten carbide tips or polyurethane blades are designed to scrape material off the conveyer belt, they are usually positioned on the head pulley. Primary cleaners are designed to scrape up to 60%-70% of material, typically removing the larger pieces. Where primary cleaners will not suffice is when the material is sticky, there is a humid climate, or there is simply not enough room to allow for one. In these circumstances, many will chose to employ a secondary or even a tertiary cleaner.
However, we can imagine you want to clean off more than 70 percent of your carryback …
Secondary cleaners are belt cleaners that are built to scrape materials left on the belt beyond the head pulley. Secondary cleaners are located just beyond where the belt leaves the head pulley, and anywhere else where necessary down the beltline. Secondary cleaners are especially good at removing fines and can, in some settings, increase cleaning efficiency to more than 90 percent. However, if you're working with extremely sticky material or in abrasive or corrosive climates you may need a heavier-duty solution.
Taking it up a Notch: Incorporating Water
Typically used alongside secondary cleaners, spray bars (also referred to as spray poles) offer another source of protection in combatting stubborn carryback. Adding water to the equation helps either break down or collect remaining carryback in a form that is easily cleaned from the belt.
Water can have drawbacks including: uncontrolled material movement, spillage, and material degradation. Issues like this can result in downtime and clean-up cost, equipment damage, and corrosion of conveyor structure and components.
However, a well thought out water management program can typically outweigh these negatives. Plans that incorporate a recycled water system and controlled runoff will negate these issues. Along with water management systems, investing in a spray bar that has a maximum inlet pressure of 1000 kPa will give you the perfect balance between having enough water to clean your belt, and avoiding nasty issues like material degradation. Allowing your site to incorporate a water-based cleaning system is often integral to the productivity of a cleaner when a standard cleaning system just won't do.
Finally, the Ultimate Cleaning System
In some settings, a primary cleaner, secondary cleaner, or spray bar just don't cut it when trying to remove carryback. Incorporating a wash box into your conveyor allows you to virtually eliminate carryback, even in the toughest applications.
A wash box is a fully enclosed system which incorporates both belt cleaners and spray bars. The spray bars flush material off the bottom pan out the drain portal, fully containing the waste wash water. This means you get a clean belt and waste water management system in one.
Most wash boxes are custom engineered. The benefits of this are getting to choose your favorite belt cleaners and rollers, as well as custom fit to mount to existing stringers for easy installation.
Manufactured in Australia, Flexco Wash Boxes have proven to be one of the most effective ways to combat carryback. The perfect example of this is the results seen at the Port Kembla Coal Terminal, where a custom-engineered wash box was installed, reducing carryback by 94 percent and saving over 720kg of product per day. Such successful results found the site's carryback being reduced to just 2kg per hour, exceeding all expectations of the Port Kembla Coal Terminal maintenance team.
To create a success story of your own, get in touch with the Flexco team to see how you could incorporate a Flexco wash box onto your conveyor and stop carryback for good.
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