Belt-washing systems function on largely the same principles as traditional belt-cleaning systems, with the crucial introduction of water into the equation. Nevertheless, they are more technically sophisticated and far more effective than traditional mechanical methods of belt cleaning alone. The addition of water to the process has three major effects on conveyor belt cleaning:
- Water can help to “soften” and loosen material, making it easier to remove by use of a scraper.
- Water prevents material from building up on the belt-cleaning blade, improving cleaning efficiency.
- Water reduces friction between the belt and cleaning blades, decreasing the forces that generate blade and belt wear. This helps to extend the life of both the blade and the belt, while increasing the intervals between maintenance.
Methods for Washing the Belt
Conveyor belts can be washed effectively in several different ways. The three accepted practices that have emerged were described in the 1987 paper by Dick Stahura entitled “Conveyor Belt Washing: Is this the Ultimate Solution?” Stahura refers to these methods as flood, bath and wash box.
- Flood Method
The flood method takes a brute force approach by using high-pressure jets of water to essentially take the role of the traditional belt scraper. Carryback is blasted off the conveyor belt using only the water and a following squeegee-type blade is used solely for scraping off remaining water.
These jets are generally sprayed at 400 to 700 kilopascals, or 60 to 100 pounds per square inch, though they can also be supplemented with the use of compressed air.
These systems are limited somewhat by their specific requirements, calling for specialized nozzles and clean water to work effectively, they also require a larger amount of water than other types of washing systems.
The adhesiveness of the conveyed materials can also pose some limitations, as can the belt speed. In order to ensure that the belt is exposed to the steam long enough to be thoroughly cleaned, belts must generally move no faster than 5 meters per second, or 1000 feet per minute. - Bath Method
The bath method consists of pulling the belt through an enclosure filled with water. It includes no spray jets, nozzles or any active parts, but rather requires only a system to maintain water level and to exchange water as necessary to prevent sediment build-up.
This enclosure could be located along the belt return or even at the gravity take-up, where the weight of the “bath tub” of water can become part of the conveyor’s counterweight tensioning system. The key consideration is more about the length of the bath, as the belt must remain under the water sufficiently long to loosen any carryback. - Wash-Box Method
The wash-box method represents the current best practice in belt-washing. These systems combine the water-spray from the flood method with a traditional belt cleaner in an enclosed box. The specifications of the wash-box can depend on the belt speed, materials conveyed, belt width and belt composition as well as the required level of cleaning and drying. Some conveyor belts might also have certain site constraints, such as water usage restrictions or environmental compliance standards.
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