THE CLEANING OF CONVEYOR BELTS – A SEVERE AND DIFFICULT PROBLEM, BUT NOT IMPOSSIBLE TO SOLVE

The cleaning of conveyor belts can at times be a major problem in many plants. Attempts have been made to develop conveyor belt cleaners, which would finally solve the problem of carry-back. Technicians at Metso Minerals have been gathering experience and testing for new solutions. The target has been to develop products with high cleaning efficiency, long wear life and a minimal need for maintenance. These efforts have now resulted in a new belt cleaner product range designated Trellex ABC – Absolute Belt Cleaning, when working in the pre-cleaner mode.

After material has been discharged from the conveyor, particles adhering to the belt (carry-back) must be removed to prevent spillage along the conveyor and material build-up on the return rollers, otherwise the result can lead to mistracking and belt edge damage. Material spillage around the conveyor means extra maintenance and clean-up cost. A description of some commonly used types of belt cleaning devices are set out below, together with their area of use and function.

Pre-Cleaner

A Pre-Cleaner is normally positioned against the drive pulley immediately below the flow of material.

As a guide the lower the belt speed, the lower the cleaner should be mounted similarly the higher the belt speed, the higher the cleaner can be mounted. This is to ensure that the cleaner is not hit by the material flow.

The Pre-Cleaner has a tough task as it removes most of the material that adheres to the belt after unloading. The Pre-Cleaner is especially suitable when coarse or moist and sticky material is transported.

In this mode of operation, Metso Minerals has developed its new belt cleaner Trellex ABC range.

Secondary Cleaner

Secondary cleaners are available in a number of different designs. What they all have in common is that they are installed immediately behind the drive pulley. Two commonly used models are the T-Cleaner and the Arm-Cleaner. The T-Cleaner is pressed directly against the belt, while the Arm-Cleaner has a twisting motion. Secondary cleaners are normally used in combination with a Pre-Cleaner for the highest cleaning efficiency, but they can also be used as stand alone if the material transported is dry and fine.

Belt Brush

A Belt Brush is a suitable method for cleaning cleated belts since scrapers do not work with this type of belt. A Belt Brush can be mounted anywhere on the return part of the conveyor, but the most suitable place is immediately behind the drive pulley. The bristles should not be pressed against the belt, but only gently touching for the best result and wear life. A Belt Brush works best on conveyors transporting relatively dry material.

Plough-Cleaner

Material that gets pinched between the belt and the tail pulley can cause the carcass of the belt to break. It therefore has to be removed before the belt reaches the tail pulley using a Plough-Cleaner. This can be combined with a scraper placed against the tail pulley, which removes any material that has managed to pass the Plough-Cleaner. Rubber or Polyurethane strips are suitable as the wearing part on a Plough-Cleaner.

No matter how sophisticated a belt cleaner may be, there are certain premises that have to be fulfilled to give it a fair chance of working well. The following factors affect the efficiency and the wear life of a belt cleaner:

The Condition of the Belt

As demands are put on the condition of the belt cleaner, certain demands must also be put on the belt. The belt must be in a condition that it is possible to scrape off the adhering particles. The cleaning efficiency is reduced if the belt is old or its surface is worn or damaged. It is also important to check that the belt splice is smooth to avoid the belt cleaner getting stuck. If the belt is spliced with mechanical belt fasteners, it is important that these are countersunk. If required, the splice can be covered with rubber cover strips.

Maintenance

As for all equipment in a plant, it is recommended to regularly check and maintain the belt cleaner. If the blades are worn, the efficiency drops and the spillage increases.

The blades should therefore be replaced regularly. In many designs the blade to belt contact pressure diminishes as the blades wear. When the pressure reduces, the risk of fine material passing between the blade and the belt increases. When this occurs, spillage along the conveyor as well as the wear rate on the blade increases dramatically. It is therefore very important to make sure that the blade to belt contact pressure is correct.

Transported Material

Belt conveyors are used in many industries. Everything from wood chips, recycled paper and garbage to iron pellets and crushed rock is moved with the help of conveyors. Obviously the characteristics of the transported material such as its hardness, shape and abrasiveness affect the wear life and efficiency of the belt cleaner.

Choice of Cleaner

It is important that the right type of cleaner is chosen, depending on the application required. The wrong choice of product can result in a shorter wear life or insufficient cleaning efficiency. Available space or other factors like temperature and working environment can also determine the choice of product.

Choice of Wear Material

It is also important to choose the correct wear material, depending on the material transported. Advanced wear materials cost more and can be unnecessary, for example, in light duty applications.

Similarly a cheaper wear material may not provide the wear life needed in a more demanding application. A number of different materials are used in today’s’ belt cleaners by various manufacturers with Metso opting for polyurethane for its hard wearing properties offering long wear life, yet at the same time, it is not abrasive against the belt.

Whilst rubber, for example, has good wear resistance it is generally too soft to be used as a belt cleaner, with poor rigidity and reduced efficiency. Another material, Tungsten Carbide, offers good resistance but it can cause belt damage. Ceramics can ensure a long wear life but is brittle and sensitive to impact which may shatter the scraper edge.

Incorrect Installation

A belt cleaner can only function if it is installed in the correct way and in the right location. Both the efficiency and wear life may be considerably reduced if the belt cleaner is incorrectly installed. A safeguard to ensure successful installation is to let experienced service technicians undertake the installation and adjustment of the belt cleaner.

Belt Speed

High belt speed can adversely affect the efficiency of a cleaner, as the time that the edge of the scraper is in contact with a specific point on the belt is extremely short. The wear life of the cleaner is therefore affected in this instance. The high speed in combination with the coefficient of friction between the belt and the blade can result in increased temperature reducing the wear life of the scraper.

Vibrations

An unsteady belt on the conveyor which may be ‘jumping and shaking’ due to uneven or damaged rollers or return roller rubber discs, will reduce the efficiency of the belt cleaner.

Service and Maintenance Increases the Profitability

It is important that after every scraper installation regular inspections and maintenance are undertaken. When the scraper system has been mounted routines must be established for servicing and maintaining the system. This is a precondition for the system to remain efficient over a long period of time and consequently increases the profitability of the plant.

This article therefore highlights that clean belts are not only a question of aesthetics, but to a high degree also contribute to more up-time, longer wear life and reduced clean-up and maintenance costs.

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Metso Minerals, part of Metso Corporation, is a global market leader in the rock and minerals processing industry. The company focuses on the supply and service of processes and related equipment. Metso Minerals has sales and service units, dealers and distributors in 150 countries, and more than 40 production units worldwide.

In September 2001, Metso Corporation purchased Svedala Industri AB, a global supplier of products for rock and minerals. The new Metso Minerals consists of the previous Nordberg and Svedala operations. The names Svedala, Nordberg, Trellex, Lindemann, Reedrill and Dynapac will continue as trademarks of Metso Minerals.

For further information please contact:

https://edir.bulk-online.com/profile...o-minerals.htm

Caption 1. Trellex ABC 70 scraper installed on a conveyor belt after a primary jaw crusher. The transported material is crushed granite 0-300 mm.

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