Beginners Guide

Reference Source = Belt Conveyors for Bulk Materials (CEMA)

Types of Belt Cleaners

Single or multiple blade belt scrapers are designed for scraping material from the belt surface. A typical single blade scraper is shown in Figure 1 below.

One or more blades are held in contact with the belt surface by counterweight or spring tension. A single blade scraper consists of one blade across the width of the belt. A multiple-blade scraper consists of two or more parallel blades across the width of the belt.

A scraper blade can be made from any of several materials. A combination of materials sometimes is used on multiple-blade scrapers, to improve cleaning results. For example, a rubber blade and a special steel blade may be used in combination.

Strips of belting should not be used for scraper blades. This is because fine particles of the material being handled on the conveyor may become embedded in the fabric of the blade, causing excessive wear on the cover of the conveyor belt. Any rubber scraper blade should be made of solid rubber with no fabric or fibre reinforcement.

Scraper blades are made of the following three designs:

• Straight blade across the belt. Refer to Figure 1 above. When used on contact with the belt on a crowned pulley, the blade wears to conform to the shape of the belt and pulley. The blade usually is made so that it can be adjusted for the most effective cleaning action.
• Sectionalised blades. Figure 2 below illustrates on form of sectionalised blades. Here, the blades are sectionalised to conform to the crown of the pulley. This design does not require a break-in period to wear the blade to the shape of the belt on a crowned pulley. It effectively cleans the belt from the time of initial installation.

• Articulated Blades. This design consists of a series of short blades, pivoted on arms which are spring-loaded to maintain contact with the belt surface. The blades are arranged in an over-lapping pattern, so that the entire width of the belt is cleaned. This type of belt cleaner must be inspected frequently and adjusted so that the blades are free to pivot and to contact the belt properly. See Figure 3 below.

Rotary belt cleaners consist of power driven shafts or tubes to which brush bristles or blades are attached. These brushes or blades are made wider than normal belt width. The brush bristles are made of nylon or bassine. The blades are made of rubber. See figure 4 below.

The rotary brushes, which have a flicking action, usually have bristles in a helical pattern.
They are of two types:

• Low-speed rotary brush. This type of rotary brush is designed to operate at peripheral speeds of 2.05 to 3.08 m/s, and is most effective on dry granular materials. It gives a longer life because the lower speed causes less wear on the bristles.
• High-speed rotary brush. The high-speed rotary brush is designed to operate at peripheral speeds of 5.13 to 7.7 m/s. It is most effective on damp granular materials. The high speed produces centrifugal dislodgement of material from the bristles.

The rotary-blade type belt cleaners use rubber blades arranged parallel to the shaft, or helically on the shaft. These rubber blades have a squeegee or scraping action.
They are also made in two types:

• Low-speed rotary cleaner. The peripheral speed of this type of rotary blade cleaner is 5.13 m/s. It is used or either dry or damp materials. the relatively low speed gives longer life to the rubber blades.
• High-speed rotary cleaner. The peripheral speed of this type of rotary blade cleaner is 7.18 m/s. This high-speed rotary blade cleaner is adapted to cleaning the belt of wet sticky materials which would adhere to build up on the bristles brushes.

The direction of motion of rotary brush and rotary blade cleaners is such that the periphery of the brushes and blades move opposite to the direction of the conveyor belt.

Rotary brushes or parallel and helical rotary blade belt cleaners may be driven by chain from the adjacent head pulley shaft; or by a separate drive.

Water spray and wiper. The use of a high-pressure water spray has been effective as a belt cleaner on certain difficult applications. The high-pressure is directed against the surface of the conveyor belt by means of nozzles with control valves. A rubber-bladed scraper is installed behind the water spray so that after the water spray washes and cleans the belt, the rubber wiper acts as a squeegee to remove the excess water.

While this type of cleaning is quite effective on certain materials, it has two disadvantages. Provision has to be made to dispose of the wash water, and freezing weather makes the whole scheme in operable.

The scraper bar should have a hardened bevel scraping edge. And, it should be adjustably fixed in position on a stiffened so that the bevelled edge of the scraper blade just clears the pulley face and works like a chisel, to shave of any material that clings to the pulley.

Belt Turn-Over Scheme

To eliminate the problems caused by a dirty belt in contact with return idlers, the belt can be twisted 180° after it passes the discharge point. This brings the clean surface of the belt in contact with the return idler rolls. The method of accomplishing this is illustrated in Figure 5 below.

The belt must be turned back again 180° before entering the tail section, to bring the conveying side of the belt up at the loading point.

Because abnormal tensions are induced in the carcass of the belt, the conveyor manufacturer should be consulted for the proper location of the snub pulleys which turn the belt. These are not shown in the figure. The distance required to accomplish the 180° turn of the belt is approximately 12 times the belt width.

Location of Belt Cleaner

The belt cleaner should be so located that the material which is removed from the belt can fall into the discharge chute or can be collected for practical disposal.

Single or multiple-blade scrapers, with spring or counter-weighted construction, should be located at points around the contact surface of belt and pulley or immediately after the belt leaves the pulley. Design of the discharge chute often determines the specific location. The articulated-blade cleaner is located on the return run of the belt, just after the belt leaves the pulley. This is shown in Figure 3.

The rotary blade cleaner is usually located behind the point where the belt breaks contact with the pulley, Figure 6.

The rotary brush cleaner should be located as described for the rotary blade cleaner. However, if necessary for reasons of chute design, snub pulley location, etc., the rotary brush may also be located to brush the belt clean while the belt still is in contact with the pulley.

Return-Belt-Run Cleaning

Even though a belt conveyor is carefully designed, spillage from the belt may occur at the loading point and elsewhere along the belt. If such spillage should strike an idler support bracket, it might land on the return run of the belt. Such material then would become trapped between the belt and tail pulley, causing possible damage to the belt or causing belt misalignment. Two methods of preventing this difficulty are through the use of cleaner plows or deck plates.

Deck plates. Made up of flat, bent, or curved plates or metal sheets, deck plates or decking can be placed between the carrying and the return run of the belt. This construction, which is conventional on all well-designed belt conveyors, provides excellent protection for the return run of the belt, both from any spill material or the weather.

Sometimes decking is applied only at the loading point and forward of it for about the next 15 m. If this design is used, then a return belt cleaner plow, as described below, should be provided.

Return-belt-cleaner plow. A return-belt-cleaner plow, located on the upper side of the return belt just forward of the tail pulley, will plow from the belt any material that may have spilled on the return run and thus prevent such spilled material from being trapped between the belt and tail pulley. This plow should be a V-type with a 60° included angle. The vertex should point toward the head-end of the conveyor. The plow should be located between the tail pulley and the first return idler from the tail pulley, and it should also ride on and be supported by the conveyor belt. See Figure 7 below.