As environmental concerns become ever more significant, the need for efficient conveyor belt cleaning is increasing in importance, but getting it right can bring production and maintenance savings.

As environmental concerns become ever more significant, the need for efficient conveyor belt cleaning is increasing in importance. Historically belt cleaners have been widely viewed as unimportant add-ons. However, in today's increasingly environmentally aware quarrying industry this view is rapidly changing.

At first sight, choosing a belt cleaner may seem a straightforward matter with a wide choice of systems on the market.

Getting it right is actually not so clear cut, but the benefits of doing so can bring environmental improvements, increased production and reduced maintenance costs, which make it well worth the investment.

If a conveyor is not cleaned efficiently, a residue of small sticky particles known as 'carry over' builds up on the top of the belt.

This can cause spillage and wastage of materials and high clean up costs.

Plus, the ongoing build up can cause return rollers to fail, potentially resulting in belt damage, higher maintenance, repair and replacement costs.

To ensure the conveyor is cleaned effectively, the cleaning system should maintain a constant angle between the scraper blade and the belt - 90 deg is optimum.

Correct installation and adjustment are critical in achieving effective belt cleaning.

Each blade should be applied to the belt with equal pressure to ensure consistent cleaning across the belt width.

To ensure cleaning is achieved efficiently and cost effectively, the system should achieve the minimum of wear to the belt cover and blades, be automatic and fail safe in operation and require minimum maintenance.

In practice, the majority of systems are given little or no maintenance priority and either do not clean effectively, or require ongoing maintenance checks and adjustments to achieve average performance.

* The lever principle, on which most belt cleaners are based, allows variation in blade angle and pressure.

Some even create a negative belt-to-blade angle, causing excessive friction and wear.

The rubber mounted conventional scraper has serious shortfalls as illustrated by the following: a) Regular maintenance checks and adjustments are needed to ensure optimal performance.

b) Some blades will have a negative blade-to-belt angle - causing belt wear.

The difference in blade-to-belt pressure per segment will increase as wear occurs.

c) Adhesive deposits onto the rubber suspension can reduce the scraper's effectiveness.

Many conventional scrapers operate with a negative blade-to-belt angle.

It is well established that the conveyor belt surface has a pre-determined roughness at installation.

As wear occurs on the belt surface, during service life, the roughness will progressively increase (3-15 micron).

The same applies to the contact area of the scraper blade on the conveyor belt (01-02 micron.

It is possible for some very small particles to pass between the belt and the cleaner blade, this is known as 'carry over'.

The abrasion of the carry over causes conventional blades to lose their cleaning edge quickly and creates the need for frequent manual maintenance and adjustment.

Using sharper blades may improve the cleaning but can also cause damage to the belt.

Carry-over is the material that passes between the belt and the scraper blade.

The pressure applied by conventional systems, which usually operate at a maximum of 1.1 - 1.4 kg/cm2 to prevent wear, however this may not be sufficient to remove the stickier deposits.

The difference in blade-to-belt pressure per segment also increases as the blades wear, again creating the need for frequent adjustments.

One system which has been specifically designed to address these problems in the most demanding environments is the 'Dirt Whacker', available in the UK through Ace Arc .

According to managing director Frank Fairbrother, it ensures the least carry over of any conveyor cleaner on the market today.

It also has the lowest running costs, with no manual adjustment required after installation and blade life of up to two years being achieved in some granite quarries.

The Dirt Whacker has a simple yet robust design, consisting of a set of articulated parallelograms mounted along a common rack with a rubber air bladder running through the middle.

Pressurisation of the air bladder ensures that each blade is always held at the optimum 90o angle to the belt and maintained at the set pressure.

The DirtWhacker Secondary belt cleaner Its scraper blades have a long-life tungsten carbide insert and have blunt edges and rounded-corners to prevent damage to the belt rubber.

This allows the system to operate safely at much higher belt/blade pressures - up to 40-60k/Pa.

The higher pressure creates a squeezing action on the belt rubber, effectively forcing the dirt to drop off the belt before it reaches the blade.

The pressure within the bladder can be precisely set and adjusted remotely if required to maintain the optimum balance of effective cleaning with minimum wear.

Less carry over means less wear on the blades, substantially prolonging their life.

Even when the blades do begin to wear, the self-compensating action of the parallelograms and inflatable bladder automatically adjusts each blade to maintain a constant pressure on the belt, again maintaining cleaning efficiency while minimising the need for replacement.

Special features include a no-load device, which senses when the belt is running empty and automatically removes the pressure from the bladder.

This eliminates unnecessary mechanical and thermal wear to both the belt and the cleaner.

A clip avoidance system can also be fitted to detect mechanical joints.

An inductive sensor senses the clip and automatically reduces pressure in the air bladder, allowing the joint to pass over the cleaner blades with a minimum of resistance and interference.

A pressure regulator and relief valve maintains the pre-determined pressure, even where on-site air pressure is intermittent, so that no manual correction is required between installation and blade change.

Where necessary, air filters and moisture traps ensure a constant supply of dry, uncontaminated air.

The Dirt Whacker is designed to be completely failsafe in operation and requires no specialist labour in between blade changes.

The only routine maintenance required is a quick check of the pressure gauge just to ensure the correct air pressure is maintained in the bladder and occasional checks on blade wear, although indicators clearly show when a blade needs replacing.

While it can be used as a primary cleaner where space is an issue, the Dirt Whacker is principally used as a secondary cleaner and, according to the manufacturers, will provide effective cleaning without the need for a pre-cleaner in the majority of installations.

It is compatible with most existing scraper mounting arrangements and the majority of belts sizes, speeds and fasteners, including reversible belt systems.

It can be retrofitted to all conveyor belt installations and can be integrated into existing programmable logic control systems.

Customised systems can also be designed to suit different applications Norwegian quarry owner Franzefoss recently installed Dirt Whacker systems on the conveyor belts at its Steinskogen rock quarry near Sandvika.

Project manager Brynjar Lund-Andersen said, 'We have two Dirt Whackers installed and are very happy with their performance.

Without proper belt cleaning we get a lot of spillage under the belt-idlers that gives us extra cleaning costs.

Spillage on the idlers also causes wear that could eventually lead to the breakdown of the conveyor.