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Belt cleaning: just deal with it

 

Why expend any time or effort into cleaning the conveyor belt when it’s only going to become dirty again? As Bradley Owen of Kinder Australia explains, producers that pay close attention to the belt will be able to employ a range of belt cleaning solutions that are cost-effective and enhance the belt’s efficiency.

The root cause of common conveyor issues can often be traced back to ineffective belt cleaning. Spillage from carryback soon becomes a safety hazard if left unchecked and can be costly for maintenance crews to remove. Build-up of bulk material on return rollers has a negative influence on belt tracking. Belt cleaning is fundamental to prolonging the life of a conveyor’s most capital-intensive component – the belt. Given today’s belt cleaning marketplace is filled with an overabundance of belt cleaning solutions to suit every application, there are no excuses for accepting poor belt cleaning performance.

Unfortunately, there is no cleaning solution on the market that can remove 100 per cent of carryback from the belt. The best belt cleaning solutions utilise a combination of different products that have been thoughtfully selected based on the demands of the application. Ultimately, this is a balance of the cost of belt cleaning products and the cost savings due to additional belt and idler life as well as the time savings created for maintenance teams and the reduction of potential downtime.

PRE-CLEANERS AND CLEANERS

The common type of cleaners on the market can be broken down into three categories: pre-cleaners, and primary and secondary cleaners. Primary cleaners are tasked to remove the majority of carryback material, typically about 60 to 80 per cent of carryback on the belt. The primary cleaner is not designed to assist with material discharge and should only be removing product that has adhered to the belt. 

As the name suggests, pre-cleaners are installed before a primary cleaner and are used to remove extremely cohesive or wet materials. Typically, these do no contact the belt and help extend the life of the primary cleaner. Secondary cleaners are tasked to remove the finer carryback that remains on the belt after passing through the primary cleaner. 

Tertiary cleaners are installed further downstream of the head pulley and take the form of brushes, spray systems, beater rollers and self-cleaning return rollers. It is worth noting that in some applications, multiple secondary or tertiary cleaners may be installed. The number of cleaners installed boils down to the properties of the bulk material and level of cleanliness
that is desired.

The head pulley diameter dictates the height of the blade or the length of the suspension arms, depending of the design of the cleaner. Blades that are too small tend to either “flip through” after a certain amount of wear or the free space between the pulley face and blade will fill with the bulk material. Once the cavity is filled, wear on the blade accelerates, leading to premature failure. A blade that is too large is typically designed for heavier duty environments. This may lead to excessive wear to the belt; a consequence of the extra tension, friction and heat that is associated with heavy-duty belt cleaners. This friction introduces additional unnecessary load to the drive unit.

The ideal blade length should match the burden width of the bulk material. It does not take much imagination to understand how a blade that is not wide enough will not deliver the desired results. The reverse is also true in that cleaning performance can diminish quickly over time if the blade length is too long, particularly with softer material blades. The leading edge of the blade wears at a quicker rate in sections that are removing the abrasive carryback. The outer edge of the blade that is scraping the relatively clean belt edge will wear only minimally. As the centre section wears, blade pressure on the belt reduces and cleaning performance is directly affected as a result. Many types of blades can be trimmed to size after installation to suit the burden width. This can be particularly helpful if the exact burden width is not yet known.

Crowned pulleys require cleaners that specifically allow the blade to conform to the crowning profile while maintaining tension across the width of the belt. Usually, this is accomplished by using a series of short segmented blades. Single piece polyurethane blades can conform to the taper of the crown but segmented polyurethane is the better option.

Most belt cleaners are designed to clean the belt while operating in one direction only. Some blades are designed not to damage the belt when operated in reverse. In these situations, two systems can be installed, one at each end of the conveyor. Other blade designs are strictly for one direction of travel and can damage the belt cleaner, belt or splice if operated in reverse.

COMMON BLADE MATERIALS

Blade material selection is generally made based on the condition of the belt, splice type, belt speed, material abrasiveness and desired blade life.

Polyurethane has many favourable properties, making it well suited to a large range of belt cleaning applications. Good abrasion resistance, high flexibility and low friction co-efficient translate to good blade life and minimal abrasion wear of the belt. The high flexibility reduces the chance of belt damage occurring from an incorrectly tensioned cleaner. Both over-tensioning and under-tensioning has its own associated issues but polyurethane has a larger margin of error compared to carbide or ceramic tips.

Tungsten carbide-tipped blades are commonly specified for applications where a higher level of abrasion resistance and thus longer blade life is desired. The lower wear rate translates to a slower loss of tension overtime as the tensioner relaxes to fill the void created by material loss of the blade. This reduces the frequency of blade change-outs and re-tensioning. The maximum permissible belt speed for a tungsten-carbide tipped cleaner is generally higher than that of a polyurethane-tipped cleaner. However, some formulas of polyurethane work successfully on belt speeds in excess of seven metres per second (m/s).

An option to tungsten carbide blades are cleaners utilising alumina ceramic chips. Alumina ceramics are incredibly hard and are used as wear liners in extreme sliding abrasion applications. In belt cleaning applications this means the wearing surface maintains its geometry, providing excellent life with the same benefits as tungsten carbide.

Mechanical belt splices and fasteners such as repair staples are incompatible with carbide and ceramic belt cleaners, due to the relatively low impact resistance of both materials. Hot vulcanised splices are a necessity when specifying either of these types of cleaners. Polyurethane blades are compatible with hot vulcanised splices and some mechanical fasteners. Edges of belt repair patches are less likely to be lifted as a polyurethane belt cleaner passes over the repaired section compared to a carbide or ceramic cleaner.

MORE TO CLEANING THAN JUST ‘SCRAPERS’

The condition of the conveyor belt covers is commonly overlooked as a selection criterion for belt cleaners. Cuts, gouges and abrasions that accumulate over the life of the belt result in an irregular surface that is difficult to clean. Fugitive material amasses in cavities created by impact damage at transfer points, groove lines from skirting and general uneven wear caused by material abrasion. Carbide and ceramic cleaners are often too stiff and may have little effect on belt cleanliness if the belt surface is uneven. These cleaners are best suited to brand new or undamaged belts. Polyurethane blades are much softer than carbide or ceramic blades and are much more effective on older belts where the surface has become uneven. As the blade wears, the polyurethane conforms to the belt surface and maintains its cleaning effectiveness over the life of the blade. Brush-type cleaners provide very good cleaning efficiency for heavily damaged or rough top belts. Motorised brush cleaners are most effective but non-powered brushes installed at an angle to the belt direction provide an economical alternative.

Conveyors with chevron belts are more difficult to keep clean as traditional “scraper”-type cleaners will damage the belt. Speciality scrapers designed specifically for chevron belts are available. Generally, these utilise very thin segmented blades which have a high degree of lateral flexibility. These thin blades allow the chevron to pass without damage. Brush cleaners with thin flexible nylon bristles are effective on belts with a small chevron height, typically less than 10mm tall. Taller cleats create difficulties cleaning into the corners and can generate too much heat when cleaned by a motorised brush. Return rollers with offset lobes can be employed to vibrate the belt and “shake off” the carryback. Also known as a beater roller, these can also be used on deep pocket belts.

There may arise a situation where it is advantageous to remove carryback further downstream or away from the head pulley. In these cases, polyurethane return rollers with spiral flutes angling towards the centre of the belt act as rotating cleaning blades. Spiral rollers can be installed on V-return systems but the frames should be designed such that the removed material does not build up. Shaker rollers and brush-type cleaners are also viable options in these situations. Furthermore, these options do not require a vulcanised splice or good belt cover condition to operate effectively.

FINAL THOUGHTS

All belt cleaners require frequent inspection and regular maintenance to perform optimally over their lives.

Cleaners should be positioned thoughtfully, ideally so that displaced material is directed back into the product stream or into a bin for easy housekeeping.

Any reputable belt cleaner manufacturer will have numerical and empirical data to make belt cleaning recommendations. They will be able to provide specific technical information about the suitability and installation of their products. Recommendations made by the manufacturer should be followed to maximise the cleaner’s performance.

No matter the application, there is a belt cleaning solution to suit.

Bradley Owen is a qualified mechanical engineer for Kinder Australia.