Saturday 23rd Mar, 2019

Conveyor dribble chute containment

Extreme build up on the dribble chute rendering the secondary cleaner inoperable.

Experts from ESS Engineering Services & Supplies explain how dribble trays or chutes can be used to divert the fines stopped by conveyor cleaners back into the main material flow.

Conveyor belts are an efficient and cost-effective method of moving bulk materials over long distances. They can transport a range of materials and integrate into other mine processes such as crushing, screening, rail car loading, stockpiling and ship loading. 

However, the inherent problem of fines or sticky material remaining on the belt after reaching the discharge point results in increased risk to operational efficiency and reduced wear life of the conveyor carcass, components and structures. When fugitive material escapes the designed material stream, it is known as carryback or spillage. This may impact on the environment, reduce safety and employee morale while increasing maintenance and replacement costs, and increased clean up costs.

Installing a belt cleaning system reduces carryback by removing the fines from the belt after the discharge point. Implementation of an efficient design must include capturing and returning fugitive material to the intended material stream. When combined with planned maintenance and inspections of the transfer point, belt cleaners will ensure continued effective bulk handling operations.

A primary cleaner is positioned so that the material recovered will simply re-join to the bulk material flow. Most primary belt cleaners will effectively remove the 90 per cent of product adhering to the belt around the head pulley.

However to eliminate fines and sticky materials, both primary and secondary cleaners are necessary.

The discharge from the secondary may be deposited outside of the containment area so capturing and directing the material may require dribble trays or chutes to divert the fines stopped by the secondary cleaner back into the main material flow.

A correctly applied industrial vibrator, in terms of size type and installation will help the material flow down the chute, by effectively increasing the angle of repose by eight degrees.
A correctly applied industrial vibrator, in terms of size type and installation will help the material flow down the chute, by effectively increasing the angle of repose by eight degrees.

Ideally, dribble chutes are installed on a steep incline angle and lined with a low-friction lining to avoid material build-up. However, the position of the secondary cleaner is often in a restricted space where the chute angle is usually less than the angle of repose of the material so it will not flow of its own volition.

This has the potential to leave material build-up on the chute wall, which, ignored long enough can result in belt wear, inoperable belt cleaners, spillage from the back of the chute and eventual transfer point blockages. 

In situations where the chute angle is inadequate, and build-up occurs, a flow aid device is required. When choosing a flow aid, a number of factors should be taken into account including safety, material characteristics, access, type of liner, and chute dimensions.

Flow aids like air cannons are unsuitable for this kind of application due to the open structure of the chute at this kind of transfer point as it poses a safety and dust risk.

A better choice is a correctly applied industrial vibrator, in terms of size type and installation will help the material flow down the chute, by effectively increasing the angle of repose by eight degrees.

Where the carryback removed by the secondary cleaners has a higher moisture content and or is inherently sticky, a pneumatic linear vibrator is appropriate, as they are typically used in the conveying and loosening of bulk materials and are especially useful for helping damp materials flow from hoppers and chutes.

The linear action of the pneumatic vibrator is selected to motivate the material by applying constant vibration to the chute.

The dribble chute becomes ‘live’ so the material does not have an opportunity to adhere to the chutes surface, preventing build-up before it can affect material flow.

Factors that need to be considered when selecting a suitable flow aid device include; structure type, build up type, material type (dry, sticky, static etc.), available power sources (electricity or compressed air), and safety requirements (noise levels).  For assistance in choosing the most suitable flow aid device, contact ESS Engineering Services & Supplies.

Established in Wollongong, Australia in 1978, ESS Engineering Services & Supplies is an expert in bulk flow aid devices, conveyor belt cleaners and skirting systems.