Sandwich Conveyors - Functional Description

Basics

Functional Description

There are a number of different branded sandwich conveyors and it is the intention of this Handbook to provide helpful information regarding the different types and the features which distinguish the brands.

In terms of its functionality, sandwich belt conveyors have certain generic similarities and these are discussed here.

Sandwich belt conveyors are so named due to the manner in which the material is 'sandwiched' between two rubber belts before it is inclined at angles up to 90 degrees.

The adjacent sketch is a typical cross-section through the inclined portion of a sandwich conveyor showing how the material is enclosed by a top and bottom belt.

Material is 'hugged' by the belts throughout the inclined section to ensure that it does not slide back down the incline, even if the conveyor trips.

This hugging pressure is achieved by either the belt tension or by means of pressing assemblies which force the belts together.

A fundamental requirement of any proposed application of sandwich belt conveyors is that the material to be transported must have a reasonable internal friction angle.

Water and aerated fly ash for example, cannot be transported on a sandwich conveyor whereas particulate materials such as grain, ore and fine sand which have surcharge angles greater than approximately 20 degrees, can be conveyed successfully. Where the material displays characteristics which do not allow the product to be 'hugged' without leaking out between the edges of the two belts, sandwich belt conveyors cannot be considered.

Sandwich belt conveyors offer the potential to load material at a considerable rate at one level and to elevate the product to a second level via an inclined section which could be angled at up to 90 degrees to horizontal.

The sketch indicates the basic anatomy of a H.A.C. - type sandwich conveyor, supplied by Continental Conveyor Company.

Material (1) is loaded onto a troughed belt (2) at the loading point via a loading chute (3). The material is accelerated to belt speed and allowed to settle on the troughed, lower belt in accordance with conventional belt theory. This section of the conveyor could range in length from a few metres to hundreds of metres.

At the point where the material is to commence elevating (4) a second conveyor belt (5) is introduced on top of the load stream and is forced down onto the lower belt and load stream. At this point the top belt is supported from above by means of inversely troughed idler sets (6) and the lower belt enters a vertical curve.

As the lower belt enters the curve it rises up off of the bottom idlers (7) and the tension in both belts ensures that the material is securely supported by the belts. The belts are supported / guided by the inverted idler sets through the first curve. As the initial vertical curve comes to an end and the required angle of inclination has been reached, the sandwich conveyor continues to support the load along the inclined section (8) until the discharge point (9) is reached.

The H.A.C. conveyor uses patented pressing mechanisms to keep the two belts together.

At the discharge, the material can be ejected in a number of different configurations i.e. a horizontal or inclined discharge.

In this case the features are similar however, the inclined portion adopts a 'snaking' profile to achieve the required hugging pressure between the belts as opposed to the H.A.C. sandwich conveyor, which uses spring-loaded pressing mechanisms to keep the belts and material securely in position.

This 'snaking' effect is the hallmark of the DSI Snake Conveyor.

The design of the inclined section is different for different brands of sandwich conveyors, as can be seen in these two examples.

Notwithstanding these differences in the two brands, both types of sandwich conveyors employ two separate, endless rubberized conveyor belts. The bottom belt (2) passes over the head / drive pulley (10) and is scraped clean (11) before it commences its return to the tail pulley (12). The return-side belt is supported on a series of flat return idlers (13) and a plough (14) cleans the return belt before it enters the tail pulley.

at the discharge the 'top' belt (5) rises above the load stream and also passes over its' drive pulley (15) and is scraped clean. As with the bottom belt, the top belt is guided along its return path via flat return idlers (13) to its tail pulley (16).

Both tail pulleys are used to impart the required tension in the belts. The take-ups (18) are either hydraulic rams or a gravity-type tower imparting the tension to the trolley-mounted tail pulleys.

This second example shows a DSI Snake conveyor offered by Dos Santos International.

At the discharge, the material can be ejected in a number of different configurations i.e. a horizontal or inclined discharge.

In the case of the 'Snake' conveyor, the features are similar to those of a H.A.C. however, the inclined portion adopts a 'snaking' profile to achieve the required hugging pressure between the belts as opposed to the H.A.C. conveyor, which uses spring-loaded pressing mechanisms to keep the belts and material securely in position. This 'snaking' effect is the hallmark of the DSI Snake Conveyor.

Notwithstanding these differences in the two brands, both types of sandwich conveyors employ two separate, endless rubberized conveyor belts. The bottom belt (2) passes over the head / drive pulley (10) and is scraped clean (11) before it commences its return to the tail pulley (12). The return-side belt is supported on a series of flat return idlers (13) and a plough (14) cleans the return belt before it enters the tail pulley.

at the discharge the 'top' belt (5) rises above the load stream and also passes over its' drive pulley (15) and is scraped clean. As with the bottom belt, the top belt is guided along its return path via flat return idlers (13) to its tail pulley (16).

Both tail pulleys are used to impart the required tension in the belts. The take-ups (18) are either hydraulic rams or a gravity-type tower imparting the tension to the trolley-mounted tail pulleys.