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Turning the hierarchy into design details
This prioritization should be incorporated into a number of design details on new conveyor architecture.
Some of these details include:
Dust resistant structure
Conventional conveyor stringers are designed from C-channel with angle iron bracing. But these shapes allow dust and spillage to accumulate, leading to long-term corrosion and safety problems, as well as the costs of cleanup. In the U.S., OSHA is currently in the midst of a campaign that mandates the cleanup of accumulations of explosive dust thicker than a paper clip.
By orientating structural members at 45 degrees to horizontal, the accumulation of dust and spillage can be reduced, without an increase in the weight, (and cost) of the structure. For example, when the angle-iron cross braces are orientated "point up" they will tend to shed, rather than accumulate fugitive materials. Granted, these 45 degree surfaces can still accumulate some material, but not nearly as much as horizontal surfaces.
The design selected for new conveyor architecture stringers combines the convenience of a standard C-channel with a flat web section and the fugitive material shedding capabilities of a 45 degree flange. This Dust-Accumulation Resistant Structure has strength comparable to common C-channels at a similar weight, so there should be little cost differential. This stringer is predrilled (laser) with mounting and connecting holes on 6″ (150 mm) centers. These holes can accommodate the mounting of standard troughing and impact idlers, impact beds and sealing cradles.
Oversized terminal pulleys
The conveyor's head and tail pulleys are typically kept to a minimum size to reduce their price, but this can increase their lifetime cost. When a tail pulley is upsized and deeper drop brackets are used, it becomes easier to install, inspect and maintain tail pulley belt plows. Similarly, oversized head pulleys allow more room for installation, inspection and service of belt cleaning systems. By selecting larger diameter pulleys, the price is slightly increased, while the lifetime cost is reduced.
Removing the transition idlers
The required transition distance from the tail pulley to the first fully troughed idler is specific to the construction and tension of each belt. Providing the proper transition distance will allow the belt to be fully-troughed before it receives any material. This eliminates transition while it improves transfer point sealing. Transition idlers should be installed before the loading zone only if dynamic analysis indicates they are necessary to control belt flap.
External wear liner
Wear liner is a sacrificial lining to reduce the abrasion of the cargo against the skirtboard and the pressure against the skirtboard sealing systems. Long-standing practice is the liners are installed on the inside of the chute and skirtboard. The new conveyor architecture proposes to install this "liner" on the outside of the skirtboard steel (yet still on the inside of the sealing system). This "external" wear liner allows easier installation, inspection and replacement, all without confined space entry. As always, wear liners must be accurately installed and well maintained to prevent trapping particles, which accelerates wear of the belt and seals.
Components ranging from belt cleaners to impact cradles can be designed with track-mounted or mandrel-style support structures, allowing them to be removed and replaced efficiently. A major prerequisite for using service-friendly designs is that there is sufficient access to take advantage of the benefits of these designs.
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