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A. In our last newsletter we presented an overview of drag conveyors and their basic design fundamentals.
Whatever style of drag conveyor you have (round bottom, flat bottom or tubular) it is made up of these basic components:
Housing options have a 10-gauge minimum, which depend on its capacity and length. The standard housing section length is typically 10 foot, with a housing flange on each end of the 10 foot length to bolt conveyor sections together. They can be galvanized, painted or stainless steel. The covers may be flat or hip.
Housing construction types are typically formed metal or welded side wall assemblies with bolted bottoms and covers. Chain returns are made up of sprockets, rollers, a feed pan, and center and side rails.
Inlet types may be direct feed, bypass or pan feeder. Direct feed inlets are used when material going into the conveyor is controlled or metered. Bypass and pan feeder inlets are used to control the flow going into the conveyors (choke loaded).
Access doors are inspection doors on the intermediate housing covers. They allow for chain inspection and the observation of material flow. The intermediate discharge assembly allows for discharge throughout the process.
The chain conveyor pull must be calculated to properly size the chain. There are many different styles available depending on the application, but the most common are cast, roller and all-steel welded.
Paddles or flights can be made from UHMW, steel, non-ferrous metal or other polymers. Tall flights and double flight spacing should be used for excessive chain weight on inclines greater than 15°.
The head section assembly includes the head sprocket, head shaft and bearings.
The sprocket diameter and head shaft RPM selection is determined by the desired capacity in TPH, CFH or BPH and correlates with housing size. More sprocket teeth will reduce the wear. Sleeve construction is two-piece split construction (hardened).
Bearings and shafts must be sized appropriately for drag conveyor capacity, length, horsepower and chain pull. The bearings should be self-aligning pillow block roller style.
Head section covers are typically a minimum 3/16” construction with 12 or 14-gauge cover. It should be easily removable and have inspection doors for ease of maintenance. The service platform that provides access to head section components should allow a minimum 24” clearance to the handrails.
This section will have a minimum 3/16” construction, depending on the capacity and housing size. It is made up of two-piece split (hardened) construction sprockets, pillow block bearings and an inspection/access cover. The sprocket size for the tail section is often the same as the head section, although it is offset in some cases. The length of the screw take-up terminal will depend on the conveyor’s length. The inlet must be located far enough away from the tail sprocket so that materials do not contact the sprocket and cause unnecessary wear.
There are a few types of gearboxes:
Motor selection is based on the classification of the area on which the conveyor is installed per NEC:
To calculate horsepower:
|Total HP||=||HP empty + HP live + HP lift
There are a number of factors in this formula, such as light friction, material friction, chain flight/weight, conveyed product weight, conveyor length, chain speed and lift.
Service factor classes are:
OSHA requires guards for belts and shafts to protect workers from pinch-points.
The V-Belt should allow for a minimum of 2.0 service factor and maximum operating speed of 5,000 RPM. It must be flame retardant and static conductive.
The following ancillary devices are available:
Specifying the proper drag conveyor style and associated components and options will result in an efficient, long lasting piece of material handling equipment.
Answered by Curtis R. Cook, Vice President of WL Port-Land Systems, Inc. He has over 36 years of experience in design, operations, and maintenance of bulk solids storage and handling facilities.