Conveyors

conveyors-header


Conveyors are used:

  • When material is to be moved frequently between specific points
  • To move materials over a fixed path
  • When there is a sufficient flow volume to justify the fixed conveyor investment


Conveyors can be classified in different ways:

  • Type of product being handled: unit load or bulk load
  • Location of the conveyor: in-floor, on-floor, or overhead
  • Whether loads can accumulate on the conveyor or no accumulation is possible


Conveyors

  1. Bucket Conveyor
  2. Vibrating Conveyor
  3. Screw Conveyor
  4. Pneumatic Conveyor
    (a) Dilute-phase Pneumatic Conveyor
    (b) Carrier-phase Pneumatic Conveyor
  5. Vertical Conveyor
    (a) Vertical Lift Conveyor
    (b) Reciprocating Vertical Conveyor
  6. Cart-on-track Conveyor
  7. Tow Conveyor
  8. Trolley Conveyor
  9. Power-and-free Conveyor
  10. Monorail
  11. Sortation Conveyor
    (a) Diverters
    (b) Pop-up Devices
    (c) Sliding Shoe Device
    (d) Tilting Device
    (e) Cross–belt Transfer Device

 






1. Chute Conveyor

  • Unit/Bulk + On-Floor + Accumulate
  • Inexpensive
  • Used to link two handling devices
  • Used to provide accumulation in shipping areas
  • Used to convey items between floors
  • Difficult to control position of the items



2. Wheel Conveyor

  • Unit + On-Floor + Accumulate
  • Uses a series of skatewheels mounted on a shaft (or axle)
  • Spacing of the wheels is dependent on the load being transported
  • Slope for gravity movement depends on load weight
  • More economical than the roller conveyor
  • For light-duty applications
  • Flexible, expandable mobile versions available



3. Roller Conveyor

  • Unit + On-Floor + Accumulate
  • May be powered (or live) or non-powered (or gravity)
  • Materials must have a rigid riding surface
  • Minimum of three rollers must support smallest loads at all times
  • Tapered rollers on curves used to maintain load orientation
  • Parallel roller configuration can be used as a (roller) pallet conveyor (more flexible than a chain pallet conveyor because rollers can be used to accommodate are greater variation of pallet widths)

(a) Gravity Roller Conveyor
  • Alternative to wheel conveyor
  • For heavy-duty applications
  • Slope (i.e., decline) for gravity movement depends on load weight
  • For accumulating loads

(b) Live Powered Roller Conveyor
  • Belt or chain driven
  • Force-sensitive transmission can be used to disengage rollers for accumulation
  • For accumulating loads and merging/sorting operations
  • Provides limited incline movement capabilities



4. Chain Conveyor

  • Unit + In-/On-Floor + No Accumulation
  • Uses one or more endless chains on which loads are carried directly
  • Parallel chain configuration used as (chain) pallet conveyor or as a pop-up device for sortation (see Sortation conveyor: Pop-up devices)
  • Vertical chain conveyor used for continuous high-frequency vertical transfers, where material on horizontal platforms attached to chain link (cf. vertical conveyor used for low-frequency intermittent transfers)



5. Slat Conveyor

  • Unit + In-/On-Floor + No Accumulation
  • Uses discretely spaced slats connected to a chain
  • Unit being transported retains its position (like a belt conveyor)
  • Orientation and placement of the load is controlled
  • Used for heavy loads or loads that might damage a belt
  • Bottling and canning plants use flat chain or slat conveyors because of wet conditions, temperature, and cleanliness requirements
  • Tilt slat conveyor used for sortation



6. Flat Belt Conveyor

  • Unit + On-Floor + No Accumulation
  • For transporting light- and medium-weight loads between operations, departments, levels, and buildings
  • When an incline or decline is required
  • Provides considerable control over the orientation and placement of load
  • No smooth accumulation, merging, and sorting on the belt
  • The belt is roller or slider bed supported; the slider bed is used for small and irregularly shaped items
  • In 1957, B.F. Goodrich, Co. patented the Möbius strip for conveying hot or abrasive substances in order to have “both” sides wear equally 13
  • Telescopic boom attachments are available for trailer loading and unloading, and can include ventilation to pump conditioned air into the trailer 14



7. Magnetic Belt Conveyor

  • Bulk + On-Floor
  • A steel belt and either a magnetic slider bed or a magnetic pulley is used
  • To transport ferrous materials vertically, upside down, and around corners



8. Troughed Belt Conveyor

  • Bulk + On-Floor
  • Used to transport bulk materials
  • When loaded, the belt conforms to the shape of the troughed rollers and idlers



9. Bucket Conveyor

  • Bulk + On-Floor
  • Used to move bulk materials in a vertical or inclined path
  • Buckets are attached to a cable, chain, or belt
  • Buckets are automatically unloaded at the end of the conveyor run



10. Vibrating Conveyor

  • Bulk + On-Floor
  • Consists of a trough, bed, or tube
  • Vibrates at a relatively high frequency and small amplitude in order to convey individual units of products or bulk material
  • Can be used to convey almost all granular, free-flowing materials
  • An Oscillating Conveyor is similar in construction, but vibrates at a lower frequency and larger amplitude (not as gentle) in order to convey larger objects such as hot castings



11. Screw Conveyor

  • Bulk + On-Floor
  • Consists of a tube or U-shaped stationary trough through which a shaft-mounted helix revolves to push loose material forward in a horizontal or inclined direction
  • One of the most widely used conveyors in the processing industry, with many applications in agricultural and chemical processing
  • Straight-tube screw conveyor sometimes referred to as an “auger feed”
  • Water screw developed circa 250 BC by Archimedes



12. Pneumatic Conveyor

  • Bulk/Unit + Overhead
  • Can be used for both bulk and unit movement of materials
  • Air pressure is used to convey materials through a system of vertical and horizontal tubes
  • Material is completely enclosed and it is easy to implement turns and vertical moves

(a) Dilute-phase Pneumatic Conveyor
  • Moves a mixture of air and solid
  • Push (positive pressure) systems push material from one entry point to several discharge points
  • Pull (negative pressure or vacuum) systems move material from several entry points to one discharge point
  • Push-pull systems are combinations with multiple entry and discharge points

(b) Carrier-system Pneumatic Conveyor
  • Carriers are used to transport items or paperwork
  • Examples: transporting money to/from drive-in stalls at banks and documents between floors of a skyscraper



13. Vertical Conveyor

  • Unit + On-Floor + No Accumulation
  • Used for low-frequency intermittent vertical transfers a load to different floors and/or mezzanines (cf. vertical chain conveyor can be used for continuous high-frequency vertical transfers)
  • Differs from a freight elevator in that it is not designed or certified to carry people
  • Can be manually or automatically loaded and/or controlled and can interface with horizontal conveyors
  • Alternative to a chute conveyor for vertical “drops” when load is fragile and/or space is limited

(a) Vertical Lift Conveyor
  • Series of flexible conveyor-carriers rotate in a loop, where empty carriers flex perpendicularly to provide access to loaded carriers moving past them in opposite direction

(b) Reciprocating Vertical Conveyor
  • Carrier used to raise or lower load
  • Can be powered (hydraulic or mechanical) or non-powered
  • Non-powered version only be used to lower a load, where counterweight used to return empty carrier to top



14. Cart-on-track Conveyor

  • Unit + In-Floor + Accumulate
  • Used to transport carts along a track
  • Carts are transported by a rotating tube
  • Drive wheel connected to each cart rests on tube and is used to vary the speed of the cart (by varying angle of contact between drive wheel and the tube)
  • Carts are independently controlled
  • Accumulation can be achieved by maintaining the drive wheel parallel to the tube



15. Tow Conveyor

  • Unit + In-Floor + Accumulate
  • Uses towline to provide power to wheeled carriers such as trucks, dollies, or carts that move along the floor
  • Used for fixed-path travel of carriers (each has variable path capabilities when disengaged from towline)
  • Although usually in the floor, the towline can be located overhead or flush with the floor
  • Selector-pin or pusher-dog arrangements used to allow automatic switching (power or spur lines)
  • Generally used when long distance and high frequency moves are required



16. Trolley Conveyor

  • Unit + Overhead + No Accumulation
  • Uses a series of trolleys supported from or within an overhead track
  • Trolleys are equally spaced in a closed loop path and are suspended from a chain
  • Carriers are used to carry multiple units of product
  • Does not provide for accumulation
  • Commonly used in processing, assembly, packaging, and storage operations



17. Power-and-free Conveyor

  • Unit + Overhead/On-Floor + Accumulate
  • Similar to trolley conveyor due to use of discretely spaced carriers transported by an overhead chain; however, power-and-free conveyor uses two tracks: one powered and the other non-powered (or free)
  • Carriers can be disengaged from the power chain and accumulated or switched onto spurs
  • Termed an Inverted Power-and-Free Conveyor when tracks are located on the floor



18. Monorail

  • Unit + Overhead + Accumulate
  • Overhead single track (i.e., mono-rail) or track network on which one or more carriers ride
  • Carriers: powered (electrically or pneumatically) or non-powered
  • Carrier can range from a simple hook to a hoist to an intelligent-vehicle-like device
  • Single-carrier, single-track monorail similar to bridge or gantry crane
  • Multi-carrier, track network monorail similar to both a trolley conveyor, except that the carriers operate independently and the track need not be in a closed loop, and a fixed-path automatic guided vehicle (AGV) system, except that it operates overhead
  • Termed an Automated Electrified Monorail (AEM) system when it has similar control characteristics as an AGV system



19. Sortation Conveyor

  • Unit + On-Floor/Overhead
  • Sortation conveyors are used for merging, identifying, inducting, and separating products to be conveyed to specific destinations. Sortation system throughput is expressed in cartons per minute (CPM). A sortation system is composed of three subsystems:
    • Merge subsystem — items transported from picking (storage) or receiving areas on conveyors and consolidated for proper presentation at the induct area
    • Induct subsystem — destination of each item identified by visual inspection or automatic identification system (e.g., bar code scanner), then a proper gap between items is generated using short variable speed conveyors as they are released to the sort subsystem
    • Sort subsystem — items are diverted to outbound conveyors to shipping, palletizing, staging, and/or secondary sort subsystems
  • There is a trend towards more use of mixed-item loads that eliminate the need for sortation: instead of a producer sending pallet loads of a single item to a distribution center for subsequent sortation or consolidation into multi-item customer loads, single pallets can be loaded at a producer with a different mix of items for each customer. This also can enable greater use of cross docking
(a) Diverters
  • Stationary or movable arms that deflect, push, or pull a product to desired destination
  • Since they do not come in contact with the conveyor, they can be used with almost any flat surface conveyor
  • Usually hydraulically or pneumatically operated, but also can be motor driven
  • Simple and low cost

(b) Pop-up Devices
  • One or more rows of powered rollers or wheels or chains that pop up above surface of conveyor to lift product and guide it off conveyor at an angle; wheels are lowered when products not required to be diverted
  • Only capable of sorting flat-bottomed items
  • Pop-up rollers (not shown) are generally faster than pop-up wheels

(c) Sliding Shoe Sorter
  • Sliding shoe sorter (a.k.a. moving slat sorter) uses series of diverter slats that slide across the horizontal surface to engage product and guide it off conveyor
  • Slats move from side to side as product flows in order to divert the product to either side
  • Gentle and gradual handling of products

(d) Cross-belt Transfer Device
  • Trays or slats provide combined sorting mechanism and product transporter
  • Can accommodate elevation changes
  • Tilt tray sorters usually designed in continuous loops with compact layout and recirculation of products not sorted first time
  • Tilt slat sorters carry products on flat-surface slat conveyor and can handle wider variety of products compared to tilt tray

(e) Tilting Device
  • Either continuous loop, where individual carriages are linked together to form an endless loop, or train style (asynchronous), where a small number of carriers tied together with potential for several trains running track simultaneously
  • Each carriage equipped with small belt conveyor, called the cell, that is mounted perpendicular to direction of travel of loop and discharges product at appropriate destination
  • Automatically separates single line of products into multiple in-line discharge lines