Screw Conveyor Flight Types
The screw of the conveyor flight may be right hand or left hand, the right hand type being the usual design. The threads of the screw may be single, double or triple.
The flight of the screws may be made in either of the two ways:
1. As Helicoids
2. As Sectional flight
Helicoids Flight | Screw conveyor Flight types:
They are formed from a flat bar or strip into a continues helix. The threads are thinner at the outer edge and thicker at the inner edge.
Sectional flights | Screw conveyor Flight types:
Sectional flights are formed from a flat disc and the thickness of the thread is uniform throughout. A continuous helix is made by joining a number of sectional flights together on a piece of pipe and butt welded them. Various styles of screw flights are in use, depending on the service required.
Some of the typical configurations in screw conveyor Flight types are:
1. Short pitch or continuous flight | Screw conveyor Flight types:
If the conveyor is required to handle dry granular or powdered materials that do not pack, this style of flight may be selected. It is of regular construction and recommended for inclined conveyors having a slope of 20 or more, including vertical conveyors. This style is extensively used as feeder screw.
2. Ribbon flight | Screw conveyor Flight types:
If the conveyor is to handle lumpy, clinging, sticky, gummy or viscous substances, this type flight may be selected. It consists of continuous helical flight formed from steel bar and secured to the pipe by supporting lugs.
3. Cut Flight | Screw conveyor Flight types:
In this type of flight screws have notches cut in the periphery of the flight. These notches supplement the conveying with moderate mixing action. They are recommended for conveyors required to handle light, fine, granular or flaky materials.
4. Cut and folded flights | Screw Conveyor Flight Types:
This type of flight is characterized by notches as in cut flight, together with folded segments. This type of flight creates agitation and aeration resulting in better mixing. This type of flight is used to handle light or medium weight materials having fine, granular or flaky materials.
5. Some screw conveyors have cut flight with paddles mounted at regular intervals. The paddles counteract the flow of material past the flight resulting in greater agitation and mixing.
6. Sometimes screws are made of stainless steel to suit special requirements, like the sanitation requirements for handling food, drugs and other hygienic materials.
7. Standard Screw conveyor flight | Screw conveyor Flight types – Screws sectional flight with a pitch spacing equal to the diameter are considered standard and are suitable for most screw conveyors of conventional horizontal design.
8. Screw conveyor tapered flight | Screw Conveyor Flight types – Tapered flight spirals provide a continuous incremental change in swept volume of the screw conveyor auger. This promotes even draw down in a full hopper situation. Tapered flights leave residual material in the screw conveyor unless the casing is tapered to suit.
9. Screw conveyor short pitch flight | Screw Conveyor Flight Types – Short pitch screws are used in inclined screw conveyors. They are also used to control the feed at the inlet and to reduce flushing of free flowing materials. The shorter the pitch the more efficient is the screw augers.
10. Screw conveyor paddles | Screw Conveyor Flight Types – Paddles are set in a helical form around a square or round center tube to form a segmented spiral. They are used in mixers and pug mills to mix and condition dry products when liquid is added during the process.
11. Variable pitch flights | Screw Conveyor Flight Types – The screw conveyor with Variable pitch flights are used to control the amount of material drawn down along the length of a hopper. By increasing the pitch at each flight along a screw you can incrementally increase the volume of product that is allowed to enter the screw.
12. Screw conveyor double start flight | Screw Conveyor Flight Types – The screw auger conveyor with Double start flights are used to accelerate the conveying process at the conveyor inlet and even out the pulsing effect at the outlet. They are also typically used in drilling and post-hole augers to equalize the torsional forces on the screw auger.
13. Screw conveyor notched and folded flights – The screw augers with Notched and folded flights provide a more aggressive mixing action where material that passes through the notch is lifted and mixed with the trailing material. They can also be used for aerating or cooling materials.
14. Screw Conveyor Notched Flight – The screw conveyors with Notched flights are used to provide a gentle mixing action. Notched flights are useful in blending different materials during the conveying process.
15. Screw Conveyor Center-less Flights (Shaft-less) – The Screw conveyor Center-less flights (Shaft-less) are used for extremely sticky or fibrous materials that tend to wrap around or build up on a center pipe.
16. Screw conveyor hollow spiral flight – The screw conveyor with Hollow spiral flights are used to pass heating or cooling liquids around the helix. Typically both the hollow center pipe and the hollow spiral flight are used as a heat exchanger to cool, heat or thaw the material being conveyed.
17. Screw conveyor ribbon flight – The screw conveyor with Ribbon flights with integral support legs are used for sticky or cohesive materials that tend to build up on the flight-pipe interface.
18. Screw conveyor Coned flight | Screw Conveyor Flight Types – The screw conveyor conical flight centers provide a continuous incremental change in swept volume of the screw. This promotes even draw down in a full hopper situation. Combined with variable pitch the coned screw provides the best possible solution to even hopper draw down. Standard troughs can be used with coned flights.