Frequently Asked Questions About Screw Conveyors

1. What is a screw conveyor?

A screw conveyor is an enclosed bulk-material handling system that uses a rotating helical screw flight to move powder, granules or semi-solid material from one location to another.

2. How does a screw conveyor work?

The electric motor and gearbox rotate the screw inside a tube or trough. As the screw rotates, its flights push the material from the inlet towards the discharge outlet.

3. What is another name for a screw conveyor?

A screw conveyor is also known as an auger conveyor, spiral conveyor, helix conveyor, screw feeder, screw-type conveyor or screw conveying system.

4. Where are screw conveyors used?

Screw conveyors are used in concrete batching plants, ready-mix concrete plants, cement plants, fly ash handling systems, dry-mix mortar plants, food plants, chemical plants, wastewater plants and other bulk-material handling industries.

5. What are the different types of screw conveyors?

Common screw conveyor types include:

Tubular screw conveyor

U-trough screw conveyor

Horizontal screw conveyor

Inclined screw conveyor

Vertical screw conveyor

Cement screw conveyor

Screw feeder

Shafted screw conveyor

Shaftless screw conveyor

Flexible screw conveyor

Ribbon screw conveyor

Paddle screw conveyor

Variable-pitch screw conveyor

Live-bottom screw feeder

Portable screw conveyor

Stainless-steel screw conveyor

Heavy-duty screw conveyor

Jacketed screw conveyor

The correct type depends on the material, capacity, conveying distance, inclination and process requirements.

6. What is a cement screw conveyor?

A cement screw conveyor is specially designed to transfer cement powder from a silo to a weighing hopper, batching plant or another processing point. It normally has an enclosed tubular body to control dust leakage.

7. Where is a cement screw conveyor installed?

It is commonly installed below the cement silo butterfly valve. The inlet receives cement from the silo, while the outlet discharges it into the cement weigh hopper or batching plant.

8. What is a tubular screw conveyor?

A tubular screw conveyor has a fully enclosed circular casing containing a rotating screw. It is commonly used for cement, fly ash, filler, lime, gypsum and other powders requiring dust-tight conveying.

A tubular screw conveyor generally includes a tubular casing, screw flights, inlet, outlet, end-bearing assemblies, seals, drive unit and intermediate supports where required.

9. What are the advantages of a tubular screw conveyor?

A tubular screw conveyor provides enclosed material transfer, compact installation, reduced dust leakage and protection of the conveyed material from outside contamination.

10. What is a U-trough screw conveyor?

A U-trough screw conveyor has a U-shaped casing with a removable top cover. It is commonly used for horizontal and low-incline conveying applications where easy inspection and maintenance are required.

11. What is the difference between tubular and U-trough screw conveyors?

A tubular screw conveyor has a completely enclosed circular casing and is commonly used for dusty powders and inclined conveying.

A U-trough conveyor has a removable cover and provides easier access for inspecting the screw, bearings and internal components. U-trough designs are widely used for horizontal conveying and lower inclination angles.

12. What is a horizontal screw conveyor?

A horizontal screw conveyor moves material along a level or nearly level path. It is one of the most commonly used screw conveyor designs because it provides reliable and controlled bulk-material transfer.

13. What is an inclined screw conveyor?

An inclined screw conveyor transfers material from a lower level to a higher level at an angle. Its diameter, screw pitch, speed and motor power must be selected according to the inclination and material characteristics.

14. Does screw conveyor capacity decrease at an incline?

Yes. Material tends to fall backwards between the screw flights as the inclination increases. Therefore, an inclined screw conveyor may require a larger diameter, modified screw pitch, higher speed or additional power compared with a horizontal conveyor.

15. What is a vertical screw conveyor?

A vertical screw conveyor lifts bulk material vertically within a compact installation area. It requires a controlled and consistent material-feeding arrangement at its inlet.

16. Can a standard screw conveyor be installed vertically?

No. A vertical screw conveyor requires a specialized screw design, speed, casing, inlet feeder and drive arrangement. A standard horizontal conveyor should not be installed vertically without engineering evaluation.

Horizontal or inclined feeders are commonly used to meter material into a vertical screw conveyor.

17. What is a shafted screw conveyor?

A shafted screw conveyor has screw flights welded or formed around a central pipe or shaft. Intermediate hanger bearings may support the rotating shaft in longer conveyors.

18. What is a shaftless screw conveyor?

A shaftless screw conveyor uses a heavy-duty spiral without a central pipe. It is suitable for sticky, fibrous, irregular or difficult-to-handle materials that could become wrapped around a centre shaft.

Shaftless conveyors can be designed for horizontal, inclined and certain vertical applications.

19. What is the difference between shafted and shaftless screw conveyors?

A shafted conveyor is commonly used for powders and free-flowing bulk materials such as cement and fly ash.

A shaftless conveyor is more suitable for sticky, wet, fibrous or irregular materials because it does not have a centre pipe or internal hanger bearings obstructing the material path.

20. What is a flexible screw conveyor?

A flexible screw conveyor uses a flexible helical screw rotating inside a flexible or rigid tube. It can follow inclined or curved routes and is often used where plant space is limited.

Flexible screw conveyors are also known as spiral conveyors, helix conveyors or auger conveyors. Some designs have no internal bearings or seals within the material-contact area.

21. What is the difference between a rigid and flexible screw conveyor?

A rigid screw conveyor uses a solid steel casing and rigid shaft or screw assembly. It is suitable for heavy-duty industrial conveying.

A flexible screw conveyor uses a flexible spiral and tube, making it suitable for lighter-duty applications and layouts requiring curved or movable conveying routes.

22. What is a screw feeder?

A screw feeder is used to withdraw material at a controlled rate from a silo, hopper or storage bin. Unlike a standard conveyor, its inlet is normally flood-loaded with material.

23. What is the difference between a screw conveyor and a screw feeder?

A screw conveyor transfers material that is supplied to it at a controlled rate.

A screw feeder receives material directly from a flood-loaded hopper or silo and controls the rate at which the material is discharged.

24. What is a variable-pitch screw feeder?

A variable-pitch screw feeder has gradually increasing spacing between the screw flights. It helps withdraw material more evenly across the complete length of a hopper or bin outlet.

25. What is a short-pitch screw conveyor?

A short-pitch screw conveyor has a smaller distance between consecutive screw flights. It is commonly considered for inclined conveying, controlled feeding and applications requiring reduced material movement per rotation.

26. What is a standard-pitch screw conveyor?

A standard-pitch screw has a pitch approximately equal to the screw diameter. It is widely used for horizontal conveying of suitable free-flowing bulk materials.

27. What is a ribbon screw conveyor?

A ribbon screw conveyor uses an open helical ribbon connected to the centre pipe by supporting bars. It can be used for sticky, viscous or cohesive materials and for applications requiring additional material movement or mixing.

28. What is a paddle screw conveyor?

A paddle screw conveyor uses adjustable paddles instead of continuous full flights. It is mainly used for mixing, blending, conditioning or gently moving bulk material.

29. What is a cut-flight screw conveyor?

A cut-flight screw has sections removed from the outer edge of the flights. It provides additional agitation and can help mix or break up certain bulk materials during conveying.

30. What is a cut-and-folded flight screw conveyor?

A cut-and-folded flight screw has sections of the flight cut and bent to create lifting and mixing action. It is used where material agitation or blending is required during conveying.

31. What is a tapered-flight screw conveyor?

A tapered-flight screw has flights that gradually change in diameter. It may be used for controlled material withdrawal and special feeding applications.

32. What is a live-bottom screw feeder?

A live-bottom screw feeder uses two or more parallel screws below a wide hopper or storage bin. It provides controlled withdrawal across a larger outlet area and helps reduce stagnant material zones.

33. What is a multiple-screw feeder?

A multiple-screw feeder contains two or more screws operating below the same hopper. It is used when a single screw cannot provide uniform material extraction across the full hopper width.

34. What is a portable screw conveyor?

A portable screw conveyor is mounted on a movable frame or wheels. It can be shifted between different feeding and discharge locations according to site requirements.

35. What is a stainless-steel screw conveyor?

A stainless-steel screw conveyor has product-contact components manufactured from a suitable stainless-steel grade. It is used where corrosion resistance, cleanliness or material compatibility is important.

36. What is a mild-steel screw conveyor?

A mild-steel screw conveyor is manufactured primarily from carbon-steel components. It is commonly used for cement, fly ash, mineral powders and general industrial bulk-material handling.

37. What is a wear-resistant screw conveyor?

A wear-resistant screw conveyor uses thicker flights, replaceable liners, hard-facing or abrasion-resistant materials in areas exposed to high wear.

38. What is a jacketed screw conveyor?

A jacketed screw conveyor has an external heating or cooling jacket around the trough or tube. It may be used when the material temperature must be controlled during conveying.

39. What materials can be handled by a screw conveyor?

Depending on its design, a screw conveyor can handle:

Cement

Fly ash

GGBS

Lime powder

Gypsum

Microsilica

Mineral filler

Sand

Ash

Grain

Flour

Chemical powders

Plastic granules

Sludge

Biomass

Food ingredients

Material characteristics must be evaluated before final conveyor selection.

40. Can the same screw conveyor handle cement and fly ash?

It may be possible when the conveyor capacity and construction are suitable. Separate conveyors are recommended when material mixing or cross-contamination must be avoided.

41. Can a screw conveyor handle wet or sticky materials?

Yes, but the screw type, trough design, liner, shaft arrangement and cleaning access must be selected specifically for the material. Shaftless or ribbon-type conveyors may be considered for some sticky applications.

42. What are the main components of a screw conveyor?

The main components may include:

Tubular casing or U-trough

Screw flights

Centre pipe or shaft

Drive motor

Gearbox

Inlet and outlet

End bearings

Intermediate hanger bearings

Coupling shafts

Seals

Inspection covers

Support brackets

Flexible connections

Protective guards

Screw conveyor manufacturers offer different flight, pitch, casing, bearing, seal and material-construction options according to the application.

43. What is a screw conveyor flight?

The flight is the helical steel blade that rotates inside the conveyor casing and pushes the material towards the outlet.

44. What is the difference between helicoid and sectional screw flights?

Helicoid flighting is continuously formed from steel strip.

Sectional flights are individually manufactured sections that are welded together. Sectional flights can be suitable for thicker, heavier-duty and customized screw designs.

45. What is a screw conveyor pitch?

Pitch is the axial distance between two corresponding points on consecutive screw flights. Standard, short, long and variable-pitch arrangements are available for different conveying and feeding applications.

46. What is a hanger bearing?

A hanger bearing supports the screw shaft between conveyor sections. It is generally used in longer shafted screw conveyors where additional internal support is required.

47. Does every screw conveyor require a hanger bearing?

No. Short conveyors may operate with end bearings only. Longer shafted conveyors may require one or more intermediate hanger bearings depending on the length, shaft design and operating load.

48. What is an intermediate bearing in a screw conveyor?

An intermediate bearing supports connected screw sections inside a long conveyor. Its material and design should be suitable for the conveyed product, operating temperature and wear conditions.

49. What is the function of a screw conveyor gearbox?

The gearbox reduces the motor speed and increases the available torque required to rotate the screw under the expected material load.

50. What is a direct-drive screw conveyor?

A direct-drive screw conveyor has the motor and gearbox connected directly to the conveyor drive shaft, reducing the need for an external chain-and-sprocket transmission.

51. What is a chain-drive screw conveyor?

A chain-drive system transfers power from the gearbox to the conveyor shaft through sprockets and a chain. It may provide flexibility in drive position and speed selection.

52. How is screw conveyor capacity calculated?

Capacity depends on the screw diameter, pitch, rotational speed, trough loading, inclination, material bulk density and material-flow characteristics.

The conveyor should be selected using application-specific engineering calculations rather than only the required tonnes-per-hour figure.

53. How do I select the correct screw conveyor diameter?

The diameter is selected according to the required conveying capacity, material density, screw speed, inclination, particle size and allowable trough loading.

54. How is screw conveyor motor power selected?

Motor power depends on the conveyor diameter, length, inclination, material load, material friction, bearing resistance, starting condition and required capacity.

55. How is screw conveyor speed selected?

Screw speed is selected according to the screw diameter, material characteristics, required capacity, inclination and allowable material degradation.

A higher speed does not always provide better performance and may increase wear, power consumption or material damage.

56. What is the maximum length of a screw conveyor?

The practical length depends on the screw diameter, shaft design, bearings, alignment, drive power, conveying angle and material.

Long conveying distances may require multiple conveyor sections or transfer points.

57. Can one screw conveyor have multiple inlets?

Yes. Multiple inlets can be provided to receive material from different silos, hoppers or process equipment, provided the total loading is properly controlled.

58. Can one screw conveyor have multiple outlets?

Yes. Multiple outlets with slide gates, butterfly valves or diverter arrangements can be provided to discharge material at different locations.

59. Can a screw conveyor be made dust-tight?

Yes. Enclosed casings, suitable covers, flange gaskets, shaft seals and flexible inlet and outlet connections can help control dust leakage.

60. Can a screw conveyor connect directly to a cement silo?

Yes. A cement screw conveyor is normally connected below the silo butterfly valve using a suitable inlet adaptor or flexible connection.

61. Can a screw conveyor feed a cement weigh hopper?

Yes. Cement screw conveyors are commonly used to transfer cement or fly ash from storage silos into batching plant weigh hoppers.

62. Can one screw conveyor receive material from two silos?

Yes. A conveyor may be arranged below two silos, but suitable isolation valves, inlet design and feed controls are required to prevent overloading.

63. Why is the screw conveyor capacity low?

Low capacity may be caused by:

Insufficient material supply

Incorrect screw speed

Excessive inclination

Worn screw flights

Material buildup

Blocked inlet or outlet

Motor or gearbox problems

Incorrect screw pitch

Excessive clearance between the screw and casing

64. Why is cement coming back through the screw conveyor inlet?

Material fallback may occur because of excessive inclination, low screw speed, incorrect pitch, an overloaded inlet or an unsuitable screw design.

65. Why is the screw conveyor getting blocked?

Blockage may be caused by moisture, hardened cement, excessive feeding, a restricted outlet, incorrect rotation, material compaction or foreign objects inside the conveyor.

66. How can cement screw conveyor blockage be prevented?

Keep cement dry, avoid overfeeding, maintain the correct operating sequence, inspect the outlet, check screw rotation and clean remaining material before extended shutdowns.

67. Why is the screw conveyor vibrating?

Excessive vibration may result from misalignment, a bent screw shaft, worn bearings, loose supports, material buildup, damaged flights or an unbalanced screw assembly.

68. Why is the screw conveyor making noise?

Abnormal noise may be caused by worn bearings, screw contact with the casing, damaged couplings, loose bolts, lack of lubrication, misalignment or foreign material.

69. Why is the screw conveyor motor tripping?

The motor may trip because of overloading, blocked material, incorrect electrical protection settings, low voltage, phase failure, seized bearings or gearbox problems.

70. Why is cement leaking from the screw conveyor?

Leakage may be caused by damaged seals, loose flanges, worn gaskets, open inspection covers, cracked welding joints or misaligned inlet and outlet connections.

71. Why are screw flights wearing quickly?

Rapid wear may result from abrasive material, excessive speed, thin flight material, incorrect conveyor loading or contact between the screw and casing.

72. Can worn screw flights be replaced?

Yes. Individual screw sections or the complete screw assembly can be repaired or replaced, depending on the wear level and conveyor construction.

73. Can screw conveyor liners be replaced?

Replaceable liners may be provided in U-trough and shaftless conveyors. The liner material should be selected according to abrasion, friction and operating temperature.

74. What maintenance is required for a screw conveyor?

Regular maintenance should include checking:

Motor and gearbox

End and hanger bearings

Screw flights

Coupling bolts

Shaft seals

Mounting supports

Inlet and outlet

Lubrication

Alignment

Protective covers and guards

75. How often should a screw conveyor be inspected?

Inspection frequency depends on operating hours, material abrasiveness, dust conditions and production requirements. Frequently used cement conveyors should be included in the plants regular preventive-maintenance schedule.

76. Can the screw conveyor run empty?

Brief empty running may be permitted for certain designs, but continuous empty operation can create unnecessary wear and heat. The operating instructions for the specific conveyor should be followed.

77. Can a fully loaded screw conveyor be restarted?

Restarting under full load requires sufficient motor torque and a correctly selected gearbox. Frequent loaded starts can increase stress on the drive and conveyor components.

78. What safety precautions are required?

The screw conveyor must be isolated and electrically locked out before opening covers or performing maintenance. Guards should remain fitted during operation, and personnel must never enter or reach into the conveyor while it can start.

79. Can a screw conveyor be customized?

Yes. The diameter, length, inclination, screw pitch, flight thickness, body material, inlet, outlet, motor, gearbox, supports and surface finish can be customized according to the application.

80. What is the price of a screw conveyor in India?

The price depends on the conveyor type, diameter, length, inclination, capacity, material of construction, flight thickness, motor, gearbox, bearings, liners and accessories.

81. Does RA Enterprises manufacture customized screw conveyors?

Yes. RA Enterprises manufactures and supplies customized screw conveyors for cement, fly ash and other dry bulk-material handling applications according to customer requirements and site conditions.

82. What details are required for a screw conveyor quotation?

Please provide:

Material name

Required conveying capacity

Horizontal length

Vertical height

Conveyor inclination

Inlet and outlet locations

Screw diameter, if already specified

Material bulk density

Motor and gearbox requirement

Electrical supply

Material of construction

Site location

Existing drawing or sample, if available

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