Inclined Screw conveyors

Inclined Screw Conveyors

A screw in the horizontal is a conveyor or feeder, but as a screw is inclined it very quickly becomes a lift or pump. All of the charts & formulas for calculating speed and capacity for a screw, in the horizontal are no longer applicable, what now comes into play is product knowledge and experience for sizing and calculating speed and horse power for incline and vertical screws.

The need to elevate material can pose many challenges. Some of the things that must be determined are:

  • How high must the material be lifted?
  • How far horizontally is the material to be moved?
  • What is the material to be conveyed?
  • What are its characteristics?
  • Is close clearance of the screw to the housing required?

How is the material going to be fed into the screw

The answers to these questions will tell you the   degree of incline of the screw and the true length of the screw. Based on product knowledge the size and speed of the screw can be estimated. Incline screw should never have internal screw supports, as they pose an obstruction to the product flow (product flow vertically and or up an incline is always critical). Product flow is controlled by speed, but speed can only be estimated, once you know the true length of the screw, the degree of incline and the material flow characteristics. Speed of the screw = horsepower required. Also when estimating horse power the number of starts and stops, the time in-between stops and restarts, and the estimated amount of residual material in the conveyor when starting all must be considered.

Since the initial screw speed was estimated based on the information provided and experience the drive for an incline or vertical screw should always have the ability for screw speed changes, i.e. “v” belts and sheaves. This gives the ability to make speed adjustments in order to get the desired product through put at the desired housing loading.

It can be very hard to use a vertical or incline screw as a feeder. The speed necessary to convey the material may produce a greater product flow than desired, the speed necessary to convey the material may cause “tip rejection” and there for no flow of material. If a vertical or incline screw needs to deliver a uniform feed rate this is a good example for the use of a cantilevered screw feeder to provide the uniform positive force feed into the incline or vertical screw conveyor.

  • More horsepower is required for Inclined Screw Conveyors: This is due to both lifting the product and “re-conveying” product that falls back.
  • Hangers should be eliminated: They create a “dead flow” area that is emphasized with inclined conveyors. This often results in the use of longer screws which require their own design considerations.

Examples of applications where such experience is required include:

  1. Corrosive Products –Screw conveyors must be fabricated from alloys not affected by the corrosive product. Typical materials of construction for corrosive products are 304, 310, 316, 410 and 430 stainless steels. Also, high nickel alloys such as Inconel, Monel and Hastalloy may be used.
  2. Abrasive Products –Screw conveyors must be fabricated from abrasion resistant alloys when handling abrasive products. Typical materials of construction are AR235, AR360, AR500, cobalt based or chromium carbide based hard surfacing materials. These materials are harder and tougher than A36 carbon steel for resisting abrasion. The carrying face of the screw may be hard surfaced with a weld-on hard surfacing material. Lining of all surfaces in contact with the product with rubber of special resins also reduces abrasion. It is also very important to reduce the trough loading and the speed of the screw conveyor when handling abrasive products.
  3. Hygroscopic Products –Screw conveyors must be sealed from the outside atmosphere. In extreme cases, it is necessary to provide jacketed troughs or housings with an appropriate circulating heat transfer medium to maintain the material at an elevated temperature. Purging of the conveyor with a suitable dry gas is also used in some installations.
  4. Products That Emit Harmful Vapors or Dusts –Screw conveyors must be sealed to contain the harmful vapors or dust. These may be safely handled in dust-tight U-troughs or tubular housings. Special shaft seals may be required.
  5. Products That Emit Explosive Dusts –Screw conveyors may be fabricated from non-sparking materials. Screw conveyors must be sealed to contain the harmful vapors or dust. These products may be safely handled in dust-tight U-troughs or tubular housings. Special shaft seals may be required. Exhaust systems are also advisable for the removal of explosive dusts.
  6. Products Subject to Packing –Screw conveyors may utilize ribbon flights, mixing paddles, cut flights or cut and folded flights to breakup products that tend to pack. Larger inlets and discharges may be required in order to provide a larger area for the product.
  7. Products Subject to Fluidizing or Aerating –Screw conveyors may utilize short-pitch close tolerance screws and tubular housings to reduce the possibility of product flowing around the screw. Also, the screw conveyor may be inclined to reduce the head pressure of the product. This condition may be used to advantage in some installations by declining the screw conveyor toward the discharge end.
  8. Products That Degrade –Screw conveyors for handling products that easily degrade are typically oversized and operated at reduced speeds. The trough loading is also kept to a minimum.
  9. Products at Elevated Temperature –Screw conveyors may be fabricated from high temperature alloys depending upon the operating temperature. Special consideration is required for handling thermal expansion of the screw and housing. High temperature seals and gasketing are required. Extensive industry specific experience with “exotic” alloy fabrication that includes all stainless steel grades, including 254SMO, Hastalloy, Inconel, Alloy 20, Monel, etc. (pipe, plate and overlay).

Common industry uses for screw conveyors:

FoundriesMold sand handling
BreweriesGrain & hops handling/storage
Wood ProductsWaste & sawdust
PaperPulp & chip handling
GypsumGypsum conveying for wallboard
Lead ProductsRecycled lead
Food HandlingVarious food-grade applications
Salt MinesMixing, conveying, blending
Steel MillsDust collection & storage
Sewage PlantsSludge conveying & storage
Chemical PlantsPrevents contamination
Feed & GrainVarious applications
RenderingExtensive use, washes down
Glass PlantsConveying & metering

Common industry uses for screw conveyors:

FoundriesMold sand handling
BreweriesGrain & hops handling/storage
Wood ProductsWaste & sawdust
PaperPulp & chip handling
GypsumGypsum conveying for wallboard
Lead ProductsRecycled lead
Food HandlingVarious food-grade applications
Salt MinesMixing, conveying, blending
Steel MillsDust collection & storage
Sewage PlantsSludge conveying & storage
Chemical PlantsPrevents contamination
Feed & GrainVarious applications
RenderingExtensive use, washes down
Glass PlantsConveying & metering

The screw conveyor has many benefits over other types of bulk material handling equipment. Some of the advantages are:

  • Screw conveyors are capable of handling a great variety of bulk materials from sluggish to free-flowing.
  • Screw conveyors can have multiple inlet and discharge points. Bulk materials can be conveyed and distributed to various locations as required. Slide gates or valves can be added to control the flow into and out of a screw conveyor.
  • When a screw conveyor is used as a metering device, it is considered a screw feeder. Screw feeders are used to initiate a material process by metering product from a bin or hopper.
  • Screw conveyors are very compact and adaptable to congested locations. Screw conveyors do not have a return similar to a belt or drag conveyor.
  • Screw conveyors are totally enclosed to contain the product and prevent spillage. Screw conveyors can be utilized in the horizontal, vertical or any inclined position depending upon the characteristics of the product being conveyed.
  • Screw conveyors can be used for mixing various products together and for breaking up large lumps.
  • Screw conveyors can be designed without a center pipe. This type of conveyor is called a shaftless screw conveyor and is designed for conveying wet, sticky, sluggish products such as industrial sludges and biosolids.
  • Screw conveyors can be used to cool, heat or dry products in transit. Depending on the heat transfer requirements, a screw conveyor can be jacketed, or a hollow-flight design utilized to provide the necessary heat transfer for the application.
  • Screw conveyors can be designed to be vapor-tight or hold an internal pressure. This is very important when conveying toxic or hazardous products such as those in the chemical industry.
  • Screw conveyors can provide an air lock between upstream and downstream equipment.

” Since 1996 Miteck systems have earned a reputation on designing & manufacturing of Inclined Screw Conveyors also we have expertise in Deep Bucket Chain Conveyors, Submerged Ash Conveyors, Chain Belt Conveyors, Live Bottom Screw Conveyors, Rotary Airlock Valves

please send us an email on [email protected] for more information “