is one of the most cost-effective methods for transporting bulk materials. Screw conveyors are used in thousands of applications in almost every industry. MITECK SYSTEMS has provided successful bulk material handling solutions for over 20 years. If you have a difficult application, please Contact Us. We have the solution. From replacement parts to complete systems, MITECK SYSTEMS will meet all of your bulk material handling needs.
Primary considerations for the selection of a screw conveyor are:
- Type and condition of the material to be handled, including maximum particle size, and, if available, the specific bulk density of the material to be conveyed.
- Quantity of transported material, expressed in pounds or tons per hour.
- The distance for which the material is to be conveyed.
In the next sections is the necessary information for the selection of a screw conveyor system, presented in a series of five steps. These steps are arranged in logical order, and are divided into separate sections for simplicity.
The five steps are:
- Establishing the characteristics of the material to be conveyed through Screw conveyors.
- Locating conveyor capacity (conveyor size and speed) on capacity tables.
- Selection of conveyor components.
- Calculation of required horsepower.
- Checking of component torque capacities (including selection of shaft types and sizes).
All necessary calculations are expressed in graphic and equation form, and use of all charts, graphs, etc. will be explained fully at the end of each section.
Engineering data regarding the design of screw feeders and their selection, is presented in a separate section, immediately following the screw conveyor data.
Any unusual applications, or special designs, should be referred to Miteck Systems Mfg’s. Engineering Department
APPLICATIONS OF Screw conveyors
- Examples of applications where such experience is required include:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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:
|Foundries||Mold sand handling|
|Breweries||Grain & hops handling/storage|
|Wood Products||Waste & sawdust|
|Paper||Pulp & chip handling|
|Gypsum||Gypsum conveying for wallboard|
|Lead Products||Recycled lead|
|Food Handling||Various food-grade applications|
|Salt Mines||Mixing, conveying, blending|
|Steel Mills||Dust collection & storage|
|Sewage Plants||Sludge conveying & storage|
|Chemical Plants||Prevents contamination|
|Feed & Grain||Various applications|
|Rendering||Extensive use, washes down|
|Glass Plants||Conveying & metering|
The body of Screw conveyor is fabricated from different type of material suitable for site condition and client requirement. Standard materials of construction for critical parts of Screw conveyor are-
- Body: A36, IS 2062, A516, IS 2002, Corten, SS 304, SS 316, Inconel etc.2. Blade: A36, IS 2062, A516, IS 2002, Corten, SS 304, SS 316, Inconel etc.
- Shaft/Screw: En8, En24, SS 304, SS 316, etc.
- Seal: SS 316Ti, Inconel etc.
- Bearing: C.I lined Bush type with Grafoil Sheet, maintenance free / Antifriction
Other materials of construction can be used as required by client.
These Screw conveyor are designed for sealing up to 99.9% without seal air system and 100% with seal air system. Shut of blinds are also provide 100% sealing across blade & 99.9% duct to/from atmosphere. Type of seals: Bulb seal/ Flexible sea
These dampers can be provided with single or double screw / rack-pinion arrangement depending on client requirements and the size of dampers.
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.