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Screw Conveyor Design

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A screw conveyor is a volumetric conveying equipment. A fixed volume of the material is discharged with each turn of the screw flight. A screw conveyor is used to move product from one location to another, which is always managed by having another conveyor or measuring equipment feed into the entrance. Read More…

Screw Conveyor Design There are a number of factors to be considered when it comes to designing screw conveyors. These factors apply not only with regard to the design of the conveyor itself but also with the facility and how/where the equipment is going to be used.
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Leading Manufacturers

Cedar Rapids, IA  |  319-364-5600

We are a US based, family owned company specializing in the design and manufacturing of screw conveyors in all configurations: vertical, inclined, shaftless, live bottom, plug screws, feeders, mixers, heating/cooling, FDA/USDA approved, screw presses and more.

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Conveyor Engineering & Mfg. Co. $$$

Belleville, NJ  |  800-822-8629

VAC-U-MAX is a manufacturer specializing in screw conveyors and transportation systems, load filling machines, bulk bag loaders, grinders, pulverizers and sifters. The company serves the chemical, food and feedmill industries with highly efficient products.

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VAC-U-MAX $$$

Monroe, NC  |  704-246-0900

Spiroflow Systems has more than 40 years of experience in the design, manufacture & installation of bulk material handling equipment & systems. Product innovation & a thorough understanding of customers’ needs & objectives keep Spiroflow at the forefront of the industry. Spiroflow Systems offers flexible screw, aero mechanical, pneumatic, tubular cable & chain drag conveyors as well as bulk bag fillers & dischargers, automatic bag placing & sealing, robotic palletizing & auxiliary equipment.

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Spiroflow Systems, Inc. $$$

Bethlehem, PA  |  888-353-9426

A world-leading manufacturer of flexible screw conveyors with more than 10,000 installations handling free- and non-free-flowing bulk products including materials that pack, smear, cake, plug, fluidize and separate. The simple design can deliver efficient performance while at the same time reduce maintenance and cost. Stationary and mobile units to automated plant-wide systems are available.

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Flexicon Corporation $$$

Port Hope, ON  |  888-884-8168

UniTrak Corporation is a global leader in the supply of bulk material conveying equipment. Our conveyors are used by several leading manufacturers around the world. We are located in Canada and the UK and can easily reach our customers. We have been in the business since 1967 and out passion to succeed remains unshaken. Our customers can be assured of the quality of our products as we have been i n the business for such a longtime.

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UniTrak Corporation $$$
placeholder image Conveyor Engineering & Mfg. Co. VAC-U-MAX Spiroflow Systems, Inc. Flexicon Corporation UniTrak Corporation

The intake of a screw conveyor is generally connected to rotary valves, conveyors, screw feeders, or even additional screw conveyors.

Screw Conveyor

Like screw conveyors, screw feeders or feeders are constantly flood-loaded or full in the entering section.

Factors Influencing Screw Conveyors Design

The Material Classification Code Chart lists typical characteristics of the granular particles to be transported, such as abrasiveness, corrosiveness, and flowability. To choose the best machinery for the intended purpose, it is crucial to understand and carefully examine these characteristics when designing screw conveyors.

Abrasive Particulates

When carrying abrasive grains, screw conveyor compositions may experience extreme wear and strain due to the design of the screw conveyor. As a result, various screw conveyor design types are best suited for abrasion-resistant metals.

The trough of the screw conveyor accumulates and hardens certain transporting materials. They also have the propensity to absorb moisture and pack tightly. The better the ability to prevent build-up incidents in the trough, the closer the space between the trough and the screw. Additionally, a high screw conveyor torque is required to cut through the hardened particles, which is all considered while designing the screw conveyor.

Generation of Static Electricity

Static electricity can be produced throughout the conveying process as the screw augers rotate and shake the bulk materials. Therefore, it is strongly considered when designing to ground the screw conveyor's trough. It may effectively eliminate static electricity by grounding the trough in several places. In addition, lowering the trough loading and the screw conveyor speed can also be very beneficial.

Flammability

Flammable and explosive materials will burn whenever oxygen and ignition sources are present. Screw conveyors should be made of non-sparking materials to stop the appearance of ignition sources. The tight troughs or housings of screw conveyors outfitted with shaft seals are also necessary to keep oxygen outside the machine. The design maybe is aided by filling the inside of the screw conveyor with inert gas, such as nitrogen.

The following properties of the transported bulk material directly determine the design of the conveyor size, speed, and horsepower requirements:

  • Maximum particle size
  • Bulk density
  • Trough loading
  • Material factor
Components of Screw Conveyor

Screw Conveyor Design

Typical Screw Conveyor Design

To design the screw feeder's size and capacity, the screw conveyor's needed capacity and the material should be known at the start; however, the screw size and properties may be unknown.

The following formula can be used to estimate the capacity of the screw conveyor, which has a standard screw flight:

Q= 60 × π⁄4 × D²×S×N×α×ρ×C

In this formula:

  • Q = Screw Capacity in kg/h
  • D = Screw Diameter in m
  • S = Screw Pitch in m
  • N = Screw speed in rpm
  • α = Loading ratio
  • ρ = Material loose density kg/m3
  • C = Inclination correction factor
  • Step 1: Define the Requirement

    • The requirement is defined after specifying the screw conveyor's needed capacity.
    • The screw's design must have a capacity equal to or greater than this figure.

    Step 2: Calculate Capacity of the Conveyor

    • Assume the diameter (D)
    • Define the screw pitch based on the diameter of the screw
    • PitchPitch Length S
      StandardS = D
      ShortS = 2/3 x D
      HalfS = D/2
      LongS = 1.5 x D
    • Estimate the screw's loading ratio based on the characteristics of the material to be conveyed.
    • MaterialMin Loading RatioMax Loading Ratio
      Not free-flowing0.120.15
      Average flowability0.250.30
      Free-flowing0.40.45
    • Values may be higher or lower than average; in extreme situations, the loading ratio may even be higher than 95%.

    Step 3: Compare Calculated Capacity to Max Screw Speed

    The table below lists a few examples of reference maximum screw speed to be used during the design:

    Screw Diameter in m15%30%A30%B45%
    0.16913969190
    0.156613266182
    0.236212262170
    0.256011860165
    0.305811158157
    0.365610456148
    0.41539753140
    0.46509050131
    0.51478247122

    The design can be maintained if the speed estimated in step 2 is less than the maximum speed allowed for the chosen screw diameter. However, suppose the calculated speed at step 2 is greater than the maximum speed for the screw diameter chosen. In that case, the design is unsuitable, and the calculation must be repeated by altering a parameter (often the diameter).

    Step 4: Power Calculations

    P= PH+PN+PSt

    PH is the power required to move the material in the conveyor horizontally.

    PN is the power required to operate the unloaded screw.

    PSt is the power required for an inclined screw conveyor.

Screw Conveyor Design Informational Video

 

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