Screw Conveyor Sizes: Standard Dimensions And Their Uses

standard screw conveyor sizes

Screw conveyors are among the most widespread equipment for transporting and dosing bulk solids. Screw conveyor sizing is a well-defined process that depends on factors such as the material being conveyed, the length, the incline, and the amount being conveyed. The first step in sizing a screw conveyor is determining its diameter, which is a function of the rate of conveyed material, density, trough fill level, screw pitch, and speed. Most screw conveyors are full pitch, running at 30%-45% trough fill level, with the recommended trough loading determined by the material being conveyed. The speed should be under the published maximum speed (RPM), with 40RPM – 80RPM being a good range for most applications. After determining the diameter and RPM, the motor horsepower (HP) must be calculated, accounting for the force required to move the material and the tumbling of the material while it is conveyed. The basic HP calculation for screw conveyors includes the hanger bearing factor and material factor, accounting for the friction of the hanger bearing and the varying frictional properties of different materials.

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Screw conveyor capacity

The capacity of a screw conveyor is defined as the weight or volume per hour of a bulk material that can be safely conveyed. Screw conveyor diameter is determined by multiple factors, including capacity.

To properly select a screw conveyor for an application, the required capacity in cubic feet per hour (ft3/hr) must first be calculated. The recommended trough loading percentage for the specific bulk material to be conveyed is then selected from the Bulk Material Table. The screw conveyor diameter that corresponds with the recommended trough loading and is less than the capacity at maximum RPM is then chosen from the Capacity Table. The actual conveyor speed is calculated by dividing the required capacity by the capacity at 1-RPM from the Capacity Table.

For example, a screw conveyor with a 12-inch diameter and a speed of 62-rpm can convey 25,600 lbs of corn meal per hour.

It is important to note that the maximum speeds shown in the Capacity Table are not intended for every application and were developed for non-abrasive, free-flowing bulk materials. Lower screw conveyor speeds are recommended for most industrial applications, which will require a larger screw conveyor diameter.

The maximum lump size must also be considered when designing a screw conveyor. The Capacity Table is only intended for designing control-fed screw conveyors, while screw feeders are flood-loaded at the inlet and require special design considerations.

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Screw conveyor horsepower

Horsepower is a measure of the rate at which work is done. In the case of a screw conveyor, it is a measure of the power needed to move material a defined distance and elevation. The horsepower required to drive a screw conveyor is called Total Shaft Horsepower (TSHP).

The TSHP is a function of the characteristics of the bulk material being conveyed and the friction inherent in the screw conveyor. It is important to design a screw conveyor with sufficient horsepower to prevent downtime and loss of production.

The TSHP is calculated by adding Friction Horsepower (FHP) and Material Horsepower (MHP) and dividing the result by the drive efficiency. The FHP is the horsepower required to turn a screw conveyor when empty, and the MHP is the horsepower required to convey the bulk material the full length of the screw conveyor.

The FHP and MHP can be calculated using the following formulas:

Friction HP Calculation:

FHP = DF x HBF x L x S x 5.37

Where:

  • DF = Conveyor Diameter Factor
  • HBF = Hanger Bearing Factor
  • L = Conveyor Length (feet)
  • S = Conveyor Speed (RPM)

Material HP Calculation:

MHP = CFH x W x MF x 0.000247

Where:

  • CFH = Conveyor Capacity (ft3/hr)
  • W = Bulk Density (lbs/ft3)
  • MF = Material Factor (from Bulk Material Table)

The TSHP is then calculated as follows:

Total Shaft HP Calculation:

TSHP = (FHP + MHP) / e

Where:

  • FHP = Friction Horsepower
  • MHP = Material Horsepower
  • E = Drive Efficiency (typically between 85% and 95%)

If the calculated MHP is less than 5 HP, it should be corrected for potential overload using the Corrected Material HP Chart. The TSHP calculation should then be adjusted as follows:

Total Shaft HP Calculation:

TSHP = (FHP + Corrected MHP) / e

Additionally, if the screw conveyor has special flights, the MHP must be multiplied by the appropriate Special Flight Factor (SF) before being added to the FHP to obtain the TSHP.

It is important to note that the horsepower requirements for screw conveyors will vary depending on the specific application and the type of screw conveyor used (shafted or shaftless). The calculations outlined above are for control-fed screw conveyors only; screw feeders may require additional considerations.

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Screw conveyor torque

Torque is the twisting force exerted by the drive unit on the conveyor screw of a screw conveyor. It is transmitted through the drive shaft of the drive unit to the screw and converted to force to convey the bulk material.

The equation for Full Motor Torque is:

HP = Nameplate Horsepower of the motor on the screw conveyor x S = Conveyor Speed

Torque is measured in inch-lbs. for screw conveyor components. The torque rating of the drive shaft, coupling shafts, coupling bolts and conveyor screw must be greater than Full Motor Torque for proper design and to avoid mechanical failure.

There are several methods to calculate the required torque for a screw conveyor. One method is to use the following formula:

M = P x 9550 / n

Where:

  • M = Torque needed (Newton-meter)
  • P = Power (kW) of your motor
  • N = rpm of the screw axe

Another method is to use an online calculator, such as the one provided by KWS Manufacturing, which offers engineering guides and interactive calculators for designing screw conveyors.

It is important to properly select screw conveyor components to minimize downtime and maintenance. The Industrial standard series of conveyor components provides a choice of power-transmitting component sizes and materials of construction to ensure adequate torque capacities without undue additional cost.

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Screw conveyor diameter

The diameter of a screw conveyor is one of the most important factors in designing a screw conveyor. It is calculated based on the rate of the conveyed material, density, trough fill level, screw pitch, and speed of the screw. The diameter directly affects the capacity and speed of the conveyor, which is why it is crucial to assume a diameter to begin the calculations.

The first step in determining the diameter is to define the capacity requirement for the screw conveyor. This involves understanding the characteristics of the material being conveyed, such as its density and flow properties. The capacity of a screw conveyor with a standard screw flight can be estimated using the 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 in kg/m3

C = inclination correction factor

Once the capacity requirement is defined, the next step is to calculate the capacity of the screw conveyor. This involves selecting a suitable screw pitch based on the diameter of the screw and estimating the loading ratio according to the flow properties of the material. The speed of the screw can then be adjusted to ensure the capacity of the screw meets or exceeds the requirement.

After determining the diameter and RPM of the screw conveyor, the motor horsepower (HP) needs to be calculated. This calculation accounts for the force required to move the material, as well as the tumbling of the material as it moves along the conveyor. The basic HP calculation for screw conveyors consists of three parts: the HP to convey the material, the HP to turn the screw, and the combination of these two for the total required HP.

It is important to note that these calculations are based on assumptions and design decisions, and they provide an estimate of the screw conveyor's diameter and speed. For detailed design and manufacturing, it is recommended to engage a specialized company that adheres to industry standards, such as CEMA in the US or SHAPA in the UK.

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Screw conveyor speed

The speed of a screw conveyor is crucial in determining its capacity and performance. The speed is measured in revolutions per minute (RPM) and can be calculated using the following 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 in kg/m3

> C = inclination correction factor

To design a screw conveyor, the first step is to define the required capacity, which is the amount of material that needs to be conveyed per unit of time. Once the capacity requirement is established, the next step is to calculate the capacity of the screw conveyor. This involves defining the screw pitch, estimating the loading ratio, and determining the correction factor for inclined screw conveyors, if applicable.

The screw speed can then be adjusted to ensure the conveyor's capacity meets or exceeds the requirement. It is important to note that the screw speed should not exceed the maximum speed for the given screw diameter. The recommended maximum screw speed for a 0.1-meter diameter screw, for example, is 190 RPM.

Additionally, when handling explosive powders, the maximum speed should result in a conveyor tip speed of less than 1 m/s. The CEMA association provides an alternative formula for calculating the capacity of a screw conveyor:

> C = 0.7854*(Ds2-Dp2).P.K.60/1728

Where C is the capacity in ft3/h/RPM, Ds is the diameter of the screw flight in inches, Dp is the diameter of the pipe or shaft supporting the screw flight in inches, P is the pitch of the screw in inches, and K is the percent trough loading.

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Frequently asked questions

Screw conveyor sizes vary depending on the application and material being conveyed. The diameter of the screw conveyor is typically determined by the rate of conveyed material, density, trough fill level, screw pitch, and speed. Standard screw conveyor diameters range from 9 inches to 12 inches, with corresponding pipe sizes of 2.5 inches and 2.875 inches, respectively.

To choose the right size screw conveyor, you need to consider the material being conveyed, the length of the conveyor, the incline, and the amount of material being conveyed. The capacity of a screw conveyor is calculated based on the screw diameter, pitch, speed, and loading ratio, among other factors. It is important to ensure that the calculated speed does not exceed the maximum speed for the selected screw diameter.

The key factors that affect screw conveyor size include the rate and density of the conveyed material, trough fill level, screw pitch, and speed. The choice of screw pitch and inclination can also impact the size and speed of the screw conveyor. Additionally, the characteristics of the material being conveyed, such as flow properties and particle size, play a role in determining the appropriate screw conveyor size.

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