Enter the screw diameter, shaft diameter, pitch, rpm, fill factor (loading ratio), material loose density, and inclination factor into the calculator to determine the screw conveyor mass flow rate (mass capacity).
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Screw Conveyor Flow Rate Formula
The following equation is used to estimate the screw conveyor mass flow rate (mass capacity) from the theoretical volumetric throughput and the material bulk (loose) density.
Q = 60 \cdot \frac{\pi}{4} \cdot (D^2 - d_s^2) \cdot S \cdot N \cdot a \cdot \rho \cdot C- Where Q is the mass flow rate (kg/hr)
- D is the outside diameter of the screw (m)
- ds is the shaft diameter (m)
- S is the screw pitch (m)
- N is the screw speed (RPM)
- a is the fill factor (loading ratio), from 0 to 1
- ρ is the loose material density (kg/m³)
- C is the inclination factor (typically 0 to 1, with 1 for horizontal)
Unit consistency is required for hand calculations (length units for D, ds, and S must match the density volume units). This calculator converts your selected input units internally and outputs either kg/hr or lb/hr.
What is a Screw Conveyor Flow Rate?
Definition:
A screw conveyor flow rate is the amount of material the conveyor moves per unit time. “Capacity” is often reported as a volumetric rate (e.g., m³/h), but this calculator reports mass flow rate (e.g., kg/hr) by multiplying the volumetric throughput by the material’s bulk density.
How to Calculate Screw Conveyor Flow Rate?
Example Problem:
The following example outlines the steps and information needed to calculate Screw Conveyor Flow Rate.
First, determine the screw diameter. In this example, the screw diameter is 1 m.
Next, determine the shaft diameter. In this example, the shaft diameter is 0.30 m.
Next, determine the conveyor pitch. This conveyor has a pitch of 0.35 m.
Next, determine the rotational speed. This rotational speed is measured to be 50 RPM.
Next, determine the fill factor (loading ratio). This conveyor is specified at a fill factor of 0.25 (25% full).
Next, determine the material density. This material has a density of 150 kg/m³.
Next, determine the inclination factor. There is no inclination in this example; this factor is 1.
Finally, calculate the conveyor screw mass flow rate using the formula above:
Q = 60 * pi/4 * (D^2 – ds^2) * S * N * a * ρ * C
Q = 60 * 3.14159/4 * (1^2 – 0.3^2) * 0.35 * 50 * 0.25 * 150 * 1
Q ≈ 28,141.77 kg/hr
FAQ
What factors can affect the efficiency of a screw conveyor?
The efficiency of a screw conveyor can be affected by several factors including the design of the screw (pitch, diameter), the speed of operation (RPM), the type and moisture content of the material being moved, the loading ratio, and the inclination of the conveyor. Environmental factors such as temperature and humidity can also play a role.
Can screw conveyors be used for all types of materials?
Screw conveyors are versatile and can be used to move a wide range of materials, including dry to semi-dry bulk material. However, they are not suitable for materials that are extremely sticky or have a high moisture content that may cause clogging. The material’s abrasiveness and temperature are also considerations, as they can affect the conveyor’s wear and operational efficiency.
How does the inclination of a screw conveyor affect its capacity?
The inclination of a screw conveyor has a direct impact on its capacity. As the angle of inclination increases, the capacity of the conveyor generally decreases. This is because gravity plays a more significant role in resisting the movement of the material. The inclination factor (C) in the flow rate formula adjusts the capacity based on the angle, with higher inclinations leading to reduced flow rates.
