What is Screw Feeder (Mass Flow & Bottom Live)

Screw feeder for dosing of bulk materials

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   Screw feeders are used in thousands of material handling applications and are designed to meter bulk materials at a controlled feed rate. A standard screw conveyor is normally fed by another screw conveyor and the amount of material that is discharged is directly proportional to the amount that is fed into the inlet.

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   In contrast, the inlet of a screw feeder is always 100 percent or flood loaded and is typically mounted directly to a storage device, such as a hopper, bin, or silo. The amount of material discharged by a screw feeder is completely controlled by design parameters.

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   A hopper is typically square or rectangular in shape with a sloping bottom and limited storage capacity. A container is very similar to a hopper but with greater storage capacity. A silo is cylindrical in shape with a conical or mass flow bottom and a large storage capacity.

   Since the screw feeder inlet is flood loaded, the desired feed or discharge rate directly influences the screw design. The discharge rate of a screw feeder can be accurately determined by speed control and screw conveyor pitch design. The use of variable speed drives improves measurement accuracy and can provide a wide range of feed rates. Pitch control is also an important consideration in screw feeder design.

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   If a Screw Conveyor is designed to handle bulk materials, it is carried out in relation to the rotation speed of the screw with a controlled percentage of load in the tundish and under these conditions the power was calculated and a standard pitch was placed, this conveyor should not force yourself to handle more bulk material, because it is only designed to handle and not feed bulk material.

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   Consequently, it is not recommended to design screw feeders with outside diameter and standard pitch (avoid designing with outside diameter equal to the lead pitch), because bulk materials will fill the helical screw from the back of the inlet opening first. , creating holes or caverns, stagnant material and possibly a "bridging" of bulk materials above the screw feeder.

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Figure 1 shows the improper design of a screw feeder with uniform outside diameter and constant pitch. To extract bulk materials evenly throughout the entire intake, each auger flight must increase the available volume as the screw conveyor moves toward the discharge. An effective and efficient system requires a variable pitch, tapered outside diameter (OD), or mass flow screw design.

Figure 2 shows a properly designed screw feeder.

The screw feeder is mainly used for powder and granule feeding, and it is used for feeding equipment with certain high requirements in the food, plastic, chemical, packaging and other industries. Understand the conveying process of the screw feeder.

Different from the horizontal conveying screw conveyor, the inclination angle of the conveyor is generally between 30-90°. Let's introduce its working principle.

The principle of screw feeder

The screw feeder moves the product upward through a completely closed helical rotating shaft. The speed of the screw body is higher than that of the ordinary screw conveyor. Under the action of centrifugal force, the conveyed material and the casing produce friction, which prevents the material from rotating with the screw blade and overcomes the problem of the material. Falling gravity, thus realizing the inclined or vertical conveying of materials.

Reminder: For materials with poor fluidity, the inclination angle can reach 50°, but when using an inclined screw feeder to convey materials, it is necessary to apply a certain pressure to the feeding port. However, when conveying materials vertically, the lifting height can reach 8 meters. When the lifting height needs to be increased, the vertical screw conveyor often needs intermediate hangers or stabilizer bearings to eliminate excessive screw deflection.

The following is a case show of screw feeders in different industries: