Screw Conveyor

Equipment Introduction

A screw conveyor, commonly known as an "auger," is a continuous conveying machine that uses a motor to drive a rotating screw to push materials for transport. Unlike belt and chain conveyors with flexible traction components, it uses a rigid screw as its main component, hence the term "conveyor with a rigid traction component."

Screw conveyors can perform horizontal, inclined, or vertical conveying. Their core advantages include: simple structure, small size, low cost, good sealing, multi-point feeding and unloading, and a mixing effect on materials during conveying. However, their conveying distance is relatively short, the blades and casing are prone to wear, energy consumption is relatively high, and they can cause some material breakage.

This equipment is widely used in building materials, chemical, power, metallurgy, coal, grain, and food industries, and is an important unit for mechanized transportation in various industrial and agricultural sectors.

Structural Composition

A complete screw conveyor typically consists of three main parts: the screw conveyor body, the inlet/outlet device, and the drive unit. The screw conveyor body is the core component, composed of a head section, an intermediate section, and a tail section.

Specifically, its main components include:

Screw (Auger): The main component for material conveying, consisting of screw blades and a screw shaft. Screw blades come in various types depending on the material, such as solid (full-surface) and ribbon-face. The screw shaft is usually made of hollow steel tubing with a diameter of 30–70 mm.

Bearings: Used to support the screw, and are classified into three types according to their location:

Head Bearing: Installed at the discharge end, bearing radial and axial forces, using a radial thrust bearing.

Tail Bearing: Installed at the inlet end, bearing only radial forces, using a radial spherical bearing.

Intermediate Hanger Bearing: When the screw shaft length exceeds 3 meters, it needs to be installed in the middle to prevent bending.

Material trough (casing): Usually made of thin steel plate, with a semi-circular bottom cross-section, used to hold the conveyed material.

Drive unit: Consists of an electric motor, reducer, and transmission components, providing power to the equipment.

Working Principle

The working principle of a screw conveyor can be summarized as "screw rotation—friction constraint—axial displacement":

1. Power Input: The drive unit drives the screw shaft to rotate within a fixed trough.

2. Friction Constraint: Due to its own weight and the external friction between the material and the trough wall, the material does not rotate with the screw shaft.

3. Axial Displacement: The rotating screw blades generate axial thrust on the material, causing it to move along the trough towards the discharge port, much like a "non-rotating nut moving along the screw."

Key Design Principles: The drive unit and discharge port are usually located at the same end, while the feed port is placed near the tail end of the other end. This ensures that the screw shaft primarily bears tensile force rather than compressive force during conveying, preventing buckling and instability of the shaft.

Suitable Materials

Screw conveyors have a wide range of applications, but they have specific requirements for the materials they handle.

✔️ Suitable Materials:

Mainly suitable for conveying loose materials such as powders, granules, and small lumps. Specific examples include: cement, fertilizer, grain, flour, coal powder, ash, and sand. For sticky or easily entangled materials (such as sludge, biomass, and garbage), a shaftless screw conveyor should be selected.

❌ Unsuitable Materials:

Screw conveyors are not suitable for conveying materials that are easily perishable, excessively sticky, or prone to caking. They are also unsuitable for conveying large pieces of material, materials containing many fibrous impurities, or highly abrasive materials, to avoid blockages and excessive wear.

Applications in Fertilizer Production Lines

Standard configuration for the three core sections of the entire production line: batching, granulation, and fine powder recovery:

1. Batching Section (Core Purpose): A screw feeder below the silo provides quantitative feeding, precisely proportioning various organic and chemical fertilizer powders, replacing manual feeding;

2. Granulation Feeding and Conveying: The discharge screw from the mixer feeds the material at a uniform speed into the disc/drum granulator, stabilizing the granulation feed flow;

3. Fine Powder Recycling: Fine powder generated during screening is returned to the mixer via a short screw for secondary granulation;

4. Coating Support: A powder coating agent (talc) is quantitatively conveyed to the inside of the coating machine;

5. Short-Distance Transfer: Small quantities of material are conveyed in a closed system between silos and at the front end of the drying process.

Supporting Process Link: Raw Material Silo → LS Screw Quantitative Batching → Mixer → LS Screw → Granulator → Dryer → Cooler → Screening Machine → Fine Powder Screw Return → Mixer

Operation and Maintenance

While screw conveyors are relatively easy to maintain, the following points directly impact equipment lifespan and operational stability:

1. Lubrication Management: Regularly lubricate bearings, gears, chains, and other transmission components.

2. Blade Inspection: Periodically check the wear of the screw blades. Repair or replace severely worn blades promptly.

3. Overloading Prohibited: Do not overload the conveying capacity; otherwise, material will not be able to discharge, leading to screw shaft bending and casing damage.

4. Temperature Monitoring: Under high-temperature conditions, ensure the casing expands and contracts freely to prevent thermal expansion and jamming.

5. Abnormal Handling: If a harsh noise is emitted during operation, immediately stop the machine for inspection, eliminating faults such as blade interference with the casing or bearing damage.

6. Shutdown Cleaning: After conveying viscous or easily agglomerated materials, clean the trough promptly to prevent residual material from hardening and causing jamming.

Summary of Equipment's Comprehensive Technical Features:

1. Enclosed and environmentally friendly, zero dust generation during powder conveying, suitable for environmental control measures in organic fertilizer plants;

2. Multi-functional, capable of conveying, batching, and light mixing, simplifying production line equipment configuration;

3. Minimal footprint, multi-point inlet and outlet design suitable for small batching workshops;

4. Precise quantitative control, variable frequency speed regulation achieves accurate fertilizer proportioning, improving the stability of nutrient content in the finished product;

5. Different models are available to handle dry and wet materials. The LS shafted model is suitable for dry powder materials, while the WLS shaftless model is suitable for high-moisture, sticky manure materials, covering the conveying needs of all fertilizer categories.