What is a double-shaft screw conveyor?

A double-shaft screw conveyor is a device used for material transfer in industrial production. Its basic function is to realize horizontal or inclined conveying of powdered, granular or small block materials. According to the internal structure and material, the equipment is mainly divided into shafted double-screw conveyors and shaftless double-screw conveyors, as well as carbon steel double-screw conveyors and stainless steel double-screw conveyors to adapt to different material characteristics and working conditions. Compared with other conveying methods, double-shaft screw conveyors usually show greater capacity in conveying volume and have better adaptability to sticky, easy-to-wind or easy-to-agglomerate materials.

What types of double-shaft screw conveyors are there?

A double-shaft screw conveyor is a conveying device that uses rotating spiral blades to push materials forward along the inside of a closed casing. According to whether there is a central axis, it can be divided into shafted double-screw conveyors and shaftless double-screw conveyors; according to the material, it can be divided into carbon steel double-screw conveyors and stainless steel double-screw conveyors.
 
The shafted twin-screw conveyor uses two spiral blades with a central shaft to rotate synchronously, pushing the material to move axially in a closed tank, and realizing horizontal or inclined conveying of the material. The double screw can stir and mix the material to a certain extent, which helps to break up lumps or evenly mix materials of different components. For a horizontal shafted twin-screw conveyor with a diameter of 200mm and a speed of 60r/min, the processing capacity of conveying fly ash with a bulk density of 1.5 t/m³ is between 10-25 t/h, and the specific value will vary depending on the material filling factor and actual working conditions. A single shafted twin-screw conveyor is mainly suitable for medium and short distance transportation. The common single-machine conveying length is usually between 2 meters and 30 meters, which is based on the strength of the screw shaft, torque transmission and intermediate support layout.
 
The shaftless twin-screw conveyor is a conveying equipment that uses a spiral body without a central shaft to push the material forward. It is mainly used to handle special materials that are difficult for traditional shafted screw conveyors to handle. Since there is no obstruction of the central axis, the material has a larger circulation space in the conveying trough, which greatly reduces the risk of material blockage and entanglement. The design of the shaftless screw also enables the equipment to have a certain stirring and breaking effect on the material during operation, which helps to prevent the material from agglomerating. For a shaftless double screw conveyor with a diameter of 250mm, the processing capacity is between 5-15 m³/h. For handling low-density and loose materials, the processing capacity can reach 10-30 m³/h. A single shaftless double screw conveyor is usually suitable for medium and short-distance transportation, and the general design conveying length is between 2 meters and 20 meters. This is because the shaftless screw body needs higher strength and rigidity to overcome the resistance of the material, and at the same time, it needs to have enough support points to ensure smooth operation. The carbon steel double screw conveyor uses two carbon steel spiral blades, which rotate synchronously under the drive of the motor, so as to promote various non-corrosive, conventional powder, granular and small block materials in the closed trough for horizontal or inclined transportation. A horizontal carbon steel double screw conveyor with a diameter of 200mm and a speed of 60r/min can handle 15-30 t/h when conveying cement with a bulk density of about 1.2 t/m³. If it is conveying granular, light-density materials such as grains, the processing capacity may be between 5-15 m³/h. A single carbon steel double screw conveyor is usually suitable for medium and short distance material transportation. Generally speaking, the effective conveying length of a single device can reach 5 meters to 30 meters.
 
Stainless steel double screw conveyors have good corrosion resistance and can resist the erosion of chemicals such as acids and alkalis. At the same time, the surface is smooth and easy to clean, ensuring that the material is not contaminated during the conveying process and meets strict hygiene standards. The double screw design also gives it a certain mixing ability and reduces the bridging and blockage of materials during transportation. A horizontal stainless steel double screw conveyor with a diameter of 150mm and a speed of 50r/min can handle 3-8 t/h when conveying starch with a bulk density of about 0.8 t/m³. If viscous sludge is processed, the processing capacity can reach 2-6 m³/h. The effective conveying length of the stainless steel double screw conveyor is between 3 meters and 25 meters.

What are the advantages of double-axis screw conveyors?

Compared with single-axis screw conveyors and other types of conveying equipment, double-axis screw conveyors show some specific advantages. It usually provides greater conveying capacity because the two screw shafts work at the same time, which can push the material more effectively, thereby conveying more material per unit time. The equipment has a stronger adaptability to materials, especially for materials with strong viscosity, easy to agglomerate or easy to bridge. The stirring and arch-breaking effect of the double shaft helps to reduce blockage and can achieve relatively stable conveying of materials with high water content and poor fluidity. In addition, the relative movement of the two spiral blades during rotation helps to peel off the materials adhering to the blades and the trough wall, thereby achieving self-cleaning to a certain extent and reducing the frequency of material residue and manual cleaning. In terms of structure, screw conveyors are usually more compact and occupy less space than belt conveyors or bucket elevators, especially in situations where inclined or vertical conveying is required, and the space utilization rate has certain advantages. At the same time, its fully enclosed casing design can effectively prevent dust leakage, avoid material pollution of the environment, or prevent external impurities from entering the material, which is of great significance for conveying toxic, harmful, volatile or clean materials.

How does a double-axis screw conveyor work?

The double-axis screw conveyor is based on the thrust generated by the spiral blades on the material when it rotates. Its core components are two parallel and synchronously rotating spiral shafts (or spiral blades). The two spiral shafts usually have opposite rotation directions, such as one is left-handed and the other is right-handed, or both are in the same direction, but the blade angles are opposite, to ensure that the material moves in the same direction in the casing. When the motor drives the two spiral shafts to rotate at a certain speed through the reducer, the spiral blades attached to the spiral shafts will continuously apply axial thrust to the material entering the casing. Due to the gravity of the material itself and the friction with the inner wall of the casing, the material will not rotate with the spiral blades, but move forward along the direction of rotation and axial direction of the spiral blades. In the dual-axis system, the staggered movement of the two spirals not only pushes the material forward, but also stirs, mixes or loosens the material to a certain extent, which helps to break up the material agglomerates and reduce the accumulation and blockage of the material during transportation. The material enters from the feed port, moves along the conveying trough under the continuous push of the spiral blades, and finally discharges from the discharge port. Factors such as the inclination angle of the conveyor, the speed of the spiral, the pitch and diameter of the spiral blades will affect the conveying speed and conveying volume of the material. As a material conveying tool, the dual-axis screw conveyor provides a feasible material transfer solution in a variety of industrial scenarios. The equipment has characteristics in conveying capacity, material adaptability and environmental control, and provides a variety of types according to the nature of the material and on-site needs, so that it can adapt to the conveying needs under different material characteristics and working conditions. In practical applications, the correct selection of a twin-shaft screw conveyor requires the physical and chemical properties of the material to be conveyed (such as viscosity, humidity, particle size, corrosiveness, etc.), the required hourly processing volume, and the conveying distance and angle to be determined. At the same time, factors such as the equipment installation space limitations, the temperature and humidity of the operating environment, etc. need to be considered.