Double Shaft Mixer

Double Shaft Mixer

The double shaft mixer is a core piece of equipment in organic fertilizer, compound fertilizer, and blended fertilizer production lines, responsible for the batch homogenization of multi-component materials. This equipment uses a horizontaldouble axis structure as the container and counter-rotating helical blades as the mixing tool, achieving rapid and uniform mixing of materials through three-dimensional convection circulation. In the entire fertilizer production line, thedouble shaft mixer is typically located after the crushing process and before the granulation process, playing a crucial role in bridging these processes.

In organic fertilizer production lines, thedouble shaft mixer is a game-changer in overcoming the challenges of mixing highly moist and viscous materials. Livestock manure such as chicken, pig, and cow manure has high moisture content and high viscosity; when piled alone, it easily cakings and has poor aeration. In contrast, auxiliary materials such as straw and sawdust are loose and fibrous, resulting in significant differences in their physical properties. Thedouble shaft mixer, with its unique mixing structure, perfectly solves the production problems of uneven mixing, material blockage, and clumping inherent in traditional methods.

Component composition and functional zoning

From a production process perspective, a double shaft mixer can be divided into the following functional units:

(I) Feeding and Distribution Unit: Includes the feed inlet and top feeding device. Material enters the mixing tank evenly through this unit; feeding should be uniform and continuous. The feed inlet adjustment mechanism controls the production volume.

(II) Double axis Convection Mixing Unit: This is the core unit of the equipment, including two parallel mixing shafts and counter-rotating spiral blades. The outer spiral pushes the material from both ends towards the center, while the inner spiral returns the material from the center to both ends, forming an axial convection circulation.

(III) Atomizing, Humidifying, and Conditioning Unit: Includes stainless steel atomizing cone nozzles and water supply pipelines. The nozzles are axially arranged along the spiral shaft direction, forming a water curtain mist to evenly wet the material.

(IV) Conveying and Discharging Unit: Includes the discharge port and conveying mechanism. The mixing blades push the material towards the discharge end while mixing.

(V) Power Transmission Unit: Includes the motor, reducer, gears, and sprocket guard.

Production line roles and processes

The double shaft mixer plays a crucial role in the mixing stage of a fertilizer production line. The complete organic fertilizer production process is as follows: raw material crushing → screening → twin-shaft mixing and humidification → granulation → drying → cooling → screening → packaging.

In the mixing stage, the twin-shaft mixer performs several key tasks: rapidly and uniformly mixing the main materials, various nutrient additives, and binders; adding water or steam during the mixing process to condition the materials, increasing their viscosity and resulting in a better forming rate when entering the granulator; and effectively breaking up any small lumps in the material, providing soft and fine raw materials for the granulation process. The equipment can be used in conjunction with compound fertilizer production lines and is suitable for mixing nitrogen, phosphorus, and potassium powders, inorganic salt raw materials, and finely crushed powders from agglomerated return materials.

Hybrid Process and Stage Description

The mixing process of a double shaft mixer can be divided into the following stages:

Feeding and Distribution Stage: Powdered material enters the mixing tank at a uniform speed through the feed inlet. Materials are added in a dry-to-wet order, while liquids are sprayed evenly through atomizing nozzles.

Convective Mixing Stage: The two main shafts rotate synchronously in opposite directions. The outer spiral pushes the material from both ends towards the center, while the inner spiral returns the material from the center to both ends. The material is repeatedly dispersed and mixed vertically and horizontally within the drum. The cross-action of the two shafts creates three-dimensional convection within the drum.

Humidification and Conditioning Stage: When the material is pushed into the humidification section, nozzles arranged axially along the spiral shafts inside the upper part of the casing form a water curtain mist to wet the material. The water spray is uniform and the water volume is controllable, solving problems of uneven moisture content, localized over-wetting leading to clumping, and over-drying making it difficult to form.

Conveying and Discharging Stage: The mixing blades push the material towards the discharge end while mixing, achieving simultaneous mixing and conveying. The material is discharged from the discharge port after reaching a controllable moisture content.

Preparatory materials and requirements

The double shaft mixer has specific process requirements for the feed materials. Material particle size: No hard foreign objects larger than 5mm should enter the machine during operation. Material moisture content: It can adapt to the mixing and conveying needs of materials with moisture content ranging from 10-25%. Material characteristics: The moisture content of raw materials for organic fertilizer varies greatly; fresh cow manure may have a moisture content of over 70%, while fermented compost may only have around 30%, and the twin-shaft mixer can adapt to both. Feeding sequence: The mixer should run first, then spray the liquid; after spraying, continue running and mixing for 3-5 minutes.

Operating procedures and key control points

Proper operation of the double shaft mixer is crucial for ensuring mixing quality and extending equipment lifespan:

Pre-start preparation: Check all bolts for looseness and ensure the main unit's door is secure. Check the bolts on the mixing blades for looseness and ensure all components are intact. Before starting, briefly run the equipment to confirm there are no abnormalities before starting the main unit. Use the handwheel to idle the main shaft several times to ensure there are no obstructions or abnormal phenomena before starting the main unit.

Operation: After starting and operating normally, begin feeding. The material should be fed evenly and in appropriate amounts; no hard foreign objects larger than 5mm should enter the machine. If any abnormal noises such as metallic clanging or friction are heard during operation, stop the machine immediately for inspection and troubleshooting.

Shutdown procedure: When not in use, empty the material from the machine completely. After long-term shutdown, thoroughly clean the material from the tank.