Double Shafts Mixer

Equipment Introduction

The double-shaft mixer, also known as a double-shaft paddle mixer, is a high-efficiency mixing device with two horizontal parallel main shafts as its core mixing elements. Its greatest advantage lies in its ability to achieve extremely high mixing uniformity (coefficient of variation ≤ 5%) in a very short time (typically 30–120 seconds/batch), and it is highly adaptable to differences in material specific gravity and particle size.

This equipment can be designed as a batch mixer for use in the feed, food, and pharmaceutical industries, or as a continuous mixer widely used in production lines for bulk materials such as fertilizers and building materials. The continuous mixer continuously receives material at the feed end, agitates and propels it with the propeller blades, and then discharges it immediately at the discharge end, combining the dual functions of mixing and short-distance conveying.

Equipment Structure and Components: 

The entire machine can be divided into two main modules: the drive unit and the main body. These components work together to achieve efficient three-dimensional mixing:

1. Drive Unit

1) Motor: Provides the main power; power is matched to production capacity (commonly 11–30 kW).

2) Reducer: Reduces speed and increases torque; typically a hardened gear reducer.

3) Coupling and Synchronous Gear: The motor drives the drive shaft via a coupling. The synchronous gear on the drive shaft then drives the driven shaft, ensuring that the two main shafts always rotate in opposite directions at a fixed speed ratio, preventing impeller collisions due to speed differences.

2. Mixing Body

1) Horizontal Cylinder: Mostly U-shaped or W-shaped troughs, welded from high-quality carbon steel or stainless steel plates. The top has an inlet and liquid spray pipe, and the bottom has a outlet.

2) Dual Mixing Shafts: Two parallel main shafts are horizontally arranged at the bottom of the cylinder. Each shaft is equipped with a combination of continuous spiral and blade-type spiral impellers (or pure blade impellers). The impeller inclination angle is typically 45°–60°.

3) Blade Design: Utilizing a two-blade structure (base + replaceable end blades), only the small blades need replacement after end blade wear, eliminating the need to replace the entire shaft and significantly reducing maintenance costs.

4) Water/Liquid Spray System: Composed of an inlet pipe and nozzles, it can evenly spray water, steam, molasses, oil, or bacterial agents during mixing, achieving simultaneous humidification/greasing.

3. Support and Sealing

1) Bearing Housing: Supports the dual shafts and withstands radial and axial loads. Internal labyrinth seals or packing seals prevent dust from entering the bearings.

2) Frame/Base: Welded from channel steel or H-beams and fixed to the ground with anchor bolts.

4. Discharge Device: Equipped with a pneumatic or manual flap valve at the bottom, the wide-opening design allows direct access to the side of the cylinder, ensuring rapid discharge with minimal residue (typically <0.1%), effectively preventing cross-contamination between different batches.

Working Principle of the Equipment

The core mechanism of the double-shaft paddle mixer is the combination of "convective mixing" and "weightlessness effect," which can be further divided into the following processes:

1. Power Transmission: The motor, after being reduced in speed by a reducer, drives the drive shaft through a coupling; the synchronous gear on the drive shaft drives the driven shaft, causing the two shafts to rotate relative to each other at the same speed (one shaft clockwise, the other counterclockwise).

2. Three-Dimensional Material Motion: The paddles propel the material at a specific angle and linear velocity (typically 6–10 m/s), simultaneously generating three types of flow:

1) Axial Flow: The paddles push the material back and forth along the length of the cylinder, achieving end-to-end macroscopic exchange;

2) Radial Flow: The material is thrown upwards from the bottom by the paddles, circulating and tumbling across the cross-section;

3) Lateral Convection: The counter-rotating dual shafts create a highly turbulent zone in the central area, with the material weaving back and forth between the two shafts. 3. Zero-Gravity Mixing: When the material is propelled to its highest point by the propeller, the centrifugal force and gravity instantly cancel each other out, and the material enters a "weightless state." At this time, particles of different densities and sizes freely cross, diffuse, and mix in the absence of gravity, fundamentally eliminating the tendency for segregation.

4. Continuous Discharge: In continuous operation mode, after the material enters through the inlet, it moves towards the outlet while being stirred by the propeller blades. The residence time can be controlled by adjusting the rotation speed and feed rate, and it is finally discharged uniformly from the outlet.

Applicable Raw Materials

Equipment Applications:

1. Organic fertilizer production line: Core conditioning and mixing section after batching, standardizing carbon-nitrogen ratio and moisture content for pretreatment before fermentation and granulation (Huaqiang equipment's main application scenario);

2. Raw material premixing for compound fertilizer, BB fertilizer, and high-tower compound fertilizer production lines;

3. Sludge and livestock manure harmless treatment, organic fertilizer fermentation pretreatment workshops;

4. Wet mixing of building material dry mortar and clay brick making raw materials;

5. Continuous mixing and conditioning of feed mills and chemical powders;

6. Organic waste treatment sections in garbage and sewage treatment plants.

Equipment Applications in Production Lines

1. Core Position in Organic Fertilizer and Compound Fertilizer Production Lines

In a complete organic fertilizer production line, the double-shaft paddle mixer is typically located after the crushing process and before the granulation process, playing a crucial role in bridging these two stages.

Complete Processing Flow: Livestock and poultry manure and other raw materials → Crushing and screening → Mixing and batching in a double-shaft paddle mixer (humidification, conditioning, and inoculation) → Granulation → Drying → Screening → Packaging

2. Specific Role in the Production Line

1) High-moisture material mixing: Well-rotted wet manure can be directly mixed without deep drying, greatly simplifying the production process.

2) Dry-wet blending: Dry, semi-wet, and high-moisture materials are mixed in proportion to adjust the material moisture content to the appropriate range for granulation.

3) Microbial agent application: Microbial agents or nutrient solutions are evenly sprayed through an atomizing spray system.

4) Nutrient homogenization: The main materials are fully integrated with trace elements and fermentation agents, solving problems of uneven mixing and fertility stratification.

5) Continuous production: 24-hour continuous and stable operation, seamlessly connecting the entire production line from crushing, granulation, drying, to packaging.

3. Impact on Subsequent Processes

The material uniformly mixed by the double-shaft paddle mixer has a loose, fine, and uniform texture without hard lumps or clumps. Uniform material significantly improves the granulation rate and reduces the output of broken and waste materials. Meanwhile, the material's nutrient distribution is even, resulting in stable fertilizer efficacy and preventing localized seedling burn or uneven fertilization after application.

4. Automated Configuration: The equipment is equipped with a variable frequency drive (VFD) system, allowing for flexible adjustment of operating parameters based on material moisture content and production requirements. It can be connected to conveyors, batching machines, and granulators to form a fully automated production line, achieving continuous assembly line operation for crushing, mixing, and granulation.

Common Equipment Faults, Causes and Solutions