1. Introduction
Twin-shaft mixers are widely used in concrete, dry mortar, chemical, and environmental protection industries due to their advantages of strong shearing force, no mixing dead corners, and high mixing efficiency. As the core component of the mixer, the blade directly participates in the processes of material pushing, shearing, throwing, and convection. Its structural parameters (thickness, width, angle, etc.) determine the material flow state and mixing quality. Among them, blade thickness is not only related to structural rigidity and wear resistance but also directly affects the material stirring trajectory, shear strength, and power consumption. Therefore, exploring the influence of blade thickness on mixing effect is of great significance for optimizing mixer performance.
2. Influence Mechanism of Blade Thickness on Mixing Effect
2.1 Too Thin Blade (＜12 mm)
When the blade thickness is less than the reasonable range, the overall rigidity is insufficient, and it is prone to elastic deformation or even plastic bending under the impact and friction of materials (especially hard aggregates such as stones). Its negative impacts on the mixing effect are mainly reflected in the following aspects:
Poor mixing uniformity and severe segregation: The deformed blade cannot effectively lift and throw materials, failing to form sufficient convective circulation. The gap between the blade and the liner increases, resulting in the inability to generate effective shearing force. Trace components such as cement and admixtures cannot be fully dispersed, leading to the separation of aggregates and paste, cement agglomeration, and local proportion imbalance. The mixing uniformity (CV value) is often higher than 15%, which cannot meet the production requirements.
Prolonged mixing time and reduced efficiency: To compensate for the problem of uneven mixing, the mixing time needs to be prolonged by more than 50%. The original 30-second mixing cycle is extended to more than 1 minute, disrupting the production rhythm of the mixing station, causing backlogs in subsequent batching and unloading links, and reducing the overall production efficiency by 30%–50%.
Unstable material discharge and serious residue: The thin blade has weak spiral pushing force, making it impossible to completely push the materials on the cylinder wall and bottom to the discharge port. After each mixing, 5%–15% of the materials remain, which hardens and mixes with new materials, further aggravating uneven mixing and forming a "hard grinding layer" that accelerates the wear of the blade and liner.
Severe equipment vibration and increased energy consumption: The deformed blade leads to unstable material carrying, fluctuating mixing load, and large impact load during operation. This causes severe vibration of the equipment, accelerates fatigue wear of the mixing shaft, increases bearing clearance, and ages the reducer gear. At the same time, the fluctuating load leads to a 10%–20% increase in energy consumption.
2.2 Moderate Blade Thickness (12–20 mm)
When the blade thickness is within the reasonable range (12–20 mm for small and medium-sized mixers, 20–24 mm for large mixers), it has sufficient rigidity and wear resistance, with stable material stirring and optimal mixing effect. Its advantages are as follows:
Excellent mixing uniformity and no segregation: The blade has no deformation during operation, maintaining a reasonable gap (3–5 mm) with the liner. It can effectively lift and throw materials, forming a strong convective circulation and shearing action. The materials are fully mixed in all directions (axial, radial, and circumferential), with a mixing uniformity (CV value) of 8%–12%, no aggregate segregation or cement agglomeration, and stable product quality.
Short mixing time and high efficiency: The moderate-thickness blade has a strong material stirring capacity, completing uniform mixing within the designed time (30–60 seconds). The production rhythm is stable, and the efficiency is maximized while ensuring mixing quality.
Stable discharge and low residue: The blade has sufficient pushing force, effectively scraping the materials on the cylinder wall and bottom, with a discharge residue of less than 3%, avoiding the problem of hardened residue affecting mixing quality.
Stable equipment operation and low energy consumption: The load is stable during operation, with uniform torque, no severe vibration, and normal service life of transmission components such as the shaft, bearings, and reducer. The energy consumption is within the rated range, with high cost-effectiveness.
2.3 Too Thick Blade (＞24 mm)
Excessively increasing the blade thickness (greater than 24 mm) will lead to redundant weight and excessive stirring resistance, which will adversely affect the mixing effect and equipment performance:
Increased stirring resistance and local dead corners: The overly thick blade has a large contact area with materials, significantly increasing stirring resistance and power consumption (increased by more than 20%). At the same time, the thick blade is prone to material jamming and accumulation at the root, forming local mixing dead corners, resulting in uneven mixing of materials in some areas.
Reduced material throwing height and weakened convection: The overly heavy blade has a slow rotation response, reducing the material lifting and throwing height, weakening the convective circulation effect, and prolonging the mixing time to a certain extent.
Increased equipment load and accelerated wear: The self-weight of the blade and the stirring resistance are excessively large, resulting in long-term high-load operation of the mixing shaft, bearings, and reducer, accelerating fatigue wear and shortening the service life of transmission components. In addition, the accumulated hardened materials on the inner wall of the cylinder aggravate the abrasion of the cylinder structure.
Poor cost-effectiveness: The excessively thick blade has extremely high wear redundancy, and the blade body is hardly worn, but the weight redundancy is excessive, increasing manufacturing and maintenance costs, and reducing economic benefits.
3. Optimal Blade Thickness Range and Engineering Selection
3.1 Optimal Thickness Range
Combined with theoretical analysis and engineering practice, the optimal blade thickness of twin-shaft mixers is as follows:
Small mixer (＜2 m³): 12–16 mm (material: 65Mn steel, surface hardening).
Medium mixer (2–5 m³): 16–20 mm (material: 65Mn steel, surfacing tungsten carbide, hardness HRC58–62).
Large mixer (＞5 m³): 20–24 mm (material: high-strength manganese steel, integral casting + wear-resistant coating).
3.2 Engineering Selection Principles
In actual engineering selection, the following factors should be comprehensively considered:
Material characteristics: For materials with high hardness and large abrasiveness (such as concrete with large stone), select a thickness close to the upper limit; for materials with low hardness and small abrasiveness (such as dry mortar), select a thickness close to the lower limit.
Mixer model: Match the thickness according to the mixer volume, and avoid "small mixer with thick blades" or "large mixer with thin blades".
Production efficiency: On the premise of ensuring mixing quality, select a moderate thickness to balance efficiency and energy consumption.
Maintenance cost: Select a thickness with sufficient wear resistance to reduce the frequency of blade replacement and maintenance costs.