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In the coatings production industry, we often focus on formula design, raw material selection, and process parameters. Yet, we frequently overlook a seemingly ordinary but critical detail—the choice of materials for dispersion equipment.
Today, we take a closer look at how the material selection of dispersion shafts and discs subtly influences the final quality of coating products.
Dispersion is a crucial step in coatings production that significantly influences product quality. Dispersion equipment uses high-speed rotation to generate strong shear forces. These forces break down pigment agglomerates and distribute them evenly within the resin system.
In this process, the material properties of the dispersion shafts and discs directly affect three aspects: dispersion efficiency, product purity, and production costs.
Consider this: if these components wear down during high-speed operation, metal particles may mix into the product. Or, if they corrode, they can contaminate the raw materials.
Even with an optimal formula, poor material choice can compromise product quality. That’s why selecting the right materials for dispersion shafts and discs is the first line of defense in ensuring coating quality.
1. Wear Resistance: Impacts Product Purity and Equipment Lifespan
Most pigments and fillers used in coatings have high hardness. For example:
Titanium Dioxide (Mohs hardness: 5.5-6.0)
Carbon Black (Mohs hardness: 2.0-2.5)
Calcium Carbonate (Mohs hardness: 3.0)
Iron Oxide (Mohs hardness: 5.0-6.0)
During high-speed shearing, these materials continuously wear down the equipment surface. If ordinary carbon steel is used, the wear rate can be very high.
Here’s a real case:
One coatings manufacturer used carbon steel dispersion discs to produce white paint. In less than three months, the product started showing dark grey particles. Testing confirmed that these were metal contaminants from disc wear.
Solution:
Choose highly wear-resistant materials like hard alloys or specially hardened stainless steel. Although the initial investment is higher, it extends equipment life, reduces downtime for maintenance, and ensures consistent product quality. In the long run, this approach actually lowers overall costs.
2. Corrosion Resistance: Ensures Product Stability and Consistency
Coatings formulations contain various corrosive chemical components, including:
Solvents (e.g., alcohols, ketones, esters)
Additives (e.g., dispersants, defoamers)
Resin systems (e.g., water-based systems, which are often alkaline)
These components can corrode the metal surfaces of the equipment.
In one instance, we worked with a coatings manufacturer to identify the cause of impurities in their product. The investigation revealed that pitting corrosion on the dispersion shaft was releasing particles into the mixture.
Solution:
316 stainless steel, which contains molybdenum, offers significantly better corrosion resistance than 304 stainless steel. It has become the preferred choice for most coatings producers. For highly corrosive environments, more advanced materials such as duplex stainless steel or Hastelloy can be considered.
3. Mechanical Strength and Toughness: Ensure Operational Stability and Safety
Dispersion equipment operates at high speeds, generating immense centrifugal force and torque. This places high demands on the mechanical properties of the materials used. The selected material must provide:
High strength: to resist deformation and maintain stable operational clearance
High toughness: to prevent brittle fractures and improve operational safety
Good fatigue resistance: to withstand long-term alternating loads
4. Cleanliness and Contamination: Zero Tolerance Between Batches
Residual Risk:
Resins (such as acrylic) in solvent-based coatings can easily adhere to metal surfaces, leading to cross-contamination. PTFE coatings reduce surface energy to 18 mN/m (compared to 60 mN/m for stainless steel).
Cleaning Solutions:
Ultrasonic Cleaning: Most effective for ceramic materials, removing up to 98% of micron-level residue.
Case Study: A food-packaging coatings manufacturer switched to PTFE-coated shafts, increasing product pass rates for heavy metal testing from 92% to 99.8%.
5. Compatibility: Avoiding Chemical Reactions
Critical Cases:
Aluminum reacts with strongly alkaline coatings, generating hydrogen gas and posing explosion risks.
Polyethylene (PE) swells in ester-based solvents, with volume expansion rates of up to 15%.
Compatibility Testing:
Follow the ASTM D543-20 standard: immerse material samples in the coating for 72 hours and observe changes in mass.
6. Dispersion Efficiency: Amplifying Shear Forces
Hydrodynamic Model:
The turbulence intensity (Reynolds number) at the edge of the dispersion disc correlates with material surface roughness. Ceramic materials, with their micron-level textures, can increase shear force by up to 20%.
Design Optimizations:
Toothed Discs: Ideal for low-viscosity systems (e.g., water-based latex paints), achieving shear rates of up to 10⁴ s⁻¹.
Turbine Discs: Paired with tungsten carbide shafts, suitable for high-solid coatings (e.g., marine paints).
7. Coating Performance: The Double-Edged Sword of Electrostatic Effects
Charge Influence:
Stainless steel carries a positive charge, which can attract negatively charged pigments (e.g., carbon black). However, excessive charge may cause flocculation. PTFE materials offer excellent electrical insulation, making them ideal for dispersing sensitive pigments.
Performance Data:
Iron oxide pigments dispersed with ceramic discs show a reduction in D90 particle size from 8μm to 5μm.
Carbon steel shafts can reduce coating water resistance by 30% (per ASTM D870 testing).
Beyond directly impacting product quality, material selection also indirectly influences dispersion efficiency. Different materials vary significantly in machinability, which directly affects how optimally a dispersion disc can be designed.
Advanced stainless steels offer excellent machinability. This allows for the manufacture of discs with complex structures, such as:
Multi-layer (Toothed Discs): Increases shear area and improves dispersion efficiency.
Specially Shaped Holes: Optimizes hydrodynamic performance.
Precision Tooth Profiles: Creates a more uniform shear force field.
In contrast, lower-grade materials have limited machine ability. These often restrict manufacturers to simple flat discs or paddle structures. As a result, dispersion efficiency is significantly compromised.
Based on years of industry experience, we offer the following practical recommendations:
For General Coatings Production
Recommended Material: 316 Stainless Steel
Suitable Systems: Most solvent-based and water-based coatings
Advantages: Offers a good balance of performance and cost-effectiveness
Notes: Regularly inspect surface condition; full inspection recommended every 6 months
For High-Hardness Pigment Systems
Recommended Material: Surface-Hardened Materials
Suitable Systems: Formulations containing hard pigments like carbon black or iron oxide
Advantages: Excellent wear resistance and extended service life
Notes: Avoid impact loads to prevent delamination of the hardened layer
For Highly Corrosive Systems
Recommended Material: Duplex Stainless Steel or Special Alloys
Suitable Systems: Coatings with strong solvents or aggressive chemical ingredients
Advantages: Superior corrosion resistance
Notes: Monitor chloride ion levels to avoid stress corrosion cracking
For Food-Grade and Specialty Coatings
Recommended Material: Polymer Materials or Special Coatings
Suitable Systems: Food-contact coatings, electronic-grade coatings, etc.
Advantages: Ensures absolute freedom from metallic contamination
Notes: Respect temperature limits to prevent material degradation
No matter which material is chosen, proper maintenance can significantly extend the service life of the equipment:
Regular Inspection: Check the surface condition of dispersion discs and shafts monthly.
Timely Cleaning: Clean thoroughly after each use to prevent material buildup.
Standardized Operation: Avoid dry running and dry grinding to reduce abnormal wear.
Professional Repair: Always rely on professional technicians for repairs when damage is detected.
Cost-Benefit Analysis
Many companies focus only on the initial procurement cost but overlook the total lifecycle cost. We recommend using the following method for a comprehensive evaluation:
Total Cost of Ownership (TCO) = Procurement Cost + Maintenance Cost + Downtime Loss + Quality Risk Cost
Using this formula, it becomes clear that although high-quality materials require a higher initial investment, they are often more economical in the long run. One customer who upgraded to 316 stainless steel based on our advice reported that the equipment’s service life increased threefold, the product defect rate decreased by 70%, and annual comprehensive savings exceeded RMB 200,000.
As the coatings industry moves toward higher quality and greater environmental sustainability, requirements for dispersion equipment materials are also increasing:
Composite Material Applications: Advances in surface coating technology allow the use of different materials for the base and working surfaces.
Intelligent Monitoring: Embedded sensors enable real-time monitoring of equipment wear.
Customized Designs: Materials and structures are optimized for specific formulations.
Eco-Friendly Materials: Recyclable and environmentally friendly materials are gaining more attention.
The choice of materials for dispersion shafts and discs may seem like a small detail, but it directly affects the quality of coating products and production costs. In an increasingly competitive market, these details often determine a company’s core competitiveness.
We recommend that coatings manufacturers:
Choose the most suitable materials based on their specific product systems.
Establish sound equipment maintenance and monitoring systems.
Evaluate cost-effectiveness from a total lifecycle perspective.
Stay informed about new materials and technologies.
Paying attention to every production detail is essential to remaining competitive in the market. If you have any questions about selecting materials for dispersion equipment, please feel free to contact us. We are here to provide professional technical advice and solutions.
