In the rubber, plastics, and composite materials industries, the internal mixer is one of the most critical pieces of equipment. Its rotor, operating under continuous high temperature, high pressure, and intense shear forces, is exposed to severe abrasive wear. Over time, the rotor blades experience progressive wear, substrate fatigue, and reduced surface hardness. As clearance increases and material flow becomes unstable, the internal mixer may face higher energy consumption, vibration, and even unexpected shutdowns.
Therefore, improving rotor surface performance, enhancing wear resistance, and extending equipment service life have become essential goals in both manufacturing and remanufacturing.
Working Conditions and Challenges of Internal Mixer Rotors
Internal mixer rotors—such as Banbury and Intermix designs—must withstand extreme conditions during rubber mixing:
- Abrasive particles like carbon black, silica, zinc oxide, and additives constantly impact and grind the rotor blade surfaces.
- The rotor is simultaneously subjected to high shear stress, elevated temperature, and tight contact with the mixing chamber wall, leading to fatigue cracks and surface spalling.
- Traditional repair approaches, including local welding or heat treatment, provide limited durability and require frequent maintenance.
These challenges highlight the demand for a surface strengthening method that offers high hardness, toughness, shear resistance, and long-term operational stability.
What Is PTA (Plasma Transferred Arc) Welding?
Plasma Transferred Arc (PTA) welding is an advanced surface alloying and strengthening technology.
Using a high-energy plasma arc, metal powders—such as Ni-based alloys, Co-based alloys, or WC/Ni composites—are melted and precisely deposited onto the rotor surface. Once solidified, the material forms a dense, defect-free alloy layer with a strong metallurgical bond to the rotor substrate.
Key Advantages of PTA Welding
- Strong metallurgical bonding between coating and substrate;
- Adjustable coating thickness, typically 0.8–3 mm;
- Low dilution rate and uniform microstructure;
- Compatibility with automated or robotic systems for stable production.
PTA welding has therefore become one of the most reliable surface strengthening techniques for improving the durability of internal mixer rotors.
Limitations of Traditional Rotor Repair Methods
Although overlay welding, thermal spraying, and surface hardening are commonly used to improve rotor wear resistance, these methods often suffer from:
Weak mechanical bonding, making the coating prone to peeling under high load;
• High dilution, reducing alloy hardness and wear resistance;
• Thermal deformation, affecting dimensional accuracy;
• Relatively short service life, resulting in repeated repairs and costly downtime.
These limitations encourage the industry to adopt a more advanced and economical strengthening solution.
Application Principles of PTA Welding on Internal Mixer Rotors
PTA welding is applied to the most critical and wear-intensive areas of the rotor:
• Leading edges and side surfaces of helical blades;
• Rotor end faces that contact the mixing chamber;
• High-friction and high-impact zones where material flow is most aggressive.
During processing, alloy powder is fed into the plasma arc, melted instantly, and fused onto the rotor surface.
The resulting coating offers high hardness, improved shear resistance, and consistent surface quality, ensuring stable rotor operation during continuous mixing cycles.
Performance Benefits of PTA Strengthening
PTA surface strengthening significantly improves the overall performance of internal mixer rotors:
- Surface Hardness: HRC 55–65, customizable through alloy selection;
- Wear Resistance: Service life extended by 3–6 times;
- Bond Strength: Greater than 70 MPa, ensuring long-term adhesion;
- Operational Efficiency: Smoother rotor surfaces enhance material flow, improving mixing efficiency by around 10%.
With a PTA-reinforced surface, the rotor remains stable even in extreme operating environments, reducing the frequency of shutdowns and lowering maintenance costs.
Conclusion
For internal mixer rotors operating under intense wear and shear conditions, PTA plasma transferred arc welding provides a powerful and cost-effective surface strengthening solution.
Whether used for new rotor manufacturing or remanufacturing worn components, PTA technology delivers substantial improvements in wear resistance, operational stability, and service life.
Shanghai Duomu Industrial Co., Ltd. provides customized PTA welding surface solutions, offering tailored alloy systems and optimized process parameters to help customers maximize equipment efficiency and long-term reliability.
Post time: Nov-14-2025