High Velocity Flame Spraying — also known as HVOF coating (High Velocity Oxy Fuel) — is one of the most advanced surface engineering technologies for extrusion screws. Due to extremely high particle velocities, the process creates exceptionally dense, wear-resistant, and highly adhesive coatings specifically designed for the demanding conditions of plastics and rubber processing.
During the HVOF process, powdered coating materials are accelerated to supersonic speeds using an oxygen-fuel flame and projected onto the screw surface. This produces a highly dense and nearly pore-free protective layer with outstanding wear and corrosion resistance.
Advantages of HVOF Coating
- Extremely high wear and abrasion resistance
- Very dense and low-porosity coatings
- Excellent adhesion to the base material
- Minimal oxidation of the coating
- High corrosion resistance
- Low coefficient of friction
- Long service life even with highly abrasive compounds
- Excellent temperature resistance
- Precise and dimensionally stable coating application
Due to the high density of HVOF coatings, material attack and abrasive wear are significantly reduced. At the same time, process stability is improved in demanding extrusion applications.
Typical Coating Materials
The following materials are commonly used for HVOF coating of extrusion screws:
- Tungsten carbide (WC-Co / WC-CoCr)
- Chromium carbide (Cr₃C₂-NiCr)
- Nickel-based alloys
- Cobalt-based hard alloys
- Special materials for highly corrosive applications
These materials combine extreme hardness with high toughness, allowing optimal adaptation to the respective process and material requirements.
Technical Characteristics
HVOF technology produces coatings with exceptionally high density and adhesion strength.
Typical properties:
- Coating hardness up to more than 1,200 HV
- Very low porosity
- High compressive residual stress
- Excellent bond strength
- Coating thickness typically 50–500 µm
- Excellent surface finish after final machining
- Temperature-resistant protective layers
The combination of hardness, toughness, and low porosity makes HVOF coatings ideal for highly stressed screw surfaces.
Applications in Plastics and Rubber Processing
HVOF-coated extrusion screws are particularly suitable for:
- Glass fiber reinforced plastics
- Highly filled compounds
- Recycling materials
- Engineering plastics
- PVC extrusion
- Abrasive and corrosive materials
- Rubber and elastomer processing
Especially when processing abrasive fillers such as glass fibers, minerals, or flame-retardant additives, HVOF coatings significantly extend screw service life.
Advantages Compared to Conventional Surfaces
Compared to nitrided or hard chrome-plated surfaces, HVOF coatings offer substantially higher wear resistance and superior adhesion strength. The extremely dense coating structure minimizes corrosion and substrate attack, ensuring maximum service life even under extreme process conditions.
In modern high-performance extrusion systems, High Velocity Flame Spraying is now considered one of the most efficient solutions for durable and highly wear-resistant extrusion screws.
ige und hochbelastbare Extrusionsschnecken.