Chemical nickel coating — also known as electroless nickel plating — is a highly effective surface treatment for extrusion screws used in plastics and rubber processing. Unlike conventional electroplating, the nickel-phosphorus layer is deposited through a purely chemical process, resulting in an exceptionally uniform coating thickness, even on complex geometries, deep flights, and internal contours.
The coating provides an outstanding combination of corrosion resistance, wear protection, and improved sliding properties. This makes chemically nickel-plated extrusion screws especially suitable for demanding processing applications involving corrosive polymers, abrasive fillers, flame retardants, or adhesive compounds.
Advantages of Chemical Nickel Coatings
- Uniform coating thickness across the entire screw geometry
- Excellent corrosion resistance against aggressive process media
- High wear resistance and increased service life
- Improved sliding and release properties
- Diffusion-tight coating structure
- Very smooth and homogeneous surface finish
- Suitable for complex screw geometries and internal surfaces
- Heat treatment possible for significantly increased hardness
- Dimensional accuracy remains virtually unchanged
Depending on the phosphorus content and heat treatment, hardness values of up to approx. 950 HV can be achieved.
Technical Characteristics
Chemical nickel coatings are based on a nickel-phosphorus alloy deposited through an autocatalytic chemical reaction without electrical current. The process creates a highly uniform and low-porosity layer with excellent adhesion to the base material.
Typical properties:
- Coating thickness: approx. 25–50 µm
- Hardness as plated: approx. 500 HV
- Hardness after heat treatment: up to approx. 950 HV
- Excellent dimensional stability
- Very low surface roughness
- High chemical resistance
- Temperature-resistant and oxidation-resistant
Applications in Extrusion Technology
Chemical nickel coatings are particularly suitable for extrusion screws processing:
- PVC compounds
- Flame-retardant materials
- Filled polymers with abrasive additives
- Rubber and elastomer compounds
- Adhesive or sensitive polymer melts
- Corrosive plastics and aggressive additives
The coating significantly reduces material build-up, improves cleaning behavior, and minimizes wear caused by friction and aggressive media. This results in longer maintenance intervals, improved process stability, and extended screw lifetime.
Advantages Compared to Hard Chrome Plating
Compared to conventional hard chrome plating, chemical nickel coatings offer more uniform layer distribution and superior corrosion protection, especially in recessed areas and complex geometries. In addition, electroless nickel coatings are considered a more environmentally friendly alternative, as they avoid chromium(VI)-based processes.