Surface Roughness: Challenges and Solutions
26/03/2025 - 09:28
Most rotary valves are made from cast iron due to its excellent wear resistance and favorable cost. While cast iron offers many advantages, it also presents challenges, particularly in terms of surface roughness.
Cast iron naturally has a rough surface, a direct result of the production process. This is not an issue for most applications, but in areas where precise tolerances are required, the rough structure becomes unusable. Therefore, essential surfaces are machined using turning, milling and boring. In the majority of applications, the resulting roughness after machining is sufficient for optimal operation, such as in flow applications and pneumatic transport.
In some cases, surface roughness remains too high, especially due to the porous nature of cast iron and the presence of micro-perforations caused by graphite inclusions. This can be problematic when processing very fine materials, which can accumulate in these perforations. The impact depends on the type of material:
- Lubricating substances (such as fine flour) even improve the lifespan of the rotary valve and do not pose a problem.
- Sticky substances (such as wet cement or salt) can, however, lead to rotor jamming, downtime or accelerated wear.
To avoid issues with sticky substances, several solutions are available:
- Use of steel plate: a welded construction with steel plate eliminates porosity and can be ground to a very low roughness.
- Chrome coating: applying a chrome coating on cast iron parts reduces roughness and prevents the accumulation of substances.
- Thermal spraying: a machinable layer, such as Wolram, can be applied and then ground to achieve an extremely smooth surface.
By making the right choice of material and finish, you can significantly improve the performance and durability of your rotary valve!
