Russian Anti-Friction Solid-Film Coatings improve reliability of the oil-free screw compressors’ rotors

The oil-free screw compressors are indispensable in medicine and various industries such as electronic, food, textile and the others. Such units create absolutely pure air necessary for the production processes to go properly.

The oil-free compressors' rotors are manufactured with improved accuracy because when there is no oilfunctioning as a sealer, the gap between them must be minimal.

It is possible to achieve high efficiency and at the same time to reduce compressor’s prime cost by using the specialcoatings for rotors which we are going to consider in this article.

Main functions of the coatings for oil-free screw compressors’ rotors

The foreign manufacturers of the screw compressors started treating the rotors with the special coatings long agoenough. It enabled to cut the costs for precise mechanical treatment of the surfaces, and reduced probability of their contact followed by the scuffing forming.

The polymer coatings including the finest particles of the solid lubricating materials in their compositionhad high anti-friction properties and provided the following:

• Easy rotors running-in during which the surfaces got the optimal form to minimize the gaps
• No scuffings and seizures
• Friction and noise reducing
• Protection for metals against corrosion

During running-in the initial factory coatings can get worn which causes corrosion (see. Fig.1), and reduction of the rotors operational efficiency. That is exactly why one of the main operations while complete overhaul of the compressors is restoring a protective solid lubricating layer.

Fig. 1 Coating wear, and rotor’s working surface corrosion

MODENGY Anti-Friction Solid-Film Coatings properties and features

The Modeling & Engineering (Modengy, LLC) Russian company has developed a series of Anti-Friction Solid-Film Coatings (ASCs) for screw compressors. They can be used both at rotor production and at their repairs.

The coating is applied onto the component surfaces by a layer of up to 100 µm thickness. During running-in itsthickness reduced by 2 to 2.5 times.

The Anti-Friction Solid-Film Coatings is a polymer matrix that strongly retains the particles of the solid lubricating materials (such asmolybdenum disulfide, graphite, polytetrafluorethylene (PTFE)) in its cells. These are the substances exactly that provide the anti-frictional and anti-scuffing functions of the coating.

The scheme of the Anti-Friction Solid-Film Coating structure is presented on Fig.2.

Fig.2. The Anti-Friction Solid-Film Coating structure

The main features of the MODENGY coatings for screw compressor rotors are presented in Table 1.

Table 1. The main features of the MODENGY coatings for screw compressor rotors

The Anti-Friction Solid-Film Coating applying technology

The coating is applied with the painting methods according to the required layer’s thickness and uniformity.

For the complicated surfaces, accuracy is provided by automated spraying out the Anti-Friction Solid-Film Coating while the movements ofthe spraying injector and the part to be covered are kept coordinated.

The treatment process includes several obligatory stages:

• Removing the previous coating (if necessary)
• Forming an optimal surface microrelief
• Cleaning, degreasing, and activating the part surface
• Applying the coating in several layers with in-between drying
• Coating curing at heating
• Controlling Anti-Friction Solid-Film Coating’s quality on following three parameters: adhesion, thickness, and curing completeness

Fig.3 demonstrates the rotors after the first and the final stages of the coating applying process.

Fig.3. The compressor rotors before and after applying the MODENGY Anti-Friction Solid-Film Coating

The technology described above solves the tasks of additional protection and improved efficiency for not only theoil-free screw compressors but also the other equipment including:

• Gear and vacuum pumps
• Blade pneumatic engines
• Hydraulic motors
• Rotor feeders
• Pipeline fittings, etc.

Conclusion

MODENGY Anti-Friction Solid-Film Coatings application on the oil-free screw compressors’ rotors enables not only to improve their efficiency but also reduce their prime cost due to decreasing the costs for the mechanical treatmentof the surfaces.

The surfaces to be covered can be far from perfect from the point of micro-geometry – the coating makes themeven and smoothy, and in this way makes running-in process easier, and creates dynamic sealing.

The Modeling & Engineering, LLC releases the AFSLCs according to its own specification at the production site in Bryansk. At the same place, the company provides the services on applying the coatings.