Corrosion-Resistant Film on Cast Iron Compressor Casings
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Solution Overview
Problem
Oil-free screw compressors face challenges with rust generation on cast iron casings due to temperature differences and moisture condensation, leading to galling and reduced maintenance-free operation, especially with complex structures that complicate surface treatments.
Innovation Solution
A corrosion-resistant film is formed on the surface of the casing using a combination of gas soft-nitriding treatment and oxidation, creating a layer of iron nitride and triiron tetraoxide, which enhances rust prevention without requiring separate outer coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid lubrication film is formed on the rotor surface to prevent contact and seizure, then reliability is improved, but manufacturing complexity increases due to additional surface treatment processes
Solution Approach 1:
The patent combines the formation of solid lubrication film and corrosion-resistant film into a single integrated surface treatment process. The treatment simultaneously creates both functional layers on the rotor and casing surfaces, eliminating the need for separate lubrication and corrosion protection steps, thus improving reliability while controlling manufacturing complexity.
Solution Approach 2:
The surface treatment creates a composite structure with a solid lubrication film layer and a corrosion-resistant film layer. This multi-layer composite surface structure provides both anti-seizure lubrication properties and corrosion resistance, addressing multiple requirements through a single material system.
2Strength
If the casing is made of cast iron for structural strength, then strength is improved, but corrosion resistance deteriorates due to rust generation from temperature differences and moisture condensation
Solution Approach 1:
The patent applies local quality by creating a corrosion-resistant film specifically on the inner surface of the cast iron casing where corrosion occurs due to temperature differences and moisture condensation. The outer structure maintains cast iron for strength, while the inner surface gains corrosion resistance through the applied film, allowing each region to have optimized properties.
Solution Approach 2:
The casing becomes a composite structure with cast iron providing structural strength and a corrosion-resistant film providing protection against rust. This combination allows the casing to maintain its structural integrity while gaining resistance to corrosion from temperature cycling and moisture.
3Reliability
If a corrosion-resistant film is formed on the casing surface to prevent rust, then reliability is improved, but manufacturing complexity increases due to additional treatment steps
Solution Approach 1:
The patent merges the corrosion-resistant film formation with the solid lubrication film formation into a single integrated surface treatment process. This combined approach applies both protective layers simultaneously, improving corrosion resistance while minimizing the number of manufacturing steps and reducing overall process complexity.
4Productivity
If very small gaps are formed between rotors and casing to improve volumetric efficiency, then productivity is improved, but reliability deteriorates due to risk of contact and seizure from thermal expansion and machining errors
Solution Approach 1:
The patent applies beforehand cushioning by forming a solid lubrication film on the rotor and casing surfaces before operation. This film acts as a protective cushion that prevents direct metal-to-metal contact even when gaps become very small, accommodating thermal expansion and machining errors while maintaining the small gap configuration needed for high volumetric efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses rust generation, reducing galling and improving the reliability of the compressor by providing a high corrosion-resistant surface on complex-shaped casings, ensuring efficient operation and reduced maintenance.
Implementation Method 1
gas soft-nitriding treatment...creating a layer of iron nitride
Implementation Method 2
oxidation...creating a layer of...triiron tetraoxide
Data Source
AI summary
An object of the invention is to provide a compressor that includes a corrosion-resistant film formed on the surface of a casing having a complicated shape. A compressor pumps gas in a compression chamber formed by a casing, the casing is made of cast iron, and a layer made of a mixture of iron nitride and a compound of iron, nitrogen, and carbon and an oxide layer made of triiron tetraoxide are formed on the surface of the casing. Accordingly, since the corrosion resistance of the casing, which includes a film formed by a gas soft-nitriding treatment and an oxidation treatment, is improved, the generation of rust is suppressed. Therefore, it is possible to provide a compressor in which galling or sticking caused by rust occurs less.