In specialized industrial refrigeration applications that use flammable refrigerants such as hydrocarbons (R290, R1270) and A2L synthetic blends, equipment design must comply with strict explosion-proof directives. Frascold's ATEX-certified semi-hermetic screw compressors are engineered to eliminate ignition risks in hazardous Zone 1 and Zone 2 environments. This technical analysis examines the structural modifications, sealing materials and monitoring parameters that enable safe operation under severe thermal and mechanical loads.
Explosion-Proof Enclosure and Electrical Architecture
The main hazard when working with flammable refrigerants is the risk of ignition caused by electrical sparks. Frascold ATEX compressors mitigate this risk by enclosing internal electrical components in heavy-duty terminal boxes built to IP65 or IP66 ingress protection standards.
- Enclosure Construction: The terminal casing is made of high-grade ductile cast iron treated with anti-spark surface coating. Flame gap clearances at joint surfaces are machined to tolerances smaller than 0.05 mm, ensuring that any internal arc cannot ignite the external explosive gas atmosphere.
- Cable Glands and Wiring: ATEX-rated Ex-d cable glands with an ambient temperature rating of -40°C to +80°C are required to maintain the explosion-proof containment for power supply lines.
Mechanical Shaft Sealing and Tribological Protection
For open-type and semi-hermetic configurations designed for flammable gas compression, dynamic gas containment along the drive shaft requires specialized mechanical seals.
- Seal Materials: Contact rings are made of silicon carbide matched with carbon-graphite mating faces. This material combination delivers a low friction coefficient and high thermal conductivity, preventing the formation of localized hot spots.
- Elastomer Integrity: Static and dynamic seal rings are made of fluorocarbon rubber (FKM) or hydrogenated nitrile butadiene rubber (HNBR). These compounds resist chemical degradation and swelling when exposed to synthetic polyolester (POE) lubricants and hydrocarbon refrigerants at pressures up to 28 bar.
- Rotor Machining Precision: The screw rotors of semi-hermetic compressors adopt a 5:6 asymmetric profile, machined to a dimensional tolerance of ±0.005 mm, with surface roughness controlled below Ra 0.4 microns. This minimizes internal gas leakage and frictional heat generation.
Thermal Management and System Safety Integration
To guarantee long-term reliability in cold storage and process cooling applications, operating temperatures must be strictly controlled. ATEX directives require that surface temperatures remain below the specified auto-ignition limit (Temperature Class T3 or T4).
- Temperature Sensors: Built-in PT100 resistance temperature detectors continuously monitor the temperature of discharge gas and motor windings, and trigger automatic shutdown when the temperature exceeds 120°C.
- Lubrication Monitoring: Differential oil pressure switches ensure continuous oil supply to rotor bearings. During regular compressor maintenance, oil acidity and moisture content must be checked to prevent dielectric breakdown of motor winding insulation.
Conclusion
Frascold ATEX screw refrigeration compressors integrate robust mechanical design with specialized material technology to meet the strict standards for hazardous areas. Choosing certified equipment equipped with micro-tolerance rotors, SiC mechanical seals and IP65 terminal enclosures allows industrial refrigeration operators to safely use environment-friendly refrigerants without sacrificing efficiency or reliability.
