Overview
The explosion-proof self-locking worm gearbox is a critical component for industrial applications where flammable substances pose ignition risks. Its design incorporates flame-path suppression technology and non-sparking materials to comply with ATEX, IECEx, or other regional explosion-proof standards. Unlike standard worm gearboxes, this variant undergoes rigorous testing to ensure its housing can contain internal explosions and maintain surface temperatures below the auto-ignition point of surrounding gases. The self-locking feature provides inherent braking capability, eliminating the need for additional holding brakes in vertical or inclined conveyors.
Structure and Working Principle
The gearbox consists of a hardened steel worm screw meshing with a bronze wheel, enclosed in a flameproof cast iron housing with machined flanges. Gaskets and labyrinth seals prevent gas ingress while allowing thermal expansion. Torque transmission occurs through the 90° engagement of the worm and wheel, with the self-locking effect achieved when the lead angle is smaller than the friction angle. Explosion-proofing is ensured by flame arrestor discs and pressure-relief channels that cool escaping gases below ignition temperatures.
Key Features
Certified models feature temperature class ratings (T1-T6) indicating maximum surface temperatures, typically ranging from 450°C to 85°C. Dual sealing systems combine lip seals with labyrinth designs to exclude dust while permitting thermal movement. The gearbox often incorporates thermal overload protection via fusible plugs or PTC sensors. Anti-static coatings and grounding terminals dissipate electrostatic charges, while special lubricants maintain viscosity across the rated temperature range (-20°C to +120°C common).
Application Areas
Primary installations include petrochemical pump drives, coal mine conveyor systems, grain elevator mechanisms, and pharmaceutical powder processing lines. In offshore platforms, they operate mud pumps and crane slewing drives. Zone 1 applications require gearboxes with Ex d (flameproof) certification, while Zone 2 areas may use Ex nR (restricted breathing) variants. Food processing plants often select stainless steel models with NSF-approved lubricants for washdown environments.
Maintenance and Precautions
Inspection intervals should follow the IEC 60079-17 standard, typically every 6-12 months. Maintenance includes checking seal integrity, verifying terminal box integrity, and measuring gear backlash with dial indicators. Never open the housing in hazardous areas—service must occur in safe zones after proper gas clearance. Use only manufacturer-approved replacement parts to maintain certification validity. Lubricant changes require complete removal of old grease to prevent incompatible mixtures.
B2B Procurement Guide
Specify the required protection level (Ex db vs. Ex dc), gear ratio (common ranges: 5:1 to 100:1), and mounting position (foot, flange, or shaft-mounted). Provide ambient temperature ranges and duty cycle information (S1 continuous or S2 intermittent). Leading manufacturers include SEW-Eurodrive, Nord Gear, and Bonfiglioli. Lead times for certified units often exceed 8-12 weeks. Consider total cost of ownership—premium models offer longer service intervals and higher efficiency (up to 92% for double-enveloping designs).
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