Bonfiglioli C-series ATEX gearbox selection and explosion-proof application guide

For C-series reducers with IEC motor flange input, two inequalities must be satisfied simultaneously:

According to the rated power meter, the selected gearbox has a rated input power Pn ₁ ≥ Pr ₁ × fs at the required output speed.

According to the rated torque table, the selected gearbox has a rated output torque Mn ₂ ≥ Mr ₂.

Finally, verify the overall safety factor S=Pn ₁/P ₁ ≥ fs (where P ₁ is the actual selected motor power). Only when this condition is met can it be considered a thermodynamically safe match.

Step 4: Peak torque verification

Although the C-series gearbox is sturdy, its mechanical limits cannot be ignored. The manual clearly states that the instantaneous peak torque should not exceed 200% of the rated torque Mn ₂. If the application experiences frequent start/stop or emergency stop conditions, a torque limiter must be installed to prevent irreversible damage to the gears or bearings.

Step 5: Axle Load Verification

Selection should not only focus on the gears in the "belly", but also on the "skeleton" - bearings and shafts.

Radial Load (Rn): The manual provides the maximum allowable radial load for the output shaft (Rn ₂) and input shaft (Rn ₁). It should be noted that these values are measured at the axis centerline. If the pulley or sprocket is installed in the cantilever position, the "load position factor" provided in the manual must be used for equivalent conversion.

Axial load (An): The allowable axial thrust is usually 20% of the allowable radial load (i.e. An=0.2 × Rn). Special case: When there is no radial load on the shaft, the pure axial thrust can be increased to 50% of the radial load.

Special design and construction under ATEX operating conditions

To meet the explosion-proof requirements of ATEX Zone 2/22 or Zone 1/21, the C series reducers have undergone multiple targeted enhancements in their design, and these details are the key to distinguishing between ordinary reducers and explosion-proof reducers.

1. Upgrade of sealing system

One of the core ideas for explosion prevention is "isolation". C series ATEX version is equipped with fluorine rubber (FKM) oil seal as standard, which is superior to ordinary NBR (nitrile rubber) in high temperature resistance and aging resistance. More importantly, a double seal rings design is adopted on the output shaft. On the one hand, this enhances the ability to prevent lubricant leakage, and on the other hand, it effectively prevents external dust or moisture from entering the interior of the box, reducing the risk of sparks caused by friction.

2. Temperature control and grade identification

Explosive gases have their own ignition temperatures. The C-series products have passed strict surface temperature testing and defined two gas explosion-proof temperature levels:

T3 level: Surface temperature not exceeding 200 ° C. Suitable for most industrial gas environments.

T4 grade: Surface temperature not exceeding 135 ° C. Suitable for gases with lower ignition temperatures (such as ether, carbon disulfide, etc.).

When ordering, the corresponding grade (such as code 2G3G-T4) must be selected based on the ignition temperature of the gas on site.

3. No plastic parts and joint surface control

To prevent static electricity accumulation or spark generation, the exterior of the C series ATEX gearbox housing does not contain any plastic components. At the same time, all static joint surfaces (such as the box body and the box cover) are strictly controlled for clearance to ensure that in the event of an internal explosion, flames will not escape to the external environment through the joint surfaces (explosion-proof principle).

Engineering Practice of Installation, Lubrication, and Maintenance

Even if the selection is correct, deviations in on-site installation and maintenance can lead to the invalidation of ATEX certificates.

1. Installation Position

The lubrication system of the gearbox depends on the installation direction. Each ATEX gearbox that leaves the factory is filled with a corresponding amount of synthetic lubricating oil according to the installation position specified in the order. The nameplate indicates the allowed installation positions for the equipment. Do not change the installation orientation without authorization from Bonfiglioli's technical department, as this can result in the bearings not being lubricated and quickly burning out.

2. Compulsory operation of breathable plug

This is a link that is easily overlooked by installation workers. Due to transportation considerations, the gearbox top is equipped with a closed screw plug at the factory. But before the device is powered on, the user must replace it with the Vented plug that comes with the box. Forgetting to replace it can cause a sharp increase in pressure inside the box due to temperature rise, ultimately damaging the oil seal, resulting in oil leakage and damage to explosion-proof performance.

3. Hard limitations on the operation of variable frequency motors

If using a frequency converter drive, two red lines must be strictly followed:

Maximum speed limit: Regardless of the frequency setting of the inverter, the motor speed is not allowed to exceed 1500 min ⁻¹.