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

Bonfiglioli C series ATEX explosion-proof helical gear reducer

In the field of modern industrial drive, especially in industries such as petrochemicals, powder processing, pharmaceuticals, and food processing, equipment not only needs to meet strict requirements for transmission efficiency and reliability, but also must cope with the enormous challenges of potential explosive environments. As a global leader in power transmission and drive, Bonfiglioli's C-series helical gear coaxial reducers are renowned in standard industrial settings for their compact design, high torque density, and excellent reliability. However, when these devices must be deployed in hazardous areas with flammable gases, vapors, or dust, the understanding of their technical characteristics and compliance must be elevated to a whole new level - ATEX compliance and special selection logic.

This article aims to provide a deep technical interpretation of Bonfiglioli C-series ATEX explosion-proof reducers for professional engineers and technicians. We will strictly follow the core concept of its technical manual, conducting comprehensive and refined analysis from the practical application of ATEX directive, key steps of selection calculation, to structural characteristics and installation specifications, to help you safely, compliantly, and efficiently complete equipment selection and operation.

Understand the ATEX compliant architecture of C-series explosion-proof reducers

Many engineers' understanding of ATEX is limited to the word 'explosion-proof', but a deep understanding of its classification is crucial for equipment selection. The C-series gearbox complies with the EU ATEX 2014/34/EU directive, and its core value lies in providing different levels of protection based on the explosion risk level. According to the manual, Bonfiglioli C-series products mainly cover equipment categories 2 and 3, which are represented by codes such as 2G/3G and 2D/3D.

1. Distinguishing between gas and dust

G (Gas): Suitable for potential explosive environments formed by gases, vapors, or mists.

D (Dust): Suitable for potential explosive environments where combustible dust is formed.

2. Corresponding relationship between device category and zone

This is the primary legal basis for selection. The configuration of C-series products determines their installable areas:

2G class equipment: suitable for Zone 1 (places where explosive gas environments may occasionally occur during normal operation) and Zone 2 (places where explosive gas environments are unlikely to occur during normal operation, and even if they do occur, the duration is very short).

3G devices: only applicable to Zone 2.

2D class equipment: suitable for Zone 21 (explosive dust environment may occasionally occur during normal operation).

3D equipment: suitable for Zone 22 (explosive dust environment is unlikely to occur during normal operation, and even if it does occur, the duration is very short).

Key point reminder: According to the manual, Bonfiglioli C series reducers are strictly prohibited from being installed underground in coal mines (Group I) and Group II Category 1 (Zone 0 or Zone 20) areas. This red line is the basic prerequisite for selection.

Deep selection calculation: Beyond conventional torque and power matching

In standard environments, gearbox selection usually only considers power and torque. But for ATEX applications, the selection process must be more rigorous, especially when it comes to the calculation of service factor (fs) and peak torque. The following is a five step manual based professional selection process:

Step 1: Determine the Application Service Coefficient (fs)

The service coefficient is not fixed, it depends on three variables: daily working hours, number of starts per hour (Z), and load type (K factor).

Load type K:

K1 (uniform load): such as smooth running conveyor belts, fans, etc.

K2 (moderate impact load): such as mixers, screw conveyors, etc.

K3 (heavy impact load): such as crushers, high-frequency reciprocating compressors, etc.

Special correction rule: For C122, C222, or C322 models, if the transmission ratio i>40 and the number of starts per hour Z>30, the calculated service factor needs to be multiplied by a correction factor of 1.2. This point is easily overlooked, but it is a hidden danger that leads to premature failure of the gearbox.

Step 2: Calculate the required input power

Firstly, based on the required output torque (Mr2) and output speed (n2) of the application, the required power (Pr1) of the motor shaft is calculated in reverse. The formula is as follows:

Pr one=Mr two×n two nine thousand five hundred and fifty×ηd[kW]

Pr one= 9550×η d Mr two×n two [kW]

among which,ηd For dynamic efficiency. According to the manual guidelines, for the C-series helical gear reducer, the efficiency value can refer to:

2-stage transmission (i ≈ 10): approximately 0.98

3-stage transmission (i ≈ 25): approximately 0.96

4-stage transmission (i ≈ 50): approximately 0.93

Step 3: Dual verification based on power and torque (IEC motor direct connection scheme)

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.

Overload protection: The parameter setting of the frequency converter must ensure that the reducer will not exceed its mechanical design limit due to low-frequency high torque or high-frequency overspeed.

Quick search of key selection parameters and engineering guidance

For the convenience of engineers to quickly refer to, the core physical quantity definitions and their engineering significance in the selection table are listed below. These parameters are hard indicators for evaluating the performance of reducers:

Definition and Significance of Symbolic Unit Engineering

Mn ₂ [Nm] rated output torque. This is the "sea fixing needle" of the gearbox, representing the torque that can be continuously transmitted when fs=1. When selecting, the torque required by the user should be ≤ Mn ₂.

Pn ₁ [kW] rated input power. Corresponding to the mechanical power at Mn ₂. Used to match IEC motors.

Fs - Service coefficient. Considering load fluctuations and startup frequency is the core weight coefficient for selection.

Rn ₂/Rn ₁ [N] allowable radial load. Determine the force that external sprockets, gears, or belts can apply to the shaft. The applied radial force must be less than this value.

An ₂/An ₁ [N] allowable axial load. Usually 20% of the radial load, it can be increased to 50% when there is no radial force.

Mc ₂ [Nm] calculates torque. For selection with solid input shaft (without motor), Mc ₂=Mr ₂ × fs × ftp (ftp is the temperature coefficient, usually 1).