Bonfiglioli C Series ATEX Explosion proof Reducer Selection

Bonfiglioli C Series ATEX Explosion proof Diagonal Gear Reducer: Selection and Compliance Guidelines for Hazardous Area Applications

In industries such as petrochemicals, pharmaceuticals, grain processing, and spraying, combustible gases, vapors, or dust are inevitably present in the production environment. All mechanical equipment used in these hazardous areas, including reducers in the transmission system, must meet strict explosion-proof certification requirements. Bonfiglioli's C Series helical gear reducer ATEX version is a compliant transmission solution designed to meet such harsh working conditions. This article will systematically sort out the selection and application points of C Series explosion-proof reducers from the ATEX directive framework, equipment classification, selection calculation methods to installation restrictions, helping you benchmark compliance in complex projects.

ATEX Explosion proof System Fundamentals: Understanding Directive and Area Classification

The core essence of ATEX 2014/34/EU directive

The ATEX (ATmosph è res EXPLosables) Directive 2014/34/EU is a mandatory regulation developed by the European Union for equipment used in potentially explosive environments. On page 6 of the manual, it is explicitly stated that this directive for the first time includes mechanical, hydraulic, and pneumatic equipment in its regulatory scope, not just electrical equipment as before. For mechanical engineers, this means that pure mechanical products such as gearboxes also need to obtain ATEX certification in order to enter explosion-proof areas in Europe.

This instruction defines four conditions for an explosive atmosphere:

Presence of flammable substances (gas, vapor, mist, or dust)

Mixing with air

Under atmospheric conditions

After ignition, combustion will spread throughout the entire unburned mixture

2. Zones and Categories of Equipment

The manual clearly defines the division logic of hazardous areas on pages 6-7, which is the primary basis for selection:

Regional gas/vapor (G) dust (D) formation frequency corresponds to equipment category

0/20 Continuous or long-term permanent danger M1/1

1/21 Potential hazards occasionally occur during normal operation 2

2/22 Short term occurrence of minimum danger under abnormal operation 3

The Bonfiglioli C Series ATEX gearbox covers the following areas:

Zone 1&2 (Gas) → Equipment Categories 2G and 3G

Zone 21&22 (Dust) → Equipment Categories 2D and 3D

The table on page 7 of the manual further specifies that the explosion-proof protection types of the C Series explosion-proof reducer are Ex h Gb (gas) and Ex h Db (dust), where "h" represents "non electrical equipment (non electrical) protection type".

3. Temperature Class

For gas environments, ATEX certification also requires the indication of temperature class (T-Class), which means ensuring that the highest surface temperature of the equipment is below the self ignition temperature of the surrounding combustible gases/vapors.

T3 (maximum surface temperature ≤ 200 ℃): Suitable for most common industrial gases

T4 (maximum surface temperature ≤ 135 ℃): Higher level, suitable for occasions requiring lower temperature thresholds

The option code on page 14 of the manual shows:

2G3G-T3: Suitable for Zone 1/2 gas environment, temperature level T3 (200 ℃)

2G3G-T4: Suitable for Zone 1/2 gas environment, temperature level T4 (135 ℃)

2D3D-160: Dust environment, surface temperature<160 ℃

2D3D-130: Dust environment, surface temperature<130 ℃

Selection prompt: The temperature level must be selected higher than (i.e. stricter) the self ignition temperature of combustible substances present in the environment. For example, a hydrogen environment requires T1, while carbon disulfide requires T6.

Special structural features of C Series ATEX gearbox

Compared with standard industrial reducers, the ATEX certified C Series has significant differences in materials and structure (page 12 of the manual):

Fluoroelastomer (FKM) sealing ring: equipped with Fluoroelastomer (fluororubber) sealing components, it has high temperature resistance, oil resistance, and chemical resistance characteristics, ensuring that the sealing integrity can be maintained even under high temperature conditions.

Output shaft double seal rings: The manual emphasizes "Double seal rings on the output shaft" - this is to form a redundant sealing barrier at the shaft end, reducing the risk of dust or gas entering the reducer interior along the shaft.

Plastic free components: completely eliminate the risk of static electricity accumulation - plastic components may generate static electricity in friction or airflow, becoming potential ignition sources.

Special nameplate information: The nameplate clearly indicates the product category (such as II 2G) and protection type (Ex h Gb) for on-site inspection and compliance audit.

Pre oiling in the factory: Add long-lasting synthetic lubricating oil according to the installation location specified in the order, and seal it with a blind plug for transportation. The user needs to replace it with a breathable plug on site.

Core logic of selection calculation: complete derivation from required torque to rated power

The selection calculation of C Series explosion-proof reducers is consistent with standard industrial reducers, but the selection of service factor needs to be particularly cautious, as explosion-proof applications often involve critical safety functions such as emergency ventilation, fire pumps, etc.

1. Determine the service coefficient [fs]

The manual provides a graphical method for selecting service coefficients on page 11. The service coefficient depends on three factors:

Daily running time (hours/day)

Number of starts per hour (Z)

Mass acceleration coefficient (K):

K=Jc/Jm, i.e. the ratio of load inertia to motor inertia

The three curves K1 (uniform load), K2 (moderate impact load), and K3 (heavy impact load) correspond to different load characteristics. The manual specifically states that for applications involving lifting, if the failure of the gearbox may pose a risk of injury to personnel, the technical department should be contacted directly - this means that such applications require far greater safety margins than usual.

2. Selection of IEC motor flange with reducer (most commonly used configuration)

When the C Series is equipped with IEC standard motor flanges (IM B5), the selection steps are as follows:

Step 1: Calculate the required power on the motor side

Pr one

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 Mr two

To achieve the required output torque (Nm) for the application,n two

To output the rotational speed (min ⁻¹),ηd

To improve the dynamic efficiency of the gearbox (manual recommendations: 0.98 for level 1 transmission, 0.96 for level 2, 0.93 for level 3, and 0.90 for level 4).

Step 2: Select a gearbox from the rated power meter (pages 19-26 of the manual) that satisfies the following equation:

Pn one≥Prone×fs among which

Pn one Rated power of the gearbox (kW), corresponding service factor

fs=one

f s=1.

Step 3: Select the rated power of the motor

Pone≥Pr one And finally verify:

S=Pnone

P one≥fs

In the formula

S is the safety factor, which must be greater than or equal to the service factor required for the application.

Special constraint: If C122, C222, or C322 is selected and the speed ratio is i>forty

i>40， And the number of starts per hour

Z> thirty

Z>30， Then the service coefficient needs to be multiplied by a correction factor of 1.2 before verification.

3. Selection of solid input shaft reducer (power source not directly connected to motor flange)

For situations where a solid input shaft is used, the calculated torque (Mc ₂) needs to be calculated:

Mc two=Mr two×fs×ftp  

among which

ftp Correction factor for ambient temperature (page 10 of the manual):

When the ambient temperature is ≤ 30 ℃,

ftp=one

f tp=1.0

When the ambient temperature is 40 ℃,

ftp=one point zero six

f tp=1.06 (uniform load) or

one point zero four

1.04 (heavy impact load)

Then select from the rated torque table

Mntwo≥Mc two

The gearbox.

Key post selection checks after selection

After completing the preliminary selection, page 10 of the manual requires three mandatory verifications:

1. Instantaneous peak torque verification

The instantaneous peak torque that the reducer can withstand is approximately the rated torque Mn two 200% of it. If the peak load of the application exceeds this limit (such as the impact when the crusher is stuck), a torque limiter must be installed to protect the gearbox.

2. Radial Load (OHL) Verification

The radial force generated by external transmission components (such as sprockets, gears, and synchronous pulleys) on the shaft must be less than or equal to the allowable radial bearing capacity of the gearbox (pages 17-18 of the manual). The calculation formula is:

Rc=two thousand×M×Ktd[N] among which

M is the transmitted torque (Nm),

d D is the pitch diameter of the transmission component (mm),

Kt The transmission type coefficient is 1.25 for sprocket/gear and 1.5-2.0 for belt transmission.

Rc Must be less than the rated value in the manual table

Rn one(Input shaft) or Rn two(Output shaft).

Important note: On page 18 of the manual, it is stated that when the load application point is not at the axis centerline but at an eccentric position, it needs to be multiplied by a position coefficient (see table for values a, b, and c). For example, the C 22 2 model has output shaft load position coefficients of a=253, b=285, and c=50.

3. Axial Load Verification

Allowable axial thrust An

An is the coaxial radial load Rn 20% of Rn (page 18 of the manual). If under pure axial force conditions without radial load, the allowable value can be increased to Rn 50% of Rn. If the axial force exceeds this limit, it is necessary to contact Bonfiglioli's technical department for a special calculation of bearing life.

Strict restrictions on ATEX explosion-proof applications

The mandatory constraints for ATEX certified gearboxes during operation are specifically listed on page 10 of the manual, and any deviation will result in certification failure:

Environmental temperature: must be within−twenty℃∼+forty℃

Operate within the range of -20 ℃ to+40 ℃.

Installation position: It must be completely consistent with the installation position specified in the order and cannot be changed arbitrarily - because the design of the lubricating oil circuit, the position of the vent plug, and the oil level height are all bound to the installation orientation.

Do not tilt installation: Unless authorized in writing by Bonfiglioli's technical department, do not tilt the gearbox at any angle.

Maximum motor speed limit: Input speed

n≤one thousand and five hundred

min−one n≤1500 min  −1

This is the hard boundary of ATEX certification, exceeding this speed may result in temperature exceeding the standard.

Additional restrictions on the use of variable frequency drives: If variable frequency drives are used, the parameters of the variable frequency drive must not allow the motor to exceed its maximum speed (1500 min ⁻¹), nor overload the gearbox. At the same time, the frequency converter motor must be clearly labeled as "frequency converter specific" and comply with ATEX usage requirements.

Dual constraints of geometry and power for motor availability matching

1. Geometric compatibility

The matrix table on page 27 of the manual lists the geometric compatibility between different C Series specifications and IEC motor frame numbers. For example:

C 12 2 supports motor flanges from P63 to P132

C 22 2 supports P71 to P112

C 61 2 supports P90 to P180

It cannot be assumed that installation is possible solely based on matching bolt hole positions. It is necessary to verify whether there are corresponding horizontal and vertical intersection points in the table.

2. Maximum installable power

On page 28 of the manual, it is listed that n one=one thousand and four hundred min−one n one=1400 min −1

The maximum input power that each reducer size can withstand. For example:

C 12 2 with P100 flange, maximum allowable input power is 2.2 kW

C 51 2 with P160 flange, maximum allowable input power is 15 kW

If a higher power motor (such as 18.5kW) is forcibly installed on the C 51 2, even if the flange holes can align, the gears and bearings inside the gearbox will quickly be damaged due to overload.

Common selection misconceptions and pitfalls avoidance guide

Misconception 1: Ignoring the distinction between ATEX explosion-proof temperature rating and operating temperature

The T3/T4 on the ATEX nameplate refers to the highest surface temperature, not the internal oil temperature. Even if the internal oil temperature is only 80 ℃, if external dust accumulation leads to poor heat dissipation, the surface temperature may exceed the limit. The surface temperature is affected by installation conditions, and even small changes (such as insufficient heat dissipation space) may significantly alter the heat dissipation effect, "emphasized on page 10 of the manual

Misconception 2: Applying the wrong formula when verifying the radial load of shaft extension

Many engineers adopt F=two T/d The simplified formula for calculating belt tension with F=2T/d ignores the additional load caused by belt pre tension. Recommended by the manual Kt Coefficient (belt drive)one point five∼two

1.5-2.0) The influence of pre tension has been taken into account.

Misconception 3: Mixing solid shaft input and IEC flange input for selection

The selection basis for solid shaft input is torque（Mn two）The selection of IEC flange input is based on power（Pn one）. If the power meter is mistakenly used to select the actual spindle model, it will lead to serious deviation - because the torque at different speed ratios under the same power varies several times.

Misconception 4: Neglecting the pre startup action of "replacing the breathable plug"

ATEX reducers are shipped with Dummy plugs to prevent lubricant leakage during transportation. On page 16 of the manual, it is emphasized that users must replace the blind plug with the Vented Plug that comes with the product before turning it on. If not replaced, the increase in pressure inside the box during operation will cause oil seal failure and oil splashing, which is neither safe nor compliant.