Bonfiglioli VF-W series ATEX explosion-proof reducer selection guide



Bonfiglioli VF-W series ATEX worm gear reducer: professional selection and explosion-proof application

In industrial fields such as chemical, petroleum, natural gas, grain processing, and pharmaceuticals where there is a potential for explosive environments, the safety and reliability of driving equipment are the primary considerations in engineering design. As a globally renowned provider of power transmission solutions, Bonfiglioli's VF-W series worm gear reducer is an ideal choice for such application scenarios due to its compact structure, large speed ratio range, and comprehensive ATEX explosion-proof certification. This article aims to provide engineers with a systematic technical reference, covering core aspects such as ATEX directive requirements, gearbox selection calculations, installation specifications, and load verification.

Product positioning of ATEX explosion-proof system and VF-W series

According to the EU ATEX Directive 2014/34/EU, a potentially explosive environment is defined as an area where flammable substances (gases, vapors, dust) mix with air and can spread combustion upon contact with a source of ignition under specific conditions. Equipment manufacturers must select products of the corresponding category based on the risk level of their installation area.

1. Regional division and equipment category

Zone 0/20: Continuous or long-term presence of explosive environment (highest risk).

Zone 1/21: Occasional occurrence during normal operation (moderate risk).

Zone 2/22: It is unlikely to occur during normal operation, and even if it does occur, it only exists briefly (with low risk).

The Bonfiglioli VF-W series ATEX gearbox is suitable for zones 1, 21, 2, and 22 (corresponding to equipment categories 2G/3G and 2D/3D). The manual clearly states that this series of products is not suitable for high-risk areas in Group I and Group II Category 1 mines.

2. Temperature Class and Surface Temperature Limits

For gas environments, the temperature level (T level) determines the maximum allowable surface temperature of the equipment, which must be lower than the ignition source temperature. The VF-W series can provide:

T3: Maximum surface temperature ≤ 200 ℃

T4: Maximum surface temperature ≤ 135 ℃ (applicable to higher requirements)

For dust environments (Class D), the self ignition of the dust layer is prevented by limiting the surface temperature of the shell (such as 130 ℃ or 160 ℃). When selecting, users need to clearly indicate the required temperature level in the ordering code.

Structural characteristics and installation requirements of VF-W series

1. Core elements of explosion-proof design

All sealing rings come standard with FKM, which is resistant to high temperatures and chemical corrosion.

No plastic parts, avoiding the risk of static electricity accumulation or melting.

Equipped with oil level check plugs, breathable plugs, and drain plugs for easy daily maintenance.

The nameplate clearly indicates the product category, temperature level, and certification number to ensure traceability on site.

2. Installation positions

The VF series (without base) and W series (with base) support multiple installation orientations, including B3 (horizontal), B6/B7/B8 (vertical, different shaft directions), and V5/V6 (suspended). Key limitations:

The installation location must be specified at the time of ordering and indicated on the nameplate. It is strictly prohibited to change the installation direction without the approval of Bonfiglioli's technical department.

Specifically, when the W110 machine base is installed in the V5/V6 position and equipped with a B14 flange motor, no oil is added at the factory. Users need to add the specified lubricating oil according to the actual installation direction.

The input shaft speed shall not exceed 1500 min ⁻¹ (four pole motor). If used in conjunction with a variable frequency motor, the maximum frequency must be limited by parameter settings to prevent overspeed.

3. Environmental temperature limit

The long-term operating environment temperature allowed for ATEX equipment is -20 ℃~+40 ℃. If it exceeds this range, the thermal power needs to be recalculated and the manufacturer consulted.

Selection process and calculation of gearbox

Whether the selection is correct directly affects the service life and explosion-proof safety of the equipment. The standard process includes the following key steps:

1. Determine the Service Factor (f ₛ)

The service factor is a comprehensive measure of load fluctuations, startup frequency, and daily running time. The determination basis is as follows:

Acceleration coefficient K: K=J-c/Jm (load inertia/motor inertia). The larger the K value, the heavier the impact.

Select the load type based on the K value:

K1: Uniform load (such as light load on conveyor belt)

K2: Medium impact load (such as agitator)

K3: Heavy impact loads (such as crushers and elevators)

By combining the number of starts per hour (Z ₕ) and daily operating hours, refer to the f ₛ curve in the manual to obtain the service coefficient. For situations involving personal safety (such as promotion), the choice of f ₛ should be particularly conservative.

2. Calculate the required input power (P ᵣ₁)

Based on the required output torque (M ᵣ₂) and output speed (n ₂) for the application, combined with the dynamic efficiency of the worm gear reducer (η d_d, please refer to the efficiency curve), calculate the required motor power:

Pr one=Mr two×n two

nine thousand five hundred and fifty×ηd[kW]

P r1= 9550×η d M r2×n two [kW]

3. Choose the specifications of the gearbox

For models with IEC motor flanges: refer to the Rating Charts to find the machine base number and speed ratio that satisfies the rated input power Pn ₁ ≥ P ᵣ₁× f ₛ at the required output speed n ₂. Then select the actual motor power P ₁ ≥ P ᵣ₁, and finally verify the safety factor S=Pn ₁/P ₁ ≥ f ₛ.

For solid shaft input models: Calculate and calculate the torque M c ₂=M ᵣ₂ × f ₛ× f_tp (f_tp is the temperature correction factor, and the worm gear is taken as 1.0~1.17). Select a gearbox with a rated output torque Mn ₂ ≥ M ₂ c ₂.

4. Post selection verification (key steps)

After the selection is completed, the following three checks must be carried out:

Peak torque: The gearbox should be able to withstand an instantaneous peak of at least 200% of the rated torque. If there is frequent impact in the application, it is recommended to install a torque limiter.

Radial Load: The radial force exerted by external transmission components (sprockets, pulleys, gears) on the input/output shaft must be less than the allowable value (Rn ₁/Rn ₂) specified in the manual. When calculating, it is necessary to consider the distance between the load application point and the axle shoulder (load position coefficient, see manual). The formula for calculating the actual radial force Rc is: Rc=(2000 × M × Kr)/d, where d is the pitch diameter of the transmission component and Kr is the transmission type coefficient (sprocket takes 1.0~1.25, gear takes 1.25~1.5).

Thrust Load: The allowable axial thrust is usually 20% of the corresponding radial allowable value. If there is no radial load, the maximum allowable axial thrust can reach 50% of the radial allowable value. If exceeding this limit, please contact the manufacturer.

Key points of lubrication management

Worm gear reducers are extremely sensitive to lubrication, especially in ATEX environments, where the correct oil level can effectively control temperature rise.

When the VF-W series leaves the factory, synthetic oil (Shell Omala S4 WE 320) is added according to the installation position ordered, and it is equipped with a closed transport plug. Before trial operation, the user must replace it with the breathable plug that comes with the box to prevent internal pressure accumulation.

The amount of lubricating oil varies depending on the seat number and installation position. For example, the B3 installation position of VF 30 requires 0.045 liters, while the B3 position of W110 (high speed ratio) requires 2.8 liters. The user manual provides a detailed fuel quantity table, please make sure to fill according to the table.

Special attention: When W110 is in V5/V6 position and equipped with B14 flange, due to structural limitations, there is no lubricating oil available at the factory. Users must fill it to the specified oil level by themselves.

Common errors and maintenance tips

Unauthorized change of installation position: It may alter the circulation of the oil circuit and the position of the vent hole, which may result in poor lubrication or oil leakage, directly violating ATEX compliance.

Neglecting the replacement of breathable plugs: If the transport plug does not exhaust, the increase in internal pressure during operation will damage the oil seal, causing lubricant leakage and increasing the risk of fire.

Overspeed operation: Even short-term overspeed may cause the worm bearing to overheat, with surface temperature exceeding the T-level limit, becoming a potential ignition source.

Radial load exceeding limit: Without considering the offset of the load center (such as the pulley being too convex), the actual radial force far exceeds the manual value, which can lead to premature bearing failure, shaft fracture, and even spark ignition.

Selection Examples and Decision Suggestions

Assuming a certain chemical mixer needs to output a speed of 20 min ⁻¹, an output torque of 300 Nm, run for 8 hours a day, start 10 times per hour, and a load inertia ratio K ≈ 2 (moderate impact). According to the table, f ₛ ≈ 1.2. Calculate P ᵣ₁=(300 × 20)/(9550 × 0.55) ≈ 1.14 kW (efficiency estimated at 0.55). Then Pn ₁ needs to be ≥ 1.14 × 1.2=1.37 kW. Check that the W 63 series has Pn ₁ of 1.1 kW (insufficient) when n ₂=20, and the W 75 series has Pn ₁ of 2.2 kW (satisfied) when n ₂=20. The final selection is W 75 with a 1.5 kW motor, with a safety factor S=2.2/1.5=1.47>1.2, which is qualified. Simultaneously verify the radial load: If a sprocket is selected with a pitch diameter of 100mm and a torque of 300Nm, then Rc=2000 × 300 × 1.25/100=7500N. The allowable radial load Rn ₂ (at n ₂=20) for the W 75 output shaft is 3050N, which is obviously insufficient. At this point, it is necessary to increase the diameter of the sprocket or switch to gear transmission, or choose a larger machine base size. Radial load is often the real bottleneck in selection, and engineers must be vigilant.