Selection and Calculation of Bonfiglioli RAN Right Angle Gearbox



Bonfiglioli RAN series right angle gearbox selection calculation and engineering application guide

Introduction: Engineering Challenges of Right Angle Transmission

In industrial transmission systems, when power transmission requires changing direction between orthogonal axes, the Mitre Gears/Marvel Gears become an indispensable core component. Unlike traditional worm gears or planetary gearboxes, right angle gearboxes need to balance multiple goals such as high efficiency, low backlash, and high load-bearing capacity while achieving 90 ° steering.

The Bonfiglioli RAN series, as a representative of its right angle gearbox product line, covers a wide range of scenarios from small power precision transmission to high thrust heavy-duty lifting applications. From the compact design of RAN 8 to the ultra large axial load capacity of RAN 2R, this series fully embodies Bonfiglioli's over sixty years of technical accumulation in the field of bevel gear transmission. This article will provide engineers with a complete engineering application methodology based on the RAN series technical manual, covering three core dimensions: selection process, load verification, and lubrication strategy.

Three basic parameters before selection

The correct selection begins with precise definitions of three basic parameters: torque, power, and service factor.

1.1 Rated torque and required torque

Rated torque [M ₙ₂]: refers to the torque that can be transmitted at the output end of the gearbox under uniform continuous load, based on the service coefficient f ₛ=1 and a specific input speed [n ₁]. This is the 'nominal capacity' of the gearbox.

Required torque [M ᵣ₂]: The output torque determined by the actual application requirements. When selecting, it is necessary to ensure that M ₙ₂ ≥ M ᵣ₂.

1.2 Input power [P ₙ₁]

The rated power data of the RAN series corresponds to the available input power at a specific input speed [n ₁] and a service factor f ₛ=1. When selecting, engineers need to ensure that the output power of the motor does not exceed this value, or adjust it based on the actual working conditions through a service factor.

1.3 Determination of Service Coefficient [f ₛ]

The service coefficient is a key parameter that quantifies the severity of application conditions. Its determination requires comprehensive consideration of three major factors:

Daily operating hours: The longer the operating time, the more severe the heat dissipation and wear accumulation, and the higher the required service factor.

Hourly startup frequency [Z ᵢ]: Frequent start stop will significantly increase the impact load on gears and bearings.

Quality Acceleration Factor [K]: This is the core link between load properties and selection curves.

K=Jc Jm

among which

J-c: The moment of inertia of the load converted to the motor shaft

J'm: The moment of inertia of the motor

According to the magnitude of the K value, the corresponding load curve can be determined:

K ≤ 0.25: K1 curve - uniform load (such as a continuously running conveyor belt)

0.25<K ≤ 3: K2 curve - moderate impact load (such as agitator, compressor)

3<K ≤ 10: K3 curve - strong impact load (such as crusher, stamping equipment)

When K>10, it is necessary to contact Bonfiglioli Technical Service Center for special verification.

The Four Step Process for Selecting Right Angle Gearboxes

Step 1: Determine the calculated torque

Based on the required output torque [M ᵣ₂] and service factor [f ₛ] for the application, calculate the calculated torque [M ꜀₂] for selection:

Mc two=Mr two×fs 

M c2=M r2×f s 

Step 2: Calculate the speed ratio

Calculate the speed ratio [i] based on the input speed [n ₁] and the required output speed [n ₂]:

i=n one n two

Step 3: Match by looking up the table

In the RAN series performance table, find the gear closest to the calculated speed ratio [i] and confirm whether the rated output torque [M ₙ₂] at that gear satisfies M ₙ₂ ≥ M ꜀.

Step 4: Motor compatibility verification

If direct connection to IEC motors is required, refer to the "Motor Adapter" section in the manual to confirm whether the input interface of the selected gearbox is geometrically compatible with the motor flange (such as B5, B14). For larger machine bases such as RAN 28/38/48, the range of suitable motors needs to be confirmed by Bonfiglioli's technical department.

Load verification: engineering considerations beyond torque

After the selection is completed, engineers must verify the following three types of loads to ensure the reliability and lifespan of the gearbox under actual working conditions.

3.1 Radial load [R] verification

When external transmission components (sprockets, gears, pulleys) are installed on the gearbox shaft, they will generate radial forces acting on the shaft. The calculation formula is:

Rc[N]=two thousand×M[Nm]×Krd[mm]

R c[N]= d[mm]2000×M[Nm]×K r

among which

M: The torque acting on the shaft

d: The pitch diameter of the transmission component

K ᵣ: Transmission type coefficient

K ᵣ=1.0: Chain Drive

K ᵣ=1.25: Gear transmission

K ᵣ=1.5~2.0: Belt drive

The calculated radial load must be less than the corresponding rated radial bearing capacity [R ₙ₁] (input shaft) and [R ₙ₂] (output shaft) in the performance table:

Rc one≤Rn one and

Rc two≤Rn two 

R c1≤R n1 And Rc2≤R n2

3.2 Axial Load [A] Verification

For applications that require axial thrust, such as screw conveyors and lifting screws, the RAN series provides clear guidance on axial bearing capacity.

General principle:

When the axial load and the rated radial load act simultaneously, the allowable axial load is about 20% of the radial bearing capacity.

If there is no radial load on the shaft, the maximum allowable axial load can reach 50% of the rated radial bearing capacity.

RAN 1/RAN 2/RAN 2R Special Axial Heavy Duty Series:

These three products are designed specifically for applications that primarily involve axial loads, such as ball screw lifting systems. The bearing system has been strengthened for axial force, and under the condition of input speed n ₁ ≤ 100 min ⁻¹, the allowable axial loads are:

RAN 1：50,000 N

RAN 2：80,000 N

RAN 2R：150,000 N

When the input speed exceeds 100 min ⁻¹, it is necessary to consult Bonfiglioli's technical department for accurate calculation of bearing life.

3.3 Peak torque verification

The instantaneous peak torque (impact load) that the gearbox is allowed to withstand should not exceed 200% of the rated torque. If there are frequent impact loads in the application, it is recommended to add hydraulic couplings, friction clutches, or torque limiters in the transmission chain to protect the gearbox from damage.

Lubrication Strategy: The Key to Long Life Operation

There are significant differences in lubrication methods for different machine base numbers in the RAN series, and engineers need to choose the correct maintenance strategy based on the product model.

4.1 "Lifetime lubrication" model (maintenance free)

Suitable for RAN 8, 15, 18.14, 20, 20CAVO, 25:

Lubricating medium: synthetic grease (GADUS S5 V142W 00)

Maintenance requirement: Under normal operating conditions without pollution, there is no need to regularly replace lubricating grease, and the product is maintenance free within its expected service life.

4.2 "Lifetime oil bath lubrication" model

Suitable for RAN 24, RAN 1, RAN 2, RAN 2R:

Lubricating medium: Synthetic oil (OMALA S4 WE 320)

Special design: RAN 1/2/2R is equipped with an oil level observation window, which facilitates visual inspection of the oil level, but does not require oil change under normal operating conditions.

4.3 Models that require on-site lubrication

Applicable to RAN 28, 38, 48:

Factory condition: Does not contain lubricating oil, customers need to add it themselves before installation.

Recommended oil: OMALA S4 WE 320

Oil quantity reference (B3 installation position):

RAN 28：1.7 L

RAN 38：3.0 L

RAN 48：4.5 L

Important reminder: Different installation positions (B6, B7, etc.) require different amounts of oil, and the installation orientation must be clearly marked when ordering to provide Bonfiglioli with correct oil level guidance.

4.4 Suggestions for Oil Change Interval

For gearboxes that are not "lifetime lubricated" and require regular oil changes, Bonfiglioli recommends determining the oil change interval based on the oil temperature:

Oil temperature [° C] Mineral oil change cycle [h] Synthetic oil change cycle [h]

< 65 8,000 25,000

65 - 80 4,000 15,000

80 - 95 2,000 12,500

Safety warning: Regardless of the lubrication method, when the ambient temperature is below -10 ° C, the gearbox must be gradually and uniformly preheated before starting, or run without load until the internal temperature rises above -10 ° C before loading, otherwise it may cause lubricant viscosity to be too high and lead to lubrication failure.

Installation and Storage Engineering Specification

5.1 Key points of installation

Fit tolerance: The inner hole of the transmission component installed on the output shaft must comply with ISO H7 tolerance to avoid interference fit and damage to the bearing or gear.

Anti corrosion treatment: Before installation, all mating surfaces should be cleaned and coated with anti rust protective agent.

Outdoor installation: Rain cover and sun shading device should be equipped to avoid direct exposure of the gearbox to rainwater and strong solar radiation.

5.2 Long term storage specifications

If the gearbox needs to be stored for more than 6 months:

Rust prevention treatment: All exposed machined surfaces (flange faces, shaft extensions, couplings, etc.) must be coated with Mobilarma 248 or equivalent rust inhibitor.

Moisture proof placement: The gearbox should be placed on a wooden pallet and direct contact with the ground is strictly prohibited.

Oil seal protection: Place the gearbox with the oil drain plug facing upwards and completely fill it with lubricating oil to prevent the seals from drying out. Before reactivation, drain to the correct oil level.

Selection checklist

After completing the selection and system design, it is recommended that engineers check the following items one by one:

Is the calculated torque [M ꜀₂] less than or equal to the rated torque [M ₙ₂] in the performance table?

Is the actual radial load less than the rated radial bearing capacity?

Is the actual axial load (if any) within the allowable range (generally not exceeding 20% of the radial capacity)?

Does the peak torque exceed 200% of the rated torque? If exceeded, has a torque limiting device been installed?

Has the installation orientation (B3/B6/B7, etc.) been clearly marked in the order?

Does the lubrication method and oil selection match the working environment temperature?