Bonfiglioli KRG/KCG/KSD Hydraulic Coupling Selection and Integration Guide

During maintenance, the hydraulic coupling body can be extracted without moving the motor or reducer

Significantly reduce maintenance downtime

No need to realign, maintain the original axis accuracy

Suitable for occasions that require frequent maintenance or replacement of couplings

3. KSD series (pulley type)

KSD is designed for installation scenarios where the motor and gearbox shafts are not aligned (parallel axes). Its output end is a reserved interface for installing the pulley (the pulley is not randomly provided), and users can choose a standard triangular pulley according to the speed ratio. KSD also supports single/double delay chambers, but it should be noted that delay chambers cannot be selected for vertical installation.

Selection process and technical verification

1. Preliminary selection (based on power and speed)

According to the selection diagram in the user manual (see Fig. 7 in the original text), the base size (Size 8-24) of the hydraulic coupling can be preliminarily determined based on the motor power (kW) and input speed (min ⁻¹). If the selection point falls on the boundary between two curves, it is recommended to choose a larger machine base size and reduce oil filling to achieve lower temperature rise and longer service life.

2. Start time calculation (t_acc)

The startup time is calculated according to the following formula:

tacc=two π⋅nMOT⋅JLOAD sixty⋅MACC[s]

t acc= 60⋅M ACC 2π⋅n MOT⋅J LOAD [s]

among which

JLOAD

Convert the load to the total inertia of the motor shaft (including couplings and reducers)

MACC

Acceleration torque=average coupling torque - load torque (to be found through the slip torque curve of the coupling)

Engineering experience value: The startup time is generally controlled within 5-20 seconds. Too long may cause the oil temperature to exceed the standard, while too short may lose the meaning of smooth start-up.

3. Temperature rise verification (Δ T)

Hydraulic couplings generate heat during start-up and operation, and it is necessary to verify whether the temperature rise is within a safe range.

Temperature rise during startup phase (Δ T-acc):

ΔTacc=QaccTC[°C]

among which

Qacc

The heat generated during the acceleration phase (which can be obtained by integrating the torque slip curve),

TC is the total heat capacity of the coupling.

Steady state operating temperature rise (Δ T_uts):

ΔTuts=Ploss⋅tutsTC[°C]

among which

Ploss

For steady-state slip loss (approximately 2% to 6% of rated power).

End temperature of cycle:

Tuts=Tamb+ΔTacc+ΔTuts[°C]

This value must be lower than the maximum allowable operating temperature of the coupling (usually 120 ° C~140 ° C).

4. Maximum allowable startup times (Z-MAX)

If the application needs to be started frequently (such as devices that work periodically), the maximum allowed number of starts per hour needs to be calculated:

ZMAX=TC⋅(TMAX−Tamb)−Ploss⋅tutsQacc

Z MAX= Q acc TC⋅(T MAX−T amb)−P loss⋅t uts

If the actual number of starts exceeds Z-MAX, the coupling will accumulate overheating and eventually trigger the melting plug protection. The solution includes choosing a larger machine base size, adding delay chambers, extending the start-up interval, or adding external cooling.

Security options and maintenance points

1. Fusible plug (standard configuration)

All KRG/KCG/KSD couplings come standard with a melting plug set at a temperature of 140 ° C. When the oil temperature exceeds the standard, the melting plug melts, the oil is discharged, and the motor is disconnected from the load. During installation, a protective barrier must be installed below the coupling to prevent high-temperature oil from splashing and injuring people.

2. Switch sales+relay (SP option)

For situations where oil leakage is not allowed (such as food processing, clean environments), the Switching Pin option can be selected:

Internally equipped with easy to fuse gold rings, the spring-loaded pin is released at 120 ° C

Pin extends 16mm, triggering external micro switch (provided with coupling)

Relay contacts can be connected to alarm circuits or motor control circuits to achieve electrical protection without oil leakage

After troubleshooting, simply replace the melting ring to reset, without the need to replace the entire melting plug

3. Maintenance points

First oil filling: The coupling does not come with oil when it leaves the factory. Users need to add the specified brand and quantity of oil according to the installation position and operating conditions in the manual.

Sealing element: standard Viton ®  Fluororubber seal, resistant to high temperature and aging.

Anti corrosion treatment: Both cast iron and steel components are treated with anti-corrosion coatings, suitable for humid or corrosive environments.

Installation direction: All options and oil quantities are based on the specified installation position (horizontal/vertical). Changing the installation direction may require recalculating the oil quantity and may affect the functionality of the delay chamber.

Selection Example

Operating parameters:

Motor power: 55 kW, speed 1475 min ⁻¹

Speed ratio of reducer: 48.8, efficiency 0.91