Bonfiglioli KRG-KCG-KSD hydraulic coupling

Bonfiglioli KRG-KCG-KSD hydraulic coupling

Bangfeili KRG, KCG, KSD three series hydraulic couplings (fluid coupling/fluid coupling/Str ö mungskupplung), including principles, working modes, performance characteristics, selection calculations, three series product specifications, model codes, mechanical dimensions, safety accessories, and version revision information. Hydraulic couplings rely on working oil to transmit power, without mechanical rigid connections, and are used in motor reducer transmission chains to achieve soft start, overload protection, and multi motor load balancing. They are typically used in belt conveyors and high inertia equipment.

Symbol Definition

Complete definition of all calculation parameters: moment of inertia, input/output torque, power, speed, slip S (percentage of pump turbine speed difference), acceleration time, number of starts Z, heat capacity, temperature rise, ambient temperature, etc.

Core formula: Slip (S %= frac {n_ {MOT}-n_ {FC}}{n_{MOT}} ×100)； Without slip, torque cannot be transmitted. Normal operating slip: about 1.5% for high power and up to 6% for low power. Physical law: The transmitted torque is proportional to the square of the input speed; The transmitted power is proportional to the third power of the rotational speed and the fifth power of the impeller outer diameter.

2 Structure and Working Principle

2.1 Core components

Pump impeller (active impeller, connected to input shaft)

Turbine (driven impeller, connected to output shaft)

Sealed end cap; The roles of pump impeller and turbine can be interchanged. By relying on the centrifugal kinetic energy of hydraulic oil in the cavity to transmit torque, there is no mechanical contact and almost no wear; The efficiency loss mainly comes from slip.

2.2 Characteristics of asynchronous motors driven by ordinary hydraulic couplings

Disadvantages of starting a regular three-phase cage asynchronous motor directly with load:

The starting current can reach 6 times the rated value, causing impact on the power grid and motor overheating;

The available torque margin during the acceleration phase is very small, and high inertia loads are prone to startup failure;

Although the star delta voltage reduction start reduces the current, the output torque also decreases significantly, and in high inertia situations, the motor still needs to be amplified.

Advantages of increasing hydraulic couplings: the motor starts almost without load, and gradually drives the load after the motor quickly reaches the rated speed; Suppress the peak of starting current, improve the acceleration torque margin, and extend the life of transmission components.

2.3 Version C/CC with Delay Chamber

Standard version: The maximum starting torque is about 200% of the rated torque of the motor; Reducing oil filling can increase the pressure to 160%, but at the cost of increased slip and working temperature.

Single delay chamber C (≥ 11 specifications available): During shutdown, a portion of the oil is stored in the delay chamber, resulting in low oil in the working circuit and limiting the starting torque to 150% of the motor's rated torque; During the start-up process, oil gradually flows into the working chamber, and once the speed is normal, all oil enters the working chamber with minimal slip. Size ≥ 15, the throttle hole can be adjusted externally to change the starting time.

Double delay chamber CC (available for specifications ≥ 15): stores more oil, limits the starting torque to a minimum of 120% of the motor's rated torque, and achieves extremely smooth starting; Suitable for high inertia and belt conveyors.

The advantage of delay cavity becomes more obvious with the increase of transmission power.

Main characteristics of 3 hydraulic couplings

Extremely smooth soft start; Motor no-load starting to reduce the impact of starting current;

Built in overload protection to protect the motor and mechanical equipment in case of load stalling;

Standard cage asynchronous motors can be used directly without the need for special starting devices;

Absorb shock and vibration, extend the life of the entire transmission chain, and reduce energy consumption;

The minimum starting torque for the C/CC version is 120% of the motor's rated torque;

The input and output torques are equal, and the motor can still output the maximum torque even if the load is stuck;

Allow frequent start stop and support forward and reverse operation;

Dual motor drive can automatically achieve load balancing;

High efficiency and low maintenance workload;

Using Viton rotary seals; Apply anti-corrosion coating to cast iron/steel parts.

Important: Working oil is not included in the supply scope and the user needs to add the correct amount of oil on site according to the manual.

Selection Methods

The selection process is divided into two steps: ① preliminary selection of chart selection; ② Thermal power school nuclear (required for high inertia and frequent start stop per hour).

4.1 Preliminary selection chart

Horizontal axis motor speed nMOT, vertical axis power kW; determine the coupling specification (8-24) based on the intersection point.

If it falls within the boundary of two gears, it is recommended to choose a larger gear and reduce the fuel filling appropriately.

4.2 Engineering verification calculation (must be used for high inertia and frequent start-up conditions)

Need to calculate:

Converted to the total moment of inertia J at the coupling shaft end;

Acceleration time tACC;

Start generating heat QACC;

Temperature rise Δ TACC, steady-state operating temperature rise Δ TUTS;

The final working temperature of the coupler TUTS must be ≤ 150 ℃;

Calculate the maximum allowable number of starts per hour ZMAX; The sample provides complete calculation formulas and engineering examples (gearbox transmission i=48.8, example of load large inertia conveyor).

Different specifications have corresponding heat capacity TC, and a table of samples is provided.

major product series KRG/KCG/KSD

Specification coverage: 8, 9, 11, 12, 13, 15, 17, 19, 21, 24.

KRG series (basic model)

Output side with elastic coupling; Pre made standard motor shaft holes for input and output, or FP pre made blank holes, can be used for on-site precision machining to the target size.

Optional: Disc/Drum Brake; Single delay cavity C (≥ 11); Double delay cavity CC (≥ 15); SP safety pin device.

Installation posture: horizontal OR, vertical upward VA, vertical downward VB; supports reverse installation REV.

Output: Two connection methods: cylindrical hole and cone sleeve; Complete shaft hole size, external dimensions, weight, and maximum oil filling gauge.

KCG series (maintenance quick release type)

Both input and output sides are equipped with toothed couplings; When disassembling the coupling, there is no need to move the motor or gearbox, and the original alignment is retained, greatly reducing maintenance time.

Configurable C/CC delay cavity, SP safety device; No brake options available.

The input and output shaft hole specification table, two-dimensional drawings, and weight oil filling parameters are complete.

KSD series (pulley compatible type)

Mechanical performance equivalent to KRG; Reserved installation interface for V-shaped belt pulley on the body (user provided belt pulley); Used for transmission systems where the motor reducer shaft is parallel to different axes.

Limitation: Vertical installation condition, cannot configure delay chamber C/CC; Horizontal installation can use C/CC.

Support SP security devices; Shaft hole size, shape, weight, and oil filling gauge.

Security Protection Options (SP)

Standard: When the oil temperature rises to 140 ℃ due to long-term overload/slippage of the 140 ℃ fusible plug, the fusible alloy melts, the working oil sprays out, and the motor is disconnected from the load. Users must take protective measures to prevent injury from hot oil.

SP option: Pin type melting protection (triggered at 120 ℃, equipped with relay)

Alloy melting at a temperature of 120 ℃; Centrifugal force pushes the firing pin outward by about 16mm and touches the matching relay;

Output switch signal, used for alarm or cutting off motor power supply; It won't splash hot oil.

Installation precautions: Reverse installation (external impeller connected to motor shaft) can ensure reliable operation under any fault condition; The standard installation (internal impeller connected to motor) provides unreliable protection in the event of a stuck fault on the driven side.

After troubleshooting, replacing the firing pin component can restore the equipment without the need to replace the entire coupling; The installation of relay wiring is the responsibility of the implementing party.

After selecting SP, the melting temperature is 120 ℃, which is different from the standard 140 ℃. The document is accompanied by a dimension drawing for the installation of the SP device.

Revision R1 Explanation in Version 7

KRG15 cancels the output shaft holes with diameters of 28 and 32;

KRG17 cancels the output shaft holes with diameters of 32 and 35;

KRG24 has added an output shaft hole with a diameter of 45;

KRG8 cancels the F200 drum brake configuration.