REXROTH MKD Explosion proof Synchronous Motor Application Guide

REXROTH MKD Explosion proof Synchronous Motor Application Guide

1. Product Overview and Applicable Standards

The Bosch Rexroth MKD series synchronous motor is a servo drive solution designed specifically for potentially explosive environments, meeting the requirements of Class II, Class 3 equipment in the ATEX Directive (94/9/EC), and suitable for gas (G) and dust (D) environments. This series of motors provides efficient and reliable power output, with a maximum torque of up to 18 Nm. It comes standard with a rotary transformer encoder and can be optionally equipped with a multi turn absolute encoder, a holding brake, or a keyway output shaft.

The MKD explosion-proof motor adopts "nA" type explosion-proof protection (non spark equipment), with a maximum surface temperature limit of 155 ° C. It is suitable for situations where explosive environments do not occur during normal operation, or where they can be quickly eliminated through ventilation and monitoring even if they do occur. The protection level of the motor housing is IP65, with good dust and water spray resistance, suitable for typical application scenarios such as industrial automation, packaging machinery, printing equipment, food processing and handling systems.

2. Safety regulations and usage precautions

Safety is always the primary consideration when using electrical equipment in explosive hazardous environments. MKD motors strictly comply with international standards such as ATEX and EN 50021, and users must fully adhere to the following safety principles in design, installation, and operation:

2.1 Expected and Unintended Uses

The motor is only suitable for the application scenarios and environmental conditions specified in the technical documentation. Prohibited from use in the following situations:

The environmental requirements are higher than the explosion-proof level indicated on the motor nameplate;

Underwater, extreme temperature or frequent temperature fluctuations;

Other application areas not explicitly approved by Rexroth.

2.2 Electrical Safety and Grounding Requirements

The motor must be reliably grounded through motor cables and independent grounding wires (with a minimum cross-sectional area of 4 mm ²) to prevent leakage and spark risks. All electrical connections must be made in non explosive areas, and it is strictly prohibited to plug or unplug connectors while they are live or under load.

2.3 Protective measures

Mechanical hazard: Measures such as safety fences, light curtains, and emergency stop switches must be taken to prevent personnel from entering the hazardous area.

Hot surface protection: The motor casing may reach high temperatures during operation, and it needs to be cooled to a safe temperature (up to 140 minutes) before it can be touched after shutdown.

Magnetic field protection: The magnetic field generated by the motor may affect pacemakers, metal implants, or hearing aids, and relevant personnel must stay away from the work area.

2.4 Specific requirements for explosion-proof environment

In explosive dust environments, it is necessary to prevent dust from accumulating on the motor casing to avoid affecting heat dissipation and causing temperature rise. The installation position of the motor should be easy to clean, and the ignition temperature of the dust must be much higher than the maximum surface temperature of the motor (155 ° C).

3. Analysis of motor model and technical parameters

The MKD series covers four basic models: MKD025, MKD041, MKD071, and MKD090, corresponding to different machine base sizes and power levels. Under each model, there are multiple winding codes and length specifications to meet different torque, speed, and inertia requirements.

3.1 Basic Technical Parameter Description

Continuous stalling torque (M ₐ N): The torque that the motor can continuously output at zero speed.

Peak current (I ₘₐₓ): The maximum phase current that a motor can withstand in a short period of time.

Torque constant (K ₘ): The torque value generated per unit current, used in control system design.

Thermal time constant (T ₜₕ): The time required for the temperature of the motor casing to rise to 63% of the steady-state value, which affects the heat dissipation design and operating cycle.

Rated data: including rated speed, torque, current, power, and voltage, defined based on S1 continuous working system or S6 intermittent working system (25% load duration rate).

3.2 Performance Curve and Operating Mode

The motor provides speed torque curves under two temperature rise parameters:

60K curve: insulation structure test based on winding temperature rise of 60K and ambient temperature of about 45 ° C.

100K curve: Non insulated structure test based on winding temperature rise of 100K and ambient temperature of about 40 ° C.

It is recommended to prioritize using 60K data in precision systems to reduce the impact of thermal expansion on positioning accuracy. The curve graph also includes a constant power zone limited by the DC bus voltage, S1 continuous working zone, and S6 intermittent working zone, providing users with intuitive basis for selection.

3.3 Axle Load and Bearing Life

The radial and axial forces that the motor output shaft can withstand depend on the shaft extension form (optical axis or keyway), the position of the force point, and the speed. The rated life of the bearing is L ₁₀ h=30000 hours (based on ISO 281 standard). If the actual load exceeds the allowable value, the life will decrease in cubic relationship. Redundant constraints on the shaft or direct installation of helical gears should be avoided, and it is recommended to use couplings with self-supporting bearings for connection.

4. Installation, Connection, and Debugging Guide

4.1 Mechanical Installation

The MKD motor adopts B5 installation method, which complies with DIN 42948 standard. The installation flange must be flat and free of burrs, and fixed with screws of the specified torque (such as MKD041 using 4 × M6 screws with a torque of 10.4 Nm). During the installation process, it is necessary to keep the motor dry and clean, and avoid impacting the shaft extension and flange.

4.2 Electrical Connections

The motor provides two connection methods:

Junction box form: standard configuration, suitable for all MKD explosion-proof models.

Plug in form: Only applicable to some models of MKD025.

Power cables and encoder cables must be selected from Rexroth recommended models or equivalent products that meet EN 50021 requirements (minimum temperature resistance of 80 ° C). The cable entry device must be equipped with a stress relief structure and ensure an IP65 protection level.

4.3 Maintain Brake Options

Keep the brake in a normally closed state and release it by energizing it with 24 VDC (± 10%). The brake is only used for shaft holding during shutdown and cannot be used as a braking device during operation. In vertical axis applications, additional mechanical safety devices (such as safety nuts, external brakes) must be equipped to prevent the rear axle from sliding down after power failure.

Before installation, it is necessary to test the holding torque of the brake and perform a break in operation if necessary (manually rotate the shaft several times with the brake closed). It is recommended to activate the brake at least once every 48 hours during operation to prevent rusting of the friction surface.

4.4 Encoder System

The motor integrates a rotary transformer or an encoder system with multiple absolute values, with a resolution of 24576 (MKD025/041) or 32768 (MKD071/090) pulses per revolution, respectively. The absolute value encoder is equipped with a battery backup, which can memorize axis positions of over 4096 revolutions per minute and has a battery life of approximately 10 years. Battery replacement must be carried out while the device is powered on and only in non explosive areas.

5. Operating environment and maintenance suggestions

5.1 Environmental Conditions Limitations

The motor can operate at full load under the following conditions:

Environmental temperature: 0 ° C to+40 ° C

Altitude: ≤ 1000 meters

If the ambient temperature or altitude exceeds the above range, the output torque needs to be corrected according to the derating curve (Figure 13-1). For example, in a 60 ° C environment or at an altitude of 2000 meters, torque needs to be multiplied by a utilization factor of 0.8.

5.2 Daily Maintenance

Cleaning: Regularly clean the dust and oil stains on the heat dissipation fins to ensure heat dissipation efficiency.

Cable inspection: Regularly check the insulation status and fastening of power and encoder cables, and replace them immediately if damaged.

Bearing replacement: If there is abnormal noise or the rated service life is reached, the bearings should be replaced by professional service personnel.

Brake inspection: Regularly test the brake's holding torque and action time to ensure its reliability.

5.3 Fault Handling and Safety Reset

If the motor is overloaded, the temperature is too high, or the brake fails, the control system will trigger an alarm and shut down. Before resetting the fault, the cause must be identified, especially for parts related to explosion-proof safety (such as aging seals, dust accumulation, poor grounding, etc.). After repair, safety acceptance testing needs to be conducted again, and the testing records need to be updated.

6. Certification and Identification

Each MKD explosion-proof motor is labeled with the following markings:

CE Mark: Compliant with the EU Machinery Directive and Low Voltage Directive.

Ex mark: II3 G D EEx nA II T155 ° C, indicating that the equipment complies with the ATEX directive and is suitable for Class II, Class 3 gas and dust environments.

Model label: Contains motor model, serial number, electrical parameters, and safety information. It is recommended to copy and post it in a prominent position on the equipment.

7. Accessories and System Integration

The MKD motor can be used in conjunction with the Rexroth planetary gearbox (GTS/GTP/GTM series) to achieve low-speed and high torque output. The reducer has high rigidity, low backlash, lifetime lubrication, and IP65 protection level, suitable for high dynamic load scenarios.

The motor must be used in conjunction with the designated driver series of Rexroth (such as DIAX04, ECODRIVE, DURADRIVE, INDRADRIVE) to ensure parameter matching and functional safety. Users can obtain selection support, technical training, and maintenance services through the global service network of Rexroth.