1. Introduction
During scheduled maintenance on the hot stamping line, an emergency stop of the pneumatic distributor was recorded. The reason for the stoppage is a complete failure of the solenoid coil (opening of the winding due to thermal destruction of the insulation). Failure of this type leads to a stoppage of the technological process and significant financial losses. Given the specifics of the operation of equipment at Ukrainian enterprises, where voltage fluctuations in the power supply network are often observed, the analysis of such incidents requires a system engineering approach in accordance with DSTU and ISO standards.
2. Overview of the component and operating conditions
The electromagnetic coil of the solenoid valve is an executive converter of electrical energy into mechanical movement of the core. In industrial environments, these elements work as part of complex control and automation systems (compatible with industrial networks, such as the Allen Bradley 1783-SFP100FX communication modules for Ethernet communication and telemetry data updates).
Typical operating parameters:
- Nominal supply voltage: 24 V DC or 230 V AC (±10%).
- Insulation class of copper wire: H (allowable temperature +180°C).
- Operating ambient temperature: from -20°C to +60°C.
- MTBF (Mean Time Between Failure): 40,000 hours subject to compliance.
3. Evidence base of rejection
The following parameters and signs were removed during defect inspection:
- Winding resistance with a multimeter: tends to infinity (complete break).
- Visual inspection: the plastic case shows signs of thermal deformation (foaming, darkening), the compound is cracked.
- Measuring the temperature with a pyrometer: the surface temperature of the coil reached +145°C (with a nominal value not higher than +90°C).
- Analysis of network parameters: systematic voltage dips up to 19.2 V DC and pulse discharges up to 29 V DC were recorded.
4. Systematic investigation of root causes
To determine the deep causes of the accident, the Ishikawa diagram method and the 5 Whys analysis were used:
- Why did the coil burn? — Due to exceeding the nominal operating temperature of the insulation.
- Why did the temperature rise? — Due to an increase in current consumption (Joule overheating).
- Why did the current increase? — The valve stem was not fully retracted due to mechanical jamming or undervoltage.
- Why was the voltage low? — Long cable lines and unstable power supply from a common industrial transformer.
- Why didn't the protection work? — The rating of the protective circuit breaker has been exceeded relative to the cross-section of the control cable.
5. Identified root causes (ranked list)
- Root Cause 1 (Probability 45%): Continuous operation with low supply voltage. Decreasing the DC voltage causes the controller to increase the tripping time, causing the starting current to flow through the winding for a long time.
- Root Cause 2 (Probability 30%): Exceeded duty cycle rating (Duty Cycle 100% ED for coils designed for repeat-short duty only).
- Root cause 3 (Probability 15%): External thermal surpluses from nearby technological nodes and lack of natural ventilation in the assembly cabinet.
- Root cause 4 (Probability 10%): Mechanical hanging of the anchor due to contamination of the environment by the working environment (lubricant, condensate).
6. Corrective actions
To eliminate the identified defects, the following measures must be implemented:
- Short-term measures: Replacement of the damaged coil with a certified analogue in accordance with the CE and UkrSEPRO technical regulations. Installation of a stabilized 24 V DC power supply with filtering of impulse interference.
- Long-term measures: Switch to coils with heat resistance class C (+200°C) and integrated protective diodes (for extinguishing self-induction). Update of PLC algorithms to control the activation time of executive mechanisms.
7. Quick diagnostic card for technical personnel (Tablet-compatible)
Use this checklist during your monthly equipment walkthrough:
- [ ] Check the cold winding resistance with a multimeter (compare with the passport, ±5% tolerance).
- [ ] Measure the voltage drop across the coil terminals when it is turned on (not less than 95% of Unom).
- [ ] Carry out non-contact thermometry with a thermal imager (the working temperature should not exceed the limits of the ISO 18436-7 standard).
- [ ] Check the integrity of the rubber seals and the absence of moisture entering the connector DIN 43650.
- [ ] Test the mobility of the rod by hand (full stroke without jamming).
- [ ] Check the reliability of tightening the terminal connections (tightening torque according to ISO 4762).
- [ ] Assess the environment for the presence of aggressive vapors or abrasive dust.
- [ ] Check the actual duty cycle (ED%) with the product data sheet.
8. Prevention strategy
To minimize the risks of emergency stoppages in production, it is recommended to implement:
- Condition Monitoring: regular audit of temperature regimes of electromagnets using infrared cameras.
- Planned preventive maintenance (PRM): replacement of coils preventively every 25,000 hours in critical sections of the process line.
- Selection of components in accordance with the strict requirements of European standards (EN 60204-1 regarding the electrical safety of machines).
9. Conclusion
The reliability of pneumatic and hydraulic systems directly depends on the quality of electrical components and the stability of power grid parameters. A timely audit of the causes of failures and the use of certified spare parts allows you to avoid long-term equipment downtime. Use the UNITEC-D E-Catalog to select reliable components for the modernization of your enterprise.
10. Links
- DSTU EN 60204-1:2015 Machine safety. Electrical equipment of machines and mechanisms.
- ISO 4406:2017 Dry and oil hydraulics. A method of assessing the cleanliness of working environments.
- ISO 18436-7 Condition monitoring and machine diagnostics. Thermography.
- Technical safety regulations of low-voltage electrical equipment (PCMU No. 1067).
