Scope and purpose
This manual covers routine maintenance of spot welding machines from 15 to 200 kVA, including single-spot and multi-spot installations. Procedures are used for equipment with water cooling and transformer power according to DSTU EN ISO 14327.
Maintenance is performed every 500 working hours or when the quality of welded points decreases. Critical inspections of the cooling system are carried out weekly under conditions of intensive operation.
Safety measures
CAUTION: High-voltage equipment! Before starting work, it is necessary to perform the blocking/marking procedure (LOTO) in accordance with DSTU OHSAS 18001.
Mandatory personal protective equipment:
- Dielectric gloves (class 0, up to 1000 V)
- Safety glasses
- Protective footwear with a dielectric sole
- Clothes made of natural fibers
It is FORBIDDEN to perform live work. The minimum waiting time after turning off the power is 10 minutes to discharge the capacitors.
Necessary tools and materials
| Name | Specification | Quantity |
|---|---|---|
| Socket wrench | M8-M20, torque 5-180 Nm | 1 set |
| Torque wrench | 10-200 Nm, accuracy ±3% | 1 pc |
| megohmmeter | 500-2500 V DC | 1 pc |
| Multimeter | CAT III, 600 V | 1 pc |
| Manometer | 0-6 bar, accuracy class 1.5 | 1 pc |
| Contact thermometer | 0-100°C, ±1°C | 1 pc |
| Dresser of electrodes | Processing diameter 6-16 mm | 1 pc |
| Thickness gauge probe | 0.05-1.0 mm | 1 set |
| Insulating tape | Class A, up to 600 V | 2 rolls |
| Coolant liquid | Water-glycol mixture, -20°C | 5 liters |
Preliminary inspection checklist
| Check element | What to check | Acceptance/rejection criteria | Notes |
|---|---|---|---|
| Feeding | Disconnecting from the network | Acceptance: 0 V / Deviation: presence of voltage | Check all phases |
| Electrodes | Visual state | Deviations: cracks, deformation, wear >2 mm | Measure the diameter of the working surface |
| Cooling system | Coolant level | Acceptance: between MIN-MAX / Deviation: below MIN | Check for leaks |
| Contact surfaces | Oxidation, pollution | Deviations: visible oxides, soot | Clean before assembly |
| Cable connections | Tighten the terminals | Deviations: backlash, darkening | Check the tightening torque |
| Isolation | Condition of insulating materials | Deviations: cracks, charring | Replace damaged insulation |
Step-by-step service procedure
Stage 1: Editing and maintenance of electrodes
- Dismantling the electrodes
- Unscrew the clamping nuts with a torque of 25-30 Nm in the opposite direction
- Carefully remove the electrodes from the holders
- Inspect the seating surfaces for wear
- Avoid hitting the electrodes - microcracks may form
- Measuring electrode wear
- Measure the diameter of the working surface with a caliper
- New electrode: 6.0±0.1 mm, marginal wear: 8.5 mm
- Check the taper: the maximum allowable is 0.05 mm on a length of 10 mm
- Measure the depth of holes from erosion: a maximum of 0.3 mm
- Editing the electrodes with the dresser
- Install the electrode in the dresser cartridge
- Set the rotation speed to 300-400 rpm
- Tool feed: 0.1-0.15 mm/rev
- Process until a diameter of 6.0±0.05 mm is obtained
- Don't allow the electrode to overheat - use the SOR
- Processing quality control
- Surface roughness: Ra ≤ 1.6 μm
- Absence of burrs and microcracks
- Perpendicularity of the end to the axis: 0.02 mm
Stage 2: Checking the transformer
- Visual inspection of the transformer
- Inspect the housing for deformation and damage
- Check the condition of the HV input insulators
- Inspect the secondary winding for darkening
- Check the tightening of bolt connections: 45-60 Nm
- Insulation resistance measurement
- Connect a megohmmeter between the primary winding and the case
- Test voltage: 1000 V DC
- Minimum permissible resistance: 10 MΩ at 20°C
- Measurement time: 60 seconds
- At low values, dry the windings
- Checking the resistance of DC windings
- Measure the resistance of the primary winding: nominal 0.15±0.02 Ohm
- Measure the resistance of the secondary winding: nominal 0.008±0.002 Ohm
- Measuring temperature: 20±2°C
- The deviation from the nominal should not exceed 10%
- Checking the transformation ratio
- Apply 100 V alternating voltage to the primary winding
- Measure the voltage on the secondary winding
- Calculate the coefficient: K = U1/U2
- Nominal value: 50±2 (for standard transformer)
Stage 3: Servicing the water cooling system
- System tightness check
- Visually inspect all connections and hoses
- Check the tightening of the clamps: 8-12 Nm
- Carry out a pressure test: 4.5 bar for 15 minutes
- Permissible pressure loss: no more than 0.1 bar
- Changing the coolant
- Drain the used liquid through the drain valve
- Flush the system with distilled water
- Pour in a new liquid: a mixture of 60% water + 40% ethylene glycol
- System volume: 8-12 liters depending on the model
- Do not use water with a high salt content - scale formation
- Cooling pump check
- Connect pump power
- Check performance: 15-25 l/min at 2.5 bar
- Measure the consumed current: nominal 2.8±0.3 A
- Check the absence of cavitation and vibrations
- Setting the flow regulator
- Set the coolant flow rate: 3-5 l/min per electrode
- System pressure: 2.0-3.5 bar
- Temperature at the entrance: no higher than 25°C
- Outlet temperature: no higher than 35°C
Post-service inspection checklist
| Test | Expected result | Actual | Counted/Not counted. |
|---|---|---|---|
| Transformer insulation resistance | ≥10 MΩ at 1000 V | _____ MOm | □ |
| Pressure in the cooling system | 2.0-3.5 bar | _____ bar | □ |
| Coolant consumption | 3-5 l/min per electrode | _____ l/min | □ |
| The diameter of the electrodes | 6.0±0.1 mm | _____ mm | □ |
| Tightening of electrode connections | 25-30 Nm | _____ Nm | □ |
| The temperature of the cooler at the outlet | ≤35°C at rated load | _____ °C | □ |
| Test welding | Quality point, diameter 4-6 mm | _____ mm | □ |
| Coolant leaks | Absent | _____ | □ |
Troubleshooting Guide
| Symptom | Probable cause | Corrective actions |
|---|---|---|
| Weak weld point | Wear of electrodes beyond the norm | Editing or replacement of electrodes, checking the clamping force |
| Sticking to electrodes | Contamination of the electrode surface | Electrode cleaning, welding mode correction |
| Transformer overheating | Insufficient cooling | Checking the flow of the coolant, cleaning the heat exchanger |
| Reduction of cooling pressure | Leakage in the system or clogging of the filter | Eliminating leaks, replacing the filter, checking the pump |
| Unstable welding current | Bad contacts in the primary circuit | Cleaning and tightening of contacts, checking cables |
| Low insulation resistance | Wetting the windings | Drying the transformer at 60-80°C for 8-12 hours |
| Increased noise during operation | Loosening of fasteners or wear of bearings | Tightening of bolted connections, replacement of pump bearings |
| Corrosion of contact surfaces | Use of low-quality coolant | Changing the fluid, adding corrosion inhibitors |
Recommended maintenance schedule
| Task | Periodicity | Estimated duration | Qualification level |
|---|---|---|---|
| Visual inspection of electrodes | Every day | 5 minutes | Operator |
| Checking the coolant level | Every week | 10 minutes | Operator |
| Editing of electrodes | Every 500 points or every week | 30 minutes | Mechanic |
| Complete maintenance of the cooling system | Every 500 operating hours | 2 hours | Mechanic |
| Checking the transformer | Every 1000 operating hours | 3 hours | Electrician |
| Replacing the coolant | Once a year or every 2000 hours | 1.5 hours | Mechanic |
| Capital maintenance | Every 8,000 operating hours | 8 hours | Specialist |
| Calibration of regulators | Once a year | 2 hours | Specialist |
Directory of spare parts
| Description of the part | Typical specification | Category UNITEC |
|---|---|---|
| Spot welding electrodes | CuCrZr, cone 1:10, diameter 6-16 mm | Welding electrodes |
| Sealing rings | NBR 70 Shore A, temperature -20/+120°C | Sealing elements |
| Coolant liquid | Ethylene glycol 40%, -25°C, 20 l | Technical fluids |
| Contact tips | M1 copper, silver coating 0.1 mm | Electrical contacts |
| Cooling hoses | EPDM, DN15, working pressure 6 bar | Hydraulic hoses |
| Coolant filter | Mesh, stainless steel, 100 µm | Filter elements |
| Insulating bushings | Polyamide PA6, dielectric strength 25 kV/mm | Insulating materials |
| Flow sensor | 2-20 l/min, output 4-20 mA | Measuring devices |
To select original spare parts and their analogues, use the electronic catalog UNITEC-D. Our technical specialists provide advice on compatibility and optimal selection of components for your equipment.
Reference materials
- DSTU EN ISO 14327:2018 - Resistance welding. Procedures for determining the weldability of sheet materials up to 3 mm thick
- DSTU EN ISO 18278-2:2017 - Resistance welding. Weldability. Part 2: Alternative procedures for the evaluation of sheet steels for spot welding
- DSTU IEC 60974-1:2014 - Equipment for arc welding. Part 1: Power sources for welding
- EN 50173:2007 - General requirements for electrical installations of industrial enterprises
- ISO 14373:2015 - Resistance welding. Procedure and test for establishing welding parameters for spot welding
