Haifeng Process Standards: Quick Reference
Electrical assembly accuracy in Haifeng polyurethane equipment directly determines final metering accuracy. For every 0.05 mm that servo-drive circuit assembly deviation exceeds the specified tolerance, metering-pump ratio error increases by more than 0.1%, directly affecting product-density uniformity and mechanical-property consistency.
Quick reference for key process parameters:
| Parameter | Haifeng Standard | Industry Reference | Related Equipment Accuracy |
| Servo motor installation concentricity | ≤0.03 mm | ≤0.05 mm | Positioning accuracy ±0.1 mm; repeatability ≤±0.05 mm |
| Wiring-resistance deviation in metering-pump drive circuit | ≤0.5 Ω (three-phase) | ≤1.0 Ω | Proportioning accuracy ±0.3% (ISO 8060) |
| Ground resistance of temperature-sensor signal-cable shield | ≤0.1 Ω | ≤0.5 Ω | Temperature-control accuracy ±0.5°C |
| Horizontal/vertical cable-trunking deviation | ≤2‰ of length; ≤2 mm overall | ≤3 mm overall | Control-cabinet protection rating IP54 or higher |
| Horizontal/vertical DIN-rail installation deviation | ≤2‰ of length; ≤1 mm overall | ≤2 mm overall | Reference accuracy for component installation |
| Separation between inverter speed-control signal cables and power cables | ≥100 mm | ≥50 mm | Speed fluctuation rate ≤1% |
| Terminal crimp pull-out force | ≥80 N (1.0 mm² conductor) | ≥60 N | Ensures connection reliability |
| Ground-system continuity resistance | ≤4 Ω | ≤10 Ω | IEC 60204-1 safety compliance |
| Encoder signal-cable twist pitch | ≤50 mm | ≤100 mm | 23-bit encoder signal integrity |
| Insulation resistance of complete cabinet (500 V DC) | ≥10 MΩ | ≥5 MΩ | Mandatory factory-test item |
1. Scope
1.1 Application
This SOP applies to electrical assembly of Haifeng polyurethane equipment control systems, including electrical-cabinet assembly, field wiring and commissioning for low-pressure foaming machines, high-pressure foaming machines, elastomer casting machines and continuous foam production lines.
2. Pre-Work Preparation and Accuracy Reference Verification
2.1 Technical Documentation Review
| No. | Item to Check | Accuracy Requirement | Acceptance Criterion |
| 1 | Electrical schematic revision | Must match the BOM revision | Revision numbers match exactly |
| 2 | Component layout drawing | Component locating dimensions are marked | Tolerances are specified |
| 3 | Servo parameter configuration table | Matches motor nameplate | Encoder resolution and rated current are consistent |
| 4 | Temperature-sensor calibration certificate | Within validity period | PT1000; calibration deviation ≤±0.1°C |
Before work begins, confirm that the electrical schematic, component layout and BOM are complete and use matching revisions. Retain detailed process records, including component-adjustment records and wiring-change notes.
2.2 Environmental Accuracy Conditions
Electrical assembly of polyurethane equipment must be performed in a controlled environment. Supply-voltage fluctuation must be ≤±5% of rated voltage, and ambient temperature must be kept between 10°C and 40°C to avoid affecting equipment accuracy. The work area must be organized into material, operation and tool zones and kept orderly.
2.3 Tool and Measuring-Instrument Accuracy Calibration
| Tool / Instrument | Accuracy Requirement | Calibration Interval |
| Digital multimeter | DC voltage ±0.05%; resistance ±0.2% | Every 6 months |
| Torque wrench | ±3% of setting | Every 3 months |
| Insulation-resistance tester | 500 V DC, ±5% | Every 12 months |
| Laser alignment instrument | ±0.01 mm | Every 12 months |
| Loop-resistance tester | 0.01 Ω resolution | Every 6 months |
3. Structured Electrical Assembly Workflow
3.1 Layout and Cabinet Installation
3.1.1 Cable Trunking Installation
Cable trunking must be level and free from twisting. Its inner walls must be smooth and burr-free, and joints must be continuous with no gaps. Secure each section at no fewer than two points; use at least three fixing points for sections longer than 400 mm. Provide fixing points at corners, branches and ends.
Accuracy control: The permitted horizontal/vertical installation deviation is 2‰ of the length, with a maximum overall deviation of ≤2 mm.
3.1.2 DIN-Rail Installation
Cut ends must be straight and perpendicular to the rail, with chamfers added and burrs removed. The gap at each end between the rail and cable trunking must be ≤1 mm. Do not join separate sections along the same straight rail. Use two fixing points per section, or three for sections longer than 300 mm. Secure with M5×20 electroplated hex-socket bolts, spring washers and flat washers.
Accuracy requirement: Horizontal/vertical deviation is 2‰ of the length, with a maximum overall deviation of ≤1 mm.
3.1.3 Cabinet Installation Accuracy
The permitted verticality deviation for cabinets, desks, boxes and panels must not exceed 1.5‰. Gaps between adjacent units must not exceed 2 mm, and deviation across a row of panel faces must not exceed 5 mm. For base-channel steel, straightness must be <1 mm per meter and <5 mm overall; levelness must be <1 mm per meter and <5 mm overall.
3.2 Component Installation and Precision Positioning
3.2.1 Servo-Drive System Installation
Metering accuracy in Haifeng polyurethane equipment depends on a servo motor driving a precision metering pump. Servo-motor positioning accuracy must reach ±0.1 mm, with repeat-positioning error ≤±0.05 mm. Electrical assembly must ensure the following:
| Assembly Item | Accuracy Requirement | Inspection Method |
| Length matching of servo-drive motor power cables | Three-phase cable length difference ≤50 mm | Tape measure |
| Clearance between encoder and power cables | ≥100 mm | Visual inspection and caliper |
| Drive cooling clearance | ≥100 mm above/below; ≥50 mm on each side | Caliper |
| Brake-resistor terminal torque | M4: 1.2 N·m ±0.1 | Torque wrench |
After wiring the servo drive, use a loop-resistance tester to measure the power-circuit resistance phase by phase. The deviation among the three phases must be ≤0.5 Ω.
3.2.2 Temperature-Control Circuit Assembly
The accuracy of polyurethane raw-material temperature control directly affects mixing-reaction consistency and metering accuracy. Haifeng equipment has separate temperature-control zones for piping and metering-valve bodies. PT1000 precision sensors and a fuzzy PID algorithm provide control accuracy of ±0.5°C.
Requirements for temperature-sensor signal wiring:
1. Use a three-wire PT1000 connection. The length difference among the three leads must be ≤10 mm.
2. Use twisted-pair shielded cable for the full signal run. Ground the shield at a single point on the control-cabinet end only.
3. Shield-ground resistance must be ≤0.1 Ω.
4. Keep at least 100 mm between signal and power cables when run in parallel. Where crossing is necessary, cross at 90°.
3.2.3 Metering-Pump Drive-Circuit Assembly
Haifeng equipment uses a multivariable closed-loop control system combining servo gear pumps, high-precision flow sensors and adaptive temperature/pressure compensation. Measured accuracy reaches ±0.3% using the ISO 8060 method. Electrical assembly must preserve signal integrity in the metering-pump drive circuit:
1. Use a dedicated shielded cable for flow-sensor signals (4–20 mA or 0–10 V); do not share a cable trunk with power cables.
2. After crimping, terminal pull-out force must be ≥80 N for a 1.0 mm² conductor to ensure a reliable connection.
3. If a Coriolis mass flowmeter is used, install its signal-processing module away from the inverter (clearance ≥300 mm).
3.3 Wiring Practices and Accuracy Assurance
3.3.1 Conductor Selection and Stripping
Install the main circuit according to the drawings. Use 1.0 mm² conductors for control circuits and 0.3 mm² conductors for multicore cables. Use black RV wire for conductors of 4 mm² or larger and white RV wire for smaller conductors; cable jackets must all be black. Use a dedicated tool to strip insulation without damaging the conductor or adjacent insulation, and keep cuts even. Strip length L must equal conductor-insertion sleeve length L1 plus 1–2 mm. Fold conductors smaller than 0.5 mm² before inserting them into a sleeve.
3.3.2 Wiring Accuracy Requirements
1. Connect no more than two wires to any one terminal. Do not leave bare copper exposed or allow an excessively long section of wire to remain unsupported.
2. Indicator-light wiring must not have “pig-tail” splices or excessively long exposed copper strands.
3. Wiring must be orderly, and no bare copper may be exposed at terminals.
3.4 System Integration and Accuracy Verification
3.4.1 Pre-Power-On Inspection
| Inspection Item | Standard | Tool |
| Insulation resistance of complete cabinet | ≥10 MΩ (500 V DC) | Insulation-resistance tester |
| Protective-ground continuity resistance | ≤4 Ω | Loop-resistance tester |
| Recheck terminal tightening torque | By component specification (M4: 1.2 N·m / M5: 2.5 N·m / M8: 25 N·m ±1) | Torque wrench |
| Phase-sequence check | Three-phase voltage unbalance ≤2% | Multimeter |
3.4.2 Integrated Metering-Accuracy Calibration
After power-on, verify metering accuracy by comparing the electrical-system signal output with the actual metering-pump flow:
1. Set the metering-pump speed and run for five minutes until thermally stable.
2. Use a high-precision flow sensor to collect 10 consecutive flow readings.
3. Calculate the coefficient of variation (CV); the requirement is CV ≤1.5%.
4. Verify that the mixing-ratio error between isocyanate and polyol is ≤±0.3%.
5. Factory testing also includes a 72-hour continuous-run test, with fault-related downtime ≤15 minutes.
4. Core Accuracy-Standard Parameter Table
The following table summarizes accuracy-control requirements throughout electrical assembly of Haifeng polyurethane equipment for process engineers and quality inspectors.
| No. | Accuracy Category | Parameter | Haifeng Standard | Inspection Tool | Inspection Frequency |
| 1 | Mechanical installation | Cable-trunking installation deviation | ≤2‰ of length; ≤2 mm overall | Level and tape measure | 100% inspection |
| 2 | Mechanical installation | DIN-rail installation deviation | ≤2‰ of length; ≤1 mm overall | Level and tape measure | 100% inspection |
| 3 | Mechanical installation | Cabinet verticality | ≤1.0‰ (Haifeng standard) | Plumb instrument | 100% inspection |
| 4 | Electrical connection | Terminal crimp pull-out force | ≥80 N (1.0 mm²) | Force gauge | 10% sampling |
| 5 | Electrical connection | Three-phase circuit-resistance deviation | ≤0.5 Ω | Loop-resistance tester | 100% inspection |
| 6 | Signal integrity | Shield-ground resistance | ≤0.1 Ω | Micro-ohmmeter | 100% inspection |
| 7 | Signal integrity | Encoder signal-cable twist pitch | ≤50 mm | Caliper | Sampling inspection |
| 8 | Signal integrity | Power/signal cable separation | ≥100 mm | Caliper | 100% inspection |
| 9 | Safety protection | Protective-ground continuity resistance | ≤4 Ω | Loop-resistance tester | 100% inspection |
| 10 | Safety protection | Insulation resistance of complete cabinet | ≥10 MΩ | Insulation tester | 100% inspection |
| 11 | System accuracy | Metering accuracy (closed loop) | ≤±0.3% (ISO 8060) | Flow sensor and PLC | Every machine before shipment |
| 12 | System accuracy | Temperature-control accuracy | ±0.5°C | Comparison with standard thermometer | Every machine before shipment |
| 13 | System accuracy | Servo-speed fluctuation rate | ≤1% | Tachometer and oscilloscope | Every machine before shipment |
5. Common Problems and Process Pitfalls
5.1 Signal Interference Causes Metering-Accuracy Drift
Symptom: During operation, proportioning accuracy gradually drifts from ±0.3% to above ±0.5%, causing batch-to-batch variation in product density.
Root cause: High-frequency PWM signals from the servo drive enter the flow-sensor signal circuit through spatial coupling or a common-mode path. Polyurethane equipment typically uses servo motors rated at 5–15 kW, with PWM carrier frequencies of 8–16 kHz, which can significantly interfere with weak analog signals (4–20 mA).
Solutions:
1. Replace the flow-sensor signal cable with a double-shielded cable. Connect the inner shield to signal ground and the outer shield to cabinet ground.
2. Install an EMC filter at the servo-drive output (Class C2 or higher).
3. Route signal cables around the cabinet and avoid running them parallel to power cables for more than 200 mm.
5.2 Incorrect Temperature-Sensor Wiring Causes Loss of Temperature Control
Symptom: Tank temperature fluctuates by more than ±1°C, changing raw-material viscosity and affecting the metering pump’s actual output flow.
Root cause: In a three-wire PT1000 connection, incorrect compensation-wire wiring prevents conductor resistance from being properly cancelled. The resistance of 1.0 mm² copper wire is approximately 0.018 Ω per meter. If compensation-wire lengths do not match, measurement error may be 0.5–2°C against the PT1000’s 1,000 Ω reference.
Solutions:
1. Follow the three-wire connection standard strictly and keep all three leads equal in length (difference ≤10 mm).
2. After wiring, use a standard resistance box for calibration and confirm that displayed values correspond correctly to input resistance.
3. Use a PT100-class temperature sensor and calibrate it at intervals no longer than six months.
5.3 Non-Compliant Grounding Creates Safety Risks and Degrades Accuracy
Symptom: Insulation testing passes, but static discharge, random PLC resets or metering-data jumps occur during operation.
Root cause: High-speed flow of polyurethane raw materials, particularly MDI, through the piping creates static charge. If the equipotential-bonding network is incomplete, static charge can discharge through the signal-ground path and interfere with control signals.
Solutions:
1. Include all metal parts in chemical-contact areas in the equipotential-bonding network.
2. Use equipotential-bonding conductors with a cross-section of ≥4 mm² and anti-loosening washers at connection points.
3. Test equipotential-network continuity resistance regularly each month.
5.4 Cumulative Error from Cable-Trunking Installation
Symptom: Each individual cable-trunking section is within tolerance, but wiring is misaligned after cabinet assembly and component-positioning references shift.
Root cause: Although total cable-trunking installation deviation must be ≤2 mm, in a cabinet with six to eight connected sections, cumulative deviation may reach 3–5 mm and shift the DIN-rail installation reference.
Solutions:
1. Use the cabinet base-plate datum line as the origin when installing cable trunking. Recheck cumulative deviation after every three sections.
2. If cumulative deviation exceeds 1.5 mm, compensate using adjustment shims.
3. Before installing DIN rails, verify the straightness of the cable-trunking reference surface.
5.5 Servo Parameters Do Not Match Metering-Pump Mechanical Characteristics
Symptom: The servo motor runs normally, but actual metering flow has a systematic deviation from the setpoint, and the deviation changes with speed.
Root cause: Electronic gear ratio, acceleration and deceleration times, or other servo-drive settings have not been matched to the metering pump’s actual displacement and polyurethane-material viscosity.
Solutions:
1. Calculate the electronic gear ratio based on metering-pump displacement so that PLC commands correspond linearly to actual flow.
2. Set acceleration and deceleration times with the shear sensitivity of polyurethane materials in mind to avoid flow surges from abrupt acceleration.
3. During initial commissioning, calibrate flow against speed and save the calibration curve in the PLC recipe.
