1 Introduction
The enamel coating is the core insulation layer of enameled copper wire, and its quality directly determines the dielectric strength, heat resistance, mechanical strength, chemical stability, and long-term reliability of the wire. Enamel coating quality assessment is a crucial step in the production, inspection, procurement, and application of enameled copper wire, and is also a core aspect of winding product quality control.
A systematic evaluation system should be established for judging the quality of qualified enameled copper wire. This article, based on international standards such as NEMA MW 1000-2018, IEC 60317 series, and IEC 60851 test method series, systematically elaborates on the methods, key indicators, qualification thresholds, and judgment procedures for judging the quality of qualified enameled copper wire from five dimensions: appearance, electrical, mechanical, chemical, and environmental. This provides a systematic technical reference for enameled wire production engineers, quality inspectors, purchasing engineers, and end users.
2 Overview of the enamel coating quality assessment system
2.1 enamel coating Function and Failure Modes
The core function of enamel coating is electrical insulation, with additional functions including mechanical protection, chemical protection, and heat conduction. During winding manufacturing and operation, enamel coating withstands various stresses, including bending, tension, friction, thermal shock, chemical corrosion, and moisture erosion. Failure modes of enamel coating include: electrical failure (dielectric breakdown), mechanical failure (enamel coating cracking and peeling), chemical failure (enamel coating swelling and degradation), and thermal failure (enamel coating aging and cracking).
Quality assessment of enamel coatings requires identifying potential failure modes and establishing corresponding test items and assessment criteria. The assessment method should cover the entire lifecycle of the enamel coating, from raw material intake to finished product delivery, from manufacturing processes to operation and maintenance.
2.2 Five-Dimensional System for Quality Evaluation of enamel coating
The quality assessment of qualified enameled copper wire should establish a five-dimensional evaluation system:
Appearance dimensions: color, gloss, uniformity, surface defects, and enamel coating continuity.
Electrical dimensions: breakdown voltage, dielectric loss tangent, volume resistivity, surface resistivity, and number of defects in the enamel coating continuity test.
Mechanical dimensions: flexibility, adhesion, scratch resistance, tensile strength, elongation, and anti-winding properties.
Chemical dimensions: solvent resistance, chemical resistance, hydrolysis resistance, oil resistance, refrigerant resistance, and heat aging resistance.
Environmental dimensions: temperature resistance, damp heat resistance, salt spray resistance, UV resistance, and temperature cycling resistance.
Each dimension includes several specific test items, and each test item corresponds to a clearly defined pass/fail threshold. Quality assessment of the enamel coating should be based on a comprehensive evaluation of the results from all dimensions of the test.
2.3 enamel coating thickness grades
According to the IEC 60317 standard, the thickness of enameled copper wire is divided into three grades: Grade 1 (thin), Grade 2 (thick), and Grade 3 (extra thick). The thickness grade is directly related to key parameters such as dielectric strength, mechanical strength, and winding fill factor.
Different enamel coating thickness grades correspond to different minimum enamel coating thickness and minimum breakdown voltage requirements. Grade 1 enamel coating is suitable for low-voltage scenarios with tight winding space; Grade 2 enamel coating is suitable for medium-voltage scenarios; and Grade 3 enamel coating is suitable for high-voltage scenarios. The selection of the enamel coating thickness grade should be based on a comprehensive consideration of winding design requirements, electrical stress, and mechanical stress.
3 Appearance Judgment
Appearance assessment is the first step in judging the quality of enamel coating and is the simplest preliminary assessment method.
3.1 Color Determination
Qualified enameled copper wire should have a uniform and consistent color, conforming to the typical color characteristics of the nominal enameled coating system. Polyurethane enameled coating is typically light yellow to brownish-yellow, polyester enameled coating is typically dark brown to reddish-brown, polyester imide enameled coating is typically dark brown to brown, and polyamide-imide enameled coating is typically dark brown to black. Slight color variations may exist between different manufacturers and batches, but the color of enameled wire from the same batch should be highly consistent.
Color abnormalities in substandard enamel coatings include: severely uneven color, with obvious color differences within the same section of enameled wire; color deviations from the nominal enamel coating system, such as polyurethane enamel coating appearing dark brown or black; dark or black color with scorch marks, which may be due to excessively high curing temperature or aging of the enamel coating; and excessively light color or excessive gloss, which may be due to the enamel coating being too thin or unevenly applied.
3.2 Gloss Judgment
A qualified enameled copper wire should exhibit a typical luster, with the gloss conforming to the characteristics of the enameled coating system. Polyurethane enameled coatings have a high gloss, polyester enameled coatings have a medium gloss, and polyimide enameled coatings have a low gloss. The gloss of the enameled coating should be uniform and consistent, without obvious haze or loss of gloss.
Unqualified enamel coatings may exhibit abnormal gloss, including: surface haze or loss of gloss, which may be due to incomplete curing or moisture absorption; excessive gloss in certain areas, which may be due to uneven coating thickness; and obvious orange peel or flow marks on the surface, which may be due to abnormal coating process.
3.3 Uniformity Determination
A qualified enameled copper wire should have a uniform thickness, with no obvious unevenness. The uniformity of the enameled coating can be determined by the following methods: visually inspecting the surface for smoothness and consistency; touching the enameled coating to check for thickness consistency; and using an enameled coating thickness gauge to measure the thickness at different locations on the wire and calculating the thickness deviation.
According to IEC 60317 standard, the thickness deviation of the enamel coating should be controlled within ±10% to ±20% of the nominal thickness, depending on the enamel coating grade and conductor diameter. Severe unevenness in enamel coating thickness is unacceptable and may lead to insufficient local dielectric strength and weak mechanical strength.
3.4 Surface Defect Judgment
A qualified enameled copper wire should have a surface free of obvious defects. Common surface defects include: bubbles (pores on or inside the enameled coating, possibly due to air entrapment during the coating process); particles (particles or protrusions on the enameled coating surface, possibly due to environmental or paint contamination); flow marks (marks of flow on the enameled coating surface, possibly due to abnormal coating process); pinholes (tiny holes on the enameled coating surface, possibly due to poor defoaming of the paint or abnormal curing process); and exposed copper (localized missing areas of the enameled coating, exposing the copper conductor, possibly due to missed areas or damage during the coating process).
Surface defects in enamel coatings significantly reduce dielectric strength, mechanical strength, and chemical stability, and are an important indicator of enamel coating quality. According to IEC 60317, the number of surface defects in enamel coatings should be below a specified threshold.
3.5 Continuity Determination of enamel coating
Continuity of the enamel coating is a key aspect of appearance assessment. According to IEC 60851-5, the enamel coating continuity test is conducted in a mercury or brine bath. At the point of enamel coating defect, the copper conductor becomes conductive with the test solution, triggering an alarm. The number of defects in the continuity test should be below the standard threshold, typically no more than 1 to 5 defects per 30 meters of enameled wire.
4 Electrical Judgment
Electrical performance is a core dimension of enamel coating quality assessment, directly verifying the dielectric insulation performance of the enamel coating.
4.1 Breakdown Voltage Determination
Breakdown voltage is a core indicator of dielectric strength and directly determines the insulation reliability of enameled copper wire. According to IEC 60317, the breakdown voltage requirements for enameled round copper wire are as follows: Class 1: approximately 1500 to 7500 volts; Class 2: approximately 2350 to 12000 volts; Class 3: approximately 3000 to 14000 volts, depending on the conductor diameter.
Breakdown voltage test method: According to IEC 60851-3 standard, an increasing AC voltage is applied between the two electrodes of the enameled wire until the enamel coating breaks down, and the breakdown voltage value is recorded. The breakdown voltage value should not be lower than the standard value. A breakdown voltage lower than the standard value indicates that the dielectric strength of the enamel coating is unqualified.
The following points should be considered when determining the breakdown voltage: The test should be conducted under standard environmental conditions, with a temperature of 20 to 25 degrees Celsius and a relative humidity of 50% to 70%; the test voltage should be increased uniformly from zero, with a boost rate typically ranging from 100 to 500 volts per second; the number of test samples should be no less than 5, and the average or median should be used as the judgment value; the breakdown voltage test is destructive to the enamel coating, and the tested samples cannot be reused.
4.2 Determination of the tangent of the dielectric loss angle
The dielectric loss tangent, tan δ, is a key indicator of the dielectric performance of an enamel coating, reflecting its energy loss in an alternating current electric field. A lower dielectric loss tangent indicates better AC insulation performance. According to the IEC 60317 standard, the dielectric loss tangent of an enamel coating is typically no higher than 0.01, depending on the coating system and frequency.
Dielectric loss tangent test method: According to IEC 60851-2 standard, a precision LCR meter or dielectric loss tester is used to measure the dielectric loss tangent of the enamel coating at a specified frequency. Common test frequencies are 1 kHz, 100 kHz, 1 MHz, etc. A dielectric loss tangent higher than the standard value indicates that the dielectric performance of the enamel coating is unqualified.
4.3 Determination of Volume Resistivity
Volume resistivity is a key indicator of enamel coating insulation performance, reflecting its ability to impede current. According to IEC 60317, the volume resistivity of enamel coatings is typically not less than 1 × 10¹³ ohm-cm, depending on the enamel coating system. Polyimide enamel coatings can achieve volume resistivity exceeding 1 × 10¹⁶ ohm-cm.
Volume resistivity test method: According to IEC 60851-2 standard, the volume resistivity of the enamel coating is measured using a high-resistivity meter. The test voltage is typically 100 to 500 volts DC, and the test time is 1 to 10 minutes. A volume resistivity lower than the standard value indicates that the enamel coating’s insulation performance is unqualified.
4.4 Surface Resistivity Determination
Surface resistivity reflects the ability of the enamel coating surface to resist current conduction, and has a significant impact on the creepage and moisture-proof performance of windings. According to IEC 60317 standard, the surface resistivity of enamel coatings is typically not less than 1 × 10¹² ohms per square centimeter. Surface resistivity decreases significantly in humid environments, and the moisture-proof performance of enamel coatings is determined by the surface resistivity after a damp heat test.
4.5 Continuous Electrical Testing of enamel coating
The enamel coating continuity test is an electrical-based method for testing the integrity of the enamel coating, detailed in the appearance assessment section. The number of defects in the enamel coating continuity test should meet the requirements of IEC 60851-5.
5 Mechanical Judgment
Mechanical assessment is an important dimension for evaluating the quality of enamel coatings, verifying their performance under mechanical stress.
5.1 flexibility determination
Flexibility is a core indicator of the mechanical properties of enamel coatings, reflecting their ability to maintain integrity under mechanical stresses such as bending, tension, and torsion. According to IEC 60851-3, enameled round copper wire should not crack or peel when wound with a mandrel diameter of 1d to 5d. d is the nominal diameter of the enameled wire.
The flexibility test method is as follows: Take a section of enameled wire and tightly wind it at least 5 turns around the specified mandrel diameter. Visually inspect the enamel coating for cracks or peeling. Cracks or peeling of the enamel coating indicate a failure to meet flexibility standards. The flexibility test should be conducted at different temperatures, including room temperature and after thermal shock, to evaluate the flexibility of the enamel coating over a wide temperature range.
5.2 Adhesion Determination
Adhesion is an indicator of the bond strength between the enamel coating and the copper conductor, reflecting the enamel coating’s ability to maintain its bond with the conductor under tensile stress. According to IEC 60851-3, the enamel coating should not crack or peel after rapid stretching to a specified elongation. Common test methods include tensile tests and peel tests.
Adhesion test method: Take a section of enameled wire and rapidly stretch it to the specified elongation on a tensile testing machine. Visually inspect the enamel coating for cracks or peeling. Cracks or peeling of the enamel coating indicate unacceptable adhesion.
5.3 Scratch Resistance Assessment
Scratch resistance is an important indicator of the mechanical strength of enamel coatings, reflecting their ability to resist mechanical scratches. According to NEMA MW 1000-2018 Table 51, Grade 1 enamel coatings should withstand at least 5 to 40 scratches, Grade 2 at least 15 to 75 scratches, and Grade 3 at least 25 to 100 scratches, depending on the conductor wire diameter.
Scratch resistance test method: Using an enamel coating scratch tester, a scratching needle is moved back and forth on the enamel coating surface, and the number of times the enamel coating is scratched is recorded. A scratch resistance test result below the standard value indicates failure to meet scratch resistance standards.
5.4 Determination of Tensile Strength and Elongation
The tensile strength and elongation of enameled copper wire reflect the overall effect of the enamel coating on the conductor’s mechanical properties. According to IEC 60317, the elongation of enameled round copper wire should be no less than 25% to 35%, depending on the conductor diameter. The tensile strength is typically no less than 200 to 250 MPa.
Tensile strength and elongation test methods: According to IEC 60851-3 standard, a tensile testing machine is used to perform tensile tests on the enameled wire, and the tensile strength and elongation are recorded. Tensile strength or elongation below the standard value is considered unqualified.
5.5 Anti-winding performance assessment
Anti-winding property refers to the ability of the enamel coating to maintain its integrity under repeated bending. According to IEC 60851-3, the enameled wire should pass a specified repeated winding test, and the enamel coating should not crack or peel. The number of repeated windings is typically no less than 5 to 10.
6 Chemical Determination
Chemical determination verifies the stability of the enamel coating in a chemical medium.
6.1 Solvent Resistance Determination
Solvent resistance reflects the stability of the enamel coating in organic solvents. According to IEC 60851-4, the enamel coating should not soften, bubble, or peel after immersion in a standard solvent. Standard solvents typically include xylene, acetone, and ethanol.
Solvent resistance test method: Immerse the enameled wire in the specified solvent for the specified time, then remove it and visually inspect the condition of the enamel coating. Softening, blistering, or peeling of the enamel coating indicates failure to pass the solvent resistance test.
6.2 Determination of resistance to chemical media
Chemical resistance reflects the stability of enamel coatings in chemical media such as acids, alkalis, and salts. The stability of enamel coatings varies in different chemical media. Polyurethane enamel coatings are sensitive to strong acids and alkalis, polyester imides are stable to many chemical media, and polyimide enamel coatings are stable to the vast majority of chemical media.
Chemical resistance test method: Immerse the enameled wire in a specified chemical medium for a specified time, then remove it and test the breakdown voltage, adhesion, and appearance of the enamel coating. A significant decrease in performance indicates failure to pass the chemical resistance test.
6.3 Determination of Hydrolysis Resistance
Hydrolysis resistance reflects the stability of enamel coatings in water vapor and humid heat environments. Polyurethane enamel coatings have moderate hydrolysis resistance, polyester enamel coatings have poor hydrolysis resistance, and polyimide enamel coatings have excellent hydrolysis resistance.
Hydrolysis resistance test method: According to IEC 60851-4 standard, the enameled wire is exposed to 40 degrees Celsius and 95% relative humidity for a specified time, and the breakdown voltage, adhesion, and appearance of the enamel coating are tested. A significant decrease in performance indicates failure to pass the hydrolysis resistance test.
6.4 Determination of Oil Resistance and Refrigerant Resistance
Oil resistance reflects the stability of the enamel coating in oily media, which is crucial for applications such as automobiles and home appliances. Refrigerant resistance reflects the stability of the enamel coating in refrigerants, which is crucial for applications such as air conditioners and refrigerators.
According to IEC 60851-4 standard, after being immersed in oil or refrigerant for a specified time, the enamel coating of the enameled wire should not soften, blister, peel off, or exhibit a significant decrease in performance.
6.5 Determination of Heat Aging Resistance
Heat aging resistance reflects the stability of the enamel coating under long-term thermal stress. Heat aging resistance is a core verification of the enamel coating’s thermal rating. According to IEC 60172 and IEEE 1776 standards, accelerated heat aging tests should be conducted at three or more temperature points, each lasting until the enamel coating fails or reaches a predetermined endpoint.
Accelerated thermal aging test data were used to plot Arrhenius curves, and the temperature corresponding to a 20,000-hour lifespan, i.e., the enamel coating thermal rating, was extrapolated. The enamel coating thermal rating should meet the nominal thermal rating requirements.
7 Environmental Assessment
Environmental assessment verifies the stability of the enamel coating under extreme environmental conditions.
7.1 Temperature Resistance Determination
Temperature resistance refers to the stability of the enamel coating under high or low temperature conditions. According to IEC 60317 standard, the enamel coating should have a design life of 20,000 hours at its nominal thermal rating. Temperature resistance is verified through accelerated thermal aging tests.
7.2 Determination of resistance to damp heat
Resistance to damp heat reflects the stability of the enamel coating under high temperature and high humidity conditions. According to IEC 60851-4 standard, the performance of the enamel coating should not significantly decrease after exposure to 40 degrees Celsius and 95% relative humidity for a specified period of time.
7.3 Salt spray resistance assessment
Salt spray resistance reflects the stability of enamel coatings in salty and humid environments. According to IEC 60068-2-52, enamel coatings should show no significant corrosion or performance degradation after a salt spray test. Salt spray resistance is crucial for enameled copper wires used in offshore wind power, marine equipment, and chemical industries.
7.4 UV Resistance Determination
UV resistance reflects the stability of the enamel coating under ultraviolet radiation. Enameled copper wires used in outdoor equipment, high-altitude areas with strong UV radiation, and direct sunlight exposure should possess excellent UV resistance. Polyimide enamel coatings exhibit better UV resistance than polyurethane and polyester enamel coatings.
7.5 Temperature Cycling Test
Temperature cycling resistance reflects the stability of the enamel coating under repeated thermal cycling. According to IEC 60068-2-14, the performance of the enamel coating should not significantly degrade after a specified number of cycles within a temperature range of -40 to +155 degrees Celsius or wider. Temperature cycling resistance is crucial for enameled copper wires used in applications with frequent temperature cycling, such as wind power, rail transportation, and outdoor equipment.
8 enamel coating Quality Judgment Process
8.1 Judgment Process
The quality assessment of qualified enameled copper wire should follow a systematic process:
The first step is visual inspection. Inspect the color, gloss, uniformity, surface defects, and continuity of the enamel coating, and reject obviously defective products.
The second step is dimensional assessment. Measure the conductor diameter and enamel coating thickness to determine if they meet standard requirements.
The third step is electrical assessment. This involves testing the breakdown voltage, dielectric loss tangent, volume resistivity, surface resistivity, and the number of continuity defects in the enamel coating.
The fourth step is mechanical assessment. Tests include flexibility, adhesion, scratch resistance, tensile strength, elongation, and anti-winding properties.
Step 5: Chemical assessment. Tests include resistance to solvents, chemical media, hydrolysis, oil, refrigerants, and heat aging.
Step 6, Environmental Assessment. Test for temperature resistance, damp heat resistance, salt spray resistance, UV resistance, and temperature cycling resistance.
Step 7: Comprehensive Judgment. The quality of the enamel coating is comprehensively evaluated based on the results of all-dimensional testing to determine whether it is qualified or not.
8.2 Sampling Plan
The sampling plan for quality assessment of enamel coatings should be determined based on the supplier’s historical quality data and risk level. High-quality suppliers can use a lower sampling frequency and smaller sample size, while new or high-risk suppliers should use a higher sampling frequency and larger sample size.
Common sampling standards include GB/T 2828.1, ISO 2859-1, and ANSI/ASQ Z1.4. Sampling inspection typically uses the Acceptable Quality Level (AQL), which ranges from 0.65 to 2.5, depending on the quality and risk level of the enamel coating.
8.3 Handling of Non-conformities
When the enamel coating fails quality inspection, the non-conforming product handling procedure should be initiated. Non-conforming products should be immediately identified, isolated, and recorded. The cause of the non-conformity should be analyzed, and corrective measures should be taken. Non-conforming products should be handled according to regulations regarding return, acceptance with concessions, downgrading, or scrapping.
Common causes of non-conformity include: substandard raw materials, abnormal coating process, abnormal curing process, abnormal production environment, and abnormal storage conditions. Corresponding corrective actions should be taken for each cause of non-conformity, including replacing raw materials, adjusting process parameters, improving the production environment, and improving storage conditions.
8.4 Continuous Improvement
enamel coating quality assessment is a continuous improvement process. Quality data, including appearance, electrical, mechanical, chemical, and environmental compliance rates, should be regularly analyzed. Based on this data, opportunities for quality improvement should be identified, and quality improvement plans should be developed to drive continuous improvement in enamel coating quality.
9 enamel coating Quality Judgment Case
9.1 Case 1: enamel coating breakdown voltage fails to meet standard
A transformer factory purchased a batch of enameled copper wire labeled as Grade 155, Class F. The measured breakdown voltage was 1800 volts, far below the standard range of 1500 to 7500 volts for Grade 155 enameled copper wire. Visual inspection revealed that the enameled copper wire was too light in color, and thickness measurements showed that the thickness was only 60% of the standard value. Conclusion: Insufficient enameled copper wire thickness caused the breakdown voltage to fail. Reason for failure: Abnormal enameled copper wire coating process, with fewer coating passes.
9.2 Case 2: enamel coatingflexibility non-compliant
A motor factory purchased a batch of enameled copper wire labeled as Grade 180 H. During winding tests, the enamel coating cracked at a 3d mandrel diameter, failing to meet IEC 60851-3 standards. Tensile tests showed the enamel coating elongation was only 8%, far below the standard requirement of 25%. Conclusion: The enamel coating’s flexibility is unqualified. Reason for non-compliance: The enamel coating’s curing temperature was too high, causing it to become brittle.
9.3 Case 3: enamel coating fails heat aging test
A traction motor factory purchased a batch of enameled copper wire labeled as Grade 200 (N grade). After accelerated thermal aging testing at 220 degrees Celsius for 1000 hours, the breakdown voltage of the enameled copper wire decreased by 50%, far below the required lifespan of 20,000 hours. Conclusion: The enameled copper wire fails the thermal aging test; its actual thermal rating is approximately Grade 180 (H grade). Reason for failure: Abnormal enameled copper wire material formulation and insufficient thermal stability.
9.4 Case 4: enamel coating fails to meet chemical resistance standards
A car motor factory purchased a batch of enameled copper wire labeled as Grade 155, Class F. After immersing it in a refrigerant solution at 40 degrees Celsius for 168 hours, the enamel coating blistered and peeled off. Conclusion: The enamel coating fails the refrigerant resistance test. Reason for failure: The enamel coating material is unsuitable for refrigerant environments; a polyurethane-nylon composite enamel coating or a polyamide-imide enamel coating should be used instead.
10 Suggestions for Improving the Quality of enamel coating
10.1 Raw Material Control
The fundamental guarantee of enamel coating quality lies in the quality control of raw materials. The copper conductor should be TU1 oxygen-free copper with a copper content of not less than 99.97% or T2 ordinary electrolytic copper with a copper content of not less than 99.90%, and the surface should be smooth, free of oxidation and impurities. The enamel should be high-quality enamel from reputable manufacturers, with stable performance between batches. The thinner should meet the enamel’s matching requirements and be of qualified purity.
10.2 Coating Process Optimization
The coating process is crucial to the quality of the enamel coating. Coating process parameters include paint viscosity, coating speed, number of coats, curing temperature, and curing time. These parameters should be continuously optimized based on the enamel coating quality assessment results to ensure uniform coating thickness, complete coating, and stable performance.
10.3 Curing Process Optimization
The curing process is another key factor in the quality of enamel coatings. Too low a curing temperature leads to incomplete curing and insufficient performance; too high a curing temperature causes embrittlement and decreased flexibility. Curing process parameters should be continuously optimized based on the quality assessment results to ensure complete curing and excellent performance of the enamel coating.
10.4 Testing Capacity Building
The quality assessment of enamel coatings relies on robust inspection capabilities. Inspection personnel should be professionally trained and possess the necessary inspection skills and quality awareness. Inspection equipment should be regularly calibrated and maintained to ensure inspection accuracy. Inspection methods should comply with international standards, and inspection records should be complete and traceable.
10.5 Supplier Management
Assurance of enamel coating quality requires establishing long-term partnerships with reputable suppliers. Suppliers should possess ISO 9001 quality management system certification, ISO 14001 environmental management system certification, relevant product certifications, third-party type test reports, and production scale and capacity matching. Suppliers should establish a complete quality inspection system, including raw material inspection, process inspection, and final inspection.
11 Conclusion
Determining the quality of qualified enameled copper wire is a crucial step in the production, inspection, procurement, and application of enameled wire. A systematic five-dimensional evaluation system should be established for enameled wire quality assessment, comprehensively evaluating the quality from five dimensions: appearance, electrical properties, mechanical properties, chemical properties, and environmental factors.
The evaluation process includes: Appearance assessment (verifying the color, gloss, uniformity, surface defects, and continuity of the enamel coating); Electrical assessment (verifying the breakdown voltage, dielectric loss tangent, volume resistivity, and surface resistivity of the enamel coating); Mechanical assessment (verifying the flexibility, adhesion, scratch resistance, tensile strength, elongation, and anti-winding properties of the enamel coating); Chemical assessment (verifying the solvent resistance, chemical resistance, hydrolysis resistance, oil resistance, refrigerant resistance, and heat aging resistance of the enamel coating); and Environmental assessment (verifying the temperature resistance, damp heat resistance, salt spray resistance, UV resistance, and temperature cycling resistance of the enamel coating).
The quality assessment of enamel coatings should follow a systematic process, including appearance assessment, dimensional assessment, electrical assessment, mechanical assessment, chemical assessment, environmental assessment, and comprehensive assessment. The assessment process should be based on a reasonable sampling plan and non-conformance handling procedures, continuously improving the quality of enamel coatings through ongoing improvement.
Winding wire engineers and purchasers should establish a systematic quality assessment capability for enamel coating, build long-term cooperative relationships with high-quality suppliers, and jointly ensure the quality of enameled copper wire and the reliability of winding products.
Contact information: E-mail office@cnlpzz.com, WhatsApp 0086-19337889070, Zhengzhou LP Industry Co., Ltd.
Contact Information:
- E-mail: office@cnlpzz.com
- WhatsApp: 0086-19337889070
- Zhengzhou LP Industry Co., Ltd.