INSPECTION OF ENAMELED WIRE

    After the product is manufactured, whether its appearance, size and performance meet the technical standards of the product and the requirements of the user's technical agreement must be judged through inspection. After measurement and test, compared with technical standards of products or technical agreements of users, those meeting the requirements are qualified, otherwise, they are unqualified. Through inspection, it can reflect the stability of enameled wire product quality and the rationality of material technology. Therefore, quality inspection has the function of check, prevention and identification. The inspection contents of enameled wire include: Inspection and measurement of appearance and dimension and performance test. The properties include mechanical properties, chemical properties, thermal properties and electrical properties. Now we mainly explain the appearance and size.

1、 Surface

(appearance) it shall be bright and clean, uniform in color, free of particles, oxidation, hair, internal and external surfaces, black spots, depainting and other defects affecting the performance. The wire arrangement shall be flat and tightly wound on the wire plate, free of crimping, and free of collection and release. There are many factors affecting the surface, which are related to raw materials, equipment, technology, environment and other factors.

2、 Dimensions

1. The dimension of enameled round wire includes: boundary dimension (outer diameter) d, conductor diameter D, conductor deviation △ D, conductor non roundness F, paint film thickness t

A. Outer diameter refers to the diameter measured after the conductor is coated with an insulating film.

B. Conductor diameter refers to the diameter of the wire after the insulation is removed.

C. Conductor deviation refers to the difference between the measured value and the nominal value of conductor diameter.

D. The out of roundness (f) value is the maximum difference between the maximum and minimum readings measured on each section of the conductor.

2. Measurement method

A. Measuring tool: micrometer, accuracy 0.002mm

When the enameled round wire d < 0.100mm, the force is 0.1-1.0n, when D ≥ 0.100mm, the force is 1-8n, and the force is 4-8n for the enameled flat wire.

B. Outer diameter

a. (circular line) when the nominal diameter D of conductor is less than or equal to 0.200 mm, measure the outer diameter once at three locations 1 m away from each other, record three measured values, and take the average value as the outer diameter.

b. When the nominal diameter D of conductor is more than 0.200 mm, the outer diameter of each position is measured three times around the line at two positions 1 m apart, and six measured values are recorded, and the average value is taken as the outer diameter.

c. (flat line) measure the dimension of wide edge and narrow edge once at each position of 100mm3, and take the average value of the three measured values as the boundary dimension of wide edge and narrow edge.

C. Conductor size

a. (round wire) when the nominal diameter D of conductor is ≤ 0.200mm, remove the insulation by any method without damaging the conductor and measure the diameter of the conductor once at three locations 1m away from each other: take the average value as the conductor diameter.

b. When the nominal diameter of the conductor d > o.200mm, remove the insulation by any method without damaging the conductor, measure along the three equally divided positions of the conductor circumference, and take the average of the three measured values as the conductor diameter.

c. (flat wire) at each 10 mm3 position, remove the insulation by any method that does not damage the conductor, measure the size of wide side and narrow side once respectively, and take the average of the three measured values as the conductor size of wide side and narrow side.

D. Calculation

a. Deviation = D measured - D nominal

b. F value = maximum difference of any diameter reading measured on each section of conductor

: T = D-D actual measurement

Example 1: there is a set of qz-2 / 130 0.71omm enameled wire, and the measured value is as follows

Outer diameter: 0.780, 0.778, 0.781, 0.776, 0.779, 0.779;

Conductor diameter: 0.706, 0.709, 0.712. Calculate the outer diameter, conductor diameter, deviation, F value, paint film thickness, and judge whether it is qualified.

Solution: D = (0.780 + 0.778 + 0.781 + 0.776 + 0.779 + 0.779) / 6 = 0.779mm, d = (0.706 + 0.709 + 0.712) / 3 = 0.709mm, deviation = D measured - D nominal = 0.709-0.710 = -0.001mm, f = 0.712-0.706 = 0.006, t = D measured = 0.779-0.709 = 0.070mm

After measurement, the size of the enameled wire meets the standard requirements.

d. Flat line: thickened paint film 0.11 < & ≤ 0.16mm, ordinary paint film 0.06 < & ≤ 0.11mm

A max = a + △ + & Max, Bmax = B + △ + & Max, when the outer diameter of AB does not exceed Amax and Bmax, the allowable film thickness is more than & Max, the deviation of nominal dimension a (b) is less than 3.155 ± 0.030, 3.155 < a (b) < 6.30 ± 0.050, 6.30 < B ≤ 12.50 ± 0.07, 12.50 < B ≤ 16.00 ± 0.100. < p="">

For example, 2: qzyb-2 / 1802.36 × 6.30mm flat wire, the measured dimensions are a: 2.478, 2.471, 2.469; a: 2.341, 2.340, 2.340; B: 6.450, 6.448, 6.448; B: 6.260, 6.258, 6.259. Determine the thickness, outer diameter and conductor of the paint film, and judge whether it is qualified.

Solution: a = (2.478 + 2.471 + 2.469) / 3 = 2.473; b = (6.450 + 6.448 + 6.448) / 3 = 6.449;

a=（2.341+2.340+2.340）/3=2.340；b=（6.260+6.258+6.259）/3=6.259

Film thickness: a side is 2.473-2.340 = 0.133mm; B side is 6.499-6.259 = 0.190mm.

   In addition to the hidden defects or uneven specifications of the semi-finished conductor, the main reasons for the unqualified conductor size are the paying off tension during the painting process, the improper adjustment of the tightness of the felt clamp of each part, or the inflexible rotation of the paying off and guide wheel, and the fine drawing of the wire.

    The unqualified insulation size of the paint film is mainly due to the improper adjustment of the felt tightness, or the improper matching of the mold and the mold not installed properly. In addition, the changes of process speed, viscosity and solid content of paint will also affect the film thickness.

3、 Performance

1. Mechanical properties: including elongation, rebound angle, softness and adhesion, paint scraping, tensile strength and other items.

a. Elongation reflects the plasticity of the material, which is used to evaluate the ductility of enameled wire.

a. The springback angle and softness reflect the elastic deformation of the material, which are used to check the softness of enameled wire.

The elongation, rebound angle and softness reflect the quality of copper and the annealing degree of enameled wire. The main factors affecting the elongation and rebound angle of enameled wire are (1) wire quality; (2) external force; (3) annealing degree.

a. The toughness of the paint film includes winding and stretching, that is, the allowable tensile deformation of the paint film without breaking along with the conductor tensile deformation.

a. The adhesion of the paint film includes rapid breaking and peeling. It mainly tests the adhesion ability of the paint film to the conductor.

3.1.5 the scratch resistance test of the paint film of the enameled wire reflects the strength of the film against mechanical scratch.

2. Heat resistance: including thermal shock and softening breakdown test.

a. The thermal shock of enameled wire is the ability of the film to bear the heat under the action of mechanical stress.

Factors affecting thermal shock: paint, copper wire, enameled process.

b. The softening and breakdown performance of enameled wire is a measure of the ability of the film of enameled wire to withstand heat deformation under the action of mechanical force, that is, the ability of the film under pressure to plasticize and soften under high temperature. The thermal softening and breakdown properties of enameled wire film depend on the molecular structure of the film and the force between the molecular chains.

3. Electrical properties include: breakdown voltage, film continuity and DC resistance test.

a. Breakdown voltage refers to the ability of the paint film of the enameled wire to bear the voltage load. The main factors affecting the breakdown voltage are: (1) film thickness; (2) film roundness; (3) curing degree; (4) external impurities in the film.

b. The continuity test of paint film is also called pinhole test. Its main influencing factors are: (1) raw materials; (2) operation technology; (3) equipment.

c. DC resistance refers to the resistance value measured in unit length. Its main influencing factors are: (1) annealing degree; (2) enameled equipment.

4. Chemical resistance includes solvent resistance and direct welding resistance.

a. Solvent resistance: generally, the enameled wire needs to be impregnated after being wound into a coil. The solvent in the impregnated paint has different swelling effect on the paint film, especially at a higher temperature. The chemical resistance of the enameled wire film mainly depends on the characteristics of the film itself. Under certain conditions of the paint, the enameled technology also has a certain impact on the solvent resistance of the enameled wire.

b. The direct welding performance of enameled wire reflects the ability of solder in the process of winding without removing the paint film. The main factors that affect the weldability are: (1) the influence of technology, (2) the influence of paint,