Product standard
l. Enameled wire
1.1 product standard of enameled round wire: gb6109-90 series standard; zxd/j700-16-2001 industrial internal control standard
1.2 product standard of enamelled flat wire: gb/t7095-1995 series
Standard for test methods of enamelled round and flat wires: gb/t4074-1999
Paper wrapping line
2.1 product standard of paper wrapping round wire: gb7673.2-87
2.2 product standard of paper wrapped flat wire: gb7673.3-87
Standard for test methods of paper wrapped round and flat wires: gb/t4074-1995
standard
Product standard: gb3952.2-89
Method standard: gb4909-85, gb3043-83
Bare copper wire
4.1 product standard of bare copper round wire: gb3953-89
4.2 product standard of bare copper flat wire: gb5584-85
Test method standard: gb4909-85, gb3048-83
Winding wire
Round wire gb6i08.2-85
Flat wire gb6iuo.3-85
The standard mainly emphasizes the specification series and dimension deviation
Foreign standards are as follows:
Japanese product standard sc3202-1988, test method standard: jisc3003-1984
American Standard wml000-1997
International Electrotechnical Commission mcc317
Characteristic use
1. acetal enamelled wire, with heat grade of 105 and 120, has good mechanical strength, adhesion, transformer oil and refrigerant resistance. However, the product has poor moisture resistance, low thermal softening breakdown temperature, weak performance of durable benzene alcohol mixed solvent, and so on. Only a small amount of it is used for winding of oil immersed transformer and oil filled motor.
Enameled wire
Enameled wire
2. the heat grade of the ordinary polyester coating line of polyester and modified polyester is 130, and the heat level of the modified coating line is 155. The mechanical strength of the product is high, and has good elasticity, adhesion, electrical performance and solvent resistance. The weakness is poor heat resistance and impact resistance and low moisture resistance. It is the largest variety in China, accounting for about two-thirds, and widely used in various motor, electrical, instrument, telecommunication equipment and household appliances.
3. polyurethane coating wire; heat grade 130, 155, 180, 200. The main characteristics of this product are direct welding, high frequency resistance, easy coloring and good moisture resistance. It is widely used in electronic appliances and precision instruments, telecommunications and instruments. The weakness of this product is that the mechanical strength is slightly poor, the heat resistance is not high, and the flexibility and adhesion of the production line are poor. Therefore, the production specifications of this product are small and micro fine lines.
4. polyester imide / polyamide composite paint coating wire, heat grade 180 the product has good heat resistance impact performance, high softening and breakdown temperature, excellent mechanical strength, good solvent resistance and frost resistance performance. The weakness is that it is easy to hydrolyze under closed conditions and widely used in winding such as motor, electric apparatus, instrument, electric tool, dry type power transformer and so on.
5. polyester IMIM / polyamide imide composite coating coating wire system is widely used in domestic and foreign heat resistant coating line, its heat grade is 200, the product has high heat resistance, and also has the characteristics of frost resistance, cold resistance and radiation resistance, high mechanical strength, stable electrical performance, good chemical resistance and cold resistance, and strong overload capacity. It is widely used in refrigerator compressor, air conditioning compressor, electric tools, explosion-proof motor and motors and electrical appliances under high temperature, high temperature, high temperature, radiation resistance, overload and other conditions.
test
After the product is manufactured, whether its appearance, size and performance meet the technical standards of the product and the requirements of the technical agreement of the user, it must be judged by inspection. After measurement and test, compared with the technical standards of the product or the technical agreement of the user, the qualified ones are qualified, otherwise, they are unqualified. Through the inspection, the stability of the quality of the coating line and the rationality of the material technology can be reflected. Therefore, the quality inspection has the function of inspection, prevention and identification. The inspection contents of the coating line include: appearance, dimension inspection and measurement and performance test. The performance includes mechanical, chemical, thermal and electrical properties. Now we mainly explain the appearance and size.
surface
(appearance) it shall be smooth and smooth, with uniform color, no particle, no oxidation, hair, internal and external surface, black spots, paint removal and other defects affecting the performance. The line arrangement shall be flat and tightly around the online disk without pressing the line and freely retracting. There are many factors that affect the surface, which are related to raw materials, equipment, technology, environment and other factors.
size
2.1 the dimensions of enameled round wire include: external dimension (outer diameter) d, conductor diameter D, conductor deviation △ D, conductor roundness F, paint film thickness t
2.1.1 outer diameter refers to the diameter measured after the conductor is coated with an insulating paint film.
2.1.2 conductor diameter refers to the diameter of metal wire after the insulation layer is removed.
2.1.3 conductor deviation refers to the difference between the measured value of conductor diameter and the nominal value.
2.1.4 the value of non roundness (f) refers to the maximum difference between the maximum reading and the minimum reading measured on each section of the conductor.
2.2 measurement method
2.2.1 measuring tool: micrometer micrometer, accuracy o.002mm
When the paint wrapped round wire d < 0.100mm, the force is 0.1-1.0n, and the force is 1-8n when the D is ≥ 0.100mm; the force of the paint coated flat line is 4-8n.
2.2.2 outer diameter
2.2.2.1 (circle line) when the nominal diameter of conductor D is less than 0.200mm, measure the outer diameter once at 3 positions 1m away, record 3 measurement values, and take the average value as the outer diameter.
2.2.2.2 when the nominal diameter of conductor D is greater than 0.200mm, the outer diameter is measured 3 times in each position at two positions 1m apart, and 6 measurement values are recorded, and the average value is taken as the outer diameter.
2.2.2.3 the dimension of wide edge and narrow edge shall be measured once at 100mm3 positions, and the average value of the three measured values shall be taken as the overall dimension of wide edge and narrow edge.
2.2.3 conductor size
2.2.3.1 (circular wire) when the nominal diameter of conductor D is less than 0.200mm, the insulation shall be removed by any method without damage to the conductor at 3 positions 1m away from each other. The diameter of the conductor shall be measured once: take its average value as the conductor diameter.
2.2.3.2 when the nominal diameter of conductor D is greater than o.200mm, remove the insulation by any method without damage to the conductor, and measure separately at three positions evenly distributed along the conductor circumference, and take the average value of the three measurement values as the conductor diameter.
2.2.2.3 (flat wire) is 10 mm3 apart, and the insulation shall be removed by any method without damage to the conductor. The dimension of wide edge and narrow edge shall be measured once respectively, and the average value of the three measurement values shall be taken as the conductor size of wide edge and narrow edge.
2.3 calculation
2.3.1 deviation = D measured – D nominal
2.3.2 f = maximum difference in any diameter reading measured on each section of the conductor
2.3.3t = D-D measurement
Example 1: there is a plate of qz-2/130 0.71omm enameled wire, and the measurement value is as follows
The outer diameter: 0.780, 0.778, 0.781, 0.776, 0.779, 0.779; conductor diameter: 0.706, 0.709, 0.712. The outer diameter, conductor diameter, deviation, F value, paint film thickness are calculated and the qualification is judged.
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 nominal = 0.709-0.710=-0.001mm, f = 0.712-0.706=0.006, t = D-D measured value = 0.779-0.709=0.070mm
The measurement shows that the size of the coating line meets the standard requirements.
2.3.4 flat line: thickened paint film 0.11 < & ≤ 0.16mm, ordinary paint film 0.06 ＜ & < 0.11mm
Amax = a + △ + &max, Bmax = b+ △ + &max, when the outer diameter of AB is not more than Amax and Bmax, the film thickness is allowed to exceed &max, the deviation of nominal dimension a (b) a (b) ＜ 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.
For example, 2: the existing flat line qzyb-2/180 2.36 × 6.30mm, the measured dimensions 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. The thickness, outer diameter and conductor of the paint film are calculated and the qualification is judged.
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: 2.473-2.340=0.133mm on side a and 6.499-6.259=0.190mm on side B.
The reason for the unqualified conductor size is mainly due to the tension of setting out during painting, improper adjustment of the tightness of felt clips in each part, or inflexible rotation of setting out and guide wheel, and drawing the wire fine except for the hidden defects or uneven specifications of semi-finished conductor.
The main reason for the unqualified insulation size of paint film is that the felt is not properly adjusted, or the mold is not properly fitted and the mold is not installed properly. In addition, the change of process speed, viscosity of paint, solid content and so on will also affect the thickness of paint film.

performance
3.1 mechanical properties: including elongation, rebound angle, softness and adhesion, paint scraping, tensile strength, etc.
3.1.1 the elongation reflects the plasticity of the material, which is used to evaluate the ductility of the enameled wire.
3.1.2 springback angle and softness reflect the elastic deformation of materials, which can be used to evaluate the softness of enameled wire.
The elongation, springback angle and softness reflect the quality of copper and the annealing degree of enameled wire. The main factors affecting the elongation and springback angle of enameled wire are (1) wire quality; (2) external force; (3) annealing degree.
3.1.3 the toughness of paint film includes winding and stretching, that is, the allowable stretching deformation of paint film that does not break with the stretching deformation of conductor.
3.1.4 the adhesion of paint film includes rapid breaking and peeling. The adhesion ability of paint film to conductor is mainly evaluated.
3.1.5 scratch resistance test of enameled wire paint film reflects the strength of paint film against mechanical scratch.
3.2 heat resistance: including thermal shock and softening breakdown test.
3.2.1 the thermal shock of enameled wire is the thermal endurance of the coating film of bulk enameled wire under the action of mechanical stress.
Factors affecting thermal shock: paint, copper wire and enamelling process.
3.2.3 the softening and breakdown performance of enameled wire is a measure of the ability of the paint film of enameled wire to withstand thermal deformation under mechanical force, that is, the ability of the paint film under pressure to plasticize and soften at high temperature. The thermal softening and breakdown performance of enameled wire film depends on the molecular structure of the film and the force between the molecular chains.
3.3 electrical properties include: breakdown voltage, film continuity and DC resistance test.
3.3.1 breakdown voltage refers to the voltage load capacity of the enameled wire film. The main factors affecting the breakdown voltage are: (1) film thickness; (2) film roundness; (3) curing degree; (4) impurities in the film.
3.3.2 film continuity test is also called pinhole test. Its main influencing factors are: (1) raw materials; (2) operation process; (3) equipment.
3.3.3 DC resistance refers to the resistance value measured in unit length. It is mainly affected by: (1) annealing degree; (2) enameled equipment.
3.4 chemical resistance includes solvent resistance and direct welding.
3.4.1 solvent resistance: generally, the enameled wire has to go through the impregnation process after winding. The solvent in the impregnating varnish has different degrees of swelling effect on the paint film, especially at higher temperature. The chemical resistance of the enameled wire film is mainly determined by the characteristics of the film itself. Under certain conditions of the paint, the enameled process also has a certain influence on the solvent resistance of the enameled wire.
3.4.2 the direct welding performance of enameled wire reflects the solder ability of enameled wire in the process of winding without removing the paint film. The main factors affecting the direct solderability are: (1) the influence of technology, (2) the influence of paint.

performance
3.1 mechanical properties: including elongation, rebound angle, softness and adhesion, paint scraping, tensile strength, etc.
3.1.1 elongation reflects the plasticity of the material and is used to evaluate the ductility of the enameled wire.
3.1.2 springback angle and softness reflect the elastic deformation of the material and can be used to evaluate the softness of the enameled wire.
Elongation, springback angle and softness reflect the quality of copper and the annealing degree of enameled wire. The main factors affecting the elongation and springback angle of enameled wire are (1) wire quality; (2) external force; (3) annealing degree.
3.1.3 the toughness of paint film includes winding and stretching, that is, the allowable tensile deformation of paint film does not break with the tensile deformation of conductor.
3.1.4 film adhesion includes rapid fracture and spalling. The adhesion ability of paint film to conductor was evaluated.
3.1.5 the scratch resistance test of enameled wire film reflects the strength of the film against mechanical scratch.
3.2 heat resistance: including thermal shock and softening breakdown test.
3.2.1 thermal shock of enameled wire refers to the heat resistance of coating film of bulk enameled wire under mechanical stress.
Factors affecting thermal shock: paint, copper wire and enamelling process.
3.2.3 the softening and breakdown performance of enameled wire is a measure of the ability of the enameled wire film to withstand thermal deformation under the action of mechanical force, that is, the ability of the film to plasticize and soften under high temperature under the action of pressure. The thermal softening and breakdown properties of enameled wire film depend on the molecular structure and the force between molecular chains.
3.3 electrical performance includes: breakdown voltage, film continuity and DC resistance test.
3.3.1 breakdown voltage refers to the voltage loading capacity of enameled wire film. The main factors affecting the breakdown voltage are: (1) film thickness; (2) film roundness; (3) curing degree; (4) impurities in the film.
3.3.2 film continuity test is also called pinhole test. The main influencing factors are: (1) raw materials; (2) operation process; (3) equipment.
3.3.3 DC resistance refers to the resistance value measured in unit length. It is mainly affected by the following factors: (1) annealing degree; (2) enamel equipment.
3.4 chemical resistance includes solvent resistance and direct welding.
3.4.1 solvent resistance: generally, the enameled wire should be impregnated after winding. The solvent in the impregnating varnish has different swelling effect on the film, especially at higher temperature. The chemical resistance of enameled wire film is mainly determined by the characteristics of the film itself. Under certain conditions of the coating, the coating process also has a certain influence on the solvent resistance of the enameled wire.
3.4.2 the direct welding performance of enameled wire reflects the welding ability of enameled wire in the winding process without removing the paint film. The main factors affecting the direct solderability are: (1) the influence of technology, (2) the influence of coating

technological process
Pay off → annealing → painting → baking → cooling → lubrication → take up
Setting out
In a normal operation of the enameller, most of the operator’s energy and physical strength are consumed in the pay off part. Replacing the pay off reel makes the operator pay a lot of labor, and the joint is easy to produce quality problems and operation failure. The effective method is large capacity setting out.
The key to pay off is to control the tension. When the tension is high, it will not only make the conductor thin, but also affect many properties of enameled wire. From the appearance, the thin wire has poor gloss; from the performance point of view, the elongation, resilience, flexibility and thermal shock of the enameled wire are affected. The tension of pay off line is too small, the line is easy to jump, which causes the draw line and the line to touch the furnace mouth. When setting out, the most fear is that the half circle tension is large and the half circle tension is small. This will not only make the wire loose and broken, but also cause the large beating of the wire in the oven, resulting in the failure of wire merging and touching. Pay off tension should be even and proper.
It is very helpful to install the power wheel set in front of the annealing furnace to control the tension. The maximum non elongation tension of flexible copper wire is about 15kg / mm2 at room temperature, 7kg / mm2 at 400 ℃, 4kg / mm2 at 460 ℃ and 2kg / mm2 at 500 ℃. In the normal coating process of enameled wire, the tension of enameled wire should be significantly less than the non extension tension, which should be controlled at about 50%, and the setting out tension should be controlled at about 20% of the non extension tension.
Radial rotation type pay off device is generally used for large size and large capacity spool; over end type or brush type pay off device is generally used for medium size conductor; brush type or double cone sleeve type pay off device is generally used for micro size conductor.
No matter which pay off method is adopted, there are strict requirements for the structure and quality of bare copper wire reel
—-The surface should be smooth to ensure that the wire is not scratched
—-There are 2-4mm radius r angles on both sides of the shaft core and inside and outside of the side plate, so as to ensure the balanced setting out in the process of setting out
—-After the spool is processed, the static and dynamic balance tests must be carried out
—-The diameter of the shaft core of the brush pay off device: the diameter of the side plate is less than 1:1.7; the diameter of the over end pay off device is less than 1:1.9, otherwise the wire will be broken when pay off to the shaft core.

annealing
The purpose of annealing is to make the conductor harden due to the lattice change in the drawing process of the die heated at a certain temperature, so that the softness required by the process can be restored after the molecular lattice rearrangement. At the same time, the residual lubricant and oil on the surface of the conductor during the drawing process can be removed, so that the wire can be easily painted and the quality of the enameled wire can be ensured. The most important thing is to ensure that the enameled wire has appropriate flexibility and elongation in the process of using as winding, and it helps to improve the conductivity at the same time.
The greater the deformation of conductor, the lower the elongation and the higher the tensile strength.
There are three common ways to anneal copper wire: coil annealing; continuous annealing on wire drawing machine; continuous annealing on enamelling machine. The former two methods can not meet the requirements of enamelling process. The coil annealing can only soften the copper wire, but the degreasing is not complete. Because the wire is soft after annealing, the bending is increased during paying off. Continuous annealing on the wire drawing machine can soften the copper wire and remove the surface grease, but after annealing, the soft copper wire wound on the coil and formed a lot of bending. Continuous annealing before painting on the enameller can not only achieve the purpose of softening and degreasing, but also the annealed wire is very straight, directly into the painting device, and can be coated with uniform paint film.
The temperature of annealing furnace should be determined according to the length of annealing furnace, copper wire specification and line speed. At the same temperature and speed, the longer the annealing furnace is, the more fully the recovery of the conductor lattice is. When the annealing temperature is low, the higher the furnace temperature is, the better the elongation is. But when the annealing temperature is very high, the opposite phenomenon will appear. The higher the annealing temperature is, the smaller the elongation is, and the surface of the wire will lose luster, even brittle.
Too high temperature of annealing furnace not only affects the service life of the furnace, but also easily burns the wire when it is stopped for finishing, broken and threaded. The maximum temperature of annealing furnace should be controlled at about 500 ℃. It is effective to select the temperature control point at the approximate position of static and dynamic temperature by adopting two-stage temperature control for the furnace.
Copper is easy to oxidize at high temperature. Copper oxide is very loose, and the paint film can not be firmly attached to the copper wire. Copper oxide has catalytic effect on the aging of the paint film, and has adverse effects on the flexibility, thermal shock and thermal aging of the enameled wire. If the copper conductor is not oxidized, it is necessary to keep the copper conductor out of contact with oxygen in the air at high temperature, so there should be protective gas. Most annealing furnaces are water sealed at one end and open at the other. The water in annealing furnace water tank has three functions: closing furnace mouth, cooling wire, generating steam as protective gas. At the beginning of start-up, because there is little steam in the annealing tube, air can not be removed in time, so a small amount of alcohol water solution (1:1) can be poured into the annealing tube. (pay attention not to pour pure alcohol and control the dosage)
The water quality in the annealing tank is very important. Impurities in the water will make the wire unclean, affect the painting, unable to form a smooth film. The chlorine content of reclaimed water should be less than 5mg / L, and the conductivity should be less than 50 μ Ω / cm. Chloride ions attached to the surface of copper wire will corrode copper wire and paint film after a period of time, and produce black spots on the surface of wire in the paint film of enameled wire. In order to ensure the quality, the sink must be cleaned regularly.
The water temperature in the tank is also required. High water temperature is conducive to the occurrence of steam to protect the annealed copper wire. The wire leaving the water tank is not easy to carry water, but it is not conducive to the cooling of the wire. Although the low water temperature plays a cooling role, there is a lot of water on the wire, which is not conducive to the painting. Generally, the water temperature of thick line is lower, and that of thin line is higher. When the copper wire leaves the water surface, there is the sound of vaporizing and splashing water, indicating that the water temperature is too high. Generally, the thick line is controlled at 50 ~ 60 ℃, the middle line is controlled at 60 ~ 70 ℃, and the thin line is controlled at 70 ~ 80 ℃. Because of its high speed and serious water carrying problem, the fine line should be dried by hot air.

Painting
Painting is the process of coating the coating wire on the metal conductor to form a uniform coating with a certain thickness. This is related to several physical phenomena of liquid and painting methods.
1. physical phenomena
1) Viscosity when the liquid flows, the collision between molecules causes one molecule to move with another layer. Because of the interaction force, the latter layer of molecules obstructs the movement of the previous layer of molecules, thus showing the activity of stickiness, which is called viscosity. Different painting methods and different conductor specifications require different viscosity of paint. The viscosity is mainly related to the molecular weight of resin, the molecular weight of resin is large, and the viscosity of paint is large. It is used to paint rough line, because the mechanical properties of the film obtained by the high molecular weight are better. The resin with small viscosity is used for coating fine line, and the resin molecular weight is small and easy to be coated evenly, and the paint film is smooth.
2) There are molecules around the molecules inside the surface tension liquid. The gravity between these molecules can reach a temporary balance. On the one hand, the force of a layer of molecules on the surface of the liquid is subject to the gravity of the liquid molecules, and its force points to the depth of the liquid, on the other hand, it is subject to the gravity of the gas molecules. However, the gas molecules are less than the liquid molecules and are far away. Therefore, the molecules in the surface layer of the liquid can be achieved Due to the gravity inside the liquid, the surface of the liquid shrinks as much as possible to form a round bead. The surface area of the sphere is the smallest in the same volume geometry. If the liquid is not affected by other forces, it is always spherical under the surface tension.
According to the surface tension of paint liquid surface, the curvature of uneven surface is different, and the positive pressure of each point is unbalanced. Before entering the paint coating furnace, the paint liquid at the thick part flows to the thin place by the surface tension, so that the paint liquid is uniform. This process is called leveling process. The uniformity of paint film is affected by the effect of leveling, and also affected by gravity. It is both The result of the resultant force.
After the felt is made with paint conductor, there is a process of pulling round. Because the wire is coated with felt, the shape of the paint liquid is olive shaped. At this time, under the action of surface tension, the paint solution overcomes the viscosity of the paint itself and turns into a circle in a moment. The drawing and rounding process of paint solution is shown in the figure:
1 – paint conductor in felt 2 – moment of felt output 3 – paint liquid is rounded due to surface tension
If the wire specification is small, the viscosity of paint is smaller, and the time required for circle drawing is less; if the wire specification increases, the viscosity of paint increases, and the required round time is also larger. In high viscosity paint, sometimes the surface tension can not overcome the internal friction of the paint, which causes uneven paint layer.
When the coated wire is felt, there is still a gravity problem in the process of drawing and rounding the paint layer. If the pulling circle action time is short, the sharp angle of olive will disappear quickly, the effect time of gravity action on it is very short, and the paint layer on the conductor is relatively uniform. If the drawing time is longer, the sharp angle at both ends has a long time and the gravity action time is longer. At this time, the paint liquid layer at the sharp corner has the downward flow trend, which makes the paint layer in local areas thickened, and the surface tension causes the paint liquid to pull into a ball and become particles. Because gravity is very prominent when the paint layer is thick, it is not allowed to be too thick when each coating is applied, which is one of the reasons why “thin paint is used for coating more than one coat” when coating the coating line.
When coating fine line, if thick, it contracts under the action of surface tension, forming wavy or bamboo shaped wool.
If there is very fine burr on the conductor, the burr is not easy to paint under the action of surface tension, and it is easy to lose and thin, which causes the needle hole of the enameled wire.
If the round conductor is oval, under the action of additional pressure, the paint liquid layer is thin at the two ends of the elliptical long axis and thicker at the two ends of the short axis, which results in a significant non-uniformity phenomenon. Therefore, the roundness of round copper wire used for enameled wire shall meet the requirements.
When the bubble is produced in paint, the bubble is the air wrapped in the paint solution during stirring and feeding. Because of the small air proportion, it rises to the external surface by buoyancy. However, due to the surface tension of the paint liquid, the air cannot break through the surface and remain in the paint liquid. This kind of paint with air bubble is applied to the wire surface and enters the paint wrapping furnace. After heating, the air expands rapidly, and the paint liquid is painted When the surface tension of liquid is reduced due to heat, the surface of the coating line is not smooth.
3) The phenomenon of wetting is that mercury drops shrink into ellipses on the glass plate, and the water drops expand on the glass plate to form a thin layer with slightly convex center. The former is non wetting phenomenon, and the latter is humid phenomenon. Wetting is a manifestation of molecular forces. If the gravity between molecules of a liquid is less than that between liquid and solid, the liquid moistens the solid, and then the liquid can be evenly coated on the surface of the solid; if the gravity between the molecules of the liquid is greater than that between the liquid and the solid, the liquid cannot wet the solid, and the liquid will shrink into a mass on the solid surface It’s a group. All liquids can moisten some solids, not others. The angle between the tangent line of the liquid level and the tangent line of the solid surface is called contact angle. The contact angle is less than 90 ° liquid wet solid, and the liquid does not wet the solid at 90 ° or more.
If the surface of copper wire is bright and clean, a layer of paint can be applied. If the surface is stained with oil, the contact angle between the conductor and the paint liquid interface is affected. The paint liquid will change from wetting to non wetting. If the copper wire is hard, the surface molecular lattice arrangement irregularly has little attraction on the paint, which is not conducive to the wetting of the copper wire by the lacquer solution.
4) Capillary phenomenon the liquid in the pipe wall is increased, and the liquid that does not moisten the wall of the pipe decreases in the tube is called capillary phenomenon. This is due to the wetting phenomenon and the effect of surface tension. Felt painting is to use capillary phenomenon. When the liquid moistens the pipe wall, the liquid rises along the pipe wall to form a concave surface, which increases the surface area of the liquid, and the surface tension should make the surface of the liquid shrink to the minimum. Under this force, the liquid level will be horizontal. The liquid in the pipe will rise with the increase until the effect of wetting and surface tension pulling upward and the weight of the liquid column in the pipe reaches the balance, the liquid in the pipe will stop Stop rising. The finer the capillary, the smaller the specific gravity of the liquid, the smaller the contact angle of wetting, the greater the surface tension, the higher the liquid level in the capillary, the more obvious the capillary phenomenon.

2. Felt painting method
The structure of the felt painting method is simple and the operation is convenient. As long as the felt is clamped flat on the two sides of the wire with the felt splint, the loose, soft, elastic and porous characteristics of the felt are used to form the mold hole, scrape off the excess paint on the wire, absorb, store, transport and make up the paint liquid through the capillary phenomenon, and apply the uniform paint liquid on the surface of the wire.
The felt coating method is not suitable for the enameled wire paint with too fast solvent volatilization or too high viscosity. Too fast solvent volatilization and too high viscosity will block the pores of the felt and quickly lose its good elasticity and capillary siphon ability.
When using felt painting method, attention must be paid to:
1) The distance between the felt clamp and the oven inlet. Considering the resultant force of leveling and gravity after painting, the factors of line suspension and paint gravity, the distance between felt and paint tank (horizontal machine) is 50-80mm, and the distance between felt and furnace mouth is 200-250mm.
2) Specifications of felt. When coating coarse specifications, the felt is required to be wide, thick, soft, elastic, and has many pores. The felt is easy to form relatively large mold holes in the painting process, with a large amount of paint storage and fast delivery. It is required to be narrow, thin, dense and with small pores when applying fine thread. The felt can be wrapped with cotton wool cloth or T-shirt cloth to form a fine and soft surface, so that the amount of painting is small and uniform.
Requirements for dimension and density of coated felt
Specification mm width × thickness density g / cm3 specification mm width × thickness density g / cm3
0.8~2.5 50×16 0.14~0.16 0.1~0.2 30×6 0.25~0.30
0.4~0.8 40×12 0.16~0.20 0.05~0.10 25×4 0.30~0.35
20 ~ 0.250.05 below 20 × 30.35 ~ 0.40
3) The quality of felt. High quality wool felt with fine and long fiber is required for painting (synthetic fiber with excellent heat resistance and wear resistance has been used to replace wool felt in foreign countries). 5%, pH = 7, smooth, uniform thickness.
4) Requirements for felt splint. The splint must be planed and processed accurately, without rust, keeping a flat contact surface with the felt, without bending and deformation. Different weight splints should be prepared with different wire diameters. The tightness of felt should be controlled by the self gravity of splint as far as possible, and it should be avoided to be compressed by screw or spring. The method of self gravity compaction can make the coating of each thread quite consistent.
5) The felt should be well matched with the paint supply. Under the condition that the paint material remains unchanged, the amount of paint supply can be controlled by adjusting the rotation of the paint conveying roller. The position of the felt, splint and conductor shall be arranged so that the forming die hole is level with the conductor, so as to maintain the uniform pressure of the felt on the conductor. The horizontal position of the horizontal enamelling machine’s guide wheel should be lower than the top of the enamelling roller, and the height of the top of the enamelling roller and the center of the felt interlayer must be on the same horizontal line. In order to ensure the film thickness and finish of enameled wire, it is appropriate to use small circulation for paint supply. The paint liquid is pumped into the large paint box, and the circulation paint is pumped into the small paint tank from the large paint box. With the consumption of paint, the small paint tank is continuously supplemented by the paint in the large paint box, so that the paint in the small paint tank maintains uniform viscosity and solid content.
6) After being used for a period of time, the pores of the coated felt will be blocked by copper powder on the copper wire or other impurities in the paint. The broken wire, sticking wire or joint in the production will also scratch and damage the soft and even surface of the felt. The surface of the wire will be damaged by long-term friction with the felt. The temperature radiation at the furnace mouth will harden the felt, so it needs to be replaced regularly.
7) Felt painting has its inevitable disadvantages. Frequent replacement, low utilization rate, increased waste products, large loss of felt; the film thickness between lines is not easy to reach the same; it is easy to cause film eccentricity; speed is limited. Because the friction caused by relative movement between the wire and felt when the wire speed is too fast, it will produce heat, change the viscosity of paint, and even burn the felt; improper operation will bring the felt into the furnace and cause fire Accidents; there are felt wires in the film of enameled wire, which will have adverse effects on high temperature resistant enameled wire; high viscosity paint can not be used, which will increase the cost.

3. Painting pass
The number of painting passes is affected by solid content, viscosity, surface tension, contact angle, drying speed, painting method and coating thickness. The general enameled wire paint must be coated and baked for many times to make the solvent evaporate fully, the resin reaction is complete, and a good film is formed.
Paint speed paint solid content surface tension paint viscosity paint method
Fast and slow high and low size thick and thin high and low felt mold
How many times of painting
The first coating is the key. If it is too thin, the film will produce certain air permeability, and the copper conductor will be oxidized, and finally the surface of the enameled wire will flower. If it is too thick, the cross-linking reaction may not be sufficient and the adhesion of the film will decrease, and the paint will shrink at the tip after breaking.
The last coating is thinner, which is beneficial to the scratch resistance of enameled wire.
In the production of fine specification line, the number of painting passes directly affects the appearance and pinhole performance.

baking
After the wire is painted, it enters the oven. First, the solvent in the paint is evaporated, and then solidified to form a layer of paint film. Then, it is painted and baked. The whole process of baking is completed by repeating this for several times.
1. Distribution of oven temperature
The distribution of oven temperature has a great influence on the baking of enameled wire. There are two requirements for the distribution of oven temperature: longitudinal temperature and transverse temperature. The longitudinal temperature requirement is curvilinear, that is, from low to high, and then from high to low. The transverse temperature should be linear. The uniformity of transverse temperature depends on the heating, heat preservation and hot gas convection of the equipment.
The enamelling process requires that the enamelling furnace should meet the requirements of
a) Accurate temperature control, ± 5 ℃
b) The furnace temperature curve can be adjusted, and the maximum temperature of curing zone can reach 550 ℃
c) The transverse temperature difference shall not exceed 5 ℃.
There are three kinds of temperature in oven: heat source temperature, air temperature and conductor temperature. Traditionally, the furnace temperature is measured by the thermocouple placed in the air, and the temperature is generally close to the temperature of the gas in the furnace. T-source > t-gas > T-paint > t-wire (T-paint is the temperature of physical and chemical changes of paint in the oven). Generally, T-paint is about 100 ℃ lower than t-gas.
The oven is divided into evaporation zone and solidification zone longitudinally. The evaporation area is dominated by evaporation solvent, and the curing area is dominated by curing film.
2. Evaporation
After the insulating paint is applied to the conductor, the solvent and diluent are evaporated during baking. There are two forms of liquid to gas: evaporation and boiling. The molecules on the liquid surface entering the air is called evaporation, which can be carried out at any temperature. Affected by temperature and density, high temperature and low density can accelerate evaporation. When the density reaches a certain amount, the liquid will no longer evaporate and become saturated. The molecules inside the liquid turn into gas to form bubbles and rise to the surface of the liquid. The bubbles burst and release steam. The phenomenon that the molecules inside and on the surface of the liquid vaporize at the same time is called boiling.
The film of enameled wire is required to be smooth. The vaporization of solvent must be carried out in the form of evaporation. Boiling is absolutely not allowed, otherwise bubbles and hairy particles will appear on the surface of enameled wire. With the evaporation of the solvent in the liquid paint, the insulating paint becomes thicker and thicker, and the time for the solvent inside the liquid paint to migrate to the surface becomes longer, especially for the thick enameled wire. Due to the thickness of the liquid paint, the evaporation time needs to be longer to avoid the vaporization of the internal solvent and get a smooth film.
The temperature of the evaporation zone depends on the boiling point of the solution. If the boiling point is low, the temperature of the evaporation zone will be lower. However, the temperature of the paint on the surface of the wire is transferred from the furnace temperature, plus the heat absorption of the solution evaporation, the heat absorption of the wire, so the temperature of the paint on the surface of the wire is much lower than the furnace temperature.
Although there is evaporation stage in the baking of fine-grained enamels, the solvent evaporates in a very short time due to the thin coating on the wire, so the temperature in the evaporation zone can be higher. If the film needs lower temperature during curing, such as polyurethane enameled wire, the temperature in the evaporation zone is higher than that in the curing zone. If the temperature of evaporation zone is low, the surface of enameled wire will form shrinkable hairs, sometimes like wavy or slubby, sometimes concave. This is because a uniform layer of paint is formed on the wire after the wire is painted. If the film is not baked quickly, the paint shrinks due to the surface tension and wetting angle of the paint. When the temperature of the evaporation area is low, the temperature of the paint is low, the evaporation time of the solvent is long, the mobility of the paint in the solvent evaporation is small, and the leveling is poor. When the temperature of the evaporation area is high, the temperature of the paint is high, and the evaporation time of the solvent is long Evaporation time is short, the movement of the liquid paint in the solvent evaporation is large, the leveling is good, and the surface of the enameled wire is smooth.
If the temperature in the evaporation zone is too high, the solvent in the outer layer will evaporate rapidly as soon as the coated wire enters the oven, which will form “jelly” quickly, thus hindering the outward migration of the inner layer solvent. As a result, a large number of solvents in the inner layer will be forced to evaporate or boil after entering the high temperature zone along with the wire, which will destroy the continuity of the surface paint film and cause pinholes and bubbles in the paint film And other quality problems.

3. curing
The wire enters the curing area after evaporation. The main reaction in the curing area is the chemical reaction of paint, that is, the crosslinking and curing of paint base. For example, polyester paint is a kind of paint film which forms a net structure by crosslinking the tree ester with linear structure. Curing reaction is very important, it is directly related to the performance of the coating line. If curing is not enough, it can affect the flexibility, solvent resistance, scratch resistance and softening breakdown of the coating wire. Sometimes, although all the performances were good at that time, the film stability was poor, and after a period of storage, the performance data decreased, even unqualified. If the curing is too high, the film becomes brittle, flexibility and thermal shock will decrease. Most of the enameled wires can be determined by the color of the paint film, but because the coating line is baked many times, it is not comprehensive to judge only from the appearance. When the internal curing is not enough and the external curing is very sufficient, the color of the coating line is very good, but the peeling property is very poor. The thermal aging test may lead to the coating sleeve or large peeling. On the contrary, when the internal curing is good but the external curing is insufficient, the color of the coating line is also good, but the scratch resistance is very poor.
On the contrary, when the internal curing is good but the external curing is insufficient, the color of the coating line is also good, but the scratch resistance is very poor.
The wire enters the curing area after evaporation. The main reaction in the curing area is the chemical reaction of paint, that is, the crosslinking and curing of paint base. For example, polyester paint is a kind of paint film which forms a net structure by crosslinking the tree ester with linear structure. Curing reaction is very important, it is directly related to the performance of the coating line. If curing is not enough, it can affect the flexibility, solvent resistance, scratch resistance and softening breakdown of the coating wire.
If curing is not enough, it can affect the flexibility, solvent resistance, scratch resistance and softening breakdown of the coating wire. Sometimes, although all the performances were good at that time, the film stability was poor, and after a period of storage, the performance data decreased, even unqualified. If the curing is too high, the film becomes brittle, flexibility and thermal shock will decrease. Most of the enameled wires can be determined by the color of the paint film, but because the coating line is baked many times, it is not comprehensive to judge only from the appearance. When the internal curing is not enough and the external curing is very sufficient, the color of the coating line is very good, but the peeling property is very poor. The thermal aging test may lead to the coating sleeve or large peeling. On the contrary, when the internal curing is good but the external curing is insufficient, the color of the coating line is also good, but the scratch resistance is very poor. In curing reaction, the density of solvent gas or humidity in the gas mostly affect the film formation, which makes the film strength of the coating line decrease and the scratch resistance is affected.
Most of the enameled wires can be determined by the color of the paint film, but because the coating line is baked many times, it is not comprehensive to judge only from the appearance. When the internal curing is not enough and the external curing is very sufficient, the color of the coating line is very good, but the peeling property is very poor. The thermal aging test may lead to the coating sleeve or large peeling. On the contrary, when the internal curing is good but the external curing is insufficient, the color of the coating line is also good, but the scratch resistance is very poor. In curing reaction, the density of solvent gas or humidity in the gas mostly affect the film formation, which makes the film strength of the coating line decrease and the scratch resistance is affected.

4. Waste disposal
During the baking process of enameled wire, the solvent vapor and cracked low molecular substances must be discharged from the furnace in time. The density of the solvent vapor and the humidity in the gas will affect the evaporation and curing in the baking process, and the low molecular substances will affect the smoothness and brightness of the paint film. In addition, the concentration of solvent vapor is related to safety, so waste discharge is very important for product quality, safe production and heat consumption.
Considering the product quality and safety production, the amount of waste discharge should be larger, but a large amount of heat should be taken away at the same time, so the waste discharge should be appropriate. The waste discharge of catalytic combustion hot air circulation furnace is usually 20 ~ 30% of the hot air quantity. The amount of waste depends on the amount of solvent used, the humidity of the air, and the heat of the oven. About 40 ~ 50m3 waste (converted to room temperature) will be discharged when 1kg solvent is used. The amount of waste can also be judged from the heating condition of furnace temperature, scratch resistance of enameled wire and gloss of enameled wire. If the furnace temperature is closed for a long time, but the temperature indication value is still very high, it means that the heat generated by catalytic combustion is equal to or greater than the heat consumed in oven drying, and the oven drying will be out of control at high temperature, so the waste discharge should be increased appropriately. If the furnace temperature is heated for a long time, but the temperature indication is not high, it means that the heat consumption is too much, and it is likely that the amount of waste discharged is too much. After the inspection, the amount of waste discharged should be reduced appropriately. When the scratch resistance of enameled wire is poor, it may be that the gas humidity in the furnace is too high, especially in wet weather in summer, the humidity in the air is very high, and the moisture generated after the catalytic combustion of solvent vapor makes the gas humidity in the furnace higher. At this time, the waste discharge should be increased. The dew point of gas in furnace is not more than 25 ℃. If the gloss of the enameled wire is poor and not bright, it may also be that the amount of waste discharged is small, because the cracked low molecular substances are not discharged and attached to the surface of the paint film, making the paint film tarnish.
Smoking is a common bad phenomenon in horizontal enamelling furnace. According to the ventilation theory, the gas always flows from the point with high pressure to the point with low pressure. After the gas in the furnace is heated, the volume expands rapidly and the pressure rises. When the positive pressure appears in the furnace, the furnace mouth will smoke. The exhaust volume can be increased or the air supply volume can be reduced to restore the negative pressure area. If only one end of the furnace mouth smokes, it is because the air supply volume at this end is too large and the local air pressure is higher than the atmospheric pressure, so that the supplementary air can not enter the furnace from the furnace mouth, reduce the air supply volume and make the local positive pressure disappear.

cooling
The temperature of the enameled wire from the oven is very high, the film is very soft and the strength is very small. If it is not cooled in time, the film will be damaged after the guide wheel, which affects the quality of the enameled wire. When the line speed is relatively slow, as long as there is a certain length of cooling section, the enameled wire can be naturally cooled. When the line speed is fast, the natural cooling can not meet the requirements, so it must be forced to cool, otherwise the line speed cannot be improved.
Forced air cooling is widely used. A blower is used to cool the line through the air duct and cooler. Note that the air source must be used after purification, so as to avoid blowing impurities and dust on the surface of enameled wire and sticking on the paint film, resulting in surface problems.
Although the water cooling effect is very good, it will affect the quality of the enameled wire, make the film contain water, reduce the scratch resistance and solvent resistance of the film, so it is not suitable to use.
lubrication
The lubrication of enameled wire has a great influence on the tightness of take-up. The lubricant used for the enameled wire shall be able to make the surface of the enameled wire smooth, without harm to the wire, without affecting the strength of the take-up reel and the use of the user. The ideal amount of oil to achieve hand feel enameled wire smooth, but the hands do not see obvious oil. Quantitatively, 1m2 of enameled wire can be coated with 1g of lubricating oil.
Common lubrication methods include: felt oiling, cowhide oiling and roller oiling. In production, different lubrication methods and different lubricants are selected to meet the different requirements of enameled wire in the winding process.

Take up
The purpose of receiving and arranging the wire is to wrap the enameled wire continuously, tightly and evenly on the spool. It is required that the receiving mechanism should be driven smoothly, with small noise, proper tension and regular arrangement. In the quality problems of the enameled wire, the proportion of return due to the poor receiving and arranging of the wire is very large, mainly manifested in the large tension of the receiving line, the wire diameter being drawn or the wire disc burst; the tension of the receiving line is small, the loose line on the coil causes the disorder of the line, and the uneven arrangement causes the disorder of the line. Although most of these problems are caused by improper operation, necessary measures are also needed to bring convenience to operators in process.
The tension of the receiving line is very important, which is mainly controlled by the hand of the operator. According to the experience, some data are provided as follows: the rough line about 1.0mm is about 10% of the non extension tension, the middle line is about 15% of the non extension tension, the fine line is about 20% of the non extension tension, and the micro line is about 25% of the non extension tension.
It is very important to determine the ratio of line speed and receiving speed reasonably. The small distance between the lines of the line arrangement will easily cause the uneven line on the coil. The line distance is too small. When the line is closed, the back lines are pressed on the front several circles of lines, reaching a certain height and suddenly collapse, so that the back circle of lines is pressed under the previous circle of lines. When the user uses it, the line will be broken and the use will be affected. The line distance is too large, the first line and the second line line are in cross shape, the gap between the enameled wire on the coil is much, the wire tray capacity is reduced, and the appearance of the coating line is disorderly. Generally, for the wire tray with small core, the center distance between lines should be three times of the diameter of the line; for the wire disc with larger diameter, the distance between the centers between the lines should be three to five times of the diameter of the line. The reference value of linear speed ratio is 1:1.7-2.
Empirical formula t= π (r+r) × l/2v × D × 1000
T-line one-way travel time (min) r – diameter of side plate of spool (mm)
R-diameter of spool barrel (mm) l – opening distance of spool (mm)
V-wire speed (m/min) d – outer diameter of enameled wire (mm)

7、 Operation method
Although the quality of enameled wire depends largely on the quality of raw materials such as paint and wire and the objective situation of machinery and equipment, if we do not seriously deal with a series of problems such as baking, annealing, speed and their relationship in operation, do not master the operation technology, do not do a good job in tour work and parking arrangement, do not do a good job in process hygiene, even if the customers are not satisfied No matter how good the condition is, we can’t produce high quality enameled wire. Therefore, the decisive factor to do a good job of enameled wire is the sense of responsibility.
1. Before the start-up of catalytic combustion hot air circulation enamelling machine, the fan should be turned on to make the air in the furnace circulate slowly. Preheat the furnace and catalytic zone with electric heating to make the temperature of catalytic zone reach the specified catalyst ignition temperature.
2. “Three diligence” and “three inspection” in production operation.
1) Frequently measure the paint film once an hour, and calibrate the zero position of the micrometer card before measurement. When measuring the line, the micrometer card and the line should keep the same speed, and the large line should be measured in two mutually perpendicular directions.
2) Frequently check the wire arrangement, often observe the back and forth wire arrangement and tension tightness, and timely correct. Check whether the lubricating oil is proper.
3) Frequently look at the surface, often observe whether the enameled wire has grainy, peeling and other adverse phenomena in the coating process, find out the causes, and correct immediately. For the defective products on the car, timely remove the axle.
4) Check the operation, check whether the running parts are normal, pay attention to the tightness of the pay off shaft, and prevent the rolling head, broken wire and wire diameter from narrowing.
5) Check the temperature, speed and viscosity according to the process requirements.
6) Check whether the raw materials meet the technical requirements in the production process.
3. In the production operation of enameled wire, attention should also be paid to the problems of explosion and fire. The situation of fire is as follows:
The first is that the whole furnace is completely burned, which is often caused by the excessive vapor density or temperature of the furnace cross section; the second is that several wires are on fire due to the excessive amount of painting during threading. In order to prevent fire, the temperature of process furnace should be strictly controlled and the furnace ventilation should be smooth.
4. Arrangement after parking
The finishing work after parking mainly refers to cleaning the old glue at the furnace mouth, cleaning the paint tank and guide wheel, and doing a good job in the environmental sanitation of the enameller and the surrounding environment. In order to keep the paint tank clean, if you don’t drive immediately, you should cover the paint tank with paper to avoid the introduction of impurities.

Specification measurement
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm). The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 . There are direct measurement method and indirect measurement method for the specification (diameter) of enameled wire.
There are direct measurement method and indirect measurement method for the specification (diameter) of enameled wire.
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm). The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 .
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Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm).
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm). The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 .
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Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm). The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0
The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 .
The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm).
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm). The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 .
. There are direct measurement method and indirect measurement method for the specification (diameter) of enameled wire.
The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 . There are direct measurement method and indirect measurement method for the specification (diameter) of enameled wire. Direct measurement The direct measurement method is to measure the diameter of bare copper wire directly. The enameled wire should be burned first, and the fire method should be used. The diameter of enameled wire used in the rotor of series excited motor for electric tools is very small, so it should be burned for many times in a short time when using fire, otherwise it may be burnt out and affect the efficiency.
The direct measurement method is to measure the diameter of bare copper wire directly. The enameled wire should be burned first, and the fire method should be used.
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm).
Enameled wire is a kind of cable. The specification of enameled wire is expressed by the diameter of bare copper wire (unit: mm). The measurement of enameled wire specification is actually the measurement of bare copper wire diameter. It is generally used for micrometer measurement, and the accuracy of micrometer can reach 0 . There are direct measurement method and indirect measurement method for the specification (diameter) of enameled wire. Direct measurement The direct measurement method is to measure the diameter of bare copper wire directly. The enameled wire should be burned first, and the fire method should be used. The diameter of enameled wire used in the rotor of series excited motor for electric tools is very small, so it should be burned for many times in a short time when using fire, otherwise it may be burnt out and affect the efficiency. After burning, clean the burnt paint with cloth, and then measure the diameter of bare copper wire with micrometer. The diameter of bare copper wire is the specification of enameled wire. Alcohol lamp or candle can be used to burn enameled wire. Indirect measurement
Indirect measurement The indirect measurement method is to measure the outer diameter of the enameled copper wire (including the enameled skin), and then according to the data of the outer diameter of the enameled copper wire (including the enameled skin). The method does not use fire to burn the enameled wire, and has high efficiency. If you can know the specific model of enameled copper wire, it is more accurate to check the specification (diameter) of enameled wire. [experience] No matter which method is used, the number of different roots or parts should be measured three times to ensure the accuracy of measurement.