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Discussion on "Black Spot" and "Cracking" of Enamelled Wire

Category:Industry News     Publish:2022-09-05 10:29:29     View:360

Usually, both manufacturers and users of enameled wire will encounter the sudden "deterioration" of the finished enameled wire. Black spots, brown or brown stains and other defects can be seen on the conductor through the paint film, and quality accidents such as cracking and falling off of the paint film occur at the defects, resulting in product scrapping. Sometimes it is difficult to find the real cause of these defects. Because this phenomenon is not found during painting, and the occurrence of such defects is irregular. This kind of quality accident is sometimes individual, but sometimes it is batch, and even the quantity can reach several tons or even dozens of tons. This problem can be said to be a serious global problem.

After careful search and analysis, it was finally attributed to the negligence of conductor quality assurance in the manufacturing process, and only a few of the reasons were from insulating paint and solvent.

For a long time, the overall production conditions and technical level of copper conductor processing in China have lagged behind the manufacturing of finished electromagnetic wires. In addition, manufacturers of electromagnetic wires often pay great attention to insulating paint materials and electromagnetic wire coating and molding process equipment, but do not pay as much attention to the manufacturing process and finished copper wire quality from electrolytic copper to bare copper wire as the former. This problem is quite prominent, and it is also a major aspect of the gap between China and developed countries. The concept of "light before heavy" has not been well corrected up to now

By the end of the 1980s, China's high-temperature resistant electromagnetic wires had made great progress. High temperature resistant paint has more stringent requirements on conductors. The bare copper wire shall not only be free from mechanical defects such as burrs, scabs and cracks, but also shall have a clean and smooth conductor surface.

What are the ingredients called "blackspots"? It is mainly the attachment of metal cations such as oil stain, magnetized matter spot, copper cyanide, cuprous chloride, cuprous oxide, cupric oxychloride, copper sulfate, calcium and sodium. This kind of "stain" attached to the surface of bare copper conductor presents black, maroon, green, gray,...... Etc. They can be identified through transparent paint film.

The main reasons for the above "unknown substances" come from the following aspects:

1. The copper rod starts to be drawn into copper wire through multiple processes. The lubricating liquid used is constantly consumed and replenished during the circulation. If the lubricating liquid is not cleaned regularly, the acid value in the lubricating liquid will become higher and higher, and the acid radical (anion) exceeding a certain concentration will form a layer of extremely thin substance with copper.

2. The water used in annealing is not clean and contains halogen compounds, such as sodium chloride, calcium chloride,.... Or sulfate. Many electromagnetic wire factories do not attach importance to the importance of water. Less than half of the manufacturers use distilled water or deionized water in the production process, and many manufacturers use tap water, even deep well water. Even if distilled water or deionized water is used, the purity change needs to be detected at any time and updated regularly, otherwise the concentration of impurities in the purified water will become higher and higher, and the purification effect will be lost.

3. The annealed tube shall also be cleaned regularly and the damage shall be checked in time. Slight air leakage or burning with pouring alcohol to drive oxygen will generate slight and imperceptible oxide layer on the surface of bare copper conductor.

4. The storage conditions of semi-finished products can not be guaranteed, the environment is humid, the temperature is high, and there is harmful gas around ------. This is also the reason why many manufacturers cancel the semi-finished product turnover link and implement the continuous pulling, returning and coating process.

There are still many times when stains have gradually formed and are not yet noticeable. But at this time, the damage effect of the stain on the paint film has begun, and this phenomenon will increase with time until the insulation layer is damaged. If we do a comparison test, or do a comparison test before and after a certain period of storage, we will measure:

1. The flexibility and adhesion of the paint film are obviously reduced.

2. The hot stamping performance becomes worse (the winding times become larger).

3. The breakdown voltage is reduced or greatly dispersed.

4. The inflection point value of the dielectric loss becomes low.

5. When polyester imine is used as primer, the adverse consequences of this defect are more serious than when polyester paint is used as primer.

We can think that the best way to prevent "Blackspots" is to implement strict quality control over the manufacturing process and environmental impact.

The so-called "crazing" is actually the phenomenon of slight "cracks" in the paint film of enamelled wire. This is a dispute between enamelled wire manufacturers and users. It is also a quality phenomenon that can only be judged according to visual effects and is difficult to determine the magnitude.

"Cracking" usually occurs in the winding process of enamelled wire or after stretching and immersion treatment. Under strong light, the crack will appear silver gray. Users often think that the insulating paint layer has been damaged. However, in many cases, although the existence of cracks can be seen with eyes, its internal performance is not affected.

In order to better explain this problem, obtain more information and solve this quality problem, Dupout Herberts Industrial Coatings Co., Ltd. has made many tests and found that the THEIC modified polyester imide paint can solve this problem. After the dielectric loss (concentration) value of the polyester imide (PEI) paint modified by THEIC was increased by 30%, no cracks were found under the electron microscope.

For further test, the sample was immersed in styrene for 30 minutes (30 minutes) at the same humidity and then observed with an electron microscope for image analysis. There was no crack, but there was a crack 2 microns below the insulation layer. However, the crack disappeared after the wire sample was treated in a flood furnace at 220 ° C for 10 minutes. This result was also confirmed by the breakdown voltage test.

The sample wire of enamelled wire is twisted, and the breakdown voltage is treated with ethylene at 100 ℃

Modified PEIA type 1.00MM 11575 11575

Modified PEIA type 1.00MM 12179 12010

Modified peib type 1.00mm 10212 10757

Polyurethane type C 0.35mm 5976 6934

Polyamide ester D 0.35MM 5899 6305

We analyze the mechanism that the paint film is wound. Deformation under the action of external forces such as stretching, or swelling and erosion of soluble organic matter, at this time, the paint film bears the feedback of stress, especially when the resin crosslinking degree is insufficient during film formation, which will aggravate this consequence. However, if treated, this result will be improved and will not have a negative impact on the acoustic performance of the insulation layer of the ground electromagnetic wire

Of course, in the process of use, attention should be paid to preventing harmful solvents such as acetone, which have a melting effect on the paint film.

Comparison between copper clad aluminum wire (CCA) and other similar products

Copper volume ratio (%) 15 15 100 0

Specific gravity (g / cm3) 3.63 3.63 8.89 2.70

Length ratio under the same wire diameter weight 2.5:1 2.5:1 1:1 3.29:1

Conductivity (% IACS) 69 65 100 62

Resistivity (Ω mm2/m) 0.02563 0.02857 0.01724 0.02780

Tensile strength (MPA) 96-135 220-251 215-265 68-107

Elongation (%) ≥ 10 ≥ 13 ≥ 20 ≥ 8

Volume linearity ○● ○


Solderability: ●●△

DC resistance

● very good ○ good △ bad

Comparison of bimetal wires produced by cladding welding method and electroplating method: index: cladding welding method production electroplating method production

The copper layer material is of high purity, good compactness, loose copper layer and impurities

The bonding mode between the two metals is the metallurgical bonding between the copper layer and the core wire, which is solid and durable. Copper ions in the electrolyte are attached to the surface of the core wire, which is not firmly bound and easy to fall off

Uniformity of copper layer: the copper layer is evenly distributed along the circumferential direction and longitudinal direction, with good concentricity. The thickness of the copper layer is often uneven.

Environmental pollution No electroplating solution seriously pollutes the environment and is harmful to the health of workers. It is gradually included in the list of prohibited production.

Structural drawing of copper clad aluminum enameled wire:

Advantages of copper clad aluminum enameled wire:

1. DC resistivity: the DC resistivity of copper clad aluminum wire is about 1.5 times that of pure copper wire; When the resistance is the same, the weight of copper clad aluminum wire is about 1/3 of that of pure copper wire.

2. Good solderability: Copper clad aluminum wire has the same solderability as pure copper wire because its surface is concentrically coated with a layer of pure copper, without special treatment like aluminum wire.

3. Light weight: the density of copper clad aluminum wire is 1/3 of that of pure copper wire with the same wire diameter, which is very effective in reducing the weight of cable and coil.

Application fields of copper clad aluminum enameled wire:

1. It is used for making windings with light weight, high relative conductivity and good heat dissipation, especially for transmitting high-frequency signals;

2. High frequency transformer, ordinary transformer, inductance coil, motor, household motor and electromagnetic wire for micro motor;

3. Enamelled wire for micro motor rotor coil;

4. Special electromagnetic wire for audio coil and optical disc drive;

5. Electromagnetic wire for deflection coil of display;

6. Electromagnetic wire for degaussing coil;

7. Electromagnetic wire used for internal coil of mobile phone and driving element of watch;

8. Other special electromagnetic wires.

Physical properties of composite copper:

Specification copper layer volume ratio (%), copper layer mass ratio (%) and pure copper wire length specific density g / cm3 maximum current resistance Ω M m2/m200 c Minimum relative conductivity (%/ACS)

CCA-10% 8-13 27 2.65:1 3.32 0.2743 63

CCAM-15% 13-20 37 2.45:1 3.7 0.3120 63

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