Understanding and familiarity with the causes of copper wire breakage can help the wire drawing workshop make reasonable and objective analyses and judgments during the production process.
Causes of Copper Wire Breakage:
There are various reasons for copper wire breakage, including central bursting, bubble breakage, inclusion breakage, “V” shaped breakage, copper burrs or fragments, tension breakage, copper powder breakage, joint breakage, mechanical damage breakage, twisting and melting breakage, and scratches on the wire drawing die.
1. Central Bursting
Central bursting refers to the fracture occurring at the central part of the copper wire, one end is a sharp cone, one end is a sharp hole.
The hole in central bursting is often mistaken for bubble breakage. However, when the wall of the hole in central bursting is magnified, it can be observed that the material itself exhibits a concave-convex tearing phenomenon due to external force.
1.1 Types of Central Bursting
1) Central bursting caused by excessive oxygen content in the copper rod (greater than 6000PPM);
2) Central bursting caused by inclusions;
3) Central bursting caused by poor wire drawing equipment (such as inappropriate wire drawing die entry angle).
1.2. Formation Process of Central Bursting
By observing the longitudinal section of the central burst fracture in a metallographic photo, we can find that the originally well-arranged cuprous oxide particles exhibit distorted and uneven conditions under stress. The formation process of the fracture can be observed in the metallographic image (the cuprous oxide particles are visibly distorted and concentrated, and tiny cracks have appeared, but the wire has not broken yet).
If this phenomenon occurs during large-scale wire drawing, although there is sufficient strength to prevent breakage, any additional external force applied during subsequent medium-scale wire drawing will inevitably lead to wire breakage.
Similarly, if internal damage occurs during medium-scale wire drawing, problems will arise during fine-scale wire drawing. (When breakage occurs, the drawn copper wire is hard and brittle, easily breaking when bent, often mistakenly attributed to poor copper quality.)
1.3. Prevention of Central Bursting
Due to the relatively stable quality of continuous casting and continuous rolling copper rods, central bursting rarely occurs due to other reasons. Therefore, prevention of central bursting is particularly important.
Preventive measures:
1)Regularly inspect the deformation angle of the wire drawing die and promptly replace it if excessive wear occurs.
2)Regularly check the concentration, temperature, pH value, and conductivity of the wire drawing fluid, and add or replace the wire drawing oil in a timely manner.
3)Check the tower wheel of the wire drawing machine and replace it promptly when serious wear occurs.
2. Bubble Breakage (Mainly caused by copper material)
This type of breakage exhibits a hole-like shape on the fracture surface, and the enlarged image of the hole shows a very smooth surface without protrusions or cracks. The formation of bubble breakage is caused by improper control of hydrogen gas during casting, resulting in inadequate cooling and the formation of shrinkage voids. If the holes are small, they may close during subsequent heat treatment processes, but if the holes are large, they cannot close, resulting in bubble breakage.
3. Inclusion Breakage (Mainly caused by copper material)
Inclusion breakage is a relatively common type of breakage, which can be divided into two categories based on appearance: breakage with inclusions present and breakage with missing inclusions.
4. “V” Shaped Breakage
The main characteristic of this breakage is the presence of continuous “V” shaped cracks on the surface of the copper wire, with the tip of the “V” pointing in the direction of tension.
The primary cause of this type of breakage is the improper angle of the drawing die during the wire drawing process. Alternatively, if the copper wire enters the drawing die at an angle instead of horizontally, excessive friction between the wire and the die can also result in the formation of “V” shaped cracks.
Metallographic analysis reveals that the copper oxide particles are distorted in a wave-like pattern around the “V” shaped crack, indicating the effect of external forces. Additionally, if there is a high concentration of oxygen in the surface layer of the copper material, it is more prone to developing “V” shaped cracks, ultimately leading to breakage.
5. Copper Slivers or Flakes (Mainly caused by copper impurities)
The occurrence of copper slivers is similar to that of impurities and happens during the drawing or casting process. It can be classified into two types: cast-in slivers and rolled-in slivers. Cast-in slivers occur due to improper cooling or excessive oxygen content in the molten copper.
Rolled-in slivers, on the other hand, occur during the wire drawing process when the edge trimming machine is not properly adjusted or when the gap between the rolling wheels is incorrectly set, resulting in scratching, among other issues.
In general, copper slivers or long flakes are related to the presence of copper oxide particles formed during casting or wire drawing. The presence of copper oxide prevents crack closure during the wire’s processing, leading to the formation of slivers or long flakes on the surface of the copper wire. In severe cases, this can cause breakage.
6. Tension Breakage
Tension breakage is a common type of breakage that occurs during the stretching process. The characteristic feature of tension breakage is a cup-cone or pointed-cone shape at the fracture end, caused by the tension exceeding the tensile strength of the copper wire itself.
Causes: Inadequate lubrication during the wire drawing process, improper angle of the drawing die, accumulation of copper powder in front of the drawing die, excessive reduction ratio, and mismatched speeds can all lead to tension breakage.
7. Copper Powder Breakage
When there is a considerable amount of copper powder in the wire drawing lubricant, the copper powder can accumulate at the entrance angle of the drawing die, causing the copper wire to become stuck and break. Additionally, if copper slivers peel off and accumulate in front of the drawing die, it can also lead to breakage.
8. Joint Breakage
Joint breakage can be classified into four types: fish-mouth shape, flat-end shape, bevelled-edge shape, and pointed-spike shape.
The primary cause of joint breakage is the excessive concentration of copper oxide particles in the joint area. Alternatively, high temperatures during the jointing process can result in grain growth. In addition, insufficient removal of burrs after welding can also cause breakage.
9. Mechanical Damage Breakage
The main cause of this type of breakage is poor alignment of the copper rod or wire, resulting in tangled and knotted wires before entering the wire drawing machine, leading to breakage.
10. Torsion Breakage and Melting Breakage
Torsion breakage occurs when the wire breaks due to twisting forces, commonly observed during the production of communication cables on stranding machines.
Melting breakage mainly occurs in continuous annealing machines. Due to improper tension adjustment or internal defects in the copper material, sparks can occur between the wire and the guide wheel, resulting in melting of the copper wire surface
11. Scratches on wire caused by wire drawing die
The management of wire drawing dies directly affects the wire breakage rate and processing cost. If the inner bore of the wire drawing die is not smooth, it will cause severe continuous scratches on the surface of the drawn wire and lead to tension breakage.
The above are the causes of wire breakage.
To prevent wire breakage, we usually recommend the following:
- Regularly inspect and replace wire drawing dies with excessive deformation angles.
- Regularly check the concentration, temperature, pH value, and conductivity of the wire drawing lubricant and add or replace it in a timely manner.
- Regularly inspect the capstan of the wire drawing machine and promptly replace heavily worn components.
- Control the oxygen content in the original copper rod to avoid excessive central bursting.
- Pay attention to hydrogen control during the casting process to prevent bubble-induced wire breakage.
- Take precautions to prevent the generation and loss of inclusions during wire drawing and casting processes.
- Ensure the appropriate angle of the wire drawing die during stretching and wire drawing, and avoid excessive friction and cracks.
- Pay attention to temperature control during connection and welding of joints to prevent grain growth and incomplete removal of burrs that may cause joint breakage.
- Manage the wire drawing die properly, ensuring a smooth inner bore to prevent scratches and tension breakage.
By regularly maintaining and replacing high-quality wire drawing dies, unnecessary losses can be reduced and work efficiency can be improved.
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