Hollow Copper Conductor

Due to the fact that the impurities will reduce the electrical conductivity of copper, and our Cu-OFE hollow conductors have electrical conductivity of 100-102 %IACS and thermal conductivity of 390 W/Km. For, Cu-OFE (CW009A), in China, the substitute copper grade is TU00, its maximum oxygen content of 5 ppm (0.0005%) makes the material immune to hydrogen embrittlement and ensures safe joining with all brazing and welding methods. Our tight production control means we can control the whole manufacturing process from casting to signing the inspection certification and ensure the consistency of our product from batch to batch. In particular, our high purity oxygen free copper is alloyed with silver (Ag) to increase both the softening temperature and creep resistance of the alloy without any significant sacrifice of its other properties. Fabmann has been working with famous copper material manufacturers to produce top-notch hollow conductors, square & rectangular copper and copper alloy tubes, special copper & copper profiles for the most demanding applications. Hollow conductors are often referred as water-cooling conductors, hollow wire, hollow copper tube, hollow magnet copper wire, square copper tube, copper profile tube, rectangular copper tubing, tubular bus conductors, induction coil tubing, and induction heating tube.

Advantages of Hollow Copper Conductor

 

Hollow copper conductors are a unique type of conductor that offers several advantages over traditional solid copper conductors. It's normally hollow copper tube with a circular or rectangular cross-section, that carries electrical current, and it has following advantages:

 

√ High current density, carry higher current densities than solid copper conductors of the same cross-sectional area.

  This is because the hollow core allows for better heat dissipation, preventing the conductor from overheating.

√ Reduced weight, the hollow design significantly reduces the weight of the conductor compared to a solid conductor

  of the same current-carrying capacity, and this is particularly advantageous in applications where weight is a critical

   factor, such as aerospace and transportation.

√ Improved cooling, the hollow core allows for efficient cooling of the conductor, either through natural convection or

  forced air/liquid cooling. This helps maintain the conductor's operating temperature within safe limits, ensuring reliable

   performance and extended lifespan.

√ Cost-effectiveness, the initial cost of hollow copper conductors may be higher than solid conductors, but the reduced

   weight and improved efficiency can lead to significant cost savings in the long run.

Application of Hollow Copper Conductor

Hollow copper conductors offer a unique combination of high current-carrying capacity, efficient cooling, and reduced weight, making them suitable for various demanding applications below:

√ Power Transformers

Hollow conductors in transformer windings minimize energy losses, improving the overall efficiency of the transformer. A smaller size of hollow conductors allows for more compact transformer designs, reducing space requirements and installation costs. The efficient cooling of hollow conductors helps maintain optimal operating temperatures, extending the lifespan of the transformer.

√ Electric Vehicles (stator direct cooling)

Hollow copper conductors contribute to the lightweight and compact design of electric vehicle battery packs and charging systems, and they facilitate efficient and rapid charging of electric vehicle batteries, reducing charging times and improving user experience. The reduced weight of hollow conductors contributes to increased driving range for electric vehicles.

√ Aerospace

The lightweight nature of hollow copper conductors is crucial for aircraft and spacecraft, where every gram saved translates to increased fuel efficiency and payload capacity meanwhile hollow conductors can handle the high power requirements of onboard electrical systems, supporting critical functions like navigation, communication, and propulsion. Additionally, efficient cooling of hollow conductors ensures reliable operation in the harsh thermal conditions encountered during flight.

√ Pulse Magnets

Hollow copper conductors are ideal for generating high-intensity magnetic pulses in research and industrial applications due to their ability to handle large currents without overheating, meanwhile the efficient cooling of hollow conductors allows for rapid repetition rates of magnetic pulses, essential for various applications. The smaller size of hollow conductors enables the design of more compact and efficient pulse magnet systems.

√ Military Applications

Hollow copper conductors are used in high-power radar systems due to their ability to handle the high currents required for generating powerful radar signals, and the high current-carrying capacity and efficient cooling of hollow conductors make them suitable for powering lasers and other directed energy weapons. Hollow conductors are used in various other military equipment, such as communication systems, electronic warfare systems, and propulsion systems.

√ MRI devices / gradient coils

√ Particle accelerators

√ Generators

√ Induction furnaces / induction heating and melting

√ Plasma research devices

√ Electrodynamic vibration test systems

√ Ion implantation units for the microcircuit industry

√ High gradient separators

√ Waveguides

√ Liquid cooled transformers

Hollow copper conductors offer significant advantages in various applications requiring high power, efficient cooling, and weight reduction. Their unique properties make them a valuable asset in power transmission, electric vehicles, aerospace, pulse magnets, military applications, and other demanding fields. Fabmann can assist you to develop the suitable hollow conductor design for your specific needs.

Why is oxygen free copper widely used for hollow conductor?

 

First of all, oxygen free copper has very high copper content, which is minimum 99.95% with maximum oxygen content 10ppm. This high purity copper means that electrons can flow through the material more freely, reducing resistance and energy loss. Secondly, the minimized impurities and oxygen content can minimize the risk of hydrogen embrittlement which is a big threat to hollow conductors, while hydrogen embrittlement could cause following failures:

 

√ Electrical failure, loss of electrical continuity due to a broken conductor can lead to power outages, equipment

   malfunction, and potential safety hazards.

√ Mechanical failure, catastrophic failure of the conductor can result in structural damage, equipment collapse, and

   potential injuries.

√ Fire risk, overheating or arcing due to a failed conductor can ignite surrounding materials, posing a significant fire

    risk.

√ Environmental damage, leakage of hazardous fluids or gases from a damaged conductor can contaminate the

    environment and pose health risks.

Why C10100/CW009A is used for hollow conductor?

Oxygen-Free copper grade with super purity like C10100/CW009A does not contain elements that can vaporize in a vacuum environment. It is very thermally and electrically conductive and it also performs extremely well during hot

and cold forming, and it has strong capability to work against atmospheric influences and water, and is also insensitive to stress corrosion cracking. This grade (99.99 % minimum Cu, a max oxygen content less than 5 ppm) offers the advantages of both Electrolytic Tough Pitch Copper (ETP) and Phosphor deoxidized Copper, and its super purity and absence of deoxidizers accounts for electrical conductivity of 101% IACS as well as no susceptibility for hydrogen embrittlement.

Plus, this copper grade has an extremely low content of highly volatile low melting elements such as Phosphorus (P), Lead (Pb), Sulphur (S), Zinc (Zn), Cadmium (Cd) and Mercury (Hg). In a number of vacuum applications in the electronic industry, glass is directly bonded to copper, requiring an adherent oxide film on the copper surface. This oxide film can be rendered non-adherent and brittle if phosphorus, which is often used as oxidant, is present. To prevent this, Chinese copper TU00 (equivalent to CW009A/C10100) contains less than 3 ppm (0.0003%) of phosphorus, allowing for a direct bond to glass and ceramic materials. The low volatility and limited phosphorus content in this copper grade ensure the smooth functioning and long service life for vacuum components such as vacuum interrupters, X-ray tubes, radio transmitters as well as hollow conductors.

How to avoid hydrogen embrittlement (HE) in oxygen-free copper hollow conductor manufacturing process?

To answer this question, we need to understand what is hydrogen embrittlement. Hydrogen embrittlement can be described as the formation of water vapor within metal like copper including oxygen-free copper, as a result of the inward diffusion of hydrogen gas into the metal structure, the oxygen being in solid solution in the metal or in the form of precipitated nodules of metal oxide such cuprous oxide which are readily reducible by the diffused hydrogen. The hydrogen diffusing into copper combines with the oxygen therein to form steam, and the expanding steam weakens the hollow copper conductor structure at the grain boundaries thereof which causes brittle failure of the hollow conductor when subjected to stress.

Secondly, let's discuss how to detect hydrogen embrittlement for hollow copper conductor, and the test standards are ASTM B577/ISO 2626, in this standard, hydrogen embrittlement of copper is analyzed by microscopic analysis. The test is done by heating copper samples in a 10% hydrogen atmosphere for 20-40 minutes at 850°C and then bent the test sample after thermal hydrogen treatment. The sample microstructure is analyzed for the presence of voids and open grain structure that is characteristic of hydrogen embrittlement.

Thirdly, oxygen itself doesn't directly cause hydrogen embrittlement, yet, it plays a significant role in influencing the behavior of hydrogen within the metal and can exacerbate the embrittlement process. Oxygen can also trap hydrogen within the copper lattice, and the trapped hydrogen can interact with dislocations and other defects, promoting the formation of microcracks and ultimately leading to embrittlement. Plus, oxygen can react with hydrogen gas to form water vapor, which can also promote hydrogen absorption by the copper material.

The final step is see which production process could cause HE issues. To minimize hydrogen embrittlement, we need to focus on eliminating as much as possible the oxygen present in the copper which can be in reaction with hydrogen. Therefore, it's vital to use advanced melting furnaces and casting machines for maximizing deoxidation and prevent reoxidation of the copper, and milling the cast copper tube before cold drawing is also the essential process control.

Of course, the copper raw material control itself is the fundamental control before the production process control. After the hollow copper conductors are fully eddy current tested and wound into coil, they need to be vacuum soft annealed, and the vacuum annealing is also essential for minimizing the risk of HE.

Fabmann has accumulated solid experience in custom hollow conductor production, each process is carefully monitored, specially copper and oxygen content. If you have any question regarding hydrogen embrittlement test, you are welcome to consult with our material engineer team.

Equivalent Copper & Copper Alloy Designation Code

To supply the correct copper material, Fabmann can help to find the current equivalent copper and copper alloy material for desired hollow conductor, and below is universal equivalent summary:

Design Availability, Dimension & Minimum Order

Custom Hollow Copper Conductor

Fabmann can supply different shapes, and our biggest perimeter of hollow copper conductor is 180mm, and our standard minimum quantity is 500kg. But for some smaller dimension, we can accept 200kg as MOQ. Below is our minimum order for different oxygen-free copper and copper alloy:

√ CW008A/C10200/TU1, 500Kg

√ CW009A/C10100/TU1,1000Kg

√ CuAg0.10(OF), 1000Kg

Production of Hollow Conductor

Production Process

It is a long process to produce hollow copper conductor, and it starts from smelting. The furnace must reach temperatures up to 2400 degrees Fahrenheit to melt the copper, and this will enable to mold it into desired shapes and also to remove impurities such as a mixture of nickel or zinc alloys. Copper is filtered out through a process known as fire-refining. In fire-refining, the impure metals become lighter than the copper and float to the surface to be caught on "snags, and this process will generate a pool of liquid hot copper with minimum impurities. The melted copper is also deoxidized in order to remove possible defects before the casting process, and then the purified liquid copper is moved to a holding furnace to be poured into a casting pipe which will eventually become the tubing. Once it has cooled and solidified, a large machine called a piercing mandrel drills a hole in the copper rod, and then a ram forces the copper rod through an extrusion pipe, creating a long hollow copper tube.

The next step is to push the mother copper tube through metal dies to create the desired size of tubing for next drawing process depending upon hollow conductor shape and size. Before reaching final drawing process, and the copper tube often needs to annealed as it gets hardened by each drawing process, and it will be redrawn afterwards.

Going through above process, the hollow copper conductor will go through Eddy Current Testing before level winding, and the length of the hollow conductor is set according to the specification during this process. After level winding, the qualified hollow conductor will be put into vacuum furnace for final annealing before packaging. Of course, the conductor is cleaned during previous drawing processes before level winding. Depending on clients' requirement on temper condition, the annealing time and temperature will be set differently to reach soft annealed, annealed, 1/4 hard, 1/2 hard and hard.

 Production Process of Hollow Copper Conductor

 

Quality Control & Insulation Service

 

Fabmann can assist you to develop the hollow copper conductor which fits your specific application, and our quality engineers focus on following quality parameters for delivering consistent shipments:

 

1. 1. Chemical composition, oxygen and hydrogen content is under strict control
2. 2. Dimension within required tolerance
3. 3. Mechanical property
4. 4. Conductivity
5. 5. Hydrogen embrittlement check
6. 6. Endoscope check the inner surface condition

 

On top of supplying custom hollow conductor, Fabmann can provide you desired insulation service, and our standard insulation material for hollow conductor is polyester imide + glass fiber which can easily reach working temperature 200°C with minimum voltage breakthrough over 1000V.

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