All you need to know about Invar conductor
Invar conductor is also named 4J36 alloy whose curie point is about 230℃. Below this temperature, the alloy is ferromagnetic and has a very low expansion coefficient. Above this temperature, the alloy is nonmagnetic and the expansion coefficient increases.
Invar conductor has low sag characteristics, it adopts invar as its wire.
Invar core overhead conductor performance
Invar core wire uses Invar stranded wire with a smaller linear expansion coefficient to replace the steel core of ordinary steel-cored aluminum stranded wire. Because Invar core has a very low linear expansion coefficient, when the wire is working at a higher temperature, the sag of the wire is not It will increase a lot, and the application temperature range of the wire is greatly improved. In the general use process, in order to give full play to the low linear expansion advantage of the Invar core, the wire is often designed as an Invar core heat-resistant aluminum alloy wire.
The alloy is mainly used to manufacture components whose size is approximately constant within the range of temperature changes, and is widely used in the radio industry, precision instruments, meters and other industries.
Invar conductor (4J36) physical and chemical properties
- The melting temperature range is 1430～1450℃.
- Thermal conductivity λ=11W/(m•℃).
- Specific heat capacity c(20～100℃)=515J/(kg•℃).
- The linear expansion coefficient standard stipulates that α1(20～100℃)≤1.5×10-6℃-1.
- The alloy sample is heated to 880℃±20℃ in a protective atmosphere or vacuum, kept for 1h, and cooled at no more than 300℃/h. The average linear expansion coefficient is shown in the table.
Invar conductor process performance and requirements
As we mentioned above, Invar conductor is also called 4J36 alloy. Thus, you will see more information about 4J36, just remember, they are same.
4J36 formability alloy is easy to cold and hot work. Avoid heating in a sulfur-containing atmosphere during thermal processing.
4J36 welding performance
The alloy can be welded by oxyacetylene welding, arc welding, spot welding and hydrogen atom welding. Since the coefficient of expansion is related to the chemical composition of the alloy, the alloy composition should be avoided as much as possible due to welding. Therefore, it is best to use argon arc welding. The filler metal for welding should preferably contain 0.5% to 1.5% of titanium to reduce welding pores and crack.
4J36 parts heat treatment process
The alloy heat treatment can be divided into: stress relief annealing, intermediate annealing and stabilization treatment.
(1) Stress relief annealing In order to eliminate the residual stress of parts after machining, stress relief annealing is required: 530～550℃, heat preservation for 1～2h, furnace cooling.
(2) Intermediate annealing In order to eliminate the work hardening phenomenon caused by the cold rolling, cold drawing and cold stamping process of the alloy, in order to facilitate the continued processing. The workpiece is heated to 830～880℃, kept for 30min, furnace cooling or air cooling.
(3) Stabilization treatment In order to obtain a treatment with a lower expansion coefficient and stable performance. Three-stage processing is generally used.
- Homogenization: During heating, the impurities in the alloy are fully dissolved and the alloying elements tend to be uniform. The workpiece is heated to 830°C in a protective atmosphere for 20min～1h, and then quenched.
- Tempering: The stress caused by quenching can be partially eliminated during the tempering process. The workpiece is heated to 315℃, kept for 1～4h, and the furnace is cooled.
- Stabilization and aging: Make the size of the alloy stable. The workpiece is heated to 95°C for 48 hours. For high-precision parts after cold processing or mechanical processing, when high temperature treatment is not suitable, the following stress relief stabilization treatment can be used: the workpiece is heated to 315～370℃ for 1～4h.
4J36 surface treatment process
The surface treatment can be sandblasted, polished or pickled. The alloy can be pickled with 25% hydrochloric acid solution at 70℃ to remove oxide scale.
4J36 Cutting and Grinding Performance
The cutting characteristics of this alloy are similar to those of austenitic stainless steel. High-speed steel or cemented carbide tools are used for processing, and low-speed cutting is used. Coolant can be used when cutting. The alloy has good grinding performance.
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