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Copper tubes

Copper tubes

Copper tubes are rolled and fabricated into active parts and ocasionally into cooling parts of the coil. Hence, the importance of the its properties cannot be denied.  About copper tubes there are couple of points to consider:

Tube material

The copper in the tubes of coil’s active part must be of at least 99.90% of purity and 58 MΩ/m of conductivity with the most possible impurity of phosphorous, oxygen and iron. These element’s presence will drastically lower the conductivity and may cause coil overheat and explosion. Aside from chemical composition of the coil’s active part, must be annealled via heat operations under special vaccum condition after bending and forming. Otherwise, during rolling and production process or mechanical tensions, tiny cracks may appear on the surface and little by little these cracks may get wider leading in major leaks and sometimes decaying. Hence, Araz Trans Co. applies purified copper of the ETP-ASTM C11000 grade for coil’s active parts and ocasionally for special orders OFC-ASTM C10100.

Tube shapes

Amoung quality factors of  the tubes used for coil construction, shape and cross-section of the tubes has the most impact on the operation and life cycle of the active part. Aside from cross-section of the conductor being adequate for the current, the point mostly been neglected is the shape of the tube. The shape must be in a way that handle the current considering penetration depth dou to proximity effect (fully related to the frequency) and proper cooling and water flow from the inside. Tubes with internal rectangular canal (90 degrres corners), would face congestion and seimentation and consequently more erosion on the corners particularly with low quality water. Henceforth, tubes with curved cross-section are better for this intention.

About penetration depth in the conductor duo to proximity effect, it can be said that a magnetic field caused by conductor’s current will induce eddy currents on outer side of the melt opposing coil’s current. According to proximity effect between coil and melt, the current in the both part will tend to flow near both surfaces.

Considering above-mentioned issues, normally the current density on the inside surface of the coil conductor (facing melt) will be higher than the other sides. Then, more thickness on this side will lead in more efficiency of the coil. According to the literature it has been suggested that the inner side of the copper tube to have thickness at least two times of the penetration depth caused by proximity effect.

The relationships and the table below show the depth of current penetration inside the conductor due to the proximity phenomenon and also the minimum optimal value for the thickness of the side facing the melting of the copper section.

The results of the relationships indicate that the effect of the proximity phenomenon in the conductors has an inverse relationship with the frequency of the electric current passing through it. The lower the frequency of the electric current of the coil, the more thickness is needed for the side of the copper profile to be melted.

The reason for using D-shaped cross-section profiles in the coils of some European manufacturers’ network frequency furnaces is the same.

مقطع شکل مورد استفاده
foursquare section

with foursquare

water passage

Active part of most

Chinese Indian and

Turkish furnaces

foursquare section

with circular

water passage

Ajax-TOCCO

Active part of

Active part of

Ajax-TOCCO Company

foursquare section

with elliptical

water passage

Active part of midrange

frequency furnaces of

German companies

Otto-Junker and ABP

D-type section with

circular water passage

Active part of grid

frequency furnaces of

German companies

Otto-Junker and ABP

Circular section with

circular water

passage (pipe)

Active part of some

Chinese furnaces and

cooling part of some

German furnaces

Asymmetric foursquare

section with circular

water passage

Novel design for active

part of midrange

frequency furnaces by

Araz Trans

Considering point about the quality and occasions of the copper tubes to be used in the coil of the induction furnaces, below table summarizes the consideration by Araz Trans Co. All the copper tubes are available by us.