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Constantan Resistance Wire from Copper and Nickel
Constantan is a copper-nickel alloy, usually 55 % copper and 45 % nickel, whose electrical resistance stays nearly the same as it warms; that is why strain gauges, thermocouples and resistance coils are wound with it. Copper and nickel melt together in any proportion, so the alloy is made by fusing the two, casting small sticks and drawing them into wire.
The melt follows C. Morfit's copper-nickel alloy as Brannt gives it in *The Metallic Alloys* (1889): nickel and an equal weight of copper fused with borax in a graphite crucible, the rest of the copper stirred in. Hiorns (1912) adds that the nickel must be as pure as possible, which is what the Mond process gives.
Avancé
Foundry day, then drawing
Consignes
1
1
Weigh the charge
Weigh the charge
For 1 kg of 55/45 constantan weigh 450 g nickel and 550 g copper, and set aside 100 g of the copper for the second addition. Use nickel as pure as you can get: Hiorns warns that silicon, carbon, iron and sulphur in it greatly reduce how well the alloy works.
Matériaux pour cette étape :
Lingot de cuivre550 g
Nickel de procédé carbonyle450 gOutils nécessaires :
Balance à fléau2
2
Fuse nickel with an equal weight of copper
Fuse nickel with an equal weight of copper
Put the nickel and an equal weight of copper (450 g of each) into a graphite crucible with some borax, and fuse them in the furnace. This is Morfit's first stage: nickel melts far hotter than copper, and melting it among copper brings it down sooner. Constantan itself melts at about 1,220–1,300 °C.
Matériaux pour cette étape :
Borax en poudre1 as requiredOutils nécessaires :
Creuset graphite-argile
Fourneau à charbon de bois
Pince à creuset
Gants résistants à la chaleur
Tablier de cuir3
3
Stir in the rest of the copper
Stir in the rest of the copper
Add the remaining 100 g of copper to the melted mass, stirring constantly with an iron rod until it has gone in and the metal is one even liquid.
Outils nécessaires :
Agitateur en ferFourneau à charbon de boisPince à creusetGants résistants à la chaleur4
4
Cast small sticks
Cast small sticks
Pour the alloy into a warmed ingot mould as small sticks, as Morfit did. Pour in one run; the alloy chills quickly.
Outils nécessaires :
LingotièrePince à creusetGants résistants à la chaleurTablier de cuir5
5
Anneal the sticks
Anneal the sticks
Anneal the cast sticks before working them: cast copper-nickel is crystalline, and Hiorns gives careful annealing at a moderate temperature as the cure.
Outils nécessaires :
Four de recuitPince à creusetGants résistants à la chaleur6
6
Draw it like copper wire
Draw it like copper wire
Forge a stick into a round rod, file a taper and draw it through the drawplate hole by hole, as copper wire is drawn. Never take the size down too fast: Hiorns warns that metal drawn without annealing breaks unless it rests five to ten minutes between passes. Anneal it as the copper wire is annealed. Simmons's strain gauges used No. 40 gauge, about 0.08 mm.
7
7
Measure the resistance
Measure the resistance
Measure the diameter in several places, cut a measured length and find its resistance on a Wheatstone bridge. Compare the result with the ohms per metre in the next step. A wire that reads much higher than expected has a thin place or a crack in it.
Outils nécessaires :
Micromètre
Pont de Wheatstone8
8
Charge and resistance figures
Charge and resistance figures
Chargement du notebook Jupyter…
9
9
Troubleshooting
Troubleshooting
Constantan wire troubleshooting.
Flow
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10
10
History and honest limits
History and honest limits
In 1887 Edward Weston found an alloy whose resistance falls as it warms, a property, he wrote, of no other metallic conductor he knew. Wikipedia says his "Alloy No. 2" was produced in Germany and renamed Konstantan. By 1912 Hiorns listed Constantan, Eureka and Heckenham metal among the copper-nickel alloys used for resistances.
Morfit's alloy was 33 nickel to 67 copper; we keep his two-stage method and scale it to 55/45, the usual constantan and Simmons's wire. That scaling is ours. The 55/45 figure and the resistivity are from Wikipedia's Constantan article. Very fine wire like No. 40 gauge needs drawplate holes that fine.
Matériaux
3- 550 gEspace réservé
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- 1 as requiredEspace réservé
Outils requis
11- Espace réservé
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Ce plan fabrique
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