Knowledge base
CUPAL glossary
30 terms of copper-aluminium bimetal joints in four topics: the material, corrosion and contact, parts and jointing, and standards and certificates. Every term is one click from the article that covers it in depth.
The material
- CUPALCu-Al bimetal
A cold-roll-bonded copper-aluminium bimetal composite, roughly 70% aluminium and 30% copper by layer thickness. Not an alloy: the two metal layers are inseparably joined yet each keeps its own properties — one face is copper, the other aluminium. Its main job is to eliminate galvanic corrosion where a copper and an aluminium conductor meet. It goes into the joint as sheet, strip, washer or a part cut to a drawing.
- Bimetalbimetallic, clad metal
A material permanently joined from two different metals that carries the useful properties of both. In CUPAL, copper’s conductivity and solderability are combined with aluminium’s low weight and cost. Not to be confused with the bimetal strip in thermostats and thermal trips: there the point is the different thermal expansion of the two metals, here it is that each face matches a different conductor.
- Roll bondingcold roll cladding
The process that joins CUPAL’s two layers: prepared aluminium and copper sheets are rolled together at room temperature under very high pressure, forming a metallic bond between the two metals. The diffusion that takes place during the subsequent heat treatment strengthens the bond further. There is no filler, adhesive or solder between the layers.
- Diffusion weldingdiffusion bonding
During the heat treatment that follows roll bonding, copper and aluminium atoms diffuse into each other across the interface, which strengthens the bond between the layers. This gives CUPAL its bond strength of 70–110 N/cm of strip width. Time and temperature of the heat treatment are tightly limited so that the intermetallic layer stays microscopically thin.
- Intermetallic layer
A brittle copper-aluminium compound layer that forms at the boundary between the two metals. In CUPAL it is deliberately kept microscopically thin, which is why the material can be bent, punched and deep-drawn without the layers separating. It grows with sustained heating: CUPAL may be heat-treated at no more than 260 °C for no more than 4 hours; beyond that the layer thickens uncontrolled and weakens the bond.
- Cladding ratio70/30
The thickness ratio of a bimetal’s two layers. CUPAL’s is 70% aluminium and 30% copper by layer thickness, which gives a density of about 4.6 g/cm³ and a conductivity of about 41.9 m/Ω·mm². Many suppliers state no ratio at all, so a specification cannot refer to it — if a drawing calls for a minimum copper thickness, have it confirmed before ordering.
- Werkstoff numberDIN 17007 material number
An identifier per the German DIN 17007 material-numbering system. CUPAL’s aluminium carrier is 3.0255 (Al 99.5, EN AW-1050A) and its copper cladding is 2.0065 (E-Cu58, Cu-ETP). These two numbers identify the material precisely on certificates and in specifications.
- CCA (copper-clad aluminium)
A conductor with an aluminium core and a thin surrounding copper layer — mostly as wire and cable. The name is similar but the job differs from CUPAL’s: CCA is a cheaper substitute for copper, its copper surrounds the aluminium, and it does not solve a copper-aluminium transition. CUPAL has copper on one face and aluminium on the other precisely so it can sit between two different conductors.
Corrosion and contact
- Galvanic corrosionbimetallic corrosion, contact corrosion
Electrochemical corrosion that starts when two metals of different nobility (e.g. copper and aluminium) touch directly in the presence of an electrolyte — moisture, condensation, salt air. The two metals form a galvanic cell and the less noble one, aluminium, dissolves. The joint loosens, contact resistance rises and the joint heats up. A CUPAL transition element removes the direct Cu-Al contact: on each face, like metal meets like metal.
- Electrochemical seriesgalvanic series
The ranking of metals by how readily they give up electrons. The standard electrode potential is +0.34 V for copper and −1.66 V for aluminium — the two sit far apart in the series, which is why pairing them is so corrosion-prone. The voltage actually measured across an installed, oxide-covered Cu/Al pair is lower, about 0.5–1 V, but that is still enough to keep the aluminium dissolving.
- Oxide film (aluminium oxide)Al₂O₃
A hard, electrically insulating film a few nanometres thick that forms on aluminium in air almost instantly. It protects the aluminium from further oxidation but impairs conduction at a contact face — which is why an aluminium surface has to be cleaned before it is connected. CUPAL’s aluminium face is prepared just like any other aluminium surface.
- Contact resistancejoint resistance
The electrical resistance at the boundary between two clamped conductors, which arises because the surfaces touch only at microscopic points. Oxide films, corrosion products or a falling clamping force increase it. Because the heat generated in a joint scales with the current squared times the resistance, rising contact resistance leads to heating and, in severe cases, failure of the joint — the cause of the familiar “hot busbar joint”.
- Contact pasteanti-oxidant compound, jointing compound
A compound used in direct copper-aluminium joints that keeps moisture out of the contact face and slows oxidation. It does not remove the potential difference, and in time it dries out or washes away, so the joint needs maintenance. A CUPAL transition does not need it, because like metal meets like metal on every face; no lubricant should be applied to CUPAL contact faces.
- Cold flow (creep)
Aluminium’s tendency to flow slowly away from under a sustained clamping load, even at room temperature. In a bolted joint this gradually reduces the clamping force and raises the contact resistance — and the resulting heat speeds the process up. That is why joints involving aluminium use a spring washer (for example a disc spring) to keep the clamping force constant.
Parts and jointing
- Transition washerbimetallic washer, Al-Cu washer
A name used for two physically different parts. One is the copper-aluminium bimetal disc (the CUPAL washer is one): copper on one face, aluminium on the other, with the transition in the material. The other is a toothed or profiled copper-alloy washer that pierces the aluminium oxide film when tightened — there, the transition is made at assembly. A specification rarely says which is meant, so check the drawing or a sample.
- Cable lug
A connector crimped or bolted onto the end of a cable, whose palm is bolted to a busbar or device. Where a copper lug goes onto an aluminium busbar — or an aluminium lug onto a copper one — a CUPAL washer goes between them so that like metal meets like metal on both contact faces.
- Bimetallic cable lugAl-Cu lug
A cable lug with an aluminium barrel that takes an aluminium conductor and a copper palm that bolts to a copper busbar or terminal. The copper-aluminium transition is made at the factory, between barrel and palm. It is the right part when an aluminium cable has to land on a copper connection point; where the mismatch is between lug and busbar, a CUPAL washer is the simpler fix.
- Busbarbus bar
A rigid conductor bar for high-current distribution in switchgear, substations and data centres. Where a copper and an aluminium bar or lug meet, a CUPAL transition plate or washer goes between them; without it, the joint loosens and heats up over time through galvanic corrosion.
- Transition platetransition segment, bimetal sheet
A piece of CUPAL cut to the size of a busbar joint and fitted between a copper and an aluminium bar or fitting. It does what the washer does, over a larger area: the copper face sits against the copper conductor, the aluminium face against the aluminium. It is cut from sheet (500 × 500 or 500 × 2000 mm), from strip, or to a drawing.
- Spring washerdisc spring, Belleville washer
A resilient washer that keeps up the clamping force in a bolted joint even when the aluminium yields slightly through cold flow or thermal expansion. It can be used in a CUPAL joint to keep the pressure constant; it does not replace the CUPAL washer but complements it.
- ICALCU part number
The part-number prefix of CUPAL bimetal washers, followed by the bolt size and variant — for example ICALCU10CS is the M10 washer with a 23 mm outer diameter. Distributors also sell the same part under their own codes (for example NEXANS Cupal M 10 Al-Cu or Mentavill 880111); the part-number cross-reference maps them.
- Laser cutting and punchingblanking, piercing
The two processes that make a custom-contour CUPAL part. Laser cutting needs no tool, so it suits samples and small runs, and the drawing can change at any time. Punching carries a one-off tooling cost, but in large runs it is the cheapest per part. Straight-edged strips and rectangles need neither — shearing is enough.
Standards and certificates
- EN 10204material certificate
The European standard that classifies the types of inspection documents for metallic products — who issues the document, and whether it carries lot-specific measured data or generic data. For CUPAL shipments the practical choice is between the 2.2 and the 3.1 certificate.
- EN 10204 2.2test report
The manufacturer’s statement with generic, non-lot-specific test results. It ships with every CUPAL delivery by default, cut-to-size parts included, with no separate request needed.
- EN 10204 3.1inspection certificate
A certificate carrying measured data tied to the specific shipment (charge/lot), signed by an authorised representative independent of production. Issued on request, project-scoped.
- ISO 9001:2015
The international quality-management-system standard. The CUPAL base material comes from an ISO 9001:2015 certified German supply chain (WMH); the certificate attests the supplier’s system, not the material itself — the material is described by the EN 10204 certificate.
- SVHC (REACH)Substance of Very High Concern
A Substance of Very High Concern under the REACH regulation. CUPAL contains no SVHC above the 0.1 wt% reporting threshold; an SVHC-free declaration can be requested per shipment or tied to a project.
- IEC 61238
The test standard for compression and mechanical connectors for power cables: it checks, through heat cycling and short-circuit tests, whether the joint’s resistance stays stable over time. It applies to the connector, not to CUPAL as a material; copper-aluminium transitions are judged within this framework.
- IEC 61439EN 61439
The standard series for low-voltage switchgear and controlgear assemblies. Compliance is always verified by the assembly manufacturer; CUPAL features here as a compatible transition material, not as a standalone certified product.
- DIN 43671
The German standard for sizing copper busbars for continuous current: it gives the permissible load current by cross-section. Its counterpart for aluminium busbars is DIN 43670. In a copper-aluminium busbar joint, the CUPAL transition piece is sized to match the bars it connects.