Perforated, Plated or Clad: Five Nickel Strips Compared

Five strip products turn up in the same request for quotation often enough that buyers treat them as grades of one material: nickel plated steel, nickel plated copper, copper nickel clad, perforated pure nickel, and perforated pure copper. They are not grades of one material. They differ on three independent axes, and a quotation that compares them on price alone compares almost nothing.

The first axis is where the nickel sits: through the whole section, as a coating a few micrometres thick, or as a bonded layer taking a share of the thickness. The second is the base metal underneath, because steel, copper and nickel conduct and corrode very differently. The third is whether the strip carries holes, which is the axis most often left out of the comparison and the one that changes the most.

Perforation is not a weight saving exercise. It removes conducting section, it concentrates stress at every hole edge, and it cuts through whatever surface protection the material had. That last effect is the subject of this article, because it decides which of the five can be perforated at all in a corrosive joint, and which ones fail first at the hole wall.

The table below separates the five forms by structure. Read the fourth and fifth columns together: conductivity comes from the base metal, while corrosion behaviour at a cut edge comes from what the cut exposes.

Only two of the five expose the same metal at a cut edge as they show on the face. The other three change character the moment a tool cuts them, and a punched strip is nothing but cut edges repeated several thousand times per metre.

This is why a specification written for solid strip does not transfer to perforated strip. A plated strip qualified on a flat coupon has been tested on its coating. The same strip, punched, presents bare substrate around every hole, and the corrosion test that passed the coupon says nothing about the hole wall.

Open area is the fraction of the strip surface removed by the holes. Because the holes run through the full thickness, the conducting section falls by the same fraction, and the resistance rises by the reciprocal.

A strip at 40 % open area keeps 60 % of its conducting section, so its resistance is 1 divided by 0.6, which is 1.67 times the solid value. At 60 % open area the multiplier is 2.5. The arithmetic is simple, and it is the first thing a drawing should state, because open area is often chosen for fluid passage or weight and its electrical cost is discovered later.

Two corrections belong with that table. First, the multiplier assumes current flows uniformly across the width, which holds when the hole pattern is fine and evenly distributed. A coarse pattern with wide unperforated margins carries current in the margins and the local resistance is lower than the average suggests, at the cost of a hot spot where the pattern begins.

Second, open area does not account for the hole edge itself. A punched hole has a rollover, a shear band and a burr, and the burr side has a slightly larger effective diameter in the current path while being the place where coating damage starts. Etched strip has tapered walls and no burr, and laser cut strip has a heat affected rim. The three processes are not interchangeable at the same nominal open area.

Five reasons justify perforation, and each points to a different pattern.

Fluid or electrolyte passage is the reason in battery and filtration work. The hole is a channel, so the pattern follows the flow direction and the open area is set by how much the process needs, not by weight.

Weight reduction matters in moving parts and in large area shields, where the strip is a conductor and a support at the same time. Here the open area can be high, and the electrical penalty is accepted.

Multi point contact is the reason in grounding and gasket applications. Many small contacts in parallel give a lower and more stable interface resistance than one large contact, because a single oxide patch or a single high spot no longer sets the whole joint.

Stress relief and keying appear in laminated and stacked assemblies, where the holes let resin, adhesive or a fastener pass through, or allow the strip to expand without buckling.

Access for welding is the fifth, and it is often the real reason a perforated strip is specified. A hole next to a weld spot lets the electrode reach through a stack, or vents gas that would otherwise blow the nugget apart.

This is where the five forms separate in a way no grade change can fix. The table describes the cut face, since the surface is the part a sample shows.

The steel case is the most severe and the most common. Nickel plated steel is the standard material for pocket plate battery electrodes precisely because it is cheap, formable, and weldable, and the perforation is functional. The same perforation puts bare steel in contact with electrolyte at every hole, so the plate lives or dies by how well that cut face is protected. Post punching re plating, edge sealing, or a deliberate choice of a thicker coating with a formed edge are the usual answers.

The clad case is subtler and often misread. A clad strip has no coating to breach, so it survives handling and abrasion far better than plated strip. Once punched, however, the wall is a laminate cross section: the nickel face is still nickel, while the wall and the opposite face are copper. Orienting the nickel face toward the electrolyte or the humid side preserves most of the benefit. Orienting it the other way throws the advantage away without changing the price.

The pure nickel case is the one that does not need mitigation. The cut face is the same alloy as the surface, at the same composition and the same corrosion potential, so there is no couple, no undercutting and no coating integrity question. That is the specific reason perforated pure nickel strip is chosen in alkaline electrolyte, in filter media that see aggressive fluids, and in electrodes where the cut edge sits in the working environment. Its conductivity is roughly a quarter of copper, which is the price paid for that uniformity.

Pure copper perforated strip sits at the other end. It is the best conductor of the five and has no edge couple, and it has almost no corrosion resistance of its own. It belongs in grounding, shielding, and dry current collection, where the environment is controlled and the joint is protected by housing or by plating after assembly.

Open area and strength loss are not the same number, and the gap between them is set by how the holes are arranged.

Conductivity is an average: current spreads across the full width, so the conducting fraction equals the solid fraction, one minus open area. Tension is not an average. It is carried by the narrowest continuous section across the width, and in a pattern with aligned rows that section is a single row of ligaments.

Take round holes on a square pitch at 40 % open area. The hole diameter works out at about 0.71 of the pitch, so a row of ligaments retains roughly 29 % of the full width. Conductivity retains 60 %. The strip has lost 40 % of its conductance and 71 % of its tensile capacity, and both numbers come from the same pattern.

The practical conclusion is that a perforated strip should be designed for its mechanical duty first. If the joint has to carry load or survive vibration, staggered rows with generous margins are worth the small loss in open area. If the strip only conducts and lets fluid through, aligned rows with a high open area are cheaper to tool.

There is a second mechanical effect at the hole edge itself. A circular hole in a loaded strip raises local stress by a factor of roughly 2 to 3, and a row of holes approaches the upper end. Under vibration or repeated bending this is where a crack starts, at the burr side first because the burr is a notch within a notch. This is why a perforated strip that passes a static tensile test can still fail in a vibrating assembly within weeks.

The five forms sort cleanly by application once the axes are fixed. The table below is a starting point, not a rule; the environment and the assembly method override it.

Two entries deserve a comment because they are usually decided on price and later regretted. The pocket plate electrode is the classic case: nickel plated steel is the standard, and the perforation is what makes the plate work, yet the same perforation is what limits its life. Moving to perforated pure nickel multiplies the material cost and removes the failure mode. Where the plate is replaced on a schedule that is short enough, steel is the rational choice.

The current collector case runs the other way. In an electrolyser the strip is perforated for gas and liquid transport, sits in alkaline electrolyte, and carries current at the same time. A plated product puts bare substrate in the electrolyte at every hole, and a clad product puts copper there. Only a solid nickel section survives that combination, which is why perforated pure nickel holds this application despite a quarter of copper conductivity.

A perforated strip order has six specification items that a solid strip order does not, and omitting any of them leaves the supplier to choose.

The fourth item is the one that separates a good order from an average one. Burr is a directional feature: it forms on the exit side of the punch. Two coils punched from opposite faces look identical in a photograph and stack differently. Naming the burr face, and turning it away from the mating surface and away from the coated side, removes a whole class of assembly complaints.

The fifth item is the one most often copied from a data sheet. Tensile values published for solid strip do not apply once the strip is perforated, because the critical section has changed. A supplier who quotes the solid value is not being dishonest, merely answering the question that was asked. Ask for the value on the finished perforated strip, and ask which pattern it was measured on.

DLX operates in Changzhou, Jiangsu, supplying nickel plated steel and copper strip, copper nickel clad strip built to a specified ratio, and perforated pure nickel and pure copper strip in coil or sheet. Hole patterns are produced to drawing, with open area, burr side and burr height stated on the certificate, and chemistry and mechanical values reported on the finished perforated material.

Four items make a quotation accurate: base form with the nickel position, thickness with tolerance, hole geometry with the calculated open area, and the burr side with its limit. Where the part goes into electrolyte or a humid assembly, say so, because that single fact decides whether a plated product is acceptable at all.

Yes, to a first approximation. The conducting section falls by the open area fraction, so resistance rises by one divided by one minus open area. At 40 % open the multiplier is 1.67. The estimate assumes uniform current distribution, which a fine evenly spaced pattern provides.

Perforated pure nickel, because the cut face is the same alloy as the surface and there is no couple at the hole. Nickel plated steel is the weakest, since every hole exposes bare steel that is anodic to the coating. Plated copper and clad strip fall in between and depend on orientation and sealing.

Only if the cut face is protected afterwards. Re plating, edge sealing, or a coating thick enough to form a continuous fillet into the hole are the usual routes. Without one of them the hole wall is bare substrate, and a salt spray result obtained on unpunched coupons does not describe the punched part.

Because tension is carried by the narrowest continuous section, while current spreads across the width. At 40 % open area with aligned rows, the ligament row retains about 29 % of the width, so capacity falls by 71 % while conductance falls by 40 %. Staggering the rows recovers part of the difference.

Away from the mating surface and away from any coated face that will be exposed. The burr is a stress raiser and a coating damage site, so it belongs on the side that is neither loaded in contact nor visible to the environment. State the direction on the drawing, since it is invisible in a photograph.

Six items: form with nickel position, thickness with tolerance, hole geometry with calculated open area, burr side with a height limit, temper with mechanical values measured on the perforated strip, and coil plus edge requirements. Missing any one of them leaves a decision to the supplier.

The five forms separate on three axes: where the nickel sits, what the base metal is, and whether the strip carries holes. Comparing them on price alone mixes all three, which is why quotations for the same nominal strip can differ by a factor of several and all be correct.

Perforation is the axis that changes the most. It cuts conductance in proportion to open area, it cuts tensile capacity in proportion to the narrowest ligament row, and it exposes a fresh metal face at every hole. For plated and clad products that last effect is the one that decides service life, and it is decided by orientation and edge treatment as much as by grade.

Where the hole wall sits in an aggressive environment, perforated pure nickel is the only one of the five that presents the same alloy on the surface and in the hole. It pays for that with a quarter of copper conductivity. Every other choice is a trade against that reference, and the trade should be written down before the order, not discovered at the failure analysis.

Physical property data for copper, nickel and low carbon steel, used for the conductivity comparison.

Standard electrode potentials for copper, nickel and iron, used for the galvanic sequence at a cut edge.

Sheet metal punching practice covering rollover, shear band and burr formation, used for the hole wall description.

Definitions and geometry of perforated metal patterns, used for the open area calculation.

Stress concentration data for holes and perforated strips in tension, used for the fatigue discussion.

Construction of alkaline pocket plate electrodes on a nickel plated steel substrate, used for the electrode example.

ASTM B162, Standard Specification for Nickel Plate, Sheet and Strip, used for nickel strip grades and dimensional wording.

Conductivity and capacity figures in this article are geometric estimates: conductance from the solid fraction, tensile capacity from the critical ligament section of an idealised pattern. Real values depend on hole shape, pattern tolerance, material temper, burr condition and the test method, and they should be measured on the finished perforated strip. Corrosion behaviour at a cut edge depends on the specific electrolyte, temperature and exposure time, and a salt spray result on solid coupons does not describe a punched part. Standards are revised, and the version cited in the contract applies. This article supports material selection and enquiry, and it does not replace engineering design or incoming inspection.