ZN-500 is a cyanide-free alkaline zinc plating brightener supplied as a four-part system: the main brightener, an additive for low-current-density areas, a purifier and a water treatment agent. The four are dosed from the same index, so a rack line and a barrel line can each be set to their own values without stocking two separate chemistries.
It is built for shops doing industrial metal plating on parts whose geometry fights the current — polygonal pressings, deep recesses, mixed racks — and for lines moving away from cyanide zinc that want the dosing, the control routine and the deposit to feel familiar from the first bath. There is no free cyanide in the system, which takes a handling hazard out of the plant and removes cyanide from the waste route.
The working window is deliberately wide across zinc metal, caustic, current density and temperature. The technical index below sets out the full range next to separate recommended values for rack and for barrel work, so an existing line can be matched at the point closest to how it already runs rather than rebuilt around the chemistry.
| Item | Operating Range | Recommended for Rack Plating | Recommended for Barrel Plating |
|---|---|---|---|
| Zinc metal | 5.5–18.75 g/L | 11 g/L | 13 g/L |
| NaOH | 75–152 g/L | 128 g/L | 135 g/L |
| Brightener | 12–20 ml/L | 16 ml/L | 18 ml/L |
| Additive for low-current area | 0.5–2 ml/L | 1 ml/L | 0.5 ml/L |
| Purifier | 1 ml/L | 1 ml/L | 1 ml/L |
| Water treatment agent | 1 ml/L | 1 ml/L | 1 ml/L |
| Cathode current density | 0.2–6 A/dm2 | 2 A/dm² | 1.5 A/dm² |
| Temperature | 18–52 °C | 28 °C | 28 °C |
Brightness that holds at temperature. Zinc from this bath comes out bright across the working range, and the brightness survives the top of the temperature window: a coating that is still bright at 52 °C provided the bath is kept inside its stated conditions. That matters in a plant where the tank warms through a summer shift or a heavy rack load heats the solution — the deposit does not quietly go dull in the afternoon and bright again the next morning.
Reach into low-current areas. Dispersion in low-current-density areas is the property that decides whether a recess plates at all. Polygonal workpieces and deep concave parts are the natural fit for this process in rack plating, and it is the reason shops converting from acid zinc plating chemicals notice the largest difference on parts with pockets, internal corners and shielded faces.
Impurities it will live with. The bath tolerates calcium, magnesium, lead, cadmium, iron and chromium carried in with work, anodes and make-up water — the metals that normally accumulate in a zinc bath and begin dulling deposits or darkening passivated parts.
A surface that takes a finish. Plated parts accept a range of post-passivation treatments, so the same process can feed a clear, blue or coloured finishing line without a change of bath.
Rack plating is where a plating process is asked the most. A deep concave part, a polygonal pressing or anything with a shielded face has a low-current-density area that decides whether the whole part plates or only its outside does, and this system addresses that with a dedicated component rather than with more brightener. On rack work the additive for low-current areas is normally run at 1 ml/L at the recommended setting, alongside 16 ml/L brightener, 11 g/L zinc metal and 128 g/L NaOH.
Current density is the lever the operator actually holds. The bath runs from 0.2 to 6 A/dm² with 2 A/dm² as the rack starting point. Raising it fills an exposed face quickly but does nothing for the back of a recess, which is why rack layout matters as much as bath chemistry. Face deep pockets towards the anode instead of letting the frame mask them, keep contacts off visible surfaces, and expect to set current per rack rather than per part.
Temperature is the second lever, and it is the one that usually limits a rack shop. 28 °C is the recommended point for both rack and barrel work, but brightness holds to 52 °C, so a long cycle in a warm plant does not automatically produce dull work. If your parts are large and the rack load is heavy, check the current density and the rack arrangement against your own geometry before the first production run, not after it.
A thick zinc coating is easy to specify and harder to deliver. As the deposit builds, many baths trade ductility for thickness and the coating starts to crack at edges, on bends or under a press fit. The zinc from this process is tough rather than brittle and holds that character at thicknesses above 25 µm, which is roughly the point where a brittle deposit announces itself.
Reaching that thickness in a metal plating process is a question of time at current density, not of current density alone. Pushing the current up to shorten the cycle builds a stressed, coarse layer; running longer inside the recommended window builds the same thickness with the deposit still soft. On rack work, start from 2 A/dm² and extend the cycle. In the barrel, start from 1.5 A/dm² with the richer bath so the load keeps building evenly as it turns.
Two things are worth settling before you commit. First the thickness figure: above 25 µm is what this process is built to reach, and a coupon check on your own parts is the number to trust. Second the corrosion performance: the salt-spray hours a finished component must survive depend on the passivation or topcoat applied afterwards, so agree the test method with your customer and verify on your own parts rather than on a data sheet.
One boundary worth stating plainly. This is a zinc process. Where the drawing specifies zinc nickel plating or another alloy, this bath is not the substitute.
A cyanide-free bath is still an alkaline bath, and it should be handled that way. The chemistry is built on sodium hydroxide, so the concentrated brightener, additive, purifier and water treatment agent deserve alkali-rated gloves and eye protection, should be kept away from acids both in storage and at the dosing bench, and should be added to water rather than the other way round. General ventilation over the tank covers normal operation.
Storage is simple: sealed containers, a cool dry place, out of direct sunlight, away from acid stocks, and never decanted into unlabelled containers. The four components look alike and are dosed at very different rates, which is exactly how a bath gets ruined.
Ask your sales contact for the safety data sheet for each component and read it before the first mix rather than filing it — the handling and first-aid sections are the parts a shift supervisor actually needs. Batch documentation accompanies the shipment.
Removing cyanide from the process does remove the cyanide-specific procedures from the line: there is no free cyanide to monitor or destroy. It does not make the caustic harmless, so keep the same discipline you would apply to any alkaline tank.
Choosing the right match is where most sourcing decisions stall. As a trading supplier, we keep one point of contact from first enquiry to after-sales: tell us what you are making and the conditions you work under, and we shortlist the closest matches from our supplier network, compare specifications and arrange samples before you commit to a bulk order. If something does not behave as expected, we work with the supplying partner on the cause and a practical fix, and stay with the case until it is settled. Email, WeChat or WhatsApp enquiries get a reply within 24 hours.
It is a cyanide-free alkaline zinc process for both rack plating and barrel plating. The bath has no free cyanide in it, and the rack and barrel columns of the technical index give each line type its own starting set points.
The bath runs from 18 °C to 52 °C, with 28 °C as the recommended value for both rack and barrel work. The upper end is real rather than theoretical: a bright deposit is still obtainable at 52 °C as long as the rest of the bath is inside its stated conditions.
Yes, and this is one of its stronger cases. Dispersion in low-current-density areas is good, and polygonal workpieces and deep concave parts are exactly the rack-plated geometry the process is set up for. Run the additive for low-current areas towards the top of its range and check the rack layout before blaming the chemistry.
Zinc thickness above 25 µm, with the deposit staying soft rather than brittle at that thickness. Building thickness in a plating process is a matter of time at current density rather than current density alone, so extend the cycle instead of pushing the current.
Calcium, magnesium, lead, cadmium, iron and chromium. These are the metals that arrive with work, anodes and make-up water. The bath tolerates them, but that is not a licence to let drag-in rise — good rinsing before the tank is still the cheapest control you have.
Different family, different behaviour. Acid zinc plating chemicals run at low pH in a chloride or sulfate system; this is an alkaline process built on sodium hydroxide, and the throwing power and impurity tolerance follow from that. If you are converting, expect to re-learn rinsing and caustic balance rather than simply swapping one brightener for another.
In the same plant, yes; in the same tank, no. Where the drawing calls for zinc nickel plating, this bath is not the substitute, because it deposits zinc rather than a zinc alloy. Keep dedicated tanks, barrels and racks, or at the very least a thorough cleaning routine between processes — cross-contamination shows as off-colour work long before it shows in analysis.
Titrate zinc metal and caustic on a fixed schedule — daily in heavy production, less often on a light line — and top up from the analysis rather than from the calendar. In a metal plating process, the pattern of additions over a month tells you more than any single reading: it shows whether the bath is drifting or whether the work coming through has changed.
