A Tinplate Lacquering Machine is a roller-coater line that applies a thin organic lacquer film to electrolytic tinplate sheet before the metal is cut and formed into can bodies, ends, or closures. Two counter-rotating rolls — a rubber applicator and a steel doctor roll — meter lacquer onto the sheet as it passes through, then a wicket oven cures the film at 190-205°C. The purpose is to protect the food product from metal contact and the metal from corrosion. A modern line coats 4,000-6,000 sheets per hour at film weights of 4-12 g/m².
Tinplate Lacquering Machine Interactive Calculator
Vary doctor-roll gap, drift, sheet size, and line speed to estimate wet film, dry film weight, lacquer use, and coating variation.
Equation Used
The calculator maps the article coating-head window to a simple linear model: a 30-80 um doctor-roll gap corresponds to about 8-25 um wet film and 4-12 g/m2 dry film weight. Dry lacquer use is then film weight times sheet area times sheets per hour.
- Linear interpolation is used across the article range of 30-80 um gap, 8-25 um wet film, and 4-12 g/m2 dry film.
- Sheet area is rectangular using entered width and length.
- Dry lacquer consumption is based on coated area and dry film weight only.
The Tinplate Lacquering Machine in Action
The machine handles tinplate in flat sheet form, typically 0.18-0.32 mm thick, in sizes around 800 × 1000 mm. A magnetic feeder lifts one sheet at a time off the stack and pushes it into the coating head. Inside the head, a rubber applicator roll picks lacquer from a pan or chamber, transfers it across a steel doctor roll that meters the film thickness, and rolls it onto the upper face of the sheet as the sheet passes underneath at line speed. The film weight depends on the gap between applicator and doctor — that gap is set in the 30-80 µm range and the wet film deposited on the sheet is a fraction of that, around 8-25 µm wet, which dries down to roughly 4-12 g/m².
From the coater the sheet drops onto a wicket conveyor — a row of vertical wire fingers that hold each sheet on edge with minimal contact — and rides through a gas-fired or electric oven for 8-12 minutes at 190-205°C peak metal temperature. The lacquer is most often an epoxy phenolic, polyester, or modern BPA-NI coating, and the cure schedule has to hit a defined PMT (peak metal temperature) for a defined dwell time or the film will under-cure. Under-cured lacquer fails the MEK rub test and tastes through into the food product. Over-cured film goes brittle and cracks at the can-body flanger.
If the doctor-roll gap drifts by even 10 µm across the roll face you get visible stripes of heavy and light coverage, the film weight check at the QC bench falls outside the ±0.5 g/m² window, and downstream the can ends fail enamel rater testing. The most common failures we see are worn rubber on the applicator (it goes glassy after 6-9 months and stops transferring evenly), lacquer viscosity drift in the pan as solvent flashes off through the shift, and oven temperature profile errors when burner trim falls out of calibration.
Key Components
- Magnetic Sheet Feeder: Lifts single sheets of 0.18-0.32 mm tinplate off the infeed stack using permanent magnet rollers. Has to deliver one sheet at a time with no doubles — a double-feed jams the coater head and tears the rubber applicator.
- Applicator Roll: Rubber-covered steel roll, typically 60-70 Shore A hardness, that transfers metered lacquer onto the sheet face. The rubber must be solvent-resistant nitrile or EPDM and the durometer drift over its life must stay within ±3 points or coating weight goes off.
- Doctor Roll: Hard chrome-plated steel roll running against the applicator. The gap between the two is set with micrometer adjusters at 30-80 µm and controls how much lacquer the applicator carries forward. Roll runout must be under 5 µm TIR.
- Lacquer Pan and Recirculation: Holds working lacquer at controlled viscosity, usually 25-35 seconds in a Zahn 2 cup, and feeds the rolls. Solvent is dosed in to compensate for flash-off across the shift.
- Wicket Conveyor: Carries coated sheets vertically on edge through the cure oven on wire fingers. Contact area is under 3 mm² per sheet so wet lacquer is not marked off. Wicket pitch sets oven dwell time.
- Cure Oven: Gas-fired or electric convection oven with multiple zones. Hits a peak metal temperature of 190-205°C for 8-12 minutes. PMT is verified weekly with a Datapaq tracker — the defined cure window is the contract between the coating supplier and the can plant.
- Cooling Section and Stacker: Forced-air cooling drops the sheet back below 40°C before stacking. Hot stacking causes block — sheets glue together and the next operator strips the top layer of lacquer when separating.
Real-World Applications of the Tinplate Lacquering Machine
Lacquered tinplate is the substrate behind almost every steel food can, beverage end, aerosol, and screw closure on the shelf. The lacquering machine sits between the tin mill and the press shop in a metal-decorating plant, and the choice of lacquer chemistry, film weight, and cure schedule is locked to the product going inside the can — fish, tomato, lager, paint, hairspray each want a different system.
- Food Cans: Crown Holdings three-piece food cans for tomato and pet food — gold epoxy phenolic internal lacquer at 6-8 g/m² coated on a Mailänder LTG2 line.
- Beverage Ends: Ardagh Metal Packaging beer-can ends coated with BPA-NI polyester at 4-5 g/m² before scoring and tab attachment.
- Aerosol Cans: Ball Corporation tinplate aerosol bodies for personal-care brands, internally lacquered with a phenolic-modified epoxy to handle propellant pressure and product chemistry.
- Screw Closures: Silgan twist-off lug caps for jars of baby food, coated with a low-migration BPA-NI vinyl organosol over a sealing compound carrier.
- Decorative Tins: Massilly biscuit and confectionery tins, where the lacquer doubles as a base coat for offset-printed graphics on a Crabtree Marquess press.
- Industrial Pails: 20 L paint and chemical pails coated with a chemical-resistant epoxy phenolic to handle solvent-based contents over multi-year shelf life.
The Formula Behind the Tinplate Lacquering Machine
The number that runs the planning office is line throughput in sheets per hour, but the number that runs the coater is film weight per square metre. Both come from the same line speed, and the operating window is narrow. At the low end of the typical speed range the oven over-cooks the film and you see brittleness at the flanger. At the high end the dwell drops below the cure threshold and the film under-cures. The sweet spot is where line speed, oven length, and cure schedule line up so PMT is reached for the full required dwell.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Q | Throughput in sheets per hour | sheets/h | sheets/h |
| v | Line speed | m/min | ft/min |
| Ls | Sheet length plus gap between sheets on the wicket | m | ft |
| Loven | Effective heated length of the cure oven | m | ft |
| tdwell | Time each sheet spends in the oven | min | min |
Worked Example: Tinplate Lacquering Machine in a Tinplate Lacquering Line for Tuna Cans
A sardine and tuna cannery supplier in Vigo, Spain is commissioning a Mailänder 222 roller coater feeding a 36 m wicket oven. They are coating 0.22 mm tinplate sheets at 880 × 1020 mm with a wicket pitch of 1.10 m, applying a BPA-NI epoxy phenolic gold lacquer at a target film weight of 7.0 g/m² and a required cure of 200°C PMT for 10 minutes. They want to know the throughput and dwell time at nominal line speed and at the edges of the practical operating window.
Given
- Ls = 1.10 m
- Loven = 36 m
- vnom = 60 m/min
- vlow = 40 m/min
- vhigh = 90 m/min
- Target PMT = 200 °C
- Required dwell = 10 min
Solution
Step 1 — at the nominal 60 m/min line speed, calculate throughput:
Step 2 — calculate dwell time in the 36 m oven at nominal speed:
That is a long way short of the 10-minute cure spec — the oven on this Mailänder is a multi-pass wicket type, so the actual sheet path through the oven is closer to 600 m as the wickets snake back and forth on overhead chains. Recompute with effective path length Lpath = 600 m:
Step 3 — at the low end of the operating window, 40 m/min:
At 40 m/min the line is loafing — throughput drops by a third, and dwell stretches to 15 minutes. The film over-bakes, you'll see a gold lacquer that has shifted toward amber, and the flanger downstream starts cracking the coating at the can-body bead.
Step 4 — at the high end, 90 m/min:
Throughput jumps 50% but dwell falls to 6.7 minutes — well below the 10-minute spec. PMT may still hit 200°C in the hot zones but total time-above-temperature is too short, the film under-cures, and an MEK double-rub test will fail at under 30 rubs against a 50-rub minimum.
Result
At nominal 60 m/min the line delivers 3,273 sheets/h with a 10. 0-minute oven dwell — exactly on the cure spec for the BPA-NI epoxy phenolic. That is the sweet spot: throughput the planner can hit comfortably, with cure fully inside the contract window. At 40 m/min you over-bake and lose flexibility for the can-body flanger; at 90 m/min you under-cure and fail MEK rub testing. If your measured film weight or cure quality drifts at nominal speed, look at three things first: applicator-roll durometer drift below 60 Shore A (gives heavy patches and uneven transfer), lacquer viscosity climb above 35 seconds Zahn 2 as solvent flashes off through the shift (gives heavy film and orange peel), or oven burner trim that has lost calibration so the upper wicket bank reads 195°C while the lower bank sits at 208°C (gives mixed cure on every other sheet).
When to Use a Tinplate Lacquering Machine and When Not To
Roller coating is the default for flat sheet metal decorating, but it is not the only way to put lacquer on tinplate. The choice between roller coater, electrostatic spray, and continuous coil coating comes down to substrate format, throughput, film weight tolerance, and what end product the plant is feeding.
| Property | Tinplate Lacquering Machine (sheet roller coater) | Coil Coating Line | Electrostatic Spray |
|---|---|---|---|
| Throughput | 3,000-6,000 sheets/h (~120-200 m/min sheet) | 60-180 m/min continuous strip | Low — limited by spray gun coverage |
| Film weight tolerance | ±0.5 g/m² across sheet | ±0.3 g/m² across width | ±1.0-2.0 g/m², harder to control |
| Capital cost | $2-5M for line including oven | $15-40M for full coil line | $200k-1M depending on automation |
| Substrate format | Pre-cut sheets, 0.18-0.32 mm tinplate | Coil only, 0.15-0.50 mm strip | Formed cans, drums, irregular shapes |
| Cure method | Wicket oven, 8-12 min at 200°C PMT | Catenary or floater oven, 20-60 s at 220-240°C PMT | Convection or IR, varies |
| Best application fit | Three-piece food cans, ends, closures | DWI beverage can stock, large-volume single-spec | Internal coating of formed cans, drums, fittings |
| Reliability / uptime | 95-98% with proper roll maintenance | 98%+ on modern lines | 85-92%, gun fouling drives downtime |
Frequently Asked Questions About Tinplate Lacquering Machine
Film weight is an average across a coupon, but enamel rater detects pinholes and thin spots — they measure different things. The most common cause is a worn rubber on one end of the applicator roll, which transfers a thinner film along one edge of the sheet while the average across the full sheet still lands inside the ±0.5 g/m² window. Cut a 25 mm strip from each edge and the centre, weigh each separately, and you'll see the edge strip 1-2 g/m² lighter.
The second cause is air entrainment in the lacquer pan when recirculation pumps suck near a low fluid level. Microbubbles burst in the wet film and leave craters too small for the QC weight check to flag but big enough for the enamel rater electrolyte to find.
The harder roll runs cleaner against the doctor and gives tighter film weight control, but it transfers less lacquer for a given gap so you need to open the gap up. Softer rolls bed in to the doctor better and tolerate a slightly out-of-true doctor roll, which matters on older machines.
Rule of thumb: high-solids modern BPA-NI lacquers run better on 65-70 Shore A because the lacquer is sticky and a softer roll smears. Traditional epoxy phenolics in the 25-35 second viscosity range run fine on 60 Shore A. If you are switching chemistries on the same machine, expect to re-set the gap by 10-15 µm and re-trim the lacquer viscosity.
Two mechanisms. First, lacquer viscosity in the open pan climbs as solvent flashes off — by the end of a 4-hour shift you can be 5-8 seconds higher on the Zahn cup, which raises wet film weight by 1-2 g/m² and that extra mass takes longer to reach PMT. Second, the oven heats up during a long run as wall losses fall, so the back end of a shift actually runs 3-5°C hotter than the front end at the same burner setpoint.
The fix is automatic solvent dosing tied to a viscosity probe in the pan, plus oven control on PMT readback from a periodic Datapaq tracker, not just air temperature thermocouples.
Blocking means the film is not fully cooled before the sheet hits the next sheet in the stack. The lacquer is still soft enough that contact pressure under the weight of the stack lets two faces bond. Three usual suspects: cooling section is too short or fans are dirty so sheet exit temperature is above 40°C; stack height is excessive so bottom sheets see too much pressure; or the cure was actually slightly under and the film never fully crosslinked, leaving residual tack.
Quick check: pull a sheet off the stacker and press your thumb on the lacquered face for 5 seconds. If you leave a print, the film is not cured or not cooled. Either is a problem you find at the can plant the next morning when stacks won't separate cleanly.
Only if the second lacquer is solvent-compatible with the first and the colour shift is tolerable. Going from a clear size coat to a gold epoxy phenolic, you can usually run through with a few hundred sheets of cross-contamination at the start. Going from a pigmented white base coat to a clear interior lacquer, you cannot — pigment particles will contaminate the clear for hours.
Practical rule: same solvent system and same or darker colour, run through. Different solvent system, lighter colour, or different chemistry family (epoxy to polyester for example), do a full wash-up with the appropriate thinner. The lost time of a 30-minute wash is cheaper than scrapping 5,000 contaminated sheets.
Dwell at line speed only tells you how long the sheet is in the oven. It does not tell you the temperature profile the sheet actually sees. PMT — peak metal temperature — and time-above-temperature (typically time above 180°C) are what crosslink the resin. A sheet can sit in the oven for the full 10 minutes but if the burners are out of trim, peak metal temp may only hit 188°C and the resin never fully reacts.
Run a Datapaq tracker through the oven on a representative sheet. You want to see PMT of 198-205°C and at least 6-7 minutes above 180°C for a standard epoxy phenolic. If the tracker shows you're short on either, retrim the burners zone by zone before you blame the lacquer supplier.
References & Further Reading
- Wikipedia contributors. Tinplate. Wikipedia
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