Opening a food can may take only a few seconds, but producing a safe, attractive and process-ready three-piece can requires coordinated control of steel, tin coating, lacquer, printing, forming, welding, end making and double seaming. This guide follows the complete journey from flat tinplate to a filled and thermally processed food can, while explaining why food manufacturers increasingly specify BPA-free or BPA-NI coating systems.
A three-piece can consists of a welded body, a bottom end and a top end. The can maker normally supplies the body with the bottom already double-seamed. The food processor then fills the open can, applies the top end and processes the sealed product according to a validated schedule. This distinction matters because empty-can manufacture and food sterilization are separate operations with different equipment, controls and responsibilities.
Tinplate, also called ETP or SPTE, is low-carbon cold-reduced steel coated on both sides with controlled amounts of tin. The steel core provides strength and rigidity, while the tin-coated surface supports corrosion protection, lacquering, printing and resistance welding. Buyers can review GDD Metal’s ETP tinplate sheet options for can bodies, ends and printed packaging.
Tin coating alone is not a universal food-contact solution. Tomatoes, fruit, fish, meat, vegetables, sauces and pet food expose a can to different combinations of acid, salt, sulfur compounds, oil and heat. The internal lacquer must therefore be matched to the recipe, filling temperature, retort process and required shelf life.
Production begins with approval of the tinplate specification. The can maker checks thickness, width, temper, tin-coating mass, surface finish, flatness, hardness, rolling direction and visible defects. The selected material must suit the can diameter, height, bead design, welding speed, packed food and thermal process. Single-reduced material offers broad forming options, while thinner double-reduced grades can provide higher strength but require compatible tooling and tighter line control.
The food-contact side receives a selected lacquer, and the outside may receive a white or transparent base coat. Each layer is cured under controlled oven conditions. Industrial offset printing then applies artwork, followed by an overvarnish that protects the graphics during cutting, forming and distribution. A welding margin is normally kept free from incompatible coating and ink so the side seam can be welded consistently. Learn more about artwork and coating preparation in our guide to printed tinplate sheets.
Printed sheets are cut into accurate rectangular blanks, often using a duplex slitter. Cut length determines the body circumference plus welding allowance, while blank width determines can height plus forming allowance. Squareness, burr height, print registration, grain direction and the position of the welding margin must remain within the approved drawing.
A body former rolls each blank into a cylinder and presents the two longitudinal edges with a small controlled overlap. A resistance welder applies current and pressure to create a continuous side seam. Welding current, wire condition, overlap, pressure and line speed must be stable; an attractive print cannot compensate for an incomplete or overheated weld.
Welding disrupts the protective layers along the side seam. The line therefore applies an internal protective side stripe, and often an external stripe where required, before curing it in an oven. Stripe width, cure and continuity are important because the weld area is a potential corrosion path if protection is incomplete.
The cylinder edges are flanged outward so they can interlock with the end curl during double seaming. Beads may be formed around the body to improve panel stiffness and resistance to pressure changes. Some designs are necked-in to match the selected end diameter. Operators monitor flange width, cracks, body roundness, bead geometry and coating damage.
Can ends are stamped in a shell press, formed with the specified countersink and curl, and lined with sealing compound. Easy-open ends undergo additional conversion operations to create the score, rivet and pull tab. At the can plant, the bottom end is normally double-seamed to the body. The empty open-top can then passes dimensional, coating, seam and leak checks before packing and shipment to the food processor.
At the cannery, empty cans are depalletized, cleaned or inverted as required, inspected and filled with the product and any brine, oil or sauce. The line controls fill weight and headspace, removes excess air by the selected exhausting or steam-flow method, feeds the top end and forms the final double seam. Low-acid foods in hermetically sealed containers are then processed using a scientifically established schedule appropriate to the product, can size and equipment. Acid foods and other products may use different validated heat treatments. Cooling, drying, coding, inspection and case packing follow.
The retort process belongs to the filled-food operation, not to every empty-can production line. A can supplier can provide a process-ready package, but the food processor and its qualified processing authority remain responsible for establishing the scheduled process, sanitation program and closure-control plan.
Three-piece cans are widely used for vegetables, fruit, tomato paste, fish, meat, beans, pet food, edible products and powders because one body diameter can be combined with different heights. This allows broad capacity planning without changing every end-tool set. Flat sheets are also easy to decorate before forming, and the welded construction suits many round and selected non-round packages.
The tradeoff is added process control. A three-piece can has a welded side seam and two end seams, so weld quality, weld-stripe coverage and both double seams must be verified. Two-piece cans eliminate the side seam and integrate the body with the bottom, but they use different drawing equipment and tooling. The better design depends on can geometry, volume, line configuration and investment plan.
BPA is not normally introduced by the steel substrate or metallic tin coating. It has historically been associated with certain epoxy-based organic coatings applied to metal food packaging. These coatings provide valuable corrosion and barrier performance, but regulators, food brands and consumers increasingly require alternative coating chemistries and better migration documentation.
The European Union adopted Regulation (EU) 2024/3190, which restricts BPA and certain other hazardous bisphenols in food-contact materials, including varnishes and coatings used on metal cans, with transition periods and limited exceptions. Requirements differ by destination, so an export project should define the applicable law, transition date, food type, processing conditions and test method before production.
In commercial discussions, “0 BPA” is often used as shorthand. A more precise specification states BPA-Free, BPA-NI / No Intentionally Added BPA, or BPA not detected at a stated analytical detection limit. Buyers should identify which claim is required and request documentation for the exact lacquer, production lot and intended food-contact conditions.
GDD Metal can supply BPA-free and BPA-NI food-packaging tinplate options with relevant food-contact test documentation according to the product and report scope. A material MTC supports traceability and reports agreed substrate properties; it does not replace coating-composition declarations or migration testing.
An easy-open end must remain strong during filling, seaming, retorting, stacking and transport, yet fracture predictably when the consumer lifts the tab. Tinplate can provide the required rigidity, stamping response and surface protection when thickness, temper, score residual, tab geometry and coating are designed as one system.
An EOE is a precision component rather than a generic lid. Excessive score residual can raise opening force; insufficient residual can weaken the panel. Coating damage at the score, rivet or formed areas can also reduce corrosion resistance. Samples should be tested on the intended seamer and through the actual thermal process before mass production. GDD Metal supplies tinplate easy-open ends in multiple diameters and opening configurations.
The following values describe common GDD supply options and ordering points. They are not a claim that every combination is available or suitable for every food. Final material, coating and end specifications must be confirmed against the can drawing, packed product, seaming line, thermal process and destination-market rules.
| Parameter | Typical Options | Selection Note |
|---|---|---|
| Base Material | ETP / SPTE electrolytic tinplate | Select body, conventional-end or EOE grade by application |
| Tinplate Thickness | 0.13–0.50 mm or customized | Match can diameter, height, beads, load and line capability |
| Temper | T1, T2, T2.5, T3, T4, T5, DR8, DR9 or agreed grade | Balance formability, springback, panel strength and score performance |
| Tin Coating | 1.1/1.1, 2.8/2.8, 5.6/5.6, 8.4/8.4 g/m², equal or differential | Confirm with corrosion exposure, lacquer and welding requirements |
| Surface Finish | Bright, stone, silver, matte | Match coating, printing appearance and forming process |
| Food-Contact Coating | Clear, gold, BPA-free or BPA-NI options | Confirm food chemistry, retort conditions and regulatory market |
| Printing | CMYK, spot colors, white base, gloss or matte overvarnish | Artwork must include trim, seam and forming allowances |
| EOE Thickness | Approximately 0.18–0.32 mm or customized | Confirm diameter, temper, score design and pressure duty |
| Common EOE Diameters | 52, 65, 73, 83, 99, 126 mm or customized | End profile must match can flange and seamer tooling |
| Reference Standards | ISO 11949:2026, EN 10202:2022, ASTM A623/A623M, ISO 90-1 | Use the contract edition and customer specification |
| Available Documents | MTC, relevant test reports, Certificate of Origin, export license documentation where applicable | Confirm document scope and destination requirements before ordering |
Material specifications and food-contact rules address different risks. ISO 11949:2026 and EN 10202:2022 cover cold-reduced tinmill products, while ASTM A623/A623M provides general requirements for tin mill products. ISO 90-1 defines terminology and methods for dimensions and capacities of open-top cans. These standards do not by themselves approve a finished can for every food.
For the United States, applicable resinous and polymeric food-contact coatings may be assessed against 21 CFR 175.300 and other relevant provisions. Thermally processed low-acid foods in hermetically sealed containers are subject to 21 CFR Part 113. EU projects should review Regulation (EC) No 1935/2004, GMP Regulation (EC) No 2023/2006, Regulation (EU) 2024/3190 on BPA and other applicable national or product-specific requirements.
A robust approval plan typically includes material identity and MTC review, lacquer declaration, coating weight and cure checks, adhesion and porosity inspection, weld evaluation, side-stripe coverage, flange and end dimensions, double-seam teardown, leak testing, opening-force checks for EOE products and retort validation with the actual food. Production records should link the can lot, end lot, coating lot and food batch.
Henan GDD Metal Materials Co., Ltd. supplies raw tinplate coils and sheets, cut-to-size body stock, printed tinplate, finished three-piece food-grade tinplate cans, bottom ends and compatible easy-open ends. Available options include food-contact lacquer systems described commercially as 0 BPA, BPA-free or BPA-NI, subject to the agreed specification and supporting documentation.
We can provide MTCs for the applicable material, relevant food-contact test reports according to their stated scope, Certificate of Origin, export license documentation where required and agreed commercial and shipping documents. Buyers should send the can drawing, packed food, filling medium, pH or product description, retort conditions, target shelf life, destination market, annual volume and required end type so the material, coating and closure can be reviewed together.
To discuss a new can line, replacement material or EOE compatibility trial, contact GDD Metal with your technical requirements and destination port.
