The appendix contains (i) a comparison of tinmill standards; (ii) a glossary of tinplate terms; (iii) detail on temper; (iv) detail on finish; and (v) detail on coating. All information is presented based on Titan Steel’s interpretation. Other participants in the industry may have a different understanding or adherence to this information. Steel mills in particular may have a separate set of standards for their production.
The information contained on this page is for general guidance on matters of interest only. Titan Steel is not responsible for any errors or omissions, or for the results obtained from the use of this information. For more information, please contact Titan Steel or consult official tinmill standards.
- Acetyl Tributyl Citrate (ATBC) Oil – A lubricating film applied to both surfaces of tinmill products to prevent abrasion during transit or handling.
- Anode – The electrode, in an electrolytic process, that has the positive charge – in tin plating the metallic tin is the anode, and the steel strip the cathode, or negative electrode.
- Base Weight – The term used to describe the thickness of tinmill products is base weight. The designated base weight multiplied by .00011 (see table on page 10) is the exact decimal thickness in inches of the material. Although it is still customary to use the word “pound” following the base weight designation, base weight is used only to describe material thickness and is not a measure of the weight of a base box.
- Black Plate – A low-carbon cold-reduced steel intended for use in the uncoated state or for coating with tin or chromium.
- Box Annealing – A process to soften steel and relieve stresses produced during cold rolling, which involves slow heating to, holding at, and cooling of coils from a high temperature. It is accomplished in a closed box and a relatively bright surface is maintained by introducing a slightly reducing gas during the annealing process.
- Butyl Stearate (BSO) Oil – A lubricating film applied to both surfaces of chromium coated black plate.
- Cathode – See Anode.
- Chemical Treatment – A chemical or electrochemical treatment that stabilizes the tinplate surface, minimizing the oxidation of tin during storage or lacquer baking, and improves lacquer performance.
- Chromium Coated Steel – Single or double reduced black plate having a coating of chromium and chromium oxide applied electrolytically. Also referred to as TFS, tin-free steel, electrolytic chromium-coated steel or ECCS.
- Coating Weight – A term used in reference to the specified amount of tin per base box of plate.
- Cold Reduction – The process of reducing the thickness of the strip at ambient temperature, generally accomplished by rolling through a series of four-high or six-high rolling mills arranged in tandem.
- Continuous Annealing – This process consists of passing the cold reduced strip continuously and in a single thickness through a series of vertical passes within a furnace consisting of heating, soaking, and cooling zones. A slightly reducing gas is maintained in the furnace to obtain a relatively bright strip.
- Differentially Coated Tinplate: Electrolytic tinplate with a different weight of tin coating on each surface.
- Double Cold Reduced – A product that is given a cold reduction to an intermediate gauge then annealed and given another cold reduction to the final gauge. The resulting product is stiffer, harder, and stronger than single reduced product and offers economies, in many instances, to the consuming industry by enabling the use of lighter base weight plate.
- Drawing – Forming a cup from a flat circular blank so that the cup bottom and sidewalls possess essentially the same thickness as the original blank.
- Earing – The formation of scallops (ears) around the top edge of a drawn part caused by directional differences in the strength properties of the sheet metal used.
- Electrolyte – The conductive medium employed in an electrolytic process.
- Electrolytic Tinplate – Black plate on which tin has been electrolytically deposited.
- Elongation – Test of ductility that measures extension of material before breaking, usually expressed as a percentage of the original length.
- Hot Rolling – Method of reducing thickness by hot rolling the steel (usually above 1400°F).
- Ironing – Reducing can sidewall thickness by advancing a punch-supported cup through progressively smaller diameter dies or “ironing” rings.
- Melted Finish – A bright or fused finish, generally on a smooth finish (#7C) base steel, though it can be on a rough finish (#5).
- Pickling – A process of removing scale (iron oxide) from sheets or coils by immersion in an acid solution. The process may be accelerated by introduction of an electric current.
- Rockwell Hardness Test – A test for determining temper. For most tinmill products, the hardness is measured on the 30-T scale.
- Single Reduced – Steel sheet that is rolled in multiple-stand reduction mills while cold, then annealed and temper rolled to produce thin gauges for canmaking. Besides reducing gauge and permitting fabrication of lighter weight cans, cold rolling also improves the steel’s surface and metallurgical properties.
- Temper – A number designation to indicate the mechanical properties of tinplate.
- Temper Mill – A four-high mill for rolling strip after annealing to obtain proper temper, flatness, and surface qualities. It usually consists of two stands arranged in tandem.
- Tensile – Maximum stress a material can withstand while being stretched before breaking, usually expressed in N/m^2 or PSI.
- Tin Coating Weight – The amount of tin per base box of plate, e.g., no. 25 designates 0.25 lb. per base box (0.125 lb. is distributed on each side of the strip).
- Tin-free Steel – Electrolytic chromium coated black plate (TFS).
- Unmelted Finish – An as-deposited tin coating that has a dull matte appearance, generally on a roughened base steel. The tin is not reflowed.
- Yield – Stress at which a material starts to deform, usually expressed in N/m^2 or PSI.
Tempers dictate strength of the steel. Lower tempers increase the drawing capabilities and formability. Higher tempers create a stronger steel that is more resistant.
Lower tempers are usually used for deeply drawn parts such as valves and hoses. Higher temper products are used as bodies for large cans.
In addition, batch annealing will make for a softer, more forgiving steel. Continuous annealing makes for a stronger steel.
Most international standards do not detail the properties of the different tempers. Instead, the standard rely on surface testing methods, such as Rockwell testing, to determine the tempers. Nonetheless most steels of a certain temper fall within a general range of properties.
The most significant change due to temper is the change in elongation. Double reduced material loses almost all its elongation.
The finish of the product is dictated both by the substrate as well as the coating. The substrate can be ground rolled making it very smooth or sand blasted to increase the roughness.
Tin coating is applied to the ground rolled substrate and can be reflowed (melted) creating a lustrous finish. Non-melted tin can be applied to a sand blasted substrate for a matte finish. Chrome is always applied to ground rolled substrate.
While chrome coating is always applied in a uniform fashion, tin coating comes in many different levels. Additionally, the tin can be equally coated on both side or there can be differential coating. Differential coatings are generally indicated by marking on the steel, usually curved or crossed lines on the side with light coating or straight lines on the side with heavy coating.
The tin coating will have almost no affect on the thickness of steel coil; the difference between an 05 coating and a 100 coating is less than 0.0001”. However, the tin coating can have a significant impact on the properties of the steel and the potential end uses. In general, thinner coating are used for most traditional applications. Thicker coating are often used for abrasive or corrosive end uses .
Comparison of International Tinmill Standards