Tin mill products include electrolytic tinplate, electrolytic chromium
coated steel (also referred to as tin free steel or TFS), and black plate,
the uncoated steel. About 90% of tin mill products made in the world are
used by the container industry in the manufacture of cans, ends, and
closures for the food and beverage industry. The balance of production is
used for automotive components, shelving, computer chassis,
telecommunications cable, cookware, etc.
Tin-coated vessels are
known to have existed as early as 23 A.D., but the tin was apparently only
used for decoration. The first tinplate appears to have been made in
Bavaria in the fourteenth century, and by the sixteenth century, a
thriving tinplate industry existed in Saxony and Bohemia. Tinplate
manufacture spread to England in the late seventeenth and early eighteenth
The tinplate industry as we know it today is founded on
the invention of the process of preserving sterilized food for long
periods of time by Nicolas Appert in 1810. By 1812, Appert was
successfully packaging a variety of products in glass containers for a
The Appert process was adapted to the preservation
of food in tinplate containers by John Hall in 1812 in London. By the
1820's, canned foods were widely sold in England and France, and by 1839,
foods were being canned in the United States. The American can industry
grew explosively as a result of the Civil War, the subsequent settling of
the west, and the growth of the oil industry.
Starting in the
1880's, a series of technical innovations transformed the tinplate
industry. These included the replacement of wrought iron with steel for
the black plate in about 1880; the development of continuous cold
reduction in 1927, that eliminated hot-pack rolling; the introduction of
continuous electro-tinning on a small scale in Germany in 1934 and on a
commercial scale in the United States in 1937, which replaced the hot dip
process; the invention of double cold reduction in 1960; and the invention
of TFS in the early 1960's in Japan and the United
Concurrently, many advances occurred in canmaking
technology that exploited the improvements in the quality of tin mill
products. Tin mill products are also used by the automotive, building,
appliance, and furniture industries, all of which take advantage of the
unique properties of these light-gauge steel products.
Black plate (basically a
clean, light gauge cold rolled steel, see Steelmaking)
destined for coating goes directly from either the temper mill or double
cold reduction mill to the coating line. The sequence of operations that
occurs in a tinplating line, at speeds up to 2000 feet per minute, are the
- Charging the Coil - The black plate coil is placed
on an uncoiling mandrel and fed into the unit. The charged coil is then
welded to the preceding coil in order to run the facility continuously.
Looping towers accumulate a length of material that is varied to enable
the welding of two coils while not stopping the operation.
- Side Trimming - The material is side trimmed to the
final width. The scrap is automatically baled, removed, and recycled to
the steelmaking furnaces.
- Clean & Pickle - The strip is next
electrolytically cleaned, pickled, and rinsed by running through a
series of tanks to ensure the surface is clean and suitable to accept
the electro-deposition of tin.
Electroplating - The strip passes
through tanks containing tin anodes on either side of the strip and in
electrolyte. Tin dissolves from the anode and is transported through the
electrolyte to deposit on the strip. The quantity of tin that deposits
on the strip is determined by the quantity of electric current flowing
between the anode and the strip. To produce differential coatings,
different current settings are used for each of the anode banks. The
dull as-plated tinplate is sometimes referred to as having a matte
- Melting Tower (Tin Reflow) - The electrolytic
tinplate next passes through a melting tower. In this section, the
temperature of the strip is raised by resistance or induction heating to
just above the melting point of tin, then is immediately quenched in
cold water. The tin begins to melt and reflows uniformly across the
strip. The product now takes on the more typical bright or shiny surface
appearance. Should a customer require a matte or unmelted tin finish,
the melting tower can be turned off. When differentially coated tinplate
is being produced, an identifying mark may be placed on either side just
prior to melting.
- Chemical Treatment - A sodium dichromate solution
is next applied to the electrolytic tinplate to create a light
protective chromium oxide film. This passivation process protects the
surface from the formation of tin oxides, which will decrease
lacquerability. Two commonly used chemical treatments for electrolytic
tinplate that have been adopted by the industry are:
- Sodium Dichromate Dip (Abbr: SDCD)
moderate resistance to tin oxide formation with limited storage
stability and is used where a highly passivated tin surface is not
required or is detrimental to the end use. Sodium Dichromate Dip has
an aim not to exceed 0.15 milligrams (mg) of chromium/sq. ft. of
- Cathodic Sodium Dichromate (Abbr:CDC)
addition of a cathodic electric current, a highly passivated surface
against the formation of tin oxide is provided. Cathodic Sodium
Dichromate treatment normally has an aim of 0.5 milligrams (mg) of
chromium/sq. ft. of surface.
- Oiling - A very thin film of oil is then
electrostatically applied to the finished tinplate. The oil is applied
to minimize scratching the tin surface in transit and handling. The
primary function of oiling is not prohibiting rust formation as it is
with uncoated products. The oil applied to electrolytic tinplate, almost
exclusively, is acetyl tributyl citrate or ATBC. The oil is applied
uniformly to both sides.
Recoiling - The finished tinplate
product is finally recoiled at the exit end of the electrolytic tin line
on a take up reel that most commonly has a 16-1/2 inch inside diameter
- Quality Inspection - The entire process is
monitored automatically and manually to ensure that the material
conforms to specification and meets customer expectations.
Electrolytic Tin Coated Sheet
Sheet and tin mill
products are differentiated by gauge. Electrolytic tinplate has a maximum
thickness of 135 lb. base weight or 0.0149 inch nominal thickness. Tin
coated sheet starts at 0.0150 inch nominal thickness and is produced up to
0.0359 inch nominal thickness.
Use of Chromium
Chromium and chromium oxide coatings, developed for
food packaging in the 1960's, offer superior lacquer adhesion and good
storage properties. These coatings are mixtures of chromium metal and
chromium oxides. Unlike tinplate with its multiplicity of coating weights,
only a single standardized chromium-coated product is
Electrolytic Chromium Coated Black
This product, commonly referred to as tin-free steel or
TFS, follows the same processing sequence as electrolytic tinplate. The
coating lines are mechanically similar. During the electrolytic deposition
process, chromium and chromium oxide are deposited. The metallic chromium
coating on each surface is applied 5.0 milligrams (mg)/sq. ft. of area.
The oxide film ranges from 0.7 to 2.0 milligrams (mg)/sq. ft., but is
generally on the lower side of this range.
Unlike tin, the chromium
layers cannot be reflowed, therefore a coating line dedicated to chromium
coating will not have melting towers as used on the tin line to reflow the
tin into a bright state.
The product is also electrostatically
oiled before it exits the coating line. Historically, the industry used
butyl stearate oil (BSO), which was developed for its lubricity to prevent
scratching. In some instances, it has been determined that acetyl tributyl
citrate (ATBC) oil used on electrolytic tinplate is more compatible with
some specific lacquering and paint systems. In this case, ATBC has been
preferred at the expense of the greater lubricity of the BSO.
Tin mill products are produced with certain standardized product
characteristics, including terminology, composition, mechanical
properties, surface finish, coating weights, and the like. These
characteristics are covered in detail in the ASTM Standard
CLASSIFICATION OF TIN MILL
The steel industry has adopted standard product names, nomenclature,
and order sequencing as published by
Single Reduced Black Plate (1 CR BP) - through 135
lb. base weight
Double Reduced Black Plate (2 CR BP) - through 100 lb.
Single Reduced Electrolytic Tinplate (1 CR ETP) -
through 135 lb. base weight
Double Reduced Electrolytic Tinplate (2 CR
ETP) - through 100 lb. base weight
Single Reduced Electrolytic Tin
Coated Sheet (1 CR TCS) - starting at 0.0150 inch
Single Reduced Electrolytic Chromium Coated Black
Plate (1 CR ECCS) - through .020 inch nominal
Electrolytic Chromium Coated Black Plate (2 CR ECCS) - through 100 lb.
Yield Strength, ksi*
49 +/- 4
57 +/- 4
61 +/- 4
65 +/- 4
25 - 42
40 - 52
48 - 60
57 - 58
70 - 85
85 - 100
*The values shown are the approximate range only and are not
30 - 60
surface for black plate and some tinplate and TFS
requirements. For tinplate, when the tin is unmelted, and when
the 5C finish is used for black plate and TFS, the finish is often
referred to as “matte” finish. On tinplate only, when the tin
is melted, the finish is sometimes referred to as “silver” or “SBF”,
or “brite grit”.
5 or less
A lustrous, smooth
surface typically found only on black plate intended for
electroplating. It is currently not available in the U.S.
7 - 15
A smooth finish that
may contain fine grit lines. Usually used only for tinplate
that is melted after plating and then it’s often referred to as
“bright” finish because the surface is very smooth and
reflective. Limited availability, only made by a few mills.
12 - 22
A smooth finish with
grit lines. This is the most common finish for tin mill products,
especially tinplate and TFS though black plate can be ordered with
this finish. When used for tinplate that is melted after
plating, or for black plate or TFS, the finish is commonly referred
to as "stone" finish
0.0061 / 0.155
0.0063 / 0.16
0.0066 / 0.17
0.0072 / 0.18
0.0075 / 0.19
0.0077 / 0.195
0.0083 / 0.21
0.0086 / 0.22
0.0088 / 0.22
0.0094 / 0.24
0.0102 / 0.26
0.0105 / 0.27
0.0108 / 0.275
0.0113 / 0.29
0.0116 / 0.295
0.0118 / 0.30
0.0127 / 0.32
0.0130 / 0.33
0.0135 / 0.34
0.0149 / 0.38
For base weights not included in the
table, the decimal thickness can be calculated by multiplying the
base weight by 0.00011.
TIN COATINGS - STANDARD COATING
Designation (US) [EURO]
Tin Coating Weight
Each Surface, Lb./Base Box (US)
One pound of tin per base box
(shared over both surfaces) is equivalent to approximately 0.000060
inch thickness on each surface.
This list represents standard
coating weights. Others available upon inquiry.
TIN PLATE TYPICAL MECHANICAL
Download the Chart in PDF Format / Download Adobe
Acetyl Tributyl Citrate (ATBC) Oil - A lubricating
film applied to both surfaces of tin mill 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
Base Weight - The term used to
describe the thickness of tin mill 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
Chemical Treatment - A chemical or
electrochemical treatment that stabilizes the tinplate surface, minimizing
the oxidation of tin during storage or lacquer baking, and improves
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.
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.
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.
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
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.
The formation of scallops (ears) around the top edge of a drawn part
caused by directional differences in the strength properties of the sheet
Electrolyte - The conductive medium
employed in an electrolytic process.
Tinplate - Black plate on which tin has been electrolytically
Hot Rolling - Method of reducing
thickness by hot rolling the steel (usually above
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
Rockwell Hardness Test - A test
for determining temper. For most tin mill 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
Temper - A number designation to
indicate the mechanical properties of tinplate.
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.
Weight - The amount of tin per base box of plate, e.g., no. 25
designates 0.25 lb. per base box (.125 lb. is distributed on each side of
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.