Electrolytic Tinplate

Electrolytic TinPlate: Features

The features of Electrolytic Tinplate (ETP) are clearly defined and can be measured. Some of the most outstanding factors include:






Type of Steel

The steel used to manufacture Electrolytic Tinplate (ETP) can be produced using the continuous cast or ingot mould methods. According to their chemical composition, the most widely used types of steel are indicated in the next chart.

Types of Steel

Types of steel	Features
D	Aluminum killed steel (deoxidized). This is used for deep drawn cans (two-piece cans, aerosol, etc.) or in those processes where wrinkles –de Luders– are likely to appear during machining.
L	Contains small quantities of metalloids and residual elements such as: Cu, Ni, Cr, Mo. Used to improve the internal corrosion resistance of cans for certain food products.
MR	Contains low percentages of residual elements and has a good corrosion resistance. It is the most common in the market and is used for general purposes, including cans.

Chemical Composition of Steel used for Electrolytic Tinplate and Tin Free Steel

Element

Type D Max %

Type L (1) Max %

Type MR (1) Max %

Carbono	0.12	0.13	0.13
Manganese	0.60	0.60 (2)	0.60
Phosphorus	0.02	0.015	0.02
Sulfur	0.03	0.03	0.03
Silicon (3)	0.02	0.02	0.02
Copper	0.20	0.06	0.20
Nickel	0.15	0.04	0.15
Chromium	0.10	0.06	0.10
Molybdenum	0.05	0.05	0.05
Aluminum	0.2	0.10	0.2
Others, each	0.02	0.02	0.02

Policy ASTM A623 -2009.

(1) Double reduction products are obtained in type L and MR
(2) Unless there is a different agreement between the manufacturer and the consumer
(3)

Thickness

The thickness of Electrolytic Tinplate (ETP) is defined by conventional standards and found in the range of 0.12 mm to 0.50 mm in simple reduction and from 0.12 mm to 0.29 mm for doubly reduced steel plate. In the metric system, thickness is reported in mm. In some parts of the world, the English system is still used where the base unit is known as the base case (CB), whose area is equivalent to 112 sheets of 20 x 14 inches.

Area of CB 112 x 20 x 14 inches 31.360 inches2

When electrolytic tinplate is sold by base case, the thickness is known as substance or base weight, which is defined as the number of pounds that a base case weight. The equivalence between lb/CB and mm is given by the expression:

lb/CB 349.85551 x thickness (mm)

Hardening

Base steel for Electrolytic Tinplate (ETP) is classified by hardness, which is a characteristic indicator of the material’s mechanical properties.

Chart 3 shows the various degrees of hardness for simply reduced and doubly reduced steel, and its applications.

Types of Hardness

Name	Desired Rockwell Hardness 30 T	Application
SIMPLY REDUCED
T1-BA	45-53	Necks, nozzles, taps, toys bottoms for 5 gal. cans for oil and other uses that require deep drawing.
T2-BA	49-57	Small, square cans, cans for fish (0) salted meat, rings and other uses, with moderate draw.
T2 2.5-BA	52-58	Crowns, for cans and other applications that require moderate draw and harness.
T3-BA,CA	53-61	Bodies for 5 gal oil cans, large cans and other applications that require an appropriate level of hardness.
T4-CA (1)	57-65	Bodies and bottoms for cans that require relatively high strength, and crown caps.
T5-CA (1)	61-69	Bodies and bottoms of for cans that require a combination of high hardness, strength, and good formability.
T6-CA (1)	66-74	Bodies, bonds and lists for high stiffness cans.

Name	Desired Rockwell hardness 30 T	Application
DOUBLE REDUCED
DR 8 (2)	69-75	Bodies and bottoms of small diameter cans requiring high strength.
DR 9 (2)	73-79	Bodies and bottoms of a large diameter cans requiring high strength.
DR 9.5 (2)	74-80	Bodies and bottoms of large diameter cans requiring high strength.

(1) CA means continuous annealing.
(2) DR: Base metal produced using the double cold reduction process; provides greater stiffness and strength than conventional base material and, therefore, provides the same strength using smaller cross sections. These advantages make it possible to produce more cans per unit weight of electrolytic tinplate. Service characteristic, thickness distribution and chemical characteristics are similar to those of conventional steel.

Tin Covering

Until recently, there were serious limitations on the various types of tin coverings. But a research carried at Duke by electrolytic tinplate producers users - for the purpose of reducing costs - it was possible to drop from 5,6 g/m2 tin layers to very low 0,.275 g/m2 layers. This brought considerable innovation into the Electrolytic Tinplate and can manufacturing processes.

The units most commonly used to express the tin coating are g/m2 and lb/CB. The next chart shows the most common and commercial coatings, as well as the differential and special types with their respective equivalencies.

Thanks to the properties of the iron-tin film, it is possible to manufacture L.T.S. or lightly tin coated steel, which is material with a very small tin coating and high passivation. The tin film may or may not be completely alloyed but the completely alloyed film has shown the best results in the market.

This type of electrolytic tinplate has the same or better behavior than the tin-free steel and normal coated plates (2.8/2.8 g/m2) when used with lacquer.

L.T.S. has been produced in Colombia since 1981, which represents significant savings in can manufacturing due to its low cost and high versatility.

HOLASA offers electrolytic tinplate that has the same coating on both sides, or differential coatings, in the weights shown in Graph 4, according to ICONTEC and international norms.

Types of Coatings

		COATING WEIGHT
	American designation numeric coating	ICONTEC G/M2 equivalent to ASTM A624m			AISI		Prior European Standard designation
		Name	Total both sides	Per side	Per side lb/CB	Total both sides
		*E 0.275/0.275	0.55	0.275/0.275
		* E 0.55/0.55	1.1	0.55/0.55
		* E 1.1/1.1	2.2	1.1/1.1	<0.10	<0.10
		* E 1.4/1.4	2.8	1.4/1.4
		* E 2.2/2.2	4.4	2.2/2.2
	# 25	E 2.8/2.8	5.6	2.8/2.8	0.125/0.125	0.25	E 1
	# 50	E 5.6/5.6	11.2	5.6/5.6	0.250/0.250	0.50	E 2
	# 75	E 8.4/8.4	16.8	8.4/8.4	0.375/0.375	0.75	E 3
	# 100	E 11.2/11.2	22.4	11.2/11.2	0.500/0.500	1.00	E 4
		** D 1.1/0.55	-	1.1/0.55
		** D 2.2/0.275	-	2.2/0.275
		** D 2.2/0.55	-	2.2/0.55
		** D 2.2/1.4	-	2.2/1.4
		** D 2.8/0.55	-	2.8/0.55
		** D 2.8/1.1	-	2.8/1.1
		** D 2.8/1.4	-	2.8/1.4
		** D 2.8/2.2	-	2.8/2.2
	# 50/25	D 5.6/2.8	-	5.6/2.8	0.250/0.125	-	E 2/1
	# 75/25	D 8.4/2.8	-	8.4/2.8	0.375/0.125	-	E 3/1
	# 100/25	D 11.2/2.8	-	11.2/2.8	0.500/0.125	-	E 4/1
	# 75/50	D 8.4/5.6	-	8.4/5.6	0.375/0.500	-	E 3/2
	# 100/50	D 11.2/5.6	-	11.2/5.6	0.500/0.250	-	E 4/2
	# 100/75	D 11.2/8.4	-	11.2/8.4	0.500/0.375	-	E 4/3

Notes
1. Coating in grams per square meter (g/m2), which corresponds to ICONTEC Standard 647 of 1988 (fifth revision) and its AISI equivalent in pounds per base case (lb/CB).
2. The values with a slash (/) indicate the coating weight on each surface, respectively. Values without the slash indicate the total coating weight on both surfaces.
3. HOLASA also offers, by order previously agreed with the electrolytic tinplate users, coatings other than the standard specified by ICONTEC Standard 647.

* Special low tinning coatings, standardized by ICONTEC but which do not have equivalent international standards
** Special low tinning differential coatings not shown in this table could be produced by agreement between the customer and HOLASA.

FIinishing

Finishing is a physical characteristic of the raw materials. Chart 5 shows the various types of finishes for electrolytic tinplate, their main uses, and characteristics. Chart 6 shows the roughness ranges for various types of steel –black plate– used for making electrolytic tinplate.

Electrolytic Tinplate Finishes

Type	Main Uses	Characteristics
MIRROR* (BRIGHT)	General purpose cans	Finishing with melded tin, with a bright shine
MATTE	Crown caps	Matte finish, without shine, with electrolytically deposited tin without melting on the matte finishes steel plate.
SILVER	Cans for different applications, crown caps	Finish with melded tin produced using a special treatment on the base metal.
STONE	General use cans	Finish with melded tin, produced on the base metal, with a slightly matte appearance.

*Availability of mirror finish electrolytic tinplate is subject to consultation with HOLASA’s Sales Management.

Finish on Black Plate

Type	Roughness (Ra) um
BRIGHT	0.18 - 0.35
STONE 1	0.25 - 0.55
STONE 2	0.50 - 0.76
MATTE 1	0.76 - 1.27
MATTE 2	1.01 - 1.52
EXTRA-MATTE	1.52 - 2.54