Overview of metal packaging materials and their ap

Summary of metal packaging materials and their applications (6)

(2) sheet specifications and dimensions

the specification and size of tinplate includes the thickness, width and length of the plate. It can be selected according to the requirements of purpose, tank type and tank number

mm is now used internationally as the unit of sheet size. The thickness of tinplate in foreign countries has been expressed by (pound/base box). Base box is a specific area unit, which is equal to (Table 6):

Table 6 conversion of foreign tinplate units

20in × 14In 112 sheets

28In × 20in 56 sheets

30in × 20in 49 sheets

1 base box = 31360in2 = 20.2324m2

generally speaking, the British thickness refers to the total mass of the sheet of a base box, and its corresponding comparison relationship with the metric thickness is as follows (Table 7):

Table 7 Comparison of British and metric sheet thickness units

comparison of unit thickness

pound/base box 70 80 90 100

mm 0.2 0.23 0.25 0.28

the thickness of sheet for empty cans is generally between 0.15 ~ 0.3mm, The most commonly used thicknesses are 0.2mm, 0.23mm, 0.25mm and 0.28mm, which are selected according to the size of the tank and the nature of the contents

the length and width of the sheet can be ordered according to the user's requirements, that is, the can factory can calculate the size of the sheet used to produce the minimum leftover material during can making according to various tank types. At present, the most commonly used specification in China is 714 × 510mm and 827 × 730mm。 The width depends on the width of the rolling mill roll. The width of the sheet supplied by WISCO is 775, 800, 825, 850, 875, 900, 950, 975, 1000, 1025 and 1050mm, and the length is arbitrarily selected in the range of 400 ~ 1200mm. Generally, the difference between length and width shall not exceed 200mm. The tinplate making the bottom cover was originally cut into a square, but the square plate usually produces many leftovers after punching the circular bottom cover. In recent years, the corrugated plate with special size for the special bottom cover has been developed to minimize the leftovers. The size and shape of the corrugated plate vary with the cover diameter. Users can order according to the size of different cover diameters

(3) tempering degree

quenching and tempering degree refers to the comprehensive mechanical properties of tinplate after rolling plastic deformation or heat treatment, such as hardness, plasticity, resilience, etc. It is usually expressed by Rockwell surface hardness hr30t (expressed by hr15t when the plate thickness is ≤ 0.22mm) and measured on the surface Rockwell hardness tester. Hr30t (hr15t) uses a steel ball with a diameter of 1/16in as the indenter, the main load of the hardness tester is 30kg (15kg), and the initial load is 3kg. The surface Rockwell hardness standard and the quenching and tempering index of tinplate can be found out from the relevant standards. At present, there are four kinds of quenching and tempering degree specifications of tinplate supplied by WISCO, including T52, t57, T61 and T70. T52 has good plasticity and medium drawing performance. It can be used for one-time drawing cans with covers, rings and screw covers (such as fish cans). T57 is used for three piece can body, can bottom cap, large diameter bottle cap, crown cap, etc. T61 can be used for three piece tank body, tank bottom, tank cover and large container with good rigidity. T70 has strong rigidity and is mainly used for beer or inflatable tank bottom and tank cover

(4) steel grade

refers to the original steel grade of tinplate. Different steel grades have certain differences in composition, quality and application. Table 8 shows the raw sheet steel based on this steel (tinplate) and its chemical composition

Table 8 tinplate steel and its chemical composition (%)

steel carbon manganese phosphorus sulfur silicon copper titanium

w08fa 0.05 ~ 0.08 0.25 ~ 0.40 ≤ 0.02 ≤ 0.025 ≤ 0.03 TBD -

w08fb 0.08 ~ 0.12 0.25 ~ 0.45 ≤ 0.03 ≤ 0.03 TBD -

w08al ≤ 0.08 0.20 ~ 0.40 the accuracy of the weight is 1% ≤ 0.02 ≤ 0.03 ≤ 0.03 TBD aluminum 0.02 ~ 0.07

(5) coating

according to whether the surface of tinned sheet is coated or not, it can be divided into two categories: plain iron and coated iron. It is assumed that the accuracy of load sensor does have problems

plain iron is mainly applicable to most canned fruits without coating. In this way, the reducibility of tin on the surface of plain iron can be used to dissolve a small amount of tin into the can, which can enhance the luster of fruits

coated iron is a tinplate coated with organic coating on one side of the inner wall, which is suitable for most food cans. The coating is made of organic polymer resin (such as epoxy resin, phenolic resin), solvent (such as cyclohexanone, xylene, etc.) and a small amount of additives. It is baked at a temperature of more than 200 ℃ according to a certain inner wall surface. The function of the coating is to isolate the tank wall and contents, prevent corrosion and prevent the pollution of heavy metal ions such as lead, iron and zinc to food

according to different types and properties of coatings, they can be divided into acid resistant and sulfur resistant dual-purpose coating iron, sulfur resistant coating iron, anti sticking coating iron and sulfur resistant coating iron for cupping. They are suitable for different food cans, of which the amount of dual-purpose coating iron is the largest

due to the differences of the above indicators, tinplate can be divided into many different categories. When using, various standards should be reasonably selected according to different specific uses and requirements, that is, the so-called "iron selection"

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