Test Items

ISV(Iron Solution Value)

Corrosive solution: H2SO4 + H2O2 + NH4SCN at 27 ℃ for 2 hours

Fe solved from colorimetric determination: If ug Fe / 3in2 (lin2 = 64516cm2), then the corrosion area is 57.3mm2

TCS(Tin crystal size)

Etchant: 84ml concentrated HCL + 100gFeCl3.XH2O + 0.5 ~ 1.0gNa2S or NaHSO3 / L

Slight corrosion by the etchant (5 ~ 15S) shows that compared with ASTM standard, the most typical tin crystallite size range is between 6 and 12.

ATC(Alloy Tin Couple test)

Electrolyte: Grapefruit juice (containing Sn2 + 100ppm) (3 servings of deionized water +1 serving of frozen concentrated grapefruit juice)

Test time: 20 ℃; temperature: 26 ℃ ± 1 ℃

ATC is a special tinplate indicator that is used to determine corrosion resistance of inner walls of cans.

Principle: ATC measurement; the amount of the coupling current passing through one pure tin electrode (anode) and a FeSn2 alloy electrode (which is produced from the exposure of the alloy layer after the pure tin coating of the test sample is removed) (uA/cm2). A lower ATC current value means good corrosion resistance of the tinplate to acidic foods.

Requirements: ATC≤0.12uA / cm2; average: less than 0.05 uA / cm2. (On a monthly basis)

The major determinant of the corrosiveness or etching speed (tin solution rate) is the amount of current through the tin alloy layer and the exposed steel base. The potential of Sn is higher than that of Fe, so Fe is the anode. However, when tin is in contact with iron in a can, especially in a can that has been vacuum exhausted, Sn becomes the anode while Fe is the cathode. Sn dissolution protects the Fe cathode. Method for removal of the free tin coating of the test sample: Control the potential in the solution of NaOH (0.4v – 0.2v) to achieve anodic dissolution.

The test is performed on base steel of ETP

Etching solution: 6MHCL 90 ℃, with the time expressed as S.

Principle: Detin the test piece, and then immerse it in 6MHCL at 90℃. Measure the time (S) required for its iron solution rate (or hydrogen evolution rate) to become stable.

According to statistics, cans made of tinplates produced from base steel with a long pickling lag (referring to cans with inner walls not painted and mainly used for acidic foods) tend to have a short shelf life, which means that base steel that can reach a constant pickling rate in a short time has good corrosion resistance.

Coating Adhesion Test

Bar coating → baking → Cross-cut test, impact test, tape stripping

a) Solution Analysis

1. Automatic titration (volumetric method): Determine the end with PH

NaOH (cleaning fluid) H2SO4 (pickling solution)

Electroplating solution: free acid

2. PH meter: measure PH values

3. Measure the picking solution Fe2 +, electroplating solution Fe2 +, and the total Sn (Sn2 +)

ICP method (Shimadzu UV-2201)

Recycling liquid Na2Cr2O7

4. Spectrophotometric method (Shimadzu UV-2201): chromium coating weight, ISV, PSA, ENSA

5、Electronic scales: oil content, sediment, SO4 ^2-

6. Ion chromatography: SO42-, PSA, ENSA, Sｎ ²⁺