Forword
This document is drafted in accordance with GB/T 1.1-2020 Guidelines for Standardization Part 1: Structure and Drafting Rules of Standardization Documents.
Please note that some of the contents of this document may involve patents. The issuing agency of this document does not assume the responsibility of identifying the patent. This document is proposed and under the centralized management of the National Technical Committee for Food Industry Standardization (SAC/TC 64).
1 Scope
This document describes the method for determining the corrosion resistance and density of the inner wall coating and film covering of food metal containers.
This document is applicable to the determination of food (cans, beverages, etc.) metal containers coated with tinned or chrome plated steel sheets (aluminum) and coated iron (aluminum) substrates.
2 Normative References
The contents in the following documents, through normative references, constitute indispensable provisions of this document. Where, for dated references, only the version corresponding to that date applies to this document; For undated references, the latest version (including all amendments) is applicable to this document.
GB/T 6682 Specification and Test Methods of Water for Analytical Laboratory
QB/T 2763 Tin (or chromium) coated steel sheet
3 Terms and definitions
There are no terms and definitions to be defined in this document.
4 Principle
The corrosion resistance of food metal containers was characterized by accelerating the electrochemical corrosion of their inner walls. The surface double electron layer capacitance and dielectric loss tangent were measured by applying a weak voltage on the inner wall of the metal container to characterize its compactness.
5 Reagents and materials
Unless otherwise specified, only analytically pure reagents shall be used.
5.1 Reagents
5.1.1 Water, GB/T 6682, Grade III.
5.1.2 Sodium nitrate (NaNO): purity ≥ 99%.
5.1.3 Citric acid monohydrate (C, HsO; · H: O): purity>98%. 5.1.4 Ascorbic acid (CHsO): purity>99%.
5.2 Test solution (mixed solution of citric acid 50.00 g/L, sodium nitrate 0.14 g/L, ascorbic acid 0.50 g/L)
6 Instruments and equipment
6.1 Corrosion resistance tester
The corrosion resistance tester is an instrument for testing metal containers and metal corrosion resistance. It consists of a stable power supply and a test electrode. The range of the stable power supply should be greater than 15V. The test electrode is a stainless steel electrode with a diameter of 4 mm and a length of 10 mm. When testing the corrosion resistance of metal covers, special clamps for testing metal covers of different specifications shall be provided.
6.2 Digital bridge
The digital bridge is a double electrode system, with a test range of 10-pF~10 'mF capacitance, 0.01 mQ~100 MQ resistance, and a test accuracy of 0.1%. The digital bridge shall be preheated and calibrated before testing.
6.3 Electronic balance
The sensitivity is 0.1 mg.
6.4 Volumetric flask
The specification is 1000 mI.
7 Test procedures
7.1 Corrosion resistance
7.1.1 At the mouth edge of the metal container, cut the film with a knife, connect the wire at the exposed iron part, and connect the positive pole of the stable power supply.
7.1.2 At room temperature, pour the test solution (5.2) into the metal container until the liquid level is 5 mm~7 mm from the tank mouth; The metal cover shall clamp the sample on the special fixture, pour the test solution (5.2), and immerse the entire test plane. The sample piece is used as the anode, and the stainless steel electrode with a diameter of 4 mm and a length of 10 mm is used as the cathode, which is connected to the 15V DC power supply to cause anodic corrosion. After 1h, take out the metal container, wash and dry it, and observe the size and number of corrosion spots.
7.1.3 For some specific products, other corrosive media (such as canned food contents) can be used by mutual consent. The test steps are the same as those in 7.1.1 and 7.1.2.
7.1.4 The corrosion resistance of the sample shall be rated according to the arithmetic mean of the number of corrosion spots of the same size of three metal containers.
7.2 Compactness
7.2.1 At the mouth edge of the metal container, cut the film with a knife, connect the wire at the exposed iron part, and connect the test electrode of the numerical bridge.
7.2.2 At room temperature, pour the test solution (5.2) into the empty tank until the liquid level is 3 mm~8 mm from the tank mouth; The metal cover shall clamp the sample on the special fixture, pour the test solution (5.2), and immerse the entire test plane. Keep soaking for 24 hours at room temperature.
8 Expression of results
The test report shall include the following parts:
a) Number of this document
b) Complete description of the test sample, such as substrate material, film thickness, coating type and coating method
c) Test date;
d) Environmental status of the test; e) Test conditions;
f) Test results;
g) Any difference from the specified test procedure.
Forword
1 Scope
2 Normative References
3 Terms and definitions
4 Principle
5 Reagents and materials
6 Instruments and equipment
7 Test procedures
8 Expression of results
