GB/T 728-2020 in English

Core changes in the standard revision

Analysis of key technical requirements

1. Grade grading system

The standard divides tin ingots into three basic grades according to purity: Sn99.90, Sn99.95, and Sn99.99, and subdivides them according to lead content:

• Grade A: high lead type (Pb≤0.0250%)
• Grade AA: low lead type (Pb≤0.0100%)

2. Key indicator control

Sulfur content limit is relaxed to 0.0010% (except Sn99.99) to adapt to modern smelting technology; newly added Ni+Co total amount control (≤0.0006%)

Key points for quality inspection implementation

1. Arbitration detection method

New cutting method sampling specification:

1. Sampling volume ≥ 2% of the batch and not less than 6 ingots
2. Use 3-6mm non-lubricated saw blade for cutting
3. Cutting depth＜1/2 of ingot width

2. Appearance acceptance standard

Clearly define the requirements for "T"-shaped cross-section (25kg±1.5kg), and the surface must be free of burrs and inclusions

Application suggestions

Background of standard evolution

This revision responds to the international ISO/TC18/SC1 technical trend. The main changes are:

• The lead content limit is aligned with the EU RoHS Directive
• Sulfur index adjustment is based on measured data of Yunnan Tin Industry
• New cutting method is added to solve the oxidation problem of high-purity tin sampling