Sampling Method

1. A batch is defined as products of the same specification delivered at the same time.
2. Randomly select three pieces from each batch as samples for surface quality inspection. From these three pieces, select three sets for mechanical performance testing.
3. Reinspection
a. Surface Quality: If any (or more than one) non-conforming sample exceeds one piece, increase the sample size from the same batch and perform reinspection. If reinspection still shows more than one non-conforming sample, the batch is considered defective.
b. Mechanical Performance: If any (or more than one) performance indicator is non-conforming, increase the sample size from the same piece and perform reinspection. If reinspection still shows a non-conforming sample, the batch is considered defective for its physical and chemical properties.
c. If both appearance and physical/chemical indicators are qualified, the batch is considered qualified.

Testing Methods

1. Surface Quality
a. Direct visual inspection
b. Surface quality requirements:

The wire surface should be smooth and clean, without cracks, peeling, burrs, rough drawing marks, folding, or inclusions.

Minor defects such as localized dents, spots, pits, and scratches should not cause the wire diameter to exceed the allowable deviation and should not affect welding quality.

Minor redness, darkening, oxidation color, or small localized water or oil marks are not considered defects that affect welding.
The wire break should be compact, with no tailing, porosity, delamination, or inclusions.

2. Wire Diameter
a. Instruments: Micrometer or digital caliper with precision of 0.01mm or micrometer.

b. Testing method: Measure the diameter of the wire at three different points on the sample, and the average of these measurements is the wire diameter.

c. The wire diameter requirements should comply with Table 5-11.

Table 5-11 Wire Diameter and Allowable Deviation

3. Mechanical Performance
a. Instruments: Testing machine.

b. Two samples (200mm × 25mm) are cut from the edge and center of each test steel plate along the rolling direction. Perform a tensile test on parallel parts with a width of 12.5mm × 1mm and a gauge length of 50mm according to GB/T 228—2002.

c. The tensile test results should comply with Table 5-12.

Table 5-12 Wire Mechanical Performance Indicators Requirements