Judgment criteria and key factors for hot-dip galvanizing
The judgment criteria and reasons for hot-dip galvanizing mainly include the following three points:
1、 Adhesion amount
Corrosion resistance mainly depends on the thickness of the coating, and thickness measurement is usually based on the quality of galvanizing, composition of the galvanizing layer, organizational structure, and different reactions on the surface of the steel plate, which have a significant impact on the angle and speed of the imported zinc solution. Therefore, it is impossible to have a completely uniform coating thickness. Therefore, the adhesion amount is measured at a single point (position) to determine the average value of zinc (g) attached per unit area (m).
There are many methods for measuring adhesion, such as destructive slice metallographic observation, acid washing method, non-destructive film thickness measurement method, electrochemical method, and estimation of weight difference between import and export. The commonly used methods are film thickness measurement and acid washing.
The film thickness gauge method is a convenient method for measuring the thickness of zinc layers through magnetic induction. The basic condition is that the surface of the steel is smooth and complete in order to obtain more accurate numbers. Therefore, it is unlikely to obtain accurate numbers in steel angles or rough, angle steel, steel parts or castings, etc. Ordinary iron sheets and raw iron, Angelica sinensis, and zero base can still provide fairly accurate numbers, resulting in inaccurate casting.
The pickling method is an accurate method for formal inspection reports, but when slicing, attention should be paid to the fair selection of upper and lower components, so as to obtain accurate values. But there are also drawbacks, such as time-consuming, complex steel areas that are difficult to obtain, too large to be fully pickled. Therefore, making full use of thickness gauges to control on-site processing and testing with acid pickling methods is sufficient.
2、 Uniformity
Hot dip galvanized steel is the fragile part or thin part of the zinc layer, and it is necessary to measure its thin part to meet the standards.
Generally, Copper(II) sulfate test is used to test homogeneity, but this galvanizing method and the test of alloy layer consisting of galvanized coating are a problem. The dissolution rate of zinc layer and alloy layer in Copper(II) sulfate test solution is different, and the alloy layer is also different from the ratio of zinc to iron. Therefore, it is unreasonable to judge uniformity at a certain number of times.
3、 Solidity
The so-called solidity refers to the tightness between the galvanized layer and steel. The main requirement is that the galvanized components must have a non peeling property during sorting, transportation, storage, and use. The general inspection methods include hammering, bending, and rolling.
The hammering method is to hit the test piece with a hammer to check the condition of the surface coating. Fix the test piece so that the hammer supports Taiwan high, with the hammer level supporting Taiwan as the center. Handle the heavy vertical position and naturally fall, and score 5 points in parallel at 4mm intervals. Observe the film peeling thought for judgment. However, this test shall not be conducted at an angle of 10mm or within the range of the end, and shall not be impacted more than twice in the same place. This method is common and suitable for solid testing of zinc and aluminum coatings. Other methods, such as extrusion and winding, are rarely used, so they have not been mentioned temporarily.
Adhesion, uniformity and solidity are the quality inspection items of Hot-dip galvanization defined in general specifications. It is also the standard for general formal inspection reports. Relevant specifications.
