Standard and measurement method for zinc layer thickness of hot-dip galvanized bolts
1、 Definition of bolts
A bolt is a type of fastener composed of a head and a screw, which needs to be matched with a nut to fasten and connect two parts with through holes. Bolts mainly serve as connections and fasteners, and their quality has a direct impact on the connected parts. In order to prevent surface wear and corrosion of bolts, surface treatment is chosen for bolts, and hot-dip galvanizing treatment is a commonly used method.
2、 Mechanism of bolt hot-dip galvanizing
Among various coating methods for protecting steel substrates, hot-dip galvanizing is a very excellent one. It undergoes complex physical and chemical reactions in the liquid state of zinc, and a thick pure zinc layer is deposited on steel. A uniform alloy part is formed, and then the zinc reacts with the air to form a protective layer of zinc oxide and basic Zinc carbonate, thus providing high-quality performance of rust prevention and corrosion prevention.
3、 Zinc coating standard for hot-dip galvanized bolts
The executive standard for the zinc layer thickness of hot-dip galvanized bolts is: GB/T5267.3-2008
According to the zinc layer thickness standard, the local thickness of the zinc layer should not be less than 40 μ m. The average thickness of the coating batch should not be less than 50 μ The measurement of the local thickness of the m coating is shown in Figure 3
If the construction environment of the workpiece has personalized requirements for salt spray testing, the required zinc layer thickness can also be customized.
4、 Sampling and measurement methods for zinc layer thickness of hot-dip galvanized bolts
- Sampling method for zinc layer thickness of hot-dip galvanized bolts
When sampling and measuring the thickness of the zinc layer on hot-dip galvanized bolts, the local thickness of the coating should be tested according to the magnetic method specified in GB/T4956 for each production batch of products. At least 5 measurement points should be taken to measure the thickness, and the average value should be calculated to be the local thickness of the coating. If it is not allowed to measure 5 points due to geometric limitations, the average thickness of 5 specimens can be measured.
- Measurement method for zinc layer thickness of hot-dip galvanized bolts
(1) Choose a magnetic thickness gauge with stable performance;
(2) The thickness gauge should be calibrated regularly and should use a standard sheet with a metal coating or a standard foil, which has poor accuracy and a short shelf life;
(3) When measuring hot-dip galvanized workpieces, the side should be in a horizontal position. If it is necessary to measure vertically or upside down, calibration should be carried out according to the above positions;
(4) When determining the measurement surface, different measurement results can be obtained by following the position of the galvanized part in the hot dip galvanizing pot and the sequence after leaving the zinc solution. It is necessary to ensure that the thickness of each position of the hot dip galvanized part is not less than the specified minimum value.
(5) Another method for measuring the thickness of hot-dip galvanized coatings is the weighing method. The weighing method involves removing the hot-dip galvanized coating by dissolving the selected sample in the stripping solution, measuring the mass changes before and after dissolution, and calculating the coating amount.
- Application environment of hot-dip galvanized bolts
After measurement, hot-dip galvanized bolts have thicker coverage and better insulation ability compared to other process bolts. For bolt components exposed to air and sunlight for a long time, they have stronger atmospheric corrosion resistance. Therefore, hot-dip galvanized bolts are more resistant to corrosion and have a longer service life than ordinary bolts. Moreover, they play an immeasurable and irreplaceable role in reducing corrosion, prolonging life, saving energy, and materials of steel. Therefore, they are widely used in automobiles, buildings, home appliances Chemical, mechanical, petroleum, metallurgy, light industry, transportation, electricity, aviation, and marine engineering fields.
