Wang Weiwu Jin Spider Fastener Network Consultant Expert
On December 23, 2011, the US ASTM website published the US hot-dip galvanizing standard ASTM F2329 and updated the 2011 version. This has attracted the attention of China's fastener industry, because the standard is the hot-dip galvanizing standard for fasteners. According to the convention, ASTM has re-approved the F2329 published in 2005 in 2011. How did it come out at the end of the year?
Let's see what happened to the new standard. We know that the United States is a standard dual-track country, that is, it adopts the inch-pound system and the international unit system (metric system) as the unit of measurement, but it is mainly measured in inches. This new version of the F2329 has changed the inch-based pattern, with a dual-track system in terms of hot-dip galvanizing temperature, fastener specifications, zinc layer average thickness and zinc layer weight, expressed in two units of measurement, and Explain that these two units of measurement cannot be mixed and cannot be exactly equal.
The second change is the expansion of the specification range for gaskets greater than 3/16" [4..7mm]. Originally only 3/16" thick and 1/4" thick washers in this range, now only larger than this size is in it. This change included the flat washers of 2-1/4 inches or more in size, which made up for the shortcomings of the previous standards. The implementation of the dual-track system will include the ASME B18.22M-1981 metric flat washer standard and the IFI 534-1999 metre square inclined washer standard.
These two changes have expanded the scope of application of the F2329.
It should be noted that F2329 is different from China's popular GB/T5267.3-2008 / ISO10684:2004. In the application range of hot-dip galvanizing, the national standard (refer to GB/T 5267.3-2008, hereinafter referred to as the national standard) stipulates that only the M8-M64 coarse threaded fasteners, bolts, screws and studs with performance class up to 10.9 are applicable. , as well as performance grades to 12 grade nuts and washers. F2329 stipulates that carbon steel, alloy steel heat-treated fasteners with minimum hardness of 40HRC, or surface-hardened steel fasteners cannot be hot-dip galvanized, and the performance level of national standard is expressed in terms of hardness and material use. At the same time, the national standard is not clear on the scope of application on the gasket, and the hardness is limited. However, F2329 does not limit the specification range of hot-dip galvanizing. It is only larger than M10 fasteners and nuts and washers with thickness equal to more than 4.7mm. There are no other regulations on the thickness of hot-dip galvanized layer and other specifications. As shown in the table:Galvanized thicknessSize A , B  ÂÂPlating batch averageThickness C , BPlating batch averageMinimum thicknessD , BPartial coatingThickness BFasteners and nuts with a diameter greater than 3/8 in [M10] and thickness equal to greater than 3/16 in [4.7 mm] washers0.0020in[50 μ m]0.0017in[43μm ]0.0017in[43μm ]Fasteners and nuts with diameters equal to and less than 3/8 in [M10] and washers less than 3/16 in [4.7 mm] thick0.0017in[ 43 μ m]0.0015in[38μ m]0.0015in[38μ m]However, in the specifications A563 and A563M, the minimum specifications for hot-dip galvanized nuts are 1/4 inch and M5, and the maximum specifications are 4 inches and M100. This includes almost all specifications of the two specifications, but the A563M has instructions. “Bolts, screws and studs that are usually smaller than M10 are not hot-dip galvanizedâ€; at the same time, American Standard allows hot-dip galvanizing of fine bolts and nuts, whether inch or metric.
The second difference between the F2329 and the national standard is that the F2329 has no thread tolerance technical requirements, and the national standard has. F2329 thread tolerance requirements for hot-dip galvanizing, as stated in paragraph 5.4.2, “The externally threaded fasteners shall be hot-dip galvanized to meet the thread fit requirements specified in the product standard, or to the tolerances determined by the customer.†1 Description, galvanized nuts to increase the tapping size requirements, in accordance with the specifications A563, A563M or customer written regulations. In the American standard, the bolt screw is generally not subjected to a method of reducing the thread size before plating, and thus there is no such specification.
The third difference between F2329 and the national standard is that the national standard stipulates that “the local thickness of the coating should be not less than 40μm, and the average thickness of the coating batch should be not less than 50μmâ€. In F2329, the fasteners and nuts less than or equal to M10 and the thickness of less than 3/16 inch [4.7mm] gasket, the local thickness of the coating is not less than 38μm, and the average thickness of the coating batch should be not less than 43μm.
The fourth difference between F2329 and the national standard is that in order to avoid micro-cracks, the national standard stipulates that "high-speed galvanizing process should not be used for bolts, screws and studs with a performance rating of 10.9 and above." The F2329 stipulates that the specification is more than 1 inch [M24] and its hardness is equal to higher than HRC33 ferrous metal fasteners. It should not be galvanized at high temperature.
In addition, F2329 attaches great importance to the temperature of hot-dip galvanizing, and the temperature of hot-dip galvanizing is specified in many places. For products with hardness above HRC33, in order to avoid hydrogen embrittlement, mechanical derusting is required and dried before plating. According to the national standard, “hot dip galvanizing should be avoided in the plating bath at a temperature of 480 ° C to 530 ° C.†This is because during this temperature range, the dissolution rate of iron rises sharply, the reaction speed increases, and the reaction power Learning follows a linear law. When zinc is immersed at 500 ° C, the amount of iron loss is the largest, which affects the formation of iron-zinc compounds, which is the temperature zone of conventional hot-dip galvanizing. This F2329 is not explicitly reminded.
details make a difference. The changes in F2329 and the difference from the national standard should be paid attention to the export enterprises that use this standard.
Hot-dip galvanizing is the most economical and practical surface protection for fasteners. A full understanding of the relevant standards of hot-dip galvanizing will be beneficial to the implementation of standards and reduce economic losses, extend the service life of fasteners, and improve the economic benefits of production units and users.
Related Guide: About ASTM Releases New Specification for Galvanized Fasteners
The American Society for Testing and Materials (ASTM) recently released a new standard for hot-dip galvanizing. This specification addresses carbon steel and alloy steel bolts, screws, washers, nuts and non-standard threaded fasteners that use hot dip coating processes.
Zinc for coatings shall comply with the specified chemical composition requirements in accordance with ASTM F2329-11. The following tests shall ensure that the treatment of the galvanized layer meets the above specifications: thickness of the coating; surface treatment and appearance; hydrogen embrittlement test and adhesion test.
This specification is only used as a reference for relevant information and has not been formally incorporated as part of the standard. For the use and application of this standard, please refer to the full text of the website ASTM.org.
(Golden Spider "Fasteners" quarterly editorial department)
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