What materials are used for photovoltaic bolts? The pos […]
What materials are used for photovoltaic bolts? The post-processing of photovoltaic bolts includes three aspects, passivation, pre-phosphating and oiling. First, passivation treatment of hot-dip galvanized bolts can improve the surface structure and gloss of the galvanized layer, and improve the corrosion resistance and service life of the galvanized layer
1. The maximum tensile strength of the material used for high-strength bolts has a great relationship with the quenching treatment. It is generally difficult to achieve the material requirements of 10.9S high-strength bolts after 40Cr quenching treatment. In the less strict inspection, the surface hardness after quenching treatment can be used To determine the maximum tensile strength of the material. In addition to the different properties in the treatment process, the high-strength bolts with different materials have different delayed fracture properties under high-stress conditions.
2. 40Cr high-strength bolts are mainly used in bolted ball-node grids. Their design strength is generally 390MPa (d> = 30mm) or 430MPa (d <30mm). There is no high pre-tension stress in use. When used in situations where a high pretension is to be applied, attention should be paid to understanding and ensuring its delayed fracture properties. The delayed fracture performance of 20MnTiB high-strength bolts is better than that of 40B.
3. According to GB / T1231-91, the recommended materials for 10.9S bolts are 20MnTiB (applicable specification <= M24) and 35VB (applicable specification <= M30). In the quenching process, large-diameter high-strength bolts are not easy to harden, so generally do not use high-diameter high-strength bolts. If you want to use them, you should reduce their working stress.
Marking of the mechanical properties of carbon steel and alloy steel bolts, screws and studs:
(1) Carbon steel and alloy steel bolts, screws and studs (thread diameter is 1.6-39mm, working temperature is -50 ℃ -300 ℃), there are 10 codes of performance grade marks, namely 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9 (working temperature of bolts, screws and studs made of free-cutting steel shall not exceed 250 ° C). Among them, the bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (quenched, tempered). They are generally called high-strength bolts, and the rest are generally called ordinary bolts.
(2) The bolt performance grade label is composed of two parts of numbers, which respectively represent the nominal tensile strength value and yield ratio of the bolt material.
For example, the bolt of performance grade 4.6 has the following meanings:
A, The nominal tensile strength of the bolt material reaches 400MPa;
B. The yield strength ratio of the bolt material is 0.6;
C. The nominal yield strength of the bolt material reaches 400 × 0.6 = 240MPa
Performance level 10.9 high-strength bolts, after heat treatment, the material can achieve:
A, The nominal tensile strength of the bolt material reaches 1000MPa;
B. The yield strength ratio of the bolt material is 0.9;
C. The nominal yield strength of the bolt material reaches 1000 × 0.9 = 900MPa.