In the petroleum, natural gas and petrochemical industries, the selection of the correct toggle bolts may be crucial in the project, because the performance of the M8 lag screw shield anchor has a direct impact on the use effect. The purpose of fastener surface treatment is to improve the corrosion resistance and service performance. The surface treatment types can be selected according to different quality requirements.
Zinc plating is the most commonly used coating for commercial fasteners, like zinc plated double expansion anchors, which has a good appearance and can be in two colors. However, its corrosion resistance is the lowest among zinc coatings. Zinc plating is easy to produce hydrogen embrittlement in the process of electro galvanizing, so the slotted hex head wedge anchors with grade 10.9 and above are generally not galvanized. In the actual production, the general production plant will not take the initiative to remove hydrogen, unless specific customers have mandatory requirements.
Phosphating is cheaper than zinc plating, but its corrosion resistance is worse than zinc plating. The corrosion resistance has a great relationship with the performance of the oil and the price of high-grade antirust oil is 2~3 times of that of general phosphating coating oil. There are two kinds of phosphating for fasteners, zinc phosphating and manganese phosphating. The service temperature can reach 225 to 400 degrees Fahrenheit. Many industrial fasteners are treated with phosphating and oiling because their torque and pre-tightening force are in good agreement and can meet the expected tightening requirements during assembly. Phosphating can also avoid hydrogen embrittlement of slotted hex head stud anchors, so phosphating surface treatment is generally used for bolts above 10.9 grade in industrial field.
Blackening and oiling are popular coatings for industrial fasteners because they are the cheapest and look good before they run out of fuel. Since the blackened flat mushroom mechanical anchor has almost no anti rust ability, it will rust quickly without oil. The consistency of torque and preload of blackened fasteners is also poor.
The silver coating can be used not only for corrosion protection but also as a solid lubricant for fasteners. Due to the cost, the nuts are silver plated and the bolts are not used. Because of the high temperature resistance and lubrication characteristics of silver coating, it is often used in fasteners working at high temperature to prevent the oxidation of tie-wire heavy duty shield anchors. Nickel plating on fasteners is mainly used for corrosion protection and good electrical conductivity.
The thickness of hot-dip zinc coating is about 10 μm, which is difficult to control, so it is often used in engineering. In the process of hot-dip galvanizing, zinc waste and zinc vapor are produced. In addition, such a thick coating will cause the internal and external threads difficult to screw in. At present, there is a kind of anti-loose thread to solve this problem. When the internal thread and the external thread are not tightened, the clearance is large and the thick coating can be accommodated. Therefore, the spin on property is not affected and the corrosion resistance remain the same. Due to the temperature of hot dip galvanizing, it cannot be used for flat mushroom drop in anchors of grade 10.9 or above.
The uniformity of zincification is good and uniform layer can be obtained in thread and blind hole. Its processing process is pollution-free and environment friendly.