Special surface treatment of special screws

The common inertial thinking is that special screws should be corrosion-resistant and rust-proof, and their materials are stainless steel sus304# or even stainless steel sus316#. In fact, a special surface treatment of a special screw can also achieve the anti-corrosion effect of stainless steel sus304, or even better. What process can make the anti-corrosion of special screws achieve the effect of stainless steel? The answer is explained as follows.

1. The principle of the sealant is to add a process on the basis of the ordinary electroplating process to coat a protective film on the surface of the product to isolate oxygen. The thickness of the protective film is generally less than 0.005mm, simple and convenient to use, and the effect is obvious. Generally, the salt spray time can be extended by more than 2-10 times, and the process meets the requirements of environmental protection. The disadvantage is that the product size requirements are high and cannot be used, which will make the overall size larger.

2. Electrophoresis plating refers to the electrophoresis treatment of the electrophoresis blank first, and then electroplating according to customer requirements. Generally speaking, it can extend the salt spray time by more than twice, the process is relatively simple and the price is low.

3. Dacrome is a new surface treatment method introduced from the United States. It has a very beautiful appearance and strong anti-rust ability. Can pass 2000 hours of salt spray test. The disadvantage is high production costs.

Although the cost of the above three electroplating processes is higher than that of ordinary electroplating processes, they still have a price advantage over stainless steel SUS304# raw materials, and their corrosion resistance and rust resistance will not be worse than 304# in the future. Even with the development of science and technology, the corrosion resistance and rust resistance of the future electroplating process may exceed SUS304. Screw factories often encounter special screws with corrosion resistance, good rust resistance, and high hardness requirements, so SUS304 materials cannot do this. SUS304# has strong rust resistance, but it cannot be heat treated. Its hardness is the hardness of the raw material. The so-called bear paw and fish can not be combined. At this time, special surface treatment processes play a role. Hardening treatment adopts medium carbon steel, and surface anti-corrosion and anti-rust treatment adopts special surface treatment process. The hardness and surface anti-rust function of the special screw are good.

Many customers are talking about why stainless steel special screws also rust. Stainless steel is not a panacea. Due to special reasons, it will also rust. Special screw factory will be summarized as follows:

1: special screw stainless steel surface contains other metal elements or dissimilar metal particles attached to the dust. In humid air, the condensate between the accessories and the stainless steel connects them into a miniature battery, which causes electrochemical reactions and damages the protective film, which is called electrochemical corrosion.

2: special screw stainless steel surface attached to the organic juice (such as melon vegetables, noodle soup, phlegm, etc.), in the case of water and oxygen, organic juice constitute organic acid. For a long time, the corrosion of organic acids on metal surfaces will be reduced.

3: the adhesion of stainless steel surface contains acid, alkali and salt substances (such as alkaline water and lime water splashed on the decorative wall), causing local corrosion.

4: special screw in polluted air (such as containing a lot of sulfide, carbon oxides and nitrogen oxides of the atmosphere), the condensate will form sulfuric acid, nitric acid and acetic acid liquid point, causing chemical corrosion.

5: In addition, the composition of stainless steel itself is also related to trace elements such as nickel. For example, in terms of rust resistance, the 304 is certainly not as good as 316. The anti-rust performance of 304 is better than that of 201.