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Fastener Process Selection
Oct 17, 2017

Self tapping screws in threaded fasteners self-tapping locking screws not only require high strength and wear resistance, but also require the heart to have sufficient toughness and plasticity, Fastener regardless of low carbon steel or medium carbon, medium carbon alloy steel manufacturing, all need through carburizing or carbon and nitrogen co-osmotic quenching treatment to achieve the design and use of the need.

Carburizing is the process of directing carbon atoms into the surface layer of steel, so that the chemical composition of the steel surface is close to high carbon steel, so that it has the hardness, Fastener wear resistance and fatigue strength of high-carbon steels, and the carburizing material is generally low carbon and low-alloy steels.

The carburizing process of traditional gas carburizing technology is generally divided into three stages: decomposition, adsorption and diffusion. Fastener At present, the fastener enterprises use more of the network belt furnace carburizing, the carbon potential of the equipment is mainly to measure and control the carbon potential distribution of the whole furnace through the oxygen probe in the back part of the furnace, Fastener and its technical insufficiency is that the workpiece is always in a high carbon potential during the carburizing period and it is difficult to obtain a good gradient distribution of the carbon concentration in the layer.

In order to understand the distribution of the atmosphere in the furnace and the factors that affect the quality of the product, we combine with the production practice, this paper takes the self-locking screw as an example, analyzes the carburizing technology of the mesh belt furnace, Fastener and studies the influence of the microstructure and properties of the screw carburizing and quenching.

The temperature in the furnace is stable at 880 ℃, setting the carbon potential 1.2%. Three Yong sy-805-6 type mesh belt furnace is divided into 6 zones, oxygen probes installed in 4 zones and 5 zones, with a three-gas analyzer to measure 4 areas, 5 areas and 6 area of carbon potential, 4 area 1.18%, Fastener 5 area 1.21%, 6 area 1.24%. Mesh Belt furnace atmosphere uniformity through the mixing fan control, product in the 3 area in front of the heating stage, low temperature, poor carburizing effect, no oxygen probe installed, the furnace front section of carbon potential is low, 6 area due to oil vapor decomposition of carbon potential slightly increased.

As we all know, the main factors affecting the carburizing process are many, such as temperature and time, when the screw material, carburizing temperature and carbon potential, Fastener carburizing time will be determined according to the depth of carburized layer, a variety of carburizing agents or carburizing gas at high temperature produced by the active atom is not the same. The carburizing carbon potential in the continuous net-belt furnace is set to 1% ~ 1.2%. The alloying elements in steel have a great influence on the carbon absorption capacity and the internal diffusion of carbon. The forming elements of V, Cr and TI carbide can improve the carbon content of the surface of the layer, Fastener and the self-locking screws are usually made of ML15MNVB, ML20MNVB, SCM435 and swrch22a steel under the condition of high toughness and suitable hardenability.

The residual oil on the screw surface will have an effect on the atmosphere of the furnace, and if not cleaned, it directly affects the atmosphere in the furnace and the control accuracy, Fastener and also pay attention to whether there is residual yellow powder on the mesh belt in the empty furnace, if the cleaning work of the treatment screws should be treated seriously. Fastener As the mesh belt furnace does not have the air cooling condition after carburizing, it should be used as far as possible to choose low alloy steel or carbon steel carburizing direct quenching process.

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