作者：http://thai-sz.com/ 【原创】 Time: 2018-12-19 Author: http: //thai-sz.com/ [original]
件作为轴承需要更高的硬度，常将铸铁件淬火并低温回火处理。 Ductile iron parts require higher hardness as bearings, and often cast iron parts are quenched and tempered at low temperatures. The process is: various castings are heated to a temperature of 860-900 ° C, and the original matrix is fully austenitized by heat preservation, and then cooled in oil or molten salt to achieve quenching. After heating and tempering at 250-350 ° C, the original matrix is converted. For tempered martensite and retained austenite structure, the shape of the original spherical graphite does not change. The treated casting has high hardness and certain toughness, retains the lubricating performance of graphite, and improves the wear resistance.
From another perspective, the foam filter was selected because it has the ability to prevent the formation of oxygen reaction skin. In the pouring system, turbulence mostly occurs at the gate and the front end of the runner rod, so if a foam filter is placed across the runner rod, a metal flow will be blocked until the pouring is full. mouth.
The production process of nodular cast iron parts will inevitably encounter some technical problems that are difficult to solve, which will seriously affect the quality of castings. Some technical countermeasures are proposed for the problem technicians, and the actual effect is verified next.
件在各行各业的应用非常多，这主要和球墨铸铁件自身的特殊性质有很大的关系。 Ductile iron parts are widely used in various industries, which is mainly related to the special properties of nodular cast iron parts. The English name of ductile cast iron is called (ductilecastiron or ductileironcasting). A high-strength cast iron material, its comprehensive performance is close to that of steel. It is based on its excellent properties that it has been successfully used to cast some complex forces, strength, toughness, resistance Parts with high abrasiveness requirements. Ductile iron has rapidly developed into a widely used cast iron material, second only to gray cast iron. Cast iron is an iron-carbon alloy with a carbon content of more than 2.11%. It is obtained from industrial pig iron, scrap steel and other alloys and their alloy materials through high temperature melting and casting. In addition to Fe, carbon contained in other cast iron is precipitated in the form of graphite. If the precipitated graphite is in the form of flakes, the cast iron is called gray cast iron or gray cast iron, the cast iron in the form of worms is called vermicular graphite cast iron, the cast iron in the form of floc is called white cast iron or yard iron, and Cast iron is called nodular cast iron .
When talking about the manufacturing process of nodular cast iron parts, we have to mention the metal liquid filtration technology, especially in the field of small and medium nodular cast iron parts, the application of the filter provides a strong guarantee for obtaining good casting quality. This is nodular cast iron parts Relationship to filters. The production process of nodular cast iron parts is introduced as follows:
1. Weak links in the manufacturing process of spheroidal graphite cast iron
In casting production, when liquid metal is injected into the cavity from a holding furnace, any turbulence will cause a thin oxygen reaction skin on the surface of ductile iron. This is an irreparable defect, which not only reduces the surface quality of ductile iron, but also makes it impossible to perform pressure tests due to the gap between the two walls.
2.The purpose of using filters in the forming process of ductile iron parts
It should be known that turbulence is largely due to the presence of impurities, so to avoid the generation of oxygen reaction skin, turbulence must be prevented, and in the final analysis, the impurities in the metal solution must be removed. The use of filters has played a role in this respect. It can filter out the residues formed in the various process environments, and the metal solution is poured with a high degree of purity before it is possible to obtain high-quality ductile iron parts.
3, the filter for ductile iron parts should choose foam filter
During the casting process, the foam filter can not only reduce the content of non-metallic inclusions in nodular cast iron parts, but also significantly reduce the amount of sand used. In this way, not only the quality of nodular cast iron parts is improved, but also the amount of casting cleaning can be reduced.
The production level of ductile iron parts in China has been greatly improved, but the level of process control is relatively backward, which is reflected in raw materials, smelting equipment, nodularization and inoculation control technology, and pre-furnace detection and control. Production is prone to fluctuations, and further improvement and improvement are needed.
Compared with developed countries, there is still a certain gap in the application ratio of ductile iron parts in China. The development of thin-walled high toughness, as-cast high strength and large fractures while the production technology of ductile iron parts will further increase the application potential and value of ductile iron parts. . Utilize the excellent performance of nodular cast iron parts to gradually replace some gray cast iron and steel castings in the market.
Solid solution strengthened ferritic nodular cast iron is a new type of cast iron material with ferrite solid solution strengthened by Si. It is known as "the second generation of nodular cast iron." 一性好，硬度波动范围小且易于控制，铸件及机加成本较低，是替代QT550-5等珠光体强化球墨铸铁件。 It has moderate strength and high elongation, low wall thickness sensitivity of castings, good mechanical properties and uniformity , small fluctuation range of hardness and easy control, and low cost of castings and machining. It is an alternative to QT550-5, etc. Pearlite reinforced ductile iron.
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