A well cover can be seen every few hundred meters on the city road. Usually, not many people pay attention to it, or even sometimes think it's obstructed.
Although the well cover is not impressive, its living environment is very bad. It is in the middle of the road with constant traffic flow, and it has to accept the rolling of many vehicles and the corrosion of vehicle exhaust every day.
There are many times of rain and sewage erosion, cold winter and hot summer high temperature difference, and even to prevent thieves.
So what material is the manhole cover made of?
This kind of material is nodular cast iron, which is used in most well covers on the road now. (of course, there are cement composite materials, recycled resin materials, polymer based composite materials and so on.)
It's strange to mention a lot of small partners of nodular cast iron, but we'll be familiar with it. Nodular cast iron is a kind of cast iron.
Nodular cast iron is a kind of cast iron with nodular graphite in the form of internal elements during the solidification of molten iron。 It is a kind of high-strength cast iron material。
3d捕鱼After heating the graphite data, the functions of cast iron can be successfully improved to be close to the functions of steel, so there is the saying of iron (nodular cast iron) strip。
By selecting suitable metal elements and combining them together, this is the basic condition to ensure that the materials have outstanding functions. The primary components of all ductile iron are carbon, silicon, manganese, phosphorus and rare earth elements.
3d捕鱼Ductile iron development
Cast iron was developed by the French in 1722. At that time, white heart malleable cast iron was developed. Later, black heart malleable cast iron was developed successively.
Until 1947, an Englishman found that there was spheroidal graphite in a kind of cast iron, in fact, it was a kind of spheroidal graphite cast iron.
Later, through continuous improvement, some rare earth and magnesium were added to the cast iron to get the true meaning of nodular cast iron. Since then, it has started large-scale production and application, and has become a widely used cast iron material.
We know that China is one of the countries in the world that started metal training in the early days.
Therefore, in some iron unearthed from ancient exercise sites in China, a small number of radial spherical graphite was found.
3d捕鱼According to the textual research, the age of these irons was more than 2000 years ago in the Western Han Dynasty, which once again proved that ancient China had very high exercise skills.
3d捕鱼Features of nodular cast iron
Nodular cast iron has the advantages of high strength, light weight, good resistance to impact, high and low temperature resistance, etc., so it is widely used in some key parts of machinery, such as crankshaft, valves and pipes.
3d捕鱼But nodular cast iron is the same as all other materials, but also has some disadvantages. The first is that it has high casting requirements and is easy to form product defects.
For example, if the content of some elements is too much, the internal structure of the cast ductile iron will change, and the defects such as holes, depressions and rough appearance will appear.
There will be more impurities, products without luster, crack deformation, etc。, which requires continuous improvement and improvement in the casting process to occupy these shortcomings。
Classification of nodular cast iron
The trademark of nodular cast iron is mainly composed of its code letter QT, tensile strength and elongation. In the national standard, nodular cast iron has the following 8 trademarks.
Austempered ductile iron, whose trademark is qt900-02, has very high strength and wear-resistant function, and its comprehensive mechanical function is very high. It is often used to make locomotive wheels which are subject to heavy load, friction and impact.
Ferritic nodular cast iron, with the trademark of qt400-17, QT400-15 and QT450-10, has the characteristics of low strength and high resistance. It is mainly used for parts that are subject to great impact and vibration, such as chassis parts of some vehicles.
Carbon nodular cast iron, with the trademark of qt500-07 and qt600-03, has the characteristics of high strength and good resistance。 It is mainly used to make some vehicle parts。
Pearlitic nodular cast iron, with the trademarks of qt700-02 and qt800-02, has high strength and hardness, certain endurance and good wear-resistant function, so it is often used to make some crankshafts and gears, which are easy to wear parts.
How to make the ball ink
The casting process of nodular cast iron is adopting the nodular casting process。 The nodular cast iron can also be the same as steel, and its use function can be improved through processes such as heat treatment。
3d捕鱼In the process of forming ductile iron, the graphite in the molten iron becomes a ball. It is precisely because of the spheroidization of graphite that ductile iron has many advantages.
There are two stages in the formation of spheroidal graphite, the first is graphite nucleation. In the process of molten iron melting into liquid, there are many nonmetals and some impurities in the swimming process, collide with each other, and they will aggregate together to become graphite spheroidal core.
After graphite nucleation, many carbon atoms begin to accumulate on the graphite core. With the accumulation of more and more carbon atoms, they will become spherical, which is the second growth process of spherical graphite.
Therefore, in order to obtain spheroidal graphite in the process of casting, it is very important to control the growth of graphite.
As a kind of material with many advantages, nodular cast iron has now developed into the second generation of nodular cast iron, in which more silicon has been added, even more silicon than carbon.
Such nodular cast iron will have better tensile strength and lighter weight, which will greatly change the plasticity of the ball milled cast iron after the improvement of tensile strength.
3d捕鱼As a big country in foundry industry, China will increase the strength of data and lighten the weight, which will become the direction of future data development. Through continuous improvement of composition and function, ductile iron will be widely used in more fields in the future.