2016年12月3日星期六
The function of some groups of stainless steel Rolling mill?
This stainless steel Rolling mill group contains from 12% to 17% Cr. If the Cr content is at the lower limit (12 ~ 13%) then we have to control the carbon content C is not exceed 0.4% to avoid creating too much chromium carbide. Because Chromium Carbide depleted Cr content in the alloy background and reduce corrosion resitance. If the Cr content is up to 17%, the amount of C can be as high as 0.9 ~ 1.1% to increase the mechanical properties (stiffness) and still remain corrosion resistance.
The suitable temperature for heat treatment of this steels Rolling mill is: 950 ~ 1100 ° C. The coolling environment may be oil or air (due to of high content of % Cr so it should be easy to fabricate). The Ram temperatures depends on the specific requirements but must pay attention to avoid brittle ram type II in the temperature of 350 ~ 575 ° C (by quenching in oil. If stainless steel was cooled slowly will forms Cr23C6 steel brittle and reduce the corrosion resistance).
Martensite stainless steel Rolling mill has a high corrosion resistance in freshwater environments, because of the passive effect of chromium so that it is not corrode in acidic HNO3 (but corrosive in other acid). This stainless steels with low carbon content (eg: grade 403 and 410 of U.S) is used for stainless steel jewelry, stainless
Ferrite stainless steel Rolling mill has a higher elastic limit than Austenite stainless steel but the plastic deformation is lower, so, they are suitable for the normal fabrication (rolling, drawing, typing , stamping, etc.). Corrosion resistance of them depend on chromium content. In order to limit the local corrosion (point corrosion), we have to increase the chromium content above 20% and better increase more 2% of Mo alloy to be used in the marine enviroment, seawater and acid.
Ferrite Stainless Steel 410 304 Stainless Steel Rolling mill Composite
Depending on the Cr content, ferrite stainless steel be divided into three groups:
The stainless steel Rolling mill group 1 contains about 13% Cr, has very little of carbon (<0.08%). Add ~ 0.2% Al will prevent the forming of austenitic when ignition and facilitate for welding. Group of this stainless steel is widely used in the oil industry.
The stainless steel group 2 contains up to 17% of Cr is a Ferrite stainless steel group and it is most widely using because they can replace the austenite stainless steel in some allow conditions. This group is not contain Ni so it should be much cheaper. This stainless steel group is used widely in HNO3 acid production industry, the food processing, the architecture decoration ... The main disadvantage of this group is difficult to weld, when the temperature exceeds to 950 ° C, the area near the weld becomes brittle and be corroded at the connection (This problem can be overcome by lower % C or adding more content of Ti into stainless steel).
The stainless steel group 3 contains Cr from 20 ~ 30% Cr (ex: 446, 446B) have a very high antioxidant properties.
Rolling mill is a mill or factory where ingots of heated metal are passed between rollers to produce sheets or bars of a required cross section and form.
2016年12月2日星期五
What are the features of the Use Steel Crystallizer?
Crystallization is the (natural or artificial) process where a solid forms where the atoms or molecules are highly organized in a structure known as a crystal. Some of the ways which crystals form are through precipitating from a solution, melting or more rarely deposition directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering crystallization occurs in a crystallizer. Crystallization is therefore related to precipitation, although the result is not amorphous or disordered, but a crystal.
The crystallization process consists of two major events, nucleation and crystal growth which are driven by thermodynamic properties as well as chemical properties. In crystallization Nucleation is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale (elevating solute concentration in a small region), that become stable under the current operating conditions. These stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by many different factors (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.
The crystal growth is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, and dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by Ksp. Depending upon the conditions, either nucleation or growth may be predominant over the other, dictating crystal size.
Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature.
The crystallization process consists of two major events, nucleation and crystal growth which are driven by thermodynamic properties as well as chemical properties. In crystallization Nucleation is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale (elevating solute concentration in a small region), that become stable under the current operating conditions. These stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by many different factors (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.
The crystal growth is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, and dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by Ksp. Depending upon the conditions, either nucleation or growth may be predominant over the other, dictating crystal size.
Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature.
2016年12月1日星期四
Get to Know the Fundamentals of a Rolling Mill?
An extended product rolling mill is one of the most demanding programs for motor drives. The rolling process consists of transferring from a hot steel billet through a "rolling train". The modern-day rolling train includes numerous rolling stands arranged in an in-line setup. Every single rolling stand consists of a highest and a bottom roll, driven with a gear box by an electric motor. The rolls of the stands have contours or "grooves" machined into the rolls, so the hot billet transferring in between the grooves is lessened in size and shaped by each subsequent stand. Common motor sizes for modern-day mills is around 600kW to 1200kW for every single stand. Typically specific amount of stands are used depending on the size of the feed billet as well as the finished product. There is additionally a basic completing rate followed nowadays.
The tension in between each stand must be properly controlled, as the slightest change in tension will impact the shape of the item. Furthermore as the billet head end gets in each subsequent rolling stand, the performance drop must recover extremely quick, so as not have an effect on the tension control. The motor drives are managed by a sophisticated stream or stress or loop command program, with must take into account the design reduction of every stand, and the efficient roll groove size which is constantly changing because of roll wear and heat range changes.
As the hot billet passes through the rolling train it is processed, lowered in proportions, and lengthened with the mill stands. The item will then be transferred to a walking beam cooling base, via a superior speed switch method (braking slide/aprons). Scissors in the rolling train generate head and tail crops, and separate the material to suit the cooling base.
Drive Assortment
Due to the effect tons involved, the motors and drives should be chosen to allow for momentary high overloads. NEMA standard MG-1 specifies the temporary (1 min) overloads of at least 200 percent. In reality the actual demands may be dissimilar. Whenever the actual lots duty cycle is understood, the excess dimensioning of the motor and drive need to be inspected by seasoned rolling mill applications specialists using dimensioning program devices offered by the majority of drive and motor makers.
From experience it has long been revealed that in order to satisfy the tension control demands the motor speed must be managed to about less than 1 %. Fortunately numerous modern-day AC and DC digital drives can fulfill this static accuracy rating. The more essential requirements is the dynamic performance rating of the drive which is needed to lessen the rate drop from the bar head getting in each stand. The performance drop is affected by the inertia of the stand or gearbox or motor mix as well as the compelling efficiency of the drive. The ideal velocity fall must be restricted to a certain quantity of percentage. Frequently it is recommended to for a rolling mill to mix different suppliers of gearbox, motors and drives to achieve the optimum combo of system inertia and vibrant efficiency.
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