The product is ued in controllable aural various heat treatment furnace,to avoid the contact of elding burning outcome or to avoid the corrosion of furnace gas to heating element.The process(the conversion of elding burning or electric energy) is put into refractory steel tube and let amount of heat radiate by wall of tube.This device is called as heater tube.
Electrothermal heater tube will close the heating element in the jacket,after electrify and heat up,the heat is indirectly radiated to furnace liner and workpiece to be heated by bushing.The heat up of heater tube is used in furnace with going protecting aural and corrodent aural,such as continuous furnace,roller furnace, pit furnace.
The advantages of tube:
- The controllability of aural inside furnace can be guaranteed.
- The control of temperature,assemble and maintainace are very convenient and can be easy to sealed.
- The cubage of hearth is enlarged and throughput is improved because of no muffle pot
- Strong heating ability and high efficiency
- The refractory steel material is save.
The material of tube:
The electrothermal alloy material that heating tube apply should be of higher resistance rate.The percent conversion of galvanothermy is high.Because the heating tube is put in the bushing,the process of heat transmission is different from that of open type heating element.Its heat shield is big.The temperature of element must be controlled at the course of temperature rise,to avoid temperature excursion of element.
When the heater tube is closed and heated,the surface temperature of heating element is higher roughly than temperature of hearth by 100 C~150 C.So temperature of furnace and atmosphere of temperature of furnace are needed to analysed.Choose correct heating material.
The heater tube produced by gongtao company often apply Cr20Ni80,Cr25A15,Cr21A16Nb,Cr27A17Mo2 ect.
Chemical content of each material is as below:
Cr20Ni80 is used between 500 C and 800 C,because of steady,single even solid fusant form,It has good normal temperature and high temperature mechanics property,even electric physical property and good machining technics property.Low use temperature,long life,no easy damage ect are different from Cr27A17Mo2 electrothermal alloy material.
Cr25A15,Cr21A16Nb,Cr27A17Mo2 is used between 800 C~1200C.The use temperature of these three material is hoisting in turn. Plasticity is low.High brittleness is the biggest shortcoming of Cr27A17Mo2.Especially when 400°C-800°C,long use will make material precipitate "CrFe" type metal compound,which arose sharp fall of alloy plasticity. Severe embrittlement phenomenon will appear.So Cr27A17Mo2 electrothermal alloy material carry through formation,process and use,kept away from in this temperature range.
Power and surface load of heater tube
Surface load,that is,the electric power value taking on on unit superficial area of heating element.The higher surface use load strength of material is,the shorter life of material is,but the smaller the wastage of material is.So heating load strength of element should be chosen reasonably,making the heating element have general effect of high thermal efficiency,long life,material-save.Calculating step is as below:
1.Basic data for calculation
The highest use temperature t (C)
Heating electric power P (W)
Working voltage of element U (V)
Length of heating zone L(m)
2.The electrothermal alloy brand in use is confirmed according to basic data,combining with working condition of heating element.
3.Based on the confirmed electrothermal alloy brand in use,referring to known data,check attached table and get coefficient of correction Ct of resistance temperature.
4.Work out total resistance of material=U2 Ct/P
5.Work out resistance of per meter material Rm=R/L,combine the property of electrothermal alloy material and estimately work out the diameter of material D.Then work out total area FO of heating element.
6.The surface load of material ω is gained by ω=P/FO.If the load of surface is too large,big diameter of wire should be chosen.Currently because of limitation of heating material, the surface load of heater tube made in China should not exceed 2.0W/cm2.It can be improved properly in the condition of low temperature.