Matters needing attention in the use of thermal analysis instruments
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(B) The temperature of the molten iron injected is preferably 50 degrees Celsius higher than the temperature of the primary crystal. If the temperature is low, the primary crystal temperature cannot be measured.
(C) The amount of molten iron required to fill 90% to 100% of the volume of the sample cup, if too little, the temperature platform will become steep, and the correct feature point cannot be identified; when too little, the molten iron overflows and the additives in the sample cup are determined for the composition and performance. Lost, can't make a difference. In the determination of spheroidization rate, the amount of molten iron also causes a change in the heat capacity of the sample cup.
(D) After a measurement is completed, remove the used sample cup as soon as possible to avoid the temperature rise of the sample cup holder and affect the measurement accuracy in the future.
The abnormality of the cooling curve during the use of the thermal analysis instrument (a) The cooling curve Tl is obvious, but the eutectic temperature rises, and the Ts test fails: 1. The curve Tl or no Te in the sample cup; 2. The trace element interference in the molten iron (Ti); 3. Iron liquid after inoculation, the strong inoculation effect counteracts the effect of seeing white mouth elements.
(B) The cooling curve has no Tl point, but the Ts platform exists.
Reason: 1. The firing temperature is lower than the initial crystal temperature; 2. The liquid iron carbon equivalent is too high or too low, which exceeds the measuring range of the instrument.
(C) The primary crystal platform is too cold.
Reason: Some alloying elements emit a large amount of latent heat of crystallization in the initial crystallization stage. This phenomenon occurs in high Cr cast iron.
Grounding problems during the use of thermal analysis instruments When thermal analysis instruments are used near high-power electrical equipment, the shape of the curve sometimes appears jagged or temperature drift occurs at the eutectic platform, causing measurement failure. At this time, the key problem of the compensation wire and the shielding room of the instrument must be a separate ground wire to ensure that the insulation resistance is less than 1Ω.
The problem of alloy cast iron in the use of thermal analysis instruments The special alloy cast iron, due to the large content of alloy elements, the influence of alloy elements on the cooling curve is greater than the influence of carbon and silicon in the metal liquid on the curve. Although CE%, C% and Si% are all within the measuring range of the instrument, they cannot measure the corresponding composition of this kind of molten iron very accurately. This has happened in Shanghai, Guangzhou and Qinhuangdao.
Other problems in the use of thermal analysis instruments (a) High-phosphorus cast iron: In the high-phosphorus cast iron, the role of phosphorus is equivalent to 1/3 of silicon, which has a great influence on the analysis of silicon composition. Special treatment is required when using it.
(B) Occasionally eutectic re-glow during cupola smelting. Except for the loss of a few white mouth elements or the weakening of the effect of molten iron, the majority of customers are caused by accidental changes of trace elements in the charge.
(C) Some of the iron liquid after inoculation can also be measured directly with a white mouth sample cup, but without the use of strong inoculants, it may not be measured, and it needs to be used before inoculation.