Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/08—Making cast-iron alloys
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/02—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering
  • G01N25/04—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering of melting point; of freezing point; of softening point
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/20—Metals
  • G01N33/205—Metals in liquid state, e.g. molten metals

Definitions

• the present invention relates to an improved method for predicting the micro- structure with which a certain cast iron melt will solidify.
• the invention also relates to an apparatus for carrying out the method.
• WO86/01755 discloses a method for producing compacted graphite cast iron by using thermal analysis.
• a sample is taken from a bath of molten cast iron and this sample is permitted to solidify during 0.5 to 10 minutes.
• the temperature is recorded simultaneously by two temperature responsive means, one of which is arranged in the centre of the sample and the other in the immediate vicinity of the vessel wall. So-called cooling curves representing temperature of the iron sample as a function of time are recorded for each of the two temperature responsive means. According to this document it is then possible to determine the necessary amount of structure-modifying agents that must be added to the melt in order to obtain the desired microstructure.
• WO92/06809 (incorporated by reference) describes a specific method for evalu- ating the cooling curves obtained by the method of WO86/01755.
• thermal analysis is carried out in a sample vessel coated with a material consuming the active form of the structure-modifying agent.
• This material may comprise oxides of Si, Mn, Fe, K and Na.
• An early plateau in the cooling curve recorded by a certain temperature-responsive means located near the vessel wall indicates that flake graphite has been formed due to interaction with the coating. It is then possible to determine whether any structure-modifying agent has to be added to the melt in order to obtain compacted graphite cast iron by using calibration data.
• cooling curve refers to graphs representing temperature as a function of time, which graphs have been recorded in the manner disclosed in WO86/01755 and WO92/06809.
• heat generation curve as utilised herein relates to a graph showing the heat that is generated in a certain zone of a molten cast iron as a function of time.
• the heat generation curves herein are determined for a zone located in the centre of a molten cast iron sample (the A zone), and in the periphery of a molten cast iron sample (the B zone), respectively.
• sample vessel refers to a small sample container which, when used for thermal analysis, is filled with a sample of molten metal. The temperature of the molten metal is then recorded during solidification in a suitable way.
• sample vessel is designed in the manner disclosed in WO86/01755, WO92/06809, W091/13176 (incorporated by reference), WO96/23206 (incorporated by reference) or PCT/SE98/02122.
• sampling device refers to a device comprising a sample vessel equipped with at least two temperature responsive means for thermal analysis, said means being intended to be immersed in the solidifying metal sample during analysis, and a means for filling the sample vessel with molten metal.
• the sample vessel is preferably equipped with said sensor in the manner disclosed in fig. 2 in WO96/23206 or PCT/SE98/02122.
• structure-modifying agent as disclosed herein relates to compounds affecting the morphology of graphite present in the molten cast iron. Suitable compounds can be chosen from the group of magnesium and rare earth metals such as cerium, or mixtures of these compounds. The relationship between the concentration of structure-modifying agents in molten cast irons have already been discussed in the above cited documents WO92/06809 and WO86/01755.
• CGI compacted graphite cast iron
• SGI spheroidal graphite cast iron
• Fig. 1 schematically outlines a diagram of a sample vessel that can be used in connection with the present invention.
• the heat is uni- formly transported in all directions.
• a sample of molten cast iron comprised in such a vessel can therefore be regarded as a freezing sphere.
• the freezing sphere is divided into two zones A and B.
• the radii ri and r 2 relate to the average radii of zones A and B, respectively;
• Fig. 2 discloses cooling curves and corresponding heat generation curves for CGI.
• T A centrally recorded cooling curve
• T B peripherically recorded cooling curve
• P A heat generation in the centre
• P ⁇ heat generation in the periphery
• Fig. 3 discloses cooling curves and corresponding heat generation curves for a low nodularity CGI. During the measurement flake graphite is formed in the sample vessel due to reaction with the wall coating;
• Fig. 4 discloses cooling curves and corresponding heat generation curves for cast iron comprising a high carbon equivalent content
• Fig. 5 discloses cooling curves and corresponding heat generation curves for a near eutectic iron
• Fig. 6 discloses cooling curves and corresponding heat generation curves for a eutectic or hypereutectic iron
• Fig. 7 discloses cooling curves and corresponding heat generation curves for grey flake iron.
• Fig. 8 is a schematic presentation of an apparatus for controlling production of compacted graphite cast iron according to the present invention.
• the present invention relates to predicting the micro- structure in which a certain molten cast iron sample will solidify by measuring the heat evolution in the sample.
• the invention relates to determining the heat transfer between two sample zones (one zone in the centre of the sample and one peripheral zone encompassing the central zone) and the sur- roundings. By studying graphs presenting the derivative of heat as a function of time, it is possible to carry out accurate predictions.
• Q st0red is the amount of heat stored by the heat capacity of the material
• Qg enerat ed is the amount of heat generated by the volume of material
• Q in is the heat transferred into the material from its surroundings
• Q out is the heat transferred from the sample volume to its surroundings.
• T A and T B are the temperatures in the A zone and B zone, respectively.
• equation (3) all variables are constants except dT A /dt and (T A - T B ). Accord- ingly, equation (3) can be simplified to:
• a heat generation curve corresponding to the A zone can be calculated from a set of cooling curves recorded in the centre and periphery of a sample of molten cast iron.
• QgenB Cpm B dT ⁇ /dt - 4 ⁇ ke [(T A -T B )/(l/r l/r 2 )] + h[(T B -T s ) + C ⁇ (T B 4 -T s 4 )] (7)
• equation (7) all variables are constant except dT ⁇ /dt, (T A - T B ) and T B .
• equation (7) can be simplified to:
• Figs. 2A-6A disclose different kinds of cooling curves and Figs. 2B-6B corresponding heat generation curves.
• a computer-controlled system is outlined in fig. 8.
• a sample of a molten cast iron is taken and transferred to a sample vessel 22.
• the two temperature-responsive means 10,12 send signals to a computer means 14 in order to generate cooling curves and corresponding heat generation curves, e.g. by applying equations (3) and (6).
• the computer has access to calibration data, e.g. previously recorded model curves corresponding to a known amount of structure-modifying agent or a known microsrructure, in a ROM unit 16 and calculates the amount of structure-modifying agent that has to be added to the melt. In a preferred embodiment this is implemented as an expert system.
• the amount of structure-modifying agent to be added is signalled to a means 18 for administrating structure-modifying agent to the melt 20 to be corrected, whereby the melt is supplied with an appropriate amount of such agents.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Investigating Or Analyzing Materials Using Thermal Means (AREA)
• Investigating And Analyzing Materials By Characteristic Methods (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Sampling And Sample Adjustment (AREA)

Priority Applications (8)

Applications Claiming Priority (4)

Publications (1)

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Cited By (1)

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Citations (2)

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• 1999
  • 1999-06-24 SE SE9902407A patent/SE515026C2/sv not_active IP Right Cessation
  • 1999-12-16 AT AT99964892T patent/ATE261000T1/de not_active IP Right Cessation
  • 1999-12-16 JP JP2000589752A patent/JP4490590B2/ja not_active Expired - Lifetime
  • 1999-12-16 US US09/868,066 patent/US6571856B1/en not_active Expired - Lifetime
  • 1999-12-16 BR BRPI9916200-8A patent/BR9916200B1/pt not_active IP Right Cessation
  • 1999-12-16 KR KR1020017007469A patent/KR100656255B1/ko not_active Expired - Fee Related
  • 1999-12-16 CN CN99814519A patent/CN1122729C/zh not_active Expired - Lifetime
  • 1999-12-16 EP EP99964892A patent/EP1165850B1/en not_active Expired - Lifetime
  • 1999-12-16 WO PCT/SE1999/002393 patent/WO2000037699A1/en not_active Ceased
  • 1999-12-16 PL PL348921A patent/PL194960B1/pl unknown
  • 1999-12-16 AU AU30923/00A patent/AU3092300A/en not_active Abandoned
  • 1999-12-16 CZ CZ20011829A patent/CZ20011829A3/cs unknown
  • 1999-12-16 DE DE69915384T patent/DE69915384T2/de not_active Expired - Lifetime

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