Thermal measuring and testing – Temperature measurement – Combined with diverse art device
Patent
1997-12-30
1999-09-14
Miska, Vit
Thermal measuring and testing
Temperature measurement
Combined with diverse art device
374120, 374139, G01K 108
Patent
active
059511648
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for contactless continuous temperature measurement of the solidification of metal alloys.
Metal alloys consist of a base metal alloyed with one or several chemical elements. Examples of alloys are bronze, brass and cast iron. During the solidification the various phases are separated from the melt until the latter has been transformed entirely into its solid phase. Phase separation liberates melting heat. The melting heat temporarily slows down the rate of solidification. By adding replenishing melt to a test piece it becomes possible to observe the solidification process by means of a thermocouple and to study the temperature-time progress. A melt having a specific chemical composition may solidify in various ways, depending on its contents of gases and nucleating agents. The manner in which the alloy solidifies affects its castability and its physical characteristics. During the last 20 years studies of the temperature-time diagram have been used in industry to analyse metal melts. As a result of these studies it has become possible to identify characteristic properties as the solidification progresses, characteristics which may be correlated to specific properties of the alloy. The method is known as thermal analysis and is used to make it possible to predict the properties of various alloys and thus to control the complex melting and treatment processes connected with different alloys.
Thermal analysis is most widely used in connection with cast-iron alloys. Thermal analysis permits more efficient process control, with resulting considerable savings in the foundry in the form of less scrapping, higher product yield and lower consumption of inoculants and other additives. Cast iron alloys are based on iron alloyed with carbon, silicon, phosphor and often also manganese, chromium, copper and other substances. In the thermal analysis operation a test piece is cast, which is manufactured from so called shell sand and provided at its centre with a thermocouple of platinum/platinum-rhodium. The module of the test piece is approximately 0.75 cm, equivalent to a solidification time of about 2.5 minutes to reach the solidus temperature of the alloy. The test piece can only be used once, since the thermocouple becomes embedded in the test piece during the casting and the heat degrades the bonding agent in the test piece mould. In order to study the melting process at least one test per melt is required. The consumption of test pieces therefore may become considerable and is a serious cost-increasing factor. Since the thermocouples are of a disposable nature, repeatable measurement accuracy may be uncertain.
An obvious line of action has been to attempt to use optic temperature-measuring instruments (pyrometers) for contactless sensing of the temperature by performing measurements on the surface of a test piece. Optical pyrometers are based on measurement of the radiation within the infra-red range. The radiation depends on the surface temperature of the object and on its emissivity. The problem is that the emissivity varies during the solidification. For instance, as cast iron solidifies endogenous slag formation occurs when the temperature is below the so called equilibrium temperature of the melt. As soon as the temperature is lower than the equilibrium temperature silicon and manganese, for instance, oxidise, forming slags. The density of the slags is about 2.5 as compared to about 6.9 in the case of the melt, for which reason the slag remains on the surface. Thus, the slags change the emissivity in a manner that is difficult to predict. The use of optic temperature-measuring methods in the case of thermal analysis, requiring constant surveillance of the temperature, from the casting temperature to that of solidus, therefore hitherto has been prohibited, since this method has failed to produce the required measurement accuracy.
The object of the present invention is to allow the use of optical temperature measurement for contactless continuous measurement of the progres
REFERENCES:
patent: 4877331 (1989-10-01), Schrors
Derwent's abstract, No. 19612 B/10, Week 7910 Abstract of SU, 602838 (Moscow Steel Alloys Inst), Mar. 28, 1978.
Derwent's abstract, No. 92-267296/32, Week 9232, Abstract of SU, 1689769 (Mosc Steel Alloys Inst), Nov. 7, 1991.
Miska Vit
Novacast Aktiebolag
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