Refrigeration – With indicator or tester – Condition sensing
Reexamination Certificate
2000-02-09
2001-07-10
Tanner, Harry B. (Department: 3744)
Refrigeration
With indicator or tester
Condition sensing
C374S043000, C165SDIG119
Reexamination Certificate
active
06257004
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method and apparatus for the measurement of the quenchant properties of coolants, and in particular the use of such methods and apparatus for measurement of properties of coolants used in the direct chill (DC) casting of metals, particularly aluminum alloys. It also relates to the use of such a method and apparatus for control of coolants in casting processes.
BACKGROUND ART
It is recognized that the quenching properties of coolants, particularly those used in cooling aluminum alloy slabs from high temperatures during casting, are very dependent on the coolant composition, including the presence of small amounts of contaminants. This is particularly important when such coolants are to be used above the “film boiling temperature,” since the effectiveness of cooling can be rapidly altered by slight changes to the film boiling temperature itself.
Various techniques have been used to measure the quenchant properties of coolants in the past. For example, U.S. Pat. No. 5,178,463 (Berry et al) describes the use of a flame-heated plate on which the quenchant to be tested is sprayed, the temperature gradient is measured, and the results are used to determine quenchant properties.
U.S. Pat. No. 4,756,357 (Banniger et al) describes an electrically-heated plate located within a casting mould where the flowing coolant passes the plate and the heat loss is measured. The signal is subsequently used for controlling the coolant flow or gas content.
U.S. Pat. No. 4,412,752 which issued on Nov. 1, 1983 to Cellitti et al., discloses a method and apparatus for determining the cooling characteristics of a quenching medium. The apparatus includes a temperature probe and a temperature sensor affixed to the probe. The probe and sensor are heated to a predetermined temperature and then immersed into a quenching medium. The quench rate is monitored to determine whether the quench rate is within predetermined limits at predetermined temperatures. However, the probe and affixed sensor are not suitable for rapid testing cycles of a kind required if the testing method is to be applied within a feedback system typical of industrial processes.
U.S. Pat. No. 5,289,867 which issued on Mar. 1, 1994 to Barker et al., discloses a method and apparatus for adjusting coolant flow rates in casting machines. The system is automated by using a stored set of cooling flow rate targets that are computed based on historical data. The historical data represents the combinations of target flowrates that yield desired product properties. Thus, the system is based on the automation of processes that an experienced operator might follow. This requires a complex database of historical data and programming based on the information.
U.S. Pat. No. 4,722,611 which issued on Feb. 2, 1988 to Hultgren, discloses an apparatus for testing quench-cooling properties of a liquid quenchant. The apparatus includes a thermistor forming one arm of a bridge circuit. The thermistor acts as both a heater and a temperature sensor. However, if the heating function is terminated, the temperature sensing also terminates, so the apparatus is not well suited for measuring quenching properties of liquids. The apparatus really measures the power dissipation of the thermistor and does not directly measure the temperature drop of a body in contact with a liquid quenchant.
U.S. Pat. No. 4,106,331 which issued on Aug. 15, 1978 to Bunton et al., discloses a method for detecting the contamination of a liquid such as a quench oil. The “probe” employed by Bunton et al. is a stainless steel slug having an embedded thermocouple and the slug is heated in a furnace. Clearly, this arrangement is not intended for rapid testing of quenching fluids because heating of the slug in a furnace is required and this is necessarily a slow step.
Both these methods employ fairly large heated elements and require the use of substantial quantities of flowing coolant.
A paper entitled “The Effect of Cooling Water on Aluminum Ingot Casting” by H. Yu, Light Metals 1994. The Metallurgical Society of the AIME, pp. 779-786, describes a small cylindrical element containing a thermocouple which is preheated in a furnace then immersed in a sample of coolant. While this device is more compact than the devices required for the preceding methods, a separate preheating furnace is required, and the thermal response is limited because of the slow response time of the embedded thermocouple.
There is a need, therefore, for a compact and fast response system for measuring coolant quenchant properties, including properties above the film boiling temperature, that can also serve as part of a control system for altering the coolant flow or properties in response to changes in such quenchant properties.
DISCLOSURE OF THE INVENTION
It is an object of the invention to provide a method for measuring the quenchant properties of coolants that is rapid and precise.
Another object of the invention is to provide an apparatus for measuring the quenchant properties of coolants that is compact, rapid and precise.
It is a further object of the invention to provide a method and apparatus for controlling the cooling of an object by intermittent but rapid measurement of the quenchant properties of the coolant and consequent alteration of the coolant flow or properties.
According to one aspect of the invention, there is provided a method of measuring quenchability of a liquid coolant, comprising the steps of: obtaining a sample of said liquid coolant; providing a probe for immersion in said sample, said probe comprising a temperature-sensing electrical device which generates an electrical response corresponding to temperature sensed; by means of electrical resistance heating by a circuit which is electrically connected to said temperature-sensing electrical device, heating said probe in a gas to a predetermined temperature measured by the electrical response of said temperature sensing device; immersing the said probe in said sample and measuring the electrical response for a predetermined measurement period, and comparing the measured electrical response to a response of a reference liquid measured under equivalent conditions; and determining the quenchability of the liquid coolant from said responses.
According to another aspect of the invention, there is provided a method of measuring the quenchability of a liquid coolant, involving obtaining a sample of the liquid coolant, providing a probe for immersion in the sample, the probe comprising a temperature-sensing electrical device which generates an electrical response corresponding to a temperature sensed, heating the probe in a gas, at an average rate that exceeds 40° C./second, to a predetermined temperature measured by the electrical response of the temperature sensing device, immersing the probe in the sample and measuring the electrical response for a predetermined measurement period, and comparing the measured electrical response to a response of a reference liquid measured under equivalent conditions, to thereby determine the quenchability property of the liquid coolant.
According to another aspect of the invention, there is provided an apparatus for measuring quenchability of a liquid coolant, comprising: a probe for immersion in a sample of said liquid coolant; a temperature sensing electrical device contained within said probe; and an electrical resistance heating device contained within the probe.
According to another aspect of the invention, there is provided a method of controlling the cooling of an object by contacting the said object with a coolant, comprising the steps of: obtaining a substantially stagnant sample of said coolant; measuring quenchability of said coolant of said sample; and controlling a property of said coolant coming into contact with said object responsive to a measured quenchability of said coolant of said stagnant sample to achieve a desired cooling effect; wherein said quenchability is measured by providing a probe for immersion in said liquid coolant, said probe comprising a temperatur
Bourgeois Thierry
Caron Yves
Gendron Andre
Langlais Joseph
Alcan International Limited
Cooper & Dunham LLP
Tanner Harry B.
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