CA1292889C - Apparatus and process for monitoring the cooling properties of liquid quenchants and restoring used quenchants - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An apparatus for testing the quench-cooling properties of a liquid quenchant comprising a thermistor adapted to be immersed in the liquid to be tested, means for applying an electric poten-tial across the thermistor comprising means for applying an exci-tation voltage to electrical bridge circuit which contains the thermistor in one leg thereof, first timing means controlling the duration of time during which said excitation voltage is applied to said bridge circuit and means for determining the electrical resistance the thermistor, such that the quenchant properties of the liquid tested are determinable by comparison of the resist-ance of the immersed thermistor with at least one reference resistance value. A process is provided for testing liquid quen-chants, particularly used quenchants which can be restored to their original properties by the addition of additives or sol-vents such as water.

Description

APPARATUS AND PROCESS FOR MONITORING
THE COOLING PROPERTIES OF LIQUID QUENCHANTS
AND RESTORING USED QUENCHANTS

~ACKG~OUND OF THE INVENTION

This invention relates to testing apparatus for measuring thermal properties of a liquid quenchant, particularly to appa-ratus and process ~teps for monitoring the cooling properties of polymer quenchants, and apparatus and process steps for monitor-5 ing the cooling properties of used liquid quenchants and alteringtheir properties, e.g., restoring the cooling properties of the used liquid quenchants to their original, unused condition.
Thermally-responsive elements, known as thermistors, consist of semi-conductors having a negative temperature coefficient of resistance, i.e., have the characteristics of decreasing resist-ance with increasing temperature. The thermistors are hard, ceramic-like, 6emi-conductors. They are available in at least three distinct forms; bead6, di6cs or washers, and rods. All of these types are made of various mixtures of the oxides of magne-6ium, nlckel, cobalt, copper, uranium, iron, zinc, titanium, and manganese. The mixture6 of oxides are formed into the desired 6hapes and sintered under accurately controlled atmospheric and temperature condition6. They are characterized by being small and compact in size, are highly stable, are mechanically rugged and shock resistant, are provided with permanent electrical con-tacts, have a wide range of resistance to temperature coefficientand power di6sipation, and have 6ubstantially unlimited life when v~

~ 8 9 D-13850 operated within their maximum temperature rating. Typically, they are designed to have a specific negative coefficient of resistance, i.e., their re6ifitance will change from several thousand ohms at 25C. to near zero at 500C.
Thermistor6 are known to be useful for detecting various propertie6 of fluids. For example, thermistors are often posi-tioned in gas and liquid streams to detect changes in thermal conductivity as it relates ~o flow rate or flow stoppage. For 10 example, see U.S. Patent No. 3,236,099, in which a bridge circuit including two thermistors is used in apparatus for indicating material stream flow characteristics by calorimetry. In most cases, the thermistor circuit is simply used to activate an alarm or control function.
Thermistors are often used as temperature sensing probes in resistance thermometers. For example, see ~.S. Patents Nos.

2,876,327; 3,699,813 and 4,143,549, which utilize thermistors in conjunction with Wheatstone bridge circuits. In this particular application, they are subjected to external heating, but in other applications they may be subjected to internal heating by the application of an appropriate electric potential. When voltage is applied to a thermistor and resistor in series a current will flow in the circuit. This electrical current causes heat to be generated in the thermistor, which in turn causes the resistance of the thermistor to be lessened and permits more current to flow than if the resistance had remained constant. This process con-tinues until the thermistor reaches the maximum temperature po~sible for the amount of power available in the circuit, at ~Z~138~ D-13850 which time a steady 6tate will exist, i.e., the electrical energy applied i6 equal to the heat energy given off by the thermistor and resi6tor. Of cour6e, the medium surrounding the thermistor will affect the equilibrium temperature.
U.S. Patent No. q,364,677 disclo6es apparatu~ comprising a bridge circuit which includes two thermoresistant devices 6uch as thermistor~ which are used in heated probe6 for comparing the thermal conductivity of a gemstone to that of a standard stone such as a diamond. Other systems for thermal testing of 601ids are disclosed in U.S. Patent6 Nos. 4,488,821 and 3,457,770. For example, the steady 6tate temperature attained in air will be significantly higher than that for a liquid. Even minor differ-ence6 in the thermal conductivity of liquids will have an effect.
The application of thermistor6 in devices used to measure themixture ratio of a two-component gas mixture is known, (see, e.q., U.S. Patent No. 3,683,671) but no such use with liquid mixture6 ha6 been found in the prior art. In particular, no reference to the u6e of thermi6tor circuits for determination of used liquid quenchant quality ha6 been found in the prior art, nor i~ u6e of a thermi6tor known for te6ting used quenchants to determine the amount of quenchant additives to be added to the used quenchant to bring its quenching properties to the desired level.
U.S. Patent No. 2,937,334 discloses heat transfer testing apparatu6 for evaluating the heat transfer capacity of materials including quenching media, comprising a heated metal probe and electronic circuitry including a bridge circuit for determining l~Zl~h~ D-l 38 50 the occurrence of the Curie point as the metal probe cools. The u~e of a thermistor is neither disclosed nor suggested. U.S.
Patent No. 3,333,470 disclose6 a method and apparatus for sensing fluid properties, including a resi6tance-type temperature sensor and a bridge circuit for maintaining at constant temperature.
The system measures heat transfer between the sensor and its environment, which information can be u6ed in the measurement of temperature6, velocities, concentrations and like properties of fluids. The use of a thermi6tor as the sensor i6 not suggested, and a method of determining a fluid's concentration is not indicated.
Heating and subsequent cooling is a process used to change the phy~ical properties of variou6 metals, such as steel and aluminum alloys. The overall cooling rate as well as the cooling rate at intermediate temperatures is critical in the quenching proces6, a6 these quantities, in combination with the composition of the metal, control to a great degree the final structural propertie6 of the heat treated part. Many different liquids have been employed as quenchant6 over the year6, including water, variou~ oils, and even human blood.
Aqueous rolutions of 6ynthetic organic polymers have gained wide acceptance as quenching media in the last two decades.
These product6 not only provide cooling characteristics interme-diate between the fast quenching action of water and the rela-tively ~low action of oil, but also provide a high degree of flexibility in that the desired cooling rate is set by adjustment ~ s~9;~8~9 D- 13 B 5 0 s of the polymer to water ratio. The most commonly used polymer quenchant6 are polyalkylene glycols, polyvinylpyrrolidones and polyacrylates, with the polyalkyle~e glycol materials being by far the mo6t common.
When a water quenchant 106e~ it6 quenching properties due to contamination or an oil quenchant become6 contaminated or degraded, the quenchant i6 generally replaced, puri~ied or recon-ditioned. However, to in6ure the 6ati6factory operation of polymer-containing quenchants, the bath temperature, deqree of agitation and optimum polymer concentration must be established and maintained. Thi6 i6 most often done by refractive index and kinematic visco6ity measurement. The polymer concentration is mo6t often determined by the end user through the use of a hand held refractometer. Kinematic vi6cosity mea6urement i6 u6ed as an alternate method when the pre6ence of bath contaminants such a6 inorganic 6alts affect the accuracy of the refractometer.
However, after prolonged u6e or under unu6ually 6evere operating condition6, a 6ignificant increa6e in the water-601uble contam-inant6 pre6ent and/or a molecular welght change in the polymer due to degradation may alter the bath to a point that the ori-ginal v$6co6ity-quenching action relationship i6 no longer valid.
The6e mea6uring techniques, moreover, relate only to fresh polymer 601ution6 and are affected by the presence of soluble contaminants and the eventual degradation of the polymer. When this condition occurs the quenching bath is typically checked by cooling curve analysis. This a a rather cumbersome laboratory procedure that entails the use of temperature instrumented metal lZ9~889 D-13850 probe6 that are heated and immersed in baths of fresh and used quenchant solution6 for the development of comparative cooling rate values.
It would be desirable to have available a portable cooling curve apparatus for use in the field, but this approach is not particularly practical from the standpoint of unit co~t and operational complexity. However, a simple heat transfer (thermal conductivity) test designed to simulate fluid quenching action of a liquid quenchant would have merit.

SUMtlARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a device for sensing the relative heat transfer charac-teristics of liquid quenching media, including water, organic liquids such as oils and in particular aqueous polymer solutions.
It is also an object of the present invention to provide a technique wherein the heat transfer information developed with the te6t devlce of the present invention may be used to determine and alter the polymer/water relationship o an aqueous polymer quenchant solution and thereby achieve an altered cooling rate for the quenchant solution.
It is a further object of the present invention to measure the relative heat transfer characteristics of a liquid quenchant, and use the measurements obtained to restore a used quenchant solution to its original quenchant properties by addition of suitable amounts of additives, solvents or diluents based upon the measurement6 of the u~ed quenchant.

1~ Z8~39 D- 1 3 8 5 0 It i6 a still further object of the present invention to pro-vide portable apparatus and a method for quickly and conveniently testirlg the thermal properties of liquid quenchants, preferably providing greater ~ensitivity than tests of refractive index and/or vi6cosity.
In accordance with the present invention, apparatus is pro-vided for testing the quench-cooling properties of a liqu~d quen-chant, comprising:
a thermistor ~dapted to be immersed in the liquid to be tested;
means for applying an electrical potential across the ther-mistor, comprising means for applying an excitation voltage to a Wheatstone bridge circuit which contains the thermistor in one leg thereof;
first timing means controlling the duration of time during which 6aid electrical potential is applied across said ther-mi6tor; and means for determining the electrical resistance of the ther-mi6tor, whereby the quenchant propertie6 of the liquid tested are determined by comparison of the resi6tance of the immersed ther-mi6tor with at least one reference resistance value, e.g., the reference current value for water or a know quenchant solution.
The thermi6tor is positioned in direct thermal contact with the liquid to be tested. Electrical power to produce internal heating of the thermistor is provided by a variable voltage direct current power supply coupled to the bridge circuit. A

~Z~'~88g voltmeter bridged between the two parallel branches of the bridge circuit indicates when the thermistor is at the prescribed tem-perature (as indicated by a bridge balance condition) or indi-cates the degree of deviation from that temperature.
The method of fluid evaluation with the quenchant tester may be de6cribed by the 6erie6 of event6 which take place during three test operations. In the fir6t operation, the supply volt-age to the bridge circuit is adjusted to give a bridge balance condition with the thermi6tor immersed in water. Next, without changing the voltage setting the thermistor is positioned in a fresh quenchant 601ution having a known polymer concentration.
The bridge circuit unbalance shown on the voltmeter is noted. In the third operation, again without changing the voltage setting, a used quenchant(6) of the 6ame type as the fresh material is checked and the voltage unbalance reading on the voltmeter i6 noted. In the first operation, a ba6eline condition is estab-li6hed with water, i.e., no polymer pre6ent. In the second operation, a reference value i5 e6tabli6hed for a fre6h quenchant with a known polymer concentration for 6ubsequent compari60n with a u6ed material in the third operation.
The device of this invention i6 a portable, relatively inex-pensive and ea6y to use device that efficiently and accurately measures the cooling characteristics of used polymer quenchants, yet is not affected by contaminants or physical changes in the polymer solution.

8~ D- 13 ~ 5 0 Further in accordance with the invention, a process is pro-vided for te6ting the quench-cooling properties of a liquid quen-chant, comprising the 6teps of:
(a) using a thermistor to test a liquid quenchant sample, the thermistor being connected in a leg of a Wheat6tone bridge cir-cuit and adapted to be immer6ed in the ~ample;
(b) determining the electrical resistance of the thermistor u6ing mean6 for measuring the output voltage of the bridge circuit, and (c) comparing the output voltage measured to at least one compari60n measurement value, e.g., the measurement value of water or quenchant of known composition.
In a preferred embodiment, the apparatus and process of the pre6ent invention are used for testing u6ed liquid quenchant6 comprising aqueou6 polymer 601utions, 60 that the quenchants' thermal properties can be altered (e.g., re6tored to their original value6) by the addition or additives or water.
Further detail~, objects and advantage6 of the pre6ent inven-tion will be apparent from the following detailed description of a preferred embodiment 6hown 6chematically in the drawing6, and the appended claim6.

( ~Z~Z~89 D-13850 I~RIEF DESCRIPTION OF THE D~AWINGS
Fig. 1 is a ~chematic view of an electrical apparatus used in the present invention;
Fig. 2 is a schematic view of an alternative Wheatstone bridge circuit and the thermistor (schematically indicated) used in the bridge circuit;
Fig. 3 is a more detailed electrical diagram of the circuit schematically illustrated in Fig. 1, indicating specific types of electrical apparatus and their interconnection to the Wheatstone bridge circuit illustrated in Fig. 2, which is substantially reproduced a6 a part of Fig. 3;
Fig. 4 illustrates quenchant cooling curves determined by various methods to illustrate the utility of the present inven-tion;
Fig. 5 show~ a set of quenchant cooling curves similar to those 6hown in Fig. 4 but having a different bath temperature;
Fig. 6 is a fiet of quenchant cooling curves similar to Fig. 5, but having a differing bath temperature; and Fig. 7 16 a 6et of quenchant cooling curves similar to tho6e ~hown in Flg. 6 but havlng a differing bath temperature and illustrating the utility of the pre6ent process to restore the thermal properties of used quenchant to nearly those of unused or fresh quenchant.

~Z~89 D-13B50 DETAILED DESCRIPTIO~ OF THE DRAWINGS
~ he quenchant tester apparatus and method of the present invention are based upon the principle that the equilibrium values of temperature and current flow attained in a thermistor having an electric potential imposed on it and immersed in a liquid are dependent upon the thermal conductivity of the liquid.
The steady state temperature of the apparatus of the present invention with the thermistor positioned in air is significantly higher than that for a liquid. Even minor differences in the thermal conductivity of liquids wil~ have an effect. It is on this principle also that the quenchant tester of this invention is based.
The quenchant test device of this invention is based on a thermal conductivity measurement technique wherein a thermistor acts as a combined heat input and temperature measurement source for the establi6hment of heat ~low rate to the quenchant, or conversely indicate the cooling rate of the quenchant.
To implement temperature measurement and control, the quen-chant tester is equipped with a bridge circuit. The thermistor (which in one embodiment is in the form of a probe having a nega-tive coefficient of resistance) is positioned in one leg of thebridge while the other three legs are fitted with resistors chosen to match the internal resistance of the thermistor at the desired operating temperature. Accordingly, when the power to the bridge is adjusted by way of a variable resistor positioned ~9z~3~9 D--13850 in 6eries with the DC power 6upply energizing the bridge and a balanced condition is achieved, the thermistor will be at the prescribed operating temperature.
Relative thermal conductivity value6 for liquids may then be established in one of two ways; (1) the current flow to the cir-cuit can be mea6ured and the DC power in the thermistor calcu-lated, or (2) the bridge can fir6t be balanced with at least one reference fluid and bridge circuit voltage unbalance value6 observed when unknown fluids are subjected to the same power 6ettinq. For operating simplicity and c06t considerations, the latter technique has been incorporated in the present invention.
Although the bridge circuit voltage unbalance values noted are a function of the equilibrium temperature of the thermistor probe when immer6ed in the liquid, they are actually caused by and related to the thermal conductivity characteristics of the liquid. The greater the unbalance, the greater the difference in thermal conductivity between the reference and unknown liquid.
The portable quenchant tester o the present invention i6 a laboratory and field te6t device for accurately monitoring the quench-cooling performance of liquid quenchant6 in service. The tester i6 6ensitive to 6mall change6 in quenchant condition and correlates well with the large scale laboratory cooling curve apparatu6. In laboratory tests, the unit has been shown to offer a more reliable means for determining what is needed in restoring u6ed quenchants than the viscosity and refractive index tests now u6ed for field control. The tester is based upon a thermal con-ductivity measurement technique. A thermistor (thermal refii6tor) ~ 89 D-13850 6ensor electrically connected in one leg of a resistance bridge circuit is immerfied in the test fluid sample. The bridge cir-cuit, in cooperation with the thermistor sensor and a coupled power supply, act to provide a voltage deviation value across the bridge indicating the relative thermal conductivity or cooling capacity of the fluid. Incorporated electrical circuits, control and mea~urement devices ensure 6imple and reliable operation of the te6ter. The unit i6 reasonably inexpensive and compact.
10 Fluid measurement requires only a few minutes time.
The apparatus and method of the present invention can be used for te6ting the thermal conductivity propertie~ of any suitable liquid quenchant, including water, oils (i.e., hydrocarbons and high molecular weight organic compounds, both naturally-occurring and synthetic, which have similar properties), and aqueous solu-tion6 of various polymers. The method can be used with 601utions of any water-soluble polymer suitable for use as a liquid quen-chant, but the polymers are generally 6elected from polyalkyleneglycol6 6uch a6 polyethylene glycol, polypropylene glycol, poly-butylene glycol and the like; polyvinylpyrrolidone and 6ub6ti-tuted ver6ions thereof, and polyacrylate6, e.g., polymer6 of acrylic acid ~6ub6tituted or unsub6tituted) and esters thereof, and polyacrylamide6. Mixtures of these polymers, and copolymers compri6ing at lea6t two of the monomers used in their prepara--tion, can also be used. If the quenchant to be tested is elec-trically conductive (such as, e.g., salt water), the thermistorand its electrical connections should be insulated to prevent 6hort circuit6.

12~Z88~ D-13850 Once the thermal properties of such a quenchant have been determined, the quenchant can be discarded and replaced, or puri-fied, reconditioned or recycled. :[n a preferred embodiment of the present invention, a quenchant comprising an aqueous solution of a synthetic polymer is tested to determine the effec~ive con-centration of polymer (as reflected by thermal properties) and the polymer level adjusted to the desired level by adding a 6uit-able quantity of the polymer, water or other diluent.
Fig. 1 illustrates schematically an embodiment comprising all of the element6 necessary to the present invention. In particu-lar, a thermistor 100 i6 a resi6tor element which is part of a bridge circuit 6hown in Fig. 1 as having resistors 3, 4 and 5.
The thermistor 100 used in this illustrative embodiment of the present invention is a Fenwel Electronic model Gs32p62 glass bead type with a resistance of 27 ohms at 180C. and approxi-mately 10 ohms at 300C. Although test temperatures ranging from 180 to 300C. were inve6tigated, a 180C. temperature was found to be best 6uited for testing and accordingly the bridge circuit was fitted with 27 ohm resistors. However, it i6 contemplated as being within the scope of the present invention to include any suitable resistance values for the circuits and not just the particular resistance values disclosed in the present embodiment.
If desired, temperature range changes can be easily made in the field by installing new resistors in the bridge circuit.
Test sample size may be as little as one fluid ounce. Although ~ 8~9 D-13850 the ~ample temperature need not be precisely controlled, all 6ample6 in a test ~eries must be run at approximately the 6ame temperature. Room or ambient temperature is most convenient.
In Fig. 1, the numeral 1 generally designates the apparatus of the pre6ent invention. The thermi6tor 100 is shown as being immersed in a liquid test sample 2. The thermistor 100 is included a~ one leg of the bridge circuit and is connected by wires 13 and 14 to the bridge circuit. A DC (direct current) power 6upply 11 6upplies the bridge excitation volage and i6 connected along electrical lines 166 and 168 to the bridge circuit. A DC digital voltmeter 7 is connected by electrical line6 18 and 19 to the bridge circuit at terminals diagonally opposite those used to connect the power supply 11 to the bridge circuit. The digital voltmeter measures and displays the output voltage of the bridge circuit.
~lock 6 in Fig. 1 represent6 a latch control, including a timer, for controlling the voltmeter display of the voltmeter 7 to latch the voltmeter di6play at the end of a predetermined period of time, e.g., 40 6econds after the beginning of a test, which begin6 with an initial 5 6econd warm-up, 60 that all test6 will be conducted for the same predetermined period of time.
A voltage 60urce 27 supplies A~ current (usually at approxi-mately 120 volts at 60 Hertz) to a timer and relay power on/off control circuit 12. Line 26 6chematically indicates the supply of AC power to the DC power supply 11. Of course, in a detailed diagram, a return path for grounding would be shown for the power supply 11.

1~2~89 D-13B50 The controller 12 includes a timer to permit operation only during a predetermined amount of time, e.g., 45 seconds, to prevent overheating of the thermistor 100 as well as to control the length of the individual tests.
Another timer is included in the DC voltage step control unit 10. Here, for a short initial period of time, e.g., 5 seconds, a higher DC voltage i6 provided to the bridge circuit by applying the 6upply voltage through the fixed resistor 9 to rapidly raise the thermi6tor to approximately the operating temperature. The line 25 indicates generally and schematically the connection between elements 10 and 11 of Fig. 1. Also, line 22 schemati-cally indicates the connection of the variable resistor 8 along line 24 to the DC voltage step control unit 10. The fixed resistor 9 is schematically shown connected by line 23 to line 24 which in turn connects to the unit 10.
Fig. 2 is a schematic diagram of an alternate Wheatstone bridge circuit ~or use in the circuit illustrated in Fig. 1, supplied by a direct current voltage source V. Line 166 and 168 connect the voltage source to the bridge circuit at diagonally opposed terminals, alternate to the position of the terminals used in the connection of the supply voltage to the bridge cir-cuit of Fig. 1. A voltmeter is shown connected by lines 18 and l9 horizontally across the bridge circuit. While drawing vir-tually no power from the circuit, the voltmeter is capable of making very sensitive voltage measurements of the voltage across the bridge circuit indicated. The values of the resistances can be so chosen that 3 or 4 significant figures in the value of the l~Z88g D-13850 ze~i~tance of ther~i~tor 100 can be obtained. When the bridge $6 ~n balance, the u6ual bridge equation ~pplies ~ follows:
R100/R5.R3/R4.
~he po~ition6 of the battery and the voltmeter are inter-S changeable as in~icated with re6pect to the connections 6hown inFig6. 1 and 2. Furthermore, there are many modifications of the bridge chown which would adapt lt to Lea6urement~ of very low ~e6i6tance6, ~s well as to alternating current mea~urement6 ~rather than the direct current measurement6 chown). Such are well-known in the prior art.
Although the b~sic te~t circuitry a~ described i~ rather cimple ~n nature, additlonal element6 are u6eful, and in the pre~erred cmbodiment lt ~6 preferred to incorporate a number of ac60ciated clrcult~ for slmple ~nd reliable field operatlon. The unit thus preferably contains a DC power cupply, three 601id state timer6, a puch button operator cwitch, magnetic relay, two voltage ad~uctment potentlometer6, a bridge balance potentlometer and a digltal voltmeter po61tloned ~croc6 the leg6 of the bridge.
The complete ~yctem lc cont~ned ln a cabinet mea6uring approximately B~ x 9" x 12n.
Fig. 3 ic a more detailed 6chematic diagram of the apparatu6 uced ~n the precent lnventlon. Several components are listed by capital l-tterc A, B, C, D, E, F, G, H, I, J, K, L and M.
Furthermore, F$g. 3 usec numeral6 within clrcles on each time lZ9Z~389 D-I38s0 lB
delay relay A, B and C to designate contact~. The circled number6 1-6 on electric power cupply E de~ignate terminal~.
Furthermore, circled letter~ C, E, J, P and S within voltmeter D
designate termin~l6.
S ~he reference number A de~ignates h Dayton electronic time delay relay 6 x 1~ ~ that i6 cet for 5 6econds ~n the preferred embodiment. ~he device indicated by B 16 a Dayton electronic t~me delay relay 6 x 15qA, wh$ch, in the preferred embodiment, lc cet for 45 cecond~. The device indicated by C i6 ~ Dayton elec-tronic time delay relay 6 x 15~A, which, in the preferred embodi-ment, i6 6et for 40 ceconds.
The 45-second timer B permits a totDl powered operation time, e.q., of 45 6econd~. rOr the fir~t period cf 5 ~econds, timer A
provides D higher than normal value of voltage and electrical power to the thermi~tor 100 to heat it to operating temperature.
For the re~aining 40 6econds, the bridge circuit i6 6upplied with the normal operDting volt~ge. At the end of the 45-6econd period, timer B terminate6 the DC power to the bridge circuit.
Timer C provide6 D ~latchinq" control ~ign~l to cau~e the re~ding of the voltmetor that ic me~6ured after 40 ~econd6 to remain di~played after the power to the bridge circuit i6 termin~ted.
~ he voltmeter u6ed i6 indicDted as D, which ic D Simpson digit~l voltmeter 2840. A6 indic~ted in rig. 3, the voltmeter D
~ncludec a chlp LD-121, PIN 17 which permitc the Dctivation of the dicplay hold circuit ~o that latching of the voltage reading take6 place.

8~39 -13850 The DC power cupply E ic a Sol~ electricAl power supply 83-81-2250 and has ~ix terminal~. ~he6e terminal6 ~re repre-~ented by circle6 ~nd ~re numbered con6ecutively, a6 terminal6 1 to 6.- The power supply ~ i6 equipped with an AC to DC converter, S not ~hown, but conventional and well known in the art. ~he power ~upply lc provided with ~C power through termin~l 3 ~nd 4, ~nd 6upplie~ DC power through terminal~ ~ ~nd 2 for volt~ge control ~nd 6ub6equent ~pplication to the bridge circuit through terLinal~ 5 ~nd 6. Power 6upply E i6 a commercial unit, de6cribed above, ~nd its functions are well known And obvious to one of ordinary ckill in the art.
~ v~riable reci6tor F, de6ignated in Fig. 1 ~s variable re~i~tor B, $6 6hown ln rig. 3. More 6pecifically, the v~rlable re6i6tor F 16 ~ potentiometer, which, ln a preferred embodiment, i6 a 10-turn, 10K ohm potentiometer ~nd i6 well known in the ~rt.
The potentiometer F ~nd fixed re6istor 9 are used ln dual voltage control clrcult6 with timer A for step control of the 6upply voltage to the bridge circuit. Resictor 9 i~ included within the circult which 1~ completed for the flr6t 5-~econd lnterval of opor~tlon, theroby provldlng ~ relativoly higher cupply voltage to the brldge clrcuit for the purpo6e o he~ting thermi6tor 100.
Potentlonmeter F 16 lncluded wlthin the other circuit and i6 operator controlled for varying the 6upply voltage to the brldge clrcult, ~t ~ lower voltage than ic ~upplied through recl~tor 9.

1~2~9 D~13B50 In Fig. 3, relay G i~ a 2-pole, normally open (No), 120 volt 60 Hz coil relay having two opposed pairs of contacts. The normally open contact~ are 6hown as havin~ a gap between T-shaped elements connected to the circled terminals numbered 303-306 in Fig. 3. Terminals 301 and 302 are provided for energizing the 120 volt ~C powered coil, indicated by the zig-zag lines connect-ing the terminals. Terminal 302 i~ connected to ground line 150 through line lSl and terminal 301 is connected to switch K
through lins 165. The normally open contactG which are located between terminals 303 and 304, as well as those between terminals 305 and 306, are closed upon energization of the relay coil. The closing of contacts 305 and 306 permits power to flow from DC
power supply E to the Wheatstone bridge circuit by closing the circuit between terminals 5 and 6 of power supply E. Closing of contact6 303 and 304 cau6es continuous energization of the coil or latching of the relay during the 45-second interval of opera-tion. Any suitable relay can be used as relay G.
The thermi6tor 100 u6ed in this specific embodiment is a Fenwel Electronics thermistor GH32T62. However, any thermistor which i8 capable of being used, or modified to be used, in the present invention is contemplated as being within the scope of the present invention. The preferred choice of thermistor is a glass bead encased type with a negative temperature coefficient of resistance having an internal resistance of approximately 2000 ohms at 25C. The preferred measurement or test temperature of the thermistor is between 180C. and 300C. If a 180C. test l~Z8~9 D-138~0 temperature lc de6ired and the chosen thermistor ~c a 2000 ohm unit, ~uch afi ~ renwel Electronic6 model G~32P62, the three rcclctor6 in the bridge c~rcuit must have a resi6tAnce of approxlm2tely 27 ohm~. However, the exact resl~tance value mu6t be determined by an actu~l temperature-reslstance calibratlon.
Elementc represented by letters I and J respectively, are pilot llght~ of any ~uitable type. ~hese are u6ed to indicate - that power 16 belng Lupplied in the circuits ln which the li~hts are conn^cted.
Switch ~ is a pu~hbutton cwitch of the type designated as ~omentary contact, double pole single throw-normally open (MC, DPS~-NO). Switch K i~ norm311y open and, upon pushing, ~imul-taneously close two pairc of contact6, one pair connecting line 163 wlth llne 165 and the other connecting line 181 with line 180. Such cwltches are well known and convention~l. In closing the flrct palr of contact6 to connect llne~ 163 and 165, tho relay G lc energlzed. ~he llghtlng of the pilot light J lndi-cate~ that the relay G has been energized. The ~econd cet of contactc clo~ed by the cwitch K connects lines 180 and 181 to clo~e a clrcult whlch ~r common to terminals 5 and 6 of each of the timerc A, ~ and C. ~hu~, actu~tlon of the ~witch K provides a c~multaneou6 tareing c$gnal to cynchronize the tlming of each of the tlmerc A, ~ and C. ~he AC power ~upply represented by numeral 27 ~uppllec power through a ~use M which, in the present preferred e~bodiment, ic a 2 amp fuse.

~ 9 D- 13B50 In the embodiment shown in Fig. 3, resistor 9 is a 400 ohm 1/4 watt resi6tor. The fixed resistors 3, 4 and 5 of the bridge circuit are each, in the preferred embodiment, 27 ohm, 12 ~att resistors. However, the yresent invention i5 not limited to S these values, and any 6uitable re6istors may be chosen for heightened selectivity and 6ensitivity for various expected thermistor operating ranges and conditions. The resi~tances may also be suitably selected for particular thermi~tor power capaci-ties and resistances where various thermistors may be usedin6tead of the thermistor identified in the preferred embodiment.
The connections and operation of the above-identified circuit elements are described hereunder. The functions of the various componentfi of the tester of this invention and the electrical circuitry ls best described through the sequence of test events which self-initiate in the equipment after depressing pushbutton K and those which are performed by the operator. After the operator has turned on the 120 volt AC power 27 to the test unit by clo~ing switch L and has positioned the thermistor 100 in the test liquid, e.g., water, as required to initiate a test series on quenchants, the momentary contact test initiator switch push-button K is pressed and relea6ed. This action activates the 120volt AC powered time delay relays, i.e, timers A, ~ and C, and initiates the timed off delay function of their contactors. It al~o energi~es the 120 volt AC powered coil of the power relay G
causing its contactors (connected to terminals 305, 306) to close and direct DC power to the bridge circuit via lines 166, 167, 168 and thermistor 100. An electrical latch circuit to the power 1~9~8~9 D-13B50 relay coil o~ relay G ~ completed through a 5econd ~et o~ con-tactor6 (connected to termin~l~ 303, 30q) ~n the power relay ~nd the cont~ctor~ in the 45 ~ec~nd timer. ThiE provides ~ continu-ance of AC power to the relay coil and therefore ~ continuance of 5 oi' DC power to the bridge c$rcult or the timPd interval, e.g., 45 ~econd6.
More cpecif$c~11y, when the AC power 6witch L i6 closed, power ~ cupplied along lines 140, 150 to ~upply power to timer C
at tcrmin~l6 2 ~nd 10 through lines 141 and 152 respectively; to timer ~ at terminals 2 and 10 through lines 142 and 153 re6pec-tively; to timer B ~t terminal 11 through line 143; to the volt-~eter D at terminals E and C (circled) through lines lq5 and 155 respect$vely; to the DC power 6upply E at terLin~ls 3 and 4 (cir-cled) through liner~ 1~4 and 154 respectively; to timer A ht termin~l6 2 and 10; and to pilot light I through line6 147 ~nd 160 recpectlvely. ~he power ~upplled along llne~ 140, lS0 ~nd ~long each of the adjoining llne6 de~cribed above, is AC
(alternatlng current) power. ~he ground line ~6 lllustrated ~6 150 which provider. ~ ground to complete the clrcuit to allow power to flow through the v~rlou6 clrcuitc a6 de6cribed ~5 hereunder.
When the ~witch K 16 cloced, the contactor6 of timer B
oper~te for 45 ~econd6 to cupply AC current to terminal 9 (cir-cled). ~hi~ ~llowc current to flow through llnes 162 and 163 ~cro~6 the ~oment~r$1y depre66ed 6witch K to line 165 to thereby power the rel~y coil extending between terminal6 301 ~nd 302. A~

~-l3eso 2~
recult, the contectt between termln~le 303 ~nd 30~, ~nd ter-~inale 305 and 306 ~re eloeed. ~he cloeing of ~he cont~ete ~etween ter~ln~l~ 303 and 304 pro~ldee for current 1OW fro~ llne 162 ~long llne 161 through ter~n~le 30~ hnd 303. ~he current thcn flows fro~ ter~n~l 303 to 301 ~eroce D ~hort (unnu~bered) ~u~per wlre thereby ~upplylng a contlnuance of AC power to the coll, 3nd latch~ng the rel~y ln J cloced etate for the full ~5 ~econds ln the latched condit~on, the rel~y G cont~cts connected to terminalc 305 and 306 arc cloced co as to ~e ln electrical com-~unicat~on ~ith one ~nother. ~hic suppllee DC current from the DC power cupply E to the Wheatctone brldge clrcuit lncluding re61ttor~ 3, 4 and 5 ~nd thermietor 100. ~hu~, when the rel~y G
lc latched, DC power from terclnal 5 of the DC power cupply E
flowe through the cont~ctc of ter~in~le 306 ~nd 105 along line 167 nd to llnc 166, where power lc rupplled to the brldge c~r-cu~try deccrlbed ibove. Ihe circuit is cccpleted by line16B to th~ t~rm~n~l 6 of the DC powor ~upply ~.
Whon tho ~wltch ~ 1~ deprecccd, lt alco clocee the cont~ctc between llne~ lB0 nd 101, thereby pro~lding the comm~n tl~ulta-neou~ ctu~tln~ ~lgn~l to e~ch of tl~ere ~ nd C. ~h~ le done rlnce ach of t-rmln~l~ 5 and 6 tcircled) of e~ch of the tlm2r~ re connected recpectl~ely to wlree lBl nd lB0 ~imers A and C are connected through lir~e 183 to wire 180 and timer B
is connected to line 180 through line 185. Timers B and C are connected thro4~ lines 184 and 182 respectively to line 180, while time~ A is directly connected to line 1~1. Therefore, if power is peI~itted to flow through ~he conductors 180 and 181, each of the tiIers A, B and C are energized snd pcwcred and ~imLltaneously begin their t~med functions.
limer A is connected at termin21s 1 and 9 (circled) to ter-rinal 1 (circled) of power supply E through lines 171 ~nd 173.
Additionally, timer A is connected at tesmin21 11 (ciscled~ to .

D-13~50 t-r~ln~l 2 (clrcled~ of power ~upply ~ through flxed re~l~tor 9, ~y llne 172 ~l~o ters$nal 4 (clrcled) of tl~er ~ lc connccted to t~r~$nal 2 of power ~upply r, through pot~ntlo~eter r by l$ne 280. Shece connect$ons between tl~er A ~nd power upply E pro-5 ~lded for ~tep control of the ~iupply voltage to the br$dge clr-cuit ~nd co~prl-e the ~fore~entloned dual voltDge control cir-cultc Dur$ng the firct f~ve ~econds after ~nit$at$on of t$mer ~, the cont~ctor~ prov~de ~ connect$on between ter~in~lt 9 ~nd 11 (clrcled) of the tlner A ~h$c ~llow~ DC current to flow through res$stor 9, which h~s a re6ictsnce rubctantially lower than potentlo~eter F, to thereby ~llow A~ lncre~sed vDlt~ge to ~e returned to voltage cupply E for ~ubseguent appllc~tlon of ehe ~upply voltsge to the br$dge c~rcl~it through terminalc S and 6 (c$rcled) of the power supply At the terminat$on of the S-second $nterv~1, the contactors of t$ner A between terminals 9 ~nd 11 (clrcledj are opened For the re~b~ning 40 ~econd6, the contactorc ~etween term$nals 1 ~nd 4, wh$ch ~re closed for the full ~5-~ocond per$od, prov$de return ~upply of DC power through potentlo~eter F to pow~r ~upply E Ad~u~tment of the potcntloseter, then, ~llowr the operstor to control the voltage ~upplled to the brldge clrcult through ter~in~l~ 5 ~nd 6 of the power cupply. ~h~refore, the f$rst S cecond6 of t~ner A prov$de for hlgher than norual ~upply volt~ge to thc ~r$dge c$rcuit for the purpo~e of bestlng ther~fctor 100. ~hereatcr, the ~upply volt~gc can be ~d~usted to b~lanee the br$dge c~rcu$t, ~s de~lr-d Voltmeter D is cor~ected across ~ points ~ ~ ered~ of the t~heatstone bridge circuit. Ilne 18 ccnnects the pcsitive terminal P
of voltmeter D with one of the points of connection, and line 19 connects negative terminal S to the o~her point of connection. ~herefore, voltage n~asurements of the ~Dltage ~rross the bridge circuit can be ~ade using voltmeter D.

1~9Z889 ~ n eonduct~ng a teet w~th th~s ~paratu~ to deter~ine the ~ueneh-eocl$ng propert~e~ of n quenchant, ~ ~erle~ of te~t6 ~re performed to ~etabl~eh r~ference ~eaeure~ent~ ba-ed on the known quench-eeol~ng propertleb of ~r~sh quenchante ~he f~rct test, wh~eh ectabl$~he~ ~ ~a6eli~e ~or th~ ~eeult~ of the ~ub6equent teet6, ean be eonducted on water. At lea6t one additional te~t ~ then run on a freeh quenchant having ~ known quench-eooling property Theroafter, a ~ngle test run Dn an unknown quench-eooling property quenehant will yield a determination of thatquenchant'c rel~t~ve quench-eool~ng property The ~irst test 1~ eonducted by $mmer~ing thermi6tor ~00 ln a quenchant,~uch ~C ~2~ to ertabll6h a b~eel$ne for the subsequent teetc Switch L 16 eloeed to ~upply AC power to the Jppar~tu6 When lt ~e dec~red to beg~n the teet, ~witch K 1~ ~omentarily depreeced thereby ~et~vating the lnltlat~on of timerc A to C and eloeing the eontactc of eoil G ~he ~equence of the te6t begine with tieer A 6upplylng a hlgh exe~tat~on voltage to the bridge elrcu~t At the eonclueion of the high voltage lnterval, the operator ~djuete the p~nol ~ounted voltage eontrol potent~ometer F for a krldge balanee eond~tlon, ae ~ndieated by the diepl~y on the dig~tal voltmeter D, ~nd eontlnuee to do ~o until the con-taetore of the 40 ~eeond t~er C ~ct~v~te the di~play hold eir-cuit of the volt~eter D. ~h~ done by ~nterrupting the eon-neet~on made throu~v~n timer C between term~nal J ~ ich i8 connected ~Ir~u~l line l90 to ti~er COO and pin No. 7 of c~ip LD~121, whlch isconnected t~rough line 170 to the timer at terminals 1 and 3 (circled), respectively. At this point the test run 19 cou~leted and the bridge l~Z8f39 circuit voltage display is locked on the screen of the voltmeter D, 40 seconds after pressing pushbutton ~. Subsequently, timer B
interrup~s the latch circuit of relay G to the power relay coil and the DC power to the bridge circuit is terminated 45 seconds after pressing pushbutton K.
The automatic test termination and power off feature insure that all test6 in a series terminate at the same time after the initially rapid change in thermistor temperature and resistance 10 has moderated and a near equilibrium condition has been achieved.
It also protects against thermistor burn out due to the inadver-tent continuance of power to the thermistor after the run is com-pleted and the thermistor has been removed from the liquid.
As a result of conducting this first baseline test, a bridge circuit balance condition has been established with water and the bridge circuit supply voltage has been fixed by locking the setting on the operator controlled voltage adju6tment potentio-meter F. Comparative testing of fresh and used quenchants of the 6ame type may now begin. At least one test needs to be conducted on a fresh qusnchant having a known quench-cooling property. To implement this test pnase the thermistor probe 100 is immersed in the fresh fluid and the test initiate button K is depressed.
Timer A ~upplies the high level of excitation voltage to the bridge circuit. However, at the conclusion of the high voltage period the operator does not adjust the level of excitation volt-age to achieve a bridge balance condition. Instead, the bridgeunbalance is measured and the final voltage deviation appears on the display 6creen of the voltmeter D.

~Z9~8~39 D-13850 Bridge circuit unbalance occurs with the new and used quen-chants becaufie these materials have a lower thermal conductivity or cooling rate than water and accordingly the thermistor becomes hotter and lower in electrical resistance as the current flows.
5 The greater the unbalance noted the lower the cooling rate of the product. secause the variation in resistance of the thermistor with changing temperature, and the bridge circuit voltage unbal-ance with changing resistance in one leg are both nearly lGga-rithmic functions, but acting in opposite directions, the voltageunbalance value6 observed with the quenchant tester may be con-6idered a nearly linear function of the thermal conductivity of the fluid. In addition, these values may be used to establish the polymer content of fresh liquid quenchants and the apparent or effective polymer content of used quenchants. For example, the bridge i6 set for zero voltage deflection or a balance condi-tion with water alone. If 6ubsequently a bridge deflection of ~ volt6 is noted with a fresh 40 percent polymer solution and a value of 1/2 Y is observed with a used material, the used mate-rial ls calculated to have an effective cooling rate equal to a fresh 20 percent solution. Where many samples of similar quen-chant6 are to be te6ted, the voltage imbalance reading6 can beconverted directly to the polymer concentrations by means of a graph, conver6ion table or nomogram; or the voltmeter can be an analog in6trument fitted to read directly in terms of polymer & 9 D-13850 2~

concentration. With this information available the used quen-chant solution may be corrected to a desired cooling rate by the addition of a measured amount of fresh quenchant or water as required.
To test a liquld quenchant sample 2 or a series of used sample6 of the 6ame type quenchant, the operator simply estab-lishes a control or reference value for a fresh 601ution of 6imilar material having a known concentration of polymer. ~he voltage value derived with the used material(s) is then compared to the fresh material voltage value to determine the effective polymer (quenchant) concentration. This may be done by a simple proportion equation or if desired from a curve or nomogram estab-lished by running two or mor0 fresh samples having a range ofquenchant concentration.
Although ~pecific devices have been 6hown having specific electrical circuit configurations, this is merely a preferred embodiment of the present invention, and the present invention is not limited thereto. Each of the items of apparatus specifically identified in the preferred embodiment has many equivalents in the prior art, and such equivalents would clearly be matters of choice, a6 would other control arrangements having the same end re~ult a6 in the present preferred embodiment. Furthermore, although 6pecific te~t time interval periods have been set, namely 5 seconds, 40 seconds, and 45 seconds, predetermined time intervals may be used which are suitable for the particular fluid being tested and for the particular thermistor used, as well as ~ 9 D-13850 the other circuit apparatus u6ed for control purposes. An operator could manually adjust the DC voltage at the appropriate, exact time intervals and perform all of the tests, performed by the tester of this invention. However, this would be somewhat cumbersome and very difficult to do consistently and therefore the apparatus of this invention, results in a convenient, port-able test unit which preferably has the elements enclosed within a cabinet which can be carried by the test operator.
~n the tester and testing method of this invention, the ther-mi6tor 100 provide6 a very 6ensitive indication of thermal con-ductivity of the liquid in which it is immer6ed. Since it has a negative coefficient of resistance (that is, the hotter the ther-mistor becomes, the lower its resistance), the thermistor pro-vides the double function of introducing the heat into the test 6ample and providing an electrical indication of the equilibrium temperature achieved by the thermistor during its operation.
Quenchant test 6ample 6ize may be as little as one fluid ounce. Although the 6ample temperature need not be controlled at n given point, all 6ample6 in a test series must be run at the 6ame temperature. Room temperature is most convenient. Sample agitation is not required or desired during testing.
Although the basic test circuitry of the quenchant tester ofthis invention i6 uncomplex in design, other features have been lncorporated to insure repeatable high quality test results and uncomplicated operation for laboratory and field usage. The cir-cuitry is housed in a suitably small cabinet measuring 8 x 9 x 12 inches with operator control and readout equipment mounted on the 1~9~9 D-13850 front panel. Contained in the cabinet is a 120 volt AC powered variable 9 to 12 volt DC power supply, an electric power relay, the bridge circuit resistor~, and three adjustable solid state timed off delay relays; one set for 5 seconds, the second for 40 seconds and the third for 45 seconds.
The effectiveness, reliability and sensitivity of the appa-ratus and method of the present invention will be seen from the following non-limiting examples. Tests show that the novel tester accurately measures the quenchant concentration present in fresh solution6 with an accuracy of + 0.5%.

l~Z~3~9 D-13850 Using a quenchant te~ter of thle present invention as described above, quenchant ~olutions of various concentrations were tested, and it i6 determined that the concentrations of polymer in these aqueous solutions could be measured to a preci-sion of approximately +0.5 weight percent. Trials were then per-formed on samples of used quenchant solutions to determine whether the tester could provide a ufficiently sensitive indica-tion of the quench-cooling performance of 6uch material and pro-vide the base6 for the correction of used quenchant baths to re6tore their propertie6 to the desired ~tandard when necessary.
The tester was calibrated as described above with distilled (or tap) water and, as a second test standard, an aqueous solu-tion of fresh unused UC0 ~ Quenchant HT, i.e., UQHT, (an aqueous solution of a mixed polyalkylene glycol prepared by copolymeriz-ing ethylene and propylene oxides and having a weight average MW
of about 15,000). The UQHT te6t solution contained about 40 weight percent polymer. The tester was then used to test a 6ample of u~d UQHT from an automotive spring manufacturing plant. The quenchant 601ution was originally about 40 weight percent polymer, but the used sample was found to have a cooling rate equivalent to a solution containing 53 weight percent polymer.

Comparative tet6 using standard refractometer apparatus indicated that the u6ed sample had a cooling rate equivalent to a polymer concentration of 45 weight percent.
Comparative tests using standard kinematic viscosity appa-ratu6 indicated that the used sample had a cooling rate equiva-lent to a polymer concentration of 42 weight percent.
To determine the accuracy of the cooling rate information determined by the novel quenchant te6ter, compared to that devel-oped from 6tandard refractometer and viscosity te6ts, a fre6hunused quenchant 601ution containing 53 weight percent polymer was prepared to match the percent polymer indicated by the tester and a 601ution containing 42 weight percent polymer was prepared to match the percent polymer 6uggested by vi6c06ity measurement.
U6ing 6tandard laboratory te6t procedures and apparatus for cooling curve analy6is, the cooling rates of the used UQHT quen-chant 6ample and the two fresh unu6ed 601ution6 (53 wt. % and 42 wt. %) were compared. In the cooling curve analysis, a trun-cated cone of metal, approximately one inch in diameter and 1.5 inches long, having a thermocouple in the center and another on the 6urface, is heated, immer~ed in the liquid to be tested, and allowed to cool, while a plot of temperature versus time i6 ~Z9~8~3 D-13850 developed u6ing normal recording equipment. The re~ulting curve6 ~or two different bath temperatures are shown in Figs. 4 and 5.
Using a bath temperature of 62.5C., Fig. 4 shows that the cool-ing curve ~or the used UQHT quenchant sample lies just below the 5 curve for the 53 percent ~olution, and i~ considerably above the curve for the 42 percent ~olution for most of its length. Using a bath temperature of 75C., Fig. 5 shows that the cooling curve for the used sample lies slightly above that for the 53 percent sample, and is farther removed from the curve for the 42 percent solution over most of the length. In both instances, the cooling curve of the fresh unused 53% UQHT olution (suggested by the novel guench tester) more closely approximates the cooling curve o the u~ed UQHT than doefi the cooling curve of the fresh 42%
UQHT solution which wa~ sug~ested by the viscosity techniques.
It i~ therefore apparent that in addition to providing faster and more convenient testing of such samples than either refractometer or vi~cosity testing, the tester of the present invention pro-vides a more accurate evaluation of the cooling rate of the used quenchant ~ample than the vi6cosity testing method. The quen-chant tester of this invention more accurately predicted the quenchant concentration and cooling curve characteristics of this used UQHT quenchant than either the refractive index or viscosity methods of the prior art.

~2~32~9 D- 13 8 5 0 Using the sa~e novel quenchant te~ter and procedures as in Example 1, the te6ter was calibrated with water and an unused aqueous solution of UQHT as described in Example 1, the ~resh unused test solution having a polymer concentration of 20 weight percent.
The tester was then used to test a sample of u~ed UQ~ from a forging plant. The used UQHT solution was originally about 20 wt. % polymer, but the used 6ample was found to have a cooling rate equivalent to A fresh unused UQHT solution containing about 22 wt. % polymer. U~ing refractometer and viscosity measursments as described in Example 1, the used sample was determined to have a quenchant concentration equivalent to 26 and 25 ~t. % of fresh unused UQHT, respectively. Cooling curves prepared using the method described in Example 1 for the used UQHT sample showed its properties to be nearly equivalent to a polymer concentration of 20 wt. ~. Thus, the ~uenchant tester of the present invention more accurately predicted the properties of the ~ample (as described by the cooling curves, i.e., as 22 wt. ~ polymer) than did either the refractive index (26 wt. %) or viscosity (25 wt.
%) techniques.

D-13~50 ~ used sample of UC0 ~ Quenchant 8, hereinafter called UQ~, which had been used in a laboratory repeat quench (R/Q) test (a lab te6t method de6igned ~o stress the durability of the quen-chant), i.e., the repeat quench test was conducted using the novel tester and procedures of Example 1 and the quenchant was determined ~o have a quenchant concent~ation equivalent to about 10.5 wt. % polymer. Quenchant VQB is an ayueous ~olution of a mixed polyalkylene glycol a6 with Quenchant HT, but having a weight average molecular weight lMW) of approximately 22,000.
While monitoring with the novel quenchant tester, a fresh, unused, UQ~ quenchant polymer was added until the amount of bridge circuit unbalance was equal to that produced by a fresh, unused, UQB quenchant solution containing exactly 20 wt. %
polymer.
Using the apparatus and procedures described in Example 1, cooling curves were developed for (1) the used UQB quenchant sample, (2) the used UQB quenchant sample as adjusted to the equivalent of 20 wt. % polymer, and (3) a fresh, unused, UQ~
quenchant solution contairing 20 wt. % polymer, using two bath temperatures, 25C. and 50C., respectively. These curve~, shown 25 in Figs . 6 and 7l indicate that the used VQB sample adjusted to the equivalent of 20 wt.% polymer and the fresh UQB 20 wt. %
polymer ~olution provide essentially the same cooling rates, thus demonstrating that the quenchant tester and procedures of the pre6ent invention can be successfully used to adjust the quen-chant concentration and coolilng characteristics uf used quen-chant solutions.

l~9~t3~39 D-13850 The pre6ent invention is capable of achieving all of the above-enumerated objects, and while a preferred embodiment has been set forth, the scope of the present invention is not limited thereto but may be embodied within the scope of the following claim6.

Claims (25)

1. An apparatus for testing the quench-cooling properties of a liquid quenchant, comprising:
a thermistor adapted to be immersed in the liquid to be tested;
means for applying an electric potential across said thermistor, comprising means for supplying an exci-tation voltage to a Wheatstone bridge circuit which con-tains said thermistor in one leg thereof;
first timing means controlling the duration of time during which said electric potential is applied across said thermistor; and means for determining the electrical resistance of said thermistor, whereby the quenchant properties of the liquid tested are determinable by comparison of the resistance of the immersed thermistor with at least one reference resistance value.

2. An apparatus as claimed in Claim 1, wherein said means for determining the electrical resistance of said thermistor comprises means for measuring voltage across said Wheatstone bridge.

3. An apparatus as claimed in Claim 2, further comprising means for applying a first predetermined level of voltage to said thermistor through said Wheatstone bridge to preheat.

4. An apparatus as claimed in Claim 3, further comprising second timing means controlling the duration of time during which said first predetermined level of voltage is applied.

5. An apparatus as claimed in Claim 2, further comprising third timing means latching an indication of voltage at said means for measuring voltage after a predetermined time interval.

6. An apparatus as claimed in Claim 1, further comprising means for determining the electrical resistance of said thermistor at the end of a test.

7. An apparatus as claimed in Claim 1, further comprising:
means for measuring voltage across two points of said Wheatstone bridge circuit;
said first timing means comprises a first timer for controlling the total duration of time during which said excitation voltage is supplied to said Wheatstone bridge;
a second timer for controlling the duration of time during which a first predetermined level of voltage is provided to said Wheatstone bridge circuit; and a third timer for latching an indication of voltage at said means for measuring voltage after a predeter-mined interval of time.

8. An apparatus as claimed in Claim 1, wherein said ther-mistor has a negative temperature coefficient of resistance.

9. An apparatus for testing the quench-cooling properties of a liquid quenchant, comprising a thermistor adapted to be immersed in the liquid to be tested;
means for applying an electric potential across said thermistor, comprising means for supplying an excitation voltage to a Wheatstone bridge circuit that contains said thermistor in one leg thereof;
means for maintaining said excitation voltage at a first predetermined level for a first predetermined period of time;
means for maintaining a second predetermined level of excitation voltage for a second predetermined period of time;
means for measuring an output voltage across said Wheatstone bridges; and means for holding a reading of said output voltage after a third predetermined period of time, whereby the quenchant properties of the liquid tested are determinable by comparison of said voltage reading with reference voltage value

10. A process for testing the quench-cooling properties of a liquid quenchant, comprising the steps of:
(a) using a thermistor to test a liquid quenchant sample, said thermistor being included in a leg of a Wheatstone bridge circuit and adapted to be immersed in the liquid quenchant sample;

(b) determining the electrical current flow through said thermistor using means for measuring electrical current, and (c) comparing the current flow measured to at least one comparison measurement value.

11. A process for determining an amount of polymer quenchant additive or water required to be added to a quenchant comprising an aqueous solution of a polymer to alter the quenchant proper-ties of said quenchant to a desired value, comprising the steps of:
using a thermistor to test a quenchant sample, said thermistor being included in a leg of a bridge circuit and adapted to be immersed in the sample;
determining the electrical resistance of said ther-mistor using means for measuring electrical resistance;
comparing the resistance measured to at least one comparison resistance measurement value;
determining an amount of quenchant additives or water necessary to be added to said quenchant from which the sample was drawn, based upon the comparison of the resistance measurements; and whereby an amount of additives or water may be determined which amount is necessary to add to said quenchant to alter its quenchant properties to said desired value.

12. A process as claimed in Claim 11, further comprising the step of providing three resistors, each having a predetermined resistance, in a bridge circuit with said thermistor and measuring an output voltage across said bridge circuit.

13. A process as claimed in Claim 12, wherein said compari-son resistance measurement value is determined by immersing said thermistor in liquid water.

14. A process as claimed in Claim 13, further comprising the steps of:
taking third measurement value of a standard liquid quenchant;
comparing the difference of the third measurement value from the comparison measurement value with the difference of said quenchant sample measurement value from the said comparison measurement value; and whereby the ratio of said differences is used as a proportionate indicator of the amount of quenchant addi-tives or water to be added to said quenchant.

15. A process as claimed in Claim 11, further comprising in the step of using said thermistor, the step of preheating said thermistor to initially lower its resistance at the beginning of a test sequence;
subsequently reducing the voltage supplied to said thermistor to a predetermined level for a predetermined period of time; and whereby each test conducted using said thermistor is conducted for an equal predetermined period of time.

16 A process as claimed in Claim 15, further comprising the steps of:
using a voltmeter to determine said resistance of said thermistor by placing said voltmeter in elec-trical contact with two different portions of a bridge circuit, said bridge circuit having said thermistor as one leg thereof;
providing an indication with said voltmeter of the voltage across said bridge circuit; and using said voltage indication as an indirect measure of electrical current flowing through said thermistor.

17. A process as claimed in Claim 11, further comprising the steps of using at least three timing sequences including a first timing sequence employing a means for pro-viding a predetermined level of power to a bridge cir-cuit having said thermistor as one leg thereof;
a second sequence for providing power to said bridge circuit at a second adjustable level of elec-trical power for a predetermined period of time; and a third timing sequence for sending a latching signal to a voltmeter placed across said bridge circuit

18. A process as claimed in Claim 17, wherein said third sequence provides a latching signal to said voltmeter to retain the last voltage reading in its display at the termination of said third sequence.

19. A process as claimed in Claim 18, further comprising the steps of:
providing a pushbutton signal to start the testing sequence;
providing an alternating current supply;
providing three means for timing;
providing a DC power supply for converting alter-nating current into direct current for supplying to said bridge circuit; and providing a means for latching said voltmeter dis-play upon termination of said testing sequences.

20. A method of restoring quenchant properties to a used quenchant comprising an aqueous polymer solution, comprising:
testing used quenchant with a thermistor;
measuring the resistance of said thermistor and comparing said resistance to a reference value;
determining an amount of additives or water required to be added to the used quenchant by comparison of said measured resistance with a reference resistance measurement;
adding the determined amount of additives required to the used quenchant; and restoring the used quenchant's quenching properties to nearly that of the quenchant before its use.

21. A method as claimed in Claim 20, further comprising the steps of:
testing said used quenchant with said thermistor provided in a bridge circuit having three different resistors, each having a predetermined resistance; and providing a first level of excitation voltage to said bridge circuit so that electrical current flowing through said thermistor heats said thermistor.

22. A method of restoring quenchant properties as claimed in Claim 20, wherein in said step of testing said used quenchant with said thermistor, apparatus is utilized which comprises:
means for providing a direct current supply to a bridge having said thermistor as one leg thereof;
means for determining the resistance of said thermistor; and a means for cutting off electrical power to said thermistor after a predetermined period of time.

23. A method as claimed in claim 22, wherein said means for measuring the resistatnce of said thermistor includes a voltmeter connected across two different portions of said bridge circuit;
whereby the resistance of said thermistor can be determine from a voltage indication provided by said voltmeter.

24. A method as claimed in claim 20, including the step of determining a reference resistance measurement by testing an unused quenchant with said thermistor for a predetermined amount of time; and comparing measured resistance values of said used quenchant and said unused quenchant with a third refer-ence resistance of a liquid containing no quenchant additives.

25. A method for determining the relative quench-cooling property of a quenchant comprising the steps:
using a thermistor connected in a Wheatstone bridge circuit immersed in a quenchant to be tested;
immersing said thermistor in a first quenchant having a known quench-cooling property, supplying a predetermined level of excitation voltage to said Wheatstone bridge circuit for preheating said thermistor for a first period of time, and thereafter adjusting the level of said excitation voltage to a second level wherein said Wheatstone bridge is substantially balanced after a second period of time;

immersing said thermistor in a second quenchant having a known quench-cooling property, supplying said first predetermined level of excitation to said Wheatstone bridge circuit for preheating said thermistor for said first period of time and thereafter supplying said excitation voltage at said second level so that said Wheatstone bridge is unbalanced at a first level of bridge unbalance after said second period of time in an amount directly proportional to the change in the quench-cooling property of said second quenchant from said first quenchant;
immersing said thermistor in a third quenchant having an unknown quench-cooling property, supplying said first predetermined level of excitation voltage to said Wheatstone bridge circuit for preheating said thermistor for said first period of time and thereafter supplying said excitation voltage at said second level to said Wheatstone bridge circuit so that said Wheatstone bridge is unbalanced at a second level of bridge unbalance after said second period of time in an amount directly proportional to the change in the quench-cooling property of said third quenchant from said first quenchant; and determining the relative quench-cooling property of the third quenchant by comparing said first level of bridge unbalance with said second level of bridge unbalance.