WO1997004960A1 - Control of batching and curing processes - Google Patents
Control of batching and curing processes Download PDFInfo
- Publication number
- WO1997004960A1 WO1997004960A1 PCT/US1995/009712 US9509712W WO9704960A1 WO 1997004960 A1 WO1997004960 A1 WO 1997004960A1 US 9509712 W US9509712 W US 9509712W WO 9704960 A1 WO9704960 A1 WO 9704960A1
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- WIPO (PCT)
- Prior art keywords
- voltage
- substance
- electrodes
- accordance
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- Prior art date
Links
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
- B01F35/20—Measuring; Control or regulation
- B01F35/21—Measuring
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
- B01F35/20—Measuring; Control or regulation
- B01F35/21—Measuring
- B01F35/2133—Electrical conductivity or dielectric constant of the mixture
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
- B01F35/80—Forming a predetermined ratio of the substances to be mixed
- B01F35/82—Forming a predetermined ratio of the substances to be mixed by adding a material to be mixed to a mixture in response to a detected feature, e.g. density, radioactivity, consumed power or colour
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/0288—Controlling heating or curing of polymers during moulding, e.g. by measuring temperatures or properties of the polymer and regulating the process
-
- 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
- G01N33/44—Resins; Plastics; Rubber; Leather
- G01N33/442—Resins; Plastics
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
- B01F35/20—Measuring; Control or regulation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B38/00—Ancillary operations in connection with laminating processes
- B32B2038/0052—Other operations not otherwise provided for
- B32B2038/0076—Curing, vulcanising, cross-linking
Definitions
- the invention relates generally to process control and, more particularly, to methods and apparatus for recognizing a change in state of a material.
- the invention is applicable to a wide variety of industrial processes, including batch mixing processes and curing processes.
- the invention additionally can be used for evaluating consistency between batches.
- a wide variety of industrial processes require the evaluation of substances which change in at least one characteristic over time. Examples of changes include changes as one substance is added to another for mixing purposes to produce a combined substance; substances which undergo a curing process such as phenolic resins, epoxy resins, and concrete; and substances which change over time as a result of microbiological processes, such as fermentation to produce beer or wine.
- a typical process for manufacturing plastic laminate multiple stacks of phenolic resin-impregnated sheets of paper-like material are heated in a curing press at least until the phenolic resin cures, and are then cooled. Each stack thus ultimately forms a single sheet of finished plastic laminate material.
- a typical sheet size is 4 feet by 8 feet (1.2 meters x 2.4 meters).
- the press applies a pressure of approximately 400 psi (28 bar) .
- a typical curing temperature which varies depending upon the particular formulation, is within the approximate range of 270°F to 300°F (132°C to 149°C) .
- superheated hot water at approximately 400°F (204°C) is employed to heat the press, although any suitable source of heat may be employed.
- a pile including multiple stacks of resin-impregnated sheets, for example fourteen stacks, each including five or six sheets of phenolic resin-impregnated paper-like material.
- the stacks actually are placed back-to-back in double stacks separated by release paper.
- the pile includes alternating double stacks of resin-impregnated sheets and metal separator sheets, such as stainless steel sheets.
- the entire pile, including the multiple stacks, is heated between the press plates to produce a finished sheet for each stack.
- thermocouples In order to determine when curing is completed, for typical prior art press operation disposable thermocouples are employed, for example M J n -type thermocouples, inserted into one or more of the stacks among the resin-impregnated sheets.
- the thermocouple is connected through appropriate signal conditioning and interface circuitry to a controller, which is thus able to sense the temperature of the resin-impregnated sheets during the curing cycle.
- thermocouples there are two disadvantages in particular of this prior art technique for operating a plastic laminate curing press.
- One disadvantage is that, when the phenolic resin cures, the thermocouple is permanently embedded in the resultant plastic laminate product, and accordingly cannot be reused. Thus, the process consumes thermocouples.
- Another disadvantage perhaps more significant, is that press production efficiency is not as high as possible due to the intentional prolonging of the heating cycle beyond the minimum required in order to ensure the phenolic resin is completely cured. In part, this results from the indirect manner in which curing of the phenolic resin is sensed; it is simply assumed that, once a particular temperature is reached, curing is assuredly complete.
- the invention disclosed herein has broad applicability and, in particular, is applicable to a variety of processes where a material changes state or undergoes a chemical reaction. Disclosure of Invention
- the invention is based both on the discovery that many substances and the combining of many substances can produce small but measurable voltages, which typically change as a function of time as characteristics of the material change; as well as on a recognition that this passively measured voltage can be related in a practical manner to various process control and analysis implementations.
- non-reactive electrodes employed are of the same material, distinguishing the invention from an ordinary battery or power cell.
- Typical electrode materials can include stainless steel, silver, copper, aluminum, carbon, iron, gold, platinum and tungsten.
- the polarity of the voltage produced is unpredictable. Thus, in some cases one electrode is positive with reference to the other electrode, and in other cases the one electrode is negative with reference to the other electrode. In some cases, the voltage crosses zero, going from negative to positive, or vice versa.
- the voltage produced is related to the size of the electrodes, increasing as the electrode area increases.
- certain curing operations such as the curing of phenolic resins
- phenolic resins typically a family of curves is developed, some of which cross zero several times during the course of a cure, and some which do not. In most cases, it is possible to recognize within the first few minutes which of the family of curves is being produced, and thereby reach a conclusion regarding how to determine the end point of the process.
- the invention may be employed for controlling a batch mixing process wherein a first substance, such as water, is placed in a mixing container and a second substance, such as sugar, is added for combining with the first substance to produce a combined substance, in this example sugar dissolved in water.
- the method includes the steps of placing a pair of electrodes in contact with the combined substance, and monitoring voltage between electrodes produced by the combined substance while the second substance is being added. The monitored voltage changes as the second substance is being added and indicates the quantity or concentration. When the monitored voltage causes a predetermined threshold voltage, it is recognized that a sufficient quantity of the second substance has been added.
- a curve fitting approach is preferred, where voltage is monitored as a function of time while the second substance is being added, and the function is evaluated, such as by a mathematical curve fitting technique, and compared to a plurality of predetermined functions to determine the best match.
- the mixing action may interfere with or mask the measured voltage with "noise" voltage, particularly where mechanical mixing is employed.
- the electrode area in contact with the combined substance may vary. Thus large variations in measured voltage may occur that are unrelated to constituent concentration. In such cases, it is preferred to periodically withdraw a quantity of the combined substance into a monitoring vessel where mechanical disturbances are minimized, and employing a pair of electrodes to monitor voltage produced by the combined substance within the monitoring vessel.
- the invention may also be employed to recognize consistency between batches of material, such as mixed food products, including gelatin. Thus, a pair of electrodes is placed in contact with the substance, and voltage between the electrodes produced by the substance as a function of time is monitored.
- the monitored voltage as a function of time is compared to at least one predetermined function to determine a degree of conformity.
- a typical voltage function may be a relatively steady voltage being produced over time. Variations in this voltage over time could be indicative of a variation in ingredients, or even bacterial contamination.
- the invention may be employed as an analytic technique to identify an unknown substance by comparison with known samples.
- a pair of electrodes is placed in contact with a substance to be analyzed, and voltage between electrodes produced by the substance as a function of time is monitored.
- the monitored voltage as a function of time is compared to a set of predetermined functions to determine a best match.
- mathematical curve fitting techniques may be applied.
- the invention may also be employed to control various curing processes, including various polymerization reactions, detecting when concrete has cured, and detecting when the precursors of alcoholic beverages such as beer and wine have completed fermentation.
- a method for monitoring change in a substance which changes in at least one characteristic over time includes the steps of placing a pair of electrodes in contact with the substance, and monitoring voltage between electrodes produced by the substance as a function of time. In some cases, simple thresholding is appropriate. Thus, it is recognized that a sufficient change has occurred when the monitored voltage crosses a predetermined threshold.
- curve fitting may be employed to compare the monitored voltage as a function of time to a plurality of predetermined functions to determine the best match.
- the invention also contemplates an instrument for monitoring substances which change in at least one characteristic over time.
- the instrument includes a pair of electrodes made of the same material for placing in contact with a substance, a voltage measuring circuit connected to electrodes for monitoring voltage between electrodes produced by the substance, and a recorder for recording voltage as a function of time.
- the recorder may comprise, for example, a simple strip chart recorder, or a memory, such as a computer memory.
- the instrument further includes a curve-fitting device for recognizing a characteristic voltage as a function of time function.
- a method for controlling a plastic laminate curing press having a pair of press plates between which at least one stack of phenolic resin-impregnated sheets is heated includes the steps of employing a pair of metallic elements on either side of the stack as electrodes.
- these metallic elements employed as electrodes are metal separator sheets employed between stacks of resin-impregnated sheets in a pile including alternating stacks of resin-impregnated sheets and metal separator sheets.
- voltage between electrodes is monitored while the stack is being heated, and heating of the stack is terminated when the monitored voltage decreases below a predetermined threshold voltage, that is, when the monitored threshold voltage decreases to near zero.
- a predetermined delay interval must elapse before heating of the stack can be terminated.
- a controller for controlling a plastic laminate curing press having a pair of press plates between which at least one stack of phenolic resin-impregnated sheets is heated.
- the controller includes a heat control element for controlling heating of the stack, a sensing circuit connected to electrodes on either side of the stack for monitoring voltage between electrodes, and a control device connected to the heat control element and to the sensing circuit and operable to initiate heating of the stack and operable to subsequently terminate heating of the stack when the voltage between the press plates decreases below a predetermined threshold voltage.
- the control device is operable to subsequently terminate heating of the stack when the voltage between the press plates decreases below the predetermined threshold voltage after a predetermined delay interval has elapsed.
- the invention provides a method for recognizing a change in state of a material, such as the curing of a resin from liquid to solid form, for example, a phenolic resin or an epoxy resin.
- a change in state is employed herein in a broad sense to include, but without limitation, polymerization reactions.
- the method includes the steps of placing a pair of electrodes in contact with the material, monitoring voltage between the electrodes while the change in state is expected to occur, and recognizing the change in state when the monitored voltage decreases below a predetermined threshold voltage.
- a change in state is accompanied by an increase in voltage.
- a peak or a dip in the voltage signal monitored over time indicates that a particular change in state has occurred, for example the onset or completion of a constituent boiling out of a complex material, such as alcohol boiling from phenolic resin.
- a voltage signal is developed, and the rate of change of the voltage signal is determined. The change in state is recognized when the rate of change reaches zero.
- the invention thus provides methods and apparatus for control of a plastic laminate curing press for increased production efficiency.
- the invention eliminates the need for thermocouples inserted within the stacks of resin-impregnated sheets during the manufacture of plastic laminate.
- the invention further provides methods and apparatus for more directly sensing when a change in state of a material has occurred, such as the change in state of a resin, such as a phenolic resin or an epoxy resin, from liquid to solid form.
- FIG. 1 depicts generalized apparatus for recognizing a change in state of a material
- FIG. 2 is a graph plotting temperature and voltage as a function of time during a typical phenolic resin curing cycle as recorded during operation of the apparatus of FIG. 1;
- FIG. 3 depicts generalized apparatus for monitoring a batch mixing process;
- FIG. 4 depicts generalized apparatus including a separate monitoring vessel for monitoring a batch mixing process
- FIG. 5 depicts generalized apparatus wherein the walls of a mixing or monitoring vessel serve as one of the two electrodes;
- FIG. 6 depicts a shielded test vessel for measuring small voltages
- FIG. 7 depicts a generalized instrument
- FIG. 8 is a highly schematic representation of a plastic laminate curing press and a controller in accordance with the invention.
- FIG. 9 is a simplified flowchart of a control program implemented in the controller of FIG. 3.
- a beaker 10 contains a quantity of test material 12, such as phenolic resin, and is heated over a hot plate 14.
- test material 12 such as phenolic resin
- a pair of electrodes 16 and 18, such as stainless steel electrodes are connected via respective leads 20 and 22 to a strip chart recorder 24.
- a temperature sensing device 26 such as a thermocouple, is connected via a test lead 28 to the strip chart recorder 24.
- the particular strip chart recorder 24 employed has at least two channels, and is arranged to plot voltage and temperature as a function of time.
- FIG. 2 is a plot or graph depicting a typical strip chart recording produced as the material 12 is heated.
- temperature is plotted as a dash line 30, while voltage between the electrodes 16 and 18 is plotted as a solid line 32.
- a measurable voltage as represented by the plot line 32, is produced between the electrodes 16 and 18 as the phenolic resin 12 is heated and cures. This voltage eventually decreases to essentially zero when the resin 12 is completely cured, as indicated at a point 34 in the plot of FIG. 2.
- the polarity is unpredictable.
- either the electrode 16 or the electrode 18 is positive with reference to the other of the electrodes 16 and 18.
- the voltage may undergo fluctuations, including a polarity reversal, before settling out with one relative polarity or the other.
- the two electrodes 16 and 18 are of the same material, such as stainless steel.
- the magnitude of the voltage depends to some extent on the area of the electrodes, and can range from a maximum of five or ten millivolts in the case of small electrodes placed in a test beaker 10, to more than ten volts in the case of electrodes of many square feet (several square meters) in a plastic laminate press embodiment.
- the phenomenon is something other than a simple battery effect.
- the single curve of FIG. 2 which may be recognized as having a characteristic shape representative of a particular voltage as a function of time function, which can be determined employing a mathematical curve fitting technique and mathematically described, various other curve shapes may be produced during different production tests run.
- a given general type of substance may be produce six different curves during successive experimental runs, which are referred to herein as a family of curves for the particular substance.
- a family of curves for the particular substance.
- phenolic resin it has experimentally been determined that at least one of the family of curves is produced during approximately one-half of the test runs, and the remaining curves occur less frequently.
- FIG. 3 represents in generalized form a batch mixing process.
- a mixing container 40 includes a quantity of a first substance 42, which gradually becomes a combined substance 42 as a second material is added.
- a supply hopper 44 contains a quantity of the second substance, which discharges through a mixing valve 46 and a conduit 48 into the combined substance 42.
- Shown in highly schematic form is a paddle mixer 50, including a mixing blade 52 driven by a motor 54.
- a pair of electrodes 60 and 62 are placed in contact with the combined substance 42, and connected via electrical conductors 64 and 66 to an instrumentation device 68 such as a microvoltmeter, a strip chart recorder, or a computer-based data acquisition and analysis system.
- the electrodes 60 and 62 are made of the same material, such as stainless steel or carbon.
- voltage produced by the combined substance 42 as monitored across the electrodes 60 and 62 varies, as an indicator of relative concentration.
- FIG. 4 depicts an alternative arrangement where there is a separate monitoring vessel 70 connected to the mixing vessel 40 via a conduit 72, and a representative pump 74 or other device for periodically withdrawing a quantity of the combined substance 42 from within the mixing vessel 40 to the monitoring vessel 70, for making undisturbed readings.
- FIG. 5 illustrates a variation wherein the monitoring vessel 40 has conductive walls, which serve as one of the electrodes.
- the electrode 60 is made of the same material as the monitoring vessel wall. The same technique may be implied to the separate monitoring vessel 70 of FIG. 4.
- Example No. 1 A 100 ml glass beaker was filled with 50 ml of common Acetic Acid (vinegar) . The liquid was at a room temperature of approximately 25°C (77°F) . Two approximately 3.2 mm diameter 304 stainless steel probes were placed into the beaker without touching the sides of the beaker and had a gap between them of about 35 cm. The stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage. A 10,000 ohm resister also was put across these terminals to give a "load" to the circuit.
- Acetic Acid vinegar
- measured voltage was in excess of 0.5 millivolts.
- the measured voltage immediately dropped to approximately 0.04 millivolts, and then increased over a five minute interval to 0.2 millivolts.
- Additional baking soda was added, and measured voltage dropped over a five minute interval to 0.16 millivolts, then over a three minute interval increased to 0.18 millivolts.
- the measured voltage decreased and then partly rebounded over a period of time, with an overall downward-sloping voltage curve. The slope decreased with each addition of baking soda. The slope when voltage is plotted as a function of time appears to be meaningful.
- the resultant voltage as a function of time plot on the strip chart recorder reflects the formation reaction for the production of carbon dioxide.
- Example No. 2 A liter of distilled water was heated to a near boil and sucrose was added, stirred vigorously, until the solution was completely saturated. A 100 ml glass beaker was then filled with 50 ml of this hot solution of distilled water and sucrose. Two 304 stainless steel rods were placed into the beaker without touching the sides of the beaker and had a gap between them of about 35 cm. The beaker was then placed in an ice bath to cool the solution down to about 2°C.
- the stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage. A 10,000 ohm resister also was put across these terminals to give a "load" to the circuit.
- Example No. 3 A liter of distilled water was heated to a near boil and sodium chloride was added, stirred vigorously, until the solution was completely saturated. A 100 ml glass beaker was then filled with 50 ml of this hot solution of distilled water and sodium chloride. Two 304 stainless steel rods were placed into the beaker without touching the sides of the beaker and had a gap between them of about 35 cm. The beaker was then placed in an ice bath to cool the solution down to about 2°C.
- the stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage.
- a 10,000 ohm resister also was put across these terminals to give a "load" to the circuit. As the solution cooled, crystals dropped out of solution. The produced voltage went to 0.02 millivolts when at equilibrium.
- the resultant voltage as a function of time plot on the strip chart recorder reflects the formation rate of crystal production.
- Example No. 4 A liter of distilled water was heated to a near boil and magnesium sulfate was added, stirred vigorously, until the solution was completely saturated. A 100 ml glass beaker was then filled with 50 ml of this hot solution of distilled water and magnesium sulfate. Two 304 stainless steel rods were placed into the beaker without touching the sides of the beaker and had a gap between them of about 35 cm. The beaker was then placed in an ice bath to cool the solution down to about 2°C.
- the stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage.
- a 10,000 ohm resister also was put across these terminals to give a "load" to the circuit.
- crystals dropped out of solution.
- the produced voltage crossed zero several times, and settled near zero volts after about thirty minutes.
- the resultant voltage as a function of time plot on the strip chart recorder reflects the formation rate of crystal production.
- Example No. 5 A 100 ml glass beaker was filled with 20 ml of household ammonia/water (which had been distilled) . The liquid was at a room temperature of approximately 25°C (77°F) . Two 304 stainless steel rods were placed into the beaker without touching the sides of the beaker and had a gap between them of about 35 cm.
- the stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage. A 10,000 ohm resister also was put across these terminals to give a "load" to the circuit. Measured amounts (5 ml) of 3% w/w iodine solution were added to the beaker until production of precipitate ceased.
- the resultant voltage as a function of time plot on the strip chart recorder reflects the equilibrium formation rate of crystal precipitate production via consumption of the iodine component.
- Example No. 6 A 100 ml glass beaker was filled with 20 ml of w/w iodine solution. The liquid was at a room temperature of approximately 25°C (77°F) . Two 304 stainless steel rods were placed into the beaker without touching the sides of the beaker and had a gap between them of about 35 cm.
- the stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage. A 10,000 ohm resister also was put across these terminals to give a "load" to the circuit.
- the resultant voltage as a function of time plot on the strip chart recorder reflects the equilibrium formation rate of crystal precipitate production via consumption of the ammonia component.
- Example No. 7 A 250 ml plastic cup was filled with 50 ml of quick forming cement powder. While stirring the powder, 20 ml of 25°C distilled water was added to the cup until the power/water system was mixed; about 15 seconds. Two 304 stainless steel rods were placed into the cup without touching the sides of the cup and had a gap between them of about 35 cm. The stainless steel probes were connected to a strip chart recorder by solid copper wires to measure voltage. A 10,000 ohm resister also was put across these terminals to give a "load" to the circuit.
- the measured voltage was initially -13.0 millivolts.
- the measured voltage crossed zero after about one hour, and reached +3.0 volts approximately two hours from the starting time, and stabilized at +3.0 volts for an extended period of time.
- Example No. 8 As an example of making beer, wort was prepared and placed in a fermentation pot. A pair of stainless steel probes were placed in contact with the wort and connected to a strip chart recorder for recording voltage readings during fermentation. The initial voltage was 6.0 millivolts, and decreased to 0.6 millivolts after six hours. The voltage slowly decreased over a period of days, and after four days was 0.2 millivolts. The voltage held at 0.2 millivolts for one day. Fermentation (as indicated by bubbles) ceased after nine days, and the voltage crossed zero to -0.02 millivolts.
- Example No. 10 Several brands of food gelatin were compared. Gelatin was prepared in accordance with recipe directions, combining mix and distilled water in a boiling solution. The solutions were cooled until solidified. Stainless steel electrodes were used to measure voltage produced by the gelatin. With one brand, a voltage remained relatively constant over time. With another brand, the voltage produced varied significantly over a period of time, crossing zero sometimes.
- Example No. 11 50 ml 4% polyvinyl alcohol by mass was mixed with 10 ml of a 4% by weight sodium borate solution to produce a polymer solution, polyvinyl alcohol sodium borate polymer complex.
- Example No. 12 Ordinary grocery bags were cut into eight ten-inch square (25.4 cm by 25.4 cm) pieces of paper, which were soaked in phenolic resin. A squeegee was employed to remove excess phenolic resin. The eight pieces were stacked and then sandwiched between two eleven-inch by twelve-inch (27.9 cm by 30.5 cm) stainless steel sheets, with a J-type thermocouple placed midway in the stack. One input of a strip chart recorder was connected to the thermocouple to record temperature, and another input of the strip chart recorder was connected to the two stainless steel sheets to measure voltage across the stainless steel sheets. The paper sandwich, initially at a temperature of 50°F (10°C) , was placed horizontally in an oven heated to 300°F (149°C) , and a twenty-pound (nine kilogram) weight placed on top of the sandwich.
- Heating of the sandwich commenced, with an initial recorded temperature of 50°F (10°C) and an initial recorded voltage of 1 millivolt. There was an initial voltage peak of 8 millivolts at 10 minutes, with a recorded temperature of 90°F (32°C) . Voltage decreased to approximately 2.5 millivolts at 25 minutes, with a recorded temperature of 130°F (54°C). Voltage remained at approximately 2.5 millivolts for a further 10 minutes, beginning to rise at 35 minutes, with a recorded temperature of 150°F (66°C) , believed to coincide with the onset of alcohol boiling from the phenolic resin.
- Very small voltages are produced in some cases, particularly when one of the substances producing a voltage being monitored is normally considered an insulator, such as oils, alcohols or waxes, or other organic hydrocarbons.
- FIG. 6 is a conceptual diagram of a shielded test vessel 70 for monitoring small voltages.
- the device 70 of FIG. 6 includes a shielded container 72, for example made of steel, having a conductive lid 74 hinged at 76, with a ground strap 78 provided to ensure good electrical continuity between the container 72 and the lid 74.
- a pair of carbon electrodes 84 and 86 are provided, connected via shielded leads 88 and 90 to a microvolt measuring or recording device 92, which may be a computer-based data acquisition system.
- the conductors 88 and 90 are part of a shielded cable assembly, with a cable shield 94 connected to ground 96 and, via straps 98 and 100, to the outer shield container 72 and a support structure 102.
- a stainless steel funnel 104 is provided, which passes through a suitable aperture in the lid 94, and is connected to the lid 94 via a ground strap 106.
- the instrument 120 includes a pair of electrodes 122 and 124 which are made of the same material, such as stainless steel, for placing in contact with a substance.
- the electrodes 122 and 124 are connected via conductors 126 and 128 to a voltage measuring circuit for measuring voltage between the electrodes 122 and 124 produced by the substance.
- the voltage measuring circuit comprises an analog interface circuit 130, which includes an analog-to-digital converter, connected to a computer processor 132 as part of a conventional data acquisition system.
- a recorder for recording voltage as a function of time which recorder can take the form of a strip chart recorder 134 connected to the interface circuit 130, or a memory 136 supplied with data by the processor 132 in accordance with voltage data from the interface circuit 130.
- a suitable output device 138 such as a printer or a display screen is connected to the processor 138.
- a conventional plastic laminate curing press generally designated 150, includes an upper press plate 152 and a lower press plate 154 which in turn include respective heat exchangers 156 and 158 and which are controllably heated by superheated hot water circulating through a fluid flow loop 160 heated by a controllable heating device 162.
- the heating device 162 is conventional, and includes a pump for circulating hot water through the loop 160.
- the heating device 162 is also capable of circulating cooling water for cooling down the press 150 near the end of a curing cycle.
- a pile 164 of alternating double stacks 166, 168 and 170 of resin-impregnated sheets and metal separator sheets 172, 174, 176 and 178 is placed within the press 150, compressed between the press plates 152 and 154 with a pressure in the order of 4000 psi, and heated.
- Each of the double stacks 166, 168 and 170 conventionally comprises two individual stacks (not separately shown) of five or six resin-impregnated sheets each placed back-to-back and separated by release paper.
- a pattern sheet (not shown) placed directly against one of the metal separator sheets 172, 174, 176 and 178 to produce a glossy finish.
- the heating cycle commences and proceeds as is described generally above under the heading "Background of the Invention". It will be appreciated that, for purposes of illustration, the elements of the pile 164 are spaced and that, during actual press operation, the elements are all in contact.
- Each of the illustrated double stacks 166, 168 and 170 results in the production of two sheets of plastic laminate, which are typically four feet by eight feet (1.2 meters x 2.4 meters) in size. Although a total of three double stacks 166, 168 and 170 are illustrated, this particular number is for purposes of illustration only, as each pile 164 placed into the press 150 typically comprises seven double stacks, resulting in fourteen sheets of plastic laminate product being produced.
- An actual plastic laminate production press has from eighteen to thirty vertically-arranged openings (not shown) , and each opening receives one pile of double stacks. Thus, a typical plastic laminate production press with twenty-two openings produces three-hundred eight finished plastic laminate sheets per batch.
- control is based on temperature as sensed by a thermocouple (not shown) placed among the individual sheets of one or more of the stacks 166, 168 and 170.
- two or more of the separator sheets 172, 174, 176 and 178 are employed as electrodes, such as the separator sheets 174 and 176. In FIG.
- sensing leads 180 and 182 are connected to the separator sheets 174 and 176 at respective connection points 184 and 186, across which a voltage is developed, as represented by the voltmeter 188 connected to these points 184 and 186.
- the voltmeter 188 is included in FIG. 3 for purposes of illustration only, and would normally not be included in actual apparatus implementing the invention.
- a controller 190 For controlling press operation, a controller 190 is provided, which may comprise an Allen-Bradley P.L.C, such as a Model 2/30, with an analog input card depicted in FIG. 3 as an interface circuit 192.
- the interface circuit 192 serves the function of applying suitable signal conditioning to voltage signals conducted along the leads 180 and 182, and converting the voltage to digital form for further processing in the controller 190.
- the interface circuit 192 is set up for high impedance voltage sensing, although a 10 K Ohm load resistor (not shown) may be connected across the input leads 180 and 182 for noise reduction purposes. A two-second integration time is typically employed for filtering purposes.
- the controller 190 is microprocessor-based, and is programmed in a conventional manner. It will be appreciated that the controller 190 is appropriately and conventionally interfaced to generally control operation of the press 150, such as opening and closing of the press 150, as well as control of the heating device 162, via a representative control line 194.
- FIG. 9 Operation of the FIG. 8 controller 190 is represented in the program flowchart of FIG. 9.
- the FIG. 9 control program is entered in box 200.
- box 202 press operation is commenced by, among other things, turning on the press heat by activating the heating device 162.
- decision box 204 implements a predetermined delay interval, such as twenty minutes, before the controller 190 even begins to consider whether to terminate the heating operation.
- a predetermined delay interval such as twenty minutes
- the voltage across the electrodes comprising the separator plates 174 and 176 is measured via the interface circuit 192.
- this voltage is compared to a threshold voltage selected to determine when the measured voltage is near zero. So long as appreciable voltage between the electrodes comprising the separator plates 174 and 176 is sensed, the answer in decision box 210 is "no", and program execution loops back along execution flow path 212 back to box 208 where the voltage is again measured.
- box 210 When curing of the phenolic resin is completed, the answer is decision box 210 is then "yes", and box 214 is entered to initiate press cool down by turning off press heat and, typically, instituting active cool down in a conventional manner as indicated in box 216.
- cool down When cool down is completed, which takes approximately thirty five to forty minutes, the press is opened, and execution terminates at 218.
- the way in which the invention is capable of being exploited and the way in which it can be made and used will be apparent from the foregoing.
- the invention thus provides methods and apparatus for control of a plastic laminate curing press for increased production efficiency and without requiring thermocouples inserted within the stacks of resin-impregnated sheets.
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Oral & Maxillofacial Surgery (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Food Science & Technology (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Engineering & Computer Science (AREA)
- Medicinal Chemistry (AREA)
- Thermal Sciences (AREA)
- Casting Or Compression Moulding Of Plastics Or The Like (AREA)
- Moulding By Coating Moulds (AREA)
- Reinforced Plastic Materials (AREA)
- Moulds For Moulding Plastics Or The Like (AREA)
- Injection Moulding Of Plastics Or The Like (AREA)
- Lining Or Joining Of Plastics Or The Like (AREA)
- Polymerisation Methods In General (AREA)
Abstract
Description
Claims
Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP95927556A EP1007355A4 (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
JP50754697A JP3708128B2 (en) | 1995-08-01 | 1995-08-01 | Batch and curing process control |
CA002228246A CA2228246C (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
PCT/US1995/009712 WO1997004960A1 (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
AU31549/95A AU718287B2 (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002228246A CA2228246C (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
PCT/US1995/009712 WO1997004960A1 (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1997004960A1 true WO1997004960A1 (en) | 1997-02-13 |
Family
ID=25680007
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1995/009712 WO1997004960A1 (en) | 1995-08-01 | 1995-08-01 | Control of batching and curing processes |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1007355A4 (en) |
AU (1) | AU718287B2 (en) |
CA (1) | CA2228246C (en) |
WO (1) | WO1997004960A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN113021662A (en) * | 2021-02-26 | 2021-06-25 | 苏州银锐环保材料有限公司 | Method for accelerating biodegradation of plastic |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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GB576097A (en) * | 1942-10-05 | 1946-03-19 | Gen Electric Co Ltd | Improvements in methods and apparatus for subjecting materials to high-frequency electrical oscillations |
US4399100A (en) * | 1980-12-29 | 1983-08-16 | Lockheed Corporation | Automatic process control system and method for curing polymeric materials |
US4747898A (en) * | 1982-10-01 | 1988-05-31 | Isovolta Osterreichische Isolierstoffwerke Aktiengesellschaft | Method of making a plastic leaf spring |
US4971639A (en) * | 1989-02-28 | 1990-11-20 | Sampson Machine Company | Method and apparatus for joining polymeric substrates such as vinyl frames |
US5219498A (en) * | 1991-11-12 | 1993-06-15 | Keller L Brian | Process for controlling curing and thermoforming of resins and composites |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3793158A (en) * | 1971-02-05 | 1974-02-19 | Dow Chemical Co | Device and method for measuring relative concentration changes in gas stream components |
EP0084404B1 (en) * | 1982-01-05 | 1989-05-31 | University Of Manchester Institute Of Science And Technology | Corrosion monitoring |
GB2208711A (en) * | 1988-08-16 | 1989-04-12 | Plessey Co Plc | Fibre optic sensor |
US5002644A (en) * | 1989-10-30 | 1991-03-26 | Westinghouse Electric Corp. | Method for monitoring sulfates and chlorides at low concentration |
AU2060495A (en) * | 1994-02-01 | 1995-08-21 | Wyatt, Tracy A. | Control of plastic laminate curing press |
-
1995
- 1995-08-01 AU AU31549/95A patent/AU718287B2/en not_active Ceased
- 1995-08-01 CA CA002228246A patent/CA2228246C/en not_active Expired - Fee Related
- 1995-08-01 WO PCT/US1995/009712 patent/WO1997004960A1/en active Application Filing
- 1995-08-01 EP EP95927556A patent/EP1007355A4/en not_active Withdrawn
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB576097A (en) * | 1942-10-05 | 1946-03-19 | Gen Electric Co Ltd | Improvements in methods and apparatus for subjecting materials to high-frequency electrical oscillations |
US4399100A (en) * | 1980-12-29 | 1983-08-16 | Lockheed Corporation | Automatic process control system and method for curing polymeric materials |
US4747898A (en) * | 1982-10-01 | 1988-05-31 | Isovolta Osterreichische Isolierstoffwerke Aktiengesellschaft | Method of making a plastic leaf spring |
US4971639A (en) * | 1989-02-28 | 1990-11-20 | Sampson Machine Company | Method and apparatus for joining polymeric substrates such as vinyl frames |
US5219498A (en) * | 1991-11-12 | 1993-06-15 | Keller L Brian | Process for controlling curing and thermoforming of resins and composites |
Non-Patent Citations (1)
Title |
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See also references of EP1007355A4 * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN113021662A (en) * | 2021-02-26 | 2021-06-25 | 苏州银锐环保材料有限公司 | Method for accelerating biodegradation of plastic |
CN113021662B (en) * | 2021-02-26 | 2022-01-11 | 苏州银锐环保材料有限公司 | Method for accelerating biodegradation of plastic |
Also Published As
Publication number | Publication date |
---|---|
CA2228246A1 (en) | 1997-02-13 |
AU3154995A (en) | 1997-02-26 |
AU718287B2 (en) | 2000-04-13 |
CA2228246C (en) | 2006-05-09 |
EP1007355A4 (en) | 2008-03-12 |
EP1007355A1 (en) | 2000-06-14 |
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