Patent Grant
9908259
Various aspects relate generally to devices and methods for controlling the shape of ceramic precursor batch extrudates including honeycomb filter bodies by monitoring and controlling the temperatures to batch materials forced through an extruder die plate.
Localized imperfections in the shape of a ceramic-forming extruded body can occur.
One aspect of the invention is a method for controlling the shape of a ceramic precursor extrudate, the method comprising the steps of: forming an extrudate by extruding ceramic precursor batch material through at least one barrel of an extruder and an extruder die disposed at the outlet of the extruder, a barrel temperature capable of being regulated by a barrel coolant flow; measuring the batch material temperature of the material within the extruder upstream of the die; measuring the barrel temperature; determining a batch material temperature setpoint; determining a barrel temperature setpoint based on the batch material temperature and the batch material temperature setpoint; determining a barrel coolant flow setpoint based on barrel temperature setpoint and the measured barrel temperature; and regulating the heat transfer between the barrel and the batch material within the extruder by adjusting the barrel coolant flow.
In some embodiments, the batch temperature can be measured by inserting a probe into the batch to directly measure, depending upon how the probe is positioned, either or both the batch core and/or batch skin temperature. In other embodiments, the batch temperature is measured indirectly be measuring the temperature of a surface of the extruder proximate to the die and that is in either direct or indirect contact with the batch material. In some embodiments, the surface of the extruder proximate to the die is positioned between the last barrel of the extruder body and before the die. Preferably, this surface is not directly supplied with coolant.
In some embodiments, heat transfer from the extruder barrel to the batch material is regulated at a rate sufficient to maintain a difference between the extrudate core temperature and the skin temperature within an extrudate temperature range. In some embodiments, the temperature range is selected such that it produces an extrudate with a uniform shape resulting in a larger number of error free extruded products and a reduced need for product reworking. In some embodiments, the difference the methods and device disclosed herein produce a temperature difference between the extrudate core temperature and the skin temperature of not less than about 1° C. and not more than about 3° C.
In some embodiments disclosed herein, a method is provided of regulating the amount of heat transferred either into or out of the batch material sufficient to maintain a core temperature of the extrudate within a target first temperature range. In some embodiments, the core temperature of the extrudate is not less than 31° C. and not more than 37° C. In some embodiments, the heat transfer into or out of the batch material is regulated so as to maintain a skin temperature of the extrudate to be within a second target temperature range. In some embodiments, the skin temperature is not less than 27° C. and not more than 34° C.
In some embodiments disclosed herein, a method is provided of regulating the amount of heat transferred into or out of a batch material sufficient to cause the flow rate of the extrudate exiting a center portion of the die to be greater than a flow rate of the extrudate exiting the outer portion of the die. In some embodiments, this results in the formation of a substantially uniform extrudate face, resulting in less waste and extrudates of better quality. In some embodiments, the use of these methods for controlling extrudate core and skin temperatures may also obviate the need to add a die mask to the face of the die plate in order to compensate for imperfections in the die plate that lead to unacceptable defects in the extrudate.
In some embodiments disclosed herein, a method is provided of regulating heat transfer into or out of the batch material from the extruder barrel assembly sufficient to cause the flow rate of the extrudate exiting a center portion of the die to be lesser than the flow rate of the extrudate exiting an outer portion of the die. In some embodiments, this results in the formation of a substantially uniform extrudate face, resulting in less waste and extrudates of better quality. This method may also obviate the need to add a die mask to the face of the die plate to compensate for imperfections in the die plate that lead to unacceptable defects in the extrudate.
In some embodiments disclosed herein, a method is provided of controlling the shape of a ceramic precursor extrudates, comprising the steps of forming an extrudate by extruding ceramic precursor batch material through a barrel of an extruder and through an extruder die disposed at the outlet of the extruder wherein the barrel temperature setpoint is an output of a master controller, and the batch material temperature and the batch material temperature setpoint are provided as inputs to the master controller. In some embodiments, the setpoint of cooling flow rate is an output of a slave controller and the barrel temperature setpoint and the measured barrel temperature provide inputs to the slave controller. In some embodiments, the batch material temperature setpoint is an output of a supervisory controller. The supervisory controller receives process inputs.
In other embodiments disclosed herein, the process inputs comprise parameters such as the composition of the batch material, feed rate of the batch material, extrudate geometry or die characteristics, and the like or combinations thereof. The supervisory controller may provide the batch material temperature setpoint, master controller parameters, slave controller parameters or barrel weighting factors, or combinations thereof.
In one aspect disclosed herein, the extruder is provided with a plurality of barrel coolant flows. In some embodiments, the batch material temperature is determined by measuring the temperature of a structure proximate the batch material within the extruder. The batch material temperature setpoint is determined from measurements of a core temperature and a skin temperature of the extrudate.
In another aspect disclosed herein, a ceramic precursor extrudate control system comprises: an extruder comprised of a barrel of an extruder and an extruder die disposed at the outlet of the extruder; a barrel cooling device capable of providing a barrel coolant flow to the barrel; a batch material temperature sensor disposed within the extruder upstream of the die and capable of delivering a batch material temperature; a barrel temperature sensor capable of delivering a barrel temperature; a master controller capable of receiving the batch material temperature and the batch material temperature setpoint as inputs, and capable of delivering a barrel temperature setpoint; and a slave controller capable of receiving the barrel temperature setpoint and the measured barrel temperature as inputs, and capable of delivering a coolant flow setpoint. In one embodiment, the control system further includes a supervisory controller capable of delivering the batch material temperature setpoint to the master controller.
Additional features and advantages of the invention will be set forth in the detailed description which follows and, in part, will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated into and constitute a part of this specification. The drawings illustrate some aspects and embodiments of the invention and, together with the description, serve to explain the principles and operations of the invention.
Some control over the dimensions of extruded batch materials, including aluminum titanate compositions, can be achieved by the use of metal “masks” or “shrink plates” to define the part size and shape as the extrudate exits the forming die. The required mask size is determined by the final part dimensional specifications and by the amount of anticipated part shrinkage that is induced as a result of drying and firing the extruded part. Some localized imperfections in the shape of an extruded part can be corrected by utilizing a mask that compensates for and corrects the imperfections. For example, if the extruded part contains a bump on its surface, a compensated mask with an indentation at the same location as the bump is made and installed to correct the imperfection.
Also, metal dies that are used to form extruded ceramic-forming logs or parts can exhibit a certain amount of die to die flow front variability in which material at the center may flow faster than material at the periphery, the flow front can be flat, or material at the periphery may flow faster than material at the center. If the flow front is not acceptable, the die may need to undergo rework to change the die until it produces an acceptable flow front.
Although batch materials may be extruded under controlled temperatures, such as by controlling the barrel temperature of an extruder, an indirect, single loop method of batch temperature control can be difficult to regulate, and under many conditions, may provides only limited control over the temperatures of the batch materials being extruded. Some aspects disclosed herein provide devices and process control methods that enable finer control over the temperature of extruded batch materials.
Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
One embodiment includes a method for controlling the shape of a ceramic precursor extrudate. Referring to
In one embodiment, the batch temperature can be measured by inserting a probe into the batch to directly measure, depending upon how the probe is positioned, either or both the batch core and/or batch skin temperature. Devices that can be used to directly measure the temperature of the batch material include thermo-couples and even conventional thermometers. Data collected by these devices are either manually or automatically input into the temperature controller system. In still another embodiment, the batch temperature is measured indirectly by measuring the temperature of the batch material. Devices that can be used to make this type of measurement include, for example, infrared heat detectors or a temperature sensor attached to a surface of the extruder that is in contact with the batch material. In one embodiment, the batch material temperature is measured indirectly by measuring the temperature of a surface of the extruder located in proximity to the die plate of the extruder. Referring again to
In one embodiment, a relationship between the indirect temperature measured for a given ceramic precursor formulation and a temperature directly measured is determined and then used to infer the temperature of the batch material including, for example, the batch core temperature by indirectly measuring the temperature of the batch and using the known relationship for the two temperatures to estimate the batch material's core temperature.
In another embodiment, heat transfer from the extruder barrel to the batch material (or from the batch material to the barrel) is regulated at a rate sufficient to maintain a desirable difference between the batch material's core temperature and its skin temperature. The term “heat transfer,” as used herein, includes cooling the batch material's temperature by transferring heat from the material to at least one barrel of the extruder. In one embodiment, the temperature range is selected such that it produces an extrudate with a uniform shape, resulting in a larger number of error free products and a reduced need for product reworking. In one embodiment wherein the difference between the core temperature and the skin temperature of the extrudate is not less than about 1° C. and not more than about 3° C., the term “about” is used to denote a value plus or minus 20 percent of the value, (e.g., about 1° C. includes the range of 0.8° C. to 1.2° C.).
One embodiment is a method of regulating the heat transfer into the batch material sufficient to maintain a core temperature of the extrudate within a target first temperature range. In one such embodiment, the core temperature of the extrudate is not less than 31° C. and not more than 37° C. In one embodiment, the heat transfer to the batch material is regulated so as to maintain a skin temperature of the extrudate to be within a second target temperature range. In one such embodiment, the skin temperature is not less than 27° C. and not more than 34° C. In another embodiment, the skin temperature is not less than 27° C. and not more than 35° C.
One embodiment is a method of regulating the amount of heat transferred to a batch material sufficient to cause the flow rate of the extrudate exiting a center portion of the die to be greater than a flow rate of the extrudate exiting the outer portion of the die. In one embodiment, this results in the formation of a substantially uniform extrudate face, resulting in less waste and extrudates of better quality. The use of this method may also obviate the need to add die mask to the face of the die plate to compensate for imperfections in the die plate that lead to unacceptable defects in the extrudate.
Still another embodiment is a method of regulating heat transfer to the batch material from the extruder barrel assembly sufficient to cause the flow rate of the extrudate exiting a center portion of the die to be lesser than the flow rate of the extrudate exiting an outer portion of the die. In one embodiment, this results in the formation of a substantially uniform extrudate face, resulting in less waste and extrudates of better quality. The use of this method may also obviate the need to add die mask to the face of the die plate to compensate for imperfections in the die plate that lead to unacceptable defects in the extrudate.
Yet another embodiment is a method of controlling the shape of a ceramic precursor extrudate, comprising the steps of forming an extrudate by extruding ceramic precursor batch material through a barrel of an extruder and through an extruder die disposed at the outlet of the extruder wherein the barrel temperature setpoint is an output of a master controller, and the batch material temperature and the batch material temperature setpoint are provided as inputs to the master controller. In one embodiment the setpoint is an output of a slave controller, and the barrel temperature setpoint and the measured barrel temperature provide inputs to the slave controller. In another embodiment the setpoint of a cooling flow rate, and/or valve position, is an output of a slave controller, and the barrel temperature setpoint and the measured barrel temperature provide inputs to the slave controller. In one embodiment, the batch material temperature setpoint is an output of a supervisory controller. The supervisory controller receives process inputs.
In still another embodiment, the process inputs comprise parameters such as the composition of the batch material, feedrate of the batch material, extrudate geometry, die characteristics and the like, or combinations thereof. In one embodiment, the supervisory controller provides the batch material temperature setpoint, master controller parameters, slave controller parameters, barrel weighting factors and the like, or combinations thereof.
In one aspect disclosed herein, the extruder is provided with a plurality of barrel coolant flows. In one embodiment, the batch material temperature is determined by measuring the temperature of a structure proximate to the die and within the extruder. The batch material temperature setpoint may be determined from measurements of a core temperature and a skin temperature of the extrudate.
In another aspect disclosed herein, a ceramic precursor extrudate control system comprises: an extruder comprised of a barrel of an extruder; an extruder die disposed at the outlet of the extruder; a barrel cooling device capable of providing a barrel coolant flow to the barrel; a batch material temperature sensor disposed within the extruder upstream of the die and capable of delivering a batch material temperature; a barrel temperature sensor capable of delivering a barrel temperature; a master controller capable of receiving the batch material temperature and the batch material temperature setpoint as inputs, and capable of delivering a barrel temperature setpoint; and a slave controller capable of receiving the barrel temperature setpoint and the measured barrel temperature as inputs, and capable of delivering a coolant flow setpoint. In one embodiment, the control system further includes a supervisory controller capable of delivering the batch material temperature setpoint to the master controller.
For most, if not all, ceramic precursor batch materials that can be extruded to form an extrudate there is an optimal core and skin temperature. Extrudates formed at or near the optimal temperature for a given batch formulation will generally have fewer imperfections than those formed at sub-optimal temperatures. Referring now to
Still another imperfection introduced into extrudates by forming them under substantially sub-optimum core and skin temperatures is the formation of extrudates with “C” fronts, a disproportional accumulation of material along the major axis of the contour plot (example not shown). Extrudates with either “A” or “C” front imperfection can be avoided by properly controlling the extrudate's core and skin temperatures. Accordingly, controlling the core and skin temperatures of a given ceramic precursor batch formulation below its gel point can have a significant effect on the shape of the extrudate.
Various aspects/embodiments relate to devices and methods for maintaining batch material temperatures within a specific operating window of extrudate skin and core temperatures that improve the shape of the extruded part. For example, when extruding certain batch materials such as some formulations of aluminum titanate (Al2TiO5), the core temperatures of the extrudate are ideally between about 31° C. and about 37° C. Extrudate skin temperatures are ideally between about 27° C., and about 34° C. may also be desirable. For some formulation of this material, this temperature produces high quality extrudates. In some instances, a skin to core temperature delta of 1° C. to 3° C. is desired in the extruded part.
The target batch material skin and core extrusion temperatures can be determined for a batch formulation by measuring the effect of batch material skin and core temperatures on viscosity (see, for example, one embodiment illustrated in
Still referring to
Some embodiments of the present disclosure include devices and methods for improving the shape of extruded parts using existing temperature controls on the extruder. We observed that barrel only temperature control is not always sufficient to control the temperature of batch materials inside of the extruder barrels. Barrel temperature control can only directly control that the temperature of the barrel itself, and batch temperature is controlled indirectly through the exchange of heat between barrel steel and batch materials extruded through those barrels. Due in part to the variation of properties of incoming batch materials, the heat exchange behaviors between barrels and batch materials can dynamically change. Factors influencing the temperature difference between barrels and batch materials include the efficiency of heat exchange, the residence time for batch materials staying contact with barrels, ambient temperatures, etc. Thus, controlling barrel temperature alone to constant setpoints cannot always maintain constant batch temperature for an extrusion process subject to various process disturbances, including variations coming from the properties of raw materials, hardware wear, batch compositions, ambient conditions, and the like.
Still another embodiment disclosed herein provides a new control system for controlling extrudate temperature, e.g., a dual loop system that adjust barrel cooling based on the batch material's temperature. These methods provide better control of batch extrusion temperatures at the die face and enable the formation of extrudates with more uniform shape.
One advantage of better batch material temperature control is that it may obviate the need to rework extruder dies to correct minor imperfections in the dies that can make for imperfect extrudates. Still another advantage of improved batch material temperature control is that it may obviate the need for masks, which are sometimes used to correct small defects in the die plate that otherwise introduce imperfects into the extruded objects. Currently, die masks are required for a wide range of shrinkage targets, with each shrinkage target requiring all compensation options. Masks are costly, and a mask may last only 24 hours or so before it wears out and must be replaced. In addition, die reworking and mask fitting increases extruder down time, reducing run efficiency. Proper selection and control of extrudate temperatures enables the utilization of some dies that include undesirable flow front characteristics, thereby eliminating costly reworking of the dies and/or the fabrication and fitting of correctional masks to the die face is avoided. Reducing or eliminating the need for corrective masks reduces the complexity and expense of producing high quality extruded objects such as honeycomb filter bodies.
Material temperature is a critical process variable, and its variation is directly related to the variation of batch rheology which determines the stability of extrusion process and the quality of extrudates. For example, methylcellulose is used in some ceramic precursor batch formulations as a temporary binder to aid in the extrusion process. The viscosity of a typical methylcellulose formulation as it is heated to its gel temperature changes. In order maintain the temperature of such formulation under its gel temperature and to control its viscosity and rheology, it is desirable to tightly control the batch material's core and skin temperatures. Accordingly, one aspect disclosed herein relates to a process control strategy for controlling material temperature in a ceramic extrusion process.
Referring now to
Referring now to
Referring now to
Still referring to
Referring now to
We also observed in our experiments and production runs that different materials and product types exhibit different system dynamics with respect to heating and cooling as well a extruder performance. Accordingly, it is difficult, if not impossible, to develop a universal set of control parameters, which will work for all conceivable process conditions. In some embodiments disclosed herein this is addressed by providing an extrusion supervisory controller, which can take into account various factors such as the job recipe, product type, material feed rate, die number, and other process setup parameters. Next, the supervisory controller can calculate a set of appropriate control parameters for the batch material temperature controller, barrel temperature controllers, and various weighting functions or factors. The system can be adjusted to accommodate these differences by, for example, adjusting the response of the inner control loop to changes in batch temperatures detected by the outer control loop. A diagram of an extrusion temperature supervisory control system is shown in
In some embodiments, the second viscosity state corresponds to a portion of the curve where slope is greater than 300 psi/° C.
In some embodiments, the core temperature of the batch material within the barrel upstream of the die is maintained in a core temperature range which overlaps at least in part with the second region of the pressure vs. temperature curve.
In some embodiments, the peripheral temperature of the batch material within the barrel upstream of the die is maintained in a peripheral temperature range which overlaps at least in part with the first region of the pressure vs. temperature curve.
In some embodiments, the peripheral temperature of the batch material within the barrel upstream of the die is maintained in a peripheral temperature range which overlaps at least in part with the second region of the pressure vs. temperature curve.
The ceramic precursor batch material can be a material which contains one or more ceramic materials, or which forms a ceramic material upon firing or sintering. For example, the ceramic precursor batch material can comprises one or more ceramic-containing-, or one or more ceramic-forming-, material, selected from the group consisting of cordierite, aluminum titanate, titania, mullite, spinel, alumina, silica, ceria, zirconia, zirconium phosphate, calcium aluminate, magnesium aluminate, sapphirine, perovskite, magnesia, spodumene, beta spodumene, silicon carbide, zirconium carbide, titanium carbide, tantalum carbide, tungsten carbide, aluminum nitride, silicon nitride, boron nitride, titanium nitride, zeolite, and combinations and composites thereof.
In some embodiments, the core temperature lower limit is between 25 and 35° C. In some embodiments, the core temperature upper limit is between 30 and 45° C.
In some embodiments, the difference (TC−TP) between the batch material core temperature (TC) and the batch material peripheral temperature (TP) is maintained at not less than −8 and not more than +16° C.
In some embodiments, the difference (TC−TP) between the batch material core temperature (TC) and the batch material peripheral temperature (TP) is maintained at not less than −4 and not more than +16° C.
In some embodiments, the difference (TC−TP) between the batch material core temperature (TC) and the batch material peripheral temperature (TP) is maintained at not less than 0 and not more than +16° C.
In some embodiments, the difference between the core temperature upper limit and the core temperature lower limit is between 4 and 8° C.
In some embodiments, the step of regulating the temperature of the batch material comprises regulating heat transfer between the extruder barrel and the batch material. In some embodiments, the step of regulating the temperature of the batch material further comprises regulating the heat transfer between an extruder screw and the batch material; in some of these embodiments, the batch material is heated via the extruder screw.
In some embodiments, the step of regulating the temperature of the batch material further comprises maintaining the batch material peripheral temperature between a peripheral temperature lower limit and a peripheral temperature upper limit. In some embodiments, the peripheral temperature upper limit is lower than the core temperature upper limit. In some embodiments, the peripheral temperature lower limit is lower than the core temperature lower limit. In some embodiments, the peripheral temperature upper limit is lower than the core temperature lower limit. In some embodiments, the peripheral temperature upper limit is higher than the core temperature lower limit. In some embodiments, the peripheral temperature lower limit is between 19 and 30° C. In some embodiments, the peripheral temperature upper limit is between 30 and 45° C. In some embodiments, the core temperature lower limit is between 20 and 35° C. In some embodiments, the core temperature upper limit is between 30 and 70° C. In some embodiments, the core temperature upper limit is between 30 and 45° C. In some embodiments, the peripheral temperature lower limit is between 20 and 30° C., the peripheral temperature upper limit is between 30 and 35° C., the core temperature lower limit is between 30 and 35° C., and the core temperature upper limit is between 35 and 40° C. In some embodiments, the difference between the peripheral temperature upper limit and the peripheral temperature lower limit is between 4 and 10° C. In some embodiments, the ceramic precursor batch material is a cordierite-forming batch material, and the difference between the core temperature upper limit and the core temperature lower limit is between 4 and 8° C., and the difference between the peripheral temperature upper limit and the peripheral temperature lower limit is between 4 and 10° C. In some embodiments, the ceramic precursor batch material is a aluminum titanate-forming batch material, and the difference between the core temperature upper limit and the core temperature lower limit is between 4 and 8° C., and the difference between the peripheral temperature upper limit and the peripheral temperature lower limit is between 4 and 10° C. In some embodiments, the batch material peripheral temperature is maintained at greater than or equal to 20° C. and less than or equal to 45° C., and the batch material core temperature is maintained at greater than or equal to 25° C. and less than or equal to 65° C. In some embodiments, the batch material peripheral temperature is maintained at greater than or equal to 27° C. and less than or equal to 35° C., and the batch material core temperature is maintained at greater than or equal to 25° C. and less than or equal to 65° C. In
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of these inventions provided that they come within the scope of the appended claims and their equivalents.
This application claims the benefit of priority to U.S. provisional application No. 61/110,367, filed on Oct. 31, 2008.
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| PCT/US2009/062727 | 10/30/2009 | WO | 00 | 9/12/2011 |
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| WO2010/051430 | 5/6/2010 | WO | A |
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