Abstract:
Apparatus and methodologies are provided for flash drying liquid materials using a variable die. A die and a die body are provided with an adjustably configured pressure regulating variable obstruction in the material flow path that allows control of the pressure applied to the material and consequent control of the temperature of the material as it enters the die. Optimizing pressure and temperature allows optimization of the flash drying process.

Description:
PRIORITY CLAIM 
   Applicant claims priority to an application filed in the United States Patent and Trademark Office on May 30, 2003, entitled “Adjustable Extruder Die”, with application Ser. No. 60-474445 and Reference No. P50-0108. 

   FIELD OF THE INVENTION 
   The present subject matter relates to synthetic elastomers and, more particularly, to methodologies and apparatus for drying, i.e., removing moisture, from such elastomers. 
   BACKGROUND OF THE INVENTION 
   Expeller-expander technology is a processing technique that has been available in various forms dating back to the nineteenth century. The present area of concern relates to that area of an elastomer processing sequence (including synthetic and natural elastomers) where the rubber material has been combined with water and now the water is to be removed. 
   In previously used configurations, two extruders in series have been employed to remove moisture from the rubber. Generally, the first extruder, also referred to as the expeller, squeezes the rubber between a pair of intermeshed screws. This portion of the process is generally able to reduce the moisture content from about 60% to about 15%. 
   Following the first stage of the drying process by the expeller, the rubber material is passed to a second extruder referred to as an expander for additional drying. This second extruder increases pressure on and consequently the temperature of the rubber, thus creating a super heated liquid. As this super heated liquid is forced through the extruder, again commonly by using screw drive technology, the material is forced through dies or filter screens at the end of the screw where the moisture, or volatile matter, will flash dry. 
   The flash drying process corresponds to a rapid change in state from liquid to vapor as the supper heated rubber material passes through the die or filter screen and suddenly returns to normal atmospheric pressure while the water temperature may still be significantly higher than 100 degrees Celsius. The energy necessary to produce the flash drying phenomena is transferred to the rubber from the screw drive mechanism in the expander. This transfer of energy is made possible by the resistance of the rubber to exit the expander through the dies. The temperature and pressure on the super heated rubber reach a maximum at the dies, thus for a given screw speed and rubber flow rate, the resistance, and therefore the amount of energy transferred to the rubber, is dependent on the pressure at the head. 
   The pressure is fixed by the pressure drop induced by the passage of the super heated rubber through the die. In a practical system, there will be a number of dies at the exit point of the expander and thus the pressure will depend on the number of dies, their geometry and aperture size. In previously employed configurations, all of these aspects of the dies were fixed with any one processing sequence. Because the prior art is a fixed and unchangeable configuration, certain production problems have occurred that the present technology addresses and overcomes. 
   When the super heated rubber goes through the dies, the flash drying process produces decohesion of the rubber thereby creating rubber crumbs that are transported to balers for further processing. The control of the size of these crumbs is one of the aspects effecting good transportation of the rubber through the remaining processing sequences and, consequently, can have an impact on further processing. For example, reduction of conveyor fouling can occur based on production of too small a crumb size. As the currently available technology employs preset die configurations, no capability other than stopping production is available to address issues involving pressure adjustment and crumb size. Moreover, there is no capability for optimizing the overall rubber processing process outside of controlling the expeller-expander screw speed without shutting down production. 
   While various implementations of extruder-expander technology have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology. 
   SUMMARY OF THE INVENTION 
   In view of the recognized features encountered in the prior art and addressed by the present subject matter, an improved methodology for drying synthetic elastomeric materials has been developed. The present technology, therefore, is directed to methodologies and apparatus that provide for the optimization of the pressure at the die or filter screen without the necessity of shutting down production. 
   In an exemplary embodiment of the present subject matter, apparatus and accompanying methodologies are provided for dynamically optimizing the overall operation of an extruder-expander system that does not require shutting down production to achieve optimized operation of the system. 
   In a further exemplary embodiment of the present subject matter, methodologies and apparatus are provide that allows crumb size adjustment during the production process without having to resort to expander shut down to alter the die set up. 
   In yet a further exemplary embodiment of the present subject matter, pressure at the die head as well as crumb size may be automatically controlled. 
   Additional objects and advantages of the present subject matter are set forth in, or will be apparent to, those of ordinary skill in the art from the detailed description herein. Also, it should be further appreciated that modifications and variations to the specifically illustrated, referred and discussed features and elements hereof may be practiced in various embodiments and uses of the invention without departing from the spirit and scope of the subject matter. Variations may include, but are not limited to, substitution of equivalent means, features, or steps for those illustrated, referenced, or discussed, and the functional, operational, or positional reversal of various parts, features, steps, or the like. 
   Still further, it is to be understood that different embodiments, as well as different presently preferred embodiments, of the present subject matter may include various combinations or configurations of presently disclosed features, steps, or elements, or their equivalents (including combinations of features, parts, or steps or configurations thereof not expressly shown in the figures or stated in the detailed description of such figures). Additional embodiments of the present subject matter, not necessarily expressed in the summarized section, may include and incorporate various combinations of aspects of features, components, or steps referenced in the summarized objects above, and/or other features, components, or steps as otherwise discussed in this application. Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the remainder of the specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
       FIG. 1  illustrates an expander head and shows a die head set up employing four separated die heads; 
       FIG. 2  illustrates a cross sectional view taken along line  2 - 2  of  FIG. 1  and showing a die head in accordance with the present subject matter; 
       FIG. 3  illustrates a second cross sectional view of the die head illustrated in  FIG. 2  and shows the adjustability aspect of the present subject matter; 
       FIG. 4  illustrates a cross sectional view of a die head in accordance with the present subject matter in an operational state; and 
       FIG. 5  illustrates and exploded view of a die head in accordance with the present subject matter. 
   

   Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference now to  FIG. 1 , there is illustrated an expander head  100  configured to house four separate die heads  110 . It should be appreciated that, although four die heads  110  are illustrated in the present configuration, such is exemplary only as the number of die heads may vary depending on processing requirements such as the specific type of synthetic elastomer being processed. Shown also is a relief valve port  120  and operating handle  122  that may be used to make sure the pressure in the expander has been relieved at those times when it becomes necessary to shut down the production line and/or service the expander head  100 . Control shaft  130  may be coupled to a control mechanism and is employed to dynamically adjust the die settings as will be more fully explained later. It should be appreciated that control shaft  130  and its accompanying control mechanism may be associated with automated control equipment, not illustrated, for automatically controlling the opening size of the variable die of the present subject matter in accordance with specific processing requirements as will be more fully explained later. 
     FIGS. 2 and 3  are both cross sectional illustrations taken along line  2 - 2  illustrated in  FIG. 1  of the variable die in accordance with the present exemplary embodiment.  FIGS. 2 and 3  illustrate, respectively, a relatively “closed” position and a relatively “open” position of the variable die. As seen from both  FIGS. 2 and 3 , the variable die of the present subject matter is constructed from three major portions: a die body  200 , an adjustment sleeve  220 , and a filter screen  240 . Die body  200  may be secured to the extruder head  100  by means of threaded portion  202  cooperating with a matching threaded coupling means, not shown, on the extruder head. An aspect of die body  200  of particular significance to the present subject matter resides in the provision of a beveled or conical surface  204  that, together with conical surface  244  of filter screen  240  forms a pressure adjusting system as will be more fully explained later. With further reference to  FIGS. 2 and 3 , it will be noted that die body  200  is fitted with an additional threaded portion  206 , the threads of which are configured to mate with threaded portion  226  of adjustment sleeve  220 . 
   Adjustment sleeve  220 , as shown, is configured to overlie and threadedly engage die body  200  in a pressure sealed manner. Improved sealing capability is supplied through the use of O-ring seal  208  positioned between an outer lateral end portion  210  of die body  200  and an inner surface  230  of adjustment sleeve  220 . Adjustment sleeve  220  is expanded at one end portion  232  thereof and internally threaded with threads  234  that cooperate with matching threads  246  on the outer periphery of filter screen  240 . 
   Filter screen  240 , as mentioned, has outer periphery threads  246  that cooperate with threads  234  of the adjustment sleeve  220  in such manner as to hold filter screen  240  securely in place by tightly seating the threaded filter screen  240  into the threaded expanded portion  232  of the adjustment sleeve  220 . Filter screen  240  is perforated with a plurality of uniformly spaced flash channels  250 , as best seen in  FIGS. 1 and 5 . As with the previously noted exemplary illustration of four die heads  110  illustrated in  FIG. 1  as mounted in the extruder head  100 , the exact number of flash channels  250  provided in each die head  110  will vary depending on specific requirement relating to the particular type of material being processed. 
   Acting as, inter alia, a distributor to the plurality of flash channels  250  of the material being processed is another significant feature of the present subject matter seen in the form of turbulence channel  268 . By design, turbulence channel  268  is configured within the filter screen  240  in such manner as to provide at least a minimum volume regardless of the relative position of the adjustment sleeve  220  with respect to the die body  200 . Turbulence chamber  268  is where a first flash drying and decohesion of the processed synthetic elastomer takes place. As the material being processed passes through the pressure control system created by the adjustable space between conical surface  204  of the die body  200  and conical surface  244  of the filter screen  240 , a reduction in pressure occurs allowing the material being processed to break apart and form crumbs due to the rapid vaporization of a portion of the moisture trapped within the material. 
   A second flash drying of the material being processed occurs as the material passes from the turbulence chamber  268  through the plurality of flash channels  250 . Upon passage of the still super heated material through flash channels  250  and sudden exposure to atmospheric pressure, substantially all of the remaining moisture in the material being processed instantly enters a vaporous state. 
   As previously mentioned, the energy necessary to produce the flash drying effect is transferred to the material being processed from a screw drive in the expander. This energy is made possible, in part, by the resistance of the material to exit the expander through the die. This resistance is controlled in large measure in the present subject matter by the controlled spacing between conical surfaces  204  and  244 . 
   With further reference, in particular, to  FIG. 3 , it will be noted that there is illustrated an arrow “A” indicating rotation of the adjustment sleeve  220  relative to the die body  200 . Rotation of the adjustment sleeve  220  in the direction of arrow “A” produces movement of the adjustment sleeve and, consequently, movement of the attached filter screen  240 , in the direction of arrow “B.” That is rotation in the direction of the arrow “A” “opens” the space between the conical surfaces  204 ,  244 . Conversely, of course, rotation in a direction opposite to arrow “A” “closes” the space between the conical surfaces  204 ,  244 . In an exemplary configuration, the threads  206  of the die body and threads  226  of the adjusting sleeve may be configured such that a total of five (5) complete revolutions of adjustment sleeve  220  will move the filter screen  240  from a substantially closed, i.e. zero setting, position to an effectively fully open, i.e. 100%, position. During normal operation of the variable die of the present subject matter, given the “zero” and “100% open” definitions just mentioned, a normal operation range might comprise between 5% open and 95% open. 
   Rotation of the adjustment sleeve  220  may be effectively implemented by way of ring gear  260 , most clearly seen in the exploded view of die head  110  illustrated in  FIG. 5 . Ring gear  260  is configured to cooperate with additional gearing, not shown, internal to expander head  100  that acts in concert with shaft  130  to simultaneously adjust all of the die heads  110  associated with expander head  100 . As previously noted, such adjustment of the die heads  110  may be controlled by way of automated means which, although not illustrated, will be well understood by those of ordinary skill in the art to which the present subject matter pertains. 
   An important aspect of this opening and closing of the space between conical surfaces  204  and  244  is that a new mechanism has been provided permitting real time adjustment of the pressure applied to and the temperature generated in the material being processed. Prior to the teachings of the present subject matter, such control was obtainable only by stopping the production line and manually modifying the die setup. Clearly such prior modification technique was detrimental to efficient operation of the extruder-expander system. A yet more significant improvement in the operation of extruder-expander systems is possible as those of ordinary skill in the art grow to appreciate that the adjustment of the space between conical surfaces  204 ,  244  and thus the pressure and temperature of the process material, can be controlled automatically through microcontroller, computer, microprocessor or other automated processing devices. 
   Referring briefly to  FIG. 4 , there is illustrated an operational embodiment of the present invention. As shown, material  300  to be processed and containing significant amounts of moisture, is forced through die head  110  in the direction of arrow “C” by a transport mechanism, not shown, but which may include a screw conveyor device. The amount of energy necessary to force the material  300  through the die head  110  is determined, in part, by the pressure adjusting spacing between conical surfaces  204 ,  244 . As the material enters the pressure adjusting space and flows into turbulence chamber  268 , a portion of the contained moisture is released from the material  300  due to the pressure drop as the material  300  enters the turbulence chamber  268 . The pressure drop within turbulence chamber  268  and the subsequent release of moisture produces decohesion of the material  300  creating a crumbled form of the material  300 . Finally, as the now crumbled material passes through flash channels  250 , additional moisture is removed from the crumbled material as the pressure on the material is suddenly reduced to atmospheric pressure and substantially all of the remaining moisture turns to vapor. 
   While the present subject matter has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. For example, while the present invention has been described in use with drying mixtures containing elastomeric particles, the present invention is not so limited. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art using the teachings disclosed herein.