Abstract:
Systems and methods compress, freeze and store forms at sufficiently low temperatures. A system provides a storage tank of liquefied gas, a gas-liquid separation tank, and a compression chamber. The compression chamber provides compression plates chilled by flow of liquefied gas through conduits traversing an interior volume of the plates. The method comprises recirculating liquefied gas to improve cooling efficiency while lowering operation costs. The system and method further provide for integrated measurement and control of the flow of liquefied gas through the primary components of the system. In one embodiment, the forms are rubber cylinders utilized in the production of torsion axles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) to provisional application No. 60/813,940, filed Jun. 15, 2006, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Molded rubber products are required for a variety of industrial uses. For certain applications, the rubber must be highly compressed during intermediate stages of production. In order to maintain the rubber in a highly compressed form during such intermediate stages, the rubber may be held at cryogenic temperatures. In subsequent stages of production, the rubber expands as it returns to ambient temperatures. 
     Liquefied gases, such as liquid nitrogen, may be used to achieve the cryogenic temperatures required to maintain rubber in a highly compressed form. However, rubber tends to absorb liquid nitrogen upon direct contact, thereby becoming brittle and susceptible to fracturing. Existing methods for chilling highly compressed rubber forms therefore apply liquid nitrogen to the external surfaces of compression plates. The rubber is then conductively chilled by the interior surfaces of the compression plates. For example, a manifold of nozzles may spray liquid nitrogen onto the external surface of a compression plate. As the stream of liquid nitrogen flows towards the external surface, a significant portion of the stream vaporizes, thereby reducing the cooling efficiency and increasing the cost of operation of the system due to the consumption of nitrogen. Another significant portion of the stream is directed away from the surface of the plate, also reducing the cooling efficiency of the stream. Finally, once compressed and chilled, the rubber must be stored at the extremely low temperatures pending subsequent production steps, thereby requiring additional cryogenic systems. 
     Therefore, what is required is a mechanism and process for more efficiently compressing, chilling, and storing rubber or elastomer forms at extremely low temperatures. 
     SUMMARY 
     Embodiments of the present invention relate to devices and methods for compressing, freezing and storing rubber or other elastomer forms at sufficiently low temperatures. One embodiment provides a recirculation system for a liquefied gas, such as nitrogen, helium, or carbon dioxide and/or a secondary refrigerant, such as d-limonene. The system includes a first compression body of a compression chamber, wherein a fluid passageway traverses an interior volume of the first compression body between an inlet and an outlet of the fluid passageway, and a second compression body of the compression chamber, wherein the first and second compression bodies have corresponding mating faces that are moveable relative to one another and define an interface between which elastomeric forms are compressible. The system further includes a first source of refrigeration liquid fluidly coupled to the inlet of the fluid passageway via a supply line and coupled to the outlet of the fluid passageway via a return line. 
     In one embodiment, a method provides for compressing and freezing rubber forms. The method includes circulating a liquefied gas through a circulation loop by flowing the liquefied gas from a source of the liquefied gas to an inlet of a compression chamber, flowing the liquefied gas through the compression chamber, whereby the compression chamber is cooled, removing the liquefied gas from an outlet of the compression chamber, and flowing the removed liquefied gas back to the source. The method further includes compressing an elastomeric form within an interface of the compression chamber, and maintaining compression of the elastomeric form for a time period sufficient to freeze the elastomeric form in a compressed state, wherein the circulating is preformed during at least a portion of the compressing and maintaining steps. 
     For one embodiment, a method provides utilization of compressed and frozen rubber forms in the assemblage of a torsion axle. The method includes chilling a first compression plate and a second compression plate with a liquefied gas, wherein the liquefied gas flows through a plurality of conduits traversing respective interior volumes of each of the first and second compression plates, compressing a plurality of elastomeric forms between the first and second compression plates, maintaining compression of the elastomeric forms for a time period sufficient to freeze the elastomeric forms in a compressed state, storing the elastomeric forms in the compressed state in a storage chamber, maintaining the temperature of the storage chamber to a specified storage temperature range, inserting one or more of the elastomeric forms in the compressed state between a torsion axle housing and a torsion axle shaft, and expanding the elastomeric forms inserted upon warming of the elastomeric forms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein: 
         FIG. 1  illustrates the primary components of an exemplary recirculation system; 
         FIGS. 2A and 2B  illustrate an exemplary compression chamber; 
         FIGS. 3A and 3B  illustrate two possible alternative embodiments for compression plates; 
         FIGS. 4A and 4B  illustrate an exemplary torsion axle assembly; and 
         FIG. 5  diagrams the steps involved in the assemblage of torsion axles utilizing the recirculation system. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the invention provide devices and methods for compressing, freezing, and storing articles of manufacture (e.g., rubber forms) at very low temperatures. Such embodiments recirculate liquefied gas to improve cooling efficiency while lowering operation costs. 
       FIG. 1  illustrates one embodiment of an exemplary liquefied gas recirculation system  100 . As depicted, the recirculation system provides a circuit for the flow of liquefied gas, whereby liquefied gas may be provided from a source, to a point of use and then recirculated back to the source. It should be appreciated that the recirculation system  100  may include any number of inlets and outlets, e.g., to provide improved performance. It should also be appreciated that a secondary refrigerant, such as d-limonene, could be used in place of or in conjunction with (either mixed with or isolated from) the recirculated liquefied gas. The secondary refrigerant may be mechanically or cryogenically chilled and may include any liquid that is capable of being chilled to below 100° C., for example. For improved cooling efficiency, any or all of the components of the liquefied gas recirculation system  100  may be insulated from external temperatures, such as through the use of vacuum jackets or urethane coatings. 
     In one embodiment of the invention, a storage tank  110  may provide a reservoir of liquefied gas. It should be appreciated by those skilled in the art that any one of a number of liquefied gases could be selected, including gases such as nitrogen, helium, or carbon dioxide, depending on the target temperature requirements. For the purposes of illustration and without limitation, in this example, nitrogen is utilized as the recirculated liquefied gas. The rate of flow of a first liquid nitrogen stream  116  from the storage tank  110  may be controlled by a first flow control valve  115 . The first liquid nitrogen stream  116  may be introduced into a gas-liquid separation tank  120 . The amount of liquid nitrogen contained in the gas-liquid separation tank  120  may be measured by a load cell or other liquid content measurement device  121 . In one embodiment, the first flow control valve  115  and the liquid content measurement device  121  may communicate with a control device  160  to provide integrated measurement and control of the amount of liquid nitrogen introduced into the gas-liquid separation tank  120 . 
     The gas-liquid separation tank  120  may serve as a reservoir of nitrogen vapor for a cryogenic storage unit  130 . The rate of flow of a nitrogen vapor stream  126  may be controlled by a second flow control valve  125 . The temperature of the cryogenic storage unit  130  may be measured by a first temperature measurement device  131 . In one embodiment, the second flow control valve  125  and the first temperature measurement device  131  may communicate with the control device  160  to provide integrated measurement and control of the amount of nitrogen vapor introduced into the cryogenic storage unit  130 . In one embodiment, the temperature of the cryogenic storage unit  130  may be maintained at an identified temperature and pressure to retain contents within the storage unit  130  in a state of compression as introduced into the storage unit  130 , for example, at about −250° C. or about −100° C. to about −300° C. 
     The gas-liquid separation tank  120  may also serve as a recirculation reservoir for a compression chamber  150 . A second liquid nitrogen stream  141  may be drawn from the gas-liquid separation tank  120  by a pump  140 . The second liquid nitrogen stream  141  may then traverse first and second compression plates  151 ,  152 , thereby providing cryogenic convective-conductive cooling of the plates  151 ,  152 . A resultant liquid nitrogen/nitrogen vapor stream  156  may be returned to the gas-liquid separation tank  120 . The rate of flow of the liquid nitrogen/nitrogen vapor stream  156  exiting the compression chamber  150  may be controlled by a third flow control valve  155 . The temperature of the compression chamber  150  may be monitored by a second temperature measurement device  170 . In one embodiment, the pump  140 , the third flow control valve  155 , and the second temperature measurement device  170 , may communicate with the control device  160  to provide integrated measurement and control of the residence time of nitrogen in the compression plates  151 ,  152 , thereby controlling the temperature of the compression chamber  150 . It should be appreciated that the locations of the pump  140  and the third flow control valve  155  are interchangeable. Although  FIG. 1  shows the second temperature measurement device  170  directly connected to the second compression plate  152 , it should be appreciated that a variety of other configurations would provide appropriate measurements of the temperature of the compression chamber  150 . In one embodiment, the temperature of the compression chamber  150  may be maintained within a range of −260° C. to −250° C. 
     Although the streams  116 ,  126 ,  141 ,  156  are illustrated as individual streams, it should be understood that portions of each stream may be removed for other purposes not shown in  FIG. 1 . For some embodiments, the cryogenic storage unit  130  may be omitted such that the nitrogen vapor stream  126  may be vented or liquefied by cooling and compressing prior to returning to the storage tank  110 . At least the liquid nitrogen streams  116 ,  141 , the liquid nitrogen/nitrogen vapor stream  156  and passage through the compression chamber  150 , may together define a sealed or closed environment preventing loss of nitrogen. 
     In one embodiment, the control device  160  continuously communicates with the flow control valves  115 ,  125 ,  155 , the liquid content measurement device  121 , the temperature measurement devices  131 ,  170 , and the pump  140  to provide integrated measurement and control of all aspects of the liquefied gas recirculation system  100 . In an alternative embodiment, the control device  160  communicates sequentially with the various components as necessitated by the production process. 
       FIG. 2A  illustrates one example of the compression chamber  150 . The second liquid nitrogen stream  141  may enter the compression chamber  150  through flexible first and second input tubing  210 ,  212 , which may be connected respectively to the first and second compression plates  151 ,  152  via first and second input manifolds  211 ,  213 , respectively. The second liquid nitrogen stream  141  may be divided into a plurality of streams by the input manifolds  211 ,  213  for respective introduction into first and second plurality of inlet holes  220 ,  221 . Liquid nitrogen may flow through the first and second plurality of inlet holes  220 ,  221  into respective first and second plurality of conduit passageways  230 ,  231 , which may traverse the volume of the compression plates  151 ,  152 . Although  FIG. 2A  illustrates straight conduit passageways  230 ,  231 , it should be appreciated that the conduit passageways  230 ,  231  could follow curved trajectories to provide for longer path length, thereby greater residence time for any given flow rate. An example of a possible curved trajectory conduit path  232  is illustrated in  FIG. 2B . It should also be appreciated that while bore diameters may be constant across the length of the conduit passageways  230 ,  231 , the bore diameters may also vary across the length of the conduit passageways  230 ,  231  to permit flow concentration at certain locations. A mixture of liquid nitrogen and nitrogen vapor may exit the conduit passageways  230 ,  231  through respective first and second plurality of outlet holes  240 ,  241 . First and second output manifolds  250 ,  252  facilitate coalescing of exiting streams into the liquid nitrogen/nitrogen vapor stream  156 , which flows out of the compression chamber  150  through flexible first and second output tubing  251 ,  253  coupled respectively to the first and second output manifolds  250 ,  252 . 
     In one embodiment, elastomeric forms (e.g., rubber forms) may be inserted between the compression plates  151 ,  152 . Pressure may be applied to the compression plates  151 ,  152  by a pressure source  280 . This application of pressure may cause the elastomeric forms to be compressed against first and second contact surfaces  261 ,  262  of respectively the first and second compression plates  151 ,  152 . Although  FIG. 2A  illustrates the pressure source  280  working directly on the second compression plate  152 , it should be appreciated that pressure could be applied to either or both of the compression plates  151 ,  152 . In one embodiment, the aggregate pressure applied to the elastomeric forms at the contact surfaces  261 ,  262  may be in the range of 600 kPa to 60,000 kPa. 
     Although  FIG. 2A  illustrates the first input manifold  211 , for example, as a single (unitary) structure, it should be appreciated that each of the first plurality of inlet holes  220  may be individually connected to flexible first input tubing  210  via a connection substructure of a manifold assembly. The individual connections may be CGA-295 cryogenic fittings, dissimilar metal bayonet connections or other cryogenic fittings commonly known in the art. Additionally, it should be appreciated that the tubing  210 ,  212 ,  251 ,  253  may be constructed from a variety of cryogenic hoses known in the art, including both flexible and fixed transfer hoses. 
     Although  FIG. 2A  illustrates each of the first plurality of inlet holes  220 , for example, breaching the perimeter of the first compression plate  151  from only one side, it should be appreciated that the first plurality of inlet holes  220  may exist on multiple sides of the first compression plate  151 . For example, in one embodiment, gas flows in opposite directions in adjacent ones of the first plurality of conduit passageways  230 , necessitating alternating the first plurality of inlet holes  220  and first plurality of outlet holes  240  on one side of the first compression plate  151 . One skilled in the art will appreciate that the temperature at specified points on the first contact surface  261  of the first compression plate  151  can be more precisely controlled by customizing the configuration of the first plurality of conduit passageways  230  and the direction of gas flow through each of the first plurality of conduit passageways  230 . Similar variations may occur in configuration and flow direction for the second plurality of conduit passageways  231  within the second compression plate  152 . 
       FIG. 3  illustrates two possible alternative embodiments for the first compression plate  151 . It should be appreciated that similar alternatives may apply to second compression plate  152 . In one embodiment, a width W of the first compression plate  151  may be about three feet. A length L of the first compression plate  151  may be about four feet, for one embodiment. The width W and the length L may vary to accommodate rubber forms of various shapes and sizes. Similarly, the first compression plate  151  may take any variety of shapes, such as the shape of an ellipse or polygon, to better accommodate production requirements. The first compression plate  151  may be made of a heat-conductive material, such as aluminum, carbon steel, or stainless steel. 
       FIG. 3A  illustrates one embodiment, wherein the first contact surface  261  of the first compression plate  151  may be a flat surface  360 .  FIG. 3B  illustrates an alternative embodiment, wherein the first contact surface  261  of the first compression plate  151  may be a grooved surface  365  to accommodate the elastomeric forms and define the shape into which the elastomeric forms are compressed. It should be appreciated that the surface structure of the first contact surface  261  may be varied to accommodate elastomeric forms of various shapes and sizes. In one embodiment, the first contact surface  261  may be removable so that interchangeable contact surface molds may be attached to the first compression plate  151  to achieve the appropriate contact surface structure. 
     Although  FIG. 3B  illustrates a one-to-one correspondence between the first plurality of inlet holes  220  and the recesses of the grooved surface  365 , it should be appreciated that a variety of configuration alternatives exist. For example, in one embodiment, each recess may be flanked by a pair of the first plurality of conduit passageways  230 , with gas flowing in opposite directions in the two conduit paths. In another embodiment, for N recesses, there may be N+1 conduit paths, wherein a single one of the first plurality of conduit passageways  230  runs between each recess and along the lateral sides of recesses 1 and N. 
       FIG. 4  illustrates an exemplary torsion axle assembly. The recirculation system  100  may be used to compress and freeze rubber rods as an intermediate step in the production of torsion axle  400 . In one embodiment, rubber rods may be compressed and frozen in the shape of half-cylinders  430 . While still frozen, the half-cylinders  430  may be inserted between an axle housing  410  and an axle shaft  420 . With thermalization, the rubber rods may expand into full cylinders  431 , thereby providing shock protection for the torsion axel  400 . It should be appreciated that torsion axles may be constructed from square tubing, as illustrated, or from triangular, hexagonal, or other polygonal shaped tubing. 
       FIG. 5  diagrams the steps involved in the production of torsion axles utilizing the recirculation system  100 . The recirculation system  100  may be initially prepared in preliminary step  510  by flowing liquid nitrogen through the compression plates  151 ,  152  until they reach a specified target temperature. In one embodiment, the target temperature may be −260° C. Although  FIG. 5  illustrates the flow of liquid nitrogen through the compression plates  151 ,  152  as a discrete step, it should be appreciated that the control device  160  may be active throughout the production process to control the flow of gas to each of the components of the recirculation system  100 . 
     In insertion step  520 , rubber rods—previously formed in manufacturing step  560 —may be inserted between the compression plates  151 , 152 . In one embodiment, the diameter of the rubber rods may be between about one-quarter to one inch. If the first contact surface  261  of the first compression plate  151  is grooved, the rubber rods may be inserted into the recesses. 
     The pressure source  280  may act on the second compression plate  152  in compressing step  530  to compress the rubber rods between the contact surfaces  261 ,  262 . In one embodiment, pressure may be applied for up to about five seconds. While being compressed, the rubber rods may freeze to a temperature of about −260° C. to −250° C. due to conductive contact with the contact surfaces  261 ,  262 . 
     At transfer step  540 , the compressed and frozen rubber rods may be transferred from compression the chamber  150  to the cryogenic storage unit  130 . The compressed and frozen rubber rods may be stored pending other processing steps, such as formation of an axle housing and axel shaft in fabrication step  570 . The cryogenic storage unit  130  may thus only temporarily maintain the rods chilled such as may be required during transfer to an assembly location where the rods are utilized. In one embodiment, about twenty to thirty compressed and frozen rubber rods may be stored for up to about four hours. When the control device  160  does not act continuously throughout the production process, control step  550  may provide for reset of the recirculation system  100  to prepare for processing of subsequent sets of rubber rods. Finally, in assembly and warming steps  580 ,  590 , the torsion axle  400  may be assembled by inserting the axle shaft  420  in the axle housing  410  and disposing the rubber rods, while still the half-cylinders  430 , about the axle shaft  420  and within the axel housing  410 , as illustrated in  FIGS. 4A and 4B . 
     It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above and/or the attached drawings.