Abstract:
The present application relates generally rheometers. In one aspect, misalignment of the air cylinder with respect to the cross-head is accommodated using a flexible coupling between the air cylinder and the cross-head so as to prevent binding and stuttering of the machine due to misalignment.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Aspects herein generally relate to rheometer systems for testing polymers, and more particularly to a decoupled cross-head incorporated into a rheometer system. 
         [0003]    2. Discussion of Related Art 
         [0004]    Polymers are often tested according to one of several ASTM methods, namely, ASTM D1646, D2084, D5289, and D6204. Instruments operating in accordance with ASTM D2084 and D5289 are known. For example, U.S. Pat. No. 3,681,980 illustrates the application of a fixed eccentric cam to facilitate oscillation of a rotor. This amplitude of oscillation is determined by the position of the pin on the eccentric. U.S. Pat. No. 4,794,788 also illustrates the use of an eccentric to facilitate an oscillatory motion. The amplitude of oscillation can be changed between tests by changing the position of the pin on the eccentric or by changing the eccentric to one with a different off-set. 
         [0005]    ASTM D6204 describes the use of a variable frequency test, and also discloses the capability of performing a variable temperature test. ASTM D6601 describes the conditions for evaluating a specimen at more than one strain amplitude during a single test. This test may be used with the apparatus described in U.S. Pat. No. 4,794,788, U.S. Pat. No. 5,079,956 or U.S. Pat. No. 6,681,617. 
         [0006]    Many of the apparatus described in these patents and used in the foregoing ASTM test methods are referred to as moving die rheometers. In typical moving die rheometers, two opposing co-axial dies compress a test specimen between them. One die is driven in an oscillatory manner, while the opposite die is free to rotate independently of the first die. A flex arm is connected to the one die, and this flex arm is driven back and forth to create the oscillatory movement of the one die. In these existing systems, a drive system may comprise an eccentric attached to the output of a motor. The eccentric is connected to a link arm which is further connected to a flex arm. The amplitude of movement of the one die is determined by the distance between the axis of rotation of the eccentric and the post of the eccentric. 
         [0007]    In other rheometer systems, the drive shaft of the motor may be directly coupled to the one die without the use of any link arms. The desired oscillatory motion is produced by the motor. 
         [0008]    Both types of rheometers may employ a moving cross-head driven by an air cylinder to urge the opposite die toward the one die to compress a test specimen between the two dies. In existing systems, the cylinder shaft is rigidly coupled to the cross-head. In such systems, the system frequently stutters or binds up, causing problems. Also, alignment of the two opposing coaxial dies is sometimes difficult to maintain. 
       SUMMARY OF INVENTION 
       [0009]    One aspect of the invention relates to a rheometer system that includes one or more posts extending between two plates, a cross-head mounted on the posts, a drive apparatus which moves the cross-head upwardly and downwardly along the posts, an upper die disposed on the cross-head, a lower die disposed in spaced relation to the upper die, the upper and lower dies being configured to capture a test sample therebetween, and apparatus for coupling the drive apparatus to the cross-head to accommodate misalignment between the drive apparatus and the posts upon which the cross-head moves and to permit alignment of the upper die with the lower die. The coupling apparatus includes a connector having a shaft coupled to the drive apparatus, and a head enlarged with respect to the shaft, the head having a curved surface. The coupling apparatus also includes a flange disposed on the cross-head, in which the curved surface of the head bears against a surface on the flange, and a retainer having a lip overlying the head of the connector to limit upward movement of the head with respect to the surface of the flange, the lip of the retainer being spaced sufficiently from the connector to permit tilting movement of the connector with respect to the cross-head while still retaining the connector within the retainer as the cross-head moves upwardly and downwardly. In another embodiment of this aspect, the head of the connector resides in a recess on the flange. In another embodiment of this aspect, the head of the connector is spaced from inner surfaces of the recess on the flange. In yet another embodiment of this aspect, the drive apparatus is an air cylinder. In another embodiment of this aspect, the connector is a bolt. 
         [0010]    Another aspect of this invention relates to a method in which the rheometer system has a cross-head that is mounted on posts and travels along the posts in a direction of elongation of the posts, a drive apparatus for moving the cross-head and a shaft that connects the drive apparatus to the cross-head. The method accommodates misalignment of the drive apparatus with respect to the posts and includes permitting the shaft connecting the cross-head to the driver apparatus to float with respect to the cross-head at an end of the shaft coupled to the cross-head. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly-identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Various embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a front schematic view of one rheometer in accordance with one aspect of the invention; 
           [0013]      FIG. 2  is a front schematic view of another rheometer in accordance with another aspect of the invention; and 
           [0014]      FIG. 3  is a partial, cross-sectional view of the decoupled cross-head taken along the line  3 - 3  of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    This invention relates to an improved rheometer system for testing polymers. In one aspect an air cylinder is decoupled from the cross-head so that the cylinder can float relative to the cross-head. 
         [0016]    With reference now to the drawings, and more particularly to  FIG. 1  thereof, an embodiment of a moving die rheometer (MDR) will now be described. MDR  100  typically includes a main plate  102  and posts  104  and  106  mounted to and extending upwardly from main plate  102 . A cross-head  108  rides upwardly and downwardly along one or more posts  104  and  106  on bearings  110 . A cylinder mounting plate  112  sits on top of posts  104  and  106 . Mounted on top of cylinder mounting plate  112  is an air or gas cylinder  114 . Instead of an air cylinder, any other known drive apparatus could be used, such as an electric or gasoline motor, or a hydraulic system which is capable of moving cross-head  108  along posts  104  and  106 . A shaft  116  extends downwardly from air cylinder  114  through cylinder mounting plate  112 . Shaft  116  is mounted to cross-head  108  by a coupling system  150 , which will be more fully described below, so as to allow air cylinder  114  to drive cross-head  108  upwardly and downwardly along posts  104  and  106 . Suspended from cross-head  108  is an upper housing  118  which includes a torque transducer  120 . Disposed on a lower end of upper housing  118  is an upper die  74 . 
         [0017]    Mounted onto main plate  102  is a lower housing  122 , and disposed below lower housing  122  and mounted to main plate  102  is a central stack housing  70 . Disposed on the upper end of lower housing  122  is lower sample die  72 . Mounted on main plate  102  and disposed adjacent central stack housing  70  is a drive motor  12  which is coupled to an eccentric cam  20 . Typically, eccentric cam  20  is a fixed eccentric cam, although cam  20  could also be a variable eccentric cam. Drive motor  12  rotates a drive shaft  14 . Motor  12  is attached to motor mount  13 . Drive shaft  14  is rigidly affixed to eccentric cam  20  so that rotation of drive shaft  14  is directly transferred to eccentric cam  20 . Eccentric cam  20  has a central axis of rotation  17  passing through the center thereof, and through the center of drive shaft  14 . A die shaft  76  passes through the center of central stack housing  70  and is rigidly affixed to sample die  72 . Die shaft  76  in turn is coupled to eccentric cam  20 , by link assembly  80 . Link assembly  80  is coupled to post  40  on cam  20  at a distance X spaced from axis  17 . The connection of link assembly  80  to post  40  causes the link assembly  80  to rotate about an axis  19  to produce the desired eccentric motion. Rotation of drive shaft  14  by motor  12  causes rotation of eccentric cam  20 , which causes link assembly  80  to move in an oscillatory motion, which motion is then transferred by link assembly  80  through die shaft  76  to lower sample die  72 . The amount of the oscillatory motion is referred to as the strain angle and is a function of distance X. 
         [0018]    During testing of a polymer specimen  90 , specimen  90  is positioned on lower sample die. When air cylinder  114  is activated, cylinder shaft  116  drives cross-head  108  downwardly to urge upper die  74  against the polymer specimen  90  and to capture and compress specimen  90  between lower die  72  and upper die  74 . Oscillatory motion is then produced on lower die  72 . During testing, heat may be applied to the specimen  90  in a conventional manner. Torque transducer  120  measures the reaction torque that is the result of the resistance of the polymer specimen  90  to the oscillatory motion. A test method that may be used with MDR  100 , is described by ASTM D5289. When employing MDR  100 , a measurement would first be made at one amplitude of oscillation, and after a change in the amplitude of oscillation, another measurement would be made, and so forth. 
         [0019]    Another embodiment of a rheometer with which the decoupled cross-head of this invention may be used will now be described with particular reference to  FIG. 2 . Rheometer  200  is commonly known as a dynamic mechanical rheological tester or DMRT which is designed to test raw elastomers or mixed rubber. Rheometer  200  is similar in many aspects to MDR  100 , and where possible, like numbers will be used for like parts for simplicity and ease of understanding Like MDR  100 , rheometer  200  typically includes a main plate  102 , and posts  104  and  106  mounted to and extending upwardly from main plate  102 . A cross-head  108  rides upwardly and downwardly along posts  104  and  106  on bearings  110 . A cylinder mounting plate  112  may sit on top of post  104  and  106 . Mounted on top of the cylinder mounting plate is an air cylinder  114 . A cylinder shaft  116  extends downwardly from air cylinder  114  through cylinder mounting plate  112 . Cylinder shaft  116  is mounted to cross-head  108  by a coupling system  150 , which will be more fully described below with respect to  FIG. 3 . Cylinder shaft  116  allows air cylinder  114  to drive cross-head  108  upwardly and downwardly along posts  104  and  106 . Suspended from cross-head  108  is an upper housing  118  which includes a torque transducer  120 . Disposed on a lower end of upper housing  118  is an upper die  74 . Mounted onto main plate  102  is a lower housing  122 , and disposed in the upper part of lower housing  122  is a lower sample die  72  that faces upper die  74 . 
         [0020]    Disposed below main plate  102  is a direct drive stepper motor  212 , from which a drive shaft  214  extends. Shaft  214  is coupled to a lower die shaft  276  by coupling  215 . Die shaft  276  passes through main plate  102  and is rigidly affixed to lower sample die  72 . Die shaft  276  is rotated by stepper motor  212 . An encoder  226  and encoder disk  227  determine the speed of rotation of die shaft  276 , as well as the position of die shaft  276 . Encoder  226  and encoder disk  227  may be any known encoder. Die shaft  276  in turn causes movement or oscillation of lower sample die  72 . 
         [0021]    Testing of a specimen  90  is similar to the testing of polymer specimen  90  that is described with respect to  FIG. 1 . Specimen  90  is positioned on lower sample die  72 . Air cylinder  114  is then activated to cause cylinder shaft  116  to drive cross-head  108  and upper housing  118  downwardly to urge upper die  74  against specimen  90  to capture and compress specimen  90  between lower sample die  72  and upper die  74 . The desired oscillatory motion is then produced on lower die  72  by stepper motor  212 . During testing, heat may be applied to the specimen  90  in a conventional manner. Torque transducer  120  measures the reaction torque that is a result of the resistance of the specimen  90  to the oscillatory motion. Test methods that may be used in conjunction with rheometer  200  include ASTM D5289, ASTM D6204, and ASTM D7605. 
         [0022]    Both MDR  100 , and rheometer  200  may include the same coupling system  150 , which will now be described in another aspect of the invention with particular reference to  FIG. 3 . The description of coupling system  150  in  FIG. 3  applies to both MDR  100  and rheometer  200 . This same coupling system  150  also could be used with other rheometer systems not described herein. 
         [0023]    In existing rheometer systems, cylinder shaft  116  often is rigidly coupled to cross-head  108 . Cylinder shaft  116  is effectively a part of cross-head  108 . As a consequence, the assembler and user of such an existing rheometer system had to make sure that air cylinder  114  and posts  104  and  106  were properly aligned. If air cylinder  114  were not properly aligned with respect to cylinder mounting plate  112  and/or posts  104  and  106 , the system would stutter or even bind up as cross-head  108  moved upwardly and downwardly on posts  104  and  106 . Also, even if the cylinder  114  and posts  104  and  106  were properly aligned, upper die  74  could be randomly positioned with respect to lower sample die  72 . This result made it nearly impossible to align lower sample die  72  and upper die  74  and to still prevent the system from stuttering and/or binding up. 
         [0024]    These problems are overcome by the use of coupling system  150 . Coupling system  150  may include a connector such as a connector  152 , a jam nut  154 , a retainer  156 , a flange  158  and bolts  160 . Connector  152  may be a bolt and includes a shaft  151  and an enlarged head  155  which has an outer dimension or diameter larger than the diameter of shaft  151 . Shaft  151  is coupled to cylinder shaft  116 , such as by welding, threads, or the like. In one embodiment, shaft  151  is threaded into an opening  117  in the bottom of cylinder shaft  116 . When installed, jam nut  154  may be tightly screwed up against the bottom edge of cylinder shaft  116  to prevent any loosening of shaft  151  of connector  152  within opening  117  due to vibrations and the like. Head  155  of connector  152  has a lower curved surface  153  which may be hemispherical in shape. A flange  158  is mounted onto cross-head  108  such as by means of bolts  160 . Alternatively, flange  158  may be formed as an integral part of cross-head  108 . Upper housing  118  is mounted into cross-head  108 . Flange  158  includes a central portion  162  to which torque transducer  120  and upper die  74  are coupled. Head  155  may reside in a recess  161  in the upper surface of portion  162 . Recess  161  extends around the entire circumference of head  155  and may be circular in shape. Lower curved surface  153  of head  155  bears on a surface of recess  161  in portion  162  when cross-head  108  is forced downwardly by cylinder shaft  116 . In other embodiments, head  155  could rest on an upper surface of portion  162 . Surrounding head  155  is a retainer  156  which includes a lip  171  which overlies head  155  and limits upward vertical movement of head  155 . Lip  171  prevents head  155  from lifting out of recess  161  when cross-head  108  is raised upwardly by cylinder shaft  116 . Retainer  156  may be affixed to flange  158  and includes a central opening which accommodates connector  152 . While lip  171  of retainer  156  overlies portions of head  155 , there is a gap  170  between head  155  and lip  171  of retainer  156 , and another gap  172  between head  155  and interior surfaces of recess  161  of flange  158 . Gaps  170  and  172  extend around the entire circumference of head  155 . These gaps  170  and  172  allow tilting or pivoting movement of connector  152  with respect to retainer  156  and flange  158 . This movement thus allows cylinder shaft  116  and thus cylinder  114  to float with respect to cross-head  108  so that any misalignment between air cylinder shaft  116  and cross-head  108  may be accommodated without binding and/or stuttering of the machine. Therefore, upper die  74  can be properly aligned with lower sample die  72  without having a perfect alignment of air cylinder  14  with respect to cross-head  108  and posts  104  and  106 . If there is any misalignment between air cylinder  114  and cross-head  108 , it will be accommodated by the gaps  170  and  172  between flange  158  and retainer  156  with respect to connector  152  which permit connector  152  to tilt or move with respect to cross-head  108 . 
         [0025]    While connector  152  was described as having a hemispherical surface  153 , surface  153  may not necessarily be precisely hemispherical. Surface  153  could have other curved shapes. Surface  153  may be semi-elliptical or any other suitable curved shape, so long as tilting movement of connector  152  with respect to cross-head  108  is permitted while maintaining a tight connection between connector  152  and flange  158  and retainer  156 . The gaps  170  and  172  may be of any suitable size that permits accommodation of misalignment of cylinder shaft  116  and cross-head  108 , and which takes into account the nature of the curvature on surface  153 . A typical gap  170  and  172  would be approximately 1 mm or 0.040 inch. However, other smaller or larger gaps  170  and  172  may be provided so long as they allow the rheometer to function without stuttering or binding, and they allow alignment of upper die  74  with lower sample die  72 . 
         [0026]    Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.