Abstract:
A method of uniformly distributing liner on an interior of a tube includes providing an apparatus comprising a horizontal bed, a tailstock coupling mounted on the horizontal bed, a drive coupling and a drive unit connected to the drive coupling; mounting the tube in the tailstock and drive couplings; and spinning the tube using torque control of the drive unit. In one embodiment, the method includes dispensing a continuous bead of liner on the interior of the tube and spreading the liner on the interior of the tube using a brush.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties thereof. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to devices for spinning hollow, cylindrical tubes and in particular to devices for spinning rocket motor tubes to distribute, evenly, viscous liner material deposited on the interior of the tube. 
     Rocket motor tubes are lined with a fire retardant liner to prevent the propellant from burning through the tube wall. The rocket tubes are, for example, about three feet long and two to three inches in diameter. U.S. patent application Ser. No. 10/927,647 filed on Aug. 25, 2004, entitled “Apparatus For Applying Liquid Liner To Rocket Tube,” having the same inventor as the present application, discloses an apparatus for dispensing a continuous bead of liner into a rocket motor tube. The contents of the above noted previous application are hereby expressly incorporated by reference. 
     After depositing the continuous bead of liner in the rocket tube, the liner must be spread around to cover the interior of the rocket tube. U.S. patent application Ser. No. 10/985,064 filed on Nov. 10, 2004 entitled “Apparatus for Spreading Liquid Liner in Rocket Tube,” having the same inventor as the present application, discloses a brushing apparatus for spreading viscous liner over the interior of a rocket motor tube. The contents of the above noted previous application are hereby expressly incorporated by reference. 
     After the brushing operation that spreads the liner, the present invention is used to spin the tubes to uniformly distribute the liner on the interior of the tube. The spinning operation uses centrifugal force to form a uniform layer of liner on the interior of the tube. 
     SUMMARY OF THE INVENTION 
     The invention includes a torque control method for controlling an apparatus for spinning hollow, cylindrical tubes that may be balanced or unbalanced. The hollow cylindrical tubes may be, for example, rocket motor tubes. The interiors of the rocket motor tubes are coated with a viscous liner material. Initially, the viscous liner material is not evenly distributed on the interior of the rocket motor tubes. The purpose of spinning the rocket motor tubes is to distribute, evenly, the viscous liner on the interior of the tubes by a centrifugal force of spinning. The drive motor for the spinning apparatus is torque controlled, rather than speed controlled. With torque control, it is easier to achieve generally constant speed spinning with an unbalanced load. 
     The invention will be better understood, and further objects, features, and advantages thereof will become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIGS. 1 and 2  are perspective views of one embodiment of a spinning apparatus in accordance with the invention. 
         FIGS. 3 and 4  are cross-sectional views of rocket motor tubes with masks. 
         FIG. 5  is a perspective view of an adjustable bed. 
         FIG. 6  is a sectional view of a slide. 
         FIG. 7  is an exploded view of a portion of the tailstock assembly. 
         FIG. 8  shows the connection between a locking clamp and a shuttle plate. 
         FIG. 9  is an upside down perspective view showing the shuttle slide, shuttle plate and locking clamp. 
         FIG. 10  shows the locking clamp in an unlocked or open position. 
         FIG. 11  shows the locking clamp in a locked or closed position. 
         FIG. 12  is a front perspective view of the spinning apparatus. 
         FIG. 13  is a rear perspective view of the spinning apparatus. 
         FIG. 14  is a cross-section of a vertical strut. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 1 ,  2 ,  12  and  13  are perspective views of one embodiment of a spinning apparatus (spinner)  10  in accordance with the invention. The spinner  10  shown in  FIGS. 1 ,  2 ,  12  and  13  is designed to accommodate two tubes at a time. It is noted however, that the spinner  10  shown in is merely exemplary and other spinners that accommodate fewer or more tubes are within the scope of the invention. 
     Spinner  10  is mounted on a table  12  or other stable and sturdy horizontal surface. Spinner  10  includes an adjustable bed  14 , guard cover  16 , manual locking clamps  18 , tailstock bearings  20 , tailstock coupling  22 , drive coupling  24  and drive unit  26 . Drive couplings  24  are only partially visible in  FIG. 1  because of splatter shields  28  installed around drive couplings  24 . In an exemplary embodiment, drive unit  26  is torque-controlled. Drive unit  26  comprises a torque-controlled electric motor  122  with associated control components. As an alternative to an electric motor, an air motor with regulator may be used for the drive unit  26 . 
     Referring to  FIGS. 12 and 13 , one or more drive coupling bearings  112  are mounted on the drive coupling support strut  116 . Each drive coupling  24  is supported by a set of drive coupling bearings  112 . Drive unit  26  comprises, among other components, a drive motor  122 ; a drive pulley  124  connected to the drive motor  122 ; drive pulley bearings  126  mounted on the drive unit strut  130 ; and a belt  114  connecting the drive pulley  124  and the drive couplings  24 . Where more than two drive couplings  24  are used, the belt  114  would connect couplings  24  and drive pulley  124  in a known serpentine manner. 
     Motor torque is controlled by, for example, computer software or one or more appropriate hard wired controller(s). Motor speed is controlled by the balance between motor output torque and bearing friction resistance torque. In the embodiment shown, the bearing friction is supplied by tailstock bearings  20 , drive coupling bearings  112  and drive pulley bearings  126 . The drive motor  122  rotational speed equals a tube  40  rotational speed. Motor speed is proportional to the amount of drag in the bearing drive system. The greater the bearing drag, the lower the steady state speed. The lower the bearing drag, the higher the steady state speed. 
     As the motor rpm increases, the bearing friction increases due to bearing grease shear and/or tube  40  vibration, until bearing friction matches motor torque. When bearing friction equals motor torque, the rotational speed becomes approximately constant. Rotational speed should be, for example, in a range of about 3000 rpm to about 4000 rpm. If no tube  40  is mounted in the spinner, the motor may overspeed and automatically shut down by using the appropriate overspeed detection circuits. Motor overspeed occurs at, for example, about 5000 rpm. Spinning time is in general about ten seconds to about sixty seconds. 
       FIGS. 3 and 4  are cross-sectional views of rocket motor tubes with masks showing how masks  46 ,  48  couple with the tailstock and drive couplings  22 ,  24 .  FIG. 3  shows a rocket motor tube  40  of the small class. The interior of tube  40  has a coating of viscous liner  44 . Generally, the viscous liner  44  has been applied to tube  40  and brushed using the apparatuses disclosed in co-pending patent application Ser. Nos. 10/927,647 and 10/985,064, referenced and incorporated above. The liner  44 , although applied on the interior of tube  40 , is not sufficiently evenly distributed. The purpose of the spinning apparatus  10  is to evenly distribute liner  44  on the interior of tube  40 . The tubes  40  spin, for example, at about 30004000 rpm until the liner inside the tube is evenly distributed. 
     As shown in  FIG. 3 , tube  40  includes mask  46  at the tailstock end and mask  48  at the drive end. Each of masks  46 ,  48  includes angled surfaces  50 ,  52  and O-ring  151 . O-rings  151  are situated substantially adjacent masks  46 ,  48  of the tube  40 . The O-rings perform several over functions in addition to being a structural interface between the masks  46 ,  48  and the tube  40 . O-rings  151 , when installed under compression, prevent liner  44  from entering the areas of the tube  40  adjacent the masks  46 ,  48  (masking function). O-rings  151  help center the tube  40  during the spinning operation and also transfer torque from the mask  52  at the drive end to the tube  40 . 
     Tailstock coupling  22  includes a flanged portion  54  having interior angled surface  58 . Drive coupling  24  includes a flanged portion  56  having interior angled surface  60 . When tube  40  is in an operable position in spinner  10 , angled surfaces  50 ,  52  of masks  46 ,  48  contact angled surfaces  58 ,  60  of the tailstock coupling  22  and the drive coupling  24 , respectively. During the spinning operation, tailstock coupling  22  is stationary with mask  46  and tube  40  rotating against angled surface  58  of tailstock coupling  22 . Drive coupling  24  rotates angled surface  60 . Angled surface  60  drives angled surface  52  of mask  48 . O-ring  151  of mask  48  drives tube  40 . Couplings  22 ,  24  may be made of a metal, for example, stainless steel. Masks  46 ,  48  may be made of a plastic such as ultra high molecular weight polyethylene. 
     The angle of angled surfaces  58 ,  60  of the tailstock coupling and the drive coupling  22 ,  24  and the angle of the angled surfaces  50 ,  52  of the masks are substantially the same. For optimum operation, this angle alpha, as shown in  FIG. 3 , is in the range of about ten degrees to about forty-five degrees and, in particular, the angle alpha is about thirty degrees. Note that angle alpha corresponds to twice the angle between one of the angled surfaces  58 ,  60 ,  50 ,  52  and the central horizontal axis of the tube  40 . That is, the angle between the angled surfaces  58 ,  60 ,  50 ,  52  and the central horizontal axis of the tube  40  is in the range of about five to about twenty-three degrees and, in particular, about fifteen degrees. 
       FIG. 4  shows a large class rocket motor tube  42  having masks  62 ,  64 , drive coupling  24  and tailstock coupling  22 . Masks  62 ,  64  include angled surfaces  66 ,  68 , respectively and O-rings  151 . O-rings  151  function in the same manner as described above with reference to  FIG. 3 . Drive coupling  24  includes angled surface  72  and tailstock coupler  22  includes angled surface  70 . In a manner analogous to the embodiment of  FIG. 3 , angled surface  68  of mask  64  contacts angled surface  72  of drive coupling  24  and angled surface  66  of mask  62  contacts angled surface  70  of tailstock coupling  22 . Because tailstock coupling  22  and drive coupling  24  each have small diameter angled surfaces  58 ,  60 , respectively, and larger diameter angled surfaces  70 ,  72 , respectively, the couplings are able to accommodate both small class and large class tubes. 
     In another embodiment, the couplings may be constructed with only the small or only the large size of angled surfaces. Such an embodiment would not be as versatile as the couplings shown in  FIGS. 3 and 4 . In general, different types of small class tubes may have some difference in diameter, but each small class tube will have individual masks with angled surfaces that will fit the angled surfaces  58 ,  60 . Likewise, large class tubes may have differing diameters, but each large class tube will have individual masks with angled surfaces that will fit the angled surfaces  70 ,  72 . In this manner, the use of standard size masks for each tube simplifies the connection to the couplings. In addition, the standard size masks cooperate with the apparatuses disclosed in copending application Ser. Nos. 10/927,647 and 10/985,064. 
     Each pair of drive and tailstock couplings  22 ,  24  is provided with an adjustable bed  14 . Thus, in the embodiment of the invention shown in  FIGS. 1 and 2 , there are two adjustable beds  14  shown with a way cover in place to prevent liner contamination.  FIG. 5  is a perspective view of an adjustable bed  14  with no way cover. Bed  14  includes a bed housing  76 , a slide  78  axially movable along the bed housing  76 , an externally threaded rod  80 , a turning knob  88  attached to one end of rod  80  and a digital indicator  90  attached to the other end of rod  80 . Bed housing  76  includes top surfaces  84  upon which slide  78  axially moves.  FIG. 6  is a sectional view of a slide  78 . Slide  78  includes an internally threaded bushing  82  that threadingly engages rod  80  and through which rod  80  passes. Bottom surfaces  86  of slide  78  slide on the top surfaces  84  of bed housing  76 . Thus, by rotating turn knob  88 , slide  78  may be positioned axially at any point along bed housing  76 . 
     When loading a rocket motor tube into the spinner  10 , the bed  14  is adjusted to a length of the rocket motor tube by rotating turn knob  88  until digital indicator  90  indicates a numeral corresponding to the length of the rocket motor tube. Because the tailstock assembly is fixed to the top of slide  78  (as discussed in more detail below), the tailstock coupling  22  will then be in the proper position for loading the tube. A locking cover  152  ( FIG. 1 ) may be used to lock the turning knob  88  in place to prevent any unwanted axial movement of the slide  78  during operation of the spinner  10 . 
       FIG. 7  is an exploded view of a portion of the tailstock assembly. Tailstock assembly comprises a mount block  92  fixed to the top of the slide  78  by, for example, bolts or screws. A locking clamp support plate  94  is fixed to the top of the mount block  92  by bolts or screws  96 . Locking clamp  18  is fixed to the top of the locking clamp support plate  94  by bolts or screws. A shuttle slide  98  is mounted on top of the locking clamp support plate  94 . A shuttle plate  100  is fixed to the top of the shuttle slide  98 . Bearings  20  (not shown in  FIG. 7 ) are mounted on the top of shuttle plate  100 . Tailstock coupling  22  is supported in bearings  20 . 
     As shown in more detail in  FIG. 8 , the locking clamp  18  is connected to the shuttle plate  100  by, for example, a threaded stud  104  that threads into opening  106  in shuttle plate  100  and threads into tapped hole  102  in locking clamp  18 . Shuttle slide  98 , shown in more detail in  FIG. 9 , allows locking clamp  18  to move the shuttle plate  100  relative to the locking clamp support plate  94 . 
       FIG. 9  is an upside down perspective view showing the shuttle slide  98 , shuttle plate  100  and locking clamp  18 . Shuttle slide  98  comprises a slide portion  108  that is fixed to the top of the locking clamp support plate  94  (not shown in  FIG. 9 ) and a housing portion  110  that is movable with respect to the slide portion  108 . Slide portion  108  has a dovetail fit in housing portion  110  that allows the housing portion  110  and slide portion  108  to move axially relative to each other. The housing portion  110  is fixed to the shuttle plate  100 . Thus, when locking clamp  18  is moved from the unlocked position, as shown in  FIG. 10 , to the locked position, as shown in  FIG. 11 , the shuttle plate  100  with bearings  20  and tailstock coupling  22  attached, is moved towards the rocket motor tube  40  to lock it in place for spinning. 
       FIG. 12  is a front perspective view of the spinner  10  and  FIG. 13  is a rear perspective view of the spinner  10 . Some components of the spinner  10  are not shown in  FIGS. 12 and 13  so that the drive and belt tensioning features may be more clearly shown and described. Adjustable, horizontal bed(s)  14  rest on a horizontal surface such as the top of table  12 . A pair of vertical struts  118  are attached to the horizontal surface using, for example, brackets  120 . A drive coupling support strut  116  is mounted between the pair of vertical struts  118  using, for example, brackets  121 . One or more drive coupling bearings  112  are mounted on the drive coupling support strut  116 . Each drive coupling  24  is supported by a set of drive coupling bearings  112 . 
     Drive unit  26  comprises, among other components, a drive unit support plate  128  attached to the vertical struts  118 ; a drive unit strut  130  attached to the drive unit support plate  128  (using brackets, for example) and disposed between vertical struts  118 ; a drive motor  122  attached to the drive unit support plate  128 ; a drive pulley  124  connected to the drive motor  122 ; drive pulley bearings  126  mounted on the drive unit strut  130 ; and a belt  114  connecting the drive pulley  124  and the drive couplings  24 . Where more than two drive couplings  24  are used, the belt  114  would connect couplings  24  and drive pulley  124  in a known serpentine manner. 
       FIG. 14  is a cross-section of a vertical strut  118 . Each vertical strut  118  includes a generally T-shaped vertical channel  132  formed therein. Six generally T-shaped vertical channels are shown in  FIG. 14 , however, for the present invention, only one channel  132  is necessary. Disposed in channel  132  are nuts  134  placed at vertical intervals. Bolts  136  are inserted through the drive unit support plate  128  and into respective ones of the nuts  134  to thereby secure the drive unit support plate  128  to the vertical struts  118 . Bolts  136  may be directly secured to the drive unit support plate  128 , or, as shown in  FIG. 14 , bolts  136  may also directly support a control component  138  situated on support plate  128 . 
     Drive unit support plate  128  ( FIGS. 12 and 13 ) includes two threaded holes  148  ( FIG. 13 ) in a top edge  150 . A tension plate  144  is fixed to a top of each vertical strut  118 . Each tension plate  144  has an opening therein for receiving a threaded stud  142 . Stud  142  passes through the opening in the tension plate  144  and threads into hole  148  in the top edge  150  of the drive unit support plate  128 . Alternatively, stud  142  may be, for example, welded, bonded or machined as part of the drive unit support plate  128 . A nut  146  ( FIG. 12 ) is disposed on a top of each tension plate  144 . The nuts  146  engage the studs  142 . By first loosening bolts  136  ( FIG. 14 ) that attach support plate  128  to struts  118 , one may adjust the vertical position of the drive unit support plate  128  by simply rotating nuts  146 . This action allows gravity to lower the drive unit support plate  128 . Vertical adjustment of the drive unit support plate  128  adjusts the tension in belt  114 . 
     While the invention has been described with reference to certain embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof. 
     Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.