Abstract:
A screw capping head for use in a rotary capping machine includes a housing defining a longitudinal axis, a spindle rotatably carried by the housing, a first ring of magnets fixed within the housing, and a second ring of magnets coupled to the spindle for rotation with the spindle. The second ring of magnets is movable, without the use of tools, in the longitudinal direction with respect to both the spindle and the first ring of magnets to achieve a plurality of nested positions with respect to the first ring of magnets. The first and second rings of magnets define a magnetic torque coupling between the housing and the spindle, the strength of the torque coupling varying in a substantially linear relationship to the nested positions of the first and second rings of magnets.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/296,560 filed on Jun. 7, 2001, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to rotary capping machines, and more particularly to rotary capping machines that apply pre-threaded closures onto pre-threaded containers. 
     BACKGROUND OF THE INVENTION 
     Rotary capping machines for applying pre-threaded closures have been known for some time. To insure that a pre-threaded closure is not applied too loosely or too tightly and to insure product integrity, rotary capping machines are equipped with capping heads dependent upon a torque coupling. The torque coupling controls the application of torque to the closures to insure that they meet packaging specifications. Various types of torque couplings exist in the art such as mechanical clutches and magnetic clutches. 
     A magnetic clutch typically consists of axially-opposed rings that are spaced apart by some distance. Each ring comprises an array of magnets mounted horizontally along each ring whereby the arrays of magnets on the opposing rings are in a facing relationship. In a magnetic clutch, one ring is typically fixed within a housing that is driven by a machine spindle and the other ring drives a capping head spindle that holds the closures. The magnetic field established between the arrays of magnets is the connection between the torque applied to the housing by the machine spindle and the torque applied to the closure by the capping head spindle. Axial distance between the opposing rings affects the torque transmitted by the magnetic clutch. Generally, a greater distance between the rings will decrease the magnetic interaction between the opposing arrays of magnets, and subsequently will decrease the amount of transmittable torque carried by the magnetic clutch. Any resistance torque applied to the magnetic clutch by the spindle beyond that of the transmittable torque causes the clutch to slip. Generally, spacer rings are used to maintain the distance between the opposing magnetic rings. 
     In addition to the clutch, each capping head also typically utilizes a telescoping lower/upper housing design, with the clutch located in the lower housing near the spindle. A spring is usually positioned between the upper housing and lower housing to help bias the housings away from each other and to exert a top-loading force on the closure to the container. The pre-load on the spring can be adjusted to vary the top-loading force on the closure, and this is often accomplished using a rotatable collar with a locking element, such as a set screw, that must be loosened to adjust the collar and tightened after the adjustment is made. Alternatively, the spring can be removed and replaced with another spring of a different stiffness. 
     SUMMARY OF THE INVENTION 
     A typical capping head utilizing a magnetic clutch requires the use of tools for torque adjustment. To adjust the torque transmitted by the magnetic clutch, spacer rings must either be inserted or removed, depending on the design of the capping head. This often requires each capping head to be disassembled or adjusted using tools, and this extends the downtime associated with setting up a capping machine to run a specific package. After the capping head is adjusted, a torque wrench is required to verify the torque setting on the capping head. This is necessary to ensure all the capping heads on a rotary capping machine apply substantially the same amount of torque to closures on open containers. 
     Downtime is also extended when the top-loading force on the closure needs adjusting. Each capping head must be disassembled or adjusted using tools if the springs are to be replaced with springs of a different stiffness. If a capping head utilizes a collar with a locking element to adjust the top-loading force on the closure, then tooling is often required to carry out the adjustment. In either case, downtime is lengthened. 
     The typical capping head also requires seals such as o-rings and quad rings to prevent the environment and/or the product from entering and attacking the internal components of the capping head. The seals also prevent any lubrication in the capping head from escaping and contaminating the product being packaged. Failure of the seals often leads to a complete failure of the capping head. An erratic torque output also often results from worn or failed seals. To help prevent this from occurring, the capping heads require frequent maintenance to inspect and replace any worn seals and bearings. 
     The relatively large inertial mass of the capping head plus the friction of the seals often produce erratic torque output through the magnetic clutch. This is most common in high speed capping applications. To help address this problem, some capping machines have been provided with different sets of capping heads for different operating speed ranges. This approach has been helpful, but it has also been uneconomical and has unduly complicated and lengthened the changeover between packaging runs requiring two very different operating speeds. Prior attempts to reduce capping head inertia have been negligible at improving erratic torque output. 
     The magnetic clutch configuration utilizing two opposing magnetic rings that are in a facing relationship typically has a non-linear relationship between operating torque and the distance between the opposing magnets. This relationship is known in the art and has proven to be relatively unstable over time. As a result, each capping head may require frequent re-calibration to maintain accurate and repeatable closure applications on the containers. This practice also lengthens downtime and is uneconomical. 
     The invention provides for significant improvement for a screw capping head having a magnetic clutch for transmission of torque to a closure. The invention provides a capping head utilizing a single bearing and no conventional, resilient seals, therefore eliminating frictional resistance, extending maintenance intervals, reducing production downtime, and lowering the cost of operation. 
     More specifically, the invention provides in one embodiment a capping head having a torque coupling consisting of a magnetic clutch that yields a predictable torque output, thereby allowing for indexed torque adjustment and eliminating the need for frequent re-calibration of the capping heads. The magnetic clutch comprises two concentric rings with rectangular magnets affixed vertically along the rings. The rectangular magnets are preferably vacuum sealed in epoxy to provide corrosion protection from the environment. An outer ring is affixed to a lower housing while an inner ring is coupled around a spindle and positioned at least partially within the outer ring. The inner ring moves axially (and not rotationally) into and out of nested relationship with respect to the outer ring, which is fixed to the lower housing. This configuration yields a substantially linear relationship between operating torque and the axial distance or spacing between the concentric rings. This relationship is very stable over time and covers a wide range of operating torques, approximately between 5 in·lbs and 35 in·lbs. 
     In another embodiment, the invention provides a tool-less adjustment of the magnetic clutch. A torque-adjusting collar is rotatably adjustable around the spindle to initiate axial displacement of the inner magnet ring with respect to the fixed outer magnet ring, effectively eliminating the use of spacers to achieve a desired torque setting at the capping head. A detent mechanism is used to selectively lock and unlock the torque-adjusting collar, eliminating the need for any tooling or extended downtime to adjust the torque setting on the magnetic clutch to satisfy different closure specifications. 
     In another embodiment, the invention also provides a tool-less adjustment of the top-loading force applied by the spring to the closure. A combination of a spring retainer and an adjustment collar work to pre-load the spring between the upper housing and lower housing. The spring retainer is free to slide on the upper housing, while the adjustment collar is located above the retainer and is rotatably positioned using threads engaged with the upper housing. A clockwise rotation of the adjustment collar initiates a greater pre-load on the spring, and subsequently a greater top-loading force to the closure on the container. A counter-clockwise rotation yields the opposite results. One or more detent mechanisms are integrated between the adjustment collar and spring retainer to allow the collar to index between different amounts of pre-load on the spring. The detent mechanisms maintain and lock the collar in place during operation of the capping head. 
     In yet another embodiment, the invention provides a capping head without any conventional, resilient seals that require frequent replacement. Rather, a retainer positioned below the bearing includes an annular sidewall portion having a channel formed therein. The channel substantially prevents the liquid product from contaminating the bearing. Unlike a conventional resilient seal, however, the sidewall and channel of the metallic retainer do not wear over time. As a result, the magnetic clutch yields a more stable torque output for a longer period of time. To forego the use of conventional lubricants and resilient seals, while maintaining the bearing as the only conventionally lubricated component within the capping head, the other components that experience wear during normal operation can be coated to prolong their useful life. The coatings are applied directly to the wear surfaces of the respective components and will not contaminate the liquid product. 
     The invention also provides a method of adjusting the strength of the magnetic torque coupling on the capping head. The method includes rotating the torque adjusting collar relative to the spindle to impart an axial (and non-rotational) displacement of the inner ring of magnets relative to the outer ring of magnets between varying positions where the inner ring of magnets is nested within the outer ring of magnets, whereby varying the nested position of the two rings varies the strength of the torque coupling. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a screw capping head embodying the present invention. 
         FIG. 2  is an exploded view showing the lower housing mating to the upper housing via male and female splines. 
         FIG. 3  is a cross-sectional view of the torque carrier assembly of the screw capping head of FIG.  1 . 
         FIG. 4  illustrates the inner magnet assembly of the screw capping head of FIG.  1 . 
         FIG. 5  illustrates the outer magnet assembly of the screw capping head of FIG.  1 . 
         FIG. 6  is a Torque vs. Distance curve illustrating the relationship between torque applied by the capping head to a closure and the spaced distance between the inner and outer magnet assemblies. 
         FIG. 7  illustrates the spindle, torque adjusting collar with detent mechanisms, and the carrier ring. 
         FIG. 8  is a cross-section view along lines  8 — 8  of the carrier ring of FIG.  7 . 
       Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A screw capping headset, or capping head  10  embodying the present invention is shown in FIG.  1 . The capping head  10  is rotatably driven along a longitudinal axis  14  by a machine spindle (not shown) of a capping machine (not shown). The machine spindle is secured to the screw capping head  10  via a spindle adapter  18 . The spindle adapter  18  has internally formed threads  22  to secure the capping head  10  to the rotating spindle of the capping machine. 
     A knock-out rod  26  travels vertically through the capping head  10  to expel any unneeded or jammed closures (not shown) from the capping head  10 . The knock-out rod  26  is biased towards an upper position by a compression spring  30 . A spring retainer  34  axially aligns the spring  30  with respect to the knock-out rod  26  and is positioned between the knock-out rod  26  and the spring  30 . 
     During operation, the knock-out rod  26  is actuated by the capping machine. When actuated, the knock-out rod  26  travels to a lower position where the rod  26  contacts and expels the unneeded closure. The spring  30  and retainer  34  then force the rod to return to the upper position. 
     As best seen in  FIG. 2 , a lower housing  38  and an upper housing  42  are keyed together by splined shafts. The lower housing  38  includes a male splined shaft  46  and the upper housing  42  includes a female splined shaft  50 , of course the lower housing  38  could include the female splined shaft  50  and the upper housing  42  could include the male splined shaft  46 . The shafts  46 ,  50  engage each other and telescope coaxially along the longitudinal axis  14 . With reference to  FIG. 1 , the upper housing  42  includes a circumferential ridge  54  concentric with the longitudinal axis  14 . The housings  38 ,  42  are allowed to telescope a pre-determined distance as a result of a knock-out rod housing  58  contacting the ridge  54 . The knock-out rod housing  58  secures the lower housing  38  to the upper housing  42  via eight cap screws  62  and prevents telescoping beyond the pre-determined distance when the knock-out rod housing  58  comes into contact with the ridge  54 . A shock absorber  66  in the form of an polymeric disc is positioned between the knock-out rod housing  58  and the lower housing  38  to decrease wear between the metallic surfaces of the housings  58 ,  38 . 
     The upper housing  42  and portions of the lower housing  38  are coated to prolong their useful life and increase their corrosion resistance. The coatings can be applied by any conventional method such as spraying, dipping, or plating the components. In some instances, portions of a component will be coated rather than the entire component, and in other instances, the entire component will be coated for ease of application. The coated surfaces are indicated by the stippling seen in  FIGS. 2 ,  4 ,  7 - 8 . 
     The coating comprises a chrome-based coating having a thickness between about 0.0001 and 0.0003 inches and a hardness of about 78 Rc, however, different coatings having similar wear protection and corrosion resistance characteristics can also be used. The illustrated coating is marketed under the name ARMALOY and is available from Armaloy of Illinois, Inc. in DeKalb, Ill. By applying coatings to the wear surfaces of the capping head  10 , such as the male and female splined shafts  46 ,  50 , conventional lubricants like grease, oil, etc. are not required between the male and female splined shafts  46 ,  50 . As a result, conventional resilient seals are also not required in the upper housing  42  or lower housing  38 . Also, cleaning the capping heads  10  is highly simplified because the entire capping head  10  can be sprayed down using a high pressure water stream. Previously, the lubricated surfaces would have to be avoided during cleaning because the water stream could dissipate the lubrication from the lubricated surfaces. 
     A compression spring  70  is confined between a spring retainer  74  and the lower housing  38 . The spring  70  biases the housings  38 ,  42  away from each other such that a force needs to be overcome for the housings  38 ,  42  to telescope toward each other. A top load adjusting nut  78  threadably engages the upper housing  42  and is positioned above the spring retainer  74 . The nut  78  axially supports the retainer  74  against the force of the compression spring  70 . Rotation of the nut  78  results in its axial movement along the longitudinal axis  14 . The nut  78  can be rotatably adjusted to displace the retainer  74  and compress the spring  70 . This action imparts a pre-load on the spring  70 . This ensures the closure will be vertically applied to an open container (not shown) by a minimum force determined by the pre-load. 
     The pre-load can be adjusted by rotating the nut  78  to increase or decrease the pre-load as required by closure application specifications. The retainer  74  includes an anti-rotation pin  82  that prevents the spring  70  from rotating relative to the housings  38 ,  42  during operation. The retainer  74  is also coated similar to the upper housing  42  and lower housing  38 . The nut  78  includes four ball detent mechanisms  86  that engage four correlating recesses  90  in the retainer  74  and secure the nut  78  to prevent any unwanted rotation during operation of the capping head  10 . Alternatively, the nut  78  can utilize other locking mechanisms, such as one or more setscrews (not shown) to secure the nut  78 . 
     The lower housing  38  contains the components involved with the magnetic torque coupling of the capping head  10 . The components generally include an outer magnet assembly  94 , a spindle assembly  98 , and a torque carrier assembly  102 . 
     As shown in  FIGS. 1 and 5 , the outer magnet assembly  94  includes an outer carrier housing  106  having exterior threads  110  for threaded engagement with the lower housing  38 . The outer carrier housing  106  includes an outer ring  114  that is shrink fit into the interior of the housing  106 . The outer ring  114  is layered with a single row of outer magnets  118  positioned in a circular array. In the illustrated embodiment, the inside diameter of the outer ring  114  with the attached magnets  118  is about 2.125 inches. The magnets  118  are preferably made of a Sumarium Cobalt or similar magnetic material, with each magnet  118  having poles of opposite charge (e.g. a north and south pole). The magnets  118  are positioned on the outer ring  114  with either a north or south pole exposed to the interior of the outer magnet assembly  94  such that each magnet  118  has an adjacent magnet  118  with an opposite pole exposed. The magnets  118  are vacuum sealed and secured to the outer ring  114  by epoxy. 
     As best seen in  FIG. 1 , the spindle assembly  98  includes a ball bearing  122  having an outer race  126  axially disposed between the outer carrier housing  106  and the lower housing  38 . As a result, the outer race  126  is rotatably fixed with respect to the lower housing  38 . The inner race  130 , however, is free to rotate independently of the lower housing  38  and is axially disposed between an upper bearing retainer  134  and a lower bearing retainer  138 . A capping head spindle  142  (hereinafter referred to as the “spindle”) is secured to the upper bearing retainer  134  and lower bearing retainer  138  through six cap screws  144  and is free to rotate about the longitudinal axis  14 . The spindle  142  (see  FIGS. 1 and 7 ) includes both exterior threads  146  and interior threads  150  on the lower portion of the spindle  142 . The spindle  142  also includes male splines  154  on its exterior surface towards the upper portion of the spindle  142 . The spindle  142  is also coated with the ARMALOY coating like the upper housing  42  and lower housing  38  to enhance wear protection and corrosion resistance. 
     The lower bearing retainer  138  includes an annular portion or sidewall  158  having a channel  162  formed therein. The channel  162  is positioned below the bearing  122  and communicates with the outer carrier housing  106 . The sidewall  158  is closely spaced to the inner surface of the outer carrier housing  106  with the channel  162  extending radially inwardly toward the longitudinal axis  14 . The channel  162  substantially prevents the liquid product from contaminating the bearing  122  by providing a collection area for any liquid product coming in contact with the sidewall  158 . Unlike a conventional resilient seal that is typically in sliding frictional contact with another mating surface, the sidewall  158  of the lower bearing retainer  138  is not in frictional contact with another surface and subsequently does not wear over time. 
     The bearing  122  is lubricated using a food-grade type grease that substantially adheres to the lubricated surfaces of the bearing  122 . As a result, the channel  162  typically is not needed to prevent unwanted movement of bearing grease away from the bearing  122  and toward the liquid product. 
     The torque carrier assembly  102  is positioned partially within the lower housing  38  and telescopes axially with respect to the spindle  142  along the longitudinal axis  14 . The torque carrier assembly  102  includes an inner magnet assembly  166 , a carrier ring  170 , a carrier coupling  174 , and a torque-adjusting collar  178 . The torque carrier assembly  102  is shown in greater detail in FIG.  3 . 
     The inner magnet assembly  166  (see  FIG. 4 ) includes an inner magnet carrier  182  having female splines  186  on the interior of the carrier  182 . The female splines  186  engage the male splines  154  of the spindle  142  to allow the inner magnet assembly  166 , and subsequently the torque carrier assembly  102 , to telescope axially with respect to the spindle  142 . The splined engagement between the inner magnet assembly  166  and the spindle  142  also prevents rotation of the inner magnet assembly  166  relative to the spindle  142 . Of course, the inner magnet carrier  182  could have male splines  154  that engage female splines  186  of the spindle  142 . 
     The female splines  186  of the inner magnet carrier  182  and the male splines  154  of the spindle  142  are also coated with the same coating applied to the upper housing  42  and lower housing  38 . As a result, conventional resilient seals are not required in the torque carrier assembly  102  because conventional lubricants are not needed. The inner magnet carrier  182  includes an inner ring  190  that is shrink fit over the inner magnet carrier  182 . 
     The inner ring  190  is layered with a single row of inner magnets  194  positioned in a circular array. The magnets  194  are also preferably made of a Sumarium Cobalt or similar magnetic material, with each magnet  194  having poles of opposite charge (e.g. a north and south pole). The magnets  194  are also positioned on the inner ring  190  with either a north or south pole exposed to the exterior of the inner magnet assembly  166  such that each magnet  194  has an adjacent magnet  194  with an opposite pole exposed. The magnets  194  are vacuum sealed and secured to the inner ring  190  by epoxy. A sleeve  198  is shrink fit over the circular array of magnets  194  to lend additional radial support to the magnets  194 . In the illustrated embodiment, the outer diameter of the inner ring  190  with the attached magnets  194  and sleeve  198  is about 2.1 inches. As a result, about 0.0125 inches of clearance exists between the inner magnet assembly  166  and outer magnet assembly  94 . This clearance allows the inner and outer magnet assemblies  166 ,  94  to achieve a variety of coaxially nested positions with respect to one another. The inner magnet carrier  182  also includes exterior threads  202  on the lower portion of the carrier  182 . 
     Referring again to  FIGS. 1 and 3 , the carrier ring  170  includes interior threads  206  for threaded engagement with the exterior threads  202  of the inner magnet carrier  182 . The carrier ring  170  also includes a plurality of indexed recesses  210  or detents (see  FIGS. 3 and 7 ) radially positioned around the bottom surface of the carrier ring  170  for receiving spring-loaded balls described below. As shown in  FIGS. 7 and 8 , the carrier ring  170  is coated similarly to the inner magnet carrier  182  to enhance wear protection and corrosion resistance. 
     The carrier coupling  174  includes interior threads  214  for threaded engagement with the spindle  142 . The carrier coupling  174  also includes exterior threads  218 . One or more bushings  222  are positioned between the contacting surfaces of the inner magnet carrier  182  and the carrier coupling  174  to minimize wear between the carrier  182  and the coupling  174 . 
     As shown in  FIGS. 1 and 7 , the torque-adjusting collar  178  includes interior threads  226  for threaded engagement with the exterior threads  218  of the carrier coupling  174 . The torque-adjusting collar  178  is also coated similarly to the inner magnet carrier  182  to enhance wear protection and corrosion resistance. The collar  178  also includes four ball detent mechanisms  230  radially positioned on the top surface of the collar  178 . The ball detent mechanisms  230  are equiangularly spaced to coincide with the indexed recesses  210  of the carrier ring  170 . 
     The collar  178  also includes one locking ball detent mechanism  234  having a ball  235  actuated by a spring-biased push button  236 . The locking ball detent mechanism  234  rotatably locks the torque-adjusting collar  178  to the carrier ring  170 , which is coupled to the spindle  142  for rotation therewith. When the push button  236  is depressed, the ball  235  disengages the carrier ring  170  and the collar  178  is allowed to co-rotate with the carrier coupling  174  about the exterior threads  146  of the spindle  142 . This action results in an axial displacement of the inner magnet assembly  166  with respect to the outer magnet assembly  94 . Utilizing the locking ball detent mechanism  234  in conjunction with the rotatably adjustable collar  178  allows the torque coupling between the magnet assemblies  94 ,  166  to be changed by hand without using tools. 
     The combination of the ball detent mechanisms  230  in the torque-adjusting collar  178  and the indexed recesses  210  in the carrier ring  170  allows the collar  178  to selectively index the axial position of the inner magnets  194  with respect to the outer magnets  118 . This configuration allows the capping head  10  to take advantage of the substantially linear relationship between the torque coupling of the nested magnets  118 ,  194  and the vertical distance between the nested magnets  118 ,  194 . This substantially linear relationship is shown in FIG.  6 . Using this configuration, the capping head  10  can be adjusted to transmit between 5 in·lbs and 35 in·lbs of torque to a closure. 
     In the illustrated embodiment shown in  FIG. 1 , a clockwise rotation (looking from the bottom of the capping head  10 ) of the torque-adjusting collar  178  causes the inner magnets  194  to displace axially away from (upwardly in  FIG. 1 ) the outer magnets  118 . In a fully displaced position, the inner magnets  194  yield the weakest torque coupling with the outer magnets  118 , while a home position yields the strongest torque coupling between the magnets  118 ,  194 . In the illustrated embodiment, the home position is defined when the inner magnets  194  are completely nested within the outer magnets  118 , while the fully displaced position is defined by about 0.5 inches of vertical upward movement of the inner magnets  194 , where the bottom surfaces  238  of the inner magnets  194  are coplanar with the top surfaces  242  of the outer magnets  118 . 
     The position of the inner magnets  194  relative to the outer magnets  118  is generally identified by reference numerals  246  engraved on the exterior of the collar  178 , as shown in FIG.  7 . The numerals  246  are indexed and referenced to a calibration mark (not shown) on the carrier ring  170 . This allows a user to visually determine the torque setting of the capping head  10 . Generally, a lower numeral referenced to the calibration mark indicates a weaker torque coupling while a higher numeral referenced to the mark indicates a stronger torque coupling. The reference numerals  246  correlate to the actual amount of torque applied by the capping head  10  to a closure, such that the numeral “29” referenced to the calibration mark indicates that a torque of 29 in·lbs is applied to a closure. With this configuration, a torque wrench is not required to verify torque settings on individual capping heads  10  during a product changeover. 
     As shown in  FIG. 1 , the capping head  10  also includes a chuck assembly  250  rotatably supported within the spindle  142 . Exterior threads  254  on the chuck assembly  250  engage the interior threads  150  of the spindle  142  to secure the chuck assembly  250  to the spindle  142  for rotation therewith. A closure is secured within the chuck assembly  250  for application to an open container. 
     During operation, the capping head  10  is pre-set to apply an amount of torque required by a production run of a particular open container. This is done by indexing the torque-adjusting collar  178  to the level of torque coupling desired. Upon application of the closure, the chuck assembly  250  will slip with the spindle  142  when the pre-set amount of torque is applied to the closure. This occurs because the torque coupling between the inner magnets  194  and outer magnets  118  is overcome. 
     When the spindle  142  slips, the spindle  142  ratchets due to alternating attraction and repulsion between the outer magnets  118  and inner magnets  194 . For example, the outer magnets  118  with exposed “north” poles will attract the inner magnets  194  with exposed “south” poles to define a stable position between the outer magnets  118  and inner magnets  194 . Conversely, the outer magnets  118  with exposed “north” poles will repulse the inner magnets  194  with exposed “north” poles to define an unstable position between the outer magnets  118  and inner magnets  194 . The magnets  118 ,  194  alternating between stable and unstable positions cause the spindle  142  to ratchet when the spindle  142  slips. This ratcheting effect is advantageous for some closure applications and provides benefits over other prior art magnetic clutches that operate using the hysteresis phenomenon to provide smooth clutch action. 
     The absence of conventional resilient seals enhances the performance and longevity of the capping head  10 . Generally, when conventional resilient seals wear, the relationship between torque coupling and axial distance between the magnets  118 ,  194  breaks down and becomes increasingly unstable. Since the present invention does not utilize conventional resilient seals, the torque coupling relationship remains stable and the capping head  10  can utilize longer maintenance intervals between servicing or replacement. This also allows the capping head  10  to more accurately and precisely apply the closures with a pre-set amount of torque, which will subsequently decrease the number of rejected product containers due to improper application of closures to the open containers. 
     Various features of the invention are set forth in the following claims.