Abstract:
A method for taking a nozzle of a valve gated runner apparatus includes releasably attaching a valve pin to a movable part of an actuator for moving the valve pin between an open position and a closed position and detaching the valve pin from the actuator by moving the movable part of the actuator towards the open position when the valve pin is immobilized. The valve pin and the movable part valve pin may be releasably attached by a magnetic force. The step of detaching the valve pin from the actuator may be accomplished by overcoming the magnetic force. A valve pin plate can be provided for a plurality of valve pins to be releasably attached to the actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional application of U.S. application Ser. No. 12/772,102 filed Apr. 30, 2010, which is a divisional of U.S. application Ser. No. 11/876,706, filed Oct. 22, 2007, now U.S. Pat. No. 7,722,351, both of which are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    This invention is relates to an injection molding apparatus, and more particularly, an injection molding apparatus having a valve pin. 
       Related Art 
       [0003]    Injection molding apparatuses, such as hot halves and hot runners, commonly use valve pins to control flow of molding material. 
         [0004]    When a cavity, valve pin, heater, mold gate, or other related component wears or fails, the molded product may have defects and the injection molding apparatus may have to be shut down for maintenance or repair. Such downtime eats into production time, which is nearly always sought to be maximized. 
       SUMMARY OF THE INVENTION 
       [0005]    A method for taking a nozzle of a valve gated runner includes the steps of releasably attaching a valve pin to a movable part of an actuator for moving the valve pin between an open position and a closed position and detaching the valve pin from the actuator by moving the movable part of the actuator towards the open position when the valve pin is immobilized. The valve pin and the movable part valve pin may be releasably attached by a magnetic force. The step of detaching the valve pin from the actuator may be accomplished by overcoming the magnetic force. A valve pin plate can be provided for a plurality of valve pins to be releasably attached to the actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    Embodiments of the present invention will now be described more fully with reference to the accompanying drawings, where like reference numbers indicate similar structure. 
           [0007]      FIG. 1  is a cross-sectional view of an injection molding apparatus according to an embodiment of the present invention. 
           [0008]      FIG. 2  is a cross-sectional view of one of the magnetic couplings of  FIG. 1 . 
           [0009]      FIG. 3  is a cross-sectional view of the injection molding apparatus of  FIG. 1  showing the valve pins in their opened positions. 
           [0010]      FIG. 4  is a cross-sectional view showing one of the valve pins of  FIG. 1  immovable. 
           [0011]      FIGS. 5   a  and  5   b  are cross-sectional views of one of the magnetic couplings of  FIG. 1  shown in various positions. 
           [0012]      FIGS. 6   a  and  6   b  are cross-sectional views of a magnetic coupling according to another embodiment of the present invention. 
           [0013]      FIGS. 7   a  and  7   b  are cross-sectional views of a magnetic coupling according to another embodiment of the present invention. 
           [0014]      FIGS. 8   a  and  8   b  are cross-sectional views of a magnetic coupling according to another embodiment of the present invention. 
           [0015]      FIG. 9  is a cross-sectional view of a magnetic coupling according to another embodiment of the present invention. 
           [0016]      FIGS. 10   a  and  10   b  are cross-sectional views of a magnetic coupling according to another embodiment of the present invention. 
           [0017]      FIG. 11  is a cross-sectional view of an injection molding apparatus according to another embodiment of the present invention. 
           [0018]      FIG. 12  is a cross-sectional view of the injection molding apparatus of  FIG. 11  showing the valve pins in their opened positions. 
           [0019]      FIG. 13  is a cross-sectional view showing one of the valve pins of  FIG. 11  immovable. 
           [0020]      FIG. 14  is a cross-sectional view of an injection molding apparatus according to another embodiment of the present invention. 
           [0021]      FIG. 15  is a cross-sectional view of part of an injection molding apparatus according to another embodiment of the present invention. 
           [0022]      FIG. 16  is a cross-sectional view of a portion of a valve pin according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  shows an injection molding apparatus  100  according to an embodiment of the present invention. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0024]    The injection molding apparatus includes an actuator plate  102 , actuators  104 , a valve pin plate  106 , a back plate  108 , a manifold  110 , nozzles  112 , a mold plate  114 , a cavity plate  116 , cores  118 , valve pins  120 , valve pin bushings  122 , and magnetic couplings  124 . The injection molding apparatus  100  can include any number of manifolds and nozzles, in any configuration. In this embodiment, one manifold is shown for simplicity. The injection molding apparatus  100  can include additional components, such as mold plates, alignment dowels, mold gate inserts, and cooling channels, among others. 
         [0025]    The actuator plate  102  has openings for accommodating the actuators  104 . 
         [0026]    If the actuators  104  depend on a working fluid for operation (i.e., pneumatic or hydraulic types), fluid conduits can be provided in the actuator plate  102 . Should the actuators  104  be electric or magnetic or of some other design, electrical conduits can be provided. 
         [0027]    The actuators  104  are disposed in the actuator plate  102  and can be pneumatic, hydraulic, electric, magnetic, or of some other design. The actuators  104  can translate the valve pin plate  106  by linear motion (e.g., a pneumatic piston) or rotary motion (e.g., an electric screw drive). To accomplish this, each actuator  104  has a stationary part (e.g., a housing or cylinder) connected to the actuator plate  102  and has a movable part  125  (e.g., a piston) connected to the valve pin plate  106 . The number of actuators is a design choice, and in other embodiments more or fewer actuators can be used. Any style of actuator is suitable, provided that it can move the valve pin plate  106 . 
         [0028]    The valve pin plate  106  is connected to the movable part  125  of each actuator  104 . The valve pin plate  106  has a plurality of threaded openings for receiving the magnetic couplings  124 . The valve pin plate  106  can move up and down in response to the actuation of the actuators  104 . The valve pin plate  106  need not be a plate as such, but can be any rigid member capable of connecting one or more actuators to a plurality of magnetic couplings. In other embodiments, the valve pin plate  106  is an assembly of stacked plates. 
         [0029]    The back plate  108  is disposed between the valve pin plate  106  and the valve pin bushings  122  and serves to secure the valve pin bushings  122  in the manifold  110 . The back plate  108  has several bores through which the valve pins  120  extend. 
         [0030]    The manifold  110  defines a manifold channel  126  and includes a manifold heater. The manifold channel  126  receives molding material (e.g., plastic melt) from an inlet (not shown) or an upstream manifold (not shown). The manifold heater can be of any design, such as the insulated resistance wire illustrated. It should also be mentioned that, because of the plate interconnections (not shown), the manifold  110  is stationary relative to the stationary parts of the actuators  104 . 
         [0031]    The nozzles  112  are connected to the manifold  110  and each nozzle  112  defines one of a plurality of nozzle channels  128  in communication with the manifold channel  126 . In this embodiment, each nozzle  112  includes a nozzle body, a nozzle flange, a nozzle heater embedded in the nozzle body, a thermocouple, a terminal end for connecting the heater to a power source, a nozzle tip, and a tip retainer. The nozzles  112  in combination with the manifold  110  define a hot runner. 
         [0032]    The mold plate  114  has wells to accommodate and support the nozzles  112 . The wells are sized to thermally insulate the nozzles  112  from the surrounding material. 
         [0033]    The cavity plate  116  and the cores  118  define cavities  130 , and the cavity plate  116  defines mold gates leading to the cavities  130 . The cavity plate  116  and cores  118  are separable from the mold plate  114  along a parting line to allow ejection of molded products from the cavities  130 . In other embodiments, a single cavity can be fed molding material by several nozzles  112 . 
         [0034]    Each of the valve pins  120  extends from one of the magnetic couplings  124  to one of the nozzles  112  for controlling flow of molding material through the mold gates and into the cavities  130 . 
         [0035]    Each valve pin bushing  122  is held to the manifold  110  by the back plate  108 . Each valve pin bushing  122  includes a disc-shaped main body and a cylindrical bushing portion connected to and extending from the main body and into the manifold  110 . Each valve pin bushing  122  has a valve pin bore, which creates a seal with the valve pin  120  while still allowing the valve pin  120  to slide. 
         [0036]    Each magnetic coupling  124  couples a respective valve pin  120  to the valve pin plate  106 . Each magnetic coupling  124  directly transmits actuator closing force to the respective valve pin  120  when the valve pins  120  are being closed (i.e., moved down). Each magnetic coupling  124  also applies a magnetic force to move the respective valve pin  120  when the valve pins  120  are being opened (i.e., moved up). During normal operation, the magnetic force is sufficient to keep the valve pins  120  coupled to the valve pin plate  106  when the valve pins  120  are opened and closed. If one of the valve pins becomes immovable, the respective magnetic force is overcome by an actuator opening force so that the valve pin plate  106  and remaining valve pins  120  move (i.e., up) with respect to the immovable valve pin. The magnetic couplings  124  are described in more detail below. It should be noted that the directions indicated above are reversed if the valve pins  120  are designed to open flow of molding material when moved down and to close flow when moved up. 
         [0037]      FIG. 2  is a cross-sectional view of one of the magnetic couplings  124 . The magnetic coupling  124  includes a housing  202 , a first magnetic part  204 , and a second magnetic part  206 . 
         [0038]    The housing  202  connects the first magnetic part  204  to the valve pin plate  106 . The housing  202  is threaded into a threaded bore of the valve pin plate  106 . A bore  208 , which can also be threaded, is provided through the back end of the housing  202 . 
         [0039]    The first magnetic part  204  is connected to the valve pin plate  106  via the housing  202  and thus moves with the valve pin plate  106 . The first magnetic part is  204  is inserted into the housing  202  and fixed to the housing  202  by way of magnetic attraction when the housing  202  is made of a magnetically responsive material such as steel. If the housing  202  is not made of a magnetically responsive material or if additional fixing force is required, an adhesive or a tight friction fit can be used, for example. A tool can be inserted into the bore  208  of the housing  202  to push the first magnetic part  204  free from the housing  202 . 
         [0040]    The second magnetic part  206  is positioned below the first magnetic part  204  and close enough to establish a magnetic force with the first magnetic part  204 . In this embodiment, the second magnetic part  206  is attractively aligned with the first magnetic part  204  and the resulting the magnetic force is an attractive magnetic force. The second magnetic part  206  is slidable in the housing  202  and is thus moveable with respect to the first magnetic part  204 . The second magnetic part  206  has a T-shaped slot for receiving the head of the valve pin  120 , so that the second magnetic part  206  and the valve pin  120  are connected and can move together. By way of its location, the first magnetic part  204  defines a stopped position of the second magnetic part  206  relative to the first magnetic part  204  (and thus to the valve pin plate  106 ), and the attractive magnetic force tends to force the second magnetic part  206  into the stopped position. When the second magnetic part  206  is pulled away from the first magnetic part  204 , the attractive magnetic force tends to pull the second magnetic part  206  back towards the first magnetic part  204  and into the stopped position. 
         [0041]    In this embodiment, the first magnetic part  204  is a permanent magnet, such as a neodymium magnet or a samarium-cobalt magnet, and the second magnetic part  206  includes magnetically responsive material, such as steel, iron, or similar. The choice between a neodymium magnet, a samarium-cobalt magnet, and a magnet of some other material should be made addressing concerns such as temperature exposure and impact during operation. Magnetically responsive material can be ferromagnetic, ferrous material, or any other kind of material that experiences a significant force in the presence of a magnetic field. In this embodiment, the second magnetic part  206  is made of steel. In other embodiments, the first magnetic part  204  can be of a magnetically responsive material and the second magnetic part  206  can be a permanent magnet, or both parts  204 ,  206  can be some combination of permanent magnets and electromagnets. 
         [0042]    In  FIG. 1  the valve pins  120  are in their closed positions, such that molding material is prevented from flowing through the mold gates and into the cavities  130 .  FIG. 3 , on the other hand, shows the valve pins  120  in their opened positions, such that molding material can flow through the mold gates and into the cavities  130 . As can be seen in  FIG. 3 , the actuators  104  have moved the valve pin plate  106  up thereby moving the magnetic couplings  124 , which, by way of attractive magnetic forces, pull the valve pins  120  up. When the valve pins  120  are to be returned to their closed positions ( FIG. 1 ), the valve pin plate  106  moves down, which causes the magnetic couplings  124  to rigidly (i.e., independently of magnetic forces) push the valve pins  120  down. 
         [0043]      FIG. 4  is a cross-sectional view showing one of the valve pins  120  that has become immovable, held in the closed position by an immobilizing force. As can be seen, three of the valve pins  120  are open, as pulled by the valve pin plate  106  via the magnetic couplings  124 ; while one valve pin  120  is closed (at  400 ), despite the pull of the valve pin plate  106 . As shown, the magnetic coupling  124  connected to the closed valve pin  120  has reacted to the immobilizing force and has extended to compensate for the movement of the valve pin plate  106 . In one example, the immobilizing force is provided by solidified molding material resulting from the nozzle heater being shut down. That is, when a nozzle is to be taken out of service because of a worn valve pin or leaking cavity, the nozzle&#39;s heater can be shut down to stop molding material from flowing. Solidified molding material can also occur if a nozzle heater fails. When the magnetic couplings  124  are designed to have a magnetic force less than the expected immobilizing force, then the magnetic couplings  124  will allow for continued operation of valve pins when one or more nozzles are taken out of service. 
         [0044]    In this embodiment, a selected nozzle  112  can be taken out of service by closing the valve pins  120 , shutting down the selected nozzle&#39;s heater, and then waiting until molding material in the selected nozzle&#39;s channel has solidified or sufficiently cooled to provide a strong enough immobilizing force. Afterwards, the injection molding apparatus  100  can be restarted as usual, and the valve pin  120  of the immobilized nozzle will remain stationary by virtue of the magnetic coupling  124 . The magnetic coupling  124  is also amenable to use with other methods of taking a nozzle out of service. 
         [0045]      FIGS. 5   a  and  5   b  show a magnetic coupling  124  associated with an immobilized valve pin  120 .  FIG. 5   a  shows the valve pin plate  106  down and the valve pin  120  closed, while  FIG. 5   b  shows the valve pin plate  106  up and the valve pin  120  still closed. As indicated at  502 , the valve pin  120  stays in the closed position even though the valve pin plate  106  has moved upwards by a distance  504  (which, in this embodiment, is equivalent to the valve pin travel). The first magnetic part  204  has moved upwards relative to the second magnetic part  206 , which has remained stationary with the fixedly connected valve pin  120 . Viewed with the valve pin plate taken as a reference, the second magnetic part  206  has slid within the housing  202  away from the first magnetic part  204 . As such, a gap  506  (which, in this embodiment, is also equivalent to the valve pin travel) separates the first and second magnetic parts  204 ,  206 . The attractive magnetic force can be viewed as acting within the gap  506  to tend to bring the first and second magnetic parts  204 ,  206  closer together. 
         [0046]      FIGS. 6   a  and  6   b  show a magnetic coupling  600  according to another embodiment of the present invention. The magnetic coupling  600  can be used to couple a valve pin (e.g., the valve pin  120  of  FIG. 1 ) to a valve pin plate (e.g., the valve pin plate  106  of  FIG. 1 ).  FIG. 6   a  shows the valve pin plate  106  down and the valve pin  120  closed, while  FIG. 6   b  shows the valve pin plate  106  up and the valve pin  120  still closed, as in the case of an immobilized valve pin. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0047]    The magnetic coupling  600  includes a housing  602 , a first magnetic part  604 , and a second magnetic part  606 . The housing  602  connects the first magnetic part  604  to the valve pin plate  106 , and thus the first magnetic part  604  moves with the valve pin plate  106 . The magnetic coupling  600  is similar to the magnetic coupling  124  and only differences are described in detail below. 
         [0048]    The second magnetic part  606  is positioned below the first magnetic part  604  and close enough to establish an attractive magnetic force with the first magnetic part  604 . The second magnetic part  606  includes a magnet holder  608 , a permanent magnet  610 , and a valve pin holder  612 . The magnet  610  is inserted into the magnet holder  608  and secured in place by the valve pin holder  612 , which threads into the magnet holder  608 . The valve pin holder  612  has a T-shaped slot for receiving the head of the valve pin  120 . The magnet  606  is attractively aligned with the first magnetic part  604  and the resulting the magnetic force is an attractive magnetic force that tends to pull the second magnetic part  606  back towards the first magnetic part  604  and into the stopped position. 
         [0049]    In this embodiment, the first magnetic part  604  is a permanent magnet, but an electromagnet could also be used. The magnet  610  could also be an electromagnet. 
         [0050]      FIGS. 7   a  and  7   b  show a magnetic coupling  700  according to another embodiment of the present invention. The magnetic coupling  700  can be used to couple a valve pin (e.g., the valve pin  120  of  FIG. 1 ) to a valve pin plate (e.g., the valve pin plate  106  of  FIG. 1 ).  FIG. 7   a  shows the valve pin plate  106  down and the valve pin  120  closed, while  FIG. 7   b  shows the valve pin plate  106  up and the valve pin  120  still closed, as in the case of an immobilized valve pin. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0051]    The magnetic coupling  700  includes a housing  702 , a first magnetic part  704 , and a second magnetic part  706 . The housing  702  connects the first magnetic part  704  to the valve pin plate  106 , and thus the first magnetic part  704  moves with the valve pin plate  106 . The magnetic coupling  700  is similar to the magnetic coupling  124  and only differences are described in detail below. 
         [0052]    The housing  702  connects the first magnetic part  704  to the valve pin plate  106 . The housing includes a threaded cylindrical body  708  and a threaded stopper  710 . The cylindrical body  708  is threaded into a threaded bore of the valve pin plate  106 . The stopper  710  is threaded into the cylindrical body  708 . The lower portion of the cylindrical body  708  has a lip  711 . 
         [0053]    The first magnetic part  704  is a magnet that is connected to the valve pin plate  106  via the housing  702  and thus moves with the valve pin plate  106 . The first magnetic part is  704  is inserted into the cylindrical body  708  of the housing  702  and rests on the lip  711 . If the housing  702  is made of a magnetically responsive material the first magnetic part may be attracted to the lip  711 . The first magnetic part  704  need not fit tightly in the cylindrical body  708 . The first magnetic part  704  has a bore  712  to accommodate the valve pin  120 . 
         [0054]    The second magnetic part includes a valve pin holder  714  and a magnet  716 . The second magnetic part  706  is positioned above the first magnetic part  704  and close enough to establish a magnetic force with the first magnetic part  704 . In this embodiment, the second magnetic part  706  is repulsively aligned with the first magnetic part  704  and the resulting the magnetic force is a repulsive magnetic force. To achieve this, the magnet  716  is repulsively aligned with the first magnetic part  704 . The second magnetic part  706  is slidable in the housing  702  and is thus moveable with respect to the first magnetic part  704 . The valve pin holder  714  has a T-shaped slot for receiving the head of the valve pin  120 , so that the valve pin holder  714  and the valve pin  120  are connected and can move together. If the valve pin holder  714  is made of a magnetically responsive material, then the valve pin holder  714  is attractively connected to the magnet  716 , but this is not necessary. By way of its location, the stopper  710  defines a stopped position of the second magnetic part  706  relative to the first magnetic part  704  (and thus to the valve pin plate  106 ). The repulsive magnetic force tends to force the second magnetic part  706  into the stopped position and tends to force the first magnetic part  704  against the lip  711 . When the second magnetic part  706  is pushed towards the first magnetic part  704 , the repulsive magnetic force tends to push the second magnetic part  706  back towards the stopper  710  and into the stopped position. 
         [0055]    In normal operation, while the valve pin plate  106  moves up and down, the components of the magnetic coupling  700  stay in the relative positions shown in  FIG. 7   a.  The stopper  710  rigidly (i.e., independently of magnetic forces) pushes the valve pin holder  714 , and thus the valve pin  120 , down when the valve pin plate  106  moves down; while the repulsive magnetic force is strong enough to push the magnet  716 , and thus the valve pin holder  714  and the valve pin  120 , up when the valve pin plate  106  moves up. However, when the valve pin  120  is immobilized in the closed position, the immobilizing force overcomes the repulsive magnetic force so that the second magnetic part  706  is held stationary while the first magnetic part  704  moves towards it against the repulsive magnetic force. As a result, the valve pin  120  can be immobilized while the remaining valve pins connected to the valve pin plate  106  can be kept in service. 
         [0056]    In this embodiment, the first magnetic part  704  is a permanent magnet, but an electromagnet could also be used. The magnet  716  could also be an electromagnet. However, neither the first magnetic part  704  nor the magnet  716  could be replaced by magnetically responsive material, as a repulsive magnetic force would not be generated. 
         [0057]      FIGS. 8   a  and  8   b  show a magnetic coupling  800  according to another embodiment of the present invention. The magnetic coupling  800  can be used to couple a valve pin (e.g., the valve pin  120  of  FIG. 1 ) to a valve pin plate (e.g., the valve pin plate  106  of  FIG. 1 ).  FIG. 8   a  shows the valve pin plate  106  down and the valve pin  120  closed, while  FIG. 8   b  shows the valve pin plate  106  up and the valve pin  120  still closed, as in the case of an immobilized valve pin. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0058]    The magnetic coupling  800  includes a plug  802 , a first magnetic part  804 , and a second magnetic part  806 . The magnetic coupling  800  is similar to the magnetic coupling  124  and only differences are described in detail below. 
         [0059]    The plug  802  is threaded into a threaded bore of the valve pin plate  106 . 
         [0060]    The plug  802  is made of magnetically attractive material and is connected (via magnetic attraction) to the first magnetic part  804 , so that the first magnetic part  804  is connected to the valve pin plate  106 . In other embodiments, the plug  802  is not made of magnetically responsive material and is connected to the first magnetic part  804  by an adhesive or other connective means. A lock nut  808  is also provided and is threaded to the plug  802 . The lock nut  808  can be used to lock the position of the plug  802  and the first magnetic part  804 , so that the normal position of the second magnetic part  806  is adjustable. 
         [0061]    The first magnetic part is  804  is inserted into an unthreaded portion of the bore of the valve pin plate  106 . The first magnetic part  804  moves with the valve pin plate  106  via its magnetic attraction to the plug  802  secured to the valve pin plate  106 . In this embodiment, the first magnetic part  804  is a permanent magnet. 
         [0062]    The second magnetic part  806  is positioned below the first magnetic part  804  and close enough to establish a magnetic force with the first magnetic part  804 . In this embodiment, the second magnetic part  806  is made of magnetically responsive material and is thus attractively aligned with the first magnetic part  804  to establish an attractive magnetic force. The second magnetic part  806  is slidable in the unthreaded portion of the bore of the valve pin plate  106  and is thus moveable with respect to the first magnetic part  804 . The second magnetic part  806  has a T-shaped slot for receiving the head of the valve pin  120 , so that the second magnetic part  806  and the valve pin  120  are connected and can move together. By way of its location, the first magnetic part  804  defines a stopped position of the second magnetic part  806 . When the second magnetic part  806  is pulled away from the first magnetic part  804 , the attractive magnetic force tends to pull the second magnetic part  806  back towards the first magnetic part  804  and into the stopped position. 
         [0063]    To adjust the normal operational position of the second magnetic part  806  and thus the valve pin  120 , the lock nut  808  is first loosened, the plug  802  is then rotated in the required direction, and then the lock nut  808  is tightened again. 
         [0064]    In this embodiment, the first magnetic part  804  is a permanent magnet, but an electromagnet could also be used. In addition, the second magnetic part  806  could include a permanent magnet or an electromagnet. 
         [0065]    In another embodiment, the plug is made of magnetically attractive material and is considered the first magnetic part, while the second magnetic part includes a magnet that moves with a valve pin holder made of magnetically attractive material. Such embodiment is similar to that of  FIG. 8  in all respects, except that the magnet is more attracted to the valve pin holder than to the plug. 
         [0066]      FIG. 9  shows a magnetic coupling  900  according to another embodiment of the present invention. The magnetic coupling  900  can be used to couple a valve pin (e.g., the valve pin  120  of  FIG. 1 ) to a valve pin plate (e.g., the valve pin plate  106  of  FIG. 1 ). The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0067]    The magnetic coupling  900  includes a plug  902 , a first magnetic part  904 , a second magnetic part  906 , and a lock nut  908 . The magnetic coupling  900  is similar to the magnetic coupling  800  and only differences are described in detail below. 
         [0068]    The first magnetic part is  904  is an electromagnet having a coil of wire  910  wrapped around or embedded within a core  912 . Wire leads  914  extend out of the magnetic coupling  900  through a bore  916  in the plug  902  that acts as an electrical conduit. The wire leads  914  can be connected to a control circuit (not shown). The second magnetic part  906  is made of magnetically responsive material. 
         [0069]    In other embodiments, where one or more electromagnets are used, electrical conduits for wire leads can be formed in any convenient component. For example, if the second magnetic part  906  is provided with an electromagnet, an electrical conduit can be provided in the valve pin plate  106 . Design of such an electrical conduit can take into account movement of the second magnetic part  906  relative to the valve pin plate  106  should the valve pin  120  become immobilized. 
         [0070]      FIGS. 10   a  and  10   b  show a magnetic coupling  1000  according to another embodiment of the present invention. The magnetic coupling  1000  can be used to couple a valve pin (e.g., the valve pin  120  of  FIG. 1 ) to a valve pin plate (e.g., the valve pin plate  106  of  FIG. 1 ).  FIG. 10   a  shows the valve pin plate  106  down and the valve pin  120  closed, while  FIG. 10   b  shows the valve pin plate  106  up and the valve pin  120  still closed, as in the case of an immobilized valve pin. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0071]    The magnetic coupling  1000  includes a positioning mechanism  1002 , a first magnetic part  1004 , and a second magnetic part  1006 . The positioning mechanism  1002  connects the first magnetic part  1004  to the valve pin plate  106 , and thus the first magnetic part  1004  moves with the valve pin plate  106 . The magnetic coupling  1000  is similar to the magnetic coupling  124  and only differences are described in detail below. 
         [0072]    The positioning mechanism  1002  connects the first magnetic part  1004  to the valve pin plate  106 . The positioning mechanism  1002  includes a base plate  1008 , a positioning bolt  1010 , a lock plate  1012 , and a lock bolt  1014 . The base plate  1008  is bolted or otherwise fixed to the valve pin plate  106  and has a threaded bore for receiving the positioning bolt  1010 . The positioning bolt  1010  threads into the base plate  1008  and the lock plate  1012  and has a head that connects to the first magnetic part  1004 . The lock plate  1012  is located near the base plate  1008  and has threaded bores for the positioning bolt  1010  and the lock bolt  1014 . The lock bolt  1014  threads into the lock plate  1012  and can be tightened to butt against the base plate  1008 . When the normal position of the valve pin  120  is to be adjusted, the position of the first magnetic part  1004  is adjusted by first turning the lock bolt  1014  until the lock plate  1012  is parallel with the base plate  1008 , turning the positioning bolt  1010  until the valve pin  120  is in the required position, and then turning the lock bolt  1014  again to tilt the lock plate  1012  with respect to the base plate  1008  to effectively jam the thread of the positioning bolt  1010  in the threaded bore of the base plate  1008 . The jamming of the positioning bolt  1010  is nonpermanent and simply serves to inhibit rotation of the positioning bolt  1010  and thereby lock the position of the first magnetic part  1004  and thus the normal position of the valve pin  120 . 
         [0073]    The first magnetic part  1004  has a non-circular cross-section to fit in a like-shaped opening of the valve pin plate  106 . This prevents rotation of the first magnetic part  1004  when the positioning bolt  1010  is rotated for adjustment. The first magnetic part  1004  includes an open-ended T-shaped slot  1016  for removably holding the head of the positioning bolt  1010 , as well as a bore  1018  through which a tool can be inserted to push the second magnetic part  1006  free from the first magnetic part  1004 . In this embodiment, the first magnetic part  1004  is made of magnetically responsive material. 
         [0074]    The second magnetic part  1006  is positioned below the first magnetic part  1004  and close enough to establish a magnetic force with the first magnetic part  1004 . In this embodiment, the second magnetic part  1006  is attractively aligned with the first magnetic part  1004  and the resulting the magnetic force is an attractive magnetic force. The second magnetic part  1006  includes a permanent magnet  1020  that establishes the attractive magnetic force and a valve pin holder  1022 . The magnet  1020  is fixed inside a recess of the valve pin holder  1022  using a friction fit, an adhesive, or the like. O-rings  1023  or similar seals are provided between the valve pin holder  1022  and the valve pin plate  106 . The valve pin holder  1022  has a T-shaped slot for receiving the head of the valve pin  120 , so that the second magnetic part  1006  and the valve pin  120  are connected and can move together. By way of its location, the first magnetic part  1004  defines a stopped position of the second magnetic part  1006  relative to the first magnetic part  1004 , and the attractive magnetic force tends to pull the second magnetic part  1006  towards the first magnetic part  1004  and into the stopped position. 
         [0075]    In another embodiment, the first magnetic part  1004  could include a permanent magnet or an electromagnet. The magnet  1020  could also be an electromagnet or could be made from magnetically responsive material. 
         [0076]      FIG. 11  shows an injection molding apparatus  1100  according to an embodiment of the present invention. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0077]    The injection molding apparatus  1100  includes an actuator plate  1102 , an actuator  1104 , a valve pin plate  1106 , a back plate  1108 , a manifold  1110 , a nozzle  1112 , a mold plate  1114 , a cavity plate  1116 , a core  1118 , valve pins  1120 , a valve pin bushing  1122 , and magnetic couplings  1124 . The injection molding apparatus  1100  can include any number of manifolds and nozzles, in any configuration. In this embodiment, one manifold is shown for simplicity. The injection molding apparatus  1100  can include additional components, such as mold plates, alignment dowels, mold gate inserts, and cooling channels, among others. 
         [0078]    The actuator plate  1102  has an opening for accommodating the actuator  1104 . If the actuator  1104  depends on a working fluid for operation, fluid conduits can be provided in the actuator plate  1102 . Should the actuator  1104  be electric or magnetic or of some other design, electrical conduits can be provided. 
         [0079]    The actuator  1104  is disposed in the actuator plate  1102  and can be pneumatic, hydraulic, electric, magnetic, or of some other design. The actuator  1104  can translate the valve pin plate  1106  by linear motion (e.g., a pneumatic piston) or rotary motion (e.g., an electric screw drive). To accomplish this, the actuator  1104  has a stationary part connected to the actuator plate  1102  and has a movable part  1125  connected to the valve pin plate  1106 . The number of actuators is a design choice, and in other embodiments more actuators can be used. Any style of actuator is suitable, provided that it can move the valve pin plate  1106 . 
         [0080]    The valve pin plate  1106  is connected to the movable part  1125  of the actuator  1104  and can move up and down in response to the actuation of the actuator  1104 . The valve pin plate  1106  need not be a plate as such, but can be any rigid member capable of connecting one or more actuators to a plurality of magnetic couplings. In another embodiment, the valve pin plate  1106  is an assembly of stacked plates. 
         [0081]    The back plate  1108  is disposed between the valve pin plate  1106  and the valve in bushing  1122  and serves to secure the valve pin bushing  1122  in the manifold  1110 . The back plate  1108  has several bores through which the valve pins  1120  extend. 
         [0082]    The manifold  1110  defines a manifold channel  1126  and includes a manifold heater. The manifold channel  1126  receives molding material (e.g., plastic melt) from an inlet (not shown) or an upstream manifold (not shown). The manifold heater can be of any design, such as the insulated resistance wire illustrated. It should also be mentioned that, because of the plate interconnections (not shown), the manifold  1110  is stationary relative to the stationary part of the actuator  1104 . 
         [0083]    The nozzle  1112  is connected to the manifold  1110  and defines a plurality of nozzle channels  1128  in communication with the manifold channel  1126 . In this embodiment, the nozzle  1112  includes a nozzle body, a nozzle flange, one or more nozzle heaters (e.g., cartridge heaters) in the nozzle body, a thermocouple, a terminal end for connecting the heater(s) to a power source, nozzle tips, and tip retainers. The nozzle  1112  in combination with the manifold  1110  can define a hot runner. 
         [0084]    The mold plate  1114  has a well to accommodate and support the nozzle  1112 . The well is sized to thermally insulate the nozzle  1112  from the surrounding material. 
         [0085]    The cavity plate  1116  and the core  1118  define cavities  1130 , and the cavity plate  1116  defines mold gates leading to the cavities  1130 . The cavity plate  1116  and the core  1118  are separable from the mold plate  1114  along a parting line to allow ejection of molded products from the cavities  1130 . 
         [0086]    Each of the valve pins  1120  extends from one of the magnetic couplings  1124  through one of the nozzle channels  1128  for controlling flow of molding material through the mold gates and into the cavities  1130 . 
         [0087]    The valve pin bushing  1122  is held to the manifold  1110  by the back plate  1108 . The valve pin bushing  1122  includes a disc-shaped main body and cylindrical bushing portions connected to and extending from the main body and into the manifold  1110 . The valve pin bushing  1122  has valve pin bores, which create seals with the valve pins  1120  while still allowing the valve pins  1120  to slide. 
         [0088]    The magnetic couplings  1124  include a permanent magnet  1132  (first magnetic part) and a plurality of valve pin heads  1134  (second magnetic parts). The magnet  1132  is fixed to the valve pin plate  1106  and each valve pin head  1134  is fixed to or integral with one of the valve pins  1120 . The magnet  1132  can be fixed to the valve pin plate  1106  by magnetic attraction, a friction fit, an adhesive, bolts, or the like. In this embodiment, the magnet  1132  is held to the magnetically responsive valve pin plate  1106  by an attractive magnetic force. The valve pin heads  1134  are positioned below the magnet  1132  and close enough to establish a magnetic force with the magnet  1132 . In this embodiment, the valve pin heads  1134  are made of magnetically responsive material, so that each valve pin head  1134  is attractively aligned with the magnet  1132 . The resulting the magnetic force is an attractive magnetic force that tends to pull each valve pin head  1134  towards the magnet  1132  and into a stopped position against the magnet  1132 . In other embodiments, the magnet  1132  and the valve pin heads  1134  can include or be replaced by other combinations of permanent magnets, electromagnets, and magnetically responsive material. Embodiments using repulsive magnetic forces are also possible (see  FIG. 7 ). 
         [0089]    Each magnetic coupling  1124  couples a respective valve pin  1120  to the valve pin plate  1106 . The magnet  1132  directly transmits actuator closing force to the respective valve pin head  1134  when the valve pins  1120  are being closed (i.e., moved down) by pushing on the valve pin heads  1134 . The magnet  1132  also pulls the valve pins  1120  upwards by attractive magnetic forces acting on the valve pin heads  1134 , when the valve pins  1120  are being opened. During normal operation, the magnetic force is sufficient to keep the valve pins  1120  coupled to the valve pin plate  1106  when the valve pins  1120  are opened and closed. If a valve pin becomes immovable, the respective attractive magnetic force is overcome, so that the immobilized valve pin is decoupled from the magnet  1132 . 
         [0090]    During normal operation the actuator  1104  opens and closes the valve pins  1120  via the magnet  1132  and the heads  1134  of the valve pins  1120 .  FIG. 11  shows the valve pins  1120  closed, while  FIG. 12  shows the valve pins  1120  open. However, when a valve pin  1120  is immobilized (e.g., when a cavity  130  is taken out of service), the head  1134  of the valve pin  1120  decouples from the magnet  1132  when the actuator  1104  pulls the valve pin plate  1106  up, as shown in  FIG. 13 . 
         [0091]      FIG. 14  shows an injection molding apparatus  1400  according to an embodiment of the present invention. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. 
         [0092]    The injection molding apparatus includes an actuator plate  1402 , an actuator  1404 , a back plate  1408 , a manifold  1410 , a nozzle  1412 , a mold plate  1414 , a cavity plate  1416 , a core  1418 , a valve pin  1420 , a valve pin bushing  1422 , and a magnetic coupling  1424 . The injection molding apparatus  1400  can include any number of manifolds and nozzles, in any configuration. In this embodiment, one manifold and one nozzle are shown for simplicity. The injection molding apparatus  1400  can include additional components, such as mold plates, alignment dowels, mold gate inserts, and cooling channels, among others. 
         [0093]    The actuator plate  1402  has an opening for accommodating the actuator  1404 . If the actuator  1404  depends on a working fluid for operation, fluid conduits can be provided in the actuator plate  1402 . Should the actuator  1404  be electric or magnetic or of some other design, electrical conduits can be provided. 
         [0094]    The actuator  1404  is disposed in the actuator plate  1402  and can be pneumatic, hydraulic, electric, magnetic, or of some other design. The actuator  1404  can translate the magnetic coupling  1424  by linear motion (e.g., a pneumatic piston) or rotary motion (e.g., an electric screw drive). To accomplish this, the actuator  1404  has a stationary part connected to the actuator plate  1402  and has a movable part  1425 . 
         [0095]    The back plate  1408  is disposed between the magnetic coupling  1424  and the valve in bushing  1422  and serves to secure the valve pin bushing  1422  in the manifold  1410 . The back plate  1408  has a bore through which the valve pin  1420  extends. 
         [0096]    The manifold  1410  defines a manifold channel  1426  and includes a manifold heater. The manifold channel  1426  receives molding material (e.g., plastic melt) from an inlet (not shown) or an upstream manifold (not shown). The manifold heater can be of any design, such as the insulated resistance wire illustrated. It should also be mentioned that, because of the plate interconnections (not shown), the manifold  1410  is stationary relative to the stationary part of the actuator  1404 . 
         [0097]    The nozzle  1412  is connected to the manifold  1410  and defines a nozzle channel  1428  in communication with the manifold channel  1426 . In this embodiment, the nozzle  1412  includes a nozzle body, a nozzle flange, a nozzle heater, a thermocouple, a terminal end for connecting the heater to a power source, a nozzle tip, and a tip retainer. The nozzle  1412  in combination with the manifold  1410  can define a hot runner. 
         [0098]    The mold plate  1414  has a well to accommodate and support the nozzle  1412 . The well is sized to thermally insulate the nozzle  1412  from the surrounding material. 
         [0099]    The cavity plate  1416  and the core  1418  define a cavity  1430 , and the cavity plate  1416  defines a mold gate leading to the cavity  1430 . The cavity plate  1416  and the core  1418  are separable from the mold plate  1414  along a parting line to allow ejection of a molded product from the cavity  1430 . 
         [0100]    The valve pin  1420  extends from the magnetic coupling  1424  through the nozzle channel  1428  for controlling flow of molding material through the mold gate and into the cavity  1430 . 
         [0101]    The valve pin bushing  1422  is held to the manifold  1410  by the back plate  1408 . The valve pin bushing  1422  includes a disc-shaped main body and a cylindrical bushing portion connected to and extending from the main body and into the manifold  1410 . The valve pin bushing  1422  has a valve pin bore, which creates a seal with the valve pin  1420  while still allowing the valve pin  1420  to slide. 
         [0102]    The magnetic coupling  1424  includes a housing  1431 , a permanent magnet  1432  (first magnetic part), a valve pin head  1434  (second magnetic part), and a set screw  1436 . The housing  1431 , which in this embodiment is a simple tube, is fixed to the movable part  1425  of the actuator  1404  and the magnet  1432  is adjustably fixed in the housing  1431  by the set screw  1436 , such that the magnet  1432  is fixed to the movable part  1425  of the actuator  1404 . In other embodiments, the magnet  1432  can be fixed to the housing  1431  by magnetic attraction, a friction fit, an adhesive, bolts, or the like. The valve pin head  1434  is fixed to or integral with the valve pin  1420 . The valve pin head  1434  is positioned below the magnet  1432  and close enough to establish a magnetic force with the magnet  1432 . In this embodiment, the valve pin head  1434  is made of magnetically responsive material, so that the valve pin head  1434  is attractively aligned with the magnet  1432 . The resulting the magnetic force is an attractive magnetic force that tends to pull the valve pin head  1434  towards the magnet  1432  and into a stopped position against the magnet  1432 . In other embodiments, the magnet  1432  and the valve pin head  1434  can include or be replaced by other combinations of permanent magnets, electromagnets, and magnetically responsive material. Embodiments using repulsive magnetic forces are also possible (see  FIG. 7 ). 
         [0103]    The magnetic coupling  1424  couples the valve pin  1420  to the movable part  1425  of the actuator  1404 . The magnet  1432  directly transmits actuator closing force to the valve pin head  1434  when the valve pin  1420  is being closed (i.e., moved down) by pushing on the valve pin head  1434 . The magnet  1432  also pulls the valve pin  1420  upwards by the attractive magnetic force acting on the valve pin head  1434 , when the valve pin  1420  is being opened. During normal operation, the magnetic force is sufficient to keep the valve pin  1420  coupled to the movable part  1425  of the actuator  1404  when the valve pin  1420  is opened and closed. If the valve pin becomes immovable, the attractive magnetic force is overcome, so that the immobilized valve pin  1420  is decoupled from the magnet  1432  (see  FIG. 13 , for example). 
         [0104]      FIG. 15  shows part of an injection molding apparatus  1500  according to an embodiment of the present invention. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. Only differing features are described in detail. 
         [0105]    An actuator  1504  is coupled to a back plate  1502 . A valve pin  1520  (second magnetic part) is positioned adjacent a moveable part  1525  (first magnetic part) of the actuator  1504 . The valve pin  1520  is made of magnetically responsive material and is attractively aligned with the moveable part  1525 , which is a permanent magnet or an electromagnet. Therefore, the valve pin  1520  and the movable part  1525  of the actuator  1504  form a magnetic coupling. Operation is similar to the other embodiments, with the valve pin  1520  decoupling from the movable part  1525  of the actuator  1504  when the attractive magnetic force is overcome. 
         [0106]      FIG. 16  shows a portion of a valve pin  1600  according to an embodiment of the present invention. The features and aspects described for the other embodiments can be used accordingly with the present embodiment. Only differing features are described in detail. 
         [0107]    The valve pin  1600  includes an upper portion  1602 , a lower portion  1604 , and a magnet  1606  between the upper portion  1602  and the lower portion  1604 . In normal operation, when the upper portion  1602  is pushed down by an actuator (not shown), the upper portion  1602  pushes the magnet  1606  down, which pushes the lower portion  1604  of the valve pin  1600  down in a direct manner. When the upper portion  1602  is pulled up by the actuator, the attractive magnetic force provided by the magnet  1606  magnetically couples the upper portion  1602  to the lower portion  1604 , so that the lower portion  1604  is pulled up as well. In the lower portion  1604  becomes immobilized, when the upper portion  1602  is pulled up by the actuator, the magnet  1606  remains coupled to either the upper portion  1602  or the lower portion  1604  while the attractive magnetic force is overcome and upper portion  1602  and the lower portion  1604  separate. Both the upper and lower portions  1602 ,  1604  can be made of magnetically attractive material. Or one of the upper and lower portions  1602 ,  1604  can be made of magnetically attractive material while the other is not, in which case, the magnet  1606  is fixed (e.g., by adhesive, mechanically, etc) to the non-magnetically attractive portion. The magnet  1606  can be a permanent magnet or an electromagnet. 
         [0108]    In embodiments described herein, supplementary components have been omitted for clarity. For example, a designer may choose to provide many of the threaded components described with lock nuts or another mechanism to stop the threads from working free over time. 
         [0109]    In addition, the valve pins described are down-closed and up-open. 
         [0110]    Reverse gating (up-closed, down-open) and lateral gating (e.g., edge gating) are also possible. 
         [0111]    Moreover, structure, such as a valve pin plate, located near permanent magnets can be provided with cooling channels or cooling devices, if the expected operating temperature is higher than the allowable temperature for the type of magnet used. 
         [0112]    Regarding the mechanical functionality of the embodiments described above, electromagnets are equivalent to permanent magnets. Electromagnets, however, can be shut off such that a valve pin can be taken out of service regardless of the magnitude of any valve-pin immobilizing force. On the other hand, permanent magnets do not require wiring, electrical conduits, and and/or control. The choice between electromagnets and permanent magnets is left to a designer, who can take into account these differences and any others. 
         [0113]    Lastly, the terms fixed, connected, coupled, etc used herein do not exclude indirect connections between parts. For example, a part can be fixed to another part with any number of parts in between or none at all (i.e., directly fixed). In addition, parts described as fixed, connected, coupled, etc can also be integral, if the resulting functionality is not changed. 
         [0114]    Although many embodiments of the present invention have been described, those of skill in the art will appreciate that other variations and modifications may be made without departing from the spirit and scope thereof as defined by the appended claims. All patents and publications discussed herein are incorporated in their entirety by reference thereto.