Patent Publication Number: US-2023150179-A1

Title: Hot-runner assembly with compact electric actuator

Description:
FIELD OF THE DISCLOSURE 
     This disclosure pertains to a hot-runner injection molding apparatus having an actuator. 
     BACKGROUND OF THE DISCLOSURE 
     In a hot-runner injection molding apparatus, the liquid resin (molten plastic) is maintained in a molten state within channels defined in a heated manifold. The channels convey the molten plastic material from an injection molding machine to one or more nozzles that convey the molten plastic to at least one mold cavity via gates defined at an interface between the nozzle and the mold cavity. After the mold cavity is filled, only the mold cavity is cooled to allow removal of a solid molded part. The resin in the manifold channels and nozzles are maintained at a temperature sufficient to keep the plastic in a liquid state, thus reducing cycle time and waste as compared with cold runner injection molding apparatuses, wherein the resin conveying channels are defined within the mold plates. 
     Because of the susceptibility of electric actuators to degradation and failure when exposed to the high temperatures needed at the hot-runner manifold, hydraulic or pneumatic actuators are typically employed in hot-runner injection molding apparatus to control the flow of molten resin into the mold cavity (or cavities). In these hot-runner injection molding apparatuses employing electric actuators, the electric actuators are positioned remotely from the manifold and/or are provided with external cooling means (e.g., a cooled plate between the manifold and actuator), adding considerable complexity and expense as compared with the more conventionally used pneumatic or hydraulic actuators. 
     Despite these generally recognized disadvantages with electric actuators, they also have advantages, including the ability to more precisely control valve pin movement and positioning, which in turn can have associated advantages pertaining to part quality and production efficiency. 
     Electric actuators for controlling the valve pin positions of injection molding systems offer significant advantages in certain applications, including cleaner operation by avoiding the inevitable leaks that occur with hydraulic actuators, and more precise control over valve pin position and flow of resin into the mold cavities. Cleanliness is an important consideration and advantage in the manufacture of injection molded items used for pharmaceutical and medical products. Precise control of melted resin flowing into a mold cavity can also be extremely beneficial to avoid or minimize imperfections, such as flow lines (wavy patterns or discolorations) caused by more rapid cooling in thinner sections of the molded part, and knit lines (where two or more flows into a mold meet). These imperfections, which do not typically affect functionality or integrity, but can cause undesirable or even unacceptable aesthetics. 
     While electric actuators have advantages with respect to flow control and cleanliness, conventional electric actuators used for injection molding systems are bulkier than the hydraulic actuators currently used in most injection molding systems, which have a transmission for converting rotary motion of the output shaft of the electric motor into linear movement to facilitate linear movement of the valve pin along a longitudinal axis of a nozzle directing resin flow into the mold. In conventional electric actuators used for injection molding, the transmission is external to the motor assembly and is often located in a housing separate from the motor housing. As a result, assembly of the injection molding apparatus becomes more cumbersome, and the transmission occupies volume that limits or restricts flexibility in actuator positioning, and consequently, flexibility in the design of the molding apparatus. 
     SUMMARY OF THE DISCLOSURE 
     Described herein are injection molding systems employing a compact electric motor valve actuator in which the valve pin for controlling resin flow to the mold cavity is configured to directly or indirectly couple the head of the valve pin to a drive shaft located within a space defined within the internal boundaries (or surfaces) of the rotor of the electric motor. 
     In certain aspects of the disclosure, the actuator can be an electric, pneumatic or hydraulic actuator including a housing or actuator body having an integral cooling block or plate with internal conduits for circulating a coolant liquid (e.g., water). 
     In other aspects, the actuator can be an electric, pneumatic or hydraulic actuator that is supported on an insulating member that positions the actuator so that there is a gap between a surface of the actuator housing facing the hot-runner manifold and the surface of the insulating support plate facing the actuator housing. 
     In a further aspect of the disclosure, a compact contactless linear position sensor is located in the actuator housing, and configured to precisely monitor the position of the valve pin to facilitate precise control of resin flow to a mold cavity. The actuator can be an electric, pneumatic or hydraulic actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an elevational cross-section of an apparatus in accordance with this disclosure. 
         FIG.  2    is an enlarged view of the actuator and a portion of the hot-runner manifold on which the actuator is supported. 
         FIG.  3    is a perspective view of an actuator support and mechanism for fixing the valve pin to a linear drive shaft. 
         FIG.  4    is an enlarged cross-sectional view of an alternate embodiment in which the valve pin is indirectly coupled to the actuator drive shaft via a valve pin extension. 
         FIG.  5    is a perspective view of the actuator. 
         FIG.  6    is a cross-sectional perspective showing a contactless linear position sensor mounted within the actuator body to provide a compact actuator assembly that facilitates precise flow control. 
         FIGS.  7 A- 7 D  illustrate a procedure for securing an anti-rotation device or part to a support plate mounted on a hot-runner manifold to prevent rotation of a valve pin. 
         FIG.  7 E  illustrates an alternative non-anti-rotation configuration. 
         FIG.  8    is a partial cross-sectional view of an actuator mounting assembly that provides improved heat management. 
     
    
    
     DETAILED DESCRIPTION 
     Shown in  FIG.  1    is a hot-runner assembly  10  for use in delivering liquid resin (typically a molten thermoplastic composition) from an injection molding machine (not shown) to a mold cavity  12  defined by mold plates  14 ,  16 . The resin flows from the injection molding machine into a channel  18  disposed in a sprue bushing  20  heated by electrical resistance heating element  22  and is distributed through manifold channels  24  defined in heated (or heatable) manifold  26 . The heated manifold is provided with electrical resistance heating elements  28  capable of maintaining the resin at a desired temperature that facilitates flow. The resin flows from the manifold channels  24  into an annular space  30  defined between internal walls  32  of nozzles  34  and a valve pin  36  that is linearly movable within nozzle  34  along a longitudinal axis of the nozzle between an open position (shown for the nozzle on the left in  FIG.  1   ) and a closed position (shown for the nozzle on the right in  FIG.  1   ). When the valve pin  36  is in the open position, liquid resin (e.g., molten thermoplastic) flows into mold cavity  12 . Nozzles  34  are maintained at a temperature sufficient to keep the resin in a liquid (flowable) state by electrical resistance heating elements  38 . Nozzles  34  can be provided with external threads  40  on the inlet end of the nozzle which engage internal threads of a bore through the bottom of manifold  26  to provide a fluid-tight seal. The mold can define a single cavity or multiple cavities, and each cavity can be supplied with resin from a single nozzle or multiple nozzles. 
     The position and rate of movement of valve pins  36  are controlled by an actuator  100 . Actuator  100  includes a body and/or housing for an electric motor  101  and converts rotational movement of the electric motor into linear movement (up and down in  FIG.  2   ) of a drive shaft  102  (e.g., an externally threaded shaft having a cylindrical longitudinal bore inside), which in the illustrated example has an elongate internally threaded bore  104  going through the whole length of the drive shaft. Rotation of rotor  101 R relative to stator  101 S around axis  105  ( FIG.  6   ) can be converted to linear movement of drive shaft  102  such as by providing threaded structure on the rotor that directly or indirectly (e.g., planetary roller screw mechanism) engages external threads on drive shaft  102 . The extent of travel of drive shaft  102  can be limited to the confines of the body of actuator  100 . Bore  104  has a central axis  105  coincident with the central axis of pin  36  and nozzle  34 . The body and/or housing of actuator  100  has a bottom opening  107  and a top opening  109  that allows access to threaded bore  104  to allow an externally threaded valve pin nut  106  to be threaded into bore  104  from both directions. A lock nut  108  can be threaded into bore  104  from the top opening to lock the position of valve pin nut  106  and valve pin  36  after it has been adjusted. A lower end of valve pin nut  106  has an inwardly projecting semi-circumferential rim  111  that engages a circumferential groove  112  at an upper end of valve pin  36  to secure valve pin  36  to valve pin nut  106 . An opening in the rim allows the valve pin  36  to be inserted into valve pin nut  106 . The threaded connection between valve pin nut  106  and drive shaft  102  can be replaced with a fixed or other connection between the drive shaft  102  and valve pin nut  106 , although this would eliminate the possibility of manually adjusting the valve pin position (as described below). 
     Notably, the pin head  110  is coupled to valve pin nut  106 , which is fixed within elongated internally threaded bore  104  of drive shaft  102 , such that the head  110  of valve pin  36  is directly or indirectly coupled to the drive shaft within a cylindrical space defined by the interior radial boundaries of the rotor and opposite ends of the rotor. 
     Valve pin nut  106  can have a tool-head engagement structure  114  that can be engaged by a tool, such as an Allen wrench to allow manual adjustment of the position of valve pin nut  106  and pin  36 . Similarly, lock nut  108  has a tool-head engagement structure and bore  116  to allow tightening of lock nut  108  against valve pin nut  106  using a tool such as an Allen wrench to keep the valve pin nut  106  from moving or rotating. In the illustrated embodiment, engagement structures  114  and  116  are hexagonal sockets. However, other shapes or tool-engagement means are possible. Top plate  64  can be provided with openings or bores  117  to allow access to tool engagement structure (e.g., sockets  114 ,  116 ) to facilitate manual adjustment of the valve pin position without removal of plate  64  or disassembly of hot-runner assembly  10 . This arrangement can be employed with an electric, pneumatic or hydraulic actuator. 
     Electrical connectors  118 ,  120  are provided for powering and controlling the electric motor, and/or to power and receive signals from an encoder that tracks drive shaft position. 
     Actuator  100  can be provided with an integral cooling plate having a coolant inlet port  122  and a coolant outlet port  124  to allow a coolant (e.g., chilled water or oil) to be circulated through the body and/or housing of the actuator to protect the motor against degradation or failure caused by overheating. Integration of the cooling block into the actuator body also simplifies assembly and disassembly of an injection molding apparatus. 
     Actuator  100  can be supported on an insulating support plate  126  (see  FIG.  3   ). Support plate  126  can, and preferably does, have a relatively low thermal conductivity. Preferred materials for support plate  126  are stainless steel and titanium or other material having a thermal conductivity equal to or less than the thermal conductivity of titanium. Support plate  126  can be releasably secured to manifold  26 , such as with screws or bolts (not shown). 
     When assembled, the upper end of valve pin  36  extends into bore  104  through openings in manifold  26 , support plate  126  and the body or housing of actuator  100  to provide a vertically compact design for mold  10 . 
     Optionally, an anti-rotation disc or guide  130  ( FIGS.  7 A- 7 D ) can be releasably secured to support plate  126  with bolts  132 . Part  130  has an aperture (e.g., keyhole design)  134  for passage of valve pin  36 . Aperture  134  has a shape configured to engage a section of valve pin  36  having a non-circular profile (e.g., parallel flats that fit the key hole) to prevent rotation of the pin around the longitudinal axis of the pin  36  and nozzle  34 . In the illustrated embodiment, the non-circular profile includes two opposing flat or planar surfaces  136  (one of which is shown in  FIG.  3   ). While flat surfaces  136  are engaged by straight edges  134  of an aperture through the anti-rotation part  130  of the illustrated embodiment, other anti-rotational means can be provided, such as splines, grooves, and other structures that can prevent rotation of valve pin  36 . 
     The procedure of securing anti-rotation part  130  to support plate  126  and engaging surfaces of part  130  with surfaces of pin  36  to prevent rotation of pin  36  is illustrated in  FIGS.  7 A- 7 D . The first step involves lowering part  130  onto support plate  126  with pin  36  extending through an enlarged section of aperture  134  of part  130  ( FIG.  7 A ). The next step involves sliding part  130  in the direction indicated by arrow  170  in  FIG.  7 A  with the flat surfaces  135  of aperture  134  engaging the flat surfaces  136  of pin  36  (as shown in  FIG.  7 B ). It may be necessary to rotate part  130  and pin  36  together while in the conformation shown in  FIG.  7 B  so that fastener openings  172  through part  130  are aligned with threaded bores  174  in the upper surface of support plate  126 . Then fasteners  132  are aligned with openings  172  ( FIG.  7 C ) and threaded into bores  174  ( FIG.  7 D ). 
     Manifold  26  and actuators  100  are located in a space generally bounded by a top mold plate  64  and an intermediate mold plate  66 . 
     Assembly  10  can also include various lower support elements  68 , dowels  70 , and upper support elements  72  for facilitating proper alignment and spacing of the components of the assembly. 
     A pin seal  138  prevents liquid resin from leaking upwardly from channel  24  of manifold  26 . 
     The disclosed apparatus allows adjustment of the valve pin using dedicated tools/wrenches etc. from the back side of the actuator (facing the mold back plate  64 ) (opposite valve pin or valve pin elongation side). 
     The disclosed apparatus can allow coupling and decoupling of the actuator axially to the valve pin (by screwing down the valve pin nut  106  while lifting the actuator straight up which doesn&#39;t interfere with adjacent actuators). 
     The valve pin can be suspended within the height of the actuator. In particular, the valve pin can be directly or indirectly coupled to the drive shaft of the actuator within a volume radially inward of the rotor of the electric motor to provide an extremely compact design that maximizes design flexibility and minimizes labor during assembly and disassembly of the injection molding apparatus. 
     The disclosed apparatus can also allow mounting of the actuator axially to the valve pin on a thermal insulation support plate in direct contact to the hot-runner manifold; wherein the support plate can have integrated or extra support columns  180  that can protrude along the actuator corners ( FIG.  8   ). 
     Shown in  FIG.  4    is an alternative arrangement in which the valve pin  36  is indirectly coupled to drive shaft  102  (rather than directly as shown in  FIGS.  1  and  2   ) by a valve pin extension  140  outside the actuator or motor (not as compact as our design). 
     The actuator  100  can be installed and coupled to the valve pin  36  axially, i.e., without moving the actuator laterally away from axis  105 . This can be accomplished by first positioning the valve pin through the manifold and into the associated nozzle with an upper end of the valve pin projecting upwardly from the top of the manifold (i.e., the surface opposite the surface from which the nozzles extend). Thereafter, support plate  126  can be attached to the manifold (such as with screws) and anti-rotation disc can be positioned around valve pin  36  and secured to the support with bolts  132 . Next, valve pin nut  106  can be positioned onto the head (top end) of valve pin  36 . Actuator  100  is then positioned with the bore of drive shaft  110  in axial alignment with the valve pin. The tool engagement structure of valve pin nut  106  can then be accessed via the top opening  109  of actuator  100  with a tool to rotate valve pin nut  106  and thread nut  108  into the threaded bore  104  of drive shaft  102 . 
     Alternatively, as shown in  FIG.  7 E , a non-anti-rotation configuration can be employed. 
     As illustrated most clearly in  FIGS.  5  and  6   , actuator  100  can be supported on support plate member  126  with a space or gap  145  between a bottom surface of the actuator and an upper surface of the insulating support member. Supports  126   a  can be integrally machined on member  126  ( FIG.  2   ), or formed as separate components  150  ( FIGS.  5  and  6   ) to better facilitate manufacturing and reduce waste. Both support plate  126  and support columns  150  (or  126   a ) are preferably made of stainless steel, titanium, or other material exhibiting a low thermal conductivity. This structure provides sufficient separation between the hot-runner manifold  26  and actuator  100 , and avoids direct contact between the actuator housing and the hot surface like the manifold or the support plate such that both thermal loads and mechanical loads on the integral cooling block or the actuator housing with separate cooling are minimal. 
     The use of a compact linear position sensor  160  within the body of actuator  100  is illustrated in  FIG.  6   . The sensor is positioned on a side (above in the drawing) of the motor opposite the side of the housing closest to the hot-runner manifold to reduce exposure of the sensor to high temperatures. Additional cooling strategies can be used/considered for applications with high mold temperatures such as a cooling plate on the top of the actuator or if the mold is cold enough the actuator just needs to have contact to the mold in the back area to indirectly cool the actuator from the back side. Sensor  160  is preferably a contactless position sensor such as an inductive sensor (e.g., commercially available from Cambridge Integrated Circuits Ltd., Cambridge, United Kingdom), a magnetic Hall effect contactless linear position sensor (e.g., commercially available from Active Sensors Inc., Indianapolis, Ind.), etc. Optical sensors or potentiators may also be employed to detect the position of pin  36 . Sensor  160  can be positioned and configured to precisely determine the position of valve pin  36  to allow precise control of resin flow into a mold using a highly compact and reliable actuator unit, preferably having integral cooling and contactless linear position sensing means. Sensor  160  can be used with pneumatic or hydraulic actuators, as well as electric actuators. Sensor  160  can be an absolute position sensor. 
     Shown in  FIG.  8    is an actuator  100  that is mounted in a manner that reduces heat transfer from a hot-runner manifold (not shown in  FIG.  8   ) on which the actuator is mounted. A support plate  126  is fastened directly to the hot-runner manifold (such as with fasteners  190 ). Separate (i.e., non-integral) support columns  180  support actuator  100  in spaced relationship to support plate  126 , such that an air gap  145  is located between the underside of the actuator housing and support plate  126 . Support plate  126  and/or support columns  180  can be formed of a material having a low thermal conductivity (e.g., titanium or stainless steel, or possibly a ceramic material). A bore  193  extends axially through a majority of the length of support column  180 , whereas threaded fastener  194  is of a length such that it can only be threaded into a minority of the length of the bore, whereby the resulting air gap or void reduces heat transfer along support column  180  and fastener  194 . The end  195  of support column  180  coupled to plate  126  can be externally threaded to mate with internal threads of a bore extending through support plate  126 , with the threaded end  194  being a larger diameter than the diameter of bore and fastener  194  to prevent loosening of support column  180  from support plate  126  when fastener  194  is loosened from threaded bore  193 . 
     The above description is intended to be illustrative, not restrictive. The scope of the invention should be determined with reference to the appended claims along with the full scope of equivalents. It is anticipated and intended that future developments will occur in the art, and that the disclosed devices, kits and methods will be incorporated into such future embodiments. Thus, the invention is capable of modification and variation and is limited only by the following claims.