Hot-runner assembly with internally cooled axially mounted electric actuator

A hot-runner injection molding apparatus that facilitates use of electric actuators in a compact design includes a hot-runner manifold defining resin channels for conveying resin to nozzles that serve as conduits for introducing liquid resin into a mold cavity, a valve pin configured for linear movement along a longitudinal axis of the nozzle to control flow of liquid resin through the nozzle, and an electric actuator having a body containing an electric motor, wherein the electric actuator body includes channels for circulating a coolant.

FIELD OF THE DISCLOSURE

This disclosure pertains to a hot-runner injection molding apparatus having an electric actuator configured for circulating a coolant fluid within the body of the actuator to facilitate mounting of the actuator in close proximity to the hot-runner manifold while preventing overheating of the electric motor of the actuator, and more particularly to such apparatus wherein the actuator can be axially assembled on the hot-runner manifold without substantial lateral clearance, allowing a plurality of actuators to be assembled onto the manifold in very close proximity to each other.

DISCUSSION OF THE PRIOR ART

U.S. Pat. Nos. 9,492,960 and 9,937,648 disclose an apparatus for controlling fluid flow to a mold, which includes a manifold, a valve pin having a pin axis, a pin connector and a stem, the valve pin being drivable into and out of open and closed positions relative to the gate. An electric actuator comprising an electric motor comprised of a motor housing that houses a drive shaft having a drive gear and a drive axis, a transmission comprised of a gear shaft, the drive gear and the transmission gear being drivably interconnected and arranged such that the drive axis and the gear axis are non-coaxially mounted or disposed relative to each other, wherein one or the other of the motor housing or the transmission housing are removably attached to a top clamping or mounting plate that is mounted upstream of the manifold and fixedly interconnected to a mold.

U.S. Pat. No. 6,294,122 discloses an injection molding machine including an apparatus for controlling movement of a pin comprising a plastic melt flow channel having an output end for delivering molten plastic injected into the channel under pressure to a mold cavity, wherein the pin comprises an elongated rod having an axis and an end, the pin being slidably mounted within the channel for movement along its axis within the channel, an electrically driven motor drivably interconnected to an actuating mechanism, wherein the actuating mechanism is drivably interconnected to the end of the pin, the motor being controllably drivable to drive the pin through movement along its axis within the channel.

EP 2679374A1 discloses an apparatus for injection molding of plastic materials, which includes a hot runner, at least one injector, including a nozzle mobile within which is a valve pin driven by a rotary electric motor and an associated transmission including a screw-and-nut assembly for converting the rotation of the shaft of the electric motor into a translation of the valve pin. At least two from among the valve pin, the rotary electric motor and the screw-and-nut assembly are set parallel alongside one another.

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.

SUMMARY OF THE INVENTION

This disclosure addresses the need for utilizing electric actuators for controlling valve pin position and movement in a hot-runner injection molding apparatus, while protecting the actuator from overheating and providing a more compact apparatus that does not use separate cooling plates or require remote mounting of the actuator. The apparatus includes a hot-runner manifold having a resin channel for conveying a liquid resin from an injection molding machine toward a mold cavity, a nozzle for conveying the liquid resin from an outlet end of the resin channel to an inlet of a mold cavity, a valve pin configured for linear movement along a longitudinal axis of the nozzle to control flow of the liquid resin through the nozzle and into the mold cavity, and a directly cooled electric actuator having an electric motor and a linear drive shaft, wherein both the electric motor and the linear drive shaft are contained within the body of the electric actuator, and wherein the valve pin is directly or indirectly coupled to the drive shaft such that linear movement of the drive shaft produces co-linear movement of the valve pin.

The directly cooled electric actuator can be mounted in a space between the hot-runner manifold and an upper mounting plate.

In certain aspects of this disclosure, the directly cooled electric actuator is directly and releasably attached to a support having a relatively high resistance to conductive heat transfer (e.g., stainless steel or titanium).

In particular embodiments, the directly cooled electric actuator has, within the body of the actuator, a linear drive shaft and a transmission mechanism that converts rotational movement of the electric motor into translational movement of the drive shaft.

In particular aspects of this disclosure, the linear drive shaft has an internally threaded bore extending along the length of the shaft, and the body and/or housing of the actuator has openings at opposite ends (e.g., top and bottom) to allow access to the opposite ends of the threaded bore. This arrangement allows the upper end of the valve pin to extend upwardly into the internally threaded bore for engagement with an externally threaded valve pin nut. An externally threaded lock nut can be tightened against the valve pin nut on the side opposite of the valve pin to lock the position of the valve pin relative to the liner drive shaft.

The disclosed arrangement allows the actuator to be assembled onto the manifold along and coincident with the longitudinal axis of the nozzle and valve pin without requiring movement of the actuator laterally (i.e., radially) from the axis, thereby making it possible to design hot-runner injection molding systems (i.e., apparatus) having a plurality of nozzles, valve pins and actuators in closer proximity to each other than would otherwise be possible.

The arrangement allows an upper end of the valve pin (or a valve pin extension) to be positioned within the drive shaft and therefore within the body of the actuator, facilitating a vertically compact design.

DETAILED DESCRIPTION

Shown inFIG. 1is a hot-runner assembly10for use in delivering liquid resin (typically a molten thermoplastic composition) from an injection molding machine (not shown) to a mold cavity12defined by mold plates14,16. The resin flows from the injection molding machine into a channel18disposed in a sprue bushing20heated by electrical resistance heating element22and is distributed through manifold channels24defined in heated (or heatable) manifold26. The heated manifold is provided with electrical resistance heating elements28capable of maintaining the resin at a desired temperature that facilitates flow. The resin flows from the manifold channels24into an annular space30defined between internal walls32of nozzles34and a valve pin36that is linearly movable within nozzle34along a vertical longitudinal axis of the nozzle between an open position (shown for the nozzle on the left inFIG. 1) and a closed position (shown for the nozzle on the right inFIG. 1). When the valve pin36is in the open position, liquid resin flows into mold cavity12. Nozzles34are maintained at a temperature sufficient to keep the resin in a liquid (flowable) state by electrical resistance heating elements38. Nozzles34can be provided with external threads40on the inlet end of the nozzle which engage internal threads of a bore through the bottom of manifold26to 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 pins36are controlled by an actuator100. Actuator100includes a body and/or housing for an electric motor101and converts rotational movement of the electric motor into linear movement (up and down inFIG. 2) of a drive shaft102, which in the illustrated example has an elongate internally threaded bore104. Rotation of motor101generally around axis105can be connected to linear movement of drive shaft102such as by providing threaded structure on the rotor of electric motor101that engages external threads on drive shaft102. The extent of travel of drive shaft102can be limited to the confines of the body of actuator100. Bore104has a central axis105coincident with the central axis of pin36and nozzle34. The body and/or housing of actuator100has a bottom opening107and a top opening109that allows access to threaded bore104to allow an externally threaded valve pin nut106to be threaded into bore104. A lock nut108can be threaded into bore104from the top opening to lock the position of nut106and valve pin36after it has been adjusted. A lower end of nut106has an inwardly projecting semi-circumferential rim111that engages a circumferential groove112at an upper end of valve pin36to secure valve pin36to nut106. An opening in the rim allows the valve pin36to be inserted into nut106. The threaded connection between valve pin nut106and drive shaft102can be replaced with a fixed or other connection between the shaft102and nut106, although this would eliminate the possibility of manually adjusting the valve pin position (as described below).

Nut106has a tool-head engagement structure114that can be engaged by a tool, such as an allen wrench to allow manual adjustment of the position of nut106and pin36. Similarly, lock nut108has a tool-head engagement structure116to allow tightening of lock nut108against valve pin nut106using a tool such as an allen wrench. In the illustrated embodiment, engagement structures114and116are hexagonal sockets. However, other shapes or tool-engagement means are possible. Top plate64can be provided with openings or bores117to allow access to tool engagement structure (e.g., sockets114,116) to allow manual adjustment of the valve pin position without removal of plate64or disassembly of hot-runner assembly10.

Electrical connectors118,120are provided for powering and controlling the electric motor, and to power and receive signals from an encoder that tracks drive shaft position.

A coolant inlet port122and a coolant outlet port124are provided 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.

Actuator100can be supported on an insulating support member126. Support126can, and preferably does, have a relatively low thermal conductivity. Preferred materials for member126are stainless steel and titanium or other material having a thermal conductivity equal to or less than the thermal conductivity of titanium. Support126can be releasably secured to manifold26, such as with screws or bolts (not shown).

When assembled, the upper end of valve pin36extends into bore104through openings in manifold26, support126and the body or housing of actuator100to provide a vertically compact design for apparatus10.

An anti-rotation plate or guide130can be releasably secured to support126with bolts132. Plate130has an aperture134for passage of valve pin36. Aperture134has a shape configured to engage a section of valve pin36having a non-circular profile to prevent rotation of the pin around the longitudinal axis of the pin36and nozzle34. In the illustrated embodiment, the non-circular profile includes two opposing flat or planar surfaces136(one of which is shown inFIG. 3). While flat surfaces136are engaged by straight edges of aperture134in the illustrated embodiment, other anti-rotational means can be provided, such as splines, grooves, and other structures that can prevent rotation of valve pin36.

Manifold26and actuators100are located in a space generally bounded by a top mold plate64and an intermediate mold plate66.

Assembly10can also include various lower support elements68, dowels70, and upper support elements72for facilitating proper alignment and spacing of the components of the assembly.

A pin seal138prevents liquid resin from leaking upwardly from channel24of manifold26.

The disclosed apparatus allows adjustment of the valve pin using dedicated tools/wrenches etc. from the back side of the actuator (opposite valve pin or valve pin elongation side).

The disclosed apparatus can allow coupling and decoupling of the cooled actuator axially to the valve pin.

The valve pin can be suspended within the height of the actuator.

The disclosed apparatus can also allow mounting of the cooled actuator axially to the valve pin on a thermal insulation support in direct contact to the hot-runner manifold; wherein the support can protrude along the actuator corners.

Shown inFIG. 4is an alternative arrangement in which the valve pin36is indirectly coupled to drive shaft102(rather than directly as shown inFIGS. 1 and 2) by a valve pin extension140.

The actuator100can be installed and coupled to the valve pin36axially, i.e., without moving the actuator laterally away from axis105. 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, support126can be attached to the manifold (such as with screws) and anti-rotation plate130can be positioned around valve pin36and secured to the support with bolts132. Next, nut106can be positioned onto the head (top end) of valve pin36. Actuator100is then positioned with the bore of drive shaft110in axial alignment with the valve pin. The tool engagement structure of nut106can then be accessed via the top opening109of actuator100with a tool to rotate nut106and thread nut108into the threaded bore104of driveshaft102.

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.