Patent Description:
The application of ultrasonic vibrations to a polymer during an injection moulding process is known to improve the melt flow characteristics of the polymer being processed.

<CIT>, <CIT> and <CIT> each describe injection moulding apparatuses including devices for applying ultrasonic vibrations to the moulding material. Although the use of ultrasound improves the flow characteristic of the moulding material, the devices of these apparatuses cannot be retrofitted to existing injection moulding apparatus.

<CIT> and <CIT> describe alternative injection moulding apparatuses that include ultrasonic vibration devices. Each of these apparatuses suffer the disadvantage of increased cycle times and, therefore, reduced productivity.

<CIT> describes an injection moulding apparatus including an ultrasonic vibration device. A length of the ultrasonic vibration device extends into a flow path in a fixed part of the moulding tool. A substantial portion of the material that passes through the flow path passes adjacent an end surface of the vibration device and an opposing wall of the chamber. The apparatus is designed such that an end of the vibration device is in direct contact with material passing through the flow path, in use.

<CIT> discloses an injection moulding machine with an ultrasonic transducer in the melt flow. The oscillator is positioned within the molten material chamber.

According to a first aspect of the invention, there is provided an apparatus according to claim <NUM>.

Advantageously, the apparatus is configured such that ultrasonic energy is transferred to the injection moulding material from the outer wall or periphery of the ultrasonic vibration device, which improves the melt flow properties of the injection moulding material without causing degradation of the material, for example by polymer chain scission.

Preferably the ultrasonic vibration device comprises an oscillator, wherein the oscillator is positioned on a first side of a wall of the flow chamber, and the sonotrode at least partially positioned on a second side of the wall of the flow chamber such that the oscillator does not contact the injection moulding material. This allows e.g. piezoelectric oscillators to be used which would not perform at the temperatures of the melt flow.

Preferably the sonotrode is mounted to the apparatus at a mounting position, wherein the mounting position is at a null point of the sonotrode in use. More preferably the null point of the sonotrode is a null point when the sonotrode is exposed to a temperature gradient of at least <NUM> along its axial length. More preferably the sonotrode comprises a mounting flange integral therewith, the mounting flange positioned at the mounting position. The mounting flange may be clamped between two components of the apparatus, for example by metal to metal contact. Advantageously this allows the sonotrode to be clamped without causing vibration damage to the surrounding equipment.

The flow chamber may form part of a hot runner system. The chamber wall is heated in such an embodiment.

The outlet may be in communication with a hot runner body, incorporating either a valve or a hot tip outlet. A portion of the outer wall of the sonotrode may be positioned adjacent to the outlet. In this way the volume of material that is subjected to ultrasonic vibration, but not transferred to the mould tool in a single injection moulding cycle, is minimised.

The flow chamber may have a first end and a second end. The outlet may be positioned adjacent to the second end of the flow chamber.

The outlet may be in communication with an elongate valve channel, the valve channel in communication with the mould tool cavity of the injection moulding assembly. Preferably a portion of the outer wall of the sonotrode is positioned adjacent to the valve channel. An opening may be provided adjacent to the outlet valve channel, wherein the sonotrode extends through the opening into the flow chamber. The sonotrode may extend normal to the valve channel.

The sonotrode may extend towards a free end in a direction directly opposed to the flow of material through the flow chamber in use- i.e. a "contra flow" arrangement.

In one embodiment, the flow chamber is a valve channel, and the sonotrode extends along the valve channel towards the outlet. In such an embodiment the sonotrode may form part of the valve.

The sonotrode may be arranged to move between an open position, in which an end of sonotrode is spaced apart from the second end of the elongate body such that, in use, injection moulding material can flow through the elongate body and along the outer wall of the ultrasonic vibration device to the mould tool, and a closed position, in which the end of the sonotrode is adjacent to the second end of the elongate body such that injection moulding material is prevented from flowing through the elongate body to the mould tool.

The valve-type sonotrode may be mounted in a sonotrode carriage, which sonotrode carriage is configured to move to place the sonotrode in the open and closed positions, wherein the sonotrode is mounted to the carriage by a mounting formation positioned at a null point of the sonotrode. A flexible seal member may be provided between the sonotrode carriage and the chamber wall. The flexible seal member may be a metal diaphragm seal. Advantageously, this removes the need to attempt to seal a vibrating shaft against the surrounding componentry, which would present significant technical challenges.

The sonotrode may have a cap that is arranged to cover the end portion of the ultrasonic vibration device. The position of the cap relative to the end portion of the ultrasonic vibration device may be adjustable. The ultrasonic vibration device may comprise a free end, and the free end is engaged in a wall of the flow chamber.

The sonotrode may extend in a direction that is transverse to a flow path of injection moulding material that passes through the flow chamber, in use, and wherein a free end of the ultrasonic vibration device extends into an opposing surface of the flow chamber such that injection moulding material flows around an outer wall of the ultrasonic vibration device, in use.

The flow chamber may be formed in a moveable component of the injection moulding assembly.

The ultrasound vibration device may be switched on to expose the injection moulding material to ultrasonic vibrations when the ultrasonic vibration device is in the open position within the elongate body. The ultrasound vibration device is switched off when the ultrasonic vibration device is in the closed position within the elongate body. In this way, the time for which the injection moulding material is exposed to the ultrasonic vibrations can be controlled to prevent degradation of the injection moulding material. Specifically, only moving material is exposed to sonification, which eliminates the possible degradation associated with static material adjacent the sonotrode.

The ultrasonic vibration device may be a first ultrasound vibration device, and the apparatus may include at least one further ultrasound vibration device. A plurality of valve channels may be provided in fluid communication with the mould tool cavity, wherein the first ultrasound vibration device is associated with a first valve channel, and the second ultrasound vibration device is associated with a second valve channel.

The cap may be mounted in an inner surface of the flow chamber. The position of the cap relative to the inner surface of the flow chamber may, preferably, be adjustable. The cap may include an upper surface having a recess into which an end portion of the sonotrode can be slidably fitted. The cap may be adjustable such that the upper surface may either be: (a) raised such that it protrudes into the flow chamber, (b) level with an inner surface of the flow chamber, or (c) embedded or sunk below the inner surface of the flow chamber.

The flow chamber may be formed in a moveable component of the injection moulding assembly, for example the moveable component may be a barrel or a moveable component of the mould tool. According to a second aspect of the present invention, there is provided a method of injection moulding a workpiece according to claim <NUM>.

Preferably the flow chamber forms part of a hot runner system.

Preferably the sonotrode forms part of a moveable valve member having:.

Preferably the sonotrode is activated only in the open position (i.e. not in the closed position).

Examples according to the present invention will now be described with reference to the accompanying Figures, in which:.

With reference to <FIG>, there is an apparatus <NUM> according to a first embodiment of the invention.

The apparatus <NUM> forms part of a hot runner injection moulding system and thus has a hot runner system <NUM>, a fixed part <NUM> and a moving part <NUM>.

The hot runner system <NUM> includes a flow chamber <NUM> that has an inlet <NUM>, an outlet <NUM> and an ultrasonic vibration device <NUM>.

The flow chamber <NUM> is an elongate cavity and has a first end <NUM> and a second end <NUM>. The inlet <NUM> is adjacent to the first end <NUM> of the flow chamber <NUM>. The outlet <NUM> is adjacent to the second end <NUM> of the flow chamber <NUM>. The flow chamber <NUM> also has an opening <NUM> at the second end <NUM>. As known in the art, the flow chamber <NUM> is heated by independent heating means (such as resistive elements) to ensure that the material therein remains molten.

The outlet <NUM> includes a valve <NUM>. The valve <NUM> has a body <NUM> defining a valve channel <NUM> and a pin <NUM> axially disposed within the valve channel <NUM>. Actuation of the valve <NUM> causes the pin <NUM> to move away from an outlet of the valve <NUM> such that injection moulding material can be transferred out of the flow chamber <NUM> via the valve <NUM>.

The ultrasonic vibration device <NUM> includes an ultrasonic probe or sonotrode <NUM>, an oscillator <NUM> and a booster <NUM>. The sonotrode <NUM> is generally cylindrical and has a first end <NUM>, a second end <NUM> and an outer wall or surface <NUM>. The sonotrode <NUM> is constructed from titanium. The oscillator <NUM> is in the form of a piezoelectric stack that converts electrical energy into high frequency mechanical vibration (for example vibrations greater than <NUM>, or preferably between <NUM> and <NUM>). The booster <NUM> boosts the signal from the oscillator <NUM> to the sonotrode <NUM>. The sonotrode <NUM> comprises a mounting flange <NUM> that extends radially from the long axis thereof. The mounting flange <NUM> is clamped by a metal-metal contact. Such a seal can withstand the high pressures of injection (possibly around <NUM> bar).

The flange <NUM> of the sonotrode is positioned such that it lies at a "null point" or "node"- i.e. at a longitudinal position of zero, or minimal movement during activation. The position of the null point is dependent upon a range of factors, but according to the invention is determined by the following method:.

These steps may be carried out by e.g. finite element analysis. It will be noted that the temperature gradient will be affected by the melt flow temperature, which in turn is determined by the type of material being moulded. Therefore it is envisaged that the sonotrode shape is dependent on the material being moulded.

The ultrasonic vibration device <NUM> is assembled by connecting the booster <NUM> to the oscillator <NUM>. The first end <NUM> of the sonotrode <NUM> is connected to the booster <NUM>. The booster <NUM> acts to concentrate the axial vibration of the piezoelectric stack into the end of the sonotrode.

It is important to note that the oscillator <NUM> is positioned on an opposite side of the chamber wall to the chamber <NUM>. This is because the piezoelectric oscillator needs to be kept below a maximum temperature (in this case <NUM>) which is far lower than the melt temperature. Positioning of the oscillator in the melt flow would cause damage to it.

The ultrasonic vibration device <NUM> is assembled onto apparatus <NUM> such that the sonotrode <NUM> extends into the chamber <NUM> through the opening <NUM>. The sonotrode <NUM> extends through the opening <NUM> of the flow chamber <NUM> such that the second end <NUM> of the sonotrode <NUM> extends along the length of the flow chamber <NUM> from the location of the outlet <NUM> towards the inlet <NUM>. The sonotrode <NUM> therefore extends in a direction that is parallel to, and contrary to, the flow of injection moulding material that passes through the flow chamber <NUM>, in use.

The ultrasonic vibration device <NUM> also includes a cap <NUM> that is arranged to cover the second end <NUM> of the sonotrode <NUM>. Specifically, the cap <NUM> is configured to block impinging flow from the inlet <NUM> from contacting the end of the sonotrode <NUM>. The cap <NUM> therefore acts as a flow guide to guide the melt flow around to the sidewalls of the sonotrode <NUM>. This ensures that the melt flow is energised at the walls <NUM> of the sonotrode (specifically in the space between the sonotrode and walls of the chamber <NUM>) in longitudinal shear (i.e. vibrated in the same direction as the flow), which enhances the effects of energisation. The cap <NUM> is adjustable such that its position relative to the second end <NUM> of the sonotrode <NUM> can be adjusted.

The proximity of the sonotrode <NUM> to the valve <NUM> allows the volume of material that is subjected to ultrasonic vibration, but not transferred to the mould tool in a single injection moulding cycle, to be minimised.

Referring to <FIG>, the chamber <NUM> is configured such that it has a primary flow direction FD from the inlet <NUM> to the outlet <NUM>. The chamber <NUM> is configured such that the inlet <NUM> is spaced apart from the sonotrode <NUM> such that a linear, laminar flow is created in direction FD before the flow encounters the sonotrode <NUM> (or specifically the cap <NUM>). This ensures that the melt flow is homogenously energised as is passes from the inlet <NUM> to the outlet <NUM>.

The fixed part <NUM> of the apparatus <NUM> includes a fixed tool bolster <NUM> and a fixed cavity part <NUM>. The moving part <NUM> of the apparatus <NUM> includes a moving tool bolster <NUM> and a moving cavity part <NUM>. The moving cavity part <NUM> has an open position, in which the moving cavity part <NUM> is spaced apart from the fixed cavity part <NUM> and a closed position, in which the moving cavity part <NUM> abuts the fixed cavity part, as shown in <FIG>, and a mould cavity <NUM> is defined between the fixed cavity part <NUM> and the moving cavity part <NUM>.

During operation of the apparatus <NUM>, when the moving cavity part <NUM> is in the closed position, injection moulding material is transferred to the flow chamber <NUM> from the barrel (not shown) by movement of the screw (not shown). Injection moulding material flows through the flow chamber <NUM> around the outer wall <NUM> of the sonotrode <NUM> to the valve <NUM>. If the valve <NUM> is open, injection moulding material flows through the vale <NUM> to the mould cavity <NUM>.

According to the present invention, the sonotrode <NUM> is activated at the point at which the injection moulding machine begins to inject molten material into the cavity (known as the "injection consent point"). It is important that ultrasonic excitation only occurs when the material to be injected is in motion (i.e. flowing) as excitation of stationary material can be problematic (detrimentally affecting the material's polymer microstructure). The injection moulding material flowing around the outer wall <NUM> of the sonotrode is exposed to ultrasonic vibrations. In this way, the melt flow properties of the injection moulding material are improved. When injection is paused (once the mould cavity is full), and flow stops, the sonotrode is deactivated ready for the next cycle. The aim is to only energise the moving flow, and not to energise stationary material.

In embodiment of <FIG>, the sonotrode <NUM> includes a cap <NUM> that is arranged to cover the second end <NUM> of the sonotrode <NUM>. In alternative embodiments of the invention, the second end <NUM> of the sonotrode <NUM> may be embedded in a wall of the flow chamber <NUM> in order to ensure the outer wall <NUM> of the sonotrode <NUM> contacts the injection moulding material.

In the embodiment of <FIG>, the sonotrode <NUM> is a separate component to the valve <NUM>. In the embodiment of <FIG>, the sonotrode <NUM> extends through the flow chamber <NUM> in a direction that is parallel to the direction in which injection moulding material flows through the flow chamber <NUM>. In contrast, the body <NUM> of the valve <NUM> extends in a direction that is not parallel to the direction in which injection moulding material flows through the flow chamber <NUM>. In other embodiments of the invention, the body of the valve could extend in a direction that is parallel to the direction in which injection moulding material flows through the flow chamber.

In alternative embodiments of the invention, the sonotrode may be positioned in the valve channel. With reference to <FIG>, the melt flow passes from an inlet <NUM> to an outlet <NUM> of a pre-chamber before entering a valve channel <NUM>. A sonotrode <NUM> is mounted to the pre-chamber wall opposite the outlet, and extends across the pre-chamber into the valve channel. As such the sonotrode is positioned within a valve channel <NUM> defined in a body <NUM> of a valve <NUM> such that the sonotrode <NUM> extends along the length of the valve body <NUM> and terminates in a free, second end <NUM> proximate the valve outlet <NUM> (i.e. the gate tip). In this arrangement, the second end <NUM> of the sonotrode <NUM> is spaced apart from the outlet <NUM> of the valve <NUM> such that injection moulding material can flow through the valve <NUM> to the mould cavity. The valve member <NUM> is separate to the sonotrode <NUM> and is actuable in an axial direction to open and close the valve opening <NUM> at the gate tip. During the transfer of injection moulding material into the mould cavity, the sonotrode <NUM> is turned on such that the injection moulding material flowing around the outer wall <NUM> of the sonotrode <NUM> is exposed to ultrasonic vibrations. In this way, the melt flow properties of the injection moulding material are improved. It will be noted that the sonotrode <NUM> spans the pre-chamber to penetrate the valve channel <NUM>.

An alternative example will now be described with reference to <FIG>. As described with respect to <FIG>, the melt flow passes from an inlet <NUM> to an outlet <NUM> of a pre-chamber before entering a valve channel <NUM>. A sonotrode <NUM> is positioned within the channel <NUM> formed in a body <NUM> of a valve <NUM> such that the sonotrode <NUM> extends along the length (i.e. flow path) of the valve body <NUM>. In this arrangement, a projection <NUM> is provided at the second end <NUM> of the sonotrode <NUM>. The sonotrode <NUM> is arranged to move between an open position, in which the projection <NUM> of the sonotrode <NUM> is spaced apart from the outlet <NUM> of the valve <NUM> such that, in use, injection moulding material can flow through the elongate valve body <NUM> and along the outer wall <NUM> of the sonotrode <NUM> to the mould cavity, and a closed position, in which the second end <NUM> of the sonotrode <NUM> abuts a shoulder <NUM> (which may be perpendicular to the main azis of the sonotrode, or angled / tapered) adjacent to the outlet <NUM> (gate tip) of the valve <NUM> such that the outlet <NUM> is closed by the projection <NUM> and injection moulding material is prevented from flowing through the elongate valve body <NUM> to the mould cavity. When the sonotrode <NUM> is in the open position, the sonotrode <NUM> is turned on such that the injection moulding material flowing around the outer wall <NUM> of the sonotrode <NUM> is exposed to ultrasonic vibrations. In this way, the melt flow properties of the injection moulding material are improved. It will be noted that the sonotrode <NUM> spans the pre-chamber to penetrate the valve channel <NUM>.

Mounting and reliable sealing of a moving sonotrode is difficult. Specifically, placing a seal between the outer surface of a vibrating sonotrode and a stationary surface presents significant technical problems. Known seals will simply fail very quickly under the action of the vibrational shear energy thereby imparted. As such, this embodiment of the present invention utilises a sonotrode carriage <NUM> movably mounted to a wall <NUM> of the apparatus of <FIG>.

The sonotrode <NUM> comprises a flange <NUM> unitary with the sonotrode body. The flange <NUM> is positioned at a "null point" of the sonotrode- that is a point at which the amplitude of vibration during resonance is de minimis or zero. The flange <NUM> is clamped between a first carriage member <NUM> and a second carriage member <NUM> such that the sonotrode <NUM> is fixed to the carriage <NUM>.

The carriage <NUM> is received in an opening in the wall <NUM> and sealed against the opening by a metal diaphragm seal <NUM> (shown schematically only). This allows axial movement of the sonotrode in direction D whilst keeping the melt flow in the chamber <NUM>, because the diaphragm seal can deform whilst maintaining a seal. An actuator <NUM> is configured to move the carriage <NUM> in direction D.

The provision of a carriage prevents the need for sealing the moving and vibrating sonotrode directly against the chamber wall.

In a still further embodiment, based on <FIG>, the second end <NUM> of the sonotrode may simply bear against the shoulder <NUM> at the end of the flow channel without the presence of the protrusion <NUM>.

In each of the examples of <FIG>, the proximity of the sonotrodes <NUM>, <NUM> to the outlet <NUM>, <NUM> of the valves <NUM>, <NUM> allows the volume of material that is subjected to ultrasonic vibration, but not transferred to the mould tool in a single injection moulding cycle, to be minimised. This reduces the amount of material whereby the imparted energy dissipates over time.

In the embodiments described above, the apparatuses include a single sonotrode <NUM>, <NUM>, <NUM>. It will be understood that, in alternative embodiments of the invention, the apparatuses may include a plurality of ultrasonic vibration devices. Similarly, in the embodiments described above, the apparatuses include a single valve <NUM>, <NUM>, <NUM>. It will also be understood that, in alternative embodiments of the invention, the flow chamber <NUM> may include a plurality of valves.

In one exemplary embodiment of the invention, as shown in <FIG>, there may be a plurality of valves <NUM> and each valve <NUM> may be associated with a sonotrode <NUM>. Alternatively, as shown in <FIG>, a sonotrode <NUM> may be associated with two or more valves <NUM>, such that there is less than one sonotrode <NUM> per valve <NUM>. Alternatively, as shown in <FIG>, more than one sonotrode <NUM> may be provided for each valve <NUM>.

With reference to <FIG>, there is shown an apparatus <NUM> according to an alternative embodiment of the invention. The apparatus <NUM> includes a flow chamber <NUM> that has an inlet <NUM>, an outlet <NUM> and an ultrasonic vibration device <NUM>. The flow chamber <NUM> is defined in a chamber body <NUM>. The body <NUM> includes a channel <NUM> that has an axis A-A and is transverse to the flow chamber <NUM>. The channel <NUM> terminates in an annular flange seat <NUM> in a surface <NUM>. Abutting the surface <NUM> there is provided a clamping body <NUM> defining a channel <NUM> aligned with the channel <NUM>.

The ultrasonic vibration device <NUM> includes an ultrasonic probe or sonotrode <NUM>, an oscillator <NUM> and a booster <NUM>. The sonotrode <NUM> is generally cylindrical and has a first end <NUM>, a second end <NUM> and an outer wall or surface <NUM>. The oscillator <NUM> converts electrical energy into high frequency mechanical vibration (for example vibrations greater than <NUM>) using a stack of piezoelectric elements <NUM>. The booster <NUM> boosts the signal from the oscillator <NUM> to the sonotrode <NUM>. The sonotrode <NUM> comprises a mounting flange <NUM> that extends radially from the long axis thereof. The mounting flange <NUM> is nested into the annular flange seat <NUM> and clamped into position by the clamping body <NUM>.

These steps may be carried out by e.g. finite element analysis. It will be noted that the temperature gradient will be affected by the melt flow temperature, which in turn is determined by the type of material being moulded. Therefore it is envisaged that the sonotrode shape or dimensions is dependent on the material being moulded.

The ultrasonic vibration device <NUM> is assembled onto apparatus <NUM> such that the sonotrode <NUM> extends into the channel <NUM>. The sonotrode <NUM> therefore extends through the channel <NUM> and the flow chamber <NUM> towards a lower surface <NUM> of the flow chamber <NUM>. An adjustable cap or anvil <NUM> is then mounted onto the apparatus <NUM> such that the second end <NUM> of the sonotrode <NUM> is adjacent to and abuts a portion of the adjustable cap or anvil <NUM>. In use, the sonotrode <NUM> vibrates in a direction that is parallel to the vertical axis A-A of the channel <NUM>.

The ultrasonic vibration assembly <NUM> can be installed at different positions on an injection moulding apparatus <NUM> as will be described with reference to <FIG>, <FIG> and <FIG>.

An exemplary injection moulding apparatus <NUM> includes a barrel <NUM> having a hopper <NUM> at a first end and an outlet in the form of a nozzle <NUM> at a second end that is opposite the first end. A reciprocating and rotating screw <NUM> is housed within the barrel <NUM>.

The injection moulding apparatus <NUM> also includes a fixed platen <NUM>, a moving platen <NUM> and an injection moulding tool <NUM>. The injection moulding tool <NUM> includes a fixed mould half <NUM> and a moving mould half <NUM>. The fixed mould half <NUM> is fitted to the fixed platen <NUM>. The moving mould half <NUM> is fixed to the moving platen <NUM>. A mould cavity <NUM> is defined between the fixed mould half <NUM> and the moving mould half <NUM>. The movable mould half <NUM> is movable between an open position in which the mould cavity <NUM> is open and a closed position in which the mould cavity <NUM> is closed.

With reference to <FIG>, the apparatus <NUM> is installed on the barrel <NUM> by connecting the inlet <NUM> of the apparatus <NUM> to an outlet of the barrel <NUM>. The outlet <NUM> of the apparatus <NUM> is connected to an inlet of the fixed mould half <NUM> supported on a fixed platen <NUM> such that a melt stream flow path is formed between the barrel <NUM> and the mould cavity <NUM>.

In use, barrel <NUM> and apparatus <NUM> are moved together to an injection port on the fixed mould half, where the injection moulding material flows from the barrel <NUM> of the injection moulding apparatus <NUM> to the mould cavity <NUM> of the injection moulding tool <NUM>.

The sonotrode <NUM> extends through the flow chamber <NUM> such that the injection moulding material that is delivered through the melt stream flow path passes around the outer wall <NUM> of the sonotrode <NUM> and is exposed to the ultrasonic vibrations from the outer wall <NUM> of the sonotrode <NUM>.

During operation of the injection moulding apparatus <NUM>, when the injection moulding tool <NUM> is in the closed position and injection moulding material is being transferred to the mould cavity <NUM> from the barrel <NUM> by linear movement of the screw <NUM>, the sonotrode <NUM> is turned on to improve the melt flow characteristics of the moulding material. Once the injection cycle has been completed, the sonotrode <NUM> is turned off to prevent degradation of the injection moulding material.

In this arrangement, the apparatus <NUM> is, advantageously, installed on the barrel <NUM>, i.e. a moving part, of the injection moulding apparatus <NUM>. It is, therefore, possible for the apparatus <NUM> to be retrofitted to existing injection moulding apparatuses. This arrangement can be installed on injection moulding apparatuses independently of the mould tool and thus allows the ultrasonic vibrations to be applied to different mould tools. This arrangement maximises the daylight that is available within the injection moulding apparatus, for example for the production of deep draw articles.

<FIG> shows a variant of the arrangement of <FIG> in which the apparatus <NUM> is integrated between the barrel <NUM> and the nozzle tip <NUM>. This provides a more compact arrangement, and can facilitate exposure of the flow at a position closer to the mould cavity (reducing the "dwell" volume between sonotrode and cavity). In this embodment, the axis A of the apparatus <NUM> is inclined to the axis of the barrel by an angle B where B<<NUM> degrees. In this instance. B = <NUM> degrees. The angle is such that the free end of the sonotrode is directed towards the cavity. This allows the sonotrode to be positioned further towards the nozzle top <NUM> without the bulkier part of the apparatus <NUM> (e. g, the piezoelectric oscillator) contacting the platen <NUM>. Further, the melt flow first contacts the sides of the sonotrode, which is beneficial for viscosity reduction.

With reference to <FIG>, the apparatus <NUM> is installed between the fixed platen <NUM> and the fixed mould half <NUM> of the injection moulding tool <NUM>.

The apparatus <NUM> is connected to the inlet of the fixed mould half <NUM> of the injection moulding tool <NUM>. Injection moulding material can thus be transferred from the barrel <NUM> to the mould cavity <NUM> via the flow chamber <NUM> of the apparatus <NUM> and the fixed mould half <NUM> during use of the injection mould apparatus <NUM>.

As described in relation to <FIG>, the sonotrode <NUM> extends through the flow chamber <NUM> such that the injection moulding material that is delivered through the melt stream flow path passes around the outer wall <NUM> of the sonotrode <NUM> and is exposed to the ultrasonic vibrations from the outer wall <NUM> of the sonotrode <NUM>.

In this arrangement, the apparatus <NUM> can, advantageously, be installed on the fixed mould half <NUM>, i.e. a fixed part, of the injection moulding apparatus <NUM>. It is, therefore, possible for the apparatus <NUM> to be retrofitted to existing injection moulding apparatuses. The fixing of the apparatus <NUM> to the fixed mould half allows a particular mould to be used with the ultrasonic apparatus on any injection moulding assembly.

The apparatus <NUM> can, alternatively, be installed on an injection moulding apparatus <NUM> as described with reference to <FIG>. In this example, the apparatus <NUM> is installed on the moving mould half <NUM>.

Injection moulding material is transferred from the barrel <NUM> to the mould cavity <NUM> via a melt tube <NUM> that is attached to the moving mould half <NUM>. In this arrangement, there is no flow path through the fixed platen <NUM> or the fixed mould half <NUM> (other than through the melt tube <NUM>).

As described in relation to <FIG> and <FIG>, the sonotrode <NUM> extends through the flow chamber <NUM> such that the injection moulding material that is delivered through the melt stream flow path passes around the outer wall <NUM> of the sonotrode <NUM> and is exposed to the ultrasonic vibrations from the outer wall <NUM> of the sonotrode <NUM>.

In this arrangement, the apparatus <NUM> can, advantageously, be installed on the moving mould half <NUM>, i.e. a moving part, of the injection moulding apparatus <NUM>. It is, therefore, possible for the apparatus <NUM> to be retrofitted to existing injection moulding apparatuses. The fixing of the apparatus <NUM> to the moving mould half advantageously enables the production of in-mould decoration and the use of double-daylight moulds.

In each of the embodiments described above, the sonotrode extends through the flow path such that the second end of the sonotrode is adjacent to and abuts a structure, for example an adjustable cap, also known as an "anvil". With reference to <FIG>, the adjustable cap <NUM>, <NUM> may be positioned such that the sonotrode <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is received in the wall of the flow chamber <NUM>, <NUM>. Alternatively, as shown in <FIG>, the adjustable cap <NUM>, <NUM> may be positioned such that the adjustable cap <NUM>, <NUM> extends above the inner wall of the flow chamber <NUM>, <NUM>. In a yet further embodiment of the invention, the adjustable cap may have an upper surface and be positioned in the wall of the flow chamber such that the upper surface of the adjustable cap is level with the inner wall of the flow chamber. In each case, the cap <NUM>, <NUM> receives the tip of the sonotrode to inhibit significant flow past the tip, and instead focus flow around the sidewalls of the sonotrode.

In yet further embodiments of the invention, the flow path around the walls of the sonotrode may be varied. For example, and as shown in <FIG>, the flow path <NUM> to the mould cavity <NUM> may run past a central portion of the sonotrode <NUM>. In particular a chamber inlet <NUM> and chamber outlet <NUM> are defined on either side of the sonotrode <NUM>, in which the inlet <NUM> and outlet <NUM> are opposite each other (i.e. the same distance from the tip of the sonotrode). This reduces flow past the tip, and instead provides flow around the sides of the sonotrode.

Alternatively, and as shown in <FIG>, the flow path <NUM> to the mould cavity may be staggered such that an outlet <NUM> is positioned further from the tip of the sonotrode than the inlet <NUM>. This also reduces flow past the tip, and instead provides flow around the sides of the sonotrode.

In a yet further embodiment of the invention, more than one sonotrode 936a, 936b may be provided and the flow path <NUM> to the mould cavity <NUM> between an inlet <NUM> and an outlet <NUM> may be provided via a gap <NUM> between adjacent sonotrodes 936a, 936b.

In the described embodiments of the invention, the sonotrode is turned on during the injection cycle in order to optimise the melt flow properties of the injection moulding material. The sonotrode is turned off upon completion of the injection stroke in order to prevent degradation of the material. It will be understood that, in alternative embodiments of the invention, the stage of the process at which the sonotrode is turned on or turned off may be adjusted according to the characteristics of the injection moulding material.

Claim 1:
An apparatus (<NUM>) for improving the flow properties of injection moulding material, the apparatus having a flow chamber that is formed in an injection moulding assembly and includes:
an ultrasonic vibration device (<NUM>) comprising a sonotrode (<NUM>), and
an outlet (<NUM>) through which injection moulding material can pass from the flow chamber towards a mould tool cavity (<NUM>); and wherein
the sonotrode (<NUM>) is at least partially arranged in the flow chamber such that injection moulding material flows along an outer wall of the sonotrode, in use;
characterised in that the apparatus is configured to:
simultaneously with flow initiation, or after the flow has been initiated, activate the ultrasonic vibration device to expose the molten injection moulding material to ultrasonic vibration such that ultrasonic excitation only occurs when the material to be injected is in motion along the outer wall of the sonotrode.