WO2007025331A1

WO2007025331A1 - Injection device for a cold runner block

Info

Publication number: WO2007025331A1
Application number: PCT/AU2006/001251
Authority: WO
Inventors: Stephen Spain; Neil Wilson
Original assignee: Romar Engineering Pty Ltd
Priority date: 2005-08-29
Filing date: 2006-08-28
Publication date: 2007-03-08
Also published as: AU2006101106A4

Abstract

An injection device for a cold runner block comprising an injection system for transferring material to be moulded in a cold and uncured state into a plurality of mould cavities via a nozzle system. The injection device comprising a plunger operably actuated by a drive assembly. The drive assembly comprises an electric servomotor controlled by a servo-controller, a gear train, a rotary-to-linear converter in the form of first roller screw drive, and a thrust reaction bearing in the form of a second roller screw drive.

Description

INJECTION DEVICE FOR A COLD RUNNER BLOCK

TECHNICAL FIELD

The present invention relates to an injection device for a cold runner block for moulding articles, and in particular to articles made from two-part low viscosity materials such as liquid silicones and polyurethanes.

BACKGROUND

The normal method of moulding articles made of silicone and the like materials is to inject the silicone (or other material) into a heated mould using a hydraulically-powered water-cooled screw injection device at single injection point at a sufficient pressure. The mould typically has a plurality of cavities, each of them in communication with the single injection point via a series of runners. The material in the runners becomes heated and cured and must be removed from the mould with the completed articles, and trimmed off at a later time. Trimming of runners at a later stage can be very wasteful of the moulded material, particularly when that material is silicone. For example, in the case of a seal used in an automotive remote lock/key made from silicone, 50% is wasted as runners during its manufacture.

In order to overcome this problem, it is known to employ "cold runner blocks" (CRB) to produce articles by allowing direct injection into parts rather than via a runner system. However, prior art CRB are expensive, and as such can only feasibly be used when production volumes are high enough to justify the cost in material savings. The drive mechanisms employed to actuate the main drive plunger are typically hydraulic, due to the force required to actuate the plunger. This hydraulic actuation disadvantageously requires bulky components, expensive control equipment, and the potential for hydraulic leakage is an environmental disadvantage. Furthermore, the build and maintenance of the drive mechanism is generally expensive.

Another problem associated with prior art CRB injection devices is that most are limited to four or six nozzles, due to bulky size of the nozzle systems. In such systems the silicone or other material enters the nozzle radially via a tortuous path and the necessary pneumatic and cooling water galleries are external of the nozzle, making a nozzle system having an array of more than say four to six nozzles considerably bulky. Such an array of nozzles is also costly to construct and difficult to maintain and repair, as each nozzle in the array is typically designed differently and requires adjustment after fitting.

The present invention seeks to overcome at least some of the disadvantages of the prior art.

SUMMARY OF INVENTION

According to a first aspect the present invention consists of an injection device for a cold runner block comprising an injection system for transferring material to be moulded in a cold and uncured state into a plurality of mould cavities via a nozzle system, said injection device comprising a plunger operably actuated by a drive assembly, wherein said drive assembly comprises an electric servomotor controlled by a servo-controller, a gear train, a rotary-to-linear converter in the form of first roller screw drive, and a thrust reaction bearing in the form of a second roller screw drive.

Preferably, said first roller screw drive has a degree of axial travel.

Preferably, said second roller screw drive has no axial travel.

Preferably, said gear train is a pancake type harmonic drive.

Preferably, said nozzle system comprises a plurality of nozzle valves, each nozzle valve associated with a respective one of said plurality of mould cavities.

Preferably, said nozzle system is electronically controlled, and each of said nozzle valves may be independently controlled for opening and shut-off.

Preferably, said nozzle valves are needle type valves.

Preferably, each of said nozzle valves comprises an internal pnuematic actuator.

Preferably, each of said nozzles has its inlet at its rear, and the path for the material passing therethrough is along a bore following the axis of the nozzle. Preferably, said material is a multi-part low viscosity material, such as liquid silicone, polyurethane or chocolate.

According to a second aspect the present invention consists of a silicone injection device for a cold runner block comprising an injection system for transferring silicone to be moulded in a cold and uncured state into a plurality of mould cavities via a nozzle system, and said injection system comprises a plunger operably actuated by a drive assembly, and wherein said drive assembly comprises an electric servomotor controlled by a servo-controller, a gear train, a rotary-to-linear converter in the form of first roller screw drive having limited axial travel, and a thrust reaction bearing in the form of a second roller screw drive having no axial travel, and said nozzle system comprises a plurality of nozzle valves, each nozzle valve associated with a respective one of said plurality of mould cavities, and each of said nozzle valves may be independently controlled for opening and shut-off.

Preferably, said gear train is a pancake type harmonic drive.

Preferably, said nozzle valves are needle type valves.

Preferably, said nozzles have its inlet at its rear, and the path for the material passing therethrough is along a bore following the axis of the nozzle.

Preferably, said silicone is a multi-part material.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a cross-sectional view of an injection device for a cold runner block in accordance with an embodiment of the present invention.

MODE FOR CARRYING OUT INVENTION

Fig. 1 depicts an injection device for a cold runner block for use in the moulding of silicone components. The principal purpose of this device is to supply a precision volume of multi-part silicone material to a number of mould cavities in a standard injection-moulding machine. The multi-part liquid silicone material requires mixing and then heating for it to become solid and elastic. Whilst it is mixed and cold, it will remain in a liquid state for a considerable time, but that time is considerably reduced after heat is applied. The silicone is mixed prior to transport through the device, and therefore needs to be kept cold until the point in the mould is reached where heat must be applied for curing.

The total device is best separated into two distinct and independent systems, namely "the drive and plunger system", which becomes part of the moulding machine and "the nozzle valve system", which becomes part of the tooling. These two systems are interconnected by a single material transfer interface which allows interchangeability between different versions of each of the two systems.

The "drive and plunger system" provides the transfer of a precision volume of silicone at a required flow rate and at sufficient pressure to flow into the mold cavity. It consists of several major subassemblies.

• The drive motor, which is an electric servomotor 1, together with its accompanying electronic programmable drive system. This motor includes timing belt transmission and mounting bracket.

• The gear train 8, which is a pancake type harmonic drive of very high ratio and very low backlash, with the capability of very high output torque.

• The rotary-to-linear converter assembly, which is a roller screw drive which has a degree of axial travel for simplicity, comprising a set of grooved rollers 13 and an externally helically grooved shaft 14, which is capable of very high axial force at low speeds.

• The thrust reaction bearing assembly, which is a roller screw drive of equivalent axial force capability, comprising an externally grooved roller nut 10, a set of grooved rollers 11 an internally grooved sleeve 12, arranged such as to allow no axial travel.

• The plunger 15, which moves axially inside cylinder block 22 with high pressure sealing by seal 18, and incorporates a silicone inlet manifold 19 with static mixer 20, a non-return valve 21 and a series of high-pressure outlets. 8

array of a large number of independently operable nozzles, say up to sixty-four nozzles, as the nozzle system is relatively very compact. This is advantageous over prior art systems, which are typically limited to four to six nozzles, which are generally not independently operable.

The arrangement of the "nozzle system" is modular and interchangeable, and the arrangement provides a path for the silicone product which is relatively straight and symmetrical, allowing for optimum balance of pressure distribution. In this embodiment, the silicone follows a path entering at the rear of the nozzle 26 and is directed through a bore along the axis of each nozzle 26. This nozzle design is what allows the nozzle system to be compact. The nozzle design also permits the rapid replacement of the nozzles 26 off the shelf, which includes an internal and integral actuator, in the form of hydraulically balanced piston 25, with no need for adjustments. To the contrary, prior art nozzle systems have the silicone injection point radially into the nozzle via a tortuous path with the actuator pneumatics and cooling water galleries added as separate components.

The major advantage of the abovedescribed injection device over the prior art devices is:

• The injection mechanism consists of an electrically powered large diameter plunger 15 ^'in place of a hydraulic screw, giving it advantages in precision, size, capacity, cost and environmental considerations.

The supply system for the two parts of the silicone material (plus any other additives such as colour dye) can be a proprietary item and needs no further design and therefore is not described in detail herein. It includes all pumps and valves for supplying the correct volumes of the two parts at a constant pressure irrespective of total flow rate. However, in a preferred silicone embodiment its design specification may be as follows:

Shot volume 2000 ml (max)

Volume flow rate 90 ml/sec (max)

Liquid pressure 40 MPa (max)

Volumetric tolerance +/- 3% 7

Once the cylinder space 17 is full, the material is ready to be ejected from the cylinder space 17 via galleries in the cylinder block 22. The cylinder block 22 is water cooled by water galleries 23.

After leaving the cylinder block 22, the material passes through the adaptor plate 24 to align the material with the multiple entry points of the injection system. The material enters each of the nozzle valve assemblies, each of which is comprised of a hydraulically balanced piston 25, a nozzle 26, a needle valve 27, a pneumatic cylinder 28 and a water jacket 29. The material then passes through the centre of hydraulically balanced piston 25 and up to nozzle 26 which is closed off by needle valve 27. The needle valve 27 is actuated by pneumatic cylinder 28, which is rigidly attached thereto. The nozzle valve assembly also contains the cooling water jacket 29.

Each pneumatic cylinder 28 is connected via a system of galleries in the nozzle block 30 to a set of solenoid operated pneumatic valves 31 which is in turn connected electronically, and controlled by, the electronic controller 2. When the controller 2 is programmed to do so, each solenoid valve 31 is operated allowing its respective needle valve 27 to open, thus admitting the material into a respective mould cavity 32 at a controlled volume, pressure, flow rate, temperature and timing.

Each cooling water jacket 29 of a respective nozzle valve assembly is connected by a system of galleries in the nozzle block 30 to a cooling water manifold 33, where the water flow to each nozzle valve assembly can be manually balanced.

As each cavity 32 has a respective independently controlled nozzle valve associated therewith, then the various cavities 32 need not be identical. For instance the mould may have a first cavity for moulding a component say having 12 grams of silicone, whilst a second cavity is for moulding a component having 10 grams. As the solenoid valves 31 are independently controlled the one associated with the "12 gram" cavity can be set to open before the "10 gram" cavity, with both being shut off at the same time, thereby each cavity having received the similar pressure to fill them prior to shut-off.

Whilst Fig. 1 depicts only two independently operable nozzles 26 for ease of clarity and reference, the "nozzle system" and its various sub assemblies could be expanded to an • The nozzle valve control manifold, which is an electric solenoid pneumatic valve manifold. Each solenoid is independently operated by a programmable electronic controller so that the valves can be opened or shut in a programmable sequence.

• The cooling water control manifold, which is a block of manually operated needle type valves so that water flow to each nozzle can be balanced.

The injection device will now be described in detail. The injection comprises an electric servomotor 1 that is controlled in its position, velocity and acceleration by an electronic controller 2. Servomotor 1 is adapted to impart a torque through driving pulley 3 and timing belt 4 to driven pulley 5 attached to shaft 6, which is in turn attached to input rotor 7 of gear train 8.

The gear train 8 is a standard harmonic drive and its action is well known and documented. The output ring of gear train 8 is bolted to an adaptor ring 9, which is in turn connected to roller nut 10 of the roller drive. The roller nut 10 rotates but does not move axially. Its axial position is maintained by a set of grooved rollers 11 which engage in grooves on the outside of the roller nut 10, and also engage in similar grooves in an internally grooved fixed sleeve 12, which is rigidly constrained against movement. The inside of the roller nut 10 is grooved with a helical groove (thread) which is engaged with another set of grooved rollers 13, which in turn engages with another helically grooved (threaded) shaft 14. This shaft 14 is rigidly attached to a plunger 15, which is constrained from rotation by keys 16, but is allowed to travel axially within the cylinder space 17, and is sealed against leakage by the hydraulic seal 18.

At least two components of a liquid (or gel) are pumped at low pressure into the material manifold 19 where the material passes through a static mixer 20. After thorough mixing, the material enters the cylinder space 17 via a non-return valve 21. The servomotor 1 is driven in reverse such that the cylinder space 17 is enlarged to accommodate the inflow of material. The drive mechanism, which is the first four of the abovementioned sub-assemblies, is based on a roller screw principle, allowing the thrust force to be in order of three times as high as the equivalent size and power of any known conventional screw drives for injection devices. The abovementioned "thrust reaction bearing assembly" advantageously provides the drive mechanism with its own reaction thrust system, not found in prior art systems. The high thrust force generated by this drive mechanism allows the ram plunger diameter of plunger 15 to be large whilst maintaining a high pressure, thus allowing maximum shot volume to be large when compared to prior art systems. The drive mechanism allows for the electric powered plunger 15 to be provided with the sort of thrust only previously found in hydraulic actuated plungers.

The "nozzle valve system" provides the independently controlled shutoff of cold silicone material right at the entry point of each cavity in the mould. It consists of several subassemblies:

• The nozzle valve assembly, which is a needle type valve controlled by an integrated pneumatic cylinder 28, and is hydraulically balanced such that the force required to open the valve is largely independent of the silicone pressure. It incorporates a water-cooling jacket 29 to keep the material cool right to the valve tip. The valve tip is of titanium alloy of sufficient strength to minimize the area of contact with the hot mould, and of low coefficient of thermal conductivity to minimize the heat transfer. Each cavity 32 has its own nozzle valve assembly.

• The nozzle block 30, which is a water-cooled block containing the nozzle valves assemblies in the required geometric pattern. This block also incorporates the pneumatic distribution to each nozzle valve assembly, and the cooling water distribution to each nozzle cooling water jacket 29.

• The adaptor plate 24, which distributes the silicone from the cylinder block 22 to the entry point of the nozzle valves assemblies. It matches the arbitrary pattern of the mould cavities 32 to the required geometric pattern of the cylinder block 22. It should also be understood that some of the components of the abovementioned embodiment may vary without affecting the scope of the present invention.

For instance gear trains other than the "harmonic pancake type" may be used. For example, a "cyclodrive" design that utilizes cam followers and lobed rotors may be used. This gear train has the necessary high ratio (up to 87:1). However, a small diameter in line input shaft can be utilized, thus not allowing for concentric injection. However, the harmonic drive in pancake configuration is more preferred because it is less complicated (fewer parts), more compact, lower backlash but somewhat higher priced than the cyclodrive design. Moreover, the "harmonic pancake type" gear train is the preferred gear train as its Ratios start at 80: 1 and can be up to 160: 1. Also, its input shaft can be large and hollow, suitable for injection of silicone mixture, and its output is a "ring flange". By ring flange, this means that the output of the gearbox is in the form of a ring, which is convenient to adopt to the next stage of the drive.

It should be understood that the rotary-to-linear converter in the abovementioned embodiment is preferably a roller screw. One such roller screw is the recirculating roller screw drive manufactured by SKF™. However, an alternative may be a "greased acme thread".

It should also be understood that whilst the injection device for a cold runner block as described in the abovementioned embodiment has been with reference to a multi-part silicone, it should be understood that the device of the present invention can also be used for other low viscosity materials that can be moulded, such as polyurethane or chocolate.

The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "having" or "including" and not in the exclusive sense of "consisting only of.

Claims

1. An injection device for a cold runner block comprising an injection system for transferring material to be moulded in a cold and uncured state into a plurality of mould cavities via a nozzle system, said injection device comprising a plunger operably actuated by a drive assembly, wherein said drive assembly comprises an electric servomotor controlled by a servo-controller, a gear train, a rotary-to-linear converter in the form of first roller screw drive, and a thrust reaction bearing in the form of a second roller screw drive.

2. An injection device for a cold runner block as claimed in claim 1 wherein said first roller screw drive has a degree of axial travel.

3. An injection device for a cold runner block as claimed in claim 1 wherein said second roller screw drive has no axial travel.

4. An injection device for a cold runner block as claimed in claim 1, wherein said gear train is a pancake type harmonic drive.

5. An injection device for a cold runner block as claimed in claim 1, wherein said nozzle system comprises a plurality of nozzle valves, each nozzle valve associated with a respective one of said plurality of mould cavities.

6. An injection device for a cold runner block as claimed in claim 5, wherein said nozzle system is electronically controlled, and each of said nozzle valves may be independently controlled for opening and shut-off.

7. An injection device for a cold runner block as claimed in claim 5 or 6, wherein said nozzle valves are needle type valves.

8. An injection device for a cold runner block as claimed in claim 5 or 6, wherein each of said nozzle valves comprises an internal pnuematic actuator.

9. An injection device for a cold runner block as claimed in claim 5, wherein each of said nozzles has its inlet at its rear, and the path for the material passing therethrough is along a bore following the axis of the nozzle.

10. An injection device for a cold runner block as claimed in claim 1, wherein the material is a multi-part low viscosity material, such as liquid silicone, polyurethane or chocolate.

11. A silicone injection device for a cold runner block comprising an injection system for transferring silicone to be moulded in a cold and uncured state into a plurality of mould cavities via a nozzle system, and said injection system comprises a plunger operably actuated by a drive assembly, and wherein said drive assembly comprises an electric servomotor controlled by a servo-controller, a gear train, a rotary-to-linear converter in the form of first roller screw drive having limited axial travel, and a thrust reaction bearing in the form of a second roller screw drive having no axial travel, and said nozzle system comprises a plurality of nozzle valves, each nozzle valve associated with a respective one of said plurality of mould cavities, and each of said nozzle valves may be independently controlled for opening and shut-off.

12. A silicone injection device for a cold runner block as claimed in claim 10, wherein said gear train is a pancake type harmonic drive.

13. A silicone injection device for a cold runner block as claimed in claim 10, wherein said nozzle valves are needle type valves.

14. An injection device for a cold runner block as claimed in claim 10, wherein each of said nozzle valves comprises an internal pnuematic actuator.

15. An injection device for a cold runner block as claimed in claim 5, wherein each of said nozzles has its inlet at its rear, and the path for the material passing therethrough is along a bore following the axis of the nozzle.

16. A silicone injection device for a cold runner block as claimed in claim 10, wherein said silicone is a multi-part material.