GB2092945A - Feeding colouring substances to injection moulding machines - Google Patents

Abstract

A device for directly supplying a colouring substance in the form of a paste in a controlled manner to the plasticising chamber (14) of a plastics material injection moulding machine (10) includes an open-top receptacle (34) removably housed in a pressurisable container (24) and the interior of which, which is able to contain a colouring paste substance, is connected to the plasticising chamber (14) by means of a tube (38) which can be disconnected from the pressurisable container and removed from the plasticising chamber. The device further includes means (54, 56) for supplying a gas under pressure into the interior of the pressurisable container (24), and metering means (62) acting on the exterior of the tube (38) to control, in use, the flow of colouring paste substance from the open-top receptacle towards the plasticising chamber of the machine. The device permits successive colouring substances of different colour to be used by replacing the container (34) and tube (38). <IMAGE>

Description

SPECIFICATION A device for supplying a colouring paste substance to the plasticising chamber of a plastics material injection moulding machine Technical field The present invention relates generally to the colouring of uncoloured thermoplastics material in granular form intended to be supplied to an injection moulding machine, for example, a machine of the type having a feed screw press.

Colouring substances used in this field are conventionally in granular form, usually called a "master", which are preliminarily mixed with the uncoloured plastics material and subsequently introduced through a feed hopper to the interior of the plasticising chamber of the injection moulding machine.

Under the action of the press screw, the uncoloured plastics material is plasticised and the colourant is melted, in this way colouring the plastics material to the desired shade.

This colouring method has three main disadvantages: a) The greater specific gravity of the colourant granules make these fall through the hopper towards the plasticising chamber of the machine more rapidly than the lighter base material. When the loading hopper is nearly empty the colouration of moulded articles is thus less intense. In order partly to obviate this disadvantage a greater quantity of colourant granules than necessary is usually introduced into the base plastics material.

b) The colourant, being in the solid state, does not perfectly amalgamate with the plastics base material so that the colouration is not always uniform. A correct plasticisation of the base material and the colourant material can be obtained by resorting to particular arrangements which, however, involve long loading times of the moulding machine and therefore an extended production cycle.

c) Forthe preliminary mixing ofthe"master" colourant with the base material, it is necessary to use suitable equipment with consequent additional burdens on the production.

In an attempt to obviate these disadvantages there have been proposed various automatic systems for performing the mixing operation directly within the feed hopper of the machine. These systems, however, have given unsatisfactory results because of the difficulty of correctly metering the colourant granules.

Recently, the producers of colouring substances have put on the market a new type of colourant in the form of a pasty liquid of high density. The inherent nature of colouring substances of this type encourages a better amalgamation with the plastics base material during plasticisation, with the evident advantage of being able to obtain a homogeneous colouration of the moulded products. Clearly this type of colouration cannot be direct, that is to say, it must take place within the interior of the plasticising chamber of the injection moulding machine.

This operation, however, involves a series of difficulties essentially tied to the necessity of having to introduce the correct quantity of colourant into the plasticising chamber at the right moment. On the other hand, it must be possible to control this quantity in dependence on the production requirements, that is to say, in dependence on the product being moulded, in such a way as to avoid both a deficiency in colouration with consequent rejects among the finished products and also a surplus with consequent wastage of colouring substance.

Another problem connected with the supplying of colouring paste is that of the associated smearing of the supply equipment which makes it extremely difficult to change from a colouring paste of a certain colour to a colouring paste of different colour without extensive delays in the production cycle.

Object of the invention The object of the present invention is that of providing a simple, reliable and functional device which allows a colouring substance to be supplied as a paste in a direct, automatic and controlled manner to the interior of the plasticising chamber of a machine for injection moulding uncoloured plastics material in granular form, and which will, moreover, be suitable to be used subsequently for the supply of colouring paste substances being a different colour without requiring long delays in the production cycle of the injection moulding machine.

The invention With a view to achieving this object, the subject of the present invention is a supply device the main characteristic of which resides in the fact that it comprises: - a pressurisable container having an openable part; - an open-top receptacle inserted in the pressurisable container and removable from this latter through the said openable part, the said receptacle being able to contain a colouring substance in the form of a paste; - a tube comprising a first section removably inserted into the pressurisable container and extend- ing into the interior of the open-top receptacle, and a second section releasably connected to the inlet of the plasticising chamber of an injection moulding machine;; - supply means for supplying a gas under pressure to the interior of the pressurisable container, and - metering means for metering, in use, the flow of colouring paste from the open-top receptacle towards the plasticising chamber of the injection moulding machine.

Thanks to this arrangement, the advantage of avoiding the use of any type of actuator members in direct contact with the colouring substance is obtained. In this way, as well as obtaining a reliable and secure operation, the device according to the invention offers a wide flexibility in use since it can be adapted easily and rapidly to colouring substances of different type.In effect, when it is necessary to change from a first colouring paste substance to a colouring substance of different colour, it is sufficient to disconnect the tube from the pressurisable container and from the injection moulding machine, to extract the open-top receptacle containing the first colouring substance from the pressurisable container and to replace it with another open-top receptacle containing the second colouring substance, and finally to insert into the pressurisable container a new tube which is then connected to the plasticising chamber.

According to the invention, the said second section of tube has at least one resiliently deformable part, and the said metering means include a throttling device acting on the exterior of the said resiliently deformable part of the second section of tube.

In this way, an effective metering action is obtained without having to resort to valves or other devices requiring direct contact with the colouring substance, and with the advantage of being able to easily vary the intensity of colouration and to obtain finished products which have a homogeneous and uniform colour, thereby reducing in a consistent manner the consumption of colouring substance.

Preferably, the resiliently deformable part of the said second section of the tube has a flattened form with a substantially elliptical transverse section, and the throttle device acts on the said flattened resilient- ly deformable part along a direction orthogonal to the major axis of the transverse section thereof.

Because of this characteristic, it is possible to obtain, as well as a better throttling effect on the flow of colouring substance consequent on the operation of the metering means, a long working life of the tube.

In fact, the substantially elliptical transverse section of the deformable part of this tube is able to resist practically limitless repeated squashings at the high pressures to which it is subjected in use, without being subject two damage or structural modifications.

On the other hand, for the purpose of ensuring an easy replacement in the event of possible damage, the flattened section resiliently deformable part of the tube is preferably connected in a rapidly releasable manner to the remaining part of the said second section of the tube.

Conveniently, the said flattened section resiliently deformable part of the tube is formed by vacuumforming a plastics material, for example, a urethane resin.

According to a further advantageous characteristic of the invention, the device further includes means for automatically controlling the activation of the said throttling means according to a predetermined cycle, and is moreover provided with security systems operable to prevent any error in the supply of the colouring substance.

Brief description of the drawings A preferred embodiment of the invention will now be described with reference to the attached drawings, provided purely by way of non-limitative example, in which: Figure 1 is a schematic view which illustrates the supply device according to the invention fitted to a plastics material injection moulding machine, and Figure 2 is a perspective view on an enlarged scale, and partially in section, of a part of Figure 1.

Detailed description ofa preferred embodiment of the invention Referring to Figure 1, there is schematically indicated a part 10 of an injection unit of a type known perse of a plastics material injection moulding machine. The unit 10 includes, inter alia, a feed screw press including a heated cylinder 12 the interior of which defines a plasticising chamber 14 in which there is rotatably mounted a plasticising feed screw 16. The plasticising screw 16 is connected at one end to an hydraulic cylinder 18 for control of the injection, and at the opposite end it is operable to inject the plasticised material into the cavity of a mould, not visible in the drawings.

A feed hopper is generally indicated 20 and this has at its lower end a cylindrical duct 22 which opens into the inlet end of the plasticising chamber 14 to supply an uncoloured plastics material to the interior thereof, the material being introduced in granular form into the feed hopper 20.

With the injection unit 10 there is associated a device for directly supplying a colouring substance in the form of a paste to the plasticising chamber 14 in a controlled manner. According to the invention, this device includes a pressurisable container 24 of substantially cylindrical form with a vertical axis, provided at the top with a cover 26. The cover 26 is fitted in a releasable manner by means of a series of screw clamping members 28 and with the interposition of an annular sealing ring 30 and a peripheral external annular flange 32 provided at the top of the side walls of the container 24.

In the interior of the container 24 there is located an open-top receptacle having a vertical axis 34 the side walls of which have a generally barrel shape.

The receptacle 34 is provided at the top with handles 36 which allow it to be raised and removed from the pressurisable container 24 following the removal of the cover 26.

The reference numeral 38 generally indicates tube comprising a rigid dip tube 40 and a flexible supply tube 42, preferably of elastomeric material or reinforced plastics material. The dip tube 40 passes through a sleeve 44 carried by a tubular connector 46 fixed to the outer face of the cover 26, and extends axially into the interior of the pressurisable container 24 and the open-top receptacle 34 down to a short distance from the bottom of this latter. The sleeve 44 is provided with a screw clamping member 48 which in the closure position fixes the dip tube 40 to the container 24, and in the open position permits the dip tube 40 to be removed axially from the container 24.

The flexible tube 42 of the tubing 38 is connected at one end to the upper end part of the dip tube 40, whilst at the other end it is inserted in a releasable mannerthrough a lateral tubular connector 50 into the central region of the lower duct 22 of the feed hopper 20. The tubular connector 50 is externally threaded and has screwed onto it a retaining member 51 and purpose of which is to lock the end of the duct 42 with respect to this tubular connector 50 in a rapidly removable manner.

The cover 26 of the pressurisable container 24 is provided with an outer tubular connector 52 to which there is permanently connected a pipe 54 in turn connected to a source of compressed air 56. In the pipe 54 there is inserted an adjustable pressure regulator 58 of known type, with which there is associated a pressure indicating instrument 60.

Further, between the regulator 58 and the connector 52 there is provided a diverter valve 53 provided with a discharge duct 61. The diverter valve 53 is manually dispiaceable between a first position, in which it opens communication between the regulator 58 and the connector 52 and interrupts communi- cation between this connector 52 and the discharge duct 61, and a second position in which communication between the regulator 58 and the connector 52 is interrupted whilst communication between the connector 52 and the discharge duct 61 is open.The presence of the diverter valve 53 permits the supply of compressed air to the interior of the pressurisable container 24 to be interrupted by means of a simple operation which simultaneously puts this latter in communication with the atmosphere atthetime when it is necessary to remove the cover 26. This cover 26 is moreover provided with an excess pressure valve 33 of conventional type.

A A metering unit associated with the supply device according to the invention is generally indicated 62.

This metering unit 62 includes a vertical axis pneumatic actuator 64 the stem of which carries a presser member in the form of a disc 66 facing a support member 68 on which rests a section 70 of the flexible tube 42.

As illustrated in detail in Figure 2, the support member 68 has a convex support surface with a radius of curvature which is significantly greater than that of the presser disc 66. Moreover, this support member 68 is provided at its ends with two positioning and retaining fork elements 69 into which the section 70 of the flexible tube 42 is inserted. The section 70 is connected by means of a pair of connectors 71 to the remaining part of the flexible tube 42, and has a particular flattened configuration. In fact, as is illustrated in detail in Figure 2, the section 70 has a squashed form with a substantially elliptical transverse section the minor axis of which is directed, when resting on the support member 68, perpendicularly with respect to the arcuate support surface of this latter.The section 70 is preferably made by means of vacuum-forming of a plastics material, for example, a urethane resin.

The pneumatic actuator 64 comprises a cylinder 80 in which there is axially slidably mounted a piston 82 to which there is rigidly connected a piston rod 84 carrying the presser member 66. The piston 82 separates the interior of the cylinder 80 into a lowr chamber 86, through which the piston rod 84 extends, and an upper chamber 88 in which is housed a helical compression spring 90 which tends to bias the piston 82 towards the first chamber 86.

This latter chamber 86 is connected to a source 56 of compressed air by means of a pipe 72 in which is inserted a solenoid control valve 74 of conventional type. When the solenoid valve 74 is in its closed position, the piston 82 is retained in its lowermost position by the action of the helical spring 90 so that the presser member 66 is disposed in its operative position, whilst opening the solenoid valve 74 causes displacement of the piston 82 upwardly against the action of the spring 90 in such a way as to carry the presser member 66 into the inoperative position illustrated in broke outline in Figure 1. In this way, security in the event of accidental interruption of the supply of compressed air from the source 56 is obtained.

The solenoid valve 74 can be controlled manually, by means of a remote control device, or else automatically by means of a programmable timer 76, in such a way as to open and close communication between the chamber 86 of the actuator 64 and the source 56 of compressed air in accordance with predetermined operating cycles.

To obtain a greater security of operation, the timer 76 is integrated with a pulse counter 92 arranged to count the number of changes of state (open-close) of the solenoid valve 74 and to hold this latter in its closed position when the number of changes of state thereof correspond to a predetermined value in dependence on the production requirements. In this way, there is obtained an effective control of the solenoid valve 74 in an entirely automatic manner which is independent of the speed of rotation of the screw 16 of the injection moulding machine 10.

Alternatively, the pulse counter 92 can be connected to a sensor, not visible in the drawings, associated with the screw 16 and arranged to send a pulse to the counter 92 whenever the screw 16 has performed one complete revolution. In this way, when the number of pulses counted by the counter 92 reaches the predetermined value, a comparison signal is sent to the timer 76, by means of which the opening of the solenoid valve 74 for the predetermined time period is controlled. At the end of this operation the timer 76 and the counter 72 are automatically returned to their initial conditions and the cycle is repeated in a similar manner.This type of control permits the opening and closure cycle of the solenoid valve 64to be adapted to the speed of rotation of the screw 16, and is particularly advantageous in cases where the machine is constituted by a screw extruder having a speed of rotation which is variable in dependence on the production requirements.

The operation of the supply device according to the invention will now be described.

After having inserted the receptacle 34 containing a colouring substance in the form of a paste, that is, in a semi-liquid state, into the interior of the pressurisable container 24, and after having closed the cover 26, the dip tube 40 is introduced into the interior of the container 24 and locked in the manner illustrated in Figure 1. The flexible tube 42 connected to the dip tube 40 is introduced at its free end through the tubular connector 50 of the hopper 20 and positioned with its section 70 resting on the support member 68 and located between the two fork elements 69. Now, during supply of the granular plastics base material contained in the hopper 20 to the plasticising chamber 14, air under pressure is supplied to the interior of the container 24 through the pipe 54.The regulator 58 permits the value of pressurisation of the container 24 to be regulated as a function of the density of the colouring substance contained in the receptacle 34.

The effect of the pressure within the interior of the container 24 is to force the colourng paste substance up the dip tube 40 to travel, through the flexible tube 42 and the lower duct 22 of the hopper 20, into the plasticising chamber 14 within which it mixes with the plastics base material. In order to interrupt the supply of colouring substance to the plasticising chamber 14 in dependence on the production requirements, it is sufficient to control the intervention of the pneumatic actuator 64 by means of the solenoid valve 74, either directly or else by means of the timer 76 and/or the pulse counter 92, in such a way as to throttle the section 70 of the flexible tube 42.The particular configuration of the metering unit 62 permits the quantity of colouring substance supplied to the plasticising chamber 14to be regulated in an extremely precise manner independently of the speed of rotation of the screw 16, with the advantage of being able to obtain a homogeneous, uniform colouration of constant in tensityofthe moulded products at the outputs of the injection unit 10. The configuration of the pneumatic actuator 64 permits the accidental introduction of an excessive quantity of colouring material into the chamber 14 to be avoided. On the other hand, the particular form and structure of the section 70 of the flexible tube 42, and of the support member 68, guarantees an effective resistance by this section 70 to repeated squashing operations in use of the presser member 66.

It should be noted that the supply device according to the invention is entirely free from mechanisms of any type in direct contact with the colouring substance, and this has evident advantages from the point of view of secure and reliable operation. This further permits the device to be adapted to use successive colouring substances of different colour by means of the simple substitution of the open top receptacle 34 and the tubing 38. These operations can be performed in an extremely rapid and simple manner so that production down times of the moulding machine are significantly reduced.

Claims (19)

1. A device for supplying a colouring substance in the form of a paste to the plasticising chamber of a plastics material injection moulding machine, characterised by the fact that it comprises: - a pressurisable container having an openable part - an open-top receptacle which can be inserted into the pressurisable container and removable therefrom through the said openable part, the said receptacle being able to contain a colouring substance in the form of a paste; - a tube comprising a first section removing inserted into the pressurisable container and extend- ing into the interior of the open-top receptacle and a second section removably connected to the input of the plasticising chamber of an injection moulding machine;; - - supply means for supplying a gas under pressure to the interior of the pressurisable container, and - metering means for metering, in use, the flow of colouring paste substance from the open-top receptacle towards the plasticising chamber of the injection moulding machine.

2. A device according to Claim 1, characterised by the fact that the said second section of the tube has at least one resiliently deformable part and the said metering means include a throttling device acting on the outside of the said resiliently deformable part of the second section of the tube.

3. A device according to Claim 2, characterised by the fact that the said resiliently deformable part of the second section of the tube has a flattened form with a substantially elliptical transverse section, and by the fact that the throttling device acts on the said resiliently deformable part in a direction perpendiculay to the major axis of the transverse section.

4. A device according to Claim 2 or Claim 3, characterised by the fact that the said resiliently deformable part of the tube is connected to the remaining part of the second section of the tube in a removable manner.

5. A device according to any of Claims 2 to 4, characterised by the fact that the said resiliently deformable part is made by vacuum-forming a plastics material, for example, a urethane resin.

6. A device according to Claim 2, characterised by the fact that it further includes means for automatically controlling the activation of the said throttling device in accordance with a predetermined cycle.

7. A device according to Claim 1, characterised by the fact that the supply means include a source of gas under pressure connected to the interior of the pressurisable container by means of a pipe in which there is inserted an adjustable pressure regulator.

8. A device according to Claim 7, characterised by the fact that there is further inserted a diverter valve in the said pipe.

9. A device according to Claims 6 and 7, characterised by the fact that the throttling device includes a pneumatic actuator which controls a presser member and is connected to the said source of gas under pressure by means of a pipe in which there is inserted a solenoid control valve controlled by means of a programmable timer.

10. A device according to Claim 9, characterised by the fact that it further includes a counter device arranged to count the number of changes in the state (open-close) of the solenoid control valve and to lock this valve in its closure position after a predetermined number of changes of state.

11. A device according to Claim 9, in which the plastics material injection moulding machine includes a plasticising feed screw the speed of rotation of which is variable, characterised by the fact that it further includes a counter device arranged to count the number of rotations of the feed screw of the moulding machine and connected to the said programmable timer in such a way as to provide this with a comparison signal enabling a change of state of the solenoid valve each time the number of revolutions of the feed screw reaches a predetermined value.

12. A device according to Claim 9, characterised by the fact that the pneumatic actuator includes a cylinder in which there is slidably axially mounted a piston to which there is rigidly connected a piston rod carrying the presser member and which subdivides the interior of the cylinder into a first chamber, through which the piston rod extends, and a second chamber opposite the first and containing a resilient means tending to bias the piston towards the first chamber, and by the fact that the solenoid control valve connected with the said source of gas under pressure is connected to the first chamber of the cylinder and normally maintains communication between the said source and the said first chamber closed, whereby the piston is held by the action of the said resilient means in the operative position of the presser member, whilst opening of the solenoid control valve causes displacement of the piston, against the action of the said resilient means, in such a a way as to carry the presser member to an inoperative position.

13. A device according to Claim 9, characterised by the fact that the presser member of the throttle device has a convex pressing surface, and by the fact that it includes a support part on which the said resiliently deformable part of the tube rests and with which the said presser member cooperates.

14. A device according to Claim 13, characterised by the fact that the said support part has an arcuate support surface for the said resiliently deformable part of the tube.

15. A device according to Claim 14, characterised by the fact that the arcuate support surface of the support part has a centre of curvature disposed on the other side of the resiliently deformable part of the tube from the centre of curvature of the pressing surface of the presser member.

16. A device according to Claim 15, characterised by the fact that the presssing surface of the said support part has a radius of curvature significantly greater than that of the pressing surface of the presser member.

17. A device according to Claim 14, characterised by the fact that the support part has two fork elements at its ends for positioning and retaining the resiliently deformable part of the tube.

18. A device according to Claim 1, in which the colouring paste substance is supplied to an injection moulding unit including a plasticising chamber and a a loading hopper for supplying an uncoloured plastics material in granular form to the said plasticising chamber, characterised by the fact that the second section of the said tube is inserted transversely in a removable manner into the base of the feed hopper of the said plasticising chamber.

19. A device substantially as described with reference to the attached drawings.