PLANT FOR TREATMENT OF POLYMERIC MATERIALS

Abstract

A plastics material transformation plant (100) comprises a transformation machine (10) for the plastics material by means of moulding or extrusion, a feeding hopper (13) which is positioned upstream of the transformation machine and a metering device (1) which is arranged to add a liquid additive to the transformation machine. The metering device (1) comprises a container (4) in which the liquid additive is contained, a metering pump (5) which is connected to the container in order to take the liquid additive and to supply it to the transformation machine (10), and a thermo-regulation system of the liquid additive which is arranged to maintain the temperature of the liquid additive in a range of 2° C. more or 2° C. less than a predetermined temperature value.

Claims

1. A plastics material transformation plant (100) comprising: a transformation machine (10) which is provided to transform the plastics material by means of molding or extrusion, a feeding hopper (13) which is positioned upstream of the transformation machine in order to supply the plastics material to the transformation machine, and a metering device (1) for liquid additives which is provided to add a liquid additive to the transformation machine, wherein the metering device (1) comprises: a container (4) in which the liquid additive is contained, a metering pump (5) which is connected to the container in order to take the liquid additive and to supply it to the transformation machine (10), and a thermo-regulation system of the liquid additive which is arranged to maintain the temperature of the liquid additive in a range of 2° C. more or 2° C. less than a predetermined temperature value.

2. The plant according to claim 1, wherein the thermo-regulation system is associated with the container (4) in order to maintain the temperature of the liquid additive in the predetermined temperature range inside the container.

3. The plant according to claim 2, wherein the thermo-regulation system comprises an insulating coating (7) which is provided around the container (4).

4. The plant according to claim 1, wherein the thermo-regulation system comprises a heating element (8), a temperature sensor (9) and a controller (20) which is associated with the temperature sensor (8) and with the heating element (9) in order to activate or deactivate the heating element (8) in accordance with the temperature value detected by the temperature sensor (9).

5. The plant according to claim 4, wherein the heating element (8) comprises an electrical resistance.

6. The plant according to claim 4, wherein the heating element (8) is immersed in the liquid additive.

7. The plant according to claim 1, wherein the thermo-regulation system comprises a thermal cover which is provided to be wrapped around the container (4).

8. The plant according to claim 2 wherein the thermo-regulation system is provided to maintain the temperature of the liquid additive inside the container (4) in a temperature range which is approximately from 3 to 5° C. greater than the temperature of the environment in which the container is positioned.

9. The plant according to claim 1, wherein the liquid additive is a dye.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The features and advantages of the invention will be better appreciated from the detailed description of a preferred embodiment thereof which is illustrated by way of non-limiting example with reference to the appended drawing, in which FIG. 1 is a schematic view of a plastics material transformation plant which is realised according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0047] In the appended FIGURE, there is generally designated 100 a plastics material transformation plant which is realised according to the present invention.

[0048] In this preferred example, the transformation plant 100 is a moulding or extrusion plant for polymer material in granules of polyethylene terephthalate (PET) for producing bottle preforms.

[0049] However, the present invention may similarly be used in a moulding or extrusion plant which is supplied with any other thermoplastic polymer material, such as, for example, polypropylene, polyethylene, polyvinyl chloride, polyamide, etc.

[0050] The transformation plant 100 comprises: [0051] a transformation machine 10, for example, an extruder, [0052] a feeding hopper 13 which is positioned upstream of the transformation machine 10 and in which there is stored the polymer material which is intended to be transformed and which is provided to supply the granules of plastics material to the transformation machine 10, and [0053] a metering device 1 for liquid additives provided to add a liquid additive to the plastics material which is supplied to the transformation machine 10.

[0054] In particular, the metering device 1 supplies the liquid additive to the plastics material by means of a supply pipe 11 which is open, for example, in the region of a rotary valve 12 which is positioned between the outlet of the feeding hopper 13 and the inlet of the transformation machine 10.

[0055] The metering device 1 comprises a movable carriage 2, on the frame 3 of which there are positioned a container 4 comprising the liquid additive to be metered in the polymer material and a metering pump 5, the intake of which is connected to the inner side of the container 4 by means of a withdrawal pipe 6 and the delivery of which is connected to the supply pipe 11.

[0056] The metering pump 5 is preferably a peristaltic pump and, in the preferred example described herein, the liquid additive is a dye to be introduced into the polymer material in order to confer the desired colouration on the product which is obtained at the end of the processing thereof.

[0057] The metering device 1 further comprises a thermo-regulation system of the liquid additive which is contained in the container 4, which system is arranged to maintain the temperature of the liquid additive in a predetermined temperature range.

[0058] In a first embodiment of the invention, illustrated in FIG. 1, the thermo-regulation system comprises an insulating coating 7 which is provided around the container 4, a heating element 8, a temperature sensor 9 and a controller 20.

[0059] The insulating coating 7 is formed, for example, by a layer of thermally insulating material having a suitable thickness, for example, between 1 and 5 cm. Examples of suitable thermally insulating materials comprise expanded polymers based on polyurethane or polystyrene, glass wool or mineral wool.

[0060] The heating element 8 is preferably an electrical resistance which is inserted in the container 4 so as to be immersed in the dye to be heated.

[0061] Similarly, the temperature sensor 9 is also inserted in the container 4 so as to detect the temperature of the dye.

[0062] The controller 20 is associated with the temperature sensor 9 and the heating element 8 and is provided to activate or deactivate the heating element in accordance with the temperature value which is detected by the temperature sensor 9.

[0063] In particular, the controller 20 is provided to maintain the internal temperature with respect to the container at a predetermined value (set temperature) which, for example, may be fixed at 30° C., with a margin of deviation of, for example, approximately 2 degrees centigrade.

[0064] The value of the set temperature is programmable by the operator and is preferably selected so as to be greater by a few degrees (for example, 5° C.) than the mean temperature of the environment, in which the metering device 1 is positioned.

[0065] Similarly, the deviation margin from the set temperature is also programmable by the operator.

[0066] The controller 20 is preferably integrated in a control unit 30 of the metering device 1, preferably mounted on the movable carriage 2, which, in addition to the thermo-regulation system, is arranged to control and/or instruct other parameters or components of the metering device, such as, for example, the metering pump 5.

[0067] The provision of the thermo-regulation system allows the dye contained in the container 4 to be maintained at a controlled temperature which is within a predefined range centred on the set temperature.

[0068] In this manner, when the metering device 1 is in operation, the quantity of dye introduced into the polymer material remains constantly proportional to the volume thereof, which in turn depends only on the metering pump 5 and is therefore readily adjustable with optimum precision.

[0069] In a second embodiment of the invention, which is similarly preferred, the thermo-regulation system comprises a thermal cover which is wrapped around the container 4.

[0070] In this case, the heating element is encased inside the insulating material of the thermal cover and the temperature sensor can be external with respect to the container, integrated in the thermal cover.

[0071] The thermal cover may be connected to the controller 20 or may have an independent control unit.

[0072] In additional construction variants of the invention, there is provision for the thermo-regulation system to comprise a heating base, on which the container 4 is supported, and/or for the thermal cover not to be in direct contact with the container, but to be arranged on a suitable frame which is mounted around the container so as to form a heated chamber around the container.

[0073] The present invention therefore allows a substantial reduction in the need for manual interventions by the operator in order to regulate the quantity of dye which is introduced into the polymer material and a reduction of the quantity of products rejected as a result of discrepancies in relation to the colouration.