AUTOMATIC PURGING METHOD FOR INJECTION MOLDING MACHINES

Abstract: Automatic purging method which is capable of injecting an arbitary material among different kinds of material into a mould without requiring a resin replacing block or a purging container and an additional material supplying means for increasing the material supply pressure, and which has a nozzle valve in a nozzle unit. The method is used to enable the automatic purging to be done smoothly and speedily by operating the nozzle valve so that it behaves according to a predetermined program. Method consists of supplying a fresh material from a hopper into a screw cylinder, rotating a screw with a nozzle valve closed, for a predetermined period of time or until the screw has been moved back a preset stroke, to plasticise the resin, and then purging the molten resin with the nozzle valve set to a predetermined degree of opening.

Description: This invention relates to a method for ejecting the molten resin used for a previous injection molding conducted in an injection molding machine according to the preamble of the claim. An automatic ejecting method for an injection molding machine is applicable when replacement of the material to be injected with another material or replacement of the material to be injected with one having a different colour is made. In case replacement of the material to be injected with one of a different kind is made while the injection molding machine is in operation, the existing material remaining in a screw cylinder in the molding machine must be ejected completely. It is publicly known that this ejecting is made automatically and a variety of means for effecting such ejecting have been proposed and carried out effectively. In particular, as for the ejecting means, it has been recognized effective to apply a high pressure to a resin (material for injection molding) remaining in the screw cylinder, and there are many technical means for automatic ejecting based on this principle. For example, the techniques described in publications of Japanese Laid-Open Patent Applications Nos. SHO-58-158228, SHO-59-87136 and SHO-59-87137 and Japanese Laid-Open Utility Models Nos. SHO-57-57926 and SHO-60-175617 require application of additional pressure into a screw cylinder. However, the prior art examples disclosed in these publications have several points desired to be improved from the viewpoint of mechanism and operation thereof. Stating in brief, the techniques described in the Japanese Laid-Open Patent Applications Nos. SHO-58-158228 and SHO-59-87136 and Japanese Laid-Open Utility Model No. SHO-57-57926 require troublesome operation of attaching a resin replacing block or an ejecting container when an automatic ejecting is made. Further, in the techniques described in Japanese Laid-open Patent Application No. SHO-59-87137, there is a problem in that an arbitrary material among different kinds of materials cannot be injected into the mold because molds having different draft angles and adapted to set different thicknesses of final products need to be used depending on the material to be subjected to injection molding. Further, the techniques described in the Japanese Laid-Open Utility Model No. SHO-60-175617 require provision of a separate material supply means for increasing the material supply pressure with the result that the apparatus per se becomes complicated and increases in the equipment cost and in the number of manufacturing steps are unavoidable. The present invention has been made in view of the above-mentioned circumstances, and has for its object to provide an automatic ejecting method for an injection molding machine which is capable of injecting an arbitrary material among different kinds of materials into a mold without having to provide a resin replacing block or a ejecting container and a separate material supply means for increasing the material supply pressure, and which has a nozzle valve in the nozzle unit thereof. Another object of the present invention is to provide an automatic ejecting method for an injection molding machine having a nozzle valve in the nozzle unit thereof which is capable of effecting automatic ejecting smoothly and speedily by operating the nozzle valve so that it may behave according to a predetermined program. To achieve the above-mentioned objects, there is provided, in accordance with the invention, a method for ejecting the molten resin used for a previous injection molding conducted in an injection molding machine having a nozzle valve which is adapted to control the flow of the molten resin and is mounted in a nozzle unit of the injection molding machine, said method including the steps of : (a) supplying a fresh resin material from a hopper accommodating the resin material into a screw cylinder of the injection molding machine ; (b) rotating a screw mounted whithin the screw cylinder under such a condition as closing the nozzle valve for a predetermined period of time or until the screw has been moved back over a preset stroke so as to plasticize the resin material; and (c) ejecting the molten resin used for the previous injection molding together with the plasticized resin under a condition such that the nozzle valve is set a predetermined degree of opening in a predetermined number of times; characterized in that the degree of opening of the nozzle valve during the ejecting operation is varied for each time of said ejecting so as to set it at a preset value and/or varied in predetermined multi-stages even during the time of ejecting operation made by the screw. A method as disclosed in the precharacterising part of the claim is known from JP-A-61-135 720 which fails however to disclose or suggest the characterizing part thereof. EP-A-0 262 229, which is to be considered under Article 54.3 EPC, shows an injection molding machine of the type used in the method of the invention but is not concerned with the same problem. Finally JP-A-61-54916 discloses a further method for changing resin in an injection molding apparatus, according to which the outlet end of the injecting nozzle is completely closed after completion of an injecting operation, after which the screw is driven at high speed so as to generate a negative pressure within the screw cylinder in the vicinity of the nozzle outlet and for withdrawing the residual resin from the nozzle. The above-mentioned and other advantages, aspects and objects of the present invention will become apparent to those skilled in the art by referring to the following description and accompanying drawing in which a preferred embodiment in compliance with the principles of the present invention is shown. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a schematic, configurational explanatory view showing one embodiment of injection molding machine having a nozzle valve in the nozzle unit thereof for carrying out the automatic ejecting method according to the present invention. The method of the present invention will now be described below by way of example. Fig. 1 shows one example of injection molding machine having a nozzle valve to which the method of the present invention is applied. This molding machine has a hopper 7 accommodating a material to be subjected to injection molding, and a screw cylinder 1 which has a nozzle 3 formed in the leading end thereof and in which a screw 2 is mounted so that it may be rotated and moved forwards and backwards freely. The nozzle 3 has a nozzle valve 4 mounted therein and which is adapted to be opened and closed by means of a nozzle valve driving mechanism 10. The screw 2 has a non-return valve in the vicinity of the leading end thereof to prevent the return or reverse flow of a molten resin. The base or trailing portion of the screw 2 passes through an injection cylinder 5 by way of a piston, and further is connected through a spline to a hydraulic motor 6. Reference numeral 13 denotes a control system adapted to control a directional control valve 11, which connects selectively a pressurized fluid supply source and a back-pressure relief valve with the injection cylinder 5 and the hydraulic motor 6, and the above-mentioned nozzle valve driving mechanism 10. The value detected by a screw position detector 12 is input as a signal to the control system 13. The control system 13 is adapted to control the operation of the injection molding machine. The control system 13 includes a timer, a comparator and an operational setting console mounted therein. The nozzle valve 4 is a valve for regulating the degree of opening of the nozzle 3, and the degree of opening of the nozzle is regulated by the nozzle valve driving mechanism 10. The directional control valve 11 serves to change the ejecting (injection of molten resin) over to the rotation of the screw 2 and vice versa. The functions of these component parts are compiled in a program which is input to the control system 13, and automatic ejecting is made by controlling the directional control valve 11 and the nozzle valve driving mechanism 10. Stating in brief, in case replacement of the material for injection molding with a different material is made, the supply of the existing material into the screw cylinder 1 is stopped, and instead a fresh material is thrown into the hopper 7. And then, the screw 2 is rotated with the nozzle valve 4 closed for a predetermined period of time or until the screw has been moved back over a preset stroke to plasticize the resin. After that, the nozzle valve 4 is opened and set at a predetermined degree of opening so as to eject the molten resin. With repeated plasticization or ejecting of the resin by the rotation of the screw 2 in this condition, the existing material within the screw cylinder 1 is replaced with a fresh material thereby achieving the ejecting operation. A variety of pressures can be applied to the molten resin within the screw cylinder 1 by varying the degree of opening of the nozzle valve for each one shot of ejecting to be made by one stroke of the screw 2 or by varying the degree of opening of the nozzle valve during one stroke of the screw 2 or by using these steps in combination. By so doing, the condition of flow of the molten resin within the screw cylinder 1 can be varied and the scraping effect can be enhanced further. Changes in the degree of opening of the nozzle valve contributes to the replacement of the material remaining in the nozzle valve 4 with a fresh, different material. Further, the stroke of the screw 2 which ensures that the ejecting is made satisfactorily can be controlled under an optimum condition by detecting the actual position of the screw 2 by means of the screw position detector 12 and inputting the detected value in the control system 13 where the programmed preset value is compared with the detected value by means of the comparator.

Claims: A method for ejecting the molten resin used for a previous injection molding conducted in an injection molding machine having a nozzle valve (4) which is adapted to control the flow of the molten resin and is mounted in a nozzle unit (3) of the injection molding machine, said method including the steps of : (a) supplying a fresh resin material from a hopper (7) accommodating the resin material into a screw cylinder (1) of the injection molding machine ; (b) rotating a screw (2) mounted within the screw cylinder (1) under such a condition as closing the nozzle valve (4) for a predetermined period of time or until the screw (2) has been moved back over a preset stroke so as to plasticize the resin material; and (c) ejecting the molten resin used for the previous injection molding together with the plasticized resin under a condition such that the nozzle valve (4) is set at a predetermined degree of opening in a predetermined number of times; characterized in that the degree of opening of the nozzle valve (4) during the ejecting operation is varied for each time of said ejecting so as to set it at a preset value and/or varied in predetermined multi-stages even during the time of ejecting operation made by the screw (2).

Inventors: FUNABASHI TETSUJI, INABA NOBUAKI - MUTSUGAWA -CHO, KAMINISHI MASASHI, MASTUDA KAZUO, TANAKA NOBUKAZU, FUNABASHI, TETSUJI, INABA, NOBUAKI 85-6, MUTSUGAWA 3-CHOME MINAMI-KU, KAMINISHI, MASASHI, MASTUDA, KAZUO, TANAKA, NOBUKAZU
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1988
Main classification: B29C45
IPC codes: B29C45