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#100 Units Relating to an Injection Molding Machine

Category : Technical Information
November 4, 2011
  1. Injecting Device
    The injecting units of a plastic injection molding machine is a unit where an injection plunger or a screw moves forward inside a cylinder to inject molten plastic into the mold.
    The performance of an injecting unit is expressed by the injection rate (the volume of molten plastic that is injected in one second, cm3/s) or the injection speed (the speed of forward movement of the plunger, mm/s).

    In the case of super engineering plastics, there are some materials that cause loss of molded article quality unless an injecting device with a high injection rate is used, or on the other hand, there are also plastics for which the suitable injecting devices are those that can inject at a low speed in a stable manner.

    It can be said that the type of injecting unit used is closely related to the molding material to be used.

    The tip of an injecting unit is provided with a nozzle, and normally the tip of the nozzle is machined to a spherical shape so that it can contact closely with the spherical seat of the sprue bush of the mold, and considerations have been given so that there is no leaking of the plastic during injection.  There are many types of nozzles, such as the open nozzle, the shut off nozzle, or the nozzle with a needle valve, etc.

  2. Mold Clamping Unit
    The mold clamping unit is a unit in charge of installing the mold in the injection machine, and of opening and closing the mold.  It is necessary to clamp the mold under a high pressure so that the mold does not open when the molten plastic is being injected into the mold.  Ordinarily, the size of an injection molding machine is expressed in terms of the claming force.  For example, "a molding machine with a mold clamping force of 160 tons", etc.

    The methods of clamping a mold can be classified into the following two types.

    1) Direct pressure type
    2) Toggle type

    The direct pressure type is one which the platen on the moving half is operated through a hydraulic cylinder for mold clamping.  In this method, since it is possible to clamp the mold with a constant pressure applied over a wide area, this method is suitable for the molds of molded articles having a large projected area.  In addition, the adjustment of the clamping force is easy, and there is the advantage that the work of installing the mold is not cumbersome even if the thickness of the mold changes.

    The toggle type is one which uses the clamping force when a toggle link mechanism extends or contracts.  This type has a high speed of opening and closing, and while it has the effect of shortening the cycle time, it takes time for set up because the work of adjusting the clamping force has to be done for each mold.

    A mold protecting device is provided in recent mold clamping units.  There are also units in which mold clamping is done at a low pressure up to a certain mold clamping process, and a protective device is provided that has a sensor that stops high pressure mold clamping if, by chance, any foreign matter or a runner, etc., has entered between the molds.

    Normally, a mold clamping unit is also provided with a molded item ejecting unit which has a structure in which a knock-out bar moves forward from the moving half and causes the ejector plate of the mold to move forward thereby ejecting the molded article.

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