IL31467A - Injection molds for the manufacture of thin-walled articles from plastics - Google Patents

Description

walled articles from Of 2 invention concerns injection molds for plastics injection particularly for the manufacture of articles such as and more particularly those Injection molds in which the bottom part of the cavity between the core and matrix has a raised central portio surrounded by a outer sloping annular channel between the outer and central parts of the the outer part of the cavity merges into an space in which the wall of the article is and an injection gate is provided in the centre of the of the These molds will be called herein of the kind referred In known molds of the kind referred to the several parts this the cavity defined between the core and matrix have a uniform width Such molds so can under certain the core becomes This is an important advantage in the manufacture plastics cups or tubes which relatively deep and as a rather The relatively long required in these cases is apt produce an uneven flow of the molten material in the cavity whereby the core is dislocated and irregularities the wall thickness of the article are In order to achieve of the a desig as been proposed in which raised central part of the matrix bottom extends relatively steeply and deeply into the core In this case relatively large surfaces of the core and raised bottom of the matrix 3 face each other across the sloping annular channel of the The idea was that a lateral dislocation of the which would entail a corresponding narrowing of the sloping channel at the opposite would throttle the flow of material through the narrowed part of the annular channel into the part of the It has been found that even when the annular channel is located relatively near to the the desired effect occurs only under especially favorable that when the location of the core is relatively great and the flow of material is checked to a large The present provides a mold avoids the disadvantages the known molds aforesaid and facilitates the of the core in respect to the e invention consists in a mold of the kind referred to in which the width of the cavity in the sloping annular channel is smaller than the width of the outer forming space of the It has been in accordance with the present that if the width of the outer space of the and hence the thickness of the wall of the article being is 2 to times the width of the sloping annular the core with be with respect to the The smallest dislocation of the core to one side closes the sloping annular channel at the opposite side and instantaneously prevents the further flow of the 4 through that side of the insures the formation of such conditions of excess pressure in the annular as cause the core to return to the correct centered A preferred embodiment of the invention is by way of example in the accompanying drawing is a fragmentary sectional view of a mold in accordance wit the The mold illustrated includes an upright cylindrical matrix 1 and a which define between them a mold cavity generally designated of a form ponding to that of the cup to be formed for has the following dimensions wall thickness bottom thickness minimum diameter height 90 mm and conicity of about In the bottom of the matrix 1 an injection gate is in an axial bottom of the matrix 1 has a raised central portion lb and an outer ortion which are spaced a central recessed portion 2b and a projecting of the core Sloping walls and of the matrix and define a sloping annular channel between the raised part the bottom of the matrix and the rim 2a of the The Includes a central part an annular elopin channel an outer channel and a conical outer space In accordance with the the sloping channel a angle o inclined wall and a vertical in the range between 5 and preferably 7 to The sloping annular channel is much narrower than the remaining parts of the the central part the outer channel d shaped Preferably the width of the sloping 3a is 2 times smaller thn that of the space in which the wall of the cup The spacing the annular channel from the space between which the rim 2a of the core will be in accordance with desired width of the bottom rim of the cup to upon which depends the mechanical strength of the In the widt of the rim 2a is usually from about 1 to example a finished cup may following dimensionsί Wall thickness mm Thickness of sloping torn part in the annular channel Length of sloping par of about times measured between the outer face the wall of the central part 1 to d the and the inner face of the bottom rim in the channel A greate length of the sloping bottom the cup is desirable the cu would then have high bottom Similar considerations apply to injection molds for the production of relatively narrow and deep tubular hollow bodies whose cylindrical wall somewhat for from to 1 for tubes for medicinal When the injection of the melted material proceeds through the gate in the bottom of the the flow of the material is apt tp dislocate the core 2 towards one side whereby the annular channel is made still narrower at that an assumed dislocation of the at the of less than mm would reduce the width of the annular channel to approximatel that to less than with a concomitant drastic reduction of the of material the channel at this Since the annular channel is too high and too narro to enable a flow of material within this the pressure in the adjacent parts o the cavity will be reduced On the other on the diametrically opposite side towards which the core is the channel is widened The flow of material in this widened part of the channel is suddenly and ill eventually lead to a pressure increase in the space 3d in the side of the mold where the flow of material is thus pressur conditions thus created not only prevent further dislocation of the but immediately about the return of to its axially centered It has been found that with this design of the the core becomes without any additional 7 measures and all even very walled cups can be produced with a much more uniform wall thickness than could be achieved 8 insufficientOCRQuality

Claims (1)

1. CLAIMS An injection mold of the kind wherein the width of the cavity in the sloping annular channel smaller than the width of the outer wall space of the cavit An injection according to wherein the width of the sloping annular channel is about 2 to times smaller than that of the outer space of the An injection mold according to Claim 1 or wherein the sloping annular channel has an angle of slope of 5 to preferably 7 to An injection mold according to any of Claims 1 to wherein the length of the sloping annular channel is equal to about times the Applicants insufficientOCRQuality