MXPA96000426A - Apparatus to detect pressure in cavity of mold during injection of molded parts - Google Patents

Abstract

The present invention relates to equipment for injection molding and more particularly to equipment for measuring pressure in a mold cavity, during injection of molded parts.

Description

APPARATUS TO DETECT PRESSURE IN CAVITY OF MOLD DURING INJECTION OF MOLDED PARTS BACKGROUND OF THE INVENTION Injection molding processes generally involve the injection of a liquid material into a mold cavity for curing. The resulting molded article must be removed or ejected from the open mold after curing. The equipment to remove items * Molded * of a mold is referred to as the ejector assembly. Often, the ejector assembly includes ejector pins that are retracted during molding and extend during ejection to force the article out of the open mold.

In the case of concave molded parts that are formed on a core pin, the ejector assembly includes a sleeve 5 that encloses and runs through the entire core. The sleeve retracts during molding and extends during function to traverse the core and force the article out of the core. In order to achieve the parts with higher or higher quality finish, the liquid material must be injected into the mold cavity at the proper pressure. In extreme cases, insufficient pressure can lead to porous, pitted or incomplete parts. On the other hand, excessive pressure can damage the molding apparatus or result in a seam line on matching or corresponding portions of the mold half. Under normal process conditions, the dimensions of parts, strength and quality in general depend on a consistent mold pressure. A prior art for measuring pressure within a mold cavity during injection employs a level-mount style transducer, such as a piezo-electric voltage or transducer. The transducer is mounted directly on the interior surface of the mold cavity, in contact with the part to measure the pressure of the cavity. When mounted on a cosmetic surface of the mold cavity, the transducer leaves an undesirable mark on the surface of the article. Secondly, many molds do not allow for the installation of a level-mount style transducer. For example, the mold may include obstructions or the transducer may interfere with proper operation of the mold. SUMMARY OF THE INVENTION The aforementioned problems are overcome by the present invention, wherein the pressure within a mold cavity during injection is approximated by measuring the force applied to the ejector assembly and core pin by the injected liquid. More particularly, the force applied to the ejector assembly is measured using conventional tension measurement technology. In the described embodiment, the invention further includes an attachment for force translation, which sits between the ejector sleeve and the ejector plate of the ejector assembly. The force translation attachment, in general, is ring-shaped and includes a series of fulcrums that move half the total force of the ejector sleeve on the dome button of a conventional load cell mold pressure transducer. The mold pressure transducer is placed between the ejector plate and the force translation attachment to verify the mold cavity pressure transferred through the ejector sleeve and the fitting. In a first alternate mode, the mold pressure transducer is replaced by another fulcrum to create a ring force transducer. The elastic deformation of the ring is measured by a series of conventional tension gauges that are applied or attached to the accessory. The elastic deformation of the accessory becomes mold pressure. In a second alternate mode, the ejector sleeve is modified to receive a series of strain gauges that measure its elastic deformation. The strain gauges are located in a portion of the ejector sleeve where the diameter has been bent downward to produce a concentrated compression stress path. In a third alternative mode, the ejector sleeve includes a flanged section at the base of the ejector tube. The tension gauges are placed in elbows that are incorporated in the flanged section at the base of the ejector tube. The manomeres can be located alternately on the upper or lower surfaces of the flanged portion. In a fourth alternate embodiment, the elastic deformation of the core pin is measured by a series of conventional strain gauges that are applied or attached to the core pin. Tension meters are located on a portion of the core pin where the diameter has been reduced to produce a tension path with concentrated compression. The present invention provides a simple, practical and economical way to verify the pressure inside a mold cavity during injection molding. Force concentration trajectories are easily incorporated into the force translation, ejector sleeve or core pin attachment without affecting the strength, integrity or function of the mold halves.

In addition, the present invention does not mark or otherwise deteriorate the surface of the molded article. These and other objects, advantages and features of the present invention will be more fully understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a fragmentary sectional view of a prior art molding apparatus for a concave article with a pressure transducer with level assembly in the upper mold half; Figure 2 is a fragmentary sectional view of the molding apparatus of the present invention; Figure 3 is a top plan view of the force translation attachment that is incorporated in the ejector assembly; Figure 4 is a front elevation view of the force translation attachment; Figure 5 is a bottom plan view of the attachment for force translation; Figure 6 is a top plan view of a ring force transducer according to an alternate embodiment; Figure 7 is a bottom plan view of the ring force transducer according to the alternate mode; Figure 8 is a sectional view of a second alternate embodiment showing an ejector sleeve with strain gauges located in a reduced diameter portion of the ejector tube; Figure 9 is a sectional view of a third alternating mode showing an ejector sleeve, with tension gauges located in a base section with flange having a flexural beam design; Figure 10 is a top plan view of the ejector sleeve and strain gauges of the third alternate mode; and Figure 11 is a sectional view of the core pin and voltage meters of the fourth alternate mode. DETAILED DESCRIPTION OF THE PREFERRED MODE A conventional injection molding apparatus incorporating a core pin and ejector sleeve, is illustrated in Figure 1 and is generally designated with the number 10. In this illustration the injection process is completed and a Molded article A remains in the mold cavity. In general, the mold cavity is defined by the middle of the upper mold 12a, the mold half "lower" 12b, and the ejector sleeve 20. The lower mold half 12b includes a generally cylindrical core pin 14 that is extends through a mold port 16. A cooling tube 18 extends in a recess in the core pin center 14, to supply gas or fluid to accelerate the curing process of the article A. The ejector sleeve 20 encloses the core pin 14 and slidably mounted for movement in and out of the lower portion of the mold cavity During the molding process, the upper surface 24 of the ejector sleeve 20 acts as a portion of the lower surface of the mold cavity This places the ejector sleeve 20 in direct contact with the molded article A. An ejector plate 22 is placed below and confined with the ejector sleeve 20. The ejector plate 22 is attached to hydraulic means (not shown) that lift the ejector plate 22 to push the ejector sleeve 20 into the lower portion of the mold cavity and force out the molded article A. According to the prior art, the pressure in the mold cavity is measured by a conventional level mounting detector 50, mounted directly on the surface of any mold half. Figure 1 shows the detector 50 mounted on the outer surface of the upper mold half 12a and extending inward to the surface of the mold cavity. As liquid is injected into the mold cavity, the detector 50 which is in direct contact with the liquid, measures the pressure in the mold cavity. The pressure in the mold cavity becomes a force in the ejector sleeve 20 during the injection process. Figure 2 illustrates an injection molding apparatus 10 according to the present invention, wherein an attachment for force translation 30 and mold pressure transducer 40 are incorporated in the ejector plate 22 to verify the force in the ejector sleeve 20. The ejector plate 22 is modified to include a circular recessed portion 38 for seating the accessory 30 and transducer 40. The mold pressure transducer 40 is a conventional cell-type transducer that includes a dome button 42 for receiving force. The transducer 40 is interposed between the accessory 30 and the ejector plate 22 in the recessed portion 38, to verify the pressure between the ejector plate 22 and the force translation attachment 30. Probably as best illustrated in Figures 3 to 5, the force translation attachment 30 is generally ring-shaped and includes an upper surface 32 and a lower surface 34. A series of fulcrums 36a-c are placed on the upper and lower surfaces of the accessory 30, to transfer one half of the force total on the dome button 42 of the mold pressure transducer 40. The first two fulcrums 36a and 36b are positioned at 0 and 180 ° on the upper surface 32 of the accessory 30. The third fulcrum 36c is placed 90 ° on the surface bottom of the accessory 30. The accessory is located in the recessed portion 38 of the ejector plate 22 such that the button with transducer dome 42 contacts the bottom surface 34 of the accessory 30 to 270 ° , acting as a fourth fulcrum. In operation, the pressure of the mold cavity is transferred to the ejector sleeve 20 as liquid is injected into the mold cavity. The two fulcrums 36a-b located on the upper surface 32 of the fitting are in contact with the base 21 of the ejector sleeve 20 and create force paths that focus one half of the sleeve force translated on opposite radial sides of the accessory 30. Both force trajectories are combined on the underside of the fixture to focus one-half of the force of the total ejector sleeve on the third fulcrum 36c and the other half on the dome button 42 of the transducer 40. First Alternate Modality A first alternate modality of the present invention is illustrated in Figures 6 and 7 and acquires the same detail as the force translation attachment 30. However, in this embodiment a fourth fulcrum 36d 'is added to the outer surface 34' of the accessory 30 to 270 °. In addition, the mold pressure transducer is replaced by four conventional 50a-d voltage meters wired in a four-arm Wheatstone bridge, constituting a ring force transducer. The strain gauges 50a-d are of a type well known to those of skill in the art and are placed on the upper and lower surfaces 32 'and 34' of the accessory 30 '. The first two voltage meters 50a-d are located at 90 ° and 270 ° on the upper surface 32 'of the accessory 30', and the second two voltage meters 50c-d are located at 0 and 180 ° on the lower surface 34 ' This assembly imparts an opposite tension measurement to each fulcrum 36a-d ', wherein the elastic deformation of the upper and lower surfaces 32' and 34 'of the accessory 30' will be concentrated. Alternatively, tension gauges 50a-d may be placed at spaced intervals on the inner surface 31a 'or outer surface 31b' of the circumferential wall 31 'of the accessory 30'. Figure 6 illustrates in dotted lines the tension gauges 50a-d x ~ located in alternating positions on the inner surface 31a 'of the circumferential wall 31'. The tension gauges 50a-d are placed at spaced locations, immediately adjacent to each fulcrum 36a'-d ', wherein the elastic deformation of the circumferential wall 31' will be concentrated. Second Alternating Modality In a second alternate embodiment of the present invention, tension gauges 50a-d are located in the circumferential wall 70 of the ejector sleeve 20 'Now with reference to Figure 8, the ejector sleeve 20 'includes a circumferential wall 70 and a flange 72 extending outwardly from the base of the circumferential wall 70. The circumferential wall 70 of the ejector sleeve 20 'includes a reduced diameter portion 74. The reduced diameter portion 74 is weaker than the rest of the ejector sleeve 20' and thus concentrates the elastic deformation of the sleeve 20 '. Four 50a-d voltage meters wired on a bridge Four-arm Wheatstone are placed in radially symmetrical spaced locations on the outer surface of the reduced diameter portion 74 of the ejector sleeve 20 '. Alternately, as illustrated in Figure 8, in dotted lines, the voltage meter 51a-d may placed in spaced locations on the inner surface '"-' of the reduced diameter portion 74 of the ejector sleeve 20 'Third Alternate Modality A third alternate embodiment of the present illustrates in Figures 9 and 10. In this embodiment the flange 72 includes a pair of lobes 80a-b connected together by bending beams 82a-b. The bending beams 82a-b have a thickness substantially less than that of the lobes 80a-b. In addition, the lobes 80a-b are radially or spaced apart from the circumferential wall 70 of the ejector sleeve 20"by through holes 84a-b. In this way, the elastic deformation of the flange 72 is concentrated in the bending beams 82a-b. As probably best illustrated in Figure 10, four 50a-d 5 voltage meters wired in a four-arm heatstone bridge are placed at spaced locations on the upper surface 76 of the flange 72. Preferably, a simple strain gauge is located on each lobe 80a-b and each bending beam 82a-b. As will be readily apparent to a person with ordinary skill in the art, the voltage meters may alternatively be located on the inner surface 78 of the flange 72. Fourth Alternating Modality A fourth alternative embodiment of the invention is illustrated in Figure 11. In this embodiment, the core pin 14 serves as a force transducer for detecting pressure in the mold cavity. Preferably, a conventional four-arm Wheatstone voltage measurement bridge 50a-d is applied to a reduced diameter portion 14a of the core pin 14, as described in connection with the second alternate embodiment. The strain gauges 50a-d measure the elastic deformation of the pin 14 resulting from the compression force placed on the core pin 14 during pressurization of the mold cavity. Alternatively, strain gauges 50a-d may be applied to the flange portion 14b of the pin 14 as described in the third alternate embodiment. The above descriptions are those of preferred embodiments of the invention. Various alterations and changes may be practiced without departing from the spirit and broader aspects of the invention as set forth in the appended claims, which shall be construed in accordance with the principles of patent law, including the doctrine of equivalents.

Claims (1)

1. CLAIMS 1. Apparatus for measuring mold cavity pressure, characterized in that it comprises: an injection mold that defines a mold cavity; an ejector assembly including at least one ejector element mounted for reciprocating movement in and out of the mold cavity to eject molded articles from the mold; and means for detecting pressure to measure the pressure imparted to at least one ejection element. 2.- Apparatus in accordance with the claim 1, characterized in that the ejector assembly includes an ejector sleeve mounted adjacent to the mold cavity and an ejector plate mounted adjacent to the ejector sleeve opposite the mold cavity; and wherein the detecting means includes an attachment for force translation interposed between the ejector sleeve and the ejector plate. 3. Apparatus in accordance with the claim 2, characterized in that the force translation device is generally ring-shaped and includes a first surface in contact with the ejector sleeve and a second surface in contact with the ejector plate; and wherein the first surface includes first and second fulcrums located radially opposite each other, and the second surface includes a third fulcrum located radially in the middle between the first and second fulcrums. 4.- Apparatus in accordance with the claim 3, characterized in that in addition it comprises a pressure transducer interposed between the attachment for force translation and the ejector plate, the transducer is located radially opposite to the third fulcrum. 5. Apparatus in accordance with the claim 4, characterized in that the pressure transducer includes a button with dome, the button with dome contacts the accessory for translation of force in a point radially opposite to the third fulcrum. 6. Apparatus according to claim 3, characterized in that the attachment for force translation includes a fourth fulcrum located radially opposite to the third fulcrum; and wherein the detection means further includes a strain detecting means for detecting the elastic deformation of the force translation accessory, the deformation detecting means is fixed to a surface of the force translation attachment. Apparatus according to claim 6, characterized in that the means for detecting deformation include a plurality of tension gauges wired in a Wheatstone bridge. 8. Apparatus according to claim 1, characterized in that the ejector assembly includes an ejector sleeve and wherein the detection means are fixed to the ejector sleeve. »9.- Apparatus in accordance with the claim 8, characterized in that the ejector sleeve includes an ejector tube having a portion of reduced diameter for concentrating the tension applied to the ejector sleeve; and wherein the detection means includes a strain detecting means, for detecting the elastic deformation of the ejector tube, the deformation detection means is fixed to a surface of the portion of reduced diameter. 10. Apparatus according to claim 9, characterized in that the means for detecting deformation include a plurality of tension gauges. 11. Apparatus according to claim 8, characterized in that the ejector sleeve includes an ejector tube and a base portion, the base portion includes a plurality of beams extending radially outwardly from the ejector tube and a plurality of lobes radially detached from the ejector tube. ejector tube and extending circumferentially between the beams; and wherein the detection means includes deformation detection means, for detecting the elastic formation of the base portion of the ejector sleeve, the detection means are fixed to a surface of the base portion. 12. Apparatus according to claim 11, characterized in that the base portion includes two lobes and two beams; and wherein the strain detection means includes four voltage meters wired in a Wheatstone bridge, one of the voltage anomers is fixed to a surface of each of the lobes and beams. 13. Apparatus for approximating the pressure of mold cavity during ejection of liquid material, characterized in that it comprises: an accessory for transfer of force interposed between a first component of the ejector assembly and a second component of the ejector assembly; and a means for detecting pressure, for measuring the pressure imparted to the accessory for force translation. 14. Apparatus according to claim 13, characterized in that the force translation attachment is generally ring-shaped and includes a first surface and a second surface; and wherein the first surface includes first and second cores located radially opposite each other, and the second surface a third fulcrum locates radially in half between the first and second fulcrums. 15. Apparatus according to claim 14, characterized in that the means for pressure detection include a pressure transducer interposed between the second surface of the force translation attachment and the ejector assembly, the transducer locates radially opposite to the third fulcrum. 16. Apparatus according to claim 14, characterized in that the second surface includes a fourth fulcrum located radially opposite the third fulcrum and radially halfway between the first and second fulcrums; and wherein the means for pressure sensing include at least one voltage meter mounted on the fixture. 17.- Ejector sleeve for removing an article from a mold cavity and for checking the mold cavity pressure, characterized in that it comprises: an ejector sleeve; and a detection means for the pressure applied to the ejector sleeve, the detection means are mounted on the ejector sleeve. 18.- Apparatus in accordance with the claim 17, characterized in that the ejector sleeve includes an ejector tube having a portion of reduced diameter for concentrating the tension applied to the ejector sleeve and wherein the detection means includes a deformation detection means for detecting the elastic deformation of the ejector tube, the means for detecting deformation are fixed on a surface of the portion of reduced diameter. 19. Apparatus according to claim 18, characterized in that the means for detecting deformation include a plurality of voltage meters. 20. Apparatus in accordance with the claim 17, characterized in that the ejector sleeve includes an ejector tube and a base portion, the base portion includes a plurality of beams extending radially outward from the ejector tube and a plurality of lobes radially detached from the ejector tube and extending circumferentially between the lobes; and wherein the detection means includes means for detecting deformation, to detect the elastic deformation of the base portion of the ejector sleeve, the detection means are fixed to a surface of the base portion. 21. Apparatus according to claim 20, characterized in that the means for detecting deformation includes a plurality of tension gauges. 22. - Apparatus in accordance with the claim 21, characterized in that the base portion includes two lobes and two beams; and wherein the means for strain detection includes four strain gauges wired in a four-arm Wheatstone bridge, one of the tension gauges being fixed to a surface of each of the lobes and beams. 23. Apparatus for injection mold capable of measuring the pressure of mold cavity during injection of liquid material, the apparatus is characterized in that it comprises: an injection mold including ejector assemblies to remove a molded part of the mold; and measuring means within the transducer means for measuring the pressure exerted on the ejector means during injection of liquid material, whereby the measured pressure provides approximation of the mold cavity pressure. 24. Apparatus for injection mold capable of measuring the pressure of mold cavity during injection of liquid material, the apparatus is characterized in that it comprises: an injection mold having a core carrier defining a portion of the mold cavity; and measuring means mounted on the core pin to measure the force exerted on the core pin during injection of a liquid material, whereby the measured pressure provides an approximation of the pressure in the mold cavity.