Abstract:
A temperature and molding material pressure compensated probe for use in injection molding apparatus. The probe includes a two-part telescoping body with a molding material filled space therebetween. Longitudinal thermal expansion which formerly presented sealing problems only results in changes in the extent of telescoping overlap. Molding material pressure is applied equally to both probe parts tending to improve sealing. The molding material filled space has a greater transverse area than all outlets and passages.

Description:
BACKGROUND OF THE INVENTION 
     In the field of injection molding, particularly in multi-cavity molds of as many as 128 cavities, there has risen a problem that is heretofore unrecognized. That is, the molding pressure applied from a manifold is multiplied many times by the areas of the probe, runners, gate, and outlets with many of these areas applying force which tends to separate the probe assembly from the mold. On occasion, the separation force exceeds the capacity of the molding apparatus. 
     Additionally, it has been common practice to design a probe assembly with a large cavity adjacent to the mold gate. When this cavity is filled with molten molding material, the molding material exerts separating pressures which may exceed the holding strength off the molding machine fasteners or locking devices. Even if the molding apparatus is capable of retaining the assembly together, changes in temperature such as cooling after a molding operation can allow molding material to enter a seam line similar to flash in molding and then upon reheating, the material in the seam line acts as a block against precise, tight mold assembly. Repeated temperature cycling inherent in the molding process only aggravates the problem. 
     Also, proper temperature compensation of probe assemblies has been difficult, if not impossible, to achieve using existing probe designs. The only solution has been to design probes with the front face acting as a reference so that the probe is free to expand and contract in a rearward direction away from the mold and toward the molding material manifold. 
     BRIEF DESCRIPTION OF THE INVENTION 
     I have faced this state of the art and this critical problem present in the use of multi-cavity injection molds and have solved each of these problems in my design of a new probe assembly. This invention involves a new probe assembly for use in single or multi-cavity injection molding and is useful wherever the force tending to separate the hot side of the mold from the injector plate can become excessive. The use of this invention is likewise desirable wherever thermal expansion of the probe due to thermal cycling throughout the normal molding operation so that longitudinal expansion of the probe can affect the mold injector plate joint integrity. While these problems are more likely to exist in multi-cavity molding operations, the features of this invention are, however, equally useful in single cavity molding systems, as well. 
     The desirable effects of this invention are achieved by designing the path of the molding material from the manifold to the point of injection to provide for pressure balancing within the probe. 
     Each of the foregoing highly desirable features or characteristics is accomplished in a two-part body probe with the parts overlapping or telescoping in a longitudinal direction with respect to the molding material flow from a supply manifold to the mold hot side. The telescoping parts of the probe body define an annular recess in the molding material passage from the molding material supplying manifold to the mold proper. The annular recess has a cross sectional area in a direction normal to the longitudinal axis of the probe assembly larger than any other of the molding pressure regions between the manifold and the mold proper. 
     One feature of this invention resides in the presence of the cross sectional dimensional relationship to the runners, gates and an internal cavity which acts as an internal reservoir of molding material tending to balance molding forces within the probe. 
     Another feature relates to the overlapping or telescoping form of the probe body whereby thermal expansion occurs within the probe body without change in the overall length of the probe despite dramatic changes of probe temperature. 
     A further feature of the invention is the presence of the internal recess or reservoir between the telescoping parts to accommodate the change in volume of the probe due to thermal expansion without any change in the distance between the reference planes defined by the mold body and the molding material manifold. 
     Another feature of this invention resides in the tapered contact region between the probe body parts which maintain good thermal transfer despite changes in probe body thermal expansion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     This invention may be more clearly understood from the following detailed description and by reference to the drawing, in which: 
     FIG. 1 is a horizontal sectional view along the flow path of a probe assembly in accordance with this invention; 
     FIG. 2 is a plan view of the hot side thereof; 
     FIG. 3 is a plan view of the ejector side thereof; 
     FIG. 4 is an enlarged section through the probe of this invention and associated mold during a mold cycle; 
     FIG. 5 is a diametrical sectional view of the outer probe body; 
     FIG. 6 is a second diametrical sectional view of the outer probe body taken along a plane at 45 degrees with respect to the lane of the section of FIG. 5; 
     FIG. 7 is a diametrical sectional view of the inner probe body of the probe of this invention; 
     FIG. 8 is a front elevational view of the outer probe body of FIGS. 5 and 6; 
     FIG. 9 is diametrical sectional view of the probe locator of this invention; 
     FIG. 10 is a diametrical sectional view of the probe housing of this invention; 
     FIG. 11 is a front elevational view of the housing of FIG. 10; 
     FIG. 12 is a diametrical sectional view of the gate insert of this invention; 
     FIG. 13 is a front elevational view of the gate tip of this invention; 
     FIG. 14 is a diametrical sectional view of the gate tip of FIG. 13 taken along line 14--14 of FIG. 13; 
     FIG. 15 is a diametrical sectional view of the gate tip of FIG. 13 taken along line 15--15 of FIG. 13; 
     FIGS. 16 and 17 are diametrical sectional views of the probe body of FIGS. 5 and 7 shown with different degrees of thermal expansion during molding operation; and 
     FIG. 18 is a simplified graphical representation of the relative sizes of the various molding material filled recesses during molding operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is now made to FIGS. 1 through 4 of the drawing in combination with FIGS. 2 and 3, showing a probe assembly, generally designated 10, restrained between a front plate 11 and a rear plate 12 to provide molding material to a injection mold assembly 13 having a hot side 14 and an ejector side 15. The injection mold assembly 13, typically has a large number of cavities, for example, 128, two of which, 16a and 16b, appear in FIG. 1. The cavities, 16a, 16b, 16c, 16d are arranged in the hot side 14 in groups such as four in number as depicted in FIG. 18, to be fed in the direction of the dashed arrows in FIGS. 1 and 4 with molding material MM from a common manifold, unshown in the drawing, but simulated by manifold assembly 21 via the probe assembly 10, a central passage 32, its internal runners 22, two of which may be seen in FIG. 1 and gates 23, one associated with each mold cavity. 
     The plates 11 and 12 containing the major length of the probe assembly 10 as well as the hot side plate 14 of the injection mold assembly 13 are aligned by guide pins such as pin 50 of FIG. 1. Plates 11 and 12 are secured together and are fixed within the injection molding machine by bolts, unshown. The ejector side 15 separates from the hot side 14 at the part line, P/L, for each mold cycle to allow ejection of the molded parts 24, of FIG. 4, as is well known in the injection molding art. 
     As is indicated above, there may be tremendous separating forces present due to the cross sectional area of mold material MM at or near the zero temperature line, ZTL, between the front plate 11 and hot side plate 14. The separation forces may be as high as fifteen to twenty times the normal or high molding pressure of only 2,000 psi. These separation forces have been known to cause a separation at the zero temperature line ZTL resulting in the destruction of prior design probes as well as the molded parts in process. This problem is solved by my new probe assembly 10 which is accompanied design without any change in the mold or molding machine design. 
     FIG. 2 shows the hot side plate 14 of a typical mold assembly with four mold cavities 16a, 16b, 16c and 16d in a square array to be fed as shown in FIGS. 1 and 4 with molten molding material MM by a single probe assembly 10 through individual internal runners 22. Heater connectors 17 are shown at the top of the mold hot side 14 as well as lift straps 18. Cooling water connections 19, guide pin bushings 49 and several fasteners are also shown. 
     FIG. 3 shows the mating ejector side of the mold assembly 13 with the four cavities 16a, 16b, 16c and 16d, cooling water connections 19, guide pin bushings 49, and guide pins 50 used to insure alignment between the hot side 14 and the ejector side 15 as they come together for a molding cycle. 
     Referring now specifically to FIG. 4 in combination with FIGS. 1 and 6-9, the probe assembly 10 comprises a two-part probe body, the probe outer body 34 and the probe inner body 35 with the inner body 35 telescoping into the outer body 34 at mating surfaces 30 and 31, respectively. Both the probe outer body 34 and probe inner body 35 are fabricated with a common central passage 32 which communicates with the manifold assembly 21 and with the runners 22. The probe body parts 34 and 35 are preferably coaxially mounted withinwith the passage 32 extending along the longitudinal axis of the two body parts 35 and 35. Note that the passage 32 also communicates with a washer shaped recess 33 between the forward end of the inner probe body part 35 and the bottom of the rear recess of the outer probe body 34. The probe body parts 34 and 35 are dimensioned so that the washer like recess 33 is present and filled with molding material MM at all molding temperatures and pressures. 
     The front face 36 of probe assembly 10 is best seen in FIG. 8, but also appearing in FIGS. 1, 4, 5, 6, 16 and 17, is flat and has four orifices 40 for the four runners 22 shown in dotted lines in FIG. 5 and communicating with the central passage 32 for supplying molten molding material MM to four gates 23 and four mold cavities 16a, 16b, 16c and 16d of FIGS. 1-3 in the mold hot side 14. Behind the face 36, as best seen in FIGS. 4-6, is a reduced diameter body length, L, which contains the passage 32 and is surrounded by a band heater 41 of FIGS. 1 and 4 in conventional probe design. The band heater 41 is located in an air space, AS, of FIGS. 1 and 4. The rear or inner end 55 of the probe outer body part 34 is positioned by locator 38 within an opening in the rear plate 12. 
     The locator 38 performs a number of important functions. First, it centers and precisely positions the probe assembly 10 within the opening, AS. Next, the locator 38 provides an annular bearing surface 38B for the probe inner body part 35. Thirdly, the locator 38 provides the mating tapered surface 38CS for the tapered outer end of the outer probe body 34. Upon expansion of the probe outer and inner parts 34 and 35, these tapered surfaces provide compressive forces for sealing the slip fit joint between the mating surfaces 30 and 31 of the probe body parts 34 and 35. This is all accomplished while allowing for thermal expansion of the inner and outer probe body parts 34 and 35 as the probe assembly 10 is heated from ambient outside temperature, e.g., 77 degrees F. (25 degrees C.) to typical molding temperatures of 340 to 540 degrees F. (177 to 288 degrees C.). 
     The front face 36 of the probe assembly 10 is positioned within the front plate 11 by tubular housing member 42 of FIGS. 1, 4, 10 and 11. An annular groove 43 in the front face of the tubular housing member 42 engages an outer lip 36L on the front face 36 of the outer probe body 34 positioning the outlets or orifices 40 adjacent to gate tips 52. The male mold member 46 in the ejector side and its associated molded part ejector 47 may be clearly seen in FIG. 1. 
     Adjacent to the gate tips 52, within the female mold 45 are gate housings 23 of FIG. 4. Just behind the gate housing 23 of each mold cavity 16a-d is a respective gate chamber 51a-d which is filled with molding material MM at all times during molding operations. Two mold cavities 16a and 16b of the four mold cavities 16a-d and two gate chambers 51a and 51b of the four gate chambers 51a-d appear in FIG. 4. Between mold shots, the molding material MM in the gate chambers 51, the outlets 40, the runners 22, the passage 32 and recess 33 will remain molten and with proper temperature control of the heater bands 41 and cooling through passages in the mold, remain at molding temperature without overheating or degradation. The balancing of temperatures is well known in the molding art; however, the probe assembly 10 of this invention facilitates temperature control as is described below. 
     The gate housing 23 is closed by gate tip 52 which is shown in two 90 degree different diametrical sections in FIGS. 14 and 15 with FIG. 15 corresponding to the view in FIG. 4. The gate tips 52 have two ports which allow the flow of molding material MM from the orifice 40 to the mold cavities 16a,b. The gate tips 52 virtually closes off the actual molding orifice 53 between mold shots by absorbing the heat of the small amount of molding material MM at the mold orifice 53 and thereby allowing opening of the mold, removal of the molded part without any dripping of excess molding material MM from the molding orifice 53. 
     TEMPERATURE COMPENSATION 
     For an understanding of the temperature compensation features of this invention, reference is again made to FIGS. 1 and 4 which shows the base or zero temperature line ZTL located at the junction of the front plate 11 and the hot side plate 14 of the mold 13. A rear reference line, RRL is located at the junction of the manifold assembly 21 and the rear face of the probe inner body 35. It is essential that the distance D between the zero temperature line ZTL and the rear reference line, RRL remain constant during all times particularly during heating for the first mold cycle and thereafter throughout the series of molding cycles or shifts as the molding operation continues. In the past, the lack of stability of this dimension, although not recognized by many molders, has been a problem which sometimes resulted in the loss of parts and, more important, by in damage to the probes or the molds. 
     Various fasteners such as internally located machine bolts, unshown in the drawing, hold the front plate 11 and the rear plate 12 together and external clamps hold the front plate 11 and the rear plate 12 with as many as 32 probe assemblies 10 to the manifold 21 so that the distance D remains constant between the zero temperature line ZTL and the rear reference line RRL of the probe assembly 10. 
     Maintaining this standard distance D is possible since the component of the entire assembly which undergoes the greatest temperature changes and cycling is the probe assembly 10. The probe outer body part 34 and the probe inner body part 35 telescope freely with temperature changes while the overall length of the probe assembly 10 does not change and essentially remains constant. A slip fit relationship is present between the cylindrical walls of the interfitting probe outer body part 34 and the probe inner body part 35 while a tapered compression fit seal exists between the probe outer wall 34 CS of the outer body part 34 at its rear end 55 which is depicted at the upper portion of FIG. 4 and the tapered inner wall 38 CS of the locator 38. As indicated above, the mating of these tapered walls 34CS and 38CS of the locator 38 also as shown in FIG. 4 and the outer body part 34 by wedging together as the temperature rises in the probe assembly 10 produces a radial compression force between the telescoping surfaces 30 and 31 of the outer and inner body parts 34 and 35, respectively, to seal the washer shaped recess 33 and to prevent any molding material MM from leaving the recess 33 via that seal. 
     An indication, although somewhat exaggerated for purposes of illustration of the extent of thermal expansion is seen by comparing FIGS. 16 and 17 in which the size of the internal washer shaped reservoir 33 for molding material MM enlarges in thickness in FIG. 17 as compared with FIG. 16. Lengths L1 and L2 will grow with heating; however, distance D remains constant. 
     INTERNAL PRESSURE COMPENSATION 
     The washer shaped reservoir or recess 33 expands and contracts in thickness with temperature changes of the probe assembly 10. The diameter of the washer shaped reservoir or recess 33 remains constant and both faces, forward face 33F and rear face 33R are exposed to the same pressure. The rear face 33R exerts pressure against the inner probe body 35 and that pressure is applied against the manifold assembly 21. The same pressure is applied by the forward face 33F against the probe outer body 34 tending to balance the pressures which are exerted in the gate housings 23 and the cavities 16. This balancing of pressures in the direction of the longitudinal axis of the probe assembly 10 is a major advantage of this invention. 
     The actual diameter of the washer shaped reservoir or recess 33 is defined by the sizes of the various other reservoirs from the manifold assembly 21 to the actual mold gate chamber 51. This relative size relationship is proportionately illustrated by graphically representation in FIG. 18. There it may be seen that the cross sectional area of the reservoir or recess 33 minus the correctional area of combined passage 32 is larger than the combined cross sectional areas of the gate chambers 51a through 51d. The principal separating force within the probe assembly 10 is the force which tends to maintain the probe assembly 10 in its stable condition and does not tend to separate the probe assembly 10 from the mold assembly 13 during normal and even abnormal, excess pressure or temperature conditions. 
     The forgoing constitute my disclosure of the best mode known by me at the time of filing this patent application for carrying out this invention. The embodiment shown is, however, only illustrative and does not limit the scope of the inventive concept. It is recognized that one of skill in the molding art may produce an operative assembly which may have differences without departing from the true concept of this invention. Therefore, this invention is defined, not by the illustrative embodiment but rather by the following claims including the protection afforded by the Doctrine of Equivalents.