CA1245819A - Injection molding apparatus - Google Patents

Abstract

ABSTRACT

INJECTION MOLDING APPARATUS
Apparatus for forming objects from molten material includes a mold frame and a movable mold side having complementary faces that define molding cavities.
The mold frame includes a mold housing having an internally heated manifold which has a plastic distribution channel for feeding plastic to an injection nozzle passageway having a restricted discharge nozzle that discharges the plastic into a molding cavity.
Within the injection nozzle passageway is a heater probe which has an internal heater, preferably an electrical cartridge heater. The probe is secured by an integral seating flange to the mold housing to hold the probe coaxially aligned in the injection nozzle passageway and to hold the probe against shifting with thermal expansion and contraction of the manifold. The integral flange may be positioned at or adjacent the exterior of the mold so that it can be pulled outwardly to remove an elongated body of the probe from the nozzle passageway for easy replacement of the internal cartridge heater disposed within the interior of the probe. The electrical caryridge heater is substantially lower in cost than external electrical band heaters used heretofore for heating plastic flowing internally through a probe.

Description

INJECTION MOLDING APPARATUS
The present invention relates to injection molding apparatus.
A large number of items are molded from molten material, typically thermoplastic of one type or another, in molding apparatus that consists of a movable mold side and a mold frame that have complementary faces which define one or more molding cavities. Molten material is injected into the molding cavities through injection nozzles within the molding frame.
In a typical molding apparatus for simultaneously molding several articles in a plurality of molding cavities, molten material is injected into the cavities by a corresponding number of individual nozzles which are each supplied with molten plastic through a channel network of a manifold distribution block~ The manifold block is disposed wi~hin a housing comprising a plurality of plates, including a front plate having passageways through which the nozzles extend~
The molten plastic is supplied to the manifold channels from a molten plastic source at a high temperature, and to keep the plastic molten and flowing, the molten plastic passageways are maintained at a high temperature by heating the manifold block and also by directly heating the nozzles. The manifold block and the channels therein are heated by resistance heating elements contained within the block itself. In an existing type of molding apparatus, the nozzles that extend from the manifold block through the front portion of the housing to the molding cavities have central hollow passageways in a probe for the flow of molten plastic, and the probe is heated by external band resistance heater that surrounds the probe.
The arrangement of nozzles having internal flow passageways and band heater elements surrounding the hollow probes is expensive to manufacture and to maintain. The band heaters are quite expensive, and have ~2~sæ~

a limited life. The band heaters are loca-ted inwardly of the mold base plate and manifold, thereby requiring a considerable amount of time and work for replacement, and thus, entailing a considerable expense each time they need to be replaced.
To assure adequate transfer of heat from surrounding external heating elements to injection nozzles, the band heater are unprotected, and if molten plastic seeps along the side of the nozzles, the band heater element may be damagedO
Because of their relatively large size, the band heaters do not extend along the entire length of probe particularly in the region of the front tip of the probe which the nozzle feeds the cavity, and as a consequence, the nozzles are made of expensive materials, such as beryllium-copper-hardened steel alloy to assure adequate transfer of heat to the front tip to keep the plastic molten. The probe tips are difficult to machine and suffer wear due to plastic flow. As stated, these band heaters are often disposed in rather inaccessible locations within a mold half and their replacement entails considerable disassembly of the mold frame, adding to the expense of heating element replacement.
It is a primary object of the present invention ~5 to provide a new and improve molding apparatus having internally heated injection nozzles receiving plastic from a heated manifold. Another object of the invention is to provide heating elements which are much more accessible for maintenance, e.g., replacement.
Molding apparatus according to the present invention includes a mold frame and a movable mold side which have complementary faces that together provide a plurality of molding cavities. The mold frame includes a mold base and a carrier plate with a heated molten material distribution block or manifold. The heated distribution block has a channel system which distributes molten plastic to heated injection nozzles for injecting plas~ic into the molding cavities. The injec-tion nozzles include a cylindrical probe that is inser-ted axially into a passageway extending from the base plate through the manifold to the mold cavity injection orifice proportioned to leave an annular channel around the probe through whici molten plastic flows to a constricted orifice leading into the molding cavity.
Because the distribution block is heated while the mold ho~using is not, the distribution block expands and contracts during heating and cooling relative to the mold housing. To accommodate its differential expansion, the distribution block is proportioned and positioned within a recess in the mold half to leave an air gap on all sides. The expansion differential between the distribution block and the surrounding mold plates causes the rear passageway segments through the distribution block to shift relative to a passageway segment through the front portion of the housing. As the front end of the heating probe cooperates with the surrounding front passageway segment to channel the molten material through the orifice, it is important that the heating probe remain centered relative to the front passageway segment. Accordingly, each heating probe is held in position by the rear portion of the housing so that it retains its position relative to the front passageway segment even as the rear manifold distribution block passageway segment shifts laterally slightly during expansion and contraction. In addition to the air gap that is provided along the sides of the manifold block, components, which are secured to the housing and function to position the distribution block in a front to rear direction within the void region and which have lateral edges that face lateral edges of the manifold block, are proportioned so as to leave air gaps between the facing lateral edges to accommodate the relative shifting of the manifold block during expansion and contraction.

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These and other objects and advantages will be more fully described in the following detailed description of the drawings in reference to the accompanying drawings of which:
FIGURE 1 iS a perspective sectional view of a portion of a mold frame, showing a single injection passageway embodying various fea~ures of the present invention;
FIGURE 2 iS a side view of molding apparatus, partially in cross section, including injection passageways, such as those shown in FIGU~E l; and FIGURE 3 is an enlarged end view, partially in section, taken along line 3-3 of FIGURE 2, Illustrated in FIGURE 1 iS a section of a mold half or frame 10 which has a mold face with a cavity or recess 12 to cooperate with another facing recess or projection 14 on a second mold half 16 to define a molding cavity 22 in which objects, e.g., container covers 24 (FIG. 2), are formed by molten plastic injection molding. The mold half 10 has a manifold 38 and a channel system 36 therein that distributes molten plastic to individual injection nozzle passageways 28 that lead to individual molding cavities 22. Heating means 56, 78 in the manifold maintain the plastic material heated in its molten state as it flows through the distribution channels 26 and into the injection noz21e passageway.
The mold half 10 includes (from right to left with respect to FIGURE 1) a front plate 32, a central or carrier plate 34 and a rear or base plate 36. The illustrated manifold 38 is a box-shaped manifold distribution block that is received in a similarly shaped space 40 defined between the carrier and base plates 34, 36.
AS best seen by the heavy arrows in FIGURE 3, the plastic is injected under pressure through an inlet port fitting 130 in the base plate 36 and through its .

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inlet channel 132 into an axially aligned channel segment 131 for ~low upwardly as viewed in FIGURE 3 through an elongated upwardly extending manifold channel 134 which has a discharge outlet 134a to discharge molten plas-tic into an annular nozzle passageway for flow principally to the right as viewed in FIGURE 3 to discharge into the mold cavity 22 through a restricted orifice 50 at the discharge end of the nozzle passageway 28. A cylindrical heating probe 52 heats the plastic.
HeretoEore, the heating probe was formed with a hollow interior through which the plastic flowed and a surrounding band heater heated the exterior of the probe at a location which would be to the right oE manifold block as viewed in FIGURE 3. One problem with band heaters at this location is that they are difficult to access for repair or replacement because i~ is necessary to remove the base plate 36 as well as the manifold 38 and the carrier plate 34 before one could remove or work on the electrical band heater encircling the probe.
2Q Further such band heaters are relatively expensive as contrasted to other types of electrical heaters.
In accordance with the present inventlon there is an easily removable injection heating probe 52 which extends from the mold base 34 through an opening in the manifold 38 and to adjacent the discharge orifice 50 of the mold cavity 22 and which is secured against shifting relative to the manifold which shifts with expansion and contraction because of hot plastic flow therein.
Further, the preferred embodiment of the invention uses an internal electric cartridge heater 56 carried within the hollow interior of the probe 52. The cartridge heater is relatively inexpensive compared to the cost of the typical band heater. As will be explained in greater detail, the preferred probe is a generally cylindrical member having a hollow interior chamber with the electrical resistance cartridge heater therein and which is held in a central axially aligned ' position within the injection passageway to define a generally annular or hollow cylindrical passageway shape through which the heated plastic flows, to the right as viewed in FIGU~E 3, to discharge at the orifice 50 into the mold cavity 220 Also as will be explained in grea-ter detail, the probe 52 has an integral enlarged base 64 which is seated in a seat in a base plate and held so that it will not be moved; and thus, the axially located position for the probe is maintained even though there may be shifting of the manifold relative to the probe because of heating and cooling of the manifold.
In the preferred embodiment of the invention, removal of the base plate 36 allows access to an enlarged end 64 of the probe 52 which then can be pulled through hollow passageway in the mani~old 38, the carrier plate 34 and in the base plate 36. Another probe may be readily installed with little down time because there is no need to remove the manifold or carrier plates as heretofore was the case with the band heaters. In other embodiments of the invention not illustrated herein, in which the molds are stacked with mold layers positioned back to back, the enlarged flanges may be facing internally and not readily removed.
The molten plastic distribution channels 26 are ~5 formed in the manifold block 38, and the individual injection passageways 28 each consist of aligned cylindrical segments, including a rear segment 44 extending entirely through the manifold block 38, and a front segment 46 that extends through the front portion 42 of the housing 30, including openings through annular bushings 48 that are attached to the central plate 34 for spacing the manifold block therefrom. The front and rear pa~sageway segments 44, 46 align to form a straight cylindrical injection passageway 28 that is of uniform diameter except at the front end 29 where the passageway is conical, narrowing to a constricted orifice 50 that opens to the molding cavity 22.

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The passageways 28 are each heated by means of an internal heating probe 52 that is received axially within the passageway 28 and is narrowly proportioned relative to the diameter of the passageway to leave an annular channel 54 through which plastic flows to the orifice 50. The heating probe 52 consists of the cylindrical resistance heating elements 56, e.g., a Calrod heating element, that is protected by an outer metal sheath 5~ which has an axial blind bore 60 o a diameter matched to that of the rod-shaped element for receiving the element in an interference fit. The front end of the sheath 58 beyond the bore 60 covers the front end of the heating element 56 and narrows to a tip 62 that functions with the narrowing diameter front end 29 of the passageway 28 as an injection nozzle 63. The rear of the sheath 58 is radially enlarged to provide an annular flange 64, the front surface 66 of which closes off the rear end of the injection passageway 2~. The sheath blind bore 60 opens to the rear end of the sheath 58 and the electrical leads 68 to the resistance heating element 56 extend from the bore.
In accordance with the present invention, in a molding assembly 20 including the movable mold side 16 and the mold frame 10 that together define at least one molding cavity 22 to which molten plastic flows through an injection passageway 28 in the mold frame, heating of the injection passageway is provided by the internal heating probe 52 that is axially insertable into the passageway and removable therefrom for periodic maintenance. The probe 52 is held in the passageway by the rear base plate 36 of the housing 30 and the rear housing portion is secured to the front portion 42 of the housing in a removable manner, allowing access to the probe and passageway when the rear portion is removed.
The invention facilitates the use of a heating probe 52 that is internally heated rather than using a conventional probe having a central flow passageway and .
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which is surrounded by and heated by an external element. Internally heated probes 52 are much less expensive than the combination of an externally heated probe and an external heating element, the internally heated probe typically being about one-~ifteenth of the cost of the external heating element itself.
Furthermore, as the internally hea-ted probe 52 is directly heated substantially throughout its length~ its outer sheath 58 need not be made of expensive alloys, such as a copper-beryllium-hardened steel alloy, which are often used in externally heated probes to assure adequate heat conduction, e.g., to the tip 62. Whereas external hea~ing elements are frequently disposed at a location within a mold frame from where replacement is time-consumin~ and expensive, the invention provides for very rapid replacement of a worn heating probe 52. The rear plate 36 is held to the front housing portion 42 by threaded members 70, e.g., bolts, and upon removal of the rear plate, the old heating probe 52 may be slid out from the passageway 28 and a new probe slid in.
The space or void region 40 that receives the manifold block 38 is defined between the ~ront surface 72 of the rear plate and a large rectangular hollow 74 formed in the central plate 34 extending internally from ~5 its rear surface 76. The manifold block 38 is heated to high temperatures during molding by resistance heating elements 78, such as a Calrod heating element, and expands when heated. The housing plates 32, 34, and 36 themselves are not directly heated by heating elements, and accordingly, there is slight but significant expansion and contraction of the manifold block 38 relative to the plates. To accommodate outward expansion of the manifold block 38 relative to the housing 30, the manifold block 38 is proportioned slightly smaller than the void region 40, leaving an air gap 82 along all sides of the manifold block. Relative shifting movement of the manifold block 38 is represented in FIGURE 1 by the arrow .
, 79 that shows the direction of movement of the illustrated upper lateral edge 80 of the manifold block relati~e to the adjacent lateral edge surface 83 of the central plate 34.
It can easily be appreciated that the relative shifting of the manifold block 38 and its passageway segment 44 creates problems in providing a straight passageway 28 that includes both the rear manifold block segment 44 and the front housing segment 46. In order that the probe 52 cooperate with the passageway 28 to best direct flow through the orifice 50~ the probe tip 62 should remain centered relative to the injection orifice 50, that is, the probe 52 should remain axially centered relative to the front passageway segment 46. If the internally heated probe 52 used in the present invention were to shift along with the manifold block, it would become misaligned with front passageway segment 46.
In accordance with an important aspect of the present invention, the molding assembly 20 includes the movable mold side 16 and the mold frame 10 that together define molding cavities 22. The mold frame 10 includes the housing 30 that defines the internal region 40 and the manifold block 38 that is positioned within this internal region. The manifold block 38 has the channel system means 26 for distributing molten plastic to injection passageway means 28 that each include a manifold passageway segment 44 and a housing passageway segment 46 which leads to the molding cavity 22. Heating means 78 heat the manifold block to a temperature whereat molding material remains molten within the channel means, and spacing means 82 provide for shifting of the manifold block 38 relative to the housing 30 during thermal expansion and contraction. To keep the molding material molten as it passes through the injection passageways 28, the internal heating probes 52 extend through the passageways leaving surrounding channels 54 through which molten material flows. In order to assure that the .. .

heating probe 52 in each passageway 2~ remains centered relative to the front housing passageway segment 46 even as the rear manifold block passageway segment 44 shifts during thermal expansion and contraction of the manifold 5 block 38, the probe 52 is affixed to the housing 30, e.g., to its rear portion 36, so that its axial position with respect to the front passageway portion 46 is unaffected by the shifting manifold block.
As a means of positioning the probe relative to the housing, the illustrated embodiment has a cylindrical recess 86 in the front surface 72 of the rear plate 36 which is matched in diameter to the rear flange 64 of the probe sheath 58. The rear sheath flange 64 is received in this recess 86 in a tight fit, restraining the probe in axial alignment through the front passageway segment 46.
The manifold block 38 has a body 88 that is closely positioned in a front-to-rear direction between the front faces 66 of the rear flanges 64 of the probe sheath 58 and the rear faces 67 of the bushings 48, the bushings being attached to the housing 30, tightly received in closely matched cylindrical indentations 92 in the internal vertical wall 84 of the central plate hollow 74. So that the flanges 64 and bushings 48 do not interfere with the lateral expansion of the manifold block 38, air gaps 94, are provided between the lateral edges 98 of the sheath flanges 64 and facing lateral edges 100 of the maniold block, and air gaps 96 are also provided between the lateral edges 102 of the bushings 48 and the facing lateral edges 104 of the manifold block.
In the illustrated embodiment, front and rear covers 106, 108 overlie the manifold block body 88, and in the regions of the bushings 48 and the rear flanges 6~ of the probe sheath 58, the front cover and rear cover have circular openings 110, 112 throuyh which the bushings and ~langes extend, and the greater diameters of the openings ': ~

relative to the encircled bushings and flanges provide the air gaps 96, 94.
During expansion of the manifold block 38, the rear manifold segment 44 of the passageway 28 rearranges relative to the housing passageway segment ~6.
Preferably, the manifold block 38 is machined so that its passageway segments 44 axially align with the front housing passageway segments 46 during those times when the manifold block is heated to the injection molding temperature. Although the rearrangement of the manifold block relative to the housing 30 and probe 52 is significant, it is nevertheless slight, and the manifold block 38 never makes contact with the probe 52. Any slight misalignment of the rear passageway segments 44 with the front passageway segments 46 during injection molding is considered inconsequential. For example, in a typical embodiment, the passageway diameter is 7/8 inch, and the probe diameter is 5/8 inch leaving a 1/4 inch annular region. Thus while the rear passageway segments 44 readjust relative to the front passageway segments 46 and to the probes 52 that are held in a fixed position relative to the housing 30, the manifold block 38 does not impinge on the probes themselves during expansion and contraction.
~5 In addition to lateral expansion of the manifold block 38, there is some front to rear expansion;
however, because the front to rear dimension of the block is significantly less than its lateral dimensions, expansion in this direction is less. The thickness of the manifold block body 88 is proportioned to take account of its expansion during heating so that when heated in anticipation of molding, its front and rear surfaces press tightly against the opposed faces 67, 66 of the bushings 48 and rear sheath flanges 64, preventing plastic from seeping from the passageway 28, while when cooled, slight gaps exists between the manifold block body and the bushings 48 and rear sheath flanges 64. The ' ., , . : ~: . :, , f~ 5~

front and rear manifold block covers 106, 108 are relatively thin and are spaced by the bushings ~8 and rear sheath flanges 64 from the vertical internal wall 8 of the central plate 3~ and the front surface 72 of the rear plate 36, respectively. While the rear passageway segment 44 extends entirely through the manifold block body 88 the channel system 26 leading to the passagewaY
28 run centrally (in a front to rear direction) through the manifold block intersecting the rear passageway segment 44 at about its midpoint. Thus, about half of each rear passageway segment 44 extends rearward of the intersection with the channel system 26.
In the illustrated embodiment, the length of the heating element 56 is such that the passageway 28 is directly heated by the element from the channel system 26 intersection forward only, and there is a tendency for the passageway region 117 rearward of the channel to become cooler and for plastic to solidy therein. To alleviate this problem, the sheath 58 in front of the flange 64 has a tapered segment 121, narrowing at a very slight angle, e.g., about 5, from the rear flange 6~
forward to closely adjacent the rear end of the heating element 56, thereby constricting the channel region 117 from the channel intersection rearward. If plastic begins to solidify as a plug in this contricted channel region 117, the natural expansion of the plastic upon solidifying creates a pressure that causes the plug of solidified plastic to slide forward from the constricted along the tapered segment 121 to a less contricted hotter region of the passageway where the plastic remelts.
Illustrated in FIGURE 2 in somewhat greater detail is the molding assembly 20 including the mold frame 10 in which a plurality of injection passageways 28 are fed through the channel network 26 within the manifold block 38 and the movable mold side 16. A pair of injection passageways 28 of the type described with reference to FIGURE 1 are illustrated in FIGURE 2 and an additional pair of passageways lie directly behind these passageways spaced longitudinally from the illustrated pair. ~lolten plastic is fed to the passageways from an external source (not shown) that is connected to a molten plastic inlet port fitting 130. From a channel 132 through the inlet port fitting 130, molten plastic flows to the channel system 26 in the manifold block 38 that includes an elongated channel 134 extending in opposite directions from adjacent to the inlet port 132 and the perpendicular branch channels 120 leading from the ends of the elongated channel into the block 38 injection passageways 28.
The inlet port fitting 130, seen in greater detail in FIGURE 3, extends through an opening 129 (FIG.
3) in the rear plate 36 and interits at its front end with the manifold block 38 to communicate its inlet channel 132 with a short channel segment 131 that extends to the elongated channel 134. The inlet port 130 is laterally restrained relative to the rear plate 36 by a collar 133 that is received in a close fit within central indentation 135 (FIG. 3) in the rear surface 137 of the rear plate 36. The inlet port 130 is attached with a bolt 141 (FIG. 3) to the manifold block 38 and, along with an opposed bushing 139 that is attached to the central plate 34, centers the manifold block 38 laterally within the void region 40. Thus during thermal expansion, the manifold block 38 expands laterally outward from its center with its four rear passageway segments 44 adjusting substantially similarly relative to each of the four front passageway segments 46 and inserted pr~bes 52.
As the means of maintaining the maniold block 38 at a temperature that assures that the plastic remains molten as it flows through the channel system 26, a network of grooves 137 (FIG 1) are formed in the front and rear faces 138, 140 of the manifold block body 38 wherein the resistance heating elements 78 are received.

The grooves 137 and resistance heating elements 78 run generally along the elongated channel 134, curving at the ends of the manifold blocks around the pairs of injection passageways 28. The front and rear manifold covers 106, 108 are attached with bolts (not shown) to the front and rear faces 138, 140 of the body 88, enclosing the heating elements 78 within the grooves 137.
The front plate 32 o the housing 30 is attached with bolts 142 (FIG 2) to the central plate 34 in the manner that the rear plate 36 is attached with bolts 37 to the central plate. The rear plate 36 has bores 144 (FIG. ~) aligned axially with the sheath-flange retaining indentations through which the electrical leads 68 to the heating elements 56 extend and also a network of grooves 146 formed in its rear surface 137 through which the leads 68 extend to an electrical power source (not shown).
The bushings 48 which help to position the manifold block 38 within the void region 40 are each secured with bolts 148 (FIG 2) within their mating cylindrical indentations 92. The rear sheath flanges 64, however, merely seat within their indentations 86 without bolting, being prevented by the manifold block 38 from dislocating from these indentations.
The movable side 16 of the mold assembly 10 will not be described in great detail herein, as it is of conventional design. Briefly, the movable side 16 has plates that define a face 160 which is complementary to the front 161 face of the mold frame 10, defining the molding cavities 22 when the complementary faces are pressed against each other. In the illustrated assembly 20, objects 24 are formed between indentations 12 in the mold frame 10 and the projections 14 of a main front plate 154 of the movable side 16. Lips 156 of the objects 24, however, are molded along edges of an ejector plate 158 that has inner surfaces 163 complementary to surfaces 162 of the main plate 154, e.g., frustoconical ~2~

in the illustrated embodiment, for mating with the main plate 154 and cooperating therewith to provide a uniform face 160 to the mold frame 10 during molding. However, the ejector plate 158 is movable relative to the main plate 154 when the movable side 16 of the mold is spread apart from the mold frame 10 after objects 24 have been molded in the cavities 22. During spreading of the movable side 16 from the mold frame 10, the newly formed objects 24 are pulled by the projections 14 from the indentations 12, and after removal of the objects from the indentations, the ejector plate 158 is spread from the main plate 15~, resulting in the ejector plate pushing against the lips 156 of the newly formed objects 24 and removing them from the projections. The ejected objects then fall vertically in~o a collection bin (not shown).
The movable side 16 is brought into contact with and spread apart from the mold frame 10 in a conventional manner, e.g., with pneumatic rams 17Q
(represented by a rod in FIG. 2). As a means for aligning the movable side 16 with the mold frame 10 during movable side travel, elongated leader pins 172 extend from the front of the mold frame into mating passageways 174 of the movable side. In the illustrated embodiment, the leader pins 172 are held by the front plate 32 of the mold frame with the leader pins extending through bores 176 through the front plate and enlarged heads 178 of the leader pins locked into countersunk bore portions 180 by the central plate 34.
Several advantages of the invention may now be more fully appreciated. The injection nozzles, consisting of passageway segments formed in the mold frame housing and manifold block and inexpensive internal heating probes, are much less expensive than nozzles formed of expensive heat-conducting alloys and encircled by very expensive cylindrical heating elements. In some embodiments, replacement of the inexpensive internal ~2~

heating element is very simple, merely requiring that the rear plate be unbolted from the front portion of the housing and the spent probe slid from the passageway and a new heating element inserted into the probe which is then returned by sliding it into the passageway. The internal heating probe is held by the housing axially centered within the front passageway segment and with respect to the injection orifice while the manifold and its passageway segment are permitted to shift laterally relative to the probe and housing passageway segment during thermal expansion and contraction.
While the invention has been described with reference to a preferred embodiment, modifications obvious to one with ordinary skill in the art may be made without departing from the scope oE the invention.
Various features of the invention are recited in the following claims.

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Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a heated plastic injection mold assembly for producing a heated flow of plastic into a mold cavity comprising: a mold housing comprising a plurality of plates including a heated manifold plate having a manifold channel therein for distributing hot plastic; a plastic injection passageway in said housing for receiving heated plastic from the manifold channel and having a discharge orifice located to discharge plastic into the mold cavity; a heater probe having an internal heater means inside of an elongated probe body, which is located within the injection passageway and which extends to adjacent the discharge orifice, for heating the plastic flowing about the elongated probe body and through the passageway; and means for securing the heater probe stationary relative to shifting movement of surfaces on the manifold plate.

2. A heated plastic injection mold assembly according to Claim 1 in which the securing means comprises: integral flange portion on the probe; and a seat in the mold housing with the flange portion on the probe abutted against the seat and held thereby against shifting.

3. A heated plastic injection mold assembly in accordance with Claim 1 in which the probe body comprises an outer cylindrical wall having a hollow interior chamber and an electrical cartridge heater inserted into the hollow interior chamber to heat the cylindrical wall, the plastic flowing about an external surface of the cylindrical wall of the probe.

4. A heated plastic injection mold assembly in accordance with Claim 2 in which the integral flange portion is secured to the mold housing and facing outwardly toward the exterior of the mold to facilitate removal of the probe body from the injection passageway and removal of the probe for replacement of the internal heater means.

5. A heated plastic injection mold assembly in accordance with Claim 3 in which the plastic injection passageway extends outwardly from the mold and the passage in the manifold, and a tapered surface faces on the passageway at a location rearwardly of the intersection of the manifold to push forwardly any plastic solidifying against the tapered surface.

6. In a heated plastic mold assembly having at least four mold assemblies; a base plate and a carrier plate having passageways therein for plastic flow; an injection inlet for receiving heated plastic; a manifold receiving plastic from the injection inlet and having internal channels for deliverying plastic to the separate passageway for each mold cavity; a probe projecting axially in each of said passageways and having an internal electrical cartridge heater within the probe to heat the plastic flowing thereabout; and, a cylindrical outer wall on the heated probe and defining with said plates and manifold an annular shape for each of the plastic flow passages from the manifold through which plastic may flow while being heated.

7. An injection molding assembly comprising a movable mold side having a first face, a mold frame having a second face which is complementary with said first face to define at least one substantially enclosed molding cavity, and means for alternately moving said movable mold side against said mold frame to define said cavity and away from said mold frame to release an object molded within said cavity, said mold frame including a straight injection passageway having a front opening communicating with said cavity and a rear end opening, a manifold means having a channel means for distributing molten molding material to said passageway, a straight heating probe axially inserted within said passageway and proportioned to leave a surrounding channel within said passageway, said heating probe being removable from said passageway through said rear opening, means for closing said rear opening with said probe inserted in said passageway, and means for holding said probe within said passageway and to close said rear opening and to hold said probe against shifting with thermal expansion and contraction of the manifold means.

8. An injection molding assembly comprising a movable mold side having a first face, a mold frame having a second face that is complementary with said first face to define at least one substantially enclosed molding cavity, and means for alternately moving said movable mold side against said mold frame to define said cavity and away from said mold frame to relase an object molded within said cavity, said mold frame comprising a front housing portion having said second face on its front side, a rear housing portion and means to removably attach the same to said front housing portion, said front and rear housing portions defining an interior void region, a molten material distribution block disposed within said void region having channel means for distributing molten material, an injection passageway including a rear segment extending through said distribution block and communicating with said channel means and having an open rear end and an aligned front segment extending through said front housing portion and opening to said second face, a straight heating probe axially inserted within said passageway proportioned to leave a surrounding channel through said passageway, said heating probe being removable from said rear end of said passageway when said rear housing portion is removed from said front housing portion, and means to close off the rear end of the said passageway when said probe is inserted within said passageway.

9, An assembly according to Claim 8 wherein said closing off means is an enlarged rear segment of said inserted probe.

10. An assembly according to Claim 8 wherein said probe comprises a central heating element enclosed in an outer heat-conducting sheath.

11. An assembly according to Claim 8 wherein said rear housing portion has means restraining said probe in alignment within said front passageway segment and wherein said block is proportioned for lateral expansion within said void region relative to said housing portions and said aligned probe.

12. An injection molding assembly comprising a movable mold side having a first face, a mold frame having a second face which is complementary with said first face to define at least one substantially enclosed molding cavity, and means for alternately moving said movable mold side against said mold frame to define said cavity and away from said mold frame to release an object molded in said cavity, said mold frame comprising a front housing portion having said second face on its front side, a rear housing portion and means to removably attach the same to said front housing portion, said front and rear housing portions defining an interior void region, a molten material distribution block disposed within said void region having channel means for distributing molten material and having means for heating said block, an injection passageway including a rear segment extending through said distribution block and communicating with said channel means and having an open rear end and an aligned front segment extending through said front housing portion and opening to said second face, spacer means for positioning said block within said cavity so as to leave an air gap around said block to provide for thermal expansion of said block within said void region, a heating probe axially inserted within said injection passageway and proportioned to leave a surrounding channel within said passageway, means for closing off the rear end of said passageway with said probe inserted therein, and means associated with said rear housing portion for holding said probe in alignment with said front passageway segment even as said rear passageway portion adjusts laterally relative to said probe as said block thermally expands and contracts relative to said housing.

13. An assembly according to Claim 12 wherein said heating probe is removable from said rear end of said passageway when said rear housing portion is removed from said front housing portion.

14. An assembly according to Claim 12 wherein said closing off means is an enlarged rear segment of said inserted probe.

15. An assembly according to Claim 14 wherein said enlarged rear probe segment spaces said block from said rear housing portion.

16. An assembly according to Claim 15 wherein said holding means comprises an indentation in said rear housing portion that receives said rear probe segment in a close fit.

17. An assembly according to Claim 16 wherein said channel means communicates with said rear passageway portion at a central location and a segment of said probe between said channel means and said enlarged rear probe segment is tapered to constrict said passageway rearward of said channel means, whereby if molten material solidifies and expands in the passageway constriction, the solidified material forces its way forward along said tapered segment into hotter regions of said passageway.

18. An assembly according to Claim 12 wherein said spacing means associated with said housing portions extend into openings in said distribution block and wherein said openings in said distribution block and said spacing means are relatively proportioned to provide gaps along the lateral edges of said spacing means for accommodating relative lateral shifting of said distribution block during expansion and contraction.