CA1044416A - Collapsible core - Google Patents

Abstract

COLLAPSIBLE CORE

ABSTRACT
Collapsible core assembly having retractable portion capable of producing plastic parts having an undercut. The core assembly comprises a segmented portion operably connected to an innercore pulling assembly wherein operation of the innercore pulling assembly first retracts the segmented core and thereafter pulls the complete core assembly out of the molded part.

Description

~0~ 6 This invention relates to plastic molding apparatus whereby a part can be made with an undercut or threaded section. Similar tooling has been developed but this invention is believed to provide apparatus with more positive use and which requires reduced maintenance.
An example of the prior art is Fields et al. 3,247,548 (1968) wherein resilient mounted molding members are used.
Another prior art device provides a collapsible core by provid-; ing helically grooved operating members capable of expanding 10 a core element by rotary movement of an innercore member. Suchrotary action results in excessive stress in s hear on the actuating members. '-SUMM~RY OF THE INVENTION
:
I have provided a collapsible core assembly capable of providing a 360 undercut in a molded plastic part. The ~'! system operates by simple axial movement of the core, the ;
I first action being retraction of circular segments in timed relationship follDwed by retraction of the core from the molded plastic part. This will provide apparatus by which an internal `~ 20 thread can be formed in a part followed by mold removal by simple axial movement rather than more complicated rotational movement. In another system the collapsible core assembly can be used to provide a plastic part with a 360 recess for ' the insertion of a preformed gasket. Such parts are used in the joining of pipe.
In its broadest aspects the present invention provides a collapsible core assembly capable of formlng in a hollow plastic part having at least one open end an internal surface ~ containing a 360 recess, said assembly comprising: -;, 30 . .
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(1) a single bi-directional inner core pulling assembly movable axially,

(2) an ~uter mold means for forming said internal surface comprising:
(a) a first mold means having a first position and a second position, wherein said first mold means when in said first position extends a greater radial distance than said first mold means when in said second position, said first mold means ~.
comprising a plurality of first and second mold segments, and (b) a plurality of grooves being equal in number to and for use with each one of said first and second mold segments and sloping radially inward toward the forward end of said collapsible core assembly, wherein said plurality of grooves are located in one of said first mold means and said inner core pulling assembly, and

(3) a means for coupling said inner core pulling assembly . ~ -and said first mold means such that axial movement of said inner . .
~ core pulling assembly causes a radial and coplanar movement of .
.~ said first mold means between said first and said second 20 positions, wherein there is a substantial time delay after an :~
initial movement from said first position toward said second :
position by said first mold segments when said second mold -::
segments begin to move from said first position toward said -. second position, said means for coupling comprising a plurality :
of projections fixedly attached to the other one of said first :
mola means and said inner core pulling assembly, and arranged ~` to be slidably contained one in each of said plurality of grooves, wherein the size of grooves, utilized by said means for coupling ~
8~1d first mold segments to said inner core pulling assembly, -- .
30 to the size of said plurality of projections slidably contained 1 . ~

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therein causes a closely coupled response upon rearward axial movement of said inner core pullin~ assembly, and the size of grooves, utiiized by said means for coupling said second mold segments to said inner core pulling ~ssembly, to said plurality ` of projections slidably contained therein causes said delay in- response upon rearward axial movement of said inner core pulling assembly.
In another aspect the present invention provides a collapsible core assembly capable of forming a 360 recess on ; 10 the inside diameter of a plastic part having a central portion and a base portion on first and second sides of said recess comprising:
` (1) an outer assembly adapted to form the inside surface .
of a said plastic part comprising from front to back in the .' longitudinal direction: .
~a) a forward end cap so shaped as to form the central .
portion of said plastic part provided with an axial counterbase, (b) a rearward base so shaped as to form the outer end of ~.
said plastic part, . 20 (c) a plurality of radially and coplanarly retractable moldsegments positioned between said cap and base which in the mold-ing position provide a mold diametèr of greater diameter than adjacent surfaces of said cap and base of said mold sections, the inner ends of said mold segments sloping inwardly toward ~ -the center line of the assembly from the base to the cap, said ~ -.
, mold segments having a T-shaped keyway on the inner end thereof, - said plurality of coplanar mold segments comprising:
. i. three small segments equidistantly placed around `
the circumference of said plurality, and :-~
. 30 ii. three large segments positioned between said small segments, and ~ - 3 -"
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10444~6 (2) a single bidirectional inner core pulling assembly movable axially of said core assembly comprising:
(a) a central core element ada~ted to travel within and extend rearwardly beyond said counterbase in said cap, (b) a travel stop on the forward end of said central core . element adapted to move within said counterbase between the forward end of the counterbase and the rearward end thereof, (c) six actuator means fixedly attached to the forward end of said inner core element, sloping radially inwardly toward the center line of the assembly from the rear to the forward ends thereof, each of said actuator means having a T-shaped projection on the radially outer surface thereof adapted to inneract with the T-shaped keyway on the retractable mold segments, said T-shaped keyways in said segments being of two dimensions wherein said actuator means comprises: .
. i. first actuator means associated to inneract with said small segments to have the relationship between the projection therein and the keyways on the mold segments such -- .
that contact therebetween occurs substantially immediately upon .~` 20 rearward movement of said inner core pulling assembly, and .: ... .
ii. second actuator means associated to inneract ~. with said large segments to have the relationship between the . projections therein and the keyways on the mold segments such ~ .
that contact therebetween occurs a substantial time after ~ .
contact has been made between said first actuators and said .
small mold segments upon rearward movement of said inner core .. :
pulling assembly. ~-:
. BRIEF DESCRIPTION OF THE DRAWING
In the Drawing :
Figure 1 is a perspective view of a coupling which can be produced using the collapsible core assem~ly of my invention.

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~)44416 Figure 2 is an enlarged sectional view on line 2-2 of Figure l.
Figure 3 is a top view of the molding system of my invention with the upper mold removed and the right hand collapsible core assembly shown in section.
Figure 4 is a section taken on line 4-4 of Figure 3.
Figure 5 is a section taken on line 5-5 of Figure 3 showing principally the end of the left hand collapsible core assembly.
Figure 6, a section view taken on line 6-6 of Figure 7 shows the collapsible core segments and the operating means therefor.
i Figure 7, is a view taken on line 7-7 of Figure 6 -i showing the collapsible core assembly in the molding position with the retractable segments extended.
Figure 8 corresponds to Figure 7 but shows the collapsible core assembly with the retractable segments in the retracted position.
Figures 9 and l0 show, in plan, the ends of each type of actuators. Figures 9 and l0 are views taken on lines 9-9 and l0-l0 of Figure 7.
DESC~IPTION OF THE INVENTION
-Broadly, my invention comprises in certain aspects ~ -a collapsible core assembly capable of forming a plastic part having at least one open end and an internal surface wherein ~ projections extending completely around said inner surface are - ~--~ of a diameter larger than a second portion of said internal surface nearer the open end comprising: -(1) an outer assembly adapted to form the internal surface of said plastic part comprising:
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1~)44416 (a) first mold means 48 having suitable dimension to form the open end, and (b) second mold means 42-47 having in a first position projecting parts to form said second portion of said internal surface and in a second position an outer circumference less than the second portion of said inner surface, and (2) an inner core pulling assembly having only a single rod movable axially of said outer assembly, and (a) means in said pulling assembly to move said second mold means from said first position to said second position.
~:, In a further aspect, my invention comprises a '~ collapsible core assembly capable of forming a plastic part having a first part having a first inner perimeter, a second part having a second inner perimeter and, between said first and ~ second parts, a third part having a third inner perimeter, said 3 third perimeter being larger than at least said second perimeter, .
.^~ said core assembly comprising~
;~ 20 (1) an outer assembly adapted to form the inside surface of said plastic part comprising from front to back in the -longitudinal direction; ^--. .:
~ (a) first mold means 48 having said first inner perimeter, 1 (b) second mold means 49 having said second inner perimeter, , and :

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444~6 (c) third mold means 42-47 having in a first posi-tion said third inner perimeter and in a -second position a perimeter less than said second perimeter said third mold means being positioned between said first 48 and second 49 mold means said third mold means having a plu-rality of coplanar retractable segments 42-47, and (2) an inner core pulling assembly having only a single ~ 10 rod movable axially of said outer assembly, and .~ (a) means in said pulling assembly to retract positively said third mold means to said perimeter less than second perimeter.
In a still further aspect, the invention comprises a - ;~ collapsible core assembly capable of forming a 360 recess on .--~ the inside diameter of a plastic part having a central portion :

`j and a base portion on first and second sides of said recess :
-:3 ::~ comprising~
:.. ~ - .
. j (1) an outer assembly adapted to form the inside surface of said plastic part comprising from front to back in ~$3 the longitudinal direction; ` :

;~ (a) a forward end cap 48 so shaped as to form the .

:j central portion of said plastic part provided :~-~ l . with an axial counterbase, (b) a rearward base 49 so shaped as to form the -~' j outer end of said plastic part, i (c) a plurality of radially and coplanarly re-~, tractable mold segments 42-47 positioned between ~. -.~ said cap 48 and base 49 which in the molding :~
.~ 30 position provide a mold diameter of greater diameter than adjacent surfaces of said cap 48 ; and base 49 of said mold sections the inner .. - , ~ ' '

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10~16 ends of said mold segments sloping inwardly - toward the center line of the assembly from the base to the cap, said mold segments having a T-shaped keyway 69 & 71 on the inner end thereof, said plurality of coplanar mold seg-ments comprising;
. (i) three small segments 42, 43 and 44 equi-distantly placed around the circumference of said plurality, and ;`
(ii~ three large segments 45, 56 and 47 posi-tioned between said small segments, and (2) an inner core pulling assembly having only a single :
. .~
` rod movable axially of said core assembly comprising; ;
(a) a central core element 61 adapted to travel ~ within and extend rearwardly beyond said counter-: base in said cap, (b) a travel stop 63 on the forward end of said ; .
:~ central core element 61 adapted to move within said counterbase 48 between the forward of the j 20 counterbase and the rearward end thereof, (c) an outer core element fixedly attached to said central core element, . :.
(d) six actuators 64 and 66 fixedly attached to -.J the forward end of said inner core element, sloping radially inwardly toward the center .~ -line of the assembly from the rear to the - ~ .
forward ends thereof, each of said actuators having a T-shaped projection 67 and 68 on the ::.
radially outer surface thereof adapted to .
, 30 inneract with the T-shaped keyway on the re- ~
-~ tractable mold segments, said T-shaped keyways . .-s 69 and 71 in said segments being of two .. ~: -.. '~ , ', ', '~' '.

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lV4~416 dimensions wherein;
(i) first actuators 64 associated to inneract with said small segments 42, 43 and 44 have -the relationship between the projection 68 therein and the keyways 71 on the mold ; segments such that contact therebetween occurs substantially immediately upon rear-ward movement of said inner core pulling assembly and (ii) actuators 66 associated to inneract with said large segments 45, 46 and 47 have the relationship between the projections 67 -therein and the keyways 69 on the mold seg- , ments such that contact therebetween occurs a substantial time after contact has been ~ made between first actuators 64 and small `~ mold segments 42, 43 and 44 upon rearward ~ movement of said inner core pulling assembly.
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$ ~ To fully understand my invention, attention is now directed to the drawing. Figure 1 shows a perspective view of ~ -a plastic coupling 15 which can be made using the collapsible ~
., ~ . .
core assembly of my invention. This coupling contains a plu-rality of ribs 16 which are made by conventional molding tech-niques. The novel feature of this part resides in the 360 recesses 17 and 18. When these recesses are provided with ; ~-~- flexible gaskets, the coupling can be used to join lengths of v pipe. Obviously, such a part could not be made by using a solid core because the portion of the core forming the recesses -could not be removed. More specifically, outer ledges 19 and 21, being of smaller diameter than recesses 17 and 18, would prevent removal of the core. As wi~ be apparent from the des-cription which follows, two collapsible core assemblies are .

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~0444~6 used in forming coupling 15, one extending into one end of the coupling, and the other extending into the other end.
Figure 3 shows the mold with the cover (not shown) removed and identical left hand collapsible core element 24, shown in full, and right hand collapsible core element 26 shown in section. Both core elements are in position for the pro-duction of the coupling by injection of molten plastic, i.e., ~-with the collapsible mold segments in the extended position.
The part shown will be more fully understood upon reference to Figures 6~8 to be subsequently described.
The operation of both collapsible core assemblies is identical and is symmetrical on both sides of the parting line between core assemblies 24 and 26. For this reason, Figure 3 illustrates only the operating mechanism for right hand core element 26. Collapsible core assembly 26 is mounted upon rod "f 27 which is connected to conventional hydraulic cylinder 28 for j movement in a reciprocating manner. When so moving, the core ~. section rides upon slides 29 and 31. Slides 29 and 31 are `' mounted respectively, on supports 32 and 33 which, in turn, are fastened to base plate 34 of the molding machine. -Figure 5, shows a plan view on line 5-5 of Figure 3 showing the molding apparatus of this invention and in parti- --cular the end view of collapsible core 24. Except for this collapsible core, the features shown are conventional and ` include the lower outer mold form 36 and the upper mold 37.
Plastic supply conduit 38 is connected to gate 39 through -which the plastic is injected into the mold. Conventional ;
ejector pins 40 and 41 are provided to eject the part from the mold upon upward movement of mold section 37.
- 30 The above description sets orth the major components used to produce the part with the 360 recess and attention --i~ now directed to Figures 6, 7 and 8 which most clearly :.

. . .

1~4416 illustrate the novel features of my invention. Figures 6 and 7 show the collapsible core assembly with a plurality of retractable mold segments in the extended or molding position.
The mold segments comprise small segments 42, 43 and 44 and large segments 45, 46 and 47. These retractable mold segments are positioned between a forward end cap 48 and a rearward base 49. In the particular design shown, this rearward base is so designed to provide a generally funnel shaped entrance into the part with a first sloping section 51, a second sloping ; 10 section 52, and a third section generally parallel to the axis of the part 53. I have identified the junctions between por-- tions 51, 52 and 53 as junctions 54 and 56.
All of retractable segments have a small undercut on the outer end thereof. This surface is indicated as 57 on large segment 45 and as 58 on small segment 44. Cap 48 and base 49 act as guides and retainers for the segments.
Central core element 61 is provided with a counterbore 62 in which moves travel stop 63. Bolted to central core element 61 are actuators 64 and 66, each of said actuators being provided with a T-shaped projection 67 and 68. This :
: projection rides in a keyway on the segment, the keyway 69 being provided in movable segment 45 and keyway 71 being provided in small segment 44.
In operation, the hydraulic cylinder, after the cooling cycle, starts to move center core element 61 from the posi-tion shown in Figure 7 toward that shown in Figure 8. Since T-shaped projection 68 and actuator 64 fits snugly in keyway 71, ~f small segment 44 starts to retract as soon as central core element 61 begins to move to the right. A short time after this movement has begun, the keyway 69 on actuator 66 contacts the T-shaped projection on said actuator and large segment 45 begins to retract.

l'~44416 In one specific model of this apparatus, the keyway - and projection associated with the small segments was 0.375 inch while the space to the projection on the actuator asso-ciated with the large segments was 0.687 inch. Thus, the large segments do not start to move for the 5/16" difference between these figures. When the travel stop 63 contacts the end of counterbore 62, the retractable segments are in the fully retracted position shown in Figure 8. While I have described the retraction by the inneraction of the T-shaped projection ` 10 on actuator 64 for the small segment 44, it will be obvious that a similar action retracts small segments 42 and 43.
`, Likewise, the operation of large segment 45 is duplicated by large segments 46 and 47.
When the apparatus has reached the position shown in Figure 8, continued movement of central core element 61 to the right withdraws the complete core assembly from the part, j cap 48 base 49 and the retracted segments moving as a unit.
i The operation in assembling the mold elements is just i opposite to that described above. The core assembly is moved into position by the hydraulic cylinder 28, first being as ~
shown in Figure 8 until surface 51 contacts the edge of -cavity elements 36 and 37. With continued movement of central . .
, core element 61 to the left, actuator 64 first begins to move the small segment 44 to its extended position. After a short ~-delay actuator 66 extends large segment 45 to its extended ' position. ~-' ~` The tooling of my invention can be made in a variety -~ of sizes but I believe that best results will be obtained using ! a minimum diameter of 6 inches. The rate of movement of the retractable segments is determined by the slope of the actua-tors 64 and 66. In one example of my invention this was a 20 ~, angle but this can range from 10 to 30. As the tooling gets _ g _ 1~44416 larger, the angle can be increased which will, in turn, increase the amount of retraction. The recess can, of course, have various configurations and can be of different widths. In one example of the tooling, the depth of the recess in the plastic part was 0.140 inch.
While I have described the production of a coupling using this molding apparatus, it could be used on longer struc-tures such as pipe. This would, of course, increase the length of the core assembly and would mean a longer withdrawal time. The core assembly can also be used in the field to thermoform plastic pipe originally made as a straight cylinder and wherein a recess or gasket groove is desired in the end of the pipe. This is done by applying heat to a band surrounding the pipe and forcing the apparatus into the pipe and expanding j the retractable segments. :
; The tooling can be used with substantially any plastic used in the production of pipe and fittings. Suit-` able resins would include high density polyethylene, polypropy-lene, polystyrene, polyvinyl chloride, etc. I have had espe-` 20 cially good results wherein a dense or structural foam product i is made using high density polyethylene in the process dis-closed by De Vita, U.S. 3,746,494 (1973). ~t While I have disclosed a particular embodiment of my `~ invention, those skilled in the art will recognize that consi-derable variations can be made without departing from the broad scope of my invention.

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Claims (6)

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

1. A collapsible core assembly capable of forming in a hollow plastic part having at least one open end an internal surface containing a 360° recess, said assembly comprising:
(1) a single bi-directional inner core pulling assembly movable axially, (2) an outer mold means for forming said internal surface comprising:
(a) a first mold means having a first position and a second position, wherein said first mold means when in said first position extends a greater radial distance than said first mold means when in said second position, said first mold means comprising a plurality of first and second mold segments, and (b) a plurality of grooves being equal in number to and for use with each one of said first and second mold segments and sloping radially inward toward the forward end of said collapsible core assembly, wherein said plurality of grooves are located in one of said first mold means and said inner core pulling assembly, and (3) a means for coupling said inner core pulling assembly and said first mold means such that axial movement of said inner core pulling assembly causes a radial and coplanar movement of said first mold means between said first and said second positions, wherein there is a substantial time delay after an initial move-ment from said first position toward said second position by said first mold segments when said second mold segments begin to move from said first position toward said second position, said means for coupling comprising a plurality of projections fixedly attached to the other one of said first mold means and said inner core pulling assembly, and arranged to be slidably contained one in each of said plurality of grooves, wherein the size of grooves, utilized by said means for coupling said first mold segments to said inner core pulling assembly, to the size of said plurality of projections slidably contained therein causes a closely coupled response upon rearward axial movement of said inner core pulling assembly, and the size of grooves, utilized by said means for coupling said second mold segments to said inner core pulling assembly, to said plurality of projections slidably contained therein causes said delay in response upon rearward axial movement of said inner core pulling assembly.

2. The collapsible core assembly of Claim 1, wherein each of said first mold segments is radially opposite one of said second mold segments.

3. The collapsible core assembly of Claim 1, wherein said first mold segments are smaller than said second mold segments.

4. The collapsible core assembly of Claim 1, wherein said outer mold means for forming comprises in addition a second mold means having a suitable radial dimension for forming said at least one open end.

5. The collapsible core assembly of Claim 1, wherein said size of grooves, utilized by said means for coupling said second mold segments to said inner core pulling assembly, are such that a surface thereof and a surface of said projections slidably contained therein, which surfaces contact one another to cause movement of said second mold segments from said first position to said second position upon axial movement of said inner core pulling assembly, are spaced apart when said mold means is in said first position and wherein said size of grooves, utilized by said means for coupling said first mold segments to said inner core pulling assembly, are such that a surface thereof and a surface of said projection slidably contained therein, which surfaces contact one another to cause movement of said first mold segments from said first position to said second position upon axial movement of said inner core pulling assembly, are in contact when said mold means is in said first position.

6. A collapsible core assembly capable of forming a 360° recess on the inside diameter of a plastic part having a central portion and a base portion on first and second sides of said recess comprising:
(1) an outer assembly adapted to form the inside surface of a said plastic part comprising from front to back in the longitudinal direction:
(a) a forward end cap so shaped as to form the central portion of said plastic part provided with an axial counterbase, (b) a rearward base so shaped as to form the outer end of said plastic part, (c) a plurality of radially and coplanarly retractable mold segments positioned between said cap and base which in the molding position provide a mold diameter of greater diameter than adjacent surfaces of said cap and base of said mold sections, the inner ends of said mold segments sloping inwardly toward the center line of the assembly from the base to the cap, said mold segments having a T-shaped keyway on the inner end thereof, said plurality of coplanar mold segments comprising:

i. three small segments equidistantly placed around the circumference of said plurality, and ii. three large segments positioned between said small segments, and (2) a single bidirectional inner core pulling assembly movable axially of said core assembly comprising:
(a) a central core element adapted to travel within and extend rearwardly beyond said counterbase in said cap, (b) a travel stop on the forward end of said central core element adapted to move within said counterbase between the forward end of the counterbase and the rearward end thereof, (c) six actuator means fixedly attached to the forward end of said inner core element, sloping radially inwardly toward the center line of the assembly from the rear to the forward ends thereof, each of said actuator means having a T-shaped projection on the radially outer surface thereof adapted to inneract with the T-shaped keyway on the retractable mold segments, said T-shaped keyways in said segments being of two dimensions wherein said actuator means comprises:

i. first actuator means associated to inneract with said small segments to have the relationship between the projection therein and the keyways on the mold segments such that contact therebetween occurs substantially immediately upon rearward movement of said inner core pulling assembly, and ii. second actuator means associated to inneract with said large segments to have the relationship between the projections therein and the keyways on the mold segments such that contact therebetween occurs a substantial time after contact has been made between said first actuators and said small mold segments upon rearward movement of said inner core pulling assembly.