CA1060624A - Apparatus for molding fluid seal elements - Google Patents

Abstract

Abstract An apparatus for molding articles, particularly those having a body portion formed from a cured material and bonded to a relatively rigid insert portion. Two mold members are arranged for relative movement along a given axis between open and closed positions. Each of the members includes surfaces at least partly directed towards each other to define in said closed position of the members, a molding cavity between the members. One of the mold members has a part for engaging a relatively rigid insert, so as to form a flash barrier on the insert when it is engaged by the mold part. The mold has surfaces for supporting the insert on at least one of its surfaces. The mold assembly includes a third mold member which is movable relative to both of the other two mold members. The moldable material from which the article is to be formed is received on one mold member, and the other member is reciprocable along a given axis and adapted to apply a predetermined closing force to the first and third members. Springs or other resilient means are disposed between a mold plate and the first mold member, and a second spring is disposed between the third mold member and the mold plate, and the first and third mold members have sealing surfaces engaging each other and separated only by a working clearance. In use, the members respectively first engage the stamping, then the rubber, and finally, under the spring force, move the rubber into the mold and hold it there under a predetermined force.

Description

APPA]~TUS FOR MOLDING FLUID SEAL_ELEMENTS
The present invention relates to an apparatus and method for minimizing or eliminating problems in the molding of rubber and other materials by the insert molding method. By "insert molding" is meant a method wherein a metal or other stiff "insert" is disposed entirely within or projects partially into the cavity in which the seal body is formed by molding.
The invention, however, is also useful with other rubber or plastic molding methods.
Insert molding techniques are commonly used in making oil seals having one or more sealing lips made from an elastomer which is bonded to a stiff casing unit. ~ -In most oil seals, the casing or cup is L-shaped in - cross section and is made by a stamping. The seal body is annular and has one or more sealing lips thereon.
- The elas~omeric seal body provides fluid retention by engaging a shaft in fluid-tight relation.
Today, most fluid seals are made by so-called com-pression molding wherein a piece of rubber is forced by the 20 simple compressing or closing action of mold closure into a -cavity which is completely defined only when the mold is fully closed.
Compression molding is desirable because of economy and relative simplicity, especially where large numbers of parts are to be made in multiple-cavity molds. For example, one "heat" or cycle of a molding press may produce 24, 36, 48 or other large number of parts.
Along with the economies of compression molding, however, certain quality control problems also occur, especially where the oil seal is finish molded to its exact size rather ,' ' . : . .
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than being molded to one size and later trimmed to its exact size.
One very common problem with compression molding is precise filling of each mold cavity and maintaining the rubber therein under a suitably high pressure.
If a mold cavity is not completely filled, the article will be characterized by voids, poc~ marks, blisters, and a generally irregular shape. If sufficient pressure is not maintained, a porous seal may result. If too much rubber is used, mold closing forces will cause the rubber material, which is substantially incompressible when totally confined, to leak or "flash" from the mold cavity, usually along the insert. This flash is undesirable, because it must either be removed from the finished product by a separate operation, or undesirably left on the finished product.
Because the size of the piece or rubber from which the molded part is made (the "prep") is not easy to control, most compression molded parts are either characterized by certain amounts of flash which must be removed subsequent to molding.
While some attempts to reduce flash have been some-what successful, most methods have one or more serious draw-backs. The present invention overcomes these drawbacks.
According to the invention, a mold apparatus is used which has a first, fixed mold member and second and third mold members movable along a given axis relative to the first member and relative to each other, resilient means are associated with each of the second and third parts, with the resilient means being adapted to be engaged by one or more parts for effecting a movement sequence so as to define a molding cavity .

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between the first and s~cond members and subsequently fill the cavity by applying a limited force to the third member to move molding material from the area in which it is received to the mold cavity.
A detailed description of certain embodiments of the invention is set forth, and the accompanying drawings show typical molds of the invention.
- BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a vertical sectional view, with portions broken away, showing one form of molding apparatus made according to the invention and showing the mold members in the closed positions thereof with an insert disposed partially within the molding cavity and bonded to the moldable material filling the cavity;
Figure 2 is a fragmentary sectional view of the mold : of Figure 1 in a fully opened position;
Figure 3 shows the mold apparatus of Figures 1 and 2 with two of the mold members thereof in the closed position and showing the third element moving toward a closed position;
Figure 4 shows another form of molding apparatus made according to the invention, with the ~lements being in a position such as that shown in Figure 3; and Figure 5 is a fragmentary sectional view of a still further form of molding apparatus, showing the apparatus in a fully closed position.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS OF THE INVENTION
For purposes of illustration, it will be assumed that the mold parts move vertically, and that the elastomer -is forced downwardly into a molding cavity as movement of the mold parts occurs vertically in the desired direction.

Figures 1 tllrough 3 show the invention to be typically embodied in a mold assembly 20, which produces a seal 22 having a rubber body portion 24 bonded to an insert 26 in the form of a flanged annular casing 28.
The molding apparatus itself includes a top plate 30, a lower plate 32, a center core 34, secured as by fastener 35 to the lower plate 32, a stripper plate 36 resting on the bottom plate 32, and an insert hold-down ring 38 disposed beneath an upper hold-down unit 40, with these parts being biased apart by a coil spring 42 received in an upper cylindrical bore 44 in the upper unit 40 and extending into a lower recess 46 in the hold-down ring 38 and disposed in a position of axial registry with the bore 44 in the upper hold-down unit 40. -~
Disposed radially inwardly of the upper hold-down unit 40 is a cylindrical mold member 48 having a top surface 50, a bottom end portion 52, and inwardly directed surfaces 54 (Figures 2 and 3) which help to define a molding cavity 56 (Figure 3). An annular shoulder 58 is disposed on the upper portion of the die member 48. Radially inwardly of the die member 48 is an inner plunger 60 having an annular, radially extending, axially facing surface 62 forming the lower part thereof. Inside the groove 64 is a stiff but lubricous seal 'L
ring 66, with an annular, radially extending shoulder 68 thereabove in oppositely facing relation to the shoulder 58 of the die member 48. An annular surface 70 forms the top of the plunger 60. ~ -A cylindrical opening 72 is defined on its outside -.
by an inner wall 74 of the upper hold-down unit 40, and on its inside by the outer surfaces of a fastener 76 having a threaded end 78 secured to the top plate 30. The fastener .

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head 80 is spaced rom a shoulder 82 extending radially inwardly on the inner surface of the plunger 60.
A collar 84 lies in the upper portion of the recess 72, with the upper surface 86 thereof engaging the lower surface 88 of the top plate 30, while the lower surface 90 of the collar 84 engages the upper ends respectively of an inner and outer stacks 92, 94 of resilient springs. A plurality of generally outwardly facing surfaces 96 in the center core 34 cooperate with the surfaces 54 on the end 52 of the die 48 to define the molding cavity 56.
Inwardly facing surfaces 98 disposed on the die member 48 above the surfaces 54 cooperate with opposite surfaces 100 located on the lower core 34 to define a transfer area or passage 102 between mold members 48, 34. This passage 102, (Figure 3) also includes at least one shoulder on the movable mold part defining an area of reduced cross section to facilitate tearing or trimming the scrap so as to separate it from the finished article along a predetermined line~
A cylindrical pin 39 rests on plate 32, and extends through the stripper plate 36 and the hold-down 38. Its upper surface engages the hold-down 40. The button 39 establishes a solid height for the mold and transmits force between plates 30 and 32 when the mold is closed.
An area 104 above the passage 102 receives the "prep" 105 from which the finished article will be made.
The area 104 is defined in part by a shoulder 106 on the mold core 34, by an axial wall 108 on the core 34, by an inner -~
surface 110 ~Figure 2) of the member 48, and by the axial end face surface 62 on the lower portion of the plunger 60.
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OPERATION
~ ssume that the assembly 20 (Figures 1 through 3) has been opened and is empty. The upper plate 30 is in a raised position (Figure 2), the collar 84 rests atop the two stacks of springs 92, 94, but lies outside the opening 72. The first mold member 48 is supported by the inner member 60 because the shoulders 58, 68 engage the outer and inner mold members 48, 60 respectively. The members 48, 60 are able to move relative to one another along a vertical movement axis.
Figure 2 also shows that the upper hold-down unit 40 is spaced from the plate 38, and that the fastener 76 supports the die member 60 which in turn swpports member 48 so that a pre-load may be placed on one or both of the spring stacks 92, 94.
Next, a stamping 26 is placed on a surface of the stripper plate 36, with the inner margin of the stamping 26 lying on a shoulder 112 which forms a part of the center core 34.
The assembly shown as the upper part of Figure 2 is then moved downwardly along the center line axis of the fastener 76. The lower surface of the ring 38 then engages and holds the upper edge of the stamping 26. The next increments of movement compress the hold-down spring 44, increasing the hold-down force, while further movement of the upper half of the mold 20 causes the lower edge 114 of the member 48 to engage the upper surface of the casing flange adjacent its inner margin.
Force to move the member 48 is supplied from the plate 30 through the springs 94. Then, the lower surface 62 of the plunger 60 begins to engage the prep 105, which becomes fluent during mold closing by reason of absorbing heat from the mold.
Continued movement of the upper plate 30 exerts a force throug]l the inner spring stack 92 to urge the plunger further downwardly ~Figure 3). This forces the prep 105 to flow through the passage 102 between the surfaces 98, 100 and into the molding cavity 56. As shown in Figure 1, the cavity 56 and tear trim area 102 are then fully filled with rubber, and a certain residual amount of rubber 114 remains in the cavity 104.
Compression of the outer stack of springs 94 moves the outer die member 48 against the stamping with sufficient force to prevent flash from forming along the surfaces of the stamping 26. Because the inner plunger 60 is also urged down by the stack of springs 92, it will tend to reach an equilibrium position such that the mold cavity 56 will be filled fully under the desired pressure, but the pressure will not rise to a level which will cause flash. Likewise, the pressure will not be so low that the cavity will not be filled nor so low that bubbles or voids will be created in the product. The exact spring forces required depend on these pressures, and the forces may be easily determined by those skilled in the art. The total force applied to members 48, 60 is limited by the springs and by the rest button 39.
The seal ring 64, usually a stiff material such as -~
"Teflon" ~ ~a polytetrafluoroethylene) prevents escape of flash between the two members 48, 60.
The rubber in the cavity is then cured to an extent sufficient to permit the mold to open. As the parts move from ~ ~
the position of Pigure 1 to that of Pigure 2, the rubber tears ~;
along the reduced cross-sectional area lying between the molding cavity 56 and the passage 102, thereby effecting a so-called tear trim between the rubber scrap and the finished ~ f~ O~

part, in a manner known to those skilled in the art.
The dotted lines 116 shown forming a part of the passage or area 102 illustrate that a plurality of notches or cutouts may be provided around the circumference of the inner core 34, if desired, to improve the flow patterns of the fluent rubber as described in U. S. Patent No. 3,773,454.
Figure 4 shows a modified form of the apparatus which differs in detail from that of Figures 1 through 3. Figure 4 shows a top plate 30a, a collar 84a disposed therebeneath and acting upon the inner and outer stacks of springs 92a, 94a, urging the inner and outer mold members 60a, 48a downwardly.
The locations of the prep 105a, the transfer area -102a and the molding cavity 54a correspond to the locations of their counterparts in Figures 1 through 3. The insert hold-down of Figure 4 is somewhat different in shape, but it in-cludes the spring 42a, the lower hold-down 38a, the cavity 46a, and provides for engagement between the spring 42a and a portion of the upper hold-down 40a with which it is associated.
A fastener 41 limits the downward motion of the lower hold-down 38a under the force of the spring 42a.
The mold of Figure 4 also includes an inner core 34a, a stripper plate 36a, and lower plate 32a. These constructions differ from those of Figures 1 through 3 in that relative move-ment between the outer and inner, axially movable mold members 48a and 60a is accomplished by registration of facing frusto-conical surfaces 49, 51. In the closed position of the mold, downward movement of the member 60a is limited by engagement between the two tapered surfaces 49 and 51. The mold of Figure 4 functions in essentially the same manner as that shown in Figures 1 through 3.

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Figure 5 shows another embodiment of the invention;
however, this embodiment differs from those of Figures 1 through 3 and 4 in the respects referred to below.
The mold 20b of Figure 5 includes a cavity 54a de-fined by surfaces on the first or outer mold part 48b and the counterpart surfaces on the center core 34b. By contrasting Figures 4 and 5 with Figures 1 through 3, it will be seen that the molding cavities 54a, 54b, respectively, are defined by three members, with the third member being the core insert 35a (Figure 4) or 35b (Figure 5). Moreover, it will be seen in all the embodiments wherein the insert lies partially within the mold cavity and partially outside of it, that the cavity is also defined in part by the insert. For purposes of the invention, these points are immaterial; however, this fact is recited merely to point out that it is not essential that the cavity be defined by two members, only that it be defined by at least two members which move relative to each other to open and close the mold.
In Figure 5, the hold-down arrangement and spring stacks 92b, 94b are similar to that of Figure 4. In Figure 5, a seal casing 26b is shown to be of the so-called "shotgun casing" type, that is, one having a double thickness flange 27 which lies radially outside of the axial flange 29 of the stampin~ 26b. Dowel pins 31 provide a casing centering function, with their inner edges engaging the outer edge of the flange 27.
The seal ring 66b, of Teflon~or the like, is engaged on one surface by a collar 67, w~ich is urged axially by a threaded sleeve or cap 6l~. As disclosed in U. S. Patent No.
3,841,809, the threaded member 69 is periodically tightened to cause the collar 67 confining the ring 66b to maintain ~ ~fa~ f~Of~

tight engagement between the ring 66b and the inner surface of part 48b with which it forms a seal. This permits compensa-tion to be made for the cold flow of the Teflon ring 66b, and insures a tight seal between these sliding parts, which is necessary to prevent flash and which permits buildup of the requisite molding pressures.
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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. An apparatus for molding articles having a body portion formed from a cured material and bonded to a relatively rigid insert portion, said apparatus comprising, in combination, first and second mold members arranged for relative movement along a given axis between open and closed positions of said members, each of said members including surfaces at least partly directed towards each other to define therebetween, in said closed position of said members, a molding cavity predetermining the exact shape of the body of said article to be formed, means on said first member for engaging a relatively rigid insert, said engaging means being adapted to form a flash barrier on said insert upon engagement thereof, means on said second member for supporting said insert along at least one surface thereof, a material pressing member movable relative to both said first and second mold members, means on said second mold member for receiving a prepared portion of moldable material from which said article is to be formed, means reciprocable along said given axis for applying a predetermined closing force to said first mold member and said press member, first resilient means disposed between said force applying means and said first mold member, second resilient means disposed between said press member and said force applying means, said first and second mold members and said press member confining said portion of moldable material, said members having mutual sealing surfaces separated from each other by a working clearance, said first and second resilient means having uncompressed, free height positions such that movement of said force applying means causes said first mold member to move from said open position to said closed position, thereby to define said molding cavity between said first and second mold member and said insert, and whereby subsequent movement of said press member causes said press member to engage said material and causes only that material able to be accommodated by said cavity to flow from the area of said material-receiving means into said molding cavity under the force applied by said press member through said second resilient means, the shape of said body portion thereby being determined solely by the predetermined shape of said cavity and not by the amount of moldable material in said portion thereof, the resiliency of said second resilient means limiting the force able to be applied to said material.

2. Apparatus as defined in Claim 1 wherein said first mold member and said press member include portions adapted for mutual engagement to limit the amount of relative movement therebetween.

3. Apparatus as defined in Claim 1 which includes means adapted to engage a portion of said insert to hold said insert in a desired position of registry within said mold prior to engage-ment of said insert by said second mold member.

4. An apparatus as defined in Claim 1 wherein said first mold member and said press member each includes a cylindri-cal portion, with the outer surface of said cylindrical portion on said press member slidingly engaging the inner surface of said cylindrical portion of said first member.

5. A compression molding apparatus adapted to form articles from a moldable material that are bonded to a relatively rigid insert, said apparatus comprising a first, stationary mold member having surfaces thereon defining respectively, a portion of a molding cavity, a transfer area, and a material-receiving area, a second mold member movable relative to said first mold member between an open position and a closed position, said second member having surfaces thereon cooperating with said surfaces on said first member to define at least a portion of said molding cavity and a portion of said transfer area, said first and second members in the closed positions thereof combining with said insert to define the shape of said article, means for moving said second member between opened and closed positions along a given axis, first spring means disposed between said moving means and said second mold member, a material press-ing member movable along said axis between open and closed positions, second spring means associated with said press member and disposed between said moving means and said press member, said press member having at least one surface adapted, in the movement along said axis between said open and closed positions, to engage a portion of said moldable material disposed in said material-receiving area and to move a portion of said material through said transfer area and into said molding cavity under the force supplied to said press member by said moving means through said second spring means to fill said cavity fully and to leave moldable material not able to be accommodated within said molding cavity outside of said cavity.

6. An apparatus as defined in Claim 5 wherein said first and second mold members each includes oppositely directed surfaces adapted to engage an insert disposed there-between in the closed position of said second mold member to establish flash barriers on said insert and prevent loss of said material from said molding cavity upon application of said mold closing force.