FR2707205A1 - Process for the overmoulding (insert moulding) of an insert, at least part of which is fragile, and overmoulding press mould suitable for the implementation of such a process - Google Patents

Abstract

According to the invention, in the moulding cavity (22) of the mould (20) employed, a shell (casing) (34) made of synthetic material is provided in order to grip, at least partially, the fragile part of the insert. Application, in particular, to the overmoulding of an electric light bulb.

Description

"Method for overmolding an insert of which at least part is fragile and mold for clean overmolding press
to the implementation of such a process "
The present invention relates generally to overmolding, that is to say at least partial coating, with thermoplastic synthetic material, of an insert duly protruding for this purpose into the molding cavity, or imprint, from an appropriate mold.

 In practice, it is done by injection, and, to resist the corresponding molding pressure, as well as to resist temperature, the mold used is metallic.

 The present invention relates more particularly to the case where at least part of the insert, that intended to remain in the open air, is fragile.

 This is the case, for example, of electric bulbs, or lamps, on the foot of which, together with the contacts with which this foot is engaged, it involves overmolding a body of insulating material in order to obtain of a "connectable" assembly, that is to say of an assembly advantageously capable of being directly connected to any suitable supply support, by simple engagement thereon.

 It is obviously necessary to leave at least a fraction of the glass part, commonly called a balloon, of such an electric bulb in the open air.

 When the mold is closed, this glass part may break.

 This is all the more so since, in practice, the light bulbs in question have a relatively uncertain geometry, their cross section being for example more or less oval instead of being strictly circular, and that, of a manufacturing to another, they jointly present significant differences in ratings.

 The overmolding of these light bulbs is also jointly complicated by the fact, on the one hand, that, to ensure all the necessary electrical continuity, it is necessary to prevent the injected thermoplastic synthetic material from being inserted between the conductors 'such a bulb and the contacts with which his foot is engaged, and that, on the other hand, it is necessary to avoid his balloon a thermal shock likely also to cause breakage.

 The present invention generally relates to provisions making it possible to overcome these difficulties in a very simple manner.

 More specifically, it firstly relates to a process for the overmolding of an insert of which at least part is fragile, this process being, according to a first aspect, generally characterized in that, in the mold cavity of the mold used, at least partially encloses the fragile part of the insert in a plastic envelope; it also relates to a mold for overmolding press characterized in that, for the implementation of the above method, it comprises, in its molding cavity, such an envelope of synthetic material.

 This envelope of synthetic material, which can be in one piece or be made of several fixed or mobile parts, and of which the constituent synthetic material is obviously chosen so as to withstand the molding temperature, advantageously assumes by itself a plurality of functions.

 First of all, it advantageously protects the fragile part of the insert when the mold is closed and, by its natural elasticity, which results in a certain compressibility at least locally, it advantageously absorbs any variations in geometry and / or dimensions of this fragile part.

 Jointly, by resisting, without yielding, to the pressure, it provides all the necessary sealing between the part of the insert which is more specifically overmolded and the fragile part of this insert which must on the contrary remain in the open air. .

This double requirement, compressibility and resistance to pressure, being at least apparently contradictory, it appeared, according to the invention, that an advantageous compromise could be found on this subject by choosing a synthetic material whose hardness is between 70 "and 90" Shore, preferably being close to 80 "
Shore.

 Finally, the plastic casing used according to the invention advantageously protects the fragile part of the insert by absorbing the thermal shock of which it is the object.

 To further minimize this thermal shock, and more specifically with regard to the overmolding of an electric bulb engaged by its foot on contacts which are in electrical connection with connection members to be left in the open air, the following is provided, a second aspect of the invention, to have the injection threshold of the molding cavity at a distance from these contacts, between these and the bottom of the molding cavity opposite the fragile part, or balloon, of the electric bulb.

 Besides this injection threshold is thus far from the balloon of the light bulb, it is also advantageously far from its contacts.

 I1 advantageously results in injection closing these contacts on the base of the light bulb rather than opening relative thereto, which ensures all the desired electrical continuity between these contacts and the conductors to which they are applied, without insertion of synthetic material between them and these conductors.

 Finally, applied to the overmolding of an electric bulb, the method according to the invention advantageously makes it possible to obtain directly in a single phase the "connectable" assembly which then constitutes this electric bulb with its contacts, the connection members in electrical connection. with these contacts, and the body of insulating material overmolded around them, ensuring in addition, by the mere fact of the corresponding overmolding, all the desired tightness around these contacts.

 This last advantage will appear better if we remember that, usually, to date, to obtain a comparable "connectable" assembly, it is normally necessary to intervene in three phases, namely a molding phase for the realization of a body of insulating material, a mounting phase for the insertion into this body of a plate carrying the contacts, and, by means of these, the electric bulb, and a bonding phase to secure this plate to this body, without a real seal being however ensured between the contacts and the conductors of the electric bulb.

The characteristics and advantages of the invention will become more apparent from the description which follows, by way of example, with reference to the appended schematic drawings in which
Figure 1 is, with a local cutaway, an elevational view of a "connectable" assembly obtained by molding an electric bulb according to the method of the invention;
Figure 2 is a side view of this single light bulb, of the contacts with which it is engaged by its foot, and of the connection members with which these are in electrical connection
Figure 3 is, like Figure 2, a side view of one of these contacts and the corresponding connection member
Figure 4 is, on a different scale, a longitudinal sectional view of a mold according to the invention;
Figure 5 is a partial cross-sectional view of this mold, along the line VV of Figure 4
Figure 6 is a partial view in longitudinal section which, similar to that of Figure 4, relates to an alternative embodiment 7
Figure 7 is a longitudinal sectional view which, also similar to that of Figure 4, relates to another alternative embodiment.

 As explained above, it is generally a question of overmolding an insert 10, at least part 11 of which is fragile.

 The figures illustrate by way of example the application of the invention in the case where the insert 10 is a light bulb 12 engaged by its foot 13 on contacts 14 for obtaining an assembly 15 capable of being directly connected to any power supply not shown.

 The glass portion of the light bulb 12, or at least a substantial fraction thereof, is to be left in the open air.

 It constitutes here the fragile part 11.

 In the embodiment shown, the conductors 16 of the light bulb 12 are simply folded into a U on the foot 13 at their exit therefrom, and the contacts 14, which are in practice two in number, and one of which is shown in isolation in FIG. 3, are lyres, which, engaged in friction on the foot 13, bear elastically on the part thus folded of these conductors 16.

 Of course, the contacts 14 are in electrical connection with connection members 17 which, too, are to be left in the open air.

 In the embodiment shown, these connection members 17 are simple flat pins.

 Each of them is in principle in one piece with the contact 14 with which it is associated, the assembly coming from one and the same metal blank, by cutting and folding thereof.

 The foregoing provisions are well known in themselves, and, not pertaining specifically to the present invention, they will not be described in more detail here.

 It is indeed here to ensure overmolding on the contacts 14 of a body 18 of insulating material.

 In the embodiment shown, this body 18 comprises, successively, by way of example, two sections, namely, around the contacts 14, a first section 18A, which, of smaller diameter, is massive, and, around the members connection 17, a second section 18B, which, having a diameter greater than the previous section 18A, while being in one piece with it, is tubular, to leave these connection members in the open air, as desired 17.

 This second section 18B of the body 18 therefore forms a cavity 19 around the connection members 17 in the embodiment shown.

 For the formation of the body 18, a mold 20 is used, in a manner known per se, of the type of those usually fitted to overmolding presses.

 Since such a mold 20 is also well known in itself, and not belonging specifically to the present invention, it will not be described in all its details here either.

 Only the elements necessary for understanding the invention will be described therein.

 Overall, and in a manner known per se, this mold 20 comprises at least two parts 20A, 20B, namely, an upper part 20A, on the side of which is injected, and a lower part 20B on the side of which is made ejection.

 These two parts 20A, 20B are movable one relative to the other in a direction D1, which is, for example, and as shown, a vertical direction, and, as shown in Figure 4, they are capable of 'be confronted to each other along a joint plane 21, then defining between them a molding cavity 22.

 For the most part, the joint plane 21 extends generally transversely with respect to the direction D1; it is therefore essentially horizontal in the embodiments shown.

 In the embodiment more particularly shown in Figures 4 and 5, the molding cavity 22 extends in the direction D1.

 The joint plane 21 therefore extends transversely relative to this molding cavity 22.

 In the embodiment more particularly shown in Figures 4 and 5, the upper part 20A of the mold 20 is also massive and integral.

On the contrary, its lower part 20B comprises, on the one hand a sole 24, and, on the other hand, for the definition of the joint plane 21 and of the molding cavity 22, two slides 25, which are mounted movable l ' one relative to the other on the sole 24 in a direction D2 orthogonal to the direction
D1.

 This direction D2 is therefore in practice horizontal.

 Externally, the slides 25 are each wedge-shaped.

 They therefore each each have locking slopes 26 by which they are engaged with locking slopes 27 provided in a complementary manner on the upper part 20A.

The upper part 20A jointly carries fingers 28, which extend obliquely on either side of the direction
D1, moving away from each other, or from each other, as they approach the lower part 20B, and which, each respectively, are slidably engaged with bores 30 of this lower part 20B after crossing the joint plane 21.

 Thus, when the two parts 20A, 20B of the mold 20 are spaced from one another, the upper part 20A causes the fingers 28 to separate the slides 25 from the lower part from one another. 20B.

 In practice, in the embodiment shown, it is the lower part 20B which must carry the insert 10, in the direction D1, and therefore perpendicular to the joint plane 21.

 The sole 24 of this lower part 20B therefore projects a core 31 for the formation of the cavity 19 of the body 18, and, at its upper surface, this core 31 has slots 32 for the engagement of the connection members 17.

 According to the invention, the fragile part 11 of the insert 10 is surrounded at least partially, in the molding cavity 22 of the mold 20, in a casing 34 made of synthetic material.

 As regards, in practice, the overmolding of an electric bulb 12, the envelope 34 is in the general shape of a cap, to enclose over its entire surface the fragile part 11, that is to say the part of the balloon of this bulb electric 12 to leave in the open air.

 This envelope 34 therefore internally forms, in the direction D1, a blind bottom imprint 35.

 In the embodiment more particularly shown in FIGS. 4 and 5, the casing 34 is embedded in the upper part 20A of the mold 20 which carries it.

 In other words, with the exclusion of the joint plane 21, up to which it extends by flush flush with it in practice, this envelope 34 is entirely confined in a cavity 36 provided for it in this upper part 20A mold 20.

 For example, it is simply engaged with a slight tightening in this cavity 36.

 As a variant, and as shown diagrammatically in broken lines in FIG. 4, it can be secured to the upper part 20A of the mold 20 by one or more screws 37.

 Whatever the case, a synthetic material whose hardness is between 70 and 90 Shore is chosen for the synthetic material constituting this envelope 34, preferably being close to 80 Shore.

 As an indication, and without this being able to result in a limitation for the invention, it will be specified that particularly satisfactory results are obtained with a synthetic material based on silicone and at least partially vulcanized.

 For example, a silicone of the type sold by RHONE-POULENC under the reference 785-80 can be chosen for the base.

 In practice, this is a pasty base to which at least one vulcanizing agent is added, and the whole is heated for the time necessary for the desired vulcanization.

 The technique in this area being well known in itself, it will not be described in more detail here.

 It will suffice to indicate that the vulcanization time is approximately 7 minutes.

 Preferably, and as shown in the embodiment of FIG. 4, a frame 38 is provided in the envelope 34.

 This frame 38, which extends annularly around the blind bottom imprint 35 of the envelope 34, extends substantially perpendicular to the joint plane 21, and therefore parallel to the direction D1.

 Preferably, while abutting against the bottom of the cavity 36 of the upper part 20A of the mold 20, it stops at a distance from the joint plane 21, in order to avoid punching of the envelope 34 to its right when closing the mold 20.

 Preferably also, and for the same reason, the end of the frame 38 is generally rounded on the side of the joint plane 21.

 In the embodiment shown, the frame 38 extends to one third of the thickness of the envelope 34 relative to the blind bottom imprint 35 thereof.

 Anyway, the frame 38 is more or less rigid.

 For example, it is made of metal.

 For example, also, the envelope 34 is overmolded on it.

 In addition to improving the pressure resistance of the envelope 34 during molding, it constitutes, for this envelope 34, a radiator capable of accelerating the evacuation of the calories to which it is subjected.

 To further promote this removal of calories, holes 40 are provided in the upper part 20A of the mold 20 for the circulation of a cooling fluid, in particular in line with the frame 38.

 Preferably, as regards, as indicated, the overmolding of an electric bulb 12 engaged by its foot 13 on contacts 14, there is the injection threshold 41 of the molding cavity 22 at a distance from these contacts 14, between those and the bottom 44 of the molding cavity 22 opposite the balloon of this electric bulb 12.

 The injection of synthetic material into the molding cavity 22 is therefore in a direction favorable to the closing of these contacts 14 and the development of a cold sheath inside this molding cavity 22 is done jointly so also favorable.

 In the embodiment more particularly shown in Figures 4 and 5, and as shown in solid lines thereon, the injection threshold 41 is located in the vicinity of the shoulder 45 corresponding to the delimitation between the two sections 18A, 18B of the body 18 to be formed, under this shoulder 45.

 As a variant, and as shown diagrammatically in broken lines in FIG. 5, it is located above this shoulder 45.

 Anyway, the injection threshold 41 is located at the junction between the two slides 25 of the lower part 20B of the mold 20, at the end of an injection channel 42 which extends over a part at less than the height of these.

 Preferably, and as shown, the injection channel 42 bends obliquely towards the bottom 44 of the molding cavity 22 at its connection to the injection threshold 41.

 The mold 20 being open, the connection members 17 of the insert 10 are engaged in the slots 32 of the core 31 of the lower part 20B of this mold 20, and the electric bulb 12, the balloon of which forms the fragile part 11 of the insert 10 is engaged by its foot 13 on the contacts 14 with which these connection members 17 are in electrical connection.

 When the mold 20 closes, the envelope 34 provided according to the invention engages on the fragile part 11 of the insert 10, and comes to enclose the latter.

 During this engagement, and due to its compressibility, the envelope 34 adapts itself to the balloon of the electric bulb 12 constituting this fragile part 11, whatever the irregularities in geometry and / or dimensions of it.

 To promote the compressibility of the envelope 34, voids may be provided therein.

 As a variant, it may have clearances in contact with the cavity 36 in which it is confined, in particular on the side of the bottom of this cavity 36 opposite the joint plane 21.

 In the foregoing, the envelope 34 is assumed to be in one piece.

 But it can also be split into several parts.

 This is the case in the variant embodiment shown diagrammatically in FIG. 6.

 In this case, and in the manner of the slides 25 of the lower part 20B of the mold 20, the constituent parts of the casing 34 are for example movably mounted on the upper part 20A of this mold 20, radially with respect to the direction D1 .

 They therefore close on their own on the fragile part 11 of the insert 10 when the mold 20 is closed.

 To promote sliding in contact with the upper part 20A of the mold 20, the constituent parts of the envelope 34 are preferably each carried by a jacket 46, as shown.

 In the alternative embodiment shown in FIG. 7, the joint plane 21 extends axially with respect to the molding cavity 22, instead of extending as previously transversely with respect to the latter.

 In addition, in this variant embodiment, the injection threshold 41 is established in line with the shoulder 45.

 Finally, in this variant embodiment, the casing 34 implemented according to the invention has a heel 43 radially, and, as shown diagrammatically in broken lines in FIG. 7, the subjection of the two shells which constitute it to the two parts 20A, 20B constituting the mold 20 is made for example by screws 47.

 Of course, the present invention is not limited to the embodiments described and shown but encompasses any variant and / or combination of their various elements.

 In addition, the application of the present invention is not limited to the overmolding of a light bulb but extends more generally to that of any insert, at least part of which must be left to the air is fragile.

Claims (14)

 1. Method for overmolding an insert of which at least part is fragile, characterized in that, in the molding cavity (22) of the mold (20) used, said fragile part is at least partially surrounded ) of the insert (10) in an envelope (34) of synthetic material.  2. Method according to claim 1, characterized in that one chooses for synthetic material constituting the envelope (34) a synthetic material whose hardness is between 70 and 90 Shore, preferably being close to 80 "Shore.  3. Method according to any one of claims 1, 2, characterized in that one chooses for synthetic material constituting the envelope (34) a synthetic material based on silicone and at least partially vulcanized.  4. Method according to any one of claims 1 to 3, characterized in that, in the case of an overmolding of an electric bulb (12), is chosen for envelope (34) an envelope in the general form of cap for enclose over its entire surface the part of the balloon of this light bulb (12) to be left in the open air.  5. Method according to claim 4, characterized in that, more specifically with regard to the overmolding of an electric bulb (12) engaged by its foot (13) on contacts (14) which are in electrical connection with organs of connection (17) to be left in the open air, the injection threshold (41) of the molding cavity (22) is placed at a distance from said contacts (14), between these and the bottom (44) of the molding cavity (22) opposite the balloon of the electric bulb (12).  6. Mold for overmolding press of the kind comprising at least two parts (20A, 20B), which define between them a molding cavity (22), and which are movable relative to each other, characterized in that , for the implementation of the method according to any one of claims 1 to 5, it comprises, in its molding cavity (22), an envelope (34) made of synthetic material.  7. Mold according to claim 6, characterized in that, one (20B) of its parts being adapted to carry the insert (10) substantially perpendicular to the joint plane (21), the other part (20A) carries the envelope (34).  8. A mold according to claim 7, characterized in that the envelope (34) extends to the joint plane (21).  9. A mold according to any one of claims 7, 8, characterized in that the envelope (34) has within it a frame (38), substantially perpendicular to the joint plane (21).  10. Mold according to claim 9, characterized in that the frame (38) of the envelope (34) stops at a distance from the joint plane (21).  11. Mold according to claim 10, characterized in that, on the side of the joint plane (21), the end of the frame (38) of the envelope (34) is rounded.  12. Mold according to any one of claims 7 to 11, characterized in that the envelope (34) is embedded in the part (20A) which carries it.  13. Mold according to any one of claims 6 to 12, characterized in that the envelope (34) is in the general form of a cap.  14. A mold according to claim 13, characterized in that the envelope (34) internally forms a blind bottom impression (35).