FR2675943A1 - METHOD OF SEALING A WORKPIECE SUCH AS AN INDUCTION COIL AND MOLD FOR IMPLEMENTING THE PROCESS - Google Patents

Abstract

Method for sealing a device such as an induction coil and mould for carrying out the method. The subject of the invention is a method for sealing a device such as an induction coil. For this purpose, the device is shrouded in a heat-settable vinyl resin (3).

Description

The present invention relates to a method of sealing a room

  such as an induction coil and a mold for carrying out this method. Induction coils, used for example in the automotive industry, are usually overmolded, after manufacture, using a plastic material intended to give it its final dimensions and appearance. Until now, this overmolding was carried out directly on the coil, possibly after applying a varnish to maintain the winding The disadvantage of this method was that it is virtually impossible to achieve a good seal between the part, especially in its plastic parts, and overmolding, moisture infiltrations may

  therefore always occur at these interfaces.

  These leakage defects were mainly located at the centering fingers of the piece in the mold, these fingers projecting, for example from the spool of the spool, to come into contact with the

mold walls.

  The present invention aims at overcoming these disadvantages by providing in particular a method making it possible to provide tight protection to any part, whether or not including a winding, in particular induction coils,

  sensors or connection elements.

  For this purpose, the present invention firstly relates to a sealing method of a part such as an induction coil, characterized in that it is an overmoulding of the part, for example by -2 - soaking followed by cooking, using a resin

thermosetting vinyl.

  As a result of the implementation of this method, the part is coated with a tight layer, for example

  a few tenths of a millimeter thick.

  In the case in particular o the original part is not fully coated with the sealing layer, for example at the locations to which it is seized during soaking, it is preferably carried out a second overmolding with a plastic material, in a known manner. Under these conditions, the finished part is completely coated with the plastic material of the second overmolding, the seal being thus almost absolute, even if parts of the original part remained

  apparent after the first overmolding.

  In the case where connection wires leave the finished part, the sealing at their outlet is carried out in a known manner using a gland. The second overmolding may also have the purpose of giving the finished part the desired appearance and dimensions. It will be noted in this regard that the invention is particularly well suited for the sealing of parts in which the distance of the internal elements from the faces of the finished piece are not critical to a few tenths of millimeters near the thickness of

the vinyl resin layer.

  The subject of the present invention is also a mold for the above-mentioned second overmolding, this mold comprising inwardly projecting fingers for centering.

  the piece overmolded by said synthetic resin.

  By way of nonlimiting example, particular embodiments of the invention will now be described with reference to the appended drawings, in which: FIG. 1 is an axial view of a coil coated with a leaktight protection according to the invention; , schematically represented in the mold of the second overmolding, and FIG. 2 is a partial view, in perspective and in section, of a coil made in accordance with FIG.

present invention.

  FIG. 1 represents a coil comprising a bobbin 1, made of plastic material, and on which is

wound a winding 2.

  The coil thus produced is dipped in a thermosetting vinyl resin, such as, for example, the resin marketed under the trade name Plastisol, by the company PPG Industries (France) S A. For this purpose, the piece is first brought to a surface. temperature, for example between 140 and 160 degrees C. The resin in which the part is soaked is at a temperature of, for example, between 28 and 30 degrees C, its viscosity then being about 35 poises. The immersion and the exit of the soaking tank is carried out slowly with if possible a slowdown on the

horizontal parts.

  4 - The soaking itself can for example last a few seconds or a few tens of seconds, after which the piece is removed and drained, and preferably pre-dried before cooking, for a few tens of minutes. The piece thus coated with vinyl resin is then subjected to cooking, for example twenty minutes, at a temperature of the order of 160 to 170 degrees C. As a result, the part is coated with a layer of hardened resin 3 , thickness for example between

3 and 8/10 th of millimeters.

  In the case shown in the drawing, the coil was dipped vertically by grasping its end 1 ', up to the level of the plane P. The only sealing defects can not therefore be

produce only at the level of this plan.

  Note also that the face 4 of the bobineau, which

  has not been immersed, remains functional and adaptable.

  This is particularly useful in the case of

  connections or the active face of a sensor.

  The coil coated with its insulating layer 3 is then placed in a mold 5 to undergo a second overmoulding by any suitable plastic This definitive overmolding allows the product, already sealed, to withstand the various chemical and mechanical stresses, and to meet the tolerances

dimensional requirements.

  It will be noted in FIG. 1 that the mold 5 comprises fingers 6, projecting towards its interior, and resting on the layer 3, in order to ensure the centering of the piece. This arrangement assumes, of course, that one admits fluctuations of position of the coil by a few tenths of a millimeter with respect to the surfaces of the definitive part, because of the thickness variations of

the sealed vinyl layer 3.

  FIG. 2 represents another coil 7, made

according to the invention.

  This coil comprises, as before, a bobbin 1 on which is wound a winding 2, the assembly being

  coated with the waterproof vinyl layer 3.

  This FIG. 2 also shows the final overmolding layer 8, made in a mold such as the mold 5, and giving the part its appearance and its dimensions.

final.

6

Claims (4)

claims   1 Method for sealing a part such as an induction coil, characterized in that the part is molded with a resin thermosetting vinyl (3).   The method of claim 1, wherein said   overmoulding is performed by dipping.   Process according to any one of claims 1   and 2, wherein overmolding is followed by baking.   4 Process according to any one of claims 1 to   3, in which the part overmolded by said vinyl resin undergoes a second overmolding with the aid of a plastic material (8).   Mold for making the second overmolding according to claim 4, characterized in that it comprises fingers (6) projecting inwardly for centering the part overmolded by said synthetic resin.