FR2778597A1 - METHOD FOR COVERING A FORMED PANTY BY GAS ASSISTED INJECTION MOLDING - Google Patents

Abstract

The invention relates to covering a pellet formed by gas assisted injection molding, and a method comprising providing a molding tool having a mold cavity and an inlet junction that accommodates a molding tool. nozzle and extending into the cavity, the junction being placed below the contoured surface (12) of the part (10) and forming a hole of predetermined size and configuration in the contoured surface (12), the molding by gas assisted injection of the part (10) through the nozzle, the extraction of the part (10) from the molding tool, and the covering of the hole of predetermined size and shape with a profiled plug (18) in order to that it fits in the hole.Application to injection molding.

Description

The present invention relates to an injection molding process

  assisted by a gas, and parts formed by

  this process. More specifically, the invention relates to a pro-

  yielded from covering a base left by a nozzle used during gas assisted injection molding of plastic parts preferably, in a way

very aesthetic.

  Gas-assisted injection molding is a low-pressure variant of conventional injection molding

  which can be used for the production of thermo parts

  hollow plastics and the like. The polymeric resin or the molten plastic material is essentially injected into the mold cavity, then is expelled or otherwise displaced by a pressurized gas (hence the name of the molding process) at the ends of the mold, while the gas causes

  digging relatively thick sections of the part.

  There are various gas assisted molding processes that are currently used in the plastics industry, and they are essentially distinguished by the manner and location of injection of the gas into the molten plastic. For example, the gas can be injected directly into the mold by a gas nozzle, the operation being known as a gas assisted molding in the article, or by a special stop nozzle fixed to the body of the press. , the process being known as gas assisted molding with a nozzle on the machine. Alternatively, the gas can be introduced into a pouring system or through a nozzle. This process is known as gas assisted molding in the

main channel.

  Each process has advantages and disadvantages.

  but all of these processes pose a fundamental problem.

  damental which is that, in all, there remains a hole in the room in which the gas was injected. In certain

  only a very small hole or the like remains.

  However, in operations using a nozzle, there is a hole of about 3 to 13 mm in diameter in the molded plastic part when the part is removed from the mold. Furthermore, this hole, sometimes called a "pellet", does not have a reproducible shape and dimension and it has

  often an irregular pattern.

  Thus, gas assisted injection molding processes have not presented advantages in certain industries for which the appearance and aesthetics of

  produced pieces are important for commercial value.

  In fact, when using the molding processes by

  gas-assisted injection, the nozzle has been placed

  in a place where the aesthetic appearance of the room is not an important consideration, usually near a

  edge or side of the part to which the base is

  so hidden. Nevertheless, there are certain operations, for example coating, in which it is necessary

  cover or seal the hole.

  As a result, in most mold operations

  lage assisted by a gas, the inlet placed between the nozzle and the material or production gas inlet of the part has been placed practically at the level of the mold cavity so that any remaining material can be removed from the part resulting from the room. Although this deburring of the part gives a smooth finish to the region surrounding the base left by the nozzle, it does not allow the closure

  watertight or plugging the hole itself.

  We have already tried to cover this entry. For example, to plug a hole, many manufacturers of

  injection molds recommend a regrowth operation

  wise in which the specialist essentially tries to melt and resolder the plastic material which surrounds the hole. This can be very expensive, however, and

  however, it is very difficult and requires

  times of years of practice for the technical operation to be perfect. In addition, the results are often not reproducible and can still give an aesthetic appearance.

  worse than if the room had kept the hole.

  Thus, it is necessary that a process allows the covering of the caps, in particular those which are left by the nozzles used for gas assisted molding.

  parts, preferably plastic.

  The present invention therefore relates to a method of covering the caps formed during the molding of a part with the assistance of a gas. It also relates to a process of this type which can be used for the aesthetic covering of a base which can

  be placed on a visible side of the room.

  It also relates to a process of the aforementioned type which allows the covering of the base whatever the dimension.

or the shape of this base.

  It also relates to a process of the aforementioned type which allows the covering of the base with a dimension and a

reproducible configuration.

  These objects of the invention, which have advantages over existing gas-assisted injection molding methods, are achieved in the following manner

  according to the invention, as the following description indicates.

  In general, the invention relates to a method of covering a base formed during the molding of a part by injection assisted by a gas. The method includes

  production of a molding tool having a mold cavity

  beam whose profile essentially corresponds to the profiled surface of the part. The molding tool further comprises an inlet junction intended to house a nozzle through which the resin or plastic and / or the gas circulate, this junction extending inside the mold cavity. In this way, the input junction is located below the shaped surface of the part when it has been shaped. After injection molding of the part, the junction which extends inside the mold cavity forms a hole of predetermined size and configuration in the shaped surface of the part of slightly

  higher than the base to be covered. After the

  lage by gas-assisted injection of the part through the nozzle, removal of the nozzle and removal of the part from the mold, the base is hollow below the surface of the part, and a dimension hole and of predetermined configuration is formed on the surface of the part above the base. The hole formed on the surface can be covered

  a plug whose profile allows adjustment on the hole.

  Other characteristics and advantages of the invention

  will be better understood on reading the description which will

  follow exemplary embodiments, made with reference to the accompanying drawings, in which: FIG. 1 is an exploded perspective view of a part molded using the principles of the invention and of a plug intended to cover a hole the contoured surface of the part;

  FIG. 2 is a section through part of a soft part

  lée according to the invention, having a plug which covers the base; and FIG. 3 is a section through a molding tool according to

  the invention having a nozzle placed inside the rod

  input of the molding tool.

  The invention relates to a method for covering a base formed in a gas-assisted injection molded part, preferably for aesthetic purposes. The base is left by the nozzle during the extraction of the molded part of the molding tool. The invention relates to the covering of the base by physical arrangement of this base below the surface of the part. In this way, the hole left on the surface of the part has a reproducible dimension and configuration and can therefore be covered by a plug.

  intended to be lodged in the hole of dimension and confi-

predetermined guration.

  We refer to the drawings; a part of the part molded or produced by implementing the invention bears the general reference 10 in FIG. 1. This part is preferably formed from a plastic material or from a polymer resin known as being a material which can be injection molded. The part 10 can have any shape and configuration and can have any dimension known in the art, the only condition being that the part 10 to be molded is prepared by a gas assisted injection molding process of the type known in the art. More specifically, the part 10 must be molded by a process in which a gas is injected directly into the molded part by a nozzle. In other words, gas assisted injection molding in the channel is not used in this process. As described in detail below and shown more precisely in FIG. 2, the part 10, which has a particular profile surface 12, is molded so that a hole 14 of selective size and shape is made on the surface 12 of the part 10 directly above a base 16 left by the nozzle 26 (Figure 3) during the removal of the part from the mold. Thus, a plug, for example an aesthetic plug 18, intended to be firmly housed in the hole 14, can be introduced directly into the hole 14 so that it

covers the base 16.

  In FIG. 3, a molding tool used for implementing the method of the invention bears the general reference 20. The tool 20 comprises a molding cavity 22 which has practically the profile of the surface 12 of the part 10 to be molded and one or more nozzle seats, such as 24,

  intended to accommodate a nozzle 26 through which the plas-

  molten tick and / or the gas is injected into the cavity 22. An inlet junction 28 enters the cavity 22 at the end of each nozzle seat 24. It should be noted that the junction 28 preferably has a wall 30 whose surface 32 communicates with the seat 24 during operation and houses at least the end 34 of the nozzle 26 when the gas assisted injection molding operation is carried out. , and a surface 36 forming a part of the cavity 22 which extends towards the inside of the rest of this cavity. Thus, it is noted that the inlet junction 28 extends below the surface 38 of the cavity 22 and, during injection molding assisted by a gas from the part 10, below the surface 12 of the molding 10. In other words, the molding 10 has a hole 14 on its surface, having a location and

  a configuration determined by the dimension and the configuration

  ration of the junction 28 which extends into the cavity 22.

  After removal of the molded part 10 from the tool 20, the tip 34 of the nozzle 26 is also removed from the part 10 and

  leaves a base 16 in the wall 30 which is set back

  below the surface 12 of the part 10. More specifically, the base 16 is defined essentially by the separation of the nozzle 26 from the end of the wall 30 which penetrates into the cavity 22 below its surface. It should be noted that a little plastic material may remain around the base 16, but this material is located below the profiled surface 12 of the part 10. The material can be easily separated from the part by deburring if necessary. , so good

  that it remains under the surface 12 of the part.

  We refer to Figures 1 and 2; a plug 18 can be inserted into the hole 14 so that it covers the base 16. It is noted that the hole 14 is necessarily a little larger than the base 16 which must be covered. However, the hole 14 also has a constant dimension and shape predetermined by the dimension and shape of the junction 28.

  Any plug known in the art

  Only suitable for use according to the invention and intended to fit in the hole 14, can be used. The

  cap 18 is preferably of a type which fits securely

  lying in the hole 14 and which has an external surface 42 which is essentially at the level of the surface 12 of the

  piece 10 or slightly below. In a mode of realization

  Preferred position, the plug 18 has a head portion 44 having an external surface, such as 42, the configuration of which corresponds practically to the profile of the profiled surface of the part 10. One or more members such as 46 penetrate the hole 14 and ensure a robust retention of the plug 18 in place by contacting the wall 48 delimiting the hole 14 or by cooperation in another way with this wall. During operation, the gas assisted injection molding of part 10 is analogous to any other gas assisted injection molding operation which employs a direct control nozzle. In particular, the molding operation can be divided into three stages. First, the polymer or plastic is injected into the cavity 22. Then, the gas is introduced into the molten core, forming a bubble. The gas bubble displaces part of the molten material and pushes it into the

  unfilled cavity 22 and completes the filling of the mold.

  This step in the process is known as primary penetration.

  mayor by a gas. Finally, the gas bubble begins to expand during the secondary penetration of the gas when the polymeric material has reached the end of the mold. The gas bubble also expands when the part cools and the material exhibits shrinkage, creating a bubble or a path in the part 10 as shown more precisely in FIG. 2. The pressure in the bubble gives the force necessary for compaction plastic and when putting

shaped as part 10.

  At the end of the seated injection molding operation

  ted by a gas from the part 10, the latter can be removed from the tool 20. In this operation, the nozzle 26 is always removed and leaves the base 16 under the surface 12 of the part and a hole 14 of dimension and of predetermined shape on the surface 12 of the part 10 above the base 16. The hole 14 of the surface 12 can then be covered with the plug 18 which has a profile allowing it to fit in the hole 14,

  as previously described.

  It is therefore obvious that the method according to the invention is very effective for covering the pellet left in a part which has been injection molded assisted by a gas. The invention is particularly suitable for a gas assisted injection molding process which uses a direct inlet nozzle, but is not necessarily limited to this process. The process according to the invention can be used separately with other devices, processes and the like, as well as for the manufacture of other parts and in many different industries. It should also be noted that, since the pellet is finally covered, the gas assisted injection molding process can be carried out on the apparent side of the part, that is to say at the place where the

  piece is visible to the consumer public.

  Of course, various modifications can be made by those skilled in the art to the methods which have just been described solely by way of nonlimiting example.

  without departing from the scope of the invention.

Claims (8)

  1. Method for covering a base (16) formed by gas-assisted injection molding of a part (10) having a predetermined profiled surface, characterized in that it comprises: the arrangement of a tool (20 ) molding having a   molding cavity (22) with a practical profile   ment to the profiled surface (12) of the part (10) and having an inlet junction (28) which houses a nozzle (26) and which extends into the mold cavity (22), the junction (28) inlet being placed below the profiled surface (12)   of the part (10) and forming a hole of dimension and confi-   predetermined guration in the profiled surface (12) of the part (10), gas-assisted injection molding of the part (10) by the nozzle (26), the extraction of the part (10) from the tool (20) molding, and   covering the hole of predetermined size and shape   terminated by a profiled plug (18) so that it fits in the hole.   2. Method according to claim 1, characterized in that   that the base (16) is below the hole formed in the sur-   profiled face (12) of the part (10).   3. Method according to claim 1, characterized in that the predetermined hole formed in the profiled surface (12) of the part (10) is at least slightly larger than the base (16).   4. Method according to claim 1, characterized in that the nozzle is a nozzle (26) with direct entry into the mold cavity (22).   5. Method according to claim 1, characterized in that the gas-assisted injection molding step is   executed on the visible side of the part (10).   6. Method according to claim 1, characterized in that the step of extracting the part (10) from the tool (20) of   molding includes extracting the nozzle (26).   7. Method according to claim 1, characterized in that the plug (18) has an external surface which is located practically at the level of the profiled surface (12) of the piece (10).   8. Method according to claim 1, characterized in that   that the plug (18) has an outer surface slightly above   under the profiled surface (12) of the part (10).