WO2012010791A1

WO2012010791A1 - Moulding process and device for moulding at least one part

Info

Publication number: WO2012010791A1
Application number: PCT/FR2011/051721
Authority: WO
Inventors: Ludovic Casier; Guillaume Pupunat; Hugues Rosier; Maxime Bonnet
Original assignee: A Raymond Et Cie
Priority date: 2010-07-23
Filing date: 2011-07-19
Publication date: 2012-01-26
Also published as: WO2012010791A4

Abstract

The invention relates to a process for moulding at least one part, in which at least one cavity of a mould (2) is filled with a thermoplastic moulding material and, before said cavity (7) is filled, a film of water is formed by condensation on the surface of said cavity (7), said film being intended to separate said moulding material from said cavity (7) so as to make it easier to demould said part. The invention also relates to a device (1) for moulding at least one part, comprising a mould (2) provided with at least one cavity (7) capable of receiving a thermoplastic moulding material, condensing means (10, 11) capable of causing water to condense on the surface of said cavity (7), forming a film of water intended to separate said moulding material from said cavity (7) in order to make it easier to demould said part.

Description

MOLDING METHOD AND DEVICE FOR MOLDING AT LEAST

A PIECE

Technical area

The invention generally relates to a method of molding at least one part according to which at least one cavity of a mold is filled with a thermoplastic molding material. The invention also relates to a device for molding at least one part comprising a mold provided with at least one cavity adapted to receive a thermoplastic molding material.

Prior art

The molding processes are widely known and used for the manufacture of molded parts of any type, for example thermoplastic material. In these processes, a two-part mold is generally used, a fixed part and a movable part, comprising one (or more) cavity (s) capable of receiving a thermoplastic molding material. The movable and fixed parts are movable between an open position and a closed position in which the cavity is said to be closed and into which a predetermined quantity of previously melted molding material is injected into the cavity. To delay the solidification of the molding material and thus facilitate its distribution in the cavity, all or part thereof can be heated by means of a hot fluid circulating in conduits provided in the mold. After cooling and solidification of the molding material, the part obtained is demolded. To be ejected from the mold, the part can be pushed by means of ejectors in the form of sliding rods passing through the mold and resting on the part to be unmolded to take off the mold.

Depending on the molding materials used, the molding operations may be more or less difficult to implement. Indeed, it is not rare that after the cooling of the molding material, this molding material has an adhesion to the cavity such that, during the demolding, a portion of this molding material remains attached to the cavity and separates from the rest of the room. Following such tearing, the piece obtained has a lack of harmful material. In addition, it is necessary to clean the mold before you can use it to make another room. Furthermore, the force to be exerted by the ejectors to eject the part, may be such that the part is marked by the support of these ejectors, leading to defects in appearance and sometimes functional defects of the piece obtained, then rendered unusable. This is particularly the case when the part is made of flexible plastic material or when the cooling time is shortened, for example to improve the production yield. To avoid this tearing problem, it is ensured that the surfaces of the cavity are not parallel to the extraction direction of the molded part and have a low angle called "draft" facilitating extraction. This draft angle is nevertheless sometimes insufficient to eliminate the risk of tearing material. Also, to overcome these adhesion problems, cavities made of different materials were tested. Similarly, cavities whose material had previously undergone different surface treatments or polishing were also tested. However, the results obtained as a function of the thermoplastic materials remain random and unsatisfactory. It has also been attempted to apply vegetable and mineral oils to the surface of the cavity. After demolding, oil residues remain on the surface of the demolded part. This is not always compatible with the end use of the product for example when the product is for food or medical use. The demolded part must then undergo cleaning operations before it can be used. These cleaning operations are often complex, sometimes impossible to implement and increase the cost of parts. Presentation of the invention

The object of the invention is to remedy these drawbacks by proposing a molding process favoring the demolding of the molded parts, to make the quality of the parts obtained more reliable, to guarantee the reproducibility of the molding and demolding operations, to reduce the cleaning times of the molds and to improve the production yields. For this purpose, the subject of the invention is a process for molding at least one part according to which at least one cavity of a mold is filled with a thermoplastic molding material, characterized in that before the filling of said cavity a film of water is formed by condensation on the surface of said cavity to separate said molding material and said cavity to facilitate demolding of said workpiece.

The process according to the invention may advantageously have the following particularities:

increasing the hygrometry of the air in contact with said surface of said cavity by vaporizing water to reach the dew point on the surface of said cavity;

to increase said hygrometry, water is sprayed above said cavity;

the temperature of the surface of said cavity is cooled to reach the dew point on the surface of said cavity;

to cool said cavity surface, circulating in said mold a coolant having a temperature lower than that of said cavity surface and adapted to remove the heat from said cavity surface;

at least one of the temperature and hygrometry parameters of the air in contact with said surface of said cavity is measured and said increase in air and / or said cooling is regulated as a function of said measurement;

using a mold having a fixed portion and a movable portion movable between an open position and a closed position in which said fixed and moving parts are in contact, and said condensation is caused in said open position. The invention also relates to a device for molding at least one part comprising a mold provided with at least one cavity adapted to receive a thermoplastic molding material, characterized in that it comprises condensation means able to cause a phenomenon condensing, on the surface of said cavity, to form a film of water for separating said molding material and said cavity to facilitate demolding of said piece.

The device according to the invention may advantageously have the following particularities:

the device comprises humidification means able to increase the hygrometry of the air in contact with said surface of said cavity by vaporizing water to reach the dew point on the surface of said cavity;

the device comprises cooling means able to cool the temperature of the surface of said cavity to reach the dew point on the surface of said cavity;

the device comprises measuring means able to perform the measurement of the temperature and hygrometry of the air in contact with said surface of said cavity, and moreover a control unit able to control at least one of said means humidification device and cooling means according to said measurement.

Brief description of the drawings

The present invention will be better understood and other advantages will appear on reading the detailed description of an embodiment taken by way of non-limiting example and illustrated by the appended drawings, in which:

Figures 1 and 2 are respectively partial schematic views of the device for molding at least one part according to the invention;

Figure 3 is a flowchart illustrating the steps of the molding method according to the invention. Description of the embodiment

With reference to FIGS. 1 and 2, the device 1 for molding at least one part according to the invention comprises a mold 2 formed of a fixed part 3 and a movable part 4 movable between an open position or a waiting position ( illustrated in FIG. 1), and a closed or working position (not shown) in which the fixed 3 and movable portions 4 are in contact with one another. The displacement of the mobile part 4 with respect to the fixed part 3 is for example obtained by translation as illustrated by the double arrow F of FIG. In the illustrated example, the fixed part 3 comprises a support 5 and an impression 6, secured to the support 5 and provided with a cavity 7 adapted to receive a molding material (not shown); the moving part 4 is flat. The molding material is thermoplastic. For example, a heated thermoplastic is used before being injected into the cavity 7 at a temperature of about 130 ° C. This thermoplastic is for example a material of EVA type (Ethylene Vinyl Acetate copolymer) without or with an additive such as for example progesterone, a material for which the molding process according to the invention is particularly well suited. In the closed position, the cavity 7 is said to be "closed" and can receive, via one or more conduits (not shown), the molten molding material. According to another embodiment not shown, the fixed part and the movable part are each provided with a cavity.

The mold 2 comprises cooling means 8, 9 for example in the form of circulation channels 8 (shown in dashed lines in Figure 2), able to allow the circulation of a cooled heat transfer fluid. This heat transfer fluid is for example water, oil or any other suitable coolant. In the illustrated example, the circulation channels 8 are provided on the fixed part 3 and intended only to cool the surface of the cavity 7. Other channels may also be provided on the movable part 4 to cool its flat surface. Traffic channels 8 are provided in or around the cavity 6 or in the support 5. They are connected, for example by means of hoses, to a cooling unit 9, able to cool the coolant and to circulate it in the channels 8 so as to obtain a temperature of the surface of the cavity 7 located between 0 and 6 ° C, and preferably about 4 ° C. According to another embodiment not shown, the cooling means comprise means for blowing cold air on the surface of the cavity or any other suitable means. The cooling of the mold goes against prejudices in the technical field of molding which, on the contrary, encourage heating of the mold to promote the distribution of the molding material in the cavity.

The device 1 for molding at least one part also comprises humidifying means 10, 1 1 for example in the form of one or more water spray nozzles 10 provided above the cavity 7 and coupled to a Humidification unit 1 1 able to supply the nozzles with water under pressure. These nozzles may also be mist-type. The spray nozzles 10 are intended to saturate the air in contact with the surface of the cavity 7 with moisture, the relative humidity then being at least 40%. The device 1 may also include any other type of suitable humidification means. The humidification of the air also goes against the prejudices in the technical field of molding which encourage on the contrary to avoid any presence of moisture to preserve the mold by avoiding for example that it does not rust and preserve the electrical installations necessary to molding operations.

The cooling means 8, 9 and the humidifying means 10, 1 1 form condensation means capable of causing a condensation phenomenon of water, on the surface of the cavity 7. This condensation of water is obtained when, by adjusting the temperature of the air and the surface of the cavity 7, the dew point is obtained on the surface of the cavity 7. The device 1 according to the invention thus makes it possible to create a film of water to the surface of the cavity 7. To regulate the temperature and humidity of the air, a control unit is used (no shown), connected to a probe 12 able to measure the temperature and humidity of the air in contact with the cavity 7 and to control the cooling unit 9 and the humidification unit 11. The device according to the invention may also comprise two separate probes, a probe dedicated to measuring the temperature, a probe dedicated to measuring the hygrometry of the air in contact with the cavity.

The molding process is described below with reference to FIG. 3. By means of the probe 12, the temperature and humidity of the air in contact with the cavity 7 are measured. According to this measurement, with the control unit, the condensation 21 is generated by controlling the cooling unit 9 and / or the humidifying unit 11 with which the temperature 22 of the surface of the cavity 7 is lowered respectively and increases the relative humidity 23 of the air in contact with the surface of the cavity 7. To increase the relative humidity 23, by means of the humidification unit 1 1 and the spray nozzles 10, one vaporizes the water above the cavity 7 until reaching a relative humidity of more than 40%. In order to reduce the temperature of the air, by means of the cooling unit 9 and the circulation channels 8, a coolant having a temperature lower than that of the cavity surface 7 is circulated in the mold 2. heat transfer fluid absorbs the calories of the cavity 7 and, circulating, evacuates them. Thus, the temperature of the surface of the cavity 7 gradually decreases to a temperature between 0 and 6 ° C, and preferably about 4 ° C. The pressure is substantially constant and corresponds to that of the place of use of the device 1 for molding. When the conditions of pressure, temperature and humidity are met, the dew point at which the water vapor in the air begins to condense is reached at the surface of the cavity 7. A film of water is then formed on the surface of the cavity 7. This film of water is for example in the form of a continuous film or a multitude of discontinuous droplets. During molding, the film of water interposes between the molding material and the surface of the cavity 7, thus reducing the adhesion between the molding material and the surface of the cavity 7. Then, the previously melted thermoplastic material 24 is poured into the cavity 7 which is allowed to cool 25. Then, the molding is demolded 26 . With the film of water, the demolding 26 can be achieved without any part of material remains attached to the surface of the cavity 7, without the need for cleaning the mold 2 in which there remain traces of tearing and without requiring the cleaning of the molded part obtained which does not have any residual release agent, such as oil, which could have been used.

Claims

1. A process for molding at least one part in which at least one cavity (7) of a mold (2) is filled with a thermoplastic molding material, characterized in that prior to filling said cavity (7), condensation form, on the surface of said cavity (7), a water film for separating said molding material and said cavity (7) to facilitate the demolding of said piece.

2. Molding method according to claim 1, characterized in that it increases the hygrometry of the air in contact with said surface of said cavity (7) by vaporizing water to reach the dew point at the surface of said cavity (7).

3. Molding method according to claim 2, characterized in that to increase said hygrometry, water is sprayed above said cavity (7).

4. Molding method according to one of the preceding claims, characterized in that the temperature of the surface of said cavity (7) is cooled to reach the dew point on the surface of said cavity (7).

5. Molding method according to claim 4, characterized in that for cooling said cavity surface (7) is circulated in said mold (2) a coolant having a temperature lower than that of said cavity surface (7) and able to evacuate the calories from said cavity surface (7).

6. Molding process according to claims 2 and 3, characterized in that at least one of the temperature and of hygrometry of the air in contact with said surface of said cavity (7) and that said increase in air and / or said cooling is regulated as a function of said measurement.

7. Molding method according to any one of the preceding claims, characterized in that one uses a mold (2) having a fixed part (3) and a movable part (4) movable between an open position and a closed position. wherein said fixed (3) and movable (4) parts are in contact, and in that said condensation is caused in said open position.

8. Device (1) for molding at least one part comprising a mold (2) provided with at least one cavity (7) adapted to receive a thermoplastic molding material, characterized in that it comprises condensation means (8). , 9, 10, 1 1) capable of causing a phenomenon of condensation, on the surface of said cavity (7), to form a film of water intended to separate said molding material and said cavity (7) to facilitate demolding of said room.

9. Device (1) according to claim 8, characterized in that it comprises humidification means (10, 1 1) adapted to increase the hygrometry of the air in contact with said surface of said cavity (7) by vaporizing water to reach the dew point on the surface of said cavity (7).

10. Device (1) according to at least one of claims 8 and 9, characterized in that it comprises cooling means (8, 9) able to cool the temperature of the surface of said cavity (7) to reach the dew point on the surface of said cavity (7).

1 1. Device (1) according to at least one of claims 9 and 10,

characterized in that it comprises measuring means (12) able to measure the temperature and hygrometry of the air in contact with said surface of said cavity (7), in that it further comprises a regulating unit able to control at least one of said means

humidification device (10, 1 1) and cooling means (8, 9) according to said measurement.