Hot molding method

Abstract

A method for hot molding an object is described, wherein a mold filled with material to be fired is closed and placed inside a firing chamber. The firing chamber is brought to a firing temperature, a cooling fluid is sent into the firing chamber to cool the mold, and the cooling fluid is evacuated from the firing chamber.

Description

[0001] HOT MOLDING METHOD

[0002] The invention refers to a method and apparatus for hot molding, which in particular are convenient for molding both an internal core and solid compound objects with the internal core and an external carbon shell.

[0003] It is known to produce cores with powdered material, see e.g. EP2697028, which are then covered with layers of carbon and put in an oven to create a compound piece. Each production step requires a specific workstation. The mold is placed in the first station, the powder is poured into it and the mold is closed. In the next station the powder goes into the oven for firing, in the next the molded core enters a chamber for cooling, in the final one the mold is opened and the core extracted.

[0004] The main object of the invention is to improve the state of the art, in particular to propose a different molding method with the aforementioned material and the apparatus for carrying it out.

[0005] Another object of the invention is a method and apparatus for molding quickly and with fewer intermediate steps.

[0006] Here we define by the term core an object obtained by molding - and made only of - material in powder form or in the form of microspheres or particles, in particular such as the one defined below.

[0007] A method is then proposed for hot molding of a core composed of powder material comprising - or consisting of - expanded particles and non-expanded particles, the particles being made of plastic material, closed in shape, hollow and filled with gas.

[0008] A method is then proposed for the hot molding of an object, wherein a mold filled of material to be fired is closed and placed inside a firing chamber, the firing chamber is brought to a firing temperature, a cooling fluid is sent into the firing chamber to cool the mold, the cooling fluid is evacuated from the firing chamber, and the mold is removed from the firing chamber and the object is removed from the mold.

[0009] Cooling serves to "stop" the firing and stabilize the shape of the molded object. Since heating and cooling occur without moving the mold, there are advantages in terms of production quality and repeatability of the molded parts, especially with carbon.

[0010] In a preferred variant, wherein the method is exploited to produce a core for use in a subsequent molding, the mold contains a core composed of powdered material comprising - or consisting of - expanded particles and unexpanded particles, the particles being made of plastic material, closed in shape, hollow and filled with gas.

[0011] In a preferred variant, wherein the method is exploited to produce a carbon object, the mold contains one or more layers of carbon laid on a solid core, preferably made according to the method defined here.

[0012] The method allows the carbon to be transformed without going through the classic autoclave and related ovens (inefficient and imprecise curing processes).

[0013] In a preferred variant, the mold contained in the firing chamber is cooled by placing it in contact with a cooling fluid or a flow of cooling fluid. In particular, the firing chamber is filled with the cooling fluid.

[0014] In a preferred variant, the cooling fluid is nitrogen, a very economical solution.

[0015] In a preferred variant, the cooling fluid is a liquid, e.g. water or oil.

[0016] In this case, the firing chamber is preferably sunk into the cooling liquid contained in a basin, and e.g. the basin is arranged in the proximity of the firing chamber, e.g. under the firing chamber. Preferably, said sinking occurs via a relative displacement between the firing chamber and the basin. In a preferred variant, the firing chamber is immersed into the basin by lowering the firing chamber towards the basin, or the basin is raised until it contains the firing chamber.

[0017] More preferably, the firing chamber is opened before contact with the cooling liquid.

[0018] In a preferred variant, the firing chamber is opened and / or closed by moving one of its walls to a position, respectively, in which it clears an opening towards the inside of the firing chamber or to a position in which it plugs such opening.

[0019] In a preferred variant, vacuum is created in the firing chamber before and / or during firing.

[0020] In a preferred variant, the mold comprises at least two shells, and the shells are mechanically pressed against each other inside the firing chamber before and / or during firing. This solves the problem of stabilizing 3D molds during firing: the shells must remain closed despite the internal pressure of the material.

[0021] In particular, vacuum is created in the firing chamber before mechanically pressing the shells against each other. This allows the carbon to be cured in a vacuum environment with the mold still open, therefore air is extracted very effectively unlike the autoclave process where vacuum is created with the mold closed.

[0022] In a more preferred variant, the shells generate heat (are heated) during firing to heat the material inside the mold.

[0023] In a preferred variant, the firing chamber and / or said shells are heated by three- dimensional induction heating.

[0024] Such heating is very fast, and economical because it uses less energy than an electric resistor. Furthermore, it can easily work even if immersed in a liquid.

[0025] Another aspect of the invention concerns a molding apparatus comprising:

[0026] - a firing chamber adapted to house (and in particular enclose) a mold and hot mold an object inside the mold,

[0027] - heating elements (preferably mounted inside the firing chamber) for bringing the firing chamber to a firing temperature, and

[0028] - means for delivering a cooling fluid into the firing chamber and evacuating the cooling fluid from the firing chamber.

[0029] In particular, said means for delivering comprise means for filling the firing chamber with the cooling fluid. Preferably the firing chamber is a watertight structure or comprises portions that can be coupled to each other to define a watertight firing chamber.

[0030] In a preferred variant, the cooling fluid is nitrogen, and the firing chamber comprises a nitrogen inlet and a nitrogen outlet. Preferably, said means for delivering and evacuating the fluid comprise a circuit for transporting nitrogen to and from the firing chamber and a pump for pushing the nitrogen into the circuit.

[0031] In a preferred variant, the cooling fluid is a liquid, e.g. water or oil. In this case, the apparatus comprises a basin of cooling liquid and means for sinking the firing chamber into the basin (e.g. actuators, pistons, or electric motors) performing relative motion between the firing chamber and the basin. In a more preferred variant, the firing chamber and the basin are movably connected to each other (e.g. via rigid guides and / or inextensible flexible elements) or unconstrained but relatively displaceable, so that the firing chamber can be lowered into the basin, or the basin can be raised to contain the firing chamber.

[0032] Preferably, the firing chamber has a closable structure, preferably hermetically.

[0033] In a preferred variant, the firing chamber comprises: an opening towards its interior and a wall movable between two positions (e.g. via actuators such as pistons or electric motors), the wall being configured to, respectively, clear or plug such opening.

[0034] In a preferred variant, the apparatus comprises means for creating vacuum in the firing chamber, e.g. a vacuum pump.

[0035] In a preferred variant, the mold comprises at least two shells, and the apparatus comprises movable elements mounted in the firing chamber that are displaceable to mechanically press the shells against each other to close the mold. More preferably, at least one of said movable elements is comprised in or constitutes a lower or upper rest support for the mold inside the firing chamber.

[0036] In a more preferred variant, the shells are provided with heating means for heating the material inside the mold. In a more preferred variant, the firing chamber and / or said shells comprise three-dimensional induction heating means, e.g. electrical conductors or cables.

[0037] Gas-filled plastic microspheres may be used as particles for the core. In particular, the powder material to be molded is preferably composed by weight of 10-70% of expanded microspheres and 90-30% of unexpanded microspheres, the microspheres being made of plastic material, closed in shape, hollow and filled with gas (flammable). These values guarantee advantageous performance and weight suitable for the applications, in particular excellent results of impact absorption and lightness. The expanded microspheres are essential to the invention, and act as a binder or filler for the other unexpanded particles. In fact, the expanded microspheres are the filling element and act as a binder, preventing the other expandable microspheres (not yet expanded), which are heavier, from falling due to gravity to the bottom of the mold and thickening. Instead, the expanded microspheres keep the expanding microspheres suspended throughout the material and in a uniform manner. This is why the presence of expanded and non-expanded microspheres guarantees the homogeneity of the density of the entire core, guaranteeing uniformity of mechanical performance.

[0038] The microspheres generally have a spherical shape and are very small (10-40 pm in diameter). Note, however, that the size is not essential.

[0039] The advantages of the invention will be even clearer from the following description of a preferred apparatus, wherein

[0040] • Fig. 1 shows a general scheme of a molding apparatus.

[0041] A molding apparatus 10 comprises a firing chamber 12 delimited by side walls 14, a ceiling 16, and a bottom 18. Two elements or platforms 20 are installed in the chamber 12 which extend substantially horizontally and are configured to receive a mold (not shown) in the space between them. The lower element 20 supports the mold from below, while the upper element 20 can block the mold from above. At least one of the elements 20 is vertically displaceable (see arrow F) relative to the other, e.g. via actuators 22, so as to create a sort of vice with which to block the mold. Preferably the actuators 22 are mounted on the ceiling 16 and / or are made with hydraulic pistons or electric motors.

[0042] This configuration of the apparatus 10 solves in particular a problem of 3D molds, which are formed of at least two opposing shells. When these 3D molds contain the expanding powder material during firing, they tend to separate because they are subjected to the pressure of the material. Instead the two elements 20 form a press that blocks the 3D mold parts in place.

[0043] The chamber 12 is kept suspended above its resting surface T by means of spacers 24, e.g. four arched or angular legs, two for each side of the chamber 12. Below the chamber 12 there is a basin 30, in use filled with cooling liquid (e.g. water or oil), which has an upper opening 32 of sufficient width to fit the bottom 18 therein and a height H sufficient to contain substantially the entire chamber 12.

[0044] An actuator 36 in the apparatus 10 is arranged to lift the basin 30 (see arrow F2) so that the chamber 12 is immersed in the liquid contained in the basin 30 (but for this purpose a manual movement is also possible).

[0045] Preferably the elements 20 are equipped with a three-dimensional induction heating system, in particular electric cables placed on the mold and / or on the elements 20.

[0046] The cables, when electrically powered, heat by induction the material forming the mold, e.g. steel. If e.g. the mold is made up of two shells that close along a common edge, the cables are arranged mainly or only above the shells, and then electrically powered during firing.

[0047] In a preferred variant, the apparatus 10 comprises a second cooling system in addition to the basin 30. For this purpose, the chamber 12 has an inlet 40 for refrigerant fluid and an outlet 42 for refrigerant fluid. The inlet 40 communicates with a source 46 of coolant fluid, e.g. nitrogen or water or oil.

[0048] A PLC or electronic unit 50 of the apparatus 10 is connected to the source 46 to control the injection of refrigerant fluid from the source 46 into the chamber 12. The electronic unit 50 allows e.g. to cool the mold according to a programmable temperature curve.

[0049] One of the side walls 14, indicated with 52 and drawn in dotted lines, is mounted movable with respect to the rest of the chamber 12 to hermetically open or close the chamber 12. In a preferred variant, the wall 52 is displaceable vertically, or it can be tilting or hinged to a part of the chamber 12 to move like a swing door. In a preferred variant, the wall 52 can be moved by an actuator 54 integrated in the apparatus 10, but manual or remote movement is also possible.

[0050] The wall 52 is moved to close and seal the chamber 12, or to open it and give access to its interior.

[0051] E.g. the wall 52 is moved to seal the chamber 12 before the injection of refrigerant fluid begins or to allow the formation of a vacuum in the chamber 12, e.g. via a vacuum pump (not shown). Instead, before mounting the mold between the elements 20, the wall 52 is displaced and moved away from the chamber 12 to give access to the inside of the chamber 12.

[0052] A preferred production method that can be accomplished with the apparatus 10 has these steps:

[0053] - a mold is filled with the powdered material necessary to form the desired core;

[0054] - the chamber 12 is opened, the mold thus filled is placed inside the chamber 12 between the elements 20, and the chamber 12 is closed by correspondingly moving the wall 52;

[0055] - the actuator 36 is activated and the elements 20 are brought closer clamping the mold between them;

[0056] - the heating of the chamber 20 is activated to heat the mold to the firing temperature for the necessary time;

[0057] - once firing is finished, before being removed the mold is cooled. For this purpose, the wall 52 is moved to open the chamber 12 and the basin 30 is raised, so that the liquid contained in the basin 30 invades the chamber 12 and cools the mold and the elements 20;

[0058] - the basin 30 is lowered again, and the liquid exits by gravity from the chamber 12 and falls back into the basin 30;

[0059] - the elements 20 are moved away to free the mold and the mold is taken out of the chamber 12,

[0060] - the mold is opened and the molded core is extracted.

[0061] The advantage offered by the apparatus 10 is evident. The cooling of the molded core takes place inside the chamber 12 immediately after firing, without moving the mould, which guarantees precision of the times and of the descending temperature ramps, as well as greatly shortening the productive cycle. The apparatus 10 is also very advantageous in a different process, which involves curing layers of carbon laid on the previously produced core. The core can then be eliminated from the obtained product, or not. To avoid bubbles in the molded carbon and to release excess resin from the mold, it is known to place the mold in an autoclave and create vacuum there. The vacuum in the autoclave occurs with the mold closed, which results in an ineffective extraction of air from the mold.

[0062] The apparatus 10 instead allows the carbon curing to be carried out in a vacuum environment with the mold open, i.e. first vacuum is created in the chamber 12 keeping the mold shells separate and then the mold is closed by pushing the elements 20 against the shells to press them together. Once the mold is closed, the carbon is cured by heating the inside of chamber 12 as indicated before. Once curing is finished, a postcure cooling phase follows, similar to that indicated before.

[0063] The advantage here too is that the cooling of the carbon piece takes place in the apparatus 10 immediately after firing, without moving the mould, which guarantees precision of times and descending temperature ramps, as well as greatly shortening the production cycle.

[0064] And above all, the process has the benefit of transforming the carbon without the classic use of an autoclave and the passage in the oven, all curing processes that are inefficient and imprecise.

[0065] An advantage of 3D induction heating is that it is very fast (about 5 minutes versus 2 hours for classic systems), and it is economical because it wastes less energy. Another advantage derives from the characteristic that 3D induction heating is fundamentally a technology with insulated conductors, which therefore can operate under water, while classic electrical resistors cannot (unless using very critical insulators given the temperatures involved). This characteristic is exploited in the apparatus 10 to cool the mold without moving it.

[0066] Overall, the apparatus 10 manages to guarantee high quality and high repeatability of the carbon pieces.

[0067] As a variant, the basin 30 can be stationary and the chamber 12 movable to be lowered into the basin 30.

[0068] Preferably the electronic unit 50 is connected to all the electrical and / or electromechanical parts of the apparatus 10 to automatically control all the functioning of the apparatus 10.

Claims

CLAIMS1 . Method for hot molding an object, wherein- a mold filled with material to be fired is closed and placed inside a firing chamber,- the firing chamber is brought to a firing temperature,- a cooling fluid is sent into the firing chamber to cool the mold,- the cooling fluid is evacuated from the firing chamber.

2. Method according to claim 1 , wherein a core is produced, thereby the mold contains a core composed of powder material comprising - or consisting of - expanded particles and unexpanded particles, the particles being of plastic material, closed in shape, hollow and filled with gas.

3. Method according to any preceding claim, wherein the mold contains one or more layers of carbon laid on a solid core obtained by molding powder material comprising - or consisting of - expanded particles and unexpanded particles, the particles being of plastic material, closed shape, hollow and filled with gas.

4. Method according to any preceding claim, wherein the firing chamber is filled with cooling fluid.

5. Method according to claim 4, wherein nitrogen is injected into the firing chamber.

6. Method according to claim 4 or 5, wherein the firing chamber is sunk into a cooling liquid contained in a basin arranged in proximity of the firing chamber.

7. Method according to any preceding claim, wherein the mold comprises at least two shells, and the shells are mechanically pressed against each other inside the firing chamber before and / or during the firing.

8. Method according to claim 7, wherein vacuum is created in the firing chamber before pressing the shells.

9. Method according to claim 7 or 8, wherein the shells generate heat during firing to heat the material inside the mold by three-dimensional induction heating.

10. Molding apparatus comprising:- a firing chamber adapted to house and enclose a mold, and to hot mold an object inside the mold,- heating elements for bringing the firing chamber to a firing temperature, and- means for delivering a cooling fluid into the firing chamber and evacuating the cooling fluid from the firing chamber.

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