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Title:
MOULDING OF CERAMIC MOULDING FORMS
Document Type and Number:
WIPO Patent Application WO/2001/090028
Kind Code:
A1
Abstract:
A method for making a ceramic moulding form (14'), e.g. for moulding or forming of composite materials, glasses or metals, comprising the following steps: force-mixing of a batch of ceramic powder (1) in the dry phase in a mixer (5) for even distribution of the powder components, to form a dry basis for a moulding mass (14); characterized by adding a water solution (2) containing a small amount of a water surface tension reducing agent (4) slowly into the powder (1) to form a batch of moulding mass (14) in the running force-mixer (5); adding reinforcing fibres (3) slowly and evenly into the batch of moulding mass (14) in the running force-mixer (5); transferring the batch of moulding mass (14) to a vacuum tob (7); extracting air by pumping vacuum in the vacuum tob (7)and transfering the vacuum tob (7) to a rolling bed (7c) for rotation for evacuation of entrapped air bubbles from the batch of moulding mass (14); and injecting the batch of moulding mass (14) into a mould form (11), leaving the moulding mass (14) to harden into a moulding form (14').

Inventors:
ANTONSEN GARD (NO)
HANSEN PAAL FRANCIS (NO)
Application Number:
PCT/NO2001/000219
Publication Date:
November 29, 2001
Filing Date:
May 25, 2001
Export Citation:
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Assignee:
HIFORM AS (NO)
ANTONSEN GARD (NO)
HANSEN PAAL FRANCIS (NO)
International Classes:
B22C1/00; B22C9/02; B28B7/34; B28B11/04; B28B11/24; B28B13/02; B28C1/08; (IPC1-7): C04B35/622; B22C1/00; B28B1/00; C04B35/76
Foreign References:
DE4037258A11991-05-29
US2893102A1959-07-07
US5238627A1993-08-24
DE19539270A11997-04-24
Other References:
DATABASE WPI Week 198718, Derwent World Patents Index; AN 1987-126226
DATABASE WPI Week 198651, Derwent World Patents Index; AN 1986-336083
Attorney, Agent or Firm:
Fluges, Patent (Postboks 214 Fredrikstad, NO)
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Claims:
Claims
1. A method for making a ceramic moulding form (14'), e. g. for moulding or forming of composite materials, glasses or metals, comprising the following steps: forcemixing of a batch of ceramic powder (1) in the dry phase in a mixer (5) for even distribution of the powder components, to form a dry basis for a moulding mass (14); characterized by adding less than 7% by weight of water (2) into the powder (1) to form a batch of moulding mass (14) in the running forcemixer (5); adding reinforcing fibres (3) into the batch of moulding mass (14) in the running forcemixer (5); transferring the batch of moulding mass (14) to a vacuum tob (7); extracting air by pumping vacuum in the vacuum tob (7) and transfering the vacuum tob (7) to a rolling bed (7c) for rotation for evacuation of entrapped air bubbles from the batch of moulding mass (14); and injecting the batch of moulding mass (14) into a mould form (11), leaving the moulding mass (14) to harden into a moulding form (14').
2. Method according to claim 1, the water (2) being a solution containing a small amount of a water surface tension reducing agent (4).
3. Method according to claim 1, the amount of water (2) being more than 5% and less than 6%.
4. Method according to claim 1, the amount of water being between 5.7% and 5.8%.
5. 5 Method according to claim 1, characterized by transferring the moulding mass (14) into a fillingtob (8) connected to the mould form (11).
6. Method according to claim 5, characterized in that the fillingtob (8) is vibrated, preferrably by a vibration bed (9) during transfer of the moulding mass from the vacuum tob (7) to the mould form (11). Method according to claim 1, characterized in that the mould form (11) is vibrated at least during the time from start of transfer of the moulding mass (14) into the mould form (11), and until the mould form (11) is partially or completely filled. Method according to claim 5, characterized in that a tob (7) containing a second or succeding batch of moulding mass (14), are inserted with the filling/pouring closure plunged into a previous batch (14) in the fillertob (8) and opened under the surface of the preceeding batch (14). Method according to claim 5, characterized in that the fillertob (8) and the connected mould form (11) is set under vacuum before and during transfer of moulding mass (14) from the tob (7) in order to avoid entrapping of air or other gases in the moulding mass (14). Method according to claim 1, characterized in leaving the moulding mass (14) to harden in the closed mould (11) for at least 24 hours, preferrably for at least 5 days. Method according to claim 1 or 9, characterized in heating the formed moulding mass (14') slowly to allow entrapped water or water vapour to escape, and then heating the formed moulding mass (14') to approximately 300 degrees Celsius to cure. lu. Method according to claim 10, characterized in heating the moulding mass (14') in steps. Method according to claim 1, characterized by the following steps: cleaning and degreasing of the surface hard mould (14') ; heating the mould (14') to approximately 80 degrees Celsius; application of liquid xylan or other PTFE or PFA or similar to a desired thickness, preferrably max. 80mu, onto the mould (14), to form a release layer or slip surface (15); heating the mould (14') with the release layer (15) to a flashoff temperature of approximately 130 degrees Celsius, and then to curing temperature of 280 degrees Celsius, and then cooling the mould slowly.
7. 19 A moulding form (14') for moulding or forming of composite materials, glasses or metals, made by the following steps: forcemixing of a batch of ceramic powder (1) and water (2), characterized by vacuumizing the batch of moulding mass (14) in a vacuum tob (7) before injecting the batch of moulding mass (14) into a mould form (11), leaving the moulding mass (14) to harden to a rigid moulding form (14') ; and removing the mould from the mould form (11). A mould according to claim 11, characterized by solving a small amount of a water surface tension reducing agent (4) to the water (2), forming a water solution (2). A mould according to claim 13, characterized by adding reinforcing fibres (3) into the mixer (5) during preparation of the batch of moulding mass (14). 't4. A mould according to claim 15, characterized in transfering the vacuum tob (7) to a rolling bed (7c) for rotation for evacuation of entrapped air bubbles from the batch of moulding mass (14) before injection into the mould form. t9. A mould according to claim 13, characterized in that the mould form (11) is set under vacuum at least before and preferrably during transfer of the moulding mass (14) from the tob (7). l. A mould according to claim 13, characterized by internal mould channels (16). DO. A mould according to claim 13, characterized by integrated electrical heater circuits (17). art. A mould according to claim 13, characterized by internal mould reinforcement metal bars (18). A mould according to claim 13, characterized by external support beams (19). A mould according to claim 13, characterized by a piston ejector (24) for releasing and ejecting the moulded, hardened product.
Description:
MOULDING OF CERAMIC MOULDING FORMS.

The present invention relates to moulding of ceramic moulding forms, hereafter called moulds, for use in moulding of composite materials like reinforced thermoplastic, and for thermoforming and metal cast moulding.

The known art.

An existing product from Elkem, a dry powder cement containing ceramic additives, is called CSA, or similar cements containing ceramic additives, and are sold in bulk and prepared for mixing with water and used for moulding of ceramic devices for high-temperature use, e. g. for molten metal. Such powder cements have the property of very little volume change during solidification which may be due to low water volume loss and the wide grain size distribution giving a well filled-in packing structure. The ceramic moulds thus formed are very temperature resistant and have a good structural integrity. Ceramic moulds are traditionally used for making transfer channels and coquille forms for raw aluminium or other metal bar moulding.

Plasma spraying is performed by mould formation by blowing a mixture of ceramic or metal powder through a flame nozzle, so-called plasma spraying, and thereby building up a ceramic or metallic layer of desired thickness against of a positive model of an object to be formed, and then removing the model, and is described in US-patents Disadvantages of the known art.

Entrapped air bubbles in the mould material incurs an uneven moulding surface. Such a surface is not suitable composite production of finer surfaces like interior parts for cars, thermal forming of glass, resin transfer moulding of boat hulls, and composite production using vacuumforming of commingled yarn of thermoplastic and reinforcing fibres, among several products having fine-structure surface.

Entrapped air bubbles also reduce the structural integrity of the mould, and gives an uneven temperature distribution of the mould and the layup during heating and cooling

cycles.

One way of getting around the problem of entrapped air bubbles is mould formation by plasma spraying mentioned above, building up a ceramic or metallic layer of desired thickness against a plug (a positive model of an object to be formed). However, often smooth surface structure of the plug or model may be neither thermally resistant to the hot plasma particles arriving at very high speeds from the flame nozzle, nor impact resistant due to the very high particle speeds.

One purpose of the invention is to make a thermally resistant mould having a desired even surface smoothnes or structure.

Another purpose of the invention is to make a thermally resistant mould being free of entrapped air, both internally and in the mould surface.

An additional purpose of the invention is to make moulds having a high wear and scratch resistance.

Another additional purpose is to make moulds having high thermal conductivity.

Another purpose of the invention is to make moulds which have a low thermal expansion coefficient.

Another purpose of the invention is to make a thermally resistant mould of improved surface smoothness and having a release layer.

Figure captions.

Fig. 1 illustrates the process according to the invention, from the mixing of basic materials, and further treatment of the mould material through various procedures.

In Fig. 2 in the right part of the same sheet, injecting of the liquid mould material into a mould is illustrated.

Fig. 3 illustrates a section of a. part of a moulding form according to the invention, illustrating supporting bars, a surface coating, and various vacuum, heating and cooling arrangements.

Fig. 4 illustrates a two-sided form acording to the invention forming a closed cavity, used in pressurized

matrix injection into a fiber reinforcing layer arranged between the moulding surfaces of the form.

Fig. 5 illustrates metal casting in a two-sided mould, and an ejection piston for releasing the product.

Fig. 6 illustrates two-sided pressure moulding using a piston for forming the material into the desired shape.

Fig. 7 illustrates thermoforming using a mould according to the invention using heat and vacuum to draw a sheet, e. g. of glass, into the desired 2-D or 3-D shape.

Short summary of the invention.

One solution to several of the above mentioned problems, and fulfilling several of the given purposes, is a method for making a ceramic moulding form, e. g. for moulding or forming of composite materials, glasses or metals, comprising the following steps: force-mixing of a batch of ceramic powder in the dry phase in a mixer for even distribution of the powder components, to form a dry basis for a moulding mass; adding less than 7% of weight of water into the powder to form a batch of moulding mass in the force-mixer; adding reinforcing fibres into the batch of moulding mass in the force-mixer; transferring the batch of moulding mass to a vacuum tob; extracting air by pumping vacuum in the vacuum tob and transfering the vacuum tob to a rolling bed for rotation for evacuation of entrapped air bubbles from the batch of moulding mass; and finally filling the batch of moulding mass into a mould form, leaving the moulding mass to harden to become a moulding form.

In an advantageous embodiment of the invention the water added is a solution containing a small amount of a water surface tension reducing agent, the water solution being added slowly into the force-mixer.

One embodiment according to the invention is a moulding form for moulding or forming of composite materials, glasses or metals, made by the following steps: force-mixing of a batch of ceramic powder and less than

7% by weight of water; and vacuumizing the batch of moulding mass in a vacuum tob before injecting the batch of moulding mass into a mould form, leaving the moulding mass to harden to a rigid mould; and removing the mould from the mould form.

Detailed description of preferred embodiments of the invention.

PROCEDURE FOR MOULD MATERIAL PREPARATION.

Some or all of the following tools and materials are needed: A vibrator bed 12 for a mould form 11 and its plug.

A vibration bed 9 for a filling-tob 8 Ceramic cement powder 1, preferrably of the trade name CSA, by Elkem, or a similar cement containing ceramic additives.

An existing product from Elkem, a dry powder cement containing ceramic additives, is called CSA, or similar cements containing ceramic additives, and are sold in bulk and prepared for mixing with water and normally used for moulding of devices for high temperature use, e. g. for molten metal. Such powder cements have the property of very little volume change during solidification which may be due to low water volume loss and the wide grain size distribution giving a well filled-in packing structure. The ceramic moulds thus formed are very temperature resistant and have a good structural integrity.

Reinforcing fibres 3, preferably about 4-6%, and most preferably 5% of the ceramic powder mass.

Water 2, preferably less than 7% by weight. The exact amount of water added to the ceramic powder mass 1 to form a moulding mass 14 may be very critical in order to obtain a sufficient quality of the ceramic mould produced, both with respect to structural strength and surface smoothness. In a preferred embodiment of the invention, the amount of water is between 5% and 6% by weight, preferrably more or equal to 5.3%, and most preferrably between 5.7% and 5.8%.

A water surface tension reducing agent 4, preferrably a dishwashing detergent, to an amount of about 1 drop per

litre of water 2. Successful test production has been conducted using a water surface tension reducing agent such as found in dishwashing detergent sold under the trade name "Zalo"in Norway, but other surface tension reducing agents may serve the purpose equally well.

A flow improving material may be added to the moulding mass 14 if necessary to ease the flow into the mould form 11.

A force-mixer 5 for mixing the moulding mass 14.

A filling tob 8.

One or more vacuum tobs 7.

For preparation of a batch of moulding material 14, a preferred procedure according to the invention is as follows: Pour ceramic powder 1 in a batch into the force-mixer 5, letting it mix the powder 1 for about 2 minutes assuring even distribution of the dry powder 1. Add water 2, preferrably with the tension reducing agent 4 slowly into the force-mixer 5 and let it run for 6 minutes, and check for a consistence for good mix and good flow properties for the moulding mass 14. Add reinforcing fibres 3 slowly and evenly into the force-mixer 5, avoiding the fibres 3 to lump into fibre balls. Mix the moulding material 14 and the reinforcing fibres for approximately 4 minutes. All mixing times may depend on the total amount of the batch of moulding materials 14, generally increasing with increasing batch mas and also increasing with reduced force-mixer capacity. The batch of moulding mass 14 is then released to a vacuum tob 7 and the vacuum tob 7 is transferred to a rolling bed 7c for slow rotation. The vacuum tob 7 is then evacuated for full evacuation of entrapped air bubbles in the mould material 14.40-50% of the tob's 7 volume may be left empty. One may leave the vacuum pump running until a vacuum gauge does not drop when the pump is shut-off for testing. The vacuum tob 7 should keep the vacuum level for at least 5 minutes at minimum 0,9 bar below athmospheric pressure. When properly sealed, the tob 7 is transferred to a rolling bed 7c assuring the fibre distribution in the material, as well as releasing all entrapped air bubbles from the mould material. The vacuum tob 7 is rolled for 5-

10 minutes at approx. 6-8 rpm. The vacuum tob is then transferred directly to the filling-tob 8, preferably placed on a vibration bed 9. The vibration bed 9 may be operating at the same frequency as a mould vibration bed 12. The first vacuum tob 7 is put into an empty filling-tob for transferring the moulding mass 14 in case of being the first batch. Several succeding tobs 7 may be prepared with batches of moulding material 14. Each succeding tob should be emptied carefully with the opening mechanism plunged into the previous batch. According to another embodiment of the invention, the filling-tob 8 and a transfer pipe 10 to the mould form 11 may be set under vacuum before transfer of the batch of moulding mass 14 from the vacuum tob 7 to the mould form 11. The entire mould form may be set under vacuum. The speed of flow from the filling-tob 8, through the mould filling system and into the mould has to be adjusted such that the filling-tob never run out of mould material, thus avoiding air entrapment. The filling-tob is transferring the mould material through a preferably wide guiding tube 10, allowing flow control of the material, which is used to adjust the filling speed. No air is to be entrapped during the filling mode. At start of the mould filling process, the vibration frequency should be low (4 Hz). One may gradually increase the frequency as the mould is filled, however the frequency should never be increased to the point where small vortexes are created in the boundary between the filler-tob and the mould material.

PROCEDURE FOR MOULD MAKING For producing a moulding form 14'according to the invention in a two-sided mould form 11, the following materials and tools are required according to a prefered embodiment of the invention: A mould form 11 and corresponding plug.

A tube insert for temperature gauge Inserts tubes 16 for heat/cooling to be arranged in the mould form 11, to be integrated in the moulding mass 14.

Insert wires 17 for integrated electrical heating of the produced ceramic moulding form 14'.

Insert material 16'may be wax bars or similar arranged for melting out, for channel making.

Mould reinforcing bar inserts 18 of metal and stabilisers or supports 19 may also be arranged inside the moulding form 11.

For producing a moulding form 14'according to the invention, assemble the two-sided mould 11 dimensioned to withstand the pressure from the fluid concrete/moulding mass 14, and preferably attached the form 11 to a vibration bed 12. Position insert elements like tubes 16, channel forming materials 16', wires 17, fasteners, reinforcing bars 18 and tube for temperature gauge etc, according to the later use of the produced mould. Preferably inserts may be provided with coating to prevent mould cracking due to material expansion. Select a convenient point for the filling of the mould material 14 in order to get an even filling mode, e. g. near the bow of a boat hull mould to be formed. The area from the filling tube 10 and further into the mould 11 should be increasing, reducing the risk of pressure buildup while filling. Vacuum suction, e. g. from the top of the mould form 11 before and during transfer from the vacuum tob 7 or the filler-tob 8. The mould form 11 may be injected from the lower part of the mould form 11.

At the beginning of the mould filling process, the vibration frequency of the supporting vibrator 12 should set low. In one test run, a frequency of 4 Hz was found to prevent separation of reinforcement fibres and cement matrix, and to assure form filling. A gradual increase of the frequency as the mould is filled may be advantageous.

However the frequency should never be increased to the point where small vortexes are created in the boundary between the mould and the mould material, which indicates the start of a separation phase. Separation will damage the structure of the mould and reduce mould strucure strength and finish.

Vibrate until the mould is filled. Ensure that no air bubbles are coming out of the mould material in case filling takes place without vacuum. Excessive vibration is not recommended as the reinforcing fibres and larger fragments in the mould material may start to sediment.

At the end of the filling and vibration phase, all open areas are covered with plastic, reducing the evaporation from the mould and preventing undesired drying-out of the surface. The moulding mass has then to be hardened by letting it rest for approximately three to seven days in a cool place before de-moulding, i. e. removing the hardened ceramic form 14'from the mould form 11.

PROCEDURE FOR MOULD HEAT TREATMENT.

For heat treatment of the moulded and hardened moulding form formed in the above mentioned processes, an oven or an in-mould integrated heat system is required, with a maximum temperature reaching at least 300C, and preferrably arranged for temperature ramping. It is essential that the moulding form 14'formed from the moulding mass 14 be dried at a low temperature, e. g. room temperature, for a minimum required period of time as described above. If needed, the mould 14' is placed on a heat resistant support system, and positioned in the oven for heat treatment. In a preferred embodiment of the invention, the oven is programmed in accordance to a heat treatment program specific for each mould application and thickness. The heat cycle will typically have 3-6 steps. It is important to have a good temperature control and good thermal distribution in the oven. The temperature sensors are connected to a control panel/PC in order to monitor heat propagation through the mould 14'. To conduct the heat treatment, start the heating and check that the programming of the heat ramping is correctly set, and that the maximum temperature is corresponding to the mould application. An uncontrolled increase in temperature may result in severe damage to the mould 14'and to the environment, e. g. due to a sudden release of entrapped water vapour from the mould 14'. The same danger is possible if the mould is not heat-treated to a sufficiently high temperature compared to the application. In case of an interrupted heating cycle, the mould 14'can be heated rapidly up to the temperature where the heat treatment was terminated and proceed from that temperature. In case of a termination of a hold sequence, the entire period has to be

repeated.

PROCEDURE FOR APPLICATION OF A PERMANENT MOULD RELEASE SURFACE.

A coating instruction for the mould release system follows. Some tools and raw materials required are listed below.

Heat-treated mould component 14'.

A pure solvent for degreasing.

Fluid xylan or other PTFE or PFA or similar coating Spray equipment Oven (settings preferably at 80C, 130C and 280C).

Cloth.

The prefabricated and heat-treated moulding form 14'is checked for dirt-spots and should be totally cleaned and degreased. The oven and mould are preheated, preferably to 80C for coating. The mould 14'is then taken to a flash-off temperature at 130C, and after the flash-off taken directly to curing temperature of 280C. The mould 14'is preheated to coating temperature. The Xylan or other PTFE or PFA or similar has to be well shear mixed and pored into the spray- cup. Application to specified thickness onto mould (max.

80m) in one layer, resulting in almost full colour coverage.

Inspect for satisfactory coverage of the release coating before proceeding. The mould 14'is heated to 130C with a temperature hold of 5-10 minutes, and then taken to cure temperature of 280C for 15 minutes. Cool the mould 14' slowly until approx. 100C and inspect release coating for failures.

Repair: Repairing possibilities of the permanent release system are limited, but possible. Scrape away the coating on the damaged area. Grain down with very fine paper (1500) the boundary area of the defect, obtaining an even crossover.

Clean the area well for debris and dust, degrease and perform the steps as indicated above. Avoid keeping the mould at cure temperature for longer time than strictly

needed.

Description of preferred embodiments.

Fig. 3 illustrates a moulding form 14'produced according to the embodiment for moulding or forming of composite materials, glasses or metals, made by force-mixing of a batch of ceramic powder 1 and water 2, by vacuumizing the batch of moulding mass 14 in a vacuum tob 7 before injecting the batch of moulding mass 14 into a mould form 11, leaving the moulding mass 14 to harden to a rigid mould 14'; and removing the mould from the mould form 11.

A moulding form produced according to the invention is characterized in that a solving a small amount of a water surface tension reducing agent 4 was added to the water 2 for preparing a water solution 2. Then reinforcing fibres 3 have been added into the mixer 5 during preparation of the batch of moulding mass 14, before transfering the vacuum tob 7 to a rolling bed 7c for rotation for evacuation of entrapped air bubbles from the batch of moulding mass 14 before injection into the mould form.

In one possible embodiment of the invention, the mould form 11 is set under vacuum at least before and preferrably during transfer of the moulding mass 14 from the tob 7.

As shown in fig 3, internal mould channels 16 formed from pipes or wax lines (to be melted out) may be integrated in the cavity of the moulding form 11 before filling with the moulding mass 14. These channels 16 may be used for heating or cooling fluids. For heating, both for hardening of the moulding mass 14 and later for ordinary production moulding, electrical heater circuits 17 may be arranged in the moulding form 11, in order to integrate in the moulding mass 14 before hardening. Internal mould reinforcement metal bars 18 and external support beams 19 may advantageously be arranged.

Fig. 4 illustrates production RTM injection of matrix into fiber reinforcement in the hardened form 14'.

A piston ejector 24 may be arranged for releasing and ejecting the moulded, hardened product, as illustrated in

fig. 5, here metal moulding.

Fig. 6 illustrates press-moulding from a plate 31 of metal, thermoplastic, or armed composite material by using a positive shaped mould piston 26 formed in ceramite according to the invention, or made in silicon, tree, or metal arranged on a cylinder 25, against a negative (or oppositely) shaped form 14 formed according to the invention.

Fig. 7 illustrates thermoforming of e. g. a plate 28 of glass, plastic or similar heated by means of an infrared heating device 29 or equivalent, and formed by a piston 14' formed according to the invention. Vacuum channels 30 draw the plate 28 to the desired shape on the piston form 14'.

List of reference numerals: 1 : ceramic mass (dry) 2 : water fibre 4 : water surface tension reducing agent, additive 5 : force mixer 6 : mixer outlet 7a: vacuum tob (illustrated during filling) 7b: vacuum tob (illustrated during rotation, vacuumized) 8: filler tob 9: vibrating support for filler tob 8b, 10: injection pipe 11 : mould forming tool (plug and/or mould form) 12: vibrating support for mould form.

13: vacuum pump 14: mixed, prepared moulding mass, later to become: 14': hardened mould 15: mould surface layer (release means, glazing, slip surface) 16 : internal mould channels 17 : electrical heater circuits 18 : internal mould reinforcement bars 19 : mould support bars 20 : internal channel for sensors in the form.

21 : procuct cavity/room for injection materials 22 : injection pump 23 : cavity for smelted metal 24 : ejector for moulded, hardened product 25 : press cylinder 26 : mould piston (for e. g. silicon, wood, metal, ceramic mass) 27: retaining formwork for press form 28: plastic material or glass plate or other material with plastic properties like glass 29: infrared heating device 30: vacuum channels