METHOD AND PRESS FOR THE MANUFACTURE OF SHELL-FORMED OBJECTS

Abstract: To obtain the possibility of manufacturing shell-formed objects of plastic material even reinforced, in such a way that no particular ventilation of the working space is required, it is suggested that a well prepared closed formation room (5) formed by a male mould (4) and a female mould (3) is applied into a press (1) and encased in a mould cassette (2) comprising said male and female moulds (4, 3) and then that the plastic material introduced into the formation room (5) is subjected to a necessary pressure either by pressurizing a press body (12) being a part of the press and having a form corresponding to one side of the mould cassette in order to press out the plastic material supplied into the formation room (5) before application of the mould cassette into the press (1) by compressing the mould cassette to a predetermined form against a second press body (7) being a part of the press and having a form corresponding to the second side of the mould cassette, or by injecting the plastic material under pressure into the formation room (5) of the mould cassette (2) being determined as to its form by said press bodies (7, 12) of the pressurized press.

Description: This invention relates to a method of manufacturing shell- formed objects of plastic material in a closed mould and to a press for carrying out the method. Manufacture of big objects regarding the area of plastic material like for instance details of coach bodies, tanks, bodies of boats and canoes, pulkers and so on has until now as a rule been made in a manual way in open moulds. In this connection a plastic material reinforced by fibres and particularly a polyester plastic reinforced by glass fibres. The fibre reinfor- cement and the plastic materials are applicated in layers in the open mould, the plastic being pressed into the fibre reinforce¬ ment by means of a tools for instance a pressure roll for wetting the fibre reinforcement through and for removing all air that can- be enclosed in each layer being under formation. Regarding the reinforcement in the form of cut reinforcement fibres the plastic material together with the reinforcement fibres can be sprayed with high pressure directly on the mould until a layer with xeguired thickness is.achieved. The use of such open moulds for manufacturing objects of plastic material, however, results in great working environmen problems and health risks due to the fact that unhealthy substances for instance styrene when using polyester plastics are co ing free during the hardening process and are allowed to mix with the air in the working room, and therefore high demands are made on the ventilation of such rooms. This results in great expenses not only for the ventilation plant as such but also for the heating of the room due to the high air exchange that a necessary ventilation gives rise to. These drawbacks can be avoided by manufacturing plastic objects in quite closed moulds from which unhealthy gases easily and effectively can be sucked out so that the air in the working room is not influenced and becomes polluted. Such closed- moulds as a rule comprise female mould and male mould which brought together to one unit between themselves creates a ormation room for forming the object that is to be formed. In this connection the plastic material is supplied to the female mould by being poured into the same and is then subjected to compression moulding pressure in connection with the application of the male mould onto the female mould. It is also possible to press the plastic material into the closed mould under pressure or to suck the plastic material into the formation room of the mould. When forming shell-formed objects in closed moulds high pressures relatively spoken are required and this fact puts very high demands upon the stability of the mould and upon the surface fineness of the formations surfaces of the mould and for that reason this type of moulds has had to be made of steel. Such steel moulds, however, are complicated to manufacture and due to that fact become too expansive to be able to be used when manufacturing objects in less number or- when manufacturing very big objects like for instance bodies of boats, canoes or dinghies, details of coach body, tanks or similar things. Furthermore, lately there have been developed closed moulds for manufacturing shell-formed products having the form of formation bodies put together and each comprising a supporting portion having a surface with a form corresponding to the object that shall be formed and a formation shell detachably applied to this surface and of a material with a surface with high fineness serving as a formation surface. It is especially this type of moulds that are intended to be used in the method according to this invention the main purpose of which is to bring about a method for a rational manufacture- of also big objects regarding the surface of reinforced plastic and which has no one of the previously mentioned drawbacks of the working method but shall be able to be practiced in working rooms without needing any particular ventilation and which besides that shall make possible an essential reduction of the necessary pressure time and despite this fact give the objects a high quality and surface fineness. This is achieved in accordance with the present invention by the fact that ' the method has the characterizing features mentioned in the claims. A further purpose with the invention is to bring about a press for carrying out the method according to this invention. In the following the present invention is describing more closely with reference to the accompanying drawings illustrating the invention schematically and in which fig 1 shows a cross section through an opened press according to the invention for manufacturing shell-formed objects of plastic; figs 2 and 3 showing cross section in cassette wagon and together illustrate the preparation of a cassette functioning as a mould; fig 4 shows the insertion of a prepared mould cassette into the press; fig 5 shows in cross section the press with the inserted mould cassette in closed position and without compression moulding pressure; fig shows in cross section the press provided with mould cassettes pressurized; fig 7 shows in cross section a press for carrying out an alternative performance of the method according to the invention and figs 8 and 9 illustrate the manufacture of a lower part and upper part respectively, of the cassette of the press. It is presumed that in the embodiments of the present invention shown in the drawings objects in the form of an elongated in cross section essentially U-formed shell shall be manufactured for instance the one half of a canoe embody of the reinforced plastic material. I accordance with the invention the manufacture is made in a press 1 with the use of a cassette 2 as a mould, which mould cassette 2 comprises a lower part 3 (the female mould) and an upper part 4 (the male mould) and a closed formation room 5 between the lower part 3 and the upper part 4 of the mould cassette corresponding to the intended shell-form. The press 1 according to the invention is very simple regarding its construction and comprises a stand 6 carrying a form stable cassette support 7 having a relatively big mass and with a smooth top side 8 which regarding its form corresponds to or is in accordance with the under-side 9 of the lower part of the cassette and which is designed as a seat for the mould cassette 2. At a distance from the top side 8 of the cassette support there are channels 1-0 for a circulating heat medium, for instance warm water, electrical conductors or similar arranged for heating the cassette support 7 to intended temperature. At the stand 6 there is pivoted a top piece 11 carrying a form stable cassette counterstay 12 which is limitedly movable and has a big mass and a smooth side 13 which regarding its form corresponds to or is in accordance with the outer side 14 of the upper part of the cassette and which impressing position comprises the under-side of the cassette counterstay. Also the cassette counterstay 12 is at a distance from its side 13 provided with channels 10 for a circulating heating medium, for instance warm water, electrical heating conductors or similar for heating the counterstay 12 to intended temperature. The cassette support 7 of the press as well as the cassette counterstay 12 of the press may consist of an inexpensive material suitable for casting, for instance concrete, and may be formed by casting, the intende ' d mould cassette being used as a mould for giving the surfaces 8 and 18 facing each other in the pressing position of the press the intended form. The cassette counterstay 12 of the press is limitedly movably connected to the top piece 11 by carrying means 15 fixedly arranged in the counterstay which means 15 is connected with pneumatic or hydraulic loosening means 16 which allows the mentioned limited movability for the counterstay 12 in relation to the top piece 11 of the press and which is arranged on cross bars 17 of longitudinal supporting bars 18 connected with the top piece 11 and together with the top piece 11 carrying a pressure plate 19. Between this one and the cassette counterstay 12 of the press there are arranged press means 20, each means preferably being positioned right in front of its supporting bar 17, which means are shown in the form of pressure tubes closed at their ends and with a connection not closely shown in the drawings to a pressure medium source for receiving necessary compression moulding pressure .by insertion of a pressure medium under pressure in the pressure tubes functioning as press means 20. For instance water can be used as a pressure medium as well as air. If pressure tubes are used as press means 20 it is suitable to have the pressure tubes somewhat longer than the cassette counterstay 12 so that the ends of the pressure tubes are outside the cassette counterstay 12 and to close the ends of the pressure tubes by means of strong end pieces which are mutually connected by means of a not extensible wire 21 for taking up the axial compressive forces. In. accordance with the method according to this invention preparation of the mould cassette 2 in a well ventilated spraying box separated from the working room as to the rest takes place as a first step. For preparation of the mould cassette there is used a cassette wagon 22 onto which the lower part 3 of the mould cassette is applied and which is then inserted into the spraying box where the waxed formation surfaces 23 of the lower part of the cassette are provided with a thin layer of gelcote, where¬ after the lower part 3 of the cassette may stand quite open in the spraying box for after hardening of the applied gelcote layer. Thus, this applied gelcote layer will form the outer surface of the object that is to be produced. After the solidification of the the gelcote layer necessary reinforcement 24 in the form of cut or preformed glass fibre and other reinforcements are applied into the lower part 3 of the cassette and/or upper part 4 of the cassette outside the spraying box. When the reinforcement 24 is in place the plastic material 25 is supplied in necessary quantity to the lower part 3 of the cassette and after that the upper part of the cassette waxed on its inside is applied onto the lower part 3 of the cassette as is apparent from fig 3. By so doing the mould cassette is made in order and ready for being lifted into the press 1 which can be made by means of a lifting yoke 26 as is shown in fig 4. At least regarding objects which for their formation require long flow ways for the plastic and therefore great press forces there are suitably arranged gaskets between the flange portions 27 of the lower and upper parts of.the cassette as is indicated at 28 in fig 3. When the mould cassette 2 has been lowered into the cassette support 7 of the press which support is heated to intended temperature, for instance 30-60°C, preferably 40-50°C, the top piece 11 of the press is pivoted by means of hydraulic or pneumatic cylinders not closely shown to closed position which is shown in fig 5 and in which position the top piece 11 is locked to the stand 6 of the press. In this position the loosening means 16 is disconnected in that way that the cassette counterstay 12 is allowed to move in relation to the top piece 11 in order to be placed against the mould cassette 2 applied into the press 1. In this connection the cassette counterstay 12 has the same temperature as the cassette support 7, for instance 30-60°C. This closed position of the press is shown in fig 5 without compres¬ sion moulding pressure applied. Having the plastic being brought into the mould cassette 2 already when it is inserted into the press 1 pressing with increasing pressure takes place by the fact that pressure medium is introduced into the pressure tubes 20 which are brought to press the cassette counterstay 12 against the mould cassette 2 supported by the cassette support 7 until intended compression moulding pressure has been achieved, whereby the plastic in the formation room 5 is brought to flow out and completely fill the formation room 5. In this connection the formation room 5 of the mould cassette is not given any possibility to change its form due to the form resistant support 7 and counterstay 12 of the press. Necessary compression moulding pressure can vary in dependence on size and form of the object that is to be manu¬ factured but by means of the press means 20 shown in the form of pressure tubes very large press forces can be achieved which gurantee that the plastic is brought to flow out in the intended way and fill the formation room completely even having very big objects regarding the area. When inserting the preparated mould cassette 2 into the press 1, especially if there are long flow ways for the plastic, it ought not to have higher temperature than 17-22°C, i e about room temperature, in order to delay the solidification of the plastic material so that this is given necessary time and by that possibility to flow out and completely fill the formation room 5 before it becomes to viscous. As far as the prepared mould cassette 2 is inserted into the press and pressurized it begins to be heated from the outside by the heated cassette support 7 and cassette counterstay 12 of the press. The time it takes for the heat from the support and the counterstay to penetrate the mould cassette 2 to the plastic material, which is flowing out, and begin influence this partly depends on the intial temperature difference between the cassette support and the cassette counterstay and inserted mould cassette, partly on the wall thickness of the mould cassette. By adapting these factors to the length of flow way of the plastic, that is to the form and the extension of the object and by that the formation room, always necessary time is achieved for making it possible for the plastic material to flow out before it becomes viscous and at last solidifies owing to raised temperature. When forming objects with big areas mould cassettes with great wall thickness and with a low entrance temperature are used while when forming small objects regarding the area mould cassettes are. used which may- have a relatively high entrance temperature and relatively thin walls. The time that the mould cassette 2 needs to be in the press 1 under pressure is accordingly determined by the mentioned temperature difference and by the thickness of the cassette walls, and when the temperature has been achieved at which the hardening starts and develops heat itself, that is in the exotermic point of the exotermic graph of the plastic, the mould cassette 2 takes out of the press after that the press means 20 having been brought to release the pressure and the loosening means 16 have been connected in order to lift up the cassette counterstay 12 of the press from the cassette. Thereafter the top piece 11 is loosened from the stand 6 in order to be brought to open position, whereafter the warm mould cassette 2 is lifted up from the press and is lowered to a cassette wagon 22 on which after hardening can take place until the plastic is completely harded through thanks to the fact that necessary heat is stored so to say in the mould cassette. At the same time as a mould cassette is lifted from the press 1 the next preparated cassette may be inserted into the press for pressing in the previously described way and by using mould cassettes in accordance with the present invention a very rational and quick manufacture of objects is achieved and also of very big objects regarding the area. Since the heat is lifted so to say out of the press with the mould cassette the press does not need to be cooled as is the case in known technique in order to remove the additional heat achieved during the hardening course. Thus, in accordance with the present invention the after hardening takes place freely from the press itself and when the hardening is completed the upper part 4 of the cassette is lifted 70 and the formed object can be taken out of the cassette 2 for being given a high polish, thereafter cassette treatment is made by cleaning and rewaxing the surfaces whereafter the cassette is again ready to be used and to be provided with a layer gelcote in previously described way. In fig 7 is illustrated an alternative performance of the method according to the present invention differing from the previously described method by the fact that the plastic material is sprayed under pressure by means of a spraying equipment 30 into the cassette mould 2 arranged in the press, which can be mentioned flowing pressing in contrast to the previously described method which can be characterized as wet pressing. When spraying the plastic material into the mould cassette with pressure, full compression moulding pressure is applied to the press which in this connection with its parts 6 and 12 functions as a counterstay. When using wet pressing, that is with the plastic introduced without spraying, the pressing is made as has been previously described with an increasing compression moulding pressure. In figs 8 and 9 is illustrated how the present press in a simple way can be utilized for manufacturing the lower part 3 and the upper part 4 respectively, of the cassette. For manufacturing a lower part 3 of the cassette the surfaces 8 of the press support 6 after having been waxed are provided with a layer 31 of glass fibre and wet plastic in a quantity giving the lower part of the cassette intended thickness. On this layer 31 there is then applied a premanufactured lower part 32 of the cassette having a reduced thickness and on this -lower part there is then arranged an upper part 4 of the cassette provided with a master object 33 determining the form of the formation room 5 of the mould cassette. Thereafter the press 1 is closed and necessary compression moulding pressure is established for forming the lower part of the cassette, the premanufactured lower part 32 of the cassette with the reduced thickness being intimately united with a layer 31 of the glass fiber reinforcement and the wet plastic in connection with the hardening of the plastic. The manufacture of an upper part 4 of the cassette in the press is illustrated in fig 9. In this connection there is arranged a lower part 3 of the cassette in the support 6 of the press and in intended position on this lower part of the cassette is the master object 33 placed. Thereafter a premanufactured upper part 35 of the cassette is applied with reduced thickness and onto the surface 13 of the cassette counterstay 12 of the press there is put a surface 36 of glass fibre and wet plastic in a quantity giving the final upper part of the cassette 4 intended thickness. Thereafter the press is closed and the compression moulding pressure is established for forming the upper part of the cassette which is made in the same way as for the lower part of the cassette. This invention is not limited to the what have been described above and shown in the drawings but can be changed and modified in many different ways within in the scope of the invention idea defined in the claims. Thus, the present inven- tion is also usable without supplying heat by instead providing the plastic material with a cold hardener which speeds up the hardening of the plastic material at room temperature and in certain cases it is also possible to let the mould cassette remain in the press until the plastic material is completely depth-hardened. In those cases the outer surface of the manu- factured object shall be painted the gelcote layer is excluded and instead a so called ' surface mat is applied.

Claims: CLAIMS: 1. Method for manufacturing shell-formed objects of plastic material, large as well as small regarding the area, preferably reinforced, in a closed formation room in which the plastic material under pressure is brought to flow out to completely fill out the same, c h a r a c t e r i z e d in that the closed formation room (5) which is formed by applying a male mould (4) onto a female mould (3), is applied into a press (1) and closed in a mould cassette (2) comprising the mentioned moulds (3,4) after that the formation room (5) has been prepared at least in order to prevent the plastic material from fastening to the formation surfaces of the formation room and possible having been provided with necessary reinforcement material and insertions, and that first thereafter the plastic material introduced into the formation room (5) is subjected to necessary pressure either by pressurizing a press body (12) being a part of the press and having a form corresponding to one side of the mould cassette in order to press out the plastic material supplied to the formation room (5) before application of the mould cassette into the press (1) by pressing the mould cassette (2) together to a previously determined form against a second press body (7) being a part of the press and having a form corresponding to the second side of the mould cassette or by spraying the plastic material under pressure into the formation room (5) of the mould cassette (2), the form of the formation room being determined by the mentioned press bodies (7,12) of the pressurized press. 2. Method according to claim 1, c h a r a c t e r i z e d in that that one of the formation surfaces of the formation room forming the outer surface of the object is after having been waxed provided with a layer of gelcote or surface mat outside the press. 3. Method according to claim 1 or 2, c h a r a c t e ¬ r i z e d in that the mould cassette (2) is given a temperature rise in the press (1) by heat transfer from the press to the press bodies (7,12) heated to a predetermined temperature. 4. Method according to anyone of the preceding claims, c h a r a c t e r i z e d in that the mould cassette (2) with the plastic material being under hardening is removed from the press (1) before the plastic material has been hardened suffe- ciently for depth-hardening of the plastic material outside the press (1). 5. Method according to claim 3 or 4, c h a r a c t e ¬ r i z e d in that particularly when manufacturing large objects regarding the area the mould cassette (2) is inserted into the press (1) with a temperature which is essentially lower than the temperature that the press bodies (7,12) have at this mentioned insertion. 6. Method according to claim 5, c h a r a c t e r i z e d in that the mentioned temperature difference between the press bodies (7,12) of the press and the inserted mould cassette (2) is adapted to the wall thickness of the mould cassette for achieving a time delay of the heat transfer to the plastic material itself in order to make possible for the plastic material to flow out and completely fill out the formation room before it begins to solidify. 7. Method according to anyone of the preceding claims 3-6, c h a r a c t e r i z e d in that when the hardening plastic material itself during the hardening force begins to emit heat the mould cassette (2) is removed from the press (1) for final hardening of the plastic material enclosed in the mould cassette (2) functioning as a heat storage. 8. Press for manufacture of shell-formed objects of plastic material, large as well as small regarding the area, preferably reinforced in a closed formation room in which the plastic material under pressure is brought to flow out and completely fill out the formation room .and which is formed by applying a male mould onto a female mould, c h a r a c t e r i z e d in that the press (1) comprises a lower press body (7) having a .form corresponding to an outer side of a mould cassette (2) with relatively thin force and comprising the mentioned moulds (3,4), and an upper press body (12) with a form corresponding to the other outer side of the mould cassette, one of these press bodies (7,12) in the closed position of the press in which the mould cassette (2) with its one outer side resting against the lower press body (7), being limitedly movable in the stand (6,11) in the press in order to press the mould cassette (2) together by press means (20) for giving the formation room (5) existing in the mould cassette (2) its intended form and maintain this form of the formation room when the plastic material in dependence of the pressure flows out in the formation room (5) in order to completely fill out the same. 9. Press according to claim 8, c h a r a c t e r i z e d in that the press means (20) comprise pressure tubes connected to a pressure medium source and which are placed between a stand (11) of the press and the press body (12) being limitedly movable in relation to the stand (11) in order to press the last mentioned press body (12) with connected pressure medium source against the mould cassette (2) resting on the lower press body (7). 10. Press according to claim 9, c h a r a c t e r i z e d in that the limitedly movable press body (12) is connected to the stand (11) of the press by means of loosening means (16) which are possible to disconnect in order allow the mentioned limitedly movability of the press body (12).

Inventors: LINDSKOG KJELL, LINDSKOG, KJELL
Applicants: RACING PLAST AB
Application year: 1988
Main classification: B29C43
IPC codes: B29C33, B29C43, B29C70, B29K105, B30B1