A METHOD FOR VACUUM MOULDING OF LARGE OBJECTS OF SYNTHETIC RESIN

Abstract: The invention relates to a method for vacuum moulding of large objects of synthetic resin in a dismountable mould (1) with reinforcing materials (5) placed in the same, in which monomer with hardening agent and possible accelerator are supplied to the cavity from below and upwards for filling said cavity held under vacuum. The method is characterized in that the synthetic resin is supplied at least at one position in said cavity situated initially in the lower portion of said cavity and then progressively moved upwards with such a speed that said position is located just below the surface of said synthetic resin as it is supplied and rises in said mould (1).

Description: A method for vacuum moulding of large objects of synthetic resin The present invention relates to a method for vacuum moulding of large objects of synthetic resin in a dismountable mould with reinforcing materials placed in the same, in which monomer with hardening agent and possible accelerator are supplied to the cavity of the mould from below and upwards for filling said cavity held under vacuum. In vacuum moulding of objects of synthetic resin, a dis¬ mountable mould is used with reinforcing materials placed in the same. The vacuum moulding is effected in such a way that vacuum is applied to the cavity through one or several connec¬ tions arranged at the upper portion of the mould, and ready- -mixed synthetic resin in the form of monomer and hardening agent is fed into the lower portion of the mould, the syn¬ thetic resin rising in the mould by way of the applied vacuum. Since the first synthetic resin supplied shall rise all the way until it reaches the uppermost part of the mould, which, when large objects shall be manufactured, takes long time, the synthetic resin will get time to become viscous, producing lumps and plugs of synthetic resin in the cavity, so that continued rising of said synthetic resin in the cavity is prevented. Thus, it is difficult to manufacture large, particularly shell-like objects, i.e. with little thickness relative to the surface area, for example domes, boat hulls, car bodies, etc. with vacuum moulding. In known methods for vacuum moulding the above-mentioned problems are avoided by using only small amounts of hardening agent in the monomer and subsequent heating of the mould after that said mould has been filled with synthetic resin for hardening the same. However, this method is circumstantial and difficult to carry out when large objects of synthetic resin shall be vacuum moulded. One of the great advantages of vacuum moulding is that it is not harmful to the environment, since no emission of monomer to the atmosphere takes place. An other advantage is that the moulding is effected in one single working step, whereby the manufactured object becomes totally homogeneous and free from voids due to the vacuum applied. The object of the invention is to provide a method for vacuum moulding, which makes it possible to manufacture large objects of synthetic resin without the above-mentioned disad¬ vantages. This is achieved according to the invention mainly in that the synthetic resin is supplied at least at one posi¬ tion in said cavity initially in the lower portion of said cavity and is then successively moved upwards at such a speed that said position is located just below the surface of said synthetic resin as it is supplied and rises in said mould. In a preferred embodiment according to the invention the synthetic resin is supplied through at least one hose, which is sealingly inserted through a wall in the upper portion of the mould as deep into the cavity that its free end is posi¬ tioned in the lower portion of said cavity, and said hose or hoses are progressively pulled upwards at such a speed that said free end or ends of said hose or hoses are positioned just below the surface of said synthetic resin as it is supp¬ lied and rises in said mould. With the method according to the invention, can for in¬ stance domes, boat hulls, flagstaffs, special types of pipes with a smooth surface, etc. , be manufactured. A non-limiting example of the invention will now be de¬ scribed with reference to the accompanying drawing, in which a sectional view of a mould for effecting the method for vacuum moulding according to the invention is shown for manu¬ facturing a half-spherical dome, the left side of the drawing illustrating the position of the hose in an initial stage and its right side illustrating the hose partly pulled up and said mould partly filled with synthetic resin. The method according to the invention is applicable to different types of known apparatuses for vacuum moulding, and will be described below in connection with a mould 1 chosen as an example, and which is dismountable in its lower portion and being composed of two complementary mould parts la, lb. At least one synthetic resin supply hose 2 is sealingly inserted through the wall of preferably the upper mould part la in its uppermost portion through any type of sealing 3. At least one connection 4 for the application of vacuum is pro¬ vided in the upper portion of said mould 1, as seen in the drawing, suitably in the wall of said upper mould part la for applying vacuum to the interior of said mould 1. The vacuum connection 4 is connected to one end of a suction pipe 6, the other end of which is connected to a vacuum apparatus (not shown) , such as a vacuum pump, which is adapted to provide vacuum in the mould. In the case of a vacuum pump its outlet is connected to suitable filters and separation apparatuses for monomer (not shown) , so that no emission to the atmosphere occurs. In the following way an object of synthetic resin is manufactured in a mould of this type by the method according to the invention. With the mould parts la, lb separated from each other, the surfaces of the mould directed towards the cavity are coated with release agent and if desired afterwards with a surface layer, for instance of gel coat, depending upon which type of surface the object to be manufactured is to have. Then, desired amount and type of reinforcing mate¬ rial 5 is placed in the mould in the form of one or more self- -supporting or spray applied fibre layers or the like on one or both mould parts. The reinforcing material 5 can for instance be glass fibre, carbon fibre, Kevlar (registered trade mark) , etc. The amount is preferably such that the object of synthetic resin to be manufactured will contain 20- 80% by weight of reinforcing material. When bringing together the mould parts la, lb for clo¬ sing the mould 1, the hose or hoses 2 are inserted through the sealings 3 and placed with their free ends quite close to the bottom of the cavity. The vacuum apparatus is then connec¬ ted through the suction pipe 6 to the vacuum connection 4, providing an underatmospheric pressure or vacuum in the mould 1. This vacuum must not be too large, since the mould l then must have a very heavy structure for avoiding deformation of said mould. The monomer with added hardening agent and pos¬ sible accelerator are introduced, preferably through pumping, through the hose or hoses 2 into the cavity. Alternatively, the adding of the hardening agent can be made at the free end of the hose 2, which then is provided with two channels 8,9 and a mixing nozzle 7 at said end (as shown to the left in the drawing) . A certain period of time after the beginning of the introduction of the synthetic resin, and when the lower portion of the cavity has been filled to such an extent that the free end of the hose or hoses 2 is positioned just below the surface of the synthetic resin, a successive pulling out of the hoses of the mould 1 is started at such a speed that the free ends of said hoses during the whole vacuum moulding remain positioned just below the surface of the synthetic resin. The vacuum applied to the cavity shall be maintained during the whole vacuum moulding. Since the mould 1 is filled with synthetic resin from the bottom and upwards, as shown in the drawing, while the hoses 2 are successively pulled out, it does not matter if the synthetic resin begins to cure at the bottom of said mould l. Even if the synthetic resin can be sucked into the mould 1 by the vacuum applied to the cavity, it is preferred, in order to avoid making the hoses 2 too coarse in order not to collapse, to supply the synthetic resin by pumping. When producing shell-like objects the hoses 2 have preferably flattened cross section with a width amounting to 60-20%, preferably 40-30%, of the width of the cavity. The synthetic resin introduced into the cavity can be mixed with chopped reinforcing material of the same kind as the reinforcement 5 for reinforcing the channels, which pos¬ sibly may be formed in the reinforcing material, when the hoses are pulled out of the mould. The number of hoses needed is depending upon the viscosity of the monomer, the amount of reinforcing material in the cavity and the dimension of the hoses 2, which in turn is depending upon the width of the cavity. By the method according to the invention homogeneous objects of synthetic resin free from voids are obtained, and rapidly as well as slowly curing synthetic resins can be used, while the emission of monomer to the atmosphere is minimized. Although the invention has be described above with reference to a mould of half-spherical shape it is obvious to the artisan that a mould of any suitable shape can be used. Also, while hoses are used for supplying the synthetic resin into the mould it is obvious that other means can be used, for instance a number of closeable inlet openings, placed horison- tally along said mould and at different heights, which openings are successively put into operation for filling said mould.

Claims: C l a i m s 1. A method for vacuum moulding of large objects of synthe¬ tic resin in a dismountable mould with reinforcing materials placed in the same, in which monomer with hardening agent and possible accelerator are supplied to the cavity from below and upwards for filling said cavity held under vacuum, c h a ¬ r a c t e r i z e d i n that the synthetic resin is supplied at least at one position in said cavity situated initially in the lower portion thereof and then successively moved upwards at such a speed that said position is located just below the surface of said synthetic resin as it is supplied and rises in said mould. 2. Method according to claim 1, c h a r a c t e r i z e d i n supplying said synthetic resin through at least one hose, sealingly inserted through a wall in the upper portion of the mould as deep into said cavity that its free end is positio¬ ned in the lower portion of said cavity, and progressively pulling up said hose or hoses with such a speed that said free end or ends of said hose or hoses are positioned just below the surface of said synthetic resin as it is supplied and rises in the mould. 3. Method according to claim l or 2, c h a r a c t e r i¬ z e d i n that the monomer and the hardening agent are supplied by pumping. 4. Method according to claim 1-3, c h a r a c t e r i z e d i n that the monomer is mixed with chopped reinforcing mate¬ rial. 5. Method according to claim 2-4, for vacuum moulding of large, shell-like objects, i.e. with little thickness relative to surface area, c h a r a c t e r i z e d i n that said hose or hoses have flattened cross section with a width amoun¬ ting to 60-20% and preferably 40-30%, of the width of said cavity. 6. Method according to claim 2-5, c h a r a c t e r i z e d i n that said hose or hoses are provided with two channels for monomer and hardening agent respectively, and that said monomer and said hardening agent are mixed continuously with each other at the free end of said hose.

Inventors: THULIN DAG, THULIN, DAG
Applicants: THULIN DAG, THULIN, DAG
Application year: 1991
Main classification: B29C39
IPC codes: B29C39, B29C70, B29K105