Apparatus for moulding plastic materials, corresponding mould and products thus obtained.

p0001The invention has for object an apparatus for molding plastic material, the mold for its implementation and the products thus obtained.

p0002The importance of the duration of the manufacturing time of industrial products made by molding of plastics has long been recognized both in the case of thermoplastic materials such as polyvinyl chloride (PVC) as plastisols or organosols liquids that for thermosetting plastics, such as polyurethanes, involving an exothermic reaction for crosslinking or polycondensation of the one or more resin (s) basis. By duration time of manufacture herein is meant not only the actual molding phase with increase in temperature but also the subsequent phase of cooling necessary in particular for plastisols. This period may be relatively high, even for small parts, since it is not unusual to provide in the case of plastisols or organosols liquids, exothermic reaction phases of the order of 10 to 15 minutes followed by cooling phases (for example in tunnels or in application of an apparatus with cooled plates) of the order of 3 to 4 minutes, comparable length is also necessary for the implementation of polyurethane elastomers by conventional methods of manufacturing parts for such materials. If one is looking for the last materials mentioned above, to reduce the manufacturing time, for example by injection molding machines with two heads, one delivering the polyol and the other isocyanate that should be reacted, it is shortened is true manufacturing time, but at the cost of technical difficulties whose operation is not always justified for certain types of products. In addition, and in this more complex technique, many factors need to be monitored, such as mold temperature, ambient temperature, etc ... so the investment and manufacturing cost per piece produced is sometimes an insurmountable obstacle the use of this technique.

p0003Since there are, however, beside the plastisols or organosols liquid of polyurethane elastomeric compositions that may be implemented in a period of 4 to 5 hours after preparation and mixtures in liquid form, said compositions being polymerizable to provide a thermoset product by heat treatment, the Applicant has sought to solve the problem of reduction in the duration of production of certain plastic articles by using techniques other than those used to date for these types base materials, in particular by developing an apparatus for applying a high-frequency electric field.

p0004If the apparatus in the production of plastic parts in a mold with the application of high-frequency electric field to said mold have already been proposed, for example in GB-A-1592383 or US-A-2,888,366, these devices are intended for the manufacture of seals, such as seals in plastic caps for which do not have to be respected with great accuracy, the shapes and / or dimensions of a series of plugs.

p0005It is therefore a general object of the invention to provide an apparatus for molding plastics which allow to reduce very significantly the time for manufacturing objects made thereof, in particular polyvinyl chloride or polyurethane elastomer.

p0006It is still an object of the invention to provide such an apparatus for implementing particularly simple and, therefore, extremely low operating and investment costs.

p0007It is also an object of the invention to provide a very suitable apparatus for the manufacture of parts of the automotive industry, for example, and without this indication has any limiting character whatsoever, filter bases in air or the like.

p0008An apparatus according to the invention for the manufacture in the open air in a room to mold plastics material from a liquid material, polyvinyl chloride (PVC) plastisol form or organisol, also mixture of at least the two basic components (polyol and isocyanate) of a polyurethane elastomer with application of an exothermic reaction to cause polymerization and / or crosslinking of the plastics material with means for applying an electric field said high frequency mold is characterized in that said mold is of a material selected from silicone resins, polyamides or polytetrafluoroethylene and in that said application of the high-frequency electric field means comprises a central portion, the inner mold, forming a ring in a clean conductive material to be connected to the mass of a high-frequency current generator or to a terminal thereof.

p0009In a preferred embodiment, the apparatus is further characterized in that said core portion is preferably a silicone resin highly charged with metallic particles such as aluminum particles or the like.

p0010The invention finds very advantageous application for the production of air filter bases of motor vehicle engines and it is, also, therefore, the specific molds for the realization of these bases or filters as filters and / or bases obtained by implementation of the apparatus.

p0011The invention will be well understood from the following description given by way of example and with reference to the accompanying drawings in which:<ul><li>- Figure 1 is a schematic view in perspective of an automobile engine air filter;</li><li>- Figure 2 is a view partly in section, partly in elevation of a filter base;</li><li>- Figure 3 is a highly diagrammatic view of an apparatus according to the invention.</li></ul>

p0012In the following description, the invention is described as applied to the manufacture of motor vehicle air filters bases, but this indication is given as to the purpose of illustration and without any limiting nature does it either naturally attached.

p0013As shown in Figures 1 and 2, an automobile engine air filter comprises, in a manner known per se, an ordinary filter paper or the like material, pleated, and whose general shape is that of an elongated cylinder (in the illustrated embodiment) or a diameter of ring many times greater than its height (in embodiments not shown, filter for a passenger car engine, for example). One or more reinforcing metal (s) (s) grid (s) may be provided outside and / or inside the cylinder or pleated paper ring. At both ends of the cylinder or paper ring, the two collars 10 and 11, plastic, or elastomer "close" the channels that spare the adjacent plies of a separate sheet of paper and ensure the cohesion mechanical filter, on the other hand, and simultaneously have a role of the air seals when the filter is placed in a removable housing cover.

p0014For the manufacture of such filters the invention provides first of all prepare a cylinder or ring 12 then packed pleated paper, if necessary, a metallic mesh reinforcement 13 and form both ends of the cylinder or of the ring the bases 10 and 11 by molding a plastics material or elastomer. To do this, one first makes the mold M of an electrically insulating material such as a silicone resin, having a circular plan shape and a cross section corresponding to that desired for the bases 10 and 11, for example, in the embodiment shown, a cylindrical inner wall 15 and cylindrical outer wall 16 joined by a beak right V-section 17, whose vertical wing (in the drawing) 18 is connected to the wall 15 by a recess 19. on the inclined face 20 of the 21 well defined ring are arranged in a regular angular distribution, studs 22.

p0015It is on the latter that is reported by its lower edge, T, the set E formed by the pleated paper sheet provided, if appropriate, his or reinforcement (s) metal grid, and that after that 'has been poured into the ring 21 a certain amount of plastisol or organosol or mixture of the two components of the polyurethane elastomer that is to be polymerized and / or crosslinked.

p0016For crosslinking and / or polymerization at the free air of the mass of liquid material, the invention is applied a high-frequency electric field applied to the mold M via a ring A adjacent to the face 16 of the mold and a ring N or interior mass to said mold and its adjacent face 15.

p0017The ring A is connected by a conductor C to one terminal of a high-frequency current generator G, for example, a generator generating a stream of frequency between 13 and 100 MHz, the other terminal of the generator G is connected grounding <u>m</u> as the core N.

p0018Alternatively, the ring A is connected to ground and the ring N to a terminal of the generator G.

p0019A first base 10 is thus produced in about ten seconds, after the temperature of the mass of liquid material dosed into the mold M remaining in the open air has been brought to a temperature of the order of 80 to 120 ° C .

p0020The base thus produced can be unmolded in a short time, on the order of one minute, a new basic quantity of material poured into the ring 21 and the process that has to be written again reproduced for manufacturing the other base.

p0021There is, of somewhat surprisingly, that the presence of or frame (s) screened (s) metal (s), when (s) exist (s) does not disturb the operation of the generator G high current -frequency.

p0022Good results were obtained using a mold M polypropylene or Teflon (a Trademark of DuPont de Nemours) ring A and N core is, in turn, made a heavily loaded silicone resin aluminum particles.

p0023While the manufacturing time by the known methods an elastomeric air filter base having a diameter of 300 mm and a height of 150 mm is about 6 minutes, the implementation of a high-frequency current 27 MHz allows for using an apparatus as just described an even base over a period of 1 minute.

p0024The invention is not limited, of course to the embodiment and examples described above.

p0025It is applicable for molding plastics of organosols type or liquid plastisol and / or polyurethane elastomers of the most varied compositions and for the manufacture of extremely varied industrial objects.

p0026The invention is preferably implemented on a machine of the carousel or linear type, arranged for the determination of the material of a base, the automatic positioning in the cylinder mold or pleated paper ring (with or without mesh reinforcement metal) extraction after polymerization and / or crosslinking cylinder or ring reversal paper and topped with a first base, metering a second quantity of material to be polymerized and / or crosslinked, implementation of the other slice pleated paper, new passage of high-frequency current, the mold extraction filter thus provided with its two bases and unloading outside the machine.