A moulding device of the type addressed by the invention is illustrated diagrammatically in FIG. 1 of the accompanying drawings.
The mould, designated as a whole by the reference numeral 1, comprises, in the configuration illustrated, two half-moulds 2 and 3 suitable respectively for forming the assembly consisting of the shoulder, of the body and of the bottom of the containers; in another possible configuration, the mould may comprise three elements, to be precise two half-moulds 2 and 3 for forming the shoulder and the body of the containers and a vertical movable mould bottom for forming the bottom of the containers.
In the example illustrated, the mould 1 is formed from two half-moulds 2, 3 which are articulated in rotation with respect to one another on a shaft 4 (jackknife mould), since this is the type of mould in most common use in the installations produced by the applicant; however, it must be understood that the invention is not aimed solely at this type of mould and may be employed in moulds of other types, especially moulds in which the half-moulds are movable linearly.
The half-moulds 2, 3 comprise two supports 5, 6 respectively and two mould blocks 7, 8 respectively which are supported by the latter. In the example illustrated, the mould blocks have a cross section of substantially rectangular general shape. The two mould blocks 7, 8 are pierced with two respective moulding recesses which together form a moulding cavity 11 of axis 12. The two mould blocks 7, 8 possess cooperating faces or bearing faces 13 and 14 respectively, which, in the mould-closing and the blowing position, are in mutual bearing contact along a parting plane P.
The supports 5, 6 are arranged so as to have, on one side, respective projecting lugs which are spaced apart from one another and to which are connected actuation means (opening/closing), designated as a whole by 9, which may be of any suitable configuration, and, on the opposite side, means for locking in the closing position, designated as a whole by 10, which themselves may have any suitable configuration.
A particular half-mould of the two half-moulds (here, the half-mould 2 located on the left in FIG. 1) is arranged such that a leak-tight chamber 20, called a “compensating chamber”, is defined between the respective assembly faces 16, 17 of its support 5 and of its mould block 7 by a seal 18 (seated in a groove 19 pierced, for example, in the assembly face 17 of the mould block 7), and such that said mould block 7 is displaceable in relation to the support 5 substantially perpendicularly to its bearing face 13. In the mould configuration of substantially quadrangular shape, illustrated by way of example in FIG. 1, the abovementioned assembly faces 16, 17 and the bearing faces 13, 14 are substantially parallel, and the compensating chamber 20 is substantially parallel to the bearing face 13 of the mould block 7.
The wall of the support 5 of the particular half-mould 2 is pierced with a passage duct 25 issuing into the compensating chamber 20. The duct 25 is connected (not shown) to a source of fluid under high pressure. In practical terms, the duct 25 may be connected to the source of blowing fluid, and in this case the situation is such that the projection of the surface of the compensating chamber 20 onto the parting plane P is greater than the projection of the surface of the moulding cavity 11 onto said parting plane P. During blowing, under the action of the pressure prevailing in the compensating chamber 20, the mould block 7 is pushed in the direction of the opposite mould block 8, and its bearing face 13 is pressed firmly against the bearing face 14 of the mould block 8.
Once blowing is completed, to ensure the mould block 7 returns into its retracted position on the bottom of the respective support 5, there is provision for the mould block 7 to be supported by the respective support 5 by elastic return means 26. A simple solution, illustrated in FIG. 1, involves, in order to form each elastic return means 26, interposing an elastic return member 22 between the head of a bolting member 21 and the outer face 23 of the support 5. The elastic return members 22 may consist of especially one-piece tubular springs made from synthetic material (typically from polyurethane), for moulds of cold-cycle use, or of exact stacks of metal spring washers, for moulds of hot-cycle use.
The mould block 8 (located on the right in FIG. 1) is itself supported fixedly by the respective support 6 by means of bolting members 24.
A mould arranged, as just described with reference to FIG. 1 of the accompanying drawings, is disclosed in the document FR 2 659 265 (FIG. 1 of the accompanying drawings being repeated in FIG. 1 of this document), to which reference may be made for fuller explanations.
However, this document omits to mention and illustrate abutment means suitable for maintaining the mould block 7 in its retracted position, such that the compensating chamber 20 formed between the aforesaid assembly faces 16 and 17 of the support 5 and of the mould block 7 respectively is represented by an interval j defined mechanically.
FIG. 2 of the accompanying drawings illustrates separately an exemplary embodiment of the abutment means 27 with which the mould 1 is equipped. Each abutment means 27 comprises a stop rod 28 screwed into a bore 29 passing through the support 5. The inner end 30 of the stop rod 28 comes to bear against the mould block 7; in particular, it may be in bearing contact, if appropriate with a bearing insert 32 being interposed, against the bottom of a clearance 31 pierced in the mould block 7 substantially coaxially to the bore 29. The rotation of the stop rod 28 makes it possible to set the value of the interval j. A lock nut 34 may be provided on the free end 33 of the stop rod 28 for blocking in the adjustment position in terms of rotation.
Of course, the arrangements which have just been explained have been incorporated in a particularly expedient way in the moulds currently manufactured by the applicant, in which each mould block is of the composite type and comprises a shell equipped with the moulding recess and a shell carrier supporting said shell and itself supported by the support. The compensating chamber is then provided between the assembly faces of the support and of the shell carrier, with elastic return means and abutment means interposed between the support and the mould block being implemented. Such moulds with a compensating chamber are described particularly in the document FR 2 733 176 in the applicant's name, although the presence of the elastic return means and of abutment means is not explained in this document.
Whatever the type of mould in question, even though this known arrangement is entirely satisfactory in operational terms, it has several disadvantages.
A first disadvantage is that the support 5 and the mould block 7 of the half-mould 2 comprise, in the embodiment illustrated in the document FR 2 659 265, elastic return means 26, of which there are eight arranged in two columns, and abutment means 27, of which there are four, all being located on either side of the compensating chamber 20. These numerous drill holes and machinings mechanically weaken these components which, moreover, are subjected to very high mechanical stresses during blowing.
In subsequent productions, the number of the elastic return means has been reduced to four; however, the total number of drill holes still remains high.
In any event, the demounting and then remounting of the mould block 7 (for example, for a change in manufacture with a different moulding cavity) make it necessary to demount and then remount the numerous elastic return means and abutment means.
Above all, another major disadvantage is that, during each remounting, it is necessary to repeat the settings of the return and abutment prestress for each of the means in question. It becomes clear that the setting of the abutment means systematically disturbs the setting of the elastic return means for compensation, thus making it necessary to repeat these settings alternately.
Furthermore, the springs made of synthetic material which are used in the moulding devices of cold-cycle operation lose their elasticity progressively and finally become slack, thus making it necessary to replace them regularly.
In turn, the metallic spring washers are assembled in the form of a stack, with their alternate positioning being adhered to. Practice shows, however, that, during the remounting operations, washers may be remounted in insufficient numbers and/or without adhering to their alternate positioning in the stack. Consequently, the elastic return means may then lose their effectiveness to a considerable extent, and it becomes necessary to redemount the elastic return means in order to complete and/or reposition the spring washers correctly.
Finally, in practice, each demounting and then remounting of the mould block 7 requires considerable work and necessitates a large amount of setting time before the mould is once again in the correct operating state. In a high-capacity moulding installation of the turntable type incorporating a large number of moulds (for example, up to 34 moulds), any alteration in manufacture involving a change of mould blocks has a highly adverse effect in terms of work and of cost because of the long period of shutdown of the installation.