FR2726783A1 - Blow moulding of bottles, etc. - Google Patents

Abstract

Prodn. of plastic hollow forms, partic. bottles or flasks, by blow moulding in which several of the preforms are blown simultaneously in the same mould as the preforms are injection moulded. The blowing stage (E3) is made in two successive operations (O1, O2), the first (O1) blows a part of the preforms then the second (O2) blows the rest. The same number of preforms are injected as are blown during stage (E3) and in the same time. The appts. for prodn. consists of at least four work stations for injection, conditioning, blowing, ejection.

Description

METHOD OF MANUFACTURING A HOLLOW BODY BY BLOWING
The present invention relates to a method of manufacturing a hollow body by blowing, and more particularly to an improvement for producing hollow bodies made of plastic material such as bottles or flasks.

 Blowing to obtain hollow bodies is a well-known process in itself since it has been used for many years for the manufacture of numerous glass articles such as bottles.

Since the appearance of plastics and the increasingly common use of such a material, manufacturers have of course been led to transpose what was done for glass and this is how blowing is currently also used as a method of making plastic bottles or flasks.

 The generally used method is of the type according to which several preforms are injected before being placed in a mold to be blown therein using pressurized air. Of course, before the preforms are put in place, they are heated in an intermediate stage.

 It is known machines intended to implement the traditional blowing process, thanks to which it is executed simultaneously all the process steps and they include, for this purpose, a swivel plate on which are provided four work stations, the injection station and blowing station. The blowing operation is a delicate operation requiring significant pressure to close the mold which includes several imprints. In fact, closing the mold, made up of two half-molds, must be able to withstand the blowing pressure. However, a new generation of plastic bottles is born which requires a blowing pressure and therefore a large mold closing force. This is, for example, the case of blowing bottles of the tulip-bottom type made of polyethylene terephthalate (PET). In order to solve the problem of closing force of the blow mold, the manufacturers responded by increasing the power of the machines, which, of course, requires the production of new larger machines than current machines.

 The object of the present invention is to overcome this drawback by proposing a new manufacturing method, according to which in the same mold, several of said hollow bodies are blown simultaneously, and according to which the blowing step is carried out in two successive operations. , a first operation during which a part of the preforms is blown followed by a second operation which consists in blowing the rest of the preforms.

 According to an additional characteristic of the process, the blowing step is preceded by a step of injecting the preforms, according to which a set of preforms is injected at the same time in a number identical to the number of preforms blown in the blowing step.

 According to another characteristic, the blowing step is carried out for substantially the same time as the step of injecting the preforms.

 The invention also relates to the device intended to implement the method and which comprises at least four work stations. Namely, a first station where the first stage of injection of the preforms is carried out, a second station where the second reconditioning stage is carried out, a third station where the actual blowing of the third stage of the process is carried out and a fourth station where the last and fourth step is done, i.e. the ejection of the bottles produced.

 According to an additional characteristic, the device comprises blowing control means in two successive operations.

 Other characteristics and advantages of the invention will emerge from the description which follows with reference to the appended drawings which are given only by way of nonlimiting examples.

 FIGS. 1 to 4 represent an example of a hollow body such as a bottle, FIG. 1 being a side view, FIG. 2 a view from below, FIG. 3 being a view in partial section along III-III, while the Figure 4 is a similar sectional view along IV-IV.

 Figure 5 is a side view of a preform.

 Figures 6, 7, 8 and 9 schematically illustrate the general principle of the process in its different stages.

 Figure 6 illustrates the first step.

 Figure 7 illustrates the second step.

 Figure 8 illustrates the third step.

 Figure 9 illustrates the fourth step.

 Figures 10 and 11 show a machine for implementing the method of the invention.

 Figure 10 is a side view.

 Figure 1 1 is a top view.

 FIG. 12 illustrates the first step of the method according to the invention.

 FIG. 13 illustrates the second step of the method according to the invention.

 Figures 14, 15, 16 and 17 illustrate the third step of the method according to the invention.

 Figure 18 is a schematic view illustrating the fourth step of the process.

 FIG. 19 is a diagram illustrating all the steps of the method.

 Figures 1 to 4 illustrate an embodiment of a hollow body which can be produced by the method of the invention. This hollow body is, for example, a bottle (1) which has a shape well known per se and which will not be described in detail, especially since the invention does not relate to the bottle itself but to its method of achievement. Note only that it is constituted by an envelope formed by a peripheral wall of plastic material such as polypropylene (PP) or polyethylene (PE) or polyethylene terephthalate (PET). The lower wall (2) is of the so-called tulip-shaped type and comprises, for example, six support projections (3) thus forming a reinforcing structure for the bottom of said bottle, which comprises at its upper part a filler neck (4 The hollow body thus defined is produced by the process according to the invention from a preform (5) as illustrated in FIG. 5. The final bottle being formed by blowing air inside the preform previously injected then heated and placed inside a mold.

The basic principle of the process to which the improvement relates is illustrated diagrammatically by FIGS. 6 to 9. This process intended for manufacturing a hollow body such as a bottle or the like from plastic material is, for example, of the type known as "injection- blowing with bi-stretch "and which consists in carrying out the following successive stages:
- 1st step (El, FIG. 6) which consists in injecting a preform.

During this step, the preform (5) is obtained by injection into a mold (6) of a plastic material (7), for example, of the thermoplastic polymer type. From a plasticized material by heat, it is injected through a nozzle of small diameter (8) into the cavity of the preform mold. Under the effect of the injection pressure, the material fills the mold cavity and solidifies by cooling on contact with the walls of the mold. The preform (5) thus produced is transferred to undergo the 2nd step.

 - 2nd stage (E2, FIG. 7) which consists in thermally reconditioning the preform, that is to say in heating to a sufficient temperature to allow the following stage (8). The heating of the wall of the preform must be uniform and is carried out by heating means (9) of the electrical type comprising an internal central heating (9a) and an external peripheral heating (9b).

 - 3rd step (E3, FIG. 8) which consists in axially stretching the preform using an elongation rod (10) and in stretching it radially by inflation using compressed air. The preform being arranged inside a mold (11).

 - 4th stage (E4, figure 9) which consists in ejecting the bottle (1) produced during the 3rd stage and allowing it to cool.

 In the industrial bottle manufacturing industry there is of course no question of making the bottles individually one after the other as could be done on an experimental basis.

 Thus, with the aid of a single machine (13), the four stages of the process (El, E2, E3, E4) are not only carried out, but several bottles are manufactured simultaneously, such as, for example, eight bottles (la, lb, lc, ld, le, lf, lg, lh).

 Thus the machine (12) comprises a movable plate (13) pivoting about a vertical axis' arranged on the frame (14) and four work stations (15, 16, 17, 18) corresponding to the four successive stages of the process ( E1, E2, E3, E4).

 Namely, a first station (15) where the first step (E1) of preform injection is carried out, a second station (16) where the second reconditioning step (E2) is carried out, a third station (17) where is the actual blowing of the third step (E3) of the process and a fourth station (18) where the last and fourth step (E4) is carried out, i.e. the ejection of the bottles produced. carried out simultaneously, in a cycle of a duration (T) on the first station (15) the first step (El) of injecting the preforms, on the second station (16) the second step (E2) of reconditioning, the preforms having been injected on the first station (15) during the previous cycle, on the third station (17) the third step (E3) of injecting the reconditioned preforms on the second station (16) during the previous cycle and injected during the cycle preceding this last cycle, on the fourth station (18), the qua third step (E4) of ejection of the bottles having been blown on the third station (17) during the previous cycle.

The pivoting plate (13) is in fact a handling plate intended simultaneously:
- passing all the preforms injected from the first work station (15) to the second work station (16),
- passing all of the thermally reconditioned preforms from the second work station (16) to the third work station (17),
- Passing the blown bottles from the third work station (17) to the fourth work station (18) for ejection.

 As we said before, the method according to the invention makes it possible to simultaneously produce several bottles and, for example, simultaneously eight bottles (la, lb, îc, ld, le, lf, lg, lh) and, on each of the workstations, there are several simultaneous executions.

 Thus, on the first station (15) is simultaneously injected, for example, eight preforms (5a, 5b, 5c, 5d, Se, Sf, Sg, 5h) by injection of plastic material in eight molds arranged side by side, like this is illustrated schematically in Figure 12.

 At the second station (16) the eight preforms produced by injection on the first station (15) are reconditioned. Reconditioning is a thermal reconditioning which consists in reheating the eight preforms (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h) so that the material constituting them is at a station at a sufficient temperature allowing the following operation blowing.

 The invention relates more particularly to the third step (E3) of the method, carried out on the third station. Thus, according to the invention, the blowing of all the reconditioned preforms is not done in a single operation, and in a single time, but at least in two stages, during two successive operations as shown in FIGS. 14 and 15 .

 The mold (11) being constituted in a manner known per se by two half-molds (1 la, 1 lob), the closure of which is effected by several jacks (110) to form the succession of the eight imprints (20a, 20b, 20c, 20d, 20th, 20f, 20g, 20h).

 Thus, after closing the mold (11) on the eight preforms (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h) as shown in FIG. 14 in the first operation and, as illustrated in FIG. Figure 16, we stretch the eight preforms (5a, 5b, 5c, 5d, 5th, 5f, 5g, 5h) by engagement down the eight elongation rods (10a, 10b, 10c, 10d, 10e, 10f, 10g , 10h) while we blow some of the preforms while in the next operation we blow the remaining preforms. Thus in the first operation (01, FIG. 16), one blows, for example, one preform out of two and, for example, the four preforms (5a, 5c, 5e, 5g). The blowing (S1) of these first preforms making at high pressure while a low pressure is maintained in the remaining preforms (5b, 5d, 5f, 5h).

In a second operation (02) which is an operation which follows the first operation, the four preforms (5b, 5d, 5f, 5h) are blown (S2) as illustrated in FIG. 17.

 At the fourth station (18), all the bottles that have been blown at the third station are ejected. During this step, the mold having served in the previous step for blowing the eight bottles opens to allow the said bottles thus produced to escape, as shown in FIG. 18.

 FIG. 19 is a diagram illustrating on the abscissa schematically the duration of the four stages (E1, E2, E3, E4) executing simultaneously. At the first station (15) is made the first step of the process which consists of injecting (step E1), to cool (step R1).

All of these actions last for a determined time (T).

 During this same time (T) is carried out on the second station (16) the thermal conditioning (E2), the withdrawal of the heating means (R2).

 During this same time (T) we proceed to the next step, which consists of blowing the preforms, which is done in two successive stages the first operation (01) of blowing (S1) of the preforms (5a, 5c, 5e, 5g ) and the second blowing operation (02) (S2) of the remaining preforms (5b, 5d, 5f, 5h).

 Of course, at the time (T) of each of the steps (E1, E2, E3) it is necessary to add a time (Tf) necessary for the opening of the molds and for the rotation of the pivoting plate.

 The device for implementing the process, that is to say the machine (12) with its various work stations (15, 16, 17, 18) comprises means for controlling the various operations and, of course, blowing control means in two operations (O 1, 02).

 Of course, the invention is not limited to the embodiments described and shown by way of examples, but it also includes all the technical equivalents and their combinations.

Claims (5)

 1. A method of manufacturing by blowing hollow plastic bodies (1) from a preform (5) of the type according to which in the same mold (11, lla, llb) is carried out the simultaneous blowing of several of said bodies hollow (la, lc, le, id - lb, id, if, lh) characterized in that the blowing step (E3) is carried out in two successive operations (01, 02), a first operation (01) during which is carried out the blowing (S1) of a part of the preforms (5a, 5c, 5e, 5g or 5b, 5d, 5f, 5h) followed by a second operation (02) which consists in carrying out the blowing (S2) from the rest of the preforms (5b, Sd, 5f, 5h or 5a, 5c, 5e, 5g).  2. Manufacturing method according to claim 1 characterized in that the blowing step (E3) is preceded by an injection step (El) of the preforms (5).  3. Manufacturing method according to claim 2 characterized in that the injection step (El) consists in injecting at the same time a set of preforms (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h) in number identical to the number of preforms blown in the blowing step (E3).  4. The manufacturing method according to claim 3 characterized in that the blowing step (E3) is performed for substantially the same time T as the injection step (El) of the preforms (5a, 5b, 5c, 5d, 5th, 5f, 5g, 5h).  5. Device for implementing the method according to any one of the preceding claims, characterized in that it comprises at least four work stations., Namely, a first station (15) where the first step is carried out (El ) injection of the preforms, a second station (16) where the second reconditioning step (E2) is carried out, a third station (17) where the actual blowing of the third step (E3) of the process is carried out and a fourth station (18) where the last and fourth step (E4) takes place, that is to say the ejection of the bottles produced.