BACKGROUND ART In the plastic bottling industry, a linear blowing machine is known comprising a number of blowing units aligned and equally spaced with a given spacing in a first direction.

Each blowing unit comprises a mold, in turn comprising two facing half-molds, which are moved, with respect to each other and in a second direction substantially crosswise to said first direction, between an open position permitting insertion of a preform or removal of a blown bottle, and a closed position in which the preform inside the mold is blown. It should be pointed out that, normally, all the molds are moved simultaneously between the open and closed positions.

The blowing machine also comprises a step-operated conveying device having a number of gripping members, each for retaining a relative preform or bottle. The

gripping members are equally spaced along the conveying device with the same spacing as the blowing units, and are fed by the conveying device along a path, a portion of which extends between the half-molds and parallel to the first direction.

At the end of each blowing operation, and when the molds are in the open position, the conveying device is operated to unload the blown bottles from the relative molds and, at the same time, load another preform into each mold.

To perform the above unloading and loading operation, the conveying device must be operated, at each operating cycle of the blowing machine, so as to impart to each gripping member a movement which substantially equals said spacing multiplied by the number of blowing units, and which therefore varies alongside a variation in the number of blowing units.

At each operating cycle, the downtime of the blowing machine corresponding to the unloading and loading operation therefore varies alongside a variation in the above movement, and, in particular, increases alongside an increase in the number of blowing units.

As a result, known linear blowing machines of the above type have an output rate whose increase by the addition of a blowing unit decreases alongside an increase in the number of blowing units.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide

a method of blowing plastic bottles, designed to eliminate the aforementioned drawbacks.

According to the present invention, there is provided a method of blowing plastic bottles on a linear blowing machine comprising at least two blowing units aligned in a given first direction, and each for blowing a respective bottle from a relative preform; the method being characterized in that each said preform and the relative said bottle are fed along respective feed paths, and are transferred between the respective feed paths and the relative said blowing unit along respective transfer paths, each of which extends at least partly in a second direction substantially crosswise to said first direction.

The present invention also relates to a machine for blowing plastic bottles from respective preforms.

According to the present invention, there is provided a linear machine for blowing plastic bottles, comprising at least two blowing units aligned in a given first direction, and each for blowing a respective bottle from a relative preform; and characterized by also comprising conveying means for feeding each said preform and the relative said bottle along respective feed paths; and transfer means for transferring each said preform and the relative said bottle between the relative said feed paths and the relative said blowing unit along respective transfer paths, each of which extends at least partly in a second direction substantially crosswise to said first

direction.

BRIEF DESCRIPTION OF THE DRAWINGS A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figures 2 and 2 show schematic plan views of a preferred embodiment of the machine according to the present invention in two different operating positions; Figure 3 shows a schematic side view of the Figure 1 machine; Figure 4 shows a schematic view in perspective of a detail of the Figure 1 machine; Figure 5 shows a schematic plan view of a variation of the Figure 1 machine.

BEST MODE FOR CARRYING OUT THE INVENTION Number 1 in Figures 1, 2 and 3 indicates as a whole a linear machine for blowing known plastic bottles 2 from respective known preforms 3.

Each bottle 2 and the relative preform 3 comprise a body 4a and 4b respectively, which is substantially cup- shaped, has a longitudinal axis 5, and has an externally threaded end 6 defined axially by an annular collar 7 extending radially outwards from the outer surface of body 4a, 4b.

Machine 1 comprises a number of (in the example shown, four) blowing units 8, each of which comprises a mold 9 and a known blowing device 10 (Figure 3) associated with mold 9.

Molds 9 have respective substantially vertical, longitudinal axes 11, which are aligned in a substantially horizontal direction 12 crosswise to axes 11, and are substantially equally spaced in direction 12 with a spacing D1. Each mold 9 comprises two half-molds 13, each of which is substantially in the form of a rectangular parallelepiped, is defined by a flat surface 14 extending crosswise to direction 12 and facing the other half-mold 13, and has a cavity 15 opening outwards at relative surface 14.

Half-molds 13 are divided into two groups, each comprising a respective number of (in the example shown, four) half-molds 13, which alternate with the half-molds 13 in the other group, and are fitted to a single supporting frame 16.

The two frames 16 are movable with respect to each other in direction 12, by a known actuating device not shown, to move each pair of half-molds 13 between a parted position (Figure 2), in which half-molds 13 are located a given distance apart, and a closed position (Figure 1), in which half-molds 13 are positioned contacting each other at relative surfaces 14.

With reference to Figure 3, each mold 9 also comprises a cup-shaped bottom 17, which is substantially coaxial with relative axis 11, is positioned with its concavity facing upwards, and is fitted to an output rod 18 of an actuating cylinder (not shown) to move, in a direction 20 parallel to axes 11, between a lowered rest

position (not shown) and a raised work position (Figure 3). When bottom 17 is in the raised work position and the two half-molds 13 in the closed position, mold 9 is closed, and bottom 17 defines, together with half-molds 13, a chamber 21 of substantially the same shape and volume as bottle 2.

Each device 10 comprises a stretch rod (not shown) extending substantially coaxially with relative axis 11, and movable axially in direction 20 with respect to relative preform 3 by a known actuating device (not shown); and a circuit for feeding compressed air into relative preform 3.

Machine 1 also comprises two conveying devices 22 located on opposite sides of molds 9 in direction 12, and one of which (hereinafter indicated 22a) conveys each preform 3 along a relative feed path P1 extending between a loading station (not shown) and a relative transfer station 23, where preform 3 is aligned with relative mold 9 in a direction 24 perpendicular to directions 12 and 20, and the other of which (hereinafter indicated 22b) conveys each bottle 2 along a relative feed path P2 extending between a transfer station 25, where bottle 2 is aligned with relative mold 9 in direction 24, and an unloading station (not shown).

Each device 22a, 22b comprises a guide 26 extending, at least at molds 9, parallel to direction 12; and a number of conveying members defined by respective slides 27 equally spaced along relative guide 26 with a spacing

substantially equal to D1, and fitted in known manner to relative guide 26 so as to move all together along relative guide 26 in steps. With reference to Figure 4, each slide 27 is substantially C-shaped, and comprises a substantially semicircular seat 28-preferably, though not necessarily, an elastically deformable seat-for receiving a bottle 2 or a preform 3, which is retained axially inside seat 28 by relative collar 7.

For each device 22a, 22b, machine 1 comprises a transfer device 29a, 29b, in turn comprising a number of transfer members 30a, 30b, which are equal in number to molds 9, are equally spaced in direction 12 with spacing D1, and are located on the opposite side of relative guide 26 to relative molds 9. Each member 30a, 30b transfers relative preform 3 and, respectively, relative bottle 2 along a transfer path P3, P4 extending in direction 24 between relative station 23,25 and relative mold 9, and comprises a known gripping member 31, which is elastically deformable to retain or release relative preform 3 or bottle 2, and is fitted to an output rod 32 of an actuating cylinder 33 fixed to a frame 34 of machine 1.

In connection with the above, it should be pointed out that member 31 and rod 32 extend through relative slide 27 when moved between an extracted position (shown in Figure 2 with reference to members 30b) and a withdrawn position (Figure 1), and that member 31 is separated from relative seat 28 by a distance, measured

parallel to direction 20, approximately equal to but no smaller than the thickness of collar 7, also measured parallel to direction 20.

Operation of machine 1 will now be described as of the instant in which: each mold 9 is closed and houses a preform 3; each device 10 is in the process of blowing preform 3 inside relative mold 9; device 22a has fed another preform 3 into each of, stations 23; the preforms 3 at stations 23 and inside seats 28 are engaged above relative collars 7 by members 30a; and the preforms 3 in molds 9 are engaged above relative collars 7 by members 30b. when the blowing operation is completed, the two frames 16 are moved with respect to each other in direction 12, and bottoms 17 are moved into the lowered rest position to open molds 9 (Figure 2). At this point, members 30b are moved in direction 24 to transfer bottles 2 along relative paths P4 into relative seats 28; and, at the same time, members 30a are moved in direction 24 to transfer the new preforms 3 along relative paths P3 into relative molds 9 and into a position coaxial with relative axes 11.

Finally, the two frames 16 are moved with respect to each other in direction 12, and bottoms 17 are moved into the raised work position to close molds 9; members 30a, 30b are moved into the withdrawn position; and devices

22a, 22b are operated to impart to-each slide 27 a movement at least equal to spacing D1 multiplied by the number of molds 9, so that device 22a feeds four new preforms 3 along relative paths P1 into relative stations 23, and device 22b feeds the blown bottles 2 along relative paths P2, and feeds four empty seats 28 into relative stations 25.

Figure 5 shows a linear machine 35 for blowing plastic bottles 2, and which differs from machine 1 solely by comprising a single transfer device 29; and a single conveying device 36 extending, at molds 9, parallel to direction 12 and between molds 9 and device 29.

Device 36 comprises a number of slides 27, which are equally spaced along guide 26 with a spacing D2 substantially equal to half spacing D1, and are loaded with preforms 3 at said loading station (not shown), so that each preform 3 is located between two empty seats 28.

Operation of machine 35 will now be described as of the instant in which each member 31 engages a preform 3 inside relative mold 9; and each station 25, which, in machine 35, coincides with relative station 23, is occupied by an empty seat 28. When the blowing operation is completed, molds 9 are opened as described previously to enable members 31 to transfer the blown bottles 2 along relative paths P4 to relative empty seats 28; and device 36 is operated to impart to each slide 27 a

movement substantially equal to spacing D2, and to feed a new preform 3 into each of stations 23,25.

At this point, members 31 transfer the new preforms 3 along relative paths P3-which, in machine 35 coincide with relative paths P4-into relative molds 9 and into a position coaxial with relative axes 11.

Machines 1 and 35 therefore have the advantage of each preform 3 and relative bottle 2 being transferred between relative mold 9 and relative stations 23,25 along respective paths P3 and P4, which extend crosswise to the direction 12 in which units 8 are aligned, and are each of constant length alongside a variation in the number of units 8.

Alongside a variation in the number of units 8, the output rate of machines 1 and 35 is therefore always substantially equal to the output rate of a machine with one unit 8 multiplied by the number of units 8.

Machine 35 also has the further advantage of one side of units 8 being substantially clear, thus enabling fast, easy access to units 8 for inspection and maintenance.