Device for transporting a parison from the tube forming head to the blow molding machine

The parison transporting device includes two opposite side wall elements whose inner surfaces facing each other are curved in accordance with the mold cavity of the blow mold. Rods which in the longitudinal direction of the parison transporting device are mounted in offset relationship in alternate fashion and form the bottom of the parison transporting device are secured to the side wall elements. The side wall elements are movable towards and away from each other. In the tube receiving position, the side wall elements are spaced apart from each other to such a degree that a parison tube can be placed in straight fashion between the side wall elements. The side wall elements are subsequently moved towards each other up to a distance corresponding to the thickness of the parison tube, whereby the parison tube is exactly shaped in the form of the mold cavity of the blow mold. The side wall elements are moved apart above the blow mold to such an extent that the parison tube drops into the mold cavity. The parison transporting device is now moved linearly.

BACKGROUND OF THE INVENTION 
The present invention relates to a parison transporting device. 
When hollow plastic articles, such as tubular pieces which are bent once or 
several times, are produced, it is difficult to insert the tubular parison 
into the blow mold. Since the mold cavity of the blow mold which 
corresponds to the hollow plastic article to be produced has more than one 
axis, and since these axes are at angles with one another in space, i.e., 
the mold cavity may consist of a plurality of sections extending upwards 
and downwards towards both sides, the part of the blow mold that is either 
in a horizontal position or in an inclined position can be moved back and 
forth and also up and down accordingly while a tubular parison is being 
discharged in straight fashion, or these movements can be performed by the 
extruder when the mold is at a standstill. Since either the whole mold 
closing support including the blow mold or the extruder with the 
associated tube forming head must be moved in three axes perpendicular to 
one another, considerable weights must be moved, as both the mold closing 
support and the extruder itself weigh several tons, even in the case of 
small machines. 
To avoid movement of one of the two heavy subassemblies extruder/tube 
forming head or mold closing support with blow mold, DE 43 05 735 C1 
suggests a lightweight interim transporting mold which includes an 
upwardly open mold trough whose bottom can be opened. This interim 
transporting mold receives the tube exiting from the tube forming head and 
is then moved to the blowing station to hand over the tube to the blow 
mold. The interim transporting mold is of little weight, one of the 
reasons being that no closing forces have to act on it and no cooling 
channels have to be accommodated therein, so that it can be moved with 
considerable smaller effort than one of the subassemblies extruder/tube 
forming head or mold closing support with blow mold. 
The mold trough of the interim transporting mold according to DE 43 05 735 
has the shape of the mold cavity of the blow mold. To receive the tube 
exiting from the tube forming head, the interim transporting mold is moved 
in its tube receiving position in both horizontal directions and is lifted 
or lowered in vertical direction until the whole tubular piece rests in 
the mold trough. The interim transporting mold is subsequently positioned 
above the lower part of the blow mold such that its mold trough lies 
vertically above the mold cavity of the blow mold, whereupon the bottom of 
the mold trough is opened, so that the parison drops into the mold cavity. 
Such an interim transporting mold has turned out to be best suited in 
practice. However, with such a prior-art solution for the problem of 
avoiding movement of great weights, the interim transporting mold must be 
moved below the tube forming head in three dimensions, requiring an 
expensive controlling and moving mechanism. 
As far as the production of pipe bends is concerned, it is suggested in DE 
30 38 590 C2 that the free end of a thermoplastic parison should be seized 
by a blow pin which is forcibly guided on an arm in such a manner that the 
blow pin inserts the parison into the mold cavity of a lower blow mold 
half. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to provide a parison transporting 
device for a blow molding machine whose moving mechanism is very 
simplified and to maintain the above-mentioned advantages at the same 
time. 
It is another object of the present invention to provide a method for 
producing hollow plastic articles, which are bent once or several times, 
at low costs. 
The parison transporting device according to the invention includes side 
wall elements whose edge contours correspond to those of the mold cavity 
of the blow mold, i.e., have the same curvature as the cavity when viewed 
from above. The side wall elements are arranged such that they can be 
moved towards and away from each other. This makes it possible to space 
apart the side wall elements in the tube receiving position below the tube 
forming head to such an extent that the parison tube can be placed in 
straight fashion between the elements on the bottom elements which close 
the bottom in this position. In a second operative position, the side wall 
elements are moved towards each other such that their distance 
substantially corresponds to the thickness of the parison tube, whereby 
the parison tube previously positioned on the bottom in straight fashion 
is given a shape whose curvature corresponds to that of the mold cavity of 
the blow mold. When the parison transporting device is then positioned 
above the blow mold such that the center line is located between the side 
wall elements or the center line of the curved parison above the center 
line of the mold cavity of the blow mold, the bottom of the parison 
transporting device is opened, so that the parison drops into the mold 
cavity. 
The parison tube can here be molded immediately after the tube has been 
placed in straight fashion between the side wall elements after clamping 
plates have been moved relative to one another for squeezing off the 
tubular piece so as to separate it from the subsequent tube and to close 
the tube thereby. So-called support air which is admitted through a nozzle 
of the tube forming head into the tube while the tube is being discharged, 
is entrapped in the parison tube, so that the latter cannot collapse. 
It is, however, within the scope of the invention to move the side wall 
elements towards the mold cavity or, however, above the mold cavity 
towards each other while the parison transporting device is being 
transported so as to change the tube into a curved parison. 
The bottom of the parison transporting device may be even, preferably 
horizontal, it may also extend in accordance with the curvature of the 
mold cavity of the blow mold in height direction (Z-direction) to avoid 
differences in length. 
The side wall elements may each be firmly connected to the associated 
bottom elements. To this end, the invention suggests in a further 
embodiment that the bottom elements should be rods which in the 
longitudinal direction of the parison transporting device are secured to 
the side elements in alternately offset relationship with each other, and 
are preferably embedded therein. As already mentioned, all of these rods 
may be arranged at the same height or may be positioned in accordance with 
the course of the mold cavity one above the other or below the other. 
The rods can have a semicircular diameter without the invention being 
restricted thereto. Rods with a rectangular cross-section may also be 
used. 
Instead of rods, plate-like elements may be used that can be secured to the 
right and left side wall elements also alternately. 
Furthermore, the bottom elements, for instance the rods, should have such a 
length that they overlap one another in the tube receiving position in 
which the side wall elements which extend in curved fashion when viewed 
from the top have thereinbetween at least a continuous straight and free 
space of a width that is slightly greater than the thickness of the tube 
to be received, so that the parison tube rests on closely adjacent points. 
To enable the side wall elements to move towards each other to such an 
extent that only a spacing preferably corresponding to the thickness of 
the tube is left between them, bores should be formed in the side wall 
elements for the entry of the bottom elements, for instance rods of the 
opposite side. 
It should be noted that the invention is not limited to the feature that 
both side wall elements are moved for reducing their distance, but there 
may also be chosen such a configuration that one side wall element is 
arranged stationary whereas the other side element is made movable. 
When the bottom elements are fixedly connected to the side wall elements, 
the bottom of the parison transporting device is expediently opened in 
that the side wall elements are moved apart to such an extent that the 
free ends of the bottom elements have formed thereinbetween a sufficient 
space through which the parison can drop into the mold cavity. 
However, it is also within the scope of the invention that the bottom 
elements are arranged to be movable relative to the side wall elements. In 
such a case rods may be provided which respectively pass through the 
associated side wall elements, to which end the rods may, for instance, be 
seated in pneumatic cylinders arranged on the outside of the side wall 
elements. In this development of the invention the rods can be moved in 
the tube receiving position inwardly to such an extent that they overlap 
in the tube receiving portion, the overlap being not absolutely necessary. 
When the side wall elements are then moved to each other to give the tube 
a curved shape, the rods can remain in the extended length and enter into 
bores of the opposite side, and it is here within the scope of the 
invention that the rods are also bent or pressed rearwards. To release the 
parison from the mold cavity of the parison transporting device downwards, 
the bottom rods can then be retracted outwards without the spacing between 
the side wall elements being varied, which has the advantage that the 
parison keeps its predetermined curved position in an absolutely reliable 
manner while the rods are being retracted, since it rests on the side 
walls of its mold cavity. 
The parison transporting device of the invention is only moved linearly, 
i.e. both in the tube receiving position below the tube forming head and 
when approaching the blowing station. 
The side wall elements are also moved back and forth only linearly, so that 
the parison transporting device only requires a simple moving mechanism. 
Further features of the invention become apparent from the following 
description of a preferred embodiment and from the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The parison transporting device includes two side wall elements 1, 2 whose 
inner sides facing each other have edge contours 3, 4 when viewed from 
above, the contours corresponding to those of the mold cavity 5 of the 
lower blow mold half 6 (FIG. 4). When viewed in vertical section, the 
inner wall surfaces 3, 5 extend in vertical direction as shown in FIG. 2. 
Rods 6, 7 which in the longitudinal direction 8 of the parison transporting 
device are secured in alternately offset relationship are embedded in side 
wall elements 1, 2. The rods 6, 7 overlap in the tube receiving state of 
the parison transporting device in the area which receives, in straight 
fashion, a parison tube 10 exiting from a tube forming head 9. The tube 
forming head 9 is arranged in horizontal direction. 
The rods 6, 7 which are secured to a respective side wall element have 
formed opposite thereto in the respectively other side wall element bores 
11 that are entered by the free end sections of rods 6, 7 when the side 
wall elements 1, 2 are moved towards each other to such a degree that the 
distance between their inner walls 3, 4 substantially corresponds to the 
thickness of the parison tube 10. This state is referred to as a "closed" 
state. 
The side wall elements 1, 2 are suspended by means of holders 12 to 
transverse bars 13 and are guided thereon, for instance, on sleeves 
provided with ball bearings. The side wall elements 1, 2 can be moved 
towards and away from each other with the aid of drive means (not shown), 
for instance, pneumatic piston/cylinder assemblies, as outlined by the 
double-headed arrow in FIG. 1. 
Two opposite clamping plates 14 are secured to the rear face side of the 
side wall elements 1, 2 with the components required for their operation, 
such as holder, guide, actuation means, etc. The clamping plates are moved 
towards each other when the tube 10 which has exited from the tube forming 
head 9 and has been placed on rods 6, 7 has reached a predetermined 
length, whereby the end 15 of the parison tube 10 as well as the beginning 
16 of the subsequent tube piece are closed. Since support air is blown 
into the tube when tube 10 is being discharged, the support air is 
entrapped in the parison tube 10 after the latter has been separated and 
closed, so that the parison tube 10 cannot collapse. 
FIG. 3 shows the closed state of the parison transporting device in which 
the parison tube 10, when viewed from above, has assumed a shape which is 
identical with that of the mold cavity 5 of the lower blow mold half 6, 
with the exception that the distance between the inner walls 3, 4 of the 
side wall elements 1, 2 is smaller than the width 17 of the mold cavity 5, 
since the parison tube 10 in the mold cavity 5 has still to be blown up to 
form the final product. 
The transverse bars 12 are movably secured to longitudinal bars 18, being 
again guided, for instance, on ball-bearing sleeves 17. The longitudinal 
bars 18 extend from the blow head 9 (strictly speaking beyond the head) to 
the blowing station. A drive means (not shown) moves the parison 
transporting device between the tube receiving position and the parison 
discharge position. 
When the parison transporting device has been positioned above the lower 
blow mold half 6 in such a manner that the center line 19 of the parison 
tube 10 is located above the center line 20 of the mold cavity 5 of the 
lower blow mold half 6, the parison transporting device is widely opened 
by moving the side wall elements 1, 2 apart to such an extent that the 
parison tube 10 can fall down between the free ends 21 of rods 6, 7. 
Alternatively, the releasing operation may be performed such that in the 
closed state (FIG. 3) the rods 6, 7 are moved outwards out of the side 
wall elements 1, 2 until the whole bottom of the space between the side 
wall elements 1, 2 is open. 
FIG. 6 shows the state in which the parison tube 10 is arranged in the mold 
cavity 5 of the lower blow mold half 6. The blow mold is now closed by 
means of the upper blow mold half (not shown), whereupon air is preferably 
introduced by a blowing needle (not shown) into the parison tube, thereby 
pressing the tube against the wall of the mold cavity 6 and shaping the 
desired hollow body. The parison transporting device is again moved into 
the tube receiving position.