Note: Descriptions are shown in the official language in which they were submitted.
7~
The present inventlon relates a method or producing
a hollow article which has a mouthpiece, con-tours and/or changes
of wall thickness from organic thermoplas-tic material, where the
plastic in a plastic state is extruded from a tubular die against
a draw-off device.
In a known process (German Pa-tent Specification No.
1,062,002) the amount of plastic extruded from the tubular die per
unit oE time is constant in practice and the draw-off speed is
carefully adjusted relative to this extruded quantity, i.e.,
is also constant. A preform is produced the wall thickness of
which is constant along its length. If the draw-off speed i5 .`
greater than would correspond to -the amount of plastic extruded,
then the preform will be stretched; if the draw-off speed is less,
then the preform will be compressed. Both the ex-trusion and the ~;
co~pression result in uneyual thickness.
In the aforesaid process, if a tube of constant diameter
is blown from a preform, then not only part of the tube wall, but
also the shoulder leading to the mouth-piece must be formed from
the part of the preform close to the draw-off apparatus, so that
the resulting part of the tube wall thus generated is thin com-
pared with the rest of the tube wallO It is undesirable for the ~
wall thickness of a tube to be thicker at the end which is remote ~'
from the mouth-l~lece than close to the mouth-piece. Hollow
vessels with con-tours, e.g., bulging bottles, can be produced by
the aforesaid process only with the disadvantage that the vessel
has thicker walls in regions of smaller cross-sections and thinner
ones in regions of larger cross-sections. Nor is it possible to
deliberately make the walls of a vessel to be produced thinner in '
some places and thicker in others. L
A method is already known (Kautex Information 1, reprint ~;
from 'IMaschinemarkt", 75th year, Issue 8, 22, 66/1969~ of
producing a hollow vessel with more or less arbitrary contours
and/or controlled changes of wall thickness by first producing a
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preform with a controlled change of wall thickness. For this
purpose, the tubular die -learance is varied during the pro-
duction of the preform, while keeping the quantity of plastic
extru~ed per unit time constant. In this known method, however,
the preEorm is worked fro~ above downwards and free, i.e., it
is not clamped between the tubular die and a draw-off device
during its production. If the preform is clamped during its pro-
duction between the tubular die and a draw-off device, no preform
with controlled wall thickness can be produced solely by changing
the tubular die clearance.
The present invention provides a method and an apparatus
of the aforesaid type in which a tube blank with generally arbi-
trary contours can be exactly produced with slight changes of
wall thickness and/or with controlled changes of wall thickness, 1
by utilizing the effect of the quantity of plastic extruded per
unit time and/or the draw-off speed and/or the tubular die cross-
section on the character of the preform. In particular the in- ~
vention provides a method for the manufacture of a preform which r
is extruded from a tubular die and is held by a draw~off device,
where, without influencing the temperature of the material in the
tu~ular die or of the preform, more or less gradual changes of the
preform wall thickness can be produced without constriction of ~
the preform, while avoiding any concertina-like deformation of the ;
preform. .-
The present invention provides a method of the aforesaid
type in which each of the two parameters subjected to change is
one of the three apparatus parameters, namely extruded quantity
of plastic, ring nozzle cross-section and draw-off speed.
The invention also provides an apparatus of the aforesaid
type in which the addition control commands act selectively on two
of the ollowin~ three deviceso conveyer device, drive device,
and if provided for, the device for adjusting the width of the
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gap aperture of the tubular die.
In the process of the Presen-t invention, whenever the
draw-off speed is reduced or -the quantity of plastic extruded
per unit time is increased, the preform wall thickness becomes
greater, and whenever the draw-off speed is increased or the
quantity of plastic extruded is reduced, the preform w~ll thick-
ness becomes smaller. Since the quantity of plastic extruded can-
not be varied as rapidly as the draw~off speed~ preferably the
draw-off speed is changed for the purpose of changing the preform
wall thickness. A change in the amount of plastic extruded is
preferably under-taken additionally to the change o~ draw-off
speed in order to attain particularly large changes in the preform
wall thickness.
According to the present inven-tion individual parts of r
the preform wall can be made thicker or thinner, depending on
how much plastic leaves the tubular die per unit time. The wall
thickness of the preform can also be varied in width in different
regions by changing the draw~off speed, because a change of draw- r
off speed primarily affects the region of the generated preform
near the tubular die rather than the preform as a whole, to the ~;
extent that it is present at the given time.
The invention also provides that in addition the cross-
section of the tubular die may be changed during production of
the preform which makes it possible to generate very distinct
variations of cross-section of the preform in a relatively short
time.
By means of the process of the present invention it is r
possible, even in the production of a clamped preform, to furnish
~ the preform with an exactly controlled tubular shape having
30 regard to the ultimate tube blank. The method of the present
invention is preferably applied when the pressure acting on the
plastic is reduced before the head mold starts to move away from
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the tubular die. Wi-th the pro(ess of the present invention pre-
forms for cylindrical finished par-ts which are desired to have
constant wall thickness over their en-tire length, for example
tubes or bottles, can be furnished with a wall that is thick at
the top and becomes conically thinner towards the bottom, by
varying the extrusion pressure, and this is possible even with a
clamped preform. Constant wall thickness in many cases is an
advantage from the standpoint of both the Einished tube blank and
printing on the blank. According to the p:rocess of the present
invention especially -tube blanks such as tubes or bottles are
produced which have a neck or a mouth-piece.
There are the following three variants of the process of
the present invention:
1) Chan~ing the quantity of plas-tic extruded and the
gap width (with constant draw-off speed): For example, iE the
quantity of plastic extruded per unit time and the gap width are
increased, there will be an increasé in the wall thickness of the
preform but there will be no concertina-like deformation of the
preform. If the quantity extruded and the gap width are decreased,
there will be a decrease in the wall thickness, but no extension ~;
of the preform as a whole, since stretching takes place only in `,:
the vicinity of the tubular die.
2) Change of draw-off speed and gap width (quantity of
plastic extruded remaining constant): If the draw-off speed is
reduced and the gap width increased~ there will then be an
increase in the wall thickness of the preform, but there will be no
concertina-like deformation of the preform. If the draw-off speed
is increased and the gap width reduced, there is then a reduction
in the wall thickness, but no extension of the preform as a whole. t
L.
3) Change of draw-off speed and quantity of plastic
extruded (the gap widtb remaining constant- If the quantity
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extruded is increased, then on account of the opposing off-take
device there is an increase in the preform wall thickness, and
a concertina-like deformation of the preform can be avoided by
increasing the dra~7-off speed. If the ~uantity extruded is
decreased, the wall thickness also decreases, and an extension
of the preform can be avoided by reducing the draw-off speed, or
an enhanced reduction of wall thickness can be attained by
increasing the draw-off speed, and, resulting therefrom, an
extension of the preform taking effect in the vicinity o~ the
tubular die.
A change in the rate of extrusion can be attained by
changing the r.p.m. of a screw conveyer or the speed of a piston
that forces the plastic through the tubular die, or by using
the screw conveyer additionally as a pis-ton. A chanye oE draw-
off speed can be attained e.g., by changing the admission of
fluid to a hydraulic piston-and-cylinder device. The storage
device by which the control is effected can comprise e.g., dogs
which cause the corresponding parts to slow down or speed up.
However, it is also possible to achieve the control commands by
means of suitably disposed switches which are activated by the
mo-tion Gf the tools during the production of a preform.
Electronically pre-established programs are also possible for
suitable control purposesO ~,
It is particularly expedient and advanta~eous when
all three apparatus parameters are subject to changeO It is
particularly expedient and advantageous also, when the tubular die
cross-section is subject to change in every case. An especially
preferred embodiment of the invention is obtained when in addition
to adjustibility of the quantity of plastic conveyed by the
30 conveyor and the adjustibility of the drive speed of the drivin~ i;
apparatus an adjusting apparatus i9 also provided for the width F
of opening of the tubular die.
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The present inven-tion will be fur-ther illus-tra-ted by
way of the accompanying drawings in which:
Figure 1 is a vertical cross-sec-tion of an essential
part of a device for producing a tube blank according to the
embodiment of the present invention and
Figure 2 is -the apparatus according to Figure 1
including additional devices.
Referring to the drawings, a tubular die is provided
at the bottom comprising a nozzle cone 1 and a concentric die
lQ nozzle 2.
The nozzle cone 1 and die nozzle 2 form an annular
die gap aperture 3 to which plastic 4 is conveyed through an
annular space between the nozzle cone 1 and the die nozzle 2.
While die nozzle 2 is in :Eixed location, i.e., is stationary,
the nozzle cone 1 can be moved up and down in the clirection of
arrow 5.
Opposite and abo~e the tubular die a draw-off device
6, also called a head mold, is provided and moves up and down
as shown by arrow 7. A mandrel 8 is provided centrally in the
nozzle cone 1 which projects forward out from the die nozzle 2
lnto a recess 9 in the draw-off device 6. Into -this recess 9 a
blow-needle 10 opens, which is disposed centrally in the draw-
off device 6. Half a blow mold 11 is indicated, which blow
mold may be closed or opened by moving the half blow molds back
and forth according to arrow 12. The blow mold has interior
contours, and in particular, has a region of relatively large
diameter~below which it is tapered inward over a slope above to
a region of smaller diameter which then tapers upward over a
slant and terminates in a region of larger diameter again.
At the side of draw-off device 6 is a trip dog 14,
which during the up and down motion slides past two proximity
switches 15 and 16 disposed at a distance from each other. The
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proximity switches form a control device and control the re-
traction motion oE draw-off device 6 and the wid-th of -the
nozzle die aperture 3.
The draw-off device 6 is first lowered and rests wi-th
recess 9 over the mandrel 8, and a plastic neck 17 or -tube head
is forced into -the space between the mandrel 8 and the recess
9. As the draw-off device 6 moves upwardly, accompanied by
additional extrusion of plastic through the nozzle die aperture
3, preform 18 is generated. This preform 18 has a changlng
wall thickness over its length. That is to say, depending on
the diameter ratios of the blow mold, a lower region of
greater wall thickness, passing through a region of decreasing
wall thickness to a region of thin walls, followed by a region
of increasing wall thickness and changing to one of thick walls,
which extends up to neck 17.
These changes of wall thickness arise when the draw-
off device 6 at first moves upward at a given speed
accompanied by a given quantity of plastic material extruded
from the noz~le die aperture 3. When trip dog 14 passes the
2Q lower proximity switches 16 this causes the draw-off speed to
be increased, and simultaneously reduces the quantity of
plastic extruded, and this results in a decrease of wall thick-
ness. When the upper proximity switch 15 is passed, the draw-
off speed increases again and the quantity of plastic extruded
is also increased. The resulting condition is retained until
preform 18 is completed. The start 19 of this preform
production takes place when draw-off de~ice 6 rests on the
mandrel 8. The conclusion of preform production takes place
when the draw-off device assumes the upper position 20
represented as shown in the drawing.
Very close to terminal position 20, in the region of
the path of motion of trip cam 14, there is another pro~imity
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switch 21, which acts on -the drive equipment of draw-off device
6, (not shown), when the latter moves into i-ts terminal
posi-tion 20. In addition, recess 9 has a -thread, i.e., it has
a shape such that it grips the preform in such a way as to be
able to pull it. ThiS pulling takes place when, under the
control of proximity switch 21, just before the termina]
position 20 its speed is greatly increased so that the entire
tube, i.e., the preform, is stretched.
The die nozzle 2 has a slope 22 in its upper region
on which the half blow molds 11 rest with a corresponding slope
23 when they are in the closed position. This slope 23 is
provided at the bottom on a floor section 24 which on -the inside
has a projection 25. These projections 25 of the two bot-tom
members 2 press against each other on closing the blow mold in
the region of mandrel 8, whicht being subject to an up and down
motion according to arrow 26 by means of a piston and cylinder
device (not shown~, has previously been retracted by the amount
of ~he projecting section 29. Thus, projections 25 press a
lower end region 27 of preform 18 together when the blow mold
closes, whence knife edges 28 of projections 25 are especially
ef~ective~
According to Figure 2, the draw-off device 6 has an
extension 30 which is guided for up and down motion on a rod 31
mounted on a platform 32. Between the draw-off device 6 and rod
31 a drive device 33 is disposed which is mounted on a platform
32 and engages extension 3Q. On platform 32 there is also
mounted an activating device 3~ which engages mandrel 8. Plat-
form 32 also holds a two--part adjusting device 35 which engages
the nozzle cone 1. The annular space between nozzle cone 1 and
the die nozzle 2 terminates below in an annular duct 36 into
which afeed hole37 opens. A delivery device 3~ is connec-ted to
feed hole 37 and is supported on platform 32. Delivery device
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38 includes a piston and cylinder arrangemen-t 39, the cylinder
of which may be filled with plastic poured -through a hole ~0,
and the piston of which conveys the plastic through feed opening
37 in-to annular duct 36 and thence into the annular space through
the die gap aperture 3.
Drive appaxatus 33, activating device 34, adjusting
device 35 and discharge device 3~ are each clouble-acting piston-
and-cylinder arrangements. Each of these piston-and-cylinder
arrangements is connected via lines 41 and ~ with a valve
arrangement ~3, 4~, ~5, 46, 47 and via these valve arrangements
to main lines 48, 49. Depending on the setting of the valve
arrangement the piston of the piston-and-cylinder arrangement is
moved forwards or backwards, and the speed of the pis-ton also
depends on the setting of the valve arrangement. Hydraulic
fluid or compressed gas serving the piston and cylinder arrange-
ment or arrangements is fed in or drained off via main lines 48,
49.
A unit 50, 51, 52, 53 of an electrical control appara-
tus is co-ordinated to each of the valve arrangements, only one
unit 52 beiny assigned to valve arrangements 46, 44 of regulating
device 35. The units act on the valve arrangemen-ts and adjust
them in -the desired manner through lines 54. The control appara-
tus is not fully described here because a suitable control device
can be designed by an expert without further instruc~ion. In
each case the control apparatus includes a storage unit to which
approximation switches 15, 16 and 21 belong, these being con-
nected through branch lines 55 to lines 56, which lead -to units
50, 51, 5~ and 53. For example, when trip dog 14 activates
approximation switch 16 r the latter sends an electrical impulse
to the units via branch lines 55 and lines 56. Depending on the
setting of the units, these give suitable con~ands to the valve
arrangements so as to adjust the latter in a desired manner.
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