Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
' 21925Q3
A blow molding m~chine operating in accordance with the
reheat method for producing hollow plastlc article~
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The present invention relate~ to the production o~ plastic
hollow articles in a spec~al type of blow molding process
wherein pa~ison6 made in an in~ection molding proce~s are
taken from a supply device and heated on a hoating path to
blow tQmperature and are subsequently transferred into one or
a plurality of blow molds in whlch they are blown to form
hollow pla~tic articles of a 6hape and size predetermined by
the mold cavity of the blow mold, subsequently cooled and
then removed. Such a method in which cold parison~ that have
b~en removed from a supply device are aga1n heated up to blow
t~mperature is mo6t of the time called "reheat m~thod".
To be able to heat the individual par~60ns evenly up to blo~
temperature over their entire length and above all o~er their
entire cross-section, and since the heat penetrates through
the cross-section only at a relatively slow pace, the
pari~ons mostly move on 8 long heating route along a straight
or circular p~th on which spaced apart heating units, mostly
i~rared radiators, are arranged, the portions of the path
between the heating units being so-called compensating or
cooling sections in which the heat, which has externally been
~pplied to the parisons, has enough time to penetrate through
the cross-section. Moreover, these sections are to ensure
that the external wall of the parison i6 not overheated,
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which happens quite often wlth many plastics that are
sens~tlve with respect to the 60-called proce~s window.
Such a ~ystffm does normally not present any difficulties in
cases where only one parison i~ transferred ~nto a blow ~old
one at a time after having passed throug~ the heating path
(e.g. EP 0 387 735 Al). By contrast, if pari~onc are to be
transferred into a plu~ality of blow molds arranged on a
spec~al blow path 60 as to incr~ase the output snd thu~
enhance the economlc e~ficiency of a reheat ~ystem, the
di~ficulty ari~es that th~ pari~ons are ~o move along the
heating p~th in A relat1vely close pitch for an e~ficient
exploitation of the radiation emitted, while the pitch of th~
cavities of the blow molds has to ~e adapt~d to the volume of
the blown ~ollow articles and thu6 to the size o~ the blow
moldc with their cavitie6 or ~old cavities and cooling
chaDnels, i.e. the parison~ are to pass along ~hs heating
path in ~elatively close pitch, whereas the blow mold
ca~ities mu~t be acco~mo~Ated on the blow path in wider p tch
in comparison therewith.
DE 31 30 129 A1 de~cribe~ this problem and suggests, as the
solution, a heating wheel which rotate~ between heating boxes
~ixedly arrsnged on the outer circumference with a clo~e
pitch ~or the parison6 or the retAinin~ mandrels receiving
said parisons, from which wheel they are trans~erred by a
tran6fer wheel to a blow wheel on which the blow molds ere
arranged in a pitch adapted to the size of said molds. As for
the 6uggestion made in DE 31 30 129 Al, a transfer is
possible for the rea~on that at the beginning not each of the
retaining mandrels is equipped with a parison fxom the supply
device, but only e.g. the first, third, fifth, 6eventh
mandrel dnd then after ~ complete rotation of the h~ating
wheel every second, ~orth, sixth, eighth ... retaining
mandrel, and a paricon i~ transferred accordingly into a blow
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mold only after two rotations. since a new parison is
simultsneou61y put onto every po6ition on the heating wheel
that has b~come free due to transfer to the blow whesl, with
the parison being tran~ferred into a blow mold on the blow
wheel ~fter t~o rotations, the m~chine operates continuously,
and since it i6 only every second pari~on that is transf~rd
from the ~oating wheel to the blow wheel ~n continuou~
sequenre, the pitch on the blow wheel can be twice a~ great
~s ~hat on the heating wheel. o~ cour~e, in this method every
pa~ison can e.g. pa58 through the heating path three tLmes
be~ore being transferred to the blow wheel, and the blow mold
pitch can be chosen accordingly.
Th16 mothod, however, has, e.g., the disadvantage that in
thi~ sy6tem, too, only one blow mold including a cavity can
be filled with a pari~on one at a time and al~o that every
parison hss to pass through two rotation6 of the heating
wheel before being removed from the he~ting wheel and
transferred to the blow wheel, with the effect that the
heating p~th consi6ts of two equal sections, 60 that, as ~ar
as a heating operation up to the blow temperature is
conc~rned, there i6 no pos6ibility of adaptively ~hanqing ~he
heating conditions and the compensating and/or cooling
section~ between the heeting devices during the ~econd run in
compari~on with the first ~un.
Moreove~, a machine which operates in accordance with this
known system requires noticeably more space ~or the same
output.
It has therefore been the object o~ the p~esent invention to
prrovide a reheat type blow molding machine with the aid of
which it i6 not only po~ible to guide the parisons in close
pitch on the heating path past the heating section~ and the
inte~po6ed compen6ating and/or cooling sections, while the
'~192sn3
blow mold or blo~ mold cavity pitch on the blow path i6
independent of the pitch of the pari6cns on the heating path,
but with which ~ plurallty of blow mold~ ~n th~ blow path or
one or a plurality of blow mold6 with a plurality of blow
cavitie~ can simultaneously be equipped with parison~ which
c~n simultan~ou61y be blown to form hollow pla~tic article~.
This ob~ect of the lnvention is sol~ed ~ith the means de~ined
in p~tent clatm 1. The subclaims relate to expedlent
embodiments o~ the inventive idea. The invention 18
illus~rated in the drawings wi~h re~erence to ~n ~mbodiment
and described wi~h reference to said embodimen~.
~ig. 1 is a partial view on a blow molding machine
~ccording to the invention, where ~ome devices thst
do not pertain to the invention, for 1nst~nce
gearing and control cabinets, have been omitted;
~ig. 2 shows a 6ection taken from Fig. 1 on an enlarged
~c~le in compa~ison with Fig. l;
~ig. 3 6how6 a cycl~ time diagram.
1 gener~lly designates a ~eating path on which an endless
conveyor device, such as a chain 2, runs over de~lection
pulley~ 3, 3'. Chain 2 carries outwardly pro~ectin~ arm~ 4,
of which only a ~ew have been drawn in. The ends of arm6 4
are fo~med a5 parison mounting6, e.g. in the form of
ret~ining mandrel~ which are put lnto rotation during the
advance movement. A parison taken from a 6upply device 1' can
be attached onto each of retaining mandrel~ 5. 6, 6~, 6~l ...
6n de6ig~ate heating means arranged in spaced-ap~rt
relation6hip along the heating path, for lnstance, infrared
radiators whose radiation will externally heat the parisons
which have been attached onto mandrels S. The drawing just
show6 heating means arranged along a side of the conveyor
2192~q3
device 2, but these mean6 may also be po6itioned next to the
advance run and the return run of chain 2 in the
illu~tration.
Each heating path has associated therewith at lea~t one blow
path generally designated ~y 7, on which in the illu6trated
c~se a blow mean~ 8 i8 arranged with a blow mold ~' having
e.g. four respective oavitioo or mold cavitie~. A ~low path 7
fu~ther includes ~ ch~in 10 ~hich ~otat6s ~round deflection
chain wheel6 9, 9' in the d~rection of the ~rrow and from
which the blown hollow pla~tic article6 are removed. In the
case of the illustrated machine a heatlng path 1 operates
along two blow paths 7, 7a, t~s 1~6t-mentioned blow path
being equipped with a blow means 8a, which is identical with
blow mean~ 8, and with deflection pulleys 9a, 9a' and a chain
10~ runn~ng around pulley~ 9a, 9a'.
Tran6fer device~ 11, lla which in controlled fashion remove
the par~on~ which have been heated to blow temperature from
the deflection portion of the heating path and put them on
chain 10 of the blow path or ch~ins 10, lOa of blow paths 7,
7~ are interpo6ed between the end of the heating path 1 ~t
the left side in the drawing and the beg~nn1ng of the blow
paths 7, 7~ at the right ~ide in the drawing, i.e. between
deflection pulley 3 of heating path 1 and deflection pulley6
9, ga of blow path 7, illustrated on an enlarged ~cale in
Fig. 2. These tran~fer devices 11, lla are o~ such a
structure that on the heating path they grip a plurality,
according to the illustxation, for example, a set of four
parisons at the same time, remove th~m from their retaining
mandrels ~nd pivot them over chain6 lo, lOa of the blow
path(~). To thi~ end, the illustrated lev~r-~haped transfe~
devices ll may e.g. have provided th~reon grippers 12 which
opexate mechanically or pneumatic~lly (negative pressure).
~lY2sa3
As chown in the drawings, the one tran6fer device, e.g.
transfer device 11, grip~ with its g~ippers, e.g. grippers
12, 12', 12", 12"', ~ ~et of ~ve~al pari60ns, e.g. foux
pari~ons 13, 13', 13", 13/", wheneve~ 6aid parisons are
equally spaced apart in the deflection posit~on on deflectlon
pulloy 3 of heating path l. In thi~ position, i.e. whe~ the
conveyor devic~ 2 is deflected ~ the deflection pulley 3,
the pitch between the parisons 13 and their retaining
mand~el6, ~espectively, becomes greater because the conveyo~-
devlce deflection radiu6 r of pulley 3 is smaller than the
radiuc R which is de~cribed by the circul~r arc through the
center axes of the parisons at~ached onto the end~ of ~rms 4.
This mean6 that as soon as the predetermined number of
pa~isons on their arms 4 have re~c~ed the deflection pulley
and all, e.g. four parisons at a t~me, occupy an angle
e~ually divided by the center pl~ne M on the deflection
pulley 3, the parisons will be transferred from the heating
path onto the blow p~th if the length of arm~ 4 ~nd thus the
deflec~ion radius of the parison~ a~Q dimensioned such that,
when the take-ovsr position has been reached, the distance
between the pa~isons is equal to the pltcb of the mold6 of
mold cavities in the blow mold or blow mold~.
The conveyor device 2 is expediently moved cyclicly in the
direct~on of the arrow, i.e. each advance movement i~
followed by a standstill pe~iod. Adv~nce and stand~till
periodc on the heating path may, for in6tance, amount to 0.2
s each.
Thus, the parisons are removed by the transfer device 11 in
spacsd-ape~t relationship ~rom the con~eyor device 2 ~nd ~re
transferred to the chain lo of blow path 7, the spacing of
said parisons corre6ponding to the one of the blow mold
cavitles in one or a plurality of blow molds that are
arranged side by side.
2192503
The conveyox device o~ the blow path, e.g. chain 10, i6 also
moved in t1med fashion, ~nd the parison8 are tran6ferred f~om
the conveyor device 2 to the conveyor device 10 wheneve~ the
two devices have a 6tandstill period at the same time o~
~lmost ~t the same time. The advan~e and 6tandstill ~eriod~
o~ chain 10, however, can be ~aried within ce~tain limit~,
since th~y are independent of tho6e of the heatlng path, and
can be adapted to the blow cycle time, i.e. the time noeded
fo~ ~eeding a blow mold with one ot 8 plurality of p~ri~on~
until the ~emoval of the hollow pla~tic art1cles blown. There
i8 enough time ~or such an operation because after each
gripping of e.g. fou~ parisons at an advance and st~nd6till
time of 0.2 s each, an ~dvanae time of 0.2 s x 4 ~ a
ctand6till time of 0.2 s x 4 = a period of 1.6 8 will pa~s on
the heating path untll there are again four pari60n~ to be
grippsd on the portion of the deflection pulley 3 fo~ ~emoval
purposes ~nd ~or the pivotal movement of the t~ansfer devices
which, of course, also needs some time, though a short one.
This ratio will be fu~ther improved in favo~ of a longer time
interval for gripping the parisons and for transferring and
processing said parisons in the blow path ~f, in accordance
with the illustratlon, a h~ating path 1 operates on two blow
paths 7, ~a, because in such-a case the transfer dovics 11,
for instance, will not grip the next four pari~3ons which have
been precycled fo~ deflection after the parisons have been
transferred to chain 10, but only those four parisons
following the n~ct ones, the above-mentioned parisons which
have been precycled after the transfer are gripped by the
transfer device lla and moved onto blow path 7a.
Hence, in the illustrated embodiment the cycle r~tio wlll be
4 : 1 if a cycle consists of an advance time and a ~tandstill
time. This mean~ that one cycle is passed on the blow path at
the ,same time at which four cycles a~e passed on t~e heating
219250~
path 1. An atte~pt is made in the diagram of Fig. 3 to
explain this proce6s; it i6 here a~sumed, but not imperative,
that a cylce i~ also divided on the blowh path into two
section6 of equal length, namely advanc~ time and ~tand6till
time. As can be seen, on the he~ting path 1, four cycles th~t
consi6t of advance (v) ~nd 6tandstill (s) are needed to brin~
four pa~is~n6 on the deflection portion into the positlon
required ~or a txansfer onto the blow path. It ~ here
important that the standst~ll (s) of the conveyo~ device 2 of
the he~t~ng path 1 and the ctandstill (S') of the chaln 10 of
the blow path 7 overlap to ~uch an extent that both de~ice~
have a ~tandstill pe~iod at the sams time, the standstill
period o~ chain 10, however, being pos~ibly longer than that
of conveyo~ device 2. During the standstill period of chain
10, it is not only the parisons already positioned on the
heating path, in the illustrated ~as~ fou~ parisons, th~t are
removed from ~aid path and put ~n chain 10, but four parl~on~
that a~e po~itioned between the opened blow mold parts are
g~ipped by the closing mold, blown, cooled and then ~emoved
from the mold a~ blown hollow articles. It would even be
possible to cyclicly move the conveyor device 2 of heating
path 1 onw~rds a~ter a transfer device has been li~ted, i.e.
even before the pari60n6 have been put on the conveyor device
10 or lOa of blow path 7, 7a. Thereupon, an advance movement
(V) of four par1son6 takes place on the blow path between or
toward6 the blow mold halves, which were opened 1n the
meantime, and the ti~ing cycle begins anew. The difference is
that in the stralght section of the he~ting p~th the p~ri60ns
which pa~s through the heating devices in close pitch ha~e
been given, on the deflection portion, a g~eater spacing from
one another (- pitch) which corresponds to the ~itch of the
mold cavities on the blow p~th, while the pari60ns on said
blow path do not change their pitch, but ~aintain lt, since
in the case of the heating path the de~lection radius of the
conveyor device 2 is ~maller than the ~adiu6 described by the
21~ZS03
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parisons on a~ms 4, while on the blow path the de~lection
~adius i8 equal to the one described by the pari~on~ carried
by chain 10. If according to the llluxtration in Fig. 1 a
heating path 6erves two blow paths, the parison6 are
transferred from the heat~ng path 1 to the blow path 7 not
durlng the standstill period of the eighth cycle, but only
du~ing that of the twel~th cycle on the deflection p~th, i.e.
twice the amount of time i8 available ~or th~ ~dvance
movement and th~ transfer o~ the parison6 into the mold
cavitiec and fo~ the blowing and cooling opera~ions.
As can be seen, this cystem is very flexible because,
e~pecially on the blow path, a cycle ne~d not cons~et of
advance and standstill times of the ~ame length. To g~in time
for thick-walled hollow plastic articles for blowing and
coollng operations in the blow mold, lt is e.g. possi~le to
interpose a co-called urgent advance between two s~and6t~11
timos, i.e. to p~olong the standstill tlmes, and it 15
equally pos~ible to prolong the ~dvance time accordingly,
e.g., ~n orde~ to gain a longer cooling or compensating time
for the paxison6 transferred to the blow path prior to their
int~oduction into the blow mold. As is gene~ally known, the
reheat method has certain difficulti~s in evenly distrlbuting
the heat, which ha6 been applied to the su~face of the
pa~i60ns from the outside, ac~o~s the entire cross-section of
the parisons down to the inner wall, which is quite easily
accomplished when the heat has enough time to propagate
across the cross-section evenly.
Moreover, the machine according to the invention is flexible
with respect to the number and arrangement of the blow molds
and the size of the mold cavities, especi~lly when a heating
path serves two blow paths. For in6tance, ~t is possible, of
cours~ within certain limits, to produce sm~ller plastic
hollow articles of a greater wall thlckness on one blow path
2192503
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~nd corre6pond~ngly greater and thu6 thinner-wallad hollow
plastic article~ on the ~econd blow p~th from the same
p~rison~ that have been h~ated on the heating path.
