Note: Descriptions are shown in the official language in which they were submitted.
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D~s; I "Jtion
Clos;~l~ lJnit for a Pl~lstic lnjection Molding ~
The invention relates to a closing unit according to the ~ .~nble of claim 1.
Injection molding m~rhi~ ~s of this type are used for plastics proc~ssin~
Plastic injection molding mach~nes o~several types are known in the art.
These m~hin~s typically include a C-shaped m~chine frame, with a hydraulic closing
unit c~rlying a fixed tool clamping plate secured to one leg for of the ms~chine frame and
~ positioning unit with a movable tool clamping plate suppotted by the other leg.
The positionin~ unit prefera~ly includes four cantilevered columns which are evenly
spaced on a reference circle and oriented in the direction of travel. The free ends of the
coluIrms are formed as claws.
The hydraulic closing unit further includes four locking sleeves fonning counter pieces of
the claws and shaped to match tlle claws, with the ~ree ends of the locking sleeves
wnnected to piston rods.
During the injection molding process, this fourfold mechanical closing assembly which
includes the columns and the hydraulic closing pistons, transmits the applied closing
force uniformly to both tool halves.
A closing unit employing this locking method is described in DD 274 ~90 Al by the
Applicant. Each of the four hydraulic loclcin{~ assemblies consists of a piston-cylinder
unit with a movable piston rod. The free end of the piston rod faces ~e corresponding
colurnn of the positioning unit and is - like the claw of the column - formed as a star-
shaped claw. ~ach of thc claws has an outer shoulder for transmitting the closing force.
The rotatable claw sleeve forms thc mcchar~cal linkage between the two claws; the
rotatable claw sleeve is supported in the fixed leg of the machine frame and has two ir ner
shoulders for transmitting the closing force.
~ 1
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In the closing position, the t~,vo opposite claws are locatcd in the claw sleeve which is
held in a pred~tc,...;-.ed radial position. By rotating the claw sleevc from the outside, the
~ho~ld~rs of the claws and the claw sleeve begin to overlap and providc a col~ncclion
bet~veen the piston-c~linder unit and the column capable of car~ying an axial load~
I his locking assembly meets atl functional req~u;l~"le.,~.
The lockin~ assembly, ho~ever, is very ex~xllsive to m~nnf~ct~e, since eaeh locking
assembly requires two cl~w pairs wilh intlicate contours.
The complexity of the manufacturing process further increases the manufacturing costs.
It is therefore an object to provide a closing unit of the type described above where each
connection has only one pair of claws.
The object is solved by the characterizing f~lu~,s of claim I .
Advantageous embodim~nts are described in the dependent claims Z to 4.
Ille invention elim;n~tt~s the disadvantages associated with conventional devices.
Most advantageously, the closing unit results can be n~nllf~ctured much more cost-
effectively. Instead of manufacturing a complete pair with expensive contours, relativcly
nsive rotationally syrn~etr~c components are used instead.
Advan~geously, the first force tr~ sion surface is also mo~ed out of the re~ion of the
fixed tool clamping plate and into the free re~ion at the sarne level as the adjacent form
tool half. Consequently, a considerable arnount of free space is gained in the open
position of the closing unit to set up tooling.
The buffer is designed to prevent the eolwnn from striking the piston rod, thereby
preventing damage to lhe COmpOnentS and also reducing noise.
The invention is described hereinafter with respect to an embodime~.
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Tt is shown in
FIG. 1 a sçh~ tic cross-section through a closing unit acco~ .g to the invention and
FIG. 2 ~ partial cross-section of the claw co....e~ion accordil1g to the invention.
Since the structure of a plastic injection molding m~chine is known in tlle art~ of the C-
shaped m~rhin~, frame and the two legs only the machine bed I is shown.
A fixed tool clarnping plate 2 is secured to one of the legs, whereas a positioning unit 3
with a movable tool clamping plate 4 is su~o.ted on the other leg.
The positioning unit 3 is guided over its cntire path in the machine bed 1. The
positioning unit 3 is driven by a hydraulic drive (not shown).
A form tool half 5 i5; n~.hçd to thc inner surface of the fixed tool clampin~ pJate 2, with
the other form tool half 6 ~t'.hed to the inside of the movable tool clamping plate 4.
The positior~ing unit 3 includes closing columns 7, ~hich are supported in the movable
tool cl~mping plate 4. On the side Facing away from the fo~n tool, the closing colurnns 7
are also connected through a yoke X, with the free ends of the closing columns 7projecl:ing over the movable forrn tool half 6. The free ends are formed as a star-shaped
claw 9 with a shoulder.
I;our hydraulic locking ~semblies 10 which incl-lde a stationary cylinder 11 and a
movable closing piston 12 with a piston rod 13, are arranged ul the fixed tool clamping
plate 2, in a similar arrangement as the closing columrls 7. The free end of the piston r~d
13 faces the corresponding closing column 7.
The closing piston 12 is in the form of a sleeve, with a stepped through-bore extending
through the center. The stepped bore supp~rts a locking sleeve l 4 which can be driven
and rotated and which has a through -bore for receiving the piston rod 13. A step is
provided on the outside diarneter of the locking sleeve 14. ~be Ytepped bore of the
closing piston 12 and the step on the outside diameter of the lc~cking sleeve 14 fo~n an
axial force t~An~mi~sion surface IS. The closing piston 12, the rotatable locking sleeve 14
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and thc piston rod 13 close flush on the sidc facing away from the form tool and arc
supported by a piston coYer 16. The closing piston 12, the piston co~er 16 and the piston
rod 13 are rigidly co....ec~ed with each other through linlcage ~ n1c and are also
conn~cte~ with the fixed tool clamping plate 2 through a safety ele~nent 17 and secured
against rotation while allowing axial ~ r~m~n~
The lockin~ sleeve 14 proje~ hwisG over the piston rod 13 on the side facing away
from the cover.
The projecting region of the locking slceve 14 forms an interiOr free space 18 which
merges with the through bote on the side of the cover and ~ith a claw opening 19 having
a contour m~tc~hing the fo~n of the claw 9 on the side of the column.
The step into the diatneter between the free space 18 and the claw opening 19 produces a
sho~llder which in conjunction with the shouldcr ~i~posed on the claw 9 forms a second
axial force tr~n~mi~sion surface 20.
The force tr~ncmicsion surface 20 located on the cla~ 9 is orientcd opposite to the force
tr~n~ission surface 15 located on the closing piston 12.
1 he free font face of the piston rod 13 is provided with an elastic buffer 21.
The two form tool halves 5 and 6 are closed by initially moving the hydraulically
operated positioning unit 3 at high speed towards the fixed tool clamping plate 2 and
subsequently switching to a lower positioning speed when the claws 9 reach the region of
the locking assemblies 10. The claws 9 pass through the co~esponding radial clawopenings 19 of the locking sleeve 14 at the lower speed. The positioning unit 3 then
stops its advance, while the elastic buffer 21 cushions a possible imp~ct of the claws 9 on
the stationary piston rod 13.
The locking sleeve 14 is subsequently rotated by a predetermined angle with the help of a
radi~l drive (not shown), so ~hat the star-shaped contours of the claws 9 and the claw
openin~s no longer overlap. Beca~se the locking sleeve 14 is not under load, it is able to
rotate and to slide ~eely in and out.
Also r~ot shown is a hydraulic drive which biases the closing piston 12 of the locking
,
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asscmbly lO on the side of the piston rod and moves the closing piston 12 in a d~rection
away from the positioning unit 3. The piston cover 16 and the piston rod 13 w~ich are
rigidly coupled, move in a similar fashion, as does the piston rod 13 since the piston rod
13 is under axial load through the second force ~r~ncmi~sion surface 15. At the same
time, the shoulders ~f the claws 9 and the claw openings 19 make conlaCt and forrn the
se~ond force ~n~ sion surface 20.
In this way, a force is transmitted from the hydraulic drive of the locking assembly lO
through the closing piston 12, the locking sleeve 13, the closing cOlllmrl9 7, to the
movable tool clarnping plate 4 of the positioning unit 3. This forcc presses the two forrn
tool halves S and ~ against each other and holds them together during the injection
molding operation.
The closing unit is opened by applying a pressure on the piston side of the closing piston
12 and thereby lifting the shouldcrs of the claws 9 and the shoulders of the claw opening
19 a~e offeach other. This relieves the locking sleeve 14 which can then be switched.
W~en the locking sleeve 14 is rotated, ~e contours of the claws 9 and the claw opening
19 overlap again and the positioning unit 3 which is now driven, separates the two form
tool halves.
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List of reft~ ce nurnerals
I m~ in~
2 fixed tool clamping plate
3 positioning ur~it
4 movable tool clamping plate
S form tool half
6 fonTI tool half
7 closing column
8 yoke
9 claw
10 locking unit
I I cylinder
1~ closing piston
13 piston rod
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14 lockin~ sleeve
15 second force ~n~mi~sion surface
16 piston cover
17 safety element
18 ~ree space
19 claw open~g
20 first force tr~ncmicsion surface
21 elastic buffer
