Injection molding machine having a rotatable turret

An apparatus for the injection moulding of synthetic products, comprising a die provided with a plurality of cavities, a discharge device and a robot device for receiving the products moulded in the cavities of the die and transferring those products to the discharge device, the robot device comprising at least two receiving plates, each capable of receiving a number of moulded products equal to at least once the number of cavities of the die, and a drive device for successively bringing the receiving plates into a receiving position next to the die, and for bringing a receiving plate from the receiving position into a take-over position and back again, in which take-over position the moulded products can be taken over from the die.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for the injection moulding of 
synthetic products, comprising a die provided with a plurality of 
cavities, a discharge device and a robot device for receiving the products 
moulded in the cavities of the die and transferring those products to the 
discharge device. 
Such an injection moulding apparatus is for instance disclosed in European 
patent application 0283644. The known apparatus is a machine for producing 
so-called "preforms" for synthetic containers such as PET (polyethylene 
terephthalate) bottles. The known apparatus has a die comprising a first 
die half, provided with a plurality of cavities, and a second die half, 
provided with the same number of cores. In the closed position of the die, 
the cores extend into the cavities, a space being present around each core 
in the cavity, which space is to be filled with synthetic material. After 
the synthetic material has been supplied in fluid form to the cavities and 
the synthetic material has cooled off sufficiently, the die is opened and 
a receiving plate of a robot device is brought before the product-carrying 
member of the die. In the apparatus described in European patent 
application 0283644, the preforms, after the die has been opened, are 
located on the cores, but it is also possible that, after the die has been 
opened, the preforms are located in the cavities. In the first case, the 
receiving plate of the robot device has cavities adapted to receive the 
products from the cores. In the second case, the receiving plate of the 
robot device has Dins or the like adapted to receive the products from the 
cavities. For this purpose, the die may be provided with ejecting means. 
Alternatively, the receiving plate may be provided with suction means for 
promoting taking of the products, optionally in combination with ejecting 
means of the die. 
It is important that after the die has been filled up, the moulded products 
are removed from the die again as quickly as possible so as to obtain a 
shortest possible cycle period. This means that the products are still 
very warm and hence soft and vulnerable at the moment when the products 
are taken away by the receiving plate of the robot device. As the robot 
device should be ready again to take over the next set of preforms at the 
end of the next injection moulding cycle, this also means that the 
preforms can stay in the robot device only briefly and that the preforms 
are still very warm and vulnerable at the moment when the robot device 
delivers the preforms again to the discharge device. Typically, the 
discharge device comprises a conveyor belt and during the stay on the 
conveyor belt the preforms are cooled by air and/or fluid. 
Because in this manner, the preforms are transferred twice before complete 
cooling and hardening has taken place, the chance of damage is relatively 
substantial. In the past, it was attempted to reduce the chance of damage 
by providing the receiving plate of the robot device with cooling means, 
such as cooling channels through which cooling fluid flows. However, in 
the case of a short cycle period, such a cooled receiving plate does not 
yet provide an optimum result. 
For this reason, in European patent application 0283644 it is proposed that 
the receiving plate be provided with a number of receiving means for 
moulded products that is a multiple of the number of cavities of the die. 
In this manner, the moulded products, such as preforms, can stay in the 
cooled carrier plate for more than one cycle period and be cooled 
relatively long before the products are transferred to the discharge 
device. 
A drawback of this known apparatus is that the receiving plate becomes 
large and heavy. Because the carrier plate should be moved back again 
between the die halves at the end of each injection moulding cycle, a 
quick reciprocating movement is necessary., which requires more energy as 
the mass of the receiving plate increases and which is moreover slowed 
down abruptly each time. Moreover, this quick reciprocating movement, 
stopping abruptly each time at the end of the path to be traversed by the 
receiving plate, increases the chance of damage to the products which are 
still located in the receiving plate. 
SUMMARY OF THE INVENTION 
The object of the invention is to overcome the above-mentioned drawbacks 
and generally to provide an improved injection moulding apparatus which on 
the one hand allows for very short cycle periods, while on the other hand 
the chance of damage to moulded products is very slight. 
To that end, according to the invention, an apparatus of the 
above-described type is characterized in that the robot device comprises 
at least two receiving plates, each adapted to receive a number of moulded 
products equal to at least once the number of cavities of the die, and 
drive means for successively bringing the receiving plates into a 
receiving position next to the die, and for bringing a receiving plate 
from the receiving position into a taking position and back again, in 
which taking position the moulded products can be taken from the die.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 schematically shows a view of a known injection moulding apparatus 1 
for preforms for PET bottles. The apparatus shown has a die 2, in this 
example mounted in vertical position on a base 3. The die 2 consists of 
two members, movable relatively to each other between a closed and an open 
position of the die, in horizontal direction transverse to the plane of 
the drawing. One die member has a plurality of substantially cylindrical 
cavities and the other die member has the same number of bar-shaped cores, 
in the closed position of the die extending into the cavities. In the 
closed position of the die, a narrow clearance is present around the 
cores, into which hot fluid synthetic material can be injected to mould 
the preforms. 
After the clearances around the pins have been filled with synthetic 
material and the thus moulded preforms have cooled to some extent, the die 
is opened. For this purpose, at least one of the die members is movable 
relatively to the other die member along guides 4. This involves the 
preforms being left behind either in the cavities or on the cores. In the 
example shown, the die comprises two rows of eight cavities and cores, 
designated by 5 and 6 respectively. 
The injection moulding apparatus further comprises a robot device, of which 
only the receiving plate 7 is shown schematically. In the present example, 
the receiving plate is provided with receiving means 8 having a receiving 
cavity adapted to take the preforms from the die member provided with 
cores. For this purpose, the receiving plate can be brought from a 
position outside the die into a position opposite the die member provided 
with cores. Taking of the preforms takes place through means known for 
that purpose, such as, for instance, a stripper plate, not shown. 
After the receiving plate has taken the moulded preforms and has been moved 
out of the die, the die can be closed again for a next cycle. During that 
next cycle, the robot device moves the receiving plate to above a 
discharge device 12. 
At 7, the receiving plate is drawn in a position in which the receiving 
plate is ready to be brought between the die halves, as indicated by an 
arrow 9. At 7', the receiving plate is shown just before the preforms, 
designated by 10, are transferred onto the discharge device. The path of 
movement between the two positions is schematically shown at 11. 
The discharge device 12 comprises a conveying belt 14 provided with pins 
13. The preforms are placed onto the pins 13 by the receiving plate and 
subsequently discharged to a collecting device 15, shown schematically. 
In the example shown, the receiving plate 7 is adapted to receive twice as 
many preforms as can be moulded in the die per injection moulding cycle. 
Therefore, the receiving plate is filled in two successive cycles and 
accordingly transfers the preforms onto the discharge device in two 
successive cycles. Hence, the preforms moulded during an injection 
moulding cycle can cool off in the receiving plate each time during the 
subsequent injection moulding cycle and are only then taken away by the 
discharge device. 
FIG. 2 schematically shows a view of an example of an apparatus 20 
according to the invention. The apparatus shown in FIG. 2 is shown 
schematically in top plan view in FIG. 3 and in this example has a die 2 
with two rows 5,6 of eight moulding cavities similar to that of the known 
apparatus of FIG. 1. 
The injection moulding apparatus 20 of FIG. 2 differs from the known 
apparatus 10 of FIG. 1 in that the robot device 21 has four receiving 
plates 22,23,24 and 25, three of which are visible in FIGS. 2 and 3. 
The receiving plates are mounted on a turret, schematically designated by 
26 in FIGS. 2 and 3, capable of rotating around a shaft 27 as indicated by 
an arrow 28. The turret 26 is disposed next to the die in such a mariner 
that when the die is open, one of the receiving plates can be inserted 
between the die halves 29,30 to receive the moulded products, as indicated 
in FIG. 3 at 23' by interrupted lines and by an arrow 31. 
In this example and in the next examples, each receiving plate has as many 
receiving locations as the number of moulding cavities of the die. 
However, it is possible to provide the receiving plates with a number of 
receiving locations that is an even multiple of the number of moulding 
cavities of the die. 
In the example shown, each receiving plate has four positions, taken up 
during successive injection moulding cycles. These are a receiving 
position, a first and a second cooling position, and an ejecting position. 
In FIGS. 2 and 3, the receiving plate 23 is in the receiving position, 
while plate 24 is in the ejecting position. The plates 22 and 25 are in 
the cooling positions. 
During the next injection moulding cycle, the plate 24 takes up the 
receiving position and the plate 25 takes up the ejecting position. 
Accordingly, the plates 22 and 23 are in the first and second cooling 
positions. In this example, the receiving plate should be available again 
for receiving newly moulded products only after four injection moulding 
cycles, so that the products can cool for a relatively long period. 
As soon as a receiving plate of the robot device has been filled with newly 
moulded products, the plate has to make only one linear movement from the 
position between the die halves to the rest position. Braking my be 
effected relatively slowly, because the same plate is moved between the 
die halves only after a number of injection moulding cycles. Between these 
two linear movements only one rotation of the turret takes place, which 
may also be effected relatively slowly. Hence, the chance of damage to the 
products, still soft, as a consequence of the movements carried out by the 
receiving plate is very small. 
Further, when the products leave the receiving plate they have already 
cooled off to such an extent that the products can be dropped loosely onto 
the discharge device 32 without causing damage. Therefore, a belt provided 
with receiving means is not necessary. 
For completeness' sake, FIGS. 4-7 once again illustrate schematically the 
operation of an apparatus according to the invention. FIG. 4 shows in side 
view a robot device with a turret according to the invention, disposed 
next to a die for moulding preforms. 
In the example shown, the robot device 40 comprises a base 41, carrying a 
turret 43 rotatable around a shaft 42. In this example, the shaft 42 is a 
horizontal shaft, but a different orientation is possible. It is important 
that the turret be positioned relatively to the die 50 in such a manner 
that the receiving plates, each in one of the positions of the turret, can 
be inserted between the die halves in a simple manner, preferably in a 
linear movement. 
In the example shown, the die has six rows of eight moulding cavities. The 
turret comprises four receiving plates, each of which also has six rows of 
eight receiving locations for moulded products. 
FIG. 5 shows the turret of FIG. 4 in end view without the base. Each plate 
successively takes up the receiving position A, the cooling positions B 
and C and the delivery position D, with the turret rotating in the 
direction of the arrow 48. 
FIG. 6 shows in top plan view the die 50 with the die halves 50a and 50b in 
the moved-apart position. Now, as indicated by an arrow 51, the receiving 
plate 44 can be moved before the die half 50a carrying the moulded 
products. For this purpose, the turret in this example is provided with at 
least one extensible arm 52, carrying the plate which is in position A, as 
is shown in FIG. 7. 
The desired movements of the receiving plates, such as the rotation of the 
turret and the reciprocating movement of the plate in the receiving 
position, can be realized in various manners known per se by means of 
pneumatic, hydraulic or electric drive means. It is possible to mount each 
plate on an extension arm, energized as soon as the plate is in the 
receiving position. It is also possible to apply a stationary extension 
arm, each time engaging and carrying the receiving plate, which is in the 
receiving position at a particular moment. 
After the foregoing, various modifications will readily occur to a skilled 
person. For instance, the receiving plates may or may not be provided with 
cooling channels or the like. 
Because after successive injection moulding cycles a different receiving 
plate is used each time to clear the die, very short cycles are possible. 
As a result, the products are still relatively soft at the moment when the 
products are received by a receiving plate. 
According to a further elaboration of the inventive concept, use can be 
made hereof to round (sharp) sprues of the product. 
The above is shown schematically in FIGS. 8 and 9. 
FIG. 8 and FIG. 9 each show a portion of a receiving plate 60 comprising 
receiving means 61 adapted to the product, in this example designed as 
loose adaptors. FIG. 8 shows a preform 62, partially accommodated in the 
adaptor 61 and having a sprue 63 at its end extending into the adaptor. 
Located within the receiving cavity, at the bottom thereof, is a 
preferably settable stop 64, receiving and smoothing or rounding the 
sprue, as shown in FIG. 9.