The present invention concerns a moulding machine for plastic objects.
It is known that, in the sector where small plastic containers and
hollow bodies are manufactured, such as flacons, pill boxes, bottles and similar,
different production systems are applied. More precisely, the techniques used
are injection moulding, blow moulding and injection combined with blow moulding.
These techniques make it possible to produce containers of various shapes, whose
production costs vary according to contingent needs.
It has been proved by experience that the most productive technique
is pure injection moulding; this technique, however, involves the construction
of relatively expensive moulds and the need to produce objects with the so-called
"slanted" geometry to permit the extraction of moulds.
The blow moulding technique requires the construction of less expensive
moulds and allows more complex shapes to be obtained; however, this process originates
waste material, that is, trims due to moulding with the use of risers.
The injection blow moulding technique combines the high productivity
typical of pure injection with the possibility to obtain complex shapes, like in
the application of the blow moulding technique, allowing at the same time to limit
production of wastes.
The machines that manufacture hollow bodies using the injection blow
moulding technique carry out, in this order, the plastification of the raw material,
the injection of the raw material into a mould, the production of a semi-finished
product or intermediate product (the so-called "preform"), the blowing of the
preform to the geometry desired, and finally the output of the finished product.
The injection moulding process takes place by injecting the plastic, that is,
plasticised material, into a mould composed of a top part, which shapes the corresponding
part of the preform, of a central male rod, which has the internal shape of the
preform, and a bottom part which, like the top part, moulds the corresponding part
of the preform. The blow moulding process involves the use of another mould, also
composed essentially of three parts: a top part, a central part (male rod) and
a bottom part. The blow moulding process takes place by means of a compressed
air jet blown through the male rod.
The typical structure of these known machines comprises a index table
which revolves on a horizontal plane in order to transfer the product (first preform
and finally container) via the moulding male rods through various processing stations
arranged in a preestablished sequence, an extruder/injector placed radially to
the index table, an injection mould with a high-power closing system, a conditioning
system for preforms (not always present because applicable to some materials only),
a blowing mould with a low-power closing system, a product output system, a conditioning
system for male rods (not always present because applicable to some materials
only). The current machines are provided with hydraulic drive and exploit the
direct application of the power by means of direct drive systems like large diameter
cylinders and similar apparatuses.
The application of power by hydraulic drive systems serves to drive
the extruder/injector and to close the injection and blowing moulds.
In some industrial sectors, particularly where the production of containers for
the pharmaceutical industry but also for the cosmetic and food industries is concerned,
hydraulic drives are not admitted or are strongly opposed due to the involved hazard
of contaminating the production environment.
In addition, the use of hydraulic power transmission, due to the high power involved,
implies the design of hydraulic control stations and conduits not easy to build
and to maintain.
Another shortcoming consists in the high noise level of these equipment, and in
the disposal and storage of hydraulic oil.
The main purpose of this invention is to provide a solution to the
above mentioned problems.
The result, consonant with the present invention has been reached from the idea
of designing a machine with the characteristics described in claim 1. Other characteristics
of the invention are described in the subordinate claims.
The advantages presented by this invention consist essentially in
the following: it is possible to apply the injection blow moulding technique even
in industrial sectors in which the use of hydraulic drives is prohibited or strongly
discouraged, as for example in the production of containers for pharmaceutical,
cosmetic and food products, where higher respect and more accurate hygiene in
the working environment are the rule; it is possible to work in productive environments
that require cleaning control according to the product typology; the machine noise
is reduced and, consequently, the environmental impact; the problems related to
the disposal and storage of the oil used in hydraulic drive systems are eliminated;
the energy consumption is reduced thanks to the increased efficiency of the machine;
a higher speed is obtained in the work cycle; increased flexibility is achieved
thanks to this system, as well as increased possibilities for monitoring the production
process; a machine designed according to this invention is relatively easy to
build, economical and reliable to run even after a prolonged period of operation.
These and additional advantages and characteristics of this invention
may be understood better and to a greater extent by every technician competent
in the trade through the following description and with the help of drawings,
enclosed for practical exemplification of the invention but not to be considered
in a limitative sense, in which:
- Fig. 1A shows a schematic lateral view of the machine according to invention;
- Fig. 1B shows a schematic plan view of the machine in Fig. 1A;
- Fig. 2 shows a longitudinal sectional view of the plasticising-injecting member;
- Figs. 3A-3F show the closing and locking systems of the injection mould and,
in particular, Fig. 3A shows a front view of the injection mould, Fig. 3B shows
a top view of part of the mould locking systems, Fig. 3C shows a partial front
view of the systems shown in Fig. 3A and a detail of the mould thickness adjusting
elements, Fig. 3D is a side view of part of the mould locking system, Fig. 3E shows
a partial plan view of a detail of the mould locking elements, Fig. 3F shows a
partial front view of a detail of the mould locking elements;
- Figs. 4A and 4B show the index table that handles the product and, in particular,
Fig. 4A shows a partial side view, while Fig. 4B shows a plan view;
- Figs. 5A-5C illustrate the elements that unload the finished products and,
in particular, Fig. 5A shows a partial front view of an extractor bar for product
extraction, Fig. 5B shows a partially sectional plan view of the cylinders used
for extracting products, Fig. 5C shows a lateral view of the details shown in
Figs. 5A and 5B;
- Fig. 6 shows a side view illustrating the kinematic connection between the
product index table and the drive elements of the injection station.
The following description makes mostly reference to the machine parts
that are directly involved with this invention; on the drawings, these parts are
identified by reference numbers. Reduced to its basic structure and with reference
to the figures on the enclosed drawings, a machine (M) according to invention is
composed of a bearing frame (1), capable of guaranteeing the rigidity necessary
for the whole machinery and provided with guard panels (10) and access doors (11)
for inspection and maintenance. The above-mentioned frame (1) supports a plasticising/injecting
assembly (2) for plastification of the raw material and injection of the plasticised
material into the injection mould, as better detailed in the following.
Fig. 1B illustrates an injection moulding station (3), a blow moulding
station (4), handling equipment (index table, 5) for transferring the products
in the course of the processing stages and unloading elements (6) for the finished
In particular, a machine for moulding plastic objects with the injection blow moulding
technique according to this invention includes:
- a plasticising/injecting unit (2), where a raw material is fluidised and injected
into an injection mould;
- an injection moulding station (3), where an intermediate product is obtained;
- a blow moulding station (4), where the intermediate product receives its final
- handling means (5) for the product in course of processing;
- unloading means (6) for the finished product.
According to the present invention and as better described below,
the plasticising/injecting unit (2), the injection moulding station (3), the blow
moulding station (4) and the handling means (5) are driven by electric motors
and are thus totally free from hydraulic type components such as, for example,
cylinders, control stations, conduits, etc.
The above-mentioned assembly (2) includes elements for plastification of the raw
material and injection of the plasticised material.
In particular, as visible in the construction example shown in Fig.
2, the raw material is introduced in solid state, that is, in pellets, into a feed
hopper (20) standing over the frame (1). More in detail, the hopper (20) is placed
on top and connected with a hollow body (22), which is subjected to the action
of electric heating elements (not illustrated) and houses a reciprocating screw
(21) in its inner cavity. The reciprocating screw (21) is driven by an electric
motor (see arrow R, Fig. 2); it can revolve around its longitudinal axis (a-a)
and be moved longitudinally along this axis (see arrow W in Fig. 2), that is,
parallel to guides (26), because it is driven by an electric motor (25) connected
with it by a ball screw (28).
During machine operation, the raw material in pellet form falls by
gravity from the hopper (20) down to the reciprocating screw (21) inside the injector
body (22). The mechanical action of the reciprocating screw (21), that is, the
interaction of the reciprocating screw with the inner walls of the body (22) and
the heating of the hollow body (22) turn the raw material into fluid state. The
reciprocating screw (21) conveys the raw material, originally in pellets and later
in fluid state, towards the injection front end (29) of the hollow body (22).
At the same time, the reciprocating screw (21) retracts from the above-mentioned
front end (with a movement to the right in the reference mark visible in Fig.
2), and forms, in correspondence with the above-mentioned injection end (29), a
chamber (27) full of fluidised plastic. The volume of the chamber (27) can be
modified depending on the type of mould into which to inject the plastic; in other
words, by lengthening or shortening the excursion of the reciprocating screw (21)
inside the hollow body (22), a larger or smaller volume of fluidised plastic to
be injected will be determined. When the plastic is injected into the moulds,
the reciprocating screw (21) will be driven in reverse direction to the one it
had so far, allowing the plastic to flow from the chamber (27) into the injection
moulds on the injection moulding station (3).
With reference to the construction example shown in Figs. 3A-3F,
the injection moulding station (3) includes a mould supporting table (31), on which
there rests the bottom part of the injection mould (32). A cross beam (34) supports
the upper part of the injection mould (33) from the top. Under the supporting
table (31) there is a block (36) with columns and, below, a lower cross beam (37).
Columns (35) with wedges are arranged vertically.
In starting condition, the upper part of the mould (33) must be in
raised position. Then, the upper mould (33) is lowered by a rigid bridge consisting
of the upper cross beam (34), of the columns with wedges (35) and of the lower
cross beam (37). The bridge movement is guaranteed by a ball screw (38) connected
with a motor (309) by a belt transmission (310). In practice, the belt (310) through
the ball screw (38) induces the revolution of the shaft (380), connected with the
ball screw (38) and, consequently, lowers the above-mentioned rigid bridge. In
this way, the upper part of the mould (33) is brought into contact with the lower
part (32) lying on the table (31) and the mould closing phase can be considered
as concluded, in that the mould upper and lower parts (33) and (32) are closed
on each other.
Lead screws (311) are used in the locking phase; they are provided with a series
of inclined planes that engage the respective planes (350) present on the columns
with wedges (35). The rotation of the lead screws (by an angle of 90°, as indicated
by arrows F in Fig. 3B), is obtained by a gear motor (314) comprising an electric
motor. The kinematic connection between gear motor (314) and lead screws (311)
consists of a gear (316), which belongs to a transmission (313) and is hinged
with two ends of two connecting rods (312), whose opposed ends are hinged with
the lead screws (311).
In this way, with reference to the Fig. 3B, to a clockwise rotation
of the gear (316) there corresponds a clockwise rotation of the two lead screws
(311): this, for example, determines the closing movement of the mould; similarly,
the counter clockwise rotation of the moulds will release the lock of the mould
at completed injection. As an example and without limiting other applications,
the system can react to an injection load as high as 50 tons. To open the mould
at the end of the injection, it must be proceeded in reverse to what described
for the closing operation.
In addition, to maintain the closing start position as constant as possible, the
injection moulding station is advantageously provided with a gear motor (315)
connected with a relative electric motor (351). The gear motor (315) allows regulation
of the height of the moulds through two threads (not illustrated) present on the
columns with wedges (35), thus maintaining the locking position constant, a gear
transmission being provided between the electric motor (351) and the said threads.
This type of mould locking feature is a novelty for this type of
machines, which usually receive power via toggle lever systems or via direct power
As concerns the blow moulding station (4), the blow mould closing system is built
in an analogous way as described for the injection moulding station (3); one difference
consists in the size of the motor that drives the mould locking elements; in fact,
this motor is remarkably smaller because of the lower power needed. As a non limitative
example, the maximum load capacity of the system is 10 tons. Also in this case,
the mould locking system is a novelty for this type of machines, which usually
receive power by means of toggle lever systems or by direct power transmission.
The handling index table (5) has the function to convey the product through the
various processing phases, making it transit between the different operating stations
of the machine.
The index table (5) includes an upper part (51) that supports a bar
(52); this bar carries more than one male rod (53). Each male rod (53) present
in the injection moulding station (3), in a way in itself known, has the task
of acting as the internal shape around which the plastic material, injected into
the mould, spreads.
In practice, in the injection phase, the male rod (53) appears interposed between
the upper half (33) and the lower half (32) of the injection mould. In the blow
moulding station (4), the task of the male rod (53) is to support the container
and to act as a blowing nozzle, whereas in the unloading station (4) it has the
task of supporting the finished container.
From a functional point of view, the product handling function of
the index table (5) is substantially the same as in the machines of the known technique.
In practice, the index table (5) is provided with handling means that allow the
passage of male rods (53) thorough the different processing stations. This purpose
is achieved by an indexer gear box (54) with a relative motor (540) for the index
table rotary motion drive; they determine the rotary motion of the index table
in known manner. For the vertical motion of the index table (5), levers (55) connect
the index table (5) with a bracket (59) (visible in Fig. 6 in proximity to the
lower cross beam (37)) of the injection moulding station (3). In this way, the
same electrical motor (314) that drives the injection mould locking system is
used. The lowering movement of the index table (5) can be advantageously achieved
by a cylinder (56), that can be operated via appropriate means of actuation when
manual intervention is called for.
As concerns the unloading station (6), this station, as mentioned before, has the
task of extracting the finished containers from the male rods and of unloading
the containers by dropping them. The unloading station functions in the same way
as foreseen on machines of the know technique and, for this reason, is not described
In Figs. 5A-C there can be seen extraction cylinders (61), an extractor
bar (62), a cylinder (63) for the rotation of extractor bar (62) and a portion
of the limit stop (64) for the containers; a fixed part of the machine has been
assigned the position (60).
During the unloading process, the extractor cylinders (61) command the traverse
movement of the extractor bar (62) which, in turn, extracts the containers from
the relative male rods (53) and brings them to the unloading position. The traverse
movement is indicated by an arrow (V) in Fig. 5B. Then, the containers are rotated
by the cylinder (63) around the axis (b-b) and arranged vertically; the rotation
operated by the cylinder (63) is represented by an arrow (K) in Fig. 5C. The extractor
cylinders (61) are then retracted and the mechanical contact between the container
and the unloading stop limit (64) allows the containers to be removed from the
extractor bar (62).
The unloading station drive cylinders are of pneumatic type; therefore, also in
this station there are no hydraulic drive components installed.