WO2007144759A2

WO2007144759A2 - Method for controlling a mould for the production of plastic material articles

Info

Publication number: WO2007144759A2
Application number: PCT/IB2007/001610
Authority: WO
Inventors: Peter Dal Bo; Dario Girelli
Original assignee: Inglass S.P.A.
Priority date: 2006-06-16
Filing date: 2007-06-15
Publication date: 2007-12-21
Also published as: EP2035207A2; WO2007144759A3; ITTV20060106A1

Abstract

Described herein is a method for controlling a mould (1) for the production of plastic material articles; the mould (1), comprising a metal body (2) provided with an impression (2a) shaped so as to reproduce in negative the form of at least one part of the article to be made, a hot runner (3) for the distribution of liquid state plastic material that is positioned on the body (2) and is structured so as to cause the plastic material to flow away, on command and in a controlled manner, to the impression (2a), and a thermoregulation system (5) that is able to cool or heat the body (2); the method comprising the steps of calculating the power absorbed (PE1 (ti) ) by the hot runner (3), calculating the power absorbed (PE2 (ti) ) by the thermoregulation system (5), calculating the deviation (ΔEP) between the power absorbed (PE1 (ti) ) by the hot runner (3) and the power absorbed (PE2 (ti) ) by the thermoregulation system (5), and detecting a condition of malfunctioning of the mould (1) when the deviation (ΔEP) calculated is different from a pre-set reference deviation (ΔEC).

Description

METHOD FOR CONTROLLING A MOULD FOR THE PRODUCTION OF PLASTIC MATERIAL ARTICLES

TECHNICAL FIELD

The present invention relates to a method for controlling a mould for the production of plastic material articles.

More specifically, the present invention relates to a method for controlling an injection mould for the production of plastic material articles, to which the following description refers purely by way of example without this implying any loss of generality.

BACKGROUND ART

As is known, injection moulds are formed basically by a first and a second metal body with a substantially parallelepipedal shape, which are designed to be brought in abutment one to the other by one of the two major faces, and are structured in such a way as to form, on the contact surface between the same bodies, a closed chamber shaped so as to reproduce in negative the form of the plastic material article to be made. At the centre of the major face, which is to come into contact with the other body, the first body of the mould moreover has an area or region, generally projecting, shaped as to reproduce in negative the form of at least one part of the plastic material article to be made, traditionally referred to as "impression" of the mould.

Injection moulds are moreover provided with a hot runner for distribution of the liquid state plastic material that is housed on the first body within a seat purposely made on the second of the two major faces of the body itself, in such a way as to be aligned with the impression of the mould mentioned above; and finally with a body thermoregulation system which is selectively able to cool or heat the first body in such a way as to maintain, during the operations for injection-moulding, the value of the average temperature of the first body within a pre-set tolerance range. More specifically, the body thermoregulation system comprises a cooling/heating pipe that develops within the first body along a path established in the design stage; a storage tank, within which a given amount of thermoregulator liquid to be circulated within the first body is to be stored; a delivery pipe and a return pipe, designed to set in communication the two ends of the cooling/heating pipe with the storage tank mentioned above; and a circulation pump, capable to circulate the thermoregulator liquid contained in the storage tank within the closed hydraulic circuit formed by the body cooling/heating pipe and by the delivery and return pipes .

The body thermoregulation system is moreover provided with a heating assembly and a cooling assembly, both positioned along the delivery pipe that takes the thermoregulator liquid from the storage tank to the body cooling/heating pipe. The heating assembly is generally constituted by an electrical resistor and is designed to transfer heat to the thermoregulator liquid at input to the body cooling/heating pipe, whilst the cooling assembly is generally constituted by a heat-pump refrigerating unit and is designed to subtract heat from the thermoregulator liquid on entry into the body cooling/heating pipe.

The body thermoregulation system is finally provided with a dedicated electronic control unit that is able to drive the circulation pump, the heating assembly, and the cooling assembly on the basis of the signals coming from a series of temperature sensors positioned in the metal body so as to bring the temperature of the first body to a pre-set value during a step of heating of the mould that precedes start of the moulding operations, and then to maintain the temperature value of the first body within a pre-set tolerance range during the subsequent use of the mould, said use obviously- envisaging continuous flowing-away of plastic material at a high temperature from the hot runner to the impression of the mould, with consequent transfer of heat and heating of the first body.

DISCLOSURE OF INVENTION

The aim of the present invention is to provide a method for controlling a mould for the production of plastic material articles that will be able to detect the onset of possible conditions of faulty operation of the mould.

According to the present invention, there is then proposed a method for controlling a mould for the production of plastic material articles, as specified in Claim 1 and preferably, thought not necessarily, in any one of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the annexed drawings, which illustrate a non-limiting example of embodiment thereof and in which:

- Figure 1 is a schematic view of a mould for the production of plastic material articles that is able to operate according to a control method provided according to the teachings of the present invention; and

- Figure 2 shows a flowchart of the control method implemented by the electronic control unit for controlling the mould illustrated in Figure 1 and built according to the teachings of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to Figure 1, number 1 indicates as a whole a mould for the production of plastic material articles via injection of plastic material in the liquid state. Mould 1 basically comprises a first body and a second body made of metal and having a substantially parallelepipedal shape, which are designed to be brought in abutment one to the other by one of the two major faces, and are structured in such a way as to form, on the contact surface between the bodies, a closed chamber shaped so as to reproduce in negative the form of the plastic material article to be made.

More specifically, the first metal body, hereinafter designated by the number 2, has, on the major face designed to come into contact with the second body (not illustrated) of the mould, a preferably, though not necessarily, projecting central area or region 2a which is shaped so as to reproduce in negative the form of at least one part of the article to be made, hereinafter referred to as impression 2a of the mould.

The mould 1 moreover comprises a hot runner 3 for the distribution of the plastic material in the liquid state that is positioned on body 2, within a seat 2b purposely made on the second major face of body 2 in such a way as to be aligned with the impression 2a of the mould, and is structured so as to cause the plastic material to flow away upon command and in a controlled manner to the impression 2a, keeping it always in the liquid state; and a main electronic control unit 4 able to drive the hot runner 3 so as to regulate, instant by instant, the flowing-away of the liquid state plastic material to impression 2a of the mould.

More specifically, electronic control unit 4 is designed to drive the electrical resistors (not illustrated) integrated in hot runner 3 , according to the signals coming from a series of temperature sensors (not illustrated) also integrated in the hot runner 3, so as to cause the plastic material to flow away upon command and in a controlled way to the impression 2a, keeping it always in the liquid state. The mould 1 is moreover provided with a system 5 for thermoregulation of the body that is selectively able to cool or heat the portion of body 2 inside the impression 2a of the mould so as to maintain, during the operations of injection- moulding, the value of the average temperature of impression 2a itself within a pre-set tolerance range around a given reference temperature, preferably, though not necessarily, coinciding with the solidification temperature of the plastic material contained in hot runner 3.

With reference to Figure 1, the thermoregulation system 5 basically comprises: a cooling/heating pipe 6 developing within body 2, around seat 2b of body 2 that houses hot runner 3, and around impression 2a of the mould; a storage tank 7, within which there is to be stored a given amount of thermoregulator liquid to be circulated within body 2; a delivery hydraulic circuit 8 and a return hydraulic circuit 9, which are designed to set tank 7 in communication with the two ends of cooling/heating pipe 6; and a circulation pump 10 preferably, thought not necessarily, with variable capacity, which is designed to cause circulation of the thermoregulator liquid contained in tank 7 within the closed hydraulic circuit formed by the cooling/heating pipe 6 and by the delivery hydraulic circuit 8 and return hydraulic circuit 9.

More specifically, circulation pump 10 is capable to circulate the thermoregulator liquid contained in tank 7 along the delivery hydraulic circuit 8, until it reaches the cooling/heating pipe 6 of body 2 , and then along the return hydraulic circuit 9 until it reaches again tank 7.

With reference to Figure 1, the thermoregulation system 5 moreover comprises: a cooling assembly 11 and a heating assembly 12both positioned along the delivery hydraulic circuit 8; and an auxiliary electronic control unit 13 able to drive circulation pump 10, cooling assembly 11 and heating assembly 12 on the basis of the signals coming from a series of temperature sensors (not illustrated) located in body 2.

More specifically, the cooling assembly 11 is able, on command, to subtract heat from the thermoregulator liquid that flows through the same delivery hydraulic circuit 8 in such a way that the temperature of the thermoregulator liquid on entry into the cooling/heating pipe 6 of body 2 is lower than the temperature of the thermoregulator liquid present within tank 7, whilst heating assembly 12 is able, on command, to transfer heat to, and hence heat, the thermoregulator liquid that flows through said delivery hydraulic circuit 8 so as that the temperature of the thermoregulator liquid on entry into cooling/heating pipe 6 is higher than the temperature of the thermoregulator liquid present within tank 7.

Electronic control unit 13 is instead designed to drive circulation pump 10, cooling assembly 11, and heating assembly 12 on the basis of the signals coming from the temperature sensors (not illustrated) located in body 2, so as to bring the temperature of body 2 to a pre-set value during a step of mould 1 heating that precedes start of the moulding operations, and then to maintain the value of body 2 temperature within a pre-set tolerance range during the subsequent use of the mould. Use that obviously envisages the continuous flowing-away of plastic material at high temperature from the hot runner 3 to the impression 2a of the mould, with consequent transfer of heat to, and heating of, the body 2.

In addition to what above, electronic control unit 13 is moreover able to detect, instant by instant, the electric power absorbed by circulation pump 10, by cooling assembly 11, and by heating assembly 12 so as to be able to determine, instant by instant, the value of the total electric power absorbed by the thermoregulation system 5 and then to communicate said values to main electronic control unit 4.

In what has been described above, it should be pointed out that auxiliary electronic control unit 13 can be constituted by a control module comprised, i.e. directly integrated, within main electronic control unit 4. Said integration advantageously enables driving of the mould 1 through a single control unit.

Hot runner 3, circulation pump 10, cooling assembly 11 and heating assembly 12 are devices already widely known in the field of injection moulds and will not be further described herein.

Preferably, thought not necessarily, thermoregulation system 5 is moreover provided with an electrically operated partializing valve 14 which is positioned along delivery hydraulic circuit 8, immediately upstream of cooling/heating pipe 6, and is designed to regulate, instant by instant, the value of the thermoregulator liquid flow on entry into cooling/heating pipe 6 on the basis of the signals coming from the electronic control unit 13.

The method for controlling mould 1 will now be described with reference to the flowchart illustrated in Figure 2, assuming that mould 1 is executing the operations of injection and moulding .

Initially, main electronic control unit 4 calculates, at each instant ti, the instantaneous value of the electric power PEl (ti) absorbed by hot runner 3 (block 100) during the operations of injection and moulding and, at the same time, receives at input the instantaneous value of the electric power PE2 (ti) , which is calculated by auxiliary electronic control unit 13 and indicates the electric power absorbed by thermoregulation system 5, in particular by auxiliary heating assembly 12, and/or by cooling assembly 11 (block 110) .

On the basis of the instantaneous values of the electric power PEl (ti) absorbed by hot runner 3, electronic control unit 4 is able to determine the evolution in time of the electric power PEl (t) corresponding to the energy evolution of hot runner 3. As for the aforesaid calculation, on the basis of the instantaneous values of the power PE2(ti) absorbed by thermoregulation system 5, main electronic control unit 4 determines the evolution in time of the power PE2 (t) corresponding to the energy evolution of thermoregulation system 5 itself.

Following upon determination of the evolution of the levels of electric power absorbed PEl (t) and PE2(t), main electronic control unit 4 calculates, at each instant ti, a deviation, i.e. a difference ΔPE, between the levels of power absorbed PEl (ti) and PE2(ti), implementing the relation ΔPE (ti) =PE1 (ti) - PE2 (ti) (block 120) and compares said difference ΔPE(ti) with a reference deviation corresponding to a value ΔPC(ti) regarding a pre-set reference evolution ΔPC(t) (block 130).

In the case in point, in the example shown the pre-set reference evolution ΔPC(t) corresponds to the difference between the reference evolution of a first and a second power levels Pcl(t) and Pc2(t), in which the reference evolution regarding the first reference power Pel corresponds to an evolution in time of the electric power absorbed by the hot runner 3 in conditions of proper operation of the mould 1, whilst the reference evolution of the second power Pc2 corresponds to the evolution of the electric power absorbed by the thermoregulation system 5 in conditions of proper operation of the mould 1 itself .

In other words, at each instant ti the pre-set reference value ΔPC(ti) corresponds to the deviation existing between the power absorbed by hot runner 3 and the power absorbed by thermoregulation system 5 in conditions of proper operation of the mould 1 and, in particular, in absence of faults in the hot runner and/or in thermoregulation system 5 and/or resulting from external events such as, for example, leakages of plastic material from hot runner 3 or leakages of the coolant.

It should be pointed out then that the reference power levels Pcl(ti) and Pc2 (ti) and the respective evolutions in time Pcl(t) and Pc2 (t) can be determined and then stored in the electronic control unit 4 during operating tests conducted on mould 1 in the aforesaid conditions of proper operation of hot runner 3 and of thermoregulation system 5.

In the case where the deviation, i.e. the difference ΔPE(ti) between the levels of power absorbed, is equal to the pre-set value ΔPC(ti) (output YES from block 130), electronic control unit 4 detects a condition of proper operation of mould 1 (block 140), whereas, instead, if the difference ΔPE(ti) between the levels of power absorbed is different from the pre-set reference value ΔPC(ti) (output NO from block 130), electronic control unit 4 detects a condition of malfunctioning of mould 1 (block 150) .

In which case, the electronic control unit 4 is able to signal said condition of malfunctioning, for example through a display monitor, or otherwise it can transmit said information to a remote processing unit (not illustrated) connected to electronic control unit 4 through a data communication system (not illustrated) .

Once the malfunctioning of mould 1 has been detected, electronic control unit 4 identifies the cause that has led to said malfunctioning, i.e. it discriminates according to the power levels PEl (ti) and PE2(ti) calculated a faulty condition of operation of hot runner 3 with respect to a faulty condition of operation verified in thermoregulation system 5.

In particular, in this step electronic control unit 4 verifies whether there has occurred a deviation between the power PEl (ti) absorbed by the hot runner 3 and the respective reference power Pcl(ti) (block 160).

In particular, if relation PEl (ti) >Pcl (t_±) - corresponding to an increase in the electric power PEl (t) with respect to its reference value Pcl(ti) - is satisfied (output YES from block 160) , then electronic control unit 4 verifies whether there has occurred or not a deviation also of the power PE2(ti) absorbed by thermoregulation system 5 (block 170) .

In the case in point, the following relation PE2 (ti) <Pc2 (ti) is verified (block 170), corresponding to a reduction of the power absorbed PE2 (ti) by thermoregulation system 5 with respect to the respective reference value Pc2(ti) .

If so (output YES from block 170), i.e. if PE2 (ti) <Pc2 (ti) , then electronic control unit 4 detects a faulty condition of operation of thermoregulation system 5 and signals it in the way described above.

If not (output NO from block 170), i.e. if PE2 (ti) =Pc2 (ti) , then electronic control unit 4 detects a faulty condition of operation of mould 1 deriving from an external event, such as, for example, a leakage of material from the hot runner, or else a leakage of coolant from the mould (block 190) .

If, instead, the comparison made in block 160 has a negative outcome, and in particular if it is verified that PEl<Pcl (output NO from block 160) , corresponding to a reduction of the electric power PEl absorbed by the hot runner 3 with respect to the respective reference evolution Pel, then electronic control unit 4 verifies whether the relation PE2>Pc2 is satisfied, i.e. it verifies whether there is in progress an increase in the electric power PE2 absorbed by thermoregulation system 5 (block 200) .

If so, i.e. if PE2 (ti)>Pc2 (ti) , (output YES from block 200) electronic control unit 4 detects a faulty condition of operation of the hot runner 3; if not, and in particular if it is verified that PE2=Pc2 (output NO from block 190) , electronic control unit 4 detects a faulty condition of operation of mould 1 associated to an external event, such as, for example, a leakage of material from the hot runner, or else a leakage of coolant from the mould (block 190) .

The method described above is extremely advantageous in so far as it enables detection, in a simple way, of a condition of malfunctioning of mould 1, and at the same time distinguishes whether said malfunctioning is caused by a fault of thermoregulation system 5 or by a fault that has arisen in hot runner 3 or by a fault regarding an external event.

Finally, it is clear that modifications and variations can be made to mould 1 described and illustrated herein, without thereby departing from the scope of the present invention.

Claims

C L A I M S

1. Method for controlling a mould (1) for the production of plastic material articles; said, mould (1) comprising a metal body (2) provided with an impression (2a) shaped in such a way as to reproduce in negative the form of at least one part of the article to be made, a hot runner (3) for the distribution of the plastic material in the liquid state, which is positioned on said body (2) and is structured so as to cause the plastic material to flow away, upon command and in a controlled manner, to said impression (2a) , and a thermoregulation system (5) able to cool or heat said body (2); said method being characterized in that it comprises the steps of:

- calculating the power absorbed (PEl (ti) ) by said hot runner (3);

- calculating the power absorbed (PE2(ti)) by said thermoregulation system (5) ;

- calculating the deviation (ΔEP) between the power absorbed (PEl (ti)) by said hot runner (3) and the power absorbed (PE2 (ti) ) by the thermoregulation system (5);

- detecting a condition of malfunctioning of said mould (1) when said deviation (ΔEP) is different from a pre-set reference deviation (ΔEC) .

2. A method according to Claim 1, comprising the steps of:

- establishing a reference power (Pcl(t)) absorbed by said hot runner (3) in conditions of proper operation of said mould

(D;

- establishing a reference power (Pc2(t)) absorbed by said thermoregulation system (5) in conditions of proper operation of said mould (1) ; and

- determining said pre-set reference deviation (ΔEC) as a function of said reference power levels (Pcl(t)) and (Pc2(t)).

3. A method according to Claim 2, comprising the step of identifying a faulty condition of operation of said thermoregulation system (5) of said mould (1) when there occurs a first condition in which the power (PEl (ti) ) absorbed by said hot runner (3) is higher than the respective reference power (Pcl(ti)) absorbed by said hot runner (3) itself, and there occurs one second condition in which the power absorbed (PE2 (ti) ) by said thermoregulation system (5) is smaller than the respective reference power (Pc2(ti)) absorbed by the thermoregulation system (5) itself.

4. Method according to Claim 2 or Claim 3, comprising the step of identifying a faulty condition of operation of said hot runner (3) of said mould (1) when there occurs a third condition in which the power (PEl (ti)) absorbed by said hot runner (3) is lower than the respective reference power (Pel) absorbed by said hot runner (3) itself, and there occurs a fourth condition in which the power absorbed (PE2 (ti) ) by said thermoregulation system (5) is higher than the respective reference power (Pc2) absorbed by the thermoregulation system (5) itself.

5. Method according to any one of Claims 2 to 4, comprising the step of identifying a faulty condition of operation deriving from an event external to the mould (1) when there occurs a fifth condition in which the power (PEl (ti)) absorbed by said hot runner (3) is different from the respective reference power (Pel) absorbed by said hot runner (3) itself, and there occurs a sixth condition in which the power absorbed (PE2(ti)) by said thermoregulation system (5) is substantially equal to the respective reference power (Pc2) absorbed by the thermoregulation system (5) itself.

6. An electronic control unit (4, 13) of a mould (1) for the production of plastic material articles, characterized in that it implements a method as specified in any one of Claims 1 to 5.

7. A software product that can be loaded into the memory of an electronic control unit (4,13) and is designed for implementation, when run, of the method according to any one of Claims 1 to 5.