WO2007144755A2

WO2007144755A2 - System and method for discriminating a faulty operational condition in a hot-runner device for plastic material injection-moulding equipments

Info

Publication number: WO2007144755A2
Application number: PCT/IB2007/001599
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: WO2007144755A3; ITTV20060108A1; EP2040903A2

Abstract

A system and method for discriminating a faulty operational condition in a hot-runner device (2), comprising a series of injectors (6), a series of tubular branches (7) for conveying the plastic material to the injectors (6), and a series of heating units (8), each of which is set on a branch (7) in a position corresponding to an injector (6) and comprises a first heating resistor (9) and a second heating resistor (10), operatively connected to a first thermocouple (11) and, respectively, to a second thermocouple (12) that measure the temperatures (T1) and (T2) of the resistors (9, 10); the method comprising the step of discriminating, as a function of the variations (ΔT1, ΔT2) of temperature measured by the first thermocouple (11) and by the second thermocouple (12) in two successive pre-set measurement instants (ti-1,ti), a faulty operational condition of the hot-runner device (2) deriving from a failure of at least one of the thermocouples (11, 12), from a faulty operational condition of the hot-runner device (2) correlated to an external event, not associated to the malfunction of the thermocouples themselves (11, 12).

Description

SYSTEM AND METHOD FOR DISCRIMINATING A FAULTY OPERATIONAL CONDITION IN A HOT-RUNNER DEVICE FOR PLASTIC MATERIAL INJECTION-MOULDING EQUIPMENTS

TECHNICAL FIELD

The present invention relates to a system and to a method for discriminating a faulty operational condition in a hot-runner device for plastic materials injection-moulding equipments.

In particular, the present invention relates to a system and to a method that enable detection of a faulty operational condition of a thermocouple installed in a heating unit of a hot-runner device for plastic material injection-moulding equipments, wherein the heating unit is provided with a pair of heating resistors, operatively connected to two respective thermocouples; to which the following treatment will make explicit reference, without implying any loss of generality.

STATE OF THE PRIOR ART As is known, some plastic material injection-moulding equipments currently known are provided with a hot-runner device, which is set in a seat made in an injection mould and comprises a series of tubular branches that selectively convey a plastic material in a fluid state to injectors that inject it into an impression made within the mould; and a series of heating units, which are installed in the tubular branches, typically in a position corresponding to the injectors, for heating upon command the plastic material to be injected.

In particular, some latest-generation heating units are each provided with a pair of heating resistors separated and independent from one another, and with a pair of thermocouples, each of which is set in the tubular branch in a position corresponding to a respective resistor for measuring the temperature thereof. For example, the Italian patent application No. TO2001A000399, filed on April 27, 2001 in the name of A. S. Attrezzature Speciali S.r.l. describes an injector of a hot-runner device provided with a heating unit having a structure of the type described above, in which the two thermocouples of the two resistors are connected to a control unit for controlling the hot-runner device, which selectively activates one or the other of the two resistors of the heating unit according to their effective functionality.

In systems for controlling hot-runner devices of the type described above, exists the problem of being able to distinguish in real time a faulty condition of measurement of the temperature deriving from a state of malfunction of one of the thermocouples, such as, for example a circuit interruption or a plastic deformation due to squeezing thereof, from a faulty condition of measurement deriving from an external event, i.e. from a cause that does not derive from a failure of the thermocouple. In the case in point, the latter condition arises when a defectiveness of the hot-runner device determines a spillage of plastic material at high temperature, accidental deposit of which on the thermocouple/thermocouples causes a sudden increase in the temperature measured, which is not interpretable by the control unit.

The possibility of making an immediate discrimination of the two different faulty conditions described above has become a need that is very much felt in the sector of injection- moulding equipments because, if on the one hand a failure of a thermocouple does not cause important and immediate irreversible effects on the equipment and can thus be repaired during any pre-set operation of ordinary maintenance, on the other hand the spillage of hot plastic material from the hot- runner device can determine, if prolonged in time, important damage to the mould, with obvious consequences from the economic standpoint. It is consequently necessary to ascertain, in a practically immediate way, any leakage of the plastic material from the hot-runner device, so as to be able to arrest the process of moulding and carry out the repair of the hot-runner device, thus limiting damage to the mould.

OBJECT OF THE INVENTION The aim of the present invention is consequently to provide a control system that will be able to discriminate immediately a faulty condition deriving from a failure of the thermocouple, from a faulty condition deriving from an "external event", i.e., from a cause that cannot be put down to a failure of the thermocouple itself, but deriving, for example, from a leakage of material from the hot-runner device or from a coolant leakage or from some other cause.

According to the present invention, a system and a method are provided for discriminating a faulty operational condition of a hot-runner device, as described in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is a schematic illustration of a system for discriminating a faulty operational condition in a hot-runner device for plastic material injection-moulding equipments, according to the present invention; and

Figures 2a and 2b show a flowchart of the operations implemented by the system of Figure 1.

PREFERRED EMBODIMENT OF THE INVENTION With reference to Figure 1, number 1 generally designates a system designed to discriminate a faulty condition deriving from malfunctioning of a temperature sensor installed in a hot-runner device from a faulty operational condition of the hot-runner device deriving from other causes and generic external events, such as, for example leakages of hot plastic material between the hot-runner device and the corresponding mould and/or a leakage of coolant of the mould itself.

In particular, the system 1 comprises an injection-moulding equipment 20 for plastic material injection-moulding, comprising, in turn, a hot-runner device 2 that is able to selectively convey and inject the plastic material in the liquid state into a series of injection points inside an injection mould 4 (represented schematically with a dashed line) for making a product of pre-set form; and a control unit 3 for controlling operation of the hot-runner device 2 that comprises at least one memory 3a, and a processing unit 3b connected, through known circuit modules (not illustrated) , to the different electrical components comprised in the hot- runner device 2 and described in detail in what follows.

In the example illustrated in Figure 1, the hot-runner device 2 is designed to be housed in a purposely provided seat 4a made in the body of the injection mould 4 and comprises, in turn, one or more injectors 6, each arranged in a corresponding point of injection provided in the injection mould 4, and one or more tubular branches 7 (two of which are illustrated schematically in Figure 1) , which convey the liquid plastic material from an input (not illustrated) to the injectors 6.

The hot-runner device 2 moreover comprises one or more heating units 8, each of which is set in a tubular branch 7 or in a position corresponding to an injector 6, and comprises one first and one second resistor designated in what follows, respectively, by 9 and 10, which are activated selectively by the control unit 3 for transmitting an amount of heat to the plastic material to be injected so as to maintain it in the liquid state at a pre-set injection temperature. In greater detail, the first and second resistors are housed within a purposely provided seat (not illustrated) , made in the tubular branch and/or in the injector. The heating unit 8 moreover comprises one first and one second thermocouple or other temperature sensor, designated in what follows, respectively, by 11 and 12, which are housed within one and the same seat made in the proximity of the seat housing the two resistors 9 and 10 and are designed to supply the relative temperatures measured Ti and T2 to the control unit 3.

With reference to Figures 2a and 2b, the method of operation implemented by the system 1, in particular by the control unit

3, will be described hereinafter for discriminating the faulty condition deriving from the malfunctioning of the first thermocouple 11 and/or of the second thermocouple 12, from a faulty condition caused by external events correlated to a leakage of plastic material between the injector 6 and the mould 4 and/or by a leakage of the coolant of the mould 4 itself or else by other generic conditions.

During the process of moulding, the control unit 3 receives at input, at pre-set regular intervals ti, the temperatures Ti and T₂, measured by the first thermocouple 11 and, respectively, by the second thermocouple 12 (blocks 100 and 110) .

At each instant ti of measurement, the control unit 3 calculates the temperature variations ΔTi and ΔT2 measured by the thermocouples 11 and 12, the first of which ΔTi corresponds to the difference between the temperature Ti detected at the current instant of measurement ti and the temperature Ti detected at the immediately preceding instant of measurement ti-i (block 120) ; whereas the second temperature variation ΔT₂ corresponds to the difference between the temperature T₂ measured at the current instant ti and the temperature T₂ measured at the preceding instant ti-i (block

130) .

At this point, it is verified whether the temperature Ti is — D ~

higher than a pre-set maximum threshold S_M, for example of approximately 450⁰C (block 140) .

In the case where the temperature T_x is higher than the maximum threshold S_M (output YES from block 140) , the control unit 3 identifies a generic condition of failure of the first thermocouple 11 and signals it (block 150); if not, i.e., if the temperature T₁ is smaller or equal to the maximum threshold S_M (output NO from block 140) the control unit 3 verifies whether the following first relation is satisfied:

a) ΔTi>S3 and ΔT₂<=S3 , where S3 is a first comparison threshold, ^' fixed for example at approximately 1O⁰C (block 160). If the first relation is satisfied (output YES from block 160) the control unit 3 detects and signals a failure deriving from a circuit interruption of the first thermocouple

11 (block 170) , whereas if the relation is not satisfied

(output NO from block 160) the control unit 3 verifies whether the following second relation is satisfied or not:

b) ΔTi<S4 and ΔT₂>=S4, where S4 is one second comparison threshold, fixed for example at approximately -1O⁰C (block 180) . If the second relation is satisfied (output YES from block 180) , the control unit 3 detects and signals a failure deriving from a plastic deformation of the first thermocouple 11, caused by a squeezing thereof (block 190) ; whereas if the second relation is not satisfied (output NO from block 180) the control unit 3 verifies whether the following third relation is satisfied or not:

c) ΔTi>S5 and ΔT₂>S5 and ΔTi<ΔT₂, where S5 is a third comparison threshold, fixed for example at approximately 0,5⁰C (block 200) .

If the aforesaid third relation is satisfied (output YES from block 200) , the control unit 3 detects a failure deriving from a plastic deformation of the first thermocouple 11 (block

210) , whereas if the third relation is not satisfied (output

NO from block 200) , the control unit 3 verifies whether a relation is satisfied or not, correlated to a faulty condition caused by a leakage of material from the hot-runner device 2

(block 220 in Figure 2b) , a condition that will be described in detail hereinafter.

At the same time, as the operations of control and comparison of the temperature variation ΔTi described above (blocks 120-

220) , the control unit 3 implements similar controls and comparisons by processing the temperature variation ΔT₂.

In detail, following upon calculation of the temperature variation ΔT₂, the control unit 3 verifies whether the temperature T₂ is higher than the maximum threshold SM (block

230) and, if so, signals a generic failure of the second thermocouple 12 (block 240) ; if not (output NO from block 230) the control unit 3 verifies whether the following fourth relation is satisfied:

d) ΔT₂>S3 and AT₁^=SS; (block 250).

If the aforesaid fourth relation is satisfied (output YES from block 250), the control unit 3 detects and signals a condition of failure deriving from a circuit interruption of the second thermocouple 12 (block 260) , whereas if the fourth relation is not satisfied (output NO from block 250) the control unit 3 verifies whether the following fifth relation is satisfied or not:

e) ΔT₂<S4 and AT₁^=SA (block 270).

If the aforesaid fifth relation is satisfied (output YES from block 270) the control unit 3 detects and signals a failure deriving from a plastic deformation of the second thermocouple 12 (block 280) , whereas if the fifth relation is not satisfied (output NO from block 270) the control unit 3 verifies whether the following sixth relation is satisfied or not:

f) ΔT₂>S5 and ΔT_!>S5 and ΔT₂<ΔTi; (block 290) .

If the aforesaid sixth relation is satisfied (output YES from block 290) the control unit 3 detects and signals a failure deriving from a plastic deformation of the second thermocouple 12 (block 300), whereas if the sixth relation is not satisfied (output NO from block 290) the control unit 3 verifies whether a relation correlated to a faulty condition caused by a leakage of material from the hot-runner device 2 (block 220) is satisfied or not.

In particular, in this step the control unit 3 verifies whether the following seventh relation is satisfied or not: g) ΔTi>S3 and ΔT₂?-S3 ; (block 220).

In the case where the seventh relation is satisfied, i.e., if both of the temperature variations AT₁ and ΔT2 are greater than the first pre-set threshold (output YES from block 220) , the control unit 3 identifies and signals a condition of leakage of material from the hot-runner device 2 (block 310) , whereas if the seventh relation is not satisfied (output NO from block 220), the control unit 3 verifies an eighth relation:

h) ΔT_!<S4 and ΔT₂<S4; (block 320);

In the case where the eighth relation h) is satisfied; i.e., if both of the temperature variations ΔTi and ΔT₂ are less than the second pre-set threshold (output YES from block 320) , the control unit 3 identifies and signals a condition of leakage of material from the hot-runner device 2 (block 310), whilst in the case where the eighth relation h) is not satisfied - S -

(output NO from block 320) , the control unit 3 verifies a ninth relation:

i) ΔTi>S6 and ΔT₂>S6; (block 330), where S6 is a fourth comparison threshold, fixed for example at approximately 5⁰C (block 330) .

In the case where the ninth relation i) is satisfied, i.e., if both of the temperature variations ΔTi and ΔT₂ are greater than the fourth pre-set comparison threshold (output YES from block

330) , the control unit 3 identifies and signals a condition of probable leakage of material from the hot-runner device 2

(block 340) , whilst in the case where the ninth relation i) is not satisfied (output NO from block 330), the control unit 3 verifies a tenth relation:

1) ΔTi<S7 and ΔT₂<S7 ; (block 350), where S7 is a fifth comparison threshold, fixed for example at approximately -5⁰C (block 350) .

In the case where the tenth relation 1) is satisfied, i.e., if both of the temperature variations ΔTi and ΔT₂ are less than the fifth pre-set comparison threshold S7 (output YES from block 350), the control unit 3 identifies and signals a condition of probable leakage of material from the hot-runner device 2 (block 340) , whilst in the case where the tenth relation 1) is not satisfied (output NO from block 350) , the control unit 3 terminates the implementation of the method, which will be repeated at the instant ti₊i.

According to a different embodiment (not illustrated) , in the case where the first temperature variation ΔTi and the second temperature variation ΔT2 are both zero ΔTi=0 ΔT₂=0 i.e., if the temperature measured is substantially constant and at the same time a pre-set variation ΔE of the power absorbed by said hot- runner device 2 is detected, then the control unit 3 identifies and signals a faulty condition of operation deriving from an event not associated to malfunctioning of the thermocouples 11 and 12 but deriving from an external event of the type described above.

In other words, the control unit 3 identifies and signals a faulty condition of operation deriving from an event not associated to malfunctioning of the thermocouples when, in the course of the moulding operations, the temperature measured is substantially constant, but there occur oscillations or perturbations of the electric power absorbed by the hot-runner device 2, this latter condition being correlated to the presence of leakages of hot plastic material and to the exit of liquid for cooling the mould.

The system 1 described above is extremely advantageous in so far as it enables identification, in extremely short times, of a condition of leakage of material from the hot-runner device, consequently enabling an immediate intervention of repair of the latter and hence limiting possible conditions of damage to the mould.

The aforesaid discrimination moreover makes it possible to establish exactly whether the condition of failure of the thermocouple or thermocouples corresponds to a plastic deformation or to a circuit interruption thereof, consequently enabling an operator to decide on the best strategy of intervention to be adopted on the hot-runner device according to the type of failure detected.

Finally it is clear that modifications and variations can be made to the system and to the method described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the annexed claims.

Claims

C L A I M S

1. A method for discriminating a faulty operational condition in a hot-runner device (2), which is designed to inject plastic material in a liquid state into a mould (4) for forming a plastic product, and comprises at least an injector (6) designed to inject said plastic material into the mould (4) , and at least a first temperature sensor (11) and, respectively, a second temperature sensor (12) arranged on said branch (7) or on said injector (6) substantially in a same point for measuring the temperatures (Ti) and (T₂) of the hot-runner device in said point; said method being characterized in that it comprises the step of discriminating, according to a temperature variation (ΔTi) measured by the first temperature sensor (11) in two successive pre-set measurement instants (ti-i,ti) and of a temperature variation

(ΔT₂) measured by the second temperature sensor (12) in the same two measurement instants (ti-i, ti) , a faulty operational condition deriving from a failure of at least one of the two temperature sensors (11,12), from a faulty operational condition of the hot-runner device (2) correlated to an external event .

2. The method according to Claim 1, further comprising the steps of: a) calculating a first temperature variation (ΔTi) measured by the first temperature sensor (11) in said two successive measurement instants (ti-i, ti) ; b) calculating a second temperature variation (ΔT2) measured by the second temperature sensor (12) in said two successive measurement instants (ti_i,ti); c) verifying whether both said first temperature variation (ΔTi) and said second temperature variation (ΔT2) satisfy a pre-set relation with a pre-set temperature variation (S3; S4) ; d) detecting a faulty operational condition of the hot-runner device (2) correlated to an external event not associated to a malfunction of said temperature sensors (11) and (12) , when said first temperature variation (ΔTi) and said second temperature variation (ΔT₂) satisfy said pre-set relation.

3. The method according to Claim 2, wherein in the step c) said pre-set relation is satisfied when both the first temperature variation (ΔTi) and the second temperature variation (ΔT₂) are higher than a first pre-set temperature variation (S3) .

4. The method according to Claim 2 or Claim 3 , wherein in the step c) said pre-set relation is satisfied when the first temperature variation (ΔTi) and the second temperature variation (ΔT₂) are lower than a second pre-set temperature variation (S4) .

5. The method according to Claim 3 or Claim 4, comprising the step of detecting a faulty condition relating to a failure corresponding to a circuit interruption of said temperature sensors (11; 12) when one of the two temperature variations

(ΔTi; ΔT₂) is higher than said first pre-set temperature variation (S3) , and the other temperature variation (ΔT₂; ΔTi) is lower than or equal to said first pre-set temperature variation (S3) .

6. The method according to any claim from 3 to 5, comprising the step of detecting a faulty condition relating to a failure corresponding to a plastic deformation of one of said temperature sensors (11; 12) when one of the two temperature variations (ΔTi; ΔT₂) is lower than a second pre-set variation (S4) of temperature, and the other temperature variation (ΔT₂; ΔTi) is higher than or equal to said second pre-set temperature variation (S4) .

7. The method according to any claim from 3 to 6, comprising the step of detecting a faulty condition relating to a failure corresponding to a plastic deformation of one of said temperature sensors (11; 12) when both the temperature variations (AT₁; ΔT₂) are higher than a third pre-set temperature variation (S5), and one of the two temperature variations (AT₁/ ΔT₂) is lower than the other temperature variation (ΔT₂; AT₁) .

8. The method according to Claim 1, comprising the steps of: a) calculating a first temperature variation (AT₁) measured by the first temperature sensor (11) in said two successive measurement instants (ti_i,ti); b) calculating a second temperature variation (AT₂) measured by the second temperature sensor (12) in said two successive measurement instants (ti_i,ti); c) verifying whether both said first temperature variation (AT₁) and said second temperature variation (AT₂) are null;

&) detecting a faulty operational condition of the hot-runner device (2) correlated to an external event not associated to a malfunction of said temperature sensors (11) and (12) when a pre-set variation (AE) of the power absorbed by said hot- runner device (2) occurs.

9. The method according to any preceding claim, characterized in that said first temperature sensor (11) and said second temperature sensor (12) are thermocouples.

10. A control unit (3) designed to discriminate a faulty operational condition in a hot-runner device (2) , characterized in that it implements a method as specified in any preceding claim.

11. A software product that can be loaded into a memory (3a) of a control unit (3) and designed to implement, when run, the method according to any one of the claims from 1 to 9.

12. A system (1) for discriminating a faulty operational condition in a hot-runner device (2) , which, is designed to inject a plastic material in a liquid state into a forming mould (4) and comprises at least an injector (6) , designed to inject the plastic material into the mould (4) ,- at least a tubular branch (7) for conveying the plastic material to the injector (6) ; aϊid at least a first (11) and, respectively, a second temperature sensor (12) arranged on said branch (7) or on said injector (6) substantially in a same point for measuring the temperatures (Ti) and (T₂) of the hot-runner device (2) in said point; said system being characterized in that it comprises a control unit (3) of said hot-runner device

(2) realized according to what is specified in Claim 10.

13. The system according to Claim 12, wherein said hot-runner device (2) comprises a first resistor (9) and a second resistor (10) arranged on said branch (7) or on said injector 16) substantially in a same point for transmitting heat to the plastic material in such a way as to bring it into and maintain it in the liquid state; said first temperature sensor (11) and said second temperature sensor (12) being operatively connected to said first (9) and, respectively, to said second resistor (10) .

14. Injection-moulding equipment (20) for plastic material injection-moulding, comprising a hot-runner device (2) able to selectively convey and inject the plastic material in the liquid state into a series of injection points inside a injection mould (4) for making a product of pre-set form; and a control unit (3) for controlling operation of the hot-runner device (2); said equipment (20) being characterized in that said control unit (3) is realized according to what is specified in Claim 10.