DE102005007747B3 - Plasticizing machine operating method using two electric motors involves accelerating axial speed of screw during injection with second motor then operating first motor to rotate screw and continue acceleration - Google Patents

Abstract

A first motor rotates the screw and a second motor moves the screw axially via a spindle and nut arrangement. During the injection stage while the screw is moved forward by the accelerating second motor, the first motor remains fixed and does not rotate. When the first motor reaches maximum acceleration the second motor starts to rotate and the axial speed of the screw increases further(72) and plasticization of melt continues during the injection stage. Operation of the first motor is such that axial screw acceleration continues after the maximum rotational speed of the second motor has been reached. The first motor starts to rotate during injection when the second motor has reached its maximum rotational speed. Axial movement of the screw in the injection direction by the electric motors may be assisted by a hydraulic system. Hydraulic power is applied continuously and the axial movement of the screw is achieved by driving the motors in the same or opposing directions. An independent claim is included for a plasticizing unit with two electric motors and including a nut and spindle system for axial screw movement of the screw. The nut and spindle unit ensures that the screw rotates in the same direction during injection, when assisted by the first motor, as it does during metering. A non-return valve at the front of the screw enables the screw to rotate during injection.

Description

The The present invention relates to a method for operating an electrical Plasticizing according to the preamble of claim 1 and an apparatus for performing this method according to the preamble of claim 6.

Plastifiziervorrichtungen for injection molding machines are well known. This is a plastic starting material a plasticizing cylinder in which a plasticizing screw rotates and axially displaceable, is supplied. The plastic material is achieved by the rotation of the plasticizing screw in the plasticizing cylinder melted and collects continuously in the cylinder chamber in front of the snail, also called snail vestibule. It will the snail continually pushed back or withdrawn, for the place for release the newly added melt into the screw antechamber. is a sufficient amount of plastic melt is present in the antechamber, so this is by axial advancement of the screw (injection stroke) in a cavity a tool mold connected to the plasticizing introduced.

Technically drive has a plasticizing unit for an injection molding machine therefore usually at least two drives for the plasticizing screw, namely a rotary drive and a drive for the axial movement of the screw in the direction of injection or opposite thereto. There are also plasticizers, in which only a single drive is provided, in which case usually a switch option must be given between the rotary drive and the axial feed.

present employed the invention with a plasticizing, at least has two electric motors, namely a first electric motor for the rotational movement of the plasticizing screw and a second Elek tromotor for the Axial movement.

In this context, we refer to the DE 43 44 335 A1 in which such a generic plasticizing is shown. The in the DE 43 44 335 A1 illustrated plasticizing device comprises two coaxially arranged electric motors with each stably housed in a housing stators and rotatable rotors. The Indian DE 43 44 335 A1 with the reference number 5 designated electric motor has an axially telescoping, but non-rotatable coupling between the rotor and the plasticizing screw. A ball screw non-rotatably connected to the plasticizing screw cooperates with a nut arranged radially outside thereof in order to be able to axially move the spindle and thus the plasticizing screw back and forth. The nut is fixed to the rotor of the second electric motor (reference number here 4 ) connected.

As in the description of DE 43 44 335 A1 can be seen, in the metering of the plastic melt - that is, in the phase in which a certain amount of melt is accumulated in the screw antechamber - the first electric motor for rotating the plasticizing screw is driven. The direction of rotation depends on the course of the worm threads in the plasticizing screw. The second electric motor rotates to an extent so that, due to a slight difference in rotational speed, a suitable retraction of the plasticizing screw to form a desired metering pressure in the screw space is made possible.

If the dosage is complete, then the first electric motor 5 held (it can also take a lock) and the axial feed of the screw is realized by the operation of the second electric motor.

In In this context, it should be noted that the Injection through a so-called backflow preventer in the area of Snail tip a backflow of the Melt from the sluice vestibule into the area between the Scheckenstege is prevented. This backflow stop continues in many embodiments between the plasticizing screw and the plasticizing cylinder. By this usual Design of a backflow lock is the plasticizing screw as a rule during the injection process not rotatable.

Another method for operating a drive for an injection molding machine is in the DE 196 52 564 specified. Again, two electric motors are provided, one of which is responsible in particular for the rotational movement of the plasticizing screw and the other for the axial feed. And here, too, the axial feed is realized using a nut-spindle combination. The DE 196 52 564 now deals with 2 objectives, namely with the increase of the dynamics in the injection process and with the increase of the injection speed. To increase the dynamics of the drive is proposed, while driving an acceleration or deceleration ramp of the translational movement of the spindle by means of one of the two electric motors to drive the other electric motor with such a rotation briefly so that an acceleration or deceleration of the translational movement is achieved. To increase the injection speed is proposed to drive during the injection process, the spindle in the opposite direction to the mother, but to Verhinde tion of the transmission of the rotary motion on the plasticizing screw a decoupling device is opened.

adversely However, with such a fast injection process, the fact that at the axial feed the plastic raw material in the catchment area the worm threads only partially filled. This leads to, when restarting the reflow, this partial filling in the initial phase must first be eliminated before the melting starts, which a delay the melting process causes. Moreover, there is a danger that trapped air promoted becomes, which on the one hand disturbs the Aufschmelzvorgang and on the other in the Snail anteroom can accumulate.

task It is the object of the present invention to provide a method and an apparatus specify, with or with the shortened injection time also the Shorten the melting phase leaves, without air pockets to fear are.

These The object is achieved by the features specified in claim 1 procedurally and solved by the device specified in claim 6 device.

With a central idea of the present invention is to melt already again during to start the injection process, so that the starting material - mostly Granules or powder - in optimally filled and a partial filling the worm threads as far as possible is prevented. The melting is operated in such a way that simultaneously the injection speed, ie the axial displacement the plasticizing screw forward, is increased. In this way you reach both an acceleration of the injection process as well as a shortening the melting process, resulting in an overall faster cycle time leads.

In the generic drive device of the aforementioned effect is achieved in that during the injection phase provided for the rotation of the plasticizing screw motor is operated so that due to the proposed nut-spindle combination, an increase in speed in the axial direction is made possible. If, for example, the second electric motor required for the axial feed turns in the first direction of rotation and the other electric motor rotates in the other direction at the same rotational speed, the axial feed rate is doubled relative to a fixed first electric motor. This is from the DE 196 52 564 known. In the present case, however, the plasticizing screw rotates at the full rotational speed, so that it comes already during the injection phase to start the further melting.

in principle Is it possible, to maintain the rotation of the plasticizing screw continuously both while the injection as well as during the melting phase and the individual phases only over one Control of the rotary drive for to realize the spindle nut. In this case, the Electric motor substantially between a substantially identical rotation Rotation and a reverse rotation are switched, where in the same rotation rotation, the dosage takes place and at the counterparts rotation the injection.

To note, however, that during the injection process the flow connection of the screw flights is suppressed to the antechamber by means of a return flow lock. So would while the entire injection time continued to melt, so it would continuous promotion from melt into the worm antechamber to a disability for functioning the backflow lock come, which then can no longer functionally close. moreover The problem arises where the newly molten material contributes closed non-return valve should be transported.

Out For this reason, according to the preferred embodiment proposed for the rotary motion of the plasticizing screw not responsible during the Total drive injection process. According to a preferred embodiment should in a first phase of the injection process, in particular while passing through the acceleration ramp for the second electric motor, the for the rotation of the spindle nut is responsible, the first electric motor not be operated or fixed. That would be during this period The plas tifizierspindel not turn and it would not melt come. That could be the backflow stop Close functionally. If the injection pressure is then built up, opening the Return valve due to the promotion no longer to be feared by new melt.

In the last period of the injection process, the rotary drive for the plasticizing screw can then be restarted, whereby the melting process is resumed and a possibly occurred partial filling is eliminated. This second period can also be connected directly to the period in which an acceleration ramp for the second electric motor is traversed. In this way, a continued acceleration of injection speed would result. Under be In certain circumstances, it would also be possible to restart the first electric motor already when the second electric motor has not yet completely passed through its acceleration ramp, so that there would be a temporal overlap in the acceleration ramps for the electric motors.

The proposed measure has in addition to the reduction of the melting time nor the effect that the maximum injection speed compared to a system as in the DE 43 44 335 A1 is indicated, can increase.

constructive to take into account is that when operating the electric motor for the metering even while the injection phase, a rotation of the plasticizing screw in this Time range results. The construction must therefore be carried out so that also the direction of rotation of the plasticizing screw during the injection in the same direction as when dosing itself. This means that the first electric motor used for the rotation of the worm responsible is, both during the dosing, as well as during injection always in the same direction of rotation must be operated. Accordingly must the second electric motor during the injection are operated in one direction of rotation, the opposite to the direction of rotation of the first electric motor.

With this measure will ensure that even while the injection phase further melted starting material and after transported in front can not and does not accumulate in the rear snail area or times.

A requirement for the operation described is the use of a non-return valve, the even while the injection process allows a rotation of the plasticizing screw in the plasticizing cylinder. In this respect, the backflow lock should not between the plasticizing screw and the plasticizing cylinder.

present is a special embodiment For example, a ball valve shown in which a ball in a receiving space at the injection-side tip of the plasticizing screw is provided. The ball can move at least slightly in the axial direction. In a first position during of the dosing is a flow channel between the worm gear (or worm threads) and the worm anteroom Approved. While In the injection phase, the ball is driven by the injection pressure in the direction a ball seat transported backwards and closes the flow channel Completely, so that no more melt material from the antechamber into the Range of screw flights can get.

A further advantageous embodiment of the invention could be realize that the plasticizing screw in addition to hydraulic manner is acted upon and in the injection direction. With such a measure could the hydraulic preload depending on the operating phase of the screw be compensated by the electric motors. In the case of injection it would but then to an addition of the forces of the hydraulic drive and the two electric motors come, which again an increase in the Allow injection speed would.

The The present invention will be described below and with reference to the accompanying drawings Drawings described in more detail. The drawings show in

1 a conventional construction of an electrically operated plasticizing device,

2 FIG. 2 is a schematic half-sectional partial view of a front screw section with the backflow lock. FIG.

3 : a time-velocity diagram for the axial velocity of the plasticizing screw,

4 a diagram showing the rotational speed and direction of the two electric motors in one embodiment of the invention and

5 : A schematic detail sectional view, which represents the catchment area of a plasticizing unit.

In 1 is in a known construction of the drive (see also DE 43 44 335 A1 ) for the plasticizing a rear part of a screw cylinder 1 shown with drive unit. In the worm cylinder 1 is a plasticizing screw 2 an injection molding machine otherwise not shown rotatably received and axially displaceable. The worm cylinder 1 is a case 3 arranged in the further course of a first hollow shaft motor 5 and a second hollow shaft motor 4 are attached.

The plasticizing screw 2 is with a ball screw 6 firmly connected via a coupling. The ball screw 6 is in a spindle nut 7 guided. It is therefore a mother-spindle drive. The spindle nut 7 is with a designed as a hollow shaft rotor 16 of the second hollow shaft motor 4 firmly coupled, with the spindle nut 7 by means of an axial bearing 8th is supported directly in the motor housing.

In one with axial grooves 9 provided recess 10 the ball screw 6 protrudes a complementary formed drive pin 11 also with axial grooves 12 provided and thus with the movement spindle 6 rotatably but axially displaceable coupled. The drive pin 11 is with the also as a hollow shaft 13 trained rotor 17 of the first hollow shaft motor 5 firmly connected. Here is the drive pin 11 with the release of an annulus 14 from the hollow shaft 13 surround.

The hollow shaft 13 is by means of an axial bearing 15 supported directly in the motor housing. The axial bearing is advantageously designed so that forces in the axial direction can be directly absorbed.

The hollow shaft motors 4 and 5 are present transversal flux with cylindrical magnets 16 and 17 , each on both sides of windings 18 and 19 are surrounded.

When metering the plastic melt is the hollow shaft motor 5 now operated in a particular direction of rotation, which is determined by the arrangement of the screw flights. The threads of the spindle nut combination 7 and ball screw 6 are now designed so that an axial feed of the plasticizing screw 2 in the injection direction is then achieved when the hollow shaft motor 4 exactly in the direction of rotation of the hollow shaft motor 5 opposite direction of rotation rotates.

The operation of the arrangement according to the invention 1 is in a very schematic and exemplary way in 4 shown. It is assumed that at a time t ' _0, the plasticizing screw 2 completely forward, so moved in the injection direction and a spray stroke is just completed. The injection stroke is then followed by another dosing phase between times t ' ₀ and t' ₁ . In this period, the hollow shaft motor 5 operated in the first direction of rotation with the angular velocity ω ₁ . So that the melt can collect in the melt antechamber, the plasticizing screw 2 withdrawn continuously during the dosing. This is done by an operation of the hollow shaft motor 4 with an angular velocity ω ' ₁ . Due to the differential angular velocity ω ₁ - ω ' ₁ results in the retraction speed of the plasticizing screw 2 depending on the thread pitch of spindle nut and ball screw 6 ,

Is then a sufficient amount of melt metered and accumulated in the Scheckenvorraum, so at the time t ' _1, the injection of the plastic melt is started. This is the hollow shaft motor 5 initially fixed. Further, the direction of movement of the first hollow shaft motor rotates 4 (ie ω ' ₂ = -ω' ₁ ) and is operated with an opposite direction of rotation and the rotational speed ω ' ₂ . Not in 4 It can be seen that the electric motors due to the inertia drive through an acceleration ramp and can not jump directly to the final speeds. Driving through the acceleration ramp takes a certain period of time. In this respect, the jumps in the rotational speeds in 4 shown incorrectly.

After a period of time t ' ₁ + δ ₁ , the rotational speed for the second hollow shaft motor of 0 is raised again, and indeed now to the rotational speed ω ₂ . From the time t ' ₂ now results in a relative rotational speed between the ball screw 6 and the spindle nut 7 of ω ' ₂ + ω ₂ , resulting in an increase in the injection speed, since the axial speed of the plasticizing screw on the thread pitch directly with the relative rotational speed of ball screw 6 and spindle nut 7 related.

At the same time, the metering is started again at the time t ' ₂ , so that in the further course of the injection a partial filling of the screw threads is prevented and any partial filling that has already taken place is eliminated.

At time t ' ₃ is then switched back from injection to dosing.

In this context, it is again pointed out that the 4 is a very idealized graph, because due to moments of inertia and other effects the flanks will have steady and flattened transitions.

In 2 a backflow valve is shown in a schematic partial sectional view, which allows a rotation of the plasticizing screw also during the injection phase. The reference number 30 denotes a front injection-side part of the plasticizing screw, which spirally revolving screw flights 32 between which a helix 34 is formed. (The plasticizing screw 30 is in 2 only half of it is shown.) The plasticizing screw is surrounded by a plasticizing cylinder, also shown cut 36 , At the front end region of the plasticizing screw, this has an approximately cylindrically shaped receiving space 38 in which a ball 50 is received slightly displaceable in the axial direction. The axial movement of the ball 50 is on the one hand by a ring projection 52 and on the other side by a roughly hemispherical ball seat 48 limited.

Radially outside the sphere 50 is a hull provided senbereich, the outside three annular grooves 42 has, in which O-ring seals 44 are received for sealing between the plasticizing screw and the plasticizing cylinder.

Between the recording room 38 and the helix 34 is a channel 46 provided, which represents a flow connection.

During the dosing process, starting material is between the plasticizing screw 30 and the plasticizing cylinder 36 in the spiral 34 melted and transported to the front. In the front end of the plasticizing screw 30 it flows through the flow channel 46 in the recording room 38 and presses the ball 50 in the axial direction forward. By not shown in detail grooves between the ball and the sleeve 42 Can the melt on the ball 50 pass into the snail vestibule.

Once the dosage has been completed and the injection phase begins, the plasticizing screw is moved axially forward and forward 30 the pressure in the antechamber increases and thereby pushes the ball 50 axially rearward so that they fit into the complementarily formed seat 48 comes. It closes the flow channel 46 , so that no more melt can pass from the antechamber into the area of the flight and vice versa. Also the construction with the O-rings 44 prevents backflow of the melt between the front part of the plasticizing screw 30 and the plasticizing cylinder 36 ,

When the injection process is completed, the pressure on the ball drops 50 , pressure-wise, the plastic melt located in the screw thread re-establishes itself and pushes the ball 50 in the axial direction forward, whereby the flow channel 46 is released again and the melt from the area of the screw can be transported back into the Schneckenvorraum.

All in all allows this construction of a backflow stop the rotary operation of the screw also during the injection phase.

The effect of increasing the injection speed will be with respect to 3 explained. 3 shows a section of the injection phase. The curve with the reference number 70 refers to the in the operation of the DE 43 44 335 A1 resulting course of the injection speed v, ie with held during the injection rotary drive.

The curve 72 illustrates the course of the injection speed, as achieved with the present invention, wherein after passing through the acceleration ramp of the intended for the axial feed electric motor immediately followed by the activation of the electric motor for the rotary drive of the plasticizing, resulting in a continuation of the overall acceleration ramp ,

With the curve 74 a course is shown, as it results, if from the time t ₀ to the electric motor for the rotary drive (reference numeral 5 ) of the plasticizing screw is used to support the Axialvorschubs. In this case, a steeper acceleration ramp would be achieved.

The positive filling effect in the filling area can with reference to 5 be explained. In 5 is a partial sectional view with a plasticizing cylinder 80 to recognize the one filling opening 82 having. In the plasticizing cylinder 80 is a plasticizing screw 84 recorded in a known manner, which screw flights and an intermediate flight 86 having. In the filling area of the filling opening 82 is schematically shown a granular material. If the plasticizing screw is moved quickly forward during the injection process (in 5 to the left), the worm webs or the worm gear travel under the filling opening. Depending on the axial velocity, the granules can only partially into the flight 86 fall and fill this. Especially in the lower part of the flight 86 will remain an unfilled space. This clearance must be removed at the start of the dosing before the plasticization can take place, resulting in an overall delay. By a rotary drive of the plasticizing screw during the injection phase, on the one hand, the period in which the partial filling can take place can be shortened. On the other hand occurring partial fillings are still eliminated during the injection phase.

With Not only the injection time of the present invention can be considered but also the time for that Reduce dosage significantly. moreover one avoids impairments by the accumulation of air in the plasticizing cylinder. This can be with the present invention, a shortening of the Cycle time can be achieved without much effort.

Claims (8)

Method for operating an electrically driven, a plasticizing screw ( 2 ) and a plasticizing cylinder ( 1 ) having two electric motors plasticizing ( 4 . 5 ), of which the first electric motor ( 5 ) for the rotary drive of the plasticizing screw ( 2 ) via a spindle ( 6 ) continuous non-rotatably with the plasticizing screw ( 2 ) and the second electric motor ( 4 ) with the interposition of a nut-spindle unit ( 6 . 7 ) for the axial displacement of the plasticizing screw ( 2 ) is formed, wherein during the metering of the plastic melt of the first electric motor ( 5 ) and at the same time the second electric motor ( 4 ) in such a way that retraction of the plasticizing screw ( 2 ), characterized by the steps; a) that during the injection process during the axial acceleration process of the plasticizing screw while passing through an acceleration ramp of the second electric motor ( 4 ) the first electric motor ( 5 ) is fixed first and does not rotate and b) the first electric motor ( 5 ) after reaching the acceleration ramp of the second electric motor ( 4 ) so that the axial speed of the plasticizing screw ( 2 ) and the plasticization is already continued during the injection process. Method according to claim 1, characterized in that the first electric motor ( 5 ) is operated so that the axial acceleration is continued after reaching the peak rotational speed of the second electric motor. Method according to claim 1, characterized in that that the first electric motor then activated during the injection process when the second electric motor is at its peak rotational speed has reached. Method according to one of claims 1 to 3, characterized in that in addition to the electrical drives ( 4 . 5 ) the plasticizing screw ( 2 ) is acted upon hydraulically in the injection direction. Method according to claim 4, characterized in that that the hydraulic loading is continuously maintained is and the actual axial displacement the plasticizing screw by an operation of the or the electric motors is achieved in the same or opposite direction. Device for carrying out the method according to one of claims 1 to 5, wherein an electrical plasticizing device comprises two electric motors ( 4 . 5 ) to the drive, of which the first electric motor ( 5 ) for the rotary drive of the plasticizing screw ( 2 ) via a spindle ( 6 ) continuously rotatable with the plasticizing screw ( 2 ) and the second electric motor ( 4 ) with the interposition of a nut-spindle unit ( 6 . 7 ) for the axial displacement of the plasticizing screw ( 2 ) is formed, characterized in that the nut-spindle unit is designed such that the plasticizing screw also in the injection assisting operation of the first electric motor ( 5 ) in the same direction as when metering, and that in the front region of the plasticizing screw a backflow lock is provided, which also during the injection phase, a rotation of the plasticizing ( 2 ) in a plasticizing cylinder ( 1 ). Apparatus according to claim 6, characterized in that the return flow lock is designed as a ball valve, wherein a ball ( 50 ) in a central recess ( 38 ) in the top of the plasticizing screw ( 30 ) and is movable such that during the metering of the plastic melt, a flow channel ( 46 ) between the flights ( 34 ) of the plasticizing screw ( 30 ) and a Schneckenvorraum is released and during injection of the flow channel ( 46 ) is closed. Device according to one of claims 6 to 7, characterized in that a hydraulic device is provided, with which the plasticizing screw ( 30 ) can be acted upon in the injection direction.