WO1993016861A1

WO1993016861A1 - Process and device for injection moulding cross-linkable compounds

Info

Publication number: WO1993016861A1
Application number: PCT/DE1993/000191
Authority: WO
Inventors: Hans-Peter Saul
Original assignee: Henniges Elastomer- Und Kunststofftechnik Gmbh & Co. Kg
Priority date: 1992-02-27
Filing date: 1993-02-27
Publication date: 1993-09-02
Also published as: DE4206447A1

Abstract

A process for the clock-actuated injection moulding of a cross-linkable compound, especially one with low heat conductivity, in which, in a first phase of the working cycle, the compound is alternately fed in and, before its entry into the mould cavity or a runner leading thereto, is heated by a heating device and, in a second phase, cross-linked under the effect of an optimum temperature and then removed from the mould cavity. As the heating device passes through the successive partial quantities of the compound, a rise in temperature takes place up to a temperature producing, specifically to the mixture, substantial cross-linking within the period of the working cycle by the alteration of the quantity of heat applied to each partial volume corresponding to a preset or calculated profile and taking account of the differing paths followed by successively conveyed partial quantities of the compound to their final positions within the mould cavity and the time needed therefor in such a way that substantially even cross-linking takes place in these different partial quantities.

Description

Method and device for the injection molding of crosslinkable molding compositions

Description

The invention relates to a method according to the preamble of claim 1 and an apparatus for performing the method.

The crosslinking of crosslinkable molding compositions, such as the vulcanization of the elastomer rubber to rubber, requires exposure to temperatures above the crosslinking temperature of the rubber molecules for a certain period of time. The temperatures and exposure times can be varied over a wide range. In the case of rubber, however, the temperature must not exceed the so-called scorch point, since otherwise the molding composition would be irreversibly damaged.

In the known method for injection molding, uniform heating of the molding compound is aimed for. However, this is not achieved due to the design-related influences in the injection unit. In addition to this disadvantage, which can lead to different crosslinking of individual volume increments of the molded part, it must be established that the time at which the temperature acts on each volume increment is different during the entire injection molding process, which leads to a further difference ¬ limit in the degree of crosslinking of the volume increments of a molded part.

However, the decisive influence on the distribution of the degree of crosslinking within an injection molded part arises from the fact that, with different wall thicknesses, in particular due to the poor thermal conductivity of the molding compound, the temperature required for crosslinking is reached at thin-walled locations sooner than in the center of thick-walled locations .

In addition, in the injection molding of special molded parts, in which flow fronts meet during the injection process, there is the need for complete to unite these flow fronts (weld line) in the uncrosslinked state in order to achieve sufficient strength at this point.

The object of the invention is to control the temperature when entering the mold cavity in a process of the type mentioned at the beginning such that for each volume increment of the molded part, taking into account the respective residence time and the course of the temperature rise during this residence time, an optimal degree of crosslinking is achieved within the shortest possible cycle time without pre-crosslinking at the flow fronts meeting and pre-damage by Scorch.

This object is achieved with the characterizing features of claim 1.

The invention includes the finding that when on. the heating of the molding compound follows a longer distance to be covered in the mold cavity, the crosslinking or vulcanization time is different for the different material volume increments - depending on whether the parts are initially in the mold , or whether the relevant volume increments only reach the mold cavity towards the end of the injection process. In this case, in particular when the molding compound enters the mold cavities on the flow front, the crosslinking must not yet be completed, since otherwise so-called "weld line defects" may arise, which are based on the fact that the crosslinking process has already been completed to such an extent that separation takes place _ -. -

Do not cross-link the flow fronts created when touched.

Starting from discontinuously supplied tempered molds or also demolding in the second phase of a work cycle, in the first phase of which the material is supplied, the energy can be added to the molding compound by a suitable variation of the heating of the supplied molding compound by means of a device introduces, can be achieved that despite different initial temperatures, different dwell times of the individual volume increments in the process between plasticization and demolding and different volume concentration in the mold, a uniform, optimal degree of crosslinking is achieved.

By means of a control according to a predetermined or online temperature profile, an optimal crosslinking process can be achieved even with low thermal conductivity of the crosslinkable molding compound, for example if a shear element is used as the heating device, with which the amount of heat transferred to a respective partial volume is briefly used by corresponding speed changes can be changed or if the conversion of supplied energy takes place in another way by dissipation into additional heat. The so-called "hot-cone method", in which the cone determining the heat transfer is kept at a relatively constant temperature, is also suitable for such applications in which no very short-term, strong changes in the heat quantities to be transmitted per unit time have to be carried out - by varying the gap width, however, a change in the mass achieved and thus the heating achieved per volume fraction can be achieved. In the following considerations, however, the preferred use of a shear element should be assumed. In the case of the "hot cone", the change in the shear energy (with constant viscosity of the molding compound: shear rate) would have to be replaced by the change in the gap width and thus the change in the throughput rate.

It is particularly advantageous in the invention that relatively large amounts of heat can be transferred into the molding composition at short notice, so that the volume filling the molding cavity obtains homogeneous vulcanization properties. A high cycle speed and thus a large material throughput is possible because of the temperature that can be defined over a short transport path.

In a preferred embodiment of the method according to the invention, the initial temperature of a portion of the molding compound which is reached with the heating upon leaving the heating element is selected such that, depending on the dwell time of the respective increment of the molding compound, on the one hand, between plasticization and demolding, and the change in temperature of the increment during the dwell time, on the other hand, the shortest possible vulcanization time is achieved for each increment, the temperature required here in each case being below the limit at which weld line defects, crosslinking in the feed channels and / or scorch occur. In another favorable embodiment of the method according to the invention, the initial temperature of a part of the molding compound reached with heating is set when leaving the heating element in such a way that the degree of crosslinking of this part upon reaching the mold parting level is already so high that the increase in the Viscosity as a result of crosslinking prevents this partial amount from penetrating into the gap in the mold parting plane, or at least reduces it (injection molding free of burrs or low in burrs).

The formation of sprouts within the mold parting line can also be reduced in that, at a sufficiently high melt temperature, a high mold temperature when the molding compound penetrates into the parting plane immediately causes the compound to solidify by vulcanization.

It can be seen that when the molding compound penetrates into the mold cavity via the feed channels, contradicting requirements have to be taken into account. By means of the measures according to the invention - and in particular by forming a model using a corresponding computer - it is possible, in most cases, to find a suitable temperature profile of the molding compound to be injected. In another embodiment of the method according to the invention, the temperature control is replaced by a quantity control of the material passage, with a constant supply of energy, so that, with a constant amount of heat emitted per unit of time, correspondingly varied temperatures. temperatures can be achieved. In a further embodiment of the method according to the invention, in particular the initial temperature of a portion of the molding composition reached with the heating is controlled when the heating element is left, so that the temperature of the molding composition rises during the injection phase. Thus, the crosslinking conditions valid for the partial quantities of the molding material leaving the heating element at different times are adapted to one another and ultimately the crosslinking conditions achievable for the last emerging partial quantities of the molding material are adjusted to those which apply to the first corresponding partial quantities.

In particular, there is a regulation for the initial temperature of a portion of the molding compound reached with the heating upon leaving the heating element according to a variable setpoint, which is determined by the output signal of a model computer, the model taking into account the further path to be currently heated Partial amount of the molding composition, the crosslinking (degree of vulcanization) which occurs as a function of time and various minimum or maximum crosslinking values (degree of vulcanization) to be observed on the way into the mold cavity.

For each molded part geometry, a model can be specified in particular, which determines the heating required for individual mass particles - according to the "finite element" process, starting from the ^' final state ^' , taking into account the path and controls the process parameters, in particular the temperature, accordingly. The temperature profile is stored in a memory of the control device for each mold cavity. tt recorded as a changeable program or is calculated in a model computer.

In the case of shear injection molding of molding compositions with low thermal conductivity, for example in multi-station injection systems, after the molds have been fed to the injection unit, the plasticized composition enters a shear gap and is there, before entering the molding cavity, by shear energy in conjunction with the previous temperature control the shear mandrel and the shear cylinder sleeve heated.

Since the temperature of the molding compound fluctuates more or less strongly over the injection cycle depending on the type of press, it is advantageous to measure the temperature before entering the shear element and to meter the additional energy so that the set temperature of the volume increment specified in the memory is reached . This setpoint temperature also depends on whether a high temperature is reached before the mass increment enters the shear gap due to the shear during plasticization or when overcoming flow resistance at narrow points in the flow path (e.g. on valves) or through longer narrow flow channels between pistons and nozzle has existed and for how long such a higher temperature has been present. This temperature history of the volume increment can be determined by a correction factor when the ^'

^• To take the target temperature into account. The invention includes the finding that in process engineering

Basic design of injection molding machines this influence of high temperatures in the early phase of the injection molding process is reduced as far as possible and the temperature height should be as close as possible to the mold cavity and as short as possible before the injection into the mold.

The temperature of the molding compound, in particular of rubber to be vulcanized, is on the one hand safely below the scorch point when entering the mold to avoid damage to the material, and on the other hand has the vulcanization when the elastomer enters the mold cavity. tion on the flow front has not yet begun, so that seam seam errors are avoided. The temperature of the preheated mold is kept low in comparison to conventional methods because the increase in the mass temperature due to heat transfer from the mold can be largely or completely dispensed with. However, the mold temperature is set so high that the molding compound immediately vulcanises out when penetrating into the thin gaps of the mold parting plane, with the result that the formation of the shoots in the parting plane (the so-called floating skin formation) is suppressed.

Of the residence time t _w in the shear gap, of the shear gap geometry (shear mandrel length 1, shear mandrel diameter d, shear gap width s) and of the shear speed n or of the torque M. and of the viscosity η, the mass flow j, the volume flow i and von Depending on the heat capacity c _w , the molding compound is heated very quickly by a power P _s given off in the shear gap. The heating of the mass flow characterizing the material throughput j = c • i from a previously lowest possible melt temperature to maximum temperature T _maχ in an immediate The vicinity of the mold cavity is measured after leaving the shear gap and the circumferential speed üo of a shear mandrel or cone is changed via the shear speed n in such a way that the melt temperature obtains the previously set optimal value. The temperature is regulated according to a predefined profile as a function of time and material throughput, since on the way to the mold cavity the duration of vulcanization for the different mass particles differs, depending on whether the components are get into the mold cavity at the beginning, or whether the mass particle in question only gets into the mold cavity towards the end of the shear spraying process.

If the hot-cone method is used, the procedure can be followed and the width of the gap and the injection speed can be changed in time according to a model. The quantities of the volume flow i, the elastomer outlet temperature ΔT from the gap with the adjustable width s, the mold temperature T _F and the information about the size and nature of the mold cavity are also taken into account.

Advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. Show it:

1 shows a preferred embodiment of a device for shear injection molding for carrying out the method according to the invention, FIG. 2 shows a diagram of the temperature profile of the individual mass particles .DELTA.m (partial quantities of the molding compound) during the respective residence time.

Figures 3a and 3b are graphs showing the dependence of the temperature increase .DELTA.T _S Dm of the mass particles to jewei- ^'time exit time from the shearing gap at constant or variable mass flow j,

FIG. 4 shows a graphical representation of the dependence of the crosslinking achieved (degree of vulcanization) on the path covered by the partial quantities of the elastomer mass or the time in the case of a constant expulsion speed,

FIG. 5 shows a block diagram of a control circuit which operates with a temperature profile which can be predetermined or calculated by modeling.

An exemplary embodiment of the invention for shear injection molding by the method according to the invention is shown in more detail below with reference to FIG. 1.

A mold arranged between a press table 1 and upper part 19, consisting of parts 2 and 5, containing mold cavities -13, is located below a feed unit 30 for the molding compound arranged above it and above an actuating and drive device 35 arranged below The above-mentioned assemblies are connected to a control unit 43, which on the one hand emits the control signals required for the clock-controlled injection molding, but on the other hand also the signals for carrying out the inventive according to the method according to the invention, the necessary signals are supplied from the individual assemblies via suitable sensors.

The molds are either firmly connected to the other assemblies, the mold being opened and the workpiece or workpieces removed after the injection and crosslinking process has been completed, or the molds are fed, filled and closed in a cyclical circulation process removed from the spray device in order to be opened after removal of the molding compound from the spray device to remove the workpiece. The molds are then closed again and filled again.

The method presented here allows a shear element 7 as part of the respective shape as well as a shear element as part of the injection molding machine 30 (as a single- or multi-station machine) as a device. The further description is intended to assume this that the shear element is part of the respective shape.

Furthermore, a cyclical mold run is to be assumed in the further description: the molds are supplied in the closed state to the injection unit 30. A corresponding opening is provided in the upper press part 19 and in the press table 1, into which the injection unit is lowered and the drive pin 15 is inserted. The injection piston is controlled by the control unit 43 with a manipulated variable for the injection speed or the injection pressure of the molding compound n _E applied.

The molding compound temperature T _{0 is} measured by means of a temperature sensor 31 arranged in the injection unit 30, and the molding temperature T _{F is} measured in the vicinity of the mold cavity by means of a further temperature sensor 34 and together with information F about the size and type of the cavity or of the weight of the product to be cast is transmitted to the control unit 43, so that further heating of the molding composition in the injection unit 30 or of the mold can optionally be initiated with the manipulated variables Hη_ or H ₂ . A sensor for querying the geometric shape parameter F is advantageously attached to the upper press part 19.

A preferred embodiment of the form is shown in the visual, sectional view. It consists of a lower tool part 2 with a rotatable, cone-shaped, rotationally symmetrical shear mandrel 7 in the center thereof and with a part of the mold cavity 13, which is closed at the top to the nozzle side with an upper tool part 5, into which the other part of the mold cavity 13 is incorporated. In the parting plane 6 between the upper and lower parts 5 and 2 of the mold there are sprue channels 14 which run in a star shape from the inside outwards to the individual mold cavities 13. The rotationally symmetrical shear mandrel 7 is part of the mold in this example and in the lower part 2 with one in the direction arranged cross section extended to the lower part of the tool. It is driven by a drive pin 15 which projects through the press table 1 into the lower tool part 2 and is adjustable at a distance from a shear cylinder sleeve 8 arranged in the upper tool part 5. An annular shear gap 16 with an adjustable width s for the mass flow j is formed between the shear cylinder sleeve 8 and the shear mandrel or cone 7. As a result of this arrangement, when the shear mandrel or cone 7 rotates, further heating takes place immediately before the mass flow j enters the mold cavity 13. The drive pin 15 protrudes from an actuating and drive unit 35, which is provided by the control device 43 with manipulated variables for the shear speed n and the shear gap width s are applied.

The molding compound has the initial temperature T _Q> before injection

During the injection molding of cross-linked molding compounds, the injection work W _E causes a temperature increase ΔT _χ according to the formula:

In addition to the injection work W _E , the specific heat capacity c _w and the density ς of the molding compound m with the injection volume V _E and the injection time t _{E also have an} influence.

In the case of a molding compound m with an injection volume V _E and the residence time t _w = t _E , the shear power P _s - should result in a temperature increase ΔT ₂ : ΔT ₂ = (P _g • t _w / t _E ) / (c "• ς • i) = P _s / (c _w • j) ( ² ) ^'

with the volume flow i = V _E / t _E (3)

and with the density ς = m / v _E (4)

At a speed n of a conical, rotationally symmetrical shear mandrel, which has the diameter d and a length 1 at half the height and, together with the cylinder sleeve, forms the shear gap s with the dynamic viscosity η, the torque M_ and from that the by Determine the shear output power P _s :

^p s = ^F R ' ^u o = [M _d / (d / 2)] ^• U _Q (5)

M _d = F _R • d / 2 [in Nm] (6) ^'

with the internal friction force F _R = (A _M • Uo • η) / s (7)

with the conical surface area A _M = π • d • / d ² + l ² (8)

or the ^' cylinder surface area A _M = π • d • 1 (9)

with the peripheral speed U _Q = π • d • n (10)

This results from shearing by means of the lateral surface

Torque M _d approximately for a cone at 1> d and exactly for a cylinder: M, IT 0, [Nm] (11)

2 p

In a first approximation, an average viscosity over the length and height of the shear gap is used.

Because of (5) with the speed n to be used in [rpm] and because of the conversion into kW:

P * Ps _s == - ^{] M} d ^{* n} [kW] (12)

9549

After inserting equations (5) to (11) in (2), there is the following temperature increase in the gap for a shear cone:

ΔT ₂ = / d ² + l ² • η • τr ³ • d ³ • n ² / (s • c _w • j) (13)

or for a cylindrical shear mandrel: ■

ΔT ₂ = i 'H • ττ ³ • d ³ • n ² / (s ^■ c _w • j) (14)

The viscosity η increases with the shear rate dU _Q / ds and due to the decreasing flow index x with increasing temperature:

For the input of measured values T _Q , F,

, ΔT _n and T _F as well as for the input of material parameters or for the output of manipulated variables H- _{j ^} and n _E as well as H ₂ , n and s the control unit 43 inter alia input and output units 37, 38, 39, 40, 41 or 36 and 42, which are controlled by a computing unit, not shown. The input units of the control unit 43 are each equipped with an analog / digital converter. The manipulated variables n and s are output as a result of the shear energy-per-time control carried out by the computing unit in accordance with the deviation of the determined temperature increases ΔT _j and ΔT ₂ from the specified target temperature values. The control unit 43 contains a programmable memory, each with a memory area for the temperature profile of the corresponding mold cavity as a function of the mass flow j. The manipulated variables E ^, n _E and H are output in accordance with a model for the necessary heating of the mass particles on average, taking into account the distance to be covered and the mass flow for a specific cavity.

Controlled by the control unit 43, but not shown in the drawings, the following method steps are also carried out in preparation for the shear injection molding:

1. Feeding the closed mold gregat to the Einspritzag- 30, which lowers the mold is abge¬ to the upper tool part 5, at the same time, a driving pin 15 has a press table 1 into the lower tool part 2 is introduced by ^■.

2. Setting the initial parameters for shear injection molding, the molding material temperature T _{Q being} Injection unit 30 and the mold temperature T _E , measured to determine the deviation from a defined initial value, and for the subsequent further heating of the molding compound according to a mold parameter F via the mold cavity in a memory of a control unit 43, a memory area for injection molding parameters is selected in accordance with the information F and the temperature T _Q in the injection unit and the temperature Tp of the mold and the injection speed n _{E are set} according to predetermined programmable setpoints.

The process for shear injection molding of crosslinkable molding compositions with low thermal conductivity, in particular rubber, with preheating before entering a mold is characterized in particular by the following steps:

1. A memory area for injection molding parameters is selected in a memory of a control unit in accordance with a shape characteristic value F in accordance with the geometry of the mold cavity in accordance with the material property value M of the molding composition.

2. The temperatures in the injection unit T _Q and the shape T _{F are set} and a variable mass flow j is set, the shear speed n is set, the shear gap width s and the speed n _{E of} the extruder screw is set according to a predetermined time changing setpoints.

3. A measurement of the temperature T _Q + ΔTη_ in the interior of a shear cylinder sleeve 8 before the elastomer mass occurs in the shear gap 16 and the temperature ΔT = T _Q + ΔT- _| _ + ΔT ₂ after exiting from the shear gap 16 and before the elastomer mass enters the cavity 13.

4. A shear energy-per-time control takes place, with a change in the setpoints for the temperatures T _Q , ΔT ₁ and ΔT ₂ according to a model stored for each mold cavity, which can be changed over time according to the path ξ to be covered and as a function Programmable values for the conveying speed n _E , the shear speed n and the shear gap width s are programmable from the mass flow j, the shear gap width s being regulated according to the temperature increase ΔT_ determined and the shear speed n corresponding to the determined temperature increase ΔT ₂ .

If the advance of the elastomer mass is interrupted, the transmitted shear energy is switched off. When the mold is opened, a skin-like layer of remaining material can be easily removed from the standing shear mandrel between the working cycles.

Alternatively, the shear element can be moved with the mold half and (in order to reduce the volume of waste) the material in the shear gap, which has not undergone additional heating due to the timely stopping of the shear element, is retained in the process.

The subsets can be recorded as finite elements in a model calculation that can be specified for each mold cavity. These must be loaded with a defined loading time or the correct times of charging are introduced into the mold cavity with a certain temperature of the mass flow j, so that the optimum vulcanization temperature prevails in these partial quantities at the end of the injection phase.

FIG. 2 shows a diagram of the time-dependent course of the temperature of the individual mass particles .DELTA.m as a function of the distance ξ traveled in the pouring channel and in terms of the shape. The residence time t _{E1 of} the mass particle Δπ ^ flowing in first is greater than that of the subsequent mass particles Δm ₂ to Δm _n .

For the model calculation, the necessary heating of the mass particles is created on the basis of the final state, taking into account the distance to be covered (shown hatched in FIG. 2a). There is an analysis of the temperature distribution on the finished product with regard to the mass particles introduced at different loading times, taking into account the dimensions of the mold cavity. The model calculation for the individual volume increments is preferably carried out according to the so-called "finite element method".

If the mass flow j and c _{w is} kept constant, the sum of the temperature increases Σ ΔT = T _Q + ΔT _χ + ΔT ₂ multiplied by the residence time t _{w of} the mass particles Δm in the shear gap can then be regarded as crosslinking energy if the shape is not for energy exchange ( Cooling) contributes. Normally, this energy exchange must be taken into account in the equation by a constant Tα _n that can be specified for each finite element and for the injection molding process can be compensated for by a corresponding temperature increase ΔT ₂ . The product time tp times temperature T _m for the vulcanization is constant for each mass particle Δm. The following applies to the nth mass particle:

^τ mn ^{* t} Pn ^{= (Σ Δτ} n ^{~ Tα} n ^{) * t} Pn ⁼ constant ⁽¹ 8 ^{) '}

The individual target values of the temperatures of the mass particles when they emerge from the shear gap are programmably recorded in a memory as a temperature profile for various mold cavities. In order to achieve a uniform quality, the mass particles .DELTA.m _{2 of} the preceding flow front are heated less highly than the .DELTA.m _{n of} the following flow front, so that the product time tp times terature temperature T _m despite the longer residence time tp of the first mass particles Δm remains approximately constant in the mold cavities.

FIGS. 3a and b show the course of the target temperature ΔT _{S of} the mass particles Δm at the respective exit time, from the shear gap s during the shear spraying process for various mold cavities A and B.

For the mold cavity A (FIG. 3a), the mass flow j remains fixed at a constant value from the beginning. The molding compound, for example rubber, is locally heated by shearing by means of a shear mandrel or cone when pressed into the mold, so that a short-term change in the shear speed n to the conditions of the mold and that of the molding compound entering the mold cavities Can be taken into account. The mass flow j is varied for the mold cavity B (FIG. 3b), which is particularly advantageous with certain molded part geometries. Due to the exact control of the mass temperature before entering the mold cavity, the mixture-specific temperature optimum for each volume increment Δm is reliably maintained despite the variation of the mass flow j.

By means of an actuating and drive device 35, the shear gap width s between the shear mandrel or cone 7 and the shear cylinder sleeve 8 and the shear speed n are adjusted in accordance with the mold cavity F such that the size of the temperature increase Δt ₂ can be varied during the shear injection molding process . The . Control unit 43 contains a programmable memory, each with a memory area for the mass flow j of the corresponding mold cavity 13 as a function of the time t _Fn . In addition, by means of temperature sensors 31, 32, 33 and .34, the sizes T _Q T _Q + ΔT- ^, .DELTA.T and Tp are measured continuously and ^'the control unit 43 transmits that cherbereichen in further Spei¬ the memory for these quantities setpoints contains.

To control the shear gap width s is taken into account that the viscosity η at increasing the width s increases the shear gap 16 and tion on the other ^'at Vergröße¬ the shear speed n according to equations (10) and (15) decreases.

For the cross-linking of each partial quantity Δm, the shear energy generated in the shear gap, plus that on the Path ξ through the form of energy supplied, provided:

* w W _v = c _w J (Σ ΔT _n - Tα _n ) • j • dt (19) o

The size of each mass element can be adjusted according to the following equation:

Δm = J j • dt (20) o

The invention in particular allows the use of a low melt temperature on the entire route from the injection unit to the shear gap. Thus, a thermal. Preloading of the molding compound safely avoided.

It is only shortly before the mold cavity that the shear temperature increases the melt temperature to the currently specified maximum temperature as quickly as possible, which causes crosslinking to begin at an early stage. If the mass which has been heated to a high degree and is about to crosslink meets the very thin gap of the mold parting plane, the mass initially penetrating here very quickly experiences a sudden increase in viscose due to the crosslinking which begins immediately here . In this way, the tendency to form floating skin can be considerably reduced. The invention enables extremely short heating times, particularly in the case of thick-walled parts. The mixture-specific temperature optimum is kept constant and reliably by the exact control of the melt temperature before entering the mold cavity, which leads to a high quality consistency.

The diagram shown in FIG. 4 shows how different crosslinking conditions can be achieved by heating the partial quantities differently before leaving the heating element. The volume increment first penetrating into the cavity is not or only slightly warmed in the shear mandrel, so that when it hits the flow front it is still sufficiently low below the scorch temperature. Shortly before the completion of the filling phase, the temperature rises above the scorch point. When hitting the mold parting level, an intensive heat transfer takes place here, which leads to a sudden crosslinking and thus to a prevention of further swimming skin formation.

The volume increment Δm _n last penetrating into the cavity, on the other hand, is already heated up by the shear element to such an extent that the scorch point is exceeded immediately after introduction into the cavity and the crosslinking begins without further heat transfer through the inner wall of the mold.

The initial temperature not only can be achieved by a change in the shear Ver¬ Dorn speed or the gap width ^'or the temperature of the heating element, but also by a change of the passing material volume at kon¬ stant power supply to achieve in Aufheizelement. The Corresponding control takes place either according to a fixed temperature / time curve defined for a system or - as described above - by means of a model computer, to which further current process parameters can be added in order to reproduce the current spraying process as precisely as possible with the aim of a particularly precise one To obtain control of the individual spraying process.

FIG. 5 shows a block diagram of a control according to a predefined or calculable temperature profile in the work cycle, in particular when using the hot-cone method. The cone and a correspondingly shaped conical sleeve form a gap which interacts with the elastomer source and the amount of heat and is adjustable in a manner (not shown in FIG. 5). Relatively large amounts of heat can likewise be transferred into the molding composition at short notice for a defined time range, so that the volume filling the molding cavity obtains homogeneous vulcanization properties. Because of the temperature, which can be set via a short transport path by changing the gap width s, a high cycle speed and thus a large material throughput is possible.

In the method for injection molding of elastomers with gerin¬ ger thermal conductivity at a heating of the molding compound in Plastifizieraggegrat on T + _Q _ΔT-] _ before ^'entering tempered forms that are successively brought in injection molding position, and in which after further heating ^up' Zung takes place in a discontinuous cycle, the heating element regulates the temperature before entry the elastomer mass into the mold cavity 13 and regulating the width s of the heating element according to a specific model and temperature profile as a function of time and volume flow i. A work cycle is output from a clock device 51 directly to the elastomer source 50 and indirectly via a device for mold transport 53 into the mold 52 and via a timing element 54 to a model computer 55 with a time delay. The form contains sensors for the size and nature of the cavity F and for the temperature Tp, which transmit information about the form 52 to the model computer 55 via corresponding connecting lines.

The molding compound ejection temperature T = T _Q + .DELTA.T _j + .DELTA.T ₂ and the volume flow i = v / t are measured with suitable measuring means immediately before entering the mold cavity 13 of the mold and are likewise supplied to the model computer 55 via connecting lines , which, taking into account the specific density ς, controls the elastomer source 50 via control lines in accordance with the optimal injection molding parameters for the mold 52, the temporal change in the required amount of heat Q / t and the volume V / t for the elastomer flow after one Model is determined.

In addition to the known regulation of the conveying speed of the molding compound and the preheating with associated measurement using thermocouples on the shower side in order to regulate the melt temperature in the injection cylinder, in the work station on the molding side during the A temperature measurement in the elastomer mass heated by shear energy as well as a The volume flow i and the local heating are realized with a short time constant in the immediate vicinity of the mold cavity in accordance with the optimal values that can be set by the model computer 55.

Due to the uniform temperature distribution over the entire cross section of the molded part, overheating of the molded part on the surface (reversion) is avoided and thus a constant, constant maintenance of the material quality is achieved.

The invention is not restricted in its implementation. to the preferred exemplary embodiment given above. Rather, a number of variants are conceivable which make use of the solution shown, even in the case of fundamentally different types.

* * * * *

Claims

Expectations

1 .. Process for the injection molding of crosslinkable molding compounds, in particular those with low thermal conductivity, the molding compound being supplied in a first phase and thereby before it enters the molding cavity or a flow channel leading to it by means of a heating device is heated and subsequently crosslinked under the influence of an optimal temperature, in order to be subsequently removed from the mold cavity,

characterized ,

that when passing through the heating device through the successive, volume increments forming partial quantities of the molding material, a temperature increase to a temperature which brings about a substantial crosslinking in the period of the working cycle takes place in a mixture-specific manner, such as by changing the heat quantity supplied to each partial volume in accordance with a predetermined or calculated profile, and

that taking into account the different paths to be covered by successively supplied portions of the molding composition, in their final position within the molding cavity and the time required for this, an essentially uniform cross-linking occurs for these various portions of the molding composition.

2. The method according to any one of the preceding claims, characterized in that the starting temperature reached with the heating of the respective partial volume of the molding compound upon leaving the Heizvorrich- 5 device is selected so that on the way of the molding compound in the mold cavity, which depends on the residence time on the flow path and the set temperature einstel¬ loin crosslinking is such kept limited such that no Anvernetzen to the flow paths or no weld line ^errors' occur 10th

3. The method according to any one of claims l or 2, d a ¬ d u r c h g e k e n n z e i c h n e t that the with

15 Heating reached the initial temperature of the respective partial volume of the molding compound when leaving the Heizvorrich¬ direction is selected such that the crosslinking achieved is high enough to prevent the molding compound from entering the mold cavity when it reaches the seams.

20th

4. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the starting temperatures reached with the heating up on one another

^{• Increase} 25 partial volumes of the molding compound when leaving the heating device.

5. The method according to any one of the preceding claims,

30 characterized in that the output temperature reached with the heating of the respective Part of the volume of the molding compound when leaving the heating device is determined by the output signal of a model computer, which takes into account the further path of the part volume of the molding mass to be heated, its cross-linking which occurs as a function of time and, if appropriate, on the way to the mold cavity location-dependent requirements of minimum or minimum maximum values of the networking is determined.

6. The method according to claim 5, characterized in that the model computer for a single partial volume passing the heating device, the current temperature and the crosslinking achieved and the distance traveled by this partial volume in the flow channels or in the mold cavity through the respective partial volume representative data records and this takes into account each other, taking into account the information of the other data records, until the final position is reached, in which the mold cavity immediately updates model data of the mold cavity,. the amount of heat actually supplied to a respective sub-volume is selected such that the sub-volume in question and also the other sub-volumes do not exceed or fall below certain specifications of the minimum or maximum values of the crosslinking in the calculation.

7. The method according to claim 6, characterized in that the calculation is carried out according to the finite element method.

8. The method according to any one of the preceding claims, characterized in that for different mold cavities (13) different models are predetermined, and / or by means of coding means present on the respective mold cavity in interaction with corresponding sensing and control means can be selected from a memory .

9. The method according to any one of the preceding claims, that the heating of the partial volumes takes place by means of shearing by internal friction and / or by heat conduction.

10. The method according to any one of the preceding claims, characterized in that within a work cycle, a regulation of the temperature of the partial volumes of the molding compound before entering the mold cavity (13) by changing the heating due to a comparison of the predetermined temperature profile with one in the range Heater or on the way of the molding compound immediately afterwards arranged temperature sensor.

11. The method according to any one of the preceding claims, characterized in that the amount of heat supplied to the partial volume in the heating device is determined by means of the energy supplied on average over time and / or the amount of molding compound carried past the heating device on average over time.

12. An apparatus for performing the method according to any one of the preceding claims, characterized in that there is provided: one temperature sensor (32, 33, 34) in front of and behind the heating ^'device as well as a computing and control unit which controls the heating device in dependence based on a predefined temperature profile for a predefined flow rate and geometry of the flow channels and the mold cavity or depending on a calculated temperature profile based on a model depending on the determined flow rate and geometry of the flow channels and the mold cavity, with input variables for the computing unit In particular, the output signals of the following modules are provided individually or in combination:

a temperature sensor (31) in one form. upstream injection unit (30),

a sensor for querying the shape information, containing a parameter (F) for the geometric shape cavity of the shape, preferably arranged between a press table (1) and top part (19),

a manipulated variable (n _E ) for the injection speed of the molding compound,

a heating device arranged shortly before the mold cavities, preferably in the form of an actuating and driving device (35) for a shear mandrel with manipulated variables for the shear speed (s) and / or the shear gap width (s).

13. The apparatus according to claim 12, characterized in that the inputs of the control. Purity (43) are each provided with an analog / digital converter for measured variables (T ₀ ), (F), (T _Q + ΔT), (ΔT _n ) and (Tp).

14. * Device according to one of claims 12 or 13, characterized. characterized in that the outputs of the control unit (43) are control units for the output of manipulated variables (K_), (n _E ) and (H ₂ ), which are generated by the computing unit in accordance with a model for the necessary current heating of the volume parts Taking into account the distance to be covered and the mass flow (j) for the respective mold cavity (13), as well as manipulated variables (n) and (s), which are calculated by the computing unit during a shear energy-per-time control according to the deviation of the determined temperature increases (ΔT_) and ( ^Δτ n) ^of ^ ^en predetermined target temperature values (T ₀ + ΔT _S ) are output.

15. Device according to one of the preceding claims 12 to 14, characterized in that the control unit (43) has a memory, each with a memory area for target values of the temperatures (T ₀ ), (ΔT _χ ), (ΔT ₂ ) and (Tp) according to the temperature profile of the corresponding mold cavity (13) as a function of time (t _Fn ).

16. The device according to one of claims 11 to 15, characterized in that the control unit (43) in the memory each have a storage area for setpoints of the mass flow (j) corresponding to the mold cavity (13) as a function of time (t _Fn ) contains.

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