DE102014001461A1 - Process for producing a molded part from polyurethane - Google Patents

Abstract

The invention relates to a method for producing a molded part from polyurethane, wherein the molded part has at least two different zones with respect to the material composition, the method comprising mixing a plurality of chemically reactive plastic components in a mixing head (1), wherein the mixing head (1) comprises a mixing chamber (1). 2) having a first axis (A) and a settling chamber (3) with a second axis (B), wherein a in the direction of the first axis (A) extending first exit direction (R) results, wherein at one end of the settling chamber ( 3) an outflow channel (8) is arranged, so that in the direction of the second axis (B) to the outflow (8) directed second outlet direction (T) results, wherein the mixing chamber (2) over its circumference nozzle bores (4, 5, 6, 7), via which a plastic component can be injected. In order to easily achieve an improved mixture of the components, the invention provides that the injection of at least two different plastic component mixtures takes place, which are generated from at least three different plastic components, wherein for the injection of the individual mass flows (ṁi) special directions be specified.

Description

The invention relates to a method for producing a molded part from polyurethane, wherein the molded part has at least two different zones with respect to the material composition (for example a motor vehicle seat cushion), the method comprising mixing a plurality of chemically reactive plastic components in a mixing head, wherein a mixing head is used comprising a cylindrical mixing chamber having a first axis and a settling chamber having a second axis, wherein the settling chamber is fluidically connectable to the mixing chamber, resulting in a first axis extending in the direction of the first axis, which directed from the mixing chamber to the settling chamber is, wherein at one end of the settling chamber, an outflow channel is arranged so that there is a directed towards the second axis to the outflow channel second outlet direction, wherein the mixing chamber has at least two nozzle bores over its circumference, over each of which a plastic component can be injected, wherein a mass flow of a plastic component is injected in an injection direction with an average injection speed over each of the nozzle holes, so that respective pulse currents of the plastic component are inputted to the mixing chamber via the nozzle bores.

The mixing principle of such mixing heads, which are usually designed to be self-cleaning, is based on the fact that the reactive plastic components are injected via the nozzles mentioned at high speeds into a small, cylindrical mixing chamber, with the jets of the individual mass flows then colliding against each other fanning, creating a large contact surface between the various component streams. This results in turbulent flows in the mixing chamber, which additionally ensure that even relatively high-viscosity materials can be mixed very well in a very small space and within a very short time.

A generic self-cleaning mixing head or the corresponding method is for example in the US 7,240,689 B2 described. There, the structure of such a mixing head is explained in detail, so that in this respect expressly made to the document. Also in the DE 2 907 938 C2 An advantageous embodiment of a generic mixing head is described.

Another embodiment of a generic mixing head is in the WO 2004/004879 A1 described. Here, the nozzles through which the reactive components are injected into the mixing chamber are inclined in two planes to achieve better mixing.

Another special embodiment of a two-component mixing head is in the DE 10 2007 023 239 A1 disclosed. Here, however, the jets first hit a baffle before fanning one another. For this special mixing head there is also taught that the components are injected at an acute angle, opposite to the outlet direction of the outlet opening, directed against a baffle wall of the mixing chamber. However, this is rather unfavorable in practice, since the component currents in this case fan out not with the greatest possible impulse, but first on said baffle. From there, initially only the respective partial flows of both component streams fan out, which are diverted inwards after the baffle wall.

Another very advantageous embodiment of such a mixing head also describes the US 5,143,946 , Here is achieved by an arranged between the mixing chamber and the outlet area annular chamber even with strong throttling of the mixing chamber and the associated high exit velocities of the reaction mixture from the mixing chamber a very good calming of the reaction mixture already on entering the outlet pipe.

A strong throttling helps in particular with regard to the mixing at the start of shooting, when the rays still enter into the empty or filled with air mixing chamber, since the strong throttling of the mixing chamber causes the mixing chamber fills faster and that at the start of shooting faster for set a good mixing necessary turbulent flows in the mixing chamber.

The aim is to further improve the mixing of the reactive plastic components, in particular at the start of firing, in order to achieve even more homogeneous mixing.

The invention is therefore based on the object, a method and a mixing head of the type mentioned in such a way that a further improved mixing of the reactive components is given if the molding has at least two with respect to the material composition different zones (for example, in the case of a motor vehicle seat cushion) , This should be done so that there is already a good and homogeneous mixing at the beginning of a shot. Another aspect is that the implementation of measures for improved mixing should be made possible in a cost-effective and simple manner.

als Summe der Teilimpulsströme

= ṁ_i·v →_i) gemäß der Beziehung

eine Komponente aufweist, die der zweiten Austrittsrichtung (T) entgegen gerichtet ist, wobei mindestens einer der Teilimpulsströme

= ṁ_i·v →_i) eine Komponente aufweist, die in Richtung der zweiten Austrittsrichtung gerichtet ist. The solution to this problem is characterized according to the method characterized in that the injection of at least two different plastic component mixtures takes place, which are generated from at least three different plastic components, wherein the injection of the individual mass flows (ṁ _i ) through the nozzle holes into the mixing chamber for each of at least two plastic component mixtures are made so that the resulting total pulse current vector

as the sum of the partial pulse currents

= ṁ _i · v → _i ) according to the relationship

a component facing the second exit direction (T), wherein at least one of the partial pulse streams

= ṁ _i · v → _i ) has a component which is directed in the direction of the second exit direction.

It is preferably provided that the resulting total pulse current vector has a component which is directed counter to the first exit direction.

Preferably, the first axis of the mixing chamber and the second axis of the settling chamber intersect at a first intersection and enclose a right angle.

In the mixing chamber can be arranged displaceable in the direction of the first axis spool, with which the at least two nozzle bores are released or closed in dependence of the axial positioning of the spool.

In the settling chamber, a throttle element which is displaceable in the direction of the second axis is preferably arranged, with which the transition surface between the mixing chamber and the settling chamber is at least temporarily closed off ("throttled"). In this case, the transition area between the mixing chamber and the settling chamber can be closed at least temporarily by at least 30% with the throttle element.

The average overflow velocity of the reactive mixture at the transition area between the mixing chamber and the settling chamber as a quotient of the exceeding volume flow of the reactive mixture and the transition surface is in this case preferably at least 5 m / s, more preferably at least 15 m / s.

The proposed mixing head for mixing at least two chemically reactive plastic components with mixing chamber and calming chamber and disposed over the circumference of the mixing chamber nozzle holes for injecting the plastic components, each nozzle bore enters at a passage point in the interior of the mixing chamber, according to the invention provides that at least two of the passage points lie different axial positions along the first axis, wherein the passage point is defined as the intersection of the axis of the nozzle bore with the lateral surface of the mixing chamber.

The first axis of the mixing chamber and the second axis of the settling chamber preferably intersect at right angles in a first intersection, wherein at least two of the penetration points have different distances from a first plane E ₁ , which is perpendicular to the first axis and includes the first intersection.

The nozzle bores preferably have bore axes, wherein the bore axes intersect a second plane E ₂ , which is perpendicular to the second axis and includes the first intersection, wherein the distances of the passage points from the first plane E ₁ are greater, the greater the distance Passage points from the second level E ₂ is.

Preferably, the bore axes of all nozzle bores meet at a second intersection, this preferably lying on the first axis.

The invention is initially based on the recognition that a similar effect, as can be generated by a strong throttling of the mixing chamber relative to the settling chamber, also with the aid of said orientation of the nozzle jets can be achieved in the mixing chamber. It has accordingly proved to be advantageous if the beams are oriented such that the resulting total pulse current of the beams does not point in the direction of the mixing chamber exit, but in the opposite direction. The total pulse current is defined by the pulse current vector resulting from vector addition of the pulse current vectors of the reactive component currents entering the mixing chamber.

Furthermore, it is achieved with the proposed procedure that the advantages mentioned are maintained, but now at least three different reactive components can be processed very advantageous. It should be noted that it is not possible to arrange any number of nozzles so that all these nozzles are oriented opposite to the outlet opening of the mixing chamber, as in appropriate position and all circuit grooves in appropriate dimensions in the spool must be introduced so that a sufficient sealing function is ensured against a passage of a component in the groove of an adjacent component. The quality of mixing results essentially from the fanning of the jets together. By the claim procedure, the driving force of the countercurrent pulse is used specifically.

While the mixing chamber is cylindrical, the settling chamber may be formed as a cylindrical or annular chamber. In the case of a cylindrically shaped settling chamber, this can merge seamlessly into the outflow channel. Settling chamber and outflow channel can then be cleaned by firing end of the same cylindrical piston.

The spool in the mixing chamber is concentric with this and has circuit grooves associated with the nozzle bores to effect rinsing in closed circuit nozzle bores. In the foaming position, the spool is positioned so that the transitions of the nozzle bores into the mixing chamber are not obscured. The throttle element for throttling the mixing chamber can be designed as a sleeve (in the case of an annularly formed settling chamber) or as a piston (in the case of a cylindrically shaped settling chamber). In the foaming position, the throttling element is positioned so that its front end (facing the outflow channel) at least partially covers the transitional cross section from the mixing chamber into the cylindrical or annular settling chamber so that this transitional cross section is subdivided into a closed curved circular section and an open curved circular section ,

als die über die Fläche gemittelte Geschwindigkeit definiert (V ._i als Volumenstrom der Komponente; ṁ_i als Massenstrom der Komponente; d_i als Durchmesser der Düsenbohrung; ρ als Dichte der Komponente). Ferner wird angenommen, dass die Richtung des Vektors der Mittelachse (Bohrungsachse) der Düsenbohrung mit Orientierung in Richtung in die Mischkammer entspricht.The velocity underlying the velocity vector v → _{i of} a component i through a nozzle bore is determined according to the formula

is defined as the velocity averaged over the surface (V _i as the volumetric flow of the component, ṁ _i as the mass flow of the component, d _i as the diameter of the nozzle bore, ρ as the density of the component). Further, it is assumed that the direction of the vector corresponds to the center axis (bore axis) of the nozzle bore oriented toward the mixing chamber.

In particular, in conjunction with a throttling of the reaction mixture by means of the throttle element can thereby achieve not only generally excellent mixing, but in particular a very good initial mixing.

A poor initial mixing is usually found again in the form of streaks or a local collapse on the component surface, which then leads to increased rejects or at least to optically inferior component quality.

As a further advantageous embodiment of the method, it is therefore proposed that the average outflow velocity of the reactive mixture from the mixing chamber, characterized by the quotient of the total volume flow to the cross-sectional area of the open curved circular section, is at least 5 m / s.

In order to optimally clean the mixing chamber after the shot end, the contour of the front control edge of the control slide usually corresponds to the shape or the radius of the fluidically arranged behind chamber. This means that in all cases in which the nozzle bores are not all arranged at the same distance to a plane E ₃ , which is spanned by the center axis of the mixing chamber and the center axis of the fluidically adjoining calming chamber, the nozzles do not open synchronously (ie fluidically connected to the mixing chamber), when the penetration points of the nozzle axes to the lateral surface of the mixing chamber are all arranged equidistant from a plane E ₁ , which is defined by that orthogonal to the central axis of the mixing chamber is oriented and that the intersection of the central axes of the Mixing chamber and the calming chamber lies in this plane. However, a non-synchronous opening of the nozzles is very disadvantageous, since not all components enter the mixing chamber simultaneously in this case.

Since there are a maximum of four points on the cylindrical surface of the mixing chamber, which are all arranged at the same distance about said plane E ₃ , it is not possible for mixing heads with more than four nozzle stations, the nozzles or nozzle holes to be arranged so that all penetration points the nozzle axis are arranged by the lateral surface of the mixing chamber at the same distance from said plane E ₃ . But even with mixing heads with fewer nozzle locations, it may be useful to arrange the nozzles differently, thereby achieving, for example, a better mixing result.

In order nevertheless to be able to ensure a synchronous opening of the nozzles, a further aspect of the present invention is a mixing head for carrying out the method described, comprising at least three nozzle bores with the associated center axes (bore axes), which open into the mixing chamber and which penetrate the lateral surface of the mixing chamber, wherein the distance from at least two of the penetration points to said plane, which is defined by that orthogonal to the central axis of the mixing chamber is oriented and that the intersection of Axes of the mixing chamber and the settling chamber in this plane is different in size.

At the start of firing, it is also important that the period of positive overlap, in which the component line is fluidically connected neither to the mixing chamber nor to the return line, is as short as possible. Decisive for this is in addition to the driving speed of the spool, the geometric distance of the front control edge of the spool to the mixing chamber facing the beginning of a circuit groove in the spool. In an advantageous embodiment of the mixing head, therefore, this distance should be as short as possible. In addition, the transition to the coverage area should be done as synchronously as possible on all nozzles. Therefore, it is advantageous if the distance of the circuit grooves in said axially movable spool to said plane E ₁ is greater, the greater the distance between the associated passage points of said second plane E ₂ .

Since a throttling of the mixing chamber - as mentioned above - has a positive effect not only on the mixing in the quasi-stationary stage in the middle of the shot, but in particular on the mixing at the start of shooting, contains the mixing head in an advantageous embodiment, the axially movable throttle element for throttling the mixing chamber in the form of a sleeve or a piston, wherein the center axis of the throttle element corresponds to the second axis of the settling chamber and wherein the throttle element is positioned in Schäumstellung so that its front end covers the transitional cross section from the mixing chamber into the settling chamber at least by 30%, so that this transitional cross-section is divided into a closed curved circle section and an open curved circle section. This throttle element can be formed both as a sleeve and as a piston.

In the drawings, embodiments of the invention are shown. Show it:

1 the top view of a mixing head with which a plurality of plastic components (shown are two components) can be mixed and discharged,

2 the too 1 associated side view,

3a the projection of the pulse currents of two components, which are input into a mixing chamber, viewed in the direction of the axis of the mixing chamber,

3b the vector addition of the individual pulse currents according to 3a .

4 the top view of a mixing head in one 1 alternative embodiment and

5 the too 4 associated side view.

In the 1 and 2 is a mixing head 1 to recognize, with the at least three plastic components, in the example polyol and isocyanate for the production of polyurethane, can be mixed. The mixing head 1 has a mixing chamber 2 which is cylindrical and which extends along a first axis A. Furthermore, the mixing head has 1 a calming chamber 3 , which is cylindrical or annular and which has a second axis B. The axes A and B of the two mixing chambers intersect at a first intersection point S; the cutting angle is 90 °. The mixing chamber 2 go to the calming chamber 3 over, with the transition surface from the section of the two chambers 2 . 3 results. However, this interface is to a considerable extent during the operation of the mixing head 1 from a throttle element 10 locked; the mixing chamber 2 is then then "throttled". The throttle element 10 is formed in the illustrated embodiment as a sleeve-shaped slide, which can be moved in the direction of the axis B, to produce the desired degree of throttling.

Three planes are defined by the axes A and B and by the first intersection S. The plane E ₁ is perpendicular to the axis A and includes the first intersection point S. The plane E ₂ is perpendicular to the axis B and includes the first intersection point S. A plane E ₃ is spanned by the axes A and B.

In the mixing chamber 2 is a control valve 9 arranged displaceably in the direction of the axis A. As is clear from the illustrations according to 1 and 2 gives, is the spool 9 at his the calming chamber 3 facing end formed so that it with its arched end face the calming chamber 3 Complemented to a cylindrical contour when it reaches the reassurance chamber 3 pushed on (what then the throttle element 10 has to be withdrawn).

From the transition of the mixing chamber 2 in the calming chamber 3 the produced mixture of plastic components enters an outflow channel 8th , Accordingly, two can be Defining the directions of flow for the mixing of the plastic components: In the mixing chamber 2 the mixture is conveyed in a first exit direction R, in the settling chamber 3 in a second exit direction T.

The chemically reactive plastic components occur at high speed (usually 80 to 200 m / s) via nozzle bores 4 . 5 . 6 . 7 into the mixing chamber 2 one for which spray nozzles 19 are provided.

About the illustrated open curved circular section surface 20 the reaction mixture exits the mixing chamber 2 from and into the following, in the illustrated embodiment annularly formed calming chamber 3 one. From the annular calming chamber 3 Then, in the example shown, the reaction mixture enters the outflow channel at a reduced rate 8th a, over which the reaction mixture finally out of the mixing head 1 flows.

The calming chamber 3 came as an alternative to the example shown also be cylindrical. In this case, the calming chamber 3 seamless into the discharge channel 8th pass. Settling chamber and outflow channel can then be cleaned by firing end of the same cylindrical piston.

= ṁ_i·v →_i mit den Bezugsziffern 21, 22, 23 und 24 bezeichnet sind. Durch (graphische) Addition ergibt sich gemäß 3b der resultierende Impulsstromvektor 25 (hier wiederum projiziert auf die genannte Fläche).The 3a and 3b show by way of example how the total momentum of the here total of four injected mass flows - projected onto a sectional surface which is perpendicular to the axis A - results from the pulses of the individual jets. This is first in 3a to see that four different reactive components are involved, their momentum current vectors

= ṁ _i · v → _i with the reference numerals 21 . 22 . 23 and 24 are designated. By (graphic) addition results according to 3b the resulting pulse current vector 25 (again projected onto the mentioned area).

It is essential that the resulting pulse current vector (total pulse current vector) 25 has a component which is directed against the second exit direction T. With regard to the first exit direction R, it is equally true that the resulting pulse current vector 25 has a component directed against this direction R.

In the 4 and 5 is a slightly different embodiment to the solution 1 and 2 to see. The mixing head 1 characterized here by the fact that the passage points 11 . 12 . 13 the nozzle holes 4 . 5 . 6 . 7 (S. 1 and 2 ) are not all at an axial location on the axis A. Rather, it can be seen that the axial position of at least two passage points 11 . 12 . 13 with respect to the distance b ₁ and b ₂ from the plane E _{1 is} different. The distances b _i are chosen so that it is despite the curved configuration of the front end of the spool 9 ie the control edge 16 , shows that during the axial displacement of the spool valve 9 all passage points 11 . 12 . 13 at the same time from the control edge 16 be reached and so simultaneously shoot or open.

The bore axes 14 . 15 the nozzle holes 4 . 5 . 6 . 7 are preferably chosen so that they all meet in a second point of intersection K.

Rinsing of the arrangement is in a conventional manner by Kreislaufnuten 17 in the spool 9 allows. Equally, a cleaning piston 18 for the calming chamber 3 intended.

LIST OF REFERENCE NUMBERS

1

mixing head

2

mixing chamber

3

settling chamber

4

nozzle bore

5

nozzle bore

6

nozzle bore

7

nozzle bore

8th

outflow

9

spool

10

Throttle element (throttle sleeve)

11

Passage point

12

Passage point

13

Passage point

14

bore axis

15

bore axis

16

control edge

17

Kreislaufnut

18

cleaning piston

19

nozzle

20

Circular section surface

21

Pulse current vector

22

Pulse current vector

23

Pulse current vector

24

Pulse current vector

25

resulting pulse current vector

• ṁ _i mass flow of the plastic component
• v → _i mean injection speed
• 
  pulse current
• 
  Total momentum flux vector
• A first axis
• B second axis
• R first exit direction
• T second exit direction
• S first intersection
• K second intersection
• E ₁ first level
• E ₂ second level
• E ₃ third level
• b ₁ distance
• b ₂ distance

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7240689 B2 [0003]
• DE 2907938 C2 [0003]
• WO 2004/004879 A1 [0004]
• DE 102007023239 A1 [0005]
• US 5143946 [0006]

Claims (6)

A method of manufacturing a polyurethane molded article, wherein the molded article has at least two zones different in material composition, the method comprising mixing a plurality of chemically reactive plastic components in a mixing head ( 1 ), wherein a mixing head ( 1 ), which is a cylindrical mixing chamber ( 2 ) with a first axis (A) and a calming chamber ( 3 ) with a second axis (B), wherein the calming chamber ( 3 ) fluidically with the mixing chamber ( 2 ) is connectable, wherein in the direction of the first axis (A) extending first outlet direction (R) results that from the mixing chamber ( 2 ) to the calming chamber ( 3 ), wherein at one end of the calming chamber ( 3 ) an outflow channel ( 8th ) is arranged, so that in the direction of the second axis (B) to the outflow channel ( 8th ) directed second exit direction (T), wherein the mixing chamber ( 2 ) over its circumference at least two nozzle bores ( 4 . 5 . 6 . 7 ), over each of which a plastic component can be injected, wherein via each of the nozzle bores ( 4 . 5 . 6 . 7 ) a mass flow (ṁ _i ) of a plastic component is injected in an injection direction with a mean injection speed (v → _i ), so that via the nozzle bores ( 4 . 5 . 6 . 7 ) respective pulse currents

= ṁ _i · v → _i ) of the plastic component into the mixing chamber ( 2 ), characterized in that the injection of at least two different plastic component mixtures takes place, which are generated from at least three different plastic components, wherein the injection of the individual mass flows (ṁ _i ) through the nozzle bores ( 4 . 5 . 6 . 7 ) into the mixing chamber ( 2 ) for each of the at least two plastic component mixtures such that the resulting total pulse current vector

as the sum of the partial pulse currents

= ṁ _i · v → _i ) according to the relationship

a component facing the second exit direction (T), wherein at least one of the partial pulse streams

= ṁ _i · v → _i ) has a component which is directed in the direction of the second exit direction (T). A method according to claim 1, characterized in that the resulting total pulse current vector

a component facing the first exit direction (R). Method according to claim 1 or 2, characterized in that a mixing head ( 1 ) is used in its mixing chamber ( 2 ) a in the direction of the first axis (A) displaceable spool ( 9 ) is arranged, with which the at least two nozzle bores ( 4 . 5 . 6 . 7 ) in dependence of the axial positioning of the spool ( 9 ) be released or closed. Method according to one of claims 1 to 3, characterized in that a mixing head ( 1 ) is used in its calming chamber ( 3 ) in the direction of the second axis (B) slidable throttle element ( 10 ) is arranged, with which the transition surface between the mixing chamber ( 2 ) and the calming chamber ( 3 ) is closed at least temporarily and at least partially. Method according to claim 4, characterized in that with the throttle element ( 10 ) the transition area between the mixing chamber ( 2 ) and the calming chamber ( 3 ) is closed at least temporarily by at least 30%. Method according to one of claims 1 to 5, characterized in that the average overflow velocity of the reactive mixture at the interface between the mixing chamber ( 2 ) and the calming chamber ( 3 ) as a quotient of the exceeding volume flow of the reactive mixture and the transition surface is at least 5 m / s.

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