DE4442536A1 - Method and device for producing molded parts from multi-component plastics - Google Patents

Description

The present invention relates to a method and an apparatus for the manufacture provision of molded parts made of solid or microcellular plastic, especially polyurethane, by reacting a flowable reaction mixture from at least two components. The device consists of a Closing unit with mold and mixing device for the Reaction components, each with a mold half on one Base plate of the clamping unit is arranged and the mold cavity when closed Shape and lack of internal pressure due to spacing blocks between the Base plates is defined. Such molds are usually called Plunging edge tools, where the sealing of the form by surfaces running parallel to the closing direction of the mold halves. At closed form overlap the sealing surfaces, i. H. the one mold half plunges into the other half of the mold.

Such a device is basically known from EP-A-0 206 100. It is also known in the manufacture of molded parts Multicomponent plastics after filling the mold the internal pressure to increase in such a way that the form while avoiding cavities, bubbles and so-called voids is well represented by the molding compound, d. H. Possibly. trapped air bubbles due to the internal mold pressure in the molding compound be solved. Due to the "chemical shrinkage", i.e. H. the volume reduction of the molding material during the reaction, it is necessary to Maintaining the internal mold pressure corresponds to the volume of the mold cavity  Reduce shrinkage. The sealing surfaces must overlap the mold halves in the closing direction, d. H. the immersion depth of one mold half in the other half of the mold, be dimensioned so that at the required initial Overfilling the shape the overlap is not yet removed.

According to EP-A-0 206 100, it was proposed to lift elements to the clamping unit assign that counteract the closing force while filling the mold and increase the volume of the mold cavity by 2 to 5%, so that an overfill development of the form with reactive mass is possible. After the filling process the effect of the lifting elements is canceled so that the closing force under Er generation of the mold pressure acts on the molded part. A disadvantage of the be known method is that a considerable amount of equipment to control the Lifting elements is required. Furthermore, the build-up of the internal mold pressure takes place with a certain delay after the filling process, so that the the very fast reacting RIM and RRIM processes used today tion already progresses before the formation of the internal mold pressure ("reprint"), with the consequence that relatively high mold internal pressures have to be generated in order to achieve the Reproduce shape safely.

According to EP-A-0 024 610, the molding tool has also already been proposed partially form as an elastic membrane, which when the shape is overfilled Trapping volume due to their deflection and absorbs the shape provides internal pressure. The disadvantage here is that, on the one hand, the constant temperature is difficult to control in the area of the membrane of the molding tool and on the other hand, especially in the production of thin-walled molded parts Shape accuracy is difficult to ensure. In addition, it comes with increasing solidification of the reactive mass to a very uneven Ver division of the mold pressure over the molded part.

According to the invention, it is now proposed to have at least one mold half a plunge edge tool against prestressed spring elements against the perform the audible base plate so that it can move, so that when the mold is closed, H. at Base plates lying on both sides of the spacer blocks, at least one  Half of the mold against the prestressed spring elements compared to the other mold half can be raised.

The prestressing of the spring elements preferably corresponds to an inner shape pressure of up to 50 bar, preferably 10 to 50 bar, particularly preferably at least 20 bar.

The spring elements can be of any design, e.g. B. can coil springs, Disc springs, leaf springs, rubber-elastic blocks or pneumatic springs elements with prestressed gas pressure can be used.

The at least one mold half is preferably against the spring elements a path movable that at least increases the volume of the mold cavity corresponds to the amount of chemical shrinkage of the reaction mixture, d. H. the minimum stroke of the mold half is intended to increase the volume by min at least 1.5%, preferably 2 to 5%, preferably not more than 4% speak. For the production of molded parts from z. B. average thicknesses from 1 to 20 mm is therefore sufficient to design the device so that a maximum stroke of 1 mm is possible.

The spring characteristic of the spring element is chosen so that at the Compensation for chemical shrinkage required overfilling the mold the desired mold pressure is set. This can be done after filling the mold about 1 to 80 bar or higher, preferably at least 25 bar. However, spring elements with a spring character are preferred according to the invention teristics, in the at least one shape due to the required stroke half the spring tension compared to the preload by only one Amount increased from 20 to 100%.

In a further preferred embodiment of the present invention, the Preload pressure of the spring elements can be selected using variable preload elements.

The present invention also relates to a method for producing Molded parts made of a solid or microcellular plastic, in particular  Polyurethane, by reaction of a flowable reaction mixture of at least two components in which the reaction mixture from a mixing device in the mold is injected, the mold initially by at least the amount of chemical shrinkage of the reaction mass is overfilled and in the mold Overpressure is generated, which is characterized in that the overpressure before Completion of the filling process is generated and maintained until demolding is obtained.

The maximum internal mold pressure is preferably from 1 to 80 bar at the end of the Filling process of the reaction mixture reached. The internal mold pressure may be up to Demolding does not fall under the preload pressure of the spring elements; preferred it should not be less than half the maximum internal mold pressure fall off.

The method according to the invention is preferably described by means of the introduction benen device according to the invention carried out without complicated tax facilities are required. The filling of the form from the mixing device first takes place in the empty mold cavity until a volume that corresponds to the volume corresponds to the later molding, is filled, essentially only against the flow pressure in the mold. After reaching this filling volume, the Overfilling the mold while increasing the internal pressure up to Maximum pressure against the preloaded spring elements.

According to a preferred embodiment of the present invention several molds assigned to a single clamping unit. Everyone by ever a mold cavity formed is a filling device (mixing head) assigned for the reactive mass.

In a further preferred embodiment, the plurality of mixing heads a mold clamping unit from common storage containers for the reactive components are fed with the reactive components via common pumps, valves are provided in the feed lines, which are controlled so that the several mixing heads are loaded one after the other.

The invention is explained in more detail below with reference to the attached figures:

Fig. 1 shows a device according to the invention without the clamping unit.

Fig. 1a shows the detail A from Fig. 1 in an enlarged view.

FIG. 2 shows a device according to FIG. 1, the upper mold half being raised by the maximum possible distance.

Fig. 3 shows a device according to the invention corresponding to Fig. 1, but the bias of the spring elements is adjustable.

FIG. 4 shows a device according to FIG. 2, with several molding tools being assigned to one clamping unit.

Fig. 1 shows the lower base plate 1 and the upper base plate 2 , which rest on the spacer blocks 3 due to the closing force of the locking unit, not shown. The lower mold half 5 fastened on the lower base plate 1 contains the mixing device 4 , by means of which the reaction mixture can be introduced into the mold cavity 12 . A clamping plate 7 is provided between the upper base plate 2 and the upper mold half 6 , to which the mold half 6 is fastened. The provision of a platen 7 allows the molds 6 and 5 z. B. to replace the production of other molded parts. The clamping plate 7 is mounted by means of preload screws 9 and spring elements 8 designed as coil springs against the upper base plate, so that a gap h is formed between the base plate 2 and the clamping plate 7 in the absence of internal mold pressure in the mold cavity 12 . The width of the gap h represents the maximum stroke by which the upper mold plate 6 can be raised against the lower mold half 5 and against the prestressed spring elements 8 by generating an internal mold pressure. The mold parting plane 11 between the lower mold half 5 and the upper mold half 6 is designed as a diving edge 10 .

FIG. 1a shows detail A from FIG. 1, namely the area around the plunge edge 10 when there is no internal mold pressure. The aim is the overlap length t of the dipping edge surface 10 and opposing surface 10 a in the closing direction of the dipping edge tool at least the width of the gap h (Fig. 1).

The same reference numerals in Fig. 3 denote the same elements as in Fig. 1. Between the base plate 2 and the mounting plate 7 , a biasing plate 13 is provided, act on the screw thread inserted into the base plate 2 before tension adjusting screws 14 to set the biasing pressure of the spring elements .

According to Fig. 4, between upper and lower base plates 1, 2 a number of molds, the mold cavities I, II and III form is provided.

A mixing head 41 , 42 , 43 belongs to each mold nest. The reactive components are supplied via common supply lines 20 (the supply line is shown for only one component), which - controlled via valves 21 , 22 , 23 - only feed into a mixing head in each case.

Depending on the operating state shown, the mold cavity I is filled with the reactive mixture. Valve 21 is closed. The upper half of the mold is raised against the spring elements. Form nest II is filled. Valve 22 is open. Valve 23 is closed.

Claims (8)

1. Apparatus for the production of molded parts from solid or micro cellular plastic, in particular polyurethane, by reaction of a flowable reaction mixture of at least two components, consisting of a clamping unit with a mold that is designed as a plunge edge tool, and mixing device for the reaction components, each in each case a mold half is arranged on a base plate of the clamping unit and the mold cavity is defined by distance blocks between the base plates when the mold is closed and in the absence of internal pressure in the mold, characterized in that at least one mold half when the clamping unit is closed against movable spring elements against the associated base plate is movable. 2. Device according to claim 1, characterized in that the preload the spring elements corresponds to an internal mold pressure of up to 50 bar. 3. Apparatus according to claim 1 or 2, characterized in that the at least one mold half is movable against the spring elements in such a way that an increase in volume of the mold cavity by at least the amount the chemical shrinkage of the reaction mixture can take place. 4. Device according to one of claims 1 to 3, characterized in that the mold is designed as a plunge edge tool. 5. Device according to one of claims 1 to 4, characterized in that the preload pressure of the spring elements is adjustable. 6. Device according to one of claims 1 to 5, characterized in that a clamping unit with associated base plates has several shapes tools are assigned.   7. Process for the production of molded parts on solid or microcellu larem plastic, especially polyurethane, by reaction of a flow capable reaction mixture of at least two components, in which the reaction mass is injected into the mold from a mixing device, the form initially being at least the amount of chemical Shrinkage of the reaction mass is overfilled and in the form Overpressure is generated, characterized in that the pressure before Been the filling process is generated and up to the demoulding is obtained. 8. The method according to claim 7, characterized in that a device is used according to claim 6, wherein the reaction mass in several of the molds assigned to the common clamping unit in succession is injected.