DD288061A7 - METHOD AND DEVICE FOR FORMING COMPONENTS FROM CERAMIC THERMOPLASTIC MOLDING MATERIALS - Google Patents

Abstract

The invention relates to a method and an apparatus for shaping tubular and rod-shaped components with Wandstaerken 2 mm of ceramic, thermoplastic compositions by low pressure hot spraying in a specific pressure range of 0.1 to 5.0 MPa excluding volume elements, according to the invention in each case only so much Molding material is fed continuously, so that always only a small amount of liquid molding compound in the form of a layer film rests on the molded parts or on the already solidified molding compound. The organic binders solidify homogeneously, predominantly glassy-amorphous and the molded parts produced show no later erroneous visual changes after thermal processes and have their own strengths to the material. Thermal spraying; Low pressure; rod-shaped components; large walls; Ausbeuteerhoehung}

Description

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Field of application of the invention

The invention relates to a method and a device for shaping ceramic tubular and rod-shaped components made of powdery material via a reachable by organic binder pourable state.

Characteristic of the known state of the art

It is known to prepare pulverulent starting materials with plasticizers. The masses thus obtained can be processed by pressing, casting, modeling, etc. and increasing the temperature of the material to form-stable parts. Also known are shaping processes for the injection molding of thermoplastics at injection pressures of> 30 MPa and corresponding closing pressures on the mold. It is also known that in the high-pressure spraying process for plastic processing is carried out with emphasis, which can reach a maximum of the height of the injection pressure and on the gate and gate on the molding until the sealing of the openings is effective. Also known are low-pressure methods for hot spraying, as described in DD-PS 67782. The molding compounds are promoted with low injection pressures in the mold and solidify there. The solidification of the molded parts takes place from the tempered walls of the molding tool in the direction of molding inside. Also in this method, the injection pressure is effective until the sealing of the openings for the mass supply. As a result, the volume contractions associated with the solidification are largely compensated by a tracking of material. Also known is the isostatic compaction and densification of powdered materials and devices for reducing stresses within ceramic blanks, as never described in DD-PS 244721. In this method, preformed components are compacted or recompressed from the outside to the inside without any further supply of material and with changes in the external dimensions.

The above methods are not suitable for the production of complicated shaped ceramic parts with wall thicknesses> 2 mm of unpiastischen powdery materials in which the determining outer contour is maintained in the following processes and does not have to be created by a post-treatment.

In contrast to filled thermoplastic molding compositions, the ceramic thermoplastic molding compositions contain filler fractions of 75 to 90% by mass. The remaining fractions consist of organic binders, with the aid of which the pulvorförmigen starting materials are converted at temperatures above the yield points of the organic binder in the pourable state. Ceramic thermoplastic moldable molding compounds, in contrast to Newtonian flowable liquid metals such as those used in the hot chamber die casting process and the pure plasticized thermoplastics, have particular rheological properties to be considered in the molding process.

Depending on the type and size of the electrostatic interactions between the powder particles and under the action of external forces, the rheograms may have all theological features. Typical flow curves show the following structure with increasing shear rate:

- yield point

- Lower, approximated Newtonian area

- plastic transition area

- Upper, approximated Newtonian area

- dilatant transition region.

For shaping, depending on the geometry of the moldings Newton's areas and the plastic Transition area used, with the work area with reduction of the specific volume to higher shear rates

and thus shifts toward the upper, approximate Newtonian area.

Dilatant flow must be avoided because of the associated "hash separation of solid-liquid Considering the increased thermal conductivity of the ceramic thermoplastic-moldable molding compounds, due to

the higher thermal conductivity of the fillers, resulting for the low-pressure hot-spraying method significantly higher Angußuud bleed cross-sections than in the die casting of metals and the injection molding of thermoplastics. To avoid the

Mold filling by jet flow behavior of the material, as it is used in the die casting of metals,

the modified sprue and gate cross-sections require a reduction of the injection pressures

Low pressure hot spraying of ceramic, thermoplastic-pourable molding compounds by a factor of 30 to 50 compared

the injection molding of thermoplastics.

Dor f οιmteilaufbau is analogous to the injection molding of thormoplasts by a thermoplastic moldable soul, which itself

trich'isrföimig of the filling opening in the molding spreads. The solidification of the thermoplastic ceramic molding material begins au the Formanwandung and migrates continuously to the center of the molding.

Vüiumiinkcütraktionen in the solidification of the molding material by a tracking of material under Forming conditions by the plastic, pourable soul until its sealing at the gate or gate

iiüsgeylir.h.en.

After the forming process, the organic binders are expelled at elevated temperatures and the moldings

you have solidified Brnrmon. Especially with thick-walled moldings with wall thicknesses> 2 mm, this process is significant

Difficulties connected. Thus, the thermally treated parts show especially when using very fine starting materials

with specific surface areas of a = 5 x 10 ^{3 to} 5 x 10 ⁴ m ^J · kg " ¹ reduced strengths and unlike the formed ones

Sharp changes due to retractions, cavities and cracks. Aim of the invention

The aim of the invention is a method in connection rr.it an appropriately designed device for molding ceramic components of thermoplastic-moldable compositions by injection molding in a pressure range of 0.1 to 5.0 MPa, in which the molded parts after the thermal processes no erroneous visual changes subject and have the material own strengths.

Explanation of the essence of the invention The invention is based on the object, a method for shaping molded parts from ceramic thermoplastic To provide molding compounds by low-pressure warm spraying, in which no sudden density change in the phase transition

solid-liquid takes place, and a device for carrying out the method.

According to the invention the object is achieved in that only as much molding material is continuously supplied, that always

only a small amount of liquid molding compound in the form of a layer film on the moldings or on the already solidified

Molding compound and the molding or the solidified molding material throughout or completely through the entire process

a m'r <is subjected to a temperature gradient to the layer film-loaded mold.

In this case, the molding process on a molding with variable coordinates done alternately. In the apparatus for carrying out the method is the volume of the mold interior to be filled with the molding material

controllable during the molding process by one or more moving parts.

The openings for supplying the pourable thermoplastic mass are attached to or in a mold

arranged tempered part.

It has been found that the crystallization of the n-alkanes used as binders in the temperature range from 308K to 328K in

the predominantly acicular hexagonal α-modification prevailing in the core-shaped parts is inhibited or completely suppressed under increased pressure, whereby the glassy-amorphous prevailing in the edge region due to the rapid cooling

Form homogeneously form throughout the molding. Due to the increased pressure, the release of adsorbed gases

prevented in the still plastic areas inside the moldings. The molded parts do not show any faulty visual changes after the thermal processes. They have their own strengths to the material.

embodiment The invention will be explained below with reference to two embodiments with reference to the drawings. Show it Fig. 1: device before and after filling of the mold Fig. 2: The heat-insulating seal with openings for the supply of the injection molding example 1

Dio Production of an annular ceramic molding of ceramic, thermoplastic, moldable molding compositions is carried out using surface-active substances and hard paraffin as organic binder. Dom ceramic material is a high alumina powder with a specific surface area a »2 × 10 ⁴ m ² × kg ^-1 , which is contained in the molding compound with Pp = 0.85 kg χ kg × ¹ mass fraction. 1, to the left of the center line, the forming tool is shown at the beginning of the molding process, the right side shows the state just before completion of the molding of the annular ceramic molding to be produced in the embodiment The molded interior 1 is thereby delimited by the cooled mold tool punches 10, scrapers 11 and ring 12 as well as by the heat-insulating seal 7 with the openings 3 The seal 7 separates the cooled tool parts from the heated tool parts mass distributor 2, distributor block 9 and A. The injection-molded in the Fcrnnenraum V mass solidifies from the cooled mold walls of parabolic in the direction of the heat-insulating seal 7. About the moving elements 6 is a continuous lowering of the mass distributor 3 with the heat-insulating seal 7 at the same time achieved continuous mass supply under the above conditions, and there is a molding in which solidify the organic binder of the ceramic, thermoplastic, moldable molding compound homogeneous glassy-amorphous. If the molding is completely formed and solidified, the injection pressure is withdrawn and the molding material flow through the distributor block 9 u broken. By opposing operation of the Bewegungselemonte 6, the mold is emptied after opening and removed with the help of the scraper 11, the finished molding.

Example 2 By the use of other movement elements that are connected to the scraper 11 and parts of the punch 10 leave

continuously with the structure shown in Figures 1 and 2 produce tubular and rod-shaped moldings.

For this purpose, as described in Ausführungsboispiel 1, a master part generated. After complete filling of the mold is in the Area of the stripping 11 of the mold solidified molding composition on moving elements with the scraper 11 and parts of the Stamp 10 led out of the original form. The prototype is in this case in a plane through completely solidified areas

closed the molding itself. Once the desired dimensions have been achieved on the molded part, the injection pressure is withdrawn, the molding compound flow through the distributor block is interrupted and, with additional use of the

Movement moments 6 emptied the original form.

Claims (4)

1. A method for shaping components of ceramic, thermoplastic molding compositions by low-pressure hot spraying in a specific pressure range of 0.1 to 5.0 MPa excluding volume elements in which moldable or thermoformable molding compositions of non-plastic molding compounds are completely surrounded and in which the organic binder homogeneous, predominantly glassy-amorphous solidified, characterized in that only so much molding composition is continuously supplied, that always only a small amount of liquid molding compound in the form of a layer film rests on the moldings or on the already solidified molding material, the supply takes place within heated moldings and the molded part or the solidified molding compound is enclosed during the entire process, in part, by a shaping tool subjected to a temperature gradient to the film layer. 2. The method according to claim 1, characterized in that the molded part or the solidified molding material is completely enclosed during the entire process by a tasked with a temperature gradient to the film layer mold. 3. The method according to claim 1 to 2, characterized in that takes place alternately on a molding with variable coordinates of the shaping process. 4. An apparatus for shaping components of ceramic, thermoplastic molding compositions by low-pressure hot spraying in a specific pressure range of 0.1 to 5.0 MPa, characterized in that the mold interior during the molding process by one or more, the outer contour of the molding partially delimiting movable, tempered parts having openings for the supply of the pourable, thermoplastic mass, is controllably changeable.