DD274814A1 - METHOD FOR PRODUCING FLUID CERAMIC SMALL PARTS THROUGH LOW PRESSURE HOT SPRAYING - Google Patents

Abstract

The invention relates to a method for producing thin-walled ceramic microparts by low-pressure hot-injection molding. The invention relates to the production of thin-walled ceramic microparticles of complicated geometry with the utmost precision, z. B. of Nadelfüuehrungen for dot matrix printers, where Wandstaerken less than 0.1 mm are required. For this purpose, a high, but closely tolerated sintering shrinkage and low segregation and sedimentation phenomena, as well as a favorable outgassing behavior of the hot injection molding compounds, are desired. According to the invention, this is achieved by mixing finely dispersed ceramic powders having a specific surface area of 80 m 2 / g and an internal fine structure of the powder particles with extremely wide voids up to molecular dimensions of at least 85 mass% of a paraffin binder, based on the ceramic powder , wherein in the binder 19 to 70% of the paraffin is replaced by low molecular weight polymers having molecular weights of 2,000 g / mol and numerous polar groups, and after the preparation of the injection molding and the injection of the bodies on documents with an open Porositaet between 45 and 50% of a temperature-time treatment up to 250C for 6 to 72 hours.

Description

Field of application of the invention

The invention relates to the production of thin-walled ceramic microparticles complicated geometry with extreme precision, z. B. needle guides for dot matrix printers, where wall thicknesses less than 0.1 mm are required.

Characteristic of the known state of the art

It is already known to produce complicated shaped parts made of ceramic by injection molding. For this purpose, preformed ceramic powders are mixed with binders or plasticizers at elevated temperatures and the degassed mass is sprayed under pressure. Thereafter, the binder is expelled from the sprayed parts at elevated temperatures, the Ausgaszeit is at least 6 hours. As a binder, paraffin is known, which is replaced by oxidized polyethylene waxes with an average molecular weight of 300 to 5000g / mol up to 10% (DD-PS 233119).

To cope with the problems of outgassing of the binder one strives for the lowest possible binder proportions. Sufficient flow properties with low percentages of birch average can only be achieved in a range of the starting powder fineness used up to 20 m ² / g and binder mixture fractions of up to 25%. Stable Spritzschlickersysteme are previously produced only within these limits. The limits of activation, dispersion and the sedimentation behavior were the non-reproducible or not reproducibly adjustable target quantities of the sprayed material preparation. In the molding of such spraying compounds segregation of flow around machine and tool parts occur. The isotropy of the workpiece was thus no longer given. The Ausgasprozeß was no longer feasible without deformation, despite Ausgaszeilen> 96h. By occurring in the individual process steps defects in the homogeneous structure of the workpiece sintering without warping is no longer possible.

With the injection molding process, therefore, only the o.g. Pulvors processed to obtain a sprayable slurry, which also passes through the Ausgasprozeß without deformation after molding and sinterable parts results. The objective function of the spray mass preparation, in addition to the flow properties, is a minimum binder content in order to enable the outgassing process without deformation. The manufacturable with this method articles are given by the construction of manageable tools and allow only in special cases to reach a wall thickness of 0.5 mm (DD-PS 67782). Working in these marginal areas of the process requires a great deal of tool design (optimal filling conditions) and is associated with a very expensive Ausgasprozeß, since the binder contents are at the upper limit. Often, an embedding of the parts is inevitable and leads in the fine structures during devesting to increased failure.

Object of the invention

The aim of the invention is to produce ceramic microparticles of complicated geometry with the utmost precision and wall thicknesses of less than 0.1 mm.

Explanation of the essence of the invention

The invention is therefore based on the object, a method for producing thin-walled ceramic microparticles by low-pressure hot-injection, being treated with a paraffin-binder mixture offset aplastic ceramic powder and the paraffin in the binder mixture partially replaced by waxes or esters and after Injection molding the binder mixture is driven out by a heat treatment, and then the sprayed body is sintered to develop by a total shrinkage of the sintered parts> 70% compared to their raw state reproducible and brought about in close tolerances, sedimentation and demixing phenomena even in complicated flow conditions in de. Avoid tools and a high dimensional stability of the manufactured parts should be ensured when expelling the organic components.

According to the invention, this is achieved by mixing finely dispersed ceramic powders having a specific surface area> 80mVg and an internal fine structure of the extremely wide voids powder particles to molecular dimensions containing at least 85% by weight of a paraffin binder based on the ceramic powder in the binder 13 to 70% Hes paraffins is replaced by low molecular weight polymers having Molmasssn to 2000g / mol and numerous polar groups, and the preparation of the injection molding compound and the injection molding the body on documents with an open. Porosity between 45 and 50% of a temperature-time treatment up to 25O ⁰ C for 6 to 72 h be subjected. Characteristic representatives of the required powder type are γ-clays and aerosils. Due to the special structure of the powder particles a sedimentation, separation tendency and Ausgasverhalten stable low viscous Spritzschlickersystem can be produced despite very high binder contents. In addition to the structure of the powder particles, the binder mixture composition and the use of surfactants are responsible for the processing capability of such a system. In addition to the paraffin, as a basic component of the binder mixture, the addition of 19-70% (based on paraffin) of oxidized degradation products of polyethylene, addition products of ethylene oxide to esters of higher fatty acids, copolymers of ethylene and vinyl acetate or maleic anhydride, rosin, polycondensation of glycerol or generally low molecular weight polymers with molecular weights around 2000g / mol and numerous polar groups required. In conjunction with the radical of the surface-active compounds projecting from the powder surface into the binder, this leads to crosslinking of the binder mixture, and a yield point of the sprayed slip is achieved. In the area of low shear stresses the spray slurry behaves like a solid body, in areas of high shear pseudoplastic, almost Newtonian flow is achieved.

The outgassing of the Pindomittels without deformation of the micro parts is carried out on the documents mentioned by the tuned to the respective binder temperature-time Beharidlung within the limits mentioned. This outgassing can usually be carried out even without embedding the parts

 The individual process characteristics:

- special structure of the powder particles

- High binder content with high replacement of the paraffin fraction by said low molecular weight polymers

- Documents with prescribed porosity for the outgassing of Bindemittegemisches

- predetermined temperature-time treatment

lead only in their combination to a thin-walled ceramic part with extremely uniform shrinkage> 70% of the sprayed part during sintering, without deformations occur. By ensuring a reproducible extremely high shrinkage within close tolerances, tools and associated pins, bushings and other special structural tooling elements can be made in a manageable form. Wall thickness of ceramic parts 0.1 mm, holes 0.3 mm, u.v.a. are thus feasible. It is thus possible to produce contours and structures already in the ceramic production, which hitherto could only be realized by expensive post-processing steps, such as, for example, B. by ultrasonic drilling, grinding, eroding.

embodiments

The embodiments for explaining the invention have been carried out according to the following technology, the process-determining parameters are summarized in a table.

The starting powder of a defined specific surface is annealed at a temperature aimed at achieving the highest surface activity. These temperatures are material-specific between 15O ⁰ C and 45O ⁰ C. In a special mixing unit in which the binder mixture at processing temperature (about 100 ⁰ C) is presented, the powder is added in three stages. The temperature of the registered powder also corresponds to the processing temperature. The time interval of the Pulverein irages is 2 h. The mixing of the components takes place at a pressure si 5Torr. The total duration of the treatment process to obtain a homogeneous spray mass is between 16 and 24 h. Before the forming process, the solidified and storable spray mass is melted and degassed at a pressure «= 1 Torr. The shaping takes place by pneumatic or hydraulic promotion of the spray slurry in a metal mold. This metal mold has the characteristic design features of the tools for the low pressure injection molding process. The required sealing pressures are article specific and are 0.6 to 2.0 MPa. For the starting powder Y-Al ₂ O ₃ , plasticized according to Example 3, the injection pressure is 0.6 MPa for producing guides for dot matrix printers of high-speed printer systems. Particularly noteworthy here are the dimensions of the needles with a diameter of 0.40 mm and a linear distance of 0.15 mm, with which the grid of holes in the sintered part is specified. These inserted needles are not bent by the mass flow and the flow cross-sections between the needles are so large that no inhomogeneities occur (streaks or segregations).

, After sintering, these parts have the outer dimensions of 4 χ 6mm and on this surface 24 holes with a diameter of 0.23 mm with a wall distance of 0.08 mrn to each other. The ausgasing process following the spraying has a cycle duration which, depending on the wall thickness of the manufactured article, is between 6 and 72 hours. The outgassing takes place on absorbent substrates of a porosity of about 50%. The sintering of the parts becomes targeted

Setting the desired crystal lattice in an oxidizing, reducing atmosphere, or carried out in a high vacuum. For

Special applications are to provide a HIP process coupled with the sintering.

The following table summarizes the process parameters during the plaetification. Here are the examples 2,6, β and 7

outside the invention and give no useful results

In Example 2, only 2% of the paraffin content was replaced. Example 5 has only a binder content of 64% by mass. in the Example β was replaced by only 8.4% of the paraffin content, and in Example 7 the ceramic powder was used

a spec. Surface of 25 mVg too coarse.

Process parameters in plasticizing No. Starting powder binder

Type / specific paraffin Surfactant Polymer Article Needle surface guidance mVg Ma .-% Ma .-% Ma .-% h (in each case based on powder weight)

comment

1 2 3 4 5 6 7 1 CiO ₂ -AroOSiIe 220 (trade name: Suprasil) 130.0 9.0 130.0 48 oxidized polyethylene wax was not sintered to parts, since as an application only foundries were eligible, but the offset had to be specially compensated 2 Y-Al ₂ O ₃ 120 95.0 12.0 2.0 copolymer of maleic anhydrite Slip shows strong sedimentation behavior and segregation behavior during conveying; not processable 3 Y-Al ₂ O ₃ 120 145.0 8.5 35.0 24 oxidized polyethylene wax good processability, the sintered products have a shrinkage of 110%.

Y-Al ₂ O-120

43.0 8.5 38.0 35

Addition product of ethylene oxide to higher fatty acids

good processability even for thicker wall parts, the shrinkage of the sintered parts is 73%

5 Y-Al ₂ O ₃ 120 35.0 12.0 17.0 oxidized polyethylene wax does not give a flowfä hifjen, d. H. processable spray slurry 6 Y-Al ₂ O ₃ 120 130.0 8.5 12.0 48 oxidized polyethylene wax After removal of the binder, parts have strong defaults and are not usable 7 Ci-Al ₂ O ₃ 25 50.0 1.5 30.0 oxidized polyethylene wax no processable spray slurry, high tendency turn demixing, not bakeable.

Claims (3)

1. A process for the preparation of dünnv / origen ceramic micro parts by low-pressure hot-injection molding, wherein processed with a paraffin-binder mixture staggered aplastic ceramic powder and the paraffin in the binder mixture is partially replaced by Wachf.e or ester and after injection molding the Binder mixture is driven out by a heat treatment, and then the injection-molded body is sintered, characterized in that finely dispersed ceramic powder having a surface area> 8OmVg and an inner fine structure of the powder particles with extremely wide voids to molecular dimensions with at least 85Ma .-% of a paraffin Binding agents are based on the ceramic powder mixed, wherein in the binder 19 to 70% of the paraffin by low molecular weight polymers having molecular weights of 2000g / mol and numerous polar groups, is erseczt and after the preparation of the injection molding and injection molding the K are subjected to documents having an open porosity between 45 UNH 50% of a time-temperature treatment up to 25O ⁰ C for 6 to 72 hours body. 2. The method according to claim 1, characterized in that are used as finely dispersed powder γ clays or aerosils. 3. The method according to claim 1, characterized in that are used as low molecular weight polymers oxidized degradation products of polyethylene, Additicnsprodukten of ethylene oxide or esters of higher fatty acids, copolymers of ethylene and vinyl acetate or maleic anhydride, rosin or polycondensation of glycerol.