DE1571366A1 - Process for the production of ceramic objects by injection molding - Google Patents

Description

Process for making ceramic articles by injection molding.

The invention relates to an improved method of manufacture of ceramic objects, in particular precision cores for metal casting molds, duroh injection molding of a mixture from the ceramic material and an organic binder, welcnes then from the molded article is burned out.

The injection molding technique for making ceramic articles with difficult and complex shapes is well known. This technique represents a fairly simple binary step process which avoids the expensive and time-consuming processing of the ho hm · ι te rial ie η ,,

BATH

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- 2 - 1S71366

So far, the finely ground keraraiache has been mixed with a plastic or resin binder that is thermoplastic, e.g., ethyl cellulose, and with a volatile liquid plasticizer, e.g. _, n-butyl stearate The mixture has the necessary fluidity at the temperature and pressure of the molding so that it can easily be injected into the injection mold to fill the cavity originated. The article was removed from the mold, subjected to a "drying step" to evaporate the calibrator by heating to about 230 ° J, and then fired to fully cure the thermoplastic material and to sinter the ceramic material.

A disadvantage of this conventional method has been the excessive amount of time required for "drying". The worm supplied to the body increased the plasticizer and also softened the thermoplastic binder, iil 3 it was therefore necessary to heat the body 1-1 rig sam a., F the maximum drying temperature, \ u \ would a more rapid increase in the vapor pressure of ¹ Yeichmaohers can escape as vapor through the pores of the body to avoid iioiist namely a übermal.! Igei cause 'vapor pressure within the body, the structure soften and Rii3- and blistering. The softened body would also

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if he was not supported, distort himself, this "Drying stage" was usually 70 hours and more,

This drying time was reduced to about 24 b'Umden by subsequent improvements by additionally a lar.i ^ s.Tii war.:.-.härtendes resin, z ₀ Ex "Schellaök, admitted as part of the binder. This heat-curing resin material hardened ciauerinf t during the first stages of drying and gao the body despite the softening of the thermoplastic stake of the binder largely rigidity "EO could aieser rigid body a more rapid increase in the vapor pressure of the ^v / calibration maker tolerated, without warping or 31 As a result, this improved process allowed the drying temperature to be increased more quickly and thus the overall drying time to be reduced, but the drying period was still undesirably long

Another flat part of conventional methods was the considerable shrinkage of the body during drying and heating, which in many cases was accompanied by cracking. "Most of this shrinkage occurred during drying in some cases, the shrinkage already set upon cooling in the mold cavity a _o This shrinkage occurs regardless of whether a thermosetting binder is contained or not, but the Rißbilaung 'is considerably less when the binder is partially wnrmehärtend. It is believed that the shrinkage is directly related to the use of the thermosetting

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Binder, as well as the fact that this binder is used during bake-out, i. h ₀ during drying vro. Br ^ rm ^ m, fvi ^ -i.-r -, 'ν · ^ ,, Beiipiel ^ vmigo, bodies which are not used with ΪΛΙν ^ tllulose as a binding agent suffer a linear shrinkage of at least

In the manufacture of molded articles complicated by very precise dimensions sets this shrinkage ausseiet difficult ο problem in designing the Spritzgußformhöhlung "In addition, not all parts shrink eii.er komplizi'erten shape, which differ in their cross section uniformly or equally _o it is therefore extremely difficult to determine the dimensions of the mold cavity in such a way that an item is obtained which has the required final, precise dimensions in all its parts after firing, without the need for further processing »

An object of this invention is to expedite the manufacture of ceramic articles by injection molding, in which the time required for baking is drastically reduced «

Another object is to provide a method of manufacturing ceramic articles by injection molding, in which case in most cases no shrinkage, d. h, a maximum of about 1 # linear shrinkage, during the bakeout of the organic constituents occurs.

Another goal is an improved 8-fuel cast iron for the production of ceramic objects »

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Other goals and advantages emerge from the description "

The single drawing is a flow scheme illustrating an exercise of the method according to the invention are wherein colloidal ceramic bodies having a particle diameter substantially less than 0.1 used / i as a "stop" -Verhinderer to be shown in detail ₀

In broad terms, the method according to the invention consists in first preparing an approach consisting of a mixture of finely comminuted ceramic material with a particle size not below O ₁ I _x U, a solid organic binder with high vapor pressure in the solid state, and a A colloidal ceramic material which acts as a "leakage" preventer and has a particle size substantially below 0.1 / 1. This batch is then heated to liquefy it and the liquid composition is injected into a mold where it is cooled to an article having the shape of the mold cavity to solidify "Then the article to a temperature below the melting point of each component of the composition heated to the solid organic binder is cast out, and then fired to the ceramic material to a zuaainmenhaftenden body to sinter.

For the purposes of the present invention, under a solid organic binder has high vapor pressure

solid state, which in the following as organlsohea connective bath

medium denotes v / grounding, an organic material that is solid at room temperature, has a melting point below about 200 ^° C., and has a vapor pressure of at least about 1 mm within the temperature range from about 20 ^° to the melting point of the material «, Examples of this class of materials are naphthalene, p-diochlorobenzene and camphor ₀

The fine2: reduced ceramic material should have a particle size distribution with a lower limit of 0.1 ^ _{or less. This is important because ceramic powders with particles smaller than 0 9} 1 Ji viä. absorb larger amounts of organic binder before the plastic flow properties required for injection molding are achieved. The consequence of these excessive amounts of organic binder is excessive porosity of the fired body and too high a fragility for practical use. The upper limit of the particle size distribution should be below 100 μ, but this limit is not very critical

The comminuted kez'amitiche Matex ^ ial may be one or more of numerous glass and crystalline ceramic materials which have the desired properties for the finished article, "B _e ispiale are: 96 $ sodium silica glass, fused silica, alumina, Beryllium oxide, magnesium oxide, mullite, petau, silicic acid and spidumene. These materials can be obtained commercially in comminuted form or prepared from raw materials by ball milling or other methods. 0 0 9 8 5 0/0 A 1 5

The colloidal ceramic mass should have a maximum particle size less than 0 ^ 1 ^, preferably less than 0.05, / U. It can be made of the same material stand, like the finely chopped ceramic mass, or from a different material, depending on the desired properties de ρ object to be manufactured. examples for commercially available, suitable materials are: 'Alon-C, finely divided Alumina, and Cab-O-SiI, finely divided silica (Trade name of Cabot Corporation, Boston, Fass.,), So ^ je D-C Fieselsäurepulver (trade name of Dow Cornirg Corporation, Midland, Mich.,).

The collecting of the batch components is preferably done in one of two ways. According to the first method, the organic binder is comminuted and mixed with the ceramic mass in a ball mill or other suitable device until a largely homogeneous mixture is obtained melted another suitable device, then the ceramic cash register is added to the molten organic binder and stirred or mixed until the ceramic mass is evenly dispersed in the binder ₀ The mixture is cooled to solidify the organic binder and is crushed or at least broken into coarse grains that allow the casting mold to be charged "

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While the choice of Kish method is free, the first method usually does not give good results when camphor is used as the organic binder. In this case, the second method is preferred, and mixing should be carried out because of the extraordinarily high vapor pressure of camphor in a closed container ₀

The resulting mixture is added to the feed cylinders of a conventional injection molding machine for ceramic articles, heated to its liquefaction, d _g h "injected above the melting point of the organic binder, and then in a conventional mold that has a the shape of the desired article corresponding cavity. The batch is preferably ^{heated to temperatures of 150 0} G to 200 ⁰ O so that good plastic flow is achieved at pressures of only 500-700 kg / cm *

Although the basic combination of organic binding agent and the finely comminuted ceramic mass already gives improved results in terms of lack of shrinkage and greatly reduced heating time, great difficulties arise when this combination of grains is sprayed as the sole approach. The reason for this is the "leakage" or flow of the organic binder, leaving behind a layer of ceramic mass which has insufficient plasticity for subsequent spraying. It has been found that it is necessary to use the colloidal ceramic material to prevent "leakage" ¹¹ to be added.

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A particularly suitable for injection molding composition consists of (in weight _o $):

(a) £ 18 to a maximum of $ 32 of any solid organic Binder with high vapor pressure in the solid state, as defined above}

(b) a spray preventing leakage material consisting of colloidal ceramic material having a particle size substantially less than 0.1 yes in an effective amount of up to 4 $, and
(c) finely comminuted ceramic material with a "particle size .not less than 0.1 / x as remainder ₀

This composition shows an excellent combination of properties, good flowability for injection molding, ox'ine detrimental "bleeding", and rapid bakeout of the organic binder within 12 hours or less, without warping, shrinkage or excessive Porosity.

Ba. ^The following example is intended to explain the invention. example 1

A semolina batch consisting of »

Powdered fused silica 66.3 parts by weight naphthalene 30.1 parts by weight

Alon-C 3.6 parts by weight

⁺ (Par tikelgrößenvertellung 0.1 to 10O _x Ui average particle size of 11 to 12yu).

was made by melting the naphthalene and slowly adding it

the powdered gesohmolzemi silicic acid and the Alon-0 " BAD OrtölNAL _Q0 9 850/0415

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Prepared 3u of the molten naphthalene, stirring the mixture constantly to make a homogeneous cup. "The composition was cooled to a solid layer and then broken into pieces linen enough to put in the feed cylinder preheated to 175 ° C will be able to _e Following the Füllung'des task cylinder with the approach of this was allowed to warm to the predetermined temperature and then injected into a mold under a pressure of 700 kg / cm. The injected composition is in the form of air-cooled solidified then taken out and ctes for expelling naphthalene at 70 ⁰ C heated "The purpose erforder-.liehe time was 3 to 12 hours at Körperdioken 0.3 to 1.25 cm ₀ Thereafter 'was the body was fired at 1125 ° 0 for two hours to sinter the ceramic particles together. The average linear shrinkage was 1 # "

It is believed that the substantial lack of shrinkage in the articles of the invention is due to this is that aas organic binder during the The bakeout remains solid while the previously used thermoplastic binder is used during this operation became liquid. Although this is only a theoretical explanation, it is assumed that under the effect of the Surface tension of a liquid binder, the ceramic Particles are drawn together when the binder is baked out of the body. Since the inventive Binder is solid during baking,

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Leash liquid phase which aes a shrinkage ^ Body can cause »

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Claims (1)

Η » Claims 1 ₀ process for the production of ceramic objects from a mixture consisting of ceramic masses with a particle size of at least 0.1 u as the main component, characterized in that one also has an organic binder which is solid at room temperature, one; Melting point below about 20O ⁰ O and a vapor pressure of at least 1 mm Hg in the temperature range of. about 20 ⁰ T to the melting point of this binder, as well as an effective tightness of a colloidal ceramic barrel with a particle size substantially below 0.1 ^ ;. only prevents "leakage" during injection molding, the composition is heated and injected into a mold ζ van Z v / corner of its liquefaction, the injected composition cools to harden it into an object with the shape of the mold cavity, the object on a Heated to a temperature below the melting point of each component of its composition to drive off the solid organic binder and fired to sinter the ceramic particles into an integral body. 2o method according to claim 1, characterized in, that the solid organic binder in an amount of 18 to a maximum of 32 wt, $, based on the composition, clogs, 3g method according to claim 1 or 2, characterized in that the colloidal ceramic mass in an amount of up to 4 wt. #, Based on the composition, · ' clogs. 009 3 BO / 0 /, 15 BAD ORiGlNAL 4ο The method according to claim 1, characterized in that the batch is heated ^{to 150 to 200 0 C.} 5ο Injection molding approach, characterized by the following composition: - (a) from 18 to at most 32 wt _o $ an organic binder which is solid at room temperature, has a melting point ° ö below about 200 and has a vapor pressure of at least about 1 mm Hg at temperatures of about 20 C to the melting point of said binder, (b) an effective amount up to 4 wt ₀ ^ a colloidal ceramic composition having a particle size below 0.1 .wesentlichen / x for preventing "leakage" during injection molding, and (c) as a residue of finely ground, ceramic · =: T.Ip.teriaü: ~? t eir-er Tsiloli ^ i ^ röH '· i.x'jVu-. \ ΰΛ? -. ι 0.1 / :, O'M'ii'-ij; "leave V / orks Corning, N.L, V. St. Lawyer BATH OO 9 H GG / OA 1 5 Blank page