JPS58168507A - Method of casting slip - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of forming a refractory material or metal molding. More specifically, the present invention relates to the forming of dense refractory materials and metal compacts by cryocasting and cryoturning.

Prior Art The patents listed below are the most relevant technology known to the applicant as of the priority date of this application.

U.S. Patent No. 2,765,512 October 9, 1956 R, A, Na
5bit No. 5bit No. 102 July 7, 1959 W,
A, Maxwell et al. No. 2948935 August 16, 1960 R, T. Carter No. 3567520 March 2, 1971 Dennery et al. No. 357665
No. 3, April 27, 1971, G. Miller et al. No. 3
No. 808143 April 30, 1974 T, R, Gar
dner No. 38850 No. 3 Hide 85005 Other publications” Urea as an Ice Nueleant
"Urea as an ice nucleating agent for supercooled clouds", Robert G.
XTechnical No. by Knollenberg
te (technical notebook) shop 29, C1oud Phygia
mLabory (Cloud Physics Library), University of Chicago, Chicago, Illinois, April 1, 1965.

Those involved in the powder metallurgy and refractory technologies have long striven to create improved methods for producing highly complex shaped metal and refractory products of high strength and quality. If the shape is simple and optimum strength is not required, the powder is pressed at room temperature, demolded and sintered; if maximum strength is required, the previous compact is hot pressed.

These methods, especially the latter, are not suitable for refractory or metal products with complex shapes. The ancient slip casting technique is probably the most effective forming method, but it is also a result of the degree of complexity of the shape being formed and the physical properties obtained with slip casting, especially mechanical strength. There is a problem with this.

The main problems associated with slip casting are the damage to complex shaped castings when attempting to remove the green casting from the mold, and the high cost of producing very complex molds that can be separated. That's expensive.

The Ne5blt reference teaches a method that allows for the successful manufacture of ceramic products of relatively complex shapes. According to Neabit, non-water-absorbing (3) molds and/or cores are prepared, for example from latex rubber. A very thick casting slip, ie a slip containing only enough water to enable casting, is made and poured into a flexible mold. Freeze the casting. The frozen body is then demolded from the mold without damaging the frozen cast body due to its inherent strength. Then N+a
According to ab it, the casting is thawed, dried, and the dried ceramic molded body is finally fired, apparently at room temperature and pressure. It is also necessary that the amount of water in the initial casting slip be small enough to prevent the formation of ice crystals large enough to crack the frozen compact. Neabit accomplishes this by partially drying the casting in the mold and then freezing it. Ne5bit's teachings are decorative plates, pots, figurines,
It is suitable for ceramics such as bottles, but it is not suitable for high-strength structural refractories.

Dowing et al. is a variation of the cryogenic casting process.

The casting slip is prepared with a relatively coarse (70 mm is much coarser than 200 (4) thick) refractory material powder, colloidal silica sol, and water. The slip is vacuum treated to remove entrained air and cast into suitably shaped non-water absorbing molds. When the mold and contents are cooled to about 15"F, the colloidal silica irreversibly precipitates, creating a strong bond between the refractory material particles or grains. The casting body and mold are then brought to a low temperature of -80"F and the casting is carried out. The water in the body is quickly frozen.The frozen molded body is removed from the mold, but it is very strong.Then it is heated to about 200℃ to melt the ice and carry away the water.1Finally, it is dried. The green compact is fired at 2000 to 3500T.

A further variation of the cryocasting method is freeze drying in a vacuum to cause sublimation of the material to be removed. This method was taught by Danny et al. and is specifically directed to the freeze drying of p1 heavy metal body slips. In related part, Dennery et al. make a paste from liquids, soluble materials, and insoluble organic materials, layering fine silver and nickel powders and rapidly freezing them to -60°C. The frozen material is lyophilized (optionally using infrared radiation) under vacuum for 12 hours. The layer thus formed is porous. A similar method is W, A, Max
“Preliminary lnv” by well et al.
eatiga mouth on ofthe' Freeze
Casting 'Method forForm
l,ng Refractory Powders (Preliminary research on "freeze casting" method for molding refractory material powder)
”, National Interrogation Committee Aerial Investigation Record E53L51 (195
4) and in the above-cited patent documents of W, A, Maxwell et al. applied to the casting of ceramic molded bodies. A thick, ie, low water content, casting slip is made of aluminum oxide, titanium carbide, or the like and is degassed by simultaneous application of vibration and vacuum. The slip is then poured into the mold and packed.

The slip and mold are then frozen in a bath, then removed and subjected to a vacuum of 2II+++1 for 4 hours at a temperature at least as low as the casting body. The dried green casting is then sintered at approximately 2300°C.

Also closely related to the present invention are several known methods of making absorbent and non-absorbent molds, such as the one taught by Carter, a type of "lost wax" method. Carter first creates an A' turn of wax, coats the i+ turn with a refractory powder mixture, hardens the powder using a method depending on the type of mixture, and then applies heat or heats the wax. Remove the wax pattern by using a solvent.

Another molding method associated with one aspect of the invention involves the use of separable molds, such as the method described by Miller et al. and Cardnet. Mi
compositions based on ternary calcium oxide,
For example, Ca-At203-S 102 is mixed with a lubricant and a temporary inder, the mixture is shaped into the desired shape, and 2
The ceramic core is made by baking at 425'F.

This core was used for casting, and then 6 N -HCl
removed from the cooled casting by immersing it in water.

Although not specifically related to slip casting, Cardnet describes the removal of gypsum deposits by dissolving them in an aqueous solution of a salt of α-hydroxycaldenic acid (7). Parts mold commonly used for slip casting
Plaster of Paris is essentially gypsum after mixing with water and drying, and Gardner's teachings can be effectively used to remove Type J silaster after slip casting. Dew.

Although Knollenberg's paper has no relevance to slip casting of complex ceramic or refractory compacts,
Its relevance to the present invention will become clear from the detailed description of the invention below.

Knollenberg is the so-called [artificial rain seeding (a
development]. An experiment using urea as an ultracold nucleating agent is described.

Spraying microscopic particles of urea into the moist, cloud-like atmosphere. The urea particles condense or coalesce from suspended fine water droplets to form larger water droplets (eg 1 tm ), which in turn form ice crystals and fall as snow. 2-6
A legitimate summary of the paper is published on page 8, including the interaction of urea with fine suspended water droplets. The general purpose of cloud nucleation with all nucleating agents is to form large water droplets and cause rainfall.

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method of making essentially flawless high strength refractory materials and metal products utilizing known slip casting techniques, the invention comprising the steps of: It includes a modified freeze-drying process by adding The presence of hydrogen bond forming substances dissolved in the slip prevents the formation of large ice crystals when freezing the casting slip, which was an inherent problem with prior art methods. Without such materials, the process of freezing the slip creates ice crystals of 1/4 to 1/2 or more size inside and on the casting body. After freeze-drying and calcination, as a result of the formation of large crystals that contain many scratches or weak surfaces, hydrogen bond-forming substances can prevent the formation of large crystals and reduce water to about (1,02~0
．． It is frozen in the form of very fine crystals of the order of 05++m+.

Examples of hydrogen bond forming substances that prevent the formation of large ice crystals are:
n-propyl sulfoxide, triethanolamine, dimethyl sulfoxide, methanol, acetamide, formic acid, dextrose, hexamethylene diamine, pyridine, formamide, raw wood, hydrogen peroxide, acetone, raffinose, tetrahydrofuran, guaninone carbonate, trimethylformamide, glycine , glycerol, ethanol, acetonitrile, agar, hexamethylenetetramine, oxalic acid, and isobutanol. These materials are added to the slip liquid in various amounts, resulting in 6-2.0 molar solutions, to evaluate their ability to prevent the formation of large ice crystals. Consistent with the solubility of the various compounds, they were more effective as the concentration of the compounds increased.

However, as a general matter, substantial amounts of organic materials can cause problems when baking the cast pieces.

Therefore, the amount of hydrogen bond formers should be kept as low as possible, between 0.1 and 10% of the total liquid used for slipping.
A weight percent range is preferred.

The reason for the formation of large ice crystals is not understood, but hydrogen bond formers form hydrogen bonds with water molecules, which therefore remove at least some of the original molecular order found in water due to the water molecules' own hydrogen bonding. This is thought to be because it destroys it.

The formation of large crystals is quite insignificant for products such as those involving Neabit, except from an aesthetic point of view, unless the crystals are large enough to cause cracking, but if the end use of the product is high. Where mechanical strength is required, such as structural refractories or turbine refractory components such as those disclosed in Maxwell et al., flaws and planes of weakness.
s) is important, even critical. until today,
There are no known essentially flawless, complex ceramic or refractory products made by slip casting and freeze drying.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In its most preferred form, the invention employs as its principal part a molding process known as slip casting. Slip casting generally involves the preparation of a mixture of a liquid (11) and a powder with a pourable consistency, where the liquid is usually water and the powder is a refractory material or metal powder. It is the body.

It is then poured into a paster absorbent mold with a casting slip. The mold absorbs water from the slip, thus drying and solidifying the paste into the desired shape. The green compact is then fired to sinter the metal or refractory material powder.

There are various variations and painstaking efforts to the basic casting method. Instead of casting a relatively fluid slip into a water-absorbing mold, a less fluid slip is injection molded (1nject).
ion mol (old ng), the mixture can be vibrated and put into molds, etc. The term "slip casting" as used herein is intended to include all such methods.

Similarly, conventional slip casting uses porous absorbent molds, but it is also known that non-absorbent molds are used, followed by freezing the cast slip and freezing it. It is disclosed in Ne5bit that the compact is removed, thawed, dried, and finally fired to promote sintering. Slip (12) Packing is usually done by a slip consisting of a ceramic or refractory material powder that is finally sintered, but it is also possible to use a powdered silicon metal as the solid phase of the slip and a refractory material powder. It can be cast and shaped in the same manner as the base slip, except that rather than simple sintering, it can be cast and nitrogenated in known manner. Optionally, if silicon carbide is the basic material, the silicon carbide compact is shaped before carbon is introduced into the pores of the workpiece, and then e.g.
r was finally siliconized by the known φ method as taught in U.S. Pat. No. 3,205,043.
n) can.

Similarly, Dennery et al. and Maxwa I
1 et al., the lost wax method of Carter, and Mll'ler et al. and Gard.
The use of separable forms such as those disclosed by ner is all within the scope of the present invention and within the skill of those skilled in the art.
and is intended to be included in the term "slip casting".

In subsequent examples, the slip-forming liquid is water. However, this does not constitute a limitation of the invention. Although water is most desirable from a practical standpoint, almost any liquid that is a solvent for hydrogen bond-forming compounds, such as methyl alcohol, glycerol, etc., can be used in the present invention.

Therefore, the ice referred to in claim 1 includes frozen liquids.

The hydrogen bond forming compound should be soluble in the slip liquid.

Example 1 Wall thickness 1.61 cIn, outer diameter 5.6 cIn, length 25,
A 40 cm silicon carbide chizo was created as follows.

A casting slip was prepared by mixing the following materials in the amounts indicated and rolling on a gloss mill for about 20 minutes.

Silicon carbide (3μm) 6637.76
g Silicon carbide (100F) 6637.76
g water, 1659
．． 44 g Sodium silicate 9.2
9 g urea 55.76
The g mold is 5p with an inner diameter of 5.16z and a length of 30.48cm.
auldite (resin-impregnated kraft paper) tube with an outer diameter of 3.55 crn and a length of 30.48 t:m formed around a steel rod of outer diameter 1.27z with a threaded end.
Consisting of a silicone rubber core and two alumina end caps with screw holes for screwing into the ends of steel rods, one end cap has the mold assembled first. Two small holes are made in the lid to allow drainage of the mold oil, and a recess approximately the diameter of the silicone rubber core is provided on each side of the lid.

A thick layer of Diesel IJ-type petroleum was applied to the bottom end lid (bottom lid), ie, the recess of the lid with two small holes.

One threaded end of the silicone rubber core was coated with wax by dipping the threaded steel end into molten wax.

The wax-covered threaded end was then firmly screwed into the screw hole in the bottom lid, and the end of the tang was fully and tightly fitted into the recess in the lid. The eyelets in the jacket allow excess sherry to drain away, thereby preventing it from oozing around the upper portion of the rubber core and ultimately contacting the refractory material slip.

Then I covered the two small holes in the bottom lid with wax. Then, both sides of the bottom lid were coated with petroleum sherry, and a kraft paper tape was pressed against the lid to seal the space between them liquid-tight.

Approximately 820 g of the previously prepared sling was passed through a 25 mesh screen. While vibrating a kraft paper cube with a bottom lid and a silicone rubber core in place, the suritsuno through the screen was poured into the mold until it was about 1/4 full. The rubber core is rotated in position to remove entrained air. Fill the rest of the mold with the slip while vibrating, and after the mold is filled, fill the slip for an additional 15 minutes.
Continue to vibrate for seconds. The top end cap was coated with petroleum sherry and screwed into place.

The assembly of the mold and its contents was placed in a CCl3F bath at approximately -8
It was cooled to 4.4° C. and kept as it was for about 40 minutes.

At this point, the assembly was removed from the bath and the frozen tube was removed from the mold and placed in a Stokes vacuum furnace.

The furnace chamber was evacuated to about 100 mnHg at room temperature, and this vacuum was maintained for an estimated 17 hours.

The dried specimen, which had no scratches due to ice crystals, was sintered by heating to 1970° C. in an argon atmosphere. Finally, the pre-sintered cheap is siliconized (AI) in a manner similar to that taught by Taylor in US Pat. No. 3,205,043.
liconiling). That is, a porous tube was impregnated with a furfural-based material, heat treated to carbonize the organic material, and exposed to silicon metal at 2070° C. in a nitrogen atmosphere.

The resulting product was a high strength refractory cheap without the flaws and weakened surfaces inherent in prior art freeze drying processes.

A silicon carbide cheap was prepared in the same manner as in Example 1 except that the slip composition was less than 1.

Silicon carbide (3 μm) 6637.76 g Silicon carbide (100F) 6637.76 g water
1659.44 g Sodium silicate 9.29 g Dimethyl sulfoxide 156.26 g The resulting dried chives were free of macroscopic defects. The final siliconized and fired product had extremely high strength as a whole.

Patent Applicant Two-Tone Company Patent Application Representative Patent Attorney Akira Aoki Patent Attorney Kazuyuki Nishidate Patent Attorney Yoshinari Koga Patent Attorney Akira Yamaguchi 1 (19) 5 Amendment to Procedure Subject to Amendment (Spontaneous) May 7, 1980 Japan Patent Office Commissioner Shima 1) Haruki Tono1, Indication of the case 1982 Patent Application No. 0502922, Name of the invention Slip casting method 3, Relationship with the person making the amendment Patent applicant name Title Two-tone Company 4, Agent Person 6, in the Detailed Description of the Invention column of the Statement of Contents of the Amendment, (1) "2-stage vacuum" and "211sHy vacuum" on page 7, line 17.
Correct to.

(2) Sentences from lines 1 to 7 on page 9 [Usually used for slip casting...It could probably be used. ``A plaster of pas mold commonly used for slip casting.''
ria mold) i'j: Plaster of Paris (calcium sulfate) mixed with water and dried is essentially gypsum, and Gardner's teachings were effective in removing plaster of Paris molds after slip casting. It will be possible to use it effectively. ”.

(3) The size of page 10, line 14, h ~ a little over %”ii
% to a little over % inch”.

Claims (1)

[Claims] 1. Creating a slip casting mother mold with an appropriate shape,
A slip comprising the steps of preparing a casting slip, casting the casting slip into the mold, freezing the cast slip, drying the frozen cast body, and baking the cowshed molded body. In the casting method, a hydrogen bond-forming compound is incorporated into the band slip in an amount sufficient to prevent the formation of ice crystals in the frozen casting body large enough to leave scars in the dry casting body. A slip casting method characterized by: 2. The hydrogen bond forming compound is n-propyl sulfoxide, triethanolamine, dimethyl sulfoxide,
Methanol, acetamide, formic acid. Dextrose, hexamethylene diamine, pyridine,
Formamide, urea, hydrogen peroxide, acetic acid. The method according to claim 1, wherein the compound is selected from the group consisting of raffinose and tetrahydrofuran. 3. The method of claim 2, wherein said hydrogen bond forming compound is present in said casting slip in an amount of about 0.1 to about 10i% of the total liquid volume. 4. The method of claim 3, wherein the liquid is water and at least a portion of the slip mold is made of a moisture permeable material. 5. The method according to claim 3, comprising the step of taking out the frozen cast body from both casting molds. 6. The method of claim 5, wherein at least a portion of the cast valve mold is moisture impermeable.