DD291261A5 - HYDROLYSIS PROCESS FOR ETHYLSILICAN BINDER - Google Patents

Abstract

The invention relates to a hydrolysis process for ethylsilicatic binders for the preparation of binder solutions for the fine casting technique. According to the invention, the hydrolysis is carried out in the presence of 0.1 to 2.0 parts by mass in% methylchlorosilane, z. As methyltrichlorosilane, dimethyldichlorosilane or trimethylchlorosilane. With the hydrolysis process according to the invention it is possible to shorten the overall treatment time of the binder solution and to increase the effectiveness of the preparation of binder suspensions. Binder solution; ceramic mask mold; Feingiesztechnik; ethyl silicate; Hydrolysis; methylchlorosilane}

Description

Field of application of the invention

The invention relates to a hydrolysis process for ethyisilicatische Bindemitte! for the production of binder solutions for the investment casting technique, which can be used for binder suspensions for the production of ceramic mask molds.

Characteristic of the known state of the art

To make ceramic mask molds, fusible or otherwise removable models are dipped in a binder suspension and then sprinkled with fine-grained refractory material. This process is repeated several times after an intermediate drying and the coating formed then cured. The quality of the ceramic mask molds and thus also the quality of the castings produced therewith depends essentially on the nature of the binder suspensions. The first coating layer formed during the dipping process essentially determines the surface quality of the castings, while the subsequent layers influence the strength and dimensional stability of the ceramic mask molds.

The binder suspension is composed of a binder solution, refractory, powdery material and optionally further additives. The binder solution contains, in addition to a binder, water, organic solvent, hydrolysis catalyst, surfactant and optionally further additives. As binders, organic silicates and silica sols are known. They are usually used individually, but can also be found in a combination as a so-called hybrid binder use. Binder suspensions containing organic silicates as the binding agent; are used because of their strong binding capacity mainly for the production of the higher coating layers used. In contrast, binder suspensions m'.t silica sol as a binder because of their favorable flow behavior and generation of elastic. Coating layer with smooth inner surface of the ceramic mask molds preferably used for the preparation of the first coating layer. Preferred in the investment casting technique is the use of binders based on organic silicates, especially of ethyl silicate. The amount of water added determines the properties of these binders. Binder based on organic silicates with a higher than for hydrolysis required water content are characterized by low mold material costs and very good processing properties.

To accelerate the hydrolysis process, inorganic acids, e.g. Hydrochloric, sulfuric and / or phosphoric acid, added as a catalyst. The problem here is the mastery of the miscibility gap organic silicate water and thus the maintenance of a constant Binderlösungsqualität. Conventional hydrolysis processes do not consistently ensure the safe and problem-free production of a high-quality homogeneous and clear binder solution.

Object of the invention

The aim of the invention is the development of a hydrolysis process for ethyisilicatic binders used for the preparation of binder suspensions in the production of ceramic mask molds. Variations in the quality of the binder suspension and thus the ceramic shell mold should be avoided and the mold breakage as well as the reject code numbers should be minimized.

Explanation of the essence of the invention

The invention has for its object to develop a hydrolysis of ethylsilicatic binder, which allows the safe and easy production of a highly qualitative and homogeneous binder solution in the further course. According to the invention the object is achieved in H-- _"Jlö hydrolysis of ethylsilicatischen binder in the presence of 0.1 to 2.0 mass fractions is performed in% methylchlorosilane. Preferably, from 0.15 to 0.60% by mass of methyltrichlorosilane, 0.20 to 0.80 parts by weight in% of dimethyldichlorosilane or 0.40 to 1.20 parts by weight in% of trimethylchlorosilane The molar ratio of water to alkoxy groups of the ethylsilicate binders is advantageously 0.4 to 1.4 The ethylsilicate binders used preferably have a SiO ₂ It has from 29 to 45% by weight of ethanol in the usual quantity and quality The ethylsilicate binder hydrolyzed according to the invention is diluted with water to an SiO ₂ content in the usual range from 12 to 17 parts by weight in% Acidify to a final pH within the acidic stability range of the silica n, preferably pH 2 to pH3, can be carried out both by means of the methylchlorosilicate additive according to the invention and by an additional acid addition. Conveniently, the finished binder solution is added 0.02 to 0.1 parts by weight in% phosphoric acid.

It has been found that with the hydrolysis process according to the invention the hydrolysis of ethylsilicate binders can be carried out much more safely and without problems than hitherto. For example, shortened by the addition of Methylchlorsiiane the duration of the heterogeneous Hydrolysestadiums caused by the miscibility gap ethylsilicatic binder water compared to those usual for acid addition to 15 to 70% and the time to reach the maximum temperature of the hydrolysis to 35 to 75%. Thus, the total processing time for the binder solution can also be significantly reduced and the effectiveness of their production can be increased. Binder suspensions, prepared from the hydrolyzate binder solution according to the invention, have a very good flow behavior, which makes it possible to introduce a high solids content and thus a considerable reduction in molding material costs. Ceramic mask molds made therefrom have high strength, green strength and hot strength are increased by about 10%, thus reducing mold manufacturing costs.

Ausführungsbelsplel

The binder solutions listed in Table 1 are prepared by mixing the starting components in the order given. The components of the hydrolysis solutions (positions 1 to 7) are mixed for at least 15 minutes before the finished binder solution is prepared.

Examples 1 to 15 of Table 1 illustrate binder solutions according to the invention, Example 16 is a comparative example. In the binder solutions according to Examples 7 to 15, the methylchlorosilane content in the hydrolysis solution was already chosen so high that the required acidity of the total binder solution (pH 2 to pH 3) is achieved without additional post-acidification. Table 2 shows the properties of the binder solutions and of the binder suspensions and ceramic mask moldings produced therefrom. The hydrolysis process according to the invention is characterized by the time until the end of the heterogeneous hydrolysis stage and the time until the temperature maximum is reached, and the quality of the hydrolyzed binder solution and the total binder solution is assessed by appearance and gelation time.

As filler for the preparation of the binder suspension, quartz powder, main grain fraction 0.005 mm to 0.080 mm was used. Platelet-shaped ceramic test specimens were prepared from the binder suspensions by five-fold dipping and basing, and the flexural strength in the green and fired states was determined therefrom by known methods. The technological viscosity range used was a flow time range of 35 to 50 seconds (Ford cup with 5 mm nozzle diameter) with a viscosity increasing from coating to coating. The binder suspensions for the higher coatings were additionally added 1.7 parts by weight in% kaolin (based on the binder solution). As Bestreumatorialien quartz sand were used in the particle size range 0.1 mm to 0.4 mm for the first coating and 0.5 mm to 1.0 mm for the subsequent coatings. As an intermediate drying condition, a short drying regime was carried out with a drying time of 30 minutes at 303K and 1.2 ms ^-1 . The results obtained are also included in Table 2.

Table 1: Composition of the blending solutions (in% by weight)

Examples 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

1. Ethyl silicate 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36,60 36, 60 with a SiO ₂ -

Content of% by mass and content of ethoxy groups of 72% by mass in%

2. Ethanol 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8,00 8, 00 (water content

5) Mass shares in%

3. methyltri), 12 0.12 0.24 0.24 0.24 chlorosilane

4. Dimethyldi- 0,16 0,16 0,32 0,32 0,32 chlorosilane

5. Trimethyl- 0.24 0.24 0.48 0.48 0.48 chlorosilane

6. Hydrochloric acid 0.27 (30 mass fractions in%)

7. Water 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 12.00 12.00 12.00 4.00 4.00 4.00 6, 00

8. Water 49.01 48.97 48.89 49.16 49.08 48.92 49.16 49.08 48.92 43.16 43.08 42.92 51.16 51.08 50.92 48, 86

9. Methyltri-0,12-chlorosilane

10. dimethyldi-0.16

chlorsifan

H.Trimethy! -0.24

chlorosilane

12. hydrochloric acid 0.27 0.27 0.27 0.27

(30 mass shares in%)

Table 2: Properties of the binder solutions and of the binder suspensions and ceramic forms produced with them Examples 1 2 3 4 6 6 7 8 9 10 11 12 13 14 15

Appearance of the hydrolyzed binder solution? " 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Appearance of the total binder solution (1-12) ¹¹ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 Gelling time of the hydrolyzed bin solution in d 4 •1 4 4 4 4 2 2 2 2 .2 2 7 7 7 4 Gel time of the total binder solution ind ²¹ 5 5 5 6 6 5 8th 7 6 7 7 6 7 7 7 4 Time to end of the heterogeneous Hy drolysestadiums inmin 2.0 2.5 3.0 2.0 2.5 3.0 0.5 0.5 0.5 1.5. 2.0 2.0 0.5 0.5 0.5 4.5 Time to maximum temperature in the hydrolysis in min 7.5 7.0 7.5 7.5 7.0 7.5 3.5 4.0 4.0 4.0 4.5 4.5 3.5 3.5 3.5 10

Quartz flour quantity 227% 228% 229% 230% 231% 231% 233% 232% 232% 231% 230% 231% 233% 233% 233% 2.33% to achieve a flow time of approx. 35 s (Ford cup, 5 mm)

Green bend 1.95 1.88 2.01 2.06 2.00 1, S8 1.83 2.09 1.78 1.81 1.75 1.70 1.90 1.81 1.78 1.85

strength in MPa

Hot bending strength 1.21 1.16 1.18 1.31 1.33 1.29 1.34 1.28 1.10 1.21 1.18 1.15 1.57 1.31 1.07 -1, 19 speed in MPa (fired at 950 "C)

# 1} 1- clear solution

jj 2 - slightly turbid solution with low soil depiction 2} after addition of 0.05 mass% In% H ₃ PO ₄

Claims (2)

1. Hydiolysis process for ethyisilicatische binder for the preparation of binder solutions for the investment casting technique, characterized in that the. Hydrolysis in the presence of 0.1 to 2.0 parts by mass in% methylchlorosilane. 2. The method according to claim 1, characterized in that 0.15 to 0.60 parts by mass in% methyltrichlorosilane, 0.20 to 0.80 parts by mass in% dimethylchlorosilane or 0.40 to 1.20 parts by mass in% trimethylchlorosilane are added.