JP5111009B2 - Manufacturing method of valve made of silicon nitride ceramic - Google Patents

Description

The present invention relates to a method for manufacturing a silicon nitride ceramic valve used mainly in internal combustion engines such as automobiles and generators.

  Conventionally, as an intake / exhaust valve (hereinafter simply referred to as a valve) used in an internal combustion engine, as shown in FIG. 3, an umbrella portion 32 and a columnar shape integrally formed at the center of the umbrella portion 32 are used. Some of them consisted of a stem portion 33. The tapered surface 34 formed on the outer periphery of the umbrella portion 32 is called a face portion, and is a portion that contacts the valve seat of the intake / exhaust port of the internal combustion engine.

  Until now, the valve 31 is generally made of metal, and for example, steel materials such as SUH-3 and SUH-11 and heat-resistant alloys such as Inconel have been used.

  However, higher output and higher rotation of the internal combustion engine are required, and accordingly, the valve 31 can withstand mechanical and thermal harsh environments, and a lighter one is desired. It has become.

  Therefore, it has been proposed that such a valve 31 is formed of a silicon nitride ceramic having excellent heat resistance, thermal shock resistance, wear resistance, and oxidation resistance and high bending strength.

As silicon nitride ceramics for forming such a valve 31, generally used is silicon nitride as a main component and a rare earth element oxide such as Y ₂ O ₃ and aluminum oxide as a sintering aid. (See Patent Document 1 and Patent Document 2).

  By the way, when manufacturing a silicon nitride ceramic valve, if the density of the molded body is uneven, the temperature in the firing furnace varies, and the heating is uneven during firing, the stem portion 33 of the valve 31 is deformed ( There is a problem that it is bent mainly), and when the coaxiality of the stem portion 33 is seen, it is deformed by 0.5 mm or more.

  In order to suppress such deformation of the stem portion 33 as much as possible, in Patent Document 3, a weight 45 is attached to the end portion of the stem portion 43 of the molded body 41 and inserted into the cylindrical jig 46 as shown in FIG. It is proposed that the umbrella portion 42 of the molded body 41 is hooked and held in the opening of the cylindrical jig 46 and fired in a state where the stem portion 43 is directly below by the tensile stress of the weight 45. ing.

  However, when the silicon nitride ceramic valve 31 is manufactured by the method disclosed in Patent Document 3, the deformation of the stem portion 33 can be suppressed, but the density of the stem portion 33 is reduced by the tensile stress of the weight 45. However, there was a problem that the mechanical strength was lowered.

Moreover, in this method, since the weight 45 must be formed at the end of the stem portion 43 of the molded body 41 and removed after firing, there is an inconvenience that waste of materials, work processes increase, and productivity is poor. there were.
JP-A-7-133550 JP-A-6-20652 Japanese Patent Laid-Open No. 3-137065

Accordingly, an object of the present invention is to provide a method for manufacturing a silicon nitride ceramic valve having high baked dimensional accuracy and high bending strength on the burned-out surface.

Therefore, in view of the above problems, the present invention provides 80 to 92.5% by weight of silicon nitride, 2 to 10% by weight of rare earth element oxide, 2 to 5% by weight of aluminum oxide, and 0% of excess oxygen in terms of silicon oxide. 0.5 to 5 wt%, and the ratio of the aluminum oxide amount to the rare earth element oxide amount and the ratio of the excess oxygen to silicon oxide equivalent amount to the rare earth oxide amount are adjusted to 0.5 to 0.8 raw material powder umbrella portion at one end of the scan Temu of the columnar formed using the said stem portion of the molded body formed integrally with an inner diameter of 0.5~3mm wider nitride than an outer diameter of the stem portion It is inserted into a cylindrical jig made of silicon ceramic and the umbrella part of the molded body is hooked and held at the opening end by the cylindrical jig, and the molded body is placed under a nitrogen atmosphere or a nitrogen atmosphere containing SiO. 1700-1800 ° C It characterized that you fired at temperature.

A method of manufacturing nitrided silicon ceramic made valves, silicon 10 to 70 wt%, the sum of the該珪element and the silicon nitride 80 to 92.5 wt%, 2-10 wt% of rare earth element oxides, Aluminum oxide is 2 to 5% by weight, excess oxygen is 0.5 to 5% by weight in terms of silicon oxide, and the ratio of the amount of aluminum oxide to the amount of rare earth element oxide and the oxidation of excess oxygen to the amount of rare earth element oxide A molded body in which an umbrella part is integrally formed at one end of a columnar stem part formed using raw material powder prepared so that the ratio of silicon equivalent amount is 0.5 to 0.8 is placed under a nitrogen atmosphere. After heat treatment at 1000 to 1400 ° C. to generate silicon nitride, the stem portion is inserted into a silicon nitride ceramic cylindrical jig whose inner diameter is 0.5 to 3 mm wider than the outer diameter of the stem portion. The cylindrical jig has the above-mentioned composition. The umbrella portion of the body is held by hooking the opening end, the molded body, characterized that you fired at a temperature of 1700 to 1800 ° C. under a nitrogen atmosphere containing nitrogen atmosphere or SiO.

As described above, according to the method for manufacturing a silicon nitride ceramic valve of the present invention, silicon nitride is 80 to 92.5% by weight, rare earth element oxide is 2 to 10% by weight, and aluminum oxide is 2 to 5% by weight. %, Excess oxygen is 0.5 to 5% by weight in terms of silicon oxide, and the ratio of the amount of aluminum oxide to the amount of rare earth element oxide and the ratio of the amount of excess oxygen to silicon oxide in terms of the amount of rare earth element oxide are 0 the stem portion of the valve head at one end of the columnar scan Temu portion formed by using the raw material powder which is prepared to have a .5～0.8 is formed integrally with the molded body, an inner diameter of said stem portion The molded body is inserted into a cylindrical jig made of silicon nitride ceramic that is 0.5 to 3 mm wider than the outer diameter of the outer diameter of the molded body, and the umbrella portion of the molded body is hooked and held on the open end by the cylindrical jig. under a nitrogen atmosphere or a SiO Ri O under nitrogen free atmosphere and baked at a temperature of 1700 to 1800 ° C., the coaxiality of the stem portion can be 0.15 mm / 100 mm or less, you can reduce the grinding after sintering, work Since the number of steps can be reduced, it is possible to provide an inexpensive and highly accurate valve, and it is possible to provide a non-breakable valve having a bending strength of the stem portion of 770 MPa or more even with the burned surface.

  Hereinafter, the present invention will be described in detail.

As shown in FIG. 1, a silicon nitride ceramic valve (hereinafter referred to as a valve) obtained by the manufacturing method of the present invention has an umbrella portion 12 and a columnar shape integrally formed at the center of the umbrella portion 12. The stem portion 13 is characterized in that the coaxial degree of the stem portion 13 is 0.15 mm / 100 mm or less and there is almost no warping or bending. A coaxiality of 15 mm / 100 mm or less is obtained.

Therefore, according to the method for manufacturing a silicon nitride ceramic valve of the present invention, since the stem portion 13 is hardly warped or bent, grinding after sintering can be reduced, and depending on the application, grinding after sintering. Can be manufactured at low cost.

By the way, in order to achieve such excellent coaxiality, it is necessary that the deformation of the silicon nitride ceramics is small during the sintering, and as a composition for that purpose, silicon nitride is 80 to 92.5% by weight. On the other hand, rare earth elements such as Y, Er, Yb, Lu, Sm, and Dy are 2 to 10% by weight in terms of oxide, preferably 5 to 9% by weight, and aluminum is 2 in terms of aluminum oxide.
Containing 5 to 5% by weight, preferably 3 to 4% by weight, and containing excess oxygen in terms of silicon oxide in the range of 0.5 to 5% by weight, preferably 2 to 4% by weight, and the rare earth element The ratio of the aluminum oxide equivalent of aluminum to the oxide equivalent of 0.5 to 0.8, and the ratio of excess oxygen to silicon oxide equivalent of the rare earth oxide equivalent to 0.5 to 0.8. It is important that it is 8. Here, if the content and ratio of silicon nitride, rare earth element, aluminum, and excess oxygen are out of the above ranges, the sinterability and the effect of suppressing deformation during sintering are small, and the concentricity of the stem portion 13 is set to 0. It is because it is difficult to make it 15 mm / 100 mm or less.

  Moreover, if each component of the sintering aid is less than the above range, the liquid phase component is insufficient at the time of firing, and firing at a high temperature is necessary for densification, and as a result, grain growth of silicon nitride particles occurs. When the bending strength is reduced and the amount of each component is larger than the above range, the liquid phase component becomes excessive during firing, so that the grain growth of the silicon nitride particles proceeds, and in the surface layer, the minor axis length or the major axis is increased. As a result of the easy formation of large crystal grains, the coarse grains serve as a fracture source and the bending strength is lowered.

Thus, by containing the content and ratio of silicon nitride, rare earth element, aluminum, and excess oxygen within the above ranges, the stem portion 13 can realize a bending strength of 770 MPa or more even when its surface is burned out. , in particular, remains grilled release surface 30% or more of the surface of the scan Temu portion, the bending strength of the stem portion is preferably at least 810MPa.

  In addition, from the viewpoint of maintaining a bending strength of 770 MPa or more, the average crystal particle diameter of the silicon nitride particles in the sintered body is 50 μm or less, preferably 30 μm or less.

Further, in the silicon nitride ceramics, other components such as metals of Group 4a, 5a, 6a of the periodic table, TiC, TiN, TaC, TaN, VC, NbC, WC, WSi ₂ , Mo _2, etc. It is also possible to improve the characteristics by containing at least one kind of carbides, nitrides and silicides of Group 4a, 5a, and 6a elements in the table, or SiC in a dispersed particle or whisker state. However, the total content of these is preferably 5% by weight or less.

Next, a description will be given manufacturing how the silicon nitride ceramic valve of the present invention.

First, silicon nitride powder is prepared. The silicon nitride powder may be in any state of α-Si ₃ N ₄ and β-Si ₃ N ₄ , the particle diameter is 0.4 to 1.2 μm, and oxygen is 0.5 to 1.. What is contained in the range of 5% by weight is preferably used.

  The silicon nitride powder is 80 to 92.5% by weight, the rare earth element oxide as a sintering aid is 2 to 10% by weight, preferably 5 to 9% by weight, and the aluminum oxide is 2 to 5% by weight. The silicon oxide is preferably added in the range of 3 to 4% by weight, and the silicon oxide is added in the range of 0.5 to 5% by weight, preferably 2 to 4% by weight. Preparation is performed such that the ratio of the amount of aluminum oxide added is 0.5 to 0.8 and the ratio of the amount of silicon oxide to the amount of rare earth element oxide is 0.5 to 0.8. However, the amount of silicon oxide is determined by a value obtained by adding the amount of silicon oxide powder added to the amount of silicon oxide powder added to the excess oxygen contained as impurities in the silicon nitride powder.

  After adding an organic solvent such as ethanol and isopropyl alcohol and a binder to the raw material powder prepared in these ranges, the raw material powder is uniformly mixed by a known pulverization method such as a ball mill, vibration mill, rotary mill, barrel mill, etc. An umbrella portion 22 is integrated with one end of a columnar stem portion 23 as shown in FIG. 2 by a known ceramic molding means such as press molding, casting molding, injection molding, cold isostatic press molding or the like. The molded body 21 formed in a standard manner is manufactured.

  Next, the stem portion 23 is inserted into the cylindrical jig 1 made of silicon nitride ceramic having a wide inner diameter Q in the range of 0.5 to 3 mm from the outer diameter W of the stem portion 23 of the obtained molded body 21. The umbrella portion 22 of the molded body 21 is hooked and held on the opening end portion of the cylindrical jig 1. Here, the cylindrical jig 1 is formed of silicon nitride ceramics. By forming the jig of the same quality silicon nitride, decomposition of the auxiliary component from the molded body 21 which is a major factor of deformation can be suppressed. Because.

Moreover, the reason why the inner / outer diameter difference between the inner diameter Q of the cylindrical jig 1 and the outer diameter W of the stem portion 23 is set to 0.5 to 3 mm is that the difference between the inner and outer diameters is smaller than 0.5 mm. 23 may be damaged when inserted into the cylindrical jig 1, and conversely, if the difference between the inner and outer diameters exceeds 3 mm, and the stem portion 23 is deformed during sintering, the coaxiality after sintering is 0.15 mm. This is because it is difficult to suppress to / 100 mm or less. In addition, since the shift | offset | difference of the gravity center at the time of a setting becomes small by using the cylindrical jig | tool 1 with a small inner-outer diameter difference, a deformation | transformation can be suppressed further.

  After that, the molded body 21 held using the cylindrical jig 1 is fired, and is fired at normal pressure at a temperature of 1700 to 1800 ° C., preferably 1750 to 1800 ° C. in a nitrogen atmosphere or an atmosphere containing SiO. Just do it. This is because if the firing temperature is less than 1700 ° C., the sinterability is insufficient and densification cannot be achieved. Conversely, if the firing temperature exceeds 1800 ° C., the cylindrical jig 1 made of silicon nitride ceramic can be used. This is because it is difficult to promote the decomposition of the auxiliary component in the molded body 21 and suppress the deformation of the stem portion 13.

If manufactured under such conditions, silicon nitride is 80 to 92.5% by weight, rare earth elements such as Y, Er, Yb, Lu, Sm, and Dy are 2 to 10% by weight in terms of oxides, aluminum In the range of 2 to 5% by weight in terms of aluminum oxide, excess oxygen in the range of 0.5 to 5% by weight in terms of silicon oxide, and the ratio of the aluminum oxide equivalent of aluminum to the oxide equivalent of the rare earth element is It is made of silicon nitride ceramics having a ratio of the amount of silicon oxide equivalent of excess oxygen to the amount of oxide equivalent of the rare earth element of 0.5 to 0.8, and is left to be an unfired surface However, the silicon nitride ceramic valve 11 in which the coaxial degree of the stem portion 13 is 0.15 mm / 100 mm or less can be obtained.

  According to the present invention, 10 to 70% by weight of the silicon nitride powder as a starting material can be replaced with silicon powder. In this case, before firing the compact 21, 1000% in a nitrogen atmosphere. A heat treatment is performed at a temperature of ˜1400 ° C. to nitride the Si powder to produce silicon nitride, and the density of the molded body 21 is increased, followed by firing under the firing conditions. According to this manufacturing method, the shrinkage | contraction at the time of baking can be suppressed, and the precise | minute and highly accurate dimensional accuracy valve | bulb 11 made from a silicon nitride ceramic can be obtained.

(Example 1) Rare earth element oxide powder (average particle diameter of 1.mm) as a sintering aid for silicon nitride powder (BET specific surface area 9m ² / g, α rate 98%, oxygen content 1.2% by weight). 5 μm), aluminum oxide powder (purity 99.9%, average particle size 2 μm), and silicon oxide powder (purity 99.9%, average particle size 2 μm) so that the composition after firing is as shown in Table 1. The figure which consists of the umbrella part 22 and the stem part 23 by the cold isostatic pressing method after compounding, adding a binder and a solvent, kneading and drying, and the outer diameter of the stem part 23 is 10 mm, and length is 100 mm. 1 was formed.

  Next, the cylindrical jig 1 made of silicon nitride ceramic is prepared, the stem portion 23 of the molded body 21 is inserted into the cylindrical jig 1, and the umbrella portion 22 is hooked on the opening end of the cylindrical jig 1. In the held state, the silicon nitride ceramic valve 11 shown in FIG. 1 was manufactured by placing it in a bowl made of silicon carbide ceramics and firing it at a temperature of 1700 ° C. to 1800 ° C. in a nitrogen atmosphere.

  The obtained silicon nitride ceramic bulb 11 was confirmed to have the composition shown in Table 1 by ICP emission spectroscopic analysis, and then contacted on the burned surface of the stem portion 13 along its longitudinal direction. After scanning the length measuring device of the type and measuring the coaxiality of the stem portion 13, the bending strength of the burned surface was measured by a four-point bending tester.

Each result is as shown in Table 1.

  As a result, first, the sample No. 1 in which the inner and outer diameter difference between the inner diameter Q of the cylindrical jig 1 and the outer diameter W of the stem portion 23 is smaller than 0.5 mm during sintering. 5, the sample No. 5 was broken when the stem portion 23 of the molded body 21 was inserted into the cylindrical jig 1, and the difference between the inner and outer diameters was larger than 3 mm. In Nos. 4 and 6, the deformation amount of the stem portion 13 after sintering was large as 0.25 mm and 0.42 mm, and the bending strength was as low as 750 MPa or less.

Sample No. As in 14-33, the oxide equivalent amount of the rare earth element is 2 to 10% by weight, the aluminum oxide equivalent amount is 2 to 5% by weight, the silicon oxide equivalent amount of excess oxygen is 0.5 to 5% by weight, The ratio of the aluminum oxide equivalent of aluminum to the oxide equivalent of the rare earth element is 0.5 to 0.8, and the ratio of the silicon oxide equivalent of excess oxygen to the oxide equivalent of the rare earth element is 0.5 to 0.8. In any case where any of these ranges was out of range, the concentricity of the stem portion 13 could not be 0.15 mm / 100 mm or less, and the bending strength was as low as 770 MPa or less.

In contrast, sample no. 1 to 3 and 7 to 13 have a silicon nitride ceramic composition of 80 to 92.5% by weight of silicon nitride, 2 to 10% by weight of rare earth element in terms of oxide, and 2 to 5 in terms of aluminum oxide. % By weight, excess oxygen is 0.5 to 5% by weight in terms of silicon oxide, and the ratio of the amount of aluminum in terms of aluminum oxide to the amount in terms of oxide of the rare earth element is 0.5 to 0.8, and the rare earth element The ratio of the equivalent amount of excess oxygen to the equivalent amount of silicon oxide in the range of 0.5 to 0.8 is 0.5 to 3 mm from the outer diameter of the stem portion 23 of the molded body 21 when the bulb 11 is fired. Since it was inserted into a silicon nitride ceramic cylindrical jig 1 having a wide inner diameter, held and sintered, the deformation of the stem portion 13 after firing was suppressed, and the stem even with the burned surface remained Coaxiality of part 13 0.15 mm / 100 mm or less and can also the transverse rupture strength at burnt releasing surface was able to achieve a high strength of at least 770 MPa.

It is a side view which shows the valve | bulb made from a silicon nitride ceramic obtained by the manufacturing method of this invention. It is sectional drawing for demonstrating the holding state by the jig | tool at the time of baking in the manufacturing method of the valve | bulb made from a silicon nitride ceramic of this invention. It is a side view which shows the valve | bulb made from a silicon nitride ceramic obtained by the conventional manufacturing method . It is sectional drawing for demonstrating the holding | maintenance state with the jig | tool at the time of baking in the manufacturing method of the conventional silicon nitride ceramic valve | bulb.

Explanation of symbols

1: Cylindrical jig 11: Silicon nitride ceramic valve 12: Umbrella part 13: Stem part 21: Molded body 22: Umbrella part of molded body 23: Stem part of molded body

Claims (2)

80 to 92.5% by weight of silicon nitride, 2 to 10% by weight of rare earth element oxide, 2 to 5% by weight of aluminum oxide, 0.5 to 5% by weight of excess oxygen in terms of silicon oxide, and the rare earth Columnar shape formed using raw material powder prepared such that the ratio of the amount of aluminum oxide to the amount of element oxide and the ratio of the amount of silicon oxide equivalent of the excess oxygen to the amount of rare earth element oxide is 0.5 to 0.8 one end of the scan Temu portion said stem portion of the valve head molded body formed integrally, the inner diameter of the stem portion 0.5~3mm wide silicon nitride ceramic cylindrical jig in than the outer diameter of the inserting the umbrella portion of the molded body cylindrical jig and by holding hook at the open end, firing at a temperature of 1700 to 1800 ° C. the molded body in a nitrogen atmosphere containing nitrogen atmosphere or SiO and said to Rukoto Method for manufacturing of siliceous ceramic valve. 10 to 70% by weight of silicon, 80 to 92.5% by weight of the total of the silicon and silicon nitride, 2 to 10% by weight of rare earth element oxide, 2 to 5% by weight of aluminum oxide, and excess oxygen to silicon oxide 0.5 to 5% by weight in terms of converted amount, and the ratio of the amount of aluminum oxide to the amount of rare earth element oxide and the ratio of the amount of silicon oxide converted to excess oxygen to the amount of rare earth element oxide are 0.5 to 0.8. The formed body in which the umbrella portion is integrally formed at one end of the columnar stem portion formed using the raw material powder thus prepared is heat-treated at 1000 to 1400 ° C. in a nitrogen atmosphere to generate silicon nitride. After that, the stem portion is inserted into a cylindrical jig made of silicon nitride ceramic whose inner diameter is 0.5 to 3 mm wider than the outer diameter of the stem portion, and the umbrella portion of the molded body is opened in the cylindrical jig. Hang it on the edge and hold it, Serial process for producing a molded article fired to you wherein Rukoto nitrided siliceous ceramic valve at a temperature of 1700 to 1800 ° C. under a nitrogen atmosphere containing nitrogen atmosphere or SiO.

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