JPH0347941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improved foundry sand used for producing castings by centrifugal casting. [Prior art] Many improvements have been made to the centrifugal casting method in recent years.
This method is currently used for cast iron pipes for water and sewage pipes, gas pipes, cable pipes, and other industrial pipes. The basic principle of centrifugal casting is a casting method in which molten metal is poured into a mold while rotating horizontally, and the centrifugal force generated by the rotation of the mold presses the metal against the walls of the mold and solidifies it. This method is
Casting yield is high because no riser or sprue is required.
Impurities in the molten metal are centrifuged, resulting in a casting with fewer defects, no core is required, and the thickness of the casting is uniform. Dividing the centrifugal casting method according to the type of mold, (1)
Sand mold and (2) mold, which combines the features of both.
(3) There are sand molds, etc. The sand mold method is said to have higher productivity and easier production control than the conventional sand mold method or metal mold method. This method uses 250-300
While rotating the metal frame heated to ℃ on a rotary machine, resin coated sand or resin mix sand containing phenol resin is uniformly spread on the inner surface of the metal frame using a long and thin gutter to a thickness of 3 to 6 mm. The fired material is used as a mold. This is placed on a separate rotary machine and rotated, and hot water is poured into the machine from the tip of a long and narrow gutter inserted into it, forming a tube using centrifugal force. Cast iron pipes made using this method have the advantage of being able to cool quickly and obtain a uniform structure due to the thinness of the mold, but on the other hand, with conventional foundry sand, stripes appear on the surface of the mold in the axial and perpendicular directions during mold making. There are areas with poor filling properties, which are referred to as floating sand phenomenon, and as a result, stripes and roughness appear on the surface of cast iron pipes manufactured after casting. [Object of the invention] In the sand mold method of centrifugal casting, the present inventors
As a result of research to solve the striped pattern on the mold surface and the floating sand phenomenon that occur when using conventional foundry sand, we found that foundry sand for centrifugal casting has a sand particle size distribution with an average particle size of 70 μm or more and 350 μm or less. Yes, the standard deviation of the particle size distribution is 50% or less of the average particle size, and the binder used is a novolac type phenolic resin, a resol type phenolic resin, or a mixed resin of a novolac type phenolic resin and a resol type phenolic resin. It has been found that the striped pattern and floating sand phenomenon on the surface of the mold can be eliminated when the number average molecular weight of each is more desirably 250 to 600. [Structure of the Invention] As the foundry sand of the present invention, any of silica sand, zircon sand, chromite sand, and olivine sand can be used. As a result of various studies on the striped pattern on the surface of a centrifugally cast mold and the floating sand phenomenon, the present inventor found that there is a close correlation between the striped pattern and floating sand phenomenon on the surface of a centrifugally cast mold, and the sand particle size distribution. Striped patterns are less likely to occur when the particle size distribution is narrow. When foundry sand is spread onto the surface of a rotating metal frame using an elongated tub, the foundry sand forms a layer of foundry sand with a uniform thickness on the surface of the metal frame due to centrifugal force in the direction of rotation. However, in the longitudinal direction, the thickness of the foundry sand layer changes depending on the particle size distribution.
Changes in the thickness of this foundry sand layer create the striped pattern on the mold surface. The narrower the particle size distribution of the sand, the smaller the change in the thickness of the foundry sand layer in the rotational direction and length direction, and the less striped patterns occur. The floating sand phenomenon tends to occur when the filling properties of the molding sand are poor during molding. Although the thickness of the foundry sand layer becomes more uniform as the grain size distribution of the sand becomes narrower, in order to improve the filling properties of the foundry sand, it is necessary that the average grain size of the sand be within a narrow range. As a method to eliminate both such striped patterns and floating sand phenomena, the average particle size of the sand particle size distribution is 70~
At 350μm, the standard deviation of the particle size distribution is 50% of the average particle size.
It has been found that it is effective to use sand with a content of less than %. If the average grain size of the sand is 70 μm or less, the grain size is too small as a whole, so even if the standard deviation of the grain size distribution is 50% or less of the average grain size, the filling property is not good and the floating sand phenomenon cannot be prevented. Further, if the particle size is 350 μm or more, the particle size is too large and tends to cause uneven filling properties of the foundry sand, which also tends to cause floating sand phenomenon. Furthermore, when the standard deviation of the grain size distribution of sand exceeds 50% of the average grain size, striped patterns on the surface of the mold increase. The thermosetting resin used in centrifugal casting is basically a phenol resin used in resin coated sand and the like. Since phenolic resin has excellent heat resistance, it exhibits good mold characteristics without damage even in a thin mold of about 3 to 6 mm. As a result of various studies regarding the phenolic resin used in centrifugal casting in order to eliminate the striped pattern and floating sand phenomenon, it was found that the melt viscosity of the phenolic resin is appropriate when the number average molecular weight of the phenolic resin is 250 to 600. It has been found that molding sand in which the resin is uniformly dispersed is obtained, and is extremely effective in preventing the above-mentioned striped pattern and floating sand phenomenon. When the number average molecular weight exceeds 600, the melt viscosity of the phenolic resin on the surface of the sprayed foundry sand is high, which reduces the uniform dispersibility of the foundry sand and makes it more likely to be unevenly distributed, making it difficult to form a uniform mold layer. Striped patterns and floating sand phenomena on the mold surface are likely to occur. When the number average molecular weight is less than 250, although the uniform dispersibility of the foundry sand improves, the content of phenolic resin on the surface of the mold differs from that inside the mold due to centrifugal force, and in particular, the resin content on the surface of the mold decreases, causing floatation. Sand phenomenon is more likely to occur. Phenols used as raw materials for producing the phenolic resin of the present invention include phenol, cresol, xylenol, etc.
Catechol, hydroquinone, aniline, urea,
Those containing melamine, cashew nut shell oil, etc. can also be used. As the aldehyde, an aldehyde substance selected from formalin, paraformaldehyde, trioxane, acetaldehyde, etc. is used. Further, the reaction catalyst between phenols and aldehydes is generally an acidic substance such as oxalic acid, hydrochloric acid, or sulfuric acid or a metal salt of an organic acid in the case of a novolac type phenolic resin, or a primary catalyst such as ammonia or ethylamine in the case of a resol type phenolic resin. secondary amines such as ethylenediamine and diethylamine, tertiary amines such as triethanolamine and triethylamine, alkali metal hydroxides such as caustic soda and caustic potassium, and alkaline earth metals such as calcium hydroxide and magnesium hydroxide. Select and use one or more types such as hydroxide. The molding sand used in the present invention includes resin coated sand made by dry hot coating method, semi-hot coating method, cold coating method, powder solvent method, etc., and resin mixed sand mixed with powdered resin. It is possible. The present invention will be explained below with reference to Examples. However, the present invention is not limited to these examples. In addition, "parts" and "%" described in each example and comparative example all indicate "parts by weight." [Example] Production Example 1 (1) Production of Sand Mikawa No. 6 silica sand was classified and adjusted to obtain silica sand with a particle size distribution having an average particle diameter of 148 μm and a standard deviation of 17 μm. (2) Production of phenolic resin Phenol 1000 in a reaction pot equipped with a cooler and a stirrer
1 part, 650 parts of 37% formalin, and then 10 parts of oxalic acid. The temperature was gradually raised, and after the temperature reached 96°C, a reflux reaction was performed for 120 minutes, a dehydration reaction was performed under vacuum, and the pot was discharged. 970 parts of a novolak type phenolic resin which was solid at room temperature and had a number average molecular weight of 523 was obtained. (3) Production of resin coated sand 7000 parts of silica sand prepared as above was heated to 150°C and charged into a Whirl mixer. After adding 210 parts of the above novolac type phenolic resin, kneading was carried out for 40 seconds, and then hexamethylenetetramine
Add an aqueous solution of 31.5 parts dissolved in 105 parts of water,
The coated sand was mixed until it disintegrated. Furthermore, 7 parts of calcium stearate was added, and 30 parts of calcium stearate was added.
The mixture was mixed for seconds and then aerated to obtain resin coated sand. Example 1 Internal diameter heated to 290°C and rotating at 60 rpm
Using a gutter in a cylindrical mold with a length of 300 mm and a length of 3000 mm, 6 kg of the resin coated sand obtained in Production Example 1 was placed.
It was inserted in 15 seconds. Rotation was continued for 60 seconds to obtain a centrifugal casting mold. Production Example 2 (1) Production of Sand Pearl No. 5.5 silica sand was classified and adjusted to obtain silica sand with a particle size distribution having an average particle diameter of 293 μm and a standard deviation of 89 μm. (2) Production of phenolic resin Phenol 1000 in a reaction pot equipped with a cooler and a stirrer
parts, 1795 parts of 37% formalin, then 160 parts of 28% aqueous ammonia, and 60 parts of 50% aqueous sodium hydroxide solution.
I prepared a section. The temperature was gradually raised, and after the temperature reached 96°C, a reflux reaction was carried out for 30 minutes, and then 40 parts of methylene bisstearamide was added, a dehydration reaction was carried out under vacuum, and the mixture was taken out of the pot and rapidly cooled. 1060 parts of a resol type phenolic resin which was solid at room temperature and had a number average molecular weight of 285 was obtained. (3) Production of resin coated sand 7000 parts of silica sand prepared as above was heated to 140°C and charged into a Whirl mixer. After adding 245 parts of the above resol type phenolic resin, the mixture was kneaded for 40 seconds, and then 105 parts of water was added and kneaded until the coated sand collapsed. Furthermore, 7 parts of calcium stearate was added, mixed for 30 seconds, and aeration was performed to obtain resin coated sand. Example 2 A centrifugal casting mold was obtained under the same manufacturing conditions as in Example 1 except that the resin coated sand obtained in Manufacturing Example 2 was used. Comparative example 1 Regenerated No. 6 silica sand (average particle size of particle size distribution 195 μm,
Standard deviation: 105 μm) 7000 parts were heated to 150°C and charged into a Whirl mixer. After adding 210 parts of the novolac type phenolic resin of Production Example 1, kneading for 40 seconds,
Next, 31.5 parts of hexamethylenetetramine was added to 105 parts of water.
An aqueous solution in which the coated sand was dissolved was added and kneaded until the coated sand was disintegrated. Furthermore, 7 parts of calcium stearate was added, mixed for 30 seconds, and aeration was performed to obtain resin coated sand. A mold for centrifugal casting was obtained under the same manufacturing conditions as in Example 1 except that this resin coated sand was used. Comparative example 2 Phenol 1000 in a reaction pot with a cooler and a stirrer
1 part, 800 parts of 37% formalin, and then 10 parts of oxalic acid. Gradually increase the temperature and after the temperature reaches 96℃
After refluxing for 150 minutes, a dehydration reaction was carried out under vacuum and the pot was discharged. Solid at room temperature, number average molecular weight is 635
1020 parts of novolac type phenolic resin was obtained. 7000 parts of Mikawa No. 6 silica sand classified product obtained in Production Example 1
It was heated to 155°C and charged into a whirl mixer. After adding 210 parts of the above novolak type phenolic resin
Knead for 40 seconds, then add hexamethylenetetramine
An aqueous solution of 31.5 parts dissolved in 105 parts water was added and kneaded until the coated sand disintegrated. Further, 7 parts of calcium stearate was added, mixed for 30 seconds, and aeration was performed to obtain resin coated sand. A mold for centrifugal casting was obtained under the same manufacturing conditions as in Example 1 except that this resin coated sand was used. Comparative Example 3 7000 parts of recycled 6 silica sand (average particle size of particle size distribution: 195 μm, standard deviation: 105 μm) was heated to 150° C. and charged into a Whirl mixer. After adding 210 parts of the novolak type phenolic resin (number average molecular weight 635) obtained in Comparative Example 2, the mixture was kneaded for 40 seconds, and then 31.5 parts of hexamethylenetetramine was added.
An aqueous solution of 105 parts of water was added thereto, mixed for 30 seconds, and aeration was performed to obtain resin coated sand. A mold for centrifugal casting was obtained under the same manufacturing conditions as in Example 1 except that this resin coated sand was used. Table 1 shows the characteristics of the foundry sand, the binder in the foundry sand, the bending strength of the mold, and the mold made by the centrifugal casting method in Examples 1 and 2 and Comparative Examples 1, 2, and 3. The test method is as follows. Average particle size, standard deviation: Toyo Ink Manufacturing Co., Ltd.
Based on "LUZEX-5000". Number average molecular weight: Based on GPC method. Bending strength: Based on JACT test method SM-1. Mold stripes and floating sand: Visually inspected. 【table】

Claims (1)

[Claims] 1. Foundry sand for centrifugal casting consisting of sand, binder, and additives, wherein the sand has an average particle size of 70 μm or more in the particle size distribution.
350 μm, and the standard deviation of the particle size distribution is 50% or less of the average particle size, and the binder is a novolac type phenolic resin, a resol type phenolic resin, or a mixed resin of a novolac type phenolic resin and a resol type phenolic resin. Characteristic foundry sand for centrifugal casting. 2. The foundry sand for centrifugal casting according to claim 1, wherein each of the novolac type phenolic resin, the resol type phenolic resin, or the mixed resin of the novolac type phenolic resin and the resol type phenolic resin has a number average molecular weight of 250 to 600.