Casting mold for cast steel and cast steel product manufacturing method

Abstract

To provide a casting mold for cast steel that can manufacture a thin-walled cast steel product while using a metal mold.SOLUTION: A casting mold for cast steel has a heat insulation layer on a cavity surface of a metal mold comprising a steel material. For example, the heat insulation layer has a thermal conductivity of 0.01 to 10 W / mk, and a permeability of 15 to 500. The thickness thereof is, for example, 0.1 to 4 mm. The heat insulation layer comprises, for example, ceramic particles, and a binder which makes the same solidify or adhere. An AFS particle fineness number of the ceramic particle is, for example, 10 to 250. For example, 0.5 to 10% by mass of the binder is included relative to the total heat insulation layer. If using the casting mold of the present invention, for example, a cast steel product having a thin-walled part with a thickness of 1 to 4.5 mm can also be manufactured. The casting mold of the present invention can be repeatedly used, since the metal mold is used, and is suitable for a circulation type economy (society).SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a mold for casting steel and the like. [Background technology]

[0002] Steel castings are used for high-strength components with complex shapes. Steel castings are obtained by pouring molten steel into a mold cavity and allowing it to solidify. Since the molten metal of steel with a low carbon content is very hot, sand molds are generally used for the molds. Related disclosures can be found in, for example, Patent Documents 1 and 2 listed below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2000-176601 [Patent Document 2] Patent Publication No. 2002-307131 [Patent Document 3] Patent Publication No. 2005-169440 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, a shaped product made of mullite sand and sodium silicate is hardened by passing carbon dioxide gas through it, and then heated to a high temperature to create a mold. Molten metal is then poured into the hot mold to produce a thin-walled cast steel product with a wall thickness of 1.5 mm.

[0005] In Patent Document 2, a molded product made from casting sand is impregnated with an inorganic binder (SiO2 / Na2O), then dried and fired to form a mold, and molten metal is poured into the hot mold to produce thin-walled cast steel exhaust system parts. The cavity spacing of the mold, which consists of a main mold and a core, is 3 mm.

[0006] Thus, steel castings (particularly thin-walled products) have been manufactured using sand molds in which a molded object made of casting sand and a binder is heated and solidified.

[0007] Such sand molds must be made for each steel casting, and the molds themselves require high-temperature heating to be made. Such sand molds do not contribute to the promotion of a circular economy or carbon neutrality (reducing CO2 emissions).

[0008] Patent Document 3 describes a mold wash for a mold into which molten cast steel is poured. The mold wash is prepared from hollow ceramic powder (hollow mullite powder, average particle size: 100 μm), finer solid ceramic powder (alumina powder, average particle size: 50 μm), adhesive (bentonite and water glass), and water. The solid ceramic powder (75 wt%) is blended in a significantly larger proportion than the hollow ceramic powder (25 wt%). When this mold wash is used, a dense coating film is formed on the surface of the mold, with fine solid ceramic particles filling the spaces between the coarse hollow ceramic particles.

[0009] As is clear from Examples 6 to 10 and Comparative Examples 4 and 5 described in Patent Document 3, a dense, thin coating (film thickness 0.5 mm) containing a mixture of coarse and fine ceramic particles prevents poor casting surface and poor molten metal flow. Conversely, coatings consisting only of coarse ceramic particles or only of fine ceramic particles cause poor casting surface and poor molten metal flow. While the truth of this is unknown, Patent Document 3 is thought to relate to a specific case in which a thick-walled cast steel product (a heat-resistant cast steel exhaust manifold) is cast at low pressure.

[0010] The present invention has been made in view of the above circumstances, and has as its object to provide a new mold for casting steel that is different from conventional molds. [Means for solving the problem]

[0011] As a result of intensive research into solving this problem, the inventors discovered that good cast steel products could be obtained by providing a heat insulating layer on the cavity surface of the mold, which is different from conventional methods. By expanding on this finding, the inventors have completed the present invention, which will be described below.

[0012] <Steel casting mold> The present invention is a mold for casting steel, which has a heat insulating layer on the cavity surface of a mold made of steel, and the heat insulating layer has a thermal conductivity of 0.01 to 10 W / m·k and an air permeability of 15 to 500.

[0013] The casting mold for steel casting of the present invention (also simply referred to as "mold") has a metal mold body, so it can be reused and regenerated. Therefore, use of the casting mold of the present invention not only reduces the manufacturing costs of steel castings, but also contributes to a recycling-based economy.

[0014] By using the mold of the present invention, it is possible to cast thin-walled steel products while suppressing defects. The reason for this is thought to be as follows.

[0015] The insulating layer on the cavity surface not only has low thermal conductivity and excellent insulating properties, but also has high air permeability, allowing it to contain gas (gas bubbles) generated during pouring. Therefore, even in a narrow cavity, the desired molten metal flow is ensured, and gas entrapment within the cavity is reduced, preventing the occurrence of casting defects (gas defects, underfill, etc.). It is believed that the use of the mold of the present invention thus makes it possible to cast (manufacture) even thin-walled steel castings with a high yield while ensuring the desired quality.

[0016] 《Manufacturing method / cast steel product》 The present invention can also be understood as a casting method (manufacturing method) using the above-mentioned mold, and a cast steel product obtained thereby. The cast steel product according to the present invention may have a thin-walled portion having a thickness of, for example, 1 to 4.5 mm or 2 to 3.5 mm. The length of the thin-walled portion may be, for example, 50 to 1000 mm, 75 to 750 mm, 100 to 500 mm, or 150 to 350 mm.

[0017] "others" Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b." Furthermore, unless otherwise specified, "x to y mm" in this specification means x mm to y mm. The same applies to other unit systems. [Brief explanation of the drawings]

[0018] [Figure 1A] FIG. 1 is a schematic diagram showing a casting (evaluation test) using a steel casting mold. [Figure 1B] This is a photo showing the actual mold. [Figure 1C] 1A and 1B are a front view and a side view of a metal mold (one half of a split mold) used in the casting process. [Figure 2] 1 is a photograph showing a portion of a thin-walled steel casting according to a first example. [Figure 3] 10 is a photograph showing a portion of a thin-walled steel casting according to a second example. [Figure 4] FIG. 10 is a scatter diagram showing the flow length ratio of the thin-walled steel casting according to the second example. DETAILED DESCRIPTION OF THE INVENTION

[0019] One or more components arbitrarily selected from this specification may be added to the above-described components of the present invention. The content described in this specification may apply to both products (molds, cast steel products) and methods. Components related to a method may also be components related to a product. Which embodiment is best depends on the target, required performance, etc.

[0020] "template" The mold has a heat insulating layer on the cavity surface of the mold. These will be described in detail below.

[0021] (1) Mold The mold (main mold) is made of steel (base material). The steel may be of any type, such as carbon steel, tool steel, alloy steel, or stainless steel. The thermal conductivity of such steel is, for example, about 50 to 60 W / m·k.

[0022] (2) Cavity The mold has a cavity shaped to correspond to the steel casting. The cavity may have narrowly spaced portions (thin portions) corresponding to the thin portions of the steel casting. The spacing of the mold cavity is set taking into account the thickness of the steel casting and the total thickness of the insulation layer.

[0023] (3) Structure The structure of the mold is not important as long as it is possible to form a heat insulating layer on the cavity surface. For example, the mold can be a one-piece mold or a split mold with two or more parts. If the mold is a split mold, it is easy to form a heat insulating layer on the cavity surface where the thin-walled part is formed.

[0024] "Thermal insulation layer" (1) Features The thermal conductivity of the heat insulating layer is sufficiently lower than that of the steel material that makes up the mold. The thermal conductivity is, for example, 0.01 to 10 W / m·k, 0.05 to 5 W / m·k, or 0.1 to 1 W / m·k. If it is possible to form a heat insulating layer, the lower the thermal conductivity, the better.

[0025] The heat insulating layer preferably has gaps that can contain gas. The air permeability is an indicator of this. The air permeability is, for example, 15 to 500, 20 to 300, 30 to 250, 50 to 200, or 70 to 180. If the air permeability of the heat insulating layer is too high, the strength of the heat insulating layer decreases, and there is a risk of peeling or collapsing during casting.

[0026] The term "air permeability" as used in this specification indicates the degree to which air passes through the insulation layer (air permeability), and is different from the air permeability (see JIS Z 2601) of its constituent raw materials (ceramic powder (such as foundry sand), binder, etc.). The air permeability of an insulation layer is determined by measuring the pressure difference that occurs when a certain air pressure is applied to the insulation layer. Specific measurement methods will be described later.

[0027] The thickness of the insulating layer is, for example, 0.1 to 4 mm, 0.5 to 3.5 mm, 0.8 to 3.2 mm, 1.3 to 3 mm, or 1.8 to 2.8 mm. The thickness of the insulating layer itself is thought to have little effect on its thermal conductivity or air permeability. However, if it is too thin, the insulating properties and ability to contain air bubbles will be poor, and if it is too thick, the amount of constituent raw materials will increase, which can increase costs.

[0028] The region where the heat insulating layer is formed may be the entire cavity surface or a part of it. The thickness and composition (components) of the heat insulating layer may vary depending on the part (region) of the cavity surface. The heat insulating layer is preferably provided at least in the region where the thin-walled portion of the steel casting is formed (specific region of the cavity surface). The thickness of the thin-walled portion is, for example, 1 to 4.5 mm, 1.5 to 3.5 mm, or 2 to 3 mm. This thickness is approximately the same as the distance between opposing heat insulating layers.

[0029] (2)Manufacturing The heat insulating layer is composed of, for example, ceramic powder and a binder (or adhesive) that solidifies or adheres it. The ceramic powder may be of any type or composition, but may be based on, for example, silica, mullite, alumina, zircon, chromite, or the like. The more heat-resistant the ceramic powder, the more preferable it is, and its refractoriness is, for example, 1700°C or higher, or even 1800°C or higher. The refractoriness here refers to the temperature that the refractory can withstand, and is determined by refractoriness measurement (softening point measurement) using a Segel cone.

[0030] The ceramic powder is not limited to foundry sand, but may be one used for other purposes. The ceramic powder may also be a mixed powder consisting of multiple types of ceramics. Furthermore, the particle size of the ceramic powder is not important as long as the properties of the heat insulating layer are ensured. For example, it is recommended to use ceramic powder (such as foundry sand) with a particle size index of 10 to 250 or 40 to 200. Unless otherwise specified, the particle size index referred to in this specification is determined by the American Foundry Society (AFS).

[0031] The ceramic powder consists of solid particles, hollow particles, or a mixture of these particles. Hollow particles have low thermal conductivity, which effectively improves the properties of the thermal insulation layer.

[0032] The binder is selected depending on the specifications of the heat insulating layer, the forming method, the type (characteristics) of ceramic powder (casting sand, etc.), etc. The binder may be inorganic or organic. Inorganic binders generate less gas during casting. Examples of such binders include silicates (water glass) and phosphates.

[0033] Even a small amount of organic binder can firmly bind the foundry sand, making it easy to form (shape) the insulating layer and maintain its shape. Examples of such binders include self-hardening resins such as phenolic resin, urethane resin, and furan resin.

[0034] The binder is contained in an amount of, for example, 0.5 to 10 mass % or 1 to 5 mass % based on the total amount of ceramic particles and binder (or the entire thermal insulation layer). In terms of volume ratio, the binder is contained in an amount of 1 to 19 volume % or 2 to 20 volume % based on the total volume of ceramic particles and binder. The binder may contain additives such as hardeners. Unless otherwise specified, the term "binder" will be used to refer to both additives and binders.

[0035] Steel Castings Steel castings are made of iron alloys with a lower carbon content than cast iron. The cast steel may be ordinary cast steel (carbon steel cast steel) or alloy cast steel, and the specific composition of the components is not important. The method for preparing the molten metal and its raw materials are not important. Scrap steel (steel plate, etc.) may be used as at least a portion of the raw materials.

[0036] The mold of the present invention can be used for any steel casting, regardless of its shape. It is preferable that the mold of the present invention be used when the steel casting has at least a thin-walled portion. The thin-walled portion may be flat or curved, and may be straight or curved.

[0037] Cast steel products can be used for any purpose. For example, cast steel products are used in structures, joints with other members, etc. The other member (mating material) to be joined to the cast steel product may be a metal substrate (iron substrate, aluminum substrate, titanium substrate, magnesium substrate, etc.), a non-metal substrate (resin, ceramics, etc.), or a composite material (FRP, etc.). [Example]

[0038] A casting test was carried out using a mold in which a coating layer (thermal insulating layer) was provided on the cavity surface of the mold, and the thin-walled castings (cast steel products) obtained were evaluated. The present invention will be described in further detail with reference to such specific examples.

[0039] [First Example] <<Sample Preparation>> An outline of the casting test is shown in Figure 1A. The actual mold used in the casting test is shown in Figure 1B. Front and side views of the split mold (metal mold) that constituted the mold are shown in Figure 1C.

[0040] (1) Mold A pair of symmetrical split dies (metal molds) was made by cutting carbon steel (JIS SS400). The cavity was a strip of 40mm wide x 300mm long (maximum flow length). The gap (spacing) between the cavities was changed depending on the thickness of the coating layer and the thickness of the thin-walled part to be cast. This was adjusted by changing the thickness of the steel spacer sandwiched between the butted split dies. A base plate (0.5mm thick) was installed at the bottom of the mold. This allowed air inside the cavity to be expelled from the bottom (air hole) when the first molten metal was poured.

[0041] (2) Covering layer Various coating layers shown in Table 1 were provided on the inner surface (cavity surface) of the split mold. The coating layers shown in Samples 11 to 18 correspond to the heat insulating layer referred to in this specification. The method of forming each coating layer will be described later.

[0042] The thermal conductivity shown in Table 1 was measured using a transient thermal conductivity tester (Quick Lambda HC-10 manufactured by Eiko Seiki Co., Ltd.) by placing the measurement probe on the surface of the coating layer before pouring.

[0043] The air permeability was measured using a digital mold sand air permeability tester (NKP-V3 / small orifice manufactured by Nakayama Co., Ltd.) by placing a mold measurement probe on the coating layer (before pouring) on ​​the mold. The thermal conductivity and air permeability thus obtained are also shown in Table 1.

[0044] The thickness of the coating layer was determined from the difference in dimensions before and after its formation.

[0045] (3) Casting The steel material (SS400) was heated to 1650℃ in a high-frequency melting furnace and completely melted. The molten metal was then cooled to 1630℃ and poured into the cavity from a sprue above the (dried) mold.

[0046] Before casting (pouring molten metal), the inside of the cavity was thoroughly heated and dried. Specifically, the mold was subjected to a flame drying process, in which water is evaporated using a burner, or to a heat treatment in a dryer (170°C x 1 hour).

[0047] After pouring the molten metal, it was allowed to cool at atmospheric pressure. The mold was then split and the solidified product (thin-walled casting) was removed from the mold. Its length (flow length; see Figures 1A and 2) was measured. The flow length was the length the molten metal flowed while keeping the cavity width (40 mm).

[0048] The appearance of each sample was also observed to check for undercuts (casting defects). The results are also shown in Table 1. The appearance of the thin-walled castings of each sample (part of the sample) is shown in Figure 2. The standard thickness of the thin-walled castings was 2.5 mm, except for sample C12.

[0049] <<Formation and evaluation of the coating layer>> The method of forming the coating layer (heat insulating layer) of each sample and the evaluation of the thin-walled casting of each sample are as follows: The thin-walled castings were evaluated mainly based on the above-mentioned flow length and the presence or absence of underfill.

[0050] [Samples 11-18] (1) Formation For Samples 11 to 16, 2 parts by mass of alkaline phenolic resin (PHENIX-621BR manufactured by Kobe Rikagaku Kogyo Co., Ltd.) and 20 parts by mass of curing agent (PHENIX C-5A manufactured by Kobe Rikagaku Kogyo Co., Ltd.) were added to 100 parts by mass of silica sand and mixed (kneaded). This mixture was placed in a mold and molded into a thin plate. The resulting molded object was attached to the inner wall surface (including the cavity surface) of a mold coated with room-temperature mold adhesive (Core Sealer SG-27 manufactured by Kobe Rikagaku Kogyo Co., Ltd.).

[0051] Each heat insulating layer shown in Table 1 was formed on the cavity surface of the mold while changing the type and composition of silica sand, molding pressure, mold depth, etc.

[0052] The Flattery Silica Sand shown in Table 1 is manufactured by Hyōya Co., Ltd., and Mikawa Silica Sand No. 6, No. 8, and No. 9 are manufactured by Mikawa Silica Sand Co., Ltd. For Sample 15, the Mikawa silica sand was sieved to a particle size of 106 μm or less to adjust the grain size index of the foundry sand. For Sample 16, a mixture of Mikawa Silica Sand No. 8 and Mikawa Silica Sand No. 9 (25% by mass of the total amount) was used.

[0053] For sample 17, a shaped object to serve as a heat insulating layer was molded using a mixture in which 8 parts by mass of the above phenolic resin was added to silica sand (100 parts by mass).

[0054] For sample 18, an inorganic binder (potassium silicate: 10% aqueous solution / Okaguard S-71 Liquid B, manufactured by Tochu Co., Ltd.) was sprayed onto the inner wall surface of the mold, and silica sand was then sprinkled on the applied surface. This procedure was repeated until the desired thickness was obtained. The surface was then leveled and smoothed. In this way, a heat insulating layer was formed.

[0055] (2) Evaluation As is clear from Table 1, all of Samples 11 to 18 had excellent molten metal running properties (flow length) and had few or no casting defects (presence or absence of underfill). As can be seen from Sample 16, even with a permeability of about 20, a thin-walled casting with sufficient flow length was obtained without underfill.

[0056] In sample 17, the grain size index of the molding sand was increased to intentionally reduce the air permeability, which resulted in gas being trapped in the cavity and causing some underfill (gas defects).Incidentally, the molding sand used in sample 17 (Mikawa silica sand No. 9) contained fine particles with a particle size of 52 μm or less, which accounted for about 50% of the total.

[0057] As can be seen from Samples 11 and 12, the thickness of the insulating layer had almost no effect on its thermal conductivity or air permeability. There was also no correlation between thermal conductivity and air permeability.

[0058] [Samples C11 and C12] (1) Formation The inner wall surface of the mold was coated with graphite spray (FC-142 manufactured by Fine Chemical Japan Co., Ltd.) to prevent seizure, and the coated surface was flame-dried. The thickness of the castings was 2.5 mm for sample C11 and 5 mm for sample C12.

[0059] (2) Evaluation No underfill was observed in samples C11 and C12. This is thought to be because the organic components contained in the graphite spray volatilized during the flame drying process, resulting in less gas being generated during casting.

[0060] When the thickness of the casting was 2.5 mm, as in sample C11, the flow length was significantly shorter. However, when the thickness of the casting was 5 mm, as in sample C12, it was found that the flow length was ensured even with the coating layer described above.

[0061] [Samples C13 to C16] (1) Formation A zircon-based mold wash (Oka Super 250 manufactured by Okazaki Mining Products Co., Ltd.) was sprayed onto the inner wall surface of the mold, and then allowed to dry naturally. This procedure was repeated to form a coating layer of the desired thickness.

[0062] (2) Evaluation As can be seen from Table 1, the thicker the coating layer made of the mold wash, the lower the thermal conductivity (improved thermal insulation). Therefore, sample C13, which has a thin coating layer and high thermal conductivity (low thermal insulation), had a significantly shorter flow length.

[0063] These coating layers all had low gas permeability, regardless of their thickness, which resulted in numerous large undercuts caused by gas in thin-walled castings (see Figure 4).

[0064] [Second Example] Thin-walled castings (steel castings) were produced by changing the coating layer (thermal insulating layer) formed on the inner surface (cavity surface) of the split mold, and the evaluation was carried out. Specifically, the casting was carried out in the same manner as in Example 1, unless otherwise specified.

[0065] <<Sample Preparation>> (1) Mold A mold was prepared in which the cavity length was extended from 300 mm to 500 mm. The other specifications were the same as those of the mold of the first embodiment (FIGS. 1A to 1C).

[0066] (2) Covering layer Each coating layer shown in Table 2 was formed on the cavity surface (inner surface of the split mold). The details are as follows. The properties of each coating layer (thermal conductivity, air permeability, etc.) were measured in the same manner as in Example 1, and the results are also shown in Table 2.

[0067] The coating layers of Samples C21 and C22 were essentially the same and were formed in the same manner as Sample 11. However, the amount of the alkaline phenol resin added was 3 parts by mass relative to the flattery sand (solid ceramic particles). In addition, a room-temperature mold adhesive (Coasealer SG-27 manufactured by Kobe Rikagaku Kogyo Co., Ltd.) was used as the adhesive.

[0068] The coating layer of sample 21 was made by replacing the Flattery sand (foundry sand) used in samples C21 (C22) with E-Spheres (SL150 manufactured by Taiheiyo Cement Corporation). E-Spheres consists of hollow ceramic particles (particle size index: 135) of a silica-alumina system (SiO2: 60%, Al2O3: 38%, balance: other oxides).

[0069] The coating layer of sample 22 was made by replacing the Flattery sand of sample C21 with yttria-stabilized zirconia (Saint-Gobain #204PR). This powder consisted of hollow ceramic particles (grain size index: 173) of yttria-zirconia (ZrO2: 92%, Y2O3: 8%).

[0070] The volume ratio of binder to ceramic powder was the same for Samples 21, 22, and C21. In other words, the blending amount (parts by mass) of binder to ceramic powder was adjusted taking into account the specific gravities of hollow ceramic particles and solid ceramic particles. However, the ratio of phenolic resin and hardener that make up the binder was the same for each sample.

[0071] (3) Casting Steel with a chemical composition (mass%) of Fe-0.09C-0.42Si-2.37Mn-0.02P-0.006S was melted in the same manner as in Example 1. The molten steel was poured into the cavities (2.3 mm thick, equivalent to the wall thickness of the casting) where each coating layer was provided. Samples 21 and C21 were poured manually, while Samples 22 and C22 were poured using the tilting mechanism of the melting furnace.

[0072] Observation and Measurement As in Example 1, each casting removed from the mold was observed and measured. The results are shown in Table 2. The appearances of the castings of Sample 21 and Sample C21 are shown in Figure 3.

[0073] The fluidity length ratios shown in Table 2 are the ratios of the fluidity lengths of the samples poured using the same method (sample 21 / sample C21 and sample 22 / sample C22). The relationship between the fluidity length ratio and the thermal conductivity of the coating layer is shown in Figure 4.

[0074] "evaluation" As can be seen from Table 2, the coating layer using hollow ceramic powder had a significantly reduced thermal conductivity. As can be seen from Figures 3 and 4, when this coating layer was formed on a mold (cavity), the flow length of thin-walled cast steel products could be increased by more than 1.5 times without causing casting defects (underfill).

[0075] From the above, it was confirmed that the desired thin-walled cast steel products can be produced by using the steel casting mold of the present invention.

[0076] [Table 1]

[0077] [Table 2]

Claims

1. A heat insulating layer is provided on the cavity surface of the mold made of steel, The heat insulating layer has a thermal conductivity of 0.01 to 10 W / m·k and an air permeability of 15 to 500.

2. 2. The mold for casting steel according to claim 1, wherein the heat insulating layer has a thickness of 0.8 to 4 mm.

3. 2. The mold for casting steel according to claim 1, wherein the heat insulating layer is provided at least in an area where a thin-walled portion having a thickness of 1 to 4.5 mm is to be formed.

4. 2. The mold for casting steel according to claim 1, wherein the heat insulating layer comprises ceramic particles and a binder that solidifies or adheres the ceramic particles.

5. 5. The mold for casting steel according to claim 4, wherein the ceramic particles are made of molding sand.

6. 5. The mold for casting steel according to claim 4, wherein the ceramic particles are hollow particles.

7. 5. The mold for casting steel according to claim 4, wherein the ceramic particles have an AFS particle size index of 10 to 250.

8. 5. The mold for casting steel according to claim 4, wherein the binder is contained in an amount of 1 to 19 volume % relative to the total volume of the ceramic particles and the binder.

9. A method for producing a cast steel product using the mold for steel casting according to any one of claims 1 to 8.

10. The method for manufacturing a steel cast product according to claim 9, wherein the steel cast product has a thin plate portion having a thickness of 1 to 4.5 mm and a length of 50 to 1000 mm.

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