JP2008231521A - Die for centrifugal casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a die for centrifugal casting provided with a die main body in the inner face of which cracks are hardly caused, and which has long service life. <P>SOLUTION: The die 2 for centrifugal casting comprises a die main body 3 composed of a chromium-molybdenum steel comprising, by mass, 0.09 to 0.12% C, 0.20 to 0.30% Si, 0.30 to 0.50% Mn, ≤0.015% P, ≤0.005% S, ≤0.40% Ni, 5.8 to 8.5% Cr, 0.85 to 0.95% Mo, 0.060 to 0.085% Nb, 0.18 to 0.22% V, ≤0.015% Al and 0.040 to 0.065% N, and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mold for centrifugal casting equipment, and more particularly to a centrifugal casting mold having a mold body having high temperature strength characteristics and high creep strength and a long life.

  Centrifugal casting equipment that manufactures ductile cast pipes such as ductile cast iron pipes is a mold that rotates with its axis as the axis of rotation, a casting carriage that mounts this mold, and contains the molten metal and tilts the mold. Equipped with a ladle for pouring the molten metal inside, and a pouring pot for relaying the molten metal flowing out of the ladle for casting into the mold, and inserts it deep into the rotating mold While injecting molten metal from the tip of the injection pouring bowl, the mold is moved to the opposite side of the pouring ladle together with the casting cart, so that the injected molten metal is solidified sequentially and a centrifugal cast tube is directly produced from the molten metal. is doing. The manufactured centrifugal cast pipe is pulled out from the mold toward the opposite side of the ladle for casting, and then subjected to a heat treatment or the like to become a product.

  The mold is composed of a cylindrical mold body, which is a part that directly receives molten metal, and a sleeve provided on the outer periphery of the mold body, and a gap between the mold body and the sleeve serves as a cooling water flow path. ing. As the mold body, chrome molybdenum steel (for example, SCM420 shown in JIS G 4105) having excellent high-temperature strength is generally used.

  Periodic thermal stress acts on the inner surface of the mold main body, which is in direct contact with the molten metal, by repeatedly applying heating and cooling. This periodic thermal stress causes cracks on the inner surface of the mold body. This cracking deteriorates the surface properties of the centrifugal cast pipe to be cast. For example, if the mold is subjected to casting for one day, the mold is removed from the casting carriage and the inner surface of the mold body is ground, or The cracks on the inner surface of the mold body are removed by, for example, grinding the inner surface after welding and depositing on the inner surface of the mold body. However, the possible range for repairing the weld overlay is limited to the end of the mold body, and generally, the inner part is mainly ground at the center of the mold body. If this number of internal grindings overlaps, the inner diameter of the mold body will increase, and the cast cast pipe that will be cast will not be able to maintain the standard size, the mold body will be discarded, and a new mold body will be renewed. Will be installed. In addition to the wear and deformation of the mold body, the number of times the mold body is used, that is, the lifetime, depends mainly on the cracks generated on the inner surface of the mold body.

In order to prevent cracking of the inner surface of the mold body, Patent Document 1 discloses that the thickness of the mold body at the position corresponding to the end of the centrifugal cast pipe to be manufactured, that is, the thick part of the centrifugal cast pipe, is centrifuged. There has been proposed a mold body that is thinner than the wall thickness at the position corresponding to the center of the cast pipe. According to Patent Document 1, the temperature distribution in the thickness direction of the mold body becomes gentle by reducing the thickness at the position corresponding to the thick part of the end portion of the centrifugal casting tube, and the occurrence of cracks in the mold body is prevented. It is going to be done. However, there is a problem that the centrifugal cast pipe to be cast is rapidly cooled by making the portion with high heat input relatively thin, and defects such as cracks are likely to occur on the surface of the centrifugal cast pipe. In addition, a relatively thin wall increases the thermal shock of the mold body, and on the other hand, the mold body tends to crack.
JP 2001-150114 A

  As described above, there is no effective means to prevent cracks on the inner surface of the mold body, and the cracks generated by grinding the inner surface of the mold body are unavoidably removed. This is the current situation, which has led to an increase in manufacturing costs.

  The present invention has been made in view of the above circumstances. The object of the present invention is to provide a centrifugal casting mold having a long-life mold body that has high-temperature strength characteristics and high creep strength, is less likely to crack. Is to provide.

  The inventors of the present invention conducted intensive studies and examinations in order to solve the above problems. As a result, it has been found that the formation of cracks can be prevented by configuring the mold body with heat-resistant steel having excellent high-temperature strength characteristics and creep strength. In addition, when comparing austenitic heat-resistant steel and ferritic heat-resistant steel, ferritic heat-resistant steel has a lower high-temperature strength than austenitic heat-resistant steel, but its thermal expansion coefficient is small, so that the oxide scale of repeated heating and cooling It has the advantage that there is little peeling, and also has the advantage that it has excellent thermal fatigue characteristics, and it has been found that it is suitable as a mold body. Furthermore, it was confirmed that the mold body must be repaired by welding for repeated use, and it is necessary to make the material excellent in weldability.

  As a result of considering these conditions, it was found that a ferritic chromium molybdenum steel containing about 9% by mass of Cr and about 1% by mass of Mo is optimal as a material for the mold body.

  The present invention has been made on the basis of the above findings, and a centrifugal casting mold according to the present invention is a centrifugal casting mold for casting a centrifugal casting pipe, and is in mass%, and C: 0.09. ˜0.12%, Si: 0.20 to 0.30%, Mn: 0.30 to 0.50%, P: 0.015% or less, S: 0.005% or less, Ni: 0.40% Hereinafter, Cr: 5.8 to 8.5%, Mo: 0.85 to 0.95%, Nb: 0.060 to 0.085%, V: 0.18 to 0.22%, Al: 0.8. It is characterized by comprising a mold body made of chromium molybdenum steel containing 015% or less and N: 0.040 to 0.065%, and the balance being Fe and inevitable impurities.

  According to the mold of the present invention, since it has a mold body made of ferritic chromium molybdenum steel having high high temperature strength and creep strength and excellent high temperature toughness and heat fatigue resistance, Even if stress acts, cracks are unlikely to occur on the inner surface of the mold body, and as a result, it can be used stably over a long period of time while suppressing the occurrence of cracks. Moreover, since it is excellent also in weldability, the overlay repair can be carried out without causing any problem. By these, the cost of a metal mold | die can be reduced significantly and the reduction of the manufacturing cost of a centrifugal cast pipe is achieved.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view of a centrifugal casting facility equipped with a mold according to the present invention, FIG. 2 is a perspective view showing a schematic structure of the mold according to the present invention, and FIG. 3 is a part of the mold according to the present invention. FIG.

  As shown in FIG. 1, a centrifugal casting facility for producing a centrifugal cast pipe such as a ductile cast iron pipe is installed substantially horizontally, and a mold 2 that rotates around its axis and a casting that holds the rotating mold 2 It accommodates a carriage 1, an electric motor 8 mounted on the casting carriage 1 as a driving apparatus for rotating the mold 2, a carriage driving apparatus 16 for moving the casting carriage 1 on the rail 11, and a molten metal 17. A triangular ladle 12 used as a pan, and a chute 13 and a trough 14 used as a pouring pot for relaying and supplying the molten metal 17 poured from the triangular ladle 12 to the inside of the mold 2 are provided. The mold 2 is cast together with the casting cart 1 and the triangular ladle using the cart driving device 16 while injecting the molten metal 17 from the tip of the trough 14 inserted deep inside the mold 2 rotating by the electric motor 8. Move to the other side of 12 By the injected molten metal 17 is sequentially solidify, manufactures centrifugal casting tube 18 directly from the molten metal 17.

  In the figure, reference numeral 5 is a pair of rotation support devices installed to fix the rotating mold 2 to the casting cart 1, and 6 is provided for supplying and discharging cooling water for cooling the mold 2. A pair of cooling water jackets, 7 is a pulley, 9 is a belt applied to the pulley 7 for transmitting the power of the electric motor 8, and 10 is a wheel. The core 15 forms the end face shape of the centrifugal cast pipe 18 to be manufactured, and prevents the molten metal 17 supplied from the trough 14 from leaking.

  As shown in FIGS. 2 and 3, the mold 2 includes a cylindrical mold body 3 that is a part that directly receives the molten metal 17, and a sleeve 4 provided on the outer periphery of the mold body 3. The gap between the mold body 3 and the sleeve 4 serves as a cooling water flow path. The cooling water supplied from one cooling water jacket 6 cools the mold body 3 through this gap and the other cooling water. The jacket 6 is discharged. The cooling water jacket 6 includes a water box 19 for supplying and discharging cooling water. The water box 19 is in close contact with the mold 2 via a plastic water sealing material 20, so that the cooling water jacket 6 is not leaked to the water box 19. The mold 2 can be rotated by joining. Reference numerals 21 and 22 in FIG. 3 are fixing hardwares for installing the mold body 3 at a predetermined position of the water box 19.

  In the present invention, as the mold body 3 constituting the mold 2, in mass%, C: 0.09 to 0.12%, Si: 0.20 to 0.30%, Mn: 0.30 to 0 .50%, P: 0.015% or less, S: 0.005% or less, Ni: 0.40% or less, Cr: 5.8 to 8.5%, Mo: 0.85 to 0.95%, Nb: 0.060 to 0.085%, V: 0.18 to 0.22%, Al: 0.015% or less, N: 0.040 to 0.065%, the balance being Fe and inevitable A mold body 3 made of chromium molybdenum steel, which is an impurity, is used.

This chromium-molybdenum steel is known as ASME T91 under the American Society of Mechanical Engineers standard name, and is a heat-resistant steel excellent in creep strength with a 10 ⁵ h creep strength at 600 ° C. exceeding 100 MPa. Moreover, since it is structurally a ferrite system, it is excellent in toughness and heat fatigue resistance. Furthermore, it is a material having a low carbon concentration and excellent weldability.

  Therefore, when the mold body 3 is made of chromium molybdenum steel having the above composition, heating and cooling are repeatedly applied each time the molten metal 17 is supplied to the inner surface of the mold body 3, and periodic thermal stress acts. However, cracks are unlikely to occur on the inner surface of the mold body 3, and as a result, the mold body 3 can be used stably over a long period of time while suppressing the occurrence of cracks.

  In addition, when a crack occurs on the inner surface of the mold body 3 due to long-term use, the mold body 3 having the same shape as the initial state is regenerated by depositing by overlay welding and then grinding the inner surface. can do. Since it has excellent weldability, no problems occur in repairing weld overlay. In areas where build-up repair is not possible, such as the central part of the mold body 3 away from the pipe end, build-up repair is not performed, and cracks are removed by internal grinding and are used again.

  Thus, according to the centrifugal casting mold 2 of the present invention, the mold body 3 made of ferritic chromium molybdenum steel having high high temperature strength and creep strength and excellent high temperature toughness and heat fatigue resistance is provided. Therefore, even if a periodic thermal stress is applied, cracks are unlikely to occur on the inner surface of the mold body 3, and as a result, the cracks can be suppressed and used stably over a long period of time. . Moreover, since it is excellent also in weldability, the overlay repair can be carried out without causing any problem. By these, the expense of the metal mold | die 2 can be reduced significantly and the reduction of the manufacturing cost of the centrifugal cast pipe 18 is achieved.

  In addition, this invention is not limited to the said description, A various change is possible. For example, the mold 2 incorporates the rotation support device 5 integrally. However, the rotation support device 5 may be disposed on the casting cart 1 and the mold 2 may be fitted therein. The shape does not need to be the shape shown in FIG. 3, and may be determined according to the outer shell of the centrifugal cast pipe to be cast.

It is the schematic of the centrifugal casting installation provided with the metal mold | die which concerns on this invention. It is a perspective view which shows schematic structure of the metal mold | die which concerns on this invention. It is sectional drawing of a part of metal mold | die which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Casting cart 2 Mold 3 Mold body 4 Sleeve 5 Rotation support device 6 Cooling water jacket 7 Pulley 8 Electric motor 9 Belt 10 Wheel 11 Rail 12 Triangle ladle 13 Chute 14 Trough 15 Core 16 Cart driving device 17 Molten metal 18 Centrifugal casting Pipe 19 Water box 20 Water seal material 21 Fixing hardware 22 Fixing hardware

Claims (1)

  A mold for centrifugal casting for casting a centrifugal casting pipe, in mass%, C: 0.09 to 0.12%, Si: 0.20 to 0.30%, Mn: 0.30 to 0.00. 50%, P: 0.015% or less, S: 0.005% or less, Ni: 0.40% or less, Cr: 5.8 to 8.5%, Mo: 0.85 to 0.95%, Nb : 0.060 to 0.085%, V: 0.18 to 0.22%, Al: 0.015% or less, N: 0.040 to 0.065%, the balance being Fe and inevitable impurities A mold for centrifugal casting comprising a mold body made of chromium molybdenum steel.

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