CN103182482A - Casting method for large double-phase steel impeller of million-kilowatt-class nuclear power station sea water circulating pump - Google Patents

Abstract

The invention discloses a casting method for a large double-phase steel impeller of a million-kilowatt-class nuclear power station sea water circulating pump. In the casting method, the appearance shrinkage rate is 2.5%, the inside shrinkage rate is 1.5%, the blade outlet shrinkage rate is 1.5%, and the blade inlet shrinkage rate is 0.1%; and the mold thickness of arbor does not exceed 50mm-70mm, feeding pasting inclination is 8%, the feeding distance of a dead head does not exceed 9 times of equivalent wall thickness of a casting piece, and the dead head enlargement coefficient f is equal to 1.35. A bottom casing way and a multi-in-gate equilibrium quick casting way are adopted; a molten steel guide plate is arranged for reducing thermal action of direct in-gates to the casting piece body; the molten steel is introduced from a position 165m from the bottommost part of the casting piece, and the mould charging time is controlled within 60 seconds; and a box opening temperature is lower than 250 DEG C. The casting method is used for solving the problem that a plurality of products are wasted due to deformation and flaws of a large casting impeller, so that much defect repairing work caused to the surface defects and the inherent defects is reduced, the production period is shortened and the production cost is reduced.

Description

The casting method of the large-scale dual phase steel impeller of million kilowatt nuclear power station sea water circulating pump

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Technical field

The present invention relates to a kind of casting method of steel impeller, be specifically related to the casting method of the large-scale dual phase steel impeller of million kilowatt nuclear power station sea water circulating pump.

Background technology

Nuclear power stations such as Ningde of China, Fuqing, Port of Fangcheng all adopt and the large-scale dual phase steel impeller of million kilowatt nuclear power station sea water circulating pump.Its specification: Φ 2730 * H1775, weight 8751kg, rated speed 176rpm/min, 40 years projected lives, material trademark GX2CrNiMoN25-6-3, chemical composition is as shown in table 1.

Table 1 impeller chemical composition (%)

C

Si

Mn

P

S

Cr

Ni

Mo

N

Ferrite

PRE

≤0.030

≤1.00

≤2.00

≤0.035

≤0.025

22.50~26.50

4.50~6.50

2.50~3.50

0.12~0.25

40~60

≥39

Conventional relatively foundry goods, the casting difficulty height of sea water circulating pump impeller mainly shows following 4 points:

(1) alloy content height (greater than 30%) in the material, it is long that melt remains on time of two-phase section when solidifying, and fluidity molten steel is poor, it is big to shrink, and easily produces defectives such as misrun, cold shut, shrinkage cavity, shrinkage porosite, crackle;

(2) impeller size is big, weight is big, and blade is thin, area is big and wall thickness change is inhomogeneous, easily forms defectives such as cold shut, shrinkage cavity, shrinkage porosite;

(3) the leaf curling angle is big, and the deflection at impeller center causes the resistance when shrinking to increase relatively, easily produces shrinkage stress, is easy to generate crackle in cooling procedure;

(4) for avoiding discontinuity equalization in the military service process, also very high to dimension precision requirement.

Domestic enterprise does not still possess the ability of producing this kind size two phase stainless steel impeller, it is the two phase stainless steel impeller of SS2377 that Wuhan Mechanical Technology Institute Co., Ltd. adopts craft of coating and laying Ceramic pulp ceramic mold hot investment casting, grouting method ceramic precision casting, resin sand, water-glass sand to mix casting technique manufacturing material, its weight only is 700kg, well below weight and the size of sea water circulating pump impeller.Harbin Engineering University also adopts the method for hot investment casting to produce the two phase stainless steel impeller of ZG0Cr25Ni5Mo2N, and this impeller also is small-sized impeller, can't meet the demands dimensionally.

Summary of the invention

The present invention aims to provide the casting method of the large-scale dual phase steel impeller of a kind of million kilowatt nuclear power station sea water circulating pump, the main technical problem of Xie Jueing: overcome thermal stress and deflation resistance cause in the casting process casting deformation, crackle, and then influence the problem of casting dimension; Overcome shrinkage porosite, shrinkage cavity problem that the casting feeding difficulty of dual phase steel material causes; Overcome defect problems such as slag inclusion that large thin wall casting cavity filling process complexity causes, misrun, prepare the large-scale dual phase steel impeller of satisfactory million kilowatt nuclear power station sea water circulating pump, satisfy the requirement of foundry goods internal soundness and dimensions.

Technical scheme of the present invention is as follows:

The casting method of the large-scale dual phase steel impeller of million kilowatt nuclear power station sea water circulating pump is characterized in that:

(1), smelts: adopt electric arc furnaces+AOD stove, perhaps electric arc furnaces+VOD stove;

(2), modelling: shrinkage: the profile reduced scale adopts 2.5%, inboard shrinkage 2.0%, blade exit shrinkage 1.5%, blade inlet shrinkage 1.0%;

(3), moulding: adopt furan no-bake resin sand, facing sand adopts chrome ore, and floor sand adopts quartz sand; The mold thickness of arbor is no more than 50～70mm, and the inboard foam that adds of arbor is to guarantee forming enough yielding spaces in the molten steel solidification contraction process;

(4), feeding: the subsidy gradient makes molten steel towards rising head direction consecutive solidification greater than 8%, and makes the feeding distance of rising head be no more than 9 times of foundry goods equivalence wall thickness; Adopt rising head sampling factor f=1.35, rising head can be shunk the foundry goods molten steel effectively compensate;

(5), cast: adopt the balanced pouring type fast of bottom filling, many ingates, eight places of the corresponding downside of eight place's ingates

Rising head, and the molten steel lead-in plate is set to reduce direct ingate to the heat effect of foundry goods body, molten steel is from highly locating introducing apart from foundry goods bottommost 165mm, and filling time was controlled in 60 seconds;

(6), unpack: unpacking temperature is lower than 250 ℃.

Good effect of the present invention is: the present invention is mainly from inherent quality, channel size, cavity filling process and the reduction stress aspect of foundry goods, integrated application by aspects such as different model shrinkages, big system of risers, rising pouring running gate system and the measures of processing sand mold deformability, finally satisfied the requirement of foundry goods internal soundness and dimensions, produce 30 products, waste product do not occurred.The application of this casting method has solved the massive casting impeller because the large-tonnage product that distortion and crackle bring is scrapped problem, and has reduced a large amount of defect repair work that surface and latent defect are brought, and has shortened the production duration, reduces production costs.Solved the production domesticization difficult problem of million kilowatt sea water circulating pump impeller.

Description of drawings

Fig. 1 is feeding design diagram of the present invention.

Fig. 2 is that running gate system is arranged.

Fig. 3 is ingate structural representation of the present invention.

The specific embodiment

Further specify the present invention below in conjunction with drawings and Examples.

(1), smelts: adopt electric arc furnaces+AOD stove, perhaps electric arc furnaces+VOD stove.

(2), modelling: shrinkage: the profile reduced scale adopts 2.5%, inboard shrinkage 2.0%, blade exit shrinkage 1.5%, blade inlet shrinkage 1.0%.The gateway spot size of blade and surface quality require high, an amount of corresponding distortion and the polishing amount of increasing.

(3), moulding: adopt furan no-bake resin sand, facing sand adopts chrome ore, and floor sand adopts quartz sand.Strengthen the deformability of sand mold and core, especially will fully reduce the deformability of core, make the mold thickness of arbor can not surpass 50～70mm, a large amount of foam of the inboard adding of arbor is to guarantee forming enough yielding spaces in the molten steel solidification contraction process.

(4), feeding: do not have shrinkage porosite class defective for guaranteeing the foundry goods interior solid, adopt the subsidy gradient greater than 8%, make molten steel towards rising head direction consecutive solidification, and make the feeding distance of rising head be no more than 9 times of foundry goods equivalence wall thickness; Adopt rising head sampling factor f=1.35, rising head can be shunk the foundry goods molten steel effectively compensate.

As shown in Figure 1, after molten steel filled the type end, the thinnest part blade at first solidified, and eight side risers are used for the molten steel contraction of compensation lower cover; The molten steel that the top annular rising head is used for the compensation upper cover plate shrinks.

(5), cast: require molten steel to fill type and want steady, rapid, avoid the oxidation of molten steel in the casting process and pollution again.For this reason, the present invention adopts the balanced pouring type fast of bottom filling, many ingates, eight place's rising heads of the corresponding downside of eight place's ingates

Molten steel lead-in plate (reducing direct ingate to the heat effect of foundry goods body) is set, and molten steel is from highly locating introducing apart from foundry goods bottommost 165mm, and filling time is controlled in 60 seconds, as shown in Figure 2.

As Fig. 3, molten steel flows up into lead-in plate over against side riser by ingate, enters the foundry goods die cavity through lead-in plate.

(6), unpack: for preventing causing distortion because of thermal stress in the cooling procedure and ftracture that the unpacking temperature of control is lower than 250 ℃.

Claims (1)

1. the casting method of the large-scale dual phase steel impeller of million kilowatt nuclear power station sea water circulating pump is characterized in that:

(1), smelts: adopt electric arc furnaces+AOD stove, perhaps electric arc furnaces+VOD stove;

(2), modelling: shrinkage: the profile reduced scale adopts 2.5%, inboard shrinkage 2.0%, blade exit shrinkage 1.5%, blade inlet shrinkage 1.0%;

(3), moulding: adopt furan no-bake resin sand, facing sand adopts chrome ore, and floor sand adopts quartz sand; The mold thickness of arbor is no more than 50～70mm, and the inboard foam that adds of arbor is to guarantee forming enough yielding spaces in the molten steel solidification contraction process;

(4), feeding: the subsidy gradient makes molten steel towards rising head direction consecutive solidification greater than 8%, and makes the feeding distance of rising head be no more than 9 times of foundry goods equivalence wall thickness; Adopt rising head sampling factor f=1.35, rising head can be shunk the foundry goods molten steel effectively compensate;

(5), cast: adopt the balanced pouring type fast of bottom filling, many ingates, eight places of the corresponding downside of eight place's ingates

Rising head, and the molten steel lead-in plate is set to reduce direct ingate to the heat effect of foundry goods body, molten steel is from highly locating introducing apart from foundry goods bottommost 165mm, and filling time was controlled in 60 seconds;

(6), unpack: unpacking temperature is lower than 250 ℃.

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