JP2882443B2 - Life extension method of metal frame for centrifugal casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for extending the life of a metal frame for centrifugal casting for producing cast iron tubes and the like.

[0002]

2. Description of the Related Art Conventionally, for example, as shown in FIG. 2, a metal frame 1 for centrifugal casting of a cast iron tube is usually made of cast steel, and a hot casting surface is prevented on its inner surface to provide a sound casting surface. To obtain it, a process called peening is applied. The inner surface of the peened centrifugal casting metal frame 1 is shown in FIGS.
As shown in FIG. 5, the surface has a plurality of hemispherical peening marks 2, and the peening marks 2 form a sound casting surface by preventing the molten metal from slipping.

[0003]

In the case of casting a cast iron pipe of, for example, φ75 to φ250 mm using the centrifugal casting metal frame 1 described above, it usually takes one to two days (about 600 times / day).
Day) After use, the centrifugal casting metal frame 1 is removed from the casting machine to perform maintenance work. The care was to grind the inner surface lightly and then peening again.

[0004] If cracks or the like are generated on the inner surface during repeated use of the centrifugal casting metal frame 1,
The metal frame life has expired and maintenance work is required. In the maintenance work, the inner surface of the centrifugal casting metal frame 1 was cut by lathing until no cracks were formed, then the weld was increased, and the inner diameter was again cut to the set inner diameter by lathing. This is generally called gold frame regeneration, and is usually 800
It is performed when it is used for casting about 0 times.

A centrifugal casting frame 1 for casting a cast iron pipe having a flange as shown in FIG.
Since cracks occur in part A on the day, partial reproduction is performed each time. The following can be considered as the reason for this.

[0006] 1. The portion A receives the heat of the molten metal from the two directions of the direction a and the direction b, so that the temperature tends to be particularly high. 2. The outer surface of the centrifugal casting metal frame 1 is in a low temperature state with water cooling, and the inner surface is alternately switched between a high temperature state and a low temperature state by repeatedly pouring the molten metal. Since the deformation due to the expansion is restricted, the generated stress increases.

An object of the present invention is to provide a method for extending the life of a metal frame for centrifugal casting, which can suppress the occurrence of cracks on the inner surface and extend the maintenance interval.

[0008]

In order to solve the above-mentioned problems, a method for extending the life of a metal frame for centrifugal casting according to the present invention comprises a plurality of hemispherical surfaces for peening the inner surface of the metal frame to prevent the molten metal from slipping. Forming a peening mark on the inside of the metal frame
Shot peening using a shot smaller in diameter than the peening trace is performed to plastically deform the inner surface of the metal frame to generate a compressive residual stress.

[0009]

According to the above construction, when the molten metal is poured into the inner surface of the metal frame in a state where the outer surface of the metal frame is cooled at the time of casting, the heat of the tensile force is applied to the inner surface of the metal frame by the difference in thermal expansion generated in the radial direction of the metal frame. Stress acts. On the other hand, in a state where the molten metal does not exist on the inner surface of the metal frame, the temperature difference between the outer surface and the inner surface of the metal frame becomes small, and thermal stress hardly acts. Therefore, since the tensile thermal stress repeatedly acts on the inner surface of the metal frame, thermal fatigue occurs and cracks occur.

Therefore, if plastic deformation is applied to the inner surface of the metal frame by shot peening, a compressive residual stress is generated on the inner surface of the metal frame, and the compressive residual stress opposes the tensile thermal stress, thereby improving the fatigue strength. In addition, the life of the metal frame can be extended by reducing thermal fatigue.

Further, unevenness is formed on the inner surface of the metal frame by peening (prevention of slipping of the molten metal), and the uneven shape becomes a source of cracks, which adversely affects the fatigue life of the metal frame. However, by performing shot peening after peening, the peening marks are not eliminated, but the inner surface of the uneven shape of the metal frame is relatively smoothly leveled, so that the number of cracks can be reduced.

[0012]

An embodiment of the present invention will be described below. Figure 2
Members having the same functions as those described with reference to FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, a plurality of hemispherical peening marks 2 are formed on the inner surface of a centrifugal casting metal frame 1 by peening in order to prevent the molten metal from slipping. This peening mark 2 is φ
It is about 1.5 mm.

[0013] Shot peening is applied to the inner surface of the peened centrifugal casting metal frame 1. As shot peening, for example, the diameter is 0.8 mm and the hardness is H _V 55.
A number of steel shots 3 having a spherical shape of 0 are made to collide with the inner surface of the metal frame at a speed of 60 m / s. As a result of the shot peening, the inner surface of the metal frame is plastically deformed to generate a compressive residual stress.
As described above, when the centrifugal casting metal frame subjected to peening and shot peening is used for casting, the compressive residual stress opposes the tensile thermal stress acting on the inner surface of the metal frame due to the pouring of the molten metal, and the fatigue strength is reduced. Therefore, thermal fatigue can be reduced, cracks can be suppressed, and the life of the metal frame can be prolonged. Further, abrasion of peening can be suppressed.

Further, peening (non-slip of molten metal)
As a result, the inner surface of the metal frame having an uneven shape is relatively smoothly leveled by shot peening, so that the number of crack sources can be reduced. In addition, since shot peening has a blast function, grinder processing as in the related art can be omitted.

As another embodiment, when the inner surface of the metal frame is hardened by nitriding or surface quenching in addition to shot peening, the fatigue strength can be further improved.

[0016]

As described above, according to the present invention, shot peening is performed after peening the inner surface of the metal frame to generate residual compressive stress due to plastic deformation on the inner surface of the metal frame. The fatigue strength is improved by the stress against the tensile thermal stress, and the thermal fatigue is reduced to extend the life of the metal frame. In addition, since the inner surface of the metal frame formed into an uneven shape by peening is relatively smoothly leveled by shot peening, the number of cracks can be reduced.
Further, since the peening wear can be suppressed, not only the life of the metal frame can be prolonged, but also the ordinary care work can be omitted.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating a method for extending the life of an embodiment of the present invention.

FIG. 2 is a sectional view of a centrifugal casting metal frame.

FIG. 3 is a sectional view of an inner surface of a metal frame.

FIG. 4 is a plan view of the inner surface of the metal frame.

[Explanation of symbols]

 1 Metal frame for centrifugal casting 2 Peening marks 3 Steel shot

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B22D 13/10 B22D 13/12

Claims (1)

(57) [Claims] (1) Peening the inner surface of a metal frame to melt
Form a plurality of hemispherical peening marks to prevent slipping , and then form a smaller diameter than the peening marks on the inner surface of the metal frame .
A method for extending the life of a metal frame for centrifugal casting, wherein shot peening using a shot is performed to plastically deform an inner surface of the metal frame to generate a compressive residual stress.