A method for reducing cracks on the inner surface of a hot mold

Abstract

A method for reducing cracks on the inner surface of a hot mold, comprising the steps of: S1, diluting a first repair material powder with a binder into a slurry, and applying it to the cracks on the inner surface of the hot mold; S2, heating the first repair material powder in step S1 to dry and solidify it; S3, spraying a release agent on the inner surface of the hot mold obtained in step S2 and casting a product, and the first repair material powder is sintered; S4, after the hot mold in step S3 is cast for several times, diluting a second repair material powder with a binder into a slurry, and applying it to the cracks generated by the sintering of the first repair material powder on the inner surface of the hot mold; S5, heating the second repair material powder applied in step S4 to dry and solidify it; S6, spraying a release agent on the inner surface of the hot mold obtained in step S5 and casting a product, and the second repair material powder is sintered. The present invention combines the repair of cracks on the inner surface of the hot mold with the working process of the hot mold, transforming heterogeneous repair into basically homogeneous repair, which is simple and energy-saving.

Description

Technical Field

[0001] The invention relates to the technical field of casting mold maintenance, in particular to a method for reducing cracks on the inner surface of a hot mold. Background Art

[0002] The hot mold used for centrifugally cast ductile iron pipes is subjected to the thermal stress of cast iron liquid and the temperature difference between the inside and outside for a long time. After long-term use, cracks will appear on the inner surface. When the cracks develop and accumulate to a certain extent, the mold needs to be repaired or scrapped.

[0003] At present, for hot molds that do not need to be patched and repaired, nano powders are used to fill and repair the cracks on the inner surface. The general procedure of this repair is: pulping - filling - sintering - heat treatment. Among the two heating steps of sintering and heat treatment, at least the sintering step requires the use of a special inner surface heating tool. Although heat treatment can be carried out with the aid of an annealing furnace, it also consumes a lot of time and energy. Moreover, even after the above-mentioned complete repair procedure, the expected repair effect may not be achieved. This depends to a large extent on the repair powder and sintering process used. Summary of the invention

[0004] In order to solve the problems in the background technology, the present invention provides a method for reducing cracks on the inner surface of a hot mold, which combines the repair of cracks on the inner surface of the hot mold with the working process of the hot mold, and achieves the purpose of repairing and reducing cracks on the inner surface of the hot mold in steps. The process difficulty is further reduced by transforming heterogeneous repair into near-homogeneous repair.

[0005] The technical solution of the present invention is as follows:

[0006] A method for reducing cracks on the inner surface of a hot mold comprises the following steps:

[0007] S1, diluting the first repair material powder with a binder into a slurry, and applying it to the cracks on the inner surface of the hot mold;

[0008] S2, heating the first repair material powder coated on the cracks on the inner surface of the hot mold in step S1 to dry and solidify it;

[0009] S3, spraying a release agent on the inner surface of the hot mold obtained in step S2 and casting the product, and sintering the first repair material powder by the high temperature during casting;

[0010] S4, after the hot mold is cast for several times in step S3, the second repair material powder is diluted with a binder to form a slurry, and is applied to the cracks on the inner surface of the hot mold generated after the first repair material powder is sintered;

[0011] S5, heating the second repair material powder coated on the sintered cracks of the first repair material powder in step S4 to dry and solidify it;

[0012] S6, spraying a release agent on the inner surface of the hot mold obtained in step S5 and casting the product, and sintering the second repair material powder by the high temperature during casting.

[0013] Further, in the method for reducing cracks on the inner surface of a hot mold as described above, in step S4, the several times is 1-20 times, preferably 5-10 times.

[0014] Further, in the method for reducing cracks on the inner surface of a hot mold as described above, the cast product is a ductile iron pipe.

[0015] Further, in the method for reducing cracks on the inner surface of a hot mold as described above, the release agent is a zircon powder release agent or a composite release agent with a zircon powder content greater than 65%.

[0016] Further, in the above-mentioned method for reducing cracks on the inner surface of a hot mold, the average particle size of the second repair material powder is not greater than 0.6 times the average particle size of the first repair material powder.

[0017] Furthermore, in the above-mentioned method for reducing cracks on the inner surface of a hot mold, the first repair material powder and the second repair material powder may contain metal powder and ceramic powder.

[0018] Further, in the method for reducing cracks on the inner surface of a hot mold as described above, the first repair material powder and the second repair material powder are composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.1-0.3.

[0019] Further, in a method for reducing cracks on the inner surface of a hot mold as described above, the first repair material powder is composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.1-0.2; the second repair material powder is composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.2-0.3, and the mass proportion of ceramic powder in the second repair material powder is higher than the mass proportion of ceramic powder in the first repair material powder.

[0020] Further, in the method for reducing cracks on the inner surface of a hot mold as described above, the average particle size of the metal powder in the first repair material powder is 20-74 μm, the average particle size of the ceramic powder is 0.01-0.6 μm, and the average particle size of the metal powder in the second repair material powder is 10-44 μm, the average particle size of the ceramic powder is 0.01-0.6 μm.

[0021] Further, in the method of reducing cracks on the inner surface of a hot mold as described above, the average particle size of the ceramic powder in the first repair material powder is greater than the average particle size of the ceramic powder in the second repair material powder, or the average particle size of the ceramic powder in the first repair material powder and the second repair material powder is the same.

[0022] The beneficial effects of the present invention are:

[0023] The method for reducing cracks on the inner surface of a hot mold provided by the present invention eliminates the two most complex and energy-consuming steps in a normal repair procedure, combines the sintering of cracks on the inner surface of the hot mold with the working process of the hot mold, and does not need to consider a one-time sintering and annealing of the sintered material to obtain a crack-free repair effect. Instead, the hot mold base is first heterogeneously repaired by a first repair material powder, and then the first repair material sintered body is basically homogeneously repaired by a second repair material powder, making the secondary repair simple, thereby achieving the purpose of repairing and reducing cracks on the inner surface of the hot mold in steps with the simplest process, the fastest effect, and the least labor and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart of the method for reducing cracks on the inner surface of a hot mold. DETAILED DESCRIPTION

[0025] Example 1

[0026] A method for reducing cracks on the inner surface of a hot mold. The hot mold in this embodiment is a tubular hot mold used for centrifugal casting of ductile iron pipes, and the cast product is a ductile iron pipe.

[0027] Specifically, the method comprises the following steps:

[0028] S1, diluting a first repair material powder composed of metal powder and ceramic powder with a binder to form a slurry, and applying the slurry to the cracks on the inner surface of the hot mold;

[0029] S2, heating the first repair material powder coated on the cracks on the inner surface of the hot mold in step S1 to dry and solidify it;

[0030] S3, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S2 and casting the product, and sintering the first repair material powder by the high temperature during casting;

[0031] S4, after the hot mold casting product in step S3 is performed 5-10 times, the second repair material powder which is also composed of metal powder and ceramic powder is diluted into slurry with a binder, and coated on the cracks generated after the first repair material powder is sintered on the inner surface of the hot mold. The average particle size of the second repair material powder in this step is not greater than 0.6 times the average particle size of the first repair material powder in the previous step, but the average particle size of the ceramic powder therein can be the same;

[0032] S5, heating the second repair material powder coated on the sintered cracks of the first repair material powder in step S4 to dry and solidify it;

[0033] S6, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S5 and casting the product, and sintering the second repair material powder by the high temperature during casting.

[0034] The zircon powder release agent sprayed in the above embodiment may also be a composite release agent with a zircon powder content greater than 65%.

[0035] In the above embodiments, the first repair material powder and the second repair material powder are preferably composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.1-0.3.

[0036] In the above embodiments, the heating in step S2 or step S5 is not limited to the heating temperature reaching only the heating temperature for removing the organic binder component, but is more preferably heated to a temperature above 200°C, especially above 300°C but not exceeding 650°C, preferably not exceeding 550°C, so that the repair material powder can be more tightly combined on the basis of sufficient degreasing and exhaust (the powder particles are slightly adhered but not to the extent of sintering).

[0037] The method for reducing cracks on the inner surface of a hot mold provided by the above-mentioned embodiment of the present invention eliminates the two most complex and energy-consuming steps of sintering and annealing in the normal repair procedure introduced in the background technology, and combines the sintering of cracks on the inner surface of the hot mold with the working process of the hot mold, and directly utilizes the pouring heat to realize the sintering of the repair material powder when pouring the product. Moreover, since the repair of the cracks is divided into at least two steps, there is no need to consider sintering and annealing the sintered material at one time to obtain a crack-free repair effect. Instead, the first repair material powder is used to perform heterogeneous repair on the hot mold substrate, and then the second repair material powder is used to perform basically homogeneous repair on the sintered body of the first repair material, so that the secondary repair becomes simple, thereby achieving the purpose of repairing and reducing cracks on the inner surface of the hot mold in steps with the simplest process, the fastest effect, and the least labor and energy consumption.

[0038] It should be noted that the method steps of the present invention are open, and in particular are not limited to termination at step S6. It does not exclude the possibility of continuing after step S6 through a repeated third slurry coating - drying and sintering - product pouring procedure to further reduce cracks on the inner surface of the hot mold according to the means disclosed in the above steps.

[0039] Example 2

[0040] A method for reducing cracks on the inner surface of a hot mold as in Example 1 comprises the following steps:

[0041] S1, diluting a first repair material powder composed of metal powder and ceramic powder with a binder into a slurry, and applying the slurry to the cracks on the inner surface of the hot mold, wherein the first repair material powder is composed of mold steel powder, iron-nickel alloy powder and zirconia ceramic powder in a mass ratio of 1:0.2-0.4:0.1-0.2, the mold steel powder and the iron-nickel alloy powder have an average particle size of 20-74 μm, and the zirconia ceramic powder has an average particle size of 0.01-0.6 μm;

[0042] S2, heating the first repair material powder coated on the cracks on the inner surface of the hot mold in step S1 to dry and solidify it, the heating temperature being 400-500° C.;

[0043] S3, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S2 and casting the product, and sintering the first repair material powder by the high temperature during casting;

[0044] S4, after the hot mold casting product in step S3 is performed 5-10 times, the second repair material powder which is also composed of metal powder and ceramic powder is diluted into a slurry with a binder, and is coated on the cracks generated after the first repair material powder is sintered on the inner surface of the hot mold, wherein the second repair material powder is still composed of mold steel powder, iron-nickel alloy powder and zirconia ceramic powder. After the first repair on the hot mold substrate, the mass proportion of ceramic powder in the second repair material powder can be increased, and the second repair material powder can be composed of mold steel powder, iron-nickel alloy powder and zirconia ceramic powder in a mass ratio of 1:0.2-0.4:0.2-0.3, the average particle size of the mold steel powder and the iron-nickel alloy powder is 10-44μm, and the average particle size of the zirconia ceramic powder is 0.01-0.6μm;

[0045] S5, heating the second repair material powder coated on the sintered cracks of the first repair material powder in step S4 to dry and solidify it;

[0046] S6, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S5 and casting the product, and sintering the second repair material powder by the high temperature during casting.

[0047] Example 3

[0048] A method for reducing cracks on the inner surface of a hot mold as in Example 2 comprises the following steps:

[0049] S1, diluting a first repair material powder composed of metal powder and ceramic powder with a binder into a slurry, and applying the slurry to the cracks on the inner surface of the hot mold, wherein the first repair material powder is composed of mold steel powder, iron-nickel alloy powder and zirconia ceramic powder in a mass ratio of 1:0.3:0.15, the mold steel powder and the iron-nickel alloy powder have an average particle size of 44 μm, and the zirconia ceramic powder has an average particle size of 0.3 μm;

[0050] S2, heating the first repair material powder coated on the cracks on the inner surface of the hot mold in step S1 to dry and solidify it, the heating temperature is 450° C.;

[0051] S3, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S2 and casting the product, and sintering the first repair material powder by the high temperature during casting;

[0052] S4, after the hot mold in step S3 is cast for 6 times, a second repair material powder which is also composed of metal powder and ceramic powder is diluted into a slurry with a binder, and coated on the cracks on the inner surface of the hot mold generated after the first repair material powder is sintered, wherein the second repair material powder is composed of mold steel powder, iron-nickel alloy powder and zirconia ceramic powder in a mass ratio of 1:0.3:0.25, the mold steel powder and the iron-nickel alloy powder have an average particle size of 20 μm, and the zirconia ceramic powder has an average particle size of 0.2 μm;

[0053] S5, heating the second repair material powder coated on the sintered crack of the first repair material powder in step S4 to dry and solidify it, the heating temperature is 450° C.;

[0054] S6, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S5 and casting the product, and sintering the second repair material powder by the high temperature during casting.

[0055] Although it is mentioned in Example 1 that there is no restriction on continuing to repeat a third slurry coating - drying and sintering - product pouring procedure after step S6 to further reduce the cracks on the inner surface of the hot mold, it has been verified by the above examples that after only two crack repairs from S1 to S6, no obvious new cracks are generated, which shows that the second crack repair has a very good repair effect.

[0056] Example 4

[0057] A method for reducing cracks on the inner surface of a hot mold in this embodiment includes the following steps:

[0058] S1, diluting a first repair material powder composed of metal powder and ceramic powder with a binder into a slurry, and applying the slurry to the cracks on the inner surface of the hot mold, wherein the first repair material powder is composed of mold steel powder, iron-nickel alloy powder and composite ceramic powder in a mass ratio of 1:0.3:0.15, the mold steel powder and the iron-nickel alloy powder have an average particle size of 44 μm, and the composite ceramic powder is composed of alumina ceramic powder and zirconia ceramic powder in a mass ratio of 4:1, and has an average particle size of 0.3 μm;

[0059] S2, heating the first repair material powder coated on the cracks on the inner surface of the hot mold in step S1 to dry and solidify it, the heating temperature is 450° C.;

[0060] S3, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S2 and casting the product, and sintering the first repair material powder by the high temperature during casting;

[0061] S4, after the hot mold in step S3 is cast for 6 times, a second repair material powder which is also composed of metal powder and ceramic powder is diluted into a slurry with a binder, and coated on the cracks on the inner surface of the hot mold generated after the first repair material powder is sintered, wherein the second repair material powder is composed of mold steel powder, iron-nickel alloy powder and zirconia ceramic powder in a mass ratio of 1:0.3:0.25, the mold steel powder and the iron-nickel alloy powder have an average particle size of 20 μm, and the zirconia ceramic powder has an average particle size of 0.2 μm;

[0062] S5, heating the second repair material powder coated on the sintered crack of the first repair material powder in step S4 to dry and solidify it, the heating temperature is 450° C.;

[0063] S6, spraying zircon powder release agent on the inner surface of the hot mold obtained in step S5 and casting the product, and sintering the second repair material powder by the high temperature during casting.

[0064] In this embodiment, on the basis of Embodiment 3, the ceramic powder in the first repair material powder is changed to be mainly alumina ceramic, and the rest remains unchanged, except for the introduction of the composite ceramic reinforcement phase. Also, since the repair surface of the crack on the hot mold body is a relatively larger repair surface for the first repair, the thermal expansion coefficient after the introduction of alumina ceramic can also be sufficiently different from the zircon powder release agent component currently used, and the mass proportion of alumina ceramic powder in the composite ceramic powder can also be adjusted, generally close to or greater than 70%.

[0065] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for reducing cracks on the inner surface of a hot mold, characterized in that: The steps include: S1, diluting the first repair material powder with a binder into a slurry, and applying it to the cracks on the inner surface of the hot mold; S2, heating the first repair material powder coated on the cracks on the inner surface of the hot mold in step S1 to dry and solidify it; S3, spraying a release agent on the inner surface of the hot mold obtained in step S2 and casting the product, and sintering the first repair material powder by the high temperature during casting; S4, after the hot mold is cast for several times in step S3, the second repair material powder is diluted with a binder to form a slurry, and is applied to the cracks on the inner surface of the hot mold generated after the first repair material powder is sintered; S5, heating the second repair material powder coated on the sintered cracks of the first repair material powder in step S4 to dry and solidify it; S6, spraying a release agent on the inner surface of the hot mold obtained in step S5 and casting the product, and sintering the second repair material powder by the high temperature during casting; The first repair material powder and the second repair material powder are composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.1-0.

3.

2. A method for reducing cracks on the inner surface of a hot mold according to claim 1, characterized in that: In step S4, the number of times is 1-20 times.

3. A method for reducing cracks on the inner surface of a hot mold according to claim 2, characterized in that: The several times is 5-10 times.

4. A method for reducing cracks on the inner surface of a hot mold according to claim 1, characterized in that: The cast product is a ductile iron pipe.

5. A method for reducing cracks on the inner surface of a hot mold according to claim 4, characterized in that: The release agent is a zircon powder release agent or a composite release agent with a zircon powder content greater than 65%.

6. A method for reducing cracks on the inner surface of a hot mold according to claim 1, characterized in that: The average particle size of the second repair material powder is not greater than 0.6 times the average particle size of the first repair material powder.

7. A method for reducing cracks on the inner surface of a hot mold according to claim 1, characterized in that: The first repair material powder is composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.1-0.2; the second repair material powder is composed of mold steel powder, iron-nickel alloy powder and ceramic powder in a mass ratio of 1:0.2-0.4:0.2-0.3, and the mass proportion of ceramic powder in the second repair material powder is higher than the mass proportion of ceramic powder in the first repair material powder.

8. A method for reducing cracks on the inner surface of a hot mold according to claim 1 or 7, characterized in that: The average particle size of the metal powder in the first repair material powder is 20-74 μm, and the average particle size of the ceramic powder is 0.01-0.6 μm. The average particle size of the metal powder in the second repair material powder is 10-44 μm, and the average particle size of the ceramic powder is 0.01-0.6 μm.

9. A method for reducing cracks on the inner surface of a hot mold according to claim 8, characterized in that: The average particle size of the ceramic powder in the first repair material powder is greater than the average particle size of the ceramic powder in the second repair material powder, or the average particle size of the ceramic powder in the first repair material powder and the second repair material powder is the same.

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