A chemical cleaning method for shells

Abstract

A chemical cleaning method for mold shells belongs to the field of silica sol mold shell cleaning technology. The chemical cleaning method includes the following steps: S.1: preparing a strong alkaline aqueous solution as a cleaning matrix, and preparing alcohols and / or ketones as cleaning accelerators; S.2: using the cleaning solution prepared by the cleaning matrix and the cleaning accelerators to clean the mold shell until the desired cleaning effect is achieved. This method can improve cleaning efficiency, reduce the leaching of chromium from stainless steel, and reduce environmental pollution.

Description

Technical Field

[0001] This invention belongs to the field of silica sol shell cleaning technology, specifically relating to a chemical cleaning method for shells. Background Technology

[0002] For castings with structures such as deep grooves, fine deep holes, blind holes and complex internal cavities, their silica sol shells (cores) are difficult to clean using mechanical or physical methods. Existing technologies usually employ strong alkaline chemical cleaning processes, which utilize alkali to react chemically with the material in the shell to generate soluble substances, thereby achieving the purpose of cleaning the shell (core).

[0003] However, this process is not without its flaws, which are mainly reflected in the following aspects:

[0004] ① The cleaning time is long, often requiring 7 to 8 hours to achieve the desired cleaning effect;

[0005] ② Prolonged cleaning with strong alkalis can cause chromium in stainless steel to dissolve, leading to environmental pollution. Summary of the Invention

[0006] To address the aforementioned technical problems, this application further improves existing silica sol shell cleaning methods, aiming to enhance cleaning efficiency and reduce chromium leaching from stainless steel. The objective of this invention is to provide a chemical cleaning method for shells.

[0007] The specific technical solutions are explained below:

[0008] A chemical cleaning method for shells includes the following steps:

[0009] S.1: Prepare a strong alkaline aqueous solution as a cleaning matrix, and prepare alcohols and / or ketones as cleaning promoters;

[0010] S.2: The shell is cleaned using a cleaning solution prepared by the cleaning matrix and the cleaning accelerator until the desired cleaning effect is achieved.

[0011] The invention primarily addresses the cleaning of silica sol mold shells. The cleaning method utilizes an alkali to react chemically with the material in the shell, generating a soluble substance, thereby completing the cleaning process. Taking sodium hydroxide as an example, the main chemical reaction formula for cleaning is:

[0012] 2NaOH + mSiO2= Na2OmSiO2+ H2O;

[0013] Na2O•mSiO2+ nH2O = mSiO2•(n-1)H2O + 2Na + +2OH - .

[0014] The chemical cleaning process of alkali cleaning consists of two stages: the first is the chemical reaction between the shell (core) material and the alkali at the interface to generate soluble reaction products (Na2O•mSiO2); the second is the diffusion of these reaction products from the interface into the alkali solution. Therefore, the overall rate of chemical cleaning is related to both the interfacial reaction rate and the diffusion rate of the reaction products.

[0015] The inventors, after analysis, believe that the main reasons for the long time and low efficiency of alkali cleaning in the prior art should include at least the following factors:

[0016] On the one hand, the reaction product (Na2O•mSiO2) forms an isolation layer that separates the shell from the alkaline solution, preventing them from continuing to react directly; if the reaction is to continue, the alkaline solution must permeate through the thin film of the reaction product.

[0017] On the other hand, this reaction takes place at the interface, where other components besides SiO2 are present. Therefore, the chemical reaction is selective. Initially, the reaction can proceed on the surface, but as the reaction time increases, the thickness of the reaction product film increases. Simultaneously, the reaction often concentrates in the pores formed by the dissolved SiO2 in the shell, where the reaction products block the channels for further reaction. Therefore, for the alkaline solution to continue reacting with SiO2, it must overcome the surface tension within these pores.

[0018] Thirdly, the gel precipitation process of the reaction product Na2O•mSiO2 is relatively slow. From the perspective of chemical reaction equilibrium, the slow gel precipitation process is not conducive to the forward progress of the cleaning reaction, thus resulting in a longer cleaning time.

[0019] Based on the above analysis and understanding of the technical problems, the inventors added alcohols and / or ketones to the alkaline cleaning solution as cleaning promoters. Their promoting effect is mainly reflected in:

[0020] ① The cleaning accelerator can change the surface tension of the cleaning liquid at the pores of the reaction product, making it easier for the alkali to penetrate / act on the area to be cleaned on the shell, thereby accelerating the cleaning speed;

[0021] ② The cleaning accelerator can promote the gelation and precipitation of silica gel particles (Na2O•mSiO2) to generate mSiO2•(n-1)H2O, thereby promoting the chemical reaction of cleaning to the unbalanced side and accelerating the cleaning speed.

[0022] ③ Alcohols can form hydrogen bonds with water, reducing the content of free water and thus promoting product gelation, which also speeds up the cleaning process.

[0023] Therefore, the above technical solution can reduce cleaning time and improve cleaning efficiency, thereby reducing the leaching of chromium from stainless steel and mitigating environmental pollution.

[0024] Ketones can generate alcohols in an alkaline environment, thus achieving the same effect.

[0025] Preferably, the strong alkaline aqueous solution is an aqueous solution of sodium hydroxide and / or potassium hydroxide with a mass content of 30-60%, which can form a suitable alkalinity. If the alkalinity is too weak, the cleaning effect will be poor; if the alkalinity is too strong, the cleaning solution will be too corrosive, which puts forward higher requirements for the corrosion resistance of the cleaning container and accelerates the dissolution of chromium in stainless steel.

[0026] Preferably, the mass of the cleaning accelerator is 0.1-2% of the cleaning matrix. As a cleaning accelerator, only a small amount needs to be added to achieve a good effect of reducing cleaning time.

[0027] Preferably, the cleaning accelerator is ethanol and / or acetone.

[0028] Preferably, the mass of the cleaning accelerator is 0.3 to 0.5% of the cleaning matrix. At this amount, the shell cleaning time is relatively minimized.

[0029] Preferably, when cleaning the shell, the shell is first immersed in the cleaning matrix, and then the cleaning accelerator is added; or, the cleaning matrix and the cleaning accelerator are first mixed to form a cleaning solution, and then the shell is first immersed in the cleaning solution.

[0030] Preferably, the shell is cleaned by boiling.

[0031] Preferably, the cleaning time for the shell is 1 to 2 hours.

[0032] Preferably, the cleaning time for the shell is less than 1 hour.

[0033] In summary, the technical solution described in this invention has the following main beneficial effects:

[0034] Compared with existing technologies, the technical solution of the present invention can reduce cleaning time and improve cleaning efficiency, thereby reducing the leaching of chromium from stainless steel and mitigating environmental pollution.

[0035] At the same time, the inventors also optimized the dosage of the cleaning accelerator.

[0036] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Detailed Implementation

[0037] The present invention will be further explained in conjunction with the embodiments:

[0038] The core technical problem faced by the technical solution of the embodiments of this application stems from the inventor's accurate understanding of the prior art. Therefore, how to reduce cleaning time and improve cleaning efficiency is a technical problem that the inventor urgently needs to solve.

[0039] At the same time, reducing the leaching of chromium from stainless steel and mitigating environmental pollution are also technical problems that the inventors need to solve simultaneously.

[0040] It should be noted that the embodiments do not constitute a limitation on the scope of protection of the claims of this invention. All technical solutions that can be reasonably expected by those skilled in the art based on the technical concepts provided / proved by the embodiments should be covered within the scope of protection of the claims of this invention.

[0041] The specific implementation examples are detailed below:

[0042] Example 1:

[0043] The chemical cleaning method for silica sol shells comprises the following steps:

[0044] S.1: Prepare a 45% (w / w) NaOH solution as the cleaning matrix, and prepare 0.05% (w / w) ethanol as the cleaning accelerator for the cleaning matrix;

[0045] S.2: NaOH solution and ethanol are mixed to form a cleaning solution. The shell is then immersed in the cleaning solution and boiled for 135 minutes to achieve the desired cleaning effect.

[0046] The main chemical reaction formula for cleaning in this embodiment is:

[0047] 2NaOH + mSiO2 = Na2OmSiO2 + H2O

[0048] Na2O•mSiO2+ nH2O = mSiO2•(n-1)H2O + 2Na + +2OH -

[0049] The silica sol shell in this embodiment comes from a precision investment casting company in Ningbo.

[0050] In this embodiment, the standard / method for achieving the expected cleaning effect of the shell is as follows: the shell cleaning effect is determined according to the principle of the standard method of HB5353.6-2004, and the cleaning time is expressed as the time when the shell is completely dissolved.

[0051] The only difference between Examples 2-15 and Example 1 lies in the selection, content, and cleaning parameters of the reagents used in the chemical cleaning method, as detailed in Table 1 below:

[0052] Table 1. Selection, content, and cleaning parameters of reagents in the chemical cleaning methods of Examples 1-15

[0053]

[0054] As shown in Table 1, in Examples 1-12, using ethanol as a cleaning promoter, the cleaning time initially decreased and then increased with increasing ethanol content. This may be because, in the initial stage, the effect of ethanol in promoting alkali penetration and gel particle precipitation also increases simultaneously with increasing ethanol content. When the ethanol content exceeds a certain value, the free water molecules between gel particles further decrease to a critical state, causing the particles to aggregate, lose fluidity, and become solid precipitates. This prevents the penetration of the reaction solution and the diffusion of reaction products, thus having an adverse effect on cleaning.

[0055] The cleaning time is shortest when the ethanol content is 0.3-0.5%, less than one hour; while the cleaning time is more than two hours when the ethanol content is 0.05% or 2.1%.

[0056] As can be seen from Examples 13 and 14, the amount of sodium hydroxide also affects the cleaning time. A comparison between Examples 13 and 5 shows that when the concentration of sodium hydroxide is reduced to 30%, the cleaning time is extended. A comparison between Examples 13 and 5 shows that when the concentration of sodium hydroxide is increased to 60%, the cleaning time is reduced, but the reduction is very small and can be ignored.

[0057] A comparison of Examples 15 and 5 shows that when sodium hydroxide is replaced with potassium hydroxide, the shell cleaning time remains almost unchanged.

[0058] The difference between Examples 16-27 and Example 1 lies in that the shell is first immersed in the cleaning matrix, then acetone is added, and the content of reagents and cleaning parameters in the chemical cleaning method are as follows: See Table 2 below for details:

[0059] Table 2. Selection of reagents, content, and cleaning parameters in the chemical cleaning methods of Examples 16-27

[0060]

[0061] As shown in Table 2, in Examples 16-27, when acetone was used as a cleaning promoter, the cleaning time also showed a trend of first decreasing and then increasing as the content of acetone increased. However, under the same conditions, the cleaning time was slightly increased compared to ethanol.

[0062] The cleaning time is shortest when the acetone content is 0.3-0.5%, less than or equal to one hour; while the cleaning time is more than two hours when the acetone content is 0.05% or 2.1%.

[0063] Comparative example:

[0064] Compared to Examples 1-12 and 16-27, the difference is that no ethanol or acetone was added as a cleaning accelerator. The cleaning time of the comparative example was 410 minutes, which is nearly seven hours. It can be seen that the cleaning accelerator in the examples can significantly reduce the cleaning time and improve the cleaning efficiency.

[0065] This reduces the leaching of chromium from stainless steel containers, which is beneficial for environmental protection.

[0066] In the description of this specification, the references to terms such as "embodiment," "basic embodiment," "preferred embodiment," "other embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0067] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0068] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A chemical cleaning method for silica sol mold shells, characterized in that, The steps include the following: S.1: Prepare a strong alkaline aqueous solution as a cleaning matrix, and prepare alcohols and / or ketones as cleaning accelerators, wherein the cleaning accelerators are ethanol and / or acetone, and the mass of the cleaning accelerators is 0.3~0.5% of the cleaning matrix; S.2: The shell is cleaned using a cleaning solution prepared by the cleaning matrix and the cleaning accelerator until the desired cleaning effect is achieved.

2. The chemical cleaning method according to claim 1, characterized in that: The strong alkaline aqueous solution is an aqueous solution of sodium hydroxide and / or potassium hydroxide with a mass content of 30-60%.

3. The chemical cleaning method according to claim 1, characterized in that: When cleaning the shell, the shell is first immersed in the cleaning matrix, and then the cleaning accelerator is added.

4. The chemical cleaning method according to claim 1, characterized in that: The cleaning matrix is ​​first compounded with the cleaning accelerator to form a cleaning solution, and then the shell is immersed in the cleaning solution.

5. The chemical cleaning method according to claim 3 or 4, characterized in that: The shell is cleaned by boiling.

6. The chemical cleaning method according to claim 5, characterized in that: The cleaning time for the shell is 1 to 2 hours.

7. The chemical cleaning method according to claim 5, characterized in that: The cleaning time for the shell is less than 1 hour.

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