Iron well lid and technological method thereof

Abstract

The invention discloses an iron well lid and a technological method thereof, and belongs to the technical field of well lids. According to the process method, by optimizing the preparation and treatment process of the sand mold, the recycling rate of used sand is increased, meanwhile, the environment-friendly paint with excellent water resistance, salt water resistance and mechanical strength is developed, the performance of the iron well lid is improved, and the service life of the iron well lid is prolonged. The specific process comprises the steps of sand treatment burdening, sand treatment sand mixing, sand mold manufacturing, molten iron melting and casting, casting cleaning, sand treatment sand returning system and the like. Compared with the prior art, the iron well lid is excellent in water resistance and salt water resistance, the mechanical property of a paint film is remarkably improved, and the production process is more environmentally friendly and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of manhole covers, and in particular to an iron manhole cover and a processing method thereof. Background Art

[0002] In modern society, iron manhole covers are widely used in urban infrastructure construction to cover underground facilities such as pipelines, cables, etc. However, existing iron manhole covers have some problems during use, which affect the service life and performance of the manhole covers.

[0003] First, existing iron manhole covers have poor corrosion resistance in harsh environments. Due to long-term exposure to outdoor conditions, the covers' surfaces are susceptible to erosion by rain, saltwater, and chemicals, leading to rust and corrosion, shortening the covers' service life. Furthermore, existing manhole cover paint films lack water and saltwater resistance, failing to effectively protect against damage from prolonged immersion.

[0004] Secondly, the existing manhole cover production process involves complex sand mold preparation and processing, resulting in low resource utilization. During the sand mold manufacturing process, the mixing ratio of new and used sand is often irrational, resulting in insufficient strength and stability. Furthermore, the recycling and reuse of used sand is inefficient, increasing production costs and wasting resources.

[0005] Furthermore, the mechanical properties of existing manhole cover paint films need to be improved. During use, manhole covers are susceptible to external physical impact and abrasion, which can damage the paint film and affect the appearance and performance of the manhole covers. Therefore, developing an environmentally friendly paint with excellent water resistance, salt water resistance, and mechanical strength, as well as optimizing the production process for manhole covers, is crucial for improving the performance and service life of iron manhole covers.

[0006] In order to solve these problems, some improvement schemes have been proposed in the prior art. For example, Chinese Patent Publication No. CN108913835A discloses a casting preparation method that reduces the generation of subcutaneous pores. By arranging a desulfurization process, baking soda is added to the molten iron to form a protective layer, so that magnesium sulfide slag floats, prevents the oxidation of the molten iron, and reduces the generation of subcutaneous pores. In addition, by adding ammonium bifluoride in the sand mold, a reducing gas film can be formed at the metal mold interface to prevent the casting from sticking sand, resist the water vapor reaction at the interface, and reduce the generation of subcutaneous pores. However, these methods still have certain limitations in actual applications and cannot completely solve the above problems. Summary of the Invention

[0007] In order to address the deficiencies in the prior art, the present invention aims to provide an iron manhole cover and a process method thereof, thereby improving the recycling rate of old sand by optimizing the preparation and treatment process of the sand mold, and developing an environmentally friendly paint with excellent water resistance, salt water resistance and mechanical strength to improve the performance and service life of the iron manhole cover.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: The production process of an iron manhole cover is as follows: Step 1: Sand preparation and batching: Send the purchased new sand and old sand to the sand mixer, and add coal powder and bentonite into the sand mixer at the same time; Step 2: Sand treatment and sand mixing: Add water into the sand mixer and mix the water, new sand, old sand, coal powder and bentonite evenly to form wet clay sand; Step 3, sand mold manufacturing: the wet clay sand is sent to the vertical molding machine, blown into the sand box with compressed air and compacted to obtain a dense sand mold; Step 4, melting and casting molten iron: melt the molten iron in a medium frequency electric furnace, add 0.1%-0.5% of the weight of the molten iron to purify the molten iron, pour the molten iron into a sand mold to complete the casting, and after the casting is completed, the casting is naturally cooled and the sand is shaken out; Step 5, cleaning of castings: remove the molding sand and pouring risers on the surface of the castings, shot blast the castings to remove sticky sand, flash and burrs, then polish them, and finally dip paint the castings; Step 6, sand processing and sand returning system: the old sand after falling sand is subjected to magnetic separation to remove iron impurities, and after screening, loosening sand and cooling treatment, it is recycled to the old sand silo and enters the next round of sand processing and batching system.

[0009] The weight ratio of the new sand to the old sand is 1-3:1.

[0010] The weight of the coal powder is 1%-3% of the total weight of the sand.

[0011] The weight of the bentonite is 2%-5% of the total weight of the sand.

[0012] The water accounts for 3%-8% of the total weight of the sand.

[0013] The slag remover is perlite, and the weight of the slag remover is 0.1%-0.5% of the weight of the molten iron.

[0014] The paint is one of environmentally friendly paint and epoxy coal tar paint, and the thickness of the paint is 80-150 μm.

[0015] The preparation method of the environmentally friendly paint is as follows: A water-based acrylic resin, 4,4',4"-triphenylmethane triisocyanate, methyl vinyl ether-maleic anhydride copolymer, vinyl-dihydroxy-methylsilane and triethylenediamine are mixed in a certain proportion and stirred at a high temperature to obtain a mixture; a polyether defoamer, fumed silica, a leveling agent and water are added to the mixture and stirred evenly to obtain an environmentally friendly paint.

[0016] Preferably, the preparation method of the environmentally friendly paint is as follows, in parts by weight: 10-15 parts of water-based acrylic resin, 10-15 parts of phenyl isocyanate, 5-10 parts of maleic anhydride copolymer, 1-5 parts of vinyl-dihydroxy-methylsilane and 0.05-0.1 parts of triethylenediamine are put into a stirrer and stirred at 80-90°C for 20-40 minutes to obtain a mixture. Then, 0.1-0.3 parts of polyether defoamer, 0.1-0.5 parts of fumed silica, 0.1-0.3 parts of leveling agent and 20-25 parts of water are added to the mixture, and the mixture is stirred at a speed of 500-1500 r / min for 5-15 minutes to obtain an environmentally friendly paint.

[0017] The phenyl isocyanate is at least one of p-phenylene diisocyanate, 1,3-bis(1-isocyanato-1-methylethyl)benzene, and 4,4ˊ,4〞-triphenylmethane triisocyanate.

[0018] The maleic anhydride copolymer is at least one of a maleic anhydride-acrylic acid copolymer and a methyl vinyl ether-maleic anhydride copolymer.

[0019] In the present invention, the functions of each substance are as follows: New sand and old sand are the main raw materials for sand molds and are used to make sand molds. Mixing new sand and old sand in a certain proportion can reduce costs while ensuring the quality of the sand molds.

[0020] Coal powder plays a certain filling and bonding role in the sand mold, which helps to improve the strength and stability of the sand mold.

[0021] Bentonite acts as a binder to improve the cohesiveness and plasticity of the sand mold, giving the sand mold better molding performance and strength.

[0022] Water is mixed with bentonite and other materials to form a binder, which gives the sand mold a certain humidity and viscosity, making it easier to form and compact the sand mold.

[0023] Slag remover is added to molten iron during the melting and casting process to purify the molten iron, remove impurities and slag in the molten iron, and improve the purity of the molten iron, thereby ensuring the quality of castings.

[0024] The paint is applied to the surface of the casting to play the role of corrosion prevention, rust prevention, protection and decoration, and extend the service life of the casting.

[0025] Water-based acrylic resin is the main film-forming substance of environmentally friendly paint, providing the basic structure and properties of the paint film, such as adhesion, hardness, gloss, etc.

[0026] 4,4′,4″-Triphenylmethane triisocyanate contains terminal isocyanate groups, which can form a stable network structure, enhance the mechanical properties and adhesion of the paint film, and improve the water resistance and salt water resistance of the paint film.

[0027] Methyl vinyl ether-maleic anhydride copolymer provides maleic anhydride groups that cross-link with isocyanate groups to form a stable network structure, enhancing the mechanical properties and adhesion of the paint film. Methyl vinyl ether-maleic anhydride copolymer also exhibits excellent hydrophobicity and chemical stability, effectively reducing water penetration and improving the water resistance of the paint film.

[0028] Vinyl-dihydroxy-methylsilane helps to form a stable paint film structure during the preparation of environmentally friendly paint.

[0029] Triethylenediamine, as a catalyst, can promote the reaction between isocyanate groups and active groups, accelerating the cross-linking process of environmentally friendly paint.

[0030] During the preparation of environmentally friendly paint, polyether defoamers prevent excessive bubbles from being generated during stirring, ensuring the uniformity and stability of the paint liquid.

[0031] As a filler, fumed silica can improve the hardness, wear resistance and scratch resistance of the paint film, while also improving the leveling and gloss of the paint film.

[0032] Leveling agents improve the leveling properties of the paint film, making the paint film surface smoother and flatter, and reducing surface defects such as orange peel.

[0033] Compared with the existing technology, it has the following beneficial effects: 1) The environmentally friendly paint of this invention exhibits excellent water and saltwater resistance. The cross-linked network structure formed by these components effectively reduces water penetration, enhances the chemical stability and adhesion of the paint film, and significantly extends the service life of iron manhole covers in harsh environments.

[0034] 2) The environmentally friendly paint of this invention, through its specific formulation and preparation process, forms a highly cross-linked network structure, significantly improving the mechanical strength and adhesion of the paint film. This allows the iron manhole cover to better withstand external physical impact and abrasion during use, maintaining its excellent appearance and performance.

[0035] 3) In the production process of iron manhole covers, the present invention realizes the recycling of resources and reduces production costs by rationally utilizing the mixing ratio of new sand and old sand and an efficient sand processing and returning system. DETAILED DESCRIPTION

[0036] Main sources of substances: New sand, specification: 40-80 mesh, item number: 26, Zhangpu County Hongxiang Quartz Sand Co., Ltd.

[0037] Bentonite, product number: PRT-1, Lingshou County Baixin New Material Technology Co., Ltd.

[0038] Coal powder, item number: 9541, Lingshou County Qiangdong Mineral Products Processing Plant.

[0039] Perlite, item number: H104, particle size: 18-30 (mesh), Xinyang Huahong Perlite Co., Ltd.

[0040] Epoxy coal tar paint, product number: 007, Langfang Huiqi Anti-corrosion Materials Co., Ltd.

[0041] Maleic anhydride-acrylic acid copolymer, model: JH-202, Changzhou Jianghu Chemical Co., Ltd.

[0042] Polyether defoamer, item number: DF-8201, Dongguan Defeng Defoamer Co., Ltd.

[0043] Leveling agent, model: BYK-333, brand: BYK, Germany.

[0044] Water-based acrylic resin, brand: J678, brand: BASF, Germany.

[0045] Methyl vinyl ether-maleic anhydride copolymer, product number: 560000, Wuhan Lanabai Pharmaceutical Chemical Co., Ltd.

[0046] Maleic anhydride grafted polyethylene, product number: ZJ006, Guangzhou Zhongjie Chemical Technology Co., Ltd.

[0047] Fumed silica, item number: 6485484, product specification: 3000 mesh, Shijiazhuang Gengcheng Chemical Technology Co., Ltd.

[0048] Vinyl-dihydroxy-methylsilane, CAS number, 3959-12-4.

[0049] The remaining raw materials in the examples and comparative examples of the present invention are all commercially available products.

[0050] Example 1 The production process of an iron manhole cover is as follows: Step 1: Sand preparation and batching: Send the purchased new sand and old sand to the sand mixer in a weight ratio of 1:1, and at the same time, add 1.5% of the total weight of the sand to the sand mixer with coal powder and 2.5% of the total weight of the sand to the sand mixer; Step 2: Sand treatment and sand mixing: Add 5% water by weight of the total sand weight into the sand mixer, mix the water, new sand, old sand, coal powder and bentonite evenly to form wet clay sand; Step 3, sand mold manufacturing: the wet clay sand is sent to the vertical molding machine, blown into the sand box with compressed air and compacted to obtain a dense sand mold; Step 4, melting and casting molten iron: melt molten iron in a medium frequency electric furnace, add 0.1% perlite by weight of the molten iron to purify the molten iron, pour the molten iron into a sand mold to complete the casting, and after the casting is completed, the casting is naturally cooled and the sand is shaken out; Step 5, cleaning the casting: remove the molding sand and pouring riser on the surface of the casting, shot blast the casting to remove sticky sand, flash and burrs, then polish it, and finally dip-coat the casting with epoxy coal tar paint with a thickness of 120μm; Step 6, sand processing and sand returning system: the old sand after falling sand is subjected to magnetic separation to remove iron impurities, and after screening, loosening sand and cooling treatment, it is recycled to the old sand silo and enters the next round of sand processing and batching system.

[0051] Example 2 The production process of an iron manhole cover is as follows: Step 1: Sand preparation and batching: Send the purchased new sand and old sand to the sand mixer in a weight ratio of 1:1, and at the same time, add 1.5% of the total weight of the sand to the sand mixer with coal powder and 2.5% of the total weight of the sand to the sand mixer; Step 2: Sand treatment and sand mixing: Add 5% water by weight of the total sand weight into the sand mixer, mix the water, new sand, old sand, coal powder and bentonite evenly to form wet clay sand; Step 3, sand mold manufacturing: the wet clay sand is sent to the vertical molding machine, blown into the sand box with compressed air and compacted to obtain a dense sand mold; Step 4, melting and casting molten iron: melt molten iron in a medium frequency electric furnace, add 0.1% perlite by weight of the molten iron to purify the molten iron, pour the molten iron into a sand mold to complete the casting, and after the casting is completed, the casting is naturally cooled and the sand is shaken out; Step 5, cleaning the casting: remove the molding sand and pouring riser on the surface of the casting, shot blast the casting to remove sticky sand, flash and burrs, then polish it, and finally dip the casting in environmentally friendly paint with a thickness of 120μm; Step 6, sand processing and sand returning system: the old sand after falling sand is subjected to magnetic separation to remove iron impurities, and after screening, loosening sand and cooling treatment, it is recycled to the old sand silo and enters the next round of sand processing and batching system.

[0052] The preparation method of the environmentally friendly paint is as follows, in parts by weight: 12 parts of water-based acrylic resin, 13 parts of 4,4ˊ,4"-triphenylmethane triisocyanate, 8 parts of methyl vinyl ether-maleic anhydride copolymer, 3 parts of vinyl-dihydroxy-methylsilane and 0.08 parts of triethylenediamine are placed in a blender and stirred at 85°C for 30 minutes to obtain a mixture. Subsequently, 0.2 parts of a polyether defoamer, 0.3 parts of fumed silica, 0.2 parts of a leveling agent and 22 parts of water are added to the mixture, and the mixture is stirred at a speed of 1200 r / min for 10 minutes to obtain an environmentally friendly paint.

[0053] Example 3 The production process of an iron manhole cover is basically the same as that of Example 2, the only difference being the preparation method of the environmentally friendly paint.

[0054] The preparation method of the environmentally friendly paint is as follows, in parts by weight: 12 parts of water-based acrylic resin, 13 parts of 1,3-bis(1-isocyanate-1-methylethyl)benzene, 8 parts of methyl vinyl ether-maleic anhydride copolymer, 3 parts of vinyl-dihydroxy-methylsilane and 0.08 parts of triethylenediamine are put into a blender and stirred at 85°C for 30 minutes to obtain a mixture. Then, 0.2 parts of polyether defoamer, 0.3 parts of fumed silica, 0.2 parts of leveling agent and 22 parts of water are added to the mixture and stirred at a speed of 1200 r / min for 10 minutes to obtain an environmentally friendly paint.

[0055] Example 4 The production process of an iron manhole cover is basically the same as that of Example 2, the only difference being the preparation method of the environmentally friendly paint.

[0056] The preparation method of the environmentally friendly paint is as follows, in parts by weight: 12 parts of water-based acrylic resin, 13 parts of p-phenylene diisocyanate, 8 parts of methyl vinyl ether-maleic anhydride copolymer, 3 parts of vinyl-dihydroxy-methylsilane and 0.08 parts of triethylenediamine are put into a blender and stirred at 85°C for 30 minutes to obtain a mixture. Then, 0.2 parts of polyether defoamer, 0.3 parts of fumed silica, 0.2 parts of leveling agent and 22 parts of water are added to the mixture and stirred at a speed of 1200 r / min for 10 minutes to obtain an environmentally friendly paint.

[0057] Example 5 The production process of an iron manhole cover is basically the same as that of Example 2, the only difference being the preparation method of the environmentally friendly paint.

[0058] The preparation method of the environmentally friendly paint is as follows, in parts by weight: 12 parts of water-based acrylic resin, 13 parts of 4,4ˊ,4"-triphenylmethane triisocyanate, 8 parts of maleic anhydride-acrylic acid copolymer, 3 parts of vinyl-dihydroxy-methylsilane and 0.08 parts of triethylenediamine are added to a blender and stirred at 85°C for 30 minutes to obtain a mixture. Subsequently, 0.2 parts of a polyether defoamer, 0.3 parts of fumed silica, 0.2 parts of a leveling agent and 22 parts of water are added to the mixture, and the mixture is stirred at a speed of 1200 r / min for 10 minutes to obtain an environmentally friendly paint.

[0059] Comparative Example 1 The production process of an iron manhole cover is basically the same as that of Example 2, the only difference being the preparation method of the environmentally friendly paint.

[0060] The preparation method of the environmentally friendly paint is as follows, in parts by weight: 12 parts of water-based acrylic resin, 13 parts of 3-(trifluoromethyl)phenyl isocyanate, 8 parts of methyl vinyl ether-maleic anhydride copolymer, 3 parts of vinyl-dihydroxy-methylsilane and 0.08 parts of triethylenediamine are put into a blender and stirred at 85°C for 30 minutes to obtain a mixture. Then, 0.2 parts of polyether defoamer, 0.3 parts of fumed silica, 0.2 parts of leveling agent and 22 parts of water are added to the mixture and stirred at a speed of 1200 r / min for 10 minutes to obtain an environmentally friendly paint.

[0061] Comparative Example 2 The production process of an iron manhole cover is basically the same as that of Example 2, the only difference being the preparation method of the environmentally friendly paint.

[0062] The preparation method of the environmentally friendly paint is as follows, in parts by weight: 12 parts of water-based acrylic resin, 13 parts of 4,4ˊ,4"-triphenylmethane triisocyanate, 8 parts of maleic anhydride-grafted polyethylene, 3 parts of vinyl-dihydroxy-methylsilane and 0.08 parts of triethylenediamine are placed in a blender and stirred at 85°C for 30 minutes to obtain a mixture. Subsequently, 0.2 parts of a polyether defoamer, 0.3 parts of fumed silica, 0.2 parts of a leveling agent and 22 parts of water are added to the mixture, and the mixture is stirred at a speed of 1200 r / min for 10 minutes to obtain an environmentally friendly paint.

[0063] Test Example 1 Water resistance test The water resistance of the paint films of the iron manhole covers prepared in the examples of the present invention and the comparative examples was tested with reference to GB / T 1733-1993 “Determination of water resistance of paint films”. The test results are shown in Table 1.

[0064] Table 1 Test Example 2 Salt water resistance: The salt water resistance of the iron manhole covers prepared in the examples of the present invention and the comparative examples was tested in accordance with the standard of GB / T10834-2008 "Determination of Salt Water Resistance of Marine Paints - Salt Water and Hot Salt Water Immersion Method". The test results are shown in Table 2.

[0065] Table 2 It can be seen from the data of test examples 1 and 2 that the iron manhole cover prepared in Example 2 has excellent water resistance and the best salt water resistance.

[0066] In the production process of iron manhole covers, the three benzene rings in the molecular structure of 4,4′,4″-triphenylmethane triisocyanate used in Example 2 are connected by methane bridges to form a stable cross-linked network. In addition, the three terminal isocyanate groups (-NCO) contained in the invention can undergo cross-linking reaction with the active groups in these components to further form a highly cross-linked network structure. This cross-linked network structure not only improves the mechanical strength and adhesion of the paint film, but also enhances the water resistance and salt water resistance of the paint film. In comparison, the 1,3-bis(1-isocyanato-1-methylethyl)benzene, para-phenylene diisocyanate and 3-(trifluoromethyl)phenyl isocyanate used in other embodiments and comparative examples have lower cross-linking, resulting in insufficient paint film performance.

[0067] The methyl vinyl ether-maleic anhydride copolymer used in Example 2 shows better water resistance and salt water resistance than the maleic anhydride-acrylic acid copolymer in Example 5 and the maleic anhydride grafted polyethylene in Comparative Example 2. This is mainly due to the chemical structure and reaction characteristics of the methyl vinyl ether-maleic anhydride copolymer. The methyl vinyl ether group in the methyl vinyl ether-maleic anhydride copolymer molecule has good hydrophobicity and chemical stability, which can effectively reduce the penetration of water molecules, thereby improving the water resistance of the paint film. At the same time, the maleic anhydride group in the methyl vinyl ether-maleic anhydride copolymer can undergo cross-linking reaction with the isocyanate group to form a stable network structure, thereby enhancing the mechanical strength and adhesion of the paint film. In contrast, the chemical stability and adhesion of the paint film of maleic anhydride-acrylic acid copolymer and maleic anhydride grafted polyethylene in water or salt water environments will decline.

Claims

1. A process for processing iron manhole covers, characterized in that: The process is as follows: Step 1: Sand preparation and batching: Send the purchased new sand and old sand to the sand mixer, and add coal powder and bentonite into the sand mixer at the same time; Step 2: Sand treatment and sand mixing: Add water into the sand mixer and mix the water, new sand, old sand, coal powder and bentonite evenly to form wet clay sand; Step 3, sand mold manufacturing: the wet clay sand is sent to the vertical molding machine, blown into the sand box with compressed air and compacted to obtain a dense sand mold; Step 4, melting and casting of molten iron: melt the molten iron in a medium frequency electric furnace, add a slag remover to purify the molten iron, pour the molten iron into a sand mold to complete the casting, and after the casting is completed, the casting is naturally cooled and the sand is shaken out; Step 5, cleaning of castings: remove the molding sand and pouring risers on the surface of the castings, shot blast the castings to remove sticky sand, flash and burrs, then polish them, and finally dip paint the castings; Step 6, sand processing and sand returning system: the old sand after the sand fall is subjected to magnetic separation to remove iron impurities, and after screening, loosening and cooling treatment, it is recycled to the old sand bin and enters the next round of sand processing and batching system; The paint is one of environmentally friendly paint and epoxy coal tar paint, and the thickness of the paint is 80-150 μm; The preparation method of the environmentally friendly paint is as follows: A water-based acrylic resin, phenyl isocyanate, maleic anhydride copolymer, vinyl-dihydroxy-methylsilane and triethylenediamine are mixed in a certain proportion and stirred at a high temperature to obtain a mixture; a polyether defoamer, fumed silica, a leveling agent and water are added to the mixture and stirred evenly to obtain an environmentally friendly paint.

2. The process for processing an iron manhole cover according to claim 1, wherein: The weight ratio of the new sand to the old sand is 1-3:

1.

3. The process for processing an iron manhole cover according to claim 1, wherein: The weight of the coal powder is 1%-3% of the total weight of the sand.

4. The process for processing an iron manhole cover according to claim 1, wherein: The weight of the bentonite is 2%-5% of the total weight of the sand.

5. The process for processing an iron manhole cover according to claim 1, wherein: The water accounts for 3%-8% of the total weight of the sand.

6. The process for processing an iron manhole cover according to claim 1, wherein: The slag remover is perlite, and the weight of the slag remover is 0.1%-0.5% of the weight of the molten iron.

7. The process for processing an iron manhole cover according to claim 1, wherein: The preparation method of the environmentally friendly paint is as follows, in parts by weight: 10-15 parts of water-based acrylic resin, 10-15 parts of phenyl isocyanate, 5-10 parts of maleic anhydride copolymer, 1-5 parts of vinyl-dihydroxy-methylsilane and 0.05-0.1 parts of triethylenediamine are put into a stirrer and stirred at 80-90°C for 20-40 minutes to obtain a mixture. Then, 0.1-0.3 parts of polyether defoamer, 0.1-0.5 parts of fumed silica, 0.1-0.3 parts of leveling agent and 20-25 parts of water are added to the mixture, and the mixture is stirred at a speed of 500-1500 r / min for 5-15 minutes to obtain an environmentally friendly paint.

8. The process for processing an iron manhole cover according to any one of claims 1 or 7, characterized in that: The phenyl isocyanate is at least one of p-phenylene diisocyanate, 1,3-bis(1-isocyanato-1-methylethyl)benzene, and 4,4ˊ,4〞-triphenylmethane triisocyanate.

9. The process for processing an iron manhole cover according to any one of claims 1 or 7, characterized in that: The maleic anhydride copolymer is at least one of a maleic anhydride-acrylic acid copolymer and a methyl vinyl ether-maleic anhydride copolymer.

10. An iron manhole cover, characterized in that: The invention is prepared by the process according to any one of claims 1 to 9.

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