Surface strengthening method for cast steel special-shaped pipe fitting

Abstract

The invention provides a cast steel special-shaped pipe fitting surface strengthening method, and relates to the field of cast steel surface strengthening. Step 2, preparing a solution: sequentially adding nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, a siloxane coupling agent and polyvinyl alcohol into deionized water, and stirring and mixing; step 3, preparing a coating film; and step 4, curing. According to the method, the enhanced functional coating film with high temperature resistance, thermal shock resistance and strong binding force is prepared on the surface of the cast steel special-shaped pipe fitting matrix, the binding strength of the coating film and the matrix is high, the heat insulation performance is excellent, the problems of cracking, deformation, falling and the like are not prone to occurring, the performance is stable and long-acting, and the method can be applied to the surfaces of cast steel special-shaped pipe fittings in various fields and is wide in application range.

Description

Technical Field

[0001] The invention relates to the technical field of cast steel surface strengthening, in particular to a method for strengthening the surface of a cast steel special-shaped pipe fitting. Background Art

[0002] Cast steel special-shaped pipe fittings are irregular or non-standard pipe fittings made of cast steel materials. They have the characteristics of complex and diverse shapes, high strength and toughness, excellent processability, good corrosion resistance, and strong structure. At present, some cast steel special-shaped pipe fittings mainly use multi-layer coating materials to achieve thermal insulation. The coating materials can effectively inhibit radiation heat transfer and convection heat transfer, thereby significantly isolating the transfer of heat; however, since the surface of cast steel special-shaped pipe fittings is composed of many continuous irregular surfaces, there are problems such as insufficient coating and low bonding strength between the coating materials and the cast steel special-shaped pipe fittings, which leads to air gaps, which not only reduces the thermal insulation effect, but also easily leads to temperature accumulation in the gap, resulting in safety hazards. In the prior art, the solution is to use overlapping and staggered coating methods to coat different surfaces, and then perform integrated coating on the outer layer. Although this method can effectively avoid the formation of air gaps, when the thickness and amount of the coating material are increased, not only the cost of the thermal insulation material is increased, but it is also very easy to interfere with the surrounding adjacent components, greatly limiting the use space; at the same time, there are also means in the prior art to replace the coating material with a coating to insulate cast steel special-shaped pipe fittings. Although the coating can fit tightly with the surface of the cast steel special-shaped pipe fittings to avoid gaps between the contact surfaces, under high temperature and vibration conditions, the coating in the prior art is prone to cracking and falling off, resulting in the cast steel special-shaped pipe fittings losing protection. The substrate is directly exposed to high temperature and aging, performance degradation, and even damage. That is, the existing coating has poor thermal insulation stability and poor resistance to complex environments (i.e., fatigue, high temperature, vibration, etc.). Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for strengthening the surface of cast steel special-shaped pipe fittings. This method prepares an enhanced functional coating that is resistant to high temperature, thermal shock and has strong bonding strength on the surface of the cast steel special-shaped pipe fitting substrate. The coating has high bonding strength with the substrate and excellent thermal insulation performance. It is not easy to crack, deform, fall off and other problems under high temperature and vibration conditions, and has good thermal insulation stability.

[0004] The purpose of the present invention is achieved through the following technical solutions: A method for strengthening the surface of a cast steel special-shaped pipe fitting, comprising: Step 1: Surface pretreatment: sandblast the outer wall of cast steel special-shaped pipe fittings; Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide (MgO ) Add filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent and polyvinyl alcohol into deionized water and mix them evenly with a mechanical stirrer; Step 3, coating preparation: Use a spray gun to spray the uniformly mixed solution in step 2 onto the surface of the cast steel special-shaped pipe fitting pretreated in step 1, let it stand until the solution stops flowing, spray it again, and repeat the spraying 5 to 15 times; Step 4, curing: the cast steel special-shaped pipe fittings sprayed in step 3 are placed in an oven for curing treatment, and then taken out to obtain the pipe fittings with the surface coated with a strengthening coating.

[0005] Based on further optimization of the above scheme, the pressure of the sandblasting in step 1 is 1-4 MPa.

[0006] Based on further optimization of the above scheme, the weight percentages of the nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 15% to 25%, 8% to 15%, 3% to 6%, 2% to 4%, 15% to 25%, 2% to 3%, 2% to 3%, 1% to 2%, and the rest is deionized water.

[0007] By compounding nano zirconium dioxide, aluminum silicate fiber, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent and polyvinyl alcohol, nano zirconium dioxide particles can be evenly dispersed on the surface of aluminum silicate fiber. Aluminum silicate fiber itself has the characteristics of low thermal conductivity, high strength and high toughness. In the process of coating preparation, a specific ratio is used to make the nano zirconium dioxide particles adsorbed on the surface of aluminum silicate fiber and distributed in clusters, thereby effectively hindering heat transfer in the coating and improving thermal insulation performance; at the same time, the density of the coating can be improved through the evenly distributed cluster structure, so that when cracks are generated under high temperature vibration conditions, the expansion of the cracks is deflected and bridged, further improving the toughness of the coating and the interface bonding strength between the coating and the matrix grains, avoiding cracking, falling off and other problems of the coating under high temperature vibration conditions.

[0008] Based on further optimization of the above scheme, the modified epoxy resin includes polyurethane, polysulfone, graphene oxide, E20 bisphenol A epoxy resin and deionized water; wherein the weight percentages of polyurethane, polysulfone, graphene oxide and E20 bisphenol A epoxy resin are 10% to 20%, 5% to 15%, 0.5% to 1% and 20% to 30%, and the rest is deionized water.

[0009] By blending polyurethane, polysulfone, graphene oxide, and E20 bisphenol A epoxy resin, the interaction between the polar groups such as the carbamate group of polyurethane, the polar groups such as the sulfone group and ether bond of polysulfone and the E20 bisphenol A epoxy resin is utilized to enhance the interfacial bonding force and the adhesion between the phases, and effectively improve the overall tensile strength and fracture resistance of the modified epoxy resin; and polysulfone and graphene oxide effectively improve the dispersibility of polyurethane in E20 bisphenol A epoxy resin, avoiding the occurrence of polyurethane and E20 bisphenol A epoxy resin due to excessive crosslinking density or excessive aggregation and entanglement of polyurethane. It can eliminate problems such as being too brittle or too sticky (epoxy resin that is too brittle or too sticky not only makes subsequent spraying difficult, but also easily leads to cracking and falling off of the coating under high temperature and vibration conditions). It is convenient for subsequent spraying and further enhances the stability of the coating under high temperature and vibration conditions. At the same time, the modified epoxy resin formed by blending specific formulas can effectively form a uniform three-dimensional network structure, promote the formation of nano zirconium dioxide and aluminum silicate fiber cluster structures, and thus enhance the toughness of the final coating and the strong bonding force between the coating and the substrate, further avoiding problems such as cracking and falling off of the coating.

[0010] Based on further optimization of the above scheme, the rotation speed of the mechanical stirrer in step 2 is 500-1200 r / min, and the stirring time is 20-30 min.

[0011] Based on further optimization of the above scheme, the environment for preparing the coating in step three is: temperature not less than 20° C., and humidity not more than 60%.

[0012] Based on further optimization of the above scheme, during spraying in step three, the central axis of the spray gun is perpendicular to the sprayed surface, the distance between the spray gun and the sprayed surface is 15 to 25 cm, and the standing time after spraying is 1 to 2 hours.

[0013] Based on further optimization of the above scheme, the curing treatment in step 4 adopts a staged heating process, that is, after closing the furnace door, the temperature is first raised to 75-85°C and kept warm for 0.8-1.2 hours, then raised to 95-105°C and kept warm for 0.8-1.2 hours, then raised to 140-160°C and kept warm for 1-1.4 hours, and finally raised to 170-190°C and kept warm for 2.8-3.2 hours.

[0014] Through staged heating and temperature gradient control, not only can the problems of local violent intermolecular reactions and uneven curing caused by excessive temperature differences or instantaneous high temperatures be avoided, but also the generation of instantaneous thermal stress between molecules, which may lead to problems such as film breakage and surface wrinkles, can be effectively avoided. In addition, step-by-step heating can also effectively activate the functional groups in nano zirconium dioxide, aluminum silicate fiber, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol, increase the tightness of intermolecular links, promote full reaction between each functional group, and enhance the integrity of the entire cross-linked network, thereby forming a complete and effective three-dimensional network structure, which improves the thermal insulation performance and toughness of the entire coating while ensuring the close bonding between the layers of the coating, effectively avoiding problems such as stratification, wrinkles, deformation, and shedding during the coating preparation process.

[0015] Based on further optimization of the above scheme, when taking out the pipe fittings with the surface coated with the strengthening coating in the step 4, the heating power of the oven is turned off and the oven temperature is waited to drop below 60°C.

[0016] The following are the technical effects of the solution of the present invention: The present invention strengthens the surface of the substrate of the special-shaped cast steel pipe fittings through a coating. The coating functional layer has high bonding strength with the substrate and good thermal insulation performance. It can be effectively attached to the various special-shaped surfaces of the special-shaped cast steel pipe fittings without generating air gaps, thereby avoiding the formation of temperature concentration points. The thermal insulation performance of the entire coating functional layer is excellent. At the same time, the coating of the present invention has strong adhesion to the substrate, and the coating has high tensile strength and fracture resistance. Under extreme working conditions of high temperature-vibration coupling, the coating layer will not crack, deform, fall off, etc., thereby effectively improving the service life and weather resistance of the coating and the substrate. In addition, the coating construction process of the present application is simple, which can improve production efficiency while reducing production costs, thereby expanding the applicable scenarios of cast steel special-shaped pipe fittings and improving the application rate of cast steel special-shaped pipe fittings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a flow chart of the surface strengthening method of cast steel special-shaped pipe fittings in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0019] Embodiment 1: A method for strengthening the surface of a cast steel special-shaped pipe fitting, comprising: Step 1: Surface pretreatment: Sandblast the outer wall of cast steel special-shaped pipe fittings at a sandblasting pressure of 1MPa; visually inspect the surface after sandblasting to ensure that the color is consistent and there is no area with metallic luster, then blow the surface to remove sand and dust.

[0020] Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide ( MgO ) filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are added into deionized water, wherein the weight percentages of nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 15%, 8%, 3%, 2%, 15%, 2%, 2%, 1%, and the rest is deionized water; a mechanical stirrer is used to mix evenly (a conventional mechanical stirrer in the art can be used), the stirring speed is 500r / min, and the stirring time is 30min; Among them, the modified epoxy resin includes polyurethane, polysulfone, graphene oxide, E20 bisphenol A type epoxy resin and deionized water; the weight percentages of polyurethane, polysulfone, graphene oxide and E20 bisphenol A type epoxy resin are 10%, 5%, 0.5% and 20%, and the rest is deionized water.

[0021] Step 3, coating preparation: In an environment with a temperature not less than 20°C (for example, the temperature is 20°C) and a humidity not more than 60% (for example, the humidity is 60%), use a spray gun to spray the solution evenly mixed in step 2 onto the surface of the cast steel special-shaped pipe fitting pretreated in step 1. During spraying, the central axis of the spray gun is perpendicular to the sprayed surface, and the distance between the spray gun and the sprayed surface is 15 cm. Let it stand for 1 hour until the solution stops flowing, spray again, and repeat the spraying 5 times. During the spraying process, the unevenness is allowed to be ±30μm, and the uneven spraying can be re-coated with a scraper.

[0022] Step 4, curing: Put the cast steel special-shaped pipe fittings sprayed in step 3 into the oven for curing treatment. The curing treatment adopts a staged heating process, that is, after closing the furnace door, first heat it to 75℃ and keep it warm for 0.8h, then heat it to 95℃ and keep it warm for 0.8h, then heat it to 140℃ and keep it warm for 1h, and finally heat it to 170℃ and keep it warm for 2.8h. Then turn off the heating power of the oven, wait for the furnace temperature to drop below 60℃, and take out the pipe fittings with the surface coated with the enhanced coating. The total thickness of the coating measured by the measuring tool is 0.8mm.

[0023] Embodiment 2: A method for strengthening the surface of a cast steel special-shaped pipe fitting, comprising: Step 1: Surface pretreatment: Sandblast the outer wall of cast steel special-shaped pipe fittings at a sandblasting pressure of 2.5MPa; visually inspect the surface after sandblasting to ensure that the color is consistent and there is no area with metallic luster, then blow the surface to remove sand and dust.

[0024] Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide ( MgO ) filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are added into deionized water, wherein the weight percentages of nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 10%, 11.5%, 4.5%, 3%, 10%, 2.5%, 2.5%, 1.5%, and the rest is deionized water; a mechanical stirrer is used to mix evenly (a conventional mechanical stirrer in the art can be used), the stirring speed is 850r / min, and the stirring time is 25min; Among them, the modified epoxy resin includes polyurethane, polysulfone, graphene oxide, E20 bisphenol A type epoxy resin and deionized water; the weight percentages of polyurethane, polysulfone, graphene oxide and E20 bisphenol A type epoxy resin are 15%, 10%, 0.7% and 25%, and the rest is deionized water.

[0025] Step 3, coating preparation: In an environment with a temperature not less than 20°C (for example, the temperature is 25°C) and a humidity not more than 60% (for example, the humidity is 55%), use a spray gun to spray the solution evenly mixed in step 2 onto the surface of the cast steel special-shaped pipe fitting pretreated in step 1. During spraying, the central axis of the spray gun is perpendicular to the sprayed surface, and the distance between the spray gun and the sprayed surface is 20 cm. Let it stand for 1.5 hours until the solution stops flowing, spray again, and repeat the spraying 10 times; during the spraying process, the unevenness is allowed to be ±30μm, and the uneven spraying can be re-coated with a scraper.

[0026] Step 4, curing: Put the cast steel special-shaped pipe fittings sprayed in step 3 into the oven for curing treatment. The curing treatment adopts a staged heating process, that is, after closing the furnace door, first heat it to 80℃ and keep it warm for 1h, then heat it to 100℃ and keep it warm for 1h, then heat it to 150℃ and keep it warm for 1.2h, and finally heat it to 180℃ and keep it warm for 3h. Then turn off the heating power of the oven, wait for the furnace temperature to drop below 60℃, and take out the pipe fittings with the enhanced coating on the surface. The total thickness of the coating measured by the measuring tool is 1.5mm.

[0027] Embodiment 3: A method for strengthening the surface of a cast steel special-shaped pipe fitting, comprising: Step 1: Surface pretreatment: Sandblast the outer wall of cast steel special-shaped pipe fittings at a sandblasting pressure of 1 to 4 MPa; visually inspect the surface after sandblasting to ensure that the color is consistent and there is no area with metallic luster, then blow the surface to remove sand and dust.

[0028] Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide ( MgO ) filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are added into deionized water, wherein the weight percentages of nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 25%, 15%, 6%, 4%, 25%, 3%, 3%, and 2%, and the rest is deionized water; a mechanical stirrer is used to mix evenly (a conventional mechanical stirrer in the art can be used), the stirring speed is 1200r / min, and the stirring time is 20min; Among them, the modified epoxy resin includes polyurethane, polysulfone, graphene oxide, E20 bisphenol A type epoxy resin and deionized water; the weight percentages of polyurethane, polysulfone, graphene oxide and E20 bisphenol A type epoxy resin are 20%, 15%, 1% and 30%, and the rest is deionized water.

[0029] Step 3, coating preparation: In an environment with a temperature not less than 20°C (for example, the temperature is 30°C) and a humidity not more than 60% (for example, the humidity is 50%), use a spray gun to spray the solution evenly mixed in step 2 onto the surface of the cast steel special-shaped pipe fitting pretreated in step 1. During spraying, the central axis of the spray gun is perpendicular to the sprayed surface, and the distance between the spray gun and the sprayed surface is 25 cm. Let it stand for 2 hours until the solution stops flowing, spray again, and repeat the spraying 15 times; during the spraying process, the unevenness is allowed to be ±30μm, and the uneven spraying can be re-coated with a scraper.

[0030] Step 4, curing: Put the cast steel special-shaped pipe fittings sprayed in step 3 into the oven for curing treatment. The curing treatment adopts a staged heating process, that is, after closing the furnace door, first heat it to 85℃ and keep it warm for 1.2h, then heat it to 105℃ and keep it warm for 1.2h, then heat it to 160℃ and keep it warm for 1.4h, and finally heat it to 190℃ and keep it warm for 3.2h. Then turn off the heating power of the oven, wait for the furnace temperature to drop below 60℃, and take out the pipe fittings with the surface coated with the enhanced coating. The total thickness of the coating measured by the measuring tool is 2.2mm.

[0031] Comparative Example 1: A method for strengthening the surface of a pipe, comprising: Step 1: Surface pretreatment: This step is consistent with step 1 in Example 2.

[0032] Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide ( MgO ) filler, E20 bisphenol A type epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are added into deionized water, wherein the weight percentages of nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, E20 bisphenol A type epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 10%, 11.5%, 4.5%, 3%, 10%, 2.5%, 2.5%, 1.5%, and the rest is deionized water; a mechanical stirrer is used to mix evenly (a conventional mechanical stirrer in the art can be used), the stirring speed is 850r / min, and the stirring time is 25min.

[0033] Step 3: Coating preparation: This step is consistent with step 3 in Example 2.

[0034] Step 4: Curing: This step is consistent with step 4 in Example 2.

[0035] The total coating thickness measured by the measuring tool is 1.5 mm.

[0036] Comparative Example 2: A method for strengthening the surface of a pipe, comprising: Step 1: Surface pretreatment: This step is consistent with step 1 in Example 2.

[0037] Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide ( MgO ) filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are added into deionized water, wherein the weight percentages of nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 10%, 11.5%, 4.5%, 3%, 10%, 2.5%, 2.5%, 1.5%, and the rest is deionized water; a mechanical stirrer is used to mix evenly (a conventional mechanical stirrer in the art can be used), the stirring speed is 850r / min, and the stirring time is 25min; Among them, the modified epoxy resin includes polyurethane, graphene oxide, E20 bisphenol A type epoxy resin and deionized water; the weight percentages of polyurethane, graphene oxide and E20 bisphenol A type epoxy resin are 15%, 0.7% and 25%, and the rest is deionized water.

[0038] Step 3: Coating preparation: This step is consistent with step 3 in Example 2.

[0039] Step 4: Curing: This step is consistent with step 4 in Example 2.

[0040] The total coating thickness measured by the measuring tool is 1.5 mm.

[0041] Comparative Example 3: A method for strengthening the surface of a pipe, comprising: Step 1: Surface pretreatment: This step is consistent with step 1 in Example 2.

[0042] Step 2: Solution preparation: Nano zirconium dioxide, aluminum silicate fiber, iron oxide ( Fe 2 O 3) Filler, magnesium oxide ( MgO ) filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are added into deionized water, wherein the weight percentages of nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 10%, 11.5%, 4.5%, 3%, 10%, 2.5%, 2.5%, 1.5%, and the rest is deionized water; a mechanical stirrer is used to mix evenly (a conventional mechanical stirrer in the art can be used), the stirring speed is 850r / min, and the stirring time is 25min; The modified epoxy resin includes polyurethane, polysulfone, E20 bisphenol A epoxy resin and deionized water; the weight percentages of polyurethane, polysulfone and E20 bisphenol A epoxy resin are 15%, 10% and 25%, and the rest is deionized water.

[0043] Step 3: Coating preparation: This step is consistent with step 3 in Example 2.

[0044] Step 4: Curing: This step is consistent with step 4 in Example 2.

[0045] The total coating thickness measured by the measuring tool is 1.5 mm.

[0046] Comparative Example 4: A method for strengthening the surface of a pipe, comprising: Step 1: Surface pretreatment: This step is consistent with step 1 in Example 2.

[0047] Step 2, solution preparation: This step is consistent with step 2 in Example 2.

[0048] Step 3: Coating preparation: This step is consistent with step 3 in Example 2.

[0049] Step 4: Curing: Put the cast steel special-shaped pipes sprayed in step 3 into the oven for curing. The curing process adopts a staged heating process, that is, after closing the oven door, first heat it to 100°C and keep it for 2 hours, then heat it to 180°C and keep it for 4.2 hours. Then turn off the heating power of the oven, wait for the oven temperature to drop below 60°C, and take out the pipes with the surface coated with the strengthening coating.

[0050] The total coating thickness measured by the measuring tool is 1.6 mm.

[0051] The bonding strength of the coatings in Examples 1 to 3 and Comparative Examples 1 to 4 was tested by the pulling method, that is, firstly, the pipes coated with the reinforced coatings in Examples 1 to 3 and Comparative Examples 1 to 4 were fixed on the bonding fixture of the tensile testing machine (to ensure that the key installation is firm and the tensile force can be evenly applied to the bonding interface), and then, the tensile force was applied at a certain stretching speed, which is generally between 0.1 and 10 mm / min. During the stretching process, the tensile force value and the displacement value were recorded in real time to guide the destruction of the bonding interface, and the maximum tensile force value when the bonding interface was destroyed was recorded, and the corresponding adhesion of the coating was obtained. Z (Unit: MPa ): ; Where: F max Indicates the maximum tensile force recorded when the bonding interface fails (unit: N ); S Indicates the bonding area (unit: m 2 ); In addition, the heat insulation performance test was performed on the pipes coated with the enhanced coating obtained in Examples 1 to 3 and Comparative Examples 1 to 4, that is, thermocouples were evenly arranged on the outer wall of the pipes coated with the enhanced coating, and the inner cavity of the pipes was heated. The test results finally obtained are shown in Table 1 below: Table 1:

[0052] It can be seen from the above table that the adhesion and thermal insulation performance of the coating can be effectively improved through the coating with a specific formula of the present invention and the specific staged temperature increase and curing process.

[0053] For further testing of the thermal insulation performance, a coating layer with a thickness of 2 to 10 cm (3 cm in this embodiment) is used to coat the outer wall of the pipe fitting coated with the enhanced coating to obtain an insulated special-shaped pipe fitting. The coating layer can be made of any one of rock wool, ceramic glass wool, polystyrene foam or polyurethane foam (ceramic glass wool is used in this embodiment); the outer walls of the pipe fittings coated with the enhanced coating in Examples 1 to 3 and Comparative Examples 1 to 4 are coated respectively, and the coating is tested for thermal insulation performance. The test results are shown in Table 2 below: Table 2

[0054] It can be seen from the above table that the coating film with a specific formula of the present invention and the specific staged temperature rise and curing process can be combined with the coating layer to effectively improve the overall thermal insulation performance of the pipe.

Claims

1. A method for strengthening the surface of a cast steel special-shaped pipe, characterized in that: include: Step 1: Surface pretreatment: sandblast the outer wall of cast steel special-shaped pipe fittings; Step 2, solution preparation: add nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol into deionized water in sequence, and mix evenly with a mechanical stirrer; Step 3, coating preparation: Use a spray gun to spray the uniformly mixed solution in step 2 onto the surface of the cast steel special-shaped pipe fitting pretreated in step 1, let it stand until the solution stops flowing, spray it again, and repeat the spraying 5 to 15 times; Step 4, curing: the cast steel special-shaped pipe fittings sprayed in step 3 are placed in an oven for curing treatment, and then taken out to obtain the pipe fittings with the surface coated with a strengthening coating.

2. A method for surface strengthening of a cast steel special-shaped pipe according to claim 1, characterized in that: The pressure of the sandblasting treatment in step 1 is 1-4 MPa.

3. A method for strengthening the surface of a cast steel special-shaped pipe according to claim 1 or 2, characterized in that: The weight percentages of the nano zirconium dioxide, aluminum silicate fiber, iron oxide filler, magnesium oxide filler, modified epoxy resin, sodium hexametaphosphate, siloxane coupling agent, and polyvinyl alcohol are: 15%-25%, 8%-15%, 3%-6%, 2%-4%, 15%-25%, 2%-3%, 2%-3%, 1%-2%, and the rest is deionized water.

4. A method for strengthening the surface of a cast steel special-shaped pipe according to claim 3, characterized in that: In the step 2, the rotation speed of the mechanical stirrer is 500-1200 r / min, and the stirring time is 20-30 min.

5. The surface strengthening method of a cast steel special-shaped pipe according to claim 1, characterized in that: The environment for preparing the coating in step 3 is: temperature not less than 20° C., and humidity not more than 60%.

6. A method for strengthening the surface of a cast steel special-shaped pipe according to claim 5, characterized in that: During spraying in step three, the central axis of the spray gun is perpendicular to the sprayed surface, the distance between the spray gun and the sprayed surface is 15 to 25 cm, and the standing time after spraying is 1 to 2 hours.

7. A method for strengthening the surface of a cast steel special-shaped pipe according to claim 1 or 3, characterized in that: The curing treatment in step 4 adopts a staged heating process, that is, after closing the furnace door, the temperature is first raised to 75-85°C and kept warm for 0.8-1.2 hours, then raised to 95-105°C and kept warm for 0.8-1.2 hours, then raised to 140-160°C and kept warm for 1-1.4 hours, and finally raised to 170-190°C and kept warm for 2.8-3.2 hours.

8. A method for strengthening the surface of a cast steel special-shaped pipe according to claim 7, characterized in that: When taking out the pipe with the surface coated with the strengthening coating in the step 4, turn off the heating power of the oven and wait for the oven temperature to drop below 60°C.

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