High-melting-point precoated sand and preparation method thereof

Abstract

The invention belongs to the technical field of precoated sand casting materials, and particularly relates to high-melting-point precoated sand and a preparation method thereof. The preparation method comprises the steps that casting waste sand is subjected to high-temperature roasting treatment and then cooled, precoated sand aggregate is obtained, the precoated sand aggregate and resin are mixed, and resin-coated aggregate is obtained; and urotropine and a solvent are mixed to obtain a curing agent, the curing agent is added into the resin wrapped aggregate, mixing is conducted under the negative pressure condition, then the lubricating agent is added, dispersion is conducted, and the high-melting-point precoated sand is obtained. The preparation method provided by the invention takes the casting waste sand after high-temperature roasting as a main raw material, and has the advantages of effective utilization of solid waste resources, low carbon, energy conservation and low cost. The high-melting-point precoated sand prepared through the preparation method has the higher melting point and heat resistance, is good in fluidity and high in normal-temperature bending resistance and normal-temperature tensile strength and can be used for producing sand cores with complex outlines, and a brand-new material is provided for precise casting production.

Description

Technical Field

[0001] The present invention belongs to the technical field of coated sand casting materials, and particularly relates to a high-melting-point coated sand and a preparation method thereof. Background Art

[0002] Coated sand is a special solid particle, which is composed of a polymer, a filler and an auxiliary agent. The coated sand particles contain a coating agent, whose main function is to prevent the coated sand particles from caking and make them easy to flow during the preparation and use process, and to increase the hydrophilicity of the particle surface. Coated sand can be applied to metal parts for construction machinery such as engine castings, motor casings, exhaust pipes, turbine casings, high-speed rail brake discs, hooks, and hydraulic valves.

[0003] The melting point is a key index of coated sand, which has a significant impact on the quality of the core. If the mold temperature is high and the melting point of the coated sand is low, after the coated sand enters the mold (usually at a temperature of 220 - 300 °C), it will quickly soften and solidify on the mold surface. At this time, the heat cannot be transmitted into the internal loose sand in time, and a hollow shell will be formed. When the molten metal is poured into the sand core, the strength of the hollow shell is very low, which will cause the molten metal to fill the inner cavity, resulting in defects such as sand sticking and excessive flesh, and directly scrapping.

[0004] The invention with the patent application number: CN202111148092.4 discloses a high-melting-point coated sand with good fluidity, belonging to the technical field of coated sand manufacturing. The invention first doped carbon nanotubes into quartz sand in a certain proportion, and mixed nano-yttrium oxide with chromite sand to obtain a mixed aggregate. The obtained mixed aggregate has high refractoriness, few volatiles, high strength, and a simple preparation method and low price. The mixed aggregate is heated and mixed with a binder, a curing agent and a lubricant to obtain a high-melting-point coated sand with good fluidity. The invention effectively solves the casting defects such as sand sticking, deformation, thermal cracking, and pores of conventional coated sand, and has a simple preparation method and good application prospects. However, the yttrium oxide used in the invention is a rare earth material, and the material cost of carbon nanotubes is very high, resulting in a high preparation cost and not meeting the basic conditions for industrial use.

[0005] Based on the above, providing a preparation method of coated sand with low cost and low energy consumption becomes a problem to be solved. Summary of the Invention

[0006] Based on the above technical background, the main purpose of the present invention is to provide a high-melting-point coated sand and a preparation method thereof to overcome the deficiencies in the prior art.

[0007] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include:

[0008] In the first aspect of the present invention, a preparation method of a high-melting-point coated sand is provided, and the preparation method includes the following steps:

[0009] Step 1: Subject the foundry waste sand to high-temperature roasting treatment, and then cool it down to obtain coated sand aggregate. Mix the coated sand aggregate with resin to obtain resin-coated aggregate.

[0010] Step 2: Mix hexamine and a solvent to obtain a curing agent. Add the curing agent to the resin-coated aggregate and mix under negative pressure conditions to obtain an aggregate mixture.

[0011] Step 3: Add a lubricant to the aggregate mixture for dispersion to obtain high-melting-point coated sand.

[0012] In Step 1,

[0013] Preferably, the conditions for the high-temperature roasting treatment are: the temperature of the high-temperature roasting is 700 - 800 °C, and the time of the high-temperature roasting is 10 - 60 min.

[0014] Preferably, when the coated sand aggregate is cooled down to 140 - 160 °C, mix the resin and the coated sand aggregate, and the mass ratio of the resin to the coated sand aggregate is 2 - 3:97 - 98.

[0015] Preferably, the resin is solid phenolic resin.

[0016] Preferably, the mixing conditions are: the stirring speed of the mixing is 120 - 150 r / min, and the time of the mixing is 15 - 30 s.

[0017] In Step 2,

[0018] Preferably, the mass ratio of the hexamine to the solvent is 1:(1.5 - 3).

[0019] Preferably, when the temperature of the resin-coated aggregate is cooled down to 120 - 140 °C, add the curing agent to the resin-coated aggregate, and the added mass of the curing agent is 40 - 60% of the added amount of the resin.

[0020] Preferably, the mixing conditions are: the pressure of the mixing is -2 - -5 kPa, the temperature of the mixing is 120 - 140 °C, the speed of the mixing is 80 - 120 r / min, and the time of the mixing is 20 - 30 s.

[0021] In Step 3,

[0022] Preferably, the lubricant is selected from one or more of graphite, carbon black, magnesium silicate, and molybdenum disulfide;

[0023] Preferably, the added amount of the lubricant is 2 - 5% of the added amount of the resin.

[0024] Preferably, the dispersion conditions are: disperse for 20 - 30 s at a dispersion speed of 120 - 150 r / min.

[0025] In the second aspect of the present invention, there is provided a method for preparing a high-melting-point coated sand according to the first aspect of the present invention, and the obtained high-melting-point coated sand.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) The preparation method of the present invention uses the casting waste sand after high-temperature roasting as the main raw material, realizing the effective and reasonable utilization of solid waste resources, and having the advantages of low carbon energy conservation and low preparation cost.

[0028] (2) The preparation method of the high-melting-point coated sand of the present invention does not require heating silica sand, which can effectively save energy consumption and reduce costs.

[0029] (3) In the preparation method, by adding a lubricant, the lubricant can be evenly coated on the surface of the sand grains, making the obtained high-melting-point coated sand have a better curing effect, improving the bonding strength between the sand grains, and being beneficial to enhancing the mechanical strength of the coated sand.

[0030] (4) By adding graphite to the high-melting-point coated sand of the present invention, on the one hand, it has a good protective effect on the resin, making the high-melting-point coated sand have a higher melting point and high-temperature resistance performance. On the other hand, it can make the curing effect of the coated sand better, enabling it to have better fluidity, excellent room-temperature bending and room-temperature tensile strength, and can be used for producing sand cores with complex contours, providing a new material for the production of precision castings. Specific embodiments

[0031] The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and more definite along with these descriptions.

[0032] In the first aspect of the present invention, there is provided a method for preparing a high-melting-point coated sand, and the preparation method includes the following steps:

[0033] Step 1: Perform high-temperature roasting treatment on the casting waste sand, and then cool it to obtain coated sand aggregate. Mix the coated sand aggregate and resin to obtain resin-coated aggregate.

[0034] Step 2: Mix hexamine and a solvent to obtain a curing agent, add the curing agent to the resin-coated aggregate, and mix under negative pressure conditions to obtain an aggregate mixture.

[0035] Step 3: Add a lubricant to the aggregate mixture for dispersion to obtain high-melting-point coated sand.

[0036] The above steps are specifically described below.

[0037] In Step 1, the conditions of the high-temperature roasting treatment are: the temperature of high-temperature roasting is 700 - 800 °C, and the time of high-temperature roasting is 10 - 60 min.

[0038] Preferably, the conditions for the high-temperature roasting treatment are as follows: the temperature of the high-temperature roasting is 750 °C, and the time of the high-temperature roasting is 45 min.

[0039] In this application, the low-melting-point substances on the surface of the foundry waste sand, such as resin films, binders, etc., can be removed through high-temperature roasting to obtain a reusable coated sand aggregate. The present invention uses the foundry waste sand as the main raw material for preparing the coated sand. On the one hand, it can reduce the preparation cost, and on the other hand, it can also realize the reuse of the foundry waste sand, improve its utilization value, and is environmentally friendly.

[0040] After high-temperature roasting, the temperature is lowered to 140-160 °C, preferably to 150 °C.

[0041] After cooling, the coated sand aggregate and the resin are mixed. In the present invention, the coated sand aggregate is cooled to 140-160 °C, and then the resin is mixed into the coated sand aggregate. The heat of the coated sand aggregate can be used to melt the solid resin, and there is no need to heat and melt the resin again, which can reduce energy consumption.

[0042] The mass ratio of the resin to the coated sand aggregate is 2-3:97-98. Preferably, the mass ratio of the resin to the coated sand aggregate is 2:98.

[0043] The mixing conditions are as follows: the stirring speed of the mixing is 120-150 r / min, and the mixing time is 15-30 s.

[0044] Preferably, the mixing conditions are as follows: the stirring speed of the mixing is 130 r / min, and the mixing time is 20 s.

[0045] Through mixing and stirring in the present invention, the resin can be wrapped on the surface of the coated sand aggregate, and the coated sand aggregate can be wrapped in the resin.

[0046] The resin is solid phenolic resin.

[0047] In step 2, the solvent is selected from one or more of ethanol, ethylene glycol, and water.

[0048] Preferably, the solvent is water.

[0049] Mix hexamine and the solvent, and the mass ratio of hexamine to the solvent is 1:(1.5-3).

[0050] Preferably, the mass ratio of hexamine to the solvent is 1:2. A curing agent for the liquid mixture is obtained.

[0051] When the temperature of the resin-coated aggregate is lowered to 120-140 °C, the curing agent is added to the resin-coated aggregate, and the added mass of the curing agent is 40-60% of the added mass of the resin.

[0052] Preferably, when the temperature of the resin-coated aggregate drops to 125 - 135 °C, a curing agent is added to the resin-coated aggregate, and the added mass of the curing agent is 50% of the resin addition amount.

[0053] The mixing conditions are as follows: the mixing pressure is -2 to -5 kPa, the mixing temperature is 120 to 140 °C, the mixing speed is 80 to 120 r / min, and the mixing time is 20 to 30 s.

[0054] Preferably, the mixing conditions are as follows: the mixing pressure is -3 kPa, the mixing temperature is 125 - 135 °C, the mixing speed is 100 r / min, and the mixing time is 25 s.

[0055] Mixing is preferably carried out in a sand mixer. Air is exhausted from the top of the sand mixer to control the mixing under negative pressure, so as to fully extract the water vapor and reduce the sand temperature at the same time. The mixing speed needs to be appropriate. If the mixing speed is too fast, the coated resin film will be broken up, resulting in the resin film falling off. Preferably, the mixing speed is 80 - 120 r / min, which can not only ensure that the resin film is not broken up but also improve the preparation efficiency.

[0056] In step 3, the lubricant is selected from one or more of graphite, carbon black, magnesium silicate, and molybdenum disulfide.

[0057] Preferably, the lubricant is graphite. Flaky graphite is the best, and the mesh number of the graphite is 500 - 800 meshes.

[0058] The function of adding the lubricant in the present invention is as follows: after the mixing in step 2, the mixture is slightly cured, and a lubricant needs to be added for dispersion. After adding the lubricant, the cured and adhered sand masses are quickly dispersed into particulate matters, and finally the finished high-melting-point coated sand is obtained. In addition, adding the lubricant is also beneficial to increasing the melting point of the coated sand.

[0059] The added amount of the lubricant is 2 - 5% of the resin addition amount. Preferably, the added amount of the lubricant is 3% of the resin addition amount.

[0060] The dispersion conditions are as follows: dispersion is carried out at a dispersion speed of 120 - 150 r / min for 20 - 30 s.

[0061] Preferably, the dispersion conditions are as follows: dispersion is carried out at a dispersion speed of 130 r / min for 25 s.

[0062] The second aspect of the present invention lies in providing a high-melting-point coated sand prepared by the preparation method of the high-melting-point coated sand according to the first aspect of the present invention.

[0063] Examples

[0064] The present invention will be further elaborated by specific examples below. These examples are only for illustrating the present invention and not for limiting the scope of the present invention. The raw materials used in the embodiments of the present invention are all commercially available.

[0065] Example 1

[0066] A preparation method of high-melting-point coated sand includes the following steps:

[0067] Heat the foundry waste sand to 750 °C for high-temperature roasting treatment for 45 min. After high-temperature roasting, cool it down to 150 °C to obtain the coated sand aggregate. Put the coated sand aggregate and phenolic resin (purchased from Jinan Shengquan) into a roller mixer for mixing. Utilize the residual heat of the coated sand aggregate to melt the solid phenolic resin. The mass ratio of the resin to the coated sand aggregate is 2:98. The stirring speed of the roller mixer is 130 r / min, and the mixing time is 20 s. The phenolic resin is coated on the surface of the coated sand aggregate to obtain resin-coated aggregate.

[0068] Mix hexamine and water. The mass ratio of hexamine to the solvent is 1:2 to obtain a curing agent. When the temperature of the resin-coated aggregate cools down to 125 - 135 °C, add the curing agent to the resin-coated aggregate for mixing. The added mass of the curing agent is 50% of the resin addition amount. The mixing is carried out in a roller mixer, and air is exhausted from the top of the roller mixer to control the mixing under negative pressure. The mixing conditions are: the mixing pressure is -3 kPa, the mixing temperature is 125 - 135 °C, the mixing speed is 100 r / min, and the mixing time is 25 s to obtain an aggregate mixture.

[0069] Add lubricant graphite to the aggregate mixture for dispersion. The mesh number of the graphite is 500 - 800 meshes, and the addition amount of the graphite is 3% of the resin addition amount. Disperse it at a dispersion speed of 130 r / min for 25 s to obtain high-melting-point coated sand.

[0070] Example 2

[0071] A preparation method of high-melting-point coated sand includes the following steps:

[0072] Heat the foundry waste sand to 700 °C for high-temperature roasting treatment for 60 min. After high-temperature roasting, cool it down to 140 °C to obtain the coated sand aggregate. Put the coated sand aggregate and phenolic resin into a roller mixer for mixing. Utilize the residual heat of the coated sand aggregate to melt the solid phenolic resin. The mass ratio of the resin to the coated sand aggregate is 3:97. The stirring speed of the roller mixer is 120 r / min, and the mixing time is 30 s. The phenolic resin is coated on the surface of the coated sand aggregate to obtain resin-coated aggregate.

[0073] Mix hexamine and water. The mass ratio of hexamine to the solvent is 1:1.5 to obtain a curing agent. When the temperature of the resin-coated aggregate drops to 120 - 130 °C, add the curing agent to the resin-coated aggregate for mixing. The added mass of the curing agent is 40% of the resin addition amount. The mixing is carried out in a roller mixer, and air is exhausted from the top of the roller mixer to control the mixing under negative pressure. The mixing conditions are: the mixing pressure is -2 kPa, the mixing temperature is 120 - 130 °C, the mixing speed is 80 r / min, and the mixing time is 30 s to obtain an aggregate mixture.

[0074] Add the lubricant graphite to the aggregate mixture for dispersion. The mesh number of the graphite is 500 - 800 meshes, and the added amount of graphite is 2% of the resin addition amount. Disperse for 30 s at a dispersion speed of 120 r / min to obtain a high-melting-point coated sand.

[0075] Example 3

[0076] A preparation method of a high-melting-point coated sand includes the following steps:

[0077] Heat the foundry waste sand to 800 °C for high-temperature roasting treatment for 10 min. After high-temperature roasting, cool it down to 160 °C to obtain a coated sand aggregate. Put the coated sand aggregate and phenolic resin into a roller mixer for mixing, and use the waste heat of the coated sand aggregate to melt the solid phenolic resin. The mass ratio of the resin to the coated sand aggregate is 2.5:97.5. The stirring speed of the roller mixer is 150 r / min, and the mixing time is 15 s. The phenolic resin is coated on the surface of the coated sand aggregate to obtain a resin-coated aggregate.

[0078] Mix hexamine and water. The mass ratio of hexamine to the solvent is 1:3 to obtain a curing agent. When the temperature of the resin-coated aggregate drops to 130 - 140 °C, add the curing agent to the resin-coated aggregate for mixing. The added mass of the curing agent is 60% of the resin addition amount. The mixing is carried out in a roller mixer, and air is exhausted from the top of the roller mixer to control the mixing under negative pressure. The mixing conditions are: the mixing pressure is -5 kPa, the mixing temperature is 130 - 140 °C, the mixing speed is 120 r / min, and the mixing time is 20 s to obtain an aggregate mixture.

[0079] Add the lubricant graphite to the aggregate mixture for dispersion. The mesh number of the graphite is 500 - 800 meshes, and the added amount of graphite is 5% of the resin addition amount. Disperse for 20 s at a dispersion speed of 150 r / min to obtain a high-melting-point coated sand.

[0080] Comparative example

[0081] Comparative example 1

[0082] The aggregate (quartz sand) is roasted at 150 °C for 2 h by natural gas. The phenolic resin is melted using the sand temperature and coated on the surface of the sand grains. The mass ratio of the phenolic resin to the aggregate is 1:40. Then, 12 parts by weight of the curing agent hexamethylenetetramine and 8 parts by weight of the lubricant calcium stearate are added in sequence for dispersion, and the conventional coated sand is obtained. Among them, the mass ratio of hexamethylenetetramine, calcium stearate and phenolic resin is 1.5:1:12.5.

[0083] Experimental example

[0084] Performance test of Experimental example 1

[0085] According to the national standard of GB / T 8583-2008 for foundry coated sand, under the condition of the same addition amount of phenolic resin, the performance tests were respectively carried out on the high melting point coated sand prepared in Example 1 and the conventional coated sand prepared in Comparative Example 1. The performance test results are shown in Table 1.

[0086] The detection steps of the fluidity of the coated sand are as follows:

[0087] 1) Inner cavity size: a conical cup with a diameter of 100 mm and a height of 100 mm, and a small hole with a diameter of 2 mm at the bottom;

[0088] 2) Block the small hole at the bottom with a rubber stopper, then pour the coated sand to be tested into the cup, and scrape off the excess coated sand from the top.

[0089] 3) Remove the rubber stopper at the bottom and start timing t. The loose sand slowly leaks out at the bottom of the cup;

[0090] 4) When the loose sand inside the cup has flowed out, stop timing;

[0091] 5) The fluidity of the coated sand is this period of time. The shorter the time used, the better the fluidity of the coated sand.

[0092] Table 1

[0093]

[0094]

[0095] It can be seen from Table 1 that the normal temperature bending resistance and normal temperature tensile strength of the high melting point coated sand prepared in Example 1 are both higher than those of the conventional coated sand. The weight of the tensile test block of the high melting point coated sand prepared in Example 1 is greater, indicating that the strength of the high melting point coated sand prepared by the present invention is higher.

[0096] In Table 1, the high-melting-point coated sand prepared in Example 1 has a higher melting point, which is 17 °C higher than that of the conventional coated sand. Moreover, the high-melting-point coated sand prepared in Example 1 has a longer heat-resistant time at 1000 °C, which is 17 s longer than that of the conventional coated sand. This indicates that the high-melting-point coated sand prepared by the present invention has a higher melting point and heat resistance.

[0097] As can be seen from Table 1, the curing thickness of the high-melting-point coated sand prepared in Example 1 is thicker than that of the conventional coated sand. The thicker the curing thickness, the better the curing effect, indicating that the cross-linking reaction between phenolic resin and curing agent hexamethylenetetramine is more sufficient. The fluidity of the high-melting-point coated sand prepared in Example 1 is shorter than that of the conventional coated sand, indicating that the high-melting-point coated sand of the present invention has better fluidity.

[0098] The above results show that, compared with the conventional coated sand, the high-melting-point coated sand of the present invention has the following advantages: ① It is not necessary to heat silica sand, saving energy consumption costs; ② Since the lubricant graphite is uniformly coated on the surface of sand grains, the curing effect and the bonding strength between sand grains are improved. ③ The high-temperature resistance time of the coated sand of the present invention is significantly improved, mainly due to the good protective effect of the added graphite on phenolic resin. ④ The high-melting-point coated sand of the present invention has better fluidity, higher bending and tensile strengths at room temperature, and can be used to produce sand cores with complex contours, providing a new material for the production of precision castings.

[0099] The present invention has been described in detail above in combination with specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions of the present invention and their implementation manners, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A preparation method of high melting point coated sand, characterized in that, The preparation method includes the following steps: Step 1: High-temperature roast the foundry waste sand, then cool it down to obtain coated sand aggregate. Mix the coated sand aggregate with resin to obtain resin-coated aggregate. Step 2: Mix hexamine and solvent to obtain a curing agent. Add the curing agent to the resin-coated aggregate and mix under negative pressure conditions to obtain an aggregate mixture. Step 3: Add a lubricant to the aggregate mixture for dispersion to obtain high-melting-point coated sand.

2. The preparation method according to claim 1, characterized in that, In Step 1, The conditions for the high-temperature roasting treatment are: the temperature for high-temperature roasting is 700 - 800 °C, and the time for high-temperature roasting is 10 - 60 min.

3. The preparation method according to claim 1, characterized in that, In Step 1, When the coated sand aggregate cools down to 140 - 160 °C, mix the resin and the coated sand aggregate. The mass ratio of the resin to the coated sand aggregate is 2 - 3:97 - 98. The resin is solid phenolic resin.

4. The preparation method according to claim 1, characterized in that, In Step 1, The mixing conditions are: the stirring speed for mixing is 120 - 150 r / min, and the mixing time is 15 - 30 s.

5. The preparation method according to claim 1, characterized in that, In Step 2, The mass ratio of hexamine to the solvent is 1:(1.5 - 3).

6. The preparation method according to claim 1, characterized in that, In Step 2, When the temperature of the resin-coated aggregate cools down to 120 - 140 °C, add the curing agent to the resin-coated aggregate. The added mass of the curing agent is 40 - 60% of the added amount of the resin.

7. The preparation method according to claim 1, wherein In Step 2, The mixing conditions are: the mixing pressure is -2 - -5 kPa, the mixing temperature is 120 - 140 °C, the mixing speed is 80 - 120 r / min, and the mixing time is 20 - 30 s.

8. The preparation method according to claim 1, characterized in that, In Step 3, The lubricant is selected from one or more of graphite, carbon black, magnesium silicate, and molybdenum disulfide; The added amount of the lubricant is 2 - 5% of the added amount of the resin.

9. The preparation method according to claim 1, wherein In Step 3, The dispersion conditions are: disperse at a dispersion speed of 120 - 150 r / min for 20 - 30 s.

10. A high-melting-point coated sand prepared by the preparation method of the high-melting-point coated sand according to any one of claims 1 - 9.

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