CN113172199A - Preparation method of novel ammonia-free curing type casting precoated sand - Google Patents
Preparation method of novel ammonia-free curing type casting precoated sand Download PDFInfo
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- CN113172199A CN113172199A CN202110442024.2A CN202110442024A CN113172199A CN 113172199 A CN113172199 A CN 113172199A CN 202110442024 A CN202110442024 A CN 202110442024A CN 113172199 A CN113172199 A CN 113172199A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
- B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
- B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
- B22C1/22—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins
- B22C1/2233—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
- B22C1/2246—Condensation polymers of aldehydes and ketones
- B22C1/2253—Condensation polymers of aldehydes and ketones with phenols
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
- B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
- B22C1/10—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives for influencing the hardening tendency of the mould material
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Abstract
The invention provides a preparation method of novel ammonia-free curing type casting precoated sand, which comprises the steps of preparing a curing agent into an aqueous solution with the concentration of 10-50%, adding a curing accelerator, and uniformly stirring for later use; preheating a proper amount of raw sand at 120-150 ℃ for 30min, heating until the temperature of the sand is stabilized at 115-120 ℃, adding phenolic epoxy resin, and stirring for 30 min; then cooling while stirring to ensure that the temperature of the sand is stabilized at 60-110 ℃; then adding the curing agent aqueous solution and calcium stearate into the sand in sequence, and continuously stirring for 30min at the temperature of 60-110 ℃; and finally, stirring and cooling to about 50 ℃, and sieving by using a standard 20-mesh inspection sieve to obtain the precoated sand. The invention adopts the novolac epoxy resin as the binder of the precoated sand, correspondingly selects the compounds containing active hydrogen such as amines, acids and the like as the curing agent, adds a certain amount of curing accelerator, and utilizes the reaction of epoxy groups in the novolac epoxy resin and the curing agent to crosslink and cure the novolac epoxy resin, thereby not emitting harmful gas and not generating other micromolecules in the curing process.
Description
Technical Field
The invention belongs to the technical field of precoated sand, and particularly relates to a preparation method of novel ammonia-free curing type casting precoated sand.
Background
The precoated sand for casting is molding sand or core sand in which a layer of solid binder is coated on the surface of raw sand particles before molding or core making. The precoated sand is mainly applied to the foundry industry, particularly the automobile industry, and is used for producing iron castings, automobile parts and the like through a shell-method casting process. The manufacturing process of the precoated sand comprises the steps of mixing heated raw sand with thermoplastic phenolic resin, curing agent hexamethylenetetramine and lubricant calcium stearate, then mechanically stirring to cover a layer of resin and curing agent on the surface of sand grains, cooling and screening to obtain the precoated sand. When molding (core), the thermoplastic phenolic resin on the surface of the coated sand is heated and melted, reacts with hexamethylenetetramine to solidify and mold the coated sand, and emits organic gases such as ammonia gas and the like.
The main defects of the existing shell casting process are that organic gases such as ammonia gas generated by the reaction of hexamethylene tetramine and the like are directly discharged into the air when the precoated sand is solidified, the environment is polluted, the requirement of environmental protection is not met, the smell is pungent, the irritation to the respiratory tract of people is great, and the physical health of workers is seriously harmed.
In order to solve the problem, the existing improvement method mainly reduces the using amount of hexamethylenetetramine or prepares the precoated sand with low gas evolution by a physical blending method. Chinese patent No. CN201910449290.0 discloses modified phenolic resin-based precoated sand, which adopts low-free phenol boron modified phenolic resin and low-free phenol silicon modified phenolic resin, and the free phenol content of the phenolic resin is lower than 1%; a small amount of hexamethylenetetramine is used as a curing agent, calcium stearate and the like are used as lubricants, and the modified phenolic resin-based precoated sand is prepared. Because the modified phenolic resin with low free phenol and a small amount of curing agent are used, the gas evolution of the precoated sand is low. The invention of Chinese patent No. CN201610959026.8 adopts phenolic resin with low free phenol and low free aldehyde prepared by metal catalysis, non-ammonia curing agent, a small amount of hexamethylenetetramine and a proper amount of lubricant to prepare the low-ammonia precoated sand, the gas evolution is reduced by 60-90% compared with the precoated sand prepared by the traditional process, but the strength is slightly reduced. The invention patent of China with the patent number of CN201610748394.8 adopts the thermoplastic phenolic resin for the precoated sand and the solid thermosetting phenolic resin to be melted and mixed evenly to prepare the ammonia-free phenolic resin, and no strengthening agent is added to prepare the precoated sand, thereby obviously reducing the gas evolution of the precoated sand.
The method disclosed in the above patent can prepare the environment-friendly phenolic resin precoated sand with greatly reduced gas evolution, but can cause the strength reduction after the precoated sand is formed, and can not completely avoid the emission of small molecular byproducts, and can still pollute the environment and cause harm to the bodies of workers.
Disclosure of Invention
The invention aims to provide a preparation method of novel ammonia-free curing type casting precoated sand, which does not emit harmful gas or generate other small molecules in the curing process and has excellent strength performance of the cured precoated sand by selecting raw materials such as resin, curing agent and the like and optimizing the preparation process of the precoated sand.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of novel ammonia-free curing type casting precoated sand comprises the following steps:
s1, preparing an amine curing agent or an acid curing agent into an aqueous solution with the concentration of 10-50%, adding a curing accelerator, and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 115-120 ℃, stirring for 1-10 min, and then cooling while stirring to stabilize the temperature of the sand at 80-110 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 1.4-2% of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 80-110 ℃ for 1-10 min, wherein the mass of the curing agent is 20-30% of that of the novolac epoxy resin, and the mass of the calcium stearate is 6-9% of that of the novolac epoxy resin;
s4, keeping stirring and cooling to below 60 ℃, and sieving by using a standard inspection sieve of 15-30 meshes to obtain precoated sand;
the novolac epoxy resin comprises one or a combination of phenol novolac epoxy resin, bisphenol A novolac epoxy resin and o-cresol novolac epoxy resin, the softening point is 76-100 ℃, the epoxy equivalent is 100-220 g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
The invention innovatively adopts novolac epoxy resin as a binder of the precoated sand, correspondingly selects amines, acids and other compounds containing active hydrogen as a curing agent, adds a certain amount of curing accelerator, and utilizes the reaction of epoxy groups in the novolac epoxy resin and the curing agent to realize crosslinking and curing, so that harmful gas is not released in the curing process, and other small molecules are not generated. The invention further optimizes the selection of the novolac epoxy resin, has high crosslinking density, can fully wrap the precoated sand, and ensures that the strength performance of the precoated sand is good after curing. Particularly, long-term experimental research shows that the steps and parameter settings of the preparation process are optimized according to the properties of the novolac epoxy resin and the precoated sand, the process cost is low, the quality is controllable, and the production and popularization are facilitated.
In the present invention, the mass of the curing accelerator is preferably 5% to 15%, preferably 10%, of the mass of the curing agent. The curing accelerator needs to be matched with a curing agent for use, can accelerate the curing reaction or reduce the curing temperature, and is obtained by the inventor through a large number of experimental adjustments, so that the using effect is good.
In the invention, the novolac epoxy resin is preferably o-cresol novolac epoxy resin, the softening point is 85-95 ℃, and the epoxy equivalent is 200-220 g/mol.
The o-cresol formaldehyde epoxy resin is a polyfunctional glycidyl ether type epoxy resin developed in the foreign 70 s for adapting to the rapid development of the semiconductor industry and the electronic industry. The o-cresol novolac epoxy resin has the advantages that each benzene ring is connected with an epoxy group from the view of a molecular structure, a cross-linking point which is 2.5 times that of the o-cresol novolac epoxy resin can be provided during curing, the cross-linking density is high, a three-dimensional network structure is easily formed during curing, and the o-cresol novolac epoxy resin contains a phenolic structure, so that the o-cresol novolac epoxy resin has excellent thermal stability, mechanical strength and water resistance. The softening point can reach 85-95 ℃. In addition, the o-cresol formaldehyde epoxy resin has the advantages that when the softening point is changed, the epoxy value is basically unchanged, the melting viscosity is low, the o-cresol formaldehyde epoxy resin can uniformly and well wrap the surface of raw sand when being stirred and mixed with the raw sand, the process quality for preparing the precoated sand is controllable, and the cured performance is excellent.
In the present invention, preferably, the preparation of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 75-85 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 60-100 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin. Further, the polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.1-0.2: 1. the heat resistance of the o-cresol formaldehyde epoxy resin can be further improved by introducing polymethylphenylsiloxane, particularly, the polymethylsiloxane containing hydroxyl is introduced, the hydroxyl can react with an epoxy group, the crosslinking degree is further improved, the Tg of a cured product can be increased to 90-100 ℃, and the internal stress is reduced.
In the present invention, preferably, the amine curing agent comprises one or a combination of 4,4' -diaminodiphenyl sulfone, 3-cyclohexylamine-1-propanesulfonic acid, 2-cyclohexylamine ethanesulfonic acid, 3-cyclohexylamine-2-hydroxy-1-propanesulfonic acid; the acid curing agent comprises one or a combination of 1,2,3, 4-butanetetracarboxylic acid, L-lysine, taurine, citric acid, succinic acid and adipic acid.
In the present invention, preferably, the acid curing agent is one of citric acid, succinic acid and 1,2,3, 4-butanetetracarboxylic acid.
In the present invention, the mass of the calcium stearate is preferably 0.10% to 0.20% of the mass of the resin sand.
In the present invention, preferably, the curing accelerator includes one of HDG-a/B epoxy resin curing accelerators, benzyldimethylamine, triethylamine, triethanolamine, 2,4, 6-tris (dimethylaminomethyl) phenol, resorcinol, m-cresol, boron trifluoride triethylphosphine, boron trifluoride triisopropylphosphine, trimethylphosphine, preferably 2,4, 6-tris (dimethylaminomethyl) phenol.
The invention also provides the casting precoated sand prepared by the preparation method of the novel ammonia-free curing type casting precoated sand.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention innovatively adopts novolac epoxy resin as a binder of the precoated sand, correspondingly selects amines, acids and other compounds containing active hydrogen as a curing agent, adds a certain amount of curing accelerator, and utilizes the reaction of epoxy groups in the novolac epoxy resin and the curing agent to realize crosslinking and curing, so that harmful gas is not released in the curing process, and other small molecules are not generated.
2. The invention further optimizes the selection of the novolac epoxy resin, has high crosslinking density, can fully wrap the precoated sand, and ensures that the strength performance of the precoated sand is good after curing. Particularly, long-term experimental research shows that the steps and parameter settings of the preparation process are optimized according to the properties of the novolac epoxy resin and the precoated sand, the process cost is low, the quality is controllable, and the production and popularization are facilitated.
3. The invention solves the problems that the environment is polluted by irritant gases such as ammonia gas and the like and the health of workers is damaged when the precoated sand is cured and molded by the prior process.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments, but the scope of the present invention is not limited to the embodiments.
Example 1:
the preparation method of the ammonia-free curing type casting precoated sand comprises the following steps:
s1, preparing a citric acid curing agent into an aqueous solution with the concentration of 10%, adding a curing accelerator DMP-30 (the mass is 10% of the mass of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 120 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 115 ℃, stirring for 10min, and then cooling while stirring to stabilize the temperature of the sand at 80 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 2.0 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 80 ℃ for 10min, wherein the mass of the citric acid curing agent is 20% of that of the resin, and the mass of the calcium stearate is 6% of that of the resin;
and S4, keeping stirring, cooling to 50 ℃, and sieving by using a standard 30-mesh test sieve to obtain the precoated sand.
The phenolic epoxy resin is o-cresol formaldehyde epoxy resin, the softening point is 85-95 ℃, the epoxy equivalent is 200-220g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
The preparation method of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 75 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 100 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin. The polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.1: 1.
example 2:
the preparation method of the ammonia-free curing type casting precoated sand comprises the following steps:
s1, preparing a citric acid curing agent into an aqueous solution with the concentration of 50%, adding a curing accelerator DMP-30 (the mass is 5% of the mass of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 150 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 120 ℃, stirring for 1min, and then cooling while stirring to stabilize the temperature of the sand at 110 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 1.8 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 110 ℃ for 1min, wherein the mass of the citric acid curing agent is 30% of that of the resin, and the mass of the calcium stearate is 9% of that of the resin;
s4, keeping stirring and cooling to 60 ℃, and sieving by using a 15-mesh standard test sieve to obtain precoated sand;
the phenolic epoxy resin is bisphenol A type phenolic epoxy resin and o-cresol novolac epoxy resin according to the mass ratio of 1: 1, the softening point is 85-90 ℃, the epoxy equivalent is 195-220g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
The preparation method of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 85 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 75 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin. The polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.2: 1.
example 3:
the preparation method of the ammonia-free curing type casting precoated sand comprises the following steps:
s1, preparing a citric acid curing agent into an aqueous solution with the concentration of 30%, adding a curing accelerator DMP-30 (the mass is 15% of the mass of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 135 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 120 ℃, stirring for 3min, and then cooling while stirring to stabilize the temperature of the sand at 100 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 1.4 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 100 ℃ for 5min, wherein the mass of the citric acid curing agent is 25% of that of the resin, and the mass of the calcium stearate is 7% of that of the resin;
s4, keeping stirring and cooling to 55 ℃, and sieving by using a 20-mesh standard test sieve to obtain precoated sand;
the phenolic epoxy resin is o-cresol formaldehyde epoxy resin, the softening point is 85-95 ℃, the epoxy equivalent is 190-220g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
The preparation method of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 80 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 85 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin. The polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.15: 1.
example 4:
the preparation method of the ammonia-free curing type casting precoated sand comprises the following steps:
s1, preparing a 4,4' -diamino diphenyl sulfone curing agent into an aqueous solution with the concentration of 20%, adding a curing accelerator triethylamine (the mass of triethylamine is 12% of the mass of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 130 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 115 ℃, stirring for 7min, and then cooling while stirring to stabilize the temperature of the sand at 90 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 1.8 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 90 ℃ for 10min, wherein the mass of the 4,4' -diamino diphenyl sulfone curing agent is 20% of the mass of the resin, and the mass of the calcium stearate is 7% of the mass of the resin;
s4, keeping stirring and cooling to 55 ℃, and sieving by using a 30-mesh standard test sieve to obtain precoated sand;
the phenolic epoxy resin is phenol type phenolic epoxy resin and o-cresol novolac epoxy resin according to the mass ratio of 1: 1, the softening point is 83-88 ℃, the epoxy equivalent is 200-220g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
The preparation method of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 80 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 85 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin. The polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.1: 1.
example 5:
the preparation method of the ammonia-free curing type casting precoated sand comprises the following steps:
s1, preparing a 25% aqueous solution from a 3-cyclohexylamine-1-propanesulfonic acid curing agent, adding a curing accelerator triethanolamine (the mass of the curing accelerator triethanolamine is 10% of that of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 130 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 120 ℃, stirring for 8min, and then cooling while stirring to stabilize the temperature of the sand at 100 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 1.8 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 100 ℃ for 30min, wherein the mass of the 3-cyclohexylamine-1-propanesulfonic acid curing agent is 25% of that of the resin, and the mass of the calcium stearate is 8% of that of the resin;
s4, keeping stirring and cooling to 55 ℃, and sieving by using a 20-mesh standard test sieve to obtain precoated sand;
the phenolic epoxy resin is o-cresol formaldehyde epoxy resin, the softening point is 85-95 ℃, the epoxy equivalent is 210-220g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
The preparation method of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 85 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 80 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin. The polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.2: 1.
comparative example 1:
in comparison with example 1, no novolac epoxy resin was used, but an equivalent amount of novolac resin was used instead, with the selection of the curing agent and the process parameters being modified accordingly according to the means conventional in the art.
Comparative example 2:
compared with the example 1, the phenolic epoxy resin is not adopted, but the mixture of the phenolic resin and the epoxy resin with the same amount is used for replacing, and the mass ratio of the phenolic resin to the epoxy resin is 1: 1, and correspondingly modifying the selection of the curing agent and the process parameters according to the conventional technical means in the field.
Comparative example 3:
compared with the example 1, the preparation parameters of the ammonia-free curing type casting precoated sand are different as follows:
s1, preparing a citric acid curing agent into an aqueous solution with the concentration of 10%, adding a curing accelerator DMP-30 (the mass is 10% of the mass of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 150 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 140 ℃, stirring for 10min, and then cooling while stirring to stabilize the temperature of the sand at 60 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 2.0 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 60 ℃ for 10min, wherein the mass of the citric acid curing agent is 20% of the mass of the resin, and the mass of the calcium stearate is 6% of the mass of the resin;
and S4, keeping stirring, cooling to 50 ℃, and sieving by using a standard 30-mesh test sieve to obtain the precoated sand.
Comparative example 4:
compared with the example 1, the preparation parameters of the ammonia-free curing type casting precoated sand are different as follows:
s1, preparing a citric acid curing agent into an aqueous solution with the concentration of 10%, adding a curing accelerator DMP-30 (the mass is 10% of the mass of citric acid), and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, preheating a proper amount of raw sand at 100 ℃ for 30min, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 90 ℃, stirring for 10min, and then cooling while stirring to stabilize the temperature of the sand at 60 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 2.0 percent of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 60 ℃ for 10min, wherein the mass of the citric acid curing agent is 20% of the mass of the resin, and the mass of the calcium stearate is 6% of the mass of the resin;
and S4, keeping stirring, cooling to 45 ℃, and sieving by using a standard 30-mesh test sieve to obtain the precoated sand.
Performance testing
The novel ammonia-free curing type foundry precoated sand finally prepared in examples 1 to 5 and comparative examples 1 to 4 were subjected to the relevant performance tests. Preparing a sample strip in a precoated sand sample preparation machine, heating and curing, and testing the strength, wherein the preparation conditions comprise that the sand shooting pressure is 0.5MPa, the sand shooting time is 2s, and the temperature is kept at 210 ℃ for 2min and 30 s. And testing the hot tensile strength, tensile strength and bending strength of the precoated sand according to the GB/T8583-2008 standard.
The gas evolution refers to the gas content of all inorganic substances in the precoated sand generated under the high temperature condition, and the gas evolution is tested according to the conventional test method in the field, as follows. The porcelain boat or the steel boat is put into a heating chamber of an air-generating capacity tester to be preheated for 1 minute for standby. Weighing 1 g of sample sand (obtained by grinding a bending-resistant sample) by using a high-precision balance, pouring the weighed sample sand into a carrier, placing the carrier into a heating chamber of an outgassing amount tester, and then rapidly closing a rear cover of the heating chamber, wherein the temperature of the heating chamber is controlled to be about 115 ℃. At the moment, the gas emission tester starts to work, and the gas emission data is displayed on a digital display and gradually increases from zero. When the value is changed from increasing to attenuating, the maximum value at the moment is determined as the maximum gas value of the sample sand. The test is carried out 3 times by the same method, and the average value of the data is the final judgment value. The test results are shown in table 1.
TABLE 1
As can be seen from Table 1, the hot tensile strength of the non-ammonia solidified type casting precoated sand prepared in the examples 1 to 5 of the invention is basically consistent with that of the casting precoated sand prepared in the comparative example 1, but the bending strength at normal temperature is obviously improved, the gas evolution is obviously reduced, and more importantly, no pungent odor is generated during heating and core making, so that the operating environment of workers is practically protected. Compared with example 1, comparative example 1 adopts phenolic resin instead of novolac epoxy resin, comparative example 2 adopts a mixture of phenolic resin and epoxy resin instead of novolac epoxy resin, and comparative examples 3 and 4 change preparation parameters; in these four cases, the obtained foundry coated sand was reduced in all of the hot tensile strength, tensile strength and flexural strength and increased in gas evolution, compared with example 1 of the present invention.
Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (10)
1. A preparation method of novel ammonia-free curing type casting precoated sand is characterized by comprising the following steps:
s1, preparing an amine curing agent or an acid curing agent into an aqueous solution with the concentration of 10-50%, adding a curing accelerator, and uniformly stirring to obtain a curing agent aqueous solution for later use;
s2, heating the raw sand, adding phenolic epoxy resin after the temperature of the sand is stabilized at 115-120 ℃, stirring for 1-10 min, and then cooling while stirring to stabilize the temperature of the sand at 80-110 ℃ to obtain resin sand for later use; wherein the mass of the novolac epoxy resin is 1.4-2% of the mass of the raw sand;
s3, sequentially adding a curing agent aqueous solution and calcium stearate into the resin sand, and continuously stirring at 80-110 ℃ for 1-10 min, wherein the mass of the curing agent is 20-30% of that of the novolac epoxy resin, and the mass of the calcium stearate is 6-9% of that of the novolac epoxy resin;
s4, keeping stirring and cooling to below 60 ℃, and sieving by using a standard inspection sieve of 15-30 meshes to obtain precoated sand;
the novolac epoxy resin comprises one or a combination of phenol novolac epoxy resin, bisphenol A novolac epoxy resin and o-cresol novolac epoxy resin, the softening point is 76-100 ℃, the epoxy equivalent is 100-220 g/mol, and the inorganic chlorine is less than or equal to 0.001mol/100 g.
2. The method for preparing the novel ammonia-free curing type foundry precoated sand according to claim 1, wherein the mass of the curing accelerator is 5 to 15%, preferably 10%, of the mass of the curing agent.
3. The preparation method of the novel ammonia-free curing type foundry precoated sand according to claim 1, wherein the novolac epoxy resin is o-cresol novolac epoxy resin, the softening point is 85-95 ℃, and the epoxy equivalent is 200-220 g/mol.
4. The preparation method of the novel ammonia-free curing type foundry precoated sand according to claim 3, wherein the preparation of the o-cresol formaldehyde epoxy resin comprises the following steps:
adding the o-cresol formaldehyde epoxy resin and xylene into a container, heating while stirring, raising the temperature to 75-85 ℃, and preserving the temperature to completely melt the o-cresol formaldehyde epoxy resin; and adding polymethylphenylsiloxane into the container, adjusting the temperature to 60-100 ℃ to enable the polymethylphenylsiloxane to react with the o-cresol formaldehyde epoxy resin, removing xylene after the reaction is completed, and drying to obtain the epoxy resin.
5. The preparation method of the novel ammonia-free curing type casting precoated sand according to claim 4, wherein the polymethylphenylsiloxane is hydroxyl-terminated polymethylphenylsiloxane, and the molar ratio of the hydroxyl-terminated polymethylphenylsiloxane to the o-cresol formaldehyde epoxy resin is 0.1-0.2: 1.
6. the method for preparing the novel ammonia-free curing type foundry precoated sand according to claim 1, wherein the amine curing agent comprises one or a combination of 4,4' -diaminodiphenyl sulfone, 3-cyclohexylamine-1-propanesulfonic acid, 2-cyclohexylamine ethanesulfonic acid and 3-cyclohexylamine-2-hydroxy-1-propanesulfonic acid; the acid curing agent comprises one or a combination of 1,2,3, 4-butanetetracarboxylic acid, L-lysine, taurine, citric acid, succinic acid and adipic acid.
7. The method for preparing the novel ammonia-free curing type foundry precoated sand according to claim 6, wherein the acid curing agent is one of citric acid, succinic acid and 1,2,3, 4-butanetetracarboxylic acid.
8. The method for preparing the novel ammonia-free curing type foundry precoated sand according to claim 1, wherein the mass of the calcium stearate is 0.10-0.20% of the mass of the resin sand.
9. The method for preparing the novel ammonia-free curable foundry precoated sand according to claim 1, wherein the curing accelerator comprises one of an HDG-A/B epoxy resin curing accelerator, benzyldimethylamine, triethylamine, triethanolamine, 2,4, 6-tris (dimethylaminomethyl) phenol, resorcinol, m-cresol, boron trifluoride triethylphosphine, boron trifluoride triisopropylphosphine, and trimethylphosphine, preferably 2,4, 6-tris (dimethylaminomethyl) phenol.
10. The foundry precoated sand obtained by the process for preparing the novel ammonia-free curable foundry precoated sand according to any one of claims 1 to 9.
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