RU2292982C1 - Method for preparing carbamide-phenol-formaldehyde-furan binding agent for casting shell forms and rods - Google Patents

Abstract

FIELD: casting manufacture.

SUBSTANCE: invention relates to methods for preparing binding agents for casting shell forms and rods being both for cold-hardening and hardening articles in the hot equipment. Method involves the condensation reaction of monomers of carbamide, furfuryl alcohol, phenol and formaldehyde wherein carbamide-formaldehyde concentrate is used as formaldehyde-containing and carbamide-containing components. The condensation reaction is carried out successively into a single reactor and with absence of vacuum-drying wherein carbamide-formaldehyde concentrate is heated firstly at pH 8.0-8.5 and then at pH 5.0-5.5. Then phenol is added to a synthesized oligomer and the condensation reaction is carried out at pH 8.0-8.5 followed by addition of furfuryl alcohol and carrying out the further condensation process. Method provides carrying out the ecologically pure manufacturing and enhancing quality of a binding agent.

EFFECT: improved method of synthesis.

4 cl, 4 tbl, 1 ex

Description

The invention relates to foundry, and in particular to methods for producing binders for foundry shell molds and cores for both cold-hardening and curing in hot snap.

In all existing methods (technologies) for the synthesis of resins, formaldehyde, which is an aqueous solution of formaldehyde (usually 37%), is used as the aldehyde-containing component. In aqueous solutions in neutral or alkaline environments, formaldehyde is in hydrated form in the form of methylene glycol. Methylene glycol in aqueous solutions is prone to polycondensation with the formation of polyoxymethylene glycols. In this case, dimers and oligomers are formed. Therefore, in an aqueous solution (in formalin) there is an equilibrium mixture of free formaldehyde, methylene glycol and polyoxymethylene glycols. Under certain conditions (long-term storage, low temperature, high concentration of formaldehyde) polymers are formed which precipitate in the form of paraformal powder. When heated, paraforms dissolve in formalin, degrading to methylene glycol. Paraform precipitation slows down when methanol (methyl alcohol) is added to formalin, which forms polyoxymethylene glycols monomethyl ethers (hemiacetals) and inhibits the growth of polymer molecules. Therefore, formalin used as a feedstock has, due to the above, a low concentration of formaldehyde (about 37%) and contains 6-15% methanol (an inhibitor of polymerization of formaldehyde), which is subsequently an extremely undesirable component throughout the entire production and use of the resin .

In addition to the costs of transporting water and methanol in formalin, the formalin working conditions themselves leave much to be desired. Reception, storage and supply of formalin to reactors are accompanied by the release of free formaldehyde into the environment. And formaldehyde is a combustible and toxic gas. The explosive limit of mixtures with air is 7-73% (by volume). Formaldehyde has an irritating effect on the mucous membranes of the eyes, upper respiratory tract, and causes dermatitis. Formaldehyde has a general toxic, allergic and mutagenic effect on the human body. The maximum permissible concentration (MPC) of formaldehyde in the air of industrial premises is 0.5 mg / m ³ . In most resin plants, the actual concentration of formaldehyde is 10 times higher. Formaldehyde itself has a second hazard class among SDYA (potent toxic substances).

In the synthesis of CFS, 747 kg of formalin per 1 ton of the resulting resin are poured into the reactor. After alkaline and acid condensation of urea with formaldehyde, the reaction mixture is evaporated under vacuum (vacuum distillation drying), i.e. excess water that is forced into the reactor along with formalin must be removed in the most wasteful way — by converting it into steam, followed by condensation. As a result, 340-470 kg of harmful effluents, which are called “tar tar”, are formed per 1 ton of the obtained resin. Suprasmal waters contain 8-12% methanol and 5-8% formaldehyde. It is not always possible to ensure the collection and processing of toxic methanol- and formaldehyde-containing supra-tar waters formed during the synthesis of resins, because may not be close to formaldehyde production where these tar waters are satisfactorily processed.

Wastewater treatment at each CFS manufacturer by chemical reagents or special biological methods entails significant additional costs. Therefore, often CFS manufacturers dump their toxic methanol- and formaldehyde-containing tar tar waters into the environment, causing irreparable damage to nature. For good reason, for example, it is forbidden to transport methanol through pipes if they are in the ground, because small doses of methanol alter the development of plants at the genetic level. Methanol does not all go into the tar water and part of it remains in the resin, and the use of methanol-containing resins increases the methanol content in the working area, which adversely affects maintenance personnel.

A known method of producing a modified urea resin, which can be used as a binder in the manufacture of shell molds and rods. This method consists in the fact that the modified urea resin is obtained by condensation of urea, formaldehyde and furyl alcohol, and urea and furyl alcohol are introduced into an alkaline neutralized aqueous formalin solution in which polyvinyl alcohol taken in an amount of 0.5-30 g per 100 g is dissolved 37% formaldehyde solution (see AS USSR No. 355189, IPC 4 08 G 12/40, 1972).

The disadvantage of this method is the low quality of the obtained resins used as a binder, since the resins contain excessive formaldehyde released during the manufacture of rods. Since formaldehyde has a second hazard class among SDYaV, its allocation in the manufacture of foundry cores leads to air pollution in foundries. In addition, this method of producing resins involves the operation of drying the resin, which leads to the appearance of toxic tar tar waters and to increase the duration of the manufacturing process.

A known method of producing a urea-formaldehyde resin used as a binder in the manufacture of foundry cores and molds, which consists in loading an aqueous solution of formaldehyde and urea, adjusting the pH of the mixture to 7.2-7.8 by introducing a NaOH solution into it, and heating the mixture condensation of the reaction partners is carried out, vacuum drying is carried out, and then furyl alcohol, triethanolamine and rosin soap are introduced into it, after which it is again heated and kept at a temperature of 100 ° C with continuous stirring for an hour (see a.s. USSR No. 246833, IPC 4 C 08 G 12/40, 1969).

The disadvantage of this method is the use of an aqueous solution of formaldehyde as one of the reagents, which leads to the release of formaldehyde vapor both during the preparation of the resin and during the manufacture of the rods. The presence of the operation of vacuum drying, which leads to the appearance of toxic tar water and to increase the duration of the manufacturing process, is a significant drawback of the known method.

A known method of producing a urea-furan binder for cold-hardening sand-resin mixtures, which consists in a two-stage condensation of urea, formaldehyde and furfuryl alcohol. In the first stage, urea and formaldehyde are condensed, first in an alkaline, then in an acidic medium, and in the second stage of condensation, tetrahydrofuran is introduced simultaneously with furfuryl alcohol (see RF patent No. 2048950, IPC 6 В 22 С 1/22, 1995).

The disadvantage of this method is the conduct of the reaction in the column, thereby increasing the duration of the process, in addition, the presence of a vacuum drying operation leads to the appearance of the same toxic tar waters and also increases the preparation time of the resin.

A known method of producing a phenol-formaldehyde binder for foundry shell molds and cores, including the polycondensation of phenol with formaldehyde and modifying the resin with a mixture of urea with formaldehyde (see RF patent No. 2044588, IPC 6 B 22 C 1/22, 1995).

The disadvantage of this method is the low quality of the binder, the bulkiness of the technological scheme and the presence of a drying operation.

All of the above methods are designed to obtain resins, the quality of which does not meet the modern requirements for resins used for the preparation of sand-resin mixtures.

Therefore, resins have recently been developed that are prepared by condensing individual oligomers in different reactors. The following is an example of such a method.

A known method of producing urea-phenol-furan binder for the manufacture of foundry cores. This method consists in the fact that in one reactor the urea-furan oligomer is condensed, which is a product of the condensation of urea with formaldehyde modified with furfuryl alcohol. In the second reactor, the phenol-carbamide-formaldehyde oligomer is condensed, which is the product of the condensation of phenol with formaldehyde in an alkaline medium, followed by post-condensation of the resin with urea. Then the contents of the first and second reactors are mixed in a certain ratio in the third reactor, where they are condensed together, followed by the addition of furfuryl alcohol. When condensing oligomers in reactors, a vacuum drying operation is performed (see RF patent No. 2044590, IPC 6 V 22 C 1/22, 1995). This decision was made as a prototype.

The disadvantage of the prototype is the cumbersome, costly technology for the preparation of resin in three reactors. The presence of the operation of vacuum drying leads to additional costs, both energy, necessary for the operation, and temporary. In addition, the process of cooking the resin is accompanied by the release of harmful substances due to the use of an aqueous solution of formalin and the appearance of tar waters, which also leads to additional costs for their neutralization.

The problem solved by the invention is the simplification of the technology for the manufacture of binders, and a significant reduction in energy consumption in the manufacture of resins. It also solves the problem of obtaining high-quality environmentally friendly binders for foundry shell molds and cores of both cold curing and hot-clad mixtures, which minimize the presence of harmful impurities released during the manufacture of cores, while improving the strength characteristics of core mixtures and reducing the consumption of binders in the manufacture foundry shell molds and cores. The invention also solves the problem of eliminating the operation of vacuum drying, and as a result, the absence of tar water, as well as reducing the preparation time of the resin and reducing the cost of transportation of the reaction partners.

The problem is solved due to the fact that in the method for producing a urea-phenol-formaldehyde-furan binder for foundry shell molds and cores, including the condensation of urea, furfuryl alcohol, phenol and formaldehyde monomers, in accordance with the invention, the urea-formaldehyde-condense reaction conduction is used as the formaldehyde-containing component, and in one reactor, in the absence of a vacuum drying operation, the urea-formaldehyde concentrate is first heated at pH 8.0-8.5, then at pH 5.0-5.5, phenol is added to the oligomer obtained and condensation is carried out at pH 8.0-8.5, then furfuryl alcohol is added and further condensation is carried out.

Urea-formaldehyde concentrate is used in the form of a composition containing "total" formaldehyde in the range of 55-60 wt.% And "total" urea in the range of 20-25 wt.%.

Phenol and furfuryl alcohol are added to the reactor in two stages, loading up to 1/2 volume or weight of each component.

Condensation is carried out at a temperature of the reaction mixture from 65 ° C to 100 ° C.

The technical result from the use of the invention lies in the fact that through the use of urea-formaldehyde concentrate (CPK), firstly, they get rid of the operation of vacuum drying, which leads to the absence of tar waters and, as a result, to obtain environmentally friendly production, and, in -second, it can significantly improve the quality of the resulting binder.

Condensation in one reactor in the absence of a drying operation reduces the preparation time of binders and allows more efficient use of equipment.

In addition, obtained by the present method, binders have greater strength and cost-effectiveness when used as binders in the foundry. Tests have shown that the consumption of binders in the manufacture of rods is markedly reduced.

When implementing the proposed method for producing binders (casting resins), in comparison with existing methods of obtaining, we achieve the following technical results:

- one reactor is used, the other two are released for cooking other binders, or when cooking the same binder in three reactors at once, the production capacity increases several times;

- in the technology for producing the casting resin according to the invention there is no stage of evaporation (vacuum drying) of the reaction mixture, therefore, there are no toxic methanol and formaldehyde-containing tar waters and there are no drains;

- since methanol is practically absent in KFK, the resin is obtained without methanol, and hence the absence of air pollution in the production room when using resins;

- the air is not polluted by methanol emissions during the synthesis of the binder;

- the transition to the use of KFK instead of formalin among consumers does not require any significant costs, since the existing technological equipment is used;

- the cost of transporting raw materials is reduced, because unnecessary water is not transported forcibly;

- increased productivity of the equipment, since the volume of the reactor is not engaged in useless water, and vacuum drying equipment is excluded altogether;

- reduced consumption of steam and electricity, since there is no stage of evaporation of water.

Successive condensation of urea-formaldehyde concentrate in alkaline and then in acidic media, followed by the addition of phenol and condensation in an alkaline medium allows to obtain high quality binders. The addition of furfuryl alcohol ensures that the binders are brought up to the required composition ratios.

Comparison of the claimed method with the prior art in technical and patent documentation for the priority date in the main and related sections shows that the set of essential features of the claimed solution was not previously known, therefore, it meets the patentability condition of "novelty."

Analysis of known solutions in this field showed that the proposed method has features, the use of which in the claimed combination of features makes it possible to achieve a new result, therefore, the proposed method has an inventive step compared to the existing level of technology.

The proposed solution is applicable, workable and feasible, because it is used in the preparation of binders for the production of casting shell molds and cores, therefore, it meets the patentability condition “industrial applicability”.

In the manufacture of binders by the present method can be used conventional equipment used in the manufacture of binders by known technologies.

The following is an example of the manufacture of binders by the present method.

The urea-phenol-formaldehyde-furan binder is obtained by condensation of monomers and oligomers in a single 3.2 m ³ reactor, which is a vertical cylindrical apparatus with a spherical bottom, equipped with a stirrer and a jacket for heating and cooling the mixture.

A binder was obtained as a result of the condensation of urea with formaldehyde by heating a urea-formaldehyde concentrate (CPK) in the form of a composition containing "total" formaldehyde in the range of 55-60 wt.% And "total" urea in the range of 20-25 wt.%. First, in an alkaline (at pH 8.0-8.5), and then in an acidic (at pH 5.0-5.5) medium for 30 minutes each stage.

Then phenol is added in two portions to the obtained oligomer, and further condensation is carried out at pH 8.0-8.5. Process control is carried out by measuring the refractive index and viscosity.

Upon reaching the desired values of refractive index and viscosity of the furfuryl alcohol is added in two portions by _^half of the volume when exposed for 30 min.

The table shows the loading rate of each component per reactor volume, shown in the example.

Name of the main raw material The percentage of basic substance Recipe in kg Urea-formaldehyde concentrate (KFK) Nat. the weight 618 Phenol Nat. the weight 245.9 Furfuryl alcohol Nat. the weight 2124

CPK is poured into the reactor by weight dosing, adjusted by adding alkali to pH 8.0-8.5, then the mixture is heated to 90 ° C at a speed of 1.5-2 ° C per minute and with the refrigerator turned back on at this temperature lead the process of alkaline condensation for 30 minutes.

Then, a solution of sulfuric acid is charged into the reactor to lower the pH to a pH of 5.0-5.5, and at the same temperature, condensation is carried out in an acidic medium for 30 minutes. After completion of the condensation process in an acidic medium, a sodium hydroxide solution is loaded into the reactor to a pH of 8.0-8.5 and the mixture is cooled in the reactor to 85 ° C. The result is a kabamido formaldehyde oligomer.

Next, phenol is loaded into the same reactor in two portions of 50% each and kept at a temperature of 78-82 ° С to a refractive index of -1,500, then the temperature is raised to 88-90 ° С and kept to a viscosity set of 35-40 seconds (VZ 246 nozzle 6 mm).

The contents of the reactor are cooled to a temperature of not more than 60 ° C and the calculated amount of furfuryl alcohol is charged in portions of 50% of the total weight.

Obtained by the present method, the resins were tested in the manufacture of binders (see Appendix No. 1 - Conclusion on the test of the central factory laboratory of OJSC "VOLGOTSEMMASH").

Tables No. 1-3 show a comparative analysis of hardening mixtures made both with the use of the resin according to the prototype, and with the use of resins made by the claimed technology.

The high level of strength of the sand-tar mixtures made using the resin obtained by the implementation of the proposed method provides the possibility of reducing the consumption of the binder to 1.3% versus 2.0-2.5% in comparison with mixtures in which the resin obtained by the method is used prototype.

At the same time, the cost of hardening mixtures (TS) is almost halved and the gas content of the mixture is almost halved. The gas mode of the mold is improved, and in this regard, the likelihood of gas shells forming in the castings is minimized. Accordingly, marriage casting for gas sinks and other defects of gas origin is reduced.

The knockability of cores from castings is improved, the compliance of cores in the hardened casting is improved, as a result of which the likelihood of casting scraps along cracks is reduced. In connection with the improvement of the fluidity of the HARDWARE, the surface quality of the castings increases: the burning, roughness, and notches are reduced.

In the composition No. 1 (Table No. 1) used resin obtained by the prototype method. In compositions No. 2-6 used resin, welded by the proposed method, compositions No. 2-6 differ only in the amount of resin introduced into them.

A comparative analysis of the tensile strength showed that the composition No. 1 tensile strength is not much higher than that required by TU (see Table No. 3). In this case, mixtures with the resin introduced into them by the present method showed high strength properties at the same and lower resin consumption: about 1.5 times higher than that of the TC with the resin according to the prototype.

Thus, the tests showed that the mixtures made using resin according to the claimed method, that when the resin is used in the composition of the TS in the amount of 1.3% of the total mass, give results on tensile strength close to TU and comparable with the properties of the TS, which used a resin welded by the prototype method.

The consumption of resin according to the claimed method in an amount of 1.2% (composition No. 5), i.e. less than 1.3%, leads to a decrease in the strength of the vehicle below the level given in the technical specifications. However, this does not mean that a vehicle with a resin content of less than 1.3% is unacceptable. For specific foundry conditions, vehicles with a resin flow rate of less than 1.2% can be used.

Mix No. 4 is also prepared with a resin content of 1.3% in accordance with the claimed method, but it differs from mixture No. 6 in the increased catalyst content to 0.33%, thereby increasing the curing rate: strength after 1 and 2 hours is higher than that of composition of TS No. 6 (see Table No. 3). Accordingly, compositions No. 4 and 6 are distinguished by their survivability: composition No. 6 contains less catalyst (0.27%) and, therefore, it has survivability more than composition No. 4 with an increased catalyst content.

Compositions No. 3-6 in comparison with compositions No. 1-2 are more survivable (see Table No. 2). This is explained by the fact that during the hardening of the resin heat is generated and the temperature of the mixture rises, which leads to an increase in the polycondensation rate of the resin oligomer in the mixture. The hardening rate of the TS, determined by the strength value after 1, 2 hours, the more, the more resin in the composition of the TS, and vice versa, the smaller the resin, the lower the curing rate of the TS.

Tests of SVHK-65SL resin were performed in accordance with the requirements of TU-2223-001-14559685-2004

Table 1
Options for XTS formulations: Mixture components The composition of the mixture, wt.% No. 1 Number 2 Number 3 Number 4 Number 5 Number 6 According to TU Sand Forming enriched 1K ₂ O ₂ O25 GOST 2138-91 one hundred one hundred one hundred one hundred one hundred one hundred one hundred Catalyst
Benzosulfonic acid with a density of 1.266 g / cm ² 70% solution 0.7 0.7 0.3 0.33 0.23 0.27 0.7 Resin SVHK-65sl 2.0 2.0 1,5 1.3 1,2 1.3 2.0 Note:
No. 1 - with a prototype resin
No. 2-No. 6 - with resin produced according to a special recipe and technology.

table 2
Survivability XTS, min Mixture composition No. 1 Number 2 Number 3 Number 4 Number 5 Number 6 According to TU 5 5 6 8-10 12-13 12-13 Not regulated Table 3
Tensile strength, kg / cm ² Sample hardening time, through No. 1 Number 2 Number 3 Number 4 Number 5 Number 6 According to TU 1 hour 8.05 12.90 12.90 15.50 5.02 9.40 ≥5 2 hours 14.40 25,50 19,20 16,20 12.40 13,20 ≥10 24 hours 16,20 26.80 20.00 18.00 12.90 18.05 ≥15

Conclusion on SVHK-65SL:

The presented sample of SVHK-65SL resin meets the requirements of TU-2223-001-14559685-2004 and, in comparison with the prototype and TU, provides more than a twofold excess of strength, which allows us to offer XTC formulations with a reduced resin consumption of up to 1.2-1.3%.

Claims (4)

1. A method of producing a urea-phenol-formaldehyde-furan binder for foundry shell molds and cores, comprising condensation of urea, furfuryl alcohol, phenol and formaldehyde monomers, characterized in that as a formaldehyde-containing and urea-containing components, a urea-formaldehyde concentrate is used in a single reaction in the absence of a reaction, and vacuum drying, while the urea-formaldehyde concentrate is first heated at a pH of 8.0-8.5, then at a pH of 5.0-5.5, the resulting oligomer was added phenol and leads the condensation at pH 8.0-8.5, and then the furfuryl alcohol is added and further condensation carried out. 2. The method according to claim 1, characterized in that the use of urea-formaldehyde concentrate containing "total" formaldehyde 55-60 wt.% And "total" urea 20-25 wt.%. 3. The method according to claim 1, characterized in that phenol and furfuryl alcohol are added to the reactor in two stages, loading 1/2 of the volume or weight of the component. 4. The method according to claim 1, characterized in that the condensation is carried out at a temperature of the reaction mass of 65-100 ° C.