RU2455109C2 - Method of defining toxic gas release volume and composition - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy. At cold stage, lab tools are used to measure composition of gas release sand bled and core mixes and their binders as well as specific rates of emission for every toxic component for reduction to common feature. At hot stage, defined are teemed melt type, volume of sand blend and core mix for standard casts, range of maximum core and mol heating temperatures for selected casts, total volume of gas releases from toxic components in heating, as well as content of monoxide of carbon, phenol, formaldehyde, and total content of toxic gas releases from thermogram of destruction if said temperature range. Thereafter, vent system is designed with due allowance for MAC. Then, concentration of toxic gas release is measured to be compared with MAC. In case measured emission exceeds MAC, mixer efficiency and quantity of produced mould and cores are changed.

EFFECT: adequate dynamic control in production.

2 cl, 5 dwg, 4 tbl, 1 ex

Description

The invention relates to foundry technology, in particular to the technology of cold-hardening mixtures (CTS), as well as to measuring equipment, in particular, can be used in systems for measuring the volume and composition of toxic gas emissions.

Modern technological processes for the manufacture of foundry cores and molds (in serial and single production) are mainly based on the use of molding and core mixtures with synthetic hot and cold cured resins and liquid glass. Only in mass and large-scale production of molds does the process of making them from raw sand-bentonite mixtures prevail.

Data on the structure of the use of CTS in industry for mass and mass production workshops, for example in Germany, are given below [1],%: "Cold-box-amin" - 57; "Epoxy-SO2" - 6; "Resol-CO2" - 4; "CO2 process" - 5; “β-set” - 2. The remaining 26% is accounted for by rods manufactured in a heated snap-in (“Hot Boxes”, “Warm Boxes” and “Croning-process." According to the binder for the CTS, from which the molds are made, the structure in Germany next,%: furan resins - 42; phenolic resins - 16; “α-set" binders - 2.

Conventionally, the technological cycle can be divided into cold and hot stages. The cold stage involves mixing XTS, compacting the mixture in a core box or flask, and holding the core or mold before pouring it with the melt. The hot stage includes melt casting, cooling and knocking out the castings. In the cold stage, the decisive role is played by evaporation from mixtures of free monomers contained in polymer binders. The gas evolution in the core section and in adjacent areas depends on this indicator. In addition, some binders contain organic solvents, the content of which in the air is regulated by maximum permissible concentrations (MPC).

Binder manufacturers are constantly working to reduce the content of free monomers in the resins: phenol, formaldehyde and furyl alcohol. At the same time, the composition and technology of resin synthesis are being improved in order to increase the specific strength of the mixtures. This allows to reduce the content of binders in mixtures and proportionally - the gross volume of gas evolution. The greatest effect here is achieved due to the introduction of organosilicon adhesive adhesion hardeners - silanes. The level of free monomers in the resins and the resins themselves, which has been achieved at the present time, are shown in table 1.

Table 1 Content in foundry binders of free monomers Free monomer Type of binder furan resins for HTS phenolic resins for HTS Resins for the Croning Process Resins for Hot Boxes binder for the process "Cold-box-amin" The monomer content,% Phenol 0 <5 <0.2 <0.5 <3 Formaldehyde <0.2 <0.3 0 <0.2 <0.2 The total binder content (without catalyst),% 1.0 (1.6-1.8) 1.0 (1.8-2.0) 3.0 (4.0-5.0) 1.5 (2-2.2) 1.2 (1.6-1.8) Note. The level of 1975 is indicated in parentheses.

From the patent literature, a method is known for determining the amount, for example, of an oil product, in emissions of a steam-air mixture from a tank, including measuring the volumetric flow rate of a steam-air mixture from a tank, the concentration of oil product vapors in this mixture, and then calculating the mass flow rate of the oil product in emissions from the product of the measured values. The maximum values of the monitored parameters in the gas space of the tank are constantly compared with the set values of the parameters and, if they do not correspond, they conclude that the equipment is inoperative (see RF patent No. 2240512, publ. 2004) [2].

The known method takes into account only the volumetric parameters of the product and does not take into account others, for example temperature, and also does not analyze the composition of the vapor-air mixture.

There are two different approaches to quantifying gas evolution. The first [3, 4] is based on a laboratory experiment in which the preparation of the mixture and its subsequent exposure to complete hardening are simulated on the sample (prototype). The data obtained by determining the specific rate of emission for each toxic component and their reduction to a common indicator allow us to compare the toxicity of different types of mixtures. Thus, when designing new facilities or introducing new technologies in an existing facility, one can predict emissions and, accordingly, design local ventilation.

The second approach is instrumental measurements of the concentration of toxic substances in the air of the working area in the existing production and, if the MPC is exceeded, the implementation of appropriate measures: additional ventilation, adjusting the composition of the mixture, etc.

The second approach is a necessary addition to the first and is required to obtain permission from the sanitary-epidemiological service (SES) to use the process.

More complex is the analysis of emissions at the hot stage. Here, the nomenclature and volume of gases depend not only on the composition of the mixture and the type of binder, but also on the type of melt, design of the casting, pouring temperature, design of molds and cores, and the exposure time during crystallization of the melt and cooling. Therefore, the calculation of emissions for design, including the calculation of maximum permissible emissions (MPE) of toxic gas emissions, can only be individual for a given production.

In this regard, the current MPC for toxic gas emissions stipulates the limits for the concentration of toxic gas emissions in production, as well as the limits of the permissible error in measuring volume, temperature and other parameters that ensure the reliability of measurements and allow their control with the required accuracy.

The problem to which the invention is directed is to create a method that allows, in the process of determining the volume and composition of toxic gas emissions, to carry out operational dynamic control of compliance with MPC and measurement errors of the volume and composition of toxic gas emissions and to give recommendations on the amount of adjustment of the minimum allowable level of toxic gas emissions of the corresponding MPC .

The subject of the invention is a method for determining the volume and composition of toxic gas emissions during the production of foundry molds and cores using the technology of cold-hardening mixtures (CTS), their curing and crystallization and cooling of castings in molten cast molds, which consists in ensuring that the specified error is not exceeded measuring the volume and composition of toxic gas emissions and not exceeding the maximum permissible concentration (MPC) of toxic gas emissions determine toxic gas emissions when ying molds and core boxes and curing XTC units with the exposed surface of molds and cores, which amounts to phenol - 0,01-0,05 mg / dm 2 per hour and formaldehyde - 0.05-0.07 mg / dm2 per hour; gross gaseous emissions are determined by the performance of the mixers and the area of simultaneously cured molds and cores. Next, the total mass of gas evolution from the CTS is determined by the destruction thermogram during heating in the temperature range by conditionally dividing the mold wall into layers heated to the levels of maximum temperature ranges: 20-200; 200-400; 400-600; and above 600 degrees C; and determine for each selected temperature range a qualitative composition: carbon monoxide, phenol, formaldehyde and the total volume of toxic gas emissions. And then the obtained data on the volume of toxic gas emissions is adjusted by instrumental measurement of the concentration of toxic gas emissions in the air of the working area in the existing production and compared with the MPC data; when the error values exceed a predetermined value and / or exceeding the maximum permissible concentration, the calculated data are recorded, these parameters are displayed on the operator’s monitor and computer simulated with correction of the volume and composition of toxic gas emissions and taking into account the maximum permissible concentration, and after correction, they are compared with the specified values and the obtained data is output to the operator’s monitor.

Determination of specific emission rates separately for molds and rods for each toxic component and their reduction to a common indicator is carried out on laboratory samples.

As the melt poured into the mold, G13L steel is used. The wall thickness of the steel casting is taken equal to 100 mm.

Figure 5 schematically shows the algorithm of the method for determining the volume and composition of toxic gas emissions.

As can be seen from the drawing, the sequence of actions during the implementation of the method is as follows:

- at the cold stage, toxic gas emissions are determined when filling the molds and core boxes and curing from a unit of the open surface of the molds and rods, which are 0.01-0.05 mg / dm2 per hour for phenol and 0.05-0.07 mg / dm2 formaldehyde in hour;

- determine the gross toxic gas evolution by the performance of the mixers and the area of simultaneously cured molds and cores;

- at the hot stage, the total mass of toxic gas emissions from the CTS is determined from the destruction thermogram during heating in the temperature range by conditionally dividing the mold wall into layers heated to the levels of maximum temperature ranges: 20-200; 200-400; 400-600; and above 600 degrees C; next, for each selected temperature range, a qualitative composition is determined: carbon monoxide, phenol, formaldehyde and the total volume of toxic gas emissions;

- correct the obtained data on the volume of toxic gas emissions by instrumental measuring the concentration of toxic gas emissions in the air of the working area in the existing production and comparing them with the MPC data;

- when the values of the error are higher than the set value and / or exceeding the maximum permissible concentration, the calculated data are recorded, these parameters are displayed on the operator’s monitor and computer simulated with correction of the volume and composition of toxic gas emissions and taking into account the maximum permissible concentration, and after correction they are compared with the given values and the obtained data display on the operator’s monitor;

- upon reaching the volume and composition of toxic gas emissions above the MPC, the recommended values are given to the visual interface (operator) in the process of determining the volume and composition of toxic gas emissions at the cold and hot stages and the operator cyclically calculates and displays the values of the volume and composition of toxic gas emissions and the MPC values ( cyclicity means a repeated measurement over time of the volume and composition of toxic gas emissions, the frequency of repetition is set by the operator depending on the conditions of production );

- upon completion of determination of the volume and composition of toxic gas emissions and comparison with MPC data, information is transmitted to the operator’s monitor and then to the data accounting system.

In the process of determining the volume and composition of toxic gas emissions, tuning parameters are used, including MPC values and the values of the permissible relative error of measurements of the gas evolution volume, temperature, gas emission area, typical shapes, measuring channels of the system, etc. set by the operator.

Compliance with the recommended values allows you to avoid errors in determining the volume and composition of toxic gas emissions in terms of excess MPC and measurement error.

The presence of control (monitoring) in the process of determining the volume and composition of toxic gas emissions allows the operator, if necessary, to change the performance of the mixers, the number of manufactured molds and cores, taking into account the measurement error of the parameters, both to ensure an acceptable measurement error and in case of emergency situations - exceeding the maximum permissible concentration.

The inventive method for determining the volume and composition of toxic gas evolution can be implemented using a system that measures the volume and composition of toxic gas evolution, the temperature of the melt being poured into the molds and the CTS itself and dynamically controlling measurement errors using a microprocessor and a display device, which can be an independent structural element , and combined with the display of the measuring system (IP) or displayed on the computer display, if used.

The parameters of the volume, composition of toxic gas emissions, temperature, and other IP detectors enter the device for calculating these parameters and dynamic control of measurement errors, where they are processed.

The proposed method is carried out as follows in relation to the conditions of a real enterprise producing medium and large steel castings. The enterprise provides for the production of molds and large rods according to the α-set process (binder is a formaldehyde alkaline resin, cured by a mixture of esters) and small rods according to the β-set process (binder of the same type, hardener is gaseous methyl formate). the implementation of the method is to obtain specific emission values separately for the molds and rods for each of the toxic main components formed at the hot stage of the gas mixture.

The initial data for determination should be the composition of the molding and core mixtures, the type of melt and pouring temperature, technological drawings with the dimensions of the molds and cores for several castings - representatives. Castings should be selected in such a way as to a first approximation to characterize the entire nomenclature for a given production. With a small nomenclature, a determination can be made for all castings. The invention is illustrated by drawings, where:

figure 1 presents the thermogram of destruction for a mixture of "α-set" and "β-set";

figure 2 - thermogram of destruction for the mixture "Cold-box-amin";

figure 3 - field of maximum temperatures for castings with a wall thickness of 100 mm;

figure 4 is a generalized field of maximum temperature of the rod;

5 is an algorithm of a method for determining the volume and composition of toxic gas emissions.

The initial data also include thermal destruction parameters: the total amount of gases released during the process and the dependence of the degree of destruction on temperature. The corresponding experimental data are shown in FIG. 1 (for a mixture of “α-set” and “β-set” with a binder content of 1.8% and hardener 0.6%) and FIG. 2 (for a mixture made by the “Cold- box-amin "with a binder composition of 1.6%). The data were obtained for destruction in an atmosphere of air and nitrogen. The latter option is more consistent with the atmosphere in a mold where the gas environment is close to reducing. Therefore, it should be taken as a basis.

Using the thermogravimetric curves of the phenolic binder composition, it is easy to determine the degree of degradation in any temperature range and to determine the specific gravity of the gaseous products formed for the selected intervals. The data on the thermal degradation of the binder in the CTS ("α-set" and "β-set" processes) are given below.

In figure 2. degradation thermogram for the Cold-box-amin mixture is presented

Temperature zone, ° C The degree of thermal degradation,% The mass of gaseous products per 1 kg of the mixture, g 20-200 thirty 7.2 200-400 65 15.6 400-600 87 20.9 Over 600 one hundred 24.0

According to the newsletters of Ashland Chemical (USA), during thermal degradation of 1 g of the binder composition for the processes of "α-set" and "β-set", the following average number of products to be controlled is distinguished:

Name of substance Weight, mg per 1 g of the binder composition Weight,% per 1 g of the binder composition Monoxide 27 5,4 Carbon Phenol 1,5 0.3 Formaldehyde 0.75 0.15

Another initial parameter is the field of maximum temperatures in the rod or form, which corresponds to the maximum degree of destruction and, accordingly, the maximum volume of emission.

Figures 3 and 4 show examples of maximum temperature fields in absolute and relative coordinates (3 and 4). According to the data for the casting - mold (rod) system, the thickness of the layer heated in a given temperature range can be determined. Then you can determine the mass of gases released from the mold or rod and then the specific amount of toxic gases in the production of this casting. The calculations were carried out for a specific casting with the following characteristics: name - box; mold weight - 3450 kg; average thickness form X - 350 mm; X: R = 10 (R is the half wall thickness of the casting).

Figure 3 presents the field of maximum temperatures for castings with a wall thickness of 100 mm (steel G13L).

Figure 4. presents a generalized field of maximum temperature of the rod.

Figure 4 is determined by the thickness of the layers of the form for each temperature interval according to the formula:

L = Rδ, where δ = (X: R) is the current coordinate along the abscissa axis in Fig. 4. So, for example, for the interval 200-400 degrees C, the current coordinate is 5.5-3.7 = 1.8. Accordingly, L = 1.8 × 35 = 63 mm.

The procedure and calculation results for a particular casting are shown in the form of summary data:

room Temperature range, ° C Zone length mm Zone Length,% The mass of the mixture, kg The mass of gas, g / kg of the mixture Mass of gas, kg one 20-200 154 44 1518 7.2 10.8 2 200-400 63 eighteen 621 15.6 9.7 3 400-600 77 22 759 20.9 15.8 four Over 600 56 16 552 24.0 13,2 The total mass of gas, kg 49.5

room Name of gas Gas content,% Amount of toxic gases from the mold kg kg / t mixture one Carbon monoxide 5,4 2.67 0.77 2 Phenol 0.3 0.15 0,043 3 Formaldehyde 0.15 0,075 0,022

The final data for four (No. 1-No. 4) typical castings (mold, core) are given below:

Name of gas Gas content, kg / t the form kernel No. 1 Number 2 Number 3 Number 4 No. 1 Number 2 Number 3 Number 4 Carbon monoxide 0.77 0.53 0.35 0.35 0.26 0.25 0.45 0.46 Phenol 0,043 0,029 0.019 0.019 0.014 0.014 0,025 0,026 Formaldehyde 0,022 0.0145 0.0095 0.0095 0.007 0.007 0.0125 0.013

By analyzing the data of the selected four typical castings, the following average values of gas evolution were obtained, kg / t:

By forms:

Carbon monoxide 0.61 Phenol 0-034 Formaldehyde 0.017

On the rods:

Carbon monoxide 0.36 Phenol 0.02 Formaldehyde 0.01

The number of typical castings for calculation can be any that most adequately reflects this production. According to the data given, the total volumes of gas evolution can be calculated for a given volume of rod and molding mixtures per unit time. Moreover, the approximate distribution of gas emissions in the areas is taken as follows,%:

Metal casting 6-8 Mold cooling 85-90 Knockout 2-8

Gas evolution in the cold stage is determined as follows. When filling the core boxes and flasks, the gas evolution is determined from the unit mass of the mixture coming from the mixer. According to the data of [3, 4] for resins of the phenolic class containing about 1.0% of free phenol and 0.1-0.2% of free formaldehyde, gas evolution amounts to: phenol 0.01-0.05; formaldehyde 0.8-1.0 mg / kg of the mixture per hour.

During curing, gas evolution is determined from a unit of the open surface of the rod or mold and according to [3, 4], they are: phenol 0.01-0.05; formaldehyde 0.05-0.07 mg / dm2 per hour.

Using the results obtained, it is possible to determine gross outgassing in the cold stage from the actual performance of the mixers and the area of simultaneously cured rods and molds.

An example of determining toxic gas emissions for a molding and casting area

1. The source data

- on the site they make 20 of the same type from the CTS according to the process of "α-set";

- composition of the mixture (wt. parts): quartz sand 100; resin 2; ether catalyst 0.6.

In this example, the calculations were performed for the “box” casting: mold weight 3450 kg, average mold thickness X - 350 mm, X: R = 10 (R - half the cast wall thickness), in each casting rods weighing 500 kg.

- steel casting with a predominant wall thickness of 100 mm.

2. Analytically determine the field of maximum temperature heating forms.

The field of maximum temperatures in relative coordinates in the mold and the core for steel casting with a wall thickness of 100 mm is determined by the graph in figure 4.

3. According to the graph in figure 3, we determine the thickness of the layers of the form for each temperature interval at the current coordinate X: R. For the interval 200-400 degrees C, the current coordinate is 5.5-3.7 = 1.8. Accordingly, L = 1.8 × 35 = 63 mm. The order and determination of the masses of evolved gases for a particular casting are shown in the form of summary data.

table 2 Next, determine the mass of gas released No. p / p Temperature range, ° C Zone length mm Zone Length,% Mixture length, kg The mass of gas, g / kg of the mixture Mass of gas, kg one 20-200 154 44 1518 7.2 10.8 2 200-400 6.1 eighteen 621 15.6 9.7 3 400-600 77 22 759 20,0 15.8 four Over 600 56 16 552 24.0 13,2 Total gas mass 49.5 kg

Table 3 According to the curve of thermal destruction, we determine the discharge from the forms and the rod by types of toxic gases No. p / p Name Gas content,% Amount of toxic gases from the mold kg kg / t mixture one Carbon monoxide 5,4 2.67 0.77 2 Phenol 0.3 0.15 0,043 3 Formaldehyde 0.15 0,075 0,022 Below is a summary of 4 typical castings selected for a given molding and casting site.

Table 4 Name of gas Gas content, kg / t The form Kernel No. 1 Number 2 Number 3 Number 4 No. 1 Number 2 Number 3 Number 4 Carbon monoxide 0.77 0.53 0.35 0.35 0.26 0.25 0.45 0.46 Phenol 0,043 0,029 0.019 0.019 0.014 0.014 0,025 0,026 formaldehyde 0,022 0.0145 0.0095 0.0095 0.007 0.007 0.0125 0.013

By analyzing the data of the selected castings and the total volume of molds and cores in a given production, we determine the average values of gas evolution, kg / t:

By forms:

Carbon monoxide 3.05 Phenol 1.7 Formaldehyde 0,085

On the rods:

Carbon monoxide 1.8 Phenol 0.10 Formaldehyde 0.05

The distribution of gas emissions in areas as a first approximation can be taken as follows,%:

Melt casting 6-8 Mold cooling 85-90 Knockout 2-8

The results of the above example of determining the volume and composition of toxic gas emissions on a real molding and casting area fully confirmed the correctness of the claimed technical solution.

The results obtained should be basic when designing a new production or reconstruction, designing local and general ventilation systems, calculating and agreeing on the maximum permissible emissions allowed for the enterprise.

Thus, at the hot stage for the operations of casting, cooling and knocking out castings, the average volume and composition of gas evolution per unit mass of mold and / or rod made from HTS can be determined by the proposed method. To do this, by layer-by-layer analysis of the maximum temperature field, the gas evolution from each layer and the total for a given shape and / or rod are determined. Next, gas evolution is determined for a group of 4-5 typical forms representing the entire nomenclature of the shapes of the site or workshop. Based on the obtained average data, a specific volume for each toxic component (phenol, formaldehyde, carbon monoxide) and then the total volume for the entire production can be determined.

At the cold stage of the technological process, the volume and composition of toxic gas emissions are determined by known specific indicators. The developed technique gives indicative results. To adjust the results, additional data on the composition of the gaseous degradation products and thermal fields in the rods and molds is needed.

The proposed method for determining the volume and composition of toxic gas emissions during the production of foundry molds and / or cores by XTS technology can be used to design ventilation and agree on the permitted level of maximum permissible emissions into the environment, which is relevant from an environmental point of view for modern foundry. After mastering the XTS technological process in full, instrumental measurements should be made and the final adjustment of the data obtained should be carried out.

Information sources

1. Wilms E. // Form-und Kernherstellung-stand und trend, Giesserei, 1999, No. 6, V.86, S.131-133.

2. RF patent No. 2240512, publ. 2004.

3. Zhukovsky S.S., Lyass A.M. Molds and cores from cold-hardening mixtures of mixtures. - M.: Mechanical Engineering, 1978. - 220 p.

4. Zhukovsky S.S. Cold-hardening binders and mixtures for foundry cores and molds: Handbook. - M.: Mechanical Engineering, 2010 .-- 255 p.

Claims (2)

1. A method for determining the volume and composition of toxic gas emissions during the production of foundry molds and cores from cold-hardening mixtures (CTS) for steel castings, which includes determining at a cold stage by laboratory instrumental measurements of the gas evolution of the selected molding and core mixtures and binders, specific emission rates for each toxic component and bringing them to a common indicator, determination of the tuning parameters at the hot stage, including the type of melt to be poured, molding volume minutes and core sand in molds for castings typical field maximum temperatures warm cores and molds for castings selected by conditional dividing wall to form layers, warmed up to its maximum temperature ranges: 20-200; 200-400; 400-600 and above 600 ° С, determination for each selected temperature range of the total mass of gas released from CTC during heating and determination of the content of carbon monoxide, phenol, formaldehyde and the total volume of toxic gas emissions from the indicated temperature ranges, ventilation design taking into account the maximum permissible concentration (MPC), the implementation of instrumental measurement of concentrations of toxic gas emissions in the existing production and the comparison of the measured gas emissions with MPC, and in excess of measured gas emissions MPC change in the performance of mixers and the number of manufactured molds and cores. 2. The method according to claim 1, characterized in that the steel G13L is used as the melt.

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