1. Introduction
In the casting industry, the use of cold box resins is widespread. However, during the production process, these resins can release formaldehyde, a harmful gas. The determination of the source strength of formaldehyde in cold box resins for casting is crucial for environmental protection and the health of workers. This article aims to comprehensively study this issue through various research methods and provide practical solutions.
1.1 Background
Casting is an important manufacturing process, and cold box resin technology has been widely used due to its advantages such as high production efficiency and good sand core quality. But the problem of formaldehyde emissions has become a concern. In Cangzhou area, as investigated, there are significant differences in the determination of formaldehyde source strength among some casting enterprises, and some even fail to identify formaldehyde as a pollution factor. This situation poses challenges to environmental management and pollution control.
1.2 Research Significance
Accurately determining the formaldehyde production coefficient in the use of cold box resins for casting can help enterprises take targeted pollution prevention and control measures. It is of great significance for ensuring the stable and up – to – standard discharge of waste gas pollutants, protecting the ecological environment, and safeguarding the health of workers.
2. Classification and Introduction of Cold Box Resins for Casting
2.1 Types of Cold Box Methods
Cold box methods mainly include the triethylamine method, method, resin method, and β – set method. After investigation in the local area, it is found that the triethylamine method is the most commonly used type. The following table summarizes the characteristics of different cold box methods:
| Cold Box Method | Catalyst/Reaction Gas | Hardening Mechanism | Advantages | Disadvantages |
|---|---|---|---|---|
| Triethylamine Method | Triethylamine and other tertiary amine – type catalysts | The phenolic resin and polyisocyanate in the two – component binder cross – link into solid urethane under the action of the catalyst, hardening the sand core (mold) | High hardening speed, good sand core strength | Potential formaldehyde and amine gas emissions |
| Method | gas | The resin cross – links and hardens under the action of | Fast hardening, high – quality sand cores | Corrosive gas emissions, complex operation |
| Resin Method | gas | The binder reacts with to harden | Environment – friendly in terms of gas emissions, simple process | Lower sand core strength in some cases |
| β – set Method | Special catalysts | The resin hardens through specific chemical reactions | Good sand core quality, less pollution | High – cost process, not widely used |
2.2 Principle of the Triethylamine Cold Box Method
The main principle of the triethylamine method is that at room temperature, tertiary amine – type catalyst gases such as triethylamine are blown in. This makes the phenolic resin and polyisocyanate in the two – component binder cross – link into solid urethane, thus hardening the sand core (mold). This process is crucial for the production of high – quality sand cores in casting.
3. Basic Components of Triethylamine Cold Box Resins and the Generation of Volatile Organic Compounds and Formaldehyde
3.1 Basic Components of Triethylamine Cold Box Resins
In the triethylamine method, the binder consists of binder component I (phenolic resin), binder component II (polyisocyanate), and a catalyst (liquid triethylamine or dimethylethylamine). The ratio of component I to component II is 1:1. According to the industry standard (JB/T11738 – 2013) “Resins for the Triethylamine Cold Box Method in Foundry”, the following table shows the main physical and chemical performance indicators of the mixed sample of casting – used triethylamine cold box resins at room temperature:
| Project | Component I (Qualified Product) | Component II |
|---|---|---|
| Free Formaldehyde Content w/% | 0.5 | – |
| Isocyanate Group Content w/% | – | 22.0 – 28.0 |
| Moisture Content w/% | 0.8 | – |
It should be noted that in this article, in order to determine the maximum amount of formaldehyde, the lowest – grade qualified product is used to determine the amount of free formaldehyde.
3.2 Determination of the Generation and Emission Source Strength of Formaldehyde
3.2.1 Sources of Formaldehyde Generation
Through investigations of relevant enterprise self – monitoring reports, pollutant discharge permit implementation reports, environmental impact assessment reports, environmental protection acceptance materials, and production operation records, it is determined that formaldehyde is generated during the resin curing and casting processes. The main sources of waste gas are binder component I (phenolic resin) and binder component II (polyisocyanate).
Formaldehyde generation mainly occurs in two ways. First, during the reaction curing process, formaldehyde is produced. Second, during the casting process, due to the heat of high – temperature molten metal and the oxygen – deficient state, the hydroxymethyl groups of phenolic resin condense and cross – link into methylene, and the released formaldehyde cannot be completely burned and will volatilize into the atmosphere. The following table shows the corresponding situation of formaldehyde emissions and raw materials during the casting process in some typical enterprises:
| Annual Consumption of Triethylamine Cold Box Resin/t | Annual Consumption of Phenolic Resin/t | Formaldehyde Pollutant/t | Pollutant Generation Coefficient /(t/t Triethylamine Cold Box Resin) | Pollutant Generation Coefficient (t/t Phenolic Resin) |
|---|---|---|---|---|
| 100 | 50 | 0.21 | 0.0021 | 0.0042 |
| 200 | 100 | 0.68 | 0.0034 | 0.0068 |
| 440 | 220 | 1.23 | 0.0028 | 0.0056 |
3.2.2 Calculation of Formaldehyde Generation Coefficients
(1) Formaldehyde Generation Coefficient in the Resin Curing Process
Based on the main physical and chemical performance of triethylamine cold box resins, the free formaldehyde content in phenolic resin is 0.5%. Although phenolic resin is a thermosetting resin and not a volatile raw material, due to the presence of free formaldehyde in its components, using the extreme value method, that is, considering the most unfavorable situation where 0.5% of the free formaldehyde in the curing process of phenolic resin completely volatilizes, the formaldehyde coefficient can be determined to be 0.005t/t phenolic resin.
(2) Formaldehyde Generation Coefficient in the Casting Process
Phenolic resin decomposes at high temperatures, mainly producing a large amount of carbon dioxide and water, as well as a small amount of formaldehyde, benzene, toluene, and aromatic compounds. The casting temperature is generally around 1300 °C, which can completely pyrolyze phenolic resin.
In this article, methods such as analogy investigation, sample mean method, extreme value method, and data analysis method are used to determine the formaldehyde generation coefficient during casting. Through the analysis of the data of formaldehyde emissions and raw material usage in typical casting enterprises, the following table shows the production and pollution discharge coefficient of volatile organic compounds in casting projects:
| Pollutant Index | Formaldehyde/(t/t Triethylamine Cold Box Method Resin) | Formaldehyde/(t/t Phenolic Resin) |
|---|---|---|
| Product Coefficient | 0.0028 | 0.0055 |
According to the sample mean method, the production and pollution discharge coefficient of formaldehyde in the casting process of casting projects is 0.0028t/t triethylamine cold box method resin.
4. Formaldehyde Prevention and Control Measures
4.1 Classification of Formaldehyde Treatment Methods
According to the “List of Toxic and Harmful Air Pollutants (2018)” issued by the Ministry of Ecology and Environment, formaldehyde is clearly defined as a toxic and harmful air pollutant, and its pollution prevention and control should be taken seriously. Currently, common formaldehyde treatment methods mainly include adsorption method, ozone oxidation method, biological purification method, and catalytic oxidation method. The following table compares these methods:
| Treatment Method | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Adsorption Method | Adsorb formaldehyde through adsorbents such as activated carbon | Simple operation, relatively low cost | Limited adsorption capacity, need for regular replacement of adsorbents |
| Ozone Oxidation Method | Use ozone to oxidize formaldehyde into harmless substances | High – efficiency oxidation, fast reaction speed | High – cost equipment, potential ozone leakage problems |
| Biological Purification Method | Use microorganisms to decompose formaldehyde | Environment – friendly, low – energy consumption | Slow reaction speed, high requirements for environmental conditions |
| Catalytic Oxidation Method | Catalyze the oxidation of formaldehyde under certain conditions | High – efficiency, stable performance | High – cost catalysts, complex operation requirements |
4.2 Application in Casting Enterprises
Currently, casting enterprises generally use activated carbon adsorption to treat formaldehyde – containing waste gas. After treatment, the waste gas is discharged through the exhaust pipe in an organized manner. The following is the waste gas collection and treatment flow chart:
[Insert a simple flow chart here, with solid – phase curing process and casting process as the starting points, leading to the activated carbon adsorption device, and finally to the exhaust pipe]
According to the investigation results, when the pollution treatment measures of casting enterprises are operating stably, the waste gas emissions can meet the relevant emission standards.
5. Conclusion
Through the investigation and analysis of some casting enterprises, this article has obtained the pollutant generation coefficients between formaldehyde and raw materials in such projects. These coefficients provide a reference for casting enterprises to select reasonable and effective formaldehyde waste gas prevention and control measures, helping casting enterprises to achieve stable and up – to – standard discharge of waste gas pollutants. Future research can be further carried out on more accurate determination of formaldehyde source strength and more efficient treatment technologies to continuously improve the environmental protection level of the casting industry.
