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Protection of metals by plaforization (II)

altSecond part of the special on the preparation of metal surfaces and alternatives in paints that currently exist. This time we will delve into solvent substances and range of application.

by Mary Carpenter*
 


Another aspect of the VOC issue is that of "degradation in the air". This concept is associated with how VOCs degrade in the atmosphere and how their effect impacts the atmosphere. Chlorofluorocarbons (CFCs), for example, cause ozone depletion and the long half-life of these chemicals in the atmosphere is thought to be directly related to ozone depletion. For example, it is known that compounds that have a long half-life and therefore reach the stratosphere, decompose when exposed to UV radiation, releasing Chlorine and Bromine, which destroy ozone molecules.

Less stable compounds degrade rapidly and do not migrate into the stratosphere.  Single-stage phosphaticizing organic solvents degrade within hours to days, (depending on temperature, humidity, and sunlight), and the products of their degradation are only carbon dioxide (CO2) and water.

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While CO2 is said to be one of the largest contributors to global warming, the amount emitted by organic phosphating solvents is small compared to the large volumes generated by the combustion of natural gas, used to heat water in conventional systems. These low emissions are due to the fact that the organic phosphating process is at room temperature and uses low-emission solvents. In addition, the percentage of coal contained in special solvents is considerably lower than the amount contained in natural gas.

An analytical comparison was made between the one-stage organic phosphating process and the current process of three plants using conventional pre-treatment washes with hot water. The comparison assumed that in each plant, hypothetically using the organic phosphating process, the same amount of metal would be treated. For each of the plants studied, only 5 to 12% of the amount of carbon dioxide would have been created with the organic phosphating process, compared to the amount that those conventional plants create using the combustion of natural gas to heat water tanks.

The three Plants studied treat different amounts of metals per day, use different sizes of burners (with varied BTU consumptions), and have different production efficiencies. These factors explain the range of 5 to 12% in comparative results, and would represent normal variations in a production process.

Application Range
One-step organic phosphating technology can be used for a wide variety of metal treatment applications. Plants that have air drying instead of using an oven, can use a formulation for faster evaporation (30 minutes), as long as they have enough time for drying at room temperature. Users who use an oven to shorten the process cycle can use formulations with higher flash points, or formulas with very low vapor pressures, which emit lower amounts of VOCs and do not evaporate at room temperature.

These formulations are particularly suitable for use in areas where plant temperatures are above 29°C (85°F) for significant periods. Other formulations can be used in conjunction with a solvent recuperator in the case of high production. The recuperator is used to capture and recycle most solvent vapors that might otherwise escape. The speed of production must be reasonably high for this type of process because there is a constant loss of equilibrium that must be overcome before the recuperator becomes efficient.


The single-step organic phosphating system results in corrosion resistance in steel, which is somewhat superior to conventional iron phosphating. The actual number of hours in a saline chamber depends on the quality and thickness of the top paint layer.  In galvanized steel, because the phosphate layer is zinc, the corrosion resistance is much higher. On aluminum, tests show results above 5,000 hours with good quality powder paints (see website www.lumca.com), and a test with Kynar yielded more than 4,000 hours (AAMA 2605 standard).

Operating costs
When capital investments and operating costs are compared to the costs of conventional systems, the one-step process is cost-efficient and operational.

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For example, an ROI spreadsheet (Gross Margin of a Product) determined that a company that treats 10,000 ft2 of metal per day and pays $1 per Therma (100,000 BTU) of natural gas would save $111,000 per year using the one-step organic phosphating process.

Green technology
Minimizing the total environmental impact of a product or process involves a multi-layered approach. The concept requires taking a "global" look at the potential for pollution by technology and carefully examining the potential impact on all environmental systems it may affect – water, soil and air. The goal is to minimize the effect on all of these systems, rather than sacrificing for each other.

Environmental efficiency
A greater part of this effort involves the concept of environmental efficiency. This means minimizing the number of elements in a process and giving each element an active function (or more than one). Such a "multi-task" minimizes the number and number of components in the process that must ultimately be discarded as "waste." For example, water is used in conventional pre-treatment processes and in the end must be treated and discharged.

Part of the concept of environmental efficiency involves avoiding the creation of waste in a process. For example, conventional metal pretreatment processes create sludge, which must then be discarded. The one-stage organic phosphating process was specifically designed to prevent the creation of sludge.

Another aspect of environmental efficiency is to avoid having to periodically discard the bathroom itself. In contrast to water-based systems, the one-stage organic phosphating system uses the ingredients of the bath in proportion, so the process will not easily go out of balance. Due to this high stability, the bathroom is never thrown away, it is only checked periodically and filled and adjusted when necessary.

Resource recovery
Another layer of the global approach to the environment is that of resource recovery, which means recycling potential pollutants within the production system and reusing them in the same process or in other processes. For example, solvents in the single-stage organic phosphating process have high flash and boiling points and low vapor pressures and are therefore returned to the tank rather than evaporated.

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Material replacement
Material substitution offers the prospect of completely eliminating the problem of a given contamination by the replacement of a different element or process (as stated above, it is not allowed to simply change the problem of one system to another problem, such as air to water or vice versa). An important substitution in the single-stage organic phosphating system is that it does not use water throughout the pretreatment and is not rinsed off. Instead it uses solvents that by themselves are particularly selected for their "degradation in air", their precise functionality during the process and the fact that they do not evaporate easily.


Order and cleanliness in the plant
Finally, good material handling and order and cleanliness in a plant have a huge positive impact on pollution control. An efficient operation saves money, minimizes large capital expenditures, and can cut pollution by up to a third. The single-stage organic phosphating process was designed for simplicity of operation, and it is easier to operate efficiently when both maintenance and operations are simple.

Conclusion
The one-stage organic phosphating process is continuously gaining momentum in the metal pretreatment market in North America. From an operational point of view the process is simple and does not require the large and complex installations necessary for a conventional system. That means less maintenance, no sludge or water treatment problems, and a stable bath with very infrequent bath check-ups and adjustments. Because there is no water in the process, users do not need water permits and air permits are also generally unnecessary.  Some companies also take the initiative to seek environmentally friendly processes. Many jurisdictions provide tax incentives for such systems. Modern companies that treat and paint metal surfaces realize the value of a healthy environment and they greatly appreciate being able to pre-treat in a way that is environmentally friendly.

*Mary Carpenter is president of Carpenter Chemicals and Químicas Carpenter de México, both distributors of the single-stage organic phosphating system. For more information about this technology in Mexico, call +52 33 3699 6537, send an email to [email protected], or visit the www.cc-lc.com page.  For Colombia, call ESIN Andina S.A.S. on +57 331 202 4347 or send mail to [email protected]

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