In a galvanizing line, the coolant quality and temperature is critical to ensure the required temperature and pressure such that a uniform anti-corrosive coating of predetermined thickness is deposited on the metal sheets. Also, a mix of chemicals under finely controlled operating conditions is used to ensure that the bonding surface is clean and oxide free to guarantee the durability of the coated metal sheets.
The mix of chemicals and the associated processes in a galvanizing line, if not controlled and handled effectively, can result in poor quality products and—importantly—toxic contaminants.
Therefore, effective Coolant filtration systems for rolling mills are vital to ensure that the contaminants are properly separated out to ensure coolant purity and therefore the integrity of the galvanizing process.
Critical Subsystems and Components
Metallic contaminants in the coolant, even the finest metallic particles, are separated out using magnetic separators. These separators are robustly designed and fabricated for 24 x 7 operations.
The self-cleaning filter offers a fit-and-forget option whereby the filtering surface is constantly rotated to ensure constant & fine filtration for particles up to 80 microns. An effective backwash mechanism, using the large pressure differential between the operating & atmospheric pressure, is used to clean clogged filter elements & ensure that a clean filter media is constantly available. A recovery filter is used to recover even the small amount of fluid evacuated in the back wash, thereby maximizing the re-usability of the coolant. Operating capacity of up to 10,000 liters per minute.
An agitator is used to prevent the precipitation of contaminants to the bottom of the tank, which may lead to frequent maintenance interventions. The skimmer, on the other hand, is used to remove the floating scum on top of the contaminated coolant.
Pneumatic vacuum filters can be used to filter particles up to 5 microns in size. Apart from providing extremely fine filtration, such filters also ensure 80% recycling of the paper filter media, compared to gravity filters; the paper media are run on a conveyor and a scraping mechanism is used to clean the paper which makes this filtration media highly reusable and cost-effective—not to mention its criticality to the environment. A vacuum filter can handle up to 6000 liters of fluid per minute.
Temperature is constantly maintained to a fine degree of accuracy through various mechanisms, such as electrical heaters in tubes with thermic fluid placed inside tanks, steam heating jackets inside tanks, forced circulation PHE with steam and PRV, and/or forced circulation through heater placed in separate housings.
A typical workflow Roll Coolant Filtration System
A large tank, with rounded corners to avoid dirt accumulation and rusting, is a part of a typical galvanising line. Also, an inspection hatch, manholes, and ladders are provided to carry out periodic maintenance works easily in the tank. The dirty fluid enters into the dirty fluid compartment of this tank; then, using baffles the fluid is passed through a Magnetic separator into a semi clean compartment. This cleaner fluid is then sucked by large pumps and passed through a self-cleaning filter as well as a PHE skid to control the temperature.
The above process is carried out with agitators and skimmers working to continuously mix the coolant. The temperature of the fluid is maintained using various heating mechanisms. For finer filtration, a different set of pumps are used to transfer dirty fluid to pneumatic vacuum filters.
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