Pickling and Cleaning
Surface preparation for galvanizing typically consists of three steps:
Caustic Cleaning, Sulphuric Acid Pickling, and Fluxing.
The following surface preparation processes are designed to deliver the parts to the galvanizing kettle with only pure elemental iron on the surface. Rust (iron oxide) and mill scale will not react with zinc to produce the desired metallurgical coating. The surface preparation is done in large tanks. These tanks are 55 ft. long by 8 ft. wide by 11.5 ft. deep. These big tanks allow us to run both large parts and/or large numbers of small parts on the same rack. Large quantities on a single rack result in lower costs for our customers. As well, our specially designed racks reduce the possibility of damage to our customer’s parts.
We have lowered the overall impact of our process on the environment by close looping our processes. We do not discharge any water to either the storm or the sanitary sewers. The Ministry of the Environment gave Court Galvanizing Ltd an “Outstanding Waste Reduction Award” for the design and operation of our closed loop system.
We further reduce our footprint on the environment by utilizing the waste heat from the kettle flue to heat all process tanks. This reduces the amount of natural gas that we utilize and lowers, significantly, the amount of greenhouse gases that we release. This waste heat utilization also makes us more cost efficient.
Caustic Cleaning – Rack loads of parts are first Immersed in a hot alkali solution at a temperature of 150°F to 180°F for 15 to 30 minutes. This proprietary solution removes all organic contaminants such as dirt, paint markings, grease, and oil from the metal surfaces. Paints, Epoxies, vinyl’s, asphalts, or welding slag will not be removed by caustic cleaning. These must be physically removed before pickling by grit-blasting, sand-blasting, or other mechanical means. The parts are rinsed in a separate tank after caustic cleaning to minimize carry-over of the caustic solution into the acids.
Pickling – Scale and rust are removed from the steel surface by pickling in a dilute solution of hot sulphuric acid at a temperature of about 155°F. Pickling takes anywhere from 15 to 45 minutes depending on the material. This process cleans the steel to the equivalent of SP10 sandblast. We have three identical acid tanks so that pickling is never the bottleneck in our process. All acids are serviced by an acid recovery system that cleans the acids so that they can be constantly reused. The acid regeneration generates a by-product that is used as a zinc fertilizer supplement. After Pickling, the parts pass through three consecutive rinses to enhance recycling and greatly reduce contaminant carryover to the Flux.
Fluxing – Fluxing is the final surface preparation step before the galvanizing kettle. Fluxing is done by immersing the parts in a hot solution (160°F of zinc ammonium chloride for 5 minutes. The solution is mildly acidic and removes any small amounts of oxides that may have formed on the hot wet parts between pickling and the Flux. The Flux also coats the parts to ensure no oxidation happens between the time the parts leave the Flux tank and when they are immersed in the kettle’s molten zinc. The flux coating on the parts burns in the 850° F kettle scouring the surface of the parts further ensuring pure iron on the surface of all parts to react with the molten zinc to form the required metallurgicaly bonded coating.
The smoke is removed from the kettle exhaust air by the dust collectors prior to discharge from the plant