What are the key points for selecting and maintaining a large cast iron platform that offers great value for money?
Graphitization effect of undissolved particles in the carbon additive for large cast iron platforms: In the molten iron of a large cast iron platform, the carbon additive, in addition to the carbon already dissolved into the iron , also contains residual, undissolved carbon in the form of graphite, which is entrained in the flow as particles. Most of the undissolved, coarse graphite particles remain suspended near the furnace wall during electrification, while some adhere to the middle part of the furnace wall, which is equivalent to a stirring dead zone. Once electrification stops, these coarse graphite particles slowly float to the surface due to buoyancy.

After filling the depressions in the bed casting of a large cast iron platform with ethylene, it must be allowed to dry before sanding. After each sanding, the surface grinding slurry and dust must be removed. Water sanding technology is used for grinding. To prevent the processed surface of the large cast iron platform from rusting, rust-proof water should be used during sanding. After sanding, if any metal is exposed, the matching primer must be applied. After the putty is sanded and cleaned, a second coat of primer should be sprayed to improve the smoothness of the paint film on the large cast iron platform and enhance its gloss.
Tiny particles beyond the observation range of an optical microscope, during the graphite dissolution process, remain suspended in the iron not only during electrification but even after electrification stops. The particle size of the carbon additive is a major factor affecting its dissolution into the iron. Although the carbonization rate is the same after 15 minutes, the time required to achieve a 90% carbonization rate varies significantly. For a large cast iron platform, using untreated C carbon additive takes 13 minutes, using A carbon additive with fine powder removed takes 8 minutes, and using B carbon additive with both fine powder and coarse particles removed takes only 6 minutes.
When the surface of a large cast iron platform is relatively rough, has deep machining marks, rust, unevenness, or distortion, and the scraping allowance is above 0.005mm, the rough scraping points should be done using a long scraper with a long stroke (between 10mm and 15mm) and wide knife marks (10mm). The knife marks should be in the same direction and not repeated. The knife marks from machining can be used for spotting, and scraping should be done based on the high points revealed. When the workpiece surface shows 4–6 spots per 25㎡×25㎡ and has a fine scraping allowance, fine scraping can begin.
Choose a carbon additive with low nitrogen content: The typical nitrogen mass fraction in the iron of a large cast iron platform is below 100ppm. If the nitrogen content exceeds this concentration (150–200ppm or higher), it can easily cause cracks, shrinkage porosity, or looseness in the casting, especially in thick-walled castings. This is due to the increased addition of carbon additives when the proportion of scrap steel is increased. Coke-based carbon additives, especially pitch coke, contain a large amount of nitrogen.
Feed the furnace mouth sealing material. The working procedure for the large cast iron platform is as described above. The furnace mouth sealing material should be filled up to the furnace flange. Special attention should be paid to properly connecting it with the furnace spout and slag removal port. Install a Martin or electric vibrator inside the mold of the large cast iron platform. The vibration time varies depending on the vibrator used. First, install the vibrator at the lower part of the mold and vibrate for 20 minutes. Then, install the vibrator at the upper part and vibrate for another 20 minutes, while continuously supplementing the furnace lining material during vibration. During vibration, add furnace mouth sealing material until it reaches the same height as the furnace flange to prevent segregation of the furnace charge. After vibration compaction is completed, scrape off any excess material, leaving an expansion gap of 10–15mm below the furnace flange, and finish the transition between the furnace spout and slag removal port. Remove the vibrator. Excessive permeability of the mold is another reflection of the overly coarse sand particles in the large cast iron platform mold sand. Permeability and compactness are two interrelated factors. Lower compactness results in better permeability, and vice versa.
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