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Metal Casting Technologies : March 2005
good casting operation should not last more than 8 hours (except very large volumes) and should be uninterrupted (less than 30 minutes between mixing operation). BEFORE STARTING WORK CHECK Sufficient products are available on the site Working areas are clean Formwork has been creased or waxed Drinking - quality water is available with means of measuring volume (graduated bucket, water meter) -- ideal water: 15° to 25°C. Mixer is clean and correctly adjusted (vanes and blades) the voltage setting is correct, check its direction of rotation and reliability (avoid electrical trip-outs) Vibration equipment is available and ready for use and that it is suitable for the volumes to be cast (thickness to be cast = rod diameter x 2.5) PREPARE Equipment to transport the product (buckets, wheelbarrows etc) Finishing tools ( shovels, trowels, straightedges, etc) You can now start casting -- Minimum ambient temperature: 5° C. MIXING Mix the sack(s) dry before use To obtain maximum efficiency, only fill mixers to 50-60% of their capacity Wet the first batch (within the recommended range, choose the maximum average for the product quality) Progressively adjust the quantity of water over the first 2 or 3 batches until required consistency is obtained The total mixing time varies from 3 to 6 minutes, depending on the size of the mixer used If the product is to be case and rodded - use the "ball test": Throw a handful of product a dozen times from one hand to the other to form a ball This casting method aims at eliminating air bubbles and filling voids left when the product is poured. The product must be "energetically worked with a metal rod or trowel, the same result can be obtained by slightly vibrating the product. If the product is to be case and vibrated - first vibrate a bucketful: The concrete must compact and spread, forming a flat surface in less than 10 seconds - otherwise adjust the quantity of water A flat surface indicates compactness. Continuing could lead to segregation, causing a slurry on the surface Casting must be completed within 40 minutes of completion of mixing (at an ambient tempera- ture between 15° and 25° C) If the structure requires casting in several layers, separate the zones so that new material is always poured less than 30 minutes after the previous layer FINISHING Do not smooth the surface Do not leave surfaces to the open air, cover them with wet paper or jute bags In general terms, the products must be kept in a damp atmosphere for 24 hours at least, and 48 hours if possible, after setting Upon completion of work, clean the mixer, tools etc. EDUCATION A Checklist for Casting Operations Prepared by Lafarge Refractories, NSW Australia. A 39 NEW DESKTOP SPECTROMETER G & C Instrument Services Pty Ltd T: (+61 2) 4981 7255 F: (+61 2) 4981 7244 E: email@example.com for highly accurate metals analysis, including C,S,P,B - at a low cost. METAL Casting Technologies March 2005