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Cast iron is a common method to prevent casting defects

by:BoQiao Machinery     2020-12-09
Cast iron parts often can produce different kinds of casting defects, how to prevent these defects occur, has always been a concern in the casting factory. This paper introduces the author of some of the understanding and practice experience in this field. 1 stomata characteristics: porosity in the casting is inside the casting, the surface or near surface smooth holes of various sizes. Often with oxidation of hole wall color, due to different sources and formation reasons and stomatal form also each are not identical, invasive porosity, precipitation porosity, subcutaneous blowhole, etc. 1. 1 invasive quantity is less, the porosity the stomata size is larger, more parts outside the casting surface, a pear shape or round ball. Is mainly due to the mold, or a gas sand core which failed to escape the liquid metal. Prevention measures: ( 1) Reduce hair volume, control of molding sand and core sand found material content of gas, water content of green sand is not too high, the modelling and repair the mould release agent and water dosage shoulds not be too much. Sand core to ensure the drying, drying after the sand core deposit shoulds not be too long, the next day before use to the use of core oven drying, moisture absorption in sand control core, without the use of be affected with damp be affected with damp, cold rusty iron and core support, etc. ( 2) To improve permeability of sand, choosing the appropriate type of empty compactness, reasonable arrangement of the air cavity location and exhaust, ensure smooth sand core ventilation channel. ( 3) Properly increasing pouring temperature, porosity and exhaust all riser, etc. , to facilitate the gas buoyancy of liquid metal into the drain. 1. 2 precipitation stomatal this porosity and more dispersed, generally located in the most often with the pouring of the casting casting surface are found. The porosity is mainly due to in the process of smelting, metal absorption of gas before solidification all failed to precipitate, has formed many scattered small porosity in the castings. Prevention measures: ( 1) Using clean, dry furnace charge, limiting air content more burden. ( 2) Ensure & other; Three dry & throughout; : that is, the iron tank, taphole, cross the bridge to thoroughly dry. ( 3) Ladle to drying, it is better to iron liquid before use and have iron liquid package, be sure to put in liquid iron surface coating agent. ( 4) All kinds of additives ( Nodulizing agent, nucleating agent, coating agent) One is not on a regular basis to keep dry, humidity is high, want to use after drying. 1. 3 subcutaneous blowhole the porosity is mainly appear in the surface layer of casting subcutaneous 2-3 mm, about 1 ~ 3 mm in diameter. And the number is more, castings after heat treatment or rough machining to remove skin, will be clearly revealed. Prevention measures; ( 1) Properly increasing pouring temperature, strictly control the various amount of additives, as far as possible, shorten the casting time. ( 2) Inoculant addition amount of control the best ( The mass fraction) 0. 4% ~ 0. 6%, at the same time, we will strictly control the quality of the inoculant in A1 scores, w ( Al) Easy to react and moisture on the surface of the cavity: higher al 2 + 3 h2o = Al2O3 + 3 h2 & uarr; Normally, inoculant Al content should not be more than 1. 5%. ( 3) Prevent iron melt oxidation, appropriate adding relay coke, strictly control into the air.
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