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METAL CASTING






 

After metal has been melted, it is poured into a mold and allowed to cool. To remove the mold, sand castings enter a process called shakeout where the sand mold is shaken from the metal piece. During the process dust and smoke are collected by dust control equipment. Permanent molds are pried from the metal pieces without being destroyed. Investment molds and shell molds are destroyed during removal, creating solid waste.

Any additional parts used to hold the piece during casting are removed. The metal piece is cleaned using steel shot, grit or other mechanical cleaners to remove any remaining casting sand, metal flash or oxide.

A surface coating may be applied to the metal piece at the foundry; however, such coating is usually done at metal finishing plants.

The first step in metal casting involves the creation of a mold into which the molten metal will be poured and cooled. The materials used to make the molds depend on the type of metal being cast and the desired shape of the final product. Sand is the most common molding material; however, metals, investment materials, and other compounds may also be used.

Green sand mold are used in 85% of foundries. Green sand is a mixture of sand, clay, carbonaceous material and water. The sand provides the structure for the mold, the clay binds the sand together and the carbonaceous materials prevent rust. Water is used to activate the clay. The green sand mixture is packed around a pattern of the metal piece and allowed to harden. The mold is carefully removed from the pattern and prepared for the molten metal.

Sand molds are used only once. Molten metal is poured into the mold and allowed to cool. After cooling, the mold is broken away from the metal piece in a process called shakeout. Most of the sand from green sand molds is reused to make future molds.

Sand mixtures are also often used to create cores. Cores are pieces that fit into the mold to create detailed internal passages in the metal piece. Cores must be strong and hard to withstand the molten metal, and collapsible so they can be removed from the metal piece after it has cooled. To obtain these properties, resins or chemical binders are usually added to sand mixtures. Depending on the binder used, molds may be either air or thermally set.

Other molding materials include chemically bonded sand, metal or refractory. These materials are used in the remaining 15% of foundry applications. Shell molds use chemically bonded sand to make the molds. Permanent metal molds may be used in foundries that produce large quantities of the same piece. Investment molds are made from ceramic substances called refractory. They are used in high precision metal castings.

 

2. Find in the text English equivalents to the following words and word combinations:

плавити, вимикати, лиття у піщані форми, пил, тверді відходи, стальний шрот, покриття, cтворення ливарної форми, ливарна форма з вологого піску, глина, вуглецевий матеріал, запобігати ржавінню, повторне використання піску, серцевина, витримувати розплавлений метал, використання, велика кількість, керамічна речовина.

 


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