36544-Monday-11-am-12 Fe FILE HOME INSERT DES GN PAGE LAYOUT REFERENCES MAILINGS

Question

36544-Monday-11-am-12 Fe FILE HOME INSERT DES GN PAGE LAYOUT REFERENCES MAILINGS REVIEW ViEW Copy B 1 u.atx x, x, | A·_a.|: ::: 12.B- ste Clipboard Font Paragraph L. The Cast Oal Field Fitting Case study: (15 A cast iron, T-type fitting is being produced for the ol drilling industry using air-set or no-bake sand for both mold and core. Silica sand has been used in combination with a catalyzed-oil urethane binder. Tbe Figure 2 presents a cross section of the mold with the core in practice (a) and a cross section of the finished casting (b). Tbe final casting cootains several significant defects. Gas bubbles are observed in the bottom section of the horizontal tee. A penetration defect is observed near the bottom of the inside diameter, and there is an enlargement of the casting at location C. Answer the following questions: What is the most likely source of the gas bubbles? and why they are present only at the location noted? What might you recommend as a solution? What factors led to the enlargement of the casting at point C? What would you recommend to correct this problem? What factors may have caused the penetration defect? Why is the defect present near the bottom of the casting but not near the top? a b. c. (15) Mold Core Penetration Mold cavity Gas tenlargement) Figure 2. The cast 01.Field Fitting (adapted tem Black and Kaes, Materials aad Processes aufcturing pp. 282, 10E, WEey 9 OF 12 1083 WORDS ENGLISH ICANADA 0 Type here to search

Explanation / Answer

a. The gas porosity is the source of formation of bubbles.Most liquid materials can hold a large amount of gases dissolved into them but when the state changes to solid on cooling it can not hold the same amount of gas as liquid form can and hence they come out as bubbles. They are seen at a specific location shown in fig. because gas bubbles form in crevices of the mold in contact with the metal. To avoid bubble formation it is recommended to to melt material in a vaccum or in conditions of low solubility gases as argon or carbon dioxide. Also, superheat temperatures can be kept a little lower to decrease solubility of gases. While pouring the molten metal avoid turbulence as high velocity flow of molten metal will carry gases rapidly. So, while pouring flow of moltem metal should be streamlined.

b. The enlargement is due to swell defect in casting. This occurs by molten metal high pressure resulting in localized or general enlargement of casting. Broadly speaking, under the influence of metallostatic forces the mold wall may move back causing a swell in the dimension of the casting. To avoid it proper ramming of the mold is necessary. This usually occurs on vertical faces of castings.

c. Metal penetration defect occurs when molten metal enters voids between the sand grains of a mold. Factors like high temperatures and greater fluidity of molten metal can cause penetration into sand core. Lower refractoriness (ability of sand grains to withstand higher temperatures) also leads to easy penetration. It occurs near bottom because the sand is poorly compacted at the bottom as compared to the top layer of sand. So, it becomes easy for molten metal to penetrate the poorly compacted sand grains area.

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.