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5 Steps to T

he procedure of identifying, diagnosing and minimiz- ing or eliminating crucial casting defects is important

for a foundry to run in a low-cost, and high-efficiency mode. It can disprove incorrect conven-

tional wisdom and show that unex- pected methods are actually the best way to move forward. To do this, there are three keys to

remember: 1. Focus on identifying a casting

defect on the basis of its appearance. 2. Be aware of the interactive nature

of foundry processes and variables. 3. Use rigorous experimental design methods to study complex causes of defects. Foundry personnel can be quick to

label a defect cause based on a cursory examination. Terms such as slag defect and cold shut are part of the defect process. Te International Casting Defect Atlas gives a specific code/cat- egory to defects based on appearance. It also suggests foundry personnel be aware that most casting defects are due to the interaction of several process variables rather than one factor, such as temperature or gating system design. Tis allows the foundry engineer to design experiments to capture the complexity of the defect cause. AFS

32 | MODERN CASTING July 2018

Identify Casting Defects


Corporate Member CWC Textron Foundry (Muskegon, Michigan) used this process of casting defect categori- zation, identification, cause determina- tion and defect reduction to address an issue with camshaft castings. Te defects began occurring after an

upgrade from manual pouring of molds to automatic pouring of molds. Auto pouring systems are considered to be safer reliable and efficient compared to manual systems. However, in the early tests compar-

ing castings from manually poured molds to castings from automatically poured molds, the casting scrap rate was always significantly higher for the automatically poured molds. Other vari- ables, such as pouring temperature and transfer time impacted the scrap rate. Tis gray and ductile iron foundry has

been producing alloy and ductile cam- shafts for many decades. All molds are produced on a horizontally parted, high pressure, tight flask, green sand, automatic molding line. Flasks on this molding line move on a conveyor to the pouring area. Primary melting is done with a

cupola. Te base iron is held in a channel induction furnace. MgFeSi is added to a large tundish ladle as it is filled from the induction furnace. In manual pouring, the ladles were filled from the tundish ladle and inmold inoculation was used.

Te main sources of casting scrap are were simply listed as “dirt” or “slag.” Now, an automatic pouring sys-

tem has replaced the manual pouring ladles. Te equipment was acquired and installed to make mold pouring safer and more consistent from mold to mold. Te automatic pouring system ladle holds significantly more iron than the manual pouring ladles. During the transition to automatic pouring, the manual pouring area was kept intact. Whenever molds were poured using the automatic pouring system, the camshaft castings exhibited a high frequency of cope-side inclusion defects. Tese defects were small, but deep enough to cause the castings to be scrapped. To solve the slag, pinhole, and dross

defects, CWC Textron worked through a proven step-by-step approach.

FIVE-STEP PROCESS Details of each of the steps followed

are shared below. Tere may be changes in the methods and tools specific to an individual foundry.

Step 1 – Identify the Defect

Foundry personnel have a tendency to identify a defect based on cause like slag defect or sand inclusions. While this is an acceptable method, after

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