ration. This capability can reduce or eliminate expensive machining steps. The center slot of the connector is a
key feature because the gusset has to fi t cleanly but tightly into the slot for fi eld assembly. Rather than machining 10-in to 18-in. cuts, the center slot was formed with a sand core. Cores are sand shapes inserted into the mold to produce interior features in the casting. Another design choice for the con-
nector was whether and how to pro- duce the bolt holes in the connector plates. Bolt holes can be drilled into the fi nished casting or produced in the casting with features on the sand core and then fi nish drilled after casting. The connector did not have a standard bolt-hole confi guration. In actual use, each structural designer chooses the bolt size, count and confi guration based on the structural loads with which he must work. With that in mind, the designers decided to produce the con- nector without bolt holes and let the fi eld engineers drill the holes required for their design. Finally, in mold design, the orien-
tation of the part in the mold is an important factor in producing a sound casting. The part should be oriented in the mold so that metal fl ow is uni- form and even in the different sec- tions of the casting and the core can be securely positioned in the mold. In the case of the steel connector, the metalcasting engineer had two options for orientation in the mold—vertical or horizontal. In the horizontal orientation, metal
would fl ow fi rst into the lower plate and then into the top plate, producing non-uniform fl ow and fi ll into the two
Fig. 2. The casting is welded to a brace on one end and bolted to a construc- tion frame on the other.
shot-blasted for improved sur- face appearance. Heat treatment of the connectors
plate sections. In addition, the core forming the center slot would be ori- ented horizontally and tend to “fl oat” in the melt, producing variation in the slot geometry. In the vertical orientation, the de-
signers determined metal fl ow would be uniform, with the two vertical plate sections fi lling evenly together. The center core also was oriented vertically and securely seated in core prints (seat- ing slots) in the top and bottom molds. The designers therefore determined this was the preferable orientation for producing a fl aw-free casting.
Producing the Part The steel connectors are cast in a
four-step process. First, the molten steel (2,850F) is poured into the as- sembled sand mold and allowed to cool and solidify in the mold. After cooling, the casting is removed and shaken out of the sand mold. Next, the risers are cut off and the riser stubs and fl ash lines are ground smooth. Finally, the casting is
is a critical process step to produce the required microstructure, mechanical properties and Charpy impact values. The castings are heat treated per the ASTM A958 specifi cation (1,700F aus- tenitizing, water quench and 1,150F temper cycle). Following heat treating, the outside
faces of the two plates are milled to the required fl atness and thickness. The weld shoulder is an as-cast feature, while the holes in the connectors are machined by the end users to match their bolt pattern and connection con- fi guration in their structural design. Quality assurance for these struc-
tural components is driven both by building codes and specifi cations and requirements. Testing and inspection in production includes tensile tests and Charpy V-notch tests on test blocks from each heat, visual examination per ASTM A802, magnetic particle examination per ASTM A903 and ultrasonic examination per ASTM A609. First article components also were tested radiographically to the procedures prescribed in ASTM E446 and ASTM E186.
MC About the Authors
Carlos de Oliveira is chief executive offi cer of Cast Connex Corp., Toronto, Canada. Ryan Grant is a technical sales representative for Pacifi c Steel Casting Co., Berkeley, Calif. Steve Gonczy, Gateway Materials, Mount Prospect, Ill., compiled the material for online publication.
Pacifi c Steel produces the raw casting and delivers a machined part to Cast Connex. The bolt holes are drilled by end users onsite. MODERN CASTING / September 2010 33
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