Foundrymen discuss nobake molding, robotic handling.

Among other things, residents of the Pacific Northwest love to talk about the weather and sports, but the "buzz" at the 48th annual AFS Northwest Regional, held May 6-8 in Portland, Oregon, focused instead on market forecasts and "trailblazers" of a different kind - the stars of the metalcasting industry. The event, which featured tours of Esco, Columbia Steel and Varicast, was hosted by the AFS Oregon Chapter and sponsored by the British Columbia and Washington Chapters.

The conference's 325 attendees, almost 40 exhibitors and 21 speakers gathered to discuss the latest and greatest in foundry technology. Presenters covered subjects ranging from industry forecasts, government affairs, mold and core coatings, furnace safety, casting defects, binders, pouring and consumables. The theme of this year's program was "Back to the Future," and industry experts shared plenty of insight to illustrate the theme - from current methods of improving foundry quality, such as a discussion on nobake molding, to a description of what the near future may hold for the industry, including the latest in robotics.

Nobake Molding

In his discussion of the "practical side" of nobake molding, William Scott, AAA Alchemy, reviewed a paper co-authored by J. Alexander Otte, Jr., Delta Resins and Refractories, that covers casting quality issues from binder selection and casting engineering to sand mixing and testing.

Binder selection should be based on the size, shape, complexity and quantity of castings to be made, the available sand and binders, and climate, Scott said.

Two approaches to optimizing the sand used with nobake binders are:

* using a fine sand (85-100 GFN over 3-4 screens, possibly without a refractory coating for reasonable section sizes (less than 4 in.);

* using a relatively coarse, round-grained refractory (35-45 GFN over three screens) and filling in the surface with a fine refractory, potentially requiring less binder. In this approach, the mold/core must be coated.

Sand grain shape and surface area determine the minimum amount of binder to be used. Sand segregation must be engineered out of the system, and sand classification is critical. In addition, it's important to follow the same procedures every time - this means starting with the same materials with the same physical characteristics and properties and ensuring a consistent reaction temperature and mixing operation. The greatest variation in most foundries is sand compaction - get this right and you may see less burn in, penetration, hot tears, scabbing and sand erosion, Scott said.

In engineering the casting, Scott recommended using a V-shaped runner design to keep sand from eroding as the binder burns out and metal drags over it. Generally, nobake sand is not suitable for downsprues - as pouring times exceed 30 sec, a ceramic tile or shell sprue should be used, he said. The in-gate that works best for steel, according to Scott, is rectangular with generously radiused corners and a low aspect ratio. The flat gates tend to trap inclusions against the relatively cold sand, he said.

Every job should be evaluated in terms of sand-to-metal ratio, and weekly average ratios of sand mixed to metal poured should be kept. Zig-zag vents should be used at parting lines to minimize runout, and cope probe vents allow solvents to escape, completing the cure sooner. Facilities also must be well-engineered to optimize material handling, and sand storage must be free of sand segregation, Scott said.

Robots and Vision Systems

Chris Cooper, Action Machinery Co. (Vulcan Engineering Co.), discussed innovations in the use of robots and vision systems to inspect parts, remove unwanted metal and finish the parts. "The major advantage of using robots for inspection is the elimination of the human subjective decision-making of what is acceptable and not acceptable," Cooper said.

Cooper discussed the vision system used at one foundry to inspect 24 different ductile iron automotive safety parts. The parts are randomly placed onto a constant-speed, slider bed conveyor. As the parts move under the first set of cameras, the vision system captures an image of the part, inspects the part for dimensional accuracy and sends a robot the location and rotational orientation of the part on the conveyor.

The robot uses conveyor tracking software to present the part in the proper orientation to other cameras that inspect the opposite side of the casting. The robot then moves the casting into an ultrasonic test tank for a nodularity test. Depending on the results of inspection and testing, the robot places the parts in the proper bin - the complete process takes less than 10 sec, Cooper said.

Integrating vision systems with robots can offer benefits such as:

* the casting can be inspected before metal removal, allowing the removal program to be "aware" of heavy flash and/or gates;

* the elimination of simple fixtures because the vision system can tell the robot what part is present and what is the orientation of the part;

* several different parts can be processed with the same robot cell.