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Steel surfaces improve with time.

It was 25 years ago that the Green Bay Packers won the first Super Bowl, LBJ had been in office for four years, thousands of young men and women were serving their country in Vietnam, and the year's best song was "Michelle" by the Beatles.

Incidentally, 1967 was also the year that R.L. Naro and J.F. Wallace presented "The Effect of Mold-Steel Interface Reactions on Casting Surfaces." Since that time, not only have a lot of global changes been made, but there's also been quite a change in the processing technology of steel casting.

Since the original paper, considerable advances in steel casting technology were made, particularly in core and mold making. In recent years, many steel foundries converted from green sand or heat-intensive coremaking processes to chemically-curing nobake binders.

In 1967, 95% of all steel castings were produced in green sand molds incorporating core oil bonded cores. Current trends show only 51% of steel production is cast in green sand molds with the balance being cast in nobake, chemically bonded sand molds. Virtually all specialty steel castings are cast in chemically bonded molds. In addition, room temperature curing chemical binders replaced oven-baked, oil sand bonded cores used during the 1960s.

Taking a second look at the information they presented 25 years earlier in this year's molding Methods and Materials Division Silver Anniversary Paper, Naro and Wallace have drawn new conclusions. Among them are:

* new binder systems provide greater control over interface reactions, resulting in better casting finishes;

* as pouring temperature and ferrostatic head pressure are decreased, so is penetration;

* as sand fineness is increased in nobake binders, liquid penetration is reduced;

* sand temperatures affect curing properties, bench life and densities of nobake systems;

* phenolic urethane systems promote lustrous carbon defects; and

* adding 2% red iron oxide prevents pockmarking for chemical binders prone to lustrous carbon defects.
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Title Annotation:96th AFS Casting Congress Milwaukee; improvements in the steel casting technology
Publication:Modern Casting
Date:Jun 1, 1992
Previous Article:Developing into the future.
Next Article:Modifying Al-Si alloys: 25 years of progress.

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