Expanding opportunities for precision sand casting: recent advances in coldbox tool design have...

Precision sand casting (PSC) is a molding technique used to produce dimensionally accurate castings with thin sections through the use of chemical binders and dimensionally accurate and durable pattern equipment.

PSC mainly has been applied to

the casting of light alloy automotive components. The chemically-bonded sand molds and cores used in PSC usually incorporate phenolic urethane nobake (PUNB) binders due to the excellent mold rigidity and dimensional stability imparted by this binder system. More recently, such molding has advanced in volume output by utilizing vapor curing techniques and mainly phenolic urethane coldbox (PUCB) binders cured with vaporized tertiary amines. The use of these vapor-cured binders gives even better rigidity and precision and allows more rapid mold production.

In high-volume green sand casting facilities, amine-cured PUCB bonded sands have largely remained a means of core production, whereas in light alloy casting facilities, the application of these binders, using PSC techniques, has been adopted as an alternative to the more traditional molding techniques of green sand and semi-permanent molding (SPM).

The application of PSC holds opportunities for both light alloy and ferrous casting facilities for the production of medium- to high-volume components.

Capital Costs

There are three basic incarnations of PSC (Fig. 1):

* the core assembly where individual mold and core components are made on a number of core machines and then assembled into complete mold-core packages;

* conventional molds blown on larger core machines, cored and assembled with complete or partial automation;

* stack molding where vertical or horizontal stacks are made using PSC molds blown with form on both sides.

[FIGURE 1 OMITTED]

No metalcasting facility is likely to use PSC unless it offers good cost or technical advantages over conventional molding methods. The global casting industry has invested heavily in green sand molding (ferrous) and SPM (nonferrous) as the dominant techniques for high-volume cored castings. However, in an increasing number of cases, PSC has been used for:

* reduced capital costs in the case of a new installation or product;

* lower operational costs for either a new or existing process or product;