Metalcasters’ product quality and performance results are under constant review, and new technologies and techniques are always being tested, or considered. But how often are maintenance methods reconsidered? Progress Casting Group in Plymouth, MN, produces precision diecastings and sand castings it supplies to automotive, aerospace, and defense industry customers. It had a fairly standard problem — cleaning core boxes and low-pressure diecasting molds — and a fairly standard approach to addressing it.
Core boxes and casting molds are meant to be used over and over again, and so they must be cleaned frequently and effectively in order to maintain dimensional accuracy and process reliability. The refractory coatings (i.e., release agent) and resin spray buildup on the mold faces, as well as sand and binder residue on the core boxes, had been removed by sand blasting and manual brushes. Both processes are slow and not fully effective. Sand blasting degrades the urethane on the molds, and both methods routinely destroy the vents on the core boxes. More than this, the cleaning can damage machinery, and workers’ safety may be at risk in the process.
Progress Casting Group was looking for a cleaning method that would remove the refractory coatings and other residual material without damaging mold vents. In addition, uneven refractory coating should be avoided, as it may affect the quality of finished products and the speed of production. Release agents and residual materials also should be removed to leave the mold surfaces smooth, without rounding corners or introducing other shape changes, all important for finished product quality.
The area around the tool should be clean too, so that it is safe for the workers. Tools must be cleaned quickly, effectively, after every use to minimize the downtime, and the molds should retain the working temperature for best reapplication the refractory coating.
The problems with steel shot, glass bead, and sandblasting is the possibility of mold vent damage and urethane damage on molds. Rounding of mold edges leads to flash on the parts, shortens mold life, and creates secondary waste. There also is potential injury from atmospheric contaminants.
Manual cleaning with chemicals and brushes is labor intensive and potentially harmful to the workers, requires long downtime, and it’s ineffective for some cleaning tasks.
An alternative cleaning method is Cold Jet LLC’s patented shaved dry-ice technology: small, dry-ice MicroParticles clean surfaces faster than standard 3-mm blasting pellets, in a quieter process that leaves a smoother surface.
Dry-ice blast cleaning is similar in concept to sand or soda blasting, in which the media is accelerated through a pressurized airstream. The primary difference is that the ColdJet blasting media is recycled CO2 — the dry-ice MicroParticles — not sand or soda. The particles are accelerated at supersonic speeds through a specialized hose and nozzle, and on contacting the mold surface the combination of kinetic energy and thermal gradient effects of the dry-ice blast breaks the bond between the surface and the residue. Upon impact with the tool surface, the CO2 sublimates, returning to its natural gas form, leaving no secondary waste to clean up.
Progress Casting tested a Cold Jet MicroParticle dry-ice cleaning system and used it to clean delicate screen vents at full blast. Even at maximum blast aggression, there was no damage to the parts and the molds appeared like new.
“The system was shown to the president of the company and after the test, he turned around and said: Buy it immediately! Within two days, the Cold Jet dry-ice blasting system was here and at work,“ recalled tooling supervisor Daryl Hesch.
Now, it takes one worker 10 minutes to clean a mold while it remains hot and online, not two to three workers to spend three to four hours cleaning one or two molds. The tooling supervisor reckoned that Progress Casting is saving $400-$500 per mold by cleaning with dry-ice blasting.
“We estimated that it would pay for itself in six months, but it took only a month,” Hesch said.