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Dry ice blasting: a new technology for corebox cleaning.

In the past few years, there have been great strides made in corebox technology, particularly in the area of corebox cleaning.

Ten years ago, when coreboxes became caked with deposits and gas vents were plugged, an assortment of cleaning methods was used. One of the more popular methods was a combination of grit blasting, scraping and chemical treatment.

Thorough cleaning of vents was virtually impossible. Cleaning was performed by the tedious method of pulling boxes out of the machines and knifing the vents out, one slot at a time.

Now, with shorter runs, faster turn-arounds and flexible approaches to manufacturing, new corebox techniques have emerged, and optimizations prevail. At Saginaw Malleable Iron/ Central Foundry Div.- General Motors (GM), one process that was analyzed was the use and cleaning of coreboxes, especially those made of newer materials. The traditional metal cleaner used on the tooling during molding combined with the new resins in coreboxes, producing a heavy, clay-like deposit. These deposits could not be blown out, making it necessary to revert back to sand blasting and the tedious knifing process. Project Parameters

The entire core production process was reviewed during a six-month project at GM. The project focused on the most efficient way to maintain urethane coreboxes in the new coldbox process.These coreboxes are softer than the older metal boxes, and grit blasting would wear and change the box dimensions.

The initial survey of various plants in the foundry division at GM turned up a variety of methods used for cleaning coreboxes. The optimum method appeared to be a combination of chemical dipping and grit blasting with glass beads.

Simultaneously, a unique cleaning technology (CO[sub.2]Cleanblast[TM] was developed at Lockheed for aerospace applications and had been licensed to Alpheus Cleaning Technologies for general industrial use. Through joint experimentation and trials with Alpheus, a new technique evolved for cleaning coreboxes and tooling, which has dramatically improved production at GM. Dry ice Blasting Process

This new process involves the production of dry ice (solid CO[sub.2]) pellets that can be sprayed from a nozzle at high velocity as the cleaning agent. Although the process is similar in nature to grit blasting, there are two significant differences: * The dry ice pellets do not clean by

chiseling away the contaminant as

the abrasives in grit blasting do. Instead,

the pellets penetrate the contaminant,

fracture into small particles

when they impact the base material

and instantly sublime into CO2 gas'

The fracturing and sublimation of the

pellets provide the mechanical action

(in a lifting/flushing motion)

needed for effective cleaning. * There is no added waste material to

plug vents or to be swept up after

cleaning.

A patented two-hose design delivers CO[sub.2] media and air to the spray nozzle through separate hoses. The pellets and air are mixed just prior to cleaning to assure that the maximum amount of pellets is delivered to the area to be cleaned. The source of the cleaning medium is a tank of liquid CO[sub.2], which is pelletized by a proprietary circular die. Pellet flow rate, size and velocity can be specified for any cleaning application. In this case, a minimum of 120 psi was used, although lower pressures will work for most foundry applications.

This mechanical blasting process is non-abrasive, allowing for the cleaning of equipment without affecting the close tolerance of the machined surfaces.

One of the more important project developments, which greatly improved the system's usefulness, was a mobile blasting unit. One challenge was to freely move pellets, without clumping, through the air hose to the nozzle.

Once a suitable mobile storage container was developed, it allowed free access to the foundry floor and blast-cleaning of tooling could be done at the workstation. Foundry Application

Actual testing of CO[sub.2] blast technology on the foundry floor resulted in dramatic improvements by completely changing existing procedures. Most significantly, CO[sub.2] blasting eliminated the need to disassemble tooling before cleaning. Immediately after a molding cycle, a corebox can be blast cleaned while remaining on the machine. Within minutes, the equipment is clean and dry, ready for reuse.

In a test of cleaning pin, dome and gate coreboxes, the old method of disassembly and cleaning of four units took four hours. Dry ice blasting took only 45 minutes.

Conventional body corebox cleaning time was one hour, but it took only 30 minutes with CO[sub.2]techniques. Weekly cleaning of cold-set tools involved dismantling to clean vents and took up to 12 hours. With CO[sub.2] blasting, cleaning can be performed in 90 minutes. During the early test stages, tooling was dismantled to verify the cleanliness of the channels. The CO[sub.2] procedure effectively cleaned coreboxes.

Hotboxes (from eight machines) that previously required 16 hours of knifing a week are now CO2 blast cleaned in only four hours.

By adjusting the work schedules in the foundry, the O[sub.2] system could be moved into the molding area to clean cope and drag machines without masking.

The annual labor savings, for dismantling tools alone, easily justified the cost of the CO 2unit.

Other benefits were faster turnaround times in molding operations and reduced chemical usage (also eliminating previous chemical disposal costs). This system has been shown to replace chloroflourocarbon and chlorocarbon solvents, reducing waste disposal problems and eliminating solvent emissions and worker exposure. Conclusions

CO[sub.2] blasting is a new approach in industrial cleaning that deserves investigation. As with many other new technologies, the benefit scan be dramatic if industry is willing to adapt to the new techniques.
COPYRIGHT 1991 American Foundry Society, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Donnelly, Tim
Publication:Modern Casting
Date:Jun 1, 1991
Words:931
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