Will a CO2-Cured Cold Box Binder System Work for You?

Carbophen is a water-based alkaline phenolic resin system cured by passing CO₂ gas into a sealed core box. The resin is the sole binder component added to the sand for making cores and molds. Typical binder levels range from 1.5-3.0%, based on sand weight.

Recent testing has shown that binder levels can be decreased to the lower end of that range with optimization of the core box venting, gas volume, and gas retention time. Optimizing these factors is critical to fast tensile strength development and somewhat dependent on the core geometry, which is where the venting comes into play. Typical tensile strengths over time are shown in Figure 1.

The tensile strengths have been found to be comparable to methyl formate-cured phenolic ester systems and sodium-silicate systems, allowing for use in a fairly wide number of applications from small vein cores to large, chunky shaped cores. Along with CO₂ being a much lower-cost co-reactant, Carbophen becomes a good option for larger production runs, as well as job shop core- and moldmaking operations.

High Volumes and Job Shops

The appeal of using Carbophen for both larger production runs and job shop operations includes:

•  Eliminating the hazardous or flammable co-reactant: there is no capital expense for handling equipment and facilities, and reduction of annual expense (lower cost insurance).

•  Safer handling and work environment: reduction in hazard risks.

•  Reduced VOC and HAP emissions at pouring, cooling and shakeout: more opportunity to expand business with existing environmental permits.

•  Single component resin meter into the sand mix: simplified quality control, and easier equipment set-up, maintenance.

•  No scrubber required: operational cost savings.

•  Good humidity resistance and increased strength over 24 hours: longer storage time and improved handling/shipping of cores.

•  Excellent sand flowability compared to sodium-silicate resin systems: fewer compaction related defects, allows for producing delicate cores (e.g., pump impellers, small valve bodies.)

•  Good bench life of mixed sand, ranging from a few hours to a few days, depending upon how the mixed sand vessel is sealed: operational cost savings.  (Note: for automated systems, a nitrogen blanket would be ideal. For a simple batch type mixer, an airtight seal will suffice. The goal is to keep atmospheric CO₂ from reacting with the mixed sand.)

•  Superior shakeout compared to sodium-silicate resin systems:  operational cost savings. Carbophen breaks down quickly after pouring, allowing for almost immediate shakeout.

•  No odor associated with the co-reactant: operational and environmental improvement.

•  Contains no nitrogen, sulfur, or phosphorous: more versatile system compatible with a wide variety of metals and alloys.

Count On Compatibility

CO₂-cured alkaline phenolic systems are compatible with most existing equipment. The critical detail will be converting the gas injector/converter over to handle the CO₂ gas. This should include a heating unit for the CO₂ gas and feed line to the core box. When CO₂ is consumed at a steady rate from cylinders, it tends to cool quickly and will freeze up. Maintaining a temperature of 45°C is recommended. CO₂ equipment is readily available on the market. We also recommend calling CO₂ specialists for guidance when converting/installing these systems. CO₂ suppliers will be able to provide the necessary assistance for optimal operation.

This system is compatible with silica, lake, and most specialty sands. Mechanically reclaimed sand may also be used if all the sand is from the Carbophen process at typical reclaim levels. If the mechanically reclaimed sand is coming from a different resin system, i.e. used in a no-bake operation, then a smaller portion of it can be incorporated into the mix. This can be determined easily with some simple sand testing at HA International laboratories.

Tensile strength formation occurs instantaneously upon contact with the CO₂ gas on the resin.  Therefore, optimizing the gassing volume and gas retention time become critical to getting the most out of the system. In other words, gas exposure throughout the core box is necessary for best results.

As such the existing core boxes can be used but further benefits could be realized by optimizing the venting depending upon the geometry of the core. This may or may not be an expense that is worth pursuing, depending upon the desired outcome, faster curing speed, or the least possible consumption of CO₂ gas. In most cases the optimization amounts to a few trial and error experiments based on recommendations from our experienced field service and lab personnel.

With historical issues addressed, the newest CO2-cured resin system, Carbophen, has clearly demonstrated that it’s capable of performing as a viable cold box system meeting the demands of both the production and job shop foundries.  The product is produced in volume quantity and available for immediate testing and trialing.

For additional information contact HA International or visit www.ha-international.com.