For most foundrymen, the term “cold box” means a phenolic urethane cured by an amine gas, which are used in most high-production coremaking systems. Cold box as a classification, however, also includes some less widely used technologies like epoxy/acrylics cured with sulfur dioxide and alkaline phenolics cured with methyl formate. While effective in their operation, they use a hazardous curing agent.

The more environmentally friendly, carbon dioxide (CO2) cured binder systems, have been around for many years, but they have not gained much presence in the foundry market for good reason.  The earlier versions offered a few significant benefits, but the trade-offs (such as poor work-ability and increased resin levels) out-weighed the benefits. Carbophen, the latest CO2-cured cold box binder offering from HA International has addressed the earlier draw-backs, thus greatly improving CO2 systems and making them a very attractive alternative for cold box binders.

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.