Acritical hazard may be under-recognized in the foundry industry. This hazard notice explains the risks of fire and explosion in 3D printing operations where furan-type binder systems are used and provides recommendations for the safe use of these systems.

3D printers for foundry cores are being installed all over the world. This revolutionary technology offers important new capabilities, including rapid prototype development, elimination of tooling costs for one-off and small-run castings, and production of complex cores that simply cannot be produced using traditional pattern-molding methods. These benefits are so significant that we can reasonably anticipate that virtually every foundry either already has or soon will adopt this technology.  

While other binder systems are available, furan-type binders currently dominate the 3D printing market. Furans offer a package of attributes that beats the alternatives on key features such as fast cure speed and high bond strength, the viscosity and solvency appropriate for jet printing, good shelf life, and reasonable cost. This is a relatively new application area, and different binder alternatives are actively being developed.

While furan binders have been used in traditional foundry molding applications for many years, they have historically been used in a relatively small number of facilities, primarily ferrous no-bake operations. As a result, most foundries adopting 3D printing are introducing a new binder type to their facility, and many are not familiar with the hazards associated with these products. 

In normal use, roughly 1%–2% furan binder is applied to sand. In traditional molding applications, the catalyst is mixed with the sand and resin, but in 3D applications the sand is pre-treated with the catalyst. 

The relatively large thermal mass of the sand absorbs the heat generated by the resin curing reaction, which slows and controls the rate of the reaction between the resin and the catalyst. If resin and catalyst are mixed without sand to absorb the heat of the reaction, the exothermic reaction is very rapid, highly energetic, and can result in an explosion. In such cases, boiling resin erupts from the container and sprays throughout the area, and, in larger incidents vessels, can rupture––and extensive physical damage can result. The very high temperatures generated during an exothermic incident can cause a fire, particularly if a flammable cleaning solvent like isopropyl alcohol (IPA) is used in the area. Some facilities will use IPA as a cleaning solvent for the print head, though effective, non-flammable options are readily available. 

Managing the Hazards

Now that we know about the hazards, what should we be doing to manage them? Facilities currently using or installing new 3D printer systems should take precautions commensurate with the risks to manage the hazard risks associated with these systems throughout the full use cycle, from delivery to storage, use, and waste management. 

The best place to start is to check your team’s attitude and culture with respect to risk management. A plant culture that effectively manages risk will typically exhibit a healthy sense of vulnerability, evidenced by an ability to establish and consistently execute effective hazard management practices. 

If 3D printing is not a good fit for your facility’s culture, then consider purchasing 3D printed cores from a third-party supplier and avoid all the capital costs, personnel costs, and other burdens of printing cores in-house, while still enjoying most of the benefits of 3D printing technology.  

If you are moving forward with in-house 3D printing, then make sure the people designing your system have a full understanding of the hazards of these chemical systems and have both formal training and prior experience designing processes to use dangerously reactive chemicals safely. 

They should also have a working knowledge of applicable codes and standards, including local fire codes, insurance company requirements, and safety regulations. While 3D printing may not be formally subject to OSHA’s Process Safety Management standards, they are a good place to start, particularly the Process Safety Information, Operating Procedures Mechanical Integrity, Process Hazard Analysis, Pre-Startup Safety Reviews, and Change Management elements. 

If you don’t have experience with these programs in-house, then consider bringing in external resources to support your project. Process Safety consultants from the chemical processing industry work with these programs daily and would be good candidates for this work.

Recommendations

1) Consider the location of your chemical storage, printing, and waste management activities. Evaluate what would be lost if there were a fire or explosion in these areas. You wouldn’t want your server room, motor control center, major production equipment, break room, or operator control station to be located where they could be impacted by an explosion or fire. Consider the building construction, particularly the roof. A fire in an isolated part of a facility can easily spread and lead to total building loss if the roofing is combustible. 

2) Consider installing the printing operation in an area equipped with smoke detectors and an appropriate fire suppression system. Spills and accidents in transportation happen every day. Consider receiving resins and catalysts on separate delivery vehicles. At a minimum, incompatibles must be segregated in transport. 

3) Segregate acids and resins in your chemical storage areas to avoid inadvertent mixing. Provide secondary containment for the acid catalyst, and all other corrosives in your facility–– it’s an OSHA requirement. This helps prevent a resin spill from potentially contacting older acidic residues and might prevent a simple spill from developing into an explosion. 

Ensure that you maintain spill response supplies including clean, unused salvage containers in your warehouse and that your team is trained to use these supplies if they are expected to respond to a spill.  OSHA’s HAZWOPER Standard (1910.120), Section q, addresses emergency responses to chemical releases. 

4) The appropriate personal protective equipment (PPE) should be provided not only for spill response but also for routine work such as connecting lines and handling containers.

5) When spills do occur, clean them up thoroughly and ensure spill-impacted areas are properly decontaminated. If you rely on outside resources for spill response, be sure to brief them on the special hazards and precautions that apply to these products. 

6) Consider using dissimilar container types for incompatible products to reduce the risk of errors in connecting containers to the process, like using totes for resins and drums for catalysts. Use different connection sizes and types for the different transfer system components. 

7) Spill containment systems should serve only a single binder system component to avoid accidental mixing of incompatible residues. 

How It Can Happen

History suggests that a furan incident is most likely to occur when chemicals are being transferred; someone makes a mistake by attaching the wrong component to a process connection, or transfers residues from one container to another. 

Equipment vendors have done a good job of providing unique fittings for hose connections to their equipment to help manage one source of these incidents, but this is only one of several opportunities for these errors to occur. No protection is provided against inserting dip tubes into the wrong drum or tote, and nothing prevents an operator from pouring container residues into the wrong container. These errors occur most often when the regular operator is for some reason unavailable and someone else is filling in. 
Additional administrative controls such as equipment labeling, accurate written operating procedures, and training are critical safeguards to avoid inadvertent mixing. Best practice is to use different container types for resin and catalyst, and to use specific product names on pipe, drum, or tote positions, and connection points rather than generic terms like “furan,” “binder,” or other non-specific terms that a new hire or someone filling in might not recognize. 

Physically separating the resin and catalyst stations can also be helpful, and color-coding may be helpful, too, if you steer clear of colors like red and green that people with the most common types of color blindness might not be able to recognize.  

Furan no-bake foundries generally have a rule prohibiting transfer of acid or resin residues into any other container holding resin or catalyst. Unfortunately, printer equipment manufacturers have not yet developed chemical feed systems for 3D printers that leave drums and totes completely empty, and shipping these containers offsite for reclamation or disposal typically requires they be fully drained. As a result, some residue is generated each time a new container is attached. The design intent for using dip tube connections to totes is that particulate residue in the product could conceivably accumulate near the bottom of the container, and we don’t want that residue to impact the performance of the printer heads. 

These days, 3D resins are typically filtered before packaging, so these early concerns may no longer be valid. And in real life, most operators pour the residues from the container being removed into the top of the next container put up onto the process, so the design intent is compromised. Ideally, the container connections would allow each container to empty completely to prevent the need to manage any leftover container residues. Totes are designed to drain empty when placed on a flat surface; the preferred approach would be to feed printers from the bottom discharge valves of totes to eliminate the need to manage residue. 

If you use drums, then you are going to be managing residues. Probably the best solution is to provide labeled or color-coded transfer funnels dedicated to each component right at each container. The operator automatically chooses the right funnel and immediately transfers residue into the next container to reduce the chance for confusion or a possible incident. 

Awareness and Training

Ultimately, there needs to be broad awareness of the hazards of these products in the facilities that conduct 3D printing operations. Hazard communication training should be meaningful and effective and must be required for all personnel directly or indirectly impacted by resin system use, including maintenance, supervisory, and management personnel, and specifically all personnel handling chemicals and wastes generated from the process. 

This training must be included in new-worker onboarding, and training materials should be revised and revisited periodically to pick up procedural changes and to ensure that awareness remains high. Supervisors need to monitor area operations closely and coach workers right away if they are deviating from established procedures. Plant leaders should have a means of monitoring these interactions, such as routinely opening meetings with a review of recent safety coaching discussions, or through use of a behavior-based safety system.

Your emergency plans should consider the potential for an explosion resulting from mixed resin system components or residues. In the event of accidental mixing of catalyst and resin, operators may have only seconds to get away before the area is showered with boiling resin. They should know that they need to move away quickly and where to seek shelter. First responders should be informed of the hazards and should pre-plan their responses to varying levels of incidents.

Finally, sufficient powered exhaust ventilation should be provided on 3D printers to prevent worker exposure to the furfuryl alcohol and other vapors that are generated by the printing process. Emissions should be exhausted to the outside of the building without recirculation of the exhausted air.  

A good way to gauge exhaust system adequacy is to observe whether resin odors are detectable around the printer’s work area. Any persistent odor around these units indicates inadequate exhaust ventilation. Increase exhaust rates until no odors are detectable. You can confirm complete capture of vapors using a smoke pencil around all the openings in the build box enclosure; you should be able to see the smoke being pulled into the enclosure everywhere around the unit. Adequate supply air to the space must also be provided. Your printer operation should be under negative pressure relative to the rest of your facility.

3D printing brings exciting new opportunities to the foundry industry. However, a critical part of implementing this technology is understanding the hazards inherent to this process and designing systems and procedures sufficient to manage them effectively. 

Contact your printing equipment and resin system suppliers if you have specific questions about identifying, communicating, and managing these hazards. Technical assistance and model hazard communication training materials for 3D printing and other foundry chemicals may be available from your supplier.