CORE BINDERS: A Look into the Future.

Three suppliers forecast how environmental issues and demands for improved quality will shape the future of core binders.

The future for core binders will be more evolutionary than revolutionary, as they react to the demands placed upon them rather than veering off in new directions.

The foundryman who works with coldbox and nobake binders can be sure it will be necessary in the future to change his trusted concoction of polymer resins and solvents to meet demands from customers and the government. To know what demands they can place on core binders, foundries must be aware of the improvements suppliers' R&D departments, in the U.S. and abroad, are focusing on at present.

In this article, three binder suppliers--Ashland Specialty Chemical Co., Dublin, Ohio; HA International, LLC, Westchester, Illinois; and Hormel Foods Corp., Austin, Minnesota--forecast how their core binders will adapt to meet the future demands of environmental regulations, extended shelf life and tighter dimensional accuracy facing the metalcasting industry. Armed with this outlook, foundries can be aware of options that may be available to them for future binder chemistries.

The Driving Force

Core binders in the next 5-10 years will be different from those in use now. The driving force of those changes will be environmental regulations, as binders will have to become more environment-friendly to meet the demands of lower air pollutant emission levels while maintaining or exceeding the productivity demands of a competitive global marketplace.

This month the U.S. EPA plans to propose a Maximum Achievable Control Technology (MACT) standard that will include regulations on the emission of air pollutants from binders during pouring, cooling and shakeout. According to AFS Vice President of Environment, Health & Safety Gary Mosher, those standards will mandate naphthalene-depleted solvent packages for phenolic urethane coldbox binders, requiring those binders to be reformulated. EPA also will limit the amount of methanol used in furan/hotbox catalysts. If EPA meets the deadline, the rules go into effect May 15, 2002 and allow for compliance within three years. If the deadline is missed, then individual state EPAs will issue their own MACT regulations, he added. Suppliers are waiting to see exactly what the regulations will demand before they begin compliance.

The three suppliers interviewed currently market binders that conform to the Clean Air Act. This proves the balancing of environmental benefits with productivity can be achieved. By utilizing binders with reduced air pollutants, foundries can reduce the equipment investment required to collect or mitigate emissions.

With the next generation of binders (within the next 5 years), foundries can look forward to more environmentally benign solvents and solvent-free systems like acrylic epoxy binders and estercured phenolics that are water-based, said Jim Archibald, coldbox marketing manager for Ashland. Extensive development continues on the reduction of volatile organic compounds (VOCs)/hazardous air pollutants (HAPs) and benzene-toulene-xylene (BTX) with phenolic urethane binders.

Phenolic urethane binders have evolved into aromatic/ester solvent blends or all-ester solvent packages, said Archibald. This trend shall continue despite the fact that aromatic solvents are less expensive. This trend is because aromatic solvents have more VOCs and HAPs, while more stringent environmental regulations will demand less.

Ester solvents are based on materials like Dibasic ester, a "green" solvent introduced into foundry binders years ago. These esters can reduce odor and fume problems to benefit workers' health and safety. However, cost and green sand compatibility are the trade-offs as some of the esters are derived from natural oils and fats like rapeseed methyl ester.

Another environmental-friendly binder currently evolving in the market is Hormel's protein-based binder, GMBOND Sand Binder, which uses no chemicals targeted in the 1990 Clean Air Act Amendments.

Primarily developed for aluminum in automotive foundries, the binder may be used with severe applications like heavy section iron and steel casting (possibly within two years). In it, aromatic solvents are not used, as water is the solvent for the protein-based binder technology. As the chemical binders improve and the binder content in the core is reduced to 0.40.5% based on sand weight, foundries will generate less emissions, according to Jeremy Eastman, GMBOND's sales and marketing manager, and Yuliy Yunovich, metalcasting technologist with Hormel.

Testing in the next couple of years will determine which castings the protein-based binders are best suited for, said Eastman. Specifically, the casting-weight-to-core-weight ratio will be developed for the heat energy needed to break down the protein-based cores.

In the long term, Eastman and Yunovich foresee foundries incorporating protein-based binder technology derived from a renewable animal resource. The growth of binder systems will be derived from renewable resources, such as the furfuryl alcohol system that can be extracted from plants. This will mean less reliance on petroleum sources that contain VOCs/HAPs for binders. Also, new technologies that have no VOCs/HAPs will gain acceptance as the environmental compliance costs increase, forcing foundries to produce less solid and air waste.

In regard to phenolic urethane, Doug Trinowski, vice president of technical operations, HA International, pointed out that suppliers have made many environmental refinements during the last 10 years. One way that HA International improved its phenolic urethane binders was by reducing the BTX emissions at pouring, cooling and shakeout through the use of Biodiesel.

Developed by HA International's parent company, Huttenes-Albertus` in Germany, Biodiesel replaces aromatic solvents with a methyl ester solvent and is being used in castings for the European and American automotive industry.

Trinowski said this trend would continue, but not without sacrifices if foundries choose to change binder chemistry instead of changing pollution control equipment.

"Cost and performance may be the trade-off for regulation compliance. The esters are more expensive. Substituting materials that are more environmentally compliant is usually more expensive," he said.

One avenue will be for suppliers to develop stronger resins that would allow reduced content. The quality will remain, but foundries may need to use more of the binder in the sand mix for coremaking and avoid letting the cores sit around for extended times.

Best If Used By...

Cores sitting on a shelf waiting to be inserted into a mold may be a habit of the past or the wave of the future, depending who you ask. Foundries build up a core inventory to maintain a steady flow of productivity. Although an inventory prevents any delay in the casting process, it also ties up capital in sand, binders and labor.

Archibald sees a main focus in core binder quality improvement will be bench life along with productivity and casting quality. Bench life refers to the amount of time the sand and binder can be mixed prior to curing with a gas catalyst while shelf life refers to the amount of time a core can sit after it is produced before being used.

Most binder systems, like phenolic urethane, have a limited bench life when mixed with sand, ranging from minutes to hours depending upon plant conditions. In the future, mixed-sand bench life will be extended while maintaining consistent flowability in core after core and mold after mold, said Archibald. Phenolic urethane coldbox has had its bench life extended incrementally since its inception in 1968 and that will continue. Archibald said that a goal is phenolic urethane sand mixes with 24-hr bench life under extreme conditions. Since acrylic epoxy coldbox binders can provide weeks of bench life, Archibald sees the acrylic epoxy process growing for new installations and coreroom upgrades that can leverage the aluminum and iron casting benefits of the binder system.

Trinowski sees improvements with bench and shelf life based on current foundry requests. Suppliers strive to make binders more resistant to humidity (shelf life) and with better bench life, so cores and molds can sit longer. Bench and shelf life are extended by adding chemicals to the binders that usually contain VOCs/HAPs. Foundries then would be required to purchase air control devices to compensate.

At present, a silicate core may fall apart if it sits around during rainy days. "We're looking at coldbox cores that can be stored for days or weeks without any adverse effects, including humidity. That may occur in 5-10 years," Trinowski added.

Work to extend the shelf life or humidity resistance with protein-based core binders is a research priority, Eastman said. Currently, the core's strength can be regained by drying the cores in an oven, since the binder has a reversible bond. He predicts, however, that lean manufacturing will drastically reduce or eliminate large core inventories.

In addition, he said, adding anything to a binder to extend the shelf life may jeopardize its environment-friendly advantage.

Dimensional Accuracy

Foundries are finding markets like military and aerospace industries demanding tighter dimensional tolerances in producing thin-walled castings. This dimensional accuracy for cores is connected with various binder properties like tensile strength, permeability, durability, density, thermal shield and expansion. Improvements to these properties are on going without any timeline unless set by the customer's level of urgency.

According to Archibald, the demand for thin-walled castings, when requested, will be met by the elimination of coatings and the use of chemically bonded binder systems available today. This will be achieved by increasing the amount of binder and specialty sand additives or reclaimable ceramics in a core mix. Currently, 0.6-1.5% binder is used in a core. In the future, foundries may find they have to increase the amount (possibly as much as 3%) to provide casting properties that would eliminate the coatings' thickness, cost and extra labor for application, he said.

Other general property improvements for phenolic urethane and acrylic epoxy may be along the lines of balancing casting surface finish with sand removal and recycling of sand. Binders will have improved thermal properties resulting in less metal penetration and better casting surface finish. This also may eliminate the need for coatings.

Trinowski and Archibald agree that the binders of today can meet the demands for dimensional accuracy for thin-walled castings and cores. The shrinkage for binders is well defined and can be calculated. "The inherent dimensional stability of chemical binders makes it quite suitable for precise tolerance castings," Trinowski added.

Others see it differently.

Eastman and Yunovich said a foundry could produce thin-wall castings up to 3 mm when current binder technologies, like phenolic urethane, increase their specific bond strength. Such bonds with high hot strength will eliminate or, at least, noticeably reduce coating applications, especially for automotive castings. Combinations of binders' high specific bond strength and its low content levels will provide improved dimensional accuracy of castings, eliminating the possibility of hot tears and reducing harmful emissions.

They added that binders are helping sand casting compete with diecasting, investment casting and lost foam. Binder systems provide sand casting processes advantages such as lower capital investment costs, a high degree of precision and manufacturing flexibility. Binder systems of the future will help bring sand casting and diecasting processes together. Systems that exhibit high hot strength and excellent collapsibility without thermoplastic deformation also will allow for high-pressure semi-permanent mold casting.

The Future?

Foundries will be the guiding factor as to the future of core binders. Suppliers will respond to the demands and the parameters set by foundries.

Ultimately, the future of binders offers choices. Foundries will be able to choose whether; to install air pollution control devices or work with binders that have lower HAPs/VOCs: a core's shelf life needs to be extended; and a binder's properties need to be enhanced for greater dimensional accuracy and improved casting quality.

The current State of Core Binders

This list shows the latest developments in core binder
technology. From these newly introduced products, binders with
lower hazardous air pollutant emissions, longer shelf life and
stronger properties in tensile strength, durability and thermal
shielding will emerge.


Name:              Isocure/Isoset Coldbox

Manufacturer:      Ashland Specialty
                   Chemical Co.

Type:              phenolic urethane/acrylic
                   epoxy (ester solvents, new
                   base resin technology)

Environmental      no or low formaldehyde,
Benefits:          reduced VOCs/HAPs and BTX
                   casting emissions, low
                   smoke at casting

Core Shelf Life:   days/weeks depending on
                   humidity and core
                   configuration

Other Properties:  high strength, low binder
                   levels, hot strength and
                   erosion resistance for
                   thin-walled iron and steel
                   castings, increased core
                   production, improved
                   shakeout with aluminum,
                   improved humidity
                   resistance



Name:              GMBOND                    Biodiesel

Manufacturer:      Hormel Food Corp.         HA International, LLC


Type:              protein-based             phenolic urethane using
                                             methyl ester (plant
                                             material) solvent

Environmental      renewable source without  no HAPs/VOCs emissions
Benefits:          HAPs/VOCs, lower casting
                   emissions


Core Shelf Life:   days/weeks depending on   days/weeks depending on
                   humidity and core         humidity and core
                   configuration             configuration

Other Properties:  excellent shakeout        hot strength, lower odor,
                   characteristics, easy     lower fumes
                   reclamation, no disposal
                   concerns, energy cost
                   reduction

Coldbox Binder R&D Focuses on Aluminum

The current trend in R&D for coldbox binders is making them more applicable with aluminum castings. R&D is focusing on that trend because the automotive industry, which creates the greatest demand for coldbox resins, is moving away from iron and towards aluminum for both heads and blocks.

Aluminum use in automobiles was 242 lb/car in 1999 and could reach up to 880 lb/car within 5 years. The percentage of automobiles with aluminum engine blocks is expected to increased from 25 to 55% by 2007.

The primary problem with sand cores in aluminum castings revolves around collapsibility during shakeout. A coldbox core for iron uses 1.2-1.4% of the resin in the core mix. The same core for aluminum requires 0.8-1.2%. The amount is reduced, so it will become loose during shakeout. Less resin also jeopardizes the bond strength when the molten metal interacts with the core.