Green Sand Metalcasting Foundry News

Excerpt from the September 2019 Foundry Management & Technology article.

Top and bottom sand-blowing system extends the Hunter expertise with a new option for foundries' mold-filling needs.

The science of sand molding has not changed for centuries, but the process technologies involved in mold production are another matter. In that case, the changes are demand-driven. Molding machinery is developed to suit the production requirements of foundries, and foundries know where to turn for molding technology expertise.

Hunter Foundry Machinery Corp. has been innovating and refining molding machinery for more than half a century, famously with the Hunter HMP machine that introduced the "matchplate" concept that made green-sand molding faster, more reliable, and more cost-effective, and allowed foundries of all types to be competitive in terms of volume and product quality. It is a rugged, gravity-driven system that’s easy to operate and easy to understand; it is scalable to foundries’ available space; and it adapts easily to different foundries’ molding operations.

Excerpt from February 2009 Foundry Management & Technology article by Nobuyoshi Sasaki.

A novel concept uses sodium and silica to increase the heat resistance of organically bonded molds and cores, which increases hot strength and allows the production of thin-wall castings.

Historically, foundries worldwide have been forced to rely on organic-based core and mold binders, and the use of refractory coatings, along with sand additives, when the hot strengths of the binders are insufficient to produce salable castings.

In 1995, Cadic Corp., and its subsidiary CTI Inc., introduced the Cadic Convert Process, which uses a liquid mixture of silicon oxide and sodium in alcohol to treat resin-bonded molds and cores. In practice, cores and molds produced using organic heat- and amine-cured resins were dipped or immersed in the ethanol solution, dried, and subsequently fired in a kiln to convert the organic-bonded article to an inorganic bonded mold or core.

This post-production treatment of organic-bonded aggregates resulted in the formation of organo-silicates that were converted to ceramics when fired at elevated temperatures, and poured hot to produce thin-wall (2 mm or less) stainless steel castings.

Laboratory evidence, supported by foundry trials, confirmed that the silica compound formed a crystal lacuna surrounding the sodium (Na) at room temperatures and allowed the Na ion to retain its high degree of reactivity.

The subsequent high-temperature treatment resulted in the conversion of quartz to tridymite, thereby increasing the high-temperature properties of the core or mold.

Because of the high degree of reactivity, the Na ion is utilized in this process as the alkali oxide Na₂O. In this new process, the nano silica composition allows the Na ion to maintain its reactivity from room temperature to the boiling point of the compound.

With the elimination of a post-production treatment for the core or mold using ethanol as a carrier, the resulting new development makes the Cadic Convert Process considerably simpler, because the nano silica compounds can be added to the sand mix prior to the production of the core or mold in any organic resin-bonded processes, such as phenolic urethanes and shell sand mixtures.

A new water-based reclamation process offers foundries a method for recovering bentonite and carbon from foundry dust.

Excerpt from the March 2020 Foundry Management & Technology article.

Despite numerous challenges to its long-term viability — some serious and credible, others just imagined or mistaken — green sand casting is thriving, both in practical terms and in its technological progress. But one constant dilemma for producers of green sand castings is what to do with the byproducts.

For background, green-sand casting involves molds formed with silica (or chromite, or zircon) sand mixed with water and bonding compounds, notably bentonite (clay) and carbon. Finished castings ultimately leave their molds but the bonded sand remains, and what to do with that sand is one of those challenges that green-sand casters routinely discuss. Reportedly, the U.S. foundry industry consumed approximately 700,000 tons of bentonite and carbon during 2018.

Today's foundries cannot afford to sacrifice the efficiency and profits that are the consequences of poorly controlled hot molding sand.

Excerpt from the June 2004 Foundry Management & Technology article by FM&T Staff

Metalcasting researchers say hot sand is the leading sand-related problem for today’s foundries. Most metalcasters recognize a relationship between reduced casting quality, increased process variation, and other molding inefficiencies that result from using hot molding sands. Studies show that hot sand affects virtually every operation in the production line.

System sand returned to the muller for reconditioning with a temperature of 160°F (approximately 70°C) or greater is considered to be excessively hot. Return sand ranging from 120° to 160°F (approx. 49°-70°C) is hot enough to demonstrate inconsistent properties during mixing and to be very difficult to control.

A global consortium of metalcasting companies, resin and coating suppliers, additive and sand suppliers, and researchers, aims to spread the word for CPR casting porosity reduction.

Abstract from the June 2007 Foundry Management & Technology article by Charles E. Bates and Robert Burch

According to a recent survey of 121 product engineers, design engineers, metallurgists, laboratory personnel, and others associated with the design, production, and use of castings, the metalcasting industry's greatest need for improvement lies in eliminating porosity in castings. By consensus, this applies to aluminum, gray iron, and ductile iron, and to all types of steel castings. The distribution of quality issues based on this broad survey is illustrated in Figure 1. Concerns over porosity rated twice as high as any other issue in the survey.

A consortium of companies around the world is being formed to address this concern, led by AlchemCast L.L.C. The consortium is known as the Foundry Casting Porosity Reduction (CPR) Consortium, and to assure the future success of castings as structural components in engineered products, a kick-off meeting for foundries and suppliers was held in Birmingham, AL, April 12-13, 2007.

For foundries that prepare chemically bonded sand for molds and cores, optimizing the process means understanding and evaluating the primary features and options for water-based and electric-resistance systems.

Excerpt from the Foundry Management & Technology Magazine February 2019 issue by Jack Palmer

In general, there are two types of sand heaters used to prepare chemically bonded sand for molding and coremaking, and both are designed as fluid bed processes — meaning the sand is moved around the heating/cooling elements with compressed air or blower air. The more popular style is the electric-resistance fluid bed with compressed air fluidization, followed by water-pipe units in which hot or cold water is passed through piping, with fluidized sand moving around them with blower air.

The popularity of the electric-resistance type heater is due primarily to cost (compared with water-pipe designs) and size. The electric-resistance units are much smaller than the water pipe-based designs, though both offer advantages.

Cloud-based software promises to reduce green sand casting rejects and optimize additive consumption by applying predictive and prescriptive data analytics, machine learning and IoT functions to green-sand molding

Excerpt from the March 2019 issue of Foundry Management & Technology

The Smart factory "vision" is gaining global acceptance. It involves integrating data analytics, machine learning and IoT by incorporating sensors, SCADA and line-speed or near-real-time data-based analytics for process optimization. Predictive and prescriptive data decision-support, predicting highly accurate outcome has shifted the paradigm in manufacturing and many other industrial and consumer sectors. For manufacturers, rapid proliferation and advancement of information technologies, such as cloud computing, allows them to generate and store huge volumes of data.

In addition, the digitalization of the green sand casting process automation has empowered industries to collect and transmit near-real-time data. Cloud computing ensures data availability without geographic or physical limitations. By leveraging the power of data-based analytics and machine learning, industries are generating significant tangible and intangible profits.

Todays foundries cannot afford to sacrifice the efficiency and profits that are the consequences of poorly controlled hot molding sand.

Excerpt from the June 2003 issue of Foundry Management & Technology

Metalcasting researchers say hot sand is the leading sand-related problem for today’s foundries. Most metalcasters recognize a relationship between reduced casting quality, increased process variation, and other molding inefficiencies that result from using hot molding sands. Studies show that hot sand affects virtually every operation in the production line.

System sand returned to the muller for reconditioning with a temperature of 160°F (approximately 70°C) or greater is considered to be excessively hot. Return sand ranging from 120° to 160°F (approx. 49°-70°C) is hot enough to demonstrate inconsistent properties during mixing and to be very difficult to control.

Excerpt from the October 2013 issue of Foundry Management & Technology by Mark Riekert and John Kuhn

Robotic sand core setting into a mold has the potential to increase molding productivity and reduce casting scrap.

With the evolution of casting designs, driven by requirements for lower-weight parts and (in automotive applications) a desire to minimize assemblies, there follow designs with thinner walls and smaller openings/cavities.  These structures need cores to create those thin wall sections, and in some examples these walls are as thin as 4 mm.  In addition, small cores are used to create small openings and cavities. 

Adding to the difficulty of the arrangement, gripping the core was a very specific challenge. The end-of-arm tool (EOAT) or end effector uses a rubber "squash" ring to expand inside a hole in the core, and a parallel gripper to contain the tail section of the core without actually gripping it. The core was specially designed with a hole to allow the tool to grip it.

Originally published in the May 2017 issue of Foundry Management & Technology.

by Alexander Brown

Controlling raw materials is critical to the success of iron casting production from green sand systems. The base silica sand is often overlooked, with the main focus on bentonite additions. Carbonaceous additives can be considered a “necessary evil” to ensure a good surface finish and reduction in sand-related surface defects. Other additives are used when systems get out of balance, and these will further complicate the complexity of green sand systems.

For castings requiring cores, this becomes a bigger issue, as many different resin systems are employed for core production, and these must be taken into consideration when controlling both the carbonaceous levels and the overall grading of the sand system. The twin effects on additional carbon and loss-on-ignition and overall sand grading need careful understanding and control.