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Green Sand Metalcasting Foundry News

Entrainment: Inclusions of Green Sand in Casting Molds

Posted by Hill and Griffith Company on Mar 2, 2021 9:48:35 PM

Sand Inclusions

Excerpt from the Complete Casting Handbook, Second Edition by John Campbell

Inclusions of molding sand are perhaps the most common extrinsic inclusion, but whose mechanism of entrainment is probably rather complicated. It is not easy to envisage how minute sand grains could penetrate the surface of a liquid metal against the repulsive action of surface tension and the presence of an oxide film acting as a mechanical barrier. The penetration of the liquid surface would require the grain to be fired at the surface at high velocity, like a bullet. However, such a dramatic mechanism is unlikely to occur in reality. Although the following description appears complicated at first sight, a sand entrainment mechanism can occur easily, involving little energy, as described next.

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Elimination of Pinhole Porosity in Alloy Steels

Posted by Hill and Griffith Company on Feb 23, 2021 4:50:06 PM

Adding small amounts of ferroselenium and keeping charged nitrogen volumes low is effective in preventing subsurface porosity.

Excerpt from Foundry Management & Technology's February 2020 issue by Dr. R. L. (Rod) Naro and D. C. Williams

Nothing is more frustrating in foundry operations than finding an outbreak of subsurface porosity after costly machining operations. Outbreaks of subsurface porosity always seem to occur during high humidity seasons, especially during the rainy spring. The prime culprit universally blamed is hydrogen absorption into molten steels.

The hydrogen atom is the smallest and simplest of all the elements. Hydrogen can be absorbed only in its mono-atomic state. Nitrogen also can play a significant role in the development of porosity, especially in the production of high-alloy steel castings.

Hydrogen and nitrogen absorption in steel casting may result from alloy additions and reactions at the mold-metal interface. The ability of molten steel to absorb large amounts of hydrogen and nitrogen is shown in Figure 1.

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Manufacturing Processes for Light Alloys

Posted by Hill and Griffith Company on Feb 16, 2021 8:53:03 PM

7.6.2 Selected expendable mold processes

Excerpt from the publication, Materials, Design and Manufacturing for Lightweight Vehicles by G.T. Kridli, et. al.

Sand casting is the most commonly used expendable mold process. In this process, sand is bound together (as detailed in  Table 7.8 ) and shaped to conform to the negative impression of the desired component. Molten metal is then poured into the sand mold; upon solidification, the metal has the geometry of the desired component.
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High-Speed, High-Efficiency Core Box and Mold Cleaning

Posted by Hill and Griffith Company on Feb 9, 2021 5:36:28 PM

Progress Casting's dry-ice blasting operation cuts cleaning time by 86% and saves operating costs.

Excerpt from the October 2019 Foundry Management & Technology article

Metalcasters' product quality and performance results are under constant review, and new technologies and techniques are always being tested, or considered. But how often are maintenance methods reconsidered? Progress Casting Group in Plymouth, MN, produces precision die castings and sand castings it supplies to automotive, aerospace, and defense industry customers. It had a fairly standard problem — cleaning core boxes and low-pressure die casting molds — and a fairly standard approach to addressing it.

Core boxes and casting molds are meant to be used over and over again. So, they must be cleaned frequently and effectively in order to maintain dimensional accuracy and process reliability. The refractory coatings (i.e., release agent) and resin spray buildup on the mold faces, as well as sand and binder residue on the core boxes, had been removed by sand blasting and manual brushes. Both processes are slow and not fully effective. Sand blasting degrades the urethane on the molds and both methods routinely destroy the vents on the core boxes. More than this, the cleaning can damage machinery and workers' safety may be at risk in the process.

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Reexamining Shakeout to Control Time, Temperature

Posted by Hill and Griffith Company on Feb 2, 2021 3:44:11 PM

What happens to castings during shakeout may be instructive to foundries seeking to optimize production costs and process quality.

Excerpt from the March 2016 Foundry Management & Technology article by G.D. Henderieckx.

Shaking out castings is done in different ways, according to a foundry’s specific molding operation, and mold cooling may require hours or even days for batch production and larger castings. There is much to be learned about the process: In general, shakeout timing is not calculated, and it is determined mainly by older, experienced employees using very safe operating practices (i.e., a long time).

What happens during the shakeout? First, the cast iron in the mold will transform its structure from austenite to ferrite (or pearlite, bainite or martensite). This initiates a transformation stress. The amount of stress depends on the final structure: transforming to martensite leads to the highest stress; transforming to ferrite to the lowest stress level. Austenitic materials have no transformation and will not suffer from transformation stress.

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3D Printing As an Alternative to Pattern Making

Posted by Hill and Griffith Company on Jan 26, 2021 9:16:21 PM

3D printing has eliminated much of the tedium of the 3,000-year-old sand casting process

Excerpt from the January 2014 Additive Manufacturing article by Peter Zelinski.

Hoosier Pattern has changed its business in a way that dramatically expands the design freedom available to its customers. Historically, the company has machined foundry patterns. Today, it uses 3D printing to create molds and cores directly from sand.

That's sand casting in a nutshell, although journeyman pattern maker Dave Rittmeyer will tell you there's far more to it than that. Rittmeyer, the customer care and additive manufacturing manager at Hoosier Pattern Inc., Decatur, Ind., also will tell you the industry has undergone a dramatic shift over the past decade or so, thanks in part to AM.

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How 3D Printing is Changing Sand Casting

Posted by Hill and Griffith Company on Jan 19, 2021 9:33:14 AM

3D printing has eliminated much of the tedium of the 3,000-year-old sand casting process

Excerpt from the September 2020 The Additive Report article by Kip Hanson.

Humans began pouring the first sand castings approximately three millennia ago. And until recently, that technology has remained virtually unchanged:

• A replica, or "pattern," of the desired object is placed in an open-ended, steel molding box.

• A special type of sand is poured around the pattern, which is pounded firmly into place and then removed.

• A sprue is cut to allow molten metal to flow into the mold, along with a gate that joins the sprue to the mold cavity.

• A core is used to replicate parts having internal features.

• Molten metal is poured into the mold; when the metal cools, the completed part is removed.

That's sand casting in a nutshell, although journeyman pattern maker Dave Rittmeyer will tell you there's far more to it than that. Rittmeyer, the customer care and additive manufacturing manager at Hoosier Pattern Inc., Decatur, Ind., also will tell you the industry has undergone a dramatic shift over the past decade or so, thanks in part to AM.

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Casting Goes Digital with Sand 3D Printing, Nondestructive Testing

Posted by Hill and Griffith Company on Jan 12, 2021 5:04:14 PM

Tooling & Equipment International (TEI) used to make tooling for castings. Now, it casts prototype parts in a digital workflow using 3D printed sand molds in combination with simulation software, CT scanning and X-ray technology.

Excerpt from the January 2019 Additive Manufacturing article by Stephanie Hendrixson.

"In the early days, before numerically controlled machines, casting tools were made by highly skilled pattern makers carving mahogany into patterns and packing sand around them," says Oliver Johnson, president of Tooling & Equipment International (TEI). "You'd be talking six or nine months to make all the tooling for a part that we could do today with a 3D printed mold in two days."

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Novel Sprue Designs in Metal Casting Via 3D Sand-Printing

Posted by Hill and Griffith Company on Jan 5, 2021 5:07:26 PM

Excerpt from the January 2019 Additive Manufacturing article by Santosh Reddy Sama, Tony Badamo, Paul Lynch, and Guha Manogharan.

The market size of the metal casting industry was 20.23 billion USD in 2017 and is expected to grow annually at a rate of 8.87% to reach 39.94 billion USD by 2025. Engineered castings constitute about 90% of total manufactured goods and capital equipment. In United States, over 2000 metal casting facilities employ more than 200,000 people across the country. Despite having a casting market share of 80%, sand casting foundries across the globe suffer from long lead times, expensive tooling and limited flexibility. It is well known that the pattern making step in sand casting is the bottleneck and often, the most expensive component in low volume production runs. The need to remove the pattern from compacted sand mold to create casting cavity significantly restricts the geometries in traditional sand castings. The increased complexity of metal parts for industrial and mission critical applications demands new technologies. Recent advancements in 3D Sand-Printing (3DSP) which is a form of Additive Manufacturing (AM) bridges this technological gap through direct printing of sand molds in a layer-by-layer process.

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Core Design is Key to Successful Castings

Posted by Hill and Griffith Company on Dec 29, 2020 8:00:00 AM

Excerpt from the November/December 2020 Casting Source by Jiten Shah.

The green sand casting process is the most widely used high-volume process because it is versatile and cost effective. In the case of an oil pan for a combine used in the agriculture industry produced by AFS Corporate Member Wabash Castings Inc. (Wabash, Indiana), the green sand process proved it versatility after eliminating some issues in the old design, which was cast in the semi-permanent mold process. Thanks to the flexibility in gating placement and design changes in the green sand process, the new casting reduced cost by using a common core for two cavities inside the part.

Critical wall thickness is maintained repeatedly with horizontally-parted green sand molding using a rugged common core for two mold cavities.

  • Critical wall section thickness (1) in the oil pan is controlled with a massive common core that is well supported at the core print. The main body core has an overhang, like a cantilever, and if not designed carefully, it could sag or deform, resulting in uneven wall thickness. This could potentially lead to shrinkage porosities and non-uniform mechanical properties due to uneven cooling rates of thinner and thicker sections within the same casting.

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