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Green Sand Metalcasting Foundry News

Mold Coatings and Core Binders for the Green Sand Metalcasting Foundry

Posted by Hill and Griffith Company on Sep 12, 2017 2:06:16 PM

Core & Mold Coatings

EZ Kote™ Refractory Core & Mold coatings are formulated for ferrous & non-ferrous castings. The formulation permits use on small intricate cores up to heavy cores and molds.

Emulsified Core Binders

Hill and Griffith 523 and 683 Emulsified Core Binders are formulated with water, drying type oils, surfactants, cross-linking resins, hardeners and biocides to produce a stable emulsion used in making sand shapes. 523 and 683 Emulsified Core Binders were developed to meet increasing environmental demands set forth by the Environmental Protection Agency.

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Sodium Silicate Binders

Hill and Griffith Sodium Silicate Binders, Corosil and CoBond 86, are formulated with water based solutions of Sodium Silicates and collapsibility agents. These binders are available in various percentages of carbonaceous materials as well as silica to soda ratios for varied or specific applications. The sand and silicate mixture is hardened by gassing with carbon dioxide (CO2). Molds or cores produced with Silicate binders result in castings with minimal veining, scabbing and penetration. Due to lack of mold wall movement, dimensional accuracy may be improved over some other casting processes.

Other Core Binders

GOULAC* is a dark colored water soluble, material developed from the wood pulping process and used primarily as a foundry core binder. *Tradename of LiqnoTech U.S.A.


Core Binder Information From Wikipedia

Baked Cores
Special binders are introduced into core sands to add strength. The core is then baked between 200 and 250 °C (392 and 482 °F). The heat causes the binder to cross-link or polymerize.

Hot Box Cores
Another type of binder process is called the hot-box process, which uses a thermoset and catalyst for a binder. The sand with the binder is packed into a core box that is heated to approximately 230 °C (446 °F). The binder that touches the hot surface of the core box begins to cure within 10 to 30 seconds. Depending on the type of binder it may require further baking to fully cure. Cores produced using this method are sometimes referred to as "shell-core" because often, only the outside layer of the core is hardened when in contact with the hot corebox. When the corebox is opened and the core removed, the uncured sand inside the core is dumped out to be reused. This practice can also be observed in some cold-box coremaking practices, though cold box shell-core making is much less common.

Cold Box Cores
In a similar vein, the cold-box process uses a binder that is hardened through the use of special gases. The binder coated sand is packed into a core box and then sealed so that a curing gas can be introduced. These gases are often toxic (i.e. amine gas) or odorous (i.e. SO2), so special handling systems must be used. However, because high temperatures are not required the core box can be made from metal, wood, or plastic. An added benefit is that hollow core can be formed if the gas is introduced via holes in the core surface which cause only the surface of the core to harden; the remaining sand is then just dumped out to be used again. For example, a cold-box sand casting core binder is sodium silicate which hardens on exposure to carbon dioxide.

Air Set Cores
Special binders are used in air-set sands to produce cores at room temperature. These sands do not require a gas catalyst because organic binders and a curing catalyst are mixed together in the sand which initiates the curing process. The only disadvantage with this is that after the catalyst is mixed in there is a short time to use the sand. A third way to produce room temperature cores is by shell molding.


Hill and Griffith Customer Service

The Hill and Griffith Company's green sand metalcasting foundry supplies help achieve the EPA's M.A.C.T. standards and reduce Benzene emissions. Our variety of environmentally sound release agents, coatings, partings, lubricants, core oils and specialty products will help you meet your metal casting's needs. We're known for our hands on approach. Let us visit your plant and recommend products that suit your needs.

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Bulletins and Technical Papers for Metal Casting Products

 

Tags: Green Sand Casting Products, Green Sand Foundry Supply, Foundry Supply, Green Sand Release Agents, Foundry Supplies, Green Sand System, Green Sand Metalcasting, Core Binders

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