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Metal casting sand

metal casting sand Materials include gray iron, ductile iron, carbon steel and alloy steel. By dan_m, December 15, -“Metal Casting: A Sand Casting Manual for the Small Foundry” by Steve Chastain Buffalo Metal Casting Is A Single-Source Supplier Of Non-Ferrous Castings & Finished Parts Through Sand Casting & Machining Services. Arvalda Corp. is a successful family business. Supply partners with you to meet your specific metal casting quality assurance and control requirements. Learn how your tools, propellers, valve bodies, and other metal parts are produced in a foundry. to/2pHdtlz Play Sand: MetalTek offers multiple metal casting processes for you to choose from- centrifugal, sand, investment, continuous, vacuum, net shaped, HPLT, and ingot. sand casting can be used to replicate intricate objects by pressing the object Metal castings are all around us, but often taken for granted. Great castings come tramp metal or other contaminates from your sand Pickering Metal Casting, LLC. green sand casting (109) The 3 Types of Sand Used for Sand Casting. We offer strategic sourcing for sand casting, precision casting, and die casting methods for your project requirement needs. 888-588-5415. Lecture 2. Investment Casting b. The object that results from this process is also called a casting. 1 [0970220324] - Metal Casting: A Sand Casting Manual for the Small Foundry, Vol. com/kingofrandom/ Let’s make special sand for casting metal! Fragrance Free Kitty Litter: http://amzn. . Air set and green sand capability. WASTE CASTING METAL Over half the metal Metal melting, metal casting, resin sand casting and green sand casting. Burned-on sand and scale are removed to improved the surface appearance of the casting. com/processes/metal_processing/sand_casting_intro. Metal Filtration in Gating Systems 12. Easy greensand recipe for sand casting/metal casting that's not oil bonded and simple instructions on how to cast with green sand at home. 3D Printing Webinars Learn from FDM and PolyJet experts, live or on-demand. C. Stephen Chastain Metal Casting Vol. Sand casting economic for low volumesSand casting economic for low volumes shape of casting and design of process to casting practice for control of metal flow Sun Fast International is an industry leading provider of strategic offshore sourcing for custom metal castings. Suppliers of die castings, investment castings, sand castings. They pay close attention to detail which will make your job easier. The Sand Casting Operation: The sand casting operation involves the pouring of the molten metal into the sand mold, the solidification of the casting within the mold, and the removal of the casting. METAL CASTING . 2. Mainly products: die casting, sand casting, investment casting, precision casting, forging, machining and OEM offered. Product Description Silica Sand, Resin and Oil Great for casting Jewelry, Coins, Metal Parts Get a T-Shirt: http://try. Expandable pattern. A sand casting mold requires placing a duplicate of the object to be created into sand. Metal casting foundry, free step by step sand casting instructions. Sand Casting and machining: 6 – 8 weeks. DIDION International manufactures machinery including shakeouts, reclamation, sand screens, casting cleaning/cooling, and sand blending/cooling for the foundry industry. Nearly any part configuration can be reduced to a pattern and created as a sand casting. General Kinematics sand handling, cooling, and reclamation solutions your sand. The Hazleton Casting Company augments its traditional foundry operations with additive manufacturing, via a new sand 3D printing system. Seattle Foundry and Metal Casting Service Company - Morel Industries Arvalda Corp. [165 Pages Report] Metal Casting Market report categorizes the global market by Material (Iron, Al, Mg, Zn), Component, ICE & EV (Passenger Car, LCV, HCV, BEV, HEV & PHEV), Process (Gravity, High & Low Pressure, Sand), Application (Body Assembly, Engine, and Transmission), and Region Kassico Casting are Prefessional manufacture of die casting, sand casting, investment casting, precision casting, aluminum die casting,aluminum sand castings, aluminum investment castings and the CNC machining in China. FAQ (Frequently Asked Questions) If you think you'll have a real interest in metal casting and you If you have good molding sand but the casting comes out From Investment Casting to Sand Casting, Forging and Precision Machining, Metal Cast & Forge provides a reliable single-source solution for various applications. , LTD is specialized in producing casting products and machining part. Other sand is used as an abrasive in sandblasting and to Metal casting! Molten aluminum poured into a sand mold, very fun,safe and SO easy! You are only limited by your imagination Sand casting definition: Sand casting is a process in which a molten metal is poured into a mold made from sand. Sand Casting is the process of making cast metal parts using sand molds. 3D Sand-Printing (3DSP) is a relatively new Additive Manufacturing (AM) technology that enables direct digital manufacturing (DDM) of complex sand molds and cores for sand casting applications. Affordable furnaces, crucibles and complete foundry kits. optimized sand for the casting being • However, if the porosity of the mold is too great, metal may penetrate the sand grains and cause a burn‐in 1992. RP investment casting is the only metal casting process that is both cost effective at low quantities and yields metal casting properties METAL CASTINGS DIVISION. Permanent Pattern a. Reclassifying spent sand in West Virginia ALUMINUM SAND CASTING. Sand casting definition: Sand casting is a process in which a molten metal is poured into a mold made from sand. 4. Harrison Castings is one of the largest gravity and aluminium sand casting companies in the UK, with clients worldwide and a strong reputation built over 100 years. 3. Sand casting method plays an important role in the production of large metal forms to those goldsmiths who take the time to master it. Contact Us Today! [165 Pages Report] Metal Casting Market report categorizes the global market by Material (Iron, Al, Mg, Zn), Component, ICE & EV (Passenger Car, LCV, HCV, BEV, HEV & PHEV), Process (Gravity, High & Low Pressure, Sand), Application (Body Assembly, Engine, and Transmission), and Region METAL CASTING PROCESS 1. An article discussing the process of DIY green sand casting and lost foam casting of molten aluminium and the relative benefits and drawbacks of each. A wide variety of casting metal in sand options are available to you, such as souvenir, art & collectible, and business gift. Our metal casting methods include die casting, investment casting, sand casting, permanent mold, and metal Injection molding, as well as hot forging and cold forging. Sand casting is a process to manufacture rough metal castings by pouring molten metal into a natural or a fabricated sand mold. A Basic Overview Metal casting is the process in which molten metal is poured into a mold and allowed to solidify into an object. As a quality metal casting company, ChinaSavvy offers different types of metal casting processes. The four main decisive elements in the casting process are patterns, chills, cores, and molding box and materials. Follow Me. metal casting industry experi- Permanent Mold Compared to sand casting operations, Rubber plaster molding, also known as plaster mold casting, is an alternative to sand casting and investment casting, and a solution for prototype die casting. Knowledgeable and experienced. RFQ LINE supports over 35 metal casting foundries. From Investment Casting to Sand Casting, Forging and Precision Machining, Metal Cast & Forge provides a reliable single-source solution for various applications. Terms. Basics of Metal-Casting The mold is made from a refractory material, for example, sand. Dandong Foundry is producing various cast iron and cast steel casting parts. Sand casting is the process of metal casting using sand as the mold material. Sand Casting Producing metal castings out of sand molds. Foundry and metal casting molding company in Seattle, WA Morel Industries. , is the world’s largest producer and supplier of green sand bond solutions for ferrous castings. Foundry Sand Casting Process: Sand casting is the most widely used metal casting process in manufacturing and almost all casting metals can be sand cast. Recent Metalcasting News. American Aluminum Casting Co. Overview of metal casting for beginners. About 11% of these are cast & forged, 2% are metal crafts, and 1% are sculptures. Permanent Mold, or Gravity Die Casting, produces parts that have better mechanical properties than sand castings, with better surface finish and a competitive part pr Steel Sand & Investment Castings. Sand casting is a versatile and economical casting method. Contact Us; Request a Quote; Castings. This blog is about metal casting, setup of a homemade, backyard aluminum foundry, sand casting methods and how to create different aluminum objects Online foundry store for ingot, flux, sand and binders, crucibles, furnace parts, and other equipment and supplies. Come see my many projests shown on this web site. METAL CASTING - MOLDING : Metal castings are used by most people everyday but very few have any idea of what they are or how they are made. In this article, Part 1, we’ll look at the background to casting, and specifically sand casting – the cheapest and easiest way of producing small runs of a casting. Metalcasting at home with mostly homemade equipment and a small budget. Once the sand hardens, metal or wax, is poured into the mold which creates an exact replica of the original object. Sand Casting – Fine Grain Sir Set. The sand is packed tight around the object creating a mold. Bernier Cast Metals, Inc. The mold is created when a pattern made out of wood or plastic — typically called a match plate — is placed inside an enclosur This article compares the various advantages and disadvantages of several industrial casting processes, including sand, plaster, investment, and die casting. Sun Fast International is an industry leading provider of strategic offshore sourcing for custom metal castings. The American Foundry Society (AFS) presented by Metal Casting Design & Purchasing magazine, at CastExpo 2019, April 27-30, 2019, in Atlanta. First a cavity in the sand is formed by using a pattern made of wood, or metal. About Us Casting Products Casting Workshop Machining Workshop Inspection Certificate Casting Defects - Sand Mold, Metal Casting Introducing various metal casting defects with many pictures by Dandong Foundry in China. SFE’s sand casting foundry tolerance and standards are unsurpassed in the industry. It is an unwanted irregularities that appear in the casting during metal casting and sand in the casting what is casting defects – types, causes and Avalon Precision Metalsmiths offers cost-effective die castings, sand castings, investment castings and permanent mold castings from China. Fluent English, Factory Direct Transparency, Strict control of material composition, ISO9001. View a full range of metal casting materials including carbon steels, compacted graphite iron, copper-base alloys, superalloys and austempered ductile iron. Can produce one metal casting only ; Made of sand, plaster, or other similar material ; Binders used to help material hold its form ; Examples of metal casting for firefighting equipment, plumbing parts, value parts, electrical hardware, precision machinery, gears, and other industries. We make rapid, high-quality no-bake sand casts in as little as three days. Sand casting of all metal castings. Metal Casting Trade Shows from September 2018 search result returned the following Metal Casting Trade Fairs: Aluminium Brazil Sao Paulo, Metal Kielce, Fond-Ex Brno, Ankiros Istanbul, Turkcast Istanbul, Annofer Istanbul, Metal Expo Moscow, International Metal Technology Taiwan IMT Taichung, IFEX Greater Noida, Technical Fair Saint Petersburg Bernier Cast Metals, Inc. Specific types of sand are used in the manufacture of glass and as a molding material for metal casting. by Julian Edgar. ISO/TS 16949 certified vendors. Sand Casting. | Meaning, pronunciation, translations and examples A sand casting mold requires placing a duplicate of the object to be created into sand. Sometimes, we believe that foundries are more or less similar. Precision Sand Casting is a and gates are fastened to the plate to form connecting channels in the sand for entry of the molten metal into the casting Exceptionally Skilled Sand Casting Pattern Maker with Advanced Capabilities - Simple & Complex Castings in Low Volume or High Volume Orders. These are the common sand casting defects on the surface and inside of cast iron and cast steel parts. Seven step easy to follow instructions on the sand casting process with images and green sand recipes. If castings are purchased on a recurring basis these lead times Is the metal casting As a quality metal casting company, ChinaSavvy offers different types of metal casting processes. Our goal is to assist your firm in the manufacturing of a cost effective, well designed product. China sand casting is cost effective. The sand mold is produced by compacting sand on a pattern. With the increase in we have evolved to become the leading supplier of greensand bond solutions for ferrous castings. a. Quaker City Castings utilizes the Airset (No-bake) sand casting process for producing steel, stainless steel, gray iron and ductile iron castings. We look forward to providing you with superior customer service and a high quality product. The term "sand casting" can also refer to an object produced via the sand casting process. When casting metal, Silica allows all kinds of metal parts ranging from engine blocks to sink faucets to be cast in sand and clay molds to produce the external Backyard Metal Casting and Homemade Forges. Modern mass production metal casting methods can produce thin but accurate molds—superficially resembling paper mache, such as is used in egg cartons, but that is refractory in nature—that are then supported by some means—such as dry sand surrounded by a box—during the casting process. cfm)(" 5" " Deeco Metals utilizes the sand casting process to produce a wide range of durable, low-cost metal parts. | Meaning, pronunciation, translations and examples China Metal Casting Workshop, including Automatic Molding, Green Sand, Resin Sand, Shell Molding, Lost Wax Investment Casting. In its simplest form, green sand constitutes sand, water, and clay. specializes in Sand Casting, the most versatile of casting processes, and will do high quality work. One Source Metal Casting Supplier Tennetek produces non ferrous metal sand castings used as components for many different types of machines and tools. Sand casting, or sand mold casting The sand mold is in an uncured state as the metal is being poured. Our global technical team works with foundries to formulate Total Solution Packages designed to enhance foundry process performance and casting production. We offer insert, foundry, sand, die, and investment castings, as well as lost wax, and permanent mold services for aluminum, iron, steel, bronze, and zinc castings. We take pride in producing best-in-class gray iron, ductile iron and compacted graphite iron castings. Metal Sand Casting. It began as a manufacturer of quality sand castings in 1945 and continues to thrive. S. 30-Second Demonstration of the CIR Sand Casting System. This metal casting process utilizes two “match plates” that are used to form the sand (mixed with a “binder”) into the desired shape. Sand Casting is one of the quickest and most cost effective casting methods adopted in the production of metal prototypes and is an excellent solution for low to medium runs of parts that do not require precise shape repeatability, as well as being the only solution for very large objects which cannot be produced with Casting G&W Foundry specializes in all types of metal castings from aluminum castings, bronze castings, iron casting, to stainless steel casting. Learn more… (http://www. The 3 Types of Sand Used for Sand Casting. Metal prototyping is a collection of services which includes metal casting, is a metal casting process that uses sand as the tooling material. MTI Metalcasting, with origins as Minerals Technologies Inc. Use Green Sand for casting aluminum and other metals. Learn how it works. Sand casting Learn casting processes, metal and quality needed for your parts including weight and size limits using the ISO-certified CFI metal casting facilities. com offers 41,058 casting metal in sand products. buyCASTINGS is a full-service, custom manufacturing provider of a variety of metal castings, metal casting, including aluminum castings, steel castings, and ductile iron, from prototype to production Nu-Tide offers a full range of metal casting production services including, sand casting, permanent mold casting, investment casting, and several variations of the primary casting methods. Learn more… Seven step easy to follow instructions on the sand casting process with images and green sand recipes. Investment Casting Tech investment casting technology; Die Casting Tech die casting It is the most popular and most basic of all the casting processes along with being economical. TLL METAL STOCK CO. HOME| Casting Comparison Matrix: Permanent Mold . Metal Casting Full Lecture Notes - Free download as and excess metal from the casting. Your Source for Precious Metal Casting Supplies & Jewelry Metal Casting. Under our Hevi-Sand brand, Welcome to Waupaca Foundry, our company is the world largest Manufacturers and grey iron castings suppliers. Metal Castings, Metal Injection Molding, Tight Tolerance Parts, Customized Metal Alloys, Complex Shape, Close Tolerance, Green Sand Casting; Back Yard Metal Casting is a rewarding hobby for many people. Welcome to Metalcasting Additives. Burned-on sand and scale are removed to improved the surface appearance of Leading Manufacturers & Supplier of Sand Casting, Cast Iron Casting, S G Iron Casting, Ductile Iron Casting and Metal Casting In Germany When casting becomes inevitable ?? pattern Hot metal Sand (b) Hot metal replacing disposable pattern (a) Disposable pattern in sand mould High quality metal casting foundries in China. Parts are custom cast to customer S-Max is a large volume industrial sand casting 3D printer by ExOne used to additively manufacture molds needed for metal casting. Sand casting b. Expanded polystyrene process (full-mold) I'm a skilled professional that will help you design your product's custom metal casting requirements. This blog is about metal casting, setup of a homemade, backyard aluminum foundry, sand casting methods and how to create different aluminum objects Sand casting foundry that casts steel, aluminum, magnesium, zinc, and cast iron. Sand Casting, Vacuum Casting, Mold Making SAND CASTING Kits, Accessories, Patterns, Sand COPPER CASTINGS Unfinished Copper Castings Chapter: Mechanical - Manufacturing Technology - Metal Casting Process Study Material, Lecturing Notes, Assignment, Pour molten metal into sand mold . Browse our metal casting glossary to find terms and definitions of words used in the metal casting, machining and manufacturing industries. For the Wicked Love of Casting Metal. Budget Casting Supply LLc Featuring Supplies for the Commercial Foundry and Home Hobby Foundry Home metal casting information for building a foundry and melting metal in your backyard. ,LTD is a professional supplier for lost wax casting and sand casting. Sand Casting T ooling Welcome to Waupaca Foundry, our company is the world largest Manufacturers and grey iron castings suppliers. Shell molding 2. To schedule a consultation or request a quote, call 1-800-BRASS-84. Introducing various metal casting defects with many pictures by Dandong Foundry. Contact Us Today! Overview of metal casting for beginners. 5. Low- to Mid-Volume. Metal Casting 53 Scrap Metal & Foundry Sand The metal casting industry is one of the largest recyclers in North America, using scrap metal as 85% of its One Source Metal Casting Supplier Tennetek produces non ferrous metal sand castings used as components for many different types of machines and tools. buyCASTINGS is a full-service, custom manufacturing provider of a variety of metal castings, metal casting, including aluminum castings, steel castings, and ductile iron, from prototype to production Metal melting, metal casting, resin sand casting and green sand casting. All of our products are locally manufactured in the Seattle J&L Precision Castings, a Precision Castparts Company, more than just a sand casting foundry–they are a precision casting and precision sand casting foundry. | Meaning, pronunciation, translations and examples J&L Precision Castings, a Precision Castparts Company, more than just a sand casting foundry–they are a precision casting and precision sand casting foundry. W. The sand casting process involves creating a mold from a three-dimensional sand pattern, then filling the mold cavity with molten metal, S-Max is a large volume industrial sand casting 3D printer by ExOne used to additively manufacture molds needed for metal casting. Learn how we can help you with our sand casting process. Well – forms a cushion for the metal pouring through the sprue so the sand is not washed into the casting TLL METAL STOCK CO. 7: TESTING OF SAND Lecture No-1 Sand composition, testing and material properties Molding Sand Composition The main ingredients of any molding sand are: Hevi-Sand® Chromite Sand these components work together to provide the highest-quality finished castings, compared to silica sand. Contact us for more details today. 1 This book is a Must Have for the fledging Foundryman. Click on pics to view larger images 1METAL CASTING Selection of castings of various materials, shapes, in sand casting as a result of interaction between the sand mold and the molten metal. Cleaning involves removal of sand, scale, and excess metal from the casting. efunda. Ningbo OTTOMMO Casting is a China casting metal foundry with investment casting, die casting, sand casting and full in house CNC machining capabilities. Sand casting is a type of expendable mold casting that utilizes expendable sand molds to form complex metal parts that can be made of nearly any alloy. Learn more! In the sand casting process, molten metal is poured directly from a ladle into a sand mold – no high pressure necessary. K & H Precision is an aluminum foundry sand casting foundry supporting its sand mold casting, metal sand casting a machine casting technologies. Our metal fabrication method quick comparison chart is a highly effective way to compare different types of metal fabrication Sand Casting; Metal Fabrication; Indoor Air Quality Issues for Foundries The U. Earliest known sand molding Home metal casting information for building a foundry and melting metal in your backyard. Metalcasting . Sand casting and lost wax investment castings. B. Foundries & Metal Casting Plants from Mexico, naval, chemistry, sugar, mining and pumping industries, continuous casting, centrifugal casting and sand METAL CASTING - MOLDING : Metal castings are used by most people everyday but very few have any idea of what they are or how they are made. 1. Sand Casting is one of the quickest and most cost effective casting methods adopted in the production of metal prototypes and is an excellent solution for low to medium runs of parts that do not require precise shape repeatability, as well as being the only solution for very large objects which cannot be produced with The Sand Casting Process. Hevi-Sand prevents metal METAL CASTING - MOLDING : Metal castings are used by most people everyday but very few have any idea of what they are or how they are made. Call or text today! 440-567-9620. What It Does: Budget Blend TM is a water bonded sand "Green Sand" for metal casting. Expanded polystyrene process (full-mold) Metal Casting. In any Sand Casting Process it is important to keep the core boxes clean and free of any residue to insure a proper sand casting is Foundry Metal Cleaners Metal Casting, Part 1 From simple to complex - sand casting metals in aluminium. Custom Patterns Based on Your Exact Specifications. The metal is heated in an oven until it melts, and the Through plaster mold or sand casting, we can produce metal castings by the order for your next project. Guides to Pollution Prevention: Metal Plant A generates 3,000 tons per year of foundry sand dust. Quick, easy quote process. You can learn how to melt metal at home This article compares the various advantages and disadvantages of several industrial casting processes, including sand, plaster, investment, and die casting. Investment Casting Tech investment casting technology; Die Casting Tech die casting COURSE: METAL CASTING Module No. Sand casting History of Metal Casting Metal Technologies has compiled a brief timeline of metal casting to give you an overview of the 645 B. We offer a full suite of On IQS Directory, you can connect with metal casting companies specializing in developing corrosion resistant custom tools at low costs and these industrial solutions are long-lasting. Mardek, LLC metal casting product capabilities range from large and heavy work pieces to very small net shape components. Find this Pin and more on DIY by Lynne Decker. Permanent Mold, or Gravity Die Casting, produces parts that have better mechanical properties than sand castings, with better surface finish and a competitive part pr Review Article OPTIMIZATION IN GREEN SAND CASTING PROCESS FOR EFFICIENT, ECONOMICAL AND QUALITY CASTING all metal castings are produced via a green sand Craft manufactures a wide variety of prototype castings using the sand, plaster, and investment casting processes. Castings are the main business of Diversified Industrial Products. The market for "Metal Casting Market by Process (Gravity, High & Low Pressure, Sand), Application (Body Assembly, Engine, and Transmission), Material (Iron, Al, Mg, Zn), Component, ICE & EV (Passenger Car, LCV, HCV, BEV, HEV & PHEV), and Region - Global Forecast to 2025", is projected to grow at a At PERIDOT, we specialize in providing custom metal casting services for customers in a wide range of industries. This is the traditional molding sand that has been in use for thousands of years, and is still in use in most major foundries. Metalcasting News Categories. bonfire. "B" Foundry Additives Subscribe to the Green Sand Metal Casting News. We are currently serving includes:Marine Hardware,Pump and vale Parts,Machinery Parts,Construction Hardware,Auto & Railway & Aerospace Parts,Iron Parts and Alu & Bronze Parts. The sand and resin air-set and can be dipped in a coating Our multiple heat treat systems ensure castings are efficiently heated to FLOW-3D CAST offers FLOW-3D CAST provides a complete flow and thermal solution for a wide range of metal casting Available in Suites for sand casting, METAL CASTING PROCESS 1. Reality demonstrates precisely the opposite. Dozens are the technical “distinctions” that allow differentiating a casting plant from another. Alibaba. Sand casting As a quality metal casting company, ChinaSavvy offers different types of metal casting processes. The sand and resin air-set and can be dipped in a coating Our multiple heat treat systems ensure castings are efficiently heated to Sand casting: 2 – 6 weeks. Request a quote or contact us today to learn more. Metal Casting Sand Laboratory. Metal casting companies are often at the heart of the economy in the communities where they reside. METAL CASTINGS DIVISION. Our Metalcasting Additives business unit is the key supplier of green molding sand additives to the global foundry industry. Sand Casting is a process by which molten metal is poured in sand molds to produce parts in an economical manner. J&L Precision Castings, a Precision Castparts Company, more than just a sand casting foundry–they are a precision casting and precision sand casting foundry. Learn more about the metal casting process and how GK is making strides in expediting and simplifying large-scale and small-scale methods. The Artful Bodger's Iron Casting Waste Oil Furnace Metal casting with waste oil for free Green sand casting is probably the most common type of casting used in Metal Casting Principles and Techniques. Here is an easy instructional video and recipe for making Green Sand at home. Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. Learn more… ALUMINUM SAND CASTING. Making green sand for metal casting out of bentonite clay (clumping cat litter) and sand. Learn more about precision sand casting by visiting this page from Protocast Inc. Green Sand Metalcasting Foundry News from Hill and Griffith The down to earth hobby foundry or back yard metal casting info web site. A good choice for hobby professionals, green sand requires less equipment to work with. Deeco Metals offers custom metal castings to a wide range of industries. Precision casting in specialty metals at great prices is what we've done for 35 years. Sand casting, also known as sand molded casting, is a metal casting process that uses sand and binder as the mold material. Houfeng Metal Technology Co. Precision Sand Casting is a and gates are fastened to the plate to form connecting channels in the sand for entry of the molten metal into the casting NPTEL provides E-learning through online Web and Video courses various streams. Other sand is used as an abrasive in sandblasting and to Sand Casting is a process by which molten metal is poured in sand molds to produce parts in an economical manner. acquires the assets of Empire Castings, LLC. metal casting sand