1- What Is Shell Mold Casting?
Shell molding casting is also called pre-coated resin sand casting, hot shell molding casting or core casting. The main molding material is the pre-coated phenolic resin sand, which is more expensive than green sand and furan resin sand. Moreover, this sand can not be recycle used. Therefore, the shell molding castings have higher costs than sand casting. However,compared to the green sand casting, the shell molding castings have many advantages such as higher dimensional tolerance, good surface quality and less casting defects. The shell molding casting process is specially suitable for producing castings of difficult shapes, pressure vessels, weight sensitive and castings requiring superior surface finishes.
2- What Are The Steps of Shell Mold Casting?
✔ Making Metal Patterns. The pre-coated resin sand needs to be heated in the patterns, so metal patterns are the necessary tooling to make shell molding castings.
✔ Making Pre-coated Sand Mold. After installing the metal patterns on the molding machine, the pre-coated resin sand will be shot into the patterns, and after heating, the resin coating will be molten, then the sand molds become solid sand shell and cores.
✔ Melting the Cast Metal. Using induction furnaces, the materials would be melted into liquid, then the chemical compositions of the liquid iron should be analyzed to match the required numbers and percents.
✔ Pouring Metal. When the melted iron meet the requirements, then they will be poured into the shell molds. Based on different characters of the casting design, the shell molds will be buried into green sand or stacked up by layers.
✔ Shot Blasting, Grinding and Cleaning. After the cooling and solidification of the castings, the risers, gates or additional iron should be cut off and removed. Then the iron castings will be cleaned by sand peening equipment or shot blasting machines. After grinding the gating head and parting lines, the finished casting parts would come, waiting for the further processes if needed.
3- What Are The Advantages of the Shell Mold Casting?
✔ Shell-mould castings are generally more dimensionally accurate than sand castings.
✔ A smoother surface of the finished castings can be obtained by shell casting.
✔ Lower draft angles than sand castings are required by shell mould casting.
✔ Permeability of the shell is high and therefore less or no gas inclusions occur.
✔ Shell mold casting process needs very small amount of sand.
✔ Mechanisation is readily possible because of the simple processing involved in shell moulding.
4- What Metals and Alloys Could Be Cast by Shell Mold Casting Process at RMC Shell Mold Foundry?
• Gray Cast Iron: GG15, GG20, GG25, GG30, GG35.
• Ductile Cast Iron: GGG40, GGG50, GGG60, GGG70, GGG80.
• Cast Carbon Steel: Low Carbon Steel, Medium Carbon Steel and High Carbon Steel from AISI 1020 to AISI 1060.
• Cast Steel Alloys: 20CrMnTi, 20SiMn, 30SiMn, 30CrMo, 35CrMo, 35SiMn, 35CrMnSi, 40Mn, 40Cr, 42Cr, 42CrMo...etc on request.
• Cast Stainless Steel: AISI 304, AISI 304L, AISI 316, AISI 316L and other stainless steel grade.
• Cast Aluminium Alloys.
• Brass & Copper.
• Other Materials and Standards on request
5- What Casting Tolerances Could be Reached by Shell Mold Casting Process?
As we mentioned in the casting tolerance for sand castings, the shell mold castings have much higher accuracy and tighter tolerance than sand casting. Here in the following are the general tolerances grade we could reach by our shell mould casting and no-bake furan resin sand casting:
✔ DCT Grade by Shell Mold Casting or Furan Resin Sand Casting: CTG8 ~ CTG12
✔ GCT Grade by Shell Mold Casting or Furan Resin Sand Casting: CTG4 ~ CTG7