TAILIEUCHUNG - Foseco Ferrous Foundryman's Handbook Part 9

Tham khảo tài liệu 'foseco ferrous foundryman's handbook part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 190 Foseco Ferrous Foundryman s Handbook mixed and blown into a heated core box. The heat activates the catalyst which causes the binder to cure. Sand Clean silica sand of AFS 50-60 is used. Low acid demand is advisable. Resin addition resin and 20 catalyst based on resin depending on sand quality. Nitrogen content The resin contains about N. The catalyst is N-free. Mixing procedure Continuous or batch mixers. Catalyst should be added first then resin. Bench life Typically 8 hours. Core blowing The binder has low viscosity and blow pressures of around 500 kPa 80 psi may be used. Core boxes Cast iron or steel heated to 180-200 C. Use a silicone based parting agent. A release agent is sometimes added to the sand binder mix. Curing time 10-30 seconds depending on the thickness. Thick section cores continue to cure after ejection from the core box. Core strength Surface hardness and strength is high on ejection. Final tensile strength can be 3000-4000 kPa 400-600 psi . Casting characteristics Gas evolution is low the low nitrogen content reduces incidence of gas related defects in ferrous castings. Surface finish of castings is good with low incidence of veining defects. Breakdown after casting is good. Environmental Emission of formaldehyde is low at the mixing and curing stages. Avoid skin contact with binder catalyst and mixed sand. Reclamation Core residues in green sand are not harmful. General Warm box cores have high strength and resistance to veining and are used in critical applications usually for iron castings such as ventilated brake discs. Oil sand Principle Certain natural oils such as linseed oil known as drying oils polymerise and harden when exposed to air and heat. Natural oils can be chemically modified to accelerate their hardening properties. Silica sand is Resin bonded sand 191 mixed with the drying oil a cereal binder and water. The resulting mixture is either manually packed or blown into a cold core box. The cereal binder or .

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