Modern Furan for Modern Castings

Like Phenol (C 6 H 5 OH) and Urea {(NH 2 ) 2 C=O)}, Furfuryl alcohol (C 4 H 3 OCH 2 OH), a product of agricultural origin is capable of polymerization with Formaldehyde (H 2 C = 0) under suitable PH conditions. However, usable polymers, at least as no bake for Foundry applications are obtained only when the condensations are carried out in association with Urea, Phenol or both. The series of resins obtained, having Furan ring (C 4 H 4 O) in chains, at different PH conditions and varying compositions are called Furan resins. These resins (binders) and acids (catalysts) make a two part no bake self-set system (popularly known as FNB in foundry terms) like Alkyd, Phenolic no bake (PNB), Urethane no bake (PUNB) and Alkaline Phenolic no bake (APNB) for binding sand particles for making moulds and cores in metal casting Industries. With growth of Foundry industry, several self-sets have been introduced periodically for making molds and cores. Once the most popular inorganic Binder i.e. Sodium Silicate which make binder system with CO 2 gas or organic esters as curing agents has lost favor of Foundrymen because of its inherent drawbacks, main being poor de-coring property and unsatisfactory casting finish. Other primitive binders like cement, molasses and many proprietory binders have largely been replaced by modern organic binders mentioned above, which meet requirements of faster productivity, better out of box and handling strength of molds and cores, rapid production cycle, better de-coring property and eventually better casting finish. This paper deals with evolution of Furan from introductory to modern stage, its advantages and disadvantages in comparison with other self-sets and its present market position and future trend, particularly in context to foundries based in India and Middle East. Dipak Ghosh Forace Polymers P Ltd, Haridwar, India INTRODUCTION FNB is a binder system comprising of two parts, both liquids. The resin, which is dark colored thin liquid acts as binder for sand particles and the catalyst or curing agent, is a solution of pure or mixture of organic, inorganic or organo inorganic acids in varying concentration. Introduced in world market in 1958 along with PNB, it took long time at least in India to gain popularity. Introduced in 1965 in world market, 3 Part Alkyd (nobake and semi bake) was the most popular self-set in Indian Foundries in eighties. PNB, which is also a two-part system, introduced in Indian Foundries in early eighties could not gain instant popularity mainly because of poor bench life of mixed sand, irritating smell of formaldehyde during mixing, limited storage life of binder etc. However, in introductory stage, the most important reason behind its nonacceptance was that the system did not have sufficient bench life of mixed sand suitable for use in batch mixers particularly in summer and in big jobs, which Alkyd could offer at ease. Introduction of continuous mixers (CSM) in Indian Foundries in large scale in mid-eighties offered Foundries option to think about enhanced productivity and thus to go for faster setting systems beyond Alkyd, for mold and core making, as faster mixing and mold filling cycles did allow to work Foundrymen with lower bench life of mixed sand compared to Alkyd. Binder manufacturers also