Лако-красочные материалы — производство

Furan resins have been extensively used as foundry binders in combination with formaldehyde, urea, phenol, and casein, for decades [12,13]. The main two monomers used in this field are 1 and 2. Table 3 summarizes their proportions in different commercial phenolic resins [12].

The main advantages of furan resins are due to their excellent thermal stability, and remarkable resistance to acidic conditions, as well as to fire and corrosion. These resins

have found widespread industrial applications as witnessed by the large number of both patents covering their uses and scientific publications dealing with their chemistry, structures, and properties [3,6,12,14-16].

There are three techniques associated with their production, mostly covered by patent literature, namely: (i) no-bake, (ii) hot-box, and (iii) cold-box processes. The no­bake technique is simple and relatively cheap. It consists in mixing the resin (based on 2) with the sand in the presence of an acidic catalyst. The reaction starts at room temperature and the curing is accelerated by the heat generated during the polycondensation reaction. The molds thus obtained are withdrawn after 10-30 min and left undisturbed for 3-6 h in order to accomplish a total curing. The hot-box technique is used in light (e. g., aluminum) and heavy (e. g., copper, bronze) metal casting [4,17]. The resins used for light metals are urea-modified furan resins, whereas those used for heavy metals contain only furan com­ponents. The hot-box process is well suited for mass production and it consists in mixing the moist sand with a liquid resin and a curing agent. The ensuing mixture is then cured at 180-260°C in heated core boxes. The main limitation of this process is its extremely long bench life. The cold-box (or SO2-furan) process is based on curing the reactive resin at room temperature in a closed-air system with SO2. This gas is converted in situ into a mixture of sulfurous and sulfuric acids which catalyze the curing.