Development of refractory composite materials for glass production

Abstract

The Semiluki Refractory Works produces refractories according to the technology of concrete and keeps developing compositions and refining the technology for producing large-size products by vibromolding. The Saratov Institute of Glass has performed service testing of concrete samples and determined their physicomechanical characteristics. The testing of samples fired at temperatures not higher than 1000°C has demonstrated their rather high compressive strength (from 40 to 60 N/mm 2 ).The decreasing volume of chamotte refractories produced by ramming in Russia has made it necessary to develop new refractory mixtures suitable for state-of-the-art mechanized molding technologies (vibromolding and vibrocasting) and that impart to the products strength sufficient for transportation and installation without using high-temperature firing and still preserve all refractory service properties. Refractory concretes, which are nonfired composites with refractoriness 1700°C and higher, have been known and used in glass production for over 30 years. Such concrete consists of a refractory filler and a binding material (binder) curing at a normal or increased temperature and having limited shrinkage at service temperatures. The type of the binder is selected based on the properties that the product should posses, i.e., a constant volume and a sufficient strength in the entire temperature interval: from ambient to service temperatures [1]. High-alumina cement with water acting as a dispersion medium can be conveniently used as a binder for refractory concrete. High-alumina cement is classified as a hydrationcuring binder, in which the curing process proceeds with formation of hydrates:Due to the formation of hydrates, the strength of refractory concrete varies depending on heat treatment temperature. Under relatively low curing temperatures (around 300°C) the strength grows, whereas in the interval of 400 -1000°C mainly determined by the dehydration of the binder and the loss of chemically bound water the strength decreases (the strength drop) [2]. As the temperature increases above 1000°C, the process of sintering starts and the strength increases. The strength of refractory concrete depends on the strength of the filler, the binder, the contact phase, and especially on the existence of shrinkage, thermal, and other stresses. Destructive forces in concrete do not always lead to crack formation, since stresses in concrete are nonuniformly distributed and concentrate on components with a high elasticity modulus, i.e., the filling components; consequently, high strength of the filler determines high strength of the concrete. Concrete produced by vibration molding typically has a filler of enhanced coarseness (up to 6 -8 mm). Cracks in fact do not propagate across the product thickness; emerging cracks become arrested on the filler grains. This is a positive property of vibromolded concrete, since in ramming technology, due to the presence of cracks going in different directions, a nonuniform distribution of pores and filler grains...