Research On The Bentonite Modification And Properties Of The Lost Foam Casting Coating

Coating is one of the key technologies for the Lost Foam Casting (LFC), and bentonite is the common suspension agent of the LFC coating. Effects of silicate sol and the ethyl silicate on properties and strctures of Ca-bentonite were studied. Taking the bentonite and the modified bentonite as the suspension agent, effects of refractory fillers and additions of suspension agents on properties of the LFC coating were investigated. Based on the above, properties of the self-made coating and the coating of Ashland Company were compared.Effects of the additions of silica sol and ethyl silicate, pH value and baking temperature on adsorption, suspended ability and dilatability for Ca-bentonite were tested. Results indicated that the adsorption and suspended ability of the bentonite increased first and then decreased with the increasing addition of silica sol or ethyl silicate, while dilatability was reduced all the time. When the quality ratio of the silica sol to the bentonite was 1/8 and the unit bentonite was modified with 6.5ml ethyl silicate, the modification effects were the best. Effects of the pH value on the bentonite properties were minute. With the increasing of the baked temperature, the absorbing property and dilatability increased first and then decreased, the suspended ability was improved all the time, and the comprehensive properties of the bentonite calcined at 500℃were the best. Modification effects of the silica sol or the ethyl silicate on the bentonite calcined at 500℃were better than on the unbaked bentonite.The differential thermal analysis (DTA) indicated that when the bentonite was calcined between 600℃and 700℃, dehydroxylation could be happened. The scanning electron microscopy (SEM) observation showed that dispersive capacity of the bentonite modified with the silica sol was better than that of the raw bentonite. The infrared ray (IR) analysis indicated that the ethyl silicate was combined with the bentonite, but didn't change the crystal structure of the bentonite. The X-ray diffraction (XRD) and the transmission electron microscopy (TEM) analyses verified that the silica sol and the ethyl silicate were mainly adsorbed on the montmorillonite edge.Effects of refractory fillers and additions of suspension agents on properties of the LFC coating were studied. Results indicated that the grain size and the density of...