Abstract: A mixing bowl having an outwardly flared inner surface is rotated around its axis at a speed which is great enough to cause a film of liquid within the bowl to be moved upwardly by centrifugal force to the rim of the bowl. A liquid is introduced into the bottom of the bowl at a rate that permits an unbroken film of liquid to form within the bowl and move from the bottom to the rim. Particulate material is uniformly distributed in a radial direction within the bowl to contact the liquid film and mix therewith. The rim of the bowl is shaped to interact with an adjacent stationary surface to shear the liquid and particulate material mixture to increase the uniformity of the mixture. A basin is positioned around and under the rim of the mixing bowl to collect the mixture as it is thrown off the outer edge of the rim.

Abstract: Methods of preparing Hybrid Silicate Binders are shown by admixing the following materials:1. a basic or acidic colloidal silica sol suspended in water or glycol ether;2. an organic silicate, such as ethyl silicate, hydrolyzed with water;3. a mineral acid of sufficient quantity to produce a final binder having a pH of 1 to 4; and4. the hybrid binder contains silica sol and organic silicates such that the ratio of weight contribution of SiO.sub.2 from organic compounds to weight contribution of SiO.sub.2 from colloidal silica sol is in the range between 0.09 to .9, in the final binder.That is, ##EQU1## The final binder preferably contains about 18%-21% SiO.sub.2. If basic silica sol is used it must be added to a mixture of the other ingredients.The preferred binder has a shelf-life exceeding nine months, it can be chemically polymerized or air-set and provides high binder strength and refractoriness.

Abstract: A tachometer pulse generator is coupled to the shaft of an electric motor. The output of the pulse generator is gated into a pulse counter circuit during a first fixed time interval. During a second fixed time interval which follows the first fixed time interval, the motor is speeded up if the count attained by the counter in the preceeding first time interval is less than a preset number or is slowed down if the count is equal to or greater than the preset number. The first and second time intervals follow each other periodically, thereby alternately measuring the speed of the motor and correcting the same to approach a preset speed which is proportional to the preset number of the counter circuit. Two preset numbers can be employed, one corresponding to a lower speed correction threshold and the other corresponding to an upper speed correction threshold.