To seal the gaps between the contacting surfaces of the stopper and the nozzle, mixtures easily eroded by the metal are used* [i]. In the preparation of slide valves a mixture of powdered crystalline graphite and machine oil is widely used for the sliding layer between the plates [2]. Heating of this mixture to 200-600~ leads to degradation of the oil with the formation of a resinous product sharply increasing the coefficient of friction between the rubbing surfaces of the slide valve.For the purpose of establishment of the possibility of decreasing the friction between the parts of a flat or rotating valve an investigation was made of compositions not containing machine oil or other similar petroleum products. Table 1 presents the results of a study of the influence of the individual components on the properties of the mixtures.The investigation made it possible to assume as desirable the use of a mixture with the following content of components (weight %) passing thro,~h a sieve with an opening size of 0.2 mm: powdered graphite 52-60; ground bentonite 13-17; ground asbestos 2-5; aqueous solution of sodium water glass remainder.The aqueous water glass solution contains 45-55% of water glass with a density of 1.4 g/cm 3 .The composition of the sliding layer [3] wasdeveloped onflat specimensand on rotating specimens which are stop-cock type tapered refractory valves [4]. For practical use of the results of the investigation after determination of the layer composition the investigations were made only on rotating parts.The material for preparation of the flat specimens was general purpose chamotte parts according to All-Union State Standard (GOST) 390-69 and for preparation of the rotating specimens chamotte stoppers to GOST 5500-75 and graphite-chamotte ones to Technical Specification (TU) 14-8-238--77.Variations of the mixture for application to the working surfaces of the valve parts were developed on the basis ofthe composition of [3]. An acceptable composition forobtaining a sufficiently thin layer on the parts may be assumed to be a mixture of two parts by weight of dry components and three parts by weight of solvent.These two phases were mixed in a porcelain bowl until uniformity in a quantity of 200-250 g. Such a mixture preserves its properties for 25-30 min and the consumption of it is 45-50 g for a single set, which provides a coating thickness of 0.2-0.5 mm.Application of the compeund was mechanized by the use of aspecial devicein whichthe parts were rotated around the horizontal axis during coating with the compound.This made it possible to decrease the consumption of the components of the mixture and the labor for application of the layer and to improve the quality of the contacting surfaces and the service and technical characteristics of the separating layer.The test specimens were turned on a IK62 lathe with cutters with sintered carbide plates. The cavities and dents on the working surfaces of the refractories with a size of 2-3 mm were filled with the investigated composition.The surface finish ...
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