Dissertation presents theoretical and technological generalizations in solving the scientific and technical problem of environmentally friendly molds and rods from sand-sodium-silicate mixture, structured by SMS-process, creating for castings of general engineering purposes, by properties formation regularities and kinetics of mixture structuring determining, its composition optimization and research results realization in production, which leads to environmental safety and production sanitary conditions increasing, cycle and energy consumption of casting process reducing, their quality improving and, accordingly, their cost lowering.
Using different materials samples with different masses, their heating peculiarities in microwave furnace resonator with standing wave at radiation frequency of 2.45 GHz and nominal magnetron power of 700...1200 W have been investigated. It has been established that with distancing from axis of rotating table microwave radiation power decreases from χ=0.40...0.72 to χ=029...0.36 of microwave furnace magnetron nominal power. In this case, at the same mass, temperature rising rate of heating materials is directly proportional to their relative dielectric permeability, which (for minerals) depends exclusively on their chemical composition. That must be taken into account when choosing the composition of sand-sodium-silicate mixtures structured by steam microwave environment (SMS-processing).
Kinetics of quartz sand clad with sodium silicate solute and structured by SMS-process structuring has been studied. It has been established that when using SMS-process, water separation from structured mixture takes place in three stages at 100…128 °С. At the same time, sodium silicate solute presence in quartz sand and its low apparent density significantly reduce sand-sodium-silicate mixture mass, which can be treated with fixed amount of saturated water steam, relative to pure quartz sand, which is associated with sodium silicate solute hydration-dehydration, with its amount, with mixture relative porosity and it’s heating by microwave radiation time.
Sand-sodium-silicate mixture composition at SMS-process has been optimized by simplex planning of active experiment due to rational level of its main technological parameters.
According to data obtained, functional dependences between parameters and properties of structured mold and rod mixtures, which are determined on samples by standard and conventional methods, have been developed. Integral-effective values of thermo-physical parameters of quartz sand clad with sodium silicate solute in amount of 0,5 to 3,0% and structured by SMS-process when pouring aluminum alloy and gray cast iron have been determined.
It has been established that sand-sodium-silicate mixture structured by SMS-process mechanical destruction nature does not depend on sodium silicate solute content, which has been consumed on quartz sand cladding, but depends on SMS-process duration, that is changes with time from adhesive (up to 2 min) to mixed (2...4 min) and to cohesive (more than 4 min). Knock out work of sand-sodium-silicate mixtures structured by SMS-process, containing sodium silicate solute from 0.5 to 2.5% (by weight, over 100% sand), with preheating temperature increasing from 800 to 1100 °C, decreases from 185…15 J to 0, and water resistance remains close to absolute during examination time, which allows these mixtures to be easily removed from castings by shock-vibration methods. It has been recommended to knock out the rods, which heating temperature did not exceed 600 °С, by immersing castings in water.
Partially dehydrated sodium silicate solute in thin layer in air carbonization kinetics has been studied, from which it follows that with air relative humidity increasing sodium silicate solute carbonization intensity and, accordingly, mass of carbonate and bicarbonate formed in sodium silicate solute thin films increases.
Mechanism of sodium silicate solute mass transfer in flat capillary under microwave radiation action description has been elaborated and recommendations for pairing molds and rods from sand-sodium-silicate structured mixtures by gluing them with sodium silicate solute in microwave radiation have been developed.
Surface quality of castings obtained in sand-sodium-silicate molds by SMS-process has been studied. It has been established that their burn is thermal in nature and, with exception of cast iron castings, easily removed. Such bronze, steel and cast iron castings surface accuracy level corresponds to 7...10 classes, and aluminum alloys – 5...14 classes according to DSTU 8981:2020. Current production parts and castings made in molds from sand-sodium-silicate mixtures structured by SMS-process foundry quality analysis have been carried out.
