The results of research on the effect of the type of cooling agent used during heat treatment and thermal-chemical treatment on the formation of temperature gradient and stress-deformation distribution in cast pallets, which are part of furnace accessories used in this treatment, are disclosed. During operation, pallets are exposed to the effect of the same conditions as the charge they are carrying. Cyclic thermal loads are the main cause of excessive deformations or cracks, which after some time of the cast pallet operation result in its withdrawal due to damage. One of the major causes of this damage are stresses formed under the effect of temperature gradient in the unevenly cooled pallet construction. Studies focused on the analysis of heat flow in a charge-loaded pallet, cooled by various cooling agents characterized by different heat transfer coefficients and temperature. Based on the obtained temperature distribution, the stress distribution and the resulting deformation were examined. The results enabled drawing relevant conclusions about the effect of cooling conditions on stresses formed in the direction of the largest temperature gradient.
By the very nature of their work, castings used in furnaces for heat treatment and thermo-chemical treatment are exposed to the effect of many unfavorable factors causing their deformation and cracking, significantly shortening the lifetime. The main source of damage are the micro- and macro-thermal stresses appearing in each cycle. As the cost of furnace instrumentation forms a significant part of the total furnace cost, in designing this type of tooling it is important to develop solutions that delay the damage formation process and thus extend the casting operation time. In this article, two structural modifications introduced to pallets castings to reduce thermal stresses arising at various stages of the cooling process are proposed. The essence of the first modification consists in making technological recesses in the wall connections, while the aim of the second one is to reduce the stiffness of the pallet by placing expanders in the external walls. Using the results of simulation analyses carried out by the finite element method, the impact of both proposed solutions on the level of thermal stresses was evaluated.