The results of investigations of spent moulding sands taken from the mould in which the metal core cooling system - to increase the
cooling rate of the ladle casting - was applied, are presented in the hereby paper. The changes of the spent moulding sand at the casting
external side being the result of degradation and destruction processes of organic binder, were analysed in this publication. Since the
reclaimed material, obtained as a result of the mechanical reclamation of spent sands of the same type, is used as a grain matrix of the
moulding sand, the amount of a binder left from the previous technological cycle is essential for the sound castings production. On the
bases of investigations of the thermal analysis, ignition losses, dusts contents and pH values of the samples taken from the spent sand the
conditions under which the process of gases displacing in the casting mould was realised as well as factors limiting the efficient mould
degassing - were considered in this study. The possible reason of a periodical occurrence of an increased number of casting defects due to
changing gas volume emission, being the reason of the realised technological process, was indicated.
A thermo-insulating moulding sand with a binder made of aluminosilicate microspheres with organic binder was subjected to testing. The aim of the analysis was to determine selected technological properties of the developed compounds. Compressive strength, friability and gas permeability were determined. The binder content was changed within a range of 5÷20 wt% with a 5% step. The applied matrix is characterized by good thermo-insulating properties and a small size of grains, while synthetic organic binder has favourable functional properties, among which the most noteworthy are the extended life and setting time, good rheological properties as well as high resistance to chemical agents. The intended use of the compound is the casting of 3D CRS (Composite Reinforced Skeletons), which are characterized by a well-developed heat transfer surface area, good absorption of impact energy, low mass and a target thickness of connectors within a range of 1.5÷3 mm. The construction of 3D CRS castings is an original concept developed by the employees of the Department of Foundry Engineering at the Silesian University of Technology.
The results of investigations of thermal reclamation of spent moulding sands originating from an aluminum alloy foundry plant are
presented in this paper. Spent sands were crushed by using two methods. Mechanical fragmentation of spent sand chunks was realized in
the vibratory reclaimer REGMAS. The crushing process in the mechanical device was performed either with or without additional
crushing-grinding elements. The reclaimed material obtained in this way was subjected to thermal reclamations at two different
temperatures. It was found that a significant binder gathering on grain surfaces favors its spontaneous burning, even in the case when
a temperature lower than required for the efficient thermal reclamation of furan binders is applied in the thermal reclaimer. The burning
process, initiated by gas burners in the reclaimer chamber, generates favorable conditions for self-burning (at a determined amount of
organic binders on grain surfaces). This process is spontaneously sustained and decreases the demand for gas. However, due to the
significant amount of binder, this process is longer than in the case of reclaiming moulding sand prepared with fresh components.
The results of investigations of spent moulding sands taken from the mould at various distances from the surface of the produced casting,
are presented in the paper. The casting mould was made with an application of the cooling system of the metal core in order to increase the
cooling rate of the ladle casting. As temperature measurements in the mould indicated the heat flow from the metal did not create
conditions for the complete burning of a moulding sand. The analysis was performed to find out changes of spent moulding sands caused
by degradation and destruction processes of organic binders. Conditions occurring in the casting mould were discussed on the bases of
testing: ignition losses, dusts contents, pH reactions and the surface morphology of the moulding sand samples. Factors limiting the
effective mould degassing were pointed out. Operations, possible for realization, which can limit the reasons of a periodical occurrence of
increased amounts of casting defects due to changing gas evolution rates being the result of the technological process, were also indicated.
Today, about two thirds of iron alloys casting (especially for graphitizing alloys of iron) are produced into green sand systems with usually organically bonded cores. Separation of core sands from the green sand mixture is very difficult, after pouring. The core sand concentration increase due to circulation of green sand mixture in a closed circulation system. Furthermore in some foundries, core sands have been adding to green sand systems as a replacement for new sands. The goal of this contribution is: “How the green sand systems are influenced by core sands?” This effect is considered by determination of selected technological properties and degree of green sand system re-bonding. From the studies, which have been published yet, there is not consistent opinion on influence of core sand dilution on green sand system properties. In order to simulation of the effect of core sands on the technological properties of green sands, there were applied the most common used technologies of cores production, which are based on bonding with phenolic resin. Core sand concentration added to green sand system, was up to 50 %. Influence of core sand dilution on basic properties of green sand systems was determined by evaluation of basic industrial properties: moisture, green compression strength and splitting strength, wet tensile strength, mixture stability against staling and physical-chemistry properties (pH, conductivity, and loss of ignition). Ratio of active bentonite by Methylene blue test was also determined.
The thermal reclamation process as a utilisation method of spent moulding and core sands is more costly than other reclamation methods, but in the majority of cases it simultaneously provides the best cleaning of mineral matrices from organic binders. Thus, the application of the thermal analysis methods (TG-DSC), by determining the temperature range within which a degradation followed by a destruction of bounded organic binders in moulding sands, can contribute to the optimisation of the thermal reclamation process and to the limiting its realisation costs. The thermal analysis results of furan resin, one of the most often applied binder in foundry practice, are presented in the hereby paper. The influence of the heating rate of the sample - placed in the thermal analyser - on its degradation and destruction process under oxygen-free (argon) and oxygen (air) conditions, were compared. The recorded TG and DSC curves were used for analysing these processes as the temperature as well as the time function. The obtained results were analysed with regard to determining the required temperature of the thermal reclamation of the investigated organic binder. The usefulness of the developed methodology was found out, however under conditions of meeting several essential requirements concerning the repeatability of performed analyses.
Recently, some major changes have occurred in the structure of the European foundry industry, such as a rapid development in the production of castings from compacted graphite iron and light alloys at the expense of limiting the production of steel castings. This created a significant gap in the production of heavy steel castings (exceeding the weight of 30 Mg) for the metallurgical, cement and energy industries. The problem is proper moulding technology for such heavy castings, whose solidification and cooling time may take even several days, exposing the moulding material to a long-term thermal and mechanical load. Owing to their technological properties, sands with organic binders (synthetic resins) are the compositions used most often in industrial practice. Their main advantages include high strength, good collapsibility and knocking out properties, as well as easy mechanical reclamation. The main disadvantage of these sands is their harmful effect on the environment, manifesting itself at various stages of the casting process, especially during mould pouring. This is why new solutions are sought for sands based on organic binders to ensure their high technological properties but at the same time less harmfulness for the environment. This paper discusses the possibility of reducing the harmful effect of sands with furfuryl binders owing to the use of resins with reduced content of free furfuryl alcohol and hardeners with reduced sulphur content. The use of alkyd binder as an alternative to furfuryl binder has also been proposed and possible application of phenol-formaldehyde resins was considered.