Characteristic of Core Manufacturing Process with Use of Sand , Bonded by Ecological Friendly Nonorganic Binders

Mechanization of the process of core making with the use of inorganic and organic binders is based, almost solely, on core blowing machines. Presently the core blowing machines are equipped with tools and devices that allow for application of different technologies of core making. Cold-box, hot-box and warm-air technologies require that core blowing machines shall be additionally equipped with either core-box pre-heating system or gas purging and neutralization system, or hot air purging systems. Considering the possibility of using varied, the most advantageous technologies of core making, the production of universal core blowing machines equipped with replaceable devices has been undertaken in Poland. The universal core blowing systems allow for mechanization of core making process also with the use of sand, bonded by modern, eco-friendly binder systems. The paper presents selected results-based evaluation of core blowing process showing the scope of conducted design and implementation works.


Introduction
Foundry production systems include also mechanized core making department ensuring fabrication of high-quality cores, productivity increase and reduction of the manufacturing cost.In order to meet the user's expectations, the company undertook the works aiming for presentation of an offer of mechanized equipment for universal system of core manufacturing, also with the use of eco-friendly, inorganic binders.A number of tests with the use of various core sands were carried out before development of technical documentation.The characteristics of core sands compacted by means of blowing methods were developed.The obtained results of tests were the base for improvement of design approach of the equipment as well as the parameters of the process.The scope of works of the universal core making system included selection of the parameters of core making process with the use of quick-hardened sands.Loose quick-hardened sands need elevated temperature for setting and simultaneously contain the hardening agent for increasing the time of the process [1].The basic components of quick-setting sand are mainly synthetic resins.They are applied in the following processes: Croning process (shell moulding), hot-box, warm-box, Thermoshock, warm air process [1].In warm air technology, quick-setting sands comprising organic and inorganic binders are used.In case of sands comprising organic binders, synthetic resins are used as binding agent.P-toluene sulphoric acid or orthophosphoric acid solutions (alcoholic solution are the best) are used as hardening agents.Compacted sand is purged with the use of air preheated to the temperature of 150-230ºC during 10-20 s.Air consumption -depending on sand composition, the size and shapes of the core and temperature of preheated air -amounts to 400-600 dcm 3 per 1 kg of the sand.The temperature of preheated air is about 40-150ºC but it is recommended to use higher temperature.The time of purging is 30 s -4 min [1].In case of sands with inorganic binders, sodium silicate powder or water solution of trisodium phosphate are used as a binding material.Compacted sand is purged with air preheated to the temperature of 85-130ºC.The strength of the sand increases if the cores are additionally preheated during drying in the temperature of 135ºC.Information about the process of core making with the use of warm air comes from 70's and 80's when the first description of warm-air process with the use of sands comprising, beside binder and matrix -also acid hardener, were published (Modern Casting, 10/1970); to accelerate the process of setting, the compacted sand was purged with warm air.In the Foundry Research Institute in Krakow, Poland a substitute of warm-air technology, called WZ technology was developed (Foundry Journal, 5/1982).The air consumption in this method amounted to 400-600 dcm 3 per 1 kg of sand, depending on the composition of the sand, the size and shapes of the core and the temperature of preheated air.The air temperature was 40-150ºC.The time of purging was 30 s to 4 min [2].Implementation of WZ technology included setting the level of hardening by determination of the relation between the weight of the hardened sample m utw and the total weight of the sample m c .The value m utw /m c x 100% was presented as a relation of heat flux Q provided by airflow (Fig. 1 and Fig. 2).The results of the tests performed with the aim of determining parameters of core-making process by means of blowing methods confirmed the guidelines of binder producer.The cores manufactured by means of blowing methods have the following properties [7]; cold-bending strength of 350-550 N/cm 2 with the Cordis binder content of 1,5-3%.Considering the flow behavior there is a possibility of manufacturing thin-walled cores.Alcohol-and water-based coatings can be applied at the core surface.The cores manufactured with the use of Cordis binders can be stored within 24 hours with high relative humidity of air and lose only 30% of its strength.Considering the fact that no adhering to the metal mould surface has been reported, cleaning of them is easier.Moulds reclamation is also typical with the use of standard equipment.Positive effects of using cores manufactured with the use of Cordis and other inorganic binders have been achieved with gravity die castings and low-pressure aluminum casting.The technology with Cordis binders has been also tested, under industrial conditions, with positive effects, with cast iron castings [5][6][7].

3.Conclusions
Implementation of the technology of core manufacturing with the use of inorganic binders is connected with improvement of working conditions and environment protection.Core sand on the base of inorganic binder has good parameters and is suitable for core-making with the use of blowing methods.The results of the tests indicate that implemented technology with the use of eco-friendly inorganic binders has positive scores; the cores with excellent strength properties are obtained.The conducted works confirmed the possibility of core manufacturing and determined required working parameters of core blowing machine and additional equipment -purging with hot-air depending on the size of the machine and manufactured cores.It is necessary to emphasize the fact that additional equipment enables for utilization of various technologies, including warm air and all cold and hot processes, which makes it universal and meet the requirements of many small and medium-sized foundries in Poland.

Fig. 1 .
Fig. 1.Influence of the way to provide air to the sample on the results of hardening process; I -air supply to the front of the φ50×50mm sample, II -extended surface of air influence on the sample

Fig. 2 .
Fig. 2. Change of quantity of the hardened sample φ50×50mm depending on air-hardening process parameters The heat flux provided by air has been evaluated by determining its weight m and enthalpy change Δi.Molier diagram (i-x chart) for humid air was used for determining of entalphy change.The analysis of air-hardening process indicated the essential influence of the process conditions for the level of core hardness; core sand hardening depends on:− time and flow rate of the preheated air, − air temperature for the given air flow rate, − airpressure, − the way of airsupply.The knowledge of the above parameters allows for precise determination of the air-hardening process conditions as well as range of parameters of core-making process.

Fig. 5 .
Fig. 5. Bending strength of the samples on the base of inorganic binder 1 -100 parts by mass of quartz sand H 33, 2.5 parts by mass of Cordis 7820 (shooting pressure 6 bar); 2 -100 parts by mass of quartz sand H33, 2.5 parts by mass of Cordis 8323, Anorgit 8322 (shooting pressure 5 bar) [7]