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Published on 03/04/2014 by Euskatfund

SphereOx a solution to the defects of the foundry

SphereOx a solution to the defects of the foundry

Veining, calcinations, penetrations and pinholes are common defects of the pieces of cast iron, and the daily struggle of foundries to control them. Unfortunately, many variables can contribute to the cause of the fault, starting from the choice of the sand. Because of the cost, silica sand is commonly used as the arid chosen but pure silica sand is expanded by an average of 4-5%. When the smelt metal enters a mould, a brutal sand heat shock occurs and is followed by rapid expansion thereof. This contraction / expansion causes flex the core matrix of the bonded sand to fracture and break, causing veining defects. Although there are other options silica sand that offer lower and more controllable growth rates, such as zirconium and olivine and chromite sand, its cost is almost 10 times higher. Even when more stable sands are used, it is still possible to find defects veining and calcinations in the castings because there are other variables, such as compaction and particle size distribution of sand, which need to be controlled.
Irons and steel very alloy (eg high levels of chromium) in base metals will have lower viscosities. Castings made with these types of alloys are more prone to veining. High temperatures pouring smelt metal also promote veining and penetrations.
The resins were formulated to provide a higher adhesive strength than a cohesive force. The more resin is used, the stronger the core and less chance of breakage during handling and transport. Excess resin does not allows core to be plasticity enough to allow expansion of the sand, causing the fracture of the core and causing smelt metal into the mould. The choice and the amount of resin used to bind the sand in a core, or mould, is very critical. When attempting to limit or eliminate negative influences on its use are considered calcinations, pinholes and other defects relationships gases. When the resin is burnt, is created where the resin was empty. The smelt metal penetrates into the voids and defects part undergoes calcination. Pinholes defects are created when the gas generated by the burning of resin (in the mould or core) can not escape prior to solidification. Ideally, use enough resin to remove the breakage of core, but not so much that the core is so hard it can be broken by thermal expansion takes place, breaking the cohesive force of the resin.
Because of the many variables involved in the process of casting, is difficult to control all the variables that can lead to a defect in the casting. The best way to combat the defects is to design a strategy in making the core/mould strategy that limits the influence that these variables can have on the casting.
For starters, the foundry must monitor and control the temperature and time of casting, and the type of metal. Once the casting temperature is under control, the control of other "process" variables can be treated.
Secondly, the addition of the system is recommended SphereOx. The SphereOx is manufactured by a very unique and precise chemical specifications under controlled and excellent uniformity of particle size process. The SphereOx is a spherical particle with a core composed of pure FeO.
As mentioned above, silica sand is expanding at an approximate average of 5%. When the molten metal enters a mould, is carried out and the thermal expansion often causes the bond between the sand particles to fracture, causing veining. Years, were introduced sand additives to soften the core and allow expansion and prevent fracture. Most additives and iron oxides existing on the market are angular in shape and require large amounts of resin to achieve tensile strengths, with SphereOx is not necessary. Unlike with angular particles, when the resin is burned in SphereOx spherical particles, these not only promote the free passage of harmful gases that are generated in the phase metal/mould to escape through the mould, but plus the SphereOX absorb some of the generated gas. This is even more remarkable when SphereOx used in conjunction with a grain of mostly spherical silica, 20-30% less resin is required to achieve adequate adhesion between sand and resin. Even with angular sand, using 10% SphereOx less resin is required. Less burning resin equals less amount of harmful gases and VOC generated. The end result is moldings without pores or defects glossy carbon. Maintain minimum levels of resin has many benefits, both economically and ecologically.
Dimensional stability of the mould/core is another critical factor for the parts without defects. In many cases zirconium sand foundries use high priced as a replacement for silica sand when the dimensional stability is critical. The SphereOx has a higher specific gravity than the sand zirconium (5.2 vs 4.7) and higher thermal conductivity - the result is a greater cooling power without any expansion. Hence, many foundries use a less expensive mixture of SphereOx and silica sand as a substitute for zirconium sand when dimensional stability is critical. Zirconium sand is increasingly limited and overpriced, about $ 2,000 €/ton compared with the mixture of SphereOx and silica sand, the average price is less than 200 €/ton.
The heat distortion is a measurement method of the propensity of a core, in a foundry of iron or steel, the fracture at the time of fusion. Thermal distortion data (see table below) were evaluated in three different samples, and shows undulations of each sample and thermal distortion in time. At 40 seconds, the curve "silica sand" is broken and can not resist the forces of thermal expansion (produce penetration), however, core samples having a "5% SphereOx /silica sand" and "zirconium sand" continues to respond, and allows thermal expansion and contraction, which ends in solidification. This assay provides evidence that it is possible to substitute a mixture of silica sand and SphereOx the more expensive zirconium sand, and achieve very similar results.
Historically foundries require strengths atraction of the core,to determine the percentage of resin needed to produce a core that is strong enough for immediate handling and transportation to the casting line without breakage. The core must be strong enough to withstand the thermal distortion under the pressures generated by the incoming molten metal. In many cases, the casting process uses sand recovered through a recovery system and then a mechanical sand percentage of the reclaimed sand is mixed with new sand, with a cost saving. A mechanical recovery system reduces metal sand and impurities retained in the sand particles used, but often did not significantly reduce the resin retained. Further LOI (loss on ignition) indicates the percentage of resin remaining in the reclaimed sand. The LOI value is added at the resin percentage of new resin is added. The LOI values over 1.50% is considered high, with a greater propensity to defects related to gas. Studies by many foundries that use SphereOx indicate that SphereOx actually produce a GOI (Gain on calcination) of about 10%, demonstrating his ability as a gas scrubber to prevent gas defects.
The SphereOx has a neutral pH (7.1), making it compatible with most resin binder systems.
Furthermore, recent studies in a massive piece of steel, high section, provided the data through a EPMA (Electron Probe Micro Analyzer) shows that the SphereOx sand particles used in contact at elevated temperatures, penetrate the core of the part and create a more effective barrier to prevent penetration of metal. Data from EPMA verify that there is no sign of calcination (burn-in) in samples in which the SphereOx was used as an additive in sand contact, however, the samples where no SphereOx is used as an additive, exhibit a high calcinations defects (burn-in). Was also observed during this study SphereOx particles that improve the chemical homogeneity of the core piece, and also a better surface finish thereof.
It is important to be constant and controlling the amount (percentage) and additive resin is mixed with sand to make a mould or core. Because the SphereOx is spherical, has a constant measure, and no dust or dirt flows well and flow rates are easy to control. Traditional iron oxides and other additives are commercially available fine-grained and angular shape. These materials do not flow easily and tend to reduce power systems, resulting in uneven levels of distribution from batch to batch. The uneven distribution causes variations in the process and a much higher chance of casting defects. In almost all cases when the SphereOX is used to replace other additives, a decrease in the percentage of binder is observed between 10-20% for optimum results.
For nearly two decades, the use of SphereOx has shown an unprecedented level of success worldwide in preventing casting defects, significantly reducing the cost of the raw material (resin). In Spain and Portugal may buy SphereOx through our EUSKATFUND distributor, SL
For more information, please contact EUSKATFUND, SL or phone + 34 945 465581

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