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Optimization of the Shooting and Curing Process for a Complex Core

Figure 1. First Core Blowing Test. The bottom of the core collapsed due to a lack of strength.

Figure 1. First Core Blowing Test. The bottom of the core collapsed due to a lack of strength.

Brazilian steel giant Usiminas recently introduced the new foundry core making simulation software MAGMASOFT® as part of their strategy to establish robust designs and processes for their core production line. The first project on which this software was utilized was already in progress at that time.

The main goal was to optimize the process conditions for the existing tooling layout. This core, called the thin waist core, represents some of the biggest challenges for Usiminas core production: its length (920 mm), substantial changes in the sand flow direction during blowing, the need to fill certain parts of the core through counter-flow and big variations in the cross section within the core.

First trials showed problems with the process, which led to a complete collapse of the lower part of the core. The core blowing and curing steps for the PU coldbox process were analyzed, making it possible to draw preliminary conclusions regarding the existing defects.

Figure 2. Curing Gas Concentration. The curing gas does not penetrate into the core to the same extent everywhere.

Figure 2. Curing Gas Concentration. The curing gas does not penetrate into the core to the same extent everywhere.

The lack of core strength was related to a poor curing process. The first simulation (Figure 2) already showed that the problematic regions experienced only very low curing gas concentrations during gassing, which was the root cause for the failure.

On the production line, various process conditions such as the curing and purging times and gassing pressure were changed. These attempts provided better results (Figure 3). However, a perfect core could still not be produced. The further analysis with MAGMASOFT® focused on the evaluation of the local concentration of adsorbed curing gas, as it shows the regions where the catalyzing gassing agent cannot activate the chemical reaction. This result clearly demonstrated that only a very small quantity of catalyst was available for accelerating curing in the defect regions (Figure 3).

Figure 3. Core Blown with new parameters in comparison with the local concentration of adsorbed curing gas. The problematic area corresponds exactly with low concentrations in the simulation.

Figure 3. Core Blown with new parameters in comparison with the local concentration of adsorbed curing gas. The problematic area corresponds exactly with low concentrations in the simulation.

Evaluating simulated curves for the gas mass flow through the vents made it clear that the catalyzing gas was not reaching the critical area. The open venting cross section of the top and central vents was allowing the gas to escape before it reached the bottom of the core.

Instead of making costly modifications to the core box, Usiminas determined that a possible – and simple – solution was to close some vents in the top and center regions, in order to increase the gas concentration in the bottom. However, it was clear that these changes obviously would also influence the core blowing step.

The optimization led to a considerable increase of the curing gas concentration in the lower regions of the core (~36%) (Figure 4). Also, the amount of adsorbed curing gas increased in comparison to the original project. Applying these modifications, Usiminas produced another core, which did not show any gassing defects. Since the venting area was reduced, some filling defects were present, as expected.

Figure 4. Total gas mass flow through the lower vents. The change in mass flow becomes clear. Removing some of the upper and middle vents resulted in a 36% increase in the gas escaping through the lower vents.

Figure 4. Total gas mass flow through the lower vents. The change in mass flow becomes clear. Removing some of the upper and middle vents resulted in a 36% increase in the gas escaping through the lower vents.

Having solved the curing related defects, a further core blowing analysis was carried out. The simulation results showed a very good match between the real defects and areas of low packing density. The flow animation also showed that the problems occurred because these areas had to be filled by a counter flow of the sand (Figure 5).

Another characteristic of the defects was that they all occurred next to the parting line of the core box.  Some of the defects showed a smooth surface, indicating that the sand had been removed by a strong air flow. The core blowing simulation results supported the Usiminas conclusion that an improper sealing of the tool was the root cause for these defects. Air could escape with high speed through the parting lines, resulting in the defect formation.

This hypothesis was tested using a silicone rubber band to obtain an improved sealing of the relevant areas of the tool. With this modification, a new core was produced which was absolutely free of any defects.

About software for casting process simulation

Casting process simulation software considers the complete casting process including mold filling, solidification and cooling, and also provides the quantitative prediction of mechanical properties, thermally induced casting stresses and the distortion of cast components. Simulation accurately describes a cast component’s quality upfront before production starts, thus the casting layout can be designed with respect to the required component properties. This results in a reduction in pre-production sampling, but also the precise layout of the complete casting system leads to energy, material and tooling savings for the foundry.

The range of application of MAGMA solutions comprises all cast alloys, from cast iron to aluminum sand casting, permanent mold and die casting up to large steel castings. The software supports the user in component design, the determination of melting practice and casting methodology through to mold making, heat treatment and finishing. This saves costs consequently along the entire casting manufacturing line.

During the last 10 years, the use of casting process simulation has become a valuable business asset for many foundries worldwide. MAGMA5 constantly expands the capabilities of casting process simulation and will further accelerate the acceptance of this technology, in the future.

About Usiminas

With 50 years of operation, Usiminas is the leader in the Brazilian flat steel market and one of the largest steel companies in Latin America. It has a nominal capacity of 9.5 million tons of steel per year. Usiminas Mecânica is a leading provider of capital goods and services to the steel, railway, mining, automotive, energy, petrochemical, marine and infrastructure industries in Brazil. With recent substantial investments, the foundry of Usiminas Mecânica has become one of the largest manufacturers of both small and large steel castings in the country. The yearly production capacity is 30,000 tons, representing about 10% of the projected production in Brazil.

About MAGMA

MAGMA offers comprehensive solutions to the metal casting industry, casting buyers and casting designers worldwide. The MAGMA product and service portfolio includes the powerful modular simulation software MAGMASOFT®,with the newest release MAGMA5, as well as engineering services for casting design and optimization.

Today, MAGMASOFT® is used throughout the metal casting industry, especially for the optimization of cast components in automotive and heavy industry applications.

MAGMA Giessereitechnologie GmbH was founded in 1988 and is headquartered in Aachen, Germany. A global presence and support are guaranteed by offices and subsidiaries in the USA, Singapore, Brazil, Korea, Turkey, India and China. Additionally, more than 30 qualified partners represent MAGMA around the world.

For more information on this release, please contact:

Christof Heisser
President
MAGMA Foundry Technologies, Inc.
10 N. Martingale Road, Suite 425
Schaumburg, IL 60173
Phone: 847-969-1001 ext. 225
Email: cheisser@magmasoft.com
Web: www.magmasoft.com

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