DOI

10.17077/etd.b7x8x3eo

Document Type

Thesis

Date of Degree

Fall 2016

Degree Name

MS (Master of Science)

Degree In

Mechanical Engineering

First Advisor

Christoph Beckermann

First Committee Member

Albert Ratner

Second Committee Member

H. S. Udaykumar

Abstract

To produce cast steel crankshafts, risering and gating systems are developed. Filling and solidification simulations of the steel crankshaft rigging are carried out to confirm that the rigging developed will produce a low porosity casting. A sand mold is created with Computer-aided design software, based on the developed crankshaft and rigging. Two prototype crankshafts are cast from the sand molds, and analyzed for porosity. The porosity analysis results are compared directly to the simulated porosity, and found to be in good agreement. From the analysis of the prototype crankshaft, rigging systems for a two-on and single-throw crankshaft are developed.

A new casting method for steel is developed. The counter-gravity with pressurization during solidification casting method utilizes vacuum pressure of 7.3 psia to draw liquid steel into a mold, where it is held until the inlet has solidified. Once the inlet has solidified, the vacuum pressure is released, and the pressure of the entire system is raised to 45 psia. Exothermic hot topping keeps the top of the riser liquid while the rest of the casting forms a solid shell. Therefore, the pressure only acts on the liquid metal at the top of the riser, forcing the liquid metal to feed farther into the casting. The new method is tested with simple bar castings. Analysis of cast bars shows that centerline porosity is fed by the riser when pressurized, while the gravity-filled control casting is not.

Public Abstract

Crankshafts of the modern engine are either cast iron or forged steel. As the automotive industry continues to move towards higher-performance and more efficient engines, the weaker cast iron crankshaft will no longer meet the durability requirements needed for high-performance engines. On the other hand, forged steel crankshafts meet these requirements, however they are costly to produce and the nature of their production does not allow for hollow sections, which improve fuel efficiency. A cast steel crankshaft combines the benefits of both cast iron and forged steel crankshafts. Steel castings are cheaper than forging and can be made to meet the mechanical properties of forgings with good casting techniques and processes.

Counter-gravity filling and applying pressure while the casting is solidifying are both beneficial casting processes. Counter-gravity filling allows the liquid steel to be pulled gently into a mold, as opposed to dumping the metal down a sprue. Steel shrinks when it solidifies, therefore it is necessary to add extra reservoirs of steel above the mold cavity, called risers. Traditionally the weight of the riser presses the liquid metal down into the casting to compensate for the shrinking steel. This effect is limited, so applying extra pressure to the top of the riser increases the effectiveness of the riser and can reduce the defects caused by the shrinking steel. In a newly developed method, vacuum pressure is used to draw molten steel smoothly into a mold and after the mold inlet has solidified the casting is pressurized, which forces the liquid steel in the riser down into the casting.

Keywords

counter-gravity, pressurization, Steel casting

Pages

x, 90 pages

Bibliography

Includes bibliographical references (pages 89-90).

Copyright

Copyright © 2016 Lucas Andrew Archer

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