Printer Friendly

Coating quality, pressure assure dimensionally stable castings; carefully applied refractory coating and the use of isostatic pressure during casting solidification combats deformation, gas pinholing and microshrinkage.

Coating Quality, Pressure Assure Dimensionally Stable Castings

Carefully applied refractory coating and the use of isostatic pressure during casting solidification combats deformation, gas pinholing and microshrinkage.

Aluminium Pechiney of France has made a strong research effort to improve the results of foam pattern casting (FPC), developing in the process a patented system to increase the advantages of this expanding segment of the metal-casting industry.

The company's initial research has focused on doing a better job of refractory coating formulation and application. Its second area of emphasis has been to perfect a method of applying pressure to the casting as it solidifies.

The refractory coating applied to foam patterns is the principal influence on the dimensional stability of the resultant casting. Well-designed and formulated coatings applied to carefully engineered patterns can eliminate casting deformation, assure the uniform inflow of molten metal and exclude blisters and inclusions. Application and formulation of refractory coatings is important since the coating is so essential to the quality of castings made by the FPC process.

A coating affects the control of gas-induced pinholing and microshrinkage, two factors that can scrap castings. Additionally, refractory coatings have the following effects: * improve pattern rigidity; * control the metal-filling rate; * minimize or eliminate the pattern's decomposition products; * control the thermal exchange between the metal and the casting material; * influence the size and presence of defects in the casting.

Making Sound Castings

The FPC process normally uses unbonded silica sand as a filler around the pattern. This results in low solidification rates and low thermal gradients compatible to those obtained with sand casting without chills.

To improve the soundness of castings, it was found that defects could be minimized by accelerating the solidification time and by applying pressure (isostatic compression) during the solidification phase.

Isostatic Compaction

Aluminium Pechiney has developed an innovative FPC system, called Castyral, which employs the use of isostatic pressure on a casting as it solidifies. Isostatic pressure is obtained by applying a gas pressure of several bars (14.4 psi per bar) on a metal casting while it is solidifying. This consists of placing the casting flask containing the casting cluster and the compacted sand surrounding it into a tightly-sealed vessel.

The part is cast at normal atmospheric pressure, but, immediately after filling, the pressure on the sand in the flask is increased gradually and held until solidification is completed. Initial testing in pilot production confirmed that several types of cast parts, i.e., heat exchangers, intake manifolds and cylinder heads, had superior mechanical properties compared to parts produced using the standard FPC cooling cycle.

Jacques Thomas Aluminium Pechiney Compiegne, France
COPYRIGHT 1989 American Foundry Society, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Author:Thomas, Jacques
Publication:Modern Casting
Date:Dec 1, 1989
Previous Article:Research testifies to cored wire's applicability in ductile iron production; magnesium-containing wire is emerging as an effective, technically...
Next Article:NC-designed tooling cuts scrap, improves quality in FPC manifold manufacturing; production tooling can reduce rejects, improve casting quality and...

Related Articles
Wealth of molding methods meet every casting need.
Coating chemistry key to FPC consistency.
Upgrading castings by hot isostatic processing.
Product category index.
94th Casting Congress Preprints.
Refractory coatings: making the right choice.
Aluminum casters discuss porosity, melt quality.
Evaluating refractory coatings: a practical approach.
M/G vs. Z: comparing refractory coatings on shell sand systems.
Controlling heat transfer with refractory coating.

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters