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MeasureMent of Gas evolution froM PunB Bonded sand as a function of teMPerature

G. Samuels and C. Beckermann Dept. of Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA, USA Copyright © 2012 American Foundry Society abstract

Gas evolved from the thermal decomposition of the binder can greatly deteriorate the quality of sand castings. Binder gas models used in casting simulations require knowledge of the binder gas mass and molecular weight evolution, but available data are limited. In the present study, the mass and molecular weight of gas evolved from phenolic urethane no-bake (PUNB) bonded sand are measured as a function of temperature. Thermogravimetric analysis is used to deter- mine the changes in the binder mass with temperature. The binder is found to be fully pyrolyzed at temperatures above 710C (1310F), with its mass reduced by 82%. Up to 100°C/ min (180°F/min), the binder decomposition does not appear to be a strong function of the heating rate. The evolved vol- ume of the binder gas during heating and cooling is mea-


Resin binders used to make sand molds and cores thermally decompose when subjected to the high temperature condi- tions in metalcasting, and a significant amount of gas is pro- duced when the binders degrade.1

It is well understood that

the evolved binder gas can profoundly influence the quality of castings.2-4

scrap and are of great concern to the casting industry.

In response to these issues, binder gas models have been in- corporated into metalcasting simulation software in order to better predict the occurrence of gas defects.10-12

Crucial ele-

ments required in binder gas evolution models are the mass and molecular weight of the evolved gas as a function of temperature. Unfortunately, temperature resolved binder gas mass evolution and molecular weight data corresponding to the conditions experienced during sand casting processes are very limited. The objective of the present study is to measure the mass and molecular weight of the gas evolved during de- composition of phenolic urethane no-bake (PUNB) bonded sand as a function of temperature at conditions similar to those experienced during sand casting. The experimental re- sults will provide improved input data for binder gas evolu- tion models used in casting simulations.

International Journal of Metalcasting/Spring 2012

from bonded sand molds and cores, with blowholes and pin- holes being the most common,5-9

Defects associated with binder gas generation result in large amounts of

sured using a specially designed quartz manometer with a liquid metal as the working fluid. During heating at 2°C/min (3.6°F/min), the binder gas molecular weight is found to de- crease in a complex manner from 375 g/mol at 115C (239F) to 33.3 g/mol at 898C (1648F). When the binder pyrolysis is complete above 710C (1310F), the binder gas is incondens- able, but continues to decompose to lower molecular weight compounds until at least 1350C (2462F). If the binder is heated to a temperature not exceeding 510C (950F), the binder gas partially condenses during subsequent cooling; this condensation occurs below 165C (329F).

Keywords: sand casting, phenolic urethane no-bake binder, PUNB, binder gas, molecular weight, binder mass evolution

Knowledge of the evolved binder gas composition facili- tates the determination of the molecular weight of the gas. Early studies by Bates and Scott,13,14 and Scott et al.16

Bates and Monroe,15 involved pouring aluminum, gray iron,

and steel into molds made using different binder systems and periodically sampling the gas generated at the mold- metal interface. The gas samples were collected inside evacuated glass tubes and subsequently analyzed by gas chromatography (GC) to determine the volume concentra- tions (% V/V) of hydrogen, oxygen, nitrogen, carbon mon- oxide, carbon dioxide, and total hydrocarbons (measured as equivalent concentration of methane) in the binder gas. The measured average composition and mixture molecu- lar weight of the gas evolved within two minutes after pouring metal into phenolic urethane cold-box (PUCB) and PUNB bonded sand molds are shown in Table 1. The reported volume concentrations are converted to mass fractions for the present analysis. The molecular weights calculated from the average gas compositions within the first two minutes after pour should approximately corre- spond to the pouring temperatures of the metal.19


the specific chemical formulations employed in PUCB and PUNB binder systems are different, these binder systems are based on the same urethane bonding chemis- try.17,18

This allows the composition and molecular weight

of the gas evolved from PUCB and PUNB bonded sand to be reasonably compared.


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