Engineered sand additives (ESAs)
were developed to address some of the negative issues of iron oxides and organic additives. Tey may have particle sizes similar to sand and have less impact on mold/core strength. However, they typically need to be used at higher levels to be effective against veining. One type of ESA is in the form of hollow spheres. It is believed these crush and provide a volume reduction and cushion when subjected to compressive stresses. Other ESAs have low expansion rates and reportedly act as fluxes to soften the surface of the sand grains at elevated temperatures. Other strategies include applying a ceramic coating or “wash” on the mold
2 Procedure Initial testing of the new
sand additives showed good results, but the researchers considered it important to
NA Wedron 540 EU Haltern SA Veiga
China 1L5W
49 46 53 52
3 3 5 3
or core surface to provide some veining resistance with a low expansion layer and insulating effects that may slow the flow of heat into the surrounding sand. Angular sand can be used to reduce core density and allow space for expansion to occur. Cores can be blown at lower than normal blow pressure to produce cores with inten- tionally low density, to allow for expansion. Tree new engineered sand addi-
tives reduce veining at relatively low additive levels. Te first, designated as ESA1 for these trials, forms fluxing agents at elevated temperatures but is relatively neutral at ambient tempera- tures. Tis minimizes interaction with the binder chemistry during molding or coremaking, but provides anti-veining
compare their performance to other sand additives currently in use. Te veining characteristics of a core depend not only on the sand additive, but the sand itself, the type and amount of
Table 1. Properties of the Four Sands Sand AFS GFN # of screens +10% pH ADV @ pH 5 ADV @ pH 7 LOI
7.8 6.4 8.3 6.9
0.1 0.6 2.0 3.1
0.0 0.4 1.2 1.8
0.07% 0.10% 0.41% 0.24%
Table 2. Bulk Density and Loss On Ignition of the Additives Alone, and pH and ADV of the Mixes of the Additives and Wedron 540
Sand Mix Wedron 540
with 1% woodflour with 1% RIO
with 1% starch with 2% BIO
with 2.5% ESA1 with 4% ESA2 with 6% ESA3
with 6% old ESA
Density g/100ml % LOI pH ADV @ pH 5 ADV @ pH 7 160 30
140 58
215 175 118 42
142
0.07 89.6 1.63 95.2 -2.7 37.5 3.5 4.4 0.3
7.8 5.5 6.8 7.0 7.0 9.4 9.8
11.3 8.4
0.1 1.8 3.1 2.8 4.3
18.6 2.7
42.2 3.2
0.0 1.1 2.7 2.2 3.8
17.9 2.3
41.6 2.8
Table 3. BCIRA Test Results for the Different Additives on NA Sand and Binder Sand Mix
No additive
1% Woodflour 1% RIO
1% starch 2% BIO
2.5% ESA1 4% ESA2 6% ESA3
6% old ESA
Max Deflection Time to Max Deflection 0.303 0.197 0.363 0.123 0.247 0.290 0.333 0.267 0.327
13.3 8.7
14.0 5.3
12.3 15.0 17.0 16.3 13.0
38 | MODERN CASTING April 2013
Time to Zero 24.0 18.3 28.0 15.7 32.7 31.0 30.7 32.0 25.3
properties when the molds are poured. Te second, designated ESA2, has a non-linear thermal expansion profile, like silica, but with the changes occur- ring at different temperatures than silica sand. When mixed with silica at relatively low levels, the combined expansion/contraction over the range of temperatures seems to give fewer problems than either material alone. ESA3 was developed to improve casting surface finish and minimize burn-in and metal penetration. It uses a combination of ingredients that help to fill the voids between the sand grains and to flux the sand. Because of the dual role, it is added at higher levels than the other new additives.
binder used and the core density. Both antiveining characteristics and the impact on coremaking are important. Tey decided to use phenolic
urethane coldbox as the platform for testing, because of its widespread use across the world. Binder formulations, as well as sand properties and avail- ability, tend to differ from region to region. Typical systems consisting of phenolic urethane coldbox (PUCB) binder, sand and binder percentage were identified for North America, Europe, South America and China. Because of import restrictions on the most common Chinese sand, the researchers selected North American lake sand that had shown similar per- formance in previous testing. For North America, Wedron 540
Time to Failure 132.7 70.7
151.7 60.7
193.7 190.0 201.3 151.7 103.0
(round grain high purity silica) was selected with 1.2% binder 10/20 and DMIPA (dimethylisopropylamine) catalyst. For Europe, Haltern H32 sand (round to subangular high purity silica) with 1.6% binder E 30/60 and DMEA (dimethylethylamine ) catalyst was used. For South America, Veiga sand (subangular to angular medium purity silica) with 1.2% binder 405/605 and DMPA (dimethylpropol- amine) catalyst was used. For China, Manley 1L5W sand (subangular lake sand) with 1.2% binder 440D/880D and DMIPA was used. Properties of the four sands including grain fineness number (GFN), pH, acid demand value (ADV), and loss on ignition (LOI ) are shown in Table 1.
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