This page contains a Flash digital edition of a book.
with increasing amounts of chromite. Looking at the expansion and viscos- ity, we can see that silica with higher amounts of chromite undergoes a sudden contraction at around (2,012F (1,100C) unlike the steady contraction seen in silica with 7.5% chromite. Also, the peak viscosity decreases and the sinter temperatures drop by as much as approximately 212F (100C) for the higher chromite content samples. Table 3 displays the veining rank-


ing for baseline silica and the various blends. Silica with 10% and 30% chro- mite could not be evaluated due to the large extent of fused sand on the cast- ings. A lower content of the specialty aggregates display better performance when compared to the higher content. Baseline silica has a high veining


index, as expected. Silica with 10% zircon and 7.5% chromite both display no indications of veining defects.


Conclusion T e quality of metal castings relates


to the high temperature performance of the refractory aggregates used. T is high temperature performance is determined by the thermal volume stability and resistance to high tem- perature softening. Silica sand with its low cost and abundant availability does have limi- tations not easily overcome. Its high rate of expansion through phase transformations results in casting defects. T e use of molds and cores produced entirely from specialty sands like chromite and zircon are expensive and in many applications do not warrant the increased cost. T e use of sand blends of inexpen- sive silica sand with higher cost specialty sands has been shown to have applications where the quality of the casting can be improved with- out the associated high cost of 100% specialty sand cores. As little as 10% of specialty sands can improve the quality of the fi nal casting by reduc- ing the extent of veining defects,


according to the research results. T e eff ect of blending silica sand and specialty sands highly depends on the thermal input of the metal and the mass of the mold that determines the heating rate of the mold and associated cooling rate of the casting. T e chemical reaction between the base sand and the specialty sand must be accurately determined, as was the case of silica and chromite sand blends. Higher heat inputs in the larger metal sections caused the mixture to fuse, leading to casting defects. Lower percentages of chromite sand


improved casting quality in the test casting. T is illustrates the importance of comparing the high temperature physical properties of the sand blend with the specifi c casting application before practicing the technology.


This article is based on the paper “The Use of Specialty Sand Blends to Reduce Vein- ing Defects in Steel Castings” (16-060) which was presented at CastExpo16.


ENGINEERING


COMPLETE TURN-KEY ENGINEERED CONVEYOR SYSTEMS MANUFACTURING


INSTALLATION


6 CE<AG<A9 8BE 5HFGB@ 53FG<A9F


4i`Ncc TNPbXQNdX^V N `NddSb^ d_ QbSNdS N Q_bS _b ]_[R gXdW _eb 6 cN^R `bX^dSb 6ScXV^ N^R `bX^d VS_]SdbXQN[[i Q_]`[Sh ]SRXN aeXQZ[i gXdW dbeS RScXV^ TbSSR_] N^R gXdWX^ _^S _T dWS [NbVScd `bX^dX^V P_hSc X^ dWS g_b[R ;C< `b_fXRSc dWS dSQW^_[_Vi d__[cN^R Sh`SbdXcS d_ WS[` i_eb PecX^Scc ceQQSSR


WEBB-STILES offers more than 60 years of practical expertise in the Overhead Conveyor and Custom Engineered Conveyor Systems.


Whether you are looking for a new system or having problems with a current system, contact a WEBB-STILES Sales Engineer for all your conveyor needs.


Sales / Engineering / Manufacturing Ph: 330-225-7761


Valley City, Ohio Corporate


sales@webb-stiles.com


Sales / Engineering / Manufacturing Ph: 256-492-6642


Webb-Stiles of Alabama Gadsden, Alabama


www.webb-stiles.com  


G_ ESaeScd N De_dS ae_dS͠W__cXSb`NddSb^Q_]


ς ;BBF<7EC3GG7EA5B@ February 2017 MODERN CASTING | 35 ;C< <^dSVbNdSR T_e^Rbi c_[edX_^c


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60