but also can result in poor casting peel, poor fi nish and poor shakeout. High combus- tibles and vola- tiles cause lower expansion but can result in pinholes, smoke, blows, brittle sand, higher cost and higher moisture requirements. Available Bond Available bond
indicates the moisture- absorbing materials in the sand system, including live, latent and dead clay and additives. T e value is derived by relating green compression to moisture using a prepared graph, slide rule or the calcula- tion (0.105 x GCS) + (1.316 x MOIST). T e live clay actively bonds the
sand, and the latent clay can be acti- vated with further energy input. T e dead clay does not add to green tensile
Expansion scabs can be caused by high compactability, low perme- ability or high loss on ignition.
or green splitting strength, but does absorb moisture. Working Bond T e working bond percent indi-
cates the amount of clay that actually is producing bond strength in the sand mix. Working bond (or eff ec- tive clay) is derived by relating green compression to compactability using
a prepared graph, slide rule or the calculation (15.29 x GCS) / (132.1 - COMP). Higher working bond
indicates more effi cient use of the clay. Large variation indicates variation in the clay
additions or in the eff ectiveness of the mulling. Mulling Effi ciency
T e higher percent mulling
effi ciency, the greater the clay utiliza- tion and the lower the clay content required. T e working bond value divided by the available bond value (and multiplied by 100) gives a percent mulling effi ciency reading. Segregation in transport, loss or buildup of fi nes due to a lack of dust collection, bond quality, temperature and muller or mixer condition all may aff ect mulling effi ciency.
T is article is based on a presentation originally given at the AFS 2014 Sand Casting Conference.
December 2014 MODERN CASTING | 29
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