| dc.description.abstract | A detailed investigation was carried out to study the solidification behaviour of narrow freezing range Aluminium-12% Silicon alloy (modified) - LM 6 plate and cylindrical castings cast in dry sand moulds, the feeding of plate castings by top-insulated cylindrical side feeders, and the influence of metallic and non-metallic chills on feeding of plate castings. The results of the investigation are presented in two parts:
Part 1: Feeding of Aluminium-12% Silicon alloy (modified) - LM 6 plate castings.
**Part 2: Influence of chills on feeding of Aluminium-12% Silicon alloy (modified) - LM 6 plate castings.
PART 1:
Results of the experiments to study the feeding of LM 6 alloy plate castings indicate the following: C hovorinov’s rule is valid for LM 6 alloy plate and cylinder castings cast in dry sand moulds. For a given (V/SA) ratio of the test casting, C hovorinov’s constant for plate casting is more than that for cylinder casting.
On using feeders below a particular size in plate-feeder combination castings, the last portion to solidify will be at the central portion of the casting, where the porosity will be maximum and the strength minimum. On increasing the feeder size, the last portion to solidify and the regions of maximum porosity and minimum strength shift towards the feeder. Further increase in the feeder size, however, tends to make the porosity uniformly low and produces uniform strength along the length of the casting.
From a systematic analysis of the mechanism of feeding in solidifying casting and the data obtained from the experiments on feeding, the following feeding equation is obtained:
fr=11 0.0354/VR
f
r
=
1 0.0354/VR
1
For the sake of practical foundrymen, a feeding nomogram has been constructed to simplify feeder dimensioning.
PART 2:
Results of experiments on the influence of end-chills on the feeding of plate castings reveal that the material and the dimensions of the chills used influence to a large extent the solidification time of LM 6 alloy plate castings. For a given end-chill material and end-chill thickness, a linear relationship exists between the solidification time and the square of the (V/SA) ratio of the plate casting, thus implying that C hovorinov’s rule is valid for end-chilled plate castings.
C hovorinov’s constant decreases with increase in chill thickness and attains a steady value when an end-chill of a given chill material beyond a particular thickness is used. In end-chill-plate-feeder combination castings, on using an end-chill of a particular thickness and feeder below a particular size, the last portion to solidify will be at the midregion of the casting, where the porosity is maximum and the strength minimum. On increasing the chill dimension, the last portion to solidify as well as the regions of maximum porosity and minimum strength shift towards the feeder.
But in end-chilled plate castings fed with suitably sized feeders, increase in chill dimension tends to make porosity uniform and low, and ultimate tensile strength (UTS) uniform and high along the length of the casting. However, for a given feeder-plate combination, increasing the chill dimension of a particular chill material beyond a particular value will not further affect the solidification time, porosity, or UTS along the length of the casting, implying that the particular chill material has reached its saturation point.
From a systematic analysis of the mechanism of feeding in solidifying castings under the influence of chills and the data obtained in the present investigation, the following feeding equations are obtained, where L = 1.168 (without any chill), 0.985, 0.887, 0.841, 0.815, and 0.800 (for cast iron chills of 1", 2", 3", 4" and 5" thickness respectively) and 1.055, 0.976, 0.925, 0.885, and 0.877 (for graphite chills of 1", 2", 3", 4" and 5" thickness respectively).
Using the nomogram, feeder dimension, and chill dimension required for producing sound LM 6 castings can be obtained with considerable ease. | |
