The practical manual of dental casting : being the recorded experiences of many able and eminent men in the dental profession.

Date:
1913
Catalogue details

Licence: In copyright

Credit: The practical manual of dental casting : being the recorded experiences of many able and eminent men in the dental profession. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    THH SHRINKAGK (JK TlUC INVKSTMENT Let US suppose Fig. 1 to represent a bar of iron 36 in. in Icngtii and 12 in. in width, and of equal density throughout the mass. Under a definite degree of heat it will expand to the extent of 3-24 of an inch in each direction from its mean line of linear expansion and 1-24 inch in each direction from its mean line of lateral expansion. The dimensions of the bar would then be 36 + 3-24 + 3-24 = 36 6-24 + 12 + 1-24 + 1-24 = 12 2-24 or 36 6-24 + 122-24 as represented by Fig. 1. Now let us suppose that the same bar is bent into the form of a ring, the inner cir- cumference of which would measure 36 in. with a consequent diameter of approxi- mately 12 in. (The diameter of a circle being determined by dividing the circum- ference by three and a fraction, the fraction being omitted to simplify.) The dimension of the outer circumference is immaterial. Now if the same definite degree of heat be applied as was to the straight bar, we will discover that while the dimen- sion of the outer circumference has increased, the dimension of the inner circum- ference remains unchanged. For the simultanpous increase of the outer and mner dimension of the respective circumferences, without taking into consideration the lateral expansion of the ring, would form a ring the inner circumference of which would measure 36 6-24 with a resultant diameter of 12 2-24 (Fig. 3). But the lateral dimensions of the ring are increased by expansion to the extent of 1-L4 inch in each direction from the mean line of lateral expansion (see Fig. 3 and note dotted lines) thereby increasing the lateral dim.-nsion of ihe ring toward the center of the