Shrink fitting is cost saving as it allows;
-No capital equipment costs
-No transport costs involve from manufacture site to assembly
-Damage free fitting
-Eliminate time lost with oil baths or heating furnaces
Metallurgical Considerations
Aluminium, copper and copper alloys (bronze, brass, monel) are not significantly affected by low temperature of liquid nitrogen. Plain carbon-steel and low alloys steels are temporarily embrittled or lose impact strength at liquid nitrogen temperature and should not then be subjected to severe blows or shock. The steel returns to normal when it reaches ambient temperature again. Our highly trained staff has the necessary expertise to carry out Liquid Nitrogen shrink fitting in your workshop or construction sites if required.
TABLE-1
Maximum shrinkage in metals cooled by Liquid Nitrogen, cooling assumed to be 15°C to -196°
Expansion Contraction Coefficient | |||
METAL | SI Units- µm/ m/ºC | British units- 10¯6in/ in/ºF |
Maximum shrinkage thous per inch |
Aluminium (unalloyed) | 18.4 | 10.2 | 3.8 |
Brass (Cu/Zn 70/30 or 60/40) | 16.0 | 8.9 | 3.4 |
Bronze (Cu/Zn 88 10 2) | 16.0 | 8.9 | 3.5 |
Cast iron (plain 3%C) | 8.5 | 4.7 | 1.8 |
Copper (unalloyed) | 14.1 | 7.8 | 3.0 |
Magnesium (unalloyed) | 21.4 | 11.9 | 4.5 |
Monel (cupronickel Cu Ni 70 30) | 13.0 | 7.2 | 2.7 |
Nickel (unalloyed) | 10.1 | 5.6 | 2.1 |
Steel, plain carbon (AS 1442, etc.) | 9.0 | 5.0 | 1.9 |
Steel, alloy (low alloy AS 618, AS 619,etc.) | 9.0 | 5.0 | 1.9 |
Steel, alloy (high alloy austenitic AS 618, AS 619, etc.) | 9.5 | 5.3 | 2.0 |
Zinc (Zn base die cast metal) | 26.4 | 14.6 | 4.1 |
To calculate the maximum shrinkage use the above table and the following the rule:
S= OD x TPI ------ (Maximum shrinkage = Outside diameter (inch) x Thous per inch)
Example: For shrinking a 6 inch iron pipe the maximum shrinkage would look as follows:
S = 6 x 1.8 = 10.8 (so the maximum shrinkage of the pipe would be 10.8 thous)