| Cryogenic shrink fitting, (or "compression fitting" | | | | usefulness of the mathematical model as a |
| as it is sometimes called), is a method used to | | | | predictor lessens. |
| insert a pin or bushing into a housing or other | | | | In addition, care should be taken when using any |
| assembly requiring an extremely tight tolerance fit. | | | | cryogen and consideration of the material and |
| It can be used as an alternative to conventional | | | | relative masses should be considered carefully. |
| press fitting, or more likely, to permit a | | | | Further, because steels may be subject to |
| mechanical fit that otherwise could not be | | | | additional transformation when exposed to |
| accomplished via the mechanical force of press | | | | cryogenic temperatures, additional processing |
| fitting. | | | | either before or after may be warranted. Heating |
| In application, the insert is cooled via exposure to | | | | of metals (for expansion) should also be controlled |
| a cryogen, typically carbon dioxide (solid or liquid) | | | | and not induce unnecessary thermal stress on the |
| or liquid nitrogen in order to reduce its size | | | | component or change their hardness or temper. |
| through the contraction usually associated with | | | | The Cryogenic Institute of New England, Inc., |
| reduced temperatures. A companion operation of | | | | located in Worcester, MA, has successfully |
| heating the housing (or other part) that receives | | | | accomplished numerous shrink-fitting jobs. These |
| the insert is conducted to enlarge the opening by | | | | include very large pipes, sized at over 24 inches |
| taking advantage of the expansion usually | | | | diameter to very intricate miniaturized parts. |
| associated with increased temperatures. | | | | Some of the customers that utilize the service |
| While it is not always necessary to use both | | | | includes large multinational companies, US |
| heating and cooling in combination, the most | | | | Department of Defense contractors, research |
| demanding applications, including those with the | | | | labs, transportation companies, including trucking, |
| tightest tolerances, often require this multi-step | | | | air and railroads, to name a few. |
| approach. | | | | Since time and transportation costs are often a |
| There are formulas that can be used to predict | | | | consideration when using shrink fitting in an |
| the rate of expansion and negative expansion | | | | industrial application, a number of customers are |
| (contraction) that materials will experience based | | | | looking to bring the capability in-house. This can be |
| on their thermal change. One must be aware, | | | | accomplished with what is usually modest |
| however, that these are often based on | | | | investment in equipment, a local source of the |
| measurements taken within a small range of | | | | cryogen of choice and appropriate safety |
| temperatures near ambient. As temperature | | | | equipment and training. There are experts |
| changes move to the extremes, be they hot or | | | | available to help you set up an internal operation if |
| cold, the rate of expansion is reduced and the | | | | that is what makes sense for you. |