One of the most difficult of all adhesive applications is the bonding of substrates with different coefficients of thermal expansion (CTE). Common examples include bonding aluminum to glass, glass to plastics, ceramic to plastics and rubbers to metals. Additionally, stresses caused by temperature extremes in service and thermal cycling sometimes make a difficult situation more complicated.
In reviewing these issues, factors such as service conditions, joint design, curing, geometry and dispensing provide a complex mix of factors to consider when selecting an appropriate candidate for bonding two dissimilar materials.
Over the years, it appears that two schools of thought have thrown their hats into the adhesive arena when it comes to bonding materials with different coefficients of thermal expansion. The first is to select adhesives with CTEs as close as possible to the materials being bonded. The second is to provide for more flexible or toughened adhesives to compensate for the mismatches. The decision is not always very clear cut.
An in-depth review of service conditions, shrink rates, CTE mismatches and other factors must be considered carefully to ensure that the best product is selected to meet the most critical phases of a specific application.
Master Bond has developed
EP30LTE for applications where low shrinkage, low thermal expansion and dimensional stability is required. It has a CTE of 15-18 x 10
-6 in/in °C. It has superior insulative properties and is easily dispensed. A NASA approved version, called
EP30LTE-LO, meeting the low outgassing requirements of ASTM E595 is now available for critical space and optical requirements.
EP30LTE-LO has the same exceptional properties of
EP30LTE.
CTE of Common Materials
| Material |
Linear coefficient α at 20°C (10-6 K-1) |
|
Material |
Linear
coefficient at 20°C (10-6 K-1) |
| Aluminum |
23.1 |
|
Kapton |
20 |
| Aluminum nitride |
5.3 |
|
Nickel |
13 |
| Brass |
19 |
|
Silicon |
2.56 |
| Copper |
17 |
|
Stainless steel |
10.1 - 17.3 |
| Glass |
8.5 |
|
Titanium |
8.6 |
| Invar |
1.2 |
|
|
|
