Automotive engine control unit manufacturer specifies Dow Corning sealant for demanding under-hood service environment.
One of the toughest operating environments in any automotive application is under the hood, where below zero ambient temperatures can quickly rise to 150ºC(302ºF) or even higher. The presence of fuel, oil, glycol coolant and solid contaminants can all create havoc for sensitive electronics, forcing device manufacturers to protect circuits and components from the harsh service conditions.
When a global leader in automotive electronics and mechatronics was looking for an adhesive to seal its engine control units (ECUs), product engineers knew the material would have to withstand dampness, heat, cold, thermal shock, vibration, automotive chemicals and even salt spray, without losing adhesion or physical properties. Often referred to as the engine’s “brain,” the ECU is the control module for fuel intake, spark timing and other critical functions, all of which directly impact vehicle performance and fuel economy.
The Dow Corning team met with company representatives and reviewed the performance and processing criteria, learning that a long tack-free time was an important additional requirement. Because the seal would be created in two passes of the automated dispensing head, it was crucial that the material not begin to cure too quickly, before the device lid could be attached.
Dow Corning technical service personnel made recommendations on processing and testing of material candidates, and the customer determined that Dow Corning® 7091 Adhesive/Sealant (“7091”) was the optimum product for this application. After conducting adhesion studies and aging tests in the Seneffe, Belgium
laboratory to confirm performance, the team also assisted the customer in implementing the product and optimizing the manufacturing process.
The one-part adhesive is applied with an industry standard dispensing machine from Threebond, using a 1.64 mm (inside diameter) head. Because the lid of the
ECU enclosure is secured with mechanical fasteners at the corners, the customer found that finished assemblies could actually be shipped before the adhesive’s room
temperature cure was fully complete.
Once the sealant skins over, cure proceeds from the surface inward, typically requiring about 24 hours (at room temperature and 50% humidity) for sections
2 mm or less in thickness. The material reacts with moisture in the ambient air, ultimately forming a tough, flexible elastomer that remains stable from -55ºC to
180ºC (-67ºF to 356ºF).
Because of the product’s excellent performance and competitive price, the customer is now considering the silicone formulation for a variety of other applications. 7091 delivers good unprimed adhesion to a variety of different substrates, including steel, aluminum, ceramic, glass and some plastics. For superior adhesive
performance, surfaces can be solvent cleaned and primed with Dow Corning® 1200 OS Primer.
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