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Alec McAllister | July 2, 2021

The Thermal Protection System used on the Space Shuttle Orbiter is perhaps the most extreme example of the importance of heat shields. During re-entry into Earth’s atmosphere, the Orbiter’s external surface temperatures reached up to 3000°F/1648°C, making the performance of the system critical to the mission’s success. The heat shields also had to withstand pyrotechnic shock loads as the Orbiter separated from the rocket’s external tank.

Back here on Planet Earth, a typical use for heat shields is to manage the sustained exhaust gas temperatures in car and truck engines.  In heavy-duty applications, diesel engine exhaust gas temperatures can average between 932-1293°F (500-700°C) at 100% load. Natural gas engines burn ever hotter, with exhaust temperatures reaching up to 1400°F/760°C. Heat management under the hood is therefore a critical task in the protection of sensitive electronics, components, and materials.

Heat is at the core of an internal combustion engine. These engines rely on the expansion of high-temperature and high-pressure gases produced by combustion to apply force to pistons or turbine blades. Generally, to generate more power from an internal combustion engine, you’ll also generate more heat. Today’s high-performance heat shields help engines strike an excellent balance between power and protection.

McAllister Mills, a global leader and single-source provider of engineered thermal fabrics and extreme temperature insulation solutions, combines expert engineering and mixed media of high-temperature materials fabricated into both flexible sewn and metal encapsulated heat shielding.

For most medium and heavy-duty truck applications, thermal fabrics are used for firewall insulation as well as the shielding of exhaust systems, manifolds, and emissions and/or after-treatment systems. These high-performance heat shields can be customized to fit application- and temperature-specific needs to help prevent heat from escaping into surrounding areas, further reducing the negative impact it can have on adjacent components. 

The reduction of diesel gas emissions is an application that is heavily reliant on high-temperature materials and heat shielding. Insulating the exhaust outlet and piping leading from the engine and into the after-treatment system contains the exhaust heat and helps maintain the necessary elevated temperatures required by any emission system. This elevated temperature is required to burn off particulate matter in the diesel particulate filter (DPF) during the regeneration cycle.

In addition to managing extreme temperatures, heat shields must also be durable enough to withstand vibration and abuse, along with potential damage from road debris and rocks found in rough off-road conditions associated with the construction, lumber, and mining industries.

In addition to stainless steel shields, McAllister Mills also offers metal encapsulated heat shields made with durable aluminum sheeting. The sheeting features a dimpled pattern that ensures easier formation around radial surfaces, while also adding rigidity and improved heat reflection. McAllister Mills’ metal heat shields are available in a 5mm basalt mat that offers service temperatures up to 1200°F/648°C and chemical resistance. Mats (7mm) made from Treo® 2000 provide thermal protection up to 1800°F/982°C, and ultrathin glass mats (3.2mm) are excellent for tight fit tolerances.

Total sales of Class 6-8 trucks in the U.S. are projected to be 404,000 units in 2021, which is an increase of approximately 118,000 units compared to 2020. While internal combustion engines will drive demand for heat shields for the foreseeable future, McAllister Mills is also working on the development of heat shields suitable for alternative power sources besides diesel, such as hydrogen fuel cells. Heat shields for electric engines—especially those being developed for on-highway trucks—is another area in which McAllister Mills is researching and developing new temperature insulation solutions.

Over the past two years, McAllister Mills has been adding capital equipment to become a vertically integrated supplier of finished heat shields. The company has added capabilities to make metal 3-D heat shields that work with their textile-based engineered solutions. From fiber production to fabrication, every aspect of the manufacturing process takes place in the company’s Virginia-based facilities, which expedites speed-to-market for both development work and deliveries.