Aerospace sealants produced by PPG Aerospace

PPG Aerospace is the leading producer of aerospace sealants with a wider product range and more qualifications than any other sealant manufacturer. PPG Aerospace’s sealants are sold under the PRC® and ProSeal ® brands and are used by all the world’s leading manufacturers. PPG Aerospace formulates sealants using polysulphide, polyurethane and silicone technologies as well as their own proprietary PERMAPOL ® polymers.

Sealants are manufactured at sites in the USA and UK and distributed via a global network of 16 Application Support Centres (ASCs). These ASCs, which are located in areas of high aerospace activity, provide technical service and add value by providing specialist support to their local customers.

The sealant product range includes Fuel Tank Sealants, Corrosion Inhibitive Sealants, Windshield and Canopy Sealants, High Temperature Sealants, Firewall Sealants, Electrically Conductive Sealants, Low Adhesion Sealants for Access Doors, Fast Cure Sealants for Flight Line Repairs and Jointing Compounds. Most sealants are two component materials and are available in a several viscosities and application lives.

Semco sealant application equipment

Recognising that good mixing and application techniques are vital to the successful use of these safety critical materials. PPG Aerospace produces a range of sealant application equipment under the SEMCO® brand name and uses several innovative forms of packaging.

SEMKITS® are plastic cartridges inside which the two sealant components, base and catalyst, are stored separately until they are needed for use. They can be mixed either manually or by an automatic machine but the mixing is enclosed and at no point does the operator come into direct contact with the chemicals.

Using sealants supplied through the SEMFREEZE® service eliminates the need for the operator to mix the sealant and puts the responsibility for mix quality and stock control onto PPG Aerospace. In this case the sealant is mixed on a dedicated machine by the local ASC, filled into numbered containers and a sample taken from each one. The containers are then immediately snap-frozen at -65°C to suspend the chemical reaction. They are then stored for 24hrs while QA checks are made on the mixed sealant and then delivered, still frozen, to freezers located alongside the assembly tracks at the customers’ premises.

When a container of sealant is needed, it is taken out and defrosted, either at ambient temperature or using a hot water-bath. Sealant deliveries are usually made on a weekly basis and each freezer topped up to an agreed stock level. This service is used by leading aircraft makers such as Boeing and British Aerospace and major subcontractors such as Spirit. Apart from the time savings and quality improvements, companies which switch to SEMFREEZE® from older types of packaging will also reduce their sealant consumption by up to 25%.

PPG Aerospace invests heavily in research and development, focusing on new sealant materials and finished products made from those materials. The current drivers are:

• higher performance, e.g. resistance to operating higher temperatures,
• better application properties, e.g. a long application life followed by a rapid cure,
• low specific gravity, e.g. the latest generation of sealants have a cured S.G. of 1.1 compared to around 1.5 for the current generation.
• Better health and safety characteristics, e.g. chromate free sealants which also inhibit corrosion.

New PPG sealants offer great benefits to the end users. For example low specific gravity sealants. A typical narrow body airliner contains about 250 litres (375 kilos) of sealant. By switching to PPG’s PR-1782 lightweight sealant, the designers can save around 100 kilos from the airframe. Operators of narrow bodies estimate that their annual fuel costs for each aircraft are 210 Euros per kilo. So reducing the weight of a single aircraft by 100 kilos will result in annual savings of 21,000 Euros. This has lead to leading manufacturers such as Boeing and Airbus using PPG’s light weight sealants.

Faster curing sealants offer even larger savings, especially to aircraft operators. Unscheduled maintenance involving sealant is sometimes necessary and the cost of delaying a narrow body for 1 hour is conservatively estimated at 2400 Euros. New generation sealants such as PR-2001B-1/2 will cure to a flyable condition in 3 hours compared with up to 30hrs for current materials. For a military aircraft operator the change to faster curing sealants can be priceless.

Custom sealant solutions

PPG Aerospace is developing a range of products under the Custom Sealant Solutions banner. These include SEALCAPS® and SEMFOAM®.

SEALCAPS are a new way of sealing the heads of fasteners. They comprise a cured outer shell made from an approved sealant which is then filled with sealant, snap-frozen and delivered in their frozen state to the customer who defrosts them immediately prior to use. Compared to the traditional way, which is to hand-apply wet sealant, SEALCAPS are quicker to apply, need less artisan skill and are entirely uniform. It is possible to achieve time savings of over 40% particularly if working in confined spaces, for example when making auxilliary fuel tanks. SEALCAPS enable the designer to control the thickness of sealant he wants over the fastener heads. This is critical in a composite structure which uses metal fasteners and one reason why they are specified on the Boeing 787 program.

SEMFOAM is a new way of sealing large apertures in critical areas quickly and safely. It is pieces of open cell polyurethane foam cut to a precise shape, impregnated with a measured amount of sealant and immediately snap-frozen. Supplied as a kit of several pieces to seal a particular joint, the operator defrosts the kit and pushes each piece into position. The polyurethane foam is compressed and acts as a carrier for the sealant holding it in position while it cures. The precise impregnation means that there are no areas in the foam matrix which are void of sealant and no also excess sealant to remove. SEMFOAM is already used by Airbus on their A320 and A400M product ranges.

PPG Aerospace is part of PPG Industries, a global supplier of paints, coatings, chemicals, optical products, specialty materials, glass and fiber glass. The company has more than 150 manufacturing facilities and equity affiliates and operates in more than 60 countries.

Access to these large resources will help PPG Aerospace continue to serve its customer base going forward.