Before inserting another rivet in the tool, be sure that the broken mandrel has been ejected from the tool. This can be done by fully extending the lever linkage and allowing the mandrel to fall clear.

The scissors or expandable type of tool is unique because it can reach hard-to-get-at areas and can set the rivets with ease. This tool is particular] y useful for installing ventilation ducting.

RIVETED SEAMS

Riveted seams are used for joining metals and have numerous applications.

Figure 2-90 shows the pattern of one of two pieces to be joined by lap and rivet. Note the cross section of the finished seam.

Figure 2-90. - Pattern for riveted lap seam.

Figure 2-91 shows the patterns for constructing a lapped and riveted comer seam. View A is the pattern for one piece and view B is the other. Note the cross section through the completed seam.

Frequent use is made of lapped and riveted seams in joining round pipe sections.

SHEET-METAL DUCT SYSTEMS

With the advent of high-tech equipment, such as computers and other specialized electronic equipment, air-conditioning systems are incorporated more than ever into many Naval Construction Force (NCF) construction projects. Many of the structures are designed for long-life usage instead of temporary buildings with a short time use. There are also some advanced base functional components (ABFC) which incorporate heating, ventilating, and air-conditioning systems (HVAC) within the facility design.

HVAC systems require close coordination between ratings. Air conditioning, air handling, and heating units are normally installed by an Utilitiesman, and the electrical connections are accomplished by a Construction Electrician. These items must be installed before the ductwork installation phase begins. The Steelworker must also coordinate with the Builder assigned to the project to ensure that all openings in walls and floors are sufficient to accommodate ducts, diffusers, and vents.

Sheet-metal HVAC systems require knowledgeable workers to fabricate and install the various ducts and

Figure 2-91. - Riveted seam for tapped and riveted corner seam.