Closing Hollow Rivets

There are a variety of hollow rivets, designed primarily for application where there is access to only one side of the job. These include Tucker-pop, Chobert, Avdel, Cherry and the Hi-Lok family of modern fasteners.

Tucker-pop

Hand-operated pop-rivet pliers or Lazy-tongs pliers can be used to close Tucker pop rivets. A procedure for using the Lazy-tongs type pliers is as follows:

• The Lazy tongs are fully extended and the mandrel shank is inserted into the chuck.
• The tongs are slightly compressed and the rivet inserted into the hole in the material being riveted.
• The chuck is held firmly and squarely against the material, while the tongs are further compressed until the head of the mandrel closes the rivet and the stem break off.

The broken off mandrel stems, swarf, rivet heads and shanks, which are discarded during a repair operation, must be removed after completion of the task. The danger of such waste material fouling items such as control cables, cannot be over-emphasised.

Chobert

Chobert rivets (refer to figure below) are very similar to Tucker Pop rivets, except that the mandrel pulls fully through the rivet and is used many times, (including some which have a magazine facility allowing repetitive operation). To operate the tool:

• The mandrel is lubricated and threaded with the rivet.
• The rivet is then threaded into the jaws of the tool with the operating handle fully anti-clockwise.
• The rivet and mandrel are pushed fully into the tool jaws.
• The rivet is place into the hole in the work and the tool is checked for square.
• The operating handle is turned clockwise to pull the mandrel through the rivet and, when the resistance ceases, the rivet is secured.

After closing the Chobert rivet, a pin is inserted through the centre of the rivet, to provide additional shear strength and some sealing properties.

FIGURE

Avdel

Where the strength of a solid rivet and a sealed joint is required, Avdel rivets (refer to figure below) are one of the possible choices. These leave part of the mandrel firmly in place, the top of which can be milled off to leave a flush surface finish.

FIGURE

Cherry Max

One of the most common riveting systems is the ‘Cherry Max’ system, produced in the USA, by Cherry Textron. The system is one of a range produced by the company, others include Friction-lock and Mechanical-lock Cherry rivets.

Cherry Max rivets (refer to figure below) consist of four components, assembled as a single unit. The components consist of a:

• Stem with a break notch shear ring and plug section.
• Locking collar, which locks the stem.
• Fastener sleeve with a locking collar dimple.
• Driving anvil, to ensure correct installation.

FIGURE

Hi-Lok

One other ‘family’ of fasteners that have taken the place of rivets in certain high load situations is the Hi-Lok (refer to figure below), Hi-Lok Hi-Tigue and Hi-Lite group. These fasteners vary from those mentioned before, not only because they are screwed down to full closure, but they are also installed using ordinary hand tools such as open-ended spanners or Allen wrenches, thus avoiding the need for complex and expensive special closing tools. The collar is tightened onto the pin to close the two sheets of metal, and when it reaches the correct torque the hexagonal drive portion shear off. The collar part of the fastener may have a fibre washer attached to aid sealing properties.

FIGURE

Rivnuts

Rivnuts are a form of blind rivet, which can be used as an anchor nut, because the internal bore is threaded to receive a bolt or screw. These fasteners can be found with either countersunk or flat heads and are installed with a special tool, fitted with a threaded mandrel.

This mandrel is screwed into the rivnut and, when the gun is operated, the pull force on the mandrel expands the shank, leaving the rivnut securely fastened and able to receive a bolt or screw after the tool is removed.