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Lockbolts

Lockbolts

  • Lockbolts are used to attach two materials permanently. They are lightweight and are equal in strength to standard bolts. Lockbolts are manufactured by several companies and conform to Military Standards, which specify the size of a lockbolt’s head in relation to the shank diameter, plus the alloy used in its construction. The only drawback to lockbolt installations is that they are not easily removable compared to nuts and bolts.
  • The lockbolt combines the features of a high-strength bolt and rivet, but it has advantages over both. The lockbolt is generally used in wing splice fittings, landing gear fittings, fuel cell fittings, longerons, beams, skin splice plates, and other major structural attachments.
  •  It is more easily and quickly installed than the conventional rivets or bolts and eliminates the use of lock washers, cotter pins, and special nuts. Like the rivet, the lockbolt requires a pneumatic hammer or “pull gun” for installation. When installed, it is rigidly and permanently locked in place. Three types of lockbolts are commonly used: the pull type, the stump type, and the blind type.
Pull Type
  • Pull-type lockbolts are used mainly in aircraft primary and secondary structures. They are installed very rapidly and have approximately one-half the weight of equivalent AN steel bolts and nuts. A special pneumatic “pull gun” is required to install this type of lockbolt. One person can accomplish installation since bucking is not required.
Stump Type
  • Stump-type lockbolts, although they do not have the extended stem with pull grooves, are companion fasteners to pull-type lockbolts. They are used primarily where clearance does not permit installation of the pull-type lockbolt. A standard pneumatic riveting hammer (with a hammer set attached for swaging the collar into the pin locking grooves) and a bucking bar are tools necessary for the installation of stump-type lockbolts.
Blind Type
  • Blind-type lockbolts come as complete units or assemblies. They have exceptional strength and sheet pull-together characteristics. Blind lockbolts are used where only one side of the work is accessible and, generally, where it is difficult to drive a conventional rivet. This type of lockbolt is installed in the same manner as the pull-type lockbolt.
Common Features
  • Common features of the three types of lockbolts are the annular locking grooves on the pin and the locking collar, which is swaged into the pin’s lock grooves to lock the pin in tension. The pins of the pull- and blind-type lockbolts are  extended for pull installation. The extension is provided with pulling grooves and a tension breakoff groove.
Composition
  • The pins of pull- and stump-type lockbolts are made of heat-treated alloy steel or high-strength aluminum alloy. Companion collars are made of aluminum alloy or mild steel. The blind lockbolt consists of a heat-treated alloy steel pin, blind sleeve and filler sleeve, mild steel collar, and carbon steel washer.
Substitution
  • Alloy-steel lockbolts may be used to replace steel high-shear rivets, solid steel rivets, or AN bolts of the same diameter and head type. Aluminum-alloy lockbolts may be used to replace solid aluminum-alloy rivets of the same diameter and head type. Steel and aluminum-alloy lockbolts may also be used to replace steel and 2024T aluminum-alloy bolts, respectively, of the same diameter. Blind lockbolts may be used to replace solid aluminum-alloy rivets, stainless steel rivets, or all blind rivets of the same diameter.

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