Introduction to Blind Rivets (part 1/2)

Introduction
The first blind fasteners were introduced in 1940 by the Cherry Rivet Company (now Cherry Aerospace) and the aviation industry quickly adopted them in a wide range of airframe assembly applications. The past decades have seen a proliferation of blind fastening systems based on the original concept, which consists of a tubular rivet sleeve incorporating a protruding (universal) or countersunk (flush) rivet head and an internal mandrel or stem. Installation consists of inserting the blind rivet into a prepared hole, engaging the serrated end of the stem with a pulling tool and pulling the stem into the sleeve to expand the sleeve on the back or blind side of the sheet assembly to fix the rivet in place. These rivets were designed to be used in blind applications where there was limited or no access to the “blind” of the assembly, such as the closing side of a box structure.

Types of Blind Rivets
Although rivet manufacturer’s produce blind rivets in a wide range of variation each with specific properties and applications, there are essentially five (5) basic types of blind rivets used in the aircraft industry:
-Self-Plugging, Mechanically-Locked Spindle, Rivets, with an Expandable Wire Draw Shank – Procurement Spec NAS1400 (Standard Sheets NAS1398/NAS1399)
-Hollow, Pull-Through, Non-Structural rivets – Procurement Spec NASM8814 (Standard Sheets NASM20604/20605)
-Self-Plugging, Mechanically-Locked Spindle, Rivets, Bulbed Shank – Procurement Spec NAS1740 (Standard Sheets NAS1738/1739)
-Self-Plugging, Mechanically-Locked Spindle, Rivets, Bulbed Shank, Nominal and 1/64” Oversize Diameter – Procurement Spec NAS1686 and NAS1687 (Standard Sheets NAS9300 Series)
-Mechanically Expanded, Self-Plugging, Mechanically-Locked Spindle, Rivets, Bulbed Shank, Nominal Diameter – Procurement Spec NAS1900 (Standard Sheets NAS1919/NAS1921)

Self-Plugging, Mechanically-Locked Spindle Rivets, Expandable Wire Draw Shank – Procurement Spec NAS1400

Procurement Specification NAS1400 establishes the requirements for procurement of self-plugging blind rivets, with a mechanically locked spindle, which can be installed in assemblies or construction where access to only one side is available. These rivets are intended for use in aircraft structural or similar applications.
Self-plugging mechanical-locked spindle blind rivets were developed to prevent from problems of losing the stem due to vibration and cyclic loading. This rivet incorporates a ring or sleeve on the stem which is formed into a groove on the stem during installation to lock the stem in place. The end of the rivet stem incorporates a “wire draw” mandrel which expands the rivet shank to form the top head and, as the stem is drawn into the shank, expands the shank to fill the hole, “drawing” or reducing the diameter of the mandrel until the break groove in the stem is flushed with the top of the rivet, the lock ring is set and the stem breaks off flush with the rivet head.

These rivets are called up by the part numbers listed on standard sheets NAS1398 for Protruding Head Rivets and NAS1399 for 100° Flush Head Rivets. They are available in 3/32” to 1/4″ diameters in normal size only. The rivets are available in Aluminum, Nickle-Copper (Monel) and A-286 CRES alloys. As the wire draw action creates high compression forces on the blind head side, these rivets are not suitable for use in thin sheets, soft material or double dimple applications. Rivets incorporating a driving anvil, code “AB” in the part number can be installed using Non-Shifting type installation tools. Rivets with a “-“ or “A” code in the part number, denoting a partial or fully serrated spindle, will require shifting type installation tooling to set the lock ring in place. Shifting type tooling is 3 to 4 times more expensive than non-shifting type and is subject to a high degree of wear in use. Refer to figure 1. for a general description of an NAS1398 protruding head “AB” code, (non-shifting), wire-draw type blind rivet.

Disclaimer
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