by Jan Zumwalt
AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair
AC 43.13-2B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair
Welding ALCOA Aluminum - Aluminum Company of America(1972 - 241 pages)
Riveting ALCOA Aluminum - Aluminum Company of America(1959 - 91 pages)
FFA-H-8083-31 - Aviation Maintenance Technician Handbook - Airframe, Volume 1
Rivet alloys and the base material they join are important to understand because it does not make since to combine mismatched material of different strength. So lets refresh our memory on the most common materials we are most apt to work with.
The material used for the majority of aircraft is aluminum alloy solid shank rivets . The strength and temper conditions of aluminum alloy rivets are identified by digits and letters similar to those adopted for the identification of strength and temper conditions of aluminum and aluminum alloy stock. The 1100, 2017-T, 2024-T, 2117-T, and 5056 rivets are the five grades usually available.
The 1100 rivet, which is composed of 99.45 percent pure aluminum, is very soft. It is for riveting the softer aluminum alloys, such as 1100, 3003, and 5052, which are used for nonstructural parts (all parts where strength is not a factor). Uses include placards, upholstery trim or decorations.
The 2117-T rivet, known as the field rivet, is used more than any other for riveting aluminum alloy structures. The field rivet is ready for use and needs no further heat treating or annealing. It also has a high resistance to corrosion.
The 2017-T and 2024-T rivets are used in aluminum alloy structures where more strength is needed than is obtainable with the same size 2217-T rivet. These rivets are annealed and must be kept refrigerated until they are to be driven. The 2017-T rivet should be driven within approximately 1 hour and the 2024-T rivet within 10 to 20 minutes after removal from refrigeration.
The 5056 rivet is used for riveting magnesium alloy structures because of its corrosion resistant qualities in combination with magnesium.
Mild steel rivets are used for riveting steel parts. The corrosion resistant steel rivets are for riveting corrosion resistant steels in firewalls, exhaust stack brackets, and similar structures.
Monel rivets are used for riveting nickel-steel alloys. They can be substituted for those made of corrosion resistant steel in some cases.
Small aircraft rarely use annealed rivets. If more strength is needed, material thickness is increased or more field rivets are used. Aluminum alloy rivets can be hardened and annealed in the same manner as other aluminum.
Common heat sources are electric air furnace, salt bath, or hot oil bath. The heat treating range, depends on the alloy but is 625° F to 950° F. The rivets are immediately quenched in cold water (70° F) then stored in a freezer until needed. Rivets that have been exposed to room temperature may be re-annealed one time but the strength is diminished by about 20%.
After installation, annealed rivets reach one-half their maximum strength in approximately 1 hour and full strength in about 4 days.
Small aircraft manufactured prior to about 2000 usually used the "Army Navy" (AN) numbering system. Newer aircraft have switched to the "Military Specification" (MS) numbering system. All new designs should use the MS system whenever possible.
Each type of rivet is identified by a part number so that the user can select the correct rivet for the job. The type of rivet head is identified by AN or MS standard numbers. The numbers selected are in series and each series represents a particular type of head. The most common numbers and the types of heads they represent are:
AN426 or MS20426 - countersunk head rivets (100°). |
AN430 or MS20430 - roundhead rivets.
AN441 or AN442 - flathead rivets.
AN455 or AN456 - brazier head rivets.
AN470 or MS20470 - universal head rivets.
There are also letters and numbers added to a part number. The letters designate alloy content; the numbers, rivet diameter and length. The letters in common use for alloy designation are:
A - Aluminum alloy, 1100 or 3003 composition.|
AD - Aluminum alloy, 2117-T composition.
D - Aluminum alloy, 2017-T composition.
DD - Aluminum alloy, 2024-T composition.
B - Aluminum alloy, 5056 composition.
M - Monel.
The rivet head identification mark designates what alloy the rivet is made from and allows the strength of the rivet to be determined.
Note: To convert KSI to PSI add three zeros to KSI. For example, 10 ksi is equal to 10,000 psi
The aluminium pieces should be clean and held firmly together.
A proper sized pilot hole should be drilled
|Rivet Pilot Hole Drill Size|
The hole does not need to be de-burred if the parts have been held firmly together during the hole drilling process and the hole has clean edges.
If the rivet is not driven properly it should be removed and replaced. Special over sized shanked rivets are available that have the same size head but allow the hole to be drilled to the next rivet size. For example if the original rivet had a 1/8" shank, a 5/32 rivet shank with a 1/8" rivet head is available. This is desirable where appearance is important.
Minor dents in the manufactured head of rivets may not require removal. A small fine jewelers file can sometimes be used to remove enough of a dented ridge, and round out the bottom of a grove, to make the rivets appearance acceptable. It helps to purchase a set of files with various shapes. A small curved (spoon) shaped file is especially helpful.
Despite the gross mishapped heads of the rivets shown in the photo above, Alcoa claims that all the heads where within 5% of the strongest. Therefore, it appears that damage to the factory head is more a matter of appearance than strength. This is NOT true for the shop side of the rivet. Any irregularities of the shop side seriously compromise strength and defect rivets should be replaced.