Blind RivetsApplicationConsiderations

Part 1 of 2 Parts

(Reprinted by Permission From ENGINEERING DIGEST(Canada), Volume 16, No. 10)

IN THE SELECTION of fastening or assembly methodsfor production lines, industry is confronted with virtual-

ly an infinite number of types and sizes of fasteners fromwhich to choose. Over 500,000 fasteners can be identifiedby type, size and material and hundreds of standardsand specifications defining fastener properties confront theuser. Under such circumstances a fastener type, whose useclearly has grown and continues to grow at a great rate in awide variety of industries, is the blind rivet, so namedbecause it can be set from one side of the work unlikemany other fasteners which require access to both sides.Furthermore, simplification of product design, higher as-sembly speeds, lower assembly costs, and the fastening ofdissimilar materials, all have contributed to high volumeusage of the blind rivet.

Blind rivets are mechanical fasteners. When a blindrivet is set, a self-contained mechanical, chemical, or otherfeature forms an upset on its inaccessible — or blind — endand also expands its shank, thus securing the parts beingjoined. However, blind rivets are increasingly being used inapplications where both sides of the joint are accessible inorder to simplify assembly, save metal, improve appearance,or decrease cost. Blind riveting has the added advantage ofportability which becomes especially valuable in the case oflarge assemblies.

Blind rivets should be considered when the fastenerswill not have to be removed for maintenance purposes, willhave to function in a high-vibration environment, will serveonly as tack or temporary fasteners, or will be used asrepair fasteners by untrained operators in the field.

BASIC TYPESBasically, blind rivets are classified by the method of

setting. There are four basic types: pull-mandrel, drive-pin,chemically expanded (explosives), and threaded (See Fig.1).

Pull-mandrel: This type consists of a rivet body and amandrel. The mandrel is pre-assembled in the body. Insetting the mandrel is gripped and pulled axially so thatits head upsets the blind end of the rivet body to forma set rivet.

Pull-mandrel rivets are subdivided into: pull-through rivets where the mandrel is pulled completely

26 AUGUST 1971

through leaving a hollow rivet; break-mandrel rivets(open or closed end) where a part of the mandrelremains a plug in the rivet body; the non-break orself-plugging rivets where the mandrel is pulled into butnot through the rivet body. The projecting mandrelend is removed in a subsequent operation.Drive-pin: Drive-pin rivets consist of a rivet body and apin assembled and located at the head side of the rivetbody. The pin is hammered into the rivet body andflares out the blind side.Chemically expanded (Explosive): A one-piece rivet(open or closed-end type), it has an explosive in itsbody. Application of heat or electricity to the rivethead activates the charge to detonate, thus expandingthe rivet walls to set the blind end.Threaded: This type consists of an internally threadedrivet and an externally threaded mandrel which istorqued or pulled, usually with a special tool. Thisaction expands the walls of the rivet body to form ablind end.Factors that can influence the choice of one of the

three types over the others are cost, structural integrity ofthe joint, speed of assembly, clinching ability of the rivet,ease with which it may be removed after setting, size rangeof available rivets, and the range of grips that each willaccommodate. Only with extensive knowledge of thesefactors can a proper choice be made.

MATERIALS AND FINISHESBlind rivets are made of various materials, including

steel, copper, stainless steel, aluminum, and Monel. Regularsteel rivets are specified where high strength with minimumcorrosion resistance is required. Such rivets can be plated,chemically treated, or painted.

Aluminum blind rivets are commonly used for exteriorwork. They are manufactured with an ordinary mill finishor any one of several special finishes, e.g., anodizing.

Monel and stainless-steel rivets provide high shear andtensile strengths and superior corrosion resistance. They canalso be used in contact with detergents and most corrosiveliquids commonly used in industry.

Fig. I—Basic blind rivet designs and how they are set.

STYLESBody style: A blind rivet is classified according to its

as-manufactured condition. The closed-end rivet has a solidend and its blind side remains closed after it has been set.The open-end rivet has the as-manufactured end open.

In a split-end rivet, a portion of the body is split axiallyinto two or more segments. The shank in a slotted-shankrivet has one or more axial slots that extend from theunderside of the head and terminate short of the open end;the remaining portion of the shank is a hollow cylindersimilar to that of the open-end body style.

Core styles: The core of a blind rivet is the axiallylocated hole in the rivet body. Styles are based on thepost-setting condition of the rivet.

A filled rivet contains enough of the mandrel or pin sothat the break point of the mandrel or the end of the pin isapproximately flush with the top of the rivet head. Thisstyle provides high shear strength. A semi-filled rivetcontains a short length of the mandrel in its core. A hollowrivet has a completely empty core, as in a pull-throughmandrel rivet, and is advantageous when light weight isimportant.

Head styles: The head of a blind rivet is the asmanufactured upset portion of the rivet body. Aftersetting, the head is located on the access side of the joint.Styles include round, truss, countersunk, brazier, flat, anddomed. These can be either flush or protruding.

End styles: The end of a blind rivet is the part of therivet body at the extremity of the shank and opposite thehead. Some rivet ends are open or split, some arecompletely enclosed, and others are plugged. When the endis set, it becomes the blind head of the rivet.

Sizes: Sizes are usually in increments of 1/32 in.Oversized rivets are also available for dimpled-sheet con-struction and for replacing standard diameter rivets in holesthat have been enlarged by the removal of those rivets.Explosive rivets are also produced oversize, i.e., the actualrivet diameter is about 1/64-in. larger than the diameterspecified. Nominal sizes of this type are 1/8, 5/32, and 3/16in.

Grip range: The minimum-to-maximum total thicknessof component materials that can be joined properly with ablind rivet of a given length is its grip range. Thus, the griprange does not correspond to the length. A wide range ofgrip means a smaller inventory for many different applica-tions. Most production requirements would dictate a lengthconsistent with the grip range involved.

STANDARDS AND SPECIFICATIONSMilitary specifications published to date have been

prepared for government applications. As blind rivetscontinue to be used in increasing volume for applicationother than aircraft, undoubtedly new specifications will beprepared and published by government and defenseagencies. At the present, it is impossible to assign typicaljoint-strength values to any of these fasteners withoutknowing the tolerances that are to be allowed on the rivetlength versus assembly thickness, hole clearance, jointconfiguration, and the type of loading. It shall be men-tioned here that the Industrial Fasteners Institute — theTechnical Committee of which prepared this article — hasissued its first IPI Standard "Glossary of Terms Relating toBlind Rivets" (IFI-110 of March 20, 1969).

(Continued on Next Page)

(a)

(b)

(e)Most common types of riveted joints: (a) lap joints; (b)single-riveted butt joint; (e) double-riveted butt joint.

SPORT AVIATION 27

DESIGN CONSIDERATIONSThe factors determining the type of rivet most suitable

for a particular application have been mentioned earlier.The designer can profit by remaining aware of certainassembly tips and techniques called from actual fieldexperience of blind riveting specialists. Such knowledge canprovide the designer with a relatively simple means ofintroducing significant improvements in the performance orappearance of an end product.

Seven examples are worthwhile to remember:1. Fastening relatively thin sections often is a stumbling

block for designers faced with reducing the overallweight of an assembly or obliged to use relatively thinsections for functional objectives. Particularly for unitsthat cannot be assembled by adhesive bonding for onereason or another, blind rivets with large flanged headscan serve to minimize the possibility of fracturing thesurfaces of the members being fastened. They alsoprovide the extra bearing strength required to ensure aquality fastening.

2. When fastening sections of dissimilar thicknesses, bestresults are obtained if the rivet is expanded with the thinsection directly under the rivet head. This causes theheavy sheet to bear the brunt of the clinching action. Toexpand the rivet on the thinner member risks damage toits surface.

3. Riveting metal to another type of material, for example,plastic, often is a problem for the designer. If the rivet isexpanded against the harder material, this can be easilysolved.

4. When fastening a flat section to a curved section, it ispossible to set the rivet from the curved side and for therivet so set to hold. However, it is strongly recom-mended that the rivet be set from the flat side.

5. When riveting corrugated material such as roofing, rivetsshould be on the flat slope if possible. Second choice isthe peak. The poorest place is the valley because waterwill accumulate at the rivet.

6. Care should be taken to use a rivet material which iscompatible with the material being riveted in order toeliminate or reduce corrosion.

7. It is sometimes most advantageous to design a part forrivet failure since the broken rivet can usually bereplaced much easier than fractured or torn sheet metal.

In addition to the rather specific tips and techniquesjust described, the designer can also profit from thefollowing design recommendations.

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Fig. 2 Fig. 3(To Be Continued Next Month)

Fig. 4

SPORT BIPLANE ENGINES

The first big change in Sport Biplane Class rules sincesouped-up engines were outlawed on January 1, 1970 isabout to take place. The Class Engine Committee of theProfessional Race Pilots Association is about to approve useof a second engine in addition to the popular Lycoming0-290 — the 235-cu. in. Franklin "Sport 4" series rated at125 hp. According to the Committee, this engine must beused in strictly stock configuration, with NO exceptions!The Committee will also be extra careful in checkingLycoming engines, especially the induction and ignitionsystems. £)28 AUGUST 1971

Helpful HintsWELDING TIPS

By Antoni Bingelis (EAA 2643/Designee 306)

8509 Greenflint LaneAustin, Texas

ALTHOUGH 4130 STEEL (chrome molybdenum or"chrome-moly") is very tough and strong when cold, it

is even weaker than mild steel in the heated condition;therefore, it must not be stressed or shocked while in awhite-hot state. The following guidelines should be heededif problems are to be avoided:

1. Do your welding in a draft-free area, otherwise themetal will chill too fast and thereby be weakened.

2. Never use tightly clamped jigs. Spring-type clamps arejust fine for holding parts to be welded, and they comein various sizes.

3. Good welders say that starting welding on an edge isnot a good technique. Rather, it is best to start at apoint away from the edge and work to it. Caution —heat builds up fast near the easily heated edges and it isvery, very easy to inadvertently burn through the edgeof the metal. Watch it and draw the flame away slightlyas needed when the edge itself is reached. If you doruin a piece, make it over. That's where the educationalpart of homebuilding comes in.

4. In all cases where parts have been tack-welded to-gether, it is most important that you melt completelythrough the tack as you complete the final weld.

5. As the thickness of the metal being welded decreases,the selection of the proper tip and the adjustment ofthe gases becomes very important. Thin metals areeasily buckled when too much heat is used.

6. Especially on thin metal and thin-wall tubing, careneeds to be taken to clean any dirt, scale, or oxidefrom the parts to be welded. Percentagewise, as theparent metal becomes thinner, the chances of havingdirty metal in the weld is increased. Take time to cleanthe weld areas.

7. Get in the habit of preheating the metal in the area tobe welded.

8. Don't clamp your work in the vise and then try to weldon the part near the jaws of the vise as the heavy metalof the vise will draw away the heat and you'll havedifficulty getting the metal hot enough to do goodwork. Remember, any large or heavy metal areas nearthe weld areas of work will draw away the heat fromthe joint and will require a larger flame, therebyincreasing the risk of burning the adjacent metal.

9. Be sure your line of weld in the parent metal is heatedto proper melting point. Try to keep the weld pool sizeas uniform as possible.

10. Heat the filler rod to the same melting point beforeintroducing it into the melted pool of metal.

11. Add filler rod as evenly and steadily as possible.12. Don't rush! Be sure that the added metal and parent

metal are puddled together properly.13. Keep playing the outer envelope flame over the pool to

protect it from the oxidizing effect of the air.14. Melt a certain portion of the parent metal on both

sides for the entire length of the weld.15. Avoid reheating of weld metal which has cooled.