Transcript
The hi-lok fastener system, the HL18, HL19, HL20, HL21 pins and theHL70 collar. The hi-lok fasteners are the second most used fasteners in structural assembly of aircraft's after the solid rivets MS20470 and MS20426. Why? What are thecharacteristics that makes this fastener the second choice after the solid rivets?Hi-lok fasteners are defined by a pin and a collar. The pin is similar to a screw and thecollar to a nut. The assembly of the pin, and the collar makes the hi-lock fastener system. The pin is like a screw but with additional advantages regarding a simple screw.The collar is not a simple nut, but a special nut with unique properties. What are thereasons to use this type of fasteners? The reasons are simple and can be summarize tothe following properties:1.Higher tension and shear strength, the material used and the geometry of the fastener gives him the best properties regarding strength.2.Lightweight fasteners, the hi-lok system as the best relation betweenweight and strength regarding the assembly between two elements. Better thatthe use of screws and nuts.3.Easy and quick assembly, with the specific tools the assembly time ismust lower that the rivet or screws/nut assembly time. The assembly is very easywith no complex steps and the final assembly is always perfect with no defects.4.Good stress concentration factor, the specific geometry of the pin elementgives to the hole an increase in fatigue life, much better that if we use thescrew/nut system.5.Fastener cost, accessible and cost effective element in the installation onthe aircraft.6.Correct torque application, the collar property gives us the guaranty thatthe correct torque is applied to the assembly, removing the problem of vibration,strength and fatigue of the pin itself.These are the mains advantages of the hi-lok fasteners. These fasteners are property of the hi-shear corporation, the company that develops this fastener. For that reason the standard designation of these fasteners is defined by the HL letters. There exist NAS or specific manufacturer specification that are equivalent to the HL designation. The hi-lokis the same but the NAS system or the manufacturer company internal systems adoptsdifferent numbering system to identify the hi-lok part number. Generally the P/N isdefined by the Hi-lok manufacturer company Part number.The P/N is specified by the sequencing letters and numbers: HL18PB-5-16. The HLletters define that we are specifying an Hi-lok fastener, the number 18 specify thegeometry and material of the fastener, the letter PB defines the finish protection of thefastener, the -5 number defines the diameter of the fastener per multiples of 32inchs( diameter =5/32 =0,156 in) and the -16 defines the grip length of the fastener per multiples of 16 inchs (length = 16/16= 1 in).This P/N is only to the pin, the collar asa similar P/N. The most used collar is the HL70-5, the letter HL defines the hi-loksystem, the number 70 defines the material and geometry of the collar and the -5defines the diameter in multiples of 32inch (diameter=5/32=0,156 in). If you need tospecify the hi-lok system in your assembly you must request the pin and the collar P/Nand not only the pin P/N. Therefore HL18 is pin and HL70 is a collar, geometry andmaterial is defined by the numbers 18 and 70. The quantity of fasteners is so great thatwe can find numbers from 1 to 1000 in the material/geometry designation.During the installation of this hi-lok fastener system we need access to both sides of thestructure, we insert the pin in the hole, with or without interference depending of thetarget of the hi-lok ( shear or tension application), we apply the collar to the pin andapply torque with the required tool. We apply the torque to a specific part of the collar, this part of the collar will break at the correct torque value. The permanent part of thecollar will continue with the pin in the assembly. This part of the collar that breakspermits that the correct torque be applied to the installation, not requiring additionalsupervision to confirm the correct torque value.There are several type of pins and several type of collars, depending of the application,you must select the correct one. The most used hi-loks are the HL18, HL19, HL20 andHL21. We can divide the hi-loks pins for tension and shear application. The tension pinshave greater heads than the shear pins. After dividing the pins for tension and shear they can be also divided in protruding head or countersunk head pins. You must selectthe tension pins when the main load applied is tension and shear pins when the shear isthe dominant load. The HL18 is the shear protruding pin, the HL20 is the tensionprotruding pin, the HL19 is the shear countersunk pin and the HL 21 is the countersunkpin.Each normal hi-lok fasteners system diameter as two oversize fasteners that can replacethe first diameter in case of a repair or damage to the hole. That means that if you dorepairs to aircraft's and you need to replace a HL18PB-6 pin because the hole as cracksor is oversize. You do not need to select the next hi-lok pin diameter the HL18PB-7. Youmust use the 1st oversize of the HL18PB-6, that presents a small increment in diameter just used for hi-lok repairs. They are called the 1st and 2nd oversize hi-lok pins, definedby a specific number after the HL letters.In shear application select the diameter of the pin according to the standard procedure: the upper higher shear strength of the bearing load failure of the plate. That means thatin your joint, the failure criterion used must be the plate bearing failure. The hi-lok mustpresent a higher shear strength than the bearing of the plate used. For that use thecloser diameter of the fastener that guaranties the failure of the assembly by bearing andnot by fastener shear.In tension application use the hi-lok with adequate tension ultimate strength for theassembly. http://www.hi-shear.com/fastener_hl_stds.htmhttp://www.gen-aircraft-hardware.com/template.asp?pagename=hilokshttp://www.gen-aircraft-hardware.com/images/pdf/hilok.pdf
