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Fastener Inserts Designed for Lightweight Aerospace Materials Reduce Risks, Costs
12/27/2012

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Spiralock 1/4-28 tapped holes are used to mount connections under the aircraft wing (circled in red) on this F-18 Hornet/AIM-120 AMRAAM air-to-air missile. (Source: Spiralock)
Spiralock 1/4-28 tapped holes are used to mount connections under the aircraft wing (circled in red) on this F-18 Hornet/AIM-120 AMRAAM air-to-air missile.
(Source: Spiralock)

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Jerry dycus
User Rank
Gold
Fasteners in composites
Jerry dycus   12/27/2012 10:10:03 AM
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              I'm not sure anything in this article is new as much if not all of it has been known for 50-100 yrs!!

              In composites one doesn't cut threads for either bolts or inserts if one is smart but instead molds them with epoxy, etc in place giving good holding and locking in many cases.  If a sandwiched material one hollows out the foam/etc core and fill it with epoxy to spead the load, then insert the bolt, insert, etc as needed.

              In other plastics drilling a smaller hole then screwing a hot bolt, insert into it  gives the needed strength in many cases.

              If higher loads than the local material can handle glue on a reinforcement piece with the threads built into it.

              As for working loose there are many types of thread lockers out there.

           

Cabe Atwell
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Blogger
Re: Fasteners in composites
Cabe Atwell   12/27/2012 3:57:26 PM
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I use steel inserts in two cases. One where a bolt will be removed repeatedly, or I have to fix a stripped out hole. I think the later is where most inserts are used. In many cases the insert has a stronger holding potential versus the original thread. I only wish I could get some of the more exotic sizes cheaper.

C

ChasChas
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Platinum
Re: Fasteners in composites
ChasChas   12/28/2012 11:46:32 AM
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This technology is a far cry from your Helicoil of yore. If you click the Spiralock link you will see the 30 degree "vibration stoppers", etc. Someone put some effort into this.

ironmandrake85
User Rank
Iron
Re: Fasteners in composites
ironmandrake85   12/28/2012 2:43:45 PM
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Check out Nord-Lock. Spiralock doesn't even compare.

007henryjones
User Rank
Iron
Re: Fasteners in composites
007henryjones   1/28/2014 3:36:06 AM
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The post is great and informative. As technology upgrades, fastener supplying companies should also check their fasteners qualities and should maintain it.

There are many fastener supply companies which provide fasteners in quantity but when one check their quality, it goes down. So, time to time, companies should also take responsibilties to provide quality in fasteners.

Tim
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Platinum
Fasteners
Tim   12/28/2012 9:16:14 AM
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The only issue that I have experienced with threaded inserts is the special tap needed for the OD of the insert. I have been in shops where they might only have one Helicoil tap for a certain ID thread. Production stops when the guy that keeps the tap in his tool box is on vacation.

bobjengr
User Rank
Platinum
FASTENER INSERTS
bobjengr   12/28/2012 12:05:01 PM
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Robert--very interesting post.  I think fastener technology has greatly improved over the last 20 or 25 years.  During my "tour of duty" in the Air Force, we would sweep the runways three times per day for components that actually fell off the aircraft.  It was amazing to me the parts we found.  Our sweeper had the capability of lifting a part weighing up to 100 pounds--and we found them.  Cowling, hundreds of screws and bolts, nuts, etc. you name it.  Believe it or not, we never had an accident, to the best of my knowledge,  as a result of components vibrating off but, I certainly don't know why not.  The technology has definitely advanced since those days--thankfully.

Ann R. Thryft
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Blogger
Re: FASTENER INSERTS
Ann R. Thryft   2/25/2013 5:36:22 PM
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bobjengr, that's a very scary story. How the heck could those aircraft fly after losing so many fasteners? What am I missing?

bobjengr
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Platinum
Re: FASTENER INSERTS
bobjengr   3/3/2013 5:48:47 PM
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 Hello Ann, I asked the very same question and sometimes they did not.  There were times, granted not  many, when emergency landings had to be made due to cowlings or flight surfaces coming loose and vibrating uncontrollably during flight.   Of course, this can affect the airworthiness of the plane and consequently provide exceptional drag.  It was always amazing to me how uninvolved some pilots were relative to pre-flight inspections.    The "walk-arounds" recommended were sometimes cursory at best.   My experience was during Viet Nam and there were so many aircraft coming and going at the Ogden Air Material Area (OAMA) it was impossible to say what part belonged to what aircraft.    They were labeled with a date and placed in a special bin. Then you wait for a phone call.   

Ann R. Thryft
User Rank
Blogger
Re: FASTENER INSERTS
Ann R. Thryft   3/4/2013 1:23:46 PM
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Thanks for the feeback, bobjengr. That's even scarier. Sounds like no one's paying enough attention, either to potential failures on individual planes, or to the entire system.

Nancy Golden
User Rank
Platinum
Apollo 13
Nancy Golden   12/29/2012 2:04:10 AM
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This statement:  "A secondary issue arises: finding safe and reliable methods of fastening assemblies that can protect against fastener loosening while minimizing assembly and maintenance costs. These methods must provide complete assurance of joint integrity under the severe conditions of shock, vibration, and thermal cycling common in aerospace environments" brought to mind Apollo 13 - if I recall correctly the explosion was caused by a defective part off the assembly line. I would be a lot more interested in maximizing safety then in minimizing the costs of the fasteners...

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