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In order to ensure that a building is safe and compliant, elements such as how a fastener is installed to the roof are key. If this is not considered properly, issues such as unwinding fasteners can occur, causing the structure of the building to be unsafe and insecure.
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Turn ideas into reality.
The problem of unwinding fastenersSFS intec
Turn ideas into reality.
Thread forming into thin materials - <2mm - the main problem?
• Very little metal to form a thread
• Coatings lubricate the thread - easy in = easy out
• Vibration and movement "work" the fastener
• Installing forces create stresses that provide a "push" backwards against the thread grip - overdriving increases force
• Soft aluminium substrates flex more easily and suffer more thermal movement.
The problem of unwinding fasteners
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•Drill tip design
•Overdrive prevention
•Non-tapping products
•"Drop through" features
•Better joint and component design
•Better installation; use of “Loctite" compounds
•Improved guidance
Fastener manufacturers cannot resolve this problem in isolation
Often, ill considered specification changes to save money erode demand for specialist purpose-made products.
Possible solutions
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Clever design - the drill point pushes metal aside to create a thicker zone
that allows better thread forming
Purpose made drill tip into 0.7mm sheet
Conventional drill tip design cuts away all metal, thread only works in sheet thickness
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main fix into 0.7mm special tip into 0.7mm
this design gives much better pull out resistance and higher grip levels into the sheet
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Overdrive prevention
•tooling control
•sheer pin drives
Possible solutions
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Non-tapping solutions
You could use rivets but,
•They require pre-drilled holes
•You can't adjust them once set
•You can't easily remove them
•They do not like slotted holes
•They have a limited grip range - up to about 15mm for basic, paintable items; up to about 30mm for bulbtite 6604 [non-painted]
•Some designs are very sensitive to hole diameters, others require special tooling.
Possible solutions
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Free spinning - "drop through" designs
After drilling and tapping, the threads drive right through the work piece, before dropping out below. This leaves the threads disengaged from the work, preventing overdriving and backing out..\..\..\Desktop\2009 presentations\podcast & videos\5 Clamping Fastener.wmv
..\..\..\Desktop\2009 presentations\podcast & videos\3 Top Hat.wmv
non-spin design
Possible solutions
Turn ideas into reality.
Better joint design, guidance and practice
One for the trade…
Image courtesy of the MCRMA
Possible solutions
Turn ideas into reality.
Summary
• Very little metal to form a thread to fix thin sheet• Coatings lubricate • Vibration and structural movement "work" the fastener • Overdriving can create stresses that provide a "push" backwards • Soft aluminium sections flex more easily and suffer high levels of thermal movement. High cyclic shear loads are transmitted to the fixing• Good fastener design can help limit problems but we can only do so much, when special products that help are ignored by price sensitive installers…
The problem of unwinding fasteners
