PolyTube Cycles

Kevin Steegmann
Braunstr. 12
41836 Hückelhoven
Germany

Deposit and pickup also in
61250 Usingen
(appointment only)

Mobile: +49 176 - 93777880
Phone: +49 2433 - 4584570
Telefax: +49 2433 - 4584571
info@polytube-cycles.de

How carbon fiber frames are repaired

When carbon fibers are overstressed, they break without deforming. The damage is not always visible but once it starts it will continue to complete failure. This does not have to happen. It is possible to make a broken frame safe again. Although the process is complex it can often result in a bike that is even stronger than the original design. The repair process can be broken down into several steps:

      
Gebrochene Sitzstrebe


Inspection: First, the damage is assessed via visual inspection. Cracks as measured and documented and an endoscope is used to look at the damaged area inside the frame when possible. The rest of the frame is also checked to ensure no further damage can be seen.

   Untersuchung des Schadens
Stiffness testing: The frame is placed in a test fixture and the stiffness of the broken frame is measured. Here the tracking and torsional stiffness values can be used to determine if further damage is likely. If the frame is shown to be weaker than the visible damage would account for, thermographic imagery can be used to show where the hidden damage is.    Messung der Spuren-Steifigkeit

Exposing the wound: Once all damaged areas have been found they are sanded to remove paint. Then carbon layers are carefully removed in successively smaller areas. This is necessary to avoid any sudden changes in stiffness along the tube. This would cause points of high stress and lead to frame failure after a short time. The lowest layer is left to provide the required surface area to which the new carbon will bond.

   Gebrochene Faser sind abgeschliffen

Clean-up: The damaged area is then cleared of dust from sanding and degreased to allow a good bond for the new layers.

   

Planning the lay-up: Based on the lay-up of the manufacturer and where the damage is, a new lay-up schedule is planned that will allow the area to be at least as strong as original without creating bulges or low areas. It is often necessary to use several different types of carbon fiber in order to achieve these goals.

   Geschnittene Kohlefasergewebe
Laying the fibers. Using special epoxies, the fibers are layed down in the predetermined order. The frame is then wrapped and placed under vacuum for the epoxy to cure. The vacuum ensures that the fibers are compacted well and the no air is trapped between the layers.

 

 

Faser für die Reparatur werden gelegt

Finishing preparation: Once the repair has had time to cure (7 days), it is unwrapped, sanded and cleaned. The frame is now ready for finishing but first new stiffness values are measured to determine if everything has gone according to plan.  

Sitzstrebe nach der Reparatur