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UV Curing and Composites Filament Winding 


Ultraviolet (UV) curing is used commercially for filament winding of a variety of products made from composite materials.  They include oxygen and liquid propane cylinders, baseball bats and PVC piping. 


UV light is part of the electromagnetic spectrum from 200nm to 400nm. In a UV curing process, photoinitiators in the ink, adhesive or resin are sensitive to UV light and generate free radicals, beginning the polymerization or "curing" process. UV curing is line of sight, meaning the entire part surface must be exposed to UV light. The filament winding process lends itself quite naturally to UV curing, since parts rotate on a mandrel and can be easily exposed to UV light. And since UV curing happens in only a few seconds, it fits easily into the high production filament winding operation. 





Cylinders with UV Cured Gel Coat 

Cylinders with UV Cured Gel Coat  



UV Curing Benefits 


There are several ways in which UV curing is applied to filament winding processes including B-stage cure, complete cure and gel coat cure. First, UV lamps can be placed after the resin bath, just prior to winding onto the mandrel to B-stage cure the resin onto the roving. The B-stage cure is not a complete cure, but partially cures the resin to a tacky stage. In addition to reducing the total cure time, there are several other benefits using this process, including: 

  • The ability to wind at high approach angles because the roving is tacky 
  • Faster winding speeds because resin no longer flies off the mandrel during winding 
  • More consistent part throughout the wall thickness because resin is no longer forced out of the rovings closest to the mandrel as the part is wound 
  • Less waste because the resin gels quickly so there is less dripping during winding and curing 

Typically, the UV lamps can be located above and/or below the rovings (either glass, aramid or carbon) immediately after the resin bath. The lamps must cover the full width of the fibers.  If the part is fabricated using fiberglass rovings, complete UV cure is usually possible. By placing the UV lamps such that the UV light strikes the rovings immediately following winding onto the mandrel, the part can be cured as it is wound. If UV B-stage curing is used as described previously, then final UV cure can take place following winding of the part. 

Producing Attractive Parts 


Another UV curing application is popular with fabricators of filament-wound cylinders, golf shafts, etc. that require a smooth, attractive appearance. A UV curable topcoat or gel coat is an ideal way to give the part a scratch-resistant, durable topcoat in a consistent, high production process. Typically, the topcoat is sprayed or manually brushed onto the fully cured part. Then the part rotates on a mandrel in front of the UV lamp. 




UV Curing Gel Station with Fusion UV F300 
UV Curing Gel Station with Fusion UV F300  


Additional Benefits of UV Curing 

Several other benefits of using UV include reducing work-in-process, since the winding and cure time is shortened. Especially important for large parts, UV curing increases capital utilization since the mandrels are freed up more quickly, resulting in more parts per mandrel. The overall worker environment improves because the operation is less messy.  Moreover, because the styrene is either eliminated or quickly becomes locked up in the resin, the smell is greatly reduced. 



Filament winding machines are available with UV curing lamps. More often, however, UV lamps are retrofitted into existing winding operations. Light shielding must be constructed to ensure worker safety. In addition, controls should be integrated to provide proper operation and safety. 


UV Curable Resins  

Polyester, vinyl ester and epoxy resins can be UV-cured. With polyester and vinyl ester it is possible to eliminate the use of the styrene with the addition of photoinitiators. Typically, the fabricator can simply add the photoinitiators once the process parameters are established. Off-the-shelf formulations are also available. In some cases – especially for B-stage curing of an aramid or carbon fiber part – a hybrid dual-cure system with both photoinitiators and a heat activated catalyst is needed. 

It has been shown that UV cure can be used to initiate and speed up the cure of epoxy resins. 

Loctite Corporation offers its AccusetTM series of additives for use with recommended epoxy resins. Loctite recommends using Heraeus Noblelight America's F300 or F600 with a D bulb for best results for a B-stage cure. Following this B-stage UV cure, the part can undergo the standard epoxy cure schedule for the final cure. 


Click here for a case study of UV gel coat curing 

Click here to learn how Advanced Composite Products and Technologies uses UV curing.   

UV Curing: Cure on Demand for Filament Winding – a paper presented by Susan Mitchell at the Automated Composite Processing Conference in Oberbruch, Germany ((pdf)) 

Download our Filament Winding brochure 


Contact us if you would like more information or have specific questions. 

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