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What to know about heavy-duty composite repair

Wednesday, August 1, 2018 - 07:00
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Although there are many similarities between heavy-duty truck and passenger autobody composite repair and bonding procedures, it’s important to understand that the scale of the repair is markedly different to ensure it’s done properly.

The procedures and adhesive products used are alike, but the size of the repairs and panels are significantly larger so they require different space considerations and the amount of repair material to be used.

On a heavy-duty truck body (also known as a tractor or cab), the repair may not be able to be completed off the vehicle because of space constraints. There are also unique challenges in terms of accessing the rear side of the panels for a structural repair. Many heavy-duty truck hoods are built in such a way that the outer panels have no backside access to perform reinforcing operations. When this is the case, either the panel can be disassembled, repairs made and reassembled, or panels are replaced because although repairable, it just isn’t a logical choice since replacement would now be faster. Traditional methods for fiberglass repair such as the use of fiberglass cloth or mat, resin and hardener can be messy and may require multiple applications.

Clean and protect damaged composite

Imagine, for example, a tractor-trailer driving down the road but focus only on the tractor or cab. The hood, fenders, roof, various ground effects, spoiler fairings, and on the tractor are typically all made of composites – and are usually very large parts.  

If a truck sustains damage to the right front and it affects the hood and front fender, it may be possible to repair these parts right on the vehicle instead of removing them. If the parts are removed, they would need to be placed on a bench or parts stand.

Repairing this way isn’t necessarily incorrect, but it is easier to access the truck when everything is all together. The reason is two-fold. Not only are the parts very large – making it easier to directly patch the truck instead of taking it off of its chassis – but they can be difficult to handle, especially if a single technician is handling the repair job.

Making repair material choices

The repair process itself to a heavy-duty composite vehicle follows the same Standard Operating Procedures (SOPs) as the automotive SOPs, with the biggest difference being the larger, thicker panels.

Technicians should keep this in mind when choosing which adhesive to use for the repair. Not only should technicians ensure the repair adhesive meets original equipment manufacturer (OEM) specifications or are OEM-approved, but it’s also best to select a product with the longest work-time possible – more work time is always better than not enough and botching a job.

The fastest-acting adhesives will most likely be unsuitable because of the large surface area involved with the repair. Shops and technicians are all different and where some may use the slowest products everywhere and then apply some heat to accelerate, others use a full range of products adjusting for size of the repair and the current shop conditions (temperature). Hotter environments require slower products and vice versa.

Related articles and blogs on adhesive repair

These articles, reports, and blog posts have information to help you learn more about composites in the automotive and heavy-duty vehicle markets and the proper use of adhesives to repair them:

Making the repairs with adhesives is relatively simple, but it is important to understand the product being used and to carefully follow instructions to guarantee the best results. It’s more than just pumping in a product to glue parts together. If the repair procedure is done properly the first time, the repair will last for the life of the vehicle.

During the actual repair process, it is important to replace the fiber and to use it with adhesive for both aesthetics and structural integrity of the vehicle. Using a generous amount of fiberglass repair cloth in a heavy-duty composite repair is critical to eliminate read-through and to ensure that there isn’t a different coefficient of expansion in the area surrounding the repair, which may result in a “halo effect” or “bullseyes.”

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