IH Hood Video
Several other posts have documented the work I performed on my 1993 International Truck Hood. I also took some video and recently got it all put together and posted on Youtube. Hopefully you can learn a couple of things.
The SMC hood was ground in preparation of work, and then I used epoxy and fiberglass to complete the work and restore the structure and shape back to original for this truck hood.
IH Hood Repair– Passenger Corner
One of the repairs on my International Hood was for the passenger corner. This portion of the hood was damaged before I got it, and was COMPLETELY MISSING!
Time, effort, epoxy, and fiberglass, allowed me to successfully completed the repair. This SMC hood will be repaired as good as new!
Damaged area to be repaired
The hood was placed upside to allow for work access. The repair area had several cracks and breakage areas. The repair began with surface preparation.
Surface Preparation on the repair area
I used a grinding disc to remove material on the front and back side of the repair to scarf the repair into the large area. Good surface preparation gives us a clean area that can hold a bond and create a transition area. I also drilled some holes in the end of the cracks to stop their propagation.
The back side was prepared too
The back side was prepared for repair by grinding the surface to allow for good bonding by the epoxy resin and glass reinforcement.
Beginning to add material
I started to add epoxy and fiberglass back onto the fender. I had to gradually move back out to where the existing fender used to be. I worked both sides bit by bit and allowed it to start curing before adding more.
Getting the shape back
I actually went a bit beyond the shape I needed. This allowed me to get the surface planes in the right spot, and later return and trim back the proper hood edge.
Back side getting rebuilt
The back side of the repair also got transitioned into the hood and out to meet the front repair area.
Grinding the repair
After most of the rebuilding was complete, some grinding got it back into shape to allow an evaluation of the repair progress.
Grinding on the back
The back side was cleaned up as well, getting the appropriate part thickness back to where it was originally intended. A nice transitioned surface was created, and all sharp edges were removed.
Bodyfiller for cosmetics
I used some bodyfiller to smooth the repair and restore the cosmetics of the hood. I could also have used epoxy, and it would have bonded better. Polyester bodyfiller is less expensive, easier to apply, and easier to sand. I smoothed the surface and feathered it back into the surrounding area to allow for a consistant surface.
Application of Primer-Surfacer
Urethane Primer-Surfacer is applied to the whole area to allow for removing the sanding/grinding scratches and preparing the surface for paint application.
The repair is complete, and the hood looks back like it was original. This repair, and many others, can be detected with some investigation of the back side of the repair area. This will be a very durable repair and will last as long as the rest of the composite body panel.
Composite electrical box
One of the composites applications that I found in a junkyard was a composite electrical box. It was discarded from a former use as an enclosure for electrical equipment in an industrial factory. Other than some minor discoloration and all of the holes from conduit, it is as good as the day it was new.
The advantages of using composites in this application include non-conductivity, protection from impact, and the ability to resist corrosion in tough environments. This is why it has outlived it’s factory setting.
Composites enclosure
An item like this where it has a good surface finish on both sides is going to be made in a set of matched-mold dies in a high-pressure and high-temperature press. It is likely to be manufactured with the Sheet Molding Compound (SMC) process, though Bulk Molding Compound (BMC) could also be at work.
Electrical panel enclosure
You can see on the front door all of the holes from its former installation. Holes on the side were used as well. It was customized for its application with all of the holes, and a new unit would arrive “blank,” without holes, as most applications are customized. The composite can be cut and drilled with metal working tools such as drill bits, holesaws, and saw blades.
Working with Chopped Strand Mat
One of my projects is repairing a composite hood for a large International Medium-Duty truck. This hood is made of SMC, and is damaged in various locations to various degrees. In doing the repairs, I am using epoxy resin and glass reinforcement. The fiberglass reinforcement I am using is referred to as Chopped Strand Mat, and is the 3 oz. per square foot version.
Chopped Strand Mat
The chopped strand mat is made up of random glass fibers held together with a light binding material. A good pair of scissors can cut the glass into manageable sizes, though the scissors will be dull when you are finished. The chopped strand mat can also be torn by hand. This leaves a “feathered” edge to create nice transitions between the patched areas and the existing surface. Pieces that are cut will leave a silhouette that will show and may require other methods to make it disappear.
The first thing that I checked was to make sure the glass was compatible with the epoxy resin. The package told me so, but I also did a small test sample to ensure that the epoxy would mix with it, was workable, and would harden properly. Testing away from the actual part can save many potential headaches and pitfalls.
Applying the glass and resin is relatively easy. Thoroughly mix some resin and apply it to the properly prepared surface (clean, dry, and sanded). Tear off an appropriate size piece of glass and place it on a piece of cardboard. Use a cheap paintbrush to get the glass wet with resin. Flip the glass over, and wet the backside. The glass will go from white to transparent on the cardboard. Now lift the glass from the cardboard and apply it to the area with the resin recently-applied resin. Use the brush to push it down against the surface to get as much contact area as possible.
Additional layers can be applied on top to build thickness, making sure to create a nice transition and limiting air bubbles in the laminate.
SMC Truck Fender
SMC (Sheet Molding Compound) works well for heavy duty truck parts, especially ones requiring complexity, strength, and impact resistance. One of the projects I am working on is a heavy truck with these SMC parts, including a hood and a driver’s and passenger’s truck fender extensions. Each of these SMC parts is very complex in geometry because of its complex application. The following is a picture of one of the SMC fender extensions.
SMC Truck Fender Extension
This SMC part is all one single molded piece, having very complicated geometry. It can also be noted that there are not any undercuts, i.e. the mold can open and close without having to move around the part. It has a mostly constant cross section, is not supported by any metal struts, and is attached to the cab by three bolts. The geometry and details to match the cab and hood styling are molded-in so that the part can be painted and bolted on the truck.
If a part needing this much complexity was manufactured with sheetmetal, it would have many more pieces of the assembly and much more bracing. Metal would also not have the resistance to corrosion and impact that is enjoyed by this composite part.
This fender extension is from a truck that has been on the road since 1993, with over 270,000 miles on it. This part has been in the wild for over 15 years, and has been exposed to tons of road salt, debris from the tires, and lots of other environmental exposures. It has survived well, only needing an update in paint to refresh its look.
Another great application of composites!
The Green Aspects of SMC
Sheet Molding Compound (SMC) is used to create many composite parts especially for the transportation industry, and contributes heavily to a positive environmental impact. SMC has been developed over the last 25 years to replace steel/sheet metal mostly in transportation applications. It is widely used in many heavy duty semi truck hoods, agricultural equipment, and pickup trucks, SUV’s and muscle cars.
The main goal of this substitution is to reduce weight, which improves fuel efficiency. Other positive side effects include fewer assembly operations, additional design freedom, dent and impact resistance, and the elimination of corrosion. Several “green” resin formulations have been introduced that make use of bio resins, which use much more renewable resources such as soy products. The fillers and reinforcements in this material can also be made from recycled and renewable materials.
SMC has overcome several hurdles in order to get to its present use and application. General acceptance and education had to be proven to the OEM manufacturers and consumers. Paint application and adhesion was one large consideration that had to be proven out. There were issues with popping and blistering from the SMC surface. Making sure the SMC parts held dimensions and aesthetics was also an important milestone.
SMC has become widely used today for many applications, and will find its way into many more. The weight saving aspects are paramount for reducing fuel consumption. The anti-corrosion and dent resistance are loved by consumers.
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