Corrosion-Part Three

Why does steel corrode? Unless steel is protected it begins to corrode as soon as it is made from its raw materials and it is exposed to oxygen. This is called oxidation. If you want steel to have a long life, it needs to be protected from oxygen. The simplest way to stop steel from corroding is to completely coat it with paint or a protective film that keeps air and rain off all surfaces and out of the nooks and crannies of the vehicle. The way auto-makers protect their steel constructed vehicles is through a process called “electrodeposition,” which is completed after the vehicle’s metal parts are assembled and before the painting begins. As long as the metal is coated and the coatings are not breached, the steel will have a long resistance to corrosion.

If there is rust on the pinchweld, the cause is only one of two options; it is caused by bad body work or caused by the breaching of the painted surface by an auto glass installer. Rarely does corrosion happen by itself once the surface has been prepared and coated. With this in mind, we must acknowledge our culpability and develop our skills to avoid scratching the metal.
Here are some issues that we must avoid doing and guard against.

  • Use extreme caution when plunge-cutting.  Plunge-cutting is inserting a utility knife blade perpendicular to the pinchweld to cut a moulding off or make the cut out procedure easier.  It is sometimes necessary to cut off a moulding or encapsulation material to get to the glass edge and the best tool for that procedure is the utility knife. However, it should never be inserted to the point of scoring or scratching the metal surface below. If that blade scores the metal then the chance of successfully priming that scratch is very low. It would take tweezers and a considerable amount of time to properly prime the area. If you do not prime the area thoroughly, then corrosion will occur and undermine the entire bond.
  • When cutting out the glass part with a cold knife and tapered blade, remember that the taper designed into the blade will cause the blade to naturally move outwardly towards the pinchweld wall possibly causing damage to the wall of the pinchweld.  Make sure that you control your knife and blade so the vertical leg of the blade stays at the glass edge. It also may be good insurance to use padded/coated blades.
  • In close tolerance glass mountings, a wire may have to be used to eliminate the chance of paint damage. If a cold knife is chosen, make sure before you pull the knife that the blade will clear the pinchweld wall.
  • When stripping the existing urethane to the proper height, make sure that you use the “pull and cut” method of strip-out. If you pull the existing urethane while stripping it from the pinchweld it serves two purposes; it indicates if there is a bond weakness and it allows for a more controlled strip-out. It makes no difference whether you use a utility knife or a scraper the “pull and cut” method makes the strip-out easier and makes it less likely that damage to the pinchweld will occur.
  • Using power tools from the outside of the vehicle allows for the technician to see where the blade exits the bead. This allows the technician to control the tool rather than work blind and cause damage to the lower pinchweld wall or firewall.
  • I have watched installers use a reciprocal blade cutting tools on an “L” shaped pinchweld that badly damaged the pinchweld wall. I have even seen them puncture the metal. This should be the very last resort to glass removal. First, they are cutting it blind and the blade can easily damage the roof area of the vehicle. Second, I don’t care how good you are, the wall of the pinchweld will be damaged seriously and no amount of primer can completely stop the metal from corroding. Third, it just looks and sounds bad to the customer that is watching.

Obviously, the best way to deal with corrosion is it to eliminate its cause and improve your skills. I know that corrosion will always be a problem but if all of us make strides in our ability to avoiding breaching the paint and coatings, we can eliminate a lot of it and get back to what we do best and that is putting in auto glass correctly and safely.

Next week is prevention.