Working on a victorian railway bridge, as part of a restoration project. This bridge was in a poor state and needed to be restored in order to preserve its history.
SAND BLASTING OR ABRASIVE BLASTING
This structure needed to be preserved. So I was contacted and asked to undertake the first stage of the project, Abrasive Blasting or Sand Blasting the main structural areas of the bridge. These areas had to be fully blasted prior to inspection & any repair work being carried out.
HIGH PRESSURE ABRASIVE BLASTING
The main areas of this steelwork where very corroded, with heavy deep rust pitting and scale, making this structure a (Grade “D” Substrate) The class of blast required was SA 2.5
(A thorough clean with less than 5% shading) SA 2.5 is a high class of blast for such a poor substrate.
OBJECTIVE
The project plan, was to remove all the rust pitting & scale from the surface of the main structural parts of the structure. So that a full inspection could be carried out. Then all the necessary repairs could be undertaken. These areas were blasted with a nozzle pressure over a 100 psi @ the nozzle. The blast media of choice for this job was iron silicate. The structure used five tons of blast media, just to remove the heavy rust pitting and scale from the lower and underside main beams and braces. By looking at the photos in the photo gallery, you will see there was a lot of rust and scale to remove from this substrate, to gain a SA 2.5 class of blast. Some parts of the bridge, had rust scale up to 1/2 inch thick in some places on the underside.
At the start of each day the temperature was tested (humidity levels) & the nozzle pressure was measured using a hypodermic blast pressure gauge, to test the true blasting pressure at the nozzle. Anything less than 100 psi at the nozzle is inefficient in many ways, both in velocity (the speed of the air exiting the nozzle) With anything less than 100psi at the nozzle, the consumption of fuel and blast media increases, because the blast media impacts the surface of the steel with less velocity and force, requiring you to spend longer blasting the same given area. This all boils down to the simple fact of efficiency.
