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How to Significantly Reduce Surface Profile

An impossible case of surface profile.

The Case

A contractor was blasting a bridge last year and was faced with a serious issue: The bridge had previously been blasted with coarse steel grit and had a whopping 162µm profile. The contractor's specification called for a maximum profile of 125µm and it seemed impossible to achieve.

Step one was to reproduce the original results to assist in determining just how to reduce the profile.

By starting with an un-marred steel plate and marking it into three equal areas:

  1. Blasted with Copper Slag only.
  2. First blasted with Copper Slag. Second blast with SpeedBlast garnet.
  3. Blasted with SpeedBlast garnet only.

The Testing Procedure

Blast Area
Figure 1: Marking Areas
  1. We blasted the left two thirds of the plate (areas 1 & 2) with copper slag (used for test purposes only to reproduce the 162µm surface profile condition of the bridge).
  2. We then blasted the right two thirds of the plate (areas 2 & 3) with SpeedBlast garnet - this over blasted the middle one third, which had been already blasted with copper slag.
  3. The profile results for each section were then measured using X-Coarse plus TestexTM Tape.

The Results

Sample Area 1: Blasted with copper slag = 162µm (reproduced original bridge profile)

Sample Area 2: Blasted with copper slag and then with SpeedBlast garnet = 125µm (a 37µm reduction)

Sample Area 3: Blasted with SpeedBlast garnet only = 87µm

Blast Results
Figure 2: Blasted Plate

Our test showed definitively that after removing the existing coating with Speedblast Garnet the surface profile was reduced to 125µm!

NOTE: By whipping over the surface again using a pure SpeedBlast garnet, the profile of area two was further reduced to 112µm.

Did you know that the size of the abrasive is not the only contributor to surface profile?

Other main contributors to the surface profile are:

  • Nozzle Pressure
  • Hardness and density of abrasive
  • Steel tensile strength