Using Hot dip galvanization process, estimate the amount of zinc being coated on the steel sheets.
The amount of zinc coated is directly proportional to the protection it offers against corrosion on the steel sheet. This test is used in the determination of the mass of zinc coated on a steel sheet, and the results expressed in S.I units. Customers can use this test to determine their desired coating and make changes to the product if required.
A 90/ A 90M – Standard test method for weight [mass] of coating on Iron and Steel Articles with Zinc or Zinc-Alloy Coatings.
All staff involved in the testing procedures should adhere to the safety regulations established by the laboratory and should be alert to the possible dangers around them.Protection clothing, gloves and goggles should be worn all the time when working in lab. So each personnel in the lab are responsible for their own safety and actions.
Warning: Caution should be taken when handling large amounts of samples. To avoid inhaling hydrogen and other toxic gases like stibine (SbH3), fumes of Hydrochloric acid during the stripping process, a fume hood with proper ventilation should be used.
- Vernier calipers
- Analytical balance
- Digital thermometer
- Water bath
- Laboratory guillotine
5.Reagents and their preparations:
- Deionised H2O
- Hydrochloric acid (12.1 mol/l) – reagent grade
- Hydrochloric acid (1:1) – 500ml of 12.1mol/l HCL, dissolved in 500ml of deionised H2O
- Naphtha solvent – reagent grade
- Methanol – commercial grade.
- Cut the specimen to an area of 3330mm (57.7±0.1mm square).
- The area is measured using the vernier calipers and the readings recorded on a data sheet.
- The sheet of the sample is cleaned with naphtha
- Rinsed with methanol and left for drying in a dry area.
- And the preliminary observations about the thickness of sample are reported.
- All precautions should be taken in order to avoid any contaminants. The testing should be done in moisture free environment. The tests should be done in duplicates, just for the sake of cross referencing with the results.
- The sample is weighed and recorded on the data sheet(this is W1)
- The sample is cleaned using naphtha solution and rinsed with methanol and subjected for drying.
- 90% of dil.HCL is used to strip the sample if it contains less than 90% zinc
Or HCL – SbCl3 solution is used if the sample has more than 90% zinc on it.
- The samples are immersed individually into the stripping solution and the temperatures for the solution maintained at 380
- And the sample is left in the solution until the formation of violent bubbles stops.
- The sample is next washed with scrubbing under running water.
- Followed by a dip in hot H2O and blow dry.
- The final weight of the sample is determined (this is W2), which is obtained after stripping, along with the area of the metal sheet and recorded on the data sheet.
Formula: C= [(W1- W2)/A] ×K
Where, C = Mass of coating g/m2 of sheet,
W1= Mass of sample before stripping in g,
W2= Mass of sample after stripping in g,
A = Area of sheet in mm2
K = Constant = 1×106 in mm2
Calculating mass of zinc coating
Formula: C=[(W1- W2)/W2] x T x K
Where, C = weight (mass) of zinc coating in g/m2 of sheet,
W1 = Original weight of sample in g,
W2 = Weight of stripped sample in g,
T = Thickness of sheet in mm,
K = Constant= 7.83 × 103
- Report the preliminary observations about the weight of zinc coating.
- Report average mass value of the samples, to the nearest 1g/m2.
- The result is validated by the supervisor.
- Any special notes are to be specified for recording purposes.
- Calculations are done after receiving all the data.
- The precision of the test method is determined.
- The repeatability and reproducibility of the test in this case is established to be 49/m2 and 60/m2
- And the error of 5% is accepted.
- If the criteria are not met, the sample is redone and the old one will be rejected.