Determination of corner coverage (see GB6554-86)
This method is to test the sample coated with the specified coating process and conditions. Under the specified plane coating thickness, the ratio of the film thickness at the corner of the rod (9° acute angle) to the plane coating thickness.
(1) Equipment
Oven, constant temperature and humidity Test Chamber.
(2) Sample
The base material is steel, the size is 10mmX10mmXl50mm, ground into a square, the size is accurate to 0.025mm. The steel should meet the requirements of GB700-79 "Technical Conditions for Ordinary Plain Steel". Coating film thickness 0.25~0.30mm.
(3) Sample preparation steps
Measure and record the lengths of the 2 planes and 2 diagonals of the 3 wire rods (see A, B, C and D of Figure 8 in Appendix III), with an accuracy of 0.01mm. The measurement point is 38mm from the bottom of the rod, and the ambient temperature is (23±2)°C.
Use a steel wire to pass through the hole at the upper end of the rod. Hang them in the oven for preheating, and heat at the specified temperature for 30 minutes or until the required temperature is reached. The powder in the fluidized bed should be clean and dry, the fluidizing gas source should be fully dehumidified, and the powder height after fluidization should be at least 200mm.
Coat the rods one by one, that is, take the rods out of the oven and stop for (4±0.5) s, then immerse them in the fluidized bed powder, and rotate along the rod axis at a speed of 0.5 r/s within a diameter of 50 mm. Take it out after the plane thickness is required, and the speed of the rod entering and leaving the fluidized powder is not lower than 0.3m/s, so as to ensure uniform coating. Cure according to the required temperature and time. Cool to (23 ± 2) ℃, and then measure.
(4) Results
Take the average values of the 2 planes and 2 diagonals measured before and after coating each square rod. Subtract the value after coating from the value before coating, and then divide by 2 to obtain the thickness of the plane coating film and the corner coating thickness. Then calculate as follows:
Accurate to integer The error of the three calculated values should be within ±5%, otherwise all the results shall be invalidated and the sample shall be remade.
The report lists 1. Column content: powder model; preheating temperature; dipping time; curing temperature and time; film thickness by plane method; middle value, maximum value and minimum value of 3 corner coverage rates.
