Test method for performance of investment casting sol-silicon coatings

Measurement of Silica Sol Coating Viscosity

1.The concept of viscosity

It is the amount of time in seconds that the paint passes through the standard flow cup, also known as the viscosity of the paint in the flow cup.

2.Measurement of viscosity of silica sol coatings

   2.1Zahn Flowing Cup method

      2.1.1Measuring instruments

               The instruments that should be configured are:

               — —Zahn cup：4# cup，5# cup See figure 1

               — — stopwatch：accurate 0.1S

1: strap handle 2：support bar 3：stem of a cup 4：flow hole

Figure 1  Schematic diagram of Zahn cup composition

Table 1  4#/5# Zahn  Cup Specification

      2.1.2Detection process

         1)Before testing should visually check the appearance of the Zahn cup, should be kept clean, especially the cup cavity and outlet parts;；

         2)The Zahn cup should be placed in the paint and lifted and dipped back and forth (2-3) times so that its temperature is close to the temperature of the paint and the surface is fully wetted by the paint;

         3)The stopwatch should be set to zero, and then the Zahn cup should be placed in the middle of the paint bucket, and the bottom of the cup should be immersed to a depth of (100~200) mm, and then the surface of the paint should be raised smoothly and vertically upwards;

         4)In the Zahn cup bottom surface of the cup to leave the paint liquid surface of the moment to start timing, visual observation of the paint in the bottom of the cup about 10mm at the first breakpoint should stop timing, as shown in Figure 2, and record the outflow of time in seconds (read the number of seconds on behalf of the position of the viscosity value measured).

Fig. 2 Schematic diagram of timing points for coating viscosity measurement

         5)Measurements should be repeated at least 3 times, and after the results of continuous measurement error should not exceed 5%, the average value is taken for calculation;

         6)The Zahn cup should be cleaned with water immediately after the test and kept dry;；

   2.2operational requirement

         1)The paint to be tested for viscosity properties should be stirred well to ensure that it is pure and free of impurities (no wax chips, clusters or sand particles, etc.);

         2)Two Zahn cups should be prepared for testing, one for coating performance testing and one for periodic calibration of the testing cup. If the error between the calibration cup and the testing cup is found to be more than 5%, the testing cup should be replaced;

   2.3Standardized Flow Cup Method

Standard flow cup method should be implemented in accordance with the provisions of JB/T 4007, the Chinese standard cup is shown in Figure 3;

                          1: stem of a cup   2：flow hole

               Figure 3 Schematic diagram of the Chinese standard cup