The bulk density and apparent porosity of HBLT-70 aluminum carbon skateboard tiles were measured in industrial pure kerosene and tap water respectively. The results show that the apparent porosity measured using industrial pure kerosene as the immersion liquid is about 7.6% higher than that measured using tap water as the immersion liquid, but there is basically no difference in the bulk density measurement results between the two. The wettability of industrial pure kerosene to graphite is higher than that of tap water to graphite, so the degree of saturation of HBLT-70 aluminum carbon skateboard bricks is higher when impregnated in industrial pure kerosene.
Keywords: aluminum carbon slide gate plate tiles; immersion liquid; bulk density; apparent porosity
The current advancement of high-efficiency continuous casting technology and secondary refining technology has greatly promoted the development of the steel industry, but at the same time, it has also put forward higher requirements for the sliding nozzle system that accurately controls the flow of molten steel. As one of the important components of the sliding nozzle system, the slide plate directly controls the flow of molten steel. Theslide gate plate has been subjected to chemical erosion and physical erosion from high-temperature molten steel for a long time, and it is required to have good anti-erosion, anti-penetration and anti-thermal shock properties. Because the apparent porosity and volume density of a skateboard are closely related to its erosion resistance, penetration resistance and thermal shock resistance, they are also important indicators for early prediction and evaluation of slide gate plate performance. Therefore, accurately measuring the apparent porosity and volume density of the slide gate plate is particularly important for predicting the quality of the slide gate plate. The currently commonly used detection method is the hydrostatic weighing method. In actual operation, the saturation of the sample immersion has a great influence on the detection results. The main influencing factors include the concentration of the immersion liquid, temperature, surface tension, contact angle θ, as well as the vacuum pressure and immersion time during immersion. GB/T 2997-2015 “Test Methods for Volume Density, Apparent Porosity and True Density of Dense and Shaped Refractory Products” covers the volume and size ratio of the tested sample, the pressure value of the equipment and instruments, the immersion liquid and the immersion time. Detailed provisions. When there are no special requirements for testing, tap water is usually used as the immersion fluid for relevant testing. In actual use of slide gate plate, subject to service conditions, in order to extend the service life, carbon materials (graphite, carbon black, asphalt, etc.) with a mass fraction of 3% to 12% are usually added as improving agents to produce products with low porosity. , Aluminum carbon skateboard with high strength and good thermal shock resistance. Graphite has poor wettability in water, so the quality of the aluminum carbon slide immersed in tap water will have a certain impact on the test results. There has been a study on measuring carbon bricks using industrial pure kerosene with strong permeability as the impregnating liquid, and it was found that there is a big difference between the results of using tap water as the impregnating liquid. The author put the aluminum carbon slide brick samples into industrial pure kerosene and tap water to measure the apparent porosity and bulk density. To compare whether there are differences in the apparent porosity and bulk density of aluminum carbon slide gate plate tiles measured in two different immersion liquids.
First, weigh the mass of the sample, and then use the hydrostatic weighing method to calculate its apparent porosity and volume density. The bulk density ρb is the ratio of the mass of the dry material with pores to its total volume, and the unit is g*cm-3 or kg.m-3. Apparent porosity is the ratio of the volume of all open pores in a material with pores to its total volume.
The calculation formula of volume density ρb is
In the formula, ρing is the density of the liquid at the test temperature; m1 is the mass of the dry sample; m2 is the mass of the saturated sample suspended in the liquid; m3 is the mass of the saturated sample.
The calculation formula of apparent porosity ∏a is:
Test steps and methods
According to the regulations of GB/T2997-2015, the dry mass of the sample, the mass of the saturated sample in the suspension and the mass of the saturated sample m3 were measured respectively. Then according to formula (1) and formula (2), the bulk density and apparent porosity of the sample are calculated respectively.
Measurement of dry sample mass m1
The sample is dried in an electric drying oven at (110 ± 5) °C to a constant mass, that is, until the mass difference between the last two times does not exceed 0.1%, and is naturally cooled to room temperature in a desiccator. Before weighing, the dust and fine particles attached to the surface of the sample should be brushed away with a brush, and the mass of each sample should be weighed separately, accurate to 0.01 g.
Measurement of mass m 2 of saturated sample suspended in liquid
Place the sample into a vacuum container, evacuate it until the remaining pressure is less than 2500 Pa, and maintain it at this vacuum for about 5 minutes, and then slowly pour the immersion liquid into it within about 3 minutes until the sample is completely submerged. , continue to vacuum for 5 minutes, stop pumping, take out the immersion tank, and let it stand in the air for 30 min to fully saturate the sample. Quickly move the saturated sample into the immersion liquid in the container with an overflow tube. When the immersion liquid completely submerges the sample, hang the sample on the hook of the balance and weigh the mass of the saturated sample suspended in the immersion liquid, accurate to 0.01 g, and then measure the immersion temperature to an accuracy of ±1°C.
Determination of saturated sample mass
Take out the sample from the immersion liquid, carefully wipe off excess droplets with a cotton towel saturated with the immersion liquid, but do not suck out the liquid in the pores, and quickly weigh the mass of the saturated sample in air, accurate to 0.01 g.
Preparation before test
In order to make the test more representative and practical, the author chose the commonly used HBLT-70 aluminum carbon skateboard brick as the test object. The sample is the same batch of products produced by a company under the same process conditions. Three pieces were randomly selected as samples. . In accordance with the requirements of YB/T 5049-2019 “Skateboard Bricks”, the samples for measuring apparent porosity and volume density are prepared at the edge of the cast opening in the width direction of the brick. The sample is made into a rectangular parallelepiped or cylinder with a total volume of 50 to 200 cm3. The ratio of the longest dimension to the shortest dimension of the sample does not exceed 2:1. In order to facilitate the test, two standard specimens were cut from each of the three aluminum carbon skateboard tiles along the edge of the sprue. Marked as A, B, C and a, b, c respectively; that is, A and a, B and b, C and c are two parallel samples made from the same brick.
Immersion liquid selection
Industrial pure kerosene and tap water were used as the test immersion liquid, and the room temperature in the laboratory was set to (25 ± 2) °C. The density of kerosene was measured using PZ-B-5 liquid specific gravity balance to be 0.798 g*cn-3, and the density of tap water was 1.0 g.cm-3.
Test results and discussion
In order to make the test results comparable, the measurement should be carried out in the same laboratory by the same tester with the same instrument and under the same test conditions. That is, the temperature, vacuum degree, vacuum time, immersion time, and method of wiping off the sample surface for immersion during the test are exactly the same. The measured data and calculated apparent porosity and bulk density of HBLT-70 aluminum carbon skateboard tiles are shown in Table 1. After measuring with tap water, immediately put the sample into an electric drying oven and dry it to constant weight at (110±5)°C. Then use industrial pure kerosene as the immersion liquid, and follow the test conditions, operating procedures and methods when using tap water as the immersion liquid. The measured data and calculated apparent porosity and bulk density of HBLT-70 aluminum carbon slide gate plate tiles are shown in Table 2.
The influence of immersion liquid on the determination of volume density of aluminum carbon sliding plate
Comparing the test results in Table 1 and Table 2, it is found that the bulk density of the same batch of HBLT-70 aluminum carbon slide gate plate tile samples measured in tap water and industrial pure kerosene is almost exactly the same. It can be seen that the two liquids have no effect on the volume density determination of HBLT-70 aluminum carbon skateboard tiles. According to GB/T 2997-2015, bulk density is the ratio of the mass of dry material with pores to its total volume. The same batch of HBLT-70 aluminum carbon slide gate plate tile samples were used in the test. Therefore, the dry quality of the samples is basically the same. According to Archimedes’ law, the volume of the HBLT-70 aluminum carbon slide gate plate tile sample is equal to the volume of liquid displaced by the saturated sample. Calculated from formula (1), the bulk density of the HBLT-70 aluminum carbon slide gate plate tile sample measured in tap water and industrial pure kerosene is exactly the same.
Table 1 Apparent porosity and bulk density of HBLT-70 aluminum carbon skateboard tiles measured with tap water as immersion solution
Table 2 The apparent porosity and bulk density of HBLT-70 aluminum carbon skateboard tiles measured with industrial pure kerosene as immersion liquid
Effect of immersion liquid on the determination of apparent porosity of aluminum carbon slide gate platetiles
After comparing the test results in Table 1 and Table 2, it was found that the apparent porosity of the same batch of HBLT-70 aluminum carbon slide gate plate tile samples measured in industrial pure kerosene was about 7.6% higher than that measured in tap water. It shows that the immersion saturation of HBLT-70 aluminum carbon slide gate plate tile samples in different immersion liquids is different under the same measurement conditions. The wettability of industrial pure kerosene to the HBLT-70 aluminum carbon slide gate plate tile sample is better than that of tap water. This is because the wettability of the immersion liquid on the surface of the HBLT-70 aluminum carbon slide gate plate tile depends on the contact angle θ. When θ>Π/2, the solid repels the liquid; when θ<Π/2, the solid is affinity to the liquid; the smaller θ is, the higher the degree of liquid infiltration into the solid. The contact angle between kerosene and HBLT-70 aluminum carbon slide gate plate bricks is < Π/2, and is much smaller than the contact angle between tap water and HBLT-70 aluminum carbon slide gate plate bricks. In addition to the original voids during molding in the HBLT-70 aluminum carbon sliding plate, the volatile matter contained in the resin binder, additives, and impregnated asphalt decomposes, carbonizes, and escapes. This creates more pits and pores in the brick body, which also makes it more difficult for the immersion liquid to penetrate and saturate all the open pores. These tiny pits and capillary structures effectively increase their surface area, directly trapping a large amount of air on the surface of the HBLT-70 aluminum carbon slide tile sample, and converting part of the solid-liquid interface into a gas-liquid interface. Greatly increases the surface tension of the liquid. The surface tension of tap water is the largest among common liquids, much greater than that of industrial pure kerosene. Industrial pure kerosene has small surface tension, low viscosity, and strong penetration ability. It can penetrate into extremely small capillary pores, and can better infiltrate the HBLT-70 aluminum carbon slide tile sample and fully penetrate into the pores. In order to improve the performance of HBLT-70 aluminum carbon slide gate plate tiles, a certain amount of graphite is added to it. Since graphite is mainly a non-polar substance composed of non-polar hexagonal carbon network, it is a low-energy surface. The interaction force with water is smaller than the association energy between molecules, and the interaction with water is weak. Compared with tap water, industrial pure kerosene has better wettability and capillary permeability to HBLT-70 aluminum carbon slide gate plate tiles, and can fully saturate all open pores. Therefore, through experimental comparison, it was found that the apparent porosity of HBLT-70 aluminum carbon slide gate plate tiles was about 7.6% higher when industrial pure kerosene was used as the immersion liquid than when tap water was used as the immersion liquid.
(1) The apparent porosity of HBLT-70 aluminum carbon slide gate plate tiles measured when industrial pure kerosene is used as the immersion liquid is about 7.6% higher than when tap water is used as the immersion liquid. However, there is almost no difference in the volume density measurement results between the two.
(2) This measurement result has a reference effect on the selection of immersion liquid when measuring apparent porosity of other carbonaceous materials, and has certain guiding significance for designers and users in actual use.