This standard specifies the test conditions and methods for the sieve residue, standard consistency, setting time, flexural strength and compressive strength of azurite powder for ceramic molds. This standard applies to semi-hydrated gypsum powder for ceramic injection molding. QB/T 1640-1992 Test method for physical properties of gypsum powder for ceramic molds QB/T1640-1992 Standard download decompression password: www.bzxz.net

Light Industry Standard of the People's Republic of China
Test Method for Physical Properties of Gypsum Powder for Ceramic Moulds 1 Subject Content and Scope of Application
QB/T1640—1992
This standard specifies the test conditions and methods for the sieve residue, standard consistency, setting time, flexural strength and compressive strength of gypsum powder for ceramic moulds.
This standard applies to semi-hydrated gypsum powder for ceramic injection moulds. 2 Reference standards
GB/T177 Cement mortar strength test method
GB/T3350.3 Cement physical testing instrument Electric flexural testing machine QB/T1639 Gypsum powder for ceramic molds
3 Test conditions
3.1 The temperature of the test room, instruments and materials (gypsum powder, water) is (20 ± 5 ° C, and the relative humidity of the air is 55% to 75%. 3.2 Sampling is carried out according to the method specified in QB/T1639, and the samples should be kept in a sealed state. 3.3 All All test items should use clean, fresh water. 3.4 The containers and molds used in the test should be impermeable and made of materials that do not react with calcium sulfate (glass, copper, stainless steel, hard steel, etc.). 4 Instruments and tools
4.1 A copper wire mesh standard test sieve with a sieve bottom receiving tray and sieve cover (the size of the sieve holes should be selected according to the product standard). 4.2 A case scale with a maximum weighing capacity of 10kg and a sensitivity of 10g; a pharmaceutical balance with a maximum weighing capacity of 500g and a sensitivity of 0.5g; a sensitivity of 0.01 bZxz.net
4.3 An electric heating blast drying oven with a maximum temperature not less than 200℃. 4.4 A tube with an inner diameter of (50±0.1)mm and a height of (100±0.1)mm, and a piece of paper with a series of concentric circles with diameters of 50 to 250mm and intervals of 10mm.
4.5 2300mm×300mm and 150mmX150mm glass plates, three each. 4.6 A stainless steel knife with a length of about 100mm, a width of about 16mm, and a back thickness of about 1.5mm. 4.7 2000mL, 1500mL, and 500mL stirring containers, and 500mlL, 100mL, and 10mL measuring cylinders, one each. 4.8 In accordance with GB /T3350.3 flexural testing machine. 4.9 Compression testing machine with pressure not less than 200kN and indication error not greater than ±1.0%. 4.10 Two sets of test molds in accordance with GB/T177. 4.71 Two dryers; one stirring rod; one stopwatch; one scraper and one soft brush. 5 Determination method
5.1 Determination of sieve residue
5.1.1 Take about 60g of the sample to be tested and place it in an electric blast drying oven, dry it at (40±4)°C to constant weight, and place the dried sample in a dryer approved by the Ministry of Light Industry of the People's Republic of China on January 15, 1993 and implemented on September 1, 1993
to cool for use.
QB/T 1640-1992
Note: When the difference between the two weighings with an effective drying time of 1 hour does not exceed 0.2g, the weight is constant. 5.1.2 Accurately weigh (50±0.1)g of the sample and place it in the sieve. Use your fingers to gently crush the lumps, cover the sieve cover, put on the sieve plate, and operate as follows.
-Hold the sieve with one hand, tilt it slightly, and shake the sieve to make it hit the other hand. The shaking speed is 125 times/min, and the amplitude of the sieve swing is about 20cm. After every 25 shakes, the sieve should be rotated 90° in a certain direction to evenly spread the sample (it can also be sieved by mechanical vibration). Sieve until less than 0.1g of the sample passes through the sieve within 1 minute. Weigh the mass of the sieve to an accuracy of 0.01g. 5.1.3 Calculate the sieve residue according to formula (1):
Ws=m×100
Wherein: W. sieve residue, %,
Original mass of the sample, g
Mass of the material on the sieve·g.
5.2 Determination of standard consistency
5.2.1 Press a 300mm×300mm glass plate horizontally on a paper with concentric circles drawn on it, slightly moisten the copper tube and the glass plate with water, and then place the copper tube upright so that its inner circle coincides with the concentric circle with a diameter of 50mm. 5.2.2 Weigh (300 ± 1) g of the sample, sprinkle the gypsum powder evenly into a container containing the required amount of water for the predetermined consistency within 305°C, let it stand for 305°C, then stir quickly for 1 minute, immediately inject it into the copper tube, scrape the surface with a scraper, and then lift the copper tube vertically upward (the operation time from the injection of the slurry to the lifting of the copper tube should not exceed 20 seconds, and the height of the copper tube lifting should be about 20 cm). 5.2.3 Observe the expansion diameter of the slurry. When the average value of the readings of the cake diameter formed by the slurry on the two vertical lines reaches (220 ± 5) mm, it meets the requirements. If the first measurement does not meet the requirements, the amount of water can be appropriately increased or decreased according to the size of the cake diameter, and the measurement can be repeated until it meets the requirements, and then repeated once more.
5.2.4 Calculate the standard consistency according to formula (2):
m=×100
Where: C—
Standard consistency, %;
Amount of water added, :
Mass of gypsum powder, g.
5.3 Determination of setting time
(2)
5.3.1 Calculate the gypsum powder sample required for 100ml of water according to the standard consistency obtained in 5.2, pour the water into a 500ml container, sprinkle the sample evenly into the water within 1min, let it stand for 30s, stir rapidly for 30s, and then pour it into three test cakes with a diameter of 100~120mm and a thickness of about 5mm on a clean glass plate while stirring. In order to make the size of the test cake meet the requirements, the three glass plates after grouting can be swung side by side.
5.3.2 Use a knife to cut the test cakes. First, cut the first and third test cakes every 30 seconds. When the initial setting is approaching, cut the second test cake every 10 seconds. The scratches must not overlap or cross each time. The knife must be wiped clean with a cloth after each cut. During the entire operation, the test cakes must not be vibrated or moved. When the slurry on both sides of the scratch on the second test cake just stops closing, it is the initial setting. The time interval from the start of the sample being put into water to the initial setting is the initial setting time.
5.3.3 Use the thumb to wipe the three test cakes after the initial setting twice with a force of about 50N. When the first and third test cakes are wiped, it is judged that the final setting is approaching. The second test cake is used as the one. The final setting is when there is no water on the edge of the mark. The final setting time is the time interval from the start of the sample being put into water to the final setting. 5.3.4 The test result of setting time is expressed in minutes. When the number of seconds exceeds 30, it can be rounded down to 1 minute. 5.4 Determination of flexural strength
5.4.1 Calculate the amount of gypsum powder and water required for the three test pieces according to formula (3) and formula (4), and weigh them separately. Pour water into a 196
QB/T1640—1992
2000mL container, sprinkle gypsum powder evenly into the water within 30s, let it stand for 30s, then stir quickly for 1min, immediately inject gypsum slurry into the mold, lift one end of the mold by hand about 10mm and then drop it, and vibrate it 5 times to eliminate bubbles. When it reaches the initial setting, scrape off the overflow with a scraper. Demould after final setting.
mp= 0. 4 C
Where: mp—mass of gypsum powder.g
mw—water content·g;
C—…--standard consistency of the sample,%.
5.4.2 The specimens for testing wet strength and dry strength should be prepared separately, three for each. After demolding, the specimens for testing 2h wet strength should be placed vertically on the laboratory workbench, and tested on the flexural testing machine 2h after the gypsum powder is put into water. After demolding, the specimens for testing dry strength should be placed in an electric hot air drying oven and dried at a temperature of (40±4)°C to constant weight. After constant weight, the specimens are placed in a dryer to cool to room temperature and tested on the flexural testing machine.
Note: Constant weight is achieved when the difference between two weighings with an effective drying time of 24h does not exceed 0.5g. 5.4.3 After calibrating the instrument according to the instrument's operating procedures, place the test piece (pay attention to making the force-bearing surface of the test piece face the die surface, and ensure that each side of the test piece is perpendicular to the three shaft rollers on the instrument fixture). Turn on the instrument and directly read the flexural strength limit value of the test piece when it is destroyed from the instrument's reading scale.
5.4.4 Record the flexural strength values ​​of the three test pieces and calculate their average value. If the relative deviation between one of the three values ​​measured and the average value of the three values ​​is greater than 10%, take the average value of the other two values ​​as the test result; if the relative deviation between two or more of the three values ​​obtained and the average value is greater than 10%, re-sample and test. 5.5 Determination of compressive strength
5.5.1 Place the half test piece obtained after the flexural test in the compression fixture (the die surface of the test piece should be perpendicular to the pressure surface, and the pressure area is 40.0mmX62.5mm), and place the compression fixture together with the test piece on the instrument. Turn on the instrument, let the specimen break within 20-40 seconds, and record its failure load.
5.5.2 Calculate the compressive strength of the six specimens according to formula (5). P
Where: R. - compressive strength, MPa;
P—destructive load, N.
5.5.3 Calculate the average compressive strength of the six specimens. If the relative deviation between one of the six values ​​measured and the average of the six values ​​is greater than 10%, the average of the remaining five values ​​is taken as the test result; if the relative deviation between two or more of the six values ​​measured and the average is greater than 10%, re-sampling should be carried out. Additional remarks:
This standard was proposed by the Quality Standards Department of the Ministry of Light Industry. This standard is under the jurisdiction of the National Ceramic Standard Promotion Center. This standard was drafted by the Ceramic Industry Science Research Institute of the Ministry of Light Industry and the Jingdezhen Gypsum Mold Factory. The main drafters of this standard are Shen Wei, Yu Zhen, and Li Feng. From the date of implementation of this standard, the former Ministry of Light Industry standard QB972-1986 "Test Methods for Physical Properties of Stone for Daily Ceramic Moulds" shall be invalid.
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