Some standard content:
JB/T8508—1996
This standard shall be implemented from July 1, 1997. Electrical grade magnesium oxide and its products shall comply with the provisions of this standard from January 1, 1998.
This standard is proposed by the National Technical Committee for Standardization of Industrial Electric Heating Equipment. This standard is under the jurisdiction of Xi'an Electric Furnace Research Institute of the Ministry of Machinery Industry. The drafting units of this standard are Shanghai Zhentai Chemical Plant and Yangzhou Jiangdu Xingguang Electric Appliance Co., Ltd. The main drafters of this standard are Li Zaixing and Zong Wei
This standard was first issued on November 7, 1996. This standard is entrusted to Xi'an Electric Furnace Research Institute of the Ministry of Machinery Industry for interpretation. 1 Scope
Machinery Industry Standard of the People's Republic of China
Electrical Grade Magnesium Oxide
JB/T8508--1996
This standard specifies the requirements for electrical grade magnesium oxide and its products, including product classification, technical requirements, test methods, inspection rules, ordering and supply, etc.
This standard applies to electrical grade magnesium oxide for tubular electric heating elements or other electrical products manufactured in accordance with JB4088 and JB/T2379. Electrical grade magnesium oxide in tubular electric heating elements for use in special occasions shall comply with the special requirements of the corresponding standards in addition to complying with this standard.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. At the time of publication of the standard, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB1234-85
JB4088—85
High resistance electric heating alloy
Daily tubular electric heating elements
JB/T2379-93 Metal tubular electric heating elements
3 Definitions
This standard adopts the following definitions.
3.1 Electrical grade magnesium oxide
refers to the electro-melted crystallized magnesium oxide block which is crushed and mixed with different particle sizes (mesh) in a certain proportion, and is directly or modified and used in tubular electric heating elements as an insulating medium for heat conduction at high temperature, hereinafter referred to as magnesium oxide. 3.2 Electrical grade magnesium oxide products
Due to the needs of structural design and process processing, magnesium oxide is first processed into a finished product with a certain shape and strength, and the performance of magnesium oxide is basically not damaged, hereinafter referred to as products.
3.3 Test electric heating element
In order to test the relevant properties of magnesium oxide, a special tubular electric heating element is processed according to the specified design and production method, hereinafter referred to as element 3.4 Magnesium oxide modification
refers to the process of targeted doping during magnesium oxide electromelting, coating magnesium oxide with a layer of substance, or doping magnesium oxide to improve certain properties of magnesium oxide without affecting its use, or overall improvement of magnesium oxide performance. 3.5 Loss on ignition, %
The percentage of the original weight of magnesium oxide that has been removed by heating and burning is called loss on ignition.
3.6 Flow rate, s/100g
The time required for 100g of magnesium oxide to naturally pass through a standard funnel hole. 3.7 Tap density, g/cm
The density of magnesium oxide measured by passing through a funnel hole that is the same as the flow rate measurement and flowing into a standard pipe vibrating at a specified frequency, amplitude and time.
3.8 Compacted density, g/cm2
The density measured by cutting a section of the element. JB/T8508—1996
3.9 Sintering index, g
indicates the numerical value of the sintering degree of magnesium oxide at a specified temperature. Its value is equal to the sum of the weight added to the probe and the mass of the probe when a specially shaped probe penetrates the sintered magnesium oxide to a predetermined depth. 3.10 Water absorption, %
refers to the water absorption capacity of magnesium oxide under steam erosion. It is expressed as the percentage of the increase to the original weight. 3.11 Working temperature (T), ℃
The maximum temperature allowed on the heating surface of the component so that the component is not damaged within the specified life cycle when the internal heating is powered on. 3.12 Overheating test
The temperature of the component surface exceeds the working temperature by 200℃ (but the temperature of the component surface shall not be higher than 1000℃) when the internal heating is powered on, and is maintained for 0.5h.
3.13 Thermal shock test
Power on and internal heating to make the surface temperature of the component quickly reach the working temperature and maintain it for 0.5h. The heating rate shall not be less than 200℃/min. 3.14 Magnesium oxide insulation resistance, Mα
The insulation resistance of the component tested by the prescribed method is called magnesium oxide insulation resistance, which is divided into insulation resistance at working temperature, room temperature and humid state.
3.15 Insulation withstand voltage strength
The insulation withstand voltage strength of the component tested by the prescribed method is called magnesium oxide insulation withstand voltage strength, which is divided into insulation withstand voltage strength at working temperature, room temperature and humid state.
3.16 Leakage current, mA
The leakage current of the component tested by the prescribed method is called magnesium oxide leakage current, which is divided into leakage current at working temperature, room temperature and humid state.
3.17 Life, h
The cumulative working time of the component under power on and internal heating at working temperature until it is damaged. 3.18 Accelerated life test
Power on the internal heating to make the surface temperature of the component reach 927℃, and measure the electrical insulation impedance (mainly insulation resistance) of the component or the leakage current of magnesium oxide in the heating and cooling cycle until the test is damaged. 3.19 Damage
A component is considered damaged if it has any of the following conditions: a) The insulation withstand voltage is lower than 2000V, the leakage current value is greater than 5mA or the insulation resistance is lower than 1Mα, and it is not recoverable; b) The outer shell emits flames and molten materials, the surface is severely corroded or other damage that does not allow recovery. 4 Product classification
4.1 Classification
Magnesium oxide is divided into the following four categories according to its production method and main use: a) Ordinary magnesium oxide
b) Low temperature moisture-proof magnesium oxide
c) Medium temperature moisture-proof magnesium oxide
d) High temperature magnesium oxide
4.2 Classification
Classification code P;
Classification code D;
Classification code Z;
Classification code G.
Magnesium oxide is divided into three grades: A, B and C according to the content of ferromagnetic impurities. 4.3 Model
JB/T8508-—1996
The model of magnesium oxide and its meaning are as follows:DMgO
5 Technical requirements for magnesium oxide
5.1 Chemical composition
The main chemical composition of each type of magnesium oxide shall meet the requirements of Table 1. Table 1
Ordinary magnesium oxide
Low-temperature moisture-proof magnesium oxide
Medium-temperature moisture-proof magnesium oxide
High-temperature magnesium oxide,
5.2 Content of ferromagnetic impurities
The content of ferromagnetic impurities in magnesium oxide shall comply with the following provisions: Grade A: ≤0.030%
Grade B: ≤0.015%
Grade C: ≤0.005%
5.3 Particle ratio
The supplier must provide the particle ratio.
The purchaser may require the supplier to provide a special ratio. This standard recommends the following particle ratio:
40～60
40~140
40～200
40~325
32±7%
55±7%
80±6%
90±6%
97±3%
5.4 Loss on ignition
The loss on ignition of magnesium oxide should not be greater than 0.2%. 5.5 Water absorption
The water absorption of magnesium oxide shall not be higher than the following provisions: 10
Enterprise code
-Design serial number
Grade code
Working temperature, ℃
Classification code
Electrical grade magnesium oxide
SiO, etc.
Ordinary magnesium oxide
Low temperature moisture-proof magnesium oxide
Medium temperature moisture-proof magnesium oxide
High temperature magnesium oxide
5.6 Sintering index
JB/T8508-1996
The sintering index of magnesium oxide should be 100±20g. The buyer can ask the supplier to provide a special sintering index. 5.7 Flow rate
The flow rate of magnesium oxide should not be greater than 45s/100g. 5.8 Tap density
The tap density of magnesium oxide should not be less than 2.3g/cm3. 5.9 Compacted density
The compacted density of magnesium oxide should not be less than 3.05g/cm3. 5.10 Working temperature
The supplier must provide the working temperature of magnesium oxide. This standard specifies the working temperature ranges of various types of magnesium oxide as follows: Ordinary magnesium oxide
Low-temperature moisture-proof magnesium oxide
Medium-temperature moisture-proof magnesium oxide
High-temperature magnesium oxide
5.11 Insulation resistance
300～600℃
300500℃
>500~800℃
>8001100℃
The insulation resistance of various types of magnesium oxide shall not be lower than the values specified in Table 2. Table 2
Ordinary magnesium oxide
Low-temperature moisture-proof magnesium oxide
Medium-temperature moisture-proof magnesium oxide
High-temperature magnesium oxide
5.12 Insulation withstand voltage
Working temperature
Magnesium oxide shall be able to withstand the following specified test voltage of 50Hz, basic sinusoidal wave for 1min, and the operating current of 2mA without flashover and breakdown.
Working temperature
Note: The purchaser may also require testing at 60Hz. 5.13 Leakage current
The leakage current of magnesium oxide shall not exceed the value specified in Table 3. 5.14 Thermal shock
Magnesium oxide shall be able to withstand the thermal shock test. The components shall not be damaged after the test, and the electrical performance shall still meet the requirements of 5.11, 5.12 and 5.13. 11
Ordinary magnesium oxide
Low-temperature moisture-proof magnesium oxide
Medium-temperature moisture-proof magnesium oxide
High-temperature magnesium oxide
JB/T8508--1996
Working temperature
5.15 Overheating
Magnesium oxide should be able to withstand overheating tests. After the test, the components shall not be damaged, and the electrical properties shall still meet the requirements of 5.11, 5.12, and 5.13. Note: If thermal shock and overheating tests are required at the same time, the two can be combined into thermal shock first and overheating test later. 5.16 Thermal conductivity
The thermal conductivity of magnesium oxide should not be less than 2W/m℃. The test temperature is selected in the range of T minus 100℃ to T plus 50℃. Two points T, and T, and the difference between T, minus T, is 110℃. The test temperature of high-temperature magnesium oxide is T, equal to 925℃, and T, equal to 815℃. 5.17 Resistivity
The resistivity of magnesium oxide shall not be lower than the value specified in Table 4. Table 4
Resistivity
5.0×10°
1.5×10°
3.0×10°
The selected test temperature is between the above temperature points, and the resistivity is determined by linear interpolation. The test temperature is selected at two points within the range of T minus 50°C to T plus 100°C, and T: minus T, equal to 100°C, high temperature magnesium oxide T: equal to 975°C, 2
T, equal to 875°C.
5.18 Life
The life of magnesium oxide at working temperature shall not be less than 10,000h. However, the life of high temperature magnesium oxide is determined by the supplier. The supplier can also provide the accelerated life at a test temperature of 927°C.
6 Technical requirements for products
6.1 Raw materials for products
The products must be made of qualified magnesium oxide, but 5.6, 5.7 and 5.8 are not subject to assessment. 6.2 Adhesive
The adhesive should have no residue after being burned at 1000℃ and should not corrode magnesium oxide. 6.3 Sintering temperature
The sintering temperature of the product should not be lower than 1200℃. 6.4 Hardness
The hardness of the product should be such that it cannot be crushed by hand but can be processed with a chain knife. 6.5 Surface
The surface of the product should be smooth and flat, and there should be no defects deeper than 1.5mm. 6.6 Density
The density of the product after sintering should not be lower than 2.3g/cm. 6.7 Plane inclination of square products
The plane inclination of square products should not be greater than 3°6.8 Compressive strength
The compressive strength of products should not be less than 1.5MPa. 6.9 Dimensions
JB/T85081996
The dimensions of products must comply with the requirements of the drawings approved in accordance with the prescribed procedures. 7 Test methods
None of the test methods in this chapter involves safety issues during operation. The tester should determine a safe operation method on his own. 7.1 Method of sampling and reduction to test weight 7.1.1 Equipment
a) Separator containing a series of chutes fed by a single feeding funnel. These chutes should be arranged so that each separated chute can feed to one side of the sample. The spacing between the two plates must be between 1.6 and 3.2 mm. The separator should be able to obtain uniform separation; b) Stainless steel spoon;
c) Mixer, any commercially suitable mixer, with a minimum capacity of 45 kg. 7.1.2 Procedure
Reduction of a large quantity (approximately 45 kg);
Randomly take magnesium oxide from one or more packages of the product and place in a suitable mixer and mix for at least 15 min; Take at least 5 spoonfuls of 1 dm of magnesium oxide from each part of the mixer; c)
Reduction of 1 dm of sample;
Pour the above 1 dm of sample evenly into the separator through the orifice of the separator; e)
When all the sample has been poured, tap the side of the separator to confirm that there is no accumulation. f)
The portion of magnesium oxide at the beginning and end of the separation is discarded;
g) If a smaller sample is required, repeat the separation process. 7.1.3 Separation accuracy
The percentage weight of the sample retained on any one sieve measured in accordance with 7.4 shall not exceed 3% of the average percentage weight retained on the sieve. 7.2 Analysis method of chemical composition
Instruments and equipment
Burette
Volume flask
Pipette
Conical flask
50mL, 5mL;
1000mL, 500mL, 250mL, 100mL; 50mL, 25mL;
250mL;
1000mL, 500mL, 250mL, 100mL, 50mL; 500mL, 250mL, 100mL
Alumina or porcelain crucible
500mL;
Analytical balance, sensitivity 0.1mg;
Muffle furnace
1300℃
721 spectrophotometer;
Colorimetry.
Hydrochloric acid 12mol/L, 6mol/L, 1+20 (1mL concentrated hydrochloric acid + 20mL water); ammonia water: concentrated ammonia water, 6mol/L, 1+3 (1mL nitrogen water + 3mL water); ammonia monoammonium chloride buffer solution, pH equal to 10; methyl red indicator, 0.1% ethanol solution; 13
chrome black T indicator, 0.5% ethanol solution;
JB/T8508—1996
triethanolamine solution, the ratio of triethanolamine to water is 1:1; EDTA standard solution, 0.02mol/L, 0.05mol/L; mannitol;
potassium hydroxide, 15% aqueous solution;
calcium carboxyl indicator [2-carboxy-1-(2-carboxy-4-sulfonic acid 1-naphthylazo)-3 ～Naphthalene. Acid] 1% solid indicator; Hydrofluoric acid 48%;
Sodium carbonate solid;
m) Sulfuric acid, 18mol/L, 6mol/L;
Standard iron solution 0.01mg/mL;
Weigh 0.8634g (NH)Fe(SO.), ·12H,0 and place it in a cup, add 20mL water and 20mL 1:1 hydrochloric acid, transfer it to a 1000mL volumetric flask after dissolving, dilute it to the scale with water, shake well to obtain a 0.1mg/mL solution, when needed, dilute it 10 times with a volumetric flask to obtain a 0.01mg/mL solution
o) o-Phenanthroline, 0.15% solution freshly prepared; p) Hydroxylamine hydrochloride, 10% aqueous solution, prepared when used; q) Sodium acetate, 1mol/L.
7.2.3 Sampling
According to the method in 7.1, 20±1g of magnesium oxide is extracted. Note: If the modified magnesium oxide will cause inconvenience to the chemical composition analysis, the sample can be pre-treated by burning, that is, 20g of the sample is placed in an alumina or porcelain crucible, and then placed in a muffle furnace for burning. The burning temperature is 1000±25℃, the time is 2h, and the furnace is cooled to 600℃. The furnace door is opened and the furnace is cooled to room temperature. During the whole burning process, impurities should be prevented from being mixed into magnesium oxide. 7.2.4 Determination of magnesium oxide (MgO) content
Weigh 0.5±0.0001g sample is placed in a 100mL beaker, moistened with 10mL water, and then 10mL concentrated hydrochloric acid is added. Heat the sample over low heat until it is completely dissolved, add a drop of methyl red indicator and 20mL water, neutralize with 6mol/L ammonia water until it just turns yellow, and then add a little excess, transfer to a 250mL volumetric flask, dilute to the scale with water, shake well, place dry filter paper in a funnel, filter into a dry container, discard the initial 20mL, correctly transfer 25mL of the clarified liquid to a 250mL conical flask, add 50mL water and 10mL ammonium fluoride buffer solution (pH 10), heat to 50-60℃, titrate with 0.05mol/L EDTA solution while shaking, add 3-4 drops of chrome black indicator when approaching the end point, and continue to titrate until the solution changes from purple to blue as the end point. Calculate the magnesium oxide content according to the following formula: =VxM×0.,04032×100-Ca0%×40: Mg0%=
Wherein: V is the volume of EDTA standard solution consumed, mL; M is the molar concentration of EDTA standard solution, mol/L; m is the mass of the weighed magnesium oxide sample, g; 0.04032 is the mass per millimole, g;
40.32/56.08 is the mass coefficient of calcium oxide converted into magnesium oxide; Ca0% is shown in formula (2).
7.2.5 Measurement of calcium oxide (CaO) content
Measure 50 mL of magnesium oxide solution, place it in a 250 mL conical flask, add 20 mL of water, 0.5 g of mannitol, 5 mL of triethanolamine (1:2) solution, 15 mL of 15% potassium hydroxide solution and 0.1 g of calcium carboxyl indicator. After dissolving, titrate with 0.02 mol/L EDTA solution from a microburette until the solution changes from wine red to blue. Calculate the calcium oxide content according to the following formula: VXMX0.05608
JB/T8508—1996
Wherein: V—volume of EDTA standard solution consumed in titration, mL; M—molar concentration of EDTA standard solution, mol/L; m
—mass of magnesium oxide sample weighed, g.
7.2.6 Determination of silicon dioxide (SiO2) content
7.2.6.1 Weigh 1±0.0001g of magnesium oxide sample and place it in a platinum crucible. Add 5g of anhydrous sodium carbonate and mix thoroughly with magnesium oxide. Cover with a lid and heat to melt on a large gas burner until dissolved. Then cool and place the crucible in 200mL of pure water in a porcelain bath to fully rinse the crucible. Take out the rinsed crucible and wash the outer wall with water. The washing liquid should be added to the porcelain bath. Carefully add a small amount of concentrated hydrochloric acid to the crucible to wash the inner wall of the crucible again.
7.2.6.2 Cover the porcelain dish with blood, carefully add 30mL of concentrated hydrochloric acid to the porcelain dish, put the porcelain blood on a water bath and evaporate it to dryness, cool it down, wash the inner wall with 20mL of hydrochloric acid and a small amount of water, and then evaporate it on a water bath again to dryness, remove it from the water bath and cool it down, add 25mL of concentrated sulfuric acid and 175mL of water to the porcelain dish, stir and dissolve thoroughly, then filter the solution and precipitate with a funnel, wash the filter paper with (1+20) hydrochloric acid 5-6 times after filtering, the precipitate is used to determine the SiO content, and the filtrate is used to determine the iron and aluminum oxides. 7.2.6.3 Transfer the precipitate to a clean constant weight platinum, dry, carbonize, ashed and calcine, keep it at 1200℃ for 20min, cool and weigh. The residue is moistened with a small amount of water, 5 drops of concentrated H2SO4 and 15 mL of hydrofluoric acid (HF) are added to evaporate until H2SO4 is completely lost, and then burned at 1200°C for 5 min. After cooling, weigh the lost SiO2 weight and calculate the SiO2 content according to the following formula: W2-Wz×100
W2-the weight of the residue after HF treatment, g; W2-the weight of the original sample, g.
7.2.7 Determination of the content of ferric oxide (Fe2O2) and aluminum oxide (Al2O2). Weigh 2.5±0.0001 g of magnesium oxide (MgO) and place it in a clean 100 mL beaker. Add a small amount of water to make the magnesium oxide into a slurry. Then add 10 mL of concentrated hydrochloric acid to the beaker and heat and stir to dissolve the magnesium oxide. If it is found that magnesium oxide is not completely dissolved, a small amount of hydrochloric acid can be added to the beaker to make it completely dissolved. When magnesium oxide is completely dissolved, heat and boil the solution for 5 minutes, filter it while hot, filter the solution into a 250mL clean beaker, wash the filter paper with pure water 4 to 5 times after filtering, use about 10mL of water each time, drip ammonia water into the filtrate until the solution becomes slightly ammoniacal (you can also add a few drops of phenolphthalein solution to the solution, add ammonia until the solution just turns red), boil the solution for 2 minutes and filter it while hot, transfer the precipitate into the filter paper, wash the precipitate with dilute nitrogen water 4 to 5 times, after washing, put the filter paper into a pre-weighed crucible and burn it to the weight, calculate the iron and aluminum content according to the calculated weight: bzxz.net
W,-empty weight, g
R.0,%=W,W
Wz empty plus precipitate weight, g
W magnesium oxide weight, g.
7.2.8 Determination of ferric oxide (Fe:0,) content This determination method is carried out in two steps:
a) Plotting the standard curve
1) Preparation and color development of a series of standard solutions. In 5 5mL volumetric flasks, use a pipette to add 2mL, 4mL, 6mL, 8mL, and 10mL of standard iron solution (0.01mg/mL), and then add 1mL10% hydroxylamine hydrochloride, 2mL0.15% o-phenanthroline and 5mL sodium acetate solution, dilute to the scale with water, and shake well. Preparation of reference reagent solution. In a 50mL volumetric flask, add 1mL10% hydroxylamine hydrochloride, 2mL0.15% o-phenanthroline and 5mL1mol sodium acetate solution, dilute to the scale with water, and shake well. Selection of the best absorption wavelength. Take one of the above solutions (such as a solution containing 6mL of standard iron solution), use a 1cm cuvette and the reagent solution as the reference solution, measure the absorbance every 10nm in the interval of 440-560nm, and measure it every 5nm in the maximum absorption area, draw an absorption curve with absorbance as the ordinate and wavelength as the horizontal coordinate, and thus select the appropriate wavelength for measuring iron.
JB/T85081996
4) Preparation of standard curve. At the selected appropriate wavelength, use a 1cm cuvette and the reagent solution as the reference solution to measure the absorbance of the above solutions, use the milliliters of standard iron as the horizontal coordinate and the corresponding absorbance as the vertical coordinate, and draw a standard curve of absorbance versus milliliters.
b) Determination of content
Weigh 0.25±0.0001g of magnesium oxide and place it in a 100mL beaker, add 5mL of water and 5mL of concentrated hydrochloric acid, heat to dissolve the magnesium oxide, and after it is completely dissolved, transfer all the solution to a 100mL volumetric flask, dilute to the mark with water, shake well, take 4mL of the solution and place it in a 50mL volumetric flask, add 1mL of 10% hydroxylamine hydrochloride, 2mL of 0.15% o-phenanthroline and 5mL of 1mol/L sodium acetate solution to the flask, dilute to the mark with water, and shake well.
At the most suitable wavelength for iron measurement, use 1cm colorimetric blood and the reagent solution as the reference solution to measure the absorbance of the above solution. According to the measured absorbance value, find the number of milliliters of the standard solution on the corresponding horizontal axis on the standard curve to calculate the percentage of iron in magnesium oxide.
Wherein: 0.01 standard iron solution concentration;
14.3--conversion factor;
W magnesium oxide weight, g
Fe:0,% = 0. 01XViX14. 3
V,-the number of milliliters on the horizontal axis corresponding to the absorbance of the solution being tested, mL: V. The sample volume of the solution being tested (4mL).
7.2.9 Calculation of aluminum oxide content
According to the (Al20O,+Fe:O,) content determined in 7.2.7 and the Fe:O, content determined in 7.2.3, the following formula is used for calculation: Al,0,%=R0,%-Fe20,%
Precision and deviation
The chemical composition analysis of magnesium oxide should be carried out twice, and the average value of them shall be taken as the result. 7.2.10.13
7.2.10.2 Repeated measurements should be within ±1.0% of the average value. 7.2.10.31
If the variation is too large, a third measurement should be performed. 7.3 Method for determination of ferromagnetic impurity content
7.3.1 Equipment
a) Magnetic analyzer, calibrated according to the instrument's instruction manual; b)
Laboratory balance, weighing capacity of 130±0.1g. 7.3.2 Steps
According to the method in 7.1, obtain the sample:
Weigh 130±0.1g sample;
Adjust the weight scale to 130g;
Set the classification selection switch to 0.1;
Adjust the instrument zero point when the sample tube is empty;e)
Transfer the test sample to the sample tube;
(5)
g) Insert the sample tube into the instrument sample decomposer and read the percentage of magnetic material content directly from the display to an accuracy of 0.001%.
7.4 Sieve analysis method
7.4.1 Method overview
Sieve the magnesium oxide sample through a series of sieves, weigh the weight retained on each sieve, and record it as a percentage of the sample. 7.4.2 Equipment
a) Shaking sieving machine;
b) Stainless steel standard sieve, bottom plate and cover; JB/T 8508-1996
Sieve mesh (mesh size): 40 (425μ), 60 (250μ), 80 (180μ), 140 (110μ), 200 (75μ), 325 (45μ); c) Timer;
Balance;
Several stainless steel receiving plates. The overall dimensions shall not be less than the dimensions of the bottom plate matching the sieve; f)
Non-metal brush;
Small rubber stick or hammer.
7.4.3 Calibration of sieves
The test station should be equipped with two sets of sieves. The first set is used for normal use, and the second set is used as the calibration sieve. After the first set of sieves has been screened 50 times, the second set of sieves is used for sample comparison; b)
When the first set of sieves is worn, the second set of sieves is used to replace it, and a new set of sieves is prepared to replace the second set of calibration sieves; e)
The sieve mesh is checked by comparing it with a new sieve, that is, two identical 100g magnesium oxide samples are taken from the same batch of materials, and then compared through the sieve using the same steps. The sample that is being tested is The weight tolerance of the amount of magnesium oxide on the sieve and the amount passing through the new sieve should be within ±3%, or it should be sent to the metrology and appraisal unit for inspection; d) The sieve mesh should be inspected if any of the following conditions occur: 1) If the sieve is loose;
2) If the sieve is blocked;
3) When the sieve has been used 200 times or 6 months; The sieve used for testing cannot be used for other purposes; e)
The sieve should be kept clean with a soft brush. If necessary, the following methods can be used for cleaning: 1) Clean with trifluoroethylene grease;
2) Clean with ultrasonic wave;
3) Tap with a rubber hammer.
Wire brush should not be used to clean the sieve.
7.4.4 Steps
Stack all the sieves in order, with the coarse ones on top and the plate at the bottom; a)
Take 100-125g of sample according to the method in 7.1; b)
Weigh to the nearest 1mg and record;
Place the sample on the coarsest sieve, cover the top with a lid, and then install the sieve assembly in the sieve box; d)
Start the sieving machine for 15 minutes;
Weigh the weight of each part of magnesium oxide as follows: f)| |tt||Pour the magnesium oxide in each sieve into the receiving tray, then brush the back of the sieve with a brush to let the magnesium oxide fall into the tray from the front 1)
side of the sieve, tap the four sides of the sieve frame with a small rubber stick or hammer to collect all the remaining magnesium oxide in the tray;
Weigh the weight of the following parts of magnesium oxide respectively: 10, 60, 80, 140, 200, 325 mesh and bottom plate; 2)
3) Record the weight of magnesium oxide of various mesh sizes, with an accuracy of 0.1g. Calculate the percentage of magnesium oxide in various mesh sizes and bottom plate as follows: g)
Mg0%=(F/S)X100
-weight of each part, g;
Where: F-
S—sample weight, g.
Percentage calculation is accurate to 0.1%.
7.5 Determination method of loss on ignition
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