Conversion of bulk materials from m3 to tons, bulk density. Determination of bulk density Determination of bulk density of bulk materials

Bulk density determined for bulk materials using the same formula as the average. The test is carried out using a standard metal funnel in the form of a truncated cone. There is a valve at the bottom of the funnel. Place a measuring cup under the funnel. Pour the material into the funnel, open the valve and fill the measuring cup to the brim, cut off the excess using a ruler. The measuring cup is weighed empty and filled. The experiment is repeated five times.

The bulk density for each experiment is determined by the formula:

where m is sample mass, g

Vst – volume of measuring cup, cm 3

The calculation results are recorded in Table 7

Table 7. Bulk density ________________________________

(indicate the name of the material)

Determination of true density

Preparing for the test

Take a sample of about 30 g from a sand sample and sift it through a sieve with holes 5 mm in diameter. The dried sand is mixed and divided into two parts.

The sample is poured into a clean, dried and pre-weighed pycnometer (Le Chatelier device) (Fig. 1), after which it is weighed along with the sand. Then boiled water is poured into the pycnometer in such an amount that the pycnometer is filled to approximately 2/3 of its volume, the contents are mixed and placed in a slightly inclined position in a water bath. The contents of the pycnometer are boiled for 15-20 minutes to remove air bubbles.

The true density of sand in g/cm3 is calculated using the formula:

Where T - mass of pycnometer with sand, g;

T 1 - mass of empty pycnometer, g;

T 2 - mass of pycnometer with water, g;

T 3 - mass of the pycnometer with sand and water after removing air bubbles, g;

r in is the density of water equal to 1 g/cm3.

Fig.1 Le Chatelier's device

Determination of porosity and voids

Porosity hard materials and voidness (the volume of intergranular voids in bulk materials in an uncompacted state) is determined based on the values ​​of the true density and the average or bulk density of the material, previously established.

Porosity (P) and voidness ( V m.p) as a percentage by volume is calculated using the formula

Where - true density, g/cm 3 ;

Average or bulk density, kg/m3.

Humidity determination

Humidity is determined by comparing the mass of the material in the state natural humidity and after drying.

The material (product) is weighed, placed in drying cabinet and dried to constant weight at a temperature of 105 o C.

Humidity ( W) as a percentage is calculated using the formula

Where T - mass of the sample in a state of natural humidity, g

T 1 - weight of the sample in dry condition, g.

The test results are recorded in Table 8

Table 8. Porosity (voidity) and moisture content of materials

2.1. Equipment and materials

PZHRV powder. Scott volumetric meter (Figure 3). Cuvette (thickness 4 mm, depth 40.4 mm, volume V=26.5 cm 3), lever scales. Vernier caliper ShTsTs-1-125.00 PS, GOST 166-89, measurement error 0.03; scales VLA-200g-M, No. 608, error due to unequal arms of the rocker arm ≤2 g., lever scales. GOST – 19440 49.

Fig.3. Scott Volume Meter

2.2. Theoretical data

Bulk density (ρ bulk, g/cm 3) is the volumetric characteristic of the powder, and represents the mass of a unit of its volume with free filling. Its value depends on the packing density of powder particles when they freely fill any volume. The larger and more correct form particles. The presence of protrusions and irregularities on the surface of particles, as well as an increase in the surface due to a decrease in particle size, increases interparticle friction, which makes it difficult for them to move relative to each other and leads to a decrease in bulk density.

The reciprocal of bulk density is called bulk volume (V bulk, cm 3 /g), which is the volume occupied by a unit mass of powder when it is freely poured. The bulk density of the powder affects the volumetric dosing and the formation process itself, as well as the amount of shrinkage during sintering (the lower the bulk density, the greater the shrinkage).

When mechanical vibration vibrations are applied to freely poured powder, the volume decreases by 20-50%. The ratio of the mass of the powder to the value of this new, reduced volume is called tapped density. The maximum tapped density is achieved on powders with spherical particles with minimal surface roughness.

The essence of the method is to measure the mass of a certain amount of powder, which, in a freely poured state, completely fills a container of a known volume. The free-flowing state is obtained by filling a container by successively passing the powder through a system of inclined plates of a Scott volumetric meter. The ratio of mass to volume is bulk density.

2.3. Description of the method for determining bulk density

We pour a certain volume of PZHRV powder into the upper funnel of the volumetric meter. The powder, in a freely poured state, pours down and sequentially passes through the system of inclined plates of the volumetric meter, filling the cuvette located under the lower funnel. The resulting slide on the surface is removed and the surface is leveled. Next, the resulting mass of powder is weighed on a scale. The experiment is performed twice (Table 2). For each time, the value of ρ fill and V fill are calculated.

2.4. results

Table 2. Values ​​of bulk density and volume for PZHRV

Where m k is the mass of the cuvette, V k is the volume of the cuvette, m P is the mass of the powder.

Conclusion: measurements of bulk density for PZHRV powder were carried out, the resulting values ​​fall within the theoretical range: 2.71-2.90 g/cm 3 .

Powder compressibility

3.1. Equipment and materials

PZHRV powder. Manual hydraulic press 10 TNS "Karl Zeiss Jena". Cylindrical molds. Lever scales.

3.2. Theoretical data

The compactability of a powder shows its ability to change the initial packing density of particles during the pressing process. This characteristic is assessed by the density of compacts produced at various pressing pressures in a cylindrical mold.

The compressibility of a powder is assessed by its ability to form a compact under the influence of pressure. This characteristic gives a qualitative assessment of the properties of the powder, which is comprehensively related to compactability and formability.

Good compressibility makes the process of powder formation easier and cheaper. The higher the bulk density of the powder, the better the compressibility.

3.3. Description of the pressing method

Fill a cylindrical mold with powder of a certain mass (m = 8.5 g for all subsequent tests the same mass is taken). The mold is placed on the object table located under the punch. Next, the punch is lowered onto the mold and firmly fixed with levers from above. Then the pressure is selected and held on the mold for about 5 seconds. After this, the pressure must be released by pressing the lever next to the pressure gauge. Raise the punch and remove the mold. Remove the top valve from the mold and put a cylinder in its place so that the compact does not fall out of the mold. Next, place the mold under the punch in the same way and apply pressure until the pressing (Figure 4) comes out. Afterwards, measure the dimensions of the compact (diameter D and height H), write it down in Table 3.

The measurements were carried out 13 times: 12 of them with increasing pressure by a step equal to 10, and one to determine the pressing threshold (at P = 8).

Fig.4. Press form

3.4. results

Table 3. Dimensions of the resulting compacts

m (weighed portions of PZHRV powder) = 8.5 g

Volume is calculated using the formula

Fig.5. Dependence of compact sizes on pressure

Fig.6. Dependence of compaction volume on pressure

To characterize the behavior of powders during pressing, use compaction factor k, equal to the ratio of compaction density at a given pressure P to bulk density:

k= γ pr / γ us.

Table 4. Calculation of compaction coefficient

Fig.7. Dependence of compaction coefficient on applied pressure

Conclusion: the compressibility of the powders was carried out on hydraulic press"Karl Zeiss Jena". After receiving the compacts, their dimensions were measured and the volume was calculated. In accordance with the table, a graph was constructed of the dependence of the volume of compacts on the applied pressure - with increasing pressure, the volume decreases.

Shrinkage of compacts

After pressing the powder, the resulting compacts were subjected to sintering on an SNVE-131 installation at a temperature of 1200 0 C, at P = 10 -2 Pa, 1 hour. Next, the shrinkage of the compacts was calculated.

4.1. Equipment and materials

Powder compacts PZHRV (13 pcs.). Vernier caliper ShTsTs-1-125.00 PS, GOST 166-89, measurement error 0.03; scales VLA-200g-M, No. 608, error due to unequal arms ≤2 g.

4.2. Results

It is necessary to measure the dimensions of the compacts after sintering (Table 5). Then compare the volumes before and after shrinkage (Table 6), thereby calculating the amount of shrinkage.

Table 5. Dimensions of compacts after sintering

Table 6. Volumetric shrinkage

Table 7. Shrinkage due to changing the height of compacts

Fig.8. Dependence of shrinkage by volume and height

Conclusion: after sintering, the dimensions of the samples changed - the diameter increased and the height decreased accordingly. A graph was constructed of the dependence of shrinkage in volume and height - the amount of shrinkage decreases monotonically.

Bulk density is determined for bulk building materials: cement, sand, crushed stone, gravel, etc. The bulk density of such materials can be determined in the loose, compacted and natural state.

Bulk density Bulk materials are the mass of a unit volume of material in bulk, i.e. with pores and voids, this parameter can be determined in accordance with the methods given in GOST 8735-88 and GOST 8269.0-97.

Bulk density is determined using a device (Fig. 4.1), which consists of a standard funnel in the form of a truncated cone and a measuring cylinder with a volume of 1 l or 10 l. For testing, a pre-weighed graduated cylinder is installed under the funnel tube. The distance between the top edge of the cylinder and the valve should be 50 mm. Dry material is poured into the funnel, then the valve is opened, the cylinder is filled with excess, the valve is closed and the excess material is cut from the middle in both directions flush with the edges of the cylinder using a metal ruler. In this case, compaction of the material is not allowed. Then the cylinder of material is weighed with an accuracy of 1 g. The bulk density of the material in the loose-fill state is calculated using the formula:

ρ n.r. . = , [kg/l], (4.1)

Where m 1 - mass of the cylinder with material, kg;

m 2 - cylinder mass, kg;

V- cylinder volume, l.

The test is repeated at least three times and calculated final result as the arithmetic mean of three measurements.

During transportation and storage, bulk materials are compacted, and their bulk density may be 15-30% higher than in the loose state. The bulk density in the compacted state can be determined using the above method, however, after filling the cylinder with material, it should be compacted by vibration for 30-60 seconds on a vibration platform by lightly tapping the cylinder on the table 30 times. During the compaction process, the material is added, maintaining some excess in the cylinder. Next, the excess is cut off, the mass of the material in the cylinder is determined and the bulk density in the compacted state is calculated.

Based on the results obtained, it is possible to determine the compactibility of the material, which is usually characterized by the compaction coefficient

TO at =, (4.2)

Where: ρ Well.- bulk density of the material in a compacted state, kg/l;

ρ n.r.- bulk density of the material in a loose-filled state, kg/l;

Rice. 4.1. Diagram of a device for determining the bulk density of a material in a loosely poured state:

1 - standard funnel; 2 - valve; 3-dimensional cylinder

5. Determination of water absorption of a material

When determining the water absorption of materials from rocks, one should be guided by GOST 30629-99. Water absorption is determined on five cubic samples with an edge of 40 - 50 mm or cylinders with a diameter and height of 40 - 50 mm. Each sample is cleaned with a brush from loose particles and dust, and dried to a constant weight. The samples are weighed and measured after they have completely cooled in air. The test is then carried out in the following sequence. Rock samples are placed in a vessel with water room temperature 15 - 20 0 C in one row so that the water level in the vessel is 20 mm higher than the top of the samples. The samples are kept for 48 hours, after which they are removed from the vessel, moisture is removed from the wet surface soft cloth and each sample is weighed. The mass of water flowing from the pores of the sample onto the scale is included in the mass of the water-saturated sample.

Water absorption of a material by mass or volume is equal to the ratio of the mass of water absorbed by a sample of the material upon saturation, respectively, to the mass or volume of the sample.

Water absorption by mass is calculated using the formula:

=
. 100 , [%], (5.1)

Where m 1

m 2 - weight of the sample in saturated water condition, kg.

Water absorption by volume is calculated using the formula:

=
. 100 , [%], (5.2)

Where m 1 - dry weight of the sample, kg;

m 2 - mass of the sample in a water-saturated state, kg;

V- sample volume, cm 3.

The arithmetic mean of five determinations of water absorption is taken as the final result.

The amount of water absorption by mass can be more than 100%.

Bulk density is determined by weighing the mass of a dried aggregate sample in a measuring vessel.

10.1.1 Test procedure

Determination of the average bulk density of porous gravel, crushed stone or sand is carried out in accordance with work No. 2.

The size of the measuring vessel and the volume of the test sample, depending on the size of the aggregate, are taken according to Table 28.

The bulk density of the aggregate is calculated as the arithmetic mean of the results of two parallel determinations, during which a new portion of aggregate is used each time.

Table 32 - Dimensions of measuring vessels and sample volume

10.1.2 Processing results

Bulk density of filler ( r n) in kg/m3 is calculated with an accuracy of 10 kg/m3 (sand grades with a bulk density of 250 or less - up to 1 kg/m3) using the formula:

Where m 1– mass of the measuring vessel with filler, kg;

m 2 – mass of the measuring vessel, kg;

V – volume of measuring vessel, m3.

Depending on the bulk density, gravel, crushed stone and sand are divided into grades shown in Table 33.

Table 33 - Grade by bulk density of inorganic porous fillers

Limit values ​​of grades by bulk density for various types porous: gravel, crushed stone and sand - must comply with the requirements of GOST 9757–90, given in table 34. In this case, the actual bulk density grade should not exceed the maximum value, and the minimum values ​​are given as a guide.

Table 34 - Limit values ​​of grades by bulk density

Note. By agreement between the manufacturer and the consumer, for the preparation of structural lightweight concrete of classes B20 and higher, the production of expanded clay gravel and crushed stone grades 700 and 800.

Determination of the average density of coarse aggregate grains

Average density grains of coarse aggregate are determined by the hydrostatic method by the difference in the mass of the container with the sample before and after its saturation with water when weighed in water and in air.

10.2.1. Test procedure

From a 3-liter sample of aggregate dried to constant weight, particles smaller than 5 mm are sifted out on a sieve with holes 5 mm in diameter. Then the dry container with a lid is pre-weighed in air and water on a scale equipped with a device for hydrostatic weighing. After that, a 1-liter sample of filler is poured into the container, closed with a lid and weighed. Then the container with the filler is gradually immersed in a vessel with water and shaken in water to remove air bubbles. The container with the filler must be kept in water for 1 hour, and the water level must be at least 20 mm above the container lid. A container with water-saturated aggregate is weighed on a scale equipped with a hydrostatic weighing device. Next, the container with the filler is removed from the vessel with water, the excess water is allowed to drain for 10 minutes and weighed in air.

The average density of coarse aggregate grains of each fraction is calculated as the arithmetic mean of the results of two parallel determinations, each of which is carried out on a new portion of aggregate.

10.2.2 Processing results

The average density of coarse aggregate grains ( r to) in g/cm 3 is calculated using the formula

(58)

Where m 1 – the mass of the dry aggregate sample, found from the difference in the mass of the container with the dried sample and the mass of the container when weighed in air, g;

m 2 – mass of a sample of filler saturated with water, found from the difference in the mass of the container with and without a saturated sample of filler when weighed in air, g;

t 3– mass of filler in water, found from the difference in the mass of the container with and without a saturated sample of filler when weighed in water, g; r in– density of water equal to 1 g/cm3.

It is the ratio of the mass of this substance in a freshly poured state to its volume. This takes into account both the volume of the substance itself and the volume of voids inside it and the volume between individual particles (for example, in coal). For obvious reasons, this type of density is less than the true density, which excludes the above voids.

To determine bulk density, tools such as scales, a ruler, a “standard funnel” device, and a measuring vessel of a certain volume are used. The bulk density of a particular substance is determined for a material of a certain moisture content. If the sample does not meet the humidity standards, then it is moistened or, more often, dried.

When we determine what the bulk is, the algorithm of actions should be like this:

1. The measuring vessel is weighed and placed under a standard funnel (it has a shutter at the bottom).

2. Sand is poured into the funnel, after which the shutter is opened so that the sand is poured into the measuring vessel at once, fills it and forms a slide on top.

3. Excess sand is “cut off” with a ruler by moving it along the top of the measuring vessel.

4. The vessel with sand is weighed, and the weight of the vessel itself is subtracted from the total mass.

5. Bulk density is calculated.

6. The experiment is repeated 2-3 times, after which the average value is calculated.

In addition to the density in the loose state, the density in the compacted version is measured. To do this, the sand in the vessel is slightly compacted on a vibrating platform for 0.5-1 minutes. You can calculate the bulk volume using the same method.

In accordance with GOST 10832-2009, sand of a certain type (expanded) according to bulk density is divided into certain grades - from M75 (density indicator is 75 kg/m3) to M500 (density 400-500 kg/m3). To be classified as a particular brand, sand must have a certain thermal conductivity and compressive strength. For example, the thermal conductivity of grade M75 at a temperature of 25 C + -5C should be no more than 0.043 W/m x C. And the compressive strength for sand of grade M500 is defined as 0.6 MPa (not less). type (material moisture content 5%) has a bulk density of 1500. For cement, this figure is about 1200 kg/m3 in a free-fill state and about 1600 kg/m3 in a compacted state. Often, an average figure is used for calculations, which is equal to 1300 kg/cubic meter.

Why is bulk density needed? The fact is that in trade turnover it is precisely this value that is used, and not the true density (for example, if sand is sold in bags). Therefore, in order to convert prices per cubic meter into prices per ton, you just need to know what the density of the material is. In addition, for cooking mortars Volume or weight data may be needed, depending on the instructions.

All product information, including density, is applied to each package by stamping, stenciling or printing on the label. Manufacturer information is provided here. symbols, date of manufacture and batch number, amount of substance in the package and