home · Other · Density of bulk cargo. Calculation of tonnage of bulk cargo. Bulk density of sand Density depending on the type of sand

Density of bulk cargo. Calculation of tonnage of bulk cargo. Bulk density of sand Density depending on the type of sand

But it also produces biologically active food additives (BAA) in tablet and capsule form. In this regard, it seems necessary to talk about some similar terms and technological properties of these products.

Technological properties of powdered (tablets and encapsulated) medicinal substances and biologically active food additives depend on their physical and chemical properties. When producing dietary supplements in the form of tablets and hard gelatin capsules, it is necessary to take into account various technological characteristics, since the active components and many extracts medicinal plants come in the form of powders or powder mixtures.

Bulk density

The basic characteristic of all bulk materials is density. There are concepts of true and bulk density, which are measured in g/cm3 or kg/m3.

True density is the ratio of the mass of a body to the volume of the same body in a compressed state, in which the gaps and pores between particles are not taken into account. True density is constant physical quantity, which cannot be changed.

In his natural state(uncompacted) bulk materials are characterized by bulk density. The bulk density of various bulk materials refers to the amount of powder ( bulk product), which is in a freely filled state in a certain unit of volume.

The bulk density of a given powder or any bulk mixture (D sat. pl.) is determined by the ratio of the mass of freely poured powder (Bulk mass) to the volume of this powder (Vcvessel) according to the formula:

D sat. pl. = Weight of bulk / Vcvessel

Bulk density takes into account not only the volume of material particles, but also the space between them, so bulk density is much less than true. For example, the true density of rock salt is 2.3 t/m3, and bulk salt is 1.02 t/m3.

Knowing the bulk density of the bulk materials used, it is possible to calculate their volume and, accordingly, the filling height when designing containers or dispensers, as well as capsules and tablets. It is clear that if we partially know some parameters, namely the height of the backfill, as well as the backfill coefficient, then we can calculate the height of the expected volume, that is, the height of the format parts, which is very important when solving technological problems. Of course, if the bulk density of the powder is known, then technologists can easily calculate the mass for one dose, portion or package and thereby determine the dosage value for a capsule or tablet press, as well as for any other packaging equipment.

The bulk density value is determined in accordance with the standard (GOST 19440-94 "Metal powders. Determination of bulk density. Part 1. Method using a funnel. Part 2. Scott volumetric meter method") using a volumetric meter whose operating principle is based on precise definition mass of powder filling the measuring container. A volume meter consists of a funnel with a sieve and a body with several inclined glasses through which the powder, pouring, falls into a crucible with a measured volume and weight.

Bulk or Bulk Density depends on the size, shape, moisture content and density of the granule or powder particles. Based on the value of this indicator, the volume of matrix channels can be predicted and calculated. The procedure for measuring the bulk density of a powder mixture or monopowder is carried out on special device(Fig. 1).

A weighed portion of 5.0 g of powder is produced. The accuracy of the sample is up to 0.001 g. Next, the sample is poured into a measuring cylinder. Set the vibration amplitude on the device (35-40 mm) using the adjusting screw. Set a mark on the scale and fix the position using a locknut. Next, using a transformer, the oscillation frequency is set. The frequency is set in the range from 100 to 120 kol/min, according to the counter. After turning on the device with the toggle switch, the operator monitors the mark at which the powder level in the cylinder is set. As a rule, after operating the device for 10 minutes, the level of the powder or mixture becomes constant and the device must be turned off.

Bulk density is calculated using the formula:

where: ρ n – bulk density, kg/m3;

m – mass of bulk material, kg;

V is the volume of powder in the cylinder after compaction, m3.

Depending on the bulk density, powders are classified as follows:

ρ n > 2000 kg/m 3 – very heavy;

2000 > ρ n > 1100 kg/m 3 – heavy;

1100 > ρ n > 600 kg/m 3 – average;

ρ n< 600 кг/м 3 – легкие.

One of the devices used to measure bulk density (as well as other characteristics of a powder mixture or monopowder) is the VT-1000 device.

The VT-1000 analyzer (Fig. 2) is used to determine the flow properties of various bulk materials. Powder or powder mixtures are, by definition, two-phase systems. The surface properties of the particles of a powder mixture or monopowder, as well as their density, all these parameters determine its behavior in the flow and their flowability. Correct determination of flowability parameters is very important for calculations of powder processing processes, its packaging, transportation and storage.

Using VT-1000 (Fig. 3), it is possible to determine not only bulk density, but also dispersion, angle of incidence, angle natural slope, angle on the flat plate and tapped density. From these characteristics it is easy to calculate the difference angle, compressibility, volume of empty space, compressibility, uniformity. Based on the characteristics recorded on the device, the Carr index can be calculated, which allows you to determine the values ​​of flowability and aeration

(behavior of powder in an aerodynamic jet).

The powder is poured into a measuring cylinder. The ratio of the volume occupied by it to the mass of the powder is the bulk or bulk density. Fig.3

The determination of bulk density indicates the amount of material in one cubic meter of bulk material. This value is determined as the number of voids between separate elements, and the size of the available fractions. You need to know the value of this indicator for correct calculations when creating solutions and purchasing materials. Units of measurement - kg/m3.

Determination of density

It is known that the composition of sand contains grains of medium, large and small fractions that affect the change in volume bulk material every time. Conditions according to which the indicator changes:

  • degree of porosity;
  • the structure of individual grains of sand;
  • quantity and type of various impurities;
  • humidity percentage indicator;
  • sand moisture level.

The change in volume is most affected by the amount of moisture. The higher this indicator, the less construction sand density indicator, which significantly distinguishes a cube of dry material from a wet one in size.

Based on size, coarse-, medium- and fine-grained material is distinguished. How larger size grains of sand, the higher the bulk density. This is due to the presence of more significant voids. For smaller grains of sand in a unit volume, due to greater compaction, they are placed large quantity. Impurities are removed by washing the extracted sand, but this significantly increases its cost.

The porosity value indicates the nature and number of voids between individual grains. The higher this value, the lower the compaction rate. For loose sand this value is 47%, for compacted sand - 37%. Moisture reduces the number of voids as water fills them. The number of voids also decreases as a result of transportation, since due to the vibration that occurs during movement, the material sags. More compacted sand for construction purposes should be used when creating reinforced concrete and concrete products with maximum accuracy. They are able to withstand the heaviest loads with their even distribution.

What determines the degree of compaction?

The purpose of the material greatly depends on its density, for which types of buildings and types of structures its use is permissible. According to this indicator, the consumption of the amount required for certain purposes is calculated. After all, it is important to know the amount of mixture that will be obtained using a specific type starting materials. It is often necessary to convert mass to cubic meters and vice versa.

Some construction bases sell sand in tons, while others sell it in cubes.

To convert data to other units of the measuring system, you should use the school formula for volume and density:

P = m / V, Where:

  • P - bulk density or degree of compaction;
  • m is the calculated mass of bulk material;
  • V is the available volume.

For example, let's calculate the density of an arbitrary type of sand weighing 3.2 tons or 3200 kg, occupying a volume of 2 m 3. The quantitative value of density according to the formula is found as:

P = 3200 / 2 = 1600 kg/m3.

Similarly, if you have data on the volume and a known degree of density of sand, you can find its wet weight or in its natural state of moisture:

The indicator is influenced by the following factors:

  1. poured in the usual way sand has a significantly lower density than compacted during laying;
  2. After caking the material at a certain stage, the sand varies in moisture content. Weight gain occurs as a result of water entering micropores between grains of sand;
  3. On value bulk mass bulk material is affected by the presence of organic additives and soil-containing impurities. For most mortars According to the preparation technology, a fine filler of a high degree of purity is needed, which requires adjusting this indicator by sifting or washing;
  4. Depending on the breed of origin, there are materials of different densities, which directly affect the weight;
  5. The shapes, as well as the fractions of the existing grains, largely determine the density of the sand. The larger the fragments contained in the embankment, the greater the distance required between the grains filled with an air gap.

Density calculation

Different types of sand are delivered to the construction site. It can be used either immediately after delivery or after certain processing. When storing bulk material without cover outdoors, the density of sand grains constantly changes.

In practice, such calculations can be carried out independently. To do this, take a container of a certain volume. For example, this could be an 8 liter bucket. After pouring the materials into the bucket, use a ruler to level the surface of the heap. After weighing the filled bucket, as well as determining the mass of the container itself, the calculation formula takes the form:

P = (m 2 - m 1) / V, Where:

  • m 1 is the weight of the container used to measure the density of the sample;
  • m 2 is the total mass of the bucket filled with sand;
  • V is the container volume, in our case 8 liters.

First you need to convert the volume into cubic meters, 8 liters is 0.008 m 3. In kilograms this is 0.45 kg, and a filled bucket of sand weighs 12.65 kg. The resulting density is defined as:

P = (12.65 - 0.45) /0.008 = 1525 kg/m3.

Using the compaction coefficient, without weighing the sand before use, you can determine its actual mass, which constantly changes for different types grain size of the material.

To obtain the desired result, you must multiply by the coefficient average density building materials. The table contains the coefficients of the most popular types of sand. However given value does not guarantee high accuracy, having an error of 5%. Weighing, which is inconvenient and sometimes not at all possible, is the single most reliable way to determine the density indicator. At the construction site, specialists can use any of the available methods.

When purchasing material, you should carefully calculate the moisture content of the purchased sand.

Density depending on the type of sand

Most often in construction, quarry, river or construction material. River sand is formed naturally because the rock is crushed naturally, which gives the sand grains a rounded shape. This material contains a minimum amount of impurities, which does not require additional processing. Depending on the size of the grains, several groups are distinguished:

  • 2.9 - 5 - large;
  • 2 - 2.8 - average;
  • up to 2 - small.

The average bulk density is approximately 1650 kg/m3. This material has the main advantage of being environmentally friendly and safe.

The cost of this type of sand is very high, so according to technical standards it can easily be replaced by a career one.

This type of material contains various rocks - quartz, mica, spar. The name is assigned according to which element predominates in it. The main area of ​​application is the creation of bedding, foundation cushions, and gaskets. highways.

Properties of sand

There is also an indicator of the true degree of compaction. This value is determined exclusively in laboratory conditions. For this indicator, voids and gaps are not taken into account.

The grain size affects the amount of binder for a particular type of mortar. To make the structure strong, all voids must be closed with cement. This increases the cost of concrete or cement composition. IN quarry sand you need to pay attention to the degree of radioactivity. For the construction of residential buildings, it is necessary to use only quality class 1 material of this type.

Conclusion

The bulk density indicator is very important parameter sand, which affects the quality and strength of future structures. In addition, you need to know it for calculations building mixtures, the required amount of material. That is why this value cannot be ignored.

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

The average density of coarse aggregate grains is 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.

Bulk density- mass per unit volume of loosely poured granular or fibrous materials(cement, sand, gravel, crushed stone, granular mineral wool and so on.).

Determination of the bulk density of loosely poured granular or fibrous materials is carried out by weighing a certain volume of material (by the method of measuring cylinders or vessels).

Bulk density (g/cm3, kg/m3) is calculated by the formula

, (9)

where is the mass of the graduated cylinder with the material; - mass of the graduated cylinder; - volume of the cylinder.

The order of work when sandy soil loose build. The sand is dried in drying cabinet at a temperature of (110±5)°C to constant mass and sifted through a sieve with holes measuring 5 mm. Dried sand from a height of no more than 5 cm is poured into a pre-weighed measuring cylinder along an inclined tray (Fig. 5), along a chute bent from a sheet of paper or with a scoop until a cone is formed above the top of the cylinder. The sand cone (excess material) is removed flush with the edges of the cylinder with a metal ruler. The cylinder with the material is weighed.

The procedure for performing work in dense sandy soil. The experiments are carried out similarly to the previous one. The prepared sand is poured in small portions into a measuring cylinder and compacted with a rubber hammer by tapping it on the walls or bottom of the cylinder. As the material shrinks in the cylinder, it is added until the cylinder is completely filled.

The results of the experiments are recorded in Table 6.

Table 6

Bulk density determination results

Determination of bulk density using these methods is carried out three to five times, each time taking a new portion of the material. The bulk density of the material is calculated as the arithmetic mean of the results of all determinations.



Porosity determination

Porosity(total) - degree of filling of the material with pores:

Where - pore volume in the material; - volume of material in its natural state.

Open porosity is defined as the ratio of the total volume of pores saturated with water to the volume of the material , those.

. (11)

Closed porosity :

. (12)

To determine the total porosity, there is an experimental and experimental-calculation method. The experimental (direct) method is based on replacing the pore space in the material with liquefied helium and requires complex testing equipment.

The experimental-calculation method for determining porosity uses the found empirically values true density material and its average density in dry condition.

Porosity (%) is calculated using the formula

. (13)

Open porosity (%) is determined by the formula

Where - volumetric water absorption of the material, % (see clause 1.6).

The results of calculating the porosity of the material are entered in the table. 7.

Table 7

Results of material porosity calculations

Humidity determination

Material moisture characterized by the amount of water contained in the pores and adsorbed on the surface of the sample.

Sample moisture content (%) is calculated using the formula

, (15)

where is the mass of the wet sample, g; - mass of dry sample, g.

The moisture content of concrete is determined from samples or samples obtained by crushing samples after testing them for strength. The size of the pieces after crushing should be no more than 5 mm. By quartering, a 100 g sample is taken, which is dried at a temperature of (105 ± 5) ° C to constant weight. To establish that the sample has reached a constant mass during the drying process, weighings are performed at least after 4 hours. The mass is considered constant if the difference between repeated weighings is no more than 0.1%.

The results of the experiments are recorded in the table. 8.

For bulk materials (cement, sand, crushed stone, gravel, etc.), bulk density is determined. In the volume of such materials there are not only pores in the material itself, but also voids between grains or pieces of material. This determination is carried out using a device (Figure 1.5), which is a standard funnel in the form of a truncated cone. At the bottom, the cone goes into a tube with a diameter of 20 mm with a valve. A pre-weighed measuring cylinder with a volume of 1 liter (1000 cm 3) is installed under the tube. The distance between the top edge of the cylinder and the valve should be no more than 50 mm.

They pour into the funnel dry test material, then open the valve and fill the cylinder with excess, close the valve and use a metal or wooden ruler to cut off the excess material from the middle in both directions, flush with the edges of the cylinder. In this case, the ruler is held obliquely, pressing tightly against the edges of the cylinder. It is necessary that the cylinder is stationary, since shocks can compact the bulk material, which will increase its average density. The cylinder is then weighed to the nearest 1 g. The test is repeated five times and the average density of the material in the loosely poured state is r n , kg/m3, calculated as the arithmetic mean of five determinations using the formula:

ρ n = (m 1- m2)/V, (1.9)

Where: m 1 - mass of the cylinder with material, kg; m 2 - mass of the cylinder without material, kg; V - cylinder volume, m3.

Rice. 1.5. Standard funnel

1 - body; 2 - tube; 3 - valve; 4-dimensional cylinder

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

For wet material, bulk density is calculated using the formula

ρ w n = ρ n (W + 1), (1.10)

Where: W - material humidity, rel. units

Question: Is this formula always correct?

Yes, if moistening does not lead to a change in the volume of the material (this is taken into account when deriving formula (1.10)). But for finely dispersed material (this does not include sand, since its fine fraction must be at least 0.14 mm), when moistened, this condition will first be met, and then the volume will increase due to the moving apart of the grains by adsorbed water. In this case there will be a decrease ρ w n with increasing W (since the density of water is less than sand).

Derivation of formula (1.10).

1. Material moisture content: W = (m in. – m)/m, Where: m ow.– mass of wet material, g; m– mass of dry material, g.

From here we find m ow. = m(1+W).

A-priory ρ w n = m ow. /V, Where V– volume of wet bulk material (here it is tacitly accepted that the volumes of dry and wet bulk material are equal!).

After substitution we have: ρ w n = m ow. /V = m(1 + W)/V = ρ n (1 + W).