Liquidity evaluation and measurement method - Database & Sql Blog Articles

Evaluation and measurement method of fluidity

1

. Angle of repose

Angle of repose

Angleofrepose

) is the maximum angle formed by the free slope of the powder accumulation layer and the horizontal plane. Commonly used measurement methods include injection method, discharge method, tilt angle method, etc.

12-10

Shown. The angle of repose can be measured not only directly, but also by measuring the height of the powder layer and the radius of the disk. which is

Tan

θ

=

height

/

radius.

The angle of repose is measured by the gravity and the friction between the particles when the particles slide on the free slope of the volume layer of the powder pile and is in a static state. It is the easiest way to check the fluidity of the powder. The smaller the angle of repose, the smaller the friction and the better the fluidity. It is generally considered that θ ≤

40

° can meet the needs of production fluidity. Adhesive powder

Stickypowder

)

Or particle diameter is less than

100

~

200

μ

m

The following powders have large interparticle interaction forces and poor fluidity, and the measured angle of repose is correspondingly large. It is worth noting that the data obtained by the measurement method is different and the reproducibility is poor, so it cannot be regarded as a physical constant of the powder.

2

. Outflow speed

Outflow speed

Flowvelocity

It is described by adding the material to the funnel to determine the time required for all materials to flow out.

12-11

Shown. If the powder has poor fluidity and cannot flow out

100

μ

m

Glass ball assist flow, measuring the amount of glass balls required for free flow (

w%

) to indicate liquidity. The more the amount added, the worse the fluidity.

3

. Compression

Compression degree

Compressibility

) measuring the initial bulk volume after gently loading a certain amount of powder into the cylinder; using tapping

Tappingmethod

) to make the powder in the tightest state, measure the final volume; calculate the loosest density ρ

0

With the closest degree ρ

f

According to the formula

12-31

Calculating compression

c

.

(

12-31

)

The degree of compression is an important indicator of the fluidity of the powder, and its size reflects the cohesiveness and softness of the powder. Compression

20%

The following is better when the fluidity is lower, and when the degree of compression is increased, the fluidity is decreased.

C

Value reached

40%~50%

The powder is difficult to automatically flow out of the container.

4

. Internal friction coefficient μ

Internal friction coefficient

(coefficientofinternalfriction)

Measuring device

12-12

As shown, applying vertical stress σ to the stationary powder layer

(normalstress)

, applying shear stress Ï„ in the horizontal direction

(shearstress)

When the value of τ is small, the powder layer is in a static state, and when the value of τ is gradually increased to a certain value, the powder layer begins to slide. This state in which the powder layer begins to slide is called a boundary stress state. The relationship between the vertical stress σ and the shear stress τ in the bounded stress state. The relationship between τ and σ of the powder layer is a straight line passing through the origin (eg

a

When called, free flowing powder (

Freeflowingpowder

). μ represents the internal friction coefficient, called the internal friction angle. If the line does not pass through the origin (eg

b

When the line is), the powder is an adhesive powder

(cohesivepowder)

.

C

-Adhesion

(cohesiveforce)

. When the relationship between τ and σ of the powder layer is a straight line, it is called

Coulomb

Powder, according to μ, and

C

The size of the liquidity is evaluated, and the smaller the numbers, the better the liquidity. If the adhesion of the powder layer is strong, there is a non-linear relationship between τ and σ (eg

C

Line) relationship, at this time the shear properties of the powder are available

Warren-Spring

formula. σ

T

-tensile strength;

n

- shear index,

n

Value is close to

1

When the curve is near a straight line.