The Promising Application of Vortex Layer Devices with Ferromagnetic Elements for Cement Improvement.

Cement is one of the most widely used construction materials. Every year, both production and consumption of cement increase. Cement quality defines the quality of concrete and durability of concrete structures.

Some of the cement particles, 70 micron and larger, are not fully engaged in hydration and not hydrated in the concrete. There are estimates that as much as 20 to 40 percent of cement take no part in solidifying and formation of a concrete structure.

Efficiency of cement is also reduced in long-term storage, when particles gather into larger lumps. The materials is hydrated by atmospheric moisture: cement may lose up to 20 percent of its efficiency after only three months of storage, and up to 40 percent after one year in the warehouse.

Increased consumption of cement can be avoided by grinding the cement again, which increases the mean surface area of the grains, accelerates hydration and improves strength.

IMAGE

Figure 1 – Ferromagnetic particles vortex layer unit: 1) protective collar; 2) rotating EM field induction coil; 3) induction coil case; 4) non-magnetic active chamber; 5) ferromagnetic particles.

Equipment Used For Cement Grinding

There are three types of equipment that can perform fine and superfine cement grinding:

  • Impact-action equipment (jet mills, hammer mills, centrifugal mills, etc).
  • Grinding-action equipment (roller mills, bead mills, overrunner mills, ring mills, pan mills, etc).
  • Combined impact and grinding equipment (ball mills, vibration mills, bead mills, attritors, planetary mills, colloid mills, etc).

In theory, all of the above can be used to pulverize construction materials, but not all can change their chemical activity by mechanical means. Besides, industrial mills consume a lot of electric power and are often very noisy. For instance, activation of cement by vibration mills may require as much 90 kWh/ton power, while a centrifugal mill may consume 78 kWh/ton.

One promising type of equipment for pulverization and activation of cement are magnetic mills with a vortex layer of ferromagnetic particles. These units feature comparatively low power consumption, small sizes and are easily retrofitted into existing production lines, improving their efficiency by subjecting the processed media to several factors and intensifying all processes.

How the Vortex Layer Device Operates

In simple terms, the vortex layer device (Figure 1) is similar to an induction motor without the rotor. Instead of the rotor, there is the active chamber 4, made of non-magnetic material.

The chamber contains cylindrical ferromagnetic particles (5), in the amount anywhere from several dozen to several hundred, depending on chamber volume. When the induction coil (2) is energized, it generates a rotating electromagnetic field, which interacts with the ferromagnetic particles, driving them on complex trajectories. The particles collide with one another and the chamber walls, forming the vortex layer.

 

The primary electromagnetic field, created by the external power source, interacts with the fields of the ferromagnetic particles, causing several additional effects with beneficial effects on the processed media (cement):

  • Direct interaction of the particles and the processed media.
  • Magnetostriction (mechanostriction).
  • Electrophysical effects etc.

The combined power of those effects is so great that can not only pulverize and activate cement, but also intensify these processes. Each ferromagnetic particle functions as both a grinder and an agitator. It only takes the vortex layer unit seconds or minutes to do what other mills do in hours.

The efficiency of the activation process in vortex layer units is influenced by several factors:

  • Strength and rate of rotation of the electromagnetic field.
  • Volume of the active chamber.
  • The amounts and ratio of ferromagnetic particles and cement in the active chamber.
  • The ratio between ferromagnetic particle length and their diameter, etc.

These parameters can be optimized by trial and error depending on the nature of the processed material.

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Figure 2 – Cement grinding and activation processing based on AVS-150 vortex layer units.

Figure 2 shows a part of production line for grinding and activation of cement based on GlobeCore machines, including two AVS-150 vortex layer units.

Results of Experimental Research

We set out to research the efficiency of using vortex layer devices for pulverization and activation of cement. For that purpose, we used an AVS-100 (laboratory scale) unit with steel ferromagnetic particles, a 22.5 Rck cement, sand and water.

These components were used to prepare samples of concrete, later tested for flexibility and compression. Some samples were made from the original cement, others were made using cement processed for 30, 60 and 120 seconds in the vortex layer device. The results are listed in Table 1.

Table 1 – The effects on mean surface area and strength of processing cement in vortex layer devices.

Retention time, seconds

Mean surface area, cm2/g

Flex strength, MPa

Compression strength, MPa

Days

Days

1

7

28

1

7

28

0

2800

1,18

3,34

4,4

4,7

22,16

29,4

30

3300

1,62

5,68

7,58

7,36

27,46

39

60

3700

1,96

5,88

8,2

9,3

28,24

40,2

120

6800

1,5

7,45

8,86

5,88

31,38

44,4

Conclusions

The data in Table 1 demonstrates that processing of cement in the vortex layer devices for 30 to 60 seconds does not increase mean surface area significantly. However, with retention time of 120 seconds, these parameters are more than doubled.

As far as mechanical strength is concerned, its improvement is quite obvious in all instances. Strength was in fact increased from 22.5 to 42.5.

These results show how promising the vortex layer devices are in production of microcement and construction mixes.

Frank May, GlobeCore service engineer, has more than 30 years of practical experience in operation and servicing of various industrial machinery. May is involved in the research of vortex layer device applications (construction material production, wastewater processing), as well as in the equipment for electrical insulation oil regeneration and power transformer servicing.

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