High-Speed and High-Temperature Powder Metallurgy for Energy

Efficiency and Environmental Protection

DIMITAR KARASTOYANOV

Institute of Information and Communication Technologies,

Bulgarian Academy of Sciences,

Bl. 2, ac. G. Bonchev str., 1113 Sofia,

BULGARIA

Abstract: - The article examines various approaches to creating industrial products from metal powders using

powder metallurgy methods. The advantages of powder-metallurgical methods for the production of details in

comparison with classical methods are cited. Innovative grinding bodies and grinding media are presented.

Possibilities of adding micro and nano elements are considered. A high-speed and high-temperature technology

for obtaining wear-resistant materials is described. Possibilities for the utilization of waste materials - glass and

electronic boards - were discussed. Applications in industry, medicine, and agriculture are presented.

Key-Words: - metal powders, innovative grinding bodies, innovative grinding media, powder metallurgy, high-

speed compacting, high-temperature sintering, waste processing, energy efficiency.

Received: March 11, 2024. Revised: August 13, 2024. Accepted: September 7, 2024. Published: October 2, 2024.

1 Introduction

Globally, 20% of the extracted energy is used for

crushing and grinding processes. The use of

innovative grinding bodies and grinding media

makes grinding energy efficient. Also, the processes

of chip removal, forging, and similar have high

energy costs and high losses, especially for metal

products. Some waste products are harmful, break

down slowly, and pollute the environment. The

processing of other waste materials (glass,

electronic boards) contributes to environmental

protection.

Mass-spread methods for thermal and chemical-

thermal treatment of tool and structural steels are

gas carburizing and gas nitrogen carburizing. Shaft

furnaces are used with external indirect heating of

the products in retorts. Other additional equipment

is used for tempering, including second-heat

tempering furnaces, conveyors, oil baths, degreasing

equipment, retort furnaces, etc. These methods are

characterized by several disadvantages such as high

consumption of reactive gases, non-uniformity of

the diffusion layers, a high degree of environmental

pollution due to the release of poisonous gases

during quenching, the presence of technological

waste from the quenching oil, and the need to

degrease the products after quenching by using

organic and inorganic degreasers, partial

decarburization and oxidation of the surface of the

products during transportation in a heated state.

The high efficiency of powder metallurgy (PM)

lies in the production of materials or products that

are technologically impossible or economically

unprofitable to produce by other methods. A feature

is that the products are produced using practically

waste-free technologies, [1], [2], [3]. Regardless of

the higher price of powders than that of cast metals,

the price per PM unit is lower than that of cutting,

stamping, milling, etc. With PM, the coefficient of

use of materials is in the range of 95-97%, while

with processing by cutting, this value is only 50-

60%. The small number of operations (3-5), allows

for the concentration of the production of parts in

one place, and this is related to increasing

productivity and automation, reducing energy losses

and the number of staff. As a result - lowering the

price of the final product. When working with

automatic presses, the amount of powder needed to

obtain a blank with a certain density is precisely

dosed, avoiding material losses inevitable in the

mechanical processing of cast parts. The method is

unique in the production of composite materials on a

metal or ceramic basis: copper-graphite for current-

carrying parts, WC-Co for metalworking tools, W-

Cu alloys, and many more. Others, [4], [5], [6].

These materials include the methods proposed for

development with the inclusion of micro and nano

elements - based on titanium carbide (TiC) and

based on boron carbide (B4C).

In the paper, we offer the following

innovations:

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2024.20.43

Dimitar Karastoyanov

E-ISSN: 2224-3496

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- obtaining metal powders through innovative

grinding,

- obtaining blanks from metal powders by

high-speed impact pressing,

- production of powder-metallurgical details

by high-temperature sintering,

- obtaining powders from other materials -

broken glass, broken electronic boards.

2 High-Speed Metal Powders

Compacting

The developed product represents an innovative

technology for obtaining metal products by the

methods of powder metallurgy. The innovative

technology involves the energy-efficient production

of fine metal powders by grinding using patented

innovative grinding bodies (Reuleaux tetrahedron* -

Figure 1, [7] in mills with patented innovative

grinding media (Reuleaux triangle lifters** - Figure

2, [8]. The inclusion of micro- and nano-elements

(for example, titanium carbide or boron carbide) in

the metal powder material is planned to increase the

hardness and wear resistance of the parts.

Fig. 1: Reuleaux tetrahedron

Fig. 2: Lifter with a section triangle of Reuleaux

*Reuleaux tetrahedron – has the largest area of all convex 3D

figures with equal volume

**Reuleaux triangle – has the largest perimeter of all convex

2D figures with equal area.

The energy efficiency and better quality of the

metal powder are demonstrated by using a ball mill

- tandem with one drive on two drums - Figure 3. In

one drum are placed the innovative tetrahedrons of

Reuleaux and in the other - traditional spherical

grinding bodies. At the same speed and the same

grinding time, the size of the particles from the two

drums and their size distribution are compared with

a laser nano-granulometry unit with a lower limit of

10 nanometers - Figure 4. If the uniform particle

size is required, it is proven that with the innovative

grinding bodies, this is achieved in a shorter time,

correspondingly with less energy consumption.

Fig. 3: Ball mill – tandem

Fig. 4: Laser nano granulometry unit

The obtained metal powders by grinding or

atomization [9], [10] are placed in test matrices of

different shapes and compacted by a high-speed

impact press with frequency control and the ability

to set the number of impacts - Figure 5. The blanks

thus obtained are sintered in an oxygen-free

environment in a muffle furnace up to 1700-1800 0C

- Figure 6. If hardening is required, the parts are

annealed to 900 0C and reheated in an electric

furnace to 1100-1200 0C.

Fig. 5: Impulse impact press hammer

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Dimitar Karastoyanov

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Volume 20, 2024

Fig. 6: Muffle furnace

In Figure 7 the structure diagram of the

developed innovative technology is shown. Metal

powders obtained by innovative grinding (possibly

with added micro and nano elements) are poured

from a dosing device into special matrices. The

matrices are located on a four-position rotary table.

A robot takes the completed matrices and places

them in a high-speed press, where the metal powder

is compacted into blanks. The blanks are placed in a

high-temperature furnace, where they are sintered.

1-Impulse press hammer

2-Bunker for metal powder

3-Dosing device

4-Rotary table

5-Stationary robot

6-High-temperature furnace

7-Table for details

8-Control panel

Fig. 7: Innovative technology for obtaining metal

powder products

3 High-Temperature Metal Powders

Sintering

We also offer an innovative high-temperature

technology (over 2000 0C) for active sintering of

high-temperature wear-resistant boron carbide

materials using a technological line with a graphite

Tamanov furnace - Figure 8. The Taman furnace is

a thick-walled graphite tube, short-circuited to a

powerful current source. In the Work Zone, the

walls are thinned, the resistance is greater and the

zone heats - max. up to 2300 0C, a temperature that

only graphite can withstand. Graphite ships are

pushed through the Work Zone from the conveyor

with a pusher rod - Figure 9, filled with mixtures of

metal powders that are melted and homogenized.

Fig. 8: Technological line with graphite Tamanov

furnace

Fig. 9: Graphite ship

In the hierarchy of materials in terms of

hardness, boron carbide ranks third after artificial

diamonds and the cubic modification of boron

nitride, but the synthesis of B4C proceeds relatively

easily. The synthesis of (BN)c from (BN)h takes

place under higher temperatures and pressure than

the synthesis of diamonds from carbon materials. In

addition to super hard (~40 GPa), boron carbide also

belongs to hard-melting (2450 oC) materials.

The applications are:

The B4C is used in the manufacture of the nuclear

reaction control systems, [11]. The B4C is used also

in military technology for making bulletproof vests,

and armor for tanks and helicopters. Calipers,

templates, sharpening tools, thermocouple guards,

mortars, etc. are made from boron carbide. Boron

carbide produces high-quality sandblasting and

shotblasting nozzles with diligence in metallurgy,

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engineering, shipbuilding, architecture, and

dentistry. B4C is used for nozzles instead of Al2O3,

in tumor diseases instead of BNC, [12]. The high

thermal and chemical stability determine the

application of B4C in the architecture of fuel cells

as a catalytic carrier, [13].

4 Processing of Other Waste

Materials

Another innovation is grinding instead of melting a

waste product - broken glass and the idea is to use

the resulting fine glass powder in construction in the

production of concrete. The quality of the obtained

material is established through research in

specialized laboratories. Glass waste (flat glass,

bottles, jars, household baking dishes, LCD screens,

etc.) is very suitable for processing in ball mills.

Depending on the operating modes of the ball mill

and the duration of grinding, products of different

shapes and sizes can be obtained. Larger products

with a size of 4 - 20 mm are used as substitutes for

gravel. Products with smaller sizes are used as

substitutes for sand or cement (< 48 µm).

It is also an innovation to grind other

ecologically harmful waste products - crushed

electronic boards, from which metal powder can be

separated from the busbars and other metal elements

using a cyclone-type separation and filtering

through water instead of direct disposal. Metal

powders are sifted in a system of precision sieves.

5 Conclusion

Innovative grinding bodies and innovative grinding

media enable energy-efficient production of metal

powders. The addition of micro and nano elements

in metal powders, high-speed impact pressing, and

high-temperature sintering make the products harder

and wear-resistant. The reduction of waste products,

as well as the disposal of other waste materials,

contribute to the protection of the environment.

Materials with high hardness and wear

resistance, produced with energy-efficient

technologies, can be used in various industries, for

example, for elements in the construction of large

buildings in agriculture – greenhouses, and

hothouses in crop production, stables and cowsheds

in animal husbandry, etc. Materials produced from

waste products such as glass can also be used in

these industries, [14], [15].

Acknowledgment:

The paper is supported by the Bulgarian National

Science Program “Intelligent Animal Husbandry”,

Grant Agreement No D01-62/18.03.2021.

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

Dimitar Karastoyanov carried out the simulation,

the data collection, and the experiments.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflicts of interest to declare.

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Creative Commons Attribution License 4.0

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