Reduction of Environmental Impact in Hardmetal Technologies

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Metal Powder Report Volume 72, Number 4 July/August 2017 metal-powder.net

Reduction of environmental impact in

hardmetal technologies SPECIAL FEATURE

Pankaj K. Mehrotra

Kennametal Inc., Latrobe, PA, USA

As energy, environmental remediation and raw material costs for hardmetal production escalate with

increasing demand, the need for developing and implementing technologies for reducing

environmental impact becomes more urgent, while, at the same time, reducing material cost. A range of

technologies can be employed for recycling hard and soft hardmetal scrap which consume less energy

and require lower capital investment than for virgin powder. Performance and processing targets with

recycled materials must be equivalent to those from virgin material. Conventional solvent based

processing can be replaced by water based processing of hardmetal compositions to reduce

environmentally damaging emissions and associated costs. This will be particularly useful as

government regulations move to reduce or eliminate emission of organic solvents. Raw material

consumption can be reduced by employing near-net-shape or net-shape technologies, since many

hardmetal parts are ﬁnished by hard grinding, which generates grinding sludge. Partial or complete

replacement of WC/Co with other hardmetals is another strategy worthy of consideration in reducing

the impact of hardmetal production on the environment.

Hardmetals play a critical role in myriad industrial processes 30% increase over the same period [2], although recent trends are

including manufacturing, energy production, construction, wear ﬂat, possibly due to developments in oil shale exploration.

resistant applications, etc. As a result, sustainable hardmetal pro- Furthermore, the availability of W bearing ores has become

duction is of paramount importance in supporting the modern more restrictive due to non-uniform geographical distribution

industrial base, especially as it expands with global population (Fig. 3). Over 2/3 of world reserves of W are in China and Russia

growth and elevated standards of living. Concurrently, reduction [3]. Although tungsten production and demand are in balance,

of environmental impact has become more urgent as harmful about 90% of production is located in the same two countries

emissions remediation costs have escalated, or has been complete- [4].

ly outlawed. As shown in Fig. 1, a majority of W production is used Therefore, it is important that strategies be developed to reduce

to meet the demand for hardmetals, so considerations for W environmental impact of hardmetal production, while simulta-

supply chain are critical to hardmetal production. neously increase supply and lower cost. This must be done without

Starting in 2003, W precursor prices underwent dramatic esca- sacriﬁcing form and function of the end product.

lation showing an eight times increase by 2011. Fig. 2 [1] shows Hardmetal manufacturing process is schematically depicted in

this trend since 2005, although, prices have moderated recently Fig. 4, starting from ore/concentrates to hard shaping. This paper

due to global reduction in industrial activity. At the same time, will examine technologies for reducing cost and environmental

industrial electric costs (as a measure of energy costs) have seen a impact, and increasing W availability during each of the processes

in the manufacturing chain. However, change in one process may

require modiﬁcation in a subsequent process to ensure process and

product performance remain unchanged. Therefore, a holistic

E-mail address: [email protected].

SPECIAL FEATURE Metal Powder Report Volume 72, Number 4 July/August 2017 PCA FEATURE SPECIAL

FIGURE 1

Applications of tungsten.

approach is required which considers the entire process chain for

beneﬁts balanced by costs.

FIGURE 3

Raw material production

Global W deposit reserves (3 million tons).

Greater recycling of hardmetal scrap in raw material production is

one way to simultaneously reduce cost, energy consumption and

environmental impact, while concurrently increasing W availabil-

ity. By one estimate, only 35% of W used is recycled [4], however, approach is the development of a separate value stream for addi-

recent trend is for greater recycling. A range of technologies can be tional recoverable materials which accompany the scrap, such as

employed for recycling hard and soft hardmetal scrap, which Co, Ti, Ta and Nb.

consume less energy and require lower capital investment than Uncontaminated soft scrap can be recycled by certiﬁcation and

by using ore concentrates. As stated before, performance and limited additions to the milling process. Composition control and

processing targets with recycled materials must be equivalent to grain size classiﬁcation are key control parameters in this regard.

those from virgin material. Both ‘soft’ and ‘hard’ hardmetal scrap Attention must be paid to carbon level to counter oxidation during

can be cleaned and oxidized to provide high W content feedstock powder handling, and microstructural features, such as porosity,

for ammonium paratungstate production, a common precursor uncrushed granules and contamination caused by improper pow-

for WO3 and virgin W metal powder. A consideration for this der classiﬁcation.

FIGURE 2

WO3 cost escalation over 10 years.

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Metal Powder Report Volume 72, Number 4 July/August 2017 SPECIAL FEATURE

FIGURE 4

Overview of hardmetal manufacturing process.

SPECIAL FEATURE

Hard scrap can also be recycled by other, lower cost, means, characteristics which do not affect the green shaping processes.

however with limitations in quality and use [5]. In the cold stream This includes powder ﬂow, Scott density and powder compaction

process, hard scrap is crushed and screened to generate powder behaviors. Furthermore, subsequent delubing and sintering pro-

which can be used to make grade powder. This process leaves cesses, such as sintering characteristics, including shrinkage, also

chemistry and grain size unchanged, but may increase some need to remain unaffected when using water processed powder.

impurities, such as Fe, as a result of the crushing process. The zinc Development of microstructure, carbon control and sintering

process is an established method to convert sintered hardmetal distortion are some of the properties which should be considered

scrap into powder by ﬁrst bloating it by making a Co-Zn amalgam, in this regard. Partial or full replacement of WC with other hard-

followed by Zn evaporation, crushing and screening [6]. The metals, such as TiC, TiCN, NbC and Mo2C, and of Co with Fe and

resulting powder can be subsequently milled to produce grade Ni, are additional technologies which can be used to tailor cost,

powder. WC particle size and impurities/alloying additions remain availability and environmental impact.

unchanged, and therefore, its use is limited to compositions with

similar grain size and chemistry as the starting scrap material. Also, Green shaping

Zn contamination needs to be controlled. High temperature bloat- Raw material consumption can be reduced by employing near-net-

ing, crushing and screening of sintered hardmetal scrap also yields shape or net-shape technologies, since many hardmetal parts are

powders which can be used in making hardmetal powders. Chem- ﬁnished by hard grinding, which generates grinding sludge [7].

istry of hardmetal in this process remains unchanged, but a Fig. 5 conceptually shows the relationship between pressing pres-

relatively large grain size results due to the high temperature used. sure, sintering shrinkage and microstructure, which can be used

Also, intensive energy consumption maybe a concern. Selective such that near-net or net shape parts can be pressed and sintered

dissolution of Co in an electrochemical bath is another process to with acceptable microstructure.

obtain WC powder from hard scrap, where relatively pure WC can Optimization of uniaxial pressing, use of multi-axial pressing,

be obtained with original grain size. However, consideration must and side pressing are green shaping technologies which can be

be made for recovery of Co and other additives and disposition of used for making complex, net or near-net shape parts. Fig. 6

solvents. schematically illustrates these technologies. They become partic-

Considerations for powders produced by recycling hard scrap ularly useful as complexities of parts increase to meet the ever

include carbon control and microstructure, since some of these increasing demand for performance.

processes may cause oxidation of powder, and pressing and sinter-

ing behavior may be different for recycled powders than those

made with virgin powders.

Grade powder production

Conventional processes to manufacture grade powder involve

solvents as transient additives to facilitate powder milling and

spray drying. Organic solvents have been traditionally used for this

purpose, which require not only expensive building and equip-

ment to handle ﬂammable liquids and vapors, but also entail high

disposal costs. Solvent based powder processing can be replaced by

water based processing of hardmetal compositions to reduce en-

vironmentally damaging emissions and associated costs. This will

be particularly useful as government regulations move to reduce or

eliminate emission of organic solvents in the industry. Process

development and choice of additives to optimize powder milling FIGURE 5

and drying are required. Powder, thus produced, should have Optimization of pressing pressure, sintering shrinkage and microstructure.

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SPECIAL FEATURE Metal Powder Report Volume 72, Number 4 July/August 2017

composite powders, such that both cost and performance can

be optimized for desired results. Thus, required high cost pow-

der is only used where needed, with the rest of the part being

made with a lower cost powder, requiring less recycling. This

necessitates development of green shaping and sintering pro-

cesses such that part performance remains unaffected. Another

approach has been to employ modular components, such that

non-critical segments are made with lower cost materials.

PCA FEATURE SPECIAL

Sintering and grinding

FIGURE 6 Sintering and grinding processes need to be considered in light of

Near-net and net shape pressing technologies. process changes discussed above, enabling reduced energy con-

sumption and cost, with lower environmental impact and greater

recycling. This may involve development of alternative delubing

and sintering processes for carbon control, control of sintering

distortion, considerations for furnace through put, capacity and

furniture, porosity reduction and densiﬁcation. Grinding of near

shape parts entails less material removal but may require develop-

ment of alternative processes to achieve needed shapes, sizes and

tolerances. This becomes all the more important as part complexi-

ty increases in response to the availability of more advanced

shaping processes.

Summary and conclusion

Hardmetal cost and availability are critical issues which need to

be addressed as environmental and material costs escalate, and

availability becomes limited. Greater recycling of raw materials

is a viable alternative to using ores/concentrates, and water

processing can signiﬁcantly reduce cost and environmental

impact of making grade powders. Partial or complete replace-

FIGURE 7

ment of WC and Co should also be considered in reducing the

Composite and modular designs.

environmental impact. Near-net and net shaping technologies

for green shaping must be investigated so that less powder is

used for making the same parts, especially as complexity re-

Injection molding and extrusion are other green shaping quired increases. Impact of new technologies, such as additive

processes which have been used to make complex net or manufacturing and information technology will become clear as

near-net shape parts. Furthermore, these technologies allow they mature and are implemented.

manufacture of parts which will otherwise be impossible or very

difﬁcult to make. Use of these technologies requires develop- References

ment of new processes and equipment, capable of greater preci- [1] www.itia.info/tungsten-prices.html.

[2] www.eia.gov/electricity/monthly/pdf/epm.pdf.

sion and repeatability. They may also affect subsequent

[3] www.itia.info/reserves.html.

processes of sintering and grinding. Green machining is also

[4] www.itia.info/supply-and-demand.html.

extensively used to make net or near-net shape hardmetal parts, [5] T.A. Wolfe, J.L. Johnson, P.K. Mehrotra, in: P. Samal, J. Newkirk (Eds.), ASM

which allows for less hard grinding and more green powder Handbook, vol. 7, Powder Metallurgy, ASM International, 2015, pp. 711–714.

[6] G.S. Upadhyaya, Cemented Tungsten Carbide, Noyes Pub, Westwood, NJ, 1998

recycling. A clear understanding of sintering shrinkage is re-

369–379.

quired to optimize the green machining process. As Fig. 7

[7] N. Myers, P.K. Mehrotra, in: P. Samal, J. Newkirk (Eds.), ASM Handbook, vol. 7,

schematically shows, many hardmetal parts are made with Powder Metallurgy, ASM International, 2015, pp. 715–719.

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