Metal Powders Industry Overview

Background

• The European powdered metals market has an annual turnover in excess of €6billion
• In North America sales in the powder metal parts and product industry are estimated at $5billion
• Annual world-wide metal powder production exceeds one million tonnes
• New commercial aircraft engines contain between 680-200 kg of powdered metal per engine

Metal powders

Metal powders are used in a wide variety of applications which include dietary supplements in food processing, additives in paint and other coatings, as pigments in printing and packaging, in solid fuels and cements. Probably the major area though is in the cost-effective production of metal components for a vast array of end uses.

Powder metallurgy

Powder metallurgy (PM) is a highly developed method of manufacturing reliable ferrous and non-ferrous metal parts. The process entails mixing powders and compacting in a die to give shapes that are then sintered or heated to bond particles metallurgically. As more than 97% of the starting materials reach the finished product, powder metallurgy is a process that conserves both energy and materials. It is a cost-effective process that can be used to produce simple or complex parts at or close to the final dimensions with production rates from a few hundred to several thousand parts per hour.

The first modern powder metallurgy product was the tungsten filament of electric light bulbs developed in the early 1900s. Today the industry is truly international and growing in all the major industrialized countries. Companies range from those producing conventional powdered metal parts using iron and copper-based powders through to manufacturers of specialty products including superalloys, porous products, friction materials, magnetic powder cores and ferrites, tungsten carbide cutting tools and wear parts.

The growth of the powder metallurgy industry during the past few decades is largely attributable to the cost savings associated with net shape processing compared to other metalworking methods, such as casting or forging. In some cases, the conversion of a cast or wrought component to powder metal provides a cost savings of 40% or higher.

Powder metallurgy is used in the manufacture of parts for:

• Automobile industry - motors, gear assemblies, brake pads
• Abrasives - polishing and grinding wheels
• Manufacturing - cutting and drilling tools (using hard metals)
• Electric and magnetic devices - magnets, soft magnetic cores, batteries
• Medical and dental - prostheses, amalgams
• Aerospace - motors, heat shields, structural parts
• Welding - solder, electrodes
• Energy - electrodes, fuel cells
• Abrasives - polishing wheels
• Other - porous filters, bearings, sporting goods etc.

More detailed information about the industry and the powder metallurgy process are available on the website of the Metal Powder Industries Federation www.mpif.org

Raw materials

Metals commonly used in powder form include iron, steel tin, nickel, copper, aluminium and titanium. Refractory metals include tungsten, molybdenum and tantalum. Bronze, brass, stainless steel and nickel cobalt alloys are also used.

Powder particles range from 0.1 to 1000 micron in size and must be carefully controlled. Major production methods include the atomization of molten metals, reduction of oxides, electrolysis and chemical reduction. Particle size distribution is a critical parameter. Powders with narrow particle size distributions behave predictably during mixing and mould filling; perform better during hot or cold compaction and sintering; will give a uniform coating in spray applications; and ultimately will give improved final product quality.

An important area of activity is the development of metal powder mixes using additives, binders and lubricants in order to improve the flow and limit powder segregation and dusting, ease the forming process and improve the performance of parts formed by compaction. The characterization of particles and particle mixes (powder) is essential in this domain.

Trends

In addition to the emergence of new submicron and nano-sized particles for specialized applications, areas of current development include:

• Investment in research, both academic and in industry, to improve manufacturing processes
• Production of fully dense PM products for improved strength properties and quality
• Commercialization of technologies such as metal injection moulding (MIM), rapid solidification and others
• Increased use of PM parts in automobiles

Source: www.mpif.org

Demands for advanced metal powders require higher specifications and these include:

• Finer powders, D v (50) < 10µm
• Controlled reproducible and tight particles size distribution
• Rapid Solidification Processing (RSP) characteristics
• High purity - free from refractory and oxide contaminants

Making and using metal powders

Metal powders are made either by gas atomization , or grinding , and are then classified using dynamic classifiers or cyclones to obtain the precise particle size distribution. To form the final end-user product, the metal powders are then used in various consolidation processes :

• extrusion
• injection molding
• blending
• compaction
• sintering

Key characteristics of metal powders include the particle size distribution, particle shape, the structure of the powder and its surface condition. These impact bulk properties such as flowability, reactivity, compressibility, porosity and hardenability which all improve as the particle size gets smaller.

The particle size distribution is important to the end user in the following ways:

• Direct impact on finished product quality
• Ease and efficiency of filling a die
• Wide size distributions allow voids between larger particles to be filled with smaller particles
• Porosity - fine particles leave smaller pores easily closed during the sintering process
• An excess of fines has negative effects on flow properties
• Caking, environmental contamination, pyrophoricity
• Balancing the properties needs dynamic process control

Malvern Insitec particle sizing systems have applications in the following key areas:

	Metal powder production
	Ore production Improving processing and control in mineral extraction and purification through the use of on-stream diluters in conjunction with on-line particle size analyzers.
	Milling Complete online and atline particle characterization systems appropriate to the requirements of the metal powders industry and unit operations.
	Atomization Here the challenge is to increase the powder yield, improve the powder quality and reduce the production cost.
	Classification Classifiers are used increasingly in conjunction with in-line particle size analysis combined with modern advanced control techniques.