Foundries forge ahead

By Jessica Roberts
Published: Friday, 27 May 2011

A healthy resurgence for metal casting in 2011 is spurring demand for foundry raw materials, but producers are struggling to supply niche minerals as stocks dwindle

 Forging ahead: production of iron for metal casting. Ferrous products account for 83% of the foundries market.
Global metal casting output reached 80.3m. tonnes in 2009, down from 93.5m. tonnes in 2008, with the top three producing countries - China (35.3m. tonnes), India (7.44m. tonnes) and the USA (7.40m. tonnes) - representing 62% of global production. In the traditional foundry hub of Western Europe, Germany led the market with an output of 3.9m. tonnes.

The data reported are from production numbers provided by each nation’s metal casting association for 2009, collated by the World Foundry Organisation. Although production suffered falling volumes in 2009 - corresponding to lower demand for metal products in end markets such as automobiles and construction - preliminary data from 2010 indicates that casting output increased last year, with output expected to reach 2007 levels by 2012.

Production is segmented into the categories of ferrous and non-ferrous castings (see Figure 1). Foundries within the ferrous casting industry produce grey, ductile, malleable, compacted graphite iron and carbon and low alloy, corrosion resistant, heat resistant, manganese and other steel cast products. This segment accounts for 83% of the market, while non-ferrous foundries - producing copper-based alloys, aluminium, magnesium, zinc and other non-ferrous metals - account for 17% of the metal casting industry.

 Table 1: Favourable zircon properties for foundry uses
 Source: TCMS

Of the ferrous metals, 49% of production is grey iron, 38% is ductile iron, steel accounts for 12% and malleable iron for 1.3%. Among the non-ferrous metals, aluminium dominates with 82% of the total, copper alloys account for 13%, followed by zinc at 4%, and magnesium at 1%.

Despite grey iron accounting for close to half of the ferrous casting industry, its global share is shrinking. Over the last decade or so, grey iron production has increased 9.3% while ductile iron production has climbed by 39.6% and steel production has boomed 50%. Grey iron’s market share has also fallen owing to the growth of non-ferrous casting output, which has increased by 41.1% since 1999 - largely from higher aluminium casting output.

North American foundry materials supplier HA International believes the growth for metal casting is expected to be seen predominately in aluminium and magnesium applications, adding: “Iron and steel applications are expected to remain flat.”

“Traditional markets such as automotive, rail and construction continue to drive metal casting production, with newer markets - such as wind energy - growing to take a noticeable share,” HAI revealed.

 Figure 1: World casting production by metal (80.3m. tonnes)
 Source: Modern Casting

According to the American Foundry Society, new proposed fuel economy standards will further increase aluminium casting as the automotive industry moves away from iron engine blocks, cylinder heads and differential and suspension castings in passenger automobiles and light trucks.

This trend towards aluminium for motor blocks and cylinder heads has led to conversion away from green sand molding with phenolic urethane cold-box and hot-box cores, HAI explained. For aluminium blocks, a ‘precision sand’ mold is prepared.

Precision sand refers to a molding process to produce castings with low dimensional variation in a bonded molding media (usually sand). Numerous cores are held together in a flaskless package, and the internal passages and external geometry of castings are produced without the use of a traditional mold or pattern plate.

“These technological and material changes will continue to affect metal casting facilities and cause significant change in the global supply and demand of castings,” HAI revealed.

“The change to light metals in automotive applications has caused the closure of many operations and reduction in production capacity in iron casting operations, while aluminium demand and supply numbers rise to new peak levels in both die casting and permanent mold operations,” the company told IM.

 Figure 2: Global production of automobiles, 2010 (top 10 countries)*
 *provisional results
Source: International Organization of Motor Vehicle Manufacturers (OICA)

These changing trends have affected consumption of foundry raw materials, which include a number of industrial minerals used as foundry sands and as additives in the casting process (see panel).

The principal foundry sands are chromite, olivine, silica and zircon; silica represents the lowest cost and most widely used material. The remaining minerals are demanded in niche applications; speciality foundry minerals are applied in substrates to prevent expansion defects in molding materials exposed to particularly stringent thermal stresses.

New substrates are being introduced as certain mineral sands increase in cost and/or become scarce. This is seeing products such as synthetic ceramic mullites, graphite sands and andalusite sands - such as Damrec’s Kerphalite product - being offered to the market.

Chromite challenge

One mineral that has seen significant price increases over the last six months is chromite sand, which has been used in foundries for over 50 years. Chromite has steadily expanded its end market from manganese steel castings to a wide range of ferrous and non-ferrous castings.

Construction of Oregon Resources’ mineral sands processing facility in Coos Bay, Oregon, USA. The plant is scheduled to produce 75,000 tonnes of chromite concentrate in 2011, in addition to smaller amounts of garnet, ilmenite and zircon. Oregon Resources Corp.

The mineral is commonly used to face large castings or thick sections and has gained popularity over the use of olivine, owing to the latter’s incompatibility with many synthetic binder systems. Similarly, foundries have re-evaluated the mineral’s ability to replace zircon sand as the latter has become difficult and expensive to purchase.

Global consumption of chromite foundry sand is around 700,000 tpa, with the foundry sector representing less than 3% of the mineral’s market (the bulk - over 90% - is diverted to metallurgical markets primarily for ferrochrome).

South Africa is the world’s largest chromite producer and an important supplier of foundry grade sand, with companies such as Rand York SA and US group Amcol International offering material from the country’s Bushveld Igneous Complex - estimated to contain up to 70% of the world’s chromite reserves.

Last year Amcol boosted the country’s foundry supply capability with a $50m. investment into the Ruighoek Chrome project, where it established a processing facility and warehouse to supply its Hevi-sand foundry product.

The facility allows Amcol to offer tailor-made grades to the market, such as higher chrome content and lower silicate levels - sized to the foundries’ requirements - rather than a ‘one size fits all’ product.

The facility is also an attempt to help stabilise the chromite sands supply chain, which has traditionally relied on ‘just in time’ deliveries - a challenging task for a market that is dictated by the sharp demand swings of the metal casting sector.

In fact, over the last three years or so, price fluctuations and material availability have been two of the key challenges for the chromite market, and this is particularly true for South Africa at present; the country is currently balancing tight availability with logistical problems.

One producer told IM: “We are entering wage negotiations and labour strike season again and in some cases labour is looking for 20% increases - which is very unlikely - but they will strike to force the mines’ and employers’ hands.”

Figure 3: Zircon prices, 2009-2011* 
 *Zircon, standard grade, bulk, FOB Australia
Solid lines = top of range; broken lines = bottom of range
 Figure 4: Chromite prices, 2009-2011*
 *Chromite, standard foundry, 46-47% Cr2O3, wet bulk, FOB South Africa
Solid lines = top of range; broken lines = bottom of range

In the past companies had huge buffer stocks to take away some of the impact of labour talks, but owing to destocking during the downturn and better than expected demand for casting from late 2010 to present, the country’s chromite stocks are inadequate, the producer warned.

This delicate supply balance comes at a time when the mineral is in high demand; zircon sand prices have doubled over the last six months (see Figure 3) and those who can are turning to chromite, either as an alternative source of supply or as a candidate for partial zircon replacement.

Similarly, chromite has increasingly benefitted from the burgeoning wind power market, which depends on well-manufactured wind turbine blades to function. Chromite sand can provide the kind of precision this market requires - offering excellent opportunities for chromite producers in Europe and North America, where the wind power industry is focused.

In the long-term the chromite sands market is addressing a number of key issues (see Table 2). Producers are increasingly aware of customer-specified grades and are looking to improve grain integrity and reduce silica content, which requires more focus on chromite processing techniques. The influence of customer-specified grades may also start to be seen through consolidation and vertical integration of the chromite supply chain.

Environmental issues are also faced by the foundry industry, with chromite consumers looking to improve the packing density of the particles to reduce resin consumption (not only lowering emissions but also reducing resin costs). Likewise, new recycling efforts are being made to re-use spent sands or extract chromium - also reducing foundries’ disposal costs.

Zircon shortage

Zircon’s refractory properties make it an ideal material for metal casting, with approximately 150,000 tpa of zircon sand consumed in this market (see IM May 2011: Zircon substitution - myth or reality? ).

The mineral is unique in that it is not consumed in the casting process; allowing it to be recycled to remove binders and separate other foundry sands. Despite this benefit, the cost of zircon sand has forced many of its consumers to find cheaper alternatives, such as chromite - although, as discussed above, chromite has its own supply issues.

Ceramics consultant Alister MacDonald, director of Technical Ceramic Marketing Services, estimates that chromite could substitute for zircon in up to 50% of foundry applications; and with zircon now costing four to five times more than chromite, there will be increased efforts to replace zircon - where possible.

“Security of zircon supply is more important than price for most foundry uses for zircon,” MacDonald told IM. “As zircon costs 4-5 times that of chromite, most people will have switched already if they didn’t need zircon.”

“The shift to cheaper (inferior) alternatives will be forced upon users who cannot secure zircon,” he explained.

One chromite project looking to bridge this gap is USA-based Oregon Resources Corp., which is developing a suite of heavy mineral sands Ð chromite, garnet, ilmenite and zircon - at its Coos Bay project in Oregon, on the west coast.

Chromite is the flagship product of the heavy minerals mix - with ORC and its parent company Industrial Minerals Corp. looking to produce 75,000 tpa. But the company is positioning itself as premium grade chromite producer - offering an alternative to bauxite, mullite and zircon - owing to the unique size and shape of its chromite sand grains (see IM July 2010: Foundries fire up a gear).

Industrial Minerals Corp’s CEO, Philip Garratt, told IM: “ORC’s sand has a rounded grain shape and narrow particle size distribution, which allows the rounded grains to pack together tightly.”

“This provides increased grain-to-grain contact and therefore increases the contact points for the binder to form more binder bridges,” he said.

During tests the company has observed higher tensile strength for cores, improved heat transfer, and an improved casting finish, Garratt commented.

ORC’s plant is currently being commissioned and is planned to achieve capacity (at the first year run rate) by July 2011, Garratt told IM, with the first-year production of 600,000 tonnes ore expected to produce: 75,000 tonnes of SpheriChrome chromite concentrate; 10-15,000 tonnes of chromite grading >42% Cr2O3; >12,000 tonnes of high-Fe ilmenite; 3,700 tonnes of zircon; and 13,000 tonnes of garnet.

In addition, production of more than 20,000 tonnes of aluminosilicates (kyanite, staurolite, epidote) will be returned to the mine site pending integration of additional product circuits, expected in 2012.

ORC revealed that HAI is the exclusive North American distributor of SpheriChrome, while German trading group Possehl will handle European sales.

Table 2: Chromite foundry sands market trends - past vs. present 
 Source: Vincent Agnello, IM Chromite conference, 2010

Metal casting outlook

Confidence is returning to the foundries sector, with a number of industrial mineral producers reporting positive market conditions for their grades.

Stan Franey, commercial director of Minelco Ltd, told IM that the company was seeing “healthy demand” for its traditional market regions of Asia and Europe, adding: “Foundries are expecting double digit growth, based on positive news flow from end users.”

IMC’s Garratt concurred: “The global foundry market so far this year has improved on the prior corresponding period, and there is strong demand for all of our products.”

Garratt warned that the sector was yet to reach pre-crisis levels in its main markets, but that metal casting was stronger primarily in Asia and South America.

He commented: “The opportunities for raw material supply are excellent for producers located in the USA, or in locations that have a US dollar cost base; these [producers] will benefit in the short to medium term.”

The source of the metal casting sector’s renewed confidence is largely owing to the motor vehicle industry - the biggest end market for foundries - which has seen better than expected demand return from Q2 2010 to present.

Provisional results of global automobile manufacturing in 2010, released by the International Organization of Motor Vehicle Manufacturers (OICA), indicate that just over 77.6m. units (both cars and commercial vehicles) were produced in 2010 - a growth of 25.8% on 2009 levels.

Of the top ten producers (see Figure 2), China led the group with an output of 18.3m. units, followed by Japan with 9.6m. units, and the USA with almost 7.8m. units.

China’s growth in motor vehicle production has occurred with astonishing speed; in 2009 the country produced 13.8m. units - representing a 48% increase - despite poor economic conditions for the rest of the world. The country followed this with an increase of almost 33% in 2010.

While fiscal stimulus aid packages failed to help western car manufacturers in 2009, these traditional motor vehicle production hubs - Germany, the UK and the USA - all posted significantly better results in 2010.

This was particularly evident in the USA, where auto manufacturing grew 35% - just exceeding the country’s drop in production in 2009 (34%). If the US auto market performs equally well this year, it will climb to levels not seen since 2006.

In the USA, the annual Foundry Management and Technology Business Outlook Survey of metal casting executives, managers and operators was conducted in October 2010, with the results noting an improvement in the economy with noticeable acceleration.

Demand recovery was described as starting in a modest and consistent fashion, followed by acceleration, with 57% of participants saying they expected to see increases in their production for 2011. However, there remained a conservative view on increasing capital. Also noted was the modernisation of China and India as a significant impact to the global economy.

Within the top five industry concerns, raw material costs, energy prices and imported castings were listed; indicating that while metal casting production had returned to the USA, China had exposed weaknesses and inefficiencies with US capabilities.

However, when the quality and delivery of the castings was considered, the real value of castings showed the USA to be a viable producer, the survey report added.

In recent months, much of the concern has focused on prices increasing for key raw materials such as chromite and zircon (see Figures 3 and 4), but also including chemicals such as phenol, methanol and furfuryl alcohol, HAI told IM.

“The impact is seen throughout key binding systems used in foundry, cold box, no-bake, acid set and resin coated sand,” the company said.

The main causes are related to limited supply with increased demand as well as rising fuel prices; and the outlook is for continued increases globally as the foundry industry recovers.

While the increases have affected the pricing structure for castings, all indications show that the increases in raw materials have not affected overall production levels: metal casting is on the up, and producers will need to secure raw materials.

The author wishes to thank Keith McLean and Lorena O’Neill from HA International for providing extensive information on metal casting processes.

 Zircon usage by application (2008)
 Source: TZ Minerals International
 Chromite sands by market
 Olivine sands by application
 Source: Industrial Minerals HandyBook, 4th ed.
 Silica sand end markets*
 *US markets
Source: USGS
Foundry minerals at a glance

Foundry sands

Chromite sand:
used in foundries for over 50 years and has steadily expanded its end market from manganese steel castings to a wide range of ferrous and non-ferrous castings, and is commonly used to face large castings or thick sections. Improvements in product quality and consistency and the incompatibility of olivine with many synthetic binder systems have boosted chromite’s market penetration. Pricing: $480-520/tonne for standard foundry, 46-47% Cr2O3, wet bulk, FOB South Africa.

Olivine sand:
widely used in the casting of manganese steels due to its basicity. The magnesium content of the olivine enhances its bonding characteristics when used with clays, reducing bentonite usage. It is also used in the production of castings (particularly non-ferrous) that require a fine surface finish as well as in core manufacturing. Olivine has faced competition from chromite sands as producers have improved the quality of their foundry grades and have benefited from olivine’s incompatibility with acid-cured binders. Pricing: €40-80/tonne ($59-114/tonne) depending on sand size, FOB European port.

Silica sand:
the principal foundry moulding material owing to its widespread availability and low cost. Fine, naturally bonded sands have traditionally been used in the casting of aluminium, light copper alloys, and light grey iron. Heavier, naturally bonded sands are used in the moulding of large iron castings. Applications for all naturally bonded products have declined in favour of blends of washed sands, bentonites and other binders and additives, owing to better control and customisation of product characteristics. Pricing: $20-22/tonne for bulk material, FOB DaNanag, Vietnam.

Zircon sand:
niche product that is capable of withstanding long exposure to the highest casting temperatures - typically between 1,550-1,650¡C for certain low alloy and low carbon steels. Its unique characteristics (such as refractoriness, low linear thermal expansion, and chemical stability) make it an ideal non-silica foundry sand. But high prices mean it is usually reserved for the most specialised applications; such as facings for heavy iron and steel castings poured at high temperatures, as mould paints or washes to improve surface quality, high definition cores, and shell casting and investment casting. Pricing: $1,600-1,700/tonne for standard material, bulk, FOB Australia.

Other sands:
andalusite, bauxite, ilmenite, kyanite, mullite, perlite, sillimanite, fused silica and staurolite.

Foundry additives

has good bonding characteristics and fast green strength, good hot strength, high gel formation and low permeability. It is used to bind green sands (such as olivine) together during foundry molding and metal casting. Both calcium and sodium bentonites are used in foundry applications, although Na bentonite is more stable at high temperatures - such as those encountered during casting of steel, ductile iron, and medium-heavy grey iron. Ca bentonite is more commonly used for detailed intricate castings, usually with grey iron, ductile iron, and non-ferrous alloys. Pricing: $90-115/tonne for foundry grade, bagged, railcars ex-works Wyoming, per s.ton.

is traditionally used in core and mold washings and foundry ladles. Low quality flake graphite or amorphous flake graphite can be mixed with other refractory minerals and shaped to form crucibles, molds and ladles for multiple metal types. Finely ground flake graphite or amorphous graphite can also be used with other minerals to form foundry facing or coating for molds - creating a smooth finish on castings. Pricing: $2,500-3,000/tonne for large flake, 94-97% C, +80 mesh, CIF.

Other additives:
alumina (fused and white fused), gilsonite, kaolin and mica.

The casting process

Casting is performed using disposable (non-permanent) or reusable (permanent) molds. In non-permanent or disposable molding, the mold is destroyed when the metal casting is removed from the mold. The opposite is true for permanent molds, where the mold is reused after the casting is removed.

The finished mold may consist of one or more parts (mold sections), such as the cope (top), drag (bottom) and cores, which form internal passages or cavities in the metal casting. Molds and cores are generally produced from similar molding materials. In most cases, the main component of these is silica sand bound with inorganic or organic binders.

In high production foundries, molds are produced on molding lines with cores produced using ‘core shooters’ or ‘blowers’ that use compressed air to facilitate filling of the core box with the sand/binder mix prior to hardening.

The most important raw material for disposable molds is quartz sand. Quartz (α-modification) is the most common modification of silica. When heated, α-quartz undergoes a transition to the β-quartz modification at temperatures above 573ºC (1,063 ¼F).

This reversible transition is accompanied by expansion of the crystalline lattice leading to a drop in the density from 2.65 to 2.50 g/cm3. Due to this quartz transition, ‘heat cracks’ leading to casting defects such as ‘veining’ may arise when the resin-bonded molds and cores are poured, depending on the degree of compaction of the molding material, the weight and temperature of the melt, and the cross-linking density of the cured binder.

Different binder systems are generally used for specific molding processes. Molds for ferrous casting traditionally have mainly been produced using inorganic binders such as clay and in a very few remaining cases, using cement or waterglass. The use of bentonite clay, water and a carbon-producing substance such as seacoal is referred to as ‘green sand’ molding, due to the fact that the binder never hardens or cures and remains moist.