End User Focus: Scratching the surface

By Mike O'Driscoll
Published: Tuesday, 26 October 2010

Insight into the world of blasting abrasives and their key applications sees garnet fighting its corner against cheaper alternatives such as copper slag

The abrasives industry is an important consumer of industrial minerals; however, they compete with a variety of other inorganic and organic abrasive materials.

There is a wide choice of these abrasive materials and their selection is based on the end use application combined with the hardness, chemistry, particle size, and grain shape of the abrasive material.

For example, pumice blasted at a ship’s rusted hull just would not do the job, while steel shot sprayed on denim garments would render them denim ribbons very quickly. Switch around the abrasives, and then one will find that they are ideally suited for the respective applications. It is often a case of horses for courses.


Close-up of VV Mineral beach sand sourced
garnet, Tamil Nadu, India, which is exported
worldwide as a blasting abrasive.


In this article it is blasting abrasives which are the focus. This is one of the key abrasive market sectors, and one which uses relatively coarse particle sizes (12/20 and 30/60 mesh sizes) and loose abrasive grains. Other loose grain abrasive markets include the more precision-based polishing and lapping sectors, which use much finer particle sizes, and the growing use of waterjet cutting.

The other key abrasive market sectors are bonded abrasives (a mixture of abrasive grains, fillers, and bonding materials, eg. grinding wheels), coated abrasives (abrasive grain bonded to a backing material, eg. sandpaper), and superabrasives (grinding, polishing, or dressing tools manufactured using diamond or carbon boron nitride).

According to a report published by Market Technology Publications (MTP) in 2009, The Abrasives Industry in Europe and North America, the total market for loose, bonded, coated, and superabrasive products in the European Union in 2008 was valued at about €3.4bn. Germany is the largest market in the EU, with about 27% of the total.

The report considers that the overall total market is expected to shrink to around €2.9bn. in 2010 and then resume slow growth.

Another report, World Abrasives, published earlier this year by The Freedonia Group Inc., forecasts that global demand for abrasive products is to climb 5.9% annually through 2013 to $38.2bn.

Advances in developing parts of Asia, the Africa/Middle East region, Eastern Europe and Latin America are expected to considerably outperform demand in the USA, Western Europe, and Japan.

China, India, and Russia are anticipated to post some of the biggest sales gains. China, which has surpassed the USA as the largest national market for abrasives, will account for two-thirds of all additional product demand through 2013.

Anne Williams, marketing manager of leading silicon carbide and fused alumina producer Washington Mills Electro Minerals Corp., USA, told IM: “The market was down in 2009 but is recovering in 2010. We expect the market to continue to improve. The industry of pressure blasting is largely dependent on the strength of the manufacturing sector in general, such as in automotives and steel.”

V. Subramanian, managing director, of India’s largest garnet supplier, VV Minerals Ltd explained to IM: “The sand blasting market is doing well for us. Though the US market is showing a very slow recovery, the Middle East is still strong in sand blasting abrasive consumption. This is mainly due to many of the oil companies starting to revive projects which were on hold during the recession.”


One of VV Mineral’s classification plants at its
Tamil Nadu, India beach sand operation.
The company sells some 70-75,000 tpa of
blasting grade garnet.


The blasting market

According to MTP, blast cleaning and related abrasive material use in the EU is in excess of 850,000 tpa, worth approximately €285m. However, this figure also includes about 175,000 tpa of steel and cast iron abrasives.

This shows the relative competitiveness of alternative materials to abrasive industrial minerals. The accompanying table outlines the main industrial minerals used in blasting, and also the metallic and other abrasive media.

Although the end use and physical and chemical properties of abrasives are key to their selection, cost, efficiency, and availability are also important parameters.

There are very few commercial sources of garnet worldwide - Australian, Indian, and US garnets are the major ones that trade globally (see US garnet panel) - while there are even fewer for emery, olivine, and staurolite.

Synthetic industrial mineral abrasives such as fused alumina and silicon carbide are much more expensive than natural abrasive minerals (broadly speaking, natural mineral abrasives up to $200/tonne, while synthetic grades are >$700/tonne).

Therefore, alternative media such as coal slag, copper slag, iron grit, steel shot, and crushed glass, which are cheaper, much more readily available, and some of which tick the green box of potential recyclability as abrasives, can be more attractive to end users.

Another issue has been the move to using more silica free abrasives. However, the adherence to silica bans and reduction of use of certain slags owing to environmental concerns is less strictly enforced in certain countries.

Commenting on alternative materials, V. Subramanian, said: “Copper slag, though it is banned in many places, is still being used in most dry docks, due to the large volumes and very low price that manufacturers are dumping in the market. Coal slag is also a popular abrasive, mainly in Europe, but it tends to leave a coating/residue on the surface compromising the quality of the coating.”

Raymond Ding, managing director, of Chinese garnet producer Wuxi Ding Long Co. Ltd, commented to IM: “For China, the domestic sandblasting market is very limited. The existing market has been dominated by copper slag due to its very cheap price and there being no strict government regulation on pollution control. The main competitive abrasive media is still slag such as copper slag and nickel slag. Of other natural minerals, maybe olivine sand is a potential one in the future.”

The upshot is that metallic slags and coal slag have a market only because of their very low price when compared to garnet. Garnet is still claimed by producers as the only natural eco-friendly abrasive which is inert and safe for the environment.

“We do see steel slag as a new entrant and we are yet to see how the market responds to this material.” added Subramanian.


Blasting abrasive applications

End use sector Comments
Shipbuilding and maintenance shipyards for blasting coatings and stubborn mill scale and rust. Navy contracts very significant, eg. vertical launch systems, superstructures, fibreglass hulls, hangar decks, tank work and aluminium surfaces
Industry, infrastructure cleaning various industrial structures like tanks, and superstructures such as bridges, also stone and concrete structures.
Oil & gas industry rigs, platforms, pipes
Specialist industrial tasks more precise blasting required in blasting rooms and for heavy equipment cleaning (eg. construction, military vehicles); abrasive usually recycled; often utilising non-ferrous abrasives where aluminium surfaces, sensitive substrates, or installed electromagnetic components preclude the use of metallic abrasives.
Clothing use of soft abrasives to achieve desired “stonewashed” look


The silica issue

For many years, one of the primary blasting abrasives was silica sand. However, owing to its threat as a health hazard in causing silicosis its use has declined dramatically in recent decades.

Today, most blasting abrasives need to demonstrate a free crystalline silica content of <1-1.5% SiO2. Thus the term “sand blasting” refers to “sand” in the sense of the particle size of the material rather than silica sand itself.

However, there are parts of the world where silica sand remains the top abrasive of choice. This is the case in India where silica sand sourced from alluvial deposits is widely used in the treatment of garments, such as stonewashing denim jeans.

Indian media reports claim there are some 100 factories using silica sand in this application, with medium sized operations consuming 2,200 cu ft of river sand each month.

Previously, this Indian market had been outsourced to Turkey, but that country banned silica sand in this application in March 2009.

Some Indian garment companies are now using alumina abrasives instead of silica, but the investment in protective clothing and other measures is a major challenge.

Clearly, the overall phase out of silica sand as a blasting abrasive has created market opportunities for other mineral abrasives and also alternative materials.

Applications

Abrasives are used in an enormous variety of blast cleaning applications, from architectural restoration to marine hull cleaning. Each application favours a particular abrasive material for its cost efficiency and desired end result of the surface preparation.

The latter will be influenced by the abrasive particle size, shape, and hardness. The accompanying table illustrates some of the main applications for blasting abrasives.

The driver behind the blasting abrasives market is the essential requirement for proper surface preparation prior to any repainting or coating of industrial (and domestic) surfaces. In general, premature failure of a protective coating system is caused by improper or sub-standard surface preparation. One of the most effective methods of surface preparation is abrasive blast cleaning.

For large, industrial scale cleaning uses, where high iron content abrasives can be accepted, then much of the metallic abrasive media such as the slags and shot are used.

But if non-ferrous media is required, and also there is some care to be taken over avoiding damage to the structure’s substrate, then some of the industrial mineral abrasives will be favoured.

For more sophisticated blasting applications, eg. for specific components or small surface areas requiring very hard abrasives, then more expensive synthetic mineral abrasives like fused alumina and silicon carbide are applied in special blasting rooms where spent abrasive material is recycled.

Although brown fused alumina is >$700/tonne FOB (and white fused alumina around double), it is one of the hardest abrasives on the market (only silicon carbide is harder), it is relatively light, and can be recycled more often.

Fused alumina is used in specific industrial uses such as cleaning engine heads, valves, pistons and turbine blades in the aircraft industry, to lettering in monument and marker inscriptions. It is also commonly used for matte finishing.

The hardest mineral abrasive is silicon carbide, and can cost >€1,500/tonne CIF UK. Silicon carbide has a very fast cutting speed and can be recycled and reused many more times than other abrasives. The hardness of silicon carbide allows for much shorter blast times relative to softer blast media.

Silicon carbide grit is the ideal media for use on glass and stone in both suction or siphon and direct pressure blast systems.

Washington Mills Electro Minerals Corp. is the largest manufacturer and supplier of silicon carbide and fused alumina (both white and brown) to the abrasive blasting industry in North America.

Anne Williams, marketing manager Washington Mills told IM: “Brown

aluminium oxide’s high durability means that it can be used on multiple passes through the pressure blasting machine, thus increasing its efficiency as a blasting material. White fused aluminium oxide is higher purity than brown and the grains are more friable. It is used in applications where surface contamination is unacceptable such as cleaning medical devices or electrical circuit boards.”

At the other end of the scale is corn cob, an organic biodegradable blast media that will not etch or warp the surface being blasted. Corn cob is suited for applications such as wood surfaces, eg. in log homes, and thin metals and plastics.


Blasting abrasives

Abrasive material Mohs hardness (1, talc -10, diamond) Comments
Industrial mineral
Emery 7-9 naturally occurring corundum (alumina) with magnetite, haematite
Garnet 6.5-7.5 almandine and andradite varieties used
Olivine 6.5-7 used more in waterjet cutting
Pumice 5-6 “stonewashing” clothes use
Staurolite 7-7.5 byproduct of minsand operations
Brown/white fused alumina
9
synthetic; specialist use in blast rooms; recycled
Silicon carbide 9-10 synthetic; specialist use in blast rooms; recycled
Metallic
Coal slag 7 aluminosilicate waste from coal fired power stations
Copper slag 7 ferrosilicate; fast cleaning rates
Iron grit 8 made from alloy-free iron scrap; recycled
Nickel slag >7 high density, high productivity
Steel shot 8 very durable, low friability
Other inorganic/organic
Corn cobs
4.5
used as absorbent and abrasive; soft abrasive
Glass beads 5.5-6 no detectable silica
Crushed glass
6
made from recycled glass
Plastic media
3-4
eg. polyester, melamine; non-aggressive; used where underlying substrate cannot be damaged
Walnut shells
3-4
common soft abrasive


Garnet


Garnet, which can be sourced from hard rock deposits (more angular) or alluvial deposits (more rounded), is one of the most popular natural mineral abrasives used in blasting applications. Particle sizes used are mostly the mesh sizes 12/20, 20/40, and 30/60, ranging 250-1,700 microns.

Compared with fused mineral abrasives, garnet is far cheaper, eg. Chinese blasting grades (hard rock) are $185-195/tonne FOB Chinese main port; and those from India (alluvial) are 12/20 mesh, €270/tonne, 20/40 mesh, €220/tonne, and 30/60 mesh, €165-190/tonne all FOB Tuticorin. Generally, Indian coarse grades are more expensive owing to their tight availability.

Advantages in using garnet include: a wide range of grades and composition available for different uses and profiles; garnet grains create a uniform profile virtually free of embedment, providing an excellent surface for coating adhesion; cost-effective, highly effective with low consumption; non-toxic; inert; non-porous, will not draw moisture; recyclable up to five times; and low dust levels.

The mineral also has important markets in water filtration and waterjet cutting.

Although there are relatively few commercially developed garnet sources, garnet is traded worldwide, and certain players, such as Opta Minerals Inc., Canada, and GMA Garnet Group, Australia, have been very active in establishing processing and distribution plants in North America and Europe for their imported material.

GMA expands

This year was a significant one for GMA Garnet. The group’s Chinese subsidiary, GMA Garnet (China) Ltd commenced production at Rizhao, Shandong, where it operates a mine and 24,000 tpa garnet processing plant. The plant produces standard sand blast and waterjet grades, and will also produce a 20/40 mesh grade product for particularly thick sand blasting applications.

In Italy, GMA opened its upgraded Garnet Reprocessing & Recycling Plant on a new site in Aulla, Pallerone, the plant was previously located in Follo, La Spezia.

The Italian plant, operated by GMA Garnet (Europe) GmbH, will reprocess 15,000 tpa of used garnet from blasting and waterjet applications and has the capacity to upgrade production in line with demand.

In the USA, GMA Garnet Group opened a loose bulk handling and packaging facility in Fairless Hills, Pennsylvania, as a vital staging ground in the group’s distribution network for North America.

The facility receives approximately 10,000 tpa loose bulk shipments of GMA garnet shipped directly from Geraldton, Australia, which after processing, is distributed to waterjet and sandblast customers in the East Coast, Upper Mid West and Eastern Canada regions.

Elsewhere in the USA, GMA has established warehouses in Los Angeles, San Francisco, Phoenix, and Seattle.


US garnet market 2009 (tonnes)

Annual production: 56,000
Sold by producers: 28,000
Exports: 15-Apr
Imports for consumption: 41,100
Apparent consumption: 89,500
Producing companies: Emerald Creek Garnet Ltd., Idaho (WGI Heavy Minerals Inc.)
Barton Mines Co. LLC, New York
NYCO Minerals Inc., New York
Ruby Valley Garnet LLC, Montana
Processors/distributors: Opta Minerals Inc. (Canada/USA locations)
GMA Garnet Group, Perth, Australia (US locations)


Sinogarnet pursues Japan

In China, Wuxi Ding Long Co. Ltd, which produces 6-7,000 tpa of various blasting grades at Wuxi, Jiangsu, is seeing its 20/40 mesh grade perform well in export markets, especially in Japan, owing to its relatively large grain size range and lower price compared to Indian and Australian alluvial garnet.

“After so many years mining, the Indian and Australian alluvial garnets are short of coarse grades” said Raymond Ding, managing director, Wuxi Ding Long Co. Ltd.

VVM eyes Middle East

India’s leading garnet supplier is VV Mineral (VVM), which has mine and plant operations in the Tirunelveli district in Tamil Nadu, India.

VVM, and sister company Transworld Garnet India, sell about 70-75,000 tpa of blasting abrasives of which 25,000 tpa goes to the UAE, 10,000 tpa to Saudi Arabia, 20,000 tpa to the USA, 15,000 tpa to Malaysia/Singapore, and 5,000 tpa to Europe.

VVM is witnessing strong demand from the revived oil industry in the Middle East. V. Subramanian, managing director, VV Minerals Ltd told IM: “We foresee the demand will grow further in the coming months and we are already in the process of planning our next expansion ready to cater the growing demands.”

“Some of our Australian Garnet competitors are running short of coarse grades required for the sand blasting industry, which automatically puts the Indian manufacturers in a much stronger position.” Subramanian added.


US import sources 2005-08
(2009 imports 41,100 tonnes)





US consuming markets 2009
(89,500 tonnes)




Annual world production in 2009
(rounded total 1.4m. tonnes)



Source: adapated from data from USGS.