AbrasiveBlastMediaLiteratureReview.f44eb0d4.436

LITERATURE REVIEW: ABRASIVE BLAST MEDIA

DRAFT REPORT BY PERA KNOWLEDGE

Written By: J R GOULD, B WILSON

Published by: The Waste and Resources Action Programme The Old Academy, 21 Horsefair, Banbury, Oxon OX16 0AH Tel: 01295 819900 Fax: 01295 819911 www.wrap.org.uk Published: (date) ISBN:

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LITERATURE REVIEW: ABRASIVE BLAST MEDIA

Contents

Body copy – to come once report is finally approved

Summary of Research Objectives To undertake a literature review and search regarding the environmental and health and safety issues and credentials together with any other related information regarding recycled glass grit, copper slag and other competing grit blast media. The literature review will be focused on glass grit and copper slag but the scope of the work will include other key blasting media. The output of the project will be a report summarising and evaluating the findings which will be utilised by WRAP to determine the strengths and weaknesses of the product comparative to other blasting abrasive media and as such identify the strongest way to promote glass grit.

Literature review: Abrasive blast media March 2003 1

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OBJECTIVE

The principle objective of this work is to undertake a literature review of published information on the subject of industrial abrasive media, including glass grit and copper slag and other competing materials. The main aspects to be considered are health and safety, environment, recyclability and performance. This will be supported by further related information and will be presented in a report summarising and evaluating the findings.

METHODOLOGY

Pera Knowledge has undertaken a desk-based evaluation of the subject of abrasive blasting media utilising global information from reference books and journals, scientific papers and conference proceedings. The papers and conference proceedings have been initially identified as a result of several external database searches using the following sources: • World Surface Coatings Abstracts (WSCA) – this is the database of the Paint Research Association (PRA,

Teddington, Middlesex) and covers all aspects of coating technology, including the surface preparation of materials which utilises abrasive media.

• Metadex – covers the technology of metallic materials which includes several types of blast media. • Ceramic Abstracts/World Ceramic Abstracts – covers ceramic technology which also includes several

types of blast media (alumina, silicon carbide etc.). • Corrosion Abstracts – covers corrosion technology, this being a factor associated with various types of

abrasive media. • Engineered Materials Abstracts – covers the technologies of polymers, plastics and composites. Various

types of thermoplastic and thermoset materials are used as abrasive media. • Copper Data Center – covers copper technology. • Mechanical Engineering Abstracts – includes references to abrasives technology. • Health and Safety Science Abstracts – covers health and safety issues, including references to materials

used in abrasive blasting applications. • Enviroline – covers pollution, environmental management and technology issues. Other reference sources have been used and a full listing is presented in Appendix 2. Further details on the scope and coverage of these databases are given in Appendix 3. The information resulting from the above searches has been reviewed with respect to key health and safety, environmental, recycling and operational issues for each type of abrasive material and following a short discussion of key points, has been summarised in a matrix. This summary allows the main issues to be compared in a structured manner.


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AN OVERVIEW OF ABRASIVE MATERIALS CURRENTLY AVAILABLE

The term ‘abrasive’ in blasting refers to a wide range of materials (blasting media) used to establish a profile on clean steel and remove unwanted coatings or contaminants from the surface of steel or other substrates. As well as those etching and cleaning applications, abrasive blast media can also be used for deburring purposes as well as peening, the latter process being used to impart residual compressive stresses to the treated material thus resulting in an improvement in fatigue strength. During blasting, there are a number of physical considerations in the selection of suitable media. As the grains impact the surface, there is a tendency for them to break down forming a potentially harmful dust. In addition, the cleaning action is the result of energy transfer, which is transferred from the abrasive to the substrate. As the kinetic energy is proportional to the mass of the grain and the square of its velocity, a small, heavy grain moving at high speed will have more effect on a substrate than a larger, lighter grain. From this, it can be seen that heavier (denser) materials such as steel and garnet are more efficient blasting media than lighter (less dense) media such as, sand and slag. Grain shape is also very important as rounded and angular grains behave differently when they impact a substrate such as steel. Angular grains tend to give rise to more broken particles and more dust whilst more rounded particles present a larger proportion of their surface to the substrate and as such, leads to reduced problems with the embedding of media into the surface. Another very important property of abrasive media is hardness. Hardness is a relative measure of the media’s resistance to abrasion by other materials. The hardness of mineral abrasives is often quoted using Mohs Scale of Hardness, after the German mineralogist Friedrick Mohs. This scale classifies minerals based on relative hardness of the unknown to a standard set of 10 minerals, ranging from very soft (talc) to very hard (diamond). The hardness of metallic abrasives is usually measured on the Rockwell system and steel grit generally has a Rockwell C value of 45 to 55 (roughly equal to 6.0 to 6.5 on the Mohs Scale). General attributes for a successful blasting media include the following: • Low health risk, including low levels of dangerous contaminants, such as asbestos (in olivine) and

arsenic (in copper slag). • Low levels of dusting under normal usage conditions. • High rates of production and cleaning, without distortion or other damage to the workpiece. • Durability of the media to allow collection, reclamation and reuse. • Appropriate grain shape and size for the intended application. • Low environmental impact during storage, use and disposal. One of the desired properties identified above is the recycling and reclamation of media, which given current environmental concerns, is not surprising. Recycling, in abrasive blasting technology, usually applies to a material contained in a blast cabinet and routinely cycled several times. Reclaiming blast media necessitates processing through a fairly complex system to remove contaminants and grade the material to size.


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The disposal of used media can involve the use of local waste landfill sites. The type of contaminant in the waste and also the potential for leaching hazardous substances (e.g. heavy metals) in landfill situations will need to be taken into account and, under certain circumstances, alternative methods of disposal may have to be considered. Most abrasive blast media can be classified into one of four general types: • Natural minerals (e.g. silica sand, garnet, olivine). • Manufactured media (e.g. steel shot, glass grit, alumina, plastic pellets or beads, solid carbon dioxide,

sodium bicarbonate). • Mineral slags (e.g. copper slag, nickel slag, iron slag and coal slag). • Organic media (e.g. corn cobs, nut shells, starch grains). The main examples of the above four types are discussed in more detail.

Natural Minerals Silica Sand

Common quartz sand is among the most abundant minerals in the earth’s surface. For many years, Silica sand was the favoured material for blast cleaning throughout the world. The entire industry was founded on its use and the term ‘sandblasting’ was the common term for this type of operation. The material is readily available and of low-cost. However, silica sand commonly contains high concentrations of crystalline silica (quartz). Respirable silica quartz causes the disease, silicosis after repeated exposure (ref 3, 21, 32, 34, 37, 42, 43, 44). Crystalline silica is also considered a possible cause of cancer in humans (ref 34). Despite strict health and safety controls in most developed countries, silica sand is still a widely used blasting media. In the UK the use of sand or other substances containing free silica is specifically prohibited for “use as an abrasive for blasting articles in any blasting apparatus” by the Control of Substances Hazardous to Health Regulations 2002 (COSHH) (48). It is not considered a recyclable material (37). Garnet

Garnet is a hard silicate mineral quarried in several parts of the world, including Australia, India, the USA and South Africa. There are some eight different forms of garnet but the one most commonly used for abrasive blasting is almandite garnet which is an iron-based material (9). It is very heavy, very hard and durable. Specific gravity and durability are critical factors affecting both blasting and recycling performance. Because of these properties, garnet is capable of very high performance when used as a single pass (disposable) or a recycled abrasive (9). Much of the garnet used for abrasive blasting is uncrushed and alluvial, meaning it was formed on a water source. The resulting abrasive particles are sub-rounded to sub-angular in shape. Because alluvial particles are uncrushed, they contain few stress fractures and resist breakdown during blasting (9).


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Garnet is used on both ferrous and non-ferrous metal substrates and has several benefits, including the following (7, 9): • Fast cutting. • Low dusting (compared to coal slag or silica sand). • Recyclable. • Low risk to health, with no detectable amounts of heavy metals and low free-silica. Olivine

Olivine is a naturally occurring magnesium iron silicate, which is pale green in colour and contains no free silica or toxic metals (11). However, it is reported that olivine is a mineral of which concern has been expressed over asbestos impurities (45, 48, 49). A series of tests performed by the Health and Safety Executive (HSE) in June 2000 on a specific shipment of olivine showed that it contained asbestos fibres. Laboratory tests carried out by HSE showed that a range of potential uses of the material – including dry grit blasting operations – could have resulted in levels of exposure in excess of the control limit (49). The major use for olivine is a safer replacement for silica sand in the cleaning of buildings but it also finds application in the blast cleaning of steel, particularly stainless steels, for which slag abrasives are often not permitted because of ferrous contamination which leads to rust spotting – so called ‘tea stains’ (11). Olivine is very hard but tends to fracture on impact, creating much light-coloured dust (8). The major deposits of olivine for industrial uses such as blasting are located in the USA and Norway (34), making it relatively costly for use in the UK as an abrasive due to this limited availability (8). Olivine is not normally recycled after use (37). Staurolite

Staurolite is a dark coloured mineral that is a silicate of aluminium and iron. It has some free silica but much less than silica sand (8). The material, which tends to be used in niche applications, is relatively high priced but offers benefits such as low dusting (due to high hardness), low embedment and is considered environmentally friendly (34). Staurolite poses virtually no environmental hazard. One of the underlying reasons for this is that the media is not recommended for certain applications, therefore ensuring that disposal costs are kept to a minimum. For example, the mineral is not recommended for use in situations that involve the removal of lead-based paints, as it is the contaminated media from the applications that can lead to the real ecological problems (34). In spite of the material’s high hardness, the rounded shape of the grains ensures that virtually no particulate embedment takes place. Although not normally subject to recycling, this has been known but only to a small degree (34). The above minerals are the main types commonly used in industrial blasting applications, although as might be expected there are a number of other materials which have been used (e.g. specular hematite).


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Manufactured Media Metallic Grit and Shot

Grit consists of angular metallic particles with high cutting power. Grit is usually made of crushed, hardened cast iron shot, which may be malleabilised. Generally, there are three hardnesses offered in steel grit and the screen distribution and velocity of the grit impacting on the substrate surface control the finish. Applications for grit include removal of heavy forging and heat treat scale, removal of rust and controlled profiling of materials before adhesive bonding (4). Shot is normally made of the same materials as grit and is usually in the form of spherical particles. Shot removes scale and other contaminants by impact. Steel shot is the most widely used metallic abrasive medium and is the least destructive to the components of the abrasive blast system (40). Shot may also be made from aluminium or cut steel wire; the latter deforms into rounded particles during usage and is used frequently in the same manner as cast shot. Because of their durability, steel abrasives can be recycled many times (typically dozens of times) in most cleaning operations without loss of efficiency (37). One major disadvantage with steel abrasives is that they must not be allowed to become wet. It cannot lie on the ground or be used to clean wet surfaces. When wet, steel grit forms lumps that can clog equipment and harm the substrate (15). The majority of systems that make use of steel shot and grit are closed systems and as such, environmental hazards are kept to a minimum. However, if used in the open or disposed of in the ground, there is a real danger of iron leaching out into the environment (34). In a more technical sense, metallic abrasives can contaminate impacted surfaces with pieces or streaks of the media itself and such contamination can lead to corrosion of the blasted surface and subsequent coating failure (34). Glass Beads

Manufactured abrasives such as soda lime glass beads are good abrasive materials for specific operations. Glass beads are manufactured from high-grade, specially designed glass to reduce wear and fracture. The particles are heat treated in a round ball to equalise stress and resist fracture. They are reasonably free of sharp angular particles and are manufactured in a wide range of sizes. They are generally used in blast cabinets that provide recycling. They do not contain crystalline silica as they are manufactured from soda lime glass (13, 14). Glass beads work by imparting a hammering or peening action at the point of contact. This hammering causes minute flexure of the surface being impacted which tends to break the bond between the body of the workpiece and the surface coating or contamination which is to be removed (13). Unlike steel shot which is the most widely used of the spherical blasting media, glass beads contain no free iron to cause corrosion on non-ferrous surfaces; they can therefore be used on all types of metals (13). Glass Grits

Processed recycled glass is used as an industrial abrasive and is manufactured from waste container glass, mainly collected from public recycling schemes. Other waste glass streams can also be used for this application such as tempered automotive glass and recovered commercial glass that provides a safer method of cleaning than using silica sand (14). The waste container glass is initially coarse crushed and


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then screened to remove bottle tops, lids, caps, corks, labels and other contaminants. After drying the glass is finely crushed, and then screened to produce the desired particle size distribution. Glass grit can also be manufactured from primary glass (8). However, this involves further processing steps and constitutes a small stream in comparison to the use of waste container glass for this application. Cleaning trials have been undertaken using recycled glass grit as an abrasive media and it has found to perform very well in cleaning operations before painting and also in the removal of hard coatings such as epoxy and enamels (12). The crushed glass is a true low silica material that behaves somewhat like slag. Because of the low specific gravity of the crushed glass the impact per particle is reduced and it is suggested that coarser gradings are often necessary (37). However, it is estimated that the recycled glass grit could produce three to four cycles if necessary before becoming spent (12). The dust generated by the recycling glass during trials was found to be relatively clean when compared to ‘black, chalk-like’ residues left by copper slag (12). Glass does not present a specific environmental hazard, indeed crush glass grit is used as an alternative to sand in water treatment processes. The recycling of glass wastes, which may otherwise be landfilled, to produce glass grit also has positive environmental benefits (12). Aluminium Oxide (Alumina)

Aluminium oxide is usually used in its brown form when it is manufactured by fusing bauxite; coke and iron in an electric is furnace at very high temperatures. Refined grades of white and pink alumina are also available that contain very low levels of free iron. This abrasive is available in a number of grades and the main use is as a recyclable abrasive in cabinets (8). It is generally more expensive than metallic recyclable abrasives and will not recycle as many times, particularly the white material, which is very hard. Since it will not corrode and solidify in the blasting equipment, it is suitable for use where the work is intermittent (8). Because of its low iron content, alumina is often specified in high-tech applicators (e.g. the aerospace industry), particularly on non-ferrous metals. It is also commonly specified for use on stainless steel which is going to be used in sea water applications, this because it will not contaminate the steel and set up an electrolytic corrosion cell which, should it happen, would cause attack to the metal (8). Plastic Media

Plastic media blasting (PMB) comes under the heading of soft media blasting in comparison to blasting using conventional blasting media such as mineral sand, alumina, slags and steels/irons which are very hard in comparison. Such soft media will not damage the substrate surface being treated. Plastics as abrasives were originally developed in the 1980s to replace chemical stripping of paints from aircraft surfaces. There are two basic types of PMB systems – open blast and closed cabinet systems. Open blast systems are ideal for stripping large items such as buses and aircraft. In contrast, automated and manual cabinet systems are completely enclosed and well suited for stripping smaller items (24). Plastic media is durable and recyclable. Blasting with plastic media is normally performed with high air volume but low blast pressure (e.g. 10-50psi). The low pressure eliminates warpage of the substrate. Plastic media can be recycled about 5-20 times (38). The resilient plastic particles used in PMB operations are harder than walnut shells but softer than mineral abrasives. A variety of granulated plastics are available, including soft polyester, medium acrylic (polymethyl methacrylate) and urea and harder melamine formulations. Many different sizes of each plastic are available


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and they are often treated with an anti-static solution to prevent media and dust clinging to the particles during use (24). Reviews of PMB are given in references 16, 25, 24, 27 and 38. Sodium Bicarbonate (Baking Soda)

Sodium bicarbonate is a soft, white, crystalline powder that readily dissolves in water to form an alkaline solution. As a blast cleaning material, sodium bicarbonate is available in different particle sizes and incorporates flow agents and other additives to give enhanced performance. It has been used for cleaning sensitive components such as those found in the aerospace industry. However, its alkalinity has been known to cause corrosion of aluminium alloys if it is not properly removed from the substrate surface after blasting (8). Whilst too light to effectively create a profile in steel, this material fills a different niche in the market. Dry Ice

Dry Ice is the solid form of carbon dioxide. The blasting media can vary in size from that of rice grains to about 3mm. The media is very cold (-79ºC) and requires blasting equipment specific to this substrate. The technology of blasting with solid carbon dioxide utilises two distinct techniques. Thermal shock occurs when the solid pellets blast the surface and surface cracks develop. Differential thermal contraction results in failure of the bond interface. The pellets thus actually penetrate the cracked surface layer of contamination and once between this and the substrate, the pellets sublime (change from a solid to a gas without going through a liquid phase) and the expanded carbon dioxide gas blasts the surface layer away from the substrate. Because the dry ice sublimes during the cleaning process, there are no problems associated with disposal of the blasting medium, it is therefore a very environmentally friendly process.

Mineral Slags Slags are the glassy waste products of industrial smelting and combustion. Although formed in differing environments, all share common traits. Chemically, they are aluminosilicate glasses, usually enriched in iron and one or more alkaline metals (37). Like all glassy solids, slags are highly stable under most environmental conditions and like other glasses; they tend toward brittle fracture on impact and may therefore, be dusty when used as an abrasive. Because of their nature as waste products formed during smelting or industrial combustion, slags may contain small quantities of heavy metals or radioactive elements (14, 34, 37). The slag abrasives are classified as metal slags (copper, nickel) and coal boiler slags. They are usually very hard (Mohs Scale 7) and sharp edged. Copper Slag (Sulphide Ores)

Slags from the reduction of sulphide ores are found throughout the world. Since slags are almost always associated with copper mines, the general term ‘copper slag’ has come to be used even for slags that might be more accurately be called ‘lead slags’, ‘zinc slags’ or even ‘arsenic slags’. Copper slags carry small amounts of the metals that were present in the original ores and smelter concentrates (37). The purpose of


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the slag was to act as a collection mechanism of these undesirable contaminates during the recovery of the metal of interest i.e. copper (37). Copper slags are common substitutes for silica sand in countries where mines and smelters are abundant. Some metal slags may contain heavy metals such as lead, beryllium or even arsenic from solutions used in metal removing processes. In most cases, the amount of heavy metals are less than exposure limit values but the presence of trace amounts of heavy metals require the blaster to be aware of potential hazards and regulations governing the allowable exposure limits and favoured control technology (14, 37). A NIOSH (National Institute for Occupational Safety and Health, USA) report (47) identifies samples of copper slag they tested as having high airborne concentrations of arsenic, cadmium, lead and silver, also having high concentrations of beryllium, titanium and vanadium. In addition, laboratory rats have been found to develop tumours attributed to the presence of copper slag (31). The study showed that copper slag produced significantly elevated lung tumour responses when compared to vehicle controls but that responses were significantly less than quartz samples tested. The slags used in the tests were selected because they contained high levels of suspect carcinogens and on the basis of the data presented in the study, the conclusion is reached than the copper slags were indeed carcinogenic to rats (31). An assessment of the leaching behaviour of granulated non-ferrous metal slags has been undertaken to estimate metal migration from a hypothetical slag disposal site into the underlying soil (50). From this survey, in a heavy textured soil, metals leaching from the slag site were predicted to accumulate mainly in the upper level (10 cm). In more sandy soils, the metals were dispersed over larger soil depths, resulting in lower accumulate levels. When comparing the modelled migration results with soil and soil water quality standards, only the migration of zinc was considered of practical importance. This may limit the reuse of the metal slags in bulk form and can create environment problems during abrasive blasting, for example when the grit is not properly cleaned up after use, when used grit is stockpiled onsite or disposed of in landfills (35). Nickel Slag

A unique, non-sulphide metal slag is formed during the smelting of certain nickel ores, mainly for use in the USA where it is produced. The material is used regionally as a replacement for both silica sand and copper slag (37). The nickel slag does not contain the usual heavy metals associated with copper slag but does contain small quantities of chromium and nickel, both of which may require monitoring for airborne dust exposures. The NIOSH report (47) states that the nickel slag they tested had high levels of chromium, cadmium and nickel. Coal Slag

Coal slag is a mixture of ferro aluminium silicates, calcium silicate and silica and is formed as a by-product of burning coal in electric power generation plants. Inevitably, the composition will vary according to the source. Coal slag used for abrasive blasting is primarily used for etching. A secondary application is cleaning. The NIOSH report (47) states that the coal slag they tested contained high levels of beryllium.


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Organic Media

Organic products, many being derived from vegetables, including materials such as corncobs, starch, nut shells (e.g. walnuts), rice hulls and fruit pits, have long been used as abrasives in areas where loose dirt and grease are to be removed without attendant damage to the underlying coating system or to the substrate (37). Organic abrasives have low hardness and low bulk density and will not etch most industrial substrates, including wood (38). They are mainly used for removing dirt or other deposits on paint films, for cleaning valves or turbine rotor blades and for removing grease from motors (38). These abrasives are non-sparking so they also find use in hazardous areas where all parts to be cleaned are adequately grounded and there is adequate ventilation. Vegetable abrasives are used with normal abrasive blasting equipment but the abrasive must be dry to flow effectively. Some shells, such as pecan shells, contain oil or stain that may not be suitable for some surfaces, especially when repainting is required (38). Vegetable abrasives are a one-time use material and materials such as corncob grit (17) and starch (22) are environmentally benign because the media is non-toxic and biodegradable. Generally they also present little problem with regard to dust levels, which are generally low for this type of soft blasting media. A review of corncob grit (17) identifies flash and dust explosion hazards as being very remote, although theoretically possible.

TABLES

Three tables are presented in Appendix 1. Table 1 gives an overview of common abrasive characteristics showing the composition, hardness, density, potential dusting problems and an indication of recyclability (37). Table 2 gives further information directly relating to non-metallic abrasives, including references to toxicity, cost comparisons (relative) and cleaning speed (40). Table 3 lists major health and safety hazards associated with the specific abrasives covered in this report.


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CONCLUSIONS

The proper selection of a suitable abrasive prior to its use in a cleaning or etching operation is most important. Issues such as abrasive performance, cost and safety must all be taken into account. Abrasives may be tested for breakdown, dust generation, effect on profile and most important, production or cutting rate. Seldom is one abrasive best suited for all jobs. With regard to cost, while silica sand may be the least costly abrasive initially; environmental problems such as dust, health hazards and waste removal costs may significantly increase the total cost in using such a material. In the consideration of abrasive cost therefore, the overall cost must be considered as, in most cases, the actual cost of the abrasive itself is only a small proportion of the overall job cost. On safety issues, very few, if any, abrasives have particles in the respirable range before blasting. During use, however, the abrasive particle breaks down to varying degrees and the fine particles produced become a potential health hazard upon inhalation. It is essential that proper engineering controls are established and that testing is conducted with abrasive blast operators being trained in the correct use of protective equipment. This is most important when friable materials (e.g. sand, slag, minerals) are used and when some manufactured products are used which may produce a ricochet effect when impacting the substrate being blasted. In addition, the nature of the material being removed from the substrate must also be taken into account. For example, if a lead-based paint coating is being abraded this can adversely affect the operator and the presence of such a material will necessitate special disposal methods. This report has undertaken an extensive literature search using a large number of suitable external databases and covering the types of abrasives used currently in industrial applications. Of particular importance in this review is the identification of health and environmental issues connected to these materials.


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APPENDIX 1

Three tables are presented in Appendix 1. Table 1 gives an overview of common abrasive characteristics showing the composition, hardness, density, potential dusting problems and an indication of recyclability (37). Table 2 gives further information directly relating to non-metallic abrasives, including references to toxicity, cost comparisons (relative) and cleaning speed (40). Table 3 lists major health and safety hazards associated with the specific abrasives covered in this report.

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Table 1: Summary of Abrasive Characteristics Abrasive Composition Mohs

Hardness Density

(gms./cu. cm) Dusting Recycling

Silica Sand Best Quality Average Quality

Crystalline Silica Same

7.0 6.5

1.6 1.6

Low High

No No

Staurolite/Zircon Iron Aluminium Silicate 7.5 2.0 Mod No Garnet Almandite Andradite

Iron Aluminium Silicate Calcium Silicate

7.5 6.5

2.0 1.8

Low High

Yes No

Olivine Iron Silicate 6.5 1.9 High NoSpec. Hematite Iron Oxide 6.0 2.3 Mod Yes Copper Slag Nickel Slag Iron Slag Coal Boiler Slag

Iron Silicate Glass Nickel Iron Glass Iron Silicate Glass Ca, Iron Silicate Glass

6.0 6.0 6.0 6.0

1.6 1.6 1.6 1.4

Mod High High High

No No No No

Steel Grit/Shot Iron (Steel) 6.0 2.2+ Low Yes Baking Soda Sodium Carbonates 2.0-3.0 1.1 High/Low* NoCrushed Glass Alkaline Silicate Glass 6.0 1.6 High No#

Organic Media Various 2-3 0.6-1.0 N/A No *High dusting when used dry; low dusting when used with water #Pera is aware that closed blasting systems are available that allow the recovery of the blasting material for reuse. This makes these materials suitable for use in closed blasting systems Source: Journal of Protective Coatings and Linings 2000; Pera 2003


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Table 2: Physical Properties and Comparative Characteristics of Nonmetallic Abrasives Description Glass beads (a) Coarse Mineral

Abrasives (b) Fine Angular Mineral Abrasives (c)

Organic Soft Grit Abrasives (d)

Plastics Abrasives (e)

Physical Properties Shape Spherical Granular Angular Irregular Cylindrical (diameter/length = 1) Colour Clear Tan Brown/white Brown/tan Nylon: white, polycarbonate: orange Specific gravity 2.45 – 2.50 2.4 – 2.7 2.4 – 4.0 1.3 – 1.4 Nylon: 1.15 – 1.17, polycarbonate: 1.2

- 1.65 Free silica content None 100% <1% None NoneFree iron content <1% <1% <1% None NoneHardness (MOH) 5.5 7.5 9.0 1.0 R-110 to R120 Media Comparisons Toxicity None High Low Low/None NoneMetal Removal Low/None High High None Deburring Only Cleaning Speed Medium/High High High Low Low Peening Ability High None None None None Finish Achieved Range (various matte) Rough anchor Various matte Smooth Smooth Surface Contamination None Medium Medium Medium/High Low to None Suitability for Wet Blasting High Low Low Low Low Suitability for Dry Blasting High High High High High Standard Size Ranges 20-325 8-200 80-235 60-325 0.76 by 0.76 mm (0.030 by 0.030 in.) U.S. mesh U.S. mesh U.S. mesh U.S. mesh 1.1 by 1.1 mm (0.045 by 0.045 in) 1.5 by 1.5 mm (0.060 by 0.060 in) Consumption Rate Low High Medium High Very low Cost Comparison Medium Low High/Medium High/Medium High/Medium (a) Glass beads are used for cleaning, finishing, light-to-medium peening and deburring. (b) Coarse mineral abrasives such as sand are used where metal removal and surface contamination are not considered. (c) Fine angular mineral abrasives such as aluminium oxide are used in cleaning when smooth finish and surface contamination are not important. (d) Organic soft grit abrasives, for example, walnut shells, are used in light deburring and cleaning of fragile items. (e) Plastic abrasives such as nylon and polycarbonate are used to deflash thermoset plastic parts and deburr finished machine parts. Source: ASM Metals Handbook, 9th Edition, vol. 5 1982; Pera 2003


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Table 3: Abrasive Media Hazards

Material Particular Hazards Other Comments Natural Minerals Silica Sand Contains (relatively) high levels of crystalline silica.

Possible carcinogen. Illegal for use as an abrasive blasting media.

Garnet None Olivine Possible asbestos impurities. Staurolite None Manufactured Media Steel Grit/Shot None Galvanic corrosion with some metals. Glass Beads None Glass Grit None Aluminium Oxide None Plastic Beads None Sodium Bicarbonate None Dry Ice None CO2 is an asphyxiant. Use ventilation. Mineral Slags Copper Slag Heavy metal contamination possible. Nickel slag Heavy metal contamination possible. Coal Slag Heavy metal contamination possible. Organic Media Corn Cobs None Potential for dust explosion. Nut Shells None Potential for dust explosion. Starch None Potential for dust explosion. Certain abrasives such as silica sand (respirable quartz content), olivine (asbestos impurities) and mineral slags (leachable heavy metals, carcinogenicity) have been found to require special health and environmental protection measures when being used. However, all abrasives must be treated with care and used in a controlled measure, as required by legislative requirements such as the Control of Substances Hazardous to Health Regulations, Personal Protective Equipment Regulations and the Environmental Protection Act.

Source: Pera 2003

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APPENDIX 2

1. Environmental Protection Agency (EPA) studies paint removal. ANON J. Protect. Coat. Linings 1995, Vol 12 No 2, 27 (5 pp). 1995 2. Garnet safely removes coatings from aluminium. ANON J. Protect. Coat. Linings 1996, Vol 13 No 4, 42 (3 pp). 1996 3. On the issue of health and silica sand as a blasting abrasive. HANSINK J J. Protect. Coat. Linings 1998, Vol 15 No 11, 90 (5 pp). 1998 4. Evaluation of substitute materials for silica sand in abrasive blasting. ADLEY D; TRIMBER K J. Protect. Coat. Linings 1999, Vol 16 No 8, 49 (18 pp). 1999 5. Research programme studies minimising waste from mineral slags. ANON J. Protect. Coat. Linings 2000, Vol 17 No 8, 73 (4 pp). 2000 6. Finding better and safer ways to clean and depaint critical components. COLBERT K Metal Fin. 1996, Vol 94 No 4, 53-6. 1996 7. Which abrasive: sand, slag or garnet? PEREIRA J Protect. Coat. Europe 1998, Vol 3 No 5, 26-7. 1998 8. What type of abrasive to use? PADDISON R D Protect. Coat. Europe 2000, Vol 5 No 4, 10 (8 pp). 2000 9. Recycling garnet in the shop and field. SCHUSTER A J Protect. Coat. Europe 2002, Vol 7 No 7, 7 (4 pp). 2002 10. Ban on silica for abrasive blasting. ANON Corros. & Materials 2001, Vol 26 No 6, 9. 2001 11. Review of expendable abrasives. BRIGGS M Anti-Corros. 1987, Vol 34 No 5, 10-2. 1987 12. Recycled glass as an industrial abrasive. McCOACH H; McLEOD J Surface World 2000, Vol 7 No 9, 32-3. 2000 13. Glass beads: a unique cleaning medium. DYER D Surface World 1997, Vol 4 No 9, 14-5. 1997 14. Non-metallic abrasives for surface preparation.


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BENNETT P J J. Protect. Coat. Linings 1986, Vol 3 No 4, 32-9. 1986 15. Review of recent developments in surface preparation methods. REX J J. Protect. Coat. Linings 1990, Vol 7 No 10, 50-8. 1990 16. Plastic Particles Strip Paint From Sensitive Surfaces McCarty, LH Des. News, vol. 42, no. 19, pp. 200-202, 6 Oct. 1986 17. An Update on Soft Grit Blast Cleaning With Corncob Grit Foley, K M; Weaver, T Abrasive Engineering Society, pp. 107-116, 1981 18. Grit Blasting Performance on Steel Surfaces Slutzky, O; Caprari, JJ; Pessi, PL; Meda, JF Affiliation Cidepint Bull. Electrochem., vol. 4, no. 2, pp. 121-130, Feb. 1988 19. Lead, chromium, and cadmium exposure during abrasive blasting Conroy, LM; Sullivan, PM; Menezes-Lindsay, RM; Cali, S; Forst, L Univ. Illinois Chicago Sch. Public Health, Chicago, IL 60612, USA Archives of Environmental Health [ARCH. ENVIRON. HEALTH], vol. 51, no. 2, pp. 95-99, 1996 20. Surveillance of Respirable Crystalline Silica Dust Using OSHA Compliance Data (1979-1995) Linch, KD; Miller, WE; Althouse, RB; Groce, DW; Hale, JM National Institute for Occupational Safety and Health, Division of Respiratory Disease Studies, 1095 Willowdale Rd., Morgantown, WV 26505-2888, USA American Journal of Industrial Medicine [Am. J. Ind. Med.]. Vol. 34, no. 6, pp. 547-558. Dec 1998. 21. Abrasive blasting with quartz sand: Factors affecting the potential for incidental exposure to respirable silica Brantley, CD; Reist, PC U.S. Coast Guard, Eighth Coast Guard District(m), 501 Magazine St., New Orleans, LA 70130-3396, USA American Industrial Hygiene Association Journal [AM. IND. HYG. ASSOC. J.], vol. 55, no. 10, pp. 946-952, 1994 22. Starch media blast cleaning of artifically aged paint films Spelt, JK; Tangestanian, P; Papini, M University of Toronto; University of Toronto; Ryerson Polytechnic University Wear (Switzerland), vol. 248, no. 1-2, pp. 128-139, Mar. 2001 23. Utilization of copper blasting grit waste as a construction material. Madany, IM; Al-Sayed, MH; Raveendran, E Arabian Gulf Univ., Box 26671, Bahrain Waste Management [WASTE MANAGE.], vol. 11, no. 1-2, pp. 35-40, 1991 24. Stripping paint with plastic media R Dotson R. Dotson, and R. Ballard (Maxi-Blast Inc., South Bend, IN), Products Finishing (1995), Vol. 59, No. 9, 112-7 25. Recycling spent polymethylmethacrylate plastic media blasting beads Bigg, DM; Barry, RG; Conkle, HN; Rockswold, AO McClellan AFB; McClellan AFB; McClellan AFB; McClellan AFB ANTEC '95. Vol. III--Special Areas, Boston, Massachusetts, USA, 7-11 May 1995 Society of Plastics Engineers (USA), pp. 3662-3665, 1995


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26. Environmental aspects of coating removal techniques Reitz, W Babcock and Wilcox Advances in Coatings Technologies for Corrosion and Wear Resistant Coatings, Las Vegas,Nevada,USA, 12-16 Feb. 1995 Advances in Coatings Technologies for Corrosion and Wear Resistant Coatings, Minerals, Metals and Materials Society/AIME, 329-352, 1995 27. Plastic media blasting Nudelman, AK; Abbott, K Composition Materials; Envirosystems Metal Finishing (USA), vol. 100, no. 6A, pp. 545-546,548-553, June 2002 28. Abrasive blasting systems Hansel, D Clemco Industries Metal Finishing (USA), vol. 100, no. 6A, pp. 51-52,54-66, June 2002 29. Dry media blasting for the removal of paint coatings on aerospace surfaces Abbott, KE Stripping Technologies Inc, Tucson, AZ, USA Metal Finishing [MET FINISH], vol. 94, no. 7, pp. 33-35, 1996 30. Plastic Media Blasting--State of the Technology Abbott, KE Stripping Technologies Materials Performance (USA), vol. 31, no. 2, pp. 38-39, Feb. 1992, ISSN 0094-1492 31. Fibrogenicity and carcinogenic potential of smelter slags used as abrasive blasting substitutes. Stettler, LE; Proctor, JE; Platek, SF; Carolan, RJ; Smith, RJ; Donaldson, HM Appl. Biol. and Phys. Branch, Div. Biomed. and Behav. Sci., Natl. Inst. Occup. Saf. and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, USA Journal of Toxicology and Environmental Health [J. TOXICOL. ENVIRON. HEALTH.], vol. 25, no. 1, pp. 35-56, 1988 32. Contributing factors to sandblasters' silicosis: Inadequate respiratory protection equipment and standards. Glindmeyer, HW; Hammad, YY Dep. Med., Pulm. Dis. Sect., 1700 Perdido St., New Orleans, LA 70112, USA J. OCCUP. MED., vol. 30, no. 12, pp. 917-921, 1988 33. Non-Metallic Abrasives for Surface Preparation Bennett, PJ J. Prot. Coatings Linings, vol. 3, no. 4, pp. 32-39, Apr. 1986 34. Abrasive blast cleaning: evolution or revolution? Skillen, AD Ind.Miner. No.317, 1994, p.25-39 35. Recycling ferrous-nickel slag in blast cleaning. Katsikaris, K; Voutsas, E; Magoulas, K; Andronikos, G; Stamataki, S National Technical University of Athens; National Technical University of Athens; National Technical University of Athens; National Technical University of Athens; National Technical University of Athens Waste Management and Research, vol. 20, no. 3, pp. 269-278, June 2002 36. Alumina grit blasting parameters for surface preparation in the plasma spraying operation Mellali, M; Grimaud, A; Leger, AC; Fauchais, P; Lu, J LMCTS; LMCTS; LMCTS; LMCTS; University of Troyes


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Journal of Thermal Spray Technology (USA), 6, (2), 217-227, June 1997 37. An Introduction to Abrasives for Protective Coating Removal Operations. Hansink JD Journal of Protective Coatings and Linings (USA), vol 17, no 4, pp 66-73, Apr 2000 38. Soft media blasting: an introduction Journal of Protective Coatings & Linings (USA), vol. 19, no. 1, pp. 23-29, Jan. 2002 39. Fibrogenic Potential of Slags Used as Substitutes for Sand in Abrasive Blasting Operations Mackay, GR; Stettler, LE; Kommineni, C; Donaldson, HM Nat. Inst. Occup. Safety & Health, Cincinnati, OH AM. INDUST. HYG. ASSN. J., vol. 41, no. 11, pp. 836-842, 1980 40. Abrasive blast cleaning ASM Metals Handbook, 9th Edition, vol. 5 (Surface Cleaning) pp. 83-96, 1982 41. ASM Handbook, vol. 5 (Surface Engineering) pp. 55-66 SIL Industrial Minerals Inc., MSDSs for Crystalline Silica + Silica Flour

42-44. SIL Industrial Minerals Inc., MSDSs for Crystalline Silica + Silica Flour 45. Consultation Document 186 - The proposal to amend the Asbestos (Prohibition) Regulations (1992) Health and Safety Commission, 2003 46. Evaluation of Substitute Materials for Silica Sand in A/B By KTA – Tator Inc. For Department of Health & Human Service } NIOSH } USA Center for Disease Control } 47. Above Report (PB99 105553, NIOSH September 1998) 48. Control of Substances Hazardous to Health Regulations 2002 HMSO, 2002, SI 2002 No. 2677 49. Asbestos in olivine shotblasting medium [ukoh] UK Yahoo News Group – UK Occupational Hygiene email list 50. Assessment of the leaching behaviour of granulated non-ferrous metal slags F.M.G. Tack, P.H. Masscheleyn & M.G. Verloo Environmental Contamination 5th International Conference, pp. 133-135, 1992


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APPENDIX 3

A number of database sources were used during this literature review of published information on the subject of industrial abrasive media, including glass grit and copper slag and other competing materials. Details on the scope and coverage of these databases are given below. • World Surface Coatings Abstracts™, produced by the Paint Research Association, Teddington,

United Kingdom, provides comprehensive coverage of paints, coatings, pigments, inks, and adhesives. All aspects of the coatings industry are covered, from company profiles and statistics to physical properties to the latest research. The database corresponds to the printed publication: World Surface Coatings Abstracts. Each year about 10,000 new records are added to the file with intensive coverage of patents, conference proceedings, books, legislation, reports, journal articles, and standards in the fields of paint and surface coating technology and related subjects.

• METADEX (METals Abstracts/Alloy InDEX) is a bibliographic database covering the worldwide literature

on metallurgy and materials. A special classification for steels, ferrous and non-ferrous metals and their alloys, the Alloys Index, is included, allowing optimal search for alloys and steels. Abstracts are available for most citations since 1979. METADEX is the online version of ASM Review of Metal Literature (1966-1967), Metals Abstracts (1968 to the present), Alloys Index (1974 to the present) and Steels Supplement (1983-1984). Companion files to METADEX are MDF with numeric data on ferrous and non-ferrous alloys, MATBUS with techno-commercial developments in metals and materials, and EMA with engineered materials.

• Ceramic Abstracts/World Ceramics Abstracts is produced by Cambridge Scientific Abstracts in

conjunction with CERAM Research Ltd. This is a comprehensive database for the ceramics industry, providing international coverage on the manufacture, processing, applications, properties and testing of traditional and advanced ceramics. Source materials include over 300 journals, conference proceedings, books, patents, standards and company product literature. All abstracts are in English.

• Corrosion Abstracts is produced by NACE International and Cambridge Scientific Abstracts. The

database provides the world's most complete source of bibliographic information in the area of corrosion science and engineering. The database includes more than 74,000 abstracts dating back to 1980 from more than 150 sources worldwide. The abstracts cover the areas of general corrosion, testing, corrosion characteristics, preventative measures, materials construction and performance, and equipment for many industries.

• Engineered Materials Abstracts focuses on polymers, ceramics, and composites in a variety of

structural and other advanced applications. Citations regarding the research, manufacturing practices, properties and applications of these materials have been taken from 1,300 journals, plus dissertations, government reports, conference proceedings, and books indexed by expert editors from Materials Information. Begun in 1986, Engineered Materials Abstracts is an electronic database containing Ceramics, Composites and Polymers subfiles. EMA is specifically designed to serve materials sciences researchers, engineers and scientists.

• Copper Data Center (CDC) provides an online bibliographic database of the world's literature on

copper, copper alloys and copper technology since 1965. The Copper Data Center Database covers copper technology from smelting and hydrometallurgy through the performance of copper and copper alloys in their end-use applications and service environments. It references data on the properties and performance of copper and copper alloys and on applications of the copper metals. Over 52,000 documents have been indexed into this database, including 5582 documents published between 1863 and 1964.


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• Mechanical Engineering Abstracts contains the facts, figures, and discoveries engineers need in

order to make faster, more authoritative decisions. Now expanded and jointly published with Engineering Information, this is the only abstracts journal that surveys and summarizes the worldwide literature in mechanical engineering, engineering management, and production engineering. Presenting theoretical perspectives as well as specific applications, the journal reports on key developments published in journals, articles, and conference papers. Besides providing details on current research results, Mechanical Engineering Abstracts contains specific information that shows how other engineers around the world are handling opportunities as well as problems.

• Health and Safety Science Abstracts is published in association with the University of Southern

California's Institute of Safety and Systems Management. It provides a comprehensive, timely survey of recent work relating to public health, safety, and industrial hygiene. Cited studies are geared to help individuals identify, evaluate, and eliminate or control risks and hazards across the spectrum of environmental and occupational situations. The database provides the latest perspectives on topics of widespread concern such as aviation and aerospace safety, environmental safety, nuclear safety, medical safety occupational safety, and ergonomics. Health and safety related aspects of pollution, waste disposal, radiation, pesticides, epidemics - and countless other phenomena having the potential to threaten the public, the environment, or the workplace itself - are reported here. Drawing on government reports as well as journal articles, conference proceedings, books, and other publications, Health and Safety Science Abstracts synthesizes the most important new developments in safety science and human factors research.

• Enviroline® covers the world's environmental related information. It provides indexing and abstracting

coverage of more than 1,000 international primary and secondary publications reporting on all aspects of the environment. These publications highlight such fields as management, technology, planning, law, political science, economics, geology, biology, and chemistry as they relate to environmental issues. Enviroline corresponds to the print Environment Abstracts. Environment Abstracts Document Delivery Service can supply about 55% of the documents referenced in the database. Users are requested to use LIMIT/AVAIL before ordering documents from EIC.
