METgrains® unique mix of spherical and irregular-shaped steel particles was developed specifically for steel surface preparation. METgrain® Steel Abrasive is especially effective when critical profile tolerance is needed.
Precise Profile Control With Metgrain® Metgrain® Magnified Showing Blasting & Scouring Power
METgrain® enhances blast cleaning efficiency by combining impact with scouring action. The result is a cleaner surface with a superior anchor pattern at a lower cost.
Steel structures such as bridges, water towers, ships and storage tanks require painting maintenance to extend the life of the structure. Due to improper maintenance, many of these valuable structures owned by federal, state and local governments have their protective coating of paint peeling, flaking and rusting away; contaminating our environment and reducing the useful economic life of our valuable infrastructure.
The EPA mandates the minimization of waste to reduce dust and waste, protect our rivers and streams and to preserve our valuable landfills. Use of recyclable Metgrain® and METgrit® minimizes the generation of hazardous waste.
Blast cleaning and repainting protective coatings is necessary to extend the economic life of these structures. Proper blast cleaning and painting typically provides at least twenty to thirty years of protection. Failure by facility owners to repaint these valuable structures can cost million$ in lost economic life of the structure. Open abrasive blasting of structures containing lead based paint with one use mineral slag or sand violates RCRA mandates to minimize the generation of hazardous waste and exposes workers and surrounding neighborhoods to tons of potentially hazardous waste and silica dust with proven health hazards.
Reusable metallic abrasive solves all these problems and does so at less total cost. While a most enlightened state authorities mandate the use of recyclable abrasives in their bid documents, too many state, local governmental agencies, and private facility owners fail to do so. This problem can not be solved without the understanding the high economic and environmental cost of using non-recyclable abrasives.
Blast Cleaning Abrasives - An Overview
1) Two generic abrasive types - Metallic & Non-Metallic.
2) Non-Metallic abrasives consist of three classes.
a) Naturally occurring abrasive.
b) By-product abrasive.
c) Manufactured abrasives.
3) The following are examples of the three types of Non-Metallic abrasives:
a) Naturally occurring abrasives include sand, garnet, heavy mineral sands, etc.
1) Sands are low cost, readily available blast media for non critical areas, but are hazardous due to the generation of high levels of silica.
2) Garnet is more costly than sand and is generally used without recycling, though three or four cycles are possible under the right conditions. Garnet breaks down easily and causes red dusty mess. It's cost and limited recycling capabilities make garnet economically unsatisfactory in most applications.
b) By-product abrasives include metal melting slags, electric power generating boiler slags and as a host of agricultural slags such as corn cobs, peach pits and walnut shells.
1) Smelter and boiler slags are glassy, angular particles used for general blast cleaning of steel surfaces. One-use means high disposal cost and non-compliance with RCRA when blastng surfaces containing lead based paints or anti-fouling paints.
2) Agricultural abrasives are used for specialty applications to remove surface contaminants leaving the substrate intact.
c) Manufactured abrasives are costly, generally 30 to 40 times the cost of sand and include aluminum oxide, glass beads, silicon carbide, etc.
1) Aluminum oxide is used for specialty cleaning such as stainless steel.
2) Glass beads are also costly and are used for special peening operations.
3) Silicon carbide is a sharp angular product for specialty etching.
4) Metallic Abrasives
a) Two basic types of chilled iron and cast steel.
1) Chilled iron is a cost effective, very agressive, hard, durable abrasive that can be recycled hundreds of times and is recommended for most blast cleaning applications.
2) METgrit is a superior chilled iron, heat treated and tempered for aggresive blast cleaning perfomance.
2) Cast steel abrasives are tough, durable and can be recycled thousands of times.
a) Cast steel comes in two basic forms - shot and grit.
b) Steel grit is preferred for most cleaning applications because grit's irregular shape cuts and scours to give a consistent profile. Steel shot gives more of a peening action which tends to peen corrosion products into the steel surface.
c) METgrain® combines the impact of steel shot with the scouring action of grit. METgrain® will not embed in steel substrate, has excellent durability and can be recycled thousands of times.
d) METgrain® Physical Features: Irregular shape cleans better than regular shot or grit. METgrain® has a mid range hardness of 40-45 Rockwell C. It comes in a range of sizes from G-14 (coarse) to G-80 (fine).
e) METgrain performs well in a broad spectrum of applications as follows:
Maintenance - Bridges, railcar, refineries, power plants, shipyards.
New Construction - Fabricators, shipbuilders, pipe coaters, railcar.
Foundry - Cast iron, steel aluminum, brass.
B. Blast Cleaning Equipnent
1) Primary methods of propelling abrasives. High Pressure (90-150 psi) air and centrifugal wheel.
a) METgrain is currently being used in both centrifugal wheel systems and air blast applications. METgrit is primarily used in air pressure blast.
2) Recovery and reclamation of steel abrasive is critical.
a) Vacuum recovery is easy. Recycling equipment utilizing a scalping screen helps to clean waste and an air wash system removes dust and blast debris so that the used grit is as clean as new condition.
b) Problems resulting from improper cleaning of abrasive.
1) Excess dust
2) Lead problem
C. Impact of EPA land Ban
1) Hazardous waste cannot be landfilled without being first treated to make material non hazardous.
2) Recyclable steel abrasive (METgrain) greatly reduces waste. Using recyclable steel can reduce disposal from tons per day to pounds per day.
a) Most non-metallic abrasives used once and wasted.
b) Too difficult to separate reclaimed non-metallic abrasives from paint, scale and other debris.
3) Typical steel grit blast and recovery systems include:
a) ADI, ARS, IPEC, CAB, SPM, Misco
b) All are effective in recovery and reclaiming steel abrasives.
a) RCRA statute directs EPA to establish controls on the management of hazardous wastes from their point of generation, through their transportation and treatment, storage and/or disposal.
b) Waste Minimization - EPA's preferred hierarchical approach to materials management includes source reduction, recycling, energy recovery, treatment, and finally, disposal.
D. Surface Cleaning Aspects
1) Profile: Important because of paint consumption impacted by profile depth.
a) Typical profiles produced by METgrain in nozzle blast applications.
METgrain G-14/18 3 – 4 mils
METgrain G-25 2 ½ - 3 mils
METgrain G-40 1 ½ - 2 ½ mils
METgrain G-50 1 – 1 ½ mils
2) Profile measurement.
a) Testex tape method.
3) SSPC Surface Preparation Specification.
4) Cleaning rates:
a) Finer abrasives clean faster when using high air pressure (130-150 psi).
b) Larger girt is often preferred for heavy pitting, pack rust, and heavy coating systems.
E.Packaging - Shipping
1) Primary packaging is in 55 gallon drums or 50 lb. bags.
a) Also can be packaged in supersacks or bulk.
2) Shipping is either on flat bed or van trucks.