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Abrasive Blasting: Choosing the Right Equipment

TUESDAY, JULY 7, 2020

By Lane Barnholtz, Clemco Industries Corp.


courtesy of Clemco industries corp.

It’s a cliché, but it’s true: To do a job right, you need the right equipment. This is especially true of abrasive blasting. But before choosing equipment for an abrasive blasting job, it is critical to examine the target surface and the work site environment, perform a job hazard analysis and assess the goals of the job. After thoroughly considering these criteria, you will be ready to select the proper equipment for a job. This article outlines the equipment needed for most abrasive blasting jobs and offers tips for making the best choices.

Air Compressor

Use an air compressor that is large enough to produce the air volume and pressure required to adequately and safely pressurize the blast machine, convey abrasive to the blast nozzle, provide breathing air and operate valves and accessories.

To determine the compressor size needed for a job, add the air requirements of all the equipment that the compressor will supply and then add a 50% reserve, which will be needed to keep productivity high as the blast nozzle wears—and it will wear. To maintain peak air supply, the smallest internal diameter (ID) of the compressor air outlet should be at least four times the size of the nozzle orifice. (See Table 1.)

Table 1: Minimum Compressor Air Line Diameter

Blast Nozzle

Replace a blast nozzle after its orifice is worn to 1⁄16 in (1.5 mm) larger than its original size. A worn nozzle not only wastes air, but also may lower productivity and even cause injury if the liner fails. Carbide nozzles—tungsten, silicon and boron—are the most popular for the majority of blasting applications because of their longevity.

Air Line

The air line ID should be as large as possible and at least four times the nozzle orifice size. This principle applies to air lines up to 100 feet. With longer hoses, especially longer than 200 feet, check the air pressure at the blast machine while blasting to determine if the air hose ID is sufficient. Air flows best through unrestricted fittings and straight air lines, so lines should be laid out in as short a length and with as few bends as possible to reduce pressure loss. (See Table 2.)

Table 2: Approximate Pressure Loss Caused by Common Fittings
Calculations are based on 100 psi (7 bar) in 1-inch (25-mm) pipe.

Air-Preparation Components

Moisture in the compressed-air supply can travel into the blast machine. If this occurs, abrasive may clump, which can cause stoppages in abrasive flow. Air-preparation components help prevent these stoppages. Depending on the humidity level of the air where operators are working, varying levels of air-preparation equipment may be needed. Coalescing filters provide the minimum level of moisture removal. They collect some of the water vapors that have formed into small droplets before the droplets enter the air filter. Aftercoolers cool air to condense even more moisture and then trap the moisture before it is conveyed to the blast machine. Air dryers are the most effective option for removing moisture and also oil from air. 

Blast Machine

A well-engineered blast machine allows smooth air and abrasive flow throughout the system. An industrial-quality blast machine features a concave head for easy filling, and it seals automatically with a pop-up valve. Place a recessed, steel screen over the machine’s filling portal to keep out debris, and cover the machine when it’s not in use to keep out rain and condensation. Make sure the pressure vessel has National Board approval, an indication that it meets American Society of Mechanical Engineers (ASME) specifications. 

Choose a blast machine that can hold enough abrasive for 20 to 30 minutes of steady blasting. Consider the effects of compressor and nozzle size on blast machine productivity. (See Table 3.)

Table 3: Compressed-Air and Abrasive Consumption
Consumption rates are based on abrasives that weigh 100 pounds per cubic foot.

Pressure Regulator and Gauge

These components enable operators to monitor and adjust air pressure. (TIP: Use a hypodermic-needle gauge to check pressure at the nozzle.)

Abrasive Metering Valve

In a well-engineered metering valve, abrasive flows into a stream of compressed air at a steady, uniform rate via the pull of gravity. A well-designed valve also permits precise flow adjustments. Metering valves that feed abrasive at a 45-degree angle facilitate the natural pull of gravity and promote a smooth abrasive and compressed-air blend, while metering valves that feed abrasive at a 90-degree angle create erratic abrasive flow, abnormal wear on piping and inaccurate mixing of air and abrasive.

Remote Controls

OSHA requires that blast machines be equipped with remote controls that quickly halt blasting after the control handle is released. Pneumatic remote controls work well at distances up to 100 feet. Electric remote controls are recommended for distances greater than 100 feet and are mandatory for distances of 200 feet or more.

Blast Hose and Couplings

Always use appropriately sized, good-quality, static-dissipating blast hose, manufactured for abrasive blasting and rated at the appropriate working pressure. The blast hose ID should be at least three times the size of the nozzle orifice.

Operator Safety Equipment

Personal protective equipment (PPE) is necessary for blasters and everyone in the work area, especially NIOSH-approved respiratory protection. No dust is safe to breathe! Use an air-fed helmet that not only furnishes breathing air but also protects the operator’s head and face from rebounding abrasive, muffles noise and allows an unobstructed field of vision.

Carbon Monoxide Monitor Alarms

These devices trigger audible, visual and/or vibratory alarms after they detect unsafe levels of carbon monoxide (CO) in the breathing-air supply of a supplied-air respirator. CO can be produced by oil-lubricated compressors or by motor or engine exhaust that enters the intake of a compressor or ambient air pump.

Properly Prepared Operators  
+  the Right Equipment 
= Successful Abrasive Blasting

Just like any other task in life, experience, knowledge and proper training are essential to abrasive blasting. OSHA regulations state that employers are responsible for training operators and for supplying all necessary PPE. Employers must also establish a safety program and ensure their workers follow safe practices on every job. OSHA’s regulations reinforce that the best way to guarantee a safe, efficient and productive abrasive blasting operation is to use properly trained, properly protected operators who have the right equipment for the job.

Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.

 

ABOUT THE AUTHOR
Lane Barnholtz, Clemco Industries Corp.

Lane Barnholtz is the senior editor at Clemco Industries Corp., the world's largest manufacturer of air-powered abrasive blasting equipment. He writes and edits material about the abrasive blasting industry, such as articles like this for industry publications.

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