Legend has it that sandblasting was first discovered by American inventor Benjamin Tilghman. While serving in the army, he noticed the effect of desert sand on windows. At the time, sand was the most commonly used abrasive in sandblasting, hence the name “sandblasting.” Over the past 50 years, more cleaning materials have been developed.
Today, the terms “blast cleaning” and “abrasive blast cleaning” more accurately describe the process, as abrasives can include any number of products such as slag, garnets, glass beads, walnut shells, and corn cobs.
Jim Deardorff, owner of Superior Coatings Sandblasting and Painting in Chillicothe, Mo., says sandblasting can be used on virtually any tractor part with the right combination of abrasive, air pressure, volume and nozzle.
Compressor “The air compressor is the most important component in the abrasive blasting process,” says Deardorff. “It provides enough air volume and pressure to move the abrasive through the hose and nozzle at a sufficient velocity to remove scale, rust, or old coatings from the target surface.”
For cabinet crushing, 3 to 5 cubic feet per minute (cfm) of crushing volume may be sufficient, he said. Larger jobs may require 25 to 250 cfm of crushing volume.
Deardorff explains that when choosing a blast bath or chamber, there are two types to choose from: suction-fed and pressure-fed.
Feed System The suction feed system works by pulling the abrasive directly into the spray gun. The system relies on the compressor sending air into the spray gun to create a vacuum. When the spray gun is triggered, the abrasive is pulled into the spray gun’s feed line. The exhaust air then delivers the abrasive to the target surface.
“In contrast, pressure feed systems store the abrasive in a container or can,” he says. “The can operates at the same pressure as the material hose. A control valve at the bottom of the can meters the abrasive into a high-velocity air stream. The air stream then delivers the abrasive through a jet hose to the workpiece surface.”
A sandblasting nozzle is a device used to maximize the impact velocity of the sandblasting abrasive. There are many types of nozzles, but four types are the most common.
*The straight nozzle produces a dense spray pattern suitable for spot cleaning or blasting cabinets. Often used for cleaning small parts.
* Venturi nozzles are the best choice for effective cleaning of large surfaces. However, it should be remembered that when blasting at high pressure (100 psi or more), the abrasive velocity can exceed 500 mph.
* Dual Venturi nozzles can be thought of as two nozzles joined end to end. An air inlet in the nozzle body allows compressor air to mix with the atmosphere. This venturi action increases the cubic feet per minute (cfm) flow rate and expands the blasting area. Deardorff notes that dual venturi nozzles are the best choice for low-pressure cleaning. This is because the suction of the air inlet port is capable of delivering large volumes of heavy, dense abrasives through the material hose at low pressure.
* Flat fan nozzles produce a flat fan spray and are used for spraying large, flat surfaces. Flat fan nozzles require more cfm to work properly.
Deardorff says there are also a variety of nozzle liner materials to choose from, including aluminum, tungsten carbide, silicon carbide, and boron carbide. Of course, the choice depends on your budget and the intensity of your work. It’s important to note that the flow rate will increase as the nozzle wears.
The abrasive is the part of any blasting process that actually does the cleaning. There are four main types of abrasives.
* Natural abrasives include quartz sand, mineral sand, garnet and mirror hematite. These abrasives are consumable abrasives and are mainly used for external sandblasting operations.
* Man-made or industrial abrasives such as glass beads, aluminum oxide, silicon carbide, steel shot and plastic materials are recyclable and can be used in systems that allow for recovery and reuse.
* By-product abrasives (such as coal ash, which is a by-product of coal-fired power plants) are considered the most widely used abrasive after quartz sand.
* Non-metallic abrasives are generally classified as organic materials. These materials include glass beads, plastic carriers, and grains such as corn cobs, wheat starch, pecan shells, coconut shells, and walnut shells. Organic abrasives are used when minimal surface damage is desired.
“The shape of the abrasive will determine the quality and speed of the blasting process,” says Deardorff. “Abrasives with angular, sharp, or irregular shapes will clean faster and etch the target surface. Abrasives with round or spherical shapes will clean the part without removing too much substrate.”
In this case, hardness affects not only the cleaning speed, but also the amount of dust generated, as well as the rate of decomposition, which also directly affects the recycling potential.
The hardness of abrasive materials is rated on the Mohs scale, from 1 (talc) to 10 (diamond), with the higher the number, the harder the product.
It’s not uncommon to use some kind of mixed medium. In fact, Deardorff developed one himself a few years ago. Sold under the trade name Classic Blast, it’s a special blend of aluminum oxide, ground black walnut shells, and other materials he mixed himself, including some garnet.
He said that by packing the product in a closed blast tank and using a vacuum to suck the medium into the blast chamber, the pressure can be reduced to 35 pounds (about 16 kilograms) while still cleaning delicate parts without damage. He often demonstrates the effectiveness of the blasting method by removing paint from an aluminum can that is still full of liquid.
Because the walnut shells in the mixture help remove paint, which acts as a polish on the sheet metal, the cleaned surface is also less susceptible to rust than with other types of media, Deardorff said. The walnut shells also soften the impact of the more caustic substances in the mixture.
Post time: Jul-01-2025