How Does a Blast Machine Work?
Byon Mar 08 2016
It's a blast
Sandblasting is an incredibly useful process that can be used for a variety of purposes, including cleaning, deburring, removing coatings, and shot-peening, among other ways which generally finish or improve the surface of a variety of materials. Blast machines are commonly found among equipment on industrial sites, like shipyards and railyards, and in the automotive industry.
These powerful, multi-purpose machine require a certain degree of skill and safety precautions to operate, but the mechanisms of the machine itself are relatively simple enough to understand.
Despite the popularity of sandblasting (also known as abrasive blasting and media blasting), finding a good guide for the layman to understand the sandblasting process isn't as easy to come by as you might expect (you never know when you might be asked to write about sandblasting, after all).
So you might say to yourself, hey, why can't I find any intelligible information on how a blast machine works? What's a safety petcock? What the heck do all the valves and hoses do?
Well, the blast masters over at sandblastingmachines.com have realized there's a lack of basic information out there on the internet and, as a leading distributer of Clemco products, have made it their goal to educate, as well as provide excellent customer service and products.
Perhaps part of the reclusive nature of this information has to do with the varying types of blast machines and parts/accessories that vary per machine. While every machine might have different components, for the most part they operate on this simplified notion: user loaded media + pressurized air = blast.
Easy enough, right?
It's all in the name: sandblasters/abrasive blasters blast grit/media/abrasive.
In a world full of objects with misleading names (catgut string isn't actually made from cats and Guinea Pigs are neither pigs nor are they from Guinea), you might be wondering if sandblasting is a misnomer, too.
It's, uh ...complicated?
Sandblasters were originally developed for use with sand (in 1870 by a man named B.C. Tilghman whom you can read about here), however now other types of abrasives are preferred due to the potential health risks involved with using silica sand (that's why it's important to adhere to all safety measures when using sandblasting equipment, just like you would using any other type of heavy machinery). This shift away from free silica sand has led to a name shift, although currently the practice is still more popularly known as sandblasting.
What else could you put in a sandblaster (or should I say abrasive blaster)? All kinds of media: glass beads, slags, steel, silicon carbide, aluminum oxide, garnet, even corn and apricot pits. As long as it's actually manufactured for blast cleaning, you can use it (although it's important to match abrasive with the surface being used, naturally. Blasting is all about cohesion).
Clemco is the world's largest manufacturer of air-powered blast equipment. And while they manufacture a variety of different models of varying capacities and components, understanding a generic " version of one of their classic stationary blast machines is beneficial to understanding sandblasting in general (by generic I simply mean of indeterminable capacity ...a hypothetical blast machine, if you will).
Main components of a blast machine:
The blast pot is essentially the reservoir for media and maintains the pressure necessary for blasting. (Blast pots come in a variety of sizes, depending on productivity needs)
Nozzles allow media to be sprayed at varying speeds/velocities, depending on what type of nozzle is used.
Inlet and Outlet valves monitor the inflow and outflow of air and determine whether the pot is pressurized (these guys are really important components, ok?).
The pop-up valve responds to pressure put into the system and pops up " to pressurize the system.
The Media valve regulates the flow of abrasive from the blast pot. Abrasive media valves have two inlets and one outlet: one inlet is for abrasive, the other is for air, and the outlet is for the mixture of air and abrasive that will be carried through the blast hose.
The abrasive trap prevents abrasive from travelling through the outlet valve (a big no-no; the outlet valve is for air).
A blast machine is also comprised of a number of hoses: twin-line hoses, blast hose, and 18-inch hose.
After media is loaded into the machine, a number of events must occur to begin blasting.
Pressure is incredibly important throughout this entire process, and without accurate pressure, nothing would happen and you'd be left with a rusty fender.
To properly pressurize the machine, you need a remote control system. Not only are these systems super handy dandy, it's an OSHA-required safety device (so it's important in a few ways!). Pressing/depressing the control handle will pressurize/depressurize the whole machine. For this purpose, the remote control system explained is a pneumatically-operated RLX control handle.
The twin-line hoses are connected to both the inlet valve and the control handle one hose monitors air travelling towards the nozzle while the other controls the air that travels back towards the inlet valve. When the control handle is not engaged, air is released at the base of the handle and no blasting can occur (because the system is not pressurized); the control handle is designed to fail to safe, " to prevent accidental blasting or injury. When the handle is pressed down, a button seals off the airflow and the air signals back to the twin-line hose and into the inlet valve. The inlet valve opens, the outlet valve closes, and the pop up seals to pressurize the pot to begin blasting.
A mixture of air and abrasive will spray through the nozzle.
Media blast pot media valve blast hose nozzle voila!
And just remember: it's all controlled by pressure (air).
ps. the safety petcock is located on the inlet valve and, when open, will prevent the machine from turning on when being filled. When open it allows air to escape from the remote control valve, which affects the blast pot's pressure.
The more you know!