Why Buy Media Blast Cabinets
Blast cabinet machine operation and automobile engine operation often use the same descriptive terms for explanations on how they work.
The following information will give you a basic understanding on the two abrasive delivery systems used and why you need other features for proper machine operation. This will also give you a good basic knowledge for decisions on how much to spend on any machine purchase.
Often times other manufacturers supplying automotive equipment simply do not offer reasons why lesser equipment is better equipment. They also don't offer better equipment that you might want to purchase. This can be described as low price, self-selling marketing. This does not allow the customer to decide what machine features are best included for their application, only see ... look ... price and purchase!
The information that follows will help to educate you during the selection process. Just as any new car option is less to purchase when the car is purchased, so are blast machine features!
Siphon Machines operate with the abrasive open to atmosphere similar to engines using carburetors that are open to atmosphere. It would be difficult to deliver more gas to the combustion chamber than the piston can displace when passing the air through the carburetor. Carburetors function in the same manner as an abrasive mixing valve, they are used to regulate the flow of gas to point of use.... some manufactures indicate that you don't need an abrasive mixing valve or shall we say a carburetor!
Direct Pressure, Pressure Pot Machines, operate closed to atmosphere. Because they use a pressurized pot to pneumatically push the abrasive at pressures above 1-atmosphere, they can operate similar to turbocharged engines that use the blower assembly to push added gas and air into the combustion chamber. More gas, more air, more horsepower. Another simpler description would be to realize that the direct pressure machine eliminates the abrasive hose, eliminates the nozzle and gun body leaving only the air hose and compressed air jet used to determine air compressor sizing. The direct pressure unit has an abrasive mixing valve that drops the abrasive directly into the air hose, now called an abrasive hose, allowing the compressed air to pneumatically push the same abrasive in pounds per minute out of the smaller air jet, now called a nozzle. This concentrates the abrasive in a smaller ID hole that everyone simply calls the blast nozzle.
Tip: Compressed air delivers the abrasive... this is what cleans the parts with the abrasive media mixed in... Often the siphon unit will blast more parts in less time than the direct pressure type unit. Each application decides what delivery system is best or faster, not the buyer... Almost all automated and semi-automated blast machines are siphon delivery! If direct pressure were really faster for general cleaning, almost all automated equipment would be the direct pressure type....
Use a direct pressure system when the abrasive is large or heavy, i.e., steel shot or steel grit. Direct pressure units are also great for deep blind hole processing and the removal of heavy coatings like automotive undercoatings.
Always keep in mind that lots of separate machine markets exist within the automotive field...
- Auto restoration for hobby, sanity and a good classic ride.
- Large and small automotive repair shops for profit.
- Production aftermarket equipment manufactures for fast processing.
HOBBY RESTORATION: Because time is money and some of us have more time than money the cleaning speed of a blast machine is not as important as having that rebuilt part from your first car looking like new. This is a good example of Hobby Restoration. This type of unit is sold by a number of companies and can be as simple as a spot-welded box, plastic view window, trigger blast gun, outlet for vacuum dust collector connection and often with optional cabinet lighting. In the industry this constitutes a “blast cabinet”. They often boast of operation with compressed air usages as low as 6 cfm. Because frictional heat is generated by all blasting cabinets with the amount of compressed air used, exception wet blasting, the larger the amount of cfm used at any blasting pressure, the greater the frictional heat generated and the faster the cleaning rate. Just remember how much faster that sander works when you push down hard creating more frictional heat and you might re-think the compressor size!
Tip: Most Hobby restoration occurs close to the refrigerator at home in the garage with only 220-volt single-phase electrical power. Regardless of the compressor Horse Power rating, it is possible to purchase a 220-volt single phase compressor, usually a 5 HP motor, with a performance cfm rating of 23-24 cfm @ 175 psi tank pressure.It is also possible to purchase an 8 HP rated motor also single phase that has a performance rating of 9 cfm at 90 psi...which unit do you want? "Buyer beware of large motor ratings and large tank sizes. Always check the cfm delivery at 90-100 psi."
Always look at the amount of compressed air any blast machine requires for operation and remember that the compressed air is doing the work and the blast machine is only keeping the process contained. Items you should look for when shopping machines. Click the dictionary icon for definition of terms.
- 100% Welded Cabinet
- Abrasive Separator Reclaimer
- 1/2 HP Exhaust Blowers 350 cfm and larger
- Safety Plate Glass Window
- Abrasive Mixing Valve
- Foot Operated Blast Valve
When you summarize this information it helps to remember the following:
Know your air compressor volume first... When purchasing compressed air for the unit, always purchase the most volume (cfm) you can afford for the electrical power voltage you have. The compressor is more important to the process than the blast cabinet when talking speed. The importance of the cabinet relates to the cleanliness of the process.
Always look for a blast machine that includes a Separator Reclaimer. This will remove the dust and oxides from the abrasive. This is as sensible as removing the dirt from your engine oil. Abrasive not being cleaned without a separator will need to be thrown away when it's dirty!
Look for a unit that includes an Abrasive Mixing Valve. This is the same as having a carburetor to mix the fuel and air. Cars can be started with no carburetor at all but this condition is very undesirable. Some blast machines are offered without any abrasive mixing valve this makes regulation of the different blast media's impossible, also as the abrasive changes in particle size you can't adjust the feed.
Never let the size of the cabinet be the deciding factor. It's easier to make a large visual self-selling box than supply you with features needed for better overall machine operation. The machine cfm used should determine the blast chamber size.
11 cfm and lower are not advised for siphon blast machine applications, you will be disappointed!
12-15 cfm for small parts, hand held brackets, pulleys, master cylinders, generator housings, voltage regulators, covers and possibly an occasional radiator bonnet...
16-20 cfm for small parts, hand held motorcycle forks, battery boxes, jacks, valve covers, shrouds and small painted wheels...
20-25 cfm for larger parts inside larger cabinets still capable of being hand held like oil pans, motorcycle gas tanks, brake drums, timing covers, wheels, bike frames, parts for weld repair and more...
Keep in mind, that parts are being flipped and rotated during the blast cleaning cycle and having an engine block, rear-end or A-arm is a bit out of the normal feasibility for light duty unit operation...think 25 cfm and less compressor delivery when you are thinking about part flipping, 50-80 cfm with part fixtures for faster easier cleaning.
For auto restoration look to the Hobby, Space Saver and Viper for siphon machines that operate on 12-17 cfm of compressed air and include exhaust blowers, separator reclaimers, abrasive mixing valves, foot operated blast controls and 100% welded construction. Direct pressure systems using smaller amounts of compressed air can be solved by looking to the 3030 Savage model that includes the smaller flow-control valves needed to make the system work properly. If you have 20-24 cfm available, look at the Shop Standard non-production line with taller, deeper and wider siphon cabinets.
When more air is available along with 3-phase electrical power, look to the N-200 siphon and Power Peen direct pressure units for fast production processing. Production units consider time as money and less time processing is more profit!
LARGE AND SMALL REPAIR SHOPS:
Often the boulevard repair shop is in a commercial zone and only has single-phase electrical power. The information about compressor sizing still applies but often the shop will be using the true industrial air compressor that supplies a full 20-25 cfm of usable compressed air.
This shop will be looking for a larger machine cabinet size for larger part processing. This type of unit operates using a slightly larger blast gun than the Light Duty Equipment.
Sometimes the shop has 3-phase electrical power but uses the air for hoists and other critical air tool operations. If you need 25 cfm of the existing air supply to be dedicated to the blasting operation it doesn’t leave room for production type machinery unless you install a smaller gun size. In each example the shop often wants a larger cabinet size.
A good example would be the need to fit the complete radiator inside the cabinet but only cleaning sections of the assembly. The machine required is often called a panel-constructed cabinet because the dimensions are greater than 24 inches and the cabinet uses panels to make the chamber larger in size.
Standard steel widths are typically 48 inches. Smaller Light Duty models usually measure 24 x 24 x something. Machines larger than 24 inches often need to be formed using panels....
Panel cabinets are larger, 28 inches or 30 inches by 36-48 inches. This type of machine should include the desirable features of 100% welded construction, separator reclaimer, abrasive mixing valve, foot operated blast control and safety door interlocks. The only feature not included but found on production models is the large capacity negative pressure dust collector that is needed and required for production dust storage.
The type of machine now being described is often called an R&D machine or something purchased to do larger parts requiring a larger cabinet size with no requirement for daily production usage or minimum cleaning time. This type of machine often has a positive pressure tubular bag type dust collector and operates using a gun size of 20-25 cfm. What separates this unit from the production type unit is the less expensive positive pressure type tubular dust collector. Production units always include the more expensive negative pressure mostly cartridge type collectors with dust storage hoppers...
Look to the Shop Standard line of blast cabinets for machines that require 20-25 cfm of compressed air without the need for production part processing... they include features like:
- Larger cabinets to 4’ x 3’
- 550 cfm Exhaust Blowers
- Separator Reclaimers
- Abrasive Mixing Valves
- Foot Operated Blast Controls
- Available Options to prevent wear on windows and nozzles
EQUIPMENT REMANUFACTURES or PRODUCTION:
After-Market Products as well as Equipment Remanufactures have one common consideration when thinking about the purchase of any abrasive blasting cabinet.
The single most important consideration is ... TIME IS MONEY!
If you remember the information about compressed air usage and creating additional frictional heat you also want to remember that doubling the compressed air used will triple the volume of work being produced on almost any application. Creating the greatest amount of frictional heat can be the deciding factor to determine if epoxy paint will be removed. Smaller guns are not capable of frictional heat development of 300 degrees “F” and often take too long to process the part or simply can’t process the part at all.
Doubling 25 cfm to 50 cfm gets you three parts in the same time, not one! Doubling 50 cfm to 100 cfm gets you nine parts not three...when time is money production and volume count. Manual blast cabinets seldom exceed 100 cfm of compressed air usage.
Because a production machine is producing parts at a higher volume and running on a daily schedule these units require larger blowers, larger dust collector filter surface for dust storage and self-cleaning dust collector filters. Most of the maintenance on any blast machine is related to the dust collector and unless the collector is large in surface area and easy to clean you only have a blast cabinet with a large gun not a production unit.
"A comparison to the automobile would be similar to having a race car that takes 20 minutes to pit...unless the race car pits in seconds the only thing you have is a car with a large engine not a race car..."
Two types of abrasive delivery systems are most commonly used. The siphon system, 80%, and the direct pressure system or pressure pot model at about 10-15% The missing percentage is often special abrasive delivery types such as wet micro and gravity feed units.
Siphon units using the same compressed air and delivering the abrasive at the same velocity will usually out-clean the direct pressure type unit. Think of this as painting a car...do you really need a garden hose delivery system to paint a car? Would the garden hose cover faster if you needed to turn it off every 5 minutes? Pressure pots are not open to atmosphere during blasting but need to be refilled when the pot is empty.
Most applications today require the siphon system and unless you are doing a very specific job that simply can’t be processed using siphon, like shot blasting... blind hole cleaning or the removal of very heavy coatings, the siphon is almost always faster because it operates continuous. Don't count any siphon system out unless you have tried an 80-90 cfm injector gun assembly in a full production siphon system.
All pressure machines, with the exception of the double pressure pot, require pot recharge time. In addition almost all automated blast machines are siphon. If the direct pressure type was really faster in the long run, all automated machines would be direct pressure ... "Time is money".
Because Media Blast makes all types, you also need to know that part-processing time is a factor. If the part being cleaned or processed is normally cleaned or processed in less than 5 minutes and not followed by cleaning or processing another part, then direct pressure can be faster. It is possible to process and walk away from the direct pressure machine allowing it to fill the pot assembly when the unit is not being used.
Look to the N-200 Siphon and Power Peen Direct Pressure for the most commonly used models for real production work. These units are used with an abrasive size of 150 mesh and larger and are also available in cabinet sizes up to 10 feet.