Thermal Spray Powder Feeders

Rotating Disk vs. Fluidized Bed Powder Feeders

When it comes to thermal spray powder feeders, a common question that comes up is: ”What is the difference between a rotating disk powder feeder and a fluidized bed powder feeder?”  An additional common question is: “Which is better?”

Rotating Disc Powder Feeder

AT 1200 Rotating Disk Powder Feeder

PF-700 Rotating Disc Powder Feeder

The rotating disk powder feeder is a name that is rather self explanatory of how it operates. The main operating component to feed the powder is a rotating disk. The AT 1200 and the PF 700 are both examples of rotating disk powder feeders. The rotating disk has a large number of small holes or slots that rotate in a circle. The hole rotates underneath the hopper that holds the powder. Gravity simply feeds the powder into the hole as it rotates past the powder discharge tube of the powder hopper. It rotates to another discharge hole where the powder drops down into the carrier hose where it is taken to the gun via the powder carrier gas. Some say this type of powder feed arrangement lends itself to the pulsating of the powder because of the interrupted flow.  Others defend it saying that the length of the powder feed hose and the speed of the rotating disc eliminate the pulsation.

The rotating disk powder feeder is simple in design, reliable, and very easy to maintain. The man wear parts are the metal rotating disk, the plastic disk seal, felt seal, and various o-rings. With regular cleaning and preventative maintenance, the rotating disk powder feeders have proven to be reliable for many years.

Fluidized Bed Powder Feeder

4MP Fluidized Bed Powder Feeder

The fluidized bed design is a little more complicated and needs more explanation. First, let’s start with the definition of a fluidized bed:

“A fluidized bed is formed when a quantity of a solid particulate substance (usually present in a holding vessel) is placed under appropriate conditions to cause the solid/fluid mixture to behave as a fluid This is usually achieved by the introduction of pressurized fluid through the particulate medium. This results in the medium then having many properties and characteristics of normal fluids; such as the ability to free-flow under gravity, or to be pumped using fluid type technologies. The resulting phenomenon is called fluidization.”

From Wikipedia, the free encyclopedia

The fluidized bed powder feeder design utilizes a portion of the carrier gas that is directed to the bottom of the powder hopper. This back pressure allows the powder to be “fluidized” with the carrier gas. In theory, this allows a more even size distribution and flow of the powder as it is drawn up into the powder pickup shaft. The powder pick up shaft has a converging/diverging internal design that creates a lower pressure inside the pickup shaft (Bernoulli principle) that draws the powder into the carrier gas stream and delivers it to the gun.  Some say this creates a more continuous feeding of powder with less pulsation.

Even though these powder feeders have a vast array of hoses and pinch valves internally; when properly maintained they are reliable and remain workhorses in many coating shops. The complexity of the plumbing circuit is what draws the most criticism of this style powder feeder.

You will find plenty of opinions as to which is the better powder feeder; both the rotating disk and the fluidized bed powder feeders have been used successfully for many years in the thermal spray industry.  I do have to say, the largest single problem I see with any powder feeder is the lack of preventative maintenance.  Metal powders are abrasive and aggressive requiring regular cleaning and maintenance.

Click here to see more features of our new powder feeders:   Powder Feeder Info
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Filed under: Thermal Spray Powder Feeders by Bob
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What is the best way to prepare the surface before thermal spray?

Grit blast is the best way to prepare a surface for thermal spray.  This is after all oil and grease has been  removed from the part to be sprayed. The purpose of grit blasting is to remove all oxides and foreign material from the surface being sprayed. More importantly, the grit blast operation results in a surface that has many pits and textured areas where the thermal spray can attache to and lock into.  The most common material used for grit blast is aluminum oxide and chilled iron.

For a more in depth discussion, please go to this link:

Surface Preparation for Thermal Spray

Filed under: Thermal Spray Process by Bob
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At Thermal Spray Depot we are proud to be a distributor for the AT 400 twin wire electric arc spray system manufactured by Thermach. We have been asked if the AT 400 by Thermach is the same as the BP400 built by Praxair Tafa; well it is not; but they share an interesting  history in arc spraying.  In applications where you require electric arc for your metal spray application, the AT 400 is superior to the Praxair Tafa BP 400. Additionally some ask to compare the AT 400 to the 8830.

The BP 400 was originally designed in Wisconsin at Miller Thermal, which was part of Miller Welding at the time. Through various acquisitions, the Miller Thermal Group became part of Praxair.  When Praxair purchased Tafa, they decided to move the manufacturing of the Miller Thermal spray equipment to the north east.  Some of the original design group and manufacturing group of Miller Thermal decided to stay in Wisconsin and form what is now Thermach.

After Thermach was formed, they took on a project to design a new arc system.  Both units look similar, but there is significant internal changes to the AT 400. The gun parts of the two units are not interchangeable even though they look similar. In addition, improvements to the wire feed unit, such  as the quick change drive rolls, are not interchangeable.

As one final note, the lightweight and rugged design of the AT 400 make it the obvious choice over the 8830.

To see the superior features, please click on this link:

AT 400 Twin Wire Electric Arc Spray

Keep asking questions!

Filed under: Thermal Spray Equipment by Bob
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Greetings:

Thanks for taking the time to visit the blog, this one is on the topic of thermal spray wire.

The thermal spray process is used to apply molten materials to the surface of an another object in order to change the surface properties of that object.  The source of material in the  process is either wire or powder.

Wire is desirable for use in the  thermal spray process because wire is generally more cost effective to manufacture than powder.  This obviously is only true for materials that can be made into a wire.

The basic process for using wire in thermal spray is as follows:

1. Feed the wire into a melting source

2. Melt the wire

3. Atomize the molten metal

4. Apply it to the object being sprayed.

Feeding the wire into the source is accomplished by using air driven or electric driven motors.  The wire is gripped with  grooved rolls that have serrations in them.  The wire is normally on an open coil or it is wound on a spool, either way, it must feed into the motors with no tangles and as little resistance to uncoiling as possible.

Melting of the wire is an integral part of the process and is accomplished in one of two ways:

1. Electric Arc

2. Combustion flame

Atomization is accomplished using a compressed gas, usually air.  However, there are applications that will use other gases, such as argon when you want to limit the oxides.

Popular sizes for the wire is 1/8? or 1/16?, although there are several other sizes used.

These blog posts are intended to be concise and fast to read.  If you would kike more information on thermal spray wire, including a chart that shows the conversion of gauge to inches to millimeters,  just click on:

“Thermal Spray Wire”

This  link will take you to the right location on the this web site.   You can also get there by following our menu bar at the top of the web site by following the drop down menus:

Information/Articles/Thermal Spray Wire

Thanks for joining us.  If there is a specific area that you would like more information on, drop us a line and  we will evaluate making your topic that one of our posts.

Bob

Filed under: Thermal Spray Wire by Bob
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