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Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2005

Powder Puffing and Surging

Q. I have a very chronic issue at our Automatic Excel powder booths dedicated for black colour. We have a chronic burp, spit or surge and it's causing heavy rejects. Can you just advise me what critical item we are missing to fix this issue?

A. Well, where do we start? First and foremost, powder collection equipment "booths" do not cause powder to burp or spit. It is the powder application equipment may cause this phenomenon. The single most common complaint from powder coating technicians is that the powder will not stop surging, spitting, puffing, and burping. The root cause is likely one or more of the following reasons:

Improper Air Settings: Powder delivery settings may not be ideal for the powder that is being sprayed. Powder is delivered to the charging field at the tip of the gun by air. The air to powder ration is a function of the gun settings that are controlled by the operator. Too much air is as much of a problem as too little air. The goal is to get the powder to flow freely through the powder pump and feed hose to the charging system at the gun.

Delivery Hose: The powder delivery hose length may be too long and the powder flow may be disrupted by the surging caused by the powder accumulating in "dead areas" of the hose. Check to be sure that there are no obstructions that may cause kinking in the hose. The powder feed hose should not be looped in circles or hung from the booth to resemble a roller coaster. This condition will make it impossible for the powder to flow evenly without surging.

Clean Dry Air: The air must be clean and dry. The air pressure must be constant. If the volume and pressure of the compressed air are not adequate for the plant, air surges may result causing erratic spray pattern surges. Powder coating equipment requires compressed air to be provided at +38 degrees dew point or lower, and contain less that 0.1 part per million oil, and have no particulate contaminates greater than 0.3 microns.

Maintenance: All powders are abrasive, and will erode the specialty designed wear parts that will eventually cause a disruption of the flow causing puffing and surging. These parts must be checked frequently, rotated to maximize wear, and replaced when necessary. Additionally, powder may be accumulating at the tip of the gun around the deflector or charging electrode. The deflectors are designed to create the powder cloud effect. Electrode accumulation is common when metallic powders are sprayed.

Powder Condition: The powder material particle size ratio is important in first time transfer efficiency. Old powder (>12 months), or powder that may have been exposed to heat (>85 Degrees F) or moisture, will cause the powder to coagulate and may cause surging as the powder travels through the powder feed hose. Powders that have settled into the containers during transportation from the manufacturer should be sieved to allow break up the powder and allow it to travel freely.

I strongly suggest that a systems audit be conducted to identify and correct this condition. Contact you powder equipment supplier and ask for assistance. This may be the most cost effective way to solve this problem. Do not forget to document the corrective action so that future department managers can benefit from this cause and effect analysis.

May your production days be colorful, and your rejects be few.

Make it a great day...

Michael W. Cravens

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