Proper Grounding

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Harleydad
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Proper Grounding

Post by Harleydad » Sun Dec 26, 2010 11:58 pm

PCI Technical Brief #16

Grounding the Powder Coating System
Proper grounding of a powder coating system is absolutely essential for safe operation and quality finishing. Powder coating particles are electrostatically charged by passing through an electrostatic field or by frictional charging (tribocharge). The charged particles are attracted to a grounded surface (the part to be coated). Without a properly grounded surface available, a majority of the powder particles will not adhere to their target and will be drawn into the powder recover system.

Production problems caused by poor grounding
Inconsistent coating. A situation where one or more pats, in a series of parts, is not coated as evenly as the others. Faraday area problems may also be more pronounced when the part grounding is poor. If grounding is poor throughout the coating area, then all the parts will be inadequately coated.
Poor transfer efficiency. Improperly grounded parts will not attract power as they should. Less powder will adhere to the part, lowering the first-pass transfer efficiency.
Inadequate film thickness. A part with insufficient grounding may hold the same charge as the powder particles and reject (back ionize) additional powder particles sprayed on the surface. This slows, or eliminates the build-up of powder needed to attain the proper coating thickness. This may be especially important when a coating of more than 2 mils is required.

Safety problems caused by poor grounding
All equipment in the powder coating operation and area (as defined by The National Fire Protection Assocation, NFPA Bulletin Number 33. Chapter 13) must be grounded for safe operation. Any ungrounded object will store an electrostatic charge when it is subjected to an electrostatic field. When this charge reaches a sufficeint level the energy will be discharged to ground causing an arc or a spark. This may be a source of ignition that, in the presence of the right fuel to air mixture, ha the potential to cause a fire. If this occurs in a confined space, the result can be an explosion.

Equipment that must be grounded includes, but is not limited to:

• the parts being coated
• the spray booth
• the recovery equipment
• the spray equipment
• the gun motion equipment
• ductwork (if used)
• feed hopper/systems
• the convertor and part hooks
• the operator or manual spray personnel equipment and/or operator platforms
• vacuum cleaning systems

A Proper ground
NFPA Bulletin Number 33, Chapter 13, paragraph 13-4c, states, “to minimize the possibility of ignition by static electrical sparks, powder transportation, application, recover equipment, work pieces and all other conductive objects shall be grounded with a resistance to ground not exceeding one megohm.” (One megohm is 1,000,000 ohms.) This is the definition of a proper ground.

Uncoated metal parts, clean hangers and clean conveyors have very little resistance to ground and are excellent electrical conductors,. What can degrade this ideal path to ground is powder build-up on the contact points of the hangers or conveyor. Also the conveyor may have swivels or indexing assemblies that, when contaminated, can also impede grounding. All of these sources in total must not exceed one megohm resistance to ground.

Measuring Proper Ground
The device used to measure continuity to ground is an ohm meter that has a megohm scale. This can be a volt/ohm meter (VOM) or a megger. A VOM is adequate for checking electrical circuits, but its low voltage power source makes it less suited for checking the proper grounding of a powder coating system. The best device is the Megger which has a power source of 500 volts or higher. This higher voltage provides the current required to accurately measure the resistance to ground.

The proper technique for measuring resistance is to start at the end of the process and work backward. The meter is connected between a known building ground and the uncoated part to be tested using a long test lead. This procedure is used to determine that the part is correctly grounded through the entire spray booth. The amount of resistance to ground can be read on the meter.

Because the meter is attached to a know ground and to a clean part on the conveyor in the booth all of the devises in between (hanger, conveyor, swivels, etc) are in the circuit and the resistance to proper ground can be measured. If the reading less than one megohm, the grounding is correct.

If the resistance reading is greater than one megohm, hook the lead to the contact point on the hanger and read again. Repeat this procedure, working back through the system (swivel or conveyor hook, conveyor) until the resistance reads in the proper range. By this method you can determine which device needs corrective action.

A similar technique should be used to check for proper grounding of other objects and equipment in the powder coating area.

Improving the Ground
Clean, uncoated metal parts should present no grounding problems. The place to begin looking for excessive resistance to ground is the hook or hanger that carries the part on the conveyor. The key parts of the hanger are the contact points (both part and conveyor contact points).

To assure good grounding, routine hanger maintenance is very important. Maintenance can be performed in various ways:

• clean contact points only
• burn-off the entire hanger
• chemical strip the entire hanger
• sandblast the entire hanger
• mechanically break the coating off the hanger

If the conveyor itself appears to be a problem it may be necessary to provide a new ground in the area of the spray booth. This will require that the conveyor rail be wired directly to a known building ground. If after this is done a problem still exists, check the conveyor wheels, chains, swivels, or indexing devices for cleanliness. If they need cleaning or replacement, consult the conveyor manufacturer for the proper procedure.

If all else fails, a grounding bar may be required. This may be a bar or a brush connected to a known building ground that conducts a proper ground direct to the part hanger. This device brings with it some potential problems which include the possibility of metal shavings in the spray booth, impediments to color change, noise generation and the creation of a trap for dirt and contaminants.

The importance of proper grounding of the power coating system cannot be overstated. Poor grounding will have an impact on the entire powder coating operation affecting quality, efficiency, and safety.


Source: Powder Coating, The Complete Finisher’s Handbook. Third Edition. The Powder Coating Institute. pg 348-350.
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Re: Proper Grounding

Post by Harleydad » Mon Dec 27, 2010 12:00 am

Related threads:
http://powder365.com/forum/viewtopic.php?f=3&t=1806" onclick="window.open(this.href);return false;
http://powder365.com/forum/viewtopic.php?f=9&t=1809" onclick="window.open(this.href);return false;
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Re: Proper Grounding

Post by Harleydad » Fri Feb 04, 2011 11:15 pm

http://powder365.com/store/downloads/Grounding.pdf" onclick="window.open(this.href);return false;
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Re: Proper Grounding

Post by drycreek » Thu May 12, 2011 11:27 pm

I have a question, I plan on having a metal bar about 8 foot long hanging from the ceiling of my garage. Is it ok to just hook the ground clamp from the powder coat machine to the bar or should I have another type of ground that goes from the bar to the outside of the garage and hooks to a copper grounding rod?

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Proper Grounding

Post by T1CC » Fri May 13, 2011 12:47 am

drycreek wrote:I have a question, I plan on having a metal bar about 8 foot long hanging from the ceiling of my garage. Is it ok to just hook the ground clamp from the powder coat machine to the bar or should I have another type of ground that goes from the bar to the outside of the garage and hooks to a copper grounding rod?
The second scenario. Dedicated ground rod is superior.

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Re: Proper Grounding

Post by duke46 » Fri May 13, 2011 9:17 am

After you do the proper grounding using a ground rod then the only time you would ever need the ground that comes with you gun would be just in case you need to do a touch up of something because you knocked some powder off on the way to your oven or while you were placing it in your oven. and you needed to do a quick shoot. Of course if it is already in your oven then there would be a good enough ground there for the quickie hit. BUT NOT WITH THE BURNERS HOT. You would get a fire works display real quick :o
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Re: Proper Grounding

Post by SCOTTMO » Fri May 13, 2011 1:55 pm

Jeff
Did you have a ground cable coming off the back of your EUROTEC ?
Scott




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Re: Proper Grounding

Post by drycreek » Fri May 13, 2011 5:29 pm

duke46 wrote:After you do the proper grounding using a ground rod then the only time you would ever need the ground that comes with you gun would be just in case you need to do a touch up of something because you knocked some powder off on the way to your oven or while you were placing it in your oven. and you needed to do a quick shoot. Of course if it is already in your oven then there would be a good enough ground there for the quickie hit. BUT NOT WITH THE BURNERS HOT. You would get a fire works display real quick :o
ok, would it hurt to hook up the ground wire that comes off of the gun also or should just use the grounding rod. Thanks

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Re: Proper Grounding

Post by duke46 » Fri May 13, 2011 5:45 pm

drycreek wrote:
ok, would it hurt to hook up the ground wire that comes off of the gun also or should just use the grounding rod. Thanks
You could just cut it off but you might find a need for it like I said. So keep it out of the way and don't use it. I have all grounds connected and then just one and never seen any difference but I do have a good grounding system in my shop and my power panel also had an 8 footer so I was not but 40 feet from it and now I have one just for the gun.
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Re: Proper Grounding

Post by Harleydad » Fri May 13, 2011 8:36 pm

SCOTTMO wrote:Jeff
Did you have a ground cable coming off the back of your EUROTEC ?
Yes there is a terminal on the back of the control box. Didn't use it though.
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