A Good Ground Starts at the Top
Transfer efficiency isn't just a technical term, it's a management issue.
“Transfer Efficiency,” droned the speaker at the coatings conference, “is the ratio of powder deposited on a part to that directed at the part.” And on he went, mentioning the words “transfer efficiency” a total of six times. I made six tick marks on my notepaper.
Then the next speaker used the same words seven times. Seven more tick marks. The following speaker three. As the last speaker of the day approached the podium, the words “transfer efficiency” had been uttered a total of 27 times by the five preceding presenters. That convinced me that there might be something to this whole idea of transfer efficiency. I made it a point to better understand it.
This column generally sticks to topics around leadership theory and practice and leaves the finer technical analysis to the experts in those areas. However, my informal research over the last eighteen months on the topic of inadequate transfer efficiency and a primary cause—poor grounding—has led me to conclude that tending to it may pay more dividends than any other improvement one can make to a coatings line.
Consider the downsides of poor grounding. It leads to excess powder consumption because any powder not deposited on a part winds up being sprayed to waste or reclaimed. Oftentimes, the shortsighted corrective action for poor grounding is to crank up the powder guns in order to reach the minimum thickness specification, which wastes even more powder. Poor grounding results in a lack of uniformity in mil build, which in turn creates rejects, rework, scrap and excessive strip costs. Another primary cause of poor grounding, inadequately cleaned fixtures, deposits ash and residue in pretreatment chemistry, which leads to more frequent chemistry replacement in addition to powder line rejects.
As Thomas P. Frauman put it in his iconic article titled “It Pays to Become a Ground Fanatic,” “It’s important to remove any residue left by the cleaning process, such as ash in a burn-off process. Not only will this ash provide a barrier to electrical ground, but it may also fall on the coated parts and create contamination rejects.”
Credit goes to a CCAI golf outing for connecting me with John Cole who, since 2007, has served as the president of Parker Ionics, a leading manufacturer and worldwide supplier of advanced powder coating systems, spray booths, spray guns and application equipment. Turns out John and I share a passion for hook grounding and transfer efficiency. And yes, I do know how lame that sounds, but one can’t hide from the truth. Cole’s views on the topic, shared over several of my lousy tee shots, fascinated me.
“Without a good ground, without a clean hook, powder coaters will struggle,” Cole pointed out. “I’m 42 years in this industry and ground has been the first of the key elements of success. What I’ve learned through observation is that you can put powder on a part with no ground but you won’t have transfer efficiency, you won’t be uniform, you will have film builds all over the map.”
In addition to the downsides of poor transfer efficiency and film build variation, Cole talked about issues related to Faraday cages and to the opportunity for back ionization that increases the creation of craters and orange peel.
What makes Cole such an authority on grounding? “A lot of what I know about ground path is derived from a study I did for Kolene Corporation,” he explained.
“We started with virgin hooks and took one pass through a powder line and took numerous film thickness measurements. After the first pass, the standard deviation between all of the measurements was very small when we used virgin hooks.”
Cole proceeded to load coated hooks with fresh parts and sent the hooks on a second pass through the line. After the second pass, the standard deviation between measurement locations on the part started to drift just a bit.
Following the third pass, however, the standard deviation between measurement locations became significant. “On the third pass we saw ranges of mil build from 1.5 mils on the low end to 4.5 mils on the high end.” His conclusion? Variation in mil thickness, and thus the quality of the finish, can be directly correlated to the frequency and completeness of hook and hanger cleaning. Cole and his team went on to repeat the test at a second coating operation and the results were virtually identical.
This testing cemented for Cole the importance of effective grounding. “I am a real ground fanatic,” he said. “Question. Do I just want to put powder on a part—in which case it doesn’t matter—or do I want to do it uniformly and efficiently? The ground path and a clean hook are critical.”
Cole has a soft spot in his heart for the manual gun operator in the powder booth. “What I see now when I go out [to powder coating operations] is I see the painter.
“He is the company’s best resource but so often overlooked and underpaid. All he cares about is that he doesn’t get yelled at for having a bare spot on the part. He doesn’t care how much powder he puts on the part or how effectively or efficiently he does it.”
Cole’s point is that the gun operator avoids being disciplined for missing a spot on a part by blowing excess powder onto the part, which leads to waste. As long as the gun operator can compensate for poor ground simply by blowing more powder, the grounding issue and the problems it creates won’t raise any flags.
For this reason, Cole believes that the case for good ground has to start with ownership of management. As he bluntly puts it, “Unless the owner or the boss is driving it, it ain’t gonna happen.”
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