Microanalysis of Craters in Organic Coating of Aluminum Cans
||Frank McDonough, Quaker Chemical, Conshohocken, PA
Wayne D. Niemeyer, McCrone Associates, Inc., Westmont, IL
Mike Shuster, Ball Packaging International, Westminster, CO
QUAKER CHEMICAL LABORATORY RESULTS
Parallel studies were ongoing by McCrone Associates, Inc. on
the surface analysis of the defect cans, and by the Quaker Chemical research
laboratory on the analysis of the lubricant/coolant samples obtained during the
cratering problem. Fortunately, this plant was on a schedule of sending a
sample for routine analysis to the Quaker Chemical laboratory every Monday.
This turned out to be most helpful since the problem started one day after the
Monday sample was sent. During the midst of the problem, a five-gallon sample
of the in-use lubricant/coolant had been captured.
Extensive analysis of the lubricant/coolant samples was
performed, and the most relevant data are shown in Figure 17.
click image to enlarge (71K)
Elemental composition of the “before” sample versus the
“during the problem” sample showed some significant differences: Note the
absence of iron, nickel and zinc in the “before” sample and the presence of
these elements “during the problem” frame. Something else very important to
note is the ratio between the magnesium and the calcium for the “before”
problem time frame. This ratio is about 1 part calcium to 3.7 parts
magnesium. In the “problem” time frame, a significant change occurred to 1
part calcium to 1.2 parts magnesium. This was a dramatic change in the fluid
chemistry, especially in a nine-month-old lubricant/coolant that had reached a
With the surprising conclusion of a corrosive mechanism from
McCrone Associates, Inc. plus the contamination findings from the Quaker Chemical
laboratories, a meeting was held with the production plant management to share
our information. This lasted for several hours and the plant personnel shared
some information that they had discovered from their own internal investigation
on changes that had occurred in their processes. Key comments from the plant personnel
- Initially, there seemed to be a
pattern to the high ME (metal exposure)readings.
- From the review of the plant chemical
process log, it was determined that excessive make-ups on the closed
loop of the cooling tower water system had occurred.
- The bodymaker operators had noticed
sporadic color changes in the lubricant/coolant, similar to the
dye used in the cooling tower water system.
- The lubricant/coolant concentration
was dropping during the “problem” time frame, indicating
that some excess water was getting into the system.
- The heat exchanger was replaced as
the lubricant/coolant was dumped and recharged. In this plant, the
lubricant/coolant flow traveled from the central lubricant/coolant system,
through the heat exchanger, directly to the bodymakers.
The main conclusion from this meeting was that substantial
amounts of cooling tower water were clearly contaminating the bodymaker lubricant/coolant
system during the “problem” time frame.
No one knew the impact of this, but the obvious next step
was to take some samples of the cooling tower water back to the laboratory and
analyze its components. Figure 18 is similar to Figure 17 with an additional
column for the cooling tower water. Note the presence of iron, zinc and nickel
in the cooling tower water; also note the magnesium to calcium ratio of 1 to 6.
We also speculated that a borate corrosion inhibitor was used in the water,
which would explain the presence of boron detected during the SIMS analysis. Our
conclusion was that the cooling tower water contamination was the assignable
cause of this ratio change during the crater problem.
click image to enlarge (76K)
Based on these findings, we hypothesized that the cooling
tower water contamination might be the cause of the crater defect during the
can making process. Additional samples of the cooling tower water were
submitted to the Quaker Chemical laboratory to see if this defect could be
reproduced under laboratory conditions.