Dreaded Monthly Test Panels

Many of the laboratories today are lacking the ability to resolve problems associated with their analytical results. The data generated is given to the client, most of them not knowing what to do with this information to resolve their problem, nor do they really understand it. Their primary function is to be proficient in metal finishing and produce an acceptable part to a specification be it customer, industrial or government related. One of the requirements, especially if the facility is accredited to military, aerospace or some high tech industry is to maintain routine outside testing, to confirm their ability to control the process or processes they are utilizing.

The testing required generally performed on specific sized metal coupons of various alloys, temper, and thickness.

When a package of these little panels arrives at shipping and receiving, you would think the world had ended. This package of panels sends shock waves from shipping and receiving all the way up to the head of quality control, chemist or the CEO, for The dreaded monthly test panels have arrived. For some mysterious and unknown reason, the production staff can process complicated, expensive and precision parts 24/7, but only the chief chemist, head of QA/QC or the CEO himself are seemingly qualified to process these little pieces of metal and for most companies this is where the problem starts.

No matter whose responsibility of processing test coupons falls on, generally not treated as a production job but rather as a special project that requires extreme T.L.C.and special handling. Most failures occur due to special treatment (handling) rather than inadequate routine production procedures and chemistries.

First, these panels should be processed along with a lot or batch of production parts and not stand-alone. It is very difficult to adjust current and racking configuration to process relatively small flat panels, unless these types of parts are routinely processed and set-ups for them are available.

Processing test coupons (panels) along with production allows more control of current density but also will, when tested, relate back to that lot or batch of parts with which it was processed as well as a better feeling for production quality. This information is more meaningful than if non-production personnel processed the coupons stand-alone.

The line personnel, not the chemist, QA/QC or the CEO, should process coupons. Allowing personnel who run daily production for the company, who are supposed to know what they are doing, and actually produce the company’s product, run the coupons, not only gives you a feeling about the process but also how the personnel are performing.

When the coupons arrive, they should be treated just like a work order from one of the companies customers and processed just as they were a box of parts and no different.

Just to touch lightly on some common process problems caused by coupons being processed stand alone, which can have direct impact on whether the process is accepted or rejected.

Electroless Nickel Hardness:

Baking for hardness will quite often fail by laying the panels flat on the oven floor during the baking process. This quite often will cause annealing on one side of the panel and hardening on the other, the temperature on the bottom of panel will generally be higher than targeted temperature. When tested, one side will fail while the other will pass. Technically the panel is a failure.

Anodize Coating Weights:

Thickness of coating may be acceptable but yields a low coating weight, this is primarily due to coating density. The coating can have the required thickness but is very porous and lacks mass. Eliminate this by processing in the shortest time possible to reduce dissolution of the outer surface causing porosity. Current specifications require panels to be used for coating weight are not to be sealed. Sealed panels are difficult to strip and quite often lead to low results and failure.

Wear Resistance (Taber):

We will not discuss proper method(s) to perform the taber wear test at this time and assume properly performed. There are several reasons why taber abrasion tests fail, other than improper testing techniques.

  1. Excessive anodize time, racked alone, improper shielding, slow ramping. Build the coating and remove panels from electrolyte as rapidly as possible. This reduces the tendency for dissolution and softening of surface coating.
  2. Excessive chloride contamination can cause porous coating generation, which leads to low density and softer coatings.
  3. Thickness of test panels should be at least 0.060” and anodic coating uniformly applied to both sides. If these two conditions are not, there is a tendency for panel to bow or warp, causing erroneous taber results. In placing the specimen on the tabor, using large top washer it is sometimes possible to flatten the panel to within acceptable limits. However, if the panel is excessively deformed, results of the test will not be relative to the coatings resistance to wear.

Salt Spray testing on Chemical Film, Anodic Film, Electroless and Electrolytic coatings, and paints: This test has caused more concern from clients and primes than any other test. There are several reasons for this:

  1. Test is very subjective
  2. Slight variations in processing can cause pass or failure
  3. Time from processing to exposure
  4. Surface contamination due to packaging material for shipment and or handling
  5. Angles at which panels are exposed
  6. Direction at which panels are facing within the salt fog chamber
  7. Distribution of fog precipitation
  8. Uniform fog collection
  9. Precipitation rate
  10. Droplet size
  11. Critical Nozzle pressure
  12. Purity of water and salt
  13. Proper handling technique
  14. Initial surface condition of coupon material
  15. Interpretation of results

If problems do occur, evaluate your own system, before yelling at the lab for their incompetence. That is not to say laboratories do not make mistakes, but it is a natural tendency for people to blame others for problems. Evaluate as many areas as possible for a cause before calling your lab, have questions and answers ready to discuss reasons why they failed.

Other areas, which can cause poor corrosion resistance:

  1. Over etching
  2. Insufficient deoxidizing
  3. Faulty Deoxidizer
  4. Chemical contamination of anodize, Chemfilm, seals, etc.
  5. Excessive dissolved aluminum
  6. Chloride, Iron, nitrate contamination
  7. Contaminated rinses (high solids, suspended matter, etc)
  8. Oil or grease films on surface of solutions, rinses, and seals
  9. Improper sealing (poor chemistry, wrong seal, contaminated)

As you can see there are many facets to any process and the best answer I have come up with in reducing production problems are the following.

  1. Establish a process procedure and stay with it. If the process procedure works and something goes wrong, the procedure would be the last thing to look at.
  2. Establish chemical controls on each process solution, this includes rinses and drying (if utilized). Maintain the parameters for each solution at all times.
  3. Document all additions and changes, this includes line personnel and anything else involved with actual process production. This may take a little time and effort each working day but payback is more than justified, especially if a problem arises. In most cases, you can look back at the logs and find the source of the problem or at least in what direction to look. This eliminates a considerable amount of down time and finger pointing.

An Ounce of Prevention is worth a Pound of Cure