Defect Reduction Process: What’s in a name

One of the most important step steps in an effective defect reduction process in the web coater is the accurate naming of the defect. This name must be unique for a defect, unambiguous and interpreted in the same way by all who use the name. Naming is usually an easy straightforward process because most areas of science have standard naming conventions. For example, there are standard names for organic chemicals, which are used by all scientists. These are issued by the International Union of Pure and Applied Chemistry. Thus all chemical compounds can be unambiguously named.  Similarly the disciplines of Chemical Engineering, Electrical Engineering and Physics all have standard naming conventions.

27. Defect Reduction Process: What’s in a name

One of the most important step steps in an effective defect reduction process in the web coater is the accurate naming of the defect. This name must be unique for a defect, unambiguous and interpreted in the same way by all who use the name. Naming is usually an easy straightforward process because most areas of science have standard naming conventions. For example, there are standard names for organic chemicals, which are used by all scientists. These are issued by the International Union of Pure and Applied Chemistry. Thus all chemical compounds can be unambiguously named.  Similarly the disciplines of Chemical Engineering, Electrical Engineering and Physics all have standard naming conventions.

Unfortunately, there are no standard naming conventions for defects in the web coating process. Thus, there are a wide variety of names in use for the same defect, and defects that appear similar can have one name when the defects are in fact different. One of the reasons for this is that coating and drying defects are often rather nebulous, and have hard-to-define characteristics.  A specific defect can have a variety of shapes and appearances and it may be hard to define the appearance of a standard defect. The names given depend on the visual appearance and how the observer perceives the defect. Often similar defects can have a variety of names that depend on the industry and the product type, in which they are observed.

A round defect with a clear center that looks as though it had a bubble or a clear center in its center is named a bubble, event though there are other causes that will give a similar appearance. In the spray coating of automotive finishes pinholes and microfoam both describe the same defect, even though the names imply that the defects are very different.

A good example of the naming problem is Ribbing Defect which is a series of machine direction streaks. The defect occurs in several coating applicators. Visually the defect appears as follows:

However, there are eight slang names for the defect which are in use:

Ribbing         Barring         Comb lines                     Corduroy
Phonographing   Rake lines               Railroad Tracks     Rib pattern

The use of these idiom names complicates the defect elimination procedure for several reasons:

    • The defect under study can have the wrong name and technical effort is wasted tying to solve the wrong defect.

• The name may also suggest the cause of the defect, thus an incorrect name can results in wasted time by trying to solve the wrong defect.
• Communications between personnel working on the same defect are difficult.
• It is difficult to locate historical data since it may be stored under a variety of names. Therefore the advantage of previous information is lost.
• Complicates an effect defect data database.

The best way to avoid this problem is to not give it a descriptive or idiomatic name when it is initially observed. Use neutral terms to describe defects and classify it according to its attributes. Figure 1show a Classification Scheme with terms that can be used to assign defect attributes.

The next step is to analyze the defect and define it both physically and compositionally using the following    analytical techniques:

• Video microscopy
• Scanning Electron Microscopy
• Energy Dispersive X-ray
• Electron Spectroscopy for Chemical Analysis
• Infra-red microscopy

The defect can then be named and the descriptive information put into a database for sharing data and recalling past experience.  A standard PC database such as Filemaker Pro can be used to store and retrieve data, Figure 2. The AIMCAL Defects Lexicon  can also assist in this effort. It contains entries on many  defects which give standard names, idiomatic names, classification images, and  information on the defect cause and how to eliminate it, Figure 3.

                                                                        Figure 1
                                                                                    Defect CLasification

                                                                         Figure 2
                                                        FileMaker Pro Defect Record
                                                                    Roll Repeats

                                                                            Figure 3
                                                            AIMCAL Defects Lexicon