Crystalline or Molecular?

Copyright © 2004 Dave Propst. All rights reserved.

Revised 5/26/2004

Introduction

Often when explanations are offered of how to repair, fabricate or paint automotive sheetmetal body panels, references are made to one or more less-than-factual concepts about the properties of both steel and aluminum. These concepts have multiple origins. Some are taught in the collision repair industry. Others are associated with the shrinking disc. Still others are found in the paint and powder coat fields. What all of these concepts have in common is the idea that metal is molecular in structure. Much is made of how a sheetmetal panel's 'molecules' react to powder coat or paint, hammer blows, heat, etc. Additionally, among the general population, a not altogether uncommon assumption is that all matter of every type is molecular in structure. Fortunately though for those wanting to build sheetmetal panels, metal is not molecular in structure.

Why Worry about Scientific Details?

So why be concerned about molecules? Simply because some of the frequently made statements about this subject as it relates to working with sheetmetal are widely accepted but are in reality untrue. This is not so much a matter of the technical details of what a molecule is and how atomic particles in metal are arranged differently than atomic particles in some other substances. Instead, it is to recognize the fact that by frequently incorporating the phrases 'molecule' and 'molecular structure' a number of profoundly incorrect ideas about the forming properties of sheetmetal are made to seem scientific and factual to novice fabricators. The result is the novice ends up accepting fictitious explanations of metal's nature because those explanations sound very authoritative and scientific and are presented as being common knowledge among those 'in the know'. As a consequence of such misinformation, incorrect courses of action are taken when building specialty cars. Tasks are made more difficult than they need be and/or less successful than they can be.

Even if correct terms such as 'atom', 'crystalline structure', 'lattice', 'grain', etc. are substituted for the incorrect terms 'molecule' and 'molecular structure' so as to be technically accurate in describing metal -- the incorrect ideas about the forming properties of sheetmetal are still incorrect. Merely getting right the meaning and use of the word 'molecule' does not turn false concepts into true information.

No Molecules

This statement that metal is not molecular can be qualified somewhat by saying that metal is not molecular in construction as per the traditional molecular model that is commonly used for much of what we call matter. Verifying this to be true and understanding it is really quite easy. Simply look up articles on 'molecule' and 'metal' in mainstream, non-technical reference books. They need not be reference books of a scientific or engineering level. Common high-school or consumer-level encyclopedia articles such as Encarta Encyclopedia's article, Molecule will suffice.

"Molecule"  Microsoft® Encarta® Online Encyclopedia
http://encarta.msn.com © 1993-2007 Microsoft Corporation. All Rights Reserved.

Sources such as this will explain in plain, non-technical language that many materials here on Earth are made of molecules. Plants, animals, various chemicals, air and other gases are all molecular. Even materials such as wood and plastic that we use to build things with are molecular.  But... metal and some other substances are simply and emphatically not molecular. They are not made up of molecules. Their atomic particles do not form molecules. Examples of this are crystalline substances such as various minerals and plain, everyday things such as the salt we eat.

Before doing more detailed research beyond the scope of this article about this subject of why metal is not molecular (and why this even matters) it is helpful to be aware of some facts in advance in order to avoid confusion on a few points.

First, delving into technically oriented encyclopedias or books will reveal very involved, complex concepts about the 'building blocks' of matter. Some of this sort of highly technical published information is well beyond the ability of we non-scientists to even begin to understand without a very great deal of intensive study and learning. Suffice it to say that in comparison to such literature, this article, the Encarta reference above and most anything else written by or for the general public is hugely oversimplified. However, one easier-to-understand alternative concept that has been used for some time is that metal can be included in the traditional molecular model BUT... in order to do so the collection of atomic particles that make up an entire metal sample, a car fender for example, must be called a single molecule. The concept of a car fender as a single gigantic molecule, however, does not fit well into the traditional idea that molecules are so small as to be microscopic or invisible to the human eye. Also, and much more relevant to the subjects at hand, this single, gigantic molecule idea is NOT the way in which the concept of 'metal molecules' is (incorrectly) used in the false concepts found in the world of panel fabrication.

Second, there can obviously be instances in which non-metallic molecular matter (and therefore that molecular substance's individual molecules) is either accidentally or intentionally imbedded in or otherwise combined with metal. So in a 'trick question' sort of way metal can have molecules 'in it' but they are not in fact metal molecules. They are not metal.

A third potential source of confusion for some is the hyphenated, two-word term, 'metal-molecule' as used in the field of nanotechnology... as opposed to the self-contradictory, made-up phrase 'metal molecule' used in the world of automotive sheetmetal work. Nanotechnology metal-molecules are minutely small, man-made, or at least partially man-made, electronic devices consisting of a single molecule of an appropriate non-metallic substance sandwiched between two layers of metal. The word 'molecule' in this term 'metal-molecule' refers to molecules of the other substance, not to the atomic structure of the metal of the metallic outer layers.

Paint and Powder Coat Concepts

Perhaps the easiest-to-understand example of the trouble caused by this idea that metal is molecular is a claim presented with respect to painting and powder coating metal parts. The assertion in some magazine articles is that powder coat molecules or paint molecules or primer molecules can and do crosslink with the 'molecules' of the metal part being coated. This claimed crosslinking supposedly creates tremendous adhesion of the paint product to the metal without having to resort to extensive surface preparation of the metal. At times this claim is used in an effort to justify skipping metal treatments... treatments that are in fact required if maximum performance is desired.

Beyond the fact that the metal has no molecules to be crosslinked with is the fact that molecular crosslinking occurs only among products made up of chemicals that are specifically designed by chemists to react (crosslink) with themselves and/or each other under certain conditions. For example, if a catalyzed paint product is applied in the appropriate time frame over a previously applied catalyzed paint product that is compatible with the first product then indeed crosslinking within each layer and between layers can occur --and-- this does provide the dramatic increase in intercoat bond associated with intercoat crosslinking of molecules. So... not only is the reality "No molecules equals no crosslinking"... the true reality is "No entirely compatible molecules in both layers in the right time frame under the right conditions of environment equals no crosslinking." The claim that elaborate preparation of metal is not required for maximum durability for powder coat or primer or paint... the claim that their molecules will crosslink with non-existant 'molecules' in the metal and thereby provide the needed adhesion... is entirely false, having no basis in fact.

Collision Repair Concepts

The concept of sheetmetal being molecular in structure is common in the collision repair industry. This is largely because it is taught as 'fact' by a few nationally recognized collision industry training organizations. Claims made are usually one or another version of what is stated in the indented text below. Please note that this is not presented here as verification of this concept however, as the claimed reality in the indented text below is untrue and unscientific.

"Because collision damage causes sheetmetal to work-harden, in order to properly repair the metal, it (the metal) must be either heated or cold stress-relieved. This is especially critical if damage is being pulled out by use of hydraulic equipment. Cold stress-relieving is performed by rapidly hammering the damage zones of the panel with a body hammer or air hammer thereby causing the metal's molecules to vibrate and in the process effectively relax the work hardened metal."

Collision damage does indeed work-harden sheetmetal. With the exception of that fact, this entire concept is most emphatically not true and not true on a much more profound level than the relatively simple reality that, contrary to the claim, there are no molecules involved. The basis of the many extensive and profound errors in this concept is a misunderstanding of what work hardening is, what stress is, and what stress relieving is. This is mainly a matter of confusing stress with work hardening and in turn confusing stress relief with annealing. Ultimately though, this, just like the assumed ability of various metal forming tools (English wheel, power hammer, etc.) to very dramatically reverse the effects of work hardening, is a matter of completely mistaking changes in yield strength of material with changes in strength/rigidity of structure. Indeed there are changes occurring in how a sheetmetal panel reacts and feels to the repair tech or panel fabricator, but the reality of what is occurring is of a dramatically different cause and presents a dramatically different effect than what is usually mistakenly presented. In other words, not only will rattling on a panel with a body hammer not achieve 'cold stress relief', the concept of 'cold stress relief' itself, as commonly presented in this regard, is fallacy.

Shrinking Disc Concepts

A shrinking disc is used by some to smooth stretched, uneven areas of sheetmetal body panels. The process by which it does this is often claimed to be as stated in the indented text below. Again... this is not verification of this concept. The claimed reality in the indented text below is untrue and entirely unscientific.

"All kinds of metal are made up of molecules. When an existing panel is dented or creased in collision damage the metal's molecules are damaged and pushed out of alignment. Heat caused by friction in conjunction with the vibrating, hammering action of the shrinking disc's ruffled surface causes the panel's molecules to move and thereby become realigned and repositioned back to their original configuration that existed before the damage occurred. In effect the molecules remember where they were originally and heat forces them to go back to that position. This realignment of molecules in turn causes the panel itself to return to its original shape that existed prior to the damage."

The reality is molecules don't function this way. Molecules are entirely subordinate to the laws of physics and chemistry found in the real world. They don't get mysteriously 'damaged' in car crashes. They don't magically defy the laws of physics and get 'fixed', 'repositioned' and 'realigned' when confronted with spinning stainless steel discs no matter whether those discs are of the smooth or ruffled variety.

Even more to the point:

1) None of this claim of 'aligning the molecules' by the shrinking disc is valid because... again, metal is not molecular in structure. Metal has no molecules. There are no molecules contained in that door skin or fender that is being worked with a grinder/shrinking disc in hopes of 'fixing' the 'damaged' molecules.

2) Even if the mistaken terminology and lack of scientific reality is overlooked and everyone pretends for the moment that metal is molecular in structure, there are still insurmountable flaws in this claim or theory. Suppose for the moment this is all just an unfortunate mistake of wording and that the term 'molecule' has been accidentally used instead of the term 'atom'. Even after making such extreme allowances the theory just doesn't get far. In the case of a damaged OEM fender, how do the molecules 'know' which shape the panel builder/restorer considers the original shape to be? How would the molecules 'know' the pre-collision state of the fender is the right shape, since, after all, the sheetmetal was a flat sheet of stock before it was a fender. Wouldn't that be the original shape? But... before it was a flat sheet it was likely a small portion of a very large coil (rolled-up length of sheet) at the mill waiting to be delivered to the auto manufacturer's factory. Just before it was coiled, it was a continuous long flat length of sheet exiting rollers. Before being processed into a flat sheet it was likely a bar or some other non-sheet shape that was created when molten metal was cooled. There were a great many shapes prior to the supposedly 'original' fender shape. However would the metal know which of these shapes the panel builder/restorer wants it to 'return' to?

3) As if the case of repair of a damaged existing panel did not present enough of a problem for the theory, the fabrication of a new custom-made panel presents an impossible-to-resolve contradiction. Again, the theory states that the panel's molecules, when vibrated by the disc and heated by friction, will tend to return to their original position causing the panel to take on its original shape. However, when the shrinking disc is used to help smooth/shrink the remnants of mallet and shot bag work, or any other similar fabrication irregularities, the panel is being forced by the fabricator into taking on an all-new contour. Far from returning to the original shape -- a flat sheet, etc. (see above) -- it is taking on a new shape that has never even existed before. If reasoning remains true to the theory, in this case the molecules would be working against the panel builder. While he is trying to make the fabricated contours into a new fender, the molecules would be trying to force the sheetmetal to return to its original shape of a flat sheet. The reality is though, usually the reasoning does not remain true to the theory. Reasoning and the very theory itself are both adjusted as need be to attempt to reconcile the theory to those always pesky, observable results that occur in the real world. As a result, one version of the theory is used to explain what supposedly occurs when a new panel is being made. A different, contradictory version of the theory is used to explain what supposedly occurs when an existing panel is repaired. None of this particular shrinking disc theory has any basis in factual reality. (This is not to say that there are never instances in which sheetmetal exhibits what appears to be a tendency to return to a previous contour. There are such instances.)

Conclusions

Consider the significance of all of these claims of metal being molecular. If the concept of metal being molecular in structure is true, if the explanations of metal's properties based on that idea are correct and true... then... technical manuals, encyclopedias, college textbooks, high school textbooks, elementary school textbooks, trade publications, scientists, teachers, engineers, chemists, metallurgists, manufacturing processes, and even entire industries ad infinitum the world over for at least the last century or so are all incorrect and misinformed. The conclusion that a few untrue, readily refuted concepts are correct and that generations worth of mankind's accumulated scientific knowledge about metal is wrong would certainly save a lot of hours of studying mountains of technical literature to learn about metal's true nature! The problem with such a conclusion is that steel and aluminum sheet is not influenced by what uninformed people think. Believing that metal is made of molecules... does not make it so. Assuming that paint or powder coat will crosslink with molecules that don't actually exist... does not make it so. Believing that an air hammer, body hammer, wheeling machine, power hammer, etc. will vibrate molecules that don't even exist and thereby reverse a prior work-induced increase in yield strength... does not make it so-- even if the claim is from a 'certified' collision industry training organization.

To overstate the obvious, the only rules metal obeys are the laws of physics, chemistry and specifically-- metallurgy. Metal does not even 'care' if mankind properly understands those very laws of physics and chemistry. Metal is unwavering in its consistency. It is never inconsistent. It doesn't react in one way to one tool and in a contradictory manner to another tool. Metal reacts in the same way to both tools. One fabricator's knowledge or another's lack of knowledge has no effect on what metal does or does not do while being formed. Metal reacts in the same way for both fabricators. Rational thought would therefore suggest the goal is to find out what metal 'does' and use that factual knowledge to one's advantage. To that end it is only logical and beneficial to study to one degree or another metallurgy, physics, engineering and chemistry in order to learn facts, then verify those facts, then utilize those facts to form body panels out of sheetmetal.

End of Article