If you're purchasing a new standing seam metal roof or have been working as a professional in the architectural metals industry for a while, it's critical to know the most common metal substrate defects that could show up on a metal sheet or coil product.
Not only will knowing this information stop you from installing defective materials on a home or property, but it will also save you time and money spent to fix any issues it could cause.
While defective metal has ended up in the hands of installers before, the majority of coil defects are caught by the manufacturers, suppliers, or production lines before the metal is ever sold to a customer. Quality assurance measures exist to make sure that only the best material is used to rollform and install a metal roofing system.
So, what signs should you look for to spot any substrate defects?
Sheffield Metals has been supplying coated and bare metal sheet and coil products to the architectural metals market for over 20 years. While rare, metal coil being defective in one way or another is still a possibility. This is why we believe educating the industry about the most common substrate defects is the best way to ensure any bad material is caught before an installation.
In this article, we'll go through:
Before we get into the defects that can show up on painted or acrylic-coated steel (Galvalume) sheets or coils, we first want to explain the journey that steel takes from the beginning stages to the final stages.
The metal that ultimately becomes a metal roof or wall starts as a flat, cold-rolled carbon steel substrate. The raw steel that we purchase is already tension-leveled, meaning that many of the imperfections in the material have been worked out before it ever makes it to a steel mill or paint line. For reference, tension leveling is the process of pulling the metal beyond its yield point and applying immense pressure, which permanently changes the shape of the metal. In this case, the tension leveling keeps the material flat and straight as it's rolled into coil form.
Once this material is sourced/purchased by a manufacturer, it is sent for processing to a steel mill. The mill takes the raw metal and continuously hot-dips the bare steel coil/sheet with aluminum and zinc alloys until it reaches a coating consisting of 55% aluminum, 43.4% zinc, and 1.6% silicone. This process allows for one steel-based product to have some of the best characteristics of each coating material, which is why it's become one of the most popular materials in today's roofing market.
For background, two different products are produced at the steel mill:
The number after the 'AZ' refers to the coating weight that is applied to the raw substrate, so an AZ55's coating weight is .55 ounces per square foot, and AZ50's coating weight is .50 ounces per square foot. The unpainted, acrylic-coated Galvalume has a slightly thicker coating weight because it will not have the paint system to cover it, so it needs some extra exposure protection.
Once the coil is coated at the steel mill, any products intended to be painted (AZ50) are sent to the paint line, while the completed AZ55 products go to the manufacturer/distributor.
For the products that now have the AZ50 Galvalume coating on the steel substrate, the next step is going through a paint line that applies the paint system.
Coil coating paint lines have many different processes and stages, which you can watch in our video on The Metal Roofing Channel, but here is a basic explanation of what a coil goes through at the coating line:
After the material is off the paint line, the coil goes through rigorous quality assurance testing. For example, the paint line company will run these tests (and more in some cases) on the painted coil to verify:
Once the material passes all of the tests, it will be packaged and shipped to the supplier or manufacturer.
The final stage of a metal coil's production journey ends at the supplier/manufacturer who purchased the material and sent it through the steel mill and paint line. Sheffield Metals would be considered a supplier.
While all suppliers' capabilities vary from company to company, the material comes into Sheffield Metals specifically as 9,000 to 12,000-pound master coils. From there, we process most of the material after a customer submits an order (we do not require an order minimum). Plus, any of our customers have the option to purchase 40', 44', and 48' master coils to help minimize scrap and drop-cuts, and can utilize our slitting, cut-to-length, strippable PVC application, and re-rolling services.
However, before any coil is sold or shipped out of a Sheffield Metals location, the material goes through even more quality assurance measures, including:
If the metal looks good and doesn't show signs of defects, the material is approved to be sent to regional manufacturers, contractors, builders, and beyond for rollforming and eventual installation.
Now that you have a little bit of background on how metal sheets and coils start as a raw steel substrate and becomes a painted or acrylic-coated coil, let's get into some of the substrate defects that could occur.
Keep in mind: The majority of metal does NOT have any defects. But it's good to be aware of these phenomena so they can be caught before a significant amount of material is wasted and especially before any installing begins.
Coil set refers to the metal retaining its curved shape as it comes off the coil roll. Metal is processed by being subjected to very high heat, which is then cooled to the point where you can see the grain in the metal. From there, it's either rolled out further or rolled up into coil form. However, metal has a memory, so if the metal wasn't correctly tension-leveled or is uneven in thickness when rolled into a coil, the material may attempt to move back to its original shape, which is when you could see coil set come into play.
Edge wave is a metal substrate defect that creates ripples on the edges of the coil. There are several causes for edge waves, but most of them are due to the edges being longer than the central portion of the coil. This extra edge material then becomes wavy while the center of the material remains flat. To fix the edge wave, the center of the coil will require stretching.
A couple of different buckling types can occur on a coil, but the most common is a center buckle, which is when the coil center is longer than the edges. This defect can create ripples in the center of the material. Correcting a center buckle requires the edges to be stretched to meet the length of the center of the coil.
A crossbow is a defect where the top surface of the metal coil is longer than the bottom surface, which creates a bowing at the ends; it is especially noticeable during slitting. According to thefabricator.com, 'correcting it [crossbow] requires stretching the bottom width and compressing the top width. This is difficult to accomplish because the work is being done in the longitudinal direction while the problem is in the transverse.'
Coil camber is when the edges of the material are stretched on one side and curve slightly to create edges that are not parallel. To see if a coil has a camber, lay a piece of the coil flat on the ground, then put a straight material (such as a piece of lumber, pipe, or another linear object) up against the edge. If two points on the edge of the coil stay up against the straight material, but the area between the points doesn't and curves away, the coil may be cambering (see photo). Most camber issues stem from the slitters that cut the material, so ensuring that shears remain sharp is the best way to prevent this phenomenon (sharp cutting shears are less likely to pull on the coil and create unequal stresses associated with cambering).
As we mentioned, most defective metal coil material is caught before it ever makes it to a customer or end-user.
However, what should you do if you're running out a coil or running it through your rollforming machine and you notice an issue?
First and foremost, stop running your rollformer. Once you stop the rollformer from running out panels, you'll need to send a small amount of test material through the machine. Do not test the whole coil or anything more than 300 feet of metal to see if the suspected defect is only on a portion of the coil. It's difficult for manufacturers/suppliers to investigate the issue if the coil has been fully rollformed into panels. This is why it's critical to have a qualified rollforming machine operator who pays close attention and knows what defect indicators to look for during production.
Second, contact the manufacturer if you suspect there is something wrong with the coil.
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Be prepared to describe what you're seeing and what you've already tried in detail. The manufacturer will be able to provide you with a course of action that is specific to the suspected defect or situation. In the end, the manufacturer is there to work through challenges that might come up so you can get back to rollforming and installing standing seam metal roofing systems.
Keep in mind: Many issues that show up during rollforming are due to one or more adjustments that need to be made on the rollformer, which is not related to coil defects. If you suspect your rollformer is causing the issue, such as panels running out uphill/downhill or the panels are coming out of the machine crooked, please contact the machine manufacturer or the supplier where you purchased the rollformer.
Metal coil goes on a long production journey before it ever makes it into the hands of fabricators and contractors, and then ultimately on a home or property owner's structure.
Luckily, this puts many different eyes on the metal so that any imperfections or defects can be caught and remedied immediately.
However, if you notice a problem or are questioning if a defect might be present, the best thing you can do is STOP rollforming or installing panels and call the supplier/manufacturer to discuss your concerns. The last thing you want is for the problem to be ignored or brushed aside, which could lead to even bigger problems (roof failure, replacement, etc.) down the line.
After over two decades of supplying metal coils and sheets, the Sheffield Metals team knows what to look for when determining if a metal product is defective or not. While rare, it can happen, which is why we're always available to discuss your coil questions, concerns, and challenges.
By Karen Knapstein
If you don't know what to ask for, odds are you won't get what you need. Asking the right questions is the first step in getting the coil you need to fill your customers' orders to their satisfaction. Coil width and thickness are two of the most obvious factors that affect metal forming. They influence the quality of the final product, the performance of the machine, and the amount of sale-able material you can get out of a coil. 3GM Territory Manager Adam Buck, who has 15 years of experience in metal roofing manufacturing and sales, shares his insights about metal coil size and thickness.
Adam explains the standard coil widths for different gauges: 'The industry standard width for 29 ga. coil is 40.875'. Some people will order that material in 41' because they want to make the underlap and overlap on their metal panel a little bit wider.' However, he estimates more than 99% of what people use to make 29 ga. ag panel and residential panel is 40.875' wide.
The thicker 26 ga. material, commonly used to make R panel or PBR panel, comes in 41.' and 43'-wide coil.
Users should be cautioned: The wider material won't fit through all machines. The width tolerance is the difference between the lower and upper limit dimensions that a roll former will accept. The guides in the roll forming machine will determine that tolerance.
'A lot of people want an ag panel rib height of 7/8' but want it in 26 ga. but they don't want to pay a processing company to slice the material down,' Adam explains. 'So they often ask if the 26 ga. material will run through an ag panel line. The answer to that is 'Some do, some don't.' It depends on the guides in the machine.' Roll formers need to measure the guides to see if the larger coil will work in their machine.
You can count on the consistency of the coil width if you buy from a reputable supplier. Adam says if you order a coil 40 7/8' wide, it will be 40 7/8' wide ' but there could be a very small variation (+/- 1/16'). If it does vary a little bit, you may have to adjust the guides on your machine to make sure their overlap stays long enough for the panel to lap properly. 'You can't really steal from the overlap side of the panel; you must steal from the underlap side when you're adjusting your machine,' he continues. 'There's very little extra material to play with.'
When addressing coil thickness, the main thing Adam stresses is the yield ' the weight per linear foot (pounds/foot). The pounds per foot is the weight of 1' of a specific width of coil (i.e. 40.875' x 1'). 'A lot of people in the industry get caught up in the decimal thickness,' he explains. 'The common thicknesses in the industry are .', .', .', .', .', .', and .'. Thicknesses from . to . material are all 29 ga. product. On the steel service center side of things, when you're purchasing coil from mills you're buying by the pound. Our customers are typically buying it by the foot.'
He gives one example of why the reason yield matters so much: 'I was at customer's place and he had some . material on his floor. If I order that thickness I would expect to get a target yield of about 2.04 pounds/foot. I checked all the coil tags, and what I found is the coils weighed anywhere from 1.92 pounds/foot to 2.05 pounds/foot. What that shows is just because a coil tag says . thickness it doesn't mean the yield corresponds with the thickness of the material. If the coil tag says it's . thickness and it weighs 1.92 pounds/foot, it's actually not . thickness. The yield is what tells me what the thickness is.'
'Tell me what you want it to weigh per foot and that's what I'll make sure it weighs,' he continues.
3GM supplies roll formers with a lot of 29 ga. coil. 'When I'm qualifying a customer, the customer usually says they're looking for 29 ga. .' material. My next question is: What do you want that to weight per foot? The customers don't request a yield, but in the backs of their minds they have a yield that they're trying to hit. But they never communicate that unless they're asked.'
Gauge is a guide ' not a hard and fast measure. 'If the customer wants material that's 2.02 pounds/ foot and I send him 1.92 pounds/foot, he's not actually getting the material that he wants because he's not going to hit the yield that he has in mind,' explains Adam. 'A lot of people get caught up on decimal thickness. For me, as a coil supplier, the decimal thickness is a guide but it doesn't really mean a whole lot. I like to get down to the specifics: the yield and what it weighs per foot. So if I know a guy is looking for 2.04 pounds/foot, I know what yield they're looking for specifically.'
Adam continues: 'With most mills, if you order .' thickness, for the most part it's going to be a heavier 29 ga. product, say 2.04-2.05 pounds/foot. But I've seen on occasions where it's definitely not, like the example I gave earlier.'
Understanding thickness terminology will help you get the material that will give you the yields you need. 'Minimal thickness' is thickness that will be greater than or equal to the target thickness. 'Nominal thickness' can be equal to, thicker or thinner than the target thickness. For example, when you ask for .' minimal thickness, the coil will always be at least .'. If you ask for .' nominal thickness, it may measure anywhere from .' to .' from coil to coil. Nominal thickness is thickness that can vary the most; it may be plus, minus or equal to the target thickness.
'The industry as a whole typically goes with minimal thickness,' Adam says, 'but you do see a little bit of nominal thickness out in the market. Minimal definitely provides a more consistent product.'
The consistency of the thickness can vary from mill to mill. 'Mills have their own quirks, and some mills have it dialed in better than others,' he says. 'Some mills you see a lot of variance.
We try to stick with mills that really dial in their product. We don't want to see a whole lot of switching back and forth between thicknesses when we're sending customers product. We want to provide a great quality product that's very, very consistent. Whether they're buying it today or buying it six months from now, it should be about the same.'
There are a few tips and tricks to mitigate coil and width variances. Regarding thickness variances, he advises that when switching coils, if going from .' material to .', you may have to back the guides off by a thousandth. Or vice versa, you might have to tighten it down a thousandth if you're running it a little bit thinner.
'If the material is too thick and you roll form it without adjusting your machine, you could scar your panel and/or peel the paint off the material. As the material goes thicker, you have to back off the dies in order to produce a thicker product.'
Dealing with width variance can be a bit more tricky. For example, say a customer orders 40 7/8', he roll forms the product and the overlap isn't long enough. That means the coil isn't wide enough. So he has to 'borrow' material from the underlap side to put on the overlap side. 'He might not have enough underlap left,' explains Adam. 'That material is going to be tough to use. You can use it for trim or you can try to find a happy medium and use a very small underlap. The underlap is so important because that's a purlin-bearing leg ' it adds strength and rigidity to the panel. If both sides were overlaps, it would be a really flimsy product regardless of the gauge. Rigidity is important.'
Adam assures that roll formers usually have very few problems with thickness and width. 'Most of the steel mills ' internationally and domestically ' have it dialed in pretty good in a construction product they know what needs to get into customers' hands to roll form a great product.'
Buying quality coil is a critical step in running a profitable roll forming business. When something goes wrong, it can jeopardize your profitability. Keeping accurate records is cheap insurance in protecting that profitability. The importance of keeping accurate records can't be overstated. If one of your customers comes back with a complaint, you need to be able to tell your supplier specific details about the materials. 'The first question we ask on the service side is what coil tag or coil number it came off of,' Adam explains. No matter who your service center/supplier is, they will ask for this information. They can't make any an assumption about which coil is the problem; they have to provide the mill with specific, factual information in order to process a claim. Adam says once they have the specific information, then they can go back and look at the mill certifications and quality control reports released by the mills in order to track warranty claims.
Clear communication with your coil supplier is important. When you process coil into panels and trims, you need to know the profit margin on each coil. If the material you are using isn't sellable/usable, your profits won't end up where you need them to be. RF
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