Mar 1, 2005 12:00 PM, By Rick Weber
IT'S a gray, bitter-cold day in the central Oklahoma town of Chickasha. In fact, it's colder now — at 10:30 am — than it was shortly after sunrise.
Michael Terry hardly notices. He's prowling the lot at Cimarron Trailers, inspecting a group of Norstar smooth-sided living quarters trailers, all of which are made with 3M's VHB Tape.
“Where are the seams on this trailer?” he asks. “They just disappear. That's what we're looking for. No blemishes. It makes a nice, clean product. You get up close and look at a trailer, and you almost get a mirror finish out of it. If you put mechanical fasteners in that, it looks like it's dotted.
“First impressions are vital. The customer has a lot of trailers to choose from in the marketplace today. You have to have something that appeals to the customer and jumps out. Sixty-five percent of our retail buyers are women — and women are aesthetically fit-and-finish oriented.
“This just works for us. I would have a hard time backing up and going to a mechanical fastener. Someone would really have to convince me that it was better.”
And that's not going to happen. Terry, Cimarron's owner, is riveted by the benefits of not using rivets in his trailers — the appearance, smooth ride with decreased vibration, elimination of water leaks, efficiency in the building process, labor savings, noise reduction in the shop, ease of repair.
Since 2000, he has been doing it this way on every line of trailers at Cimarron. Any issues that have arisen have been quickly and effectively handled by Charlie Toney, 3M's Tulsa-based trailer market specialist. Why go back?
Terry had started using VHB Tape when he was working across town at Hart Trailers. But when he got to Cimarron, his goal was to come up with a trailer on which every component was designed from scratch with VHB tape in mind. The trailer design would have to be fresh and innovative, using his then-23 years of experience in the business. And he would need 3M's help.
Delamination issues solved
Mark Berman, an application development engineer for 3M, says that research had shown that some manufacturers had encountered side-panel buckling or delamination issues on trailers that were utilizing acrylic foam tapes — often triggered by prolonged sun exposure leading to higher temperatures, sometimes by improper tape selection, improper surface preparation, and poor application techniques. But by engineering slight modifications into the design, delamination could be reduced or eliminated.
3M discovered that one potential source of delamination was caused by the combined use of mechanical fasteners and tapes to secure the exterior walls of smooth-sided trailers to interior posts. That design features tape that is applied to bond the side panels to the interior posts and mechanical fasteners placed a few inches apart along the top and bottom of the wall extrusions. 3M's engineers, through research and discussion with customers, discovered that constraining the sidewall panel at the top and bottom of the interior post produced tremendous outward forces when the side panel expanded because of heat and sun exposure — outward forces that can cause delaminations.
Berman says that in a typical trailer, the exterior walls might be made of aluminum panels that are mechanically fastened to steel posts along the top and bottom extrusions, resulting in a constrained sidewall. 3M found that when a dark-colored trailer is exposed to heat — typically through extended periods in sunlight — the temperature of the exterior aluminum skin can rise to nearly 200° F, causing the panel to expand 0.138" on a 96" panel.
“The interior post is not directly exposed to the sun and has a lower thermal expansion rate than aluminum,” Berman says. “The post temperature rises to approximately 100 degrees and expands minimally — about 0.018” on a 96” post. The difference in these expansion amounts causes the length of the panel to expand beyond the length of the post by 0.120” to 0.138”. When a panel is mechanically constrained by being fastened to the posts at the top and bottom, this expansion differential can cause the panel to buckle outward from the post.
“While acrylic foam tapes are typically able to withstand up to several times their thickness in expansion, that still may not be enough to withstand this amount of outward force due to panel thermal expansion. In fact, 3M's preliminary investigations of other adhesive technologies, including polyurethane and structural adhesives, have shown similar delaminations on constrained designs.”
Terry created an unconstrained design solution in which the exterior walls are attached to the posts using VHB Tape, with the top and bottom of the panels being left to “float” in a notch-like component designed into the extrusions. This allows the panel to expand vertically when exposed to heat. The differential expansion of 0.120” experienced on a 96” unconstrained panel-to-post application is within the design parameters of VHB Tape.
Berman says the same expansion of 0.120” on a constrained design that utilizes mechanical fasteners at the top and bottom extrusions could cause the exterior skin to buckle. 3M believes that a design that leaves only one end of the panel to “float” — top or bottom — will also allow the panel to expand on an even plane, helping to prevent delamination.
“When my side post is on, the bottom of the sheet fits into the groove at the bottom and gives it a place to float,” Terry says. “At the top rail of the trailer, there's a very specific flange for the sheet to go in. On the inside and the outside, it gives me a clean line and lets the sheet float. Those things make a significant difference.”
Terry and Toney say preparation in the manufacturing process is critical.
They discovered that their initial problems with VHB tape were caused by employees who were not following directions, shortcutting the surface-preparation process. Toney went back to 3M's abrasive laboratory in St Paul, Minnesota, and worked until he came up with the right abrasive.
They recommend using only an approved tape and surface-preparation combination for the specific materials being bonded together. Typical surface preparations can include abrading, priming, cleaning, or a combination. Good tape roll-down pressure (15 psi) is always required. In addition, the manufacturing facility and all materials should meet the required minimum temperature for a given adhesive and surface preparation.
“We brought this into our culture right off the bat: ‘This is the procedure, and you're going to do it this way, and it's not acceptable to do it any other way,’” Terry says. “Early on, Charlie had told us, ‘You don't really need to abrade it.’ We said, ‘OK, we understand that. But if we do, is it better?’ he said, ‘Yes.’ Well, we took the high road and put in a little bit of extra time.”
Both surfaces — the sheet and the post — are abraded to get maximum adhesion.
Says Toney, “When we talk about abrading, we're not talking about sandpaper. We're talking Scotch-Brite 7447 pads. We're not taking the paint off. We're only changing it so that when you look at a high gloss and turn it on its side and look at it, it's dull. All we're doing is taking the sheen off.
“And let me tell you why abrading is such a good decision. When Mike and I started working on this, the paint systems hadn't begun to change at the aluminum sheet mills. When they changed the paint system, they don't call you up and say, ‘I've changed my paint system. Please make sure what you're doing is OK.’ So abrading equalizes Mike's sheet. He doesn't have to worry that the mill has changed on him, or if a contaminant got on it. It takes some of the guesswork out of it when you equalize the surface. If he buys his aluminum today off XYZ Company, they may have used a mill that offers a white urethane paint system. If he buys off of another mill, they may have used a white polyester paint system. White urethane and white polyester paint systems can have different surface characteristics.”
Terry says he has had numerous conversations with other manufacturers who have told him that they tried tape and it wouldn't hold. In the course of the discussion, Terry learned that they had used steel frames with aluminum skin, and they hadn't abraded.
“They set themselves up for failure,” he says.
“Mike will tell you that if you cut corners, you will not have a quality product,” Toney says.
“Oh,” Terry says, “it'll come back and bite you.”
Terry says other manufacturers have tried tape but just can't put total trust in it.
“So what do they do?” he asks. “They'll say, ‘Well, it's pretty darn good stuff, but just not perfect. We're going to put a mechanical fastener at the very top and bottom just to make sure it doesn't come loose.’ You know what they did? They held all that expansion and contraction in one place. It actually will create more problems than it solves.”
Says Toney, “The unique thing about VHB is it's so elastic. It will expand up to three times its thickness without distorting, and then it comes right back. So when Mike talks about floating panels, he's incorporating that expansion so that when the aluminum sheet expands during heat, it just floats. At the same time, when you pull on it, you'll find it extremely difficult to tear.”
“I've had some big old burly cowboys that had some issues with the ‘little tape’ that holds their trailers together,” Terry says. “One time, we had some dealers going through the shop, and I grabbed some pieces of 050 white. I didn't abrade them. I just grabbed the tape, laid it down, peeled it back, stuck it on the sheet, stepped on it, and handed it to him. I've got this 6-foot-6, 250-lb strong man turning red, trying to pull this apart. You couldn't have done a better testimonial.”
A closer look at the benefits Cimarron has experienced:
- Ease of repair.
Terry wanted to build a user-friendly product, so he believes the repairability with this design is a huge selling point.
“If a skin on a door is damaged, I can take it off and never take the door off the trailer,” he says. “Last year, 48% of our product was living quarters, and it's not uncommon for somebody to have a little accident — a fence post or on the road — and have to replace some sheets. If you use a buck rivet, there's no way to put the sheet back on. To put it back the way it was, you have to take the interior out of the trailer. It's just financially unfeasible. But with VHB Tape, we can peel the sheet back. Once you start the sheet, you can start prying with screwdrivers and break it loose. Then you can take a knife and cut it. You will destroy the sheet, but you can get it off without touching anything on the inside.”
- Smooth ride with decreased vibration.
Terry says that not only is VHB Tape stronger than a typical pop rivet, but it helps to produce a much quieter trailer because its acrylic foam core damps vibrations within the trailer walls.
“If you slam a door on a trailer with mechanical fasteners, it rattles,” he says. “When you close the door, you want it to sound like an expensive automobile.”
Says Toney, “VHB Tape is a great sound deadener. If you get any vibration from the outside skin to the inside skin, it never reaches the inside because it is absorbed into the material.”
- Waterproofing qualities.
Terry says he doesn't have any leak issues in his sidewalls.
“If he puts that in the joints, he's not going to have a water leak,” Toney says. “When you run a rivet through there, you always have the potential for a leak.”
- Noise reduction in the shop.
“We've never used buck rivets in our shop, but I've been in other plants that use buck rivets, and it's deafening,” Terry says. “And that's an OSHA nightmare. Earplugs and ear muffs are required for everybody.”
- Efficiency in the building process.
“Using mechanical fasteners, it's common for a drill bit to break, and you have to replace the sheet,” Terry says. “I feel like our failure rate is a lot less with VHB than it ever was with mechanical fasteners. It wasn't that the fastener was bad — it was human error involved. There are a thousand ways to put a rivet in crooked, and one way to put it in straight.”
- Labor savings.
Production manager Tony Hackney says it takes two workers 2Ω hours to do with VHB Tape what it took them four to six hours to do with rivets.
The cost savings is more difficult to quantify, but Terry isn't concerned because he knows he's building a better product.
“If I put all the fasteners in a pile and all the tape in a pile for a given trailer, the fasteners would be less expensive,” Terry says. “But I'm not buying drill bits. And I don't replace nearly as many bad sheets. Have I had a little place left on the sheet where I had an adhesion problem? Yes, I have. But I'll bet that in our five-year history, I haven't had 25 linear feet of seam failure. And I think that's a whole lot to be proud of.
“The thing is, what do you sell your trailer for, and how many profit dollars do you generate when you're building a better product? When you consider horse trailers that are riveted versus smooth skin, it's night and day. There is such an incredible appearance difference.
“It puts our dealers at an advantage. So far, we've had a production problem — trying to get enough made — rather than a sales problem.”
Cimarron built 920 trailers last year. Terry's goal for this year is 1000, most of them large living quarters trailers.
He sees smooth sailing in Cimarron's future.
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