MATS AND PADS

Surfacing products deliver value beyond comfort and safety.

WHERE THE BUCK STOPS:
Rick Hudson is founder and
CEO of RL Hudson.

by Rick Hudson

Something for nothing.You’ll often hear that there’s no such thing, but at RL Hudson we’ve set our sights on always giving you, our customer, more than you pay for. From complex hoses, seals, and assemblies to “low-tech” surfacing products (“low-tech”? Not necessarily, as we’ll see), our knowledge, experience, and unwavering focus on quality don’t cost extra — they come standard.

In this issue, I’d like to talk about mats and pads, which are part of our surfacing products group. When you think about mats and pads, you naturally think first about user comfort and safety, but at little or no additional cost they can also protect your product’s surfaces against wear or damage while providing eye appeal. In addition, because they’re highly visible, they’re an ideal location for your logo or for safety information.

DESIGN: Far from being a simple slab of rubber or plastic, a well-designed mat or pad can incorporate multiple appearance and functional features. Custom-designed mats and pads may be made in virtually any shape, thickness, or size by compression or injection molding, with the limitation being the size of the press and the cost of the mold. Designs can include molded or die-cut tear-outs or cut-outs, making one basic design suitable for two or more applications.

Top-surface geometry, back geometry, and thickness are key decisions in the design of a mat or pad.Whenever possible, you should minimize the amount of material used because materials are expensive, and as a rule, the thicker the material, the longer (and more costly) the molding cycle.

ON THE SURFACE: Mats and pads are part of RL Hudson’s
extensive line of Surfacing products which includes Boots &
Bellows, Grips & Handles, Trim and more.

MATERIALS: As is true with nearly every decision about materials, you must balance cost against performance and service life. For example, a mat used in an engine room faces far different conditions than a pad used to provide sure footing or impact protection on construction equipment. The materials used in mats and pads must often withstand extended exposure to the damaging effects of ozone, ultraviolet (UV), water (or saltwater), petroleum oils and fuels, impact, tearing, abrasion, or, more likely, a combination of these.

In addition to environmental resistance, your choice of materials should take into account the application’s requirements for hardness and stiffness, cushioning qualities, friction level,wet or oily traction, vibration damping, tear and cut resistance, and wear and abrasion resistance. To meet these often conflicting requirements, mats and pads may be made from SBR, chloroprene, natural rubber, nitrile, EPDM, recycled rubber, or even a blend of materials. In addition, thermoplastic elastomers and flexible PVC are also suitable for specific applications.

Our engineers can assist you with specifying materials according to ASTM D2000, which provides the benefit of ensuring that the material will meet your general requirements. When your application is difficult or demanding, call on RL Hudson to provide guidance on the specification of manufacturing methods, material grade(s), or formulations. There’s a good explanation of how to read and use the ASTM standard on our website, at: http://www.rlhudson.com/publications/ techfiles/astmd2000.htm.

EPDM is often specified for mats and pads used outdoors because of its natural resistance to the effects of oxygen,ozone, and UV. However, modern non-staining antioxidants, antiozonants, and UV inhibitors make it possible to also obtain long service life from resilient, high-traction materials such as natural rubber and SBR. For oil and fuel resistance, depending on the severity of exposure,we recommend chloroprene or nitrile.

Carbon black is highly effective against UV,which is why many rubber and plastic products intended for outdoor use are black, but there’s really no limit to the range of colors you can specify.

Most materials may be foamed to reduce weight or to improve the mat’s or pad’s cushioning qualities.For some applications, the material may be reinforced with short fibers or compounded with traction-enhancing materials such as ground nut shells or abrasive grit. It’s also possible to incorporate multiple features, such as a foamed mat with a solid top layer that carries a vivid multi-color logo.

If your application requires reinforcement in high-stress areas, fabric, plastic, or metal inserts can be added. Fasteners, color details, logos, and even bright plastic or metal trim are readily incorporated.

FASTENING: Mats may simply be held in place by gravity, often with the help of a high-friction backing surface, or placed in a shallow well or tray.They may also be fastened with screws, rivets, or adhesives. The key to mat installation is safety: a mat must not move in such a way as to cause a fall, and the retaining method must not provide a tripping hazard.

Pads may also be held in place by screws or rivets, but they may also be designed with features that can snap-fit over a mushroom post or into a drilled hole. Another common fastening method is to use a metal or plastic frame that surrounds the pad; you will often see these on boats, heavy trucks, and even classic cars!

But what about adhesives? We’ve seen many successful applications that use adhesives to hold molded rubber parts, but the choice of adhesive is important. In addition to being flexible and having low surface energy, many rubber compounds include one or more liquid or waxy ingredients that are designed to migrate to the surface to form a protective barrier. These ingredients can cause the adhesive interface to fail.

TOLERANCES: Because of the very nature of the materials used to create mats and pads, it is important to remember that parts cannot be produced with the same precision of metal or rigid plastic components. That’s why mats and pads shouldn’t be dimensioned to the same tolerances applied to rigid products. The dimensions of the finished part are affected by a variety of issues during production, including temperature, cure time, and compound composition. In addition, conditions encountered during shipping, handling, and storage can cause changes in a part’s dimensions.For all these reasons, it’s a good practice to use RMA (Rubber Manufacturers’Association) tolerances of A3 (“Commercial”) or A4 (“Basic”) unless cost is not of primary importance.When you specify unnecessarily tight tolerances, you’re adding cost with no real benefits.“Nothing for something.” And here’s something else to think about: the mating surfaces to which a mat or pad will be applied. These surfaces should be designed with shapes and tolerances that will accommodate the necessarily looser tolerances typical of molded rubber or flexible plastic. For example, a maximum gap of 0.060”around a rubber pad may be desirable, but allowing a maximum gap of 0.120”will reduce product cost without compromising its usefulness.“Something for nothing.”

POTENTIAL PROBLEMS IN APPLICATION: Mats and pads, and surfacing products in general, are sometimes called upon to mate to components with few, if any, straight or standard radius-driven arc edges. As a result, these parts are difficult to design for a precise fit and are equally difficult to inspect. The preferred method for tolerancing complex profiles is to specify a profile tolerance around the outside edge, referenced to the nominal 3D model. This allows us to efficiently inspect the parts with a Coordinate Measuring Machine. Another potential problem occurs when the mating components are fabricated to excessively loose tolerances, resulting in inconsistent size and shape. While it’s true that a flexible mat or pad will accommodate some inconsistencies, in these situations it is best to design-in even greater flexibility or use two or more smaller mats or pads.

A third problem results when, for various reasons, the customer’s 3D CAD data of mating components (on which RL Hudson engineers base their designs) does not match the actual physical components. As a result, surfacing parts may have to be revised, based on observations taken during early product builds. Doing this is straightforward, but because it usually requires changes to the mold, it will delay product introduction and can greatly increase the cost of the molded parts.

Well, it looks like I’ve run out of space.Whether your mats, pads, and other surfacing products will be manufactured to your drawing, designed in collaboration with you, or taken from concept to finished product by our engineering group, I hope you’ll call on RL Hudson. As I said at the beginning, our knowledge,experience,and unwavering focus on quality don’t cost extra — they come standard.

Solutions 1Q08

MATS AND PADS

Surfacing products deliver value beyond comfort and safety.