Wire protection grommet edging is on the face of it, a relatively simple product. It helps prevent wiring chafe that can lead to arcing/sparking/loss of function. For years the SOP has been to use nylon PE strips like MS21266 or BACG20Z
However, most assembly workers and management know this “simple” product is not quite so simple in practice because it has three basic problems:
- “Coil set” and “Straight Set” Problem
- Fit and Retention Problem
- Ease of Application Problem
1. “Coil set” and “Straight Set” Problem
Engineers and production managers often have to deal with a phenomenon called “set” in extruded or molded nylon or polyethylene (PE). Set is a by-product of the grommet manufacturing process. There are two variants: coil set and straight set. Both represent real challenges for managers charged with manufacturing and assembly.
Set causes issues across industries and solutions have been created to solve it. For example the image below is a McElroy LineTamer® machine whose sole task is to remove coil set from piping. However, no such solution exists for nylon grommets.
Coil set happens when a strip is manufactured and immediately spooled onto a reel. When it is unwound for use it will retain some degree of residual curvature- the degree of set will be a function of the material and the spool radius onto which it is wound. In other words it will want to coil as if it were still on the spool. See this related article from Science Direct.
Straight set happens when the strip is not spooled. It comes off the line or out of the mold straight/flat and so will have a tendency to want to remain straight. It will resist being bent.
Either situation creates significant assembly challenges when it comes to applying edge protection for the wiring in powered manufactured products.
See this related article from Science Direct.
Common Production Scenarios
Manufacturers buy coils or strips of PE or nylon grommets to use on various sheet thicknesses. In production the set issue means they face two very common production scenarios:
1) Penetrations: Your product has circular penetrations in its metal framework through which wiring has to pass – edge protection should be applied to prevent chafing. You have two options:
Option 1: Apply a “straight set” strip. Unfortunately, this strip will want to return to its flat shape so has to be secured to the edge with tape or clamps while any adhesive cures a.k.a. fixturing. Even after curing this “straight set” will stress the bond and compromise product integrity in the short to medium term.
Option 2: Apply a “coil set” strip. This strip wants to bend. Unfortunately, the residual coil set rarely matches the penetration radius – meaning the strip will not conform to the curve of the penetration. Again “fixturing” is required. And the coil set will stress the bond and compromise product integrity in the short to medium term.
2) Straight Edges: Your product has straight metal edges which the wiring crosses – again edge protection should be applied to prevent chafing.
Option 1: Apply a “straight set” strip. This is the best case as the strip is naturally straight and so will protect the edge without any residual set affecting the bond. However, these tend to be supplied in 12.75” lengths so long edges will need multiple strips vs. a one long easily applied “run”.
Option 2: Apply a “coil set” strip. You are seeing the issue here. The residual coil set will bend the strip away from the edge that is being protected. Again “fixturing” is needed and once again the coil set will stress the bond and compromise product integrity in the short to medium term. PSA has poor edge retention even at room temperature and this is exacerbated by the force from the coil set acting on it.
As industrial standards continually rise to increase product safety, the need for a reliable, safe, and easy-to-apply grommet edge solution without these significant drawbacks, is both needed and important.
We speak to our solution toward the end of this post.
Fit and Retention Problem
Nylon/PE grommets come in various sizes to fit the sheet metal to which it is being applied. However, it is rarely a great fit as explained in the two scenarios below:
Scenario 1. The nylon/PE grommets are wider than the sheet metal to which it is being applied. It is a “loose fit”. A straight set strip will need glue to keep it on the edge – but normally not fixturing. This may hold reasonably well. However, a coil set strip will need adhesive and fixturing to hold it in place while the adhesive cures, often 8 hours or overnight. As discussed above – coil set can affect the product integrity pretty quickly.
Scenario 2. The nylon/PE grommets fit the sheet metal almost exactly so it is “a tight fit” with no play on either side. In this case, it may be decided that an adhesive is not needed. The straight set strip will likely hold reasonably well. However, a ‘coil set’ grommet works against you. Within a matter of weeks -and often faster- the nylon grommet edging lifts off the edge and falls off leaving cabling exposed to chafing.
In some applications, the risk of data or signal loss may be low to modest. In many others, this is a recipe for disaster as it can lead to catastrophic control failure.
Ease of Application Problem
Nylon grommets have very little “give” and assembly can be complicated as installers try to line up the grommet for application onto the metal edge. However, there is no leading edge to help guide the nylon grommet onto the metal edge so application often turns into an iterative and time-consuming process. It’s one of those things assemblers just “put up with”.
However, there is a solution.
The Solution is Spring-Fast® Wire Protection Grommet Edging
Spring-Fast protects wires and cables from chafing and arcing and solves all three problems:
“Coil set” and “Straight Set” Problem
Manufactured with an encapsulated flexible spring steel core, Spring-Fast can be pre-formed and will conform to and retain the shape of the edge or opening. It can be removed and adjusted without suffering coil set or straight set. The conformance and easy application are particularly helpful when adding/replacing grommets with wiring already in place.
Fit and Retention Problem
The encapsulated spring steel core is designed with “castles” on each side. These are angled in such a way so that even if the grommet does not match the metal thickness exactly, the castles create insertion alignment for the assembly and flex wider to accommodate the sheet metal thickness while exerting a retention force onto the metal. This is why it is used without adhesives in tough high vibration conditions like military and commercial aerospace and automotive
Ease of Application Problem
Spring-Fast has an angled out “lip” on each row of castles (see the image above) which helps guide and align the installation of the grommet onto an edge. Think of it as a “docking” aid. It makes installation simple and fast.
Spring-Fast Grommet Edging
- Resolves product safety and integrity issues
- Installs faster and easier than the plastic solutions
- Saves you ~49% of the installed costs of nylon grommets and glue
- Increase productivity of grommet process by 9.5X,
- UL Component Recognized solution
- Significant retention strength without adhesive
- Tighter application range
- Improves work cell environment by reducing VOC exposure
- Spring-Fast -12 variants from High Heat to Military Spec.
Go to the Spring-Fast page to learn more.
Request free samples here.