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Merryweather Foam Blog

Since 1948, we have been industry leaders in fabricating unique, foam components for customers in the medical, sound absorption, automotive, and unique packaging industries. At Merryweather Foam, we pride ourselves on our ability to combine experience, innovation, and excellent customer service. We have the knowledge, manpower & equipment to help you get the job done. Visit our website to see our fabrication portfolio as well as our capabilities.

Should you be using PORON® Urethane Foams?

Also available in Medical Grades

When budgets get squeezed the selection and purchase of every component, spare part or piece of material is scrutinized carefully. Many times engineers and maintenance technicians have little choice but to go with the least expensive, despite knowing it's likely to fail prematurely. That in turn leads to unplanned downtime and additional repair work, the costs of which can quickly negate the initial savings realized.

Gaskets and sealing materials are a good illustration. In many applications a better quality foam material will last longer and reduce overall costs, yet it's difficult to convince management of this.

PORON® Urethane foam is an excellent example. Properties like superior uniformity and compression set resistance result in much longer life and potentially lower overall costs. Making the case for using PORON® hinges on understanding the differences between it and other foams, and the benefits that result.

Introduction to PORON® Urethane Foams
PORON®is the name of a family of urethane foams produced by Rogers Corporation. They use a proprietary process plus special additives to control bubble formation during the foaming reaction. This results in an open cell structure with small pores of very consistent size that are distributed evenly throughout the foam. In contrast, the pores in other foams have a far more random nature.

The benefit of uniform pore size and distribution is predictable properties and performance. Two pieces of the same grade of PORON® will display the same characteristics, (within limits, naturally,) regardless of when each was made. In fact it would be fair to call PORON® an engineered foam.

Performance Characterization
The piece-to-piece consistency of PORON® lets Rogers Corporation publish a broad array of test and measurement data. In addition to the density numbers put out by almost all foam manufacturers, Rogers provide ASTM test results along with other material properties.

In select applications it's important to know parameters like thermal conductivity, dielectric constant and surface and volume resistivity. More generally, users of flexible foam fabrications want to know about elasticity and recovery. Merryweather can provide detailed performance information for every grade of PORON® on request, but the numbers below for PORON® 4701 (a firmer grade,) should give a general appreciation.

  • Density: 15 – 30 lb/ft3
  • 25% Compression force deflection: 8 – 60 psi
  • Shore "A" durometer hardness: 18 – 55
  • Max compression set: 10%

In less technical terms, PORON® is quite soft and resists taking a compression set. In other words, it's good material for many gasket applications.

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Foam Gutter Guards? Absolutely!

For much of the country, it is that time of year when leaves fall and air becomes brisk as the temperature cools. What could be better? How about if your darn gutters didn't get full of leaves every year? There is a solution to the leaf problem. Put flexible foam in the gutters and leaves can't get in, but water can flow. The foam sits in the bottom of the gutter and fills the gutter up so that when leaves try to weasel their scurrilous selves into the gutter, there is no room. Yet, this is foam, so water can run out of the gutter the way it is supposed to. No ladders and gutter cleaning for you, no clogged gutters, and an affordable fix for what can be a real problem.

Some people may caution that foam is not safe to put in a gutter. That might be true if you were taking the novelty foam finger from the football game and stuffing it in the gutter, but that's not what you're doing. When you purchase foam to prevent leaf clogging in the gutter, you should check to make sure that you are purchasing fire retardant foam as many products are formulated to be fire retardant.

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Selecting Foam for Sealing and Gasket Applications

Fabricated Gaskets
​Gaskets come in a boundless array of shapes, sizes and materials, but they all do the same job. Gaskets exist to seal gaps. It might be the gap between two pipe flanges, the gap around an electrical cabinet, or even the gap between two pieces of ducting in an a/c system, but the gasket's job is always the same: fill that gap.

Flexible foam fabrications are often a good choice for gasket material. There are many different types of foam but most are lightweight, can be cut into various shapes, and may be purchased pre-laminated with pressure sensitive adhesive (PSA) for ease of installation. Most importantly, most foams compress readily and do an excellent job of sealing out, (or keeping in,) fluids, gases, dusts and other contaminants.

For a fabricated foam gasket to perform as needed it must be matched to the application. That demands a good appreciation of the following:

  • How gaskets work
  • Typical gasket applications
  • Key performance characteristics
  • Environmental factors
  • Media
  • Foam gasketing materials available from Merryweather.

How Gaskets Work
If surfaces like pipe flanges and cabinet doors could be made perfectly flat there would be no gaps for fluid to leak through. In the real world though, surfaces are far from flat. Sheet metal panels inevitably have undulations that cause varying gaps as a door is closed and pipe flanges have machining marks that create leak paths. And even if the surfaces were smooth, alignment tolerances would still create gaps of varying widths.

A gasket is a piece of compressible material fitted between two surfaces that will be clamped together. It's job is to prevent leaks from or through the joint. Being soft, it squashes down more where the gap is smaller while remaining thicker for wider spaces. Its softness also lets it flow into small indentations on the two surfaces, blocking even microscopic leak paths.
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Why Consider Cross-Linked Polyethylene Foam? A Primer on the Subject

Ever order a steak and find yourself overwhelmed by the choices? How do you want it done? Fries or baked potato? Butter and sour cream with the potato? It goes on and on. Well buying foam gets like that too, and unless you have a background in polymer chemistry some of the questions can be quite baffling.

One of the options foam fabricators throw at buyers is cross-linking. It's actually an important question as cross-linking has quite an effect on the properties of the foam. There are applications that might benefit from it while others won't. And should cross-linking be right for your application you may even be hit with another question: chemically cross-linked or irradiated?

To help you understand the questions, and decide if it's even something to consider, here's a primer on cross-linked polyethylene foam. It explains what the words mean and why you might want your next foam fabrication made from it. Individual sections address:

  • Understanding polyethylene
  • What is cross-linking?
  • Characteristics of XLPE foam
  • Benefits and applications

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Introducing Spunbond Materials

Spunbond materials are a subset of what's termed non-woven fabrics. That is, they are webs of material without the interlacing of threads produced by weaving on a loom. That means the fibers are randomly oriented and not interlocked, so a bonding process or medium is needed to fix them in place.

Non-woven fabrics are everywhere. Disposable wipes, diapers and pillow covers are just a few of the many uses around the home, but they're also used in agriculture, civil engineering and automobile interiors.

Why So Popular? 
Non-woven fabrics compete with wovens in two ways. First, they can be engineered to have practically any combination of properties needed. Tensile strength, absorption, and density are just of few of the characteristics polymer chemists are able to manipulate. In contrast, woven fabrics derive their properties mainly from the characteristics of the yarns employed.

Second, non-woven production processes are much faster than weaving. While a loom might turn out three to seven meters of woven material per hour, many non-woven processes could produce several hundred meters per hour. Naturally, this has an impact on cost.

Non-woven Production Processes 
Non-woven materials may be produced either from short lengths of fiber, (known as staple fibers,) or from continuous filament. Fibers can come from many sources, both natural and man-made, but filament is generally produced from polymers such as polypropylene, polyester and nylon.

A variety of methods are used to randomly orient fibers into a web before bond them together. One issue is that staple fibers must go through some kind of chopping process first. In contrast, spunbond materials, while lacking the randomness of fiber, are made directly from the polymer.

The Spunbond Process 
Polymer is melted and extruded through very fine holes, typically measuring 15 to 35 microns diameter. These thin continuous strands are made to spin as they solidify before landing on a moving conveyor or web of supporting material. The spinning randomizes the orientation of the strand as it lands and the conveyor motion ensures it forms a mat or web of material.

A bonding process, mechanical, chemical or thermal, joins the overlapping filament coils together, creating an engineered fabric. From polymer pellets to fabric web, it's an integrated process, and so highly cost-competitive.

Types of Spunbond Materials 

  • Polypropylene. This offers low density, good chemical and water resistance, and is readily formed as a breathable material. It works well in protective bags, sheets, pockets or pouches, is a good filter medium and absorbs oil well thanks to a porous structure. Spunbond polypropylene is also used for single-use gowns in the medical field.
  • Polyester. More expensive than polypropylene, this has higher tensile strength and better heat stability. It can be dyed or printed with conventional textile industry methods. Applications include fabric softener dryer sheets, automotive carpet backing and geotextiles.
  • Nylon. Has good tensile strength and tear resistance. Can absorb water but resists attack by alkalies and weak acids. Has good heat resistance and is air permeable. It's widely used as carpet underpad reinforcement, as quilt backing, and in automotive interiors.
  • Polyethylene. Similar to polypropylene, although with generally inferior properties, this is chemical and water resistant, and has good electrical insulation characteristics. A porous structure makes it a good oil absorber.
  • Polyurethane. This is an emerging material in spunbond form. Somewhat elastic, uses are anticipated in masks, diapers, medical tape, and also disposable clothing, thanks to textile-like properties.
  • Rayon. This creates non-wovens with textile-like properties like good drape and soft feel.
  • Bicomponent fibers. These consist of one polymer molded around a second, different, polymer. This enables a combination of properties such as the ability to take a dye combined with high strength.

Emerging Applications 
Development of spunbond manufacturing processes is continuing, with new forms of material entering the market and new applications being found. Spunbond foam offers superior handling characteristics with lower weight and increased softness. Today, we are able to laminate adhesive to spunbond materials to film, foam, and other materials as well as die cut, water jet cut, slit, and kiss cut this material in a number of application settings. The cost-effective spunbond process facilitates engineering of specific performance characteristics such as strength, water and chemical resistance, and feel. New spunbond materials are emerging constantly, and improved manufacturing methods are enabling yet more applications. Already spunbond polypropylene is seen as an alternative to polyurethane foam, and other applications are sure to follow. If you are interested in learning more about Spunbond Fabrics, give us a call and we would be happy to help you learn more.