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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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Viscoelasticity and PSA and the Role in Flexible Foam Fabrication

Example of Viscoelastic Foam

Viscoelasticity and Pressure Sensitive Adhesive
No pun intended, but it is hard to separate the relationship between viscoelasticity and pressure sensitive adhesive (PSA). What exactly is viscoelasticity and why is it important in a PSA? Let's try to take a potentially complex issue and break it down.

What is Viscoelasticity?
Viscoelasticity is a blend of the words viscosity and elasticity.

  • Viscosity refers to the resistance a liquid has to flow, generally related to the thickness of the liquid.
  • Elasticity is the ability for a solid to return to its original shape once strain is removed.

Examples of elastic materials include viscoelastic foam, rubber bands, stress balls and bungee cords. High viscous materials are generally thick liquids or gels. Honey, motor oil, and syrups are considered high viscosity liquids. Low viscosity liquids flow easily, like water.

The Affect of Heat on Viscosity
Heat reduces viscosity which you can see in daily life. Oil loses viscosity as it heats in an engine. Maple syrup will flow easier when warmed. Gels will even lose their form when subjected to heat. This is an important fact to keep in mind when discussing the relationship between viscoelasticity and PSA. Heat has an effect on both.

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PORON: When Fire is a Possibility

Many types of foam burn rapidly. Some even drip burning material on to the surface below, helping a fire spread rapidly. However, there are foams formulated to provide high levels of fire resistance. Whenever possible these should be used near potential sources of ignition.

The fire-resistance of foam for use in appliances, enclosures and equipment is measured by testing to procedures set out in the UL94 standard. (Note: this does NOT address foam used in upholstery or building construction.) Flammability (the ease with which a material burns,) is shown by a UL94 rating, such as the UL94 V-0 indication carried by PORON® 4701-V0-M.

Foam Flammability
Anything composed of carbon and hydrogen will burn if conditions are right, and that means having oxygen and an ignition source. All foams are formed from these elements and oxygen is always present in the atmosphere, so to start a fire all that's needed is an ignition source. This could be provided by an electrical spark, such as when motors or relays produce arcing. High temperatures, as caused by friction between moving parts or electrical current flowing through wiring are others possible causes.

UL94 flammability ratings
The UL organization is an independent global testing organization dedicated to improving safety. Founded in 1894 as "Underwriters Electrical Bureau" it started out by testing noncombustible insulation material and grew to become first "Underwriters Laboratories" and now just UL.

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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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What Can Pressure Sensitive Adhesive Lamination Do For You?

When you need cushioning, you choose foam. The compressible yet resilient bubbles trapped in elastic material absorb shocks and vibration, giving it thousands of uses from packaging to upholstery. Foam comes in a wide range of materials and ranges from firm and heavy to soft and light. There's a foam to suit every application, but it does have limitations: it can be difficult to fit or install, and it may not have the desired final appearance or surface properties.

The way around these problems is to specify a pressure sensitive adhesive (PSA) lamination for your foam fabrication. 

Overview of PSA foam lamination:
"Lamination" refers to adding one or more layers to a sheet or roll of foam. There are two reasons you might do this:

  1. To create a composite of two or more materials, combining the properties of foam with a second material.
  2. To make it easier to attach foam to a surface or to other foam pieces.
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