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.
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.
When to use PORON®
PORON®foam provides excellent impact absorption and energy dissipation, making it ideal for cushioning applications. It's used widely in healthcare as a load spreader and impact absorber, and more prosaically, in shoe inserts. Its reluctance to take a compression set makes it particularly valuable in gasket applications, especially where a joint is opened repeatedly or the faces move relative to one another. It's also very good at preventing adjacent surfaces from touching, so eliminating squeaks and rattles in assemblies.
PORON®is suitable for use when temperatures range between -40°F/°C and 194°F (90°C) and tolerates temperatures as high as 250°F (121°C) for short periods. It is available UL94 V0-rated for fire resistance so is a good choice in electrical installations. It can also be used outdoors as it has good UV resistance and will tolerate ozone.
Another characteristic of PORON® is it's low outgassing and non-fogging behavior. This makes it suitable for applications where display or viewing screens must remain clear. It also helps with accepting a pressure sensitive adhesive film or tape.
When a clean or attractive look is needed PORON® is a better choice than many other types of foam. It die-cuts cleanly and the small, uniform pores create a very homogenous appearance.
When NOT to use PORON®
Open cell foams tend to absorb water, and PORON® is no exception. Unless compressed, PORON® provides little to no protection against liquids and gases, and even then is not a material to use in a submerged or submersible application. Swelling can also be an issue when exposed to some organic fluids, motor oil or brake fluid, and these will reduce tensile strength.
In common with most types of foam, it is possible to add a film of pressure sensitive adhesive to PORON® to simplify mounting in-place. However, in applications where fire is a risk, (electrical cabinets for example,) with a pressure sensitive adhesive foam fabrication fire resistance may be reduced.
Benefits of using PORON®
Most foam gaskets are used to protect components from dust ingress or to retain fluids within a piping system. Others accommodate assembly tolerances and prevent rattles and squeaks. In some cases the failure of the foam means the end of the assembly's useful life, or at best impaired, performance. Dust entering an enclosure could cause an electrical malfunction with costly consequences, and likewise, fluid leaks can require expensive clean-up and remediation.
In many applications the cost of scrapping equipment or replacing a gasket far exceeds the actual cost of the part or material, especially when this forces an unplanned equipment shutdown. With their good compression set resistance PORON® gaskets can handle movement between mating faces or opening and closing of enclosure doors over a longer period than can other materials. Switching to a superior material like PORON® extends replacement intervals as well as improving the level of protection provided, so is often a cost-effective change.
Working with PORON®
PORON® foam comes in roll form and is available in thicknesses from around 0.060" (1.5 mm) up to ½" (12.7 mm.) When a greater thickness is needed, consider the possibility of creating a pressure sensitive adhesive foam fabrication.
PORON® is produced in black, although other colors are available. For further details, contact Merryweather Foam.
Consistent and Durable
PORON® foam offers greater consistency within a sheet and between sheets than do other foam materials. Along with a long list of published ASTM data, this should give engineers the confidence to use PORON® in their products and assemblies without worrying about variation.
Being soft, it provides excellent cushioning and excellent compression set resistance, plus chemical and UV resistance, give it a long service life. This saves money for users by extending equipment life and prolonging the period between scheduled replacement.
For more information on the savings possible from switching to PORON®, discuss your application with a Merryweather technical specialist today.