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7 Steps to Achieving Successful Gasket Applications
Introduction
Gasket performance is critical to a wide range of products and is becoming more important than ever with
the increasing need to control leakage to address goals such as improving product safety and reliability and
meeting environmental regulations. This article will discuss some of the key factors involved in accomplishing
a successful gasket application.
1. Begin Thinking About Gasket Design In The Early Stages Of The Design Process
A new product or equipment development project requires such an enormous effort that it’s easy to overlook
an area such as gasket design that seemingly can be left to the last minute without doing any harm. But early
stage design decisions that do not take sealing considerations into account can have a negative impact on
gasket performance and cost. For example, a product may be designed so that the gasket has a narrow
cross-section relative its overall size. Later you may discover that the gasket geometry required by this design
is expensive to produce because of the need to use high tensile strength materials and is responsible for high
scrap rates during assembly. Then you have the difficult choice of either living with a suboptimal gasket design
or making expensive late-stage design stages to the product design. Instead, design the gasket at the same
time as the mating assembly so that you can identify and correct any issues upfront.
2. Carefully Define The Function Of The Gasket
The first step is designing a gasket is to carefully define its required functionality. The acronym TAMP, which
stands for temperature, application, media and pressure, has long been used to summarize the variables
involved in a sealed connection. The range of temperatures that the gasket will be exposed to is important
because it often limits the materials that can be used. The application concerns the types of flanges, their
surface area, material and surface finish, the fasteners used and related factors. The process media that will
come into contact with the gasket plays an important role in the design specifications and any other media
that may also contact the gasket such as a cleaning solution should also be specified. Finally, the pressure
that the gasket must contain and whether that pressure is constant or varying is another critical element
in gasket design. Additional factors that are particular to an application may also play a role such as the
maximum leakage requirement.
3. Select The Right Gasket Material
With hundreds of available materials and material combinations to choose from, selecting the best gasket
material can be challenging. Elastomeric materials such as natural rubber are widely used in gaskets because
of their ability to fill out flange imperfections even under relatively low loadings. Other common elastomeric
gasket materials include styrene-butadiene -- also called synthetic rubber, chloroprene, nitrile, fluoroelastomer,
ethylene-propylene, cellulose fiber sheet and cork. Elastomers are primarily used in applications where
pressures and temperatures are relatively low. Hardness of elastomers used as gaskets is typically in the range
of 55 to 80 Shore A and thickness ranges from 1/32 inch (0.8 mm) to ¼ inch (6.4 mm).
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There are also a wide range of engineered materials that work well in specific gasket applications. Silicone has
properties that make it useful in gasketing, including the ability to withstand a wide range of temperatures. Silicone
gaskets come in both foam and sponge properties and can be reinforced with other materials to deliver specific
mechanical properties as well as electrical conductivity. Poron cellular urethane, which was developed by Rogers
Corporation, offers a very low compression set of under 2% at 73% combined with energy absorbing properties. Its
as-cast thickness tolerances are also very low. These properties are well suited to certain gasket applications such as
sensitive electronics handheld devices.
4. Optimize The Gasket Geometry
Gasket geometry plays an important role in the success of the application. The thickness of the gasket is largely
determined by the tolerances of the flanges. If the flange surfaces have relatively large tolerances, then thicker gaskets
are needed to make up for manufacturing variation. On the other hand, if tolerances are tight, then thinner gaskets
can be used. Thinner gaskets generally result in lower leakage. However, if the gasket is too thin it may be difficult to
handle, resulting in high scrap losses during manufacturing, assembly and maintenance.
The geometry of the gasket also has an impact on manufacturing costs. The internal area of a gasket usually must be
discarded, which drives up material costs. For example, a circular gasket with an outside diameter of 36 inches and
an inside diameter of 35 inches requires that a large circle be cut out of its center. This internal material that is normally
discarded constitutes 97% of the total material within the boundaries of the gasket. The cost of this gasket can be
substantially reduced by redesigning it as a series of arc segments connected by dovetail joints. The arc segments
can be very efficiently nested in a material sheet, substantially reducing manufacturing costs.
Gasket tolerances should also be carefully considered in order to keep costs under control. Tolerances of the flange
assembly are often specified as +/- 0.005 inch which are often necessary and easy to hold in machining applications.
But it’s expensive and in some cases impossible to hold these tolerances when working with elastomeric gasket
materials.
Furthermore, gaskets rarely need to be held to tolerances this tight because their contact area with the flanges is so
large. Tolerances of +/- 0.030 inch to 0.060 inch are sufficient in the vast majority of applications.
5. Define the assembly process
The method by which the flanges are attached together is important because excessive compression can rip or crush
gaskets or burst cells in closed-cell foams. The torque applied to threaded fasteners consists of the sum of the load
the fastener, thread friction and friction of the nut. Use a torque wrench or another controlled tension device to fasten
the bolts. The ideal approach is to apply torque to all bolts simultaneously. If this is not practical, then a tightening
sequence should be specified that provides relatively even distribution in the joint such as a cross-bolt pattern. Tighten
a bolt, then tighten the opposite bolt, then tighten a bolt midway between the two bolts that have been tightened, then
tighten the opposite bolt, etc. Begin by tightening the nuts loosely by hand. Then with a torque wrench apply 30% or
less of the full torque on the first pass, 60% or less of the full torque on the second pass and apply the full torque on
the third pass. Relaxation often sets in after a short time for all of the materials in the flange system including flanges,
gaskets, bolts, nuts and washers. So it is advisable to re-tighten fasteners 24 hours after the initial assembly.
6. Consider The Gasket Manufacturing Process
Consider manufacturability of the gaskets during the design process in order to ensure high quality and keep costs
low. Production volumes play a major role in selecting the right manufacturing process. No-tooling methods such as
a digital stylus and waterjet cutting are suitable for prototyping or very low volume production. Die cutting is often
used for higher volume runs and tools can be made by a variety of different methods with different tradeoffs in cost,
accuracy and life. In some applications, gasket installation can be simplified by applying an adhesive backing to the
gasket during the manufacturing process. Consult a gasket vendor with a wide range of capabilities to get feedback
on the manufacturability of different design alternatives.
7. Work With A Vendor With The Right Kind Of Experience
Look for a gasket manufacturer that is easy to do business with. The vendor should be willing to listen to and have no
difficulty in understanding your requirements. It’s hard to overestimate the value of vendor that goes the extra mile by
not just quoting your design but also by suggesting alternatives that deliver higher performance or save money.
Beyond these essentials, one thing that sets superior vendors apart is their ability to provide a wide range of
manufacturing methods that enable them to provide the right product and process for a wide range of applications.
For example, leading edge vendors can offer: 1) a digital stylus with no tooling required for prototyping and low
volume production 2) steel rule dies for short and medium runs 3) die cutting with computer numerical control (CNC)
machined tooling 4) hybrid tools that stamp out the inside dimensions of the die while they cut its outside shape 5)
class A metal machined tools made on an EDM machine for maximum accuracy and die life.
Conclusion
Gaskets protect products and the environment from leakage. This article has explored some of the major factors
that should be addressed to achieve a successful gasket application. Gasket vendors can provide more detailed
information relevant to your specific applications by analyzing your design and suggesting materials, gasket
geometries and manufacturing methods that will best accomplish your goals. Finally, well-equipped suppliers can
provide prototypes that you can use to validate the performance of design alternatives.
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