Lets take a rectangular block of rubber as a specimen. If you squeeze the small sides together this is compressive force. If you stretch the block, this is tension or tensile force. If you twist the block this is torsional force and if you apply an opposing force to the side on top and opposite side on bottom, this is shear force.
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What are the forces that may be applied to rubber?
understanding of the forces that may be applied to the rubber parts while in your application. Lets take a rectangular block of rubber as a specimen. If you squeeze the small sides together this is compressive force. If you stretch the block, this is tension or tensile force.
What force is needed to compress a round cross section elastomer seal?
The force needed to compress a round cross section elastomer seal will depend on several factors that can be condensed to cross section, percent compression, and durometer. This can be seen in Illustration 5.3 of the Apple Rubber Seal Design Guide.
What is the coefficient of friction between rubber and rubber seals?
Softer rubber has a higher coefficient of friction and harder rubber has a lower coefficient of friction. Coefficient of friction plays a factor when the rubber seal is sealing a part that moves.
How much force is needed to compress an Oring 20%?
The expected range of force needed to compress an oring 20% with a 0.070” diameter cross section (purple) that is 50 durometer is between 4.5 and 14 pounds per linear inch. The variation comes from differences in the compressive modulus of elasticity between different types of materials and different recipes.
How do you calculate rubber compression?
Gasket Compression Pecentage Calculation720 lb Clamp, Foot Print / Contact Area Foot Size: 3″ x 12″ each. ... HT-800 Silicone Pad Size: 3″ x 12″ each. ... Mounting Plate.Calculation: Load / Area = 720lb / 72 in² = 10 lb/in²Compression: From the Compression Force Deflection Curve, HT-800 will compress approximately 30%.
How much force is needed to compress a gasket?
The expected range of force needed to compress an oring 20% with a 0.070” diameter cross section (purple) that is 50 durometer is between 4.5 and 14 pounds per linear inch. The variation comes from differences in the compressive modulus of elasticity between different types of materials and different recipes.
How much does rubber compression?
Rubber gaskets are compressed or squeezed by a percentage of their original size. A gasket that compresses too much or too little will not form a proper seal. The ideal compression percentage is 40, the maximum is 50, and the minimum is between 10 to 15.
How do you calculate sealing force?
To determine the force required for proper sealing of a device, the force per centimeter can be multiplied by the overall length of the boss around the perimeter of the device.
What is compression set in rubber?
Compression set testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber material is compressed over time, it loses its ability to return to its original thickness.
How much compression should an O-ring have?
Compression should not exceed 3% of the O-ring diameter. Stretch for a smaller O-ring should not exceed 5%.
What is the strength of rubber?
Solid rubber, with a consistency of pencil erasers, has a hardness of 40 duro. By contrast, harder rubber, like that used in hockey pucks, has 90 duro hardness. Figure 1 shows rubber with different hardness.
What is compression stiffness of rubber?
What is the stiffness of rubber? The moduli of rubber are typically expressed as the stress needed to strain a rubber sample. This is measured for 25%, 50%, 100%, 200% and 300%, reported as Modulus 25%. The stiffer the material is, the higher the stress needed.
How do you calculate compression of a material?
The formula to calculate compressive strength is F = P/A, where:F=The compressive strength (MPa)P=Maximum load (or load until failure) to the material (N)A=A cross section of the area of the material resisting the load (mm2)
How do you calculate the force required to compress an O-ring?
Moving vertically to either the 70 or 90 durometer band, you will find the expected range of load in pounds per linear inch of O-ring. Multiplying this number by the O-ring circumference in inches, you are left with the approximate range of compressive force, in pounds.
How are O rings calculated?
To measure the outside diameter, use a ruler to measure from one outer edge to the other of the o-ring. You can determine the third diameter of the O-ring with 2 diameters using the following equation: Outside Diameter (OD) = Inside Diameter + (2 x Cross Section). Inside Diameter (ID) = OD - (2 x Cross Section).
How do you calculate an O-ring weight?
x O.D. – I.D. x T x 0.785 x D.A. = WT of ring in pounds.
Why is rubber made in different hardness?
Rubber is made in different hardness’ for several reasons. Some sealing surfaces may not be totally smooth. The little voids, pits and scratches allow a pathway for fluid or air to escape through. Softer materials tend to flow better into these voids and imperfections on the sealing surface creating a better seal.
What rubber products have a low tensile strength?
A few rubber products that tensile strength are important would be bungee cords, rubber tie downs, drive belts. Some elastomeric compounds, like Silicone, have a low tensile strength making them unsuitable for a dynamic types of seal because they can fracture easily.
How is tensile strength measured?
A tensometer is special machine that is designed to apply a tensional or compressive force to a specimen, in our case a die cut dumbbell shape, and measure how much force it takes to deform and fracture the specimen. The force is typically displayed on a stress-strain curve that shows how much force was required to stretch the specimen to deformation and ultimately break.
How to determine tensile set after break?
Remember the 2 bench marks 1 inch apart on the specimen in the elongation test? To determine Tensile Set after break, wait 10 minutes after the specimen breaks and then fit the two halves of the specimen back together so there is good contact along the full length of the break. Measure the distance between the bench marks. Use the same equation used in the elongation test except the Final Gage Length (L x) is the final measured distance between the bench marks.
What is the ultimate tensile strength?
Ultimate tensile strength, or just tensile strength, is the maximum force a material can withstand without fracturing when stretched. It is the opposite of compressive strength. Have you ever purchased a pair of shoes and they came joined together with a piece of string? Instead of getting a pair of scissors, did you opted to test your physical strength against the tensile strength of the string and try to break it by pulling on it? If the string has a low tensile strength you should be able to pull and break the string easily. You can apply more tensional force than the string can withstand. If it has a high tensile strength it will be much harder to break by pulling. Are you starting to understand tensile strength?
How to measure elongation?
Elongation is measured with a ruler or an extensometer. An extensometer is an electronic ruler that is attached to the tensometer and will measure the extension of the specimen while torsional force is being applied. Another way of measuring elongation is with a regular ruler.
What is elasticity in rubber bands?
Elasticity is the mechanical property of a material to return to its original shape where Tensile Set is the amount on extension remaining after being stretched. A rubber band would have a low Tensile Set percentage. After stretched it relaxes close to, if not exactly to, its original length.
When a part is compressed, does it want to expand out laterally?
When a part is compressed it wants to expand out laterally and that movement changes the shape factor. This is particularly noticeable if the surfaces are lubricated. However, if the surfaces are bonded to a substrate such as metal, the shape factor remains the same.
How thick is a 92A pad?
You have a 92A durometer (hardness) isolation pad that is 6" long by 3" wide and 2" thick, that is under a 3,600 lb load. You want to know how much deflection it will have.
Is polyurethane compressible?
Polyurethane, unlike rubber, is a non-compressible elastomer, meaning its volumne will not change. In other words if you squeeze it in one place, it will bulge the same amount in another place. For that reason, it makes an excellent material for load-bearing applications.
All Answers (5)
If you know the elastic modulus and the stress, you can calculate the strain at low deformations.
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