A Discussion of Durometer (hardness) Scales

The term durometer refers specifically to an object’s hardness measured by its indentation properties, which are defined by an object’s resistance to permanent indentation. Often times the word durometer is referred to as both the measurement of hardness and the durometer instrument which was created by Albert Ferdinand Shore in the 1920s to determine scales of Shore hardness.

While the origins of both hardness scales and the coining of the term durometer trace back a significant number of years before the Shore hardness scale was invented, the vast majority of modern science practices rely on its scales in one form or another.

There are several different types of durometer scales used to properly measure the hardness properties of materials, but the two most common scales are the ASTM D2240 type A and D scales. Scale A is designed to measure the hardness of softer plastic materials, like out urethane rollers which have a durometer hardness of 55 and 70, while Scale D is designed to measure the hardness of harder plastics.

The largest and most interesting difference between Scale A and Scale D originates from the physical size of the hardened steel rod performing the durometer. With the hardened steel rod in Scale A, the foot measures 1.1mm-1.4mm in diameter with a 30°. In Scale D, the hardened steel rod measures the same 1.1mm-1.4mm diameter but differs in that its radius has a narrower tip and has a 30° conical point instead.

The ASTM D2240 recognizes ten other different durometer scales, all differentiating in accordance to the types of material they measure. Some of these difference include diameter, extension, and spring force.

To put things into perspective, the durometer has measured properties of hardness in common objects which you may see or use daily, such as the bicycle seat, chewing gum, rubber band, door seal, skateboard wheels and much more. Each of these materials in ranked in a scale ranging from 0-100, where higher values indicate harder materials and lower values indicate softer materials.

Can you guess which materials ranked where? Check out some of the durometer values below on common objects.

• Bicycle seat: 15-30
• Chewing gum: 20
• Rubber band: 25
• Door seal: 55
• Skateboard wheel: 98

The twelve durometer types are A, C, D, B, M, E, O, OO, DO, OOO, and OOO-S. The bicycle seat and the chewing gum fit within the OO Scale, for example, while the skateboard wheel, rubber band, and door seal fit within the A Scale.

All in all, it’s intriguing to sometimes stop and wonder about how a scale might have been originally constructed to accurately describe the hardness properties of all different types of materials around you. Among even the most modern science ideologies today, the Shore hardness scales are as solidified a concept as some of the hardest objects measured to date.

Physical Properties of Urethanes Specified by ASTM

Polyurethanes are known as reaction polymers formed by synthesizing urethane links. The component polymers are isocyanates and polyols. The physical properties of urethanes which are specified by ASTM are dependent upon the specific classification for urethanes. These classifications include:

  • Microcellular urethane
  • Urethane coatings
  • Flexible cellular materials such as molded, bonded and slab urethane foams

ASTM tests each of these classifications of urethanes differently and also with different testing classifications. For example, ASTM D2370 – 98(2010) tested the tensile properties of urethane coatings. These properties include:

  • Elasticity
  • Elongation
  • Tensile strength

(Ref. https://www.astm.org/Standards/D2370.htm)

In testing microcellular urethane, ASTM D3489 – 11, the properties included plasticity, specific gravity (SpG) and density.

In ASTM testing of flexible cellular materials, the properties included hardness with a range of 20A to 75D, density, specific gravity and viscosity.

It should be noted that due to the fact that urethanes are used in a number of common products for industrial uses (ex:  urethane rollers) and home use (ex: polyurethane coated flooring), testing of the physical properties follow ASTM’s guidelines for plastics. As such, it can be expected that these diverse uses would also require physical property differentials. For example, thermoplastic polyurethane’s physical properties include resistance to oil and grease, as well as elasticity and transparency.

As an elastomer, the properties of urethane or polyurethane are resiliency and elasticity. The physical properties for urethane coatings for wood flooring would necessitate durability and resiliency. These properties are also found in thermal insulation used in homes and buildings to protect the interior from drafts and to reduce the cost of energy.

How the Physical Properties and ASTM Figure into Urethane Uses

ASTM relies on standardization to produce testing results that reflect a specified classification for each material tested. For example, when ASTM tests urethane for hardness, the results allow the producers of products to rely on the findings of ASTM’s standards as a guide to how to produce a broad range of urethane products with varying levels of hardness. This is also true for urethane coatings. Flooring designers and manufacturers rely on the durability of urethane used to produce flooring materials.

Density is another physical property of urethane that affects manufactured materials like coatings for window lineals and siding for buildings. Since urethane is used in end products, the physical properties as outlined by ASTM provide reasonable design, manufacture and buyer confidence children’s car seats, vehicle body parts and sports gear.

Generalized Urethane Roller Industry Tests

It is important to note that even though there are many tests available to test polyurethanes and urethane’s, the urethane roller industry utilizes a general set of tests (the specific testing method may vary):

  1. Hardness – ASTM D2240
  2. Tensile strength – ASTM D412
  3. Elongation – ASTM D412
  4. Tensile Stress 100%, 200% & 300% Modulus – ASTM D412
  5. Tear strength – ASTM D624
  6. Split tear –  ASTM D470
  7. Rebound – ASTM D2632
  8. Compression set – ASTM D395

Do You Have Specific Needs?

If you have further questions about your roller application, or you require assistance in creating a custom roller, contact us toll free at:

800-563-3381

Polyester Polyurethane vs Polyether Polyurethane

Polydrive Industries processes high quality, industrial grade, castable polyurethanes. These castable urethanes can be separated into two main categories as they are identified as either polyester based polyurethanes or polyether based polyurethanes. Both of these urethane chemistries are excellent for precision rollers and many other non-roller applications. Both are strong, tough and durable elastomers with excellent physical properties. They can be formulated to work equally well in some applications but there are other applications where, after considering all the physical and environmental aspects of the application, one will be a more appropriate choice than the other.

Polyester Polyurethanes – Typically, we use polyesters for our softer urethanes, where we formulate them in a durometer range from 15A to 85A . In general, the polyester polyurethanes are known to have excellent physical properties when it comes to tear and tensile strength as well as resistance to abrasion, oil, grease, fuel and organic solvents.

Polyether Polyurethanes – Typically, we use polyethers for our harder urethanes, where we formulate them in a durometer range from 70A to 60D. In general, the polyether polyurethanes have superior dynamics properties which makes them an excellent choice in heavily loaded roller applications which subject the urethane to a repetitive compression force. The polyethers are also superior in cold or wet applications.

When comparing polyether polyurethanes to polyester polyurethanes, the following is generally true, especially if you compare them at the same durometers.

Polyether Polyurethanes

  • Better for higher durometer formulations
  • Better dynamic properties (lower hysteresis)
  • Better water resistance (resists hydrolyzation)
  • Better low temperature flexibility
  • Better resistance to molds and fungi.

Polyester Polyurethanes

  • Better for lower durometer formulations
  • Better abrasion resistance
  • Better tensile strength
  • Better tear resistance
  • Better oil, grease and fuel resistance
  • Better organic solvent resistance
  • Lower cost

Polydrive manufactures polyurethane products for a wide range of applications. In general, the applications can be categorized by the type of urethane most commonly used.

 

Polyester Applications

Our polyester polyurethanes are used in the following applications.

  • Mail handling equipment rollers
  • Labeling equipment rollers
  • Magnetic tape drive rollers
  • Ticket dispensing rollers
  • Credit card handling rollers
  • Sewing equipment rollers
  • Packaging equipment rollers
  • Printer rollers
  • Banking equipment rollers
  • Paper handling equipment rollers
  • Vacuum fixtures
  • Automation clamps and hold downs
  • Capping equipment fixtures

Polyether Applications

Our polyether polyurethanes are used in the following applications.

  • Wire Feed rollers
  • Sheet metal forming rollers
  • Stone grinding equipment rollers
  • Refrigeration equipment rollers
  • Cradle rollers
  • Automation clamps and hold downs
  • Clean room conveyor rollers
  • Conveyor rollers
  • Water blast equipment rollers
  • Punch strippers
  • Marine equipment rollers

Find the Right Roller for Your Application!

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4 Uses of Polyurethane Rollers

You may be  familiar with our Polyurethane rollers, but if you aren’t and are looking for a few examples of why polyurethane rollers make a better choice then rubber or other materials.

Here are 4 of the more popular ones:

Weight Resistance

Polyurethane drive rollers are used in mounting heavy load machines. Wheels made out of other materials do not last long when fitted into heavy weight lifting machines. Wheels made of rubber wear out first thus making them unreliable and expensive for industrial use. Rubber wheels cannot withstand heavy loads for a long time. Polyurethane rollers are weight resistant. Being exposed to heavy loads does not tear them down at all. For the sake of industrial purposes, polyurethane rollers are the best choice due to their durability and tough nature.
Friction Resistance

Polyurethane rollers have a high tear strength capacity. Machines like drive belts and forklifts endure so much friction while in operation. Fitting such machines with wheels made of rubber is expensive, and nearly unrealistic. Polyurethane wheels work well in heavy duty machines. They have the capability to withstand the friction that heavy duty machines like forklifts endure while at work. Fitting heavy duty machines with polyurethane wheels is economical. For example, if heavy duty machines were fitted with rubber wheels, they would constant changes thus making them expensive to use. Polyurethane wheels are sturdy and durable thus making them efficient, and economical to use.
Noise Reduction

The construction sector is always full of activities. The presence of various activities in one designated area, leads to noise emission. The noise in a construction area can be sickening if not controlled. Machines using metal or rubber wheels produce much noise while in operation. Reducing noise in a construction site calls for the use of wheels made of a friction resistant material. To reduce the noise, machines, and other heavy duty implements at a construction site ought to be fitted with polyurethane wheels. These wheels have the capability to move through hard or cemented surfaces without making noise. Polyurethane wheels have the capacity to resist friction thus emitting little or no noise at all.
High Temperature Resistant

Machines using wheels that are made of rubber are subject to climatic changes. It is nearly impossible to use rubber wheels in hot climatic areas. Low temperatures affect the functionality of rubber-made wheels negatively. In the context, it is clear that rubber wheels operate well under specific weather conditions. Polyurethane wheels are resistant to climatic changes. They have the capability to withstand tough weather conditions. When machines like forklifts are operating in extreme weather condition, they are best suited with polyurethane wheels. These wheels give heavy duty machines the capability to perform to their full potential.

 

If you are unsure if a polyurethane roller is the right choice for your project or situation, give us a call so we can help you make a well informed decision.

Coefficient of Friction on Polyurethane Rollers

The coefficient of friction, or COF, is one of the first properties considered when determining the type of polyurethane roller needed for a particular application. Polyurethane is an extremely versatile material that can be manufactured into many different shapes, sizes, and colors, as well as be developed to varying magnitudes of hardness and degree of friction. And depending on the application, the coefficient of friction may be very important, as it is in the case of polyurethane rollers.

Polyurethane rollers are typically made to a higher coefficient of friction. Rollers, by nature, have to move something else along, and a common use of rollers is on powered or motorized conveyor systems to move the belt along smoothly regardless of the load applied to it. A lower coefficient of friction would mean that the conveyor belt would simply remain in place. On the other hand, rollers on some manual conveyor systems are made to a lower coefficient of friction, as the rollers rely on manual force to move the load along.

There are two types of friction that must be considered when deciding on a particular type of polyurethane roller for its intended application. The first is the static coefficient of friction (SCOF), which is a measure of the friction between the roller and the belt (or other equipment) while both are at a state of rest. An engineer can calculate the static coefficient of friction easily enough using the standard formula in order to get a good idea of the type of polyurethane roller needed for the final application.

The second type of friction to be considered is the dynamic (or kinetic) coefficient of friction (DCOF). This is best measured with laboratory equipment such as tribometers or other friction testers for an accurate measurement to be obtained, as it is measured while the equipment is in motion. Manufacturers and/or third-party labs would be able to accurately measure the dynamic coefficient of friction and further determine which type of roller would be best for the intended application. There are many types of polyurethane rollers, and determining the amount of friction for a particular application or piece of equipment will help narrow the field.

Why does Polyurethane material make a great roller?

The industrial world is moving us forward quite literally. From garage doors to conveyor belts and even the label machine, it is the durability of the smaller parts that make the difference. Consider a conveyor belt moving large parts down the line. The strength behind it rests solely on the drive rollers. Although available in a variety of materials, polyurethane drive rollers have proven to be the superior choice.

Conveyor belts are an excellent example of the quality of these rollers. These belts often move extremely heavy equipment down a production line providing many points of consideration. Metal rollers are by nature very noisy whereas polyurethane rollers significantly reduce noise in the workplace. The noise from metal rollers is generated from friction, which wears down metal relatively quickly. Polyurethane is manufactured with varying friction absorbing levels enabling them to last far longer than metal with less maintenance and replacements. They are also temperature tolerant, making them an excellent choice for equipment that runs constantly or for extended periods of time.

Polyurethane drive rollers are capable of withstanding heavier loads than metal as well. Under prolonged exposure to extreme weight, metal will bend, dent or become scratched and marred, severely affecting efficiency. Polyurethane is a forgiving material that will flex and resist scarring due to rigid chemical analysis tests in the formation process and Durometer tests after production, ensuring the strength performance of each roller. Because of the quality standards of each roller, they enjoy a longer lifespan than metal with less frequent need for replacement. Polyurethane rollers are also far more cost efficient to produce than metal rollers. Manufacturing metal rollers requires machining and welding of the parts, extra steps that significantly raise the price.

Spills are an unfortunate reality, but Polyurethane rollers are designed to handle it. The treated polymer is resistant to spills, water or chemical. There is almost no absorption or swelling which also means no rusting or corrosion.

The benefits of choosing Polyurethane drive rollers over metal become obvious when comparing both side by side. With superior performance, quality, durability and pricing, they are the clear choice.

Custom polyurethane rollers can help save your equipment

rollers-custom-300There’s no such thing as a perpetual motion machine: Bearings will inevitably need replaced, and gears eventually break down, regardless of the grease and maintenance they receive. When such things happen, other parts in your machines can suffer too. Modern advances in moving part technology have made it easier for designers and engineers to implement durable, safer and longer lasting parts into their plans.

Our custom polyurethane rollers are a great option when it comes to conveyors, presses and other machines that require many moving and easily replaceable parts. Polyurethane is a natural solution for when you need a material that is naturally durable, cost effective and has built-in friction grip capabilities to make it versatile and dependable.

Today it is more cost effective than ever for you to order custom sized polyurethane rollers, which is may be extremely important when you need a variety of specific sized rollers in your machines.

Another facet of the versatility of polyurethane rollers is their wide range of uses, due to multiple levels of softness available (Polydrive offers 55A & 70A).

Softer polyurethane rollers have applications that can’t be satisfied by metal rollers, such as heavily friction-dependent conveyor systems. Extra soft rollers are useful for keeping delicate equipment from being damaged, and the collateral damage from a failing polyurethane lower is considerably lower than damage from a metal alternative.

Polyurethane rollers are perfect for a company that needs a solution more durable than plastic and more cost-effective than steel or aluminum. They are also ideal for package conveyor systems, and custom-made polyurethane rollers make it extremely easy to account for logistics solutions involving tight corners and steep grades.

Have additional questions? Give us a call: 800-563-3381

How is Polyurethane Made?

Polyurethane products were invented in the 1940s after Otto Bayer and his coworkers discovered and patented the chemistry of polyurethanes in 1937. The substance becomes a flexible and very durable material that has to be manufactured to be usable in society and has continuously evolved to be used in a wide variety of items. Polyurethane is used to create rubber, metal and wood products. It is also used in paint, cotton, and other fabrics. Based on its structure and uses, Polyurethane can conform to a variety of items. It can be found in foams both rigid and flexible, chemical-resistant varnishes and coatings, special sealants, rubber adhesives and even fiberglass.

The basis of the Polyurethane substance is categorized as a polymer. A polymer is a molecule that consists of several smaller units called monomers. Polyurethanes are manufactured by mixing two types of chemical compounds of Polyols and Polymeric Isocyanates, along with other additives to create a chemical reaction. The basic material has several fairly indestructible variations that can be altered and can be presented in the forms of liquid, foam, or solid each providing its own limitations and advantages.

Polyurethane molded products typically consist of a resin base, some type of curative, and a dye or pigment colorant additive. Most manufacturers use high tech equipment that first mix the ingredients into a comparable liquid which is then heated and molded to create the finished product. Because Polyurethane is so pliable, the machines used to produce the product consist of chemical tanks that keep the raw materials at a certain high temperature for optimum processing. The tanks are linked to complex mixing chambers where the polyol and isocyanates are mixed together and the mixture is poured in to specified mold cavities for their desired shapes.
The typical methods used to mix, mold, and creates polyurethane products are:

Compression Molding: Polyurethane in liquid form is poured into a mold and placed in a compression press. The heat allows the liquid to thicken and the pressure from the press creates the completed molding process.

Open Cast Molding: In this process the liquid form of polyurethane is poured into an open mold. The mold is then placed into an oven.

Spin Casting: This process requires a spinning mold in which the liquid polyurethane is poured into. This process remove all air trapped inside the chemical as it is being poured.

Low Pressure Injection Molding: This process requires the liquid Polyurethane to be injected into a closed mold. The mold is designed with openings to allow air to slowly leak out.

Polyurethanes are best known to the general public in the form of what is called flexible foam. These polyurethane foams are manufactured in the forms of mattresses, upholstery, and other chemical resistant packaging. Again, it can conform to almost any type of structure and also comes in forms that can be used in insulation for water heaters and buildings. This substance is continuously adapting to be used in our current technology.

What is the Difference Between Polyurethane and Rubber Tires

Even though we specifically make polyurethane rollers, which are much smaller than, and have a different use than polyurethane tires, we wanted to post this article to educate people about the difference between polyurethane and rubber tires.

While polyurethane and rubber products sometimes appear to be variations of the same material, they are quite different in physical structure as well as beneficial qualities.

Rubber, as we know it, has been manufactured for more than 100 years; polyurethanes, or urethanes, have been around for about half that time. To say that polyurethanes are an improvement over rubber is an understatement. The qualities and benefits of polyurethanes are far superior to those of traditional rubber in a variety of applications. And despite the fact that urethane is technically one of 14 different materials classified as “rubber,” it is quite different as we shall see.

The differences are obvious in a number of ways with a variety of attributes, including:

  • Load Capacity – A polyurethane tire can easily support twice the weight that a rubber tire can support, making polyurethanes ideal for heavy weight-bearing lift trucks.
  • Wear and Abrasion Resistance – Poly tires will last around four times as long as rubber tires, as rubber tires tend to wear down from long distance road friction.
  • Wet Floor Conditions – Because produce warehouses, for example, usually have wet floors due to the necessity of high moisture to maintain produce freshness, polyurethane tires have to be siped to secure reliable traction. Siped is the process of making small, angular cuts across the treads. While rubber is better for moist floors, it loses efficiency in load-bearing capabilities, so siped poly treads solves the problem without compromising load-bearing benefits.
  • High Speed Operation – In this category, rubber is preferred, as poly doesn’t wear as well at high speeds; the inability of poly tires to dissipate internal heat efficiently is the issue.
  • Chemical Resistance – While harsh solvents like methylene chloride, methyl ethyl ketone, or acids can break down polyurethanes, the chemical resistance benefits of polyurethane tires make them perfect for environments where industrial chemicals are present and utilized.

While both rubber and polyurethane tires have unique qualities that make them more appropriate in certain circumstances, polyurethane has proven to be all-around more durable, flexible and pliable.

Polyurethane can also be manufactured to be as soft as a foam pillow or as hard and smooth as a table top. With the continuous expansion of high tech applications, the benefits and applications of polyurethanes continue to be explored and developed.