Factors to Consider When Bending Rubber

Bending rubber is a complex process that requires many different parameters. The bending allowance is one of the most important factors to consider.

The bend deduction is also an important factor to consider. It is calculated from a formula that accounts for the material thickness.

The bend deduction can be positive or negative, depending on the part geometry and inside radii.

What is rubber?

Rubber is a very common material used in a lot of different products and applications. It is extremely flexible and can be stretched and twisted many times without breaking or becoming deformed. It is also very tough, a quality that makes it highly resistant to many different types of damage.

Natural rubber is the most widely-used form of rubber, and it is extracted from the latex sap of certain trees. There are over 2,500 species of plant that produce latex, but the vast majority of natural rubber is made from the Hevea brasiliensis tree (also known as the rubber tree).

It can be used for a variety of purposes. The natural rubber is usually mixed with other chemicals to improve its properties, and then vulcanized. This chemical process heats the rubber with sulphur and a catalyst, to harden it while maintaining its elasticity.

The natural rubber is then pressed into slabs and dried before being masticated to make it softer. It is then mixed with other additives and then shaped to its final form.

In addition, it can be vulcanized to be harder and more durable. This is done by heating the rubber with sulphur, an accelerator and an activator at about 373-415 degrees C.

Once the rubber is vulcanized, it can be used for all sorts of different things, from tires to medical devices. It is also used in clothing to manufacture expandable clothes such as gym shorts and swimming suits, and for flooring to give padding and be waterproof and slip-resistant. In the automobile industry, it is used to create brake pads and seals. It is also used to create airbags that protect drivers from accidents.

How is rubber made?

Rubber is an important material that is used to make a variety of items including tires, elastic bands and footwear. It can be made from natural or synthetic sources, and the process for making rubber depends on what the product is used for.

Natural rubber is made from bending rubber latex from rubber trees or other plants. It is a milky liquid that is drawn off the bark of these trees by making incisions and collecting it in vessels in a process called “tapping”.

Synthetic rubber is made using chemicals to synthesise polymers instead of using natural materials. It can be made from oil, coal, or other hydrocarbons and is mainly monomers containing styrene or butadiene.

The chemical reactions involved create a chain of polymers, which are then linked together to form the rubbery substance. The final properties of a rubber article depend on the polymer and any additives, such as carbon black, that are added.

After this, the mixture is shaped into a mold of the desired shape. This is usually done by extrusion, but can also be accomplished by transfer or injection molding.

Once the rubber mixture is shaped into its final form, it must be cured. This is usually done by heating the mixture to a temperature where it will interlink with other chains of rubber, a process known as vulcanization.

This can be done by heating the rubber mix in a pressurized mold, but can also be achieved by microwave irradiation or passage through a bath of molten metal salts. The final cure of a rubber product is crucial for its strength and durability.

Bend Deduction

Bending rubber is one of the most common processes used in manufacturing. Several different methods are available, including air bending, vaccum forming, V-die bending and stretch bending. Each method has its advantages and disadvantages, and the right choice depends on your needs.

The bend deduction (BD) is a critical factor in air bending for rubber forming. It is the difference between two flange lengths before a bend, and it represents how much material you must remove from the flat pattern to form the desired flange.

For example, if you change the inside bend radius that you produce with air bending, it will alter the amount of material elongation within each bend and cause the BD to increase, thus changing the part’s flange lengths. This can wreak havoc with angle corrections and other precision work.

This is why it’s important to use a bend deduction chart for air forming. Older charts often have variances that can lead to miscalculations, which can be very dangerous for parts with multiple bends.

The elastic force is caused by a number of mechanisms, including entropy changes and molecular bond bending rubber distortions. When rubber is stretched, the entropy change increases, which causes the elastic force to increase.

Elasticity is also caused by compressive and tensile stresses. As a result, the bending process must overcome both types of forces.

Another advantage of air bending is that it requires less force than other bending techniques. This decreases the amount of material that must be bent and reduces setup time and cost.

Unlike other bending processes, air forming does not require customized bottom dies for different flange lengths. It also eliminates the need for witness marks on the resulting bend.

Bend Allowance

Bend Allowance is a calculation used to determine the length of a bend based on a material’s neutral axis. It takes into account the geometry of bending, the properties of the metal and a K-factor ratio (typically between 0.25 to 0.5).

As sheet metal is bent, it changes in both tension and compression. The outside portion of the sheet experiences tension and expands, while the inside portion undergoes compression and shortens. These two processes cause the material’s neutral axis, which is where the sheet doesn’t compress or stretch, to shift inward toward the inside radius.

This results in a bending allowance, which is the amount of material that is lost to a bend. This can be calculated by using a mathematical formula that adds the neutral axis to the flat length of the part.

When working with a newly designed or manufactured sheet metal product, bend allowance and springback calculations are critical design factors. This is because sheet metal stock transforms from a plastic state to an elastic state and then back to a plastic existence during a bending process.

During this transformation, the molecular properties of the sheet metal retain the instructions that were present in its plastic state when it was formed. This enables the metal to retain its shape and size after a bend, similar to how it can reestablish its memory.

Bend allowance is a key element for precision sheet metal fabrications such as electronic housings and custom industrial enclosures, or for original equipment manufacturers that use sheet metal products in a variety of applications. It also helps ensure that end-products function properly and meet or exceed expectations.

PDMS

Polydimethylsiloxane (PDMS) is a plastic material that has several properties that can be beneficial when bending rubber. It is pressible, durable over a wide temperature range, and is essentially non-toxic. Its chemical structure is hydrophilic, which means that it can seal to itself, glass, silicon, and some plastic materials.

PDMS is often used in composites because of its good mechanical and thermal properties. It is also flexible, which makes it easy to bend without collapsing.

The PDMS can be cured at high temperatures. Typically, 65 degC for a few hours is sufficient to cure the material. However, PDMS can also be cured at room temperature over a longer period of time.

There are a few methods that can be used to make PDMS more flexible, including surface modification. One method is the use of surfactants. A neutral surfactant can adsorb to the surface of the PDMS, making it more elastic. Another way to modify the surface is by using a plasma treatment.

When PDMS is exposed to a plasma, it will create a layer of silica-like material on its surface. This helps to improve the tackiness of the material, which is important for bonding with other materials.

In addition, plasma treatment can alter the water-polymer interaction of PDMS. It can also create a layer of atomic oxygen on the surface that can affect its wet-tability.

Lastly, PDMS can be bonded to other materials in a variety of ways. Some of these techniques include surface bonding, covalent bonding, and dynamic bonding.

The energy needed to peel a PDMS beam from its substrate can be calculated by combining the bending and adhesion energies of the beam. The equilibrium peel distance s*, or the separation position a, is determined by the balance of these energies.