What is a seal, what are its advantages?

 What is a seal?

Rubber gaskets are flexible components used to mechanically seal a microscopic gap between two mating surfaces or joints. Examples of such surfaces are the flange surfaces of pipes and fittings, the mating surfaces of the car cylinder head and engine block, the tank and its lid, door edges, frames and so on. Rubber gaskets seal surfaces by flowing into and filling surface irregularities in rigid parts.

The sealing ability of rubbers is attributed to their elastomeric nature. Natural or synthetic rubbers belong to a family of materials called elastomers. Elastomers are a class of polymers that are highly flexible in nature and are created by cross-linking long polymer chains into amorphous structures. The intermolecular forces between polymer chains are relatively weak; this allows them to be reconfigured under stress. Thanks to this property, elastomer seals easily adapt to the profile of the surfaces, thus creating a tight seal.

What are the advantages of seals?

Compared to their metallic and other non-metallic counterparts, rubber seals have many advantages due to their unique properties. Flexibility, or the ability to deform, is the most important property of rubber that allows it to form tight seals.

Below are the benefits of rubber seals.

1. Cheap and easy to manufacture

Rubber seals are made by combining raw rubber with various additives and forming the desired profile. Like all other polymers, rubber has excellent formability. In its liquid or uncured state, whether it is of the thermosetting or thermoplastic type, the rubber flows easily into the molds. After curing, the material can be easily cut or machined to almost perfect size. In contrast to metallic and other non-metallic gaskets, the production of rubber gaskets requires low heat and pressure. Thus, cheaper tools are used and operating costs are lower.

2. Seals have excellent properties

Thanks to the unique microstructure of the seals, the tires can be stretched or compressed without damage or loss of properties. This allows rubber seals to form effective seals as they can easily deform depending on the surface of the part being sealed. They provide a more effective seal than some metal seals that rely on grooved, serrated or corrugated surfaces.

3. The seal is resistant to chemicals

Rubber seals are very stable materials. They resist all kinds of chemical and environmental attacks such as acids, alkalis, oxygen, ozone, water, heat and UV light. Of course, it all depends on the type of rubber and the mixed additives. Seals made of fluorocarbon-based elastomers have excellent corrosion-resistant properties. Examples include FKM and PTFE. Other materials with good chemical and aging resistance are SBR, butyl and EPDM.

4. Different material types are available for different applications

Unlike other types of seals, it provides a certain degree of flexibility and freedom in choosing the right material for the given application. This is due to the nature of the production of elastomeric materials. Raw elastomers, such as raw synthetic rubbers, can be made from various hydrocarbon compounds. After the production of this raw material, its properties are further modified by various additives, such as stabilizers, fillers, antioxidants and enhancers. This design flexibility allows for the production of countless engineered rubber sealants, most of which are patented by major manufacturers.

In comparison, metal seals are typically limited to stainless steel, and graphite seals are limited to very pure exfoliated graphite. The only type of gaskets that are similar to rubber gaskets are compressed fiber gaskets; elastomeric materials are also used for their production.

Seal manufacturing processes

There are different types of rubber gasket manufacturing processes. Each procedure has several advantages and limitations. Some of these processes are listed below.

- Press cutting:

Die cutting is a mass production process in which shapes are cut out of a flat material with a tool. This tool is a special tool that contains the two-dimensional profile of the product. It has an edge on one side, which is called a steel rule. Cutting is done by pressing the tool into the material placed on the machine bed. A single downward motion cuts the fabric to the desired shape.

Press cutting is one of the most popular rubber gasket manufacturing processes due to its simplicity, low tooling cost, low material waste, and high production speed. Compression seals are commonly used in general purpose applications such as plumbing and tank sealing.

- Water jet cutting:

Waterjet cutting is an unconventional manufacturing process that uses a concentrated, high-velocity stream of water to cut various types of materials, including rubber. This is achieved by pumping water at high pressure and forcing it through a small nozzle that converts the fluid pressure into velocity.

Water jet cutting is suitable for making seals that are sensitive to pressure and temperature. This process puts less strain on the material than press cutting. It also does not burn the edges of the finished product. The only limitation is that the material must be waterproof.

- Laser cutting:

Laser cutting is another unconventional cutting technology that uses a highly concentrated beam of light called a laser. In this process, a cut is made by guiding the laser beam along the cut lines on the material. The exposed material quickly evaporates or sublimates, leaving a cut.

Laser cutting is desirable for its precision and clean cutting process. It does not involve wetting the product; this is desirable as wetting can lead to swelling and degradation. Compared to the equipment used in water jet cutting, the equipment used also requires little maintenance.

- Flat cutting:

Plane cutting is a mechanical cutting process that uses a small oscillating knife to cut through soft and semi-rigid materials such as rubber. The knife is mounted on a robotic system controlled by a CNC program.

Plane cutting is also a precision cutting technology similar to waterjet and laser cutting. The advantage of this process is that it does not expose the material to pressure, high temperatures or water. However, it is less efficient when cutting harder materials.

- Injection molding:

Injection molding is typically a plastic forming process that can also be used to mold rubber. This process involves melting the rubber to a manageable viscosity level so that it can be processed. Other types of rubber do not need to be melted as they are liquid in their uncured state. After the initial process, the rubber is injected into a mold. The form contains a negative image of the final product. Inside the mold, the rubber solidifies, hardens and cools. After the hardening phase, the molded rubber seal is released.

The main application of injection molding in the production of rubber seals is the production of rounded products such as O-rings or products that have a three-dimensional shape. Unlike previous machining methods, injection molding is not limited to producing flat profile gaskets.