Silicone coatings: keeping performance in check, so airbags can save lives
Silicone coatings: keeping performance in check, so airbags can save lives
Talk about a serious challenge. Airbags were indeed designed to save lives and limit the severity of injuries during a car crash, but exactly how do they fulfill this vital requirement? Silicone coatings actually play a significant role in optimal airbag performance. So, as logic would have it, if silicone helps save airbags and airbags help save lives, then silicone also helps save lives. How’s that for some food for thought?
Perhaps to the untrained eye, it does not seem like airbags are made with silicone but in fact they are. Airbag textile cushions use a silicone coating to enhance the performance of modern airbags. Although this stands true today, silicone has not always been in the picture. Prior to the 1990s, the automotive industry did not use silicone but rather another material called neoprene. This begs a few questions: What triggered the automotive industry to make the change to silicone? What is it about silicone that makes it the preferred choice today in manufacturing airbags? Join us then as we discuss these questions by taking a look at the history of airbags, the added value of silicone as an airbag component and finally the different types of airbags used in the automotive industry today.
The evolution of airbag cushions
Airbags or safety cushions for automobiles are a fairly new innovation, making their official debut in cars manufactured in the 1970s. Modern airbag cushions are made with a woven polyamide (or more recently of polyester) textile which is coated with a silicone elastomer.
After six years, Elkem Silicones’ team was granted its first patent, and has been leading since then the rapid development of silicones in airbags.
However, prior to the 1990s, airbag fabric was coated with neoprene, a synthetic rubber. In 1990, convinced that silicone technology could be offering an alternative to neoprene, Elkem Silicones decided to set up a dedicated R&D team to research into enhanced solutions. Aside from being solventless, silicone elastomers can be formulated to achieve extremely good adhesion onto synthetic substrates, including onto new polyester yarns, while being very effective even at lower add-on weights than neoprene.
In order to better understand the role silicone plays in airbags, let’s take a closer look at how an airbag works
The automotive industry opts for airbag coating silicones
An airbag consists of a cushion, a sensor and a canister filled with different chemicals. When the sensor detects a collision, the chemicals in the canister react to form gas and cause a sort of explosion. It is this explosion that ends up inflating the airbag with around 50 to 120 liters of air, depending on the type of airbag.
Silicone can, in fact, make this process more effective thanks to a number of its properties such as thermal resistance, slip and protection. First off, during deployment, airbags create heat and passengers in the car risk getting burnt. Also, the fabric of the airbag cushion must be able to withstand this heat without ripping or tearing. Applying a thin layer of silicone to the airbag will help protect the fabric from heat and prevent burn-through to passengers.
Furthermore, an airbag remains tucked away for long periods of time until a collision triggers deployment. Since the silicone coating is very stable over time, it prevents airbags from becoming stuck and ensures they smoothly deploy even after many years. Finally, silicone venting membranes in the airbag fabric allow the airbag to quickly deflate once it has reached its peak inflation pressure. Therefore, all it takes is just a thin layer of silicone to protect airbags (and passengers!) from heat, extend their useful life and improve the inflation/deflation mechanisms.
That is all good, but why silicone and not neoprene? The downside to neoprene was that it was very thick and needed to be mixed with a solvent in order to be applied onto fabric.
Plus, large quantities of neoprene had to be used in order to ensure the effectiveness of the airbag. With a very thick neoprene layer on the fabric, the airbag cushion was quite large in size making it difficult to install airbags in compact vehicles. Unlike neoprene, only a small amount of solvent-free silicone is needed, so smaller models of airbags can be designed. Silicone also lasts much better over time. Thanks to the longevity of its properties, there is no longer the need to change airbags. In terms of strength, silicone is highly resistant to pressure and heat. When the metal canister inside an airbag explodes, the heat it produces reaches to over 1000ºC. Metallic pieces may even be burnt and ejected during the explosion. Silicone protects airbags from being damaged by the high temperatures during this explosion. Therefore, silicone has long replaced neoprene in airbag manufacturing.
Spicing up airbags with variety
Modern automobiles come equipped with a variety of airbag models for a better protection of occupants. As such, airbags come in all shapes and sizes, in different locations of the cockpit. There are two main types of airbags: for short impacts, and for long impacts, or rollover.
Frontal airbags are used for short impact: when a collision occurs, they will deploy in just a few milliseconds, which is faster that the blink of an eye. Once peak pressure is reached, they start deflating in order to gradually slow down the passenger’s momentum from the driving speed of the car to zero. This prevents passengers from violently ‘banging into a brick wall’. The impact is stretched out over a longer period of time and over a larger area of the body. With this type of airbag, between 25 to 35 grams of silicone is needed per 1 square meter of fabric.
Curtain airbags, on the other hand, are intended for long impact during a rollover crash. This type of airbag needs more silicone, from about 60 to above 100 grams, to ensure that the airbag lasts and is able to withstand the longer period of impact during these types of crashes.
Today, cars in mature markets normally come equipped with between four and six airbags:
- 2 frontal airbags for the driver and the passenger
- 2 side airbags on the left and right sides of the two frontal occupants
- Thorax airbags, possibly with head protection, that deploy from the seat or the door
- Side curtain airbags intended to protect front and rear passengers’ head during a side-impact crash or a rollover event
Other airbags, although less common, include:
- Knee airbags to prevent legs and knees from the steering column
- Anti-submarining airbags, installed under the seat to prevent occupants from sliding underneath during a crash
- Pedestrian head protection airbags which inflate under the hood
When it comes down to it, what airbag manufacturers seek is the improved quality and safety of their products. Silicone can help manufacturers fulfil these two requirements whether in the form of airbag sealants, fabric coatings, venting membranes or other. The state of the airbag market today is focused on looking for new innovations, in terms of coated and sealed fabrics, and timely approaches to airbag technology. Manufacturers are also placing emphasis on developing appropriate evaluation methods that can be implemented during application, manufacturing and deployment. Thus, silicone, with its many possibilities, offers the automotive industry promising solutions for the future of airbag manufacturing…and life-saving for that matter.