Monday, June 24, 2019
Materials Matters: Titanium verses Aluminium Manual Wheelchair Frames
Right from the get-go let me say, I love titanium! From my first ride in a titanium chair some 15 years ago I remain convinced it is the best material on earth for wheelchairs. The ride in a titanium chair feels different, it has a dampening effect on bumps. When I got my first titanium chair my wife would often get surprised when she realised, I was beside her – she could hear my aluminium chairs coming as they went over the tiles and floorboards, but not the titanium chair. This was because of the vibration dampening. Apart from the “ride”, I love the fact it does not have to be powder coated, which means it does not chip, or look scratched and old. As well as that, titanium is strong – the strongest weight to strength ratio of any metal – which suits my lifestyle which involves lots of travel. After 15 years of regular plane trips I have confidence that when I arrive my chair will be good to go despite the rough handling it gets. That peace of mind is really important to me.
My chair is also ultra-light, especially with a non-folding back. With the configuration I have it is slightly under 8kg with the wheels on, about 4.5kgs with them off.
A couple of things to note, not all titanium is the same, so the type of titanium and the thickness of the tubing will impact on how the chair rides and how heavy it is. Also, my chair frame is made from titanium, but I have carbon fibre components such as side guard, wheels and backrest. Some of the parts are aluminium, such as front forks and camber clamps, so it is really a titanium frame with hybrid components.
Mal just gave a great insight into his preference. Now, let’s look at the materials and why Mal has preference for titanium versus aluminium. We have been able to learn a lot about the materials we use in manual wheelchairs through other industries, one of the big ones being the biking industry. We will start with aluminium. All types of aluminium have specific strength, low density, and resistance to corrosion. There are lots of different types of aluminium, but most manual wheelchairs are made of either 6000 or 7000 series aluminium. Many people believe that 7000 series is the best, just like how the iPhone 10 is better than the iPhone 8, but this is not true. The type that is best depends on how each manufacturer wants to use the aluminium. TiLite uses 6000 series as this allows for the aluminium to be weldable and for the greatest amount of customisability while still having a high strength. The 7000 series has a slightly higher tensile strength, but it is heat treated and therefore is harder to machine and less customisable. The difference in strengths of aluminium is minimal as compared to the difference in strength of aluminium to titanium. You can see the difference in the chart below. The chart on the left showers the ultimate strength of 6000 series aluminium, 7000 series aluminium, and then titanium. The chart on the right shows the strength-to-weight ratio.
Titanium has the highest strength to weight ratio of any metal on Earth. This gives the end-user a light weight and strong frame. Titanium is virtually immune to corrosion and is easily machined. From its ability to be easily machined and its strength to weight ratio, and vibration dampening properties, Titanium can allow us to achieve that ultimate fit. This ultimate fit along with the design of the frame of the chair leads to the optimal ride for our end-user. Although titanium has many benefits, it is a more expensive metal, and therefore the base price for a titanium frame will be more than an aluminium frame.
When deciding what type of material is right for you or your client, it is important to assess each person individually and consider the environments in which the chair will be used. It is also important to keep in mind the amount of time that will be spent in the wheelchair. We know that vibration has negative impacts on our health, and we know titanium through its material properties, design of the frame, and being easy to machine, will help to limit some of these vibrations, therefore providing the highest performance and ride for the end-user that is in the wheelchair throughout the day. We also know that strength is important as we want the frame to be able to withstand the environment that it is taken through. Finally, we want to think about the weight of the overall chair and how we can keep the weight low. This will help reduce the amount of work that we are asking the shoulders to do with every push. This is where are shoulder preservation comes back in! We want to make sure we can keep the chair as light as possible. This doesn’t just include the frame! We also need to think about what we are putting on this frame. All of the seating components, accessories, tyres, wheels, etc… have an impact on the weight of the wheelchair. Besides what goes on the wheelchair, we will also have to consider how the frame design impacts the ride, strength, and way that the wheelchair is built. We will continue this discussion next week.