What is titanium and how it is used
Titanium metal is not found alone in nature but linked to other elements. Instead the Titanium element is, however, the ninth most abundant element in the earth’s crust (0.63% by mass) and is present in most eruptive rocks and relative sediments.
In 1795 the German chemist Heinrich Klaproth managed to isolate it from rutile minerals (TiO2) and baptized the element inspired by the figures of the Titans of Greek mythology sons of Uranus (Heaven) and Gea (Earth).
The important titanium minerals are rutile, brookite, anatase, ilmenite and titanite.
The main extracted mineral, ilmenite, occurs in large sand deposits in Western Australia, Norway, Canada and Ukraine. The large rutile deposits of North America and South Africa also contribute significantly to world titanium reserves. World production of metal reaches the 90,000 tons ca. per year instead titanium dioxide production is 4.3 million tons per year.
Titanium dioxide, TiO2, is commonly found in black or brownish form is known as rutile. The least frequent natural forms in nature are anatasite and brooquite. Both pure rutile and pure anatasite are white. The black basic oxide, FeTiO3, is found in its natural form as a natural mineral called ilmenite; this is the main commercial source of titanium.
Pure titanium is obtained from ilmenite, through complex chemical processes, where the titanium element is linked to iron minerals.
The titanium available in commerce comes in different grades, i.e. different alloys starting from the purest material (CP) to that linked with other elements (TITANIUM ALLOYS).
The pure titanium grades (CP) are:
Grade 1: the purest existing. It is easily workable and presents a very high corrosion resistance.
Grade 2: the most used in the industry, it shares the strong corrosion resistance with grade 1 but is more resistant to mechanical stress.
Grade 3: mainly dedicated to aeronautics.
Grade 4: the most mechanically resistant among the pure titanium grades.
Note: Given the above characteristics, it is easy to see that these Titanium grades cannot be used in cycling.
“TITANIUM ALLOYS” are defined as all those alloys which through metallurgical processes are added with other minerals (aluminum, vanadium, chromium tin etc.) to increase their mechanical.
The BUGIA\ROSA Frame has been built using the following titanium alloys:
Grade 9
Known as 3Al – 2,5V, since it is made up of 3% aluminum and 2,5% vanadium, it is an easily weldable alloy, with a high breaking load (i.e. the maximum force capable of breaking it) and has a high corrosion resistance (stainless). Given these characteristics, it is the most used alloy in the bicycle field for the construction of the tubular frame structure.
Grade 5
Known as 6Al – 4V, since it is made up of 6% aluminium and 4% vanadium, it has a very high breaking coefficient, ideal to build the mechanical parts making up the frame such as: bottom bracket, dropouts, etc.
It also has good weldability and high resistance to corrosion (stainless) as the previously mentioned Grade 9.
Realization of a titanium frame with TIG welding
The creation of a titanium frame with TIG (Tungsten Inert Gas) technology is very particular and requires specific equipment, a very high professionalism and manual ability.
The preparation of the pipes (stripping) must be done carefully by hand: since working the pipes with grinding wheels or mechanical pipe cutters would compromise their characteristics.
During welding, titanium heats up and becomes very reactive with the atmospheric elements (oxygen, nitrogen and hydrogen present in the air), which bind and oxidize the weld, irreparably weakening the material: For this reason it is necessary to weld it in an inert and protective atmosphere of argon (Inert Gas).
The welding of the frame and its mechanical components is carried out mainly in two ways:
- Welding under a bell in a protective atmosphere
The welding of the frame takes place by inserting the pipes to be joined, the clamp with the tungsten electrode and the rods of material supply in a glass bell, in which argon is injected to saturate and expel the oxygen present in the air while, the welder, from the outside, makes the joint through special manipulators;
- “Gas Lens” Welding
The frame welding is done outside the bell – a procedure widely used in the aeronautical sector for welding the structural bases of aircraft. Using the classic TIG welding system, an argon cone is created with a very large volume (called Gas Lens), able to cover the entire weld and thus protect it from the dangers of oxygen.
Titanium Advantages (Physical and mechanical features)
- Density (weight ratio per volume unit): Titanium has a density of about 4.5 g / cm3, higher than other light metals of structural interest such as aluminum or magnesium, but almost half that of steels (about 60% of the iron density).
- Tensile and compressive strength: titanium has a high tensile strength, ie a yield strength value (ie permanent plastic deformation) of the order of 725Mpa for Grade 9. A remarkable value, which makes it perfect for the construction of bicycle frames: In fact, the most common forces acting on the frames take place along the longitudinal or transverse directions of the frame: by “pulling” or “shortening” it;
- Stiffness: when we apply a force on a frame, the material deforms to absorb it, and then returns to its original shape once the force ceases to act. This feature is called plastic deformation which works below the elastic limit, that is the maximum applicable load without permanent deformation. The higher the strength, the more the material deforms to “welcome” it, and then returns to its original position once the load is exhausted. The value of the stiffness of a material is very important when it comes to bicycles, since it represents the order of magnitude it can resist before breaking;
- Fatigue resistance: during use, bicycle frames are subjected to fatigue and must withstand repeated work cycles over time, which “tire” the material and produce a crash break that is difficult to predict. Titanium “excels” for fatigue resistance, this is why it is considered an “eternal” material, same as the carbon fiber, which however suffers the influence of UV rays (aging factor)
- Corrosion resistance: atmospheric corrosion is as subtle as fatigue because it weakens the material slowly but gradually. The oxidation, working patiently, corrodes the thickness of the tube, decreasing the resistant section and thus lowering the real value of the forces it can resist. Titanium, if worked correctly, is “immune” to atmospheric corrosion (stainless): since the outer layer of titanium is oxidized by a very resistant film
A titanium frame is not for everyone, given the intrinsic cost of the material and the expensive manufacturing techniques.
It is a precious material, with high mechanical and fatigue resistance characteristics and practically immune to atmospheric corrosion and aging.
Demanding cyclists, who want a bike with a reliable frame, which never leaves them on foot but which is light and quick, must look towards this material.
On the other hand, there are few cycling houses that offer complete models of bikes with a titanium frame, so we usually turn to specialist companies that assemble both the frame and the assembly of the components.
