Patent Application
20200130770
Bicycles have been made of a variety of different materials over the years, from wood to steel to aluminum and carbon fiber. Magnesium and its alloys, a reactive metal system that is difficult to weld, is extruded by very few companies worldwide and is forged by even fewer. Magnesium weld rod is only available from a very small number of makers and has not been met with commercial success as an alloy for bicycles. Magnesium also generally has a 30% lower modulus which adds to the list of challenges. In contrast, Aluminum needed a minimum of 8 to 10 years to become commonplace as a bicycle alloy, considering it is non corrosive in most environments, can retain polish, can be easily anodized, painted and extruded by no less than 300 firms world-wide.
Simple changes in geometry in the tubes used in bicycles for example can make a big difference. Many bicycle producers believe that 1 ¾″ Mg alloys will be too stiff, but they fail to understand that the lower modulus of elasticity (30% lower) will retain a soft feel. Overcoming consumer's lack of education by factual demonstration can help to promote Mg usage in bicycles.
In a carbon fiber composite structure, reinforcing fiber—the carbon—is encased in the matrix material, an epoxy resin. Carbon composites derive most of their strength from the carbon filaments, but those filaments are nothing without the resin that binds them together. A major factor in high quality carbon composite bicycles becoming a reality has been the advancements in the manufacture of both carbon filaments and resins over the past decade. Some carbon fiber materials have a modulus of elasticity between 200-600 GPa and a tensile strength of between 2,500-3,500 MPa.
In terms of carbon filaments, one important factor has been the ability to tailor fibers of high tensile strength of around 600 to 700 ksi (thousand pounds per square inch). Fiber filaments are also rated by their modulus (stiffness) and can be referred to as either being standard, intermediate, or high modulus fiber. The strength and stiffness of carbon filament does not always correlate with each other. Unfortunately fiber higher than intermediate modulus tend to get weaker as they get stiffer. As a result, the design of a composite structure has to balance these two attributes in order to optimize the performance and durability of the finished product.
It is to be appreciated that the filaments are nothing without the resin, and the key to a good resin job is to get it evenly compacted in just the right ratio with the carbon. With shapes as complicated as are found in modern composite structures it is easy appreciate how some areas may not get fully compacted. Those regions can lead to filament separation and failure. Depending on the area and compaction needed, foam shells, carbon shells, alongside pressure intensifiers to squeeze the composite just right are often employed.
For bicycles, most frame manufacturers use continuous sheet of filaments “pre-impregnated” (pre-preg) with uncured resin as the building block. The pre-preg is adhered to a carrier sheet, or backing paper, so that it can be more easily handled. Properly handled sheets are stored in freezers to keep the resin from curing prematurely, and in production the sheets are cut and layered up in climate controlled rooms.
To give bike frames their structural strength manufacturers employ a variety of unidirectional carbon fiber pre-preg sheets, or “plies”. Each ply is designated by the fiber orientation as being either a 0°, a plus 45°, a minus 45°, and/or a plus or minus 30°. Each orientation bestows a different mechanical attribute to the structure. 0° sheets build strength and stiffness along the length of the structure. Plus and minus 30° sheets resist twisting, and the 45° 's fend off crushing loads. Together they determine the strength and stiffness characteristics of our little mechanical structure. There can be hundreds of individual sheets of pre-preg in a single frame, each one a unique shape that goes into a predetermined location in the layup.
Composite frames are molded using layers of pre-preg in a very specific sequence and orientation. The combination of heat and pressure first causes the resin in the pre-preg to flow, compacting the laminate and fusing the plies together as the excess resin gets pressed out of the structure. As the temperature increases, the epoxy hardens by way of a non-reversible chemical reaction. When fully cured the separate pre-preg components integrate with each other into a continuous structure.
A critical aspect of composite manufacturing is the skill of the workers actually laying up the pre-preg according to the lay-up schedule and the quality controls built into the manufacturing process. This is to ensure that every frame meets the strength, stiffness and weight goals for that design. These factors add up and make a good carbon composite frame very expensive. Also, a crash can totally destroy the carbon frame.
Magnesium (Mg) bikes have existed since the 1980s, when Frank Kirk made the first cast magnesium bike frames while working at Ford in Dagenham, England. Oscar Pereiro won the 2006 Tour de France on Pinarello's Dogma FPX magnesium bicycle. The Dogma FPX offers triple butted Mg alloy frame. It features an ONDA FPX fork utilizing a 1¼″ bearing at the fork crown and a 1⅛″ at the top of the headset. Magnesium offers elongation in the 10% range, which helps make a durable frame with low notch memory for high impact and dent resistance. Magnesium can be used to engineer bike frames that are lighter than aluminum while maintaining high tensile strength and damping capabilities. All of that leads to a much smoother, more efficient ride. Magnesium also comes in at a lower price point than popular lightweight materials like carbon fiber.
Though these bikes made an appearance in the Tour de France, they could not succeed commercially due to manufacturing and build quality issues. Of late, DT Swiss, Paketa Cycles and others are addressing the challenges of magnesium bike frames through new technologies and the creation of new alloys. These developments are designed to yield better bikes that take advantage of the lightness, stiffness and high damping capacity of magnesium.
The present disclosure is directed to a novel Mg alloy frame for designing ATOMICA's (™) bicycle. Based on experience in designing novel alloys and metal matrix composites stemming from Mg as matrix with second phase for tailoring stiffness and minor alloying elements for strengthening and reducing corrosion resistance, the subject material of the present disclosure has resulted in a riding product like no other.
Embodiments of the present disclosure are directed to a design methodology to engineer a light-weight, high-strength alloy and extrude tubes with a form factor for bicycle frames with features such as internal fins offering adequate stiffness, thus riding comfort is obtained without compromising superior performance. The materials of construction are of Mg alloy matrix and will be resistant to environmental corrosion and will be weld-able using common Mg alloy electrodes. Last but not least, the alloy can be produced by different routes for added performance and tailored to meet cost targets. Various features of the present disclosure are described herein.
Below is a detailed description according to various embodiments of the present disclosure.
The first-melting projections (FMP) from phase diagrams, be it a binary, ternary or a higher-order system, predicts the temperature at which there is the first emergence of a liquid phase upon heating at any given composition at thermodynamic equilibrium. Generally, FMP are identical to solidus projections. They are often observed to obey same established topological rules as isothermal sections of phase diagrams. Only in systems with metatectic (catatectic) invariants (partial melting during cooling) or retrograde solid solubility do exceptions to these rules occur. In these regions the FMP and solidus projections are not identical. Here we usually plot the FMP which is always single-valued at all compositions.
The liquid projection of the (Zn+Mg+Al) system is shown in
Initial phase behavior is determined by simulation and predictions after production of binary and ternary phase diagrams using simulation software, for example “Thermocalc”, “FactSage” etc. Eutectic and peritectic reactions in designed alloys dictates design by PM or IM processing. Simulation predicts temperature range to consolidate blended powders (PM route) or alternatively melting temperature (IM route).
The portion of Mg of course is calculated after the other constituents have been chosen and will complete the 100%.
The materials are in powdered form which helps to promote an even blend. Each of these materials can be obtained in a powdered form using known techniques. At 102 the materials are blended together. In some embodiments the blending can be achieved by using a V-blending technique. The materials can be blended in such a way that segregation between the powders is minimized or eliminated. At 104 the mixture can be vacuum hot pressed at a temperature of 750 degrees F., ±25 degrees F. The vacuum hot pressing causes the materials to melt and fuse together and when it cools it forms a solid alloy that can be extruded or otherwise machined. At 106 the material is extruded. In some embodiments the extrusion can be performed using a die-mandrel-container configuration with the billet at 800 degrees F., the die at 700 degrees F., the mandrel at 800 degrees F., and the liner/container at 800 degrees F. The shape of the die and mandrel can form the desired shape of the tubes which can be constructed into a bicycle frame.
The foregoing disclosure hereby enables a person of ordinary skill in the art to make and use the disclosed systems without undue experimentation. Certain examples are given to for purposes of explanation and are not given in a limiting manner.
