Simple production technology for compact universal hydrogen tanks

Simple production process for tank modules made of carbon fiber-reinforced plastic (CFRP)

Mindelheim, 07.08.2020. BBG has developed a mold concept that allows compact, modular hydrogen tanks made of CFRP to be manufactured in series quickly and reproducibly. What is the benefit? The tanks can be easily adapted to various car models and thus be installed in different fuel cell vehicles.

So far, large cylindrical hydrogen storage tanks have been used commonly; however, they require a great deal of space. More compact tanks, which can be produced at low cost, therefore play an important role in the development of fuel cell vehicles. The research project Bryson, in which TU Dresden (Dresden Technical University), Hochschule München (Munich University) and Leichtbauzentrum Sachsen (Lightweight Construction Center Saxony) participate in addition to BMW, is looking for solutions to this problem.

in the floor assembly integrated tank
in the floor assembly integrated modular hydrogen tank

Simple technology and low investment cost

We at BBG have developed a simple process: CFRP tank modules can be manufactured autonomously through the use of the self-closing molds developed and made by us. This results in low investment cost since the process does not require a press or further production equipment, such as autoclaves for curing.

Self-closing HP-RTM mold suffices for series production

During our production process, cylindrical hollow bodies, i.e. the inner shells of the cylinders, which are also referred to "liners", are first overbraided with carbon fiber. Then the blanks thus prepared are inserted into the two-part mold. Up to 15 cylinders with a diameter of 50 mm and more can be produced simultaneously per operation.

A low-viscosity, resin-based mixture is then injected into the heated mold under a high level of pressure. This mixture penetrates the carbon-fiber braid, enclosing the individual fibers evenly and without defects in the process. After curing in the mold, the modular CFRP cylinders can be removed and connected to form a tank.

Cylinder braided with carbon fiber
with carbon fiber braided cylinder

Compact tanks, range similar to those of internal-combustion engines

Since tanks are assembled from individual CFRP cylinder modules, they can be tailored precisely to the installation space available in a vehicle. The modules can be integrated, for example, in the floor assembly to save space. Such a tank filled with 700 bar internal pressure facilitates a range that is similar to those offered by internal-combustion engines for hydrogen-powered passenger and commercial vehicles.

Efficient and reliable production of hydrogen tank

The mold concept for modular hydrogen tanks is based on our comprehensive expertise in the high-pressure resin transfer molding (HP-RTM) process, as we have developed and manufactured molds for this process for many years. In 2019, we presented a mold for the production of hydrogen tanks at the JEC World Composite trade show.

Gerhard Hörtrich, our project manager, likes to refer to our large competence in tool and mold making: "Since the high pressure applied to hydrogen tanks requires a great deal of component stability, we attach particular importance to maximum precision in the design and production of HP-RTM molds.

For the production of the hydrogen tanks to be as efficient as possible at the same time, we have developed and integrated a reliable sealing system, among other things. This system ensures that virtually no manual reworking is required after the resin mixture is injected", says Hörtrich.

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