Towpreg: 700 bar H2 tanks, smaller and lighter in partnership with Voith

Voith and Huntsman Advanced Materials have partnered to meet the industry's demand for safe, lightweight, and highquality hydrogen composite pressure vessels. The collaboration aimed to achieve best cost-performance ratio of the pressure vessels by implementing a new mass production process using towpreg material.

Leveraging Voith and Huntsman experience and know-how in filament winding products, the two companies are building higher storage capacity tanks without compromising safety at high pressures, aiming to reach series production. By enabling the best cost-performance ratio thanks to towpregs (high filament count pre-impregnated with an optimal quantity of resin), Carbon4Tank 700-bar H2 is an improved and sustainable solution for storing hydrogen, meeting automotive quality standards.

Higher storage density H2 tanks

The developed Type IV 700 bar H2 tanks for use in hydrogen-powered zero emission trucks show significant performance improvements vs. conventional Type IV tank designs (Figure 1).

Fig. 1: Results apply to type IV 700 bar H2 tanks with new towpreg system Voith Composites Carbon4 Tank GEN II- 700 bar type IV hydrogen tank with 15.5 kg H2 Capacity, 2,140 mm length and 555 mm in diameter

With the performance advantages of Voith’s H2 Tank design, the new towpreg resin system from Huntsman Advanced Materials supported Voith to improve Total Cost of Ownership (TCO) of the new tanks while meeting the automotive industry's quality and safety standards.

Stringent requirements for safe H2 storage

Truck manufacturers' demands on hydrogen tanks are clear and strictly defined. The so-called Type IV pressure vessels must ensure storage of compressed hydrogen at high pressures up to 700 bar. Therefore, the composite vessels need to fulfill the following requirements:

• meet the automotive standards: the UN/ECE regulation n°134 governs
• the technical requirements, for which the vessels need to withstand impact and chemical resistance test fatigue cycling at various temperatures, to ensure safe hydrogen storage and transportation;
• compatible with mass production: the project needed to meet industry output and cost targets achieved through high speed production and reproducibility;
• lightweight: lighter pressure vessels enable higher storage capacity and result in longer range and higher payload;

Voith Composites and Huntsman Advanced Materials joined forces and determined the towpreg production process as the best solution  because it offers several benefits. Since the towpreg impregnation line operates at speeds up to 100 m/min, it leads to an increased productivity. An excellent quality control ensures an optimum resin content and reproduceable high quality and safety tanks in a clean process environment.
Additional winding possibilities compared to conventional filament winding enables the reduction of composite wall thicknesses and consequently reduces material consumption and overall pressure vessel weight.
Both partners combined their knowhow and expertise to develop a new generation of carbon fibre based towpreg material dedicated to production of high performance 700 bar Type IV hydrogen storage tanks: Huntsman Advanced Materials focused on the formulation of epoxy-based resin systems with optimised thermo-mechanical performance and process ease, while Voith Composites worked on tank design, certifications and automated process for cost-effective large-scale production for a higher economic efficiency of the H2 high-pressure tanks.

Development of a new towpreg generation

A new epoxy-based formulation was developed to give the towpreg material extended storage possibilities, a specific rheology, tackiness, and cohesion of the carbon fibre filaments to optimise the tank production without sacrificing thermo-mechanical performance.
The ARALDITE® towpreg solution can be stored up to 3 months at 23°C after the production of the towpreg bobbins which reduces logistic issues, energy consumption, storage cost, and time-consuming operations.
The rheology profile leads to a very good impregnation of the carbon tow during the production of the towpregs, at a speed up to 100 m/min. The specific resin tack and viscosity at room temperature were fine tuned to end up with the optimal balance between tow stiffness and drapability. The carbon fibre filaments hold together along the winding process and can spread when being deposited on the tank layup under both low and high tension to reach a suitable band width.
The tack of the towpregs enables the maximum winding speed of the machine (up to 6 m/sec.) and places the tows accurately on the pre-determined path, during the production of the pressure tanks. Highly accurate fibre placement and the possibility to reach lower winding angles without slippage, allows for optimisation of the winding pattern and design (Figure 2).

Fig. 2: Specific winding pattern

Both the development of the resin system, as well as the design optimisation of the pressure tank benefited from the cure kinetic simulation expertise offered by Huntsman. Cure simulation provides a valuable tool to quickly assess the effects of changes to cure cycles and gain insight into all areas of the simulated part. Detailed material data models have been generated to make accurate predictions of exotherm temperature, degree of cure and glass transition temperatures (Tg). This is a powerful tool to accelerate product development and optimise manufacturing, leading to increased part quality and minimum production cycle times. Figure 3 shows the temperature distribution during the cure cycle of the tank to keep the exotherm  temperature under control and predict the cure behavior. The overall cure cycle of the tanks was optimised to increase production output and reach the optimal degree of cure of the resin system to ensure safety. Thermo-mechanical static, dynamic performance as well as chemical resistance are governed by the resin system and have been optimised to safely withstand extreme solicitations during the lifetime of the tanks.

Fig. 3: Cure simulation of pressure vessels

In summary, this new towpreg material allows an increased productivity thanks to fast in-house production of the bobbins, outstanding winding speed, and controlled cure cycles; new winding possibilities for new lay-up design; a very good control and reproducibility of the production parameters to ensure quality and safety during the lifetime of the pressure tanks and shorter curing times for higher productivity.

Optimised use of towpreg material for cost effective and fully automated production of H2 Type lV tanks

Voith identified several ways to improve TCO:

• in-house production of the towpreg material optimises the value chain of H2 tanks by reducing cost drives along the supply chain as well as storage and transportation costs;
• extremely low scrap rate through online controlled and monitored impregnation processes for highest automotive quality standards, reduction of material consumption within the impregnation process as well as in the subsequent winding process drives cost down and reduces tank weight by getting the best mechanical performance out to the carbon material;
• design capabilities given by new winding possibilities (small angles capability) allows laminate thickness reduction. This will allow superior H2 storage capability per kg of composites. Productivity increase over full production process is achieved thanks to fully automated production lines; higher winding speeds (three times faster than WFW); fast curing with new resin formulation;
• the well-thought-out production layout according to the principles of Composite 4.0 favors cost efficiency with fewer errors and defects.

Plug and drive H2 storage systems meets truck OEM requirements

Voith Composites and Voith Turbo have jointly developed a complete ready- to-ride H2 drive system for heavy duty trucks (Figure 4). With the complete system including H2 peripherals and electrical control outstanding performance and long service life are convincing features.

Fig. 4: Voith’s H2 plug and drive system

The modular, platform-based plug and drive storage system is offered with 4 to 8 Type IV hydrogen tanks. The light weight and thin wall of the 700-bar hydrogen tank enables about 5 tons more payload and additional space efficiency on the truck –compared to the battery electric version. The complete hydrogen storage module, from the tank nozzle to the fuel cell inlet, a tested and ready-toinstall system with 700 bars in automotive series quality, is ready to drive after less than 10 minutes charging time. The Voith plug and drive H2 storage system is suitable for long distances and enables a range of up to 1,000 km.

“This common project illustrates perfectly how trustful collaboration can accelerate development and time to market”, said Simon Burkel. “Sharing expertise and understanding each other’s constraints and needs were instrumental in the success of this development”, added Carolin Cichosz.

FOCUS - About Voith

Voith Composites is the expert for high-performance composites of the 1867 established Voith Group. With its experience especially in automotive and other industries, the company stands out with its broad know-how and reputable references in the field of composites. The first high-performance winding products, before winding high pressure tanks, were for paper machines. The challenge of the large dimensions and complexity of the rolls required here is met by the company with flying colors, ensuring faster running time for the paper machines and higher quality and quantity in their output for the paper manufacturers. The production of cylindrical carbon fibre products involves the efficient use of materials with an optimal production fl ow and digitally recorded and controlled processes. It is the selection of the right winding material, the precise deposition of the material and setting of the deposition angles. Together to ensure a higher outcome, better performance, and economical advantages for the customer using these CFRP rolls. Voith Composites has tremendous capabilities in the wet filament winding process and reflects these capabilities in the towpreg winding of their hydrogen tanks. The expertise in CFRP roll production and the leadership position in Composite 4.0 component manufacturing in the automotive sector combined, makes Voith Composites the number 1 high pressure (700 bar) hydrogen tank manufacturer for high volume automotive serial production.

FOCUS - About Huntsman Advanced Materials

As a pioneer and leading global supplier of epoxy resin solutions for Type III, Type IV, and even Type V filament-wound composite pressure vessels (wet filament and towpreg winding), Huntsman Advanced Materials offers innovative solutions that support manufacturers in the design and production of composite pressure vessels for hydrogen storage and transportation. The company’s solutions are trusted worldwide for material performance, efficient manufacturing, and increased productivity complemented by extended material characterisation, processing expertise, and process simulation. Huntsman Advanced Materials is also offering a range of products utilising the mass balance concept which are RedCert2 certified. It supports the chemical industry in shifting from fossil-based to biomass feedstocks ultimately this approach leads to the sourcing of more sustainable raw materials. The performance of these products matches their fossil-based counterparts, with an added benefit of a CO2 emissions footprint reduction of up to 80%, depending on chemical structures.

More information:
www.huntsman.com 
www.voith.com

ARALDITE^® is a registered trademark of Huntsman Corporation or an affiliate thereof in one or more, but not all, countries. © 2023 Huntsman Corporation or an affiliate thereof. All rights reserved.

Source: JCM152 – sept/oct 2023