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Techno-Composites Domine GmbH
Dieselstraße 34
49716 Meppen

Expertise

Just as there are different kinds of steel, there are also different kinds of fibre composite materials. The following is not a complete list, but it demonstrates the breadth of solutions that we cover. This isn’t an in-depth report; there are plenty of specialist publications for that. At this point we just want to give you an initial idea of the possible applications.

Fibre composite components

Fibre composite materials have a number of advantages over other materials. That said, they're not cheap. If used appropriately, however, they offer material properties that cannot be achieved by other materials. This gives them the potential to be remarkably cost-effective.

Fibre composite materials offer the following benefits:

  • High mechanical strength but lightweight
  • Freedom in design for customised shapes.
  • High-quality, paintable surfaces
  • High breakage resistance
  • Assessable fire protection properties
  • Resistant in corrosive environments
  • Weather-resistant
  • Low thermal conductivity
  • Electrically insulating
  • Economical to transport and handle
  • Easy to adapt on site

There are a number of reasons for using filling materials in fibre composite components. Filling materials can alter the mechanical, visual, thermal and electrical properties of the product. Fillers are added to the liquid resin mixture. Chalk is often used as a filler in order to reduce costs. Aluminium hydroxide improves the flame-retarding properties and fire behaviour. Hollow glass spheres can reduce the density and thus the weight of the fibre composite component. Graphite can alter the electrical conductivity of a GRP component. Soot turns the matrix resin black and provides UV protection.

GRP lay-ups can be provided with what is known as a gel coat. This is the first layer that is sprayed onto the GRP form and constitutes the layer of paint. Only then are further layers of fibreglass and matrix resin applied. As such, the demoulded component already has a smooth, coloured surface.

For pultruded profiles, colour pigments can be added to the liquid matrix resin mixture. In this case, please note that the fibreglass does not absorb the colour pigments; the matrix resin is coloured instead. In a matrix resin that has been coloured black, you will continue to see the pale glass fibres shimmering through the finished GRP profile. The lighter the colour pigments that have been added, the more uniform the profile will look.

GRP components can be primed and painted afterwards in order to achieve a visually perfect surface. This is especially relevant for cladding parts, e.g. for use on buses and trains, both indoors (e.g. textured paints) and outdoors, where water-based paint systems can be used.

The UV and weather resistance of GRP profiles can be adapted to the customer’s wishes.

Our GRP profiles manufactured for special GRP structures – e.g. walkways, stairs – are inherently UV- and weather-resistant, with very low moisture absorption. These profiles also have a resin-rich covering layer and polyester fleece. If increased UV radiation reduces the resin-rich covering layer over the years, so that the polyester fleece shows through, the GRP profile can simply be painted over. It will retain its mechanical load-bearing capacity.

GRP components that have a very even surface are used for outer and inner cladding parts for vehicles, and can be painted subsequently. Such smooth surfaces are achieved by adding a low-profile additive that counteracts the shrinkage of the profile within the implement. The low-profile additive has increased water absorption properties, so such components must be painted on all sides in order to avoid water ingress. Bus side panels that have been produced and painted in this way are very difficult to distinguish from painted aluminium or sheet metal panels, even for specialists.

Selecting the appropriate resin and adding substances such as aluminium trihydroxide can be beneficial to flame retardancy and fire protection properties. We already produce components that comply with the following fire protection classes:

  • EN45545 HL2 / HL3
  • DIN 5510 S4 SR2 ST2
  • BS 6853 Cat 1b
  • various NF standards.

The feasibility of fire protection can depend on the geometry and wall thickness of the component, not to mention the mechanical values and other properties. Get in touch so that we can establish the details of your project.

Fibre composite materials

Just as there are different kinds of steel, there are also different kinds of fibre composite materials. The following is not a complete list, but it demonstrates the breadth of solutions that we cover. This isn’t an in-depth report; there are plenty of specialist publications for that. At this point we just want to give you an initial idea of the possible applications.

All of the resin systems set out here are thermosets. These are materials that harden when heat is applied, but cannot be melted again afterwards.

Unsaturated polyester resins
These resin systems are often used in fibre composite components. They are easy to process and cheaper than most other resin systems.

Vinyl ester resins
GRP products based on vinyl ester resins are used in instances where higher chemical resistance is required. Please contact us for a more assessment of the chemical resistance in a specific case. It is important to factor in the following:

  • How long will the GRP component be exposed to the medium?
  • What is the concentration of the medium?
  • How hot is the medium?
  • Does regular cleaning take place? If yes, what kind?
  • What is the planned operating period?
  • How exactly will the GRP component be used? Let’s take the example of hydrochloric acid at 20 % concentration and a temperature of 24 °C, with the GRP component attached approx. 20 cm over the acid basin for a period of 10 years, where it is used as a walkway and has to bear the weight of a maximum of 3 people.

Epoxy resins
Epoxy resins have good mechanical properties and good resistance to temperatures and chemicals. They are often used for components in electrical engineering and electronics. Epoxy resins are often more expensive than polyester resins.

Polyurethane resins
Components based on polyurethane resins offer very good flexibility. A GRP profile based on a polyurethane resin can be bent much more before it breaks than a similarly constructed polyester resin profile.

Phenolic resin
Components based on phenolic resins inherently have better fire protection properties than the other resin systems mentioned here.

The different fibres and their spatial orientation have a significant impact on the mechanical properties of the fibre composite component. We’ve set some key pointers here:

Glass fibres
These almost round fibres, which have been finely spun from molten glass, come in the form of E-glass, R-glass and C-glass fibre. Glass fibres are relatively strong lengthways. The size applied to the glass fibre filaments ensures that they adhere to the resin matrix and protects the surface.

Basalt fibres
Basalt fibres are often added to glass fibre-reinforced plastic profiles as a stiffening element due to their high tensile strength and rigidity. This is useful if, for instance, the forces pulling at the profiles are very high. Basalt fibres are significantly more expensive then E-glass fibres.

Carbon fibres
Carbon fibres can be used to increase the mechanical strength of fibre composite components by an order of magnitude. At the same time, carbon fibre components are significantly lighter than equivalent glass fibre components. For this reason, they are more likely to be used in racing and the aircraft industry. Products made of carbon fibres are much more expensive than those made from other fibre composites. It is also possible to add carbon fibres at specific points of glass fibre-reinforced components in order to improve the mechanical properties in a targeted manner, while keeping costs under control. This mix of materials can be used to meet customer requirements in a highly targeted way, while meeting their budget.

Natural fibres
In principle, it is also possible to use natural fibres in fibre composite components. Difficulties arise due to their somewhat erratic mechanical properties. Their low density makes them suitable as a lightweight raw material. As other fibres can be used with much more process reliability, at present natural fibres are seldom deployed.

The fibres are further processed with the specific aim of enhancing the properties of the GRP component.

Rovings
Rovings consist of a bundle of individual glass fibres, for instance. Rovings ensure easy handling, equal tension within the strand, low abrasion and reduced fraying, plus a corresponding suppleness. They are often wound onto cylindrical spools with an internal or external outlet so that they can be processed into a pultrusion system, for example.

Glass fibre matting
Glass fibre matting consists of continuous glass threads laid out randomly on a surface and interspersed with binders. These binders dissolve when they come into contact with the styrene of the polyester resin. Glass fibre matting adjusts very effectively to the contours of a component. Generally speaking, it is slightly cheaper than reinforcement fabrics.  Among other things, it differs in weight per unit area. The most common types are 300g/m² and 450 g/m² matting.

Glass filament fabric
In this case, individual glass fibres are interwoven to form a proper fabric. The fibres typically intersect at a 90° angle. The tight mesh can be used to create different fabrics, such as plain weave, twill weave and satin weave. Strength along the different spatial directions of a fibre composite component can be further enhanced by layering individual fabrics at an angle to one another.

Peel ply
If, for instance, you want the surface of a component to be clean and adhesive at a certain point or in a particular area without having to clean and sand it beforehand, you can use peel ply there. The peel ply (a textile fabric) is simply torn directly off the component before adhesion. This gives you a clean, dry and grease-free surface to which things can be glued directly.

Non-woven fabrics
Non-woven fabrics are often used to improve the surface of a GRP component. The non-woven fabric prevents the glass fibres of matting, fabrics and rovings from being pushed to the surface. A resin-rich top layer can be created in this way.

Manufacturing process

Producing hand lay-ups is a very simply process for manufacturing small quantities of fibre composite components.  They are based on an open tool mould into which a release agent is first inserted. In the next step, the gel coat/top layer is applied, and left to reach the appropriate level of hardness. The non-woven fabric and glass fibre matting or fabric are then inserted in layers and wetted with laminating resin. The mats are pressed down using rollers and the laminating resin is vented. A top coat can be applied once the laminate has hardened. This covers the last fibre layer and serves as protection against wear and weather.

Hand lay-ups have a ‘good side’ and a ‘bad side’. Their wall thickness may vary by a few millimetres due to the manual process. The overall quality of the component is also hugely dependent on the manual dexterity of the processing technician.

The resin transfer moulding (RTM) process is used for manufacturing long and continuous fibre-reinforced, flat components in small and medium-sized series.  The usual 2-shell mould ensures that both surfaces are good quality. Pre-cut and non-impregnated fibre matting is inserted into the mould for that purpose. Once the mould is closed, the reactive resin system is injected into the mould cavity by generating negative pressure. Once it has hardened, the component can be removed from the mould.

There are some sub-forms of the RTM process, such as the RTM light process, which we won’t go into at this point. One key fact is this process can be used to manufacture small to mid-sized series of large-scale components that have two good sides, so that, for instance, a mounting support can be glued to the back with a certain degree of reproducibility. Whenever possible, such mounts can be attached in the mould, during the creation of the RTM component itself.

Pressing processes are suitable for producing a very large number of identical fibre composite components. They offer good reproducibility and can largely be automated. Cycle times are short. However, this type of production requires a hydraulic press with controls, plus very expensive tools. It is widely used in the automotive sector.

In the pultrusion process, fibre rovings and mats are passed into a tool via a feed device. The feed device ensures that any roving or mat is positioned at the intended place in the tool to ensure that its mechanical properties remain reproducible. Before the fibres are fed into the tool, they are steeped in the intended matrix resin in a resin bath. Alternatively, the resin can also be injected into the mould or a combination of both processes can be used. The resin and glass fibre mixture is then hardened in the mould, with heat applied. The profile is drawn steadily out of the mould by a trigger unit.

Pultrusion can be used to produce GRP profiles of great length in large quantities and at an economical price. As a separate mould needs to be created for every pultrusion profile, this process is cost-effective if you require at least 1,000 m per profile type.

Machining processes

Fibre composite components can be cut using small commercially available equipment such as circular saws, drills, jigsaws, angle grinders, routing machines, etc. Carbide and diamond-tipped tools are recommended, as they stay sharp for much longer. Other tools wear out very quickly due to the glass content of the products.

In terms of personal protective equipment, safety goggles, gloves, clothing that covers the entire body and, if necessary, a mouthguard should be worn at a minimum, as GRP cutting creates dust. This cannot be breathed in, but may cause skin irritation.

For more professional machining needs, CNC machines are a good fit. When using CNC machines, the key issue is clamping the GRP component to the CNC machine in a sound, simple and replicable manner. Our employees have designed and refined various different concepts for doing this over the last two decades. The correct use of tools is also especially important. This eliminates the need for subsequent work, such as deburring GRP profiles. Naturally, our CNC machines are connected to a central suction system that is designed to filter out carbon dust.

The question of which glue to use had to take a number of factors into account. First, we need to know what is being glued together (GRP and GRP; GRP and aluminium; GRP and stainless steel; and so on). In addition, the components to be joined must have a design that allows a good bonded connection. If you want to glue two GRP profiles together on their blunt end faces, it doesn’t matter how well designed the bonding point is; the component simply won’t hold together. But neither the employee nor the glue are to blame for this. In this case, the joint has not been constructed so that it is suitable for gluing.

You also need to consider the loads that will be acting on the bonded joint during its service life, and whether these are dynamic or static loads. Another factor is whether the bonding will take place under construction site conditions, or whether the gluing will be carried out, for instance, in our climate-controlled production halls, with set humidity and no draughts blowing through.

It is necessary to determine the environment in which the bonded component is to be used (temperature, weathering, chemical impacts, etc.) Knowing whether this is a one-off item or a series component is also important. And then there are the gluing devices that need to be constructed. Only once we know these basic conditions in detail can our experienced adhesive engineers go about choosing the adhesive. In other words, if you need glue-bonded components, you’re in good hands with TC. Talk to us!

Isn’t painting simply a matter of applying paint to a component? Not even close. We know that painting components requires a high level of manual skill. That’s why we greatly appreciate the value that our partners add in terms of painting technology. Whether you need a smooth painted surface with a defined level of gloss for your product, a textured paint or simply a sanded surface, just let us know. We will discuss the component and the different painting options with our painting sector partner and coordinate with you so that you get a result you’re happy with.

Without the right equipment for processing components, every piece is like a unique item. Without professionally configured workstations, we can manufacture components for our customers, but we wouldn’t be able to do so economically. We make the effort into creating equipment, workstations and transport frames so that we can produce items cost-effectively and with a high degree of repeat accuracy.

Design

If you’re designing items made of fibre composite materials, you need to be aware of their anisotropic behaviour. The properties of fibre composite components are thus dependent on their direction. This property makes it possible to design components with the specific loads of the customer application in mind. On the other hand, this also means taking the connection points into account. If, for instance, you want to connect one GRP profile to another and drill a hole at the edge of the GRP profile, your trusty book of metalworking tables won’t be of much use. When thinking about material behaviour, it’s easier to imagine a fibre composite profile as a wooden board. If you drill a hole too close to the edge, the fibres will tear in a longitudinal direction and the durability of the connection will be greatly reduced. We are happy to help you design your product.

Recycling

As a rule, our customers commission GRP products from us on the understanding that they will be doing their jobs for several decades to come. Once our products have reached the end of their life cycle, they can be recycled via co-processing, whereby shredded GRP fragments are placed in cement kilns together with other raw materials. The fragments generate additional heat when burned, while the fire residues also provide raw material for the cement itself.

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