Always Keeping Your Feet on the Ground

No one can escape it: no living thing, no element, no planet, no star. It governs direction – without it the cosmos would be in chaos, plants wouldn’t know which way to grow, and rain wouldn’t fall to the ground. We still don’t know everything about it, but one thing is for certain: since there is no way to block it, it dominates the universe. Gravity controls the world.

In front of Trinity College in Cambridge, an apple tree has been planted outside the room that English astronomer and physicist Isaac Newton once lived in. It is said to be a descendant of the tree that, according to legend, led Newton to a groundbreaking discovery in 1660. Newton was sitting in the garden of his parents’ house, lost in his own musings as usual, when an apple fell from the tree. “Why do apples always fall straight down to the ground? Why not sideways or upwards, but always down towards the center of the Earth?” Newton realized that the Earth was attracting the apple – the first step towards the law of gravity.

Gravitation, gravity, the force of attraction, weight force – these terms are generally used interchangeably. ­Gravity means two masses being mutually attracted to one another. The closer these two masses are, the ­stronger the force of gravity. The Sun attracts nearby Mercury with greater strength than it does Earth, which is further away. Size is another crucial factor: the larger an object is, the stronger its gravitational pull. This is why the little apple is drawn to the surface of the Earth. As the absolute giant of our solar system, the Sun attracts all planets and forces them into a constant orbit. In this orbit, the centrifugal force of the planets exactly equates to the gravity of the Sun. Both are in balance. The centrifugal force prevents the planets from being so strongly attracted that they hurtle into the Sun.

Gravity Is Dependent on Mass
Whether it is the Sun, the Moon, Venus or Earth: all bodies have a specific gravitational force that corresponds to their mass. It acts on all objects equally. This means, for example, that the Earth attracts a feather, a stone, an elephant, and even the Moon with the same force. The Earth’s force of attraction is six times larger than that of the Moon, because Earth is much bigger than the Moon. This is why astronauts can make large, light-footed leaps on the Moon, which is not possible on Earth.

Anyone who thinks they now understand gravity, has not seen Albert Einstein’s theory of general relativity. The physics genius was the first person to realize that gravity is not a force, but a geometric property of space and time. Space is four-dimensional. It has the directions of length, width, height – and the fourth dimension is time. Masses and all forms of energy cause “dents” in this space-time. All celestial objects have to move along these grooves. The curved space-time determines how we move.

Gravity therefore has a major impact on the universe and our lives. It is the force that keeps us on the ground, meaning it is also the force that pulls objects or a person down onto scales according to their mass. Gravity and weight are closely related. Weight makes life difficult for us in many everyday situations. We have all wished something was lighter, for example when you have to carry a large purchase home with you or take a new refrigerator up to your third-floor apartment.

Lightweight Construction Has Many Advantages
The same applies to industrial applications. Lightweight construction is becoming increasingly important these days in practically all industries because of the advantages it brings. The aim of lightweight construction is to save as many resources, materials, energy, emissions, and costs as possible during the production, use, and recovery of a product. Plastics are a particularly interesting material in this field, because they have a low density in comparison with other materials. For example, polyethylene is lighter than water with a maximum weight of 0.96 grams per cubic centimeter, and it can float.

Lightweight construction is particularly in demand for moving masses, such as cars or airplanes, because it can reduce operating costs and emissions. Wind turbines are another good example. “These turbines are getting bigger and bigger – and so are the masses being moved,” explains Dr. Axel Höfter, Director Corporate R&D at Röchling Industrial. The rotors have spans of up to 130 meters – and it is not only during the construction of turbines that dimensions like these present a huge challenge. “The lighter, the better,” or so you would think. But the rotor blades also need to be able to withstand wind speeds of up to 90 kilometers per hour and top blade speeds of up to 300 kilometers per hour.

Where Does Gravity Come from?

The source of gravity is hidden deep within the Earth. On the approach the Earth’s outer core, approximately 3,000 kilometers beneath the Earth’s crust and mantel, temperatures reach 4,000 degrees Celsius and the pressure is 1.3 million times higher than the atmospheric pressure on the Earth’s surface. The Earth’s outer core primarily consists of molten iron. Embedded within this liquid is an even hotter and even more pressurized ball of solid iron and nickel – the Earth’s inner core. Even though it is relatively small, it accounts for one third of the Earth’s mass of six trillion metric tons. This makes the Earth heavy enough and the force of attraction powerful enough to hold onto the most essential thing in life: the air that we breathe. The Earth’s atmosphere, a perfect blend of nitrogen, oxygen, CO2, water vapor, and noble gases, surrounds our planet like a protective blanket and keeps it warm. The “miracle of Earth” therefore relies heavily on its inner workings.

“We constantly need to consider the relationship between weight and strength during our developments,” says Höfter. This means that the rotor blades need to be both light and stable. This is why Röchling Industrial developed pultruded profiles for the spar caps, which are used as stabilizing elements inside the rotor blades and absorb extreme tensile forces. They are made of carbon (CFRP) or glass fiber (GFRP) reinforced Durostone®. The profiles reduce the bending of the rotor blades under a high wind load and contribute to the safe operation and high performance of the turbines.

There are other examples on a slightly smaller scale. Röchling has developed Polystone® P CubX®, a twin-wall sheet with a unique inner cube structure, for tank construction. It has a low density and combines the resulting low weight with excellent rigidity. “Tank manufacturers can save a lot of time and resources during production with CubX®. This product is unique on the market,” emphasizes Jens Korte from the Corporate R&D department at Röchling Industrial. The sheets and finished tanks are also significantly easier to handle due to the low weight. Generally, cuboid tanks that are constructed using conventional solid-plastic boards have to be laboriously reinforced with steel. Depending on their size, tanks produced from Polystone® P CubX® require no or only minimal steel reinforcement.

The Balancing Act Between Lightweight and Stability
Röchling Industrial has also mastered the balancing act between lightweight and stability when it comes to vehicle bodies, for example horseboxes or flight cases (see the report on page 26). Foamlite® is an entire product line characterized by its lightweight construction. The foamed sheet has a weight advantage of 30 percent over a compact sheet with the same dimensions. At 0.6 grams per cubic centimeter, the product is significantly lighter than fully compressed polyethylene or polypropylene. The sheet is also easy to process using wood processing tools, has high mechanical stability, a long service life, a high-quality surface, and good insulation properties.

This list shows how much Röchling can achieve with just one material. Ultimately, it’s all about finding the ideal compromise between the material properties. For example, if a plastic needs to be able to slide easily, you can reduce its coefficient of friction by adding oil to the plastic formulation. However, this also automatically decreases the strength of the material. Adjusting other elements will also influence other parameters. “Our experts determine the specific requirements together with the customers. We know the precise limits of what is feasible and advise accordingly,” says Höfter. In doing so, Röchling Industrial can draw on its profound specialist knowledge, vast industrial expertise, and wide range of materials – which includes composite materials and thermoplastics as well as material combinations.

Intelligent Material Combinations
The Automotive division also relies on intelligent material combinations, including composite plastics and thermoplastics, fiber composites and metals. The products and solutions from Röchling Automotive stand out for many reasons, including for their acoustic and aerodynamic properties. The main benefit of using plastic, which is an inherently lightweight material, is the lower weight, which in turn means lower fuel consumption and lower emissions. Automotive manufacturers and their suppliers are not getting around this issue any more.

Röchling Automotive has developed a truly lightweight material with Stratura® Hybrid. The material combines acoustically effective and thermally insulating glass fiber lightweight reinforced thermoplastics (LWRT) created using pressing technology and aluminum layers. This innovative approach achieves the same qualities as body sheet in terms of rigidity and strength and reduces the weight of the vehicle floor by 50 percent or more due to the integration of acoustic properties. One application area of Stratura® Hybrid is the Integrated Sandwich Floor (ISF), a multilayer, integrated floor that replaces the conventional car body floor. By varying the material thickness, the automotive developer can specifically influence the strength values, the acoustics and the thermal insulation properties. “Stratura® Hybrid enables us to produce highly rigid, extremely light and acoustically effective components,” explains Markus Sattel, Head of Product Line Structural Lightweight.

Stratura® Hybrid is also a beneficial material for electric vehicles. The material is perfect for protecting battery systems in the event of a crash as the material demonstrates a high degree of elasticity and a large elongation at break. Stratura® Hybrid is replacing metal housing in this area, which is reducing costs and weight.

What Falls Faster – a Hammer or a Feather?

Does an object with a higher weight, such as a hammer, hit the ground faster than an object with a lower weight, such as a feather? Italian universal scholar Galileo Galilei (1564–1642) spent a lot of time pondering this question. He is said to have performed free fall experiments from the Leaning Tower of Pisa to test whether the weight or density of an object determines how fast it falls to Earth.

The question of fall velocity cannot be answered without first clarifying the difference between mass and weight. The mass of an object is the same everywhere – it stays the same on Earth, on the Moon and everywhere in the entire universe. Weight, on the other hand, depends on the force of attraction that is acting on the object. An object with a mass of 120 kilograms weighs 120 kilograms on Earth. On the Moon, the same object would weigh just 20 kilograms, because the force of attraction on the Moon is only a sixth of that on Earth. In space, the object is weightless because there is no force of attraction acting on it. However, the object still has a mass of 120 kilograms.

The speed at which an object falls depends on the force that is acting on it and that accelerates it. On Earth, this acceleration factor is 9.81 meters per second squared on average. Fall velocity can be calculated using the acceleration factor and the fall time or the drop height – without taking air resistance into account. Mass or weight play no role in this equation. This means that hammers and feathers fall at the same speed. The astronaut Dave Scott visually demonstrated this as part of the Apollo 15 mission on the Moon. He dropped a feather and a hammer on the Moon, where there is no atmosphere and therefore no air resistance. Both landed on the ground at the same time. Therefore the only reason a feather falls much slower than a hammer on Earth is air resistance. Air density, volume, and thermal lift also play a role here. However, if you put the feather in a small box and the hammer in an identically shaped box, both boxes would have the same fall velocity, even on Earth.

Targeted Component Reinforcement Using Tapes
Röchling Automotive has very recently developed plastic solutions for structural components in cars that are reinforced with tapes. These tapes are made of polypropylenes or polyamide in combination with glass, carbon or aramid continuous fibers. “They enable us to precisely reinforce a component with minimal material usage. This not only results in cost savings, but also reduces the weight when compared with conventional reinforcement structures,” says Dirk Montan, Head of Advanced Development Aerodynamics & New Mobility.

Whether it is a cooling system, an air conditioning duct, an air intake line or underbody cladding – Röchling Automotive has been impressing its customers with a wide range of weight-reducing components and ­applications for many years. And we can expect much more from the experts in automotive plastics in terms of lightweight construction in the future.


Christiane Müller

Freelance Journalist

Phone: +49 40 32 03 95 35

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