Sustainable Lifecycle of Perforated Metal Materials

In an era of rapidly growing consumer demand and the subsequent development of production, light materials and structures with a wide range of applications are becoming increasingly important in the field of construction and mechanical engineering, including aerospace engineering. At the same time, one of the trends is the use of perforated metal materials (PMMs). They are used as finishing, decorative and structural building materials. The main feature of PMMs is the presence of through holes of a given shape and size, which makes it possible to have low specific gravity; however, their tensile strength and rigidity can vary widely depending on the source material. In addition, PMMs have several properties that cannot be achieved with solid materials; for example, they can provide considerable noise reduction and partial light absorption, significantly reducing the weight of structures. They are also used for damping dynamic forces, filtering liquids and gases and shielding electromagnetic fields. For the perforation of strips and sheets, cold stamping methods are usually used, carried out on stamping presses, particularly using wide-tape production lines. Other methods of manufacturing PMMs are rapidly developing, for example, using liquid and laser cutting. An urgent but relatively new and little-studied problem is the recycling and further efficient use of PMMs, primarily such materials as stainless and high-strength steels, titanium, and aluminum alloys. The life cycle of PMMs can be prolonged because they can be repurposed for various applications such as constructing new buildings, designing elements, and producing additional products, making them more environmentally friendly. This work aimed to overview sustainable ways of PMM recycling, use or reuse, proposing different ecological methods and applications considering the types and properties of PMM technological waste. Moreover, the review is accompanied by graphical illustrations of real examples. PMM waste recycling methods that can prolong their lifecycle include construction technologies, powder metallurgy, permeable structures, etc. Several new technologies have been proposed and described for the sustainable application of products and structures based on perforated steel strips and profiles obtained from waste products during stamping. With more developers aiming for sustainability and buildings achieving higher levels of environmental performance, PMM provides significant environmental and aesthetic advantages.

1. Introduction

Worldwide annual resource use reached almost 90 billion metric tones in 2017 and could more than double by 2050 [1]. By 2030, European Raw Materials Alliance (ERMA) activities will increase the production of raw and advanced materials and address the circular economy by encouraging the recovered processing of essential raw materials [2]. In an era of rapidly growing consumer demand and the subsequent development of production, lightweight materials and structures with a wide range of applications are becoming increasingly important in the field of construction and mechanical engineering. Unfortunately, metal recycling tends to be at a low level globally. In 2010, the International Resource Group, hosted by the United Nations Environment Programme, issued reports on the metal stocks that exist in society and their recycling rates [3].

Perforated metal is a valuable source of secondary raw materials to be processed in metallurgical enterprises. The secondary use of perforated metal makes the process less expensive than conventional remelting methods, as well as significantly reducing emissions of harmful substances into the atmosphere and making it more sustainable as well as prolonging the lifecycle. There is an urgent need to change how we use non-renewable resources, especially metals, to maintain their sustainable availability and minimize the negative impacts associated with their production and use [4].

Products made of ferrous and non-ferrous metals or alloys are a valuable source of secondary raw materials to be processed in metallurgical enterprises. The use of scrap metal makes it possible to make the technological process of smelting metals less energy-intensive compared to obtaining products from ore and significantly reduces emissions of harmful substances into the atmosphere. Metals also can be returned to the production process without impairment. The steel sector will indeed be a key contributor to Europe achieving its 2050 targets. Thanks to their unique properties, ferrous and non-ferrous metals can be recycled indefinitely. The strong recycling performance is widely recognized and long-lasting. Moreover, the industry’s business model is circular by nature as the input of steel scrap is a necessary component for making new steel at any one of more than 500 steel plants in Europe. The more quality scrap that can be used in new steel production, the less raw materials and energy are needed and in turn, this reduces emissions. Steel, for instance, is circular by nature, because it is recycled repeatedly without loss of quality. Currently, of all steel packaging put on the market in Europe, 84% is being recycled into new steel products [5].

Solid waste generation is increasing in the world today. Zero-waste strategy is a smart solution to minimizing the increasing solid waste. To keep to a minimum solid waste, even more work is needed in the long run [6]. Reducing the resource intensity of products and emissions into the environment and improving their socio-economic performance throughout the life cycle of a material or product is an important task. Its solution can significantly facilitate the links between economic, social, and environmental aspects along the entire value chain of a product. At every stage of the life cycle, there is potential to reduce resource consumption and increase productivity.

Metals can be recycled back into the manufacturing process without compromising the quality of the subsequent product. In fact, recycling represents an advantage because it takes less energy to melt the metal. The recycling quota for scrap metal sent for recycling is 90% [7].

Modern architecture uses building materials in new and innovative ways. The fascination comes from the materials themselves and how they are processed and used. The emphasis is not so much on the material to be matched to the building, but on the effect of the particular materials created for the building with their material and visual qualities [5].

One of the trends in the manufacture of products and structures is the use of perforated metal materials (PMMs). These are used as finishing, decorative and structural building materials [8]. The growing interest is due to the fact that they significantly reduce the weight of the structure [9]. In addition, PMMs have a number of properties that cannot be achieved with solid materials; for example, they provide significant noise reduction [10], and light scattering [11]. They can also be used for damping dynamic force [12], filtering liquids and gases [13], and shielding electromagnetic fields [14]. PMMs are the simplest in terms of structure and implementation. They seem to be one of the most promising for wide production and application. The main feature of PMMs is the presence of through holes of a given shape and size. PMMs have low specific gravity, but their tensile strength and rigidity can vary widely depending on the source material [12]. This allows them to find a stable application, in particular in construction ( ).

There are many examples of the effective use of PMMs in the creation of enclosing structures for buildings and mechanical structures [15], for the manufacture of facades and decorative elements, as well as in the production of fittings for pipes and panels. PMMs are increasingly used in various interior solutions for premises and urban architecture [16,17].

In addition, PMMs have become popular and common materials for construction and installation works. Perforated steel strip components are widely used to connect and reinforce individual parts of building structures [16,17]. Most often, these are joints of load-bearing and enclosing structures made of drywall, as well as wood and concrete. In mechanical engineering, PMM products have found application in the manufacture of filters [18,19], separator assemblies, dryers, and other equipment [20] ( ).

For the perforation of strips and sheets, the cold stamping method is usually used, which is implemented on stamping presses, as well as by using broad tape production lines [21]. Other methods for the production of PMMs are rapidly developing, for example, using liquid [22,23] and laser cutting [24]. The volumes of production and use of thin-sheet stamping products in the world are constantly growing and the biggest sector is the expanding automotive market ( ) [25].

The most common PMMs are steel, aluminum and copper. The main feature of PMM is the presence of through holes of a given shape and size ( ).

In practice, the following physical and mechanical properties of PMMs are of the greatest interest: density, strength, ductility, weldability, corrosion resistance, hardness and microhardness and surface roughness [26,27]. When choosing materials for further use, an important point is the deformation state and the presence of corrosion phenomena. This is especially important when they are used in aggressive environments, such as marine, space, or aviation [28,29]. Experiments have shown that the tensile strength of steel perforated bands achieved as waste after punching is in the range of 100–250 MPa according to the type of perforation, width and thickness of the band and base material [30]. The percentage of perforation (%) of perforated bands, achieved after punching, varied from 66% to 76% when the thickness is in the range of 1.00 to 1.75 mm [30]. Studies have also shown that when perforations are made in the boundary layers, an increase in the microhardness of the material is observed and cracks may form. In particular, for steel, when stamping in the area of a punched hole (0.2–0.3 mm from the edge), the microhardness values almost doubled, but at a distance of 0.7–0.9 mm, it already reached the usual values for this material [31].

Punching or cutting perforation openings directly affects the mechanical and physical properties of the perforated metallic material. In many cases, the perforation process causes an increase in the surface hardness of the material, or forging [32]. During piercing or cutting, plastic deformation of the material occurs. Its degree on the edges of the perforation holes is very large and the grains of the metal microstructure are stretched in the direction of the applied load; therefore, their boundary surface can be invisible. In the process of forging the material, the specific volume of the metal increases and the density decreases, the ultimate strength, microhardness and brittleness increase while the plasticity and viscosity decrease. The stress concentration around the perforation opening increases. Even changes in the magnetic properties of the material are possible. Gradually moving away from the edges of the openings, the degree of metal deformation decreases. For high carbon steels, the zone of obvious deformation may be 0.3 to 0.4 mm from the edge of the perforation slots.