Technological innovations for green production: The Green Foundry case study

Technological innovations aim to improve manufacturing processes. In recent times, ever ‐ increasing attention to economic, social and above all, environmental sustainability, suggests that technological innovations are techniques not only for reducing costs but also for improving company sustainability. This includes the foundry industry, which is presented with the need for technological changes that improve processes but also satisfy environmental and climate regulations. This case study attempts to analyse the technological changes necessary not only to optimise production processes but also to make them more sustainable. Starting from the introduction of a new production process that aims to reduce environmental impact, the necessary plant changes are analysed. These changes concern various areas: the introduction of new machinery, lean techniques for inventory management and management modes of production waste material. The paper analyses these changes and demonstrates the need to act in several areas to make a production process that is sustainable from an economic, social and environmental point of view.


| INTRODUCTION
The concepts of lean production and green production have been studied separately as ways to overcome problems in the production process [1]. On one side, the lean concept is known as a manufacturing solution for achieving maximum added value through the identification and elimination of losses ( [2,3]). On the other side, the green concept answers the demands and necessity of industry to create environmentally friendly manufacturing processes that follow both ecological and social perspectives and not just economic profit [3,4]. Thus, integrating these two concepts is a necessity for developing sustainable production processes: improving productivity increases economic benefit [5], while focussing on the triple bottom line (people-profit-planet) improves sustainability ( [6][7][8]).
Many lean techniques (kaizen, 5S, JIT, visual management, VSM, andon, gemba, TPM, Takt time, SMED, SCM, cellular layout) ( [2,3]) reduce losses, thus increasing a manufacturing system's productivity and quality [9]. Green practices create a sustainable manufacturing system due to the development of processes along ecological, social and economic dimensions [10,11]. Because ecology and economy are attributed to 'reduce-reuse-recycle' [12], they have a relationship with lean ( [13][14][15]). The social aspect of green is related to workplace safety [16]. Lean and green concepts can be applied in several stages along the supply chain and involve design, production, suppliers and customers [17,18].
The potential of integrating lean management concepts and sustainable logistics practices along with Industry 4.0 technologies to enhance the operational performance of business functions in the logistics industry was discussed in [19]. They proposed a conceptual framework to illustrate how lean and green concepts can be integrated in the logistics industry.
Lean and green concepts have also been introduced in the foundry industry. The environmental impact of the foundry industry is significative: high gas emissions and waste generation make the foundry one of the most environmentally polluting types of production. Therefore, within the foundry sector especially, continuous research is needed on technologies that guarantee compliance with both technological and environmental parameters. In [20], there is a preliminary study of lean and green concepts in the foundry sector. Through a survey [21], the use of lean manufacturing tools was investigated in 300 Polish foundries: only 29% of the foundries had implemented any of the lean tools. Some difficulties of implementing improvements in foundries are overcome by modifying the industrial layout and balancing the workload [22]. Pouring time [22], WIP inventories, and production time [23] are reduced, and safety and productivity are improved, using lean tools and techniques [23]. The low percentage of adoption in the Polish case indicates that lean techniques are more difficult to implement in the foundry sector, and the need to have more environmentally friendly processes often predominates. The need to prevent pollution, which in the case of foundries concerns the potential contamination of soil, air and water, is obviously preferable to having to resolve its consequences [24]. In this context, the foundry sector has been working on production processes and management procedures to reduce resource use and the generation of residues and toxic substances as it moves towards cleaner production.
The paper aims to investigate how changes in production processes that focus on a green perspective force the introduction of technological innovations and necessary changes in operations management. In other words, the paper highlights the technological innovations and plant modifications that are necessary to introduce green processes. The study aims to be a useful tool for foundry operators in terms of the technological innovations that make production processes more environmentally sustainable. The paper is an opening discussion of the implications and solutions for production processes in the foundry sector following the introduction of less-polluting technologies, as no existing literature has analysed the problem from a production management point of view.
It is known that Industry 4.0 technologies are being implemented within the foundry sector-in particular, big data analytics and machine learning technologies offer new opportunities ( [25,26]).
The remainder of the paper is organised as follows: Section 2 is dedicated to describing the methodology. In Section 3, a case study is presented, while in Section 4, process changes and other steps are discussed. Section 5 provides conclusions.

| METHODOLOGY
Attention to green production processes involves changes in the production system. Several aspects could vary for a company moving towards green production. These research questions are posed by this work: � What changes are necessary to achieve an environmentally sustainable production process? � How do technological innovations support green production?
It is necessary to start from the analysis of the production system to identify the areas where it is possible to make processes environmentally sustainable by introducing green innovation. Subsequently, the consequences generated on the entire production system must be analysed. In this way, it is possible to identify technological innovations that can support the production system in its passage towards greener production.
The research approach (see Figure 1) is therefore based on an analysis to first understand the manufacturing processes. The second step consists of the detection of green innovation, and finally there is an analysis of technological innovations that are useful in introducing more environmentally sustainable processes. These analyses and evaluations were made by the authors in collaboration with the company plant manager.
The methodological approach is qualitative. Through a case study, we wish to highlight the changes that the move towards green production makes on production processes and on the entire industrial system. To make a process more environmentally sustainable, it is also necessary to introduce changes and technological innovations to support green innovation.
The quantitative aspect is not investigated here. There are interesting studies in the literature on the analysis of environmental performance. For example, [24] measured the environmental impact generated by all businesses in the foundry sector through the development of an environmental performance analysis index.
The research is applied to an Italian foundry, supported by a European project-the Green Foundry LIFE project (LIFE17 ENV/FI/000,173) introduces novel technologies for sand-moulding systems to cut emissions, improve indoor air quality and support the circular economy through the reuse of foundry sand that is normally disposed in landfills.

| CASE STUDY
To answer the research questions, a foundry that produces automotive parts such as turbine housings (2.5 million items/ year), bearing housings (3.2 million items/year) and manifolds (1 million/year) is analysed. Figure 2 shows the foundry plant layout. In the analysis, three foundry areas (see Figure 3 for their schematisation) are considered because they allow for greater possibility of intervention to improve industrial processes: 1. core shop department: the area for core production; 2. moulding department: the area for mould preparation and for all operations before casting; 3. melting department: the area for the melting and treatment of metal.
The cores, elements used to create internal cavities where melted metal does not penetrate for a functional reasons of the piece or to reduce its overall weight, are produced in the core shop. Core production must minimise the formation of burrs and satisfy certain other requirements that vary with the casting technique. After solidification of the metal, the jet is extracted and the core removed by dirt [27]. Figure 4 shows one of the core production lines. There are three silos, each containing a different type of sand (synthetic, French and national) sent in mixture to the core blowing machine. The sand is mixed for between 1 and 2 min with a two-component binder: a phenol formaldehyde resin and a poly-isocyanate. Then the mixture enters the core blowing machine to produce the cores. The line in Figure 4 consists of three core blowing machines-even if they share the same feeding duct for the sand, each machine has an independent mixer to produce different types of cores.
Once produced, the cores are stored in a warehouse and wait to be used in the moulding department (see Figure 5 for its operation), where the moulds to produce pieces are assembled, and the cores are manually inserted by an operator.
Finally, the mould is sent to the melting department.

| 'Green' innovation
The proper mechanical resistance of the cores is ensured by binders: chemical mixtures with a content from 1% to 3% (the remaining 97%-99% is sand) that adhere to the grains. The traditional binders used for the cores emit up to 70% volatile foundry compounds (volatile organic compounds) [28] that originate from their combustion in sand moulds after coming in contact with liquid metal at temperatures over 1200°C. Also, the binder residuals in the surplus foundry sand disposed in landfills cause some greenhouse gases in ambient air. In recent years, the foundry industry has seen environmental standards become increasingly restrictive [29,30]: the goal is to replace organic binders with low-emission binders that guarantee comparable physical and mechanical properties at high temperatures and reduce some technological problems such as poor knocking out, elasticity and reclaimability [28].
Inotec™ by ASK Chemicals, Cordis by Hüttenes-Albertus, GEOPOL® by Sand Team CZ and the inorganic system developed within the Gietech-Go project are the new inorganic binders already in commercial use or in trial phases in aluminium foundries.
The Inotec system, mainly used in aluminium foundries but with some trials made in ferrous foundries, consists of a binder (i.e. alkali silicate, a modified blend of water glass) and a 100% inorganic promoter (minerals and synthetic raw materials). Curing in the Inotec binder system is done by heating at a temperature of about 170°C-175°C. Recycling of sand must be made by thermal reclamation.
The Cordis system is essentially like Inotec, but it is still in a trial phase. The Cordis binder (modified alkali silicate solution) and Anorgit additive (synthetic, inorganic additives) are the two components of the Cordis binder. The curing takes place at a temperature of 130°C-200°C. A water-based coating is necessary for ferrous castings, but drying occurs instantly after painting; otherwise, humidity destroys the strength. The Cordis system is used in about all foundries, especially ferrous foundries that serve the automotive industry.
The use of Cordis and Inotec binders is analysed in the case study supported by the Green Foundry LIFE project. The improvement of the environmental and economic impact of the ferrous foundry is the main objective of the analysis. The use of new inorganic binders reduces hazardous air emissions, casting fumes and fine particles like binder aerosols, thereby improving indoor air quality. [31] describes some benefits of using inorganic binders in the foundry.

| Necessary changes
To obtain more environmentally sustainable production, inorganic binders can be introduced. But their use influences the production process to be implemented.
Many foundries, including the analysed foundry, use the cold box method to form the cores. The cold box process, also known as the Ashland process, was tested in the United States in 1965 and appeared in Europe in 1968. The process allows the production of cores in a few seconds, ready for immediate use, without using heat.

SAETTA AND CALDARELLI
The traditional process (cold box) undergoes changes if new inorganic binders are introduced-the core blowing machines currently used for the cores must be modified, or it becomes necessary to purchase new machines suitable for the new process.
Cores obtained with inorganic binders are hygroscopic; that is, they are prone to water absorption that causes their rapid deterioration. To solve the problem of hygroscopicity of the cores, several measures concerning their storage are possible.
Another problem linked to the introduction of the inorganic binder is that it does not burn in contact with the casting metal, remaining entirely attached to the sand used to create the mould. So the inorganic binder must be recirculated together with the sand using a land recirculation plant. Figure 6 shows the necessary plant and process modifications for the introduction of inorganic binders.
Therefore, as discussed earlier and shown in Figure 6, the areas where process changes are necessary to allow the use of inorganic binders concern the moulding process, the recirculation process of waste sand and a series of possible interventions that account for the hygroscopicity of the new cores. In this way, thanks to a technological innovation and to leaner production, it is possible to insert a green production process in the foundry. Lean production combined with technological innovations also allows a green process with a lower emission of pollutants.

| DISCUSSION
In this section we want to discuss in detail the changes in the production processes and the plant that should be introduced following the choice to use inorganic binders.
The first innovation necessary for the production of inorganic cores is core blowing machine modifications within the core shop. It is possible to purchase a new machine specifically designed for use with inorganic processes or to reconvert and modify existing machines used for the cold box process. The process with inorganic binders requires a special F I G U R E 6 Necessary changes and technological innovations in the production processes SAETTA AND CALDARELLI mixer that makes it possible to combine sand, liquid binder and additive. The mixer must be discontinuous and closed to minimise the evaporation of the binder during the formation of the mixture. The metal core boxes must be heated to 150°C -200°C, and a core drying system with hot air at about 200°C is necessary in order to speed up the hardening process directly in the core box. The needed changes for the core blowing machines are the following: � Some components of the machine must be cooled. � The sand loading hopper must be closed. � A hopper cooling system must be present. � A core box heating system is required. � A hot air generator must be provided for drying the cores.
To evaluate the best choice between purchase and modification, an economic evaluation takes place. Modification of the core box is a common cost item both for the purchase of new machines and for the modification of machines already in use. The core boxes are the containers within which the cores are created. They are not independent of the type of machine used, and it is necessary to modify them when changing from a cold box to hot box process. Considering all the costs, the percentage increase in costs to buy a new machine compared with the costs to modify an existing one is about 66% (105,000 € to purchase a new machine, 63,000 € to make changes to the current machine).
To solve the problem of hygroscopicity of the inorganic cores and at the same time optimise the cast-iron production line in the plant, it was decided to reset production according to the just-in-time (JIT) approach. Because inorganic cores require an extremely short storage time in order to preserve their mechanical characteristics, we would like to proceed by innovating the production line to make it more efficient. The core shop has a slower production rate than the moulding department, with respectively 20 pieces/h for each core blowing machine and 140 pieces/h for the moulding line. For this reason, the storage of cores in a large warehouse (about 6000 m 3 ) is necessary with an average storage time of one week. This long storage time is induced by some constraints in the production of cores: 1. setup time of 2 h for each core blowing machine; 2. core box cost: the high cost of the core box involves the difficulty of producing the same product in parallel on separate core blowing machines (a large production involves multiple moulds).
The first analysis of the production processes highlights the possibility of intervening in warehouse management: the long storage time and the large size of the warehouse are critical situations on which to operate to make production leaner. A simulation model is developed to simulate the core production line to obtain a leaner warehouse with fewer pieces and with storage time reduced to 8 h [32]. The introduction of a JIT policy in the production system leads the system towards leaner production. This makes it possible to insert inorganic binders that make production green. Thus, the concepts of lean and green are closely connected.
Another possible solution to possibly counteract the tendency of inorganic cores to absorb humidity is conditioning the core storage warehouse by controlling the temperature and relative humidity. In particular, it is assumed that relative humidity is kept constant in a range of 30% to 50%, while the temperature is in a range between 17°C and 23°C. As the environment to be air-conditioned has large dimensions (6000 m 3 ), and the hygrometric conditions must be kept uniform, the air-conditioning system is of the 'full air' type. The air is sent to the environment through a distribution system consisting of a network of delivery channels and the relative input terminals, vents, haemostats or linear diffusers. By designing the air-conditioning system, the necessary power of 720 kW is obtained with an initial investment cost of 263,000 €.
In any case, air-conditioning of the warehouse presents a critical aspect-difficulty in keeping the climatic conditions of the warehouse fixed due to the frequent opening and closing of the doors to allow for storage and removal of the cores.
The hypothesis of storing cores in containers with excellent characteristics as regards insulation from the outside, water and humidity is analysed. The material chosen is expanded polypropylene that, being an apolar polymer, exhibits excellent thermal insulating properties, with low thermal conductivity and high mechanical strength that make it possible to protect the cores from possible impacts. Furthermore, this material is totally recyclable. The most important advantage of this solution lies in the possibility of minimising the humidity absorbed by the core without the need to condition the warehouse and therefore without any energy consumption due to storage. The main disadvantages is imposing a further operation on the production cycle for storage, which does not increase the value of the product and entails an increase in the volume needed within the warehouse. Especially for high production volumes, the solution appears to be not very functional, although highly effective in terms of maintaining the correct mechanical and resistance properties. The solution of the insulating boxes is the most economical solution, even if it is difficult to make a precise calculation of the costs. However, due to the large production volumes of the company and its several types of cores, the use of different containers is a solution that is difficult to implement. Storage boxes are a solution only for small orders where the company's priority is represented by the quality and maintenance of the optimal conditions of the cores.
The mixture of exhausted sand is made up of green sand of which the mould is composed, silica sand and the binders necessary for the cores. The sand can be regenerated to be reused in a subsequent production cycle. For mixed sands, recovery and regeneration are more difficult and less controllable than in the case where the sands are monotype. In addition, a further difficulty in the regeneration process is caused by the presence of the inorganic binders because they are less subject to thermal degradation. For the steel castings, in which the casting takes place in shell and the same sand is used both in the mould and in the cores, it is possible to regenerate the monotype sand with inorganic binder. Plants are 90 -SAETTA AND CALDARELLI already in use with excellent results that successfully reuse almost all the sand. The green sand regeneration process, on the other hand, is still in the initial phase, and it is not yet known how, with the increase in the regeneration cycles, the chemical characteristics of the inorganic binder affects the green sand. In this regard, there are no known layouts of plants for the regeneration of the sand for cast iron foundries. Within the Green Foundry LIFE project, an analysis of the sands coming from the casting tests was started to understand how green sand is modified by the presence of sodium silicates (inorganic binders). The current state of regeneration technology is therefore in the initial state of study: it will be necessary to analyse the technical characteristics that the plant will have to provide and then, through pilot plants, to test the actual operation after several repetitions of the recirculation cycle. Currently the problem of managing waste sand certainly represents the greatest obstacle to the diffusion of this technology for use in large series productions. Instead, it is possible to use inorganic binders for small productions, as sand mixtures will be in much lower percentages than mixtures composed of green sand and organic binders, so the effect of inorganic binders on the characteristics of the sands is negligible.

| CONCLUSIONS
The paper aims to investigate how changes in production processes towards a green perspective force the introduction of technological innovations and changes in operations management.
A case study in the foundry industry is presented, analysing the introduction of green technological innovations, in particular the use of inorganic binders in core production. The new binders cause different chemical behaviours from those of the standard process, affecting all of the production line. In fact, to guarantee the quality of the pieces obtained through the introduced technological innovation, action must be taken on the entire process. The paper analysed various interventions to be carried out to allow the use of inorganic binders. Among these interventions, the introduction of lean warehouse management is the most interesting solution. This solution, in fact, includes both sustainable logistics practices and lean management concepts, and it requires the use of Industry 4.0 technologies such as big data analytics and simulation.
All proposed changes will require further evaluation from both environmental and economic points of view. In fact, the study aims to be a useful tool for operators in the foundry sector by providing interesting plant and technological solutions. The necessary economic evaluation that follows will enrich this first part of the work.