Facilities/Equipment for Surface Treatment in the Surface Technology Processing Chain

Wet chemical processes are widely used in surface treatment of materials, particularly metallic materials and metallization of plastics. Today, semi-automatic or fully automatic systems are used for this purpose. Depending on the type of parts to be processed, working bath volumes vary from several liters to several hundred cubic meters. In wet-chemical processing sequences, active process stages are generally supported by intermediate rinsing steps. With a view to environmental protection, the collection of waste materials produced or recovery of process water, often returned to the processing sequence, as well as multiple rinsing and various processes are now standard. Active process steps consist of cleaning, activation of surfaces to be processed, and coating and conversion processes (transformation of surface layers, for example oxides), and post-process technologies, where almost exclusively water-based solutions are used. These are heated to elevated temperatures between approximately 30°C and approximately 100°C. However, in order to limit energy costs, efforts are always made to achieve lower temperatures.

In wet-chemical surface treatment, circulation and filtration of electrolytes and aqueous solutions are very important. Circulation ensures that all volumes used have uniform temperature, as well as equal concentration of active substances in the solution on the surface of parts to be processed.

This is particularly important for metal-containing electrolytes and is also very important in the activation of surfaces of completely chemical environments such as cleaning agents or acids / alkalis. Additionally, in connection with filtration, circulation removes foreign matter (dust, particles) or degradation products (filtration with activated carbon treatment) from the solution, thereby preventing it from settling, for example, on a metal layer to be deposited. As a result, facilities are equipped with numerous pump-filter systems. In extreme cases, some systems where each active station and rinsing stages are performed are equipped with their own filtration pump unit. Other important components are power sources. These are also required for all galvanic electrolytes to electrically reduce metal ions in the solution or to provide electrical charge feed for the oxidation of oxygen in the formation of anodic oxide layers (anodizing). These, systems working with wet-chemical, are structured essentially as lines consisting of containers with various active solutions and required intermediate rinsing processes. Using fully automatic or semi-automatic conveying systems, parts to be processed are either fixed on suspension or loaded onto drums and passed through individual processing steps - for bath volumes smaller than 100 liters and low part weights, transport is performed entirely manually. For material transport, conveyor robots are mounted above the baths and they also lower and raise the suspension at individual positions. The number of robots per system depends on the processing times in individual process stages - these can vary from several seconds to several days.

All facility components from the conveyor equipment's power, heating, cooling, filtration or circulation and process control for part movement in the baths are controlled by complex and highly efficient control software.

This control includes direct operating parameters such as temperature, current and voltage, circulation in electrolytes, extraction capacity, processing times, and lowering and raising speeds. Beyond this, information about the amount of energy consumed for individual processes or facility components now also plays an important role. As a result, production data is transferred to ERP systems or ERP systems have direct access to a facility's production data, or production simulations are performed to simulate the effects of fluctuations in production or changes in batch size. As a result of the high degree of automation in modern facilities, ongoing operations can be maintained with low human intervention. On the other hand, labor input for loading and unloading components from coating units is very extensive. With regard to occupational safety and environmental protection, wet chemical facilities have extensive air extraction from active stations. They exhaust vapors that may contain aerosols (for positions with higher operating temperatures) and also hydrogen gas - the latter is flammable with electrical sparks. Extracted / removed air is cleaned very efficiently and is generally discharged to the environment. As part of energy conservation efforts, heat is also removed from the air and used for heating processes or building heating. Particularly exhaust air systems contribute to the fact that modern wet chemical coating systems are very energy efficient and environmentally friendly. A brief overview of the structure and functions of a wet-chemical surface treatment facility clearly demonstrates that the facility design and layout depend significantly on the relevant combination of a processing sequence or the composition of the mixture of parts to be processed. The resulting facilities are extremely individual and each is newly designed. In addition, facilities are also extended with water treatment systems (fresh water and wastewater) or to test processing quality.

Industry 4.0

The term Industry 4.0 describes progressive networking / communication of people and machines via the internet. History shows several industrial revolutions that have already caused major changes in the business world: Mechanization with the steam engine, mass production achieved through assembly line work, and the use of micro-electronics to automate production processes. This is exactly what is expected from this networking and digitalization - in other words, a fourth industrial revolution is expected here. However, what is actually relevant for companies is what is hidden behind these terms. In the surface treatment industry there are many starting points for networking. Here, customer use typically takes center stage. Better networking of information can lead to better decision-making based on this information base. Collected information and data can provide unexpected correlations and thus reveal entirely new optimization potentials.

New internet standards provide possibilities that go far beyond the already known EDI (Electronic Data Interchange).

Innovative systems should then be able to map different information gathered from the real world. A modern ERP system forms the central point for this information and data flows in the sector. Serving as an interface for customers and also for systems and production, it offers flexible application options. Data on all process steps and individual items can be collected and evaluated. The objective is to demonstrate, on a data basis, optimization possibilities such as a company's energy consumption can be effectively reduced. Creativity is scarcely limited. Industry 4.0 is currently emerging; during this process, expectations and possibilities change, the spectrum broadens. Through networking within the supply chain, optimizations between companies are also conceivable. However, not only machines, products and data are networked. Customers can be better integrated into production processes and may even participate in processes and monitor them better. Another requirement is to achieve more flexibility in the production process. Individual parts with lot size 1 should also be produced the same way as series parts - meaning processes must be made rapidly adaptable. However, there is no requirement as to which areas of a company should be prioritized for networking. Ultimately, all areas can be made "smart". Where development begins depends on the individual.

Surface Technology ERP Systems

ERP stands for Enterprise Resource Planning. An ERP system is, in brief, an operations management system that can plan, optimize and control all business processes ongoing in a company. These are covered by numerous modules such as order processing, production planning, production control and feedback, quality management, sales, procurement / materials management, finance and accounting, and control. The ERP system integrates modules and thus provides the opportunity to track, network and optimize all processes from quotation to successful delivery at all company levels. This ensures that required information is processed in real-time across all areas - Excel lists or isolated solutions are no longer necessary. As a result, deviations in production can be responded to with immediate reaction as soon as they occur. This also facilitates target / actual comparisons. Since process networking is playing an increasingly important role in the company, modern ERP systems are particularly focused on providing solutions in this area. Individual customization such as the division of power units for facilities according to time or product carriers is an advantage of industry-specific ERP systems. Here, while working process-oriented, product-specific adjustments in the process are simultaneously provided.

Additionally, more specific data such as processing times or energy consumption can be collected and can then be used for optimization. Networking must be guaranteed not only within the company but also with customers and suppliers. Network-connected ERP systems minimize data entry costs on both sides.

For this purpose, orders, work orders, delivery notes, invoices and quality protocols are transferred electronically. This creates transparency for customers and thus they are included in processing via the "extended work station" and are always informed about production progress. This reduces the time required for obtaining information by phone and ensures greater customer loyalty. ERP systems offer the opportunity to focus on technical aspects, collect specific data and support progressive networking processes. Data can be easily transferred to facility controls or integration elements with subsystems. All data is on the same system or connected to it - these centralized access options allow data to be consolidated in the shortest possible time. Modern ERP systems can therefore already manage technical parameters and connections with intelligent subsystems. Thus they can respond to various networking possibilities and support and encourage innovations through software.

Main screen of an ERP system (Source: Softec AG - OMNITEC)

Energy-Saving Drying

Many industrial processes require drying operations. However, drying is only sometimes perceived as an independent process section. Yet high-quality drying processes help reduce energy costs, lower operating costs and increase production efficiency. Modern facility structures require both powerful, protective and energy-efficient processes. A closed system based on heat pumps provides rapid drying at low temperatures. This process, known as condensation drying, allows water collected on surfaces to be used in drying areas for process optimization. Condensation drying based on heat pumps removes excess moisture from the existing room air to an extreme degree. This excessively dry air is passed over or through the drying material and physically absorbs the moisture of the products to be dried very quickly. This achieves very short drying times. However, high-quality moisture removal is only one of two components necessary for successful drying. The second determining factor is ensuring proper air flow within the dryer. The improvement seen in a production line's performance and quality also eliminates unwanted cost and error sources. Condensation drying based on heat pumps saves energy for several reasons. On the one hand, drying air uses the existing waste heat from the condensation drying system, circulating in a closed circuit, free from emissions and without energy losses. Studies have shown that use of such dryers can provide savings of up to 75 percent in carbon dioxide (CO²). On the other hand, depending on application and customer requirements, drying takes place at low temperatures between 20°C and 90°C. This requires significantly less energy than conventional hot air drying systems. These advantages are achieved with special heat exchangers and circulation fans. Low temperatures allow sensitive and gentle drying of products.

Temperature can be adjusted variably depending on parts to be dried, thus preventing unwanted heating. Furthermore, products can be processed immediately after the drying process, which simplifies operational processes and saves time, money and energy.

Special drying technology is used in many industrial manufacturing processes requiring a drying stage; in surface treatment, drying after cleaning or painting operations. Following galvanic enrichment and cleaning operations, operators often encounter poor drying quality, stains and heat-related problems. Through effective processing, staining and unwanted temperature stress can be prevented. Paint drying must naturally take place at low temperatures so that the paint dries uniformly from inside to outside. Craters and cracks are thus avoided. Flexible condensation processing can be used for any type of operation. Drying in a drum with minimum movement is a special process; cast materials need not be centrifuged, as they can be completely dried within the drum with minimal gap movement. This process is also suitable for drying sludge-like industrial waste where the weight and volume of the dewatered substrate is reduced by up to 60 percent. This means savings of up to 60 percent in disposal costs for the user. The reduction in volume reduces transport costs and improves ease of use.

The Water Factor in Industry

Water is considered an indispensable operating and auxiliary material in almost all industrial sectors. This is particularly true of the application of water in surface treatment through wet-chemical treatment, where water serves as the main component in various process solutions and at all times as a rinsing agent in water or mostly in diluted aqueous solutions during intermediate cleaning steps between processes. Beyond this, water is used to an even greater extent as a medium for heat transfer. In most cases, closed circuits are used, but in larger water circuits, for example to prevent troublesome deposits, these must have a certain water quality with regular replenishment. Another common use of water or aqueous solutions is in the area of cooling agents and lubricants for mechanical processing such as grinding, spinning, welding or abrasion as well as mechanical surface treatment, for example vibratory grinding. Here, first of all, adjustment of water quality components, for example to prevent deposits in the form of lime or to prevent microorganism formation, is important. Along with water conservation, comprehensive efforts for efficient and economical use of water as a raw material are supported by various facilities and process technologies. These include equipment such as ion exchangers in various designs, as well as various types of filtration for separation of coarse particles and separation of ionic components.

Counter-current water softening system (Source: EnviroFALK)

Ion Exchanger

Depending on design, ion exchangers produce water at low investment costs with small amounts of mineral components up to the highest quality demineralized water (DI water). Deionized water is obtained from tap water (spring or tap water) by retaining minerals such as salts and ions found in water. Tap water is usually used as raw water. Due to frequent large demand peaks in industrial applications, surface water or well water is often used. Ion exchange technology takes advantage of the fact that substances dissolved in water can be subject to chemical bonding reactions. Tap water contains salts in varying concentrations. These contain metal ions (cations) and an acid residue (anions). Special ion exchange resins are used to eliminate these cations and anions. These are long-chain molecules with side chains containing hydrogen ions or hydroxide ions. These can be separated.

Organic molecules are processed from porous granules (called ion exchange resin) and in principle water can flow through them. In this way they absorb cations dissolved in water (e.g., Ca2+, Mg2+, Na+) and anions (e.g., Cl-, SO4 -, NO3-) and release corresponding amounts of H+ and OH- ions into the water.

As a result of this process engineering ion exchange, completely purified water is obtained, namely nearly pure H2O. Another important advantage of ion exchangers is their easy renewability. By being appropriately charged with acid or alkaline liquid, they are returned to their original state during a regeneration step, meaning new H+ and OH- ions are obtained and in return they release the cations and anions they received / absorbed. These are then available in concentrated form for processing. Depending on the size of the ion exchangers, the regeneration process is carried out by the supplier as a service provider on-site or by the user. The application areas of ion exchangers depend on water composition and the amount of water required. Mixed bed ion exchangers can be used for low to moderate demineralized water demand. For facilities with large demineralized water requirements, separate bed ion exchangers are available. In mixed bed ion exchangers, regeneration of cation exchangers and anion exchangers generally takes place in situ and depending on facility design, automatically. A parameter for measuring demineralized water quality is electrical conductivity expressed in Siemens in cm units (μS / cm). Demineralized water quality requirements can vary greatly. For example, demineralized water is used in many industrial applications. For example; as a heat transfer medium in the cooling circuit of a power plant, in metal cleaning systems, in air humidifiers, in rinsing baths and galvanic baths, or for feeding steam boilers and steam turbines.

Water Softening

Water softening achieved by ion exchange is a process in which cations responsible for water hardness, particularly calcium ions and magnesium ions, are replaced for sodium ions using cation exchange resins. Here a strong acid cation exchanger in sodium form is used. This cation exchanger is loaded with sodium ions and exchanges them for calcium and magnesium ions, the hardening agents. Since during water softening one salt is simply replaced with another salt, this is referred to as a neutral exchanger. Regeneration in the water softening process is reversed. For this purpose, excess sodium ions are supplied to the ion exchanger. A saturated table salt solution obtained, for example, by dissolving table salt tablets for regeneration, is used here. In larger facilities, bagged table salt operations are accordingly more complex. Here, the regeneration agent is fully automatically available from a rock salt container as ready salted water or brined water in large bags.

Water treatment facility consisting of softening, reverse osmosis and electrodeionization (Source: EnviroFALK)

Reverse Osmosis

Reverse osmosis (RO) is a membrane process that retains ions in addition to particulate matter in water. Reverse osmosis is based on the osmosis effect in which substances are replaced with an ion-permeable membrane. The driving force of the process is based on different concentrations on both sides of the membrane. Since membranes can be produced separately for permeability to different ions, it is possible to selectively concentrate or consume/reduce ions for desired concentration changes as long as suitable solvents are available. Instead of using different concentrations, ion separation can also be initiated with different pressures on both sides of the membrane. This effect is known as reverse osmosis. Here pressure is applied to the concentrated solution to overcome the solution's osmotic pressure. The solvent passes back through the membrane and all dissolved water components remain on the side where the concentrate is located. On a large scale, a reverse osmosis facility is operated as cross-flow filtration. Here the raw water inlet is divided into pure water, a permeation of 75 to 80 percent, and approximately 2 percent residual salt content. All other water components are continuously discharged with the facility's concentrate / concentrated solution. An important part of the reverse osmosis facility is the pre-treatment performed to prevent scaling with calcium and magnesium on membranes. For this purpose, water softening with ion exchange or hardness stabilization is also used with an antiscalant. In modern facilities, water yield can be increased, for example by using a concentrate stage. Additionally, permeate yield can be adjusted more variably using variable speed discharge pumps. Through such measures and the use of special low-pressure membranes, the overall facility's energy requirements can be improved significantly.

Reverse osmosis system (Source: EnviroFALK)

Micro-Filtration

Micro-filtration (MF) has the task of retaining all components in water that are larger than the pores in the membrane. Micro-filtration membranes separate particles or colloidal suspensions. Pore sizes are approximately between 0.05 μm and 10 μm. A characteristic feature of micro-filtration is tangential membrane flow, called cross-flow filtration. That is, here water is not forced directly through the membrane and only flows over the membrane. With this type of flow, a cleaning effect is achieved over the membrane and the service life of filtration systems increases several times.

Ultra-Filtration

Ultra-filtration (UF) is a process in which water is filtered through a polymeric membrane with a very fine pore structure. With defined separation limits and individual backwash concepts, the ultra-filtration process can demonstrate its advantages in demanding raw waters with high fluctuating particle loads. For this purpose, the process engineering has a more modular structure. This means an ultra-filtration facility can flexibly respond to changes in required quantities and fluctuations in raw water composition. Ultra-filtration is essentially characterized by higher performance in terms of particle retention. Compared to a gravel filter system, an ultra-filtration system particularly provides significantly better separation / retention of very small particles.

Electrodeionization

For electrodeionization (EDI), ion exchange resins and ion-selective membranes are combined with direct current. An EDI module consists of several chambers separated by ion-selective membranes. The chambers are filled with ion exchange resin and arranged between two DC electrodes. The applied voltage deflects ions in the EDI feed water toward the electrodes; cations move toward the cathode and anions toward the anode. Due to the opposite arrangement of ion-selective membranes, ions accumulate in channels between compartments and a partial flow from the module is discharged with EDI concentrate. Electrodeionization is preferentially used after reverse osmosis. Water is reprocessed. Water quality is characterized by low electrical conductivity and low silica values.

Pure Water Circulation Systems

Pure water circulation systems (RKA) are used for the production and circulation of completely demineralized water (demineralized water). Reverse osmosis removes more than 98 percent of unwanted substances from raw water. The permeate produced is stored in a working tank and can be heated if necessary. Circulation is carried out through a combination of absorbent resin or activated carbon and ion exchangers. Particles are filtered to <0.2 μm with filter systems. In backflow, the deionized water is sterilized with UV light, thus preventing microorganism growth. Through the use of heat-resistant resins, the circulation water is permitted to be used at temperatures up to 70°C. In smaller quantities, tap water is used as raw water. For larger quantities for industrial use, depending on the application area, surface water or well water is frequently used. İzzet Aydın General Manager Hillebrand Chemicals Kimyasal Pazarlama Ltd. Şti.

Sources: Basiswissen – Prozesskette Oberflächentechnik, Wotech Softech AG – Omnitec EnviroFALK Praktische Galvanotechnik, Leuze Verlag