What do you call the process of converting raw materials?

Abstract

The purpose of the converting process is to transform raw materials in the form of polymer pellets or film substrates (including paper and foil) into a final packaging structure. This often involves more than one process or step that may include film formation, orientation, metallization, lamination, coating, printing, winding, and slitting. The basic processes include blown and cast film, extrusion coating and lamination, adhesive lamination, orientation processes (tenter frame, double bubble, and machine direction orientation), and printing. Often there is more than one way to make a functional structure, the choice of which depends on a number of factors such as run length and existing assets of the converter. This chapter briefly describes the major converting processes, their key components, and processing parameters that affect the properties of the final product.

Thermal Depolymerization and Decarboxylation of PHB Containing Bacterial Cells

For a process converting PHB to propene to have any chance of being economically viable, it is essential that the process work not only on isolated PHB, but also on the PHB in whole cells. Isolation of PHB from the bacterial cell mass prior to the thermal conversion reaction would likely make the process too expensive for commercial production of propene. As can be seen in Table 3, significant yields of propene were obtained by thermal treatment of C. necator cells containing PHB. Thermal experiments on C. necator 428 containing various amounts of PHB resulted in the production of propene and CO2. At 350 °C, yields of 14% propene and 52% CO2 were obtained in 15 min. At 400 °C, C. necator 428 gave propene yields of 60 to 70% and CO2 yields more than 100%, based on the PHB content of the cells. The propene yields were only slightly lower than were obtained with pure CA or PHB, whereas the CO2 yields were much higher, probably due to the conversion of other cell components. A negative control was treated thermally at the same conditions, and this produced a significant amount of CO2 but no propene, confirming that all propene generated comes from PHB and that other cell components do not breakdown to give propene, but will breakdown to give CO2.

Table 3. Thermal treatment of PHB-containing Cupriavidus necator (15 min reaction time)

3.2 Copper extraction and copper slag

Copper is one of the first metals to be used by humans and the third most extensively used metal after iron and aluminum. The percentage usage of copper and copper alloys worldwide is approximately 44% in building construction, 20% in electric and electric products, 17% in transportation equipment, 12% in consumer and general products, and 7% in industrial machinery and equipment (Brininstool, 2014).

Copper is extracted from copper ores by a pyrometallurgical (dry) method or hydrometallurgical (wet) method. The pyrometallurgical method produces approximately 80% of the primary copper (Schlesinger, King, Sole, & Davenport, 2011). Pyrometallurgical production of molten copper generates slag in the stages of smelting and converting. Many copper ores contain iron that is fluxed. Typically, silica is used to flux iron and form an iron–silicate slag. During smelting, sulfur combines with copper and some iron to form a copper–iron sulfide matte, which is separated from copper slag. The matte is converted to metallic copper by oxidation, consequently removing iron and sulfur. Copper is further refined to remove impurities. Copper alloys such as bronze and brass can be made, which contains up to 25% tin and 5–30% zinc, respectively (Brandt & Warner, 2009).

3.2.1 Copper extraction process and copper slag formation

Copper ores are found as dominantly sulfide minerals, with or without other metallic sulfides. The major copper ore is copper pyrite or chalcopyrite (CuFeS2), from which a large amount of copper is obtained by smelting. Other copper ores include chalcocite (Cu2S), malachite (CuCO3⋅ Cu (OH)2), and covellite (CuS). The actual ores contain only small amount of copper. Typical copper ores contain from 0.5% Cu which is normally from open-pit mines to 1–2% Cu, which is from underground mines. Compared with iron ores, copper ores are generally too lean in copper to be smelted directly. Heating and melting the huge quantity of waste rock require prohibitive amounts of energy. Fortunately the Cu–Fe–S and Cu–S minerals in an ore can be isolated by physical means in beneficiation (concentration) into high-Cu concentrate, which can then be smelted economically (Schlesinger et al., 2011).

Normally 0.5–2.0% copper is considered satisfactory for copper extraction by concentration followed by a pyrometallurgical process that treats concentrates with 24% copper or higher, or is extracted by a hydrometallurgical process that handles lower-grade copper ores (Ray et al., 2014). Recycled scrap is becoming a source of copper production. Approximately 10–15% of scrap copper is used to produce primary copper (Schlesinger et al., 2011). Fig. 3.2 presents the major steps in the pyrometallurgical process in the extraction of copper.

Fig. 3.2. Flow sheet of major pyrometallurgical steps in extraction of copper.

Beneficiation of copper ores comprises several steps and the methods to be used vary with the mining operations, ore characteristics, and economic aspects. Beneficiation includes crushing, screening, grinding, and sorting operations. Copper ore is first crushed and ground into very fine powder. The powder is mixed with water and chemicals so that the part of the ore containing copper (copper concentrate) floats to the surface. This process is called froth flotation. In froth floatation, an ore pulp is agitated and air is blown through it to produce froth. Some mineral particles, mostly sulfides, attach to their air bubbles and are concentrated in the froth, which is skimmed off from time to time. The copper is concentrated from 0.5% to 1% Cu until 24% to 30% Cu. Once obtained, the concentrate is sent to a pyrometallurgical process where the concentrate is partially roasted in order to eliminate sulfur, and later is smelted to produce a matte that contains all the material in a liquid state. The last step is to purify electrolytically the impure metal by an acid solution of copper sulfate to obtain metallic copper having a purity of 99.999% Cu.

Copper smelting can be done in a reverberatory furnace (Fig. 3.3) or a flash smelting furnace (Fig. 3.4). Flash smelting is the predominant method used today and accounts for more than 50% of the copper matte smelting in the world (Peacey, 1989). An electric arc furnace is also used along with other smelting processes.

Fig. 3.3. Schematized reverberatory furnace.

Fig. 3.4. Schematized flash smelting furnace.

When copper concentrate is melted in a furnace, some of the impurities are driven off to form slag. The temperature during matte smelting the sulfide concentrate is approximately 1200°C to oxidize some of the iron to generate a molten matte and slag. The products from the furnace are (i) copper matte, which is molten Cu–Fe–S matte, 45–75% Cu, which is sent to oxidation converting to molten metallic copper; (ii) molten Fe silicate slag, which is treated to recover Cu and then discarded; and (iii) SO2-bearing off-gas:

CuFeS2+O2+SiO2 →Cu,Fe,Smatte+FeOSiO2slag+SO2

Copper slag from matte smelting is a solution of molten oxides. These oxides consist primarily of FeO from iron oxidation, SiO2 from flux, with small amounts of oxide impurities (eg, Al2O3, CaO, and MgO) from the concentrate. The oxides commonly found in copper slag include ferrous oxide (FeO), ferric oxide (Fe2O3), silica (SiO2), alumina (Al2O3), calcia (CaO), and magnesia (MgO). This slag is often referred to as fayalite slag as fayalite (Fe2SiO4) often precipitates from the slag on cooling.

In the converting process, the matte is converted to blister copper (99% Cu) in another furnace. The products of converting are (i) molten blister copper, which is sent to fire refining and electrorefining; (ii) molten iron–silicate slag, which is sent to Cu recovery, and then discarded with or without water quenching; and (iii) SO2-bearing off-gas.

The overall converting process may be described by schematic reaction:

Cu–Fe–S + O2 + SiO2 → Cu (l) + 2 FeO⋅SiO2 (molten slag with some solid Fe3O4) + SO2 (Schlesinger et al., 2011).

Calcium ferrite and olivine slags may occur as lime-based flux is added for two reasons: (i) copper-bearing concentrates often contain 5–10% silica and lime is added to break up silicates, take up excess silica from aluminosilicates, and reduce the viscosity of the silicarich slag (typically, 3–10% limestone or lime-bearing mix is added); and (ii) lime-based slag has a lower viscosity and a higher solubility for magnetite that has higher smelting and converting temperatures and low solubility in slag and matte may be formed in furnaces. In this case, lime-based slag separates more easily from the matte and removes arsenic, antimony, and bismuth more efficiently than siliceous slag does (Chaubal, Sohn, George, & Bailey, 1989; Turkdogan, 1983).

In converters, the particle size of flux is in the range of 6–25 mm (0.24–0.99 in.). Coarser flux is difficult to inject and to dissolve; finer flux tends to float on the bath and can be a source of dust. In some processes, smaller flux particle size may be used; for instance, the Sirosmelt process, in which limestone flux is between 5 and 10 mm (0.2–0.4 in.) in size (Kokal, 2006).

In hydrometallurgical methods, the extraction is done by acid leaching and metal precipitation. The metal copper can be precipitated from the solution by scrap iron, or by solvent extraction traded electrolytically in an acid bath. Sludge, rather than slag, is generated from hydrometallurgical process.

1.7.2.3 Converting processes for wet lay webs

A number of converting processes are applied to wet lay media as necessary for their end use filtration performances. Included are corrugating, rewinding, slitting, creping, sheet cutting, die cutting, pleating, bag making, and other operations that alter the mechanical structure and geometrical surface of the web. In addition to resin, there are other chemical treatments that add to web properties. Among them are flame retardants, water repellents, extenders, surfactants, adsorbents, and antimicrobial agents. The various converting operations for filter media will be discussed in Chapter 5.

2.4.2.1.1 Steady-State Operations

Modern matte smelting and converting processes are increasingly becoming continuous in nature and operated at steady-state conditions. In such a process, the conditions in the reactor remain constant with respect to time. Modeling of minor-element behavior during a steady-state operation will be described using the work of Kim and Sohn [10,12] on copper matte smelting as an example.

The two main functions of copper matte smelting are: (1) melting the entire sulfides and oxides of copper and iron with a flux (silica) to produce two immiscible liquid phases—slag (oxide) and copper-rich matte (Cu2S + FeS); and (2) oxidizing excess sulfur and a portion of the FeS in the matte to obtain a certain grade of matte by the blowing of oxygen. The most important undesirable minor elements in coppermaking are Pb, Zn, Bi, Sb, and As [10,12,13]. Mattemaking is usually performed as a continuous system, in which the solids are continuously charged and melted and matte and slag are continuously produced and tapped. A schematic diagram of the matte smelting process is shown in a previous section.

With the assumption that all copper in the feed enters the matte phase, the following mass balances for copper, iron, and a minor element are established:

(2.4.1)mfd%Cufd=x⋅mmt

(2.4.2)mfd%Fefd=mmt%Femt+msl%Fesl

(2.4.3)mfd%Mfd=mmt%Mmt+msl%Mmt /LMIII+yMTnoAM

where

(2.4.4)LMIII=%Mmt/%Msl

and mfd, mmt, and msl are the mass flow rates of feed, matte, and slag, respectively; x is matte grade; yMT is the mole fraction of minor element M in the output gas (= pMT/pT) where pMT is an effective total pressure of all the gas species containing a minor element M as defined below; LMIII is the distribution coefficient of minor element between matte and slag; no is the total molar flow rate of output gas; and AM is the atomic or molecular weight of species M.

The effective total pressure of all the minor element-containing gaseous species, pMT is defined by

(2.4.5) pMT=pM+pM2+βp MβOδ+μpMμOv=k1,MiMi+k2,M iMi2+k3,MiM iβ+k4,MiMiv

where i refers to a molten phase and the volatilization constants (kn,M)i are functions of temperature, pO2 and pS2 and are calculated from the equilibrium relations between the gas and condensed phase i, as described in a previous section. In copper matte smelting and converting only M, M2, MO, and MS are important [12]. Detailed mathematical relations for calculating these volatilization constants can be found in the cited references [10,12].

The molar flow rate of tonnage oxygen (or process gas) required to obtain a certain grade of matte may be expressed as

(2.4.6)Np=1/yO2mfd%Sfd−mmt%Smt100AS+0.5rslmfd%Fefd−mmt %Femt100AFe+0.5mfd %Znfd100AZn+ %Pbfd100APb+Npa

where A is atomic or molecular weight of species i, rsl is the atomic ratio of O/Fe in slag, yO2 is the mole fraction of oxygen in the process gas and Npa is the additional molar flow rate of process gas needed to burn a fuel when used.

The molar flow rate of output SO2 gas is given by

(2.4.7)nSO2=mfd%Sfd−mmt%Smt100AS

If the composition and flow rate of feed, the final matte grade, oxygen amount in the input gas and slag composition are given, all other flow rates can be calculated from the above equations because the composition of matte can be expressed as a function of matte grade [14]. Therefore, the concentrations of minor elements in matte and slag can be calculated from Equation (2.4.4) and the concentrations in slag can be calculated by use of the distribution coefficient. Further calculational details can be found in Kim and Sohn [10,12].

2.1.3.4.1 Impact of Process Material on Refractory Degradation

2.1.3.4.1.1 Ferrous Silicate or Fayalite Slag

Slags for the primary smelting and converting processes are first and foremost based on a ferrous silicate slag, referred to as fayalite slags [102,115]. In contact with fayalite slag, refractory corrosion primarily occurs through the dissolution of MgO [111], thereby showing increasing aggressivity toward MgO with increasing silica content of the slag. Under reducing conditions, magnesia dissolves in fayalite according to the reaction:

(2.1.113)MgOrefr⇌MgOslag

Once the liquid fayalite slag is saturated with forsterite (2MgO·SiO2) due to increasing MgO content in the slag or decreasing temperature, solid olivine [2(Mg,Fe)O·SiO2] will form (Figure 2.1.43b):

Figure 2.1.43. The FeO–MgO–SiO2 system: (a) calculated liquidus projection (in equilibrium with Fe; T in °C) [116]; (b) illustration of the dissolution and precipitation reactions of MgO in the FeO–MgO–SiO2 system.

(2.1.114)2MgFeOslag+SiO2slag⇌Mgo,T2MgFeO⋅SiO2prec

Next to these dissolution and precipitation reactions, FeO in the fayalite slag reacts with MgO in the refractory to form magnesiowüstite, a solid solution of FeO and MgO, according to the reaction:

(2.1.115)FeOslag+MgOrefr⇌2MgFeOrefr

Likewise to FeO, other bivalent metals such as Ni or Zn will diffuse in MgO to form a solid solution. Equations (2.1.113)–(2.1.115) are illustrated within the relevant cross-sections of the FeO–MgO–SiO2 system in Figure 2.1.43. The pseudobinary forsterite–fayalite section in Figure 2.1.43b shows how this solubility limit changes with temperature.

In the presence of O, the forsterite–fayalite and magnesiowüstite solid solutions react further to form, respectively, magnetite + silica and magnesioferrite. This silica can then combine with free MgO to form forsterite.

The chromite grains react with Fe or other bivalent metals to form new spinels. As their dissolution rate is however low, they are presumably washed away [117]. This leads to the conclusion that refractories which are higher in chrome ore and are direct-bonded with a spinel bond rich in Cr2O3 are more resistant to chemical corrosion. However, as the reaction product of MgO with the slag can freeze near the hot-face, a brick high in MgO may be desirable. With respect to this issue, the authors’ own experience with the corrosion of refractory with fayalite slag indicates that a high content of secondary chromite is beneficial, especially when the slag is rich in spinel forming elements (Fe, Ni, Zn, etc.). Equally important is the distribution of these chromites. Fused grains with evenly distributed intragranular chromite particles tend to form a spinel layer more easily at their interface with the slag, thereby forming a protective layer.

Other Coating Processes

Adhesive laminating is a subset of the broader converting process called “coating.” Coating refers to any process in which a fluid material of some sort is applied over the width of a web. The coating material functions in many ways including: barrier improvement, heat sealability, adhesion when pressed to another surface deliberate release from such “pressure-sensitive” surfaces. The fluid dynamics of the coating material dictate one of the many metering methods available to web converters for coating processes.3 Fluid-coated substrates lend themselves to dedicated high-volume manufacturing processes, unlike the job-shop traditions of flexible packaging converting. With few exceptions, such products are marketed by rollstock suppliers to converters as raw materials.

The “pattern coating” process is better suited to the manufacturing environment of the flexible packaging converter. The process imparts the coating’s functionality to only a part of the substrate, usually registered to a printed pattern. For example, a frame of pressure-sensitive adhesive coating applied to the inside of chocolate bar wrappers allows packaging of the product with pressure only. This avoids heat sealing that could melt the product. As digital electronic control of web processes allows easier, more reliable registration of a coating to a printed image, additional opportunities for converters to add value to flexible packaging emerge.

Abstract

This chapter highlights two areas where the film-converting process strongly affects adhesion: (1) adhesion of polymer to substrate in extrusion coating and lamination and (2) interlayer adhesion in coextrusion cast film, blown film, and extrusion coating. The effect of oxidation, cooling and stress development in the air gap, and rapid cooling in the nip of the extrusion coating process is examined in detail. A case study on the root cause of lower peel strength with thinner coatings underscores these effects.

Interlayer adhesion in coextrusion is shown to be influenced by time, temperature, strain history, and new area creation. The process time is an important parameter for characterizing adhesion for a given process and master curves can be generated to relate adhesion to polymer and process parameters. Interfacial reaction rates are accelerated by polymer flow during extrusion and draw down.

2 Methodology

In this work, the thermodynamic efficiency of the process converting waste tyre to methanol and power is measured using two basic metrics, mainly; carbon efficiency and chemical potential efficiency. The properties are described as follows:

(1)CarbonEfficiencyCeff=molesofCinthedesiredproduct molesofCinthefeed

(2)ChemicalPotentialEfficiencyηcp,eff=Gibbsfreeenergyofcombustion ofproductsGibbsfreeenergyof combustionoffeed

Equation 1 measures how much of the carbon in the feed stream ends up in the desired products. Less than 100% carbon conversion leads to carbon dioxide emissions. Equation 2 measures how much of the chemical potential stored in the feed material is translated to the desired products during chemical transformation (Sempuga & Yao, 2017). The thermodynamic properties of waste tyres utilised in this work can be found in (Mavukwana et al., 2020).

16.6 Guiding and Path Control

Every roller that touches the web steers the web. Since rollers are never perfectly cylindrical and are never perfectly aligned that means that the farther the web goes, the more scattered its path position will be. This is one of the many reasons for the first commandment of good web machine design is to minimize the rollers necessary to do the job [5]. However, even a perfect machine, if there were such a thing, would not result in a perfectly straight and controlled web path because the web itself can steer in different directions if it has even the slightest asymmetrical bagginess that is called camber in guiding language. Here, again how much the path moves depends on the path length going through the machine.

Allowing web path to vary through a fixed width converting process such as coating or slitting will cause an increase in trim waste; hence one reason to control path. Another is that customers often require good roll edge straightness or good registration such as color-to-color or print-to-edge. Commercial tolerances are often as tight as the thickness of a human hair, 5 mils or 125 µm for position, registration, and width. Good path control begins with good design and good webs. However, all of that may not be enough. We may need to correct the path. Either we could guide the web on the unwinder, to start the web off in a consistent position, or the winder, to give the customer had better roll edge quality. No less interesting is guiding in the middle of a process. While there are several guides, the most common in converting is a displacement guide shown in Fig. 16.5. Guiding is one of the oldest of web science and was thoroughly modeled at the PhD level in the mid-1960s [15]. The practical upshot of this is that little is left as a craft and the application rules are well known. They include:

right angle entries and exit,

the length of the vertical legs (about half web width),

the proper position of the sensor (near the second moving roller),

all aspects of the control algorithm.

While this compact guide shown as a “hat” orientation in Fig. 16.5 is the most common, there are eight different and yet entirely equivalent geometries that can be used.