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Twentieth Century Equipment Concepts
CHAPTER 3
Twentieth Century Equipment Concepts Contents 3.1 3.2 3.3 3.4 3.5 3.6 3.7
Overview Benches Blocks Multiple-Die Machines Other In-Line Processes Post-Twentieth Century Developments Questions and Problems
13 13 14 15 17 17 18
3.1 OVERVIEW As stated in Section 1.1.2, the terms “bar,” “rod,” and “wire” often imply a certain mode of processing, or process flexibility, especially regarding the ability to coil the product during process sequences. The related drawing equipment can be roughly categorized as benches, blocks, and multiple-die machines. Countless variations and subtleties exist regarding these equipment types, and a comprehensive treatment of wire drawing machinery is beyond the scope of this text. However, some useful simplifications and characteristics are shown in this chapter.
3.2 BENCHES While the term “bench” has been applied to a variety of wire processing assemblies, this text will regard drawing benches as involving the simple pulling of straight lengths, where, in the simplest cases, the length achievable is limited by the length of the bench. It should be noted, however, that continuous bench-type machines have been developed, such as systems applying a “hand-over-hand” pulling technique. In any case, simple bench drawing does not generally involve coiling of the drawn workpiece, although Wire Technology http://dx.doi.org/10.1016/B978-0-12-802650-2.00003-0
Copyright © 2016 Elsevier Inc. All rights reserved.
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benches, particularly continuous benches, are often in tandem with straightening and cutting machines. In addition to use with uncoilable workpieces (heavy-gage stock, bendsensitive stock, etc.), benches are useful for certain laboratory or development studies and for short lengths of specialty items. Drawing bench speeds do not generally exceed 100 m/min.
3.3 BLOCKS When bar or rod is sufficiently robust or of small enough diameter to permit coiling, block drawing may be employed. The block involves a capstan or bull block to which the rod is attached. The powered bull block turns, pulling the rod through the die and coiling the as-drawn rod on the bull block. Single block or capstan drawing is often undertaken, although multipleblock systems are common, with the rod wrapped a few times around each capstan before entering the next, smaller gage die. The capstans transmit pulling force to the rod by way of the frictional contact of the rod wraps on the capstan surface. A schematic illustration of block drawing was given in Figure 1.3. Figure 3.1 shows a commercial drawing machine with the
Mehrtach-Drahtziehmaschine, Modell KRT 1250/4, Multiple wire drawing machine, model KRT 1250/4
Die station
Capstan
Figure 3.1 Commercial multiple-block drawing machine with capstans and die stations indicated. (Courtesy of Morgan-Koch Corporation.)
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Twentieth Century Equipment Concepts
capstans and die stations clearly indicated. Block drawing speeds are often in the range of 100-200 m/min, with the drawing speed, v, as: v ¼ π Dω
(3.1)
where D is the block diameter and ω is the block speed in revolutions per unit time. Higher speed multiple-block systems are discussed in Section 3.4.
3.4 MULTIPLE-DIE MACHINES As the rod or wire gets smaller in diameter, high-speed, multiple-die machines become practical and necessary for commercial productivity. These may be of the multiple or tandem capstan variety or may involve a single, multiple-diameter capstan of the “stepped cone” variety. The stepped cone has a constant angular velocity (or revolutions per unit time) that generates a different pulling speed at each capstan diameter. Figures 3.2 and 3.3 show, respectively, a schematic representation of a stepped cone drawing system17 and a stepped cone in a commercial drawing system. It is fundamental that the drawing speed increases as the wire lengthens and is reduced in diameter in the upstream die. This is easily considered, since one can assume that the overall volume of the wire (equal to length multiplied by cross-sectional area) remains constant during its drawing.
Die Di
e
4
3
e Di 2
Di e1
Electric motor
4 1
2
3
Blocks
Figure 3.2 Schematic representation of a stepped cone drawing system. (From Harris JN. Mechanical working of metals. New York: Pergamon Press; 1983. p. 208. Copyright held by Elsevier Limited, Oxford, UK.)
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Figure 3.3 A stepped cone within a commercial drawing system. (Courtesy of Macchine +Engineering S.r.l.)
On this basis, the product of the drawing speed and the wire cross-sectional area remains constant. In the case of the multiple-diameter capstan, the stepped diameters provide the series of drawing speeds consistent with the increased speed needed as the wire is reduced in cross section during the multiple-die drawing; that is, the wire is pulled through the first die by the smallest diameter on the capstan, goes through the second die, is pulled by the second smallest diameter on the capstan, and so on. The respective drawing speeds, v1, v2, v3…, may be calculated from Equation (3.1) for the respective stepped cone diameters, D1, D2, D3…, with the value of ω remaining constant. With separate capstans, the series of drawing speeds is achievable largely by driving the individual capstans at progressively higher angular velocities (values of ω). All capstans may be driven by a single power source, or the capstans may be driven individually. The angular velocity may be programmed and controlled so that the capstan surface speed is essentially the same as the intended drawing speed so that the wire does not slip on the capstan (no-slip machines). Alternatively, the capstans may be driven faster so that the wire slips on the capstan by design (slip machines). Beyond this,
Twentieth Century Equipment Concepts
17
wire speed may be controlled by variable “storage” of wire between passes on dynamic accumulating systems. The design and operation of multiple-die machines vary significantly from ferrous to nonferrous practice. With ferrous drawing, conventional multiple-die drawing speeds reach 600 m/min, and with nonferrous drawing, speeds up to 2000 m/min are common. However, modern drawing machines have featured speeds several times these levels. The major limitation to such drawing speeds lies not in the drawing process but in the dynamic equipment necessary to payoff, handle, and take up the wire. The frequency of wire breakage is an increasing consideration at high speed, since production may be lost while restringing the machine. Some modern drawing machine systems also involve the drawing of several or many wires at once in parallel operation. With high drawing speeds and dozens of parallel lines, the productivity of these machines can be enormous. The basic principles of the individual drawing operations remain much the same, however. Important issues with such machines include string-up time, the amount of production lost due to wire breakage, the frequency of such breakage, and the cost and maintenance of the ancillary wirehandling equipment.
3.5 OTHER IN-LINE PROCESSES Drawing is often done directly in line with other operations. These may include shaving (circumferential machining of the outer rod surface), descaling, pickling (chemical removal of surface oxide), cleaning, and the application of coatings and lubricants prior to initial drawing. Annealing and other thermal processes may be undertaken in tandem with drawing. Other in-line processes include numerous types of electrical insulation application, straightening, cutting, and welding. Finally, some drawing systems lead continuously to wire-forming operations (for fasteners, springs, etc.).
3.6 POST-TWENTIETH CENTURY DEVELOPMENTS We are, of course, well into the twenty-first century, and it is the purpose of this book to provide orientation suitable for one to interface with current and future developments. Care has been taken to indicate models, measurements, quality and productivity issues, and engineering basics that are consistent with progress in, say, the first quarter of the current century. Examples of current technology developments are presented in Chapter 20.
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3.7 QUESTIONS AND PROBLEMS 3.7.1. A multiple-die wire drawing operation finishes at a diameter of 0.1 mm and at a speed of 2000 m/min. An upstream die has a size of 0.18 mm. What is the speed of the wire coming out of that upstream die? Answer: As stated in Section 3.4, the product of the drawing speed and the wire cross-sectional area remains constant. Therefore, final drawing speed multiplied by final area equals upstream speed multiplied by upstream area, and the upstream speed in question equals the final speed multiplied by the ratio of the final area to the upstream area. The area ratio can be replaced with the square of the diameter ratio. Therefore, upstream speed ¼ (2000 m/min) [(0.1)/(0.18)]2 ¼ 617 m/min. 3.7.2. If a stepped cone drawing machine lengthens the wire 26% in each drawing pass with five passes involved with no slip and if the largest capstan diameter is 15 cm, what will be the smallest capstan diameter? Answer: The percentage increase in length in each pass is associated with an identical increase in velocity and an identical increase in associated capstan diameter (note Equation (3.1)). After five passes, the velocity and associated capstan diameter will have increased by a factor of (1.26)5 or 3.18. Thus, the final capstan diameter divided by 3.18 will be the diameter of the smallest and first capstan. The diameter is 4.72 cm. 3.7.3. If the finishing speed in the previous problem is 1000 m/min, how many revolutions per minute is the capstan making? Answer: Rearranging Equation (3.1), the revolutions per unit time, or ω, is [v/πD]. Thus, the number of revolutions per unit time is (1000 m/min)/[(π)(0.15 m)], 2122 min1, or 35.4 s1. 3.7.4. A certain high-capacity, multi-line drawing machine is losing 4% of its productivity due to one drawing break each week. Assuming a 20-shift per week basis, with seven active manufacturing hours per shift, estimate the time it takes to string up the machine. Answer: The number of active manufacturing hours per week is 7 20 or 140 hours. Four percent of this number is 5.6 hours or the time required to string up the drawing machine.
Twentieth Century Equipment Concepts Contents 3.1 3.2 3.3 3.4 3.5 3.6 3.7
Overview Benches Blocks Multiple-Die Machines Other In-Line Processes Post-Twentieth Century Developments Questions and Problems
13 13 14 15 17 17 18
3.1 OVERVIEW As stated in Section 1.1.2, the terms “bar,” “rod,” and “wire” often imply a certain mode of processing, or process flexibility, especially regarding the ability to coil the product during process sequences. The related drawing equipment can be roughly categorized as benches, blocks, and multiple-die machines. Countless variations and subtleties exist regarding these equipment types, and a comprehensive treatment of wire drawing machinery is beyond the scope of this text. However, some useful simplifications and characteristics are shown in this chapter.
3.2 BENCHES While the term “bench” has been applied to a variety of wire processing assemblies, this text will regard drawing benches as involving the simple pulling of straight lengths, where, in the simplest cases, the length achievable is limited by the length of the bench. It should be noted, however, that continuous bench-type machines have been developed, such as systems applying a “hand-over-hand” pulling technique. In any case, simple bench drawing does not generally involve coiling of the drawn workpiece, although Wire Technology http://dx.doi.org/10.1016/B978-0-12-802650-2.00003-0
Copyright © 2016 Elsevier Inc. All rights reserved.
13
14
Wire Technology
benches, particularly continuous benches, are often in tandem with straightening and cutting machines. In addition to use with uncoilable workpieces (heavy-gage stock, bendsensitive stock, etc.), benches are useful for certain laboratory or development studies and for short lengths of specialty items. Drawing bench speeds do not generally exceed 100 m/min.
3.3 BLOCKS When bar or rod is sufficiently robust or of small enough diameter to permit coiling, block drawing may be employed. The block involves a capstan or bull block to which the rod is attached. The powered bull block turns, pulling the rod through the die and coiling the as-drawn rod on the bull block. Single block or capstan drawing is often undertaken, although multipleblock systems are common, with the rod wrapped a few times around each capstan before entering the next, smaller gage die. The capstans transmit pulling force to the rod by way of the frictional contact of the rod wraps on the capstan surface. A schematic illustration of block drawing was given in Figure 1.3. Figure 3.1 shows a commercial drawing machine with the
Mehrtach-Drahtziehmaschine, Modell KRT 1250/4, Multiple wire drawing machine, model KRT 1250/4
Die station
Capstan
Figure 3.1 Commercial multiple-block drawing machine with capstans and die stations indicated. (Courtesy of Morgan-Koch Corporation.)
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Twentieth Century Equipment Concepts
capstans and die stations clearly indicated. Block drawing speeds are often in the range of 100-200 m/min, with the drawing speed, v, as: v ¼ π Dω
(3.1)
where D is the block diameter and ω is the block speed in revolutions per unit time. Higher speed multiple-block systems are discussed in Section 3.4.
3.4 MULTIPLE-DIE MACHINES As the rod or wire gets smaller in diameter, high-speed, multiple-die machines become practical and necessary for commercial productivity. These may be of the multiple or tandem capstan variety or may involve a single, multiple-diameter capstan of the “stepped cone” variety. The stepped cone has a constant angular velocity (or revolutions per unit time) that generates a different pulling speed at each capstan diameter. Figures 3.2 and 3.3 show, respectively, a schematic representation of a stepped cone drawing system17 and a stepped cone in a commercial drawing system. It is fundamental that the drawing speed increases as the wire lengthens and is reduced in diameter in the upstream die. This is easily considered, since one can assume that the overall volume of the wire (equal to length multiplied by cross-sectional area) remains constant during its drawing.
Die Di
e
4
3
e Di 2
Di e1
Electric motor
4 1
2
3
Blocks
Figure 3.2 Schematic representation of a stepped cone drawing system. (From Harris JN. Mechanical working of metals. New York: Pergamon Press; 1983. p. 208. Copyright held by Elsevier Limited, Oxford, UK.)
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Figure 3.3 A stepped cone within a commercial drawing system. (Courtesy of Macchine +Engineering S.r.l.)
On this basis, the product of the drawing speed and the wire cross-sectional area remains constant. In the case of the multiple-diameter capstan, the stepped diameters provide the series of drawing speeds consistent with the increased speed needed as the wire is reduced in cross section during the multiple-die drawing; that is, the wire is pulled through the first die by the smallest diameter on the capstan, goes through the second die, is pulled by the second smallest diameter on the capstan, and so on. The respective drawing speeds, v1, v2, v3…, may be calculated from Equation (3.1) for the respective stepped cone diameters, D1, D2, D3…, with the value of ω remaining constant. With separate capstans, the series of drawing speeds is achievable largely by driving the individual capstans at progressively higher angular velocities (values of ω). All capstans may be driven by a single power source, or the capstans may be driven individually. The angular velocity may be programmed and controlled so that the capstan surface speed is essentially the same as the intended drawing speed so that the wire does not slip on the capstan (no-slip machines). Alternatively, the capstans may be driven faster so that the wire slips on the capstan by design (slip machines). Beyond this,
Twentieth Century Equipment Concepts
17
wire speed may be controlled by variable “storage” of wire between passes on dynamic accumulating systems. The design and operation of multiple-die machines vary significantly from ferrous to nonferrous practice. With ferrous drawing, conventional multiple-die drawing speeds reach 600 m/min, and with nonferrous drawing, speeds up to 2000 m/min are common. However, modern drawing machines have featured speeds several times these levels. The major limitation to such drawing speeds lies not in the drawing process but in the dynamic equipment necessary to payoff, handle, and take up the wire. The frequency of wire breakage is an increasing consideration at high speed, since production may be lost while restringing the machine. Some modern drawing machine systems also involve the drawing of several or many wires at once in parallel operation. With high drawing speeds and dozens of parallel lines, the productivity of these machines can be enormous. The basic principles of the individual drawing operations remain much the same, however. Important issues with such machines include string-up time, the amount of production lost due to wire breakage, the frequency of such breakage, and the cost and maintenance of the ancillary wirehandling equipment.
3.5 OTHER IN-LINE PROCESSES Drawing is often done directly in line with other operations. These may include shaving (circumferential machining of the outer rod surface), descaling, pickling (chemical removal of surface oxide), cleaning, and the application of coatings and lubricants prior to initial drawing. Annealing and other thermal processes may be undertaken in tandem with drawing. Other in-line processes include numerous types of electrical insulation application, straightening, cutting, and welding. Finally, some drawing systems lead continuously to wire-forming operations (for fasteners, springs, etc.).
3.6 POST-TWENTIETH CENTURY DEVELOPMENTS We are, of course, well into the twenty-first century, and it is the purpose of this book to provide orientation suitable for one to interface with current and future developments. Care has been taken to indicate models, measurements, quality and productivity issues, and engineering basics that are consistent with progress in, say, the first quarter of the current century. Examples of current technology developments are presented in Chapter 20.
18
Wire Technology
3.7 QUESTIONS AND PROBLEMS 3.7.1. A multiple-die wire drawing operation finishes at a diameter of 0.1 mm and at a speed of 2000 m/min. An upstream die has a size of 0.18 mm. What is the speed of the wire coming out of that upstream die? Answer: As stated in Section 3.4, the product of the drawing speed and the wire cross-sectional area remains constant. Therefore, final drawing speed multiplied by final area equals upstream speed multiplied by upstream area, and the upstream speed in question equals the final speed multiplied by the ratio of the final area to the upstream area. The area ratio can be replaced with the square of the diameter ratio. Therefore, upstream speed ¼ (2000 m/min) [(0.1)/(0.18)]2 ¼ 617 m/min. 3.7.2. If a stepped cone drawing machine lengthens the wire 26% in each drawing pass with five passes involved with no slip and if the largest capstan diameter is 15 cm, what will be the smallest capstan diameter? Answer: The percentage increase in length in each pass is associated with an identical increase in velocity and an identical increase in associated capstan diameter (note Equation (3.1)). After five passes, the velocity and associated capstan diameter will have increased by a factor of (1.26)5 or 3.18. Thus, the final capstan diameter divided by 3.18 will be the diameter of the smallest and first capstan. The diameter is 4.72 cm. 3.7.3. If the finishing speed in the previous problem is 1000 m/min, how many revolutions per minute is the capstan making? Answer: Rearranging Equation (3.1), the revolutions per unit time, or ω, is [v/πD]. Thus, the number of revolutions per unit time is (1000 m/min)/[(π)(0.15 m)], 2122 min1, or 35.4 s1. 3.7.4. A certain high-capacity, multi-line drawing machine is losing 4% of its productivity due to one drawing break each week. Assuming a 20-shift per week basis, with seven active manufacturing hours per shift, estimate the time it takes to string up the machine. Answer: The number of active manufacturing hours per week is 7 20 or 140 hours. Four percent of this number is 5.6 hours or the time required to string up the drawing machine.