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Die-less wire drawing using borosiloxane as a pressure medium
Journal of Materials Processing Technology, 33 (1992) 375-381
375
Elsevier
Die-less wire drawing using borosiloxane as a pressure medium G.R. Symmons Sheffield City Polytechnic, Sheffield, UK
and Zhang Ming Chengdu University, Chengdu, China
Industrial Summary In the conventional drawing of wire, the diameter is reduced by pulling it through a reduction die, resulting in wear. Further, the die size has to be changed for each product size, thus involving time. A process know as die-less wire drawing has been developed in which polymer melts are used as the pressure medium in a reduction unit of stepped-bore geometry. The wire size is less than the minimum bore of the reduction unit, eliminating a conventional die and hence wear problems, as metal-to-metal contact is avoided. The deformation of the wire is directly dependent on the drawing speed, being caused by the pressure generated and the shear stress developed in the polymer melt. Polymer melts are used in the process because of their inherent high viscosity, which reduces the length required for the reduction unit; because of their flexibility; and because they provide a coating to the product (this is attractive for several industrial applications). Several types of polymer melts have been tested previously to meet various industrial requirements, in which a melt chamber heated to temperatures suitable for the particular polymer has been used at the entry position of the reduction unit. However, the thermal conditions of the melt can promote degradation problems of the polymer, resulting in loss of performance of the deformation process. The present experimental investigation compares the deformation of copper wire using borosiloxane at room temperature with more conventional polymers that require heating to provide a melt form in the die-less wire-drawing process. The results show that borosiloxane produces significantly greater deformation of the wire than the previously tested polymers and that it is less prone to shear thinning due to the shear rates or thermal conditions employed. The use of borosiioxane as the pressure medium eliminates the need for a melt chamber in the process and affords a greatly improved percentage of reduction of the wire per pass. Further, the borosiloxane coating is removed easily from the output wire by wiping.
I. Introduction
When a solid continuum is pulled through an orifice filled with a viscous fluid, shearing takes place at the interface of the fluid and the solid continuum. Correspondence to: Prof. G.R. Symmons, Department of Mechanical Engineering, Sheffield City Polytechnic, Pond Street, Sheffield, UK.
0924-0136/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
376 If the fluid film is converging in the direction of pull then, in addition to the shear force, a hydrodynamic pressure is generated. The magnitude of the shearing and the pressure generated depend upon the speed with which the continuum is pulled, on the viscosity of the fluid and on the geometric configuration of the orifice that contains the fluid. The shearing causes a drag force on the continuum which, combined with the effect of hydrodynamic pressure, may be sufficient to initiate plastic yielding and produce permanent deformation of the continuum. The application of the concept to die-less drawing was introduced in Ref. [ 1 ] using a polymer melt as the fluid. The development of this process towards a practical wire-drawing process is reported in Refs. [2] and [3]. A number of analytical models have been developed to optimise the geometrical dimensions of the orifice to produce the maximum deformation of the wire. Closed-form analytical models were presented in Refs. [3] and [4] and numerical solutions in Refs. [5] and [6]. Further improvements of the process can be achieved either by modifications to the shape and sizes of the orifice along its axis or by the selection of the type of polymer melt [7,8]. The output wire is coated with the polymer used, the quality and the thickness of the coating depending upon the drawing speed and the type of polymer. Previous work has shown that low density polyethylenes produced consistent coatings with little adhesion to copper wire, whilst nylon 6 produced good adherence. The present experimental investigation compares the deformation of copper wire using borosiloxane at room temperature with more conventional polymers that require heating to produce a melt form. Borosiloxane polymers have constitutive elements of boron, silicon and oxygen with phenyl or methyl groups. The structure is organised around an Si, O, B chain with either the phenyl or methyl groups linked to the silicon atoms. The physical characteristics and properties of the phenyl-based and methyl-based borosiloxanes differ: the phenyl-based borosiloxanes are used as heat- and fire-resistant materials, whilst the methyl-based borosiloxanes are used for abrasive-flow machining where silicon carbides are added to the media to produce the deburring process. Methyl-based borosiloxanes have been used in the present investigation, their rheological properties being affected by additives such as fillers, pigments and oils. Extrudehone supplies three grades of these borosiloxanes: blue, yellow and red, where the resistance to flow is least with the red. The medium-range yellow, which has properties similar to 'bouncing putty', was used in the tests. It is known for its unusual properties: it is readily mouldable; is easily drawn into threads; rebounds as much as 80%; and when struck by a hammer it will shatter into small pieces. It is its cold-flow ability and high elastic properties that make this type ofborosiloxane particularly useful in die-less wire drawing. 2. Experimental, procedure, and equipment
A purpose-built wire-drawing machine was used to carry out the experimental programme using borosiloxane as the working fluid. Figure 1 shows a sche-
377 OIEL,ESS RF.OUCTION UNIT
/
BULL BLOCK
/
T~
S UPPOR T
FRAME
COIL \
Fig. 1. Schematic diagr~ of the drawing machine.
/
P(']IYMFR R F ~ F R V O I R
STEPPEO BORE
OF PLI! t
Fig. 2. Assembly of the die-lessreduction unit.
378
matic diagram of the drawing machine, which used a coil holder, the die-less reduction unit and a bull-block. Figure 2 shows the assembly of the die-less reduction unit, which has an effective length of 10 mm with a gap ratio of 2.6 and a land ratio of 3.0, the same unit having been used for previous tests [8] on low-density polyethylenes, EVA and nylon 6. Similarly, copper wire of 0.45 mm diameter was used for the tests, within a range of drawing speed of 0.05 to 0.8 m/s. The experimental procedure using borosiloxane was simplified by carrying out the polymer tests at room temperature only. The wire was fed through the melt chamber and reduction unit of a fixed geometry and then attached to the motorised bull-block. Measurements of percentage reduction in area and observations on the coatings on the wire were made for small increasing increments of drawing speed. The condition for wire breakage was noted to be in excess of 22% reduction in area, the latter being measured at four positions for each speed increment and an average value being plotted. 3. Experimental results and discussion The experimental results on copper wire using borosiloxane are compared with the previously obtained results for alkathene WVG 23, LD polyethylene SW 6034, elvax 650 and nylon 6. In terms of wire deformation, nylon produced the largest reductions at 17% per pass, with loss of performance with increase nylon6 and polyboroslloxane
22 20 18
416
J
14.
°
A
4-
12 10 8
<>
6 4 2 0
i 0
i 0.2
i
i 0.4
!
i 0.6
0.8
d r o w l n g Sl:MXld r n / s
F i g . 3. Experimental results in percentage reduction in area of wire against drawing speed for nylon 6 and polyborosiloxane. ( V - b o r o s i l o x a n e ; [ ] - n y l o n 2 3 0 ° C; + - n y l o n 240 ° C; O - n y l o n 2 5 0 ° C; - nylon 260°C; × - nylon 270°C)
379 e l v a x 6 5 0 (rod polybomalloxane 22
18 16
14 12 10 8 6
4 2 0
i
I
0
[
0.2
I
I
|
0.4
I
0.6
0.8
drowlng I p e e d m / .
Fig. 4. Experimental results of percentage reduction in area of wire against drawing speed for elvax 650 and polyborosiloxane. ( X - borosiloxane; [] - elvax 140°C; + - elvax 150°C; O - elvax 160°C; A - elvax 180°C)
w~g23 and polyborollioxane 22 20 18 16
14. 12 10
+
+
<>
0
:
+
8 6
4 2 0
A
+
A
Q i
i
0.2
+
'0'
~
I0 i
i
0,4
13 i
I. i
0.6
O.S
drawlng speed m / a
Fig. 5. Experimental resultsof percentage reduction in area of wire against drawing speed for W V G 23 and polyborosiloxane. ( A - borosiloxane; + - W V G 130°C; ~ - W V G 140°C; [] - W V G 180°C)
380 sW6034- a n d p o l y b o r o s l l o x a n e 22
18 16 o c
12
~
10
~
8
g
[] +
6 4 20
i
! 0.2
i
i
i
0.4
drawing l l ~ m d
i 0.6
! 0.8
rn/s
Fig. 6. Experimentalresultsof percentagereductionin area ofwire againstdrawingspeedfor SW 6034 and polyborosiloxane.( 0 - borosiloxane;[] - SW 188°C; + - SW 210°C) in temperature beyond 260 ° C. The optimum drawing speeds for this particular size of reduction unit was 0.4 m/s. Figure 3 shows the results for various melt temperatures of nylon compared with the experimental results using borosiloxane at room temperature. Similarly, Figs. 4-6 show the experimental results of percentage reduction in areas against drawing speed for borosiloxane compared with elvax 650, alkathene WVG 23 and low-density polyethylene SW 6034, respectively. In each case the same size of copper wire and reduction unit was used for each polymer. The experimental results showed a marked improvement in the deformation of the wire using borosiloxane compared with all the other polymers tested. The degree of deformation using borosiloxane increased rapidly with increase in drawing speed, reaching 22% reduction in area - at which breakage of the wire occurred - at 0.12 m/s. The borosiloxane coating was removed easily from the deformed wire by wiping. The results suggest that borosiloxane could be chosen for the deformation of high yield material such as high-tensile steel wire, where many other polymers would require more passes to produce significant reductions. Higher drawing speeds for low yield materials such as copper could be achieved at the achieved 22% reduction in area per pass by modifying the size of the stepped bore. 4. C o n c l u s i o n s
Copper wire has been deformed successfully using a stepped-bore die-less drawing process with borosiloxane at room temperature. The removal of the
381 n e e d to h e a t t h e p o l y m e r i n t o a m e l t f o r m , as in p r e v i o u s cases, s i m p l i f i e s t h e p r o c e s s a n d h a s t h e a d v a n t a g e of a v o i d i n g a n y t h e r m a l d e g r a d a t i o n d u r i n g drawing. T h e b o r o s i l o x a n e c o a t i n g o f t h e o u t p u t wire is r e m o v e d easily b y wiping.
References 1 M.S.J. Hashmi, G.R. Symmons and H. Parvinmehr, A novel technique for wire drawing, J. Mech. Eng. Sci.,24 (1982) 1. 2 M.S.J. Hashmi and G.R. Symmons, U K Patent No. 8311301, 1983. 3 G.R. Symmons, M.S.J. Hashmi and H. Parvinmehr, Plasto-hydrodynamic lubrications,dieless wire drawing, in: Proc. Int. Conf. on Developments in Drawings of Metals, Metals Society, London, 1983, p. 54. 4 M.S.J. Hashmi and G.R. Symmons, A mathematical model for the drawing of a solid continuum through Newtonian fluid filled tubular orifice, in: Proc. 4th Int. Conf. on Mathematical Modelling, Ziirich, August, 1983, pp. 627-633. 5 M.S.J. Hashmi and G.R. Symmons, A numerical solution for the plasto-hydrodynamic drawing of a rigid non linearly strain hardening continuum through a conical orifice, in: Proc. 2nd Int. Conf. on Numerical Methods for Linear Problems, Barcelona, April, 1984, 1048-1059. 6 G.R. Symmons, Y. Xie and M.S.J. Hashmi, Thermal effect on a plasto-hydrodynamic wire drawing process using a polymer melt, Xth Int. Conf. on Rheology, Sydney, Australia, August, 1988, pp. 295-297. 7 I. A1-Natour and M.S.J. Hashmi, Development of a complex geometry pressure unit hydrodynamic coating applications, in: Proc. 6th Conf. of the Irish Manufacturing Committee, (IMC6), Dublin City University, Ireland, August/September, 1989, pp. 280-297. 8 G.R. Symmons, A.H. Memon, M.S.J. Hashmi and Ming Zhang, Polymer coating of wire using a die-less drawing process, ibid., pp. 367-375.
375
Elsevier
Die-less wire drawing using borosiloxane as a pressure medium G.R. Symmons Sheffield City Polytechnic, Sheffield, UK
and Zhang Ming Chengdu University, Chengdu, China
Industrial Summary In the conventional drawing of wire, the diameter is reduced by pulling it through a reduction die, resulting in wear. Further, the die size has to be changed for each product size, thus involving time. A process know as die-less wire drawing has been developed in which polymer melts are used as the pressure medium in a reduction unit of stepped-bore geometry. The wire size is less than the minimum bore of the reduction unit, eliminating a conventional die and hence wear problems, as metal-to-metal contact is avoided. The deformation of the wire is directly dependent on the drawing speed, being caused by the pressure generated and the shear stress developed in the polymer melt. Polymer melts are used in the process because of their inherent high viscosity, which reduces the length required for the reduction unit; because of their flexibility; and because they provide a coating to the product (this is attractive for several industrial applications). Several types of polymer melts have been tested previously to meet various industrial requirements, in which a melt chamber heated to temperatures suitable for the particular polymer has been used at the entry position of the reduction unit. However, the thermal conditions of the melt can promote degradation problems of the polymer, resulting in loss of performance of the deformation process. The present experimental investigation compares the deformation of copper wire using borosiloxane at room temperature with more conventional polymers that require heating to provide a melt form in the die-less wire-drawing process. The results show that borosiloxane produces significantly greater deformation of the wire than the previously tested polymers and that it is less prone to shear thinning due to the shear rates or thermal conditions employed. The use of borosiioxane as the pressure medium eliminates the need for a melt chamber in the process and affords a greatly improved percentage of reduction of the wire per pass. Further, the borosiloxane coating is removed easily from the output wire by wiping.
I. Introduction
When a solid continuum is pulled through an orifice filled with a viscous fluid, shearing takes place at the interface of the fluid and the solid continuum. Correspondence to: Prof. G.R. Symmons, Department of Mechanical Engineering, Sheffield City Polytechnic, Pond Street, Sheffield, UK.
0924-0136/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
376 If the fluid film is converging in the direction of pull then, in addition to the shear force, a hydrodynamic pressure is generated. The magnitude of the shearing and the pressure generated depend upon the speed with which the continuum is pulled, on the viscosity of the fluid and on the geometric configuration of the orifice that contains the fluid. The shearing causes a drag force on the continuum which, combined with the effect of hydrodynamic pressure, may be sufficient to initiate plastic yielding and produce permanent deformation of the continuum. The application of the concept to die-less drawing was introduced in Ref. [ 1 ] using a polymer melt as the fluid. The development of this process towards a practical wire-drawing process is reported in Refs. [2] and [3]. A number of analytical models have been developed to optimise the geometrical dimensions of the orifice to produce the maximum deformation of the wire. Closed-form analytical models were presented in Refs. [3] and [4] and numerical solutions in Refs. [5] and [6]. Further improvements of the process can be achieved either by modifications to the shape and sizes of the orifice along its axis or by the selection of the type of polymer melt [7,8]. The output wire is coated with the polymer used, the quality and the thickness of the coating depending upon the drawing speed and the type of polymer. Previous work has shown that low density polyethylenes produced consistent coatings with little adhesion to copper wire, whilst nylon 6 produced good adherence. The present experimental investigation compares the deformation of copper wire using borosiloxane at room temperature with more conventional polymers that require heating to produce a melt form. Borosiloxane polymers have constitutive elements of boron, silicon and oxygen with phenyl or methyl groups. The structure is organised around an Si, O, B chain with either the phenyl or methyl groups linked to the silicon atoms. The physical characteristics and properties of the phenyl-based and methyl-based borosiloxanes differ: the phenyl-based borosiloxanes are used as heat- and fire-resistant materials, whilst the methyl-based borosiloxanes are used for abrasive-flow machining where silicon carbides are added to the media to produce the deburring process. Methyl-based borosiloxanes have been used in the present investigation, their rheological properties being affected by additives such as fillers, pigments and oils. Extrudehone supplies three grades of these borosiloxanes: blue, yellow and red, where the resistance to flow is least with the red. The medium-range yellow, which has properties similar to 'bouncing putty', was used in the tests. It is known for its unusual properties: it is readily mouldable; is easily drawn into threads; rebounds as much as 80%; and when struck by a hammer it will shatter into small pieces. It is its cold-flow ability and high elastic properties that make this type ofborosiloxane particularly useful in die-less wire drawing. 2. Experimental, procedure, and equipment
A purpose-built wire-drawing machine was used to carry out the experimental programme using borosiloxane as the working fluid. Figure 1 shows a sche-
377 OIEL,ESS RF.OUCTION UNIT
/
BULL BLOCK
/
T~
S UPPOR T
FRAME
COIL \
Fig. 1. Schematic diagr~ of the drawing machine.
/
P(']IYMFR R F ~ F R V O I R
STEPPEO BORE
OF PLI! t
Fig. 2. Assembly of the die-lessreduction unit.
378
matic diagram of the drawing machine, which used a coil holder, the die-less reduction unit and a bull-block. Figure 2 shows the assembly of the die-less reduction unit, which has an effective length of 10 mm with a gap ratio of 2.6 and a land ratio of 3.0, the same unit having been used for previous tests [8] on low-density polyethylenes, EVA and nylon 6. Similarly, copper wire of 0.45 mm diameter was used for the tests, within a range of drawing speed of 0.05 to 0.8 m/s. The experimental procedure using borosiloxane was simplified by carrying out the polymer tests at room temperature only. The wire was fed through the melt chamber and reduction unit of a fixed geometry and then attached to the motorised bull-block. Measurements of percentage reduction in area and observations on the coatings on the wire were made for small increasing increments of drawing speed. The condition for wire breakage was noted to be in excess of 22% reduction in area, the latter being measured at four positions for each speed increment and an average value being plotted. 3. Experimental results and discussion The experimental results on copper wire using borosiloxane are compared with the previously obtained results for alkathene WVG 23, LD polyethylene SW 6034, elvax 650 and nylon 6. In terms of wire deformation, nylon produced the largest reductions at 17% per pass, with loss of performance with increase nylon6 and polyboroslloxane
22 20 18
416
J
14.
°
A
4-
12 10 8
<>
6 4 2 0
i 0
i 0.2
i
i 0.4
!
i 0.6
0.8
d r o w l n g Sl:MXld r n / s
F i g . 3. Experimental results in percentage reduction in area of wire against drawing speed for nylon 6 and polyborosiloxane. ( V - b o r o s i l o x a n e ; [ ] - n y l o n 2 3 0 ° C; + - n y l o n 240 ° C; O - n y l o n 2 5 0 ° C; - nylon 260°C; × - nylon 270°C)
379 e l v a x 6 5 0 (rod polybomalloxane 22
18 16
14 12 10 8 6
4 2 0
i
I
0
[
0.2
I
I
|
0.4
I
0.6
0.8
drowlng I p e e d m / .
Fig. 4. Experimental results of percentage reduction in area of wire against drawing speed for elvax 650 and polyborosiloxane. ( X - borosiloxane; [] - elvax 140°C; + - elvax 150°C; O - elvax 160°C; A - elvax 180°C)
w~g23 and polyborollioxane 22 20 18 16
14. 12 10
+
+
<>
0
:
+
8 6
4 2 0
A
+
A
Q i
i
0.2
+
'0'
~
I0 i
i
0,4
13 i
I. i
0.6
O.S
drawlng speed m / a
Fig. 5. Experimental resultsof percentage reduction in area of wire against drawing speed for W V G 23 and polyborosiloxane. ( A - borosiloxane; + - W V G 130°C; ~ - W V G 140°C; [] - W V G 180°C)
380 sW6034- a n d p o l y b o r o s l l o x a n e 22
18 16 o c
12
~
10
~
8
g
[] +
6 4 20
i
! 0.2
i
i
i
0.4
drawing l l ~ m d
i 0.6
! 0.8
rn/s
Fig. 6. Experimentalresultsof percentagereductionin area ofwire againstdrawingspeedfor SW 6034 and polyborosiloxane.( 0 - borosiloxane;[] - SW 188°C; + - SW 210°C) in temperature beyond 260 ° C. The optimum drawing speeds for this particular size of reduction unit was 0.4 m/s. Figure 3 shows the results for various melt temperatures of nylon compared with the experimental results using borosiloxane at room temperature. Similarly, Figs. 4-6 show the experimental results of percentage reduction in areas against drawing speed for borosiloxane compared with elvax 650, alkathene WVG 23 and low-density polyethylene SW 6034, respectively. In each case the same size of copper wire and reduction unit was used for each polymer. The experimental results showed a marked improvement in the deformation of the wire using borosiloxane compared with all the other polymers tested. The degree of deformation using borosiloxane increased rapidly with increase in drawing speed, reaching 22% reduction in area - at which breakage of the wire occurred - at 0.12 m/s. The borosiloxane coating was removed easily from the deformed wire by wiping. The results suggest that borosiloxane could be chosen for the deformation of high yield material such as high-tensile steel wire, where many other polymers would require more passes to produce significant reductions. Higher drawing speeds for low yield materials such as copper could be achieved at the achieved 22% reduction in area per pass by modifying the size of the stepped bore. 4. C o n c l u s i o n s
Copper wire has been deformed successfully using a stepped-bore die-less drawing process with borosiloxane at room temperature. The removal of the
381 n e e d to h e a t t h e p o l y m e r i n t o a m e l t f o r m , as in p r e v i o u s cases, s i m p l i f i e s t h e p r o c e s s a n d h a s t h e a d v a n t a g e of a v o i d i n g a n y t h e r m a l d e g r a d a t i o n d u r i n g drawing. T h e b o r o s i l o x a n e c o a t i n g o f t h e o u t p u t wire is r e m o v e d easily b y wiping.
References 1 M.S.J. Hashmi, G.R. Symmons and H. Parvinmehr, A novel technique for wire drawing, J. Mech. Eng. Sci.,24 (1982) 1. 2 M.S.J. Hashmi and G.R. Symmons, U K Patent No. 8311301, 1983. 3 G.R. Symmons, M.S.J. Hashmi and H. Parvinmehr, Plasto-hydrodynamic lubrications,dieless wire drawing, in: Proc. Int. Conf. on Developments in Drawings of Metals, Metals Society, London, 1983, p. 54. 4 M.S.J. Hashmi and G.R. Symmons, A mathematical model for the drawing of a solid continuum through Newtonian fluid filled tubular orifice, in: Proc. 4th Int. Conf. on Mathematical Modelling, Ziirich, August, 1983, pp. 627-633. 5 M.S.J. Hashmi and G.R. Symmons, A numerical solution for the plasto-hydrodynamic drawing of a rigid non linearly strain hardening continuum through a conical orifice, in: Proc. 2nd Int. Conf. on Numerical Methods for Linear Problems, Barcelona, April, 1984, 1048-1059. 6 G.R. Symmons, Y. Xie and M.S.J. Hashmi, Thermal effect on a plasto-hydrodynamic wire drawing process using a polymer melt, Xth Int. Conf. on Rheology, Sydney, Australia, August, 1988, pp. 295-297. 7 I. A1-Natour and M.S.J. Hashmi, Development of a complex geometry pressure unit hydrodynamic coating applications, in: Proc. 6th Conf. of the Irish Manufacturing Committee, (IMC6), Dublin City University, Ireland, August/September, 1989, pp. 280-297. 8 G.R. Symmons, A.H. Memon, M.S.J. Hashmi and Ming Zhang, Polymer coating of wire using a die-less drawing process, ibid., pp. 367-375.