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Polymer coating of wire using a die-less drawing process
Journal of Materials Processing Technology, 26 (1991) 173-180
173
Elsevier
Polymer coating of wire using a die-less drawing process G.R. Symmons Sheffield City Polytechnic, Sheffield, UK
A.H. Menon Mehran University College of Engineering, Nawabshah, Pakistan
Zhang Ming Chengdu University, Chengdu, China
and M.S.J. Hashmi Dublin City University, Dublin, Ireland
Industrial Summary A process known as die-less wire drawing has been developed in which polymer melts are used as a pressure medium in a reduction unit of stepped bore geometry. The wire size is less than the bore of the reduction unit, eliminating a conventional die, and providing a combined deformation of the wire together with a polymer coating. Previous experimental investigations have shown significant percentages in reduction of area but polymer coating of poor adhesion to the drawn wire. The present experimental investigation compares the coating performance on copper wire with different types of polymer which vary in melt index and viscosity ranges. The results show that adhesion is good with polyamides and the quality of coat improved using a low melt index polyethylene. Significant reductions in area of wire were achieved but small variations in maximum reduction were measured with changes in the polymer melt. Temperature of the polymer and drawing speed had significant effects on both the reduction in area and quality of polymer coating on the wire.
1. I n t r o d u c t i o n
The concept of plasto-hydrodynamic wire drawing was introduced in Ref. [ 1 ] in which a die-less reduction unit was used in conjunction with a viscous fluid. Reduction in the diameter of the wire is affected by the plasto-hydrodynamic pressure and shear stress generated by drawing the wire through a stepped bore reduction unit filled with a viscous fluid. The development of this new process towards a practical wire drawing process is given in Refs. [2,3 ]. A number of analytical models have been developed to optimise the geometrical 0924-0136/91/$03.50 © 1991--Elsevier Science Publishers B.V.
174
dimension of the reduction unit to produce maximum deformation of the wire. Closed form analytical models were presented in Refs. [3,4] and numerical solutions in Refs. [5,6]. The emphasis has been on using polymer melts as the pressure medium resulting in reductions of wire size using short units comparable with conventional methods. Another advantage of using polymer melts in the die-less wire drawing process is that the output wire is coated and the thickness of coat can be varied by changing the drawing speed. Previous work has concentrated on the process as a deformation system for the reduction in diameter of wire. In this paper an experimental programme has been carried out to investigate the quality of polymer coatings produced for different types of polymer using a fixed size stepped bore reduction unit. Coating thickness on the wire which is dependent upon deformation is measured in the experiments and comparisons made for change in melt temperature and polymer.
2. Experimental procedure and equipment A purpose built wire drawing machine was used to carry out the experimental programme. Figure 1 (a) shows a schematic diagram of the drawing machine which incorporated a coil holder, the die-less reduction unit and a bullblock. The drawing speed range was 0.05 to 0.8 m s - 1. The same reduction unit was used for all polymer tests consisting of a stepped bore cylinder and a melt chamber rigidly fastened to a drawing bench as shown in Fig. 1 (b). The length of the cylinder was 10 mm with a gap ratio of 2.6 and land ratio of 3.0. The polymer was fed into the melt chamber in granular form and heated by a jacket type electrical heater band. Temperature of the polymer melt were varied by thermostat control ranging from 120-270 ° C. Copper wire 0.45 mm diameter was used for the test. Five types of polymer were tested each over the speed range, with various melt temperatures to suit the polymer. To start a test for a selected polymer, the wire was fed through the melt OZELESS ~ o u c n o .
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Fig. 1. Schematic diagram showing: (a) the drawing machine; and (b) the reduction unit and polymer melt chamber.
175
chamber and through the reduction unit of a fixed geometry. The wire was then attached to the motorised bull-block. When the process is started, the wire is pulled through the melt chamber and reduction unit and drags the molten polymer into the unit causing hydrodynamic action generating pressure and shear stresses in the polymer. If the magnitude of these pressures and shear stresses are equal to the yield stress of the wire materials then reduction in diameter takes place and an increase in polymer coating thickness is produced on the output wire. For a set stable melt temperature outputs of coated wire were measured for percentage reduction in area, coating thickness and surface quality for a change in drawing speed. The experiments were repeated for a series of melt temperatures. On completion of the tests, the melt chamber was purged and cleaned before a new polymer was used for the same experimental procedure. 3. E x p e r i m e n t a l results
Five polymers were tested in the die-less drawing machine: Alkathene WVG 23 BP D2145 SW 6034 BP D2133 SR7329 Elvax 650 Nylon 6
-
low density polyethylene low density polyethylene high density polyethylene EVA Nylon
All the polymers except the high density polyethylene produced reduction in area and coatings of the wire. The melt temperatures were varied through a wide range for BP D2133 but flow through the reduction unit proved unsuccessful hence no results are available for this polymer. Alkathene WVG 23 has been tested previously as shown in Ref. [3] with success in producing deformation and coating of the wire. Figure 2 shows the repeated test results on deformation on the selected size of reduction unit used for all the tests reported in this paper. The results for three polymer melt temperatures are shown with a maximum reduction in area of 11 percent. The other low density polyethylene BP D2145 produced higher reductions in area up to 15 percent per pass with the melt temperatures at higher values as shown in Fig. 3. Similarly Elvax 650 produced reduction in area of the wire up to 14 percent as shown in Fig. 4, but was sensitive to melt temperature. The reductions in area produced by Nylon 6 shown in Fig. 5 were of the same order of magnitude to the other polymers. Due to the wire breaking at reductions larger than 15 percent per pass indications were that this polymer would otherwise produce maximum reductions and coating thickness. Polymer coatings of the wire were produced for both the low density polyethylenes, EVA and Nylon. Experimental results are shown in Fig. 6 of the size of coatings for WVG 23 and the effects
176 polymer
material:
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Fig. 2. Experimental results of percentage reduction in area of wire against drawing speed for WVG 23 polymer at different melt temperatures ( ° C ). polymer material: BPD2145/SW6054
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177 polymer moteriol: elvax650
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Fig. 5. Experimental results of percentage reduction in area of wire against drawing speed for Nylon 6 at different melt temperatures ( ° C ).
178 polymer moteHol: wvg23 0.045
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Fig. 6. Experimental results of coating thickness against drawing speed for WVG23 polymer at different melt temperatures ( ° C ). polymer material: nylon 6 0.06
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Fig. 7. Experimental results of coating thickness against drawing speed for Nylon 6 at different melt temperatures ( ° C ).
179
of drawing speed and melt temperature. The coating results using Nylon 6 are shown in Fig. 7. The nylon coatings strongly adhered to wire in which thickness of coat was sensitive to change in drawing speed. 4. D i s c u s s i o n
The results show that polymer coatings on copper wire for four types of polymer using the die-less wire drawing process produce coat thicknesses which can be varied by drawing speed and melt temperature. The minimum coat thickness was set by the choice of outlet size of the stepped bore in the reduction unit and increases in coatings were produced by deforming the wire. Maximum change in coat thickness with speed was obtained from Nylon 6. This polymer was only limited in further reductions of the wire with increase in speed by the strength of the wire itself rather than the rheological behaviour of the polymer melt. All the polymer results indicate a maximum condition of reduction and hence coating thickness when the polymer is used just above its melt temperature. For this condition Nylon 6 trebled its coating thickness when increasing the drawing speed from 0.05 m / s to 0.3 m / s producing an even adhered coat. A similar performance was found from WVG23 over a wider speed range but with no adherence of the polymer coat to the wire. At the higher drawing speeds both EVA and BPD2145 produced a roughness in the coat surface with sharkskin appearing at the maximum speed whereas the nylon and WVG23 gave smooth surface finishes. No evidence of die swell was noticed. Although there was little difference in the maximum reductions in wire diameter for the four successful polymers over the full drawing speed range and coating thickness, there were significant differences in the rates of change with speed and the adherence of the coating to the wire. 5. C o n c l u s i o n s
Copper wire has been successfully coated using a stepped bore die-less drawing process in conjunction with a variety of polymer melts. Reductions in area of the wire have simultaneously been achieved providing an ability to produce polymer coatings in which their thickness depends upon the speed of drawing. Low density polyethylenes produced consistent coatings with little adhesion to the copper wire. Less success in producing coatings was found from a high density polyethylene. Coatings with good adherence to the wire were produced from Elvax and Nylon 6.
References 1 M.S.J. Hashmi, G.R. Symmons and H. Parvinmehr, A novel technique for wire drawing, J. Mech. Eng. Sci., 24 ( 1 ) ( 1982 ) 1.
180 2 M.S.J. Hashmi and G.R. Symmons, UK Patent No. 8311301, 1983. 3 G.R. Symmons, M.S.J. Hashmi and H. Parvinmehr, Plasto-hydrodynamic lubrication, dieless wire drawing, Proc. Int. Conf. on Developments in Drawings of Metals, Metals Society, London, P. 54, 1983. 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, Proc. 4th Int. Conf. on Mathematical Modelling, Zurich, August 1983. 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, Proc. 2nd Int. Conf. on Numerical Methods for Non Linear Problems, Barcelona, April 1984. 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.
173
Elsevier
Polymer coating of wire using a die-less drawing process G.R. Symmons Sheffield City Polytechnic, Sheffield, UK
A.H. Menon Mehran University College of Engineering, Nawabshah, Pakistan
Zhang Ming Chengdu University, Chengdu, China
and M.S.J. Hashmi Dublin City University, Dublin, Ireland
Industrial Summary A process known as die-less wire drawing has been developed in which polymer melts are used as a pressure medium in a reduction unit of stepped bore geometry. The wire size is less than the bore of the reduction unit, eliminating a conventional die, and providing a combined deformation of the wire together with a polymer coating. Previous experimental investigations have shown significant percentages in reduction of area but polymer coating of poor adhesion to the drawn wire. The present experimental investigation compares the coating performance on copper wire with different types of polymer which vary in melt index and viscosity ranges. The results show that adhesion is good with polyamides and the quality of coat improved using a low melt index polyethylene. Significant reductions in area of wire were achieved but small variations in maximum reduction were measured with changes in the polymer melt. Temperature of the polymer and drawing speed had significant effects on both the reduction in area and quality of polymer coating on the wire.
1. I n t r o d u c t i o n
The concept of plasto-hydrodynamic wire drawing was introduced in Ref. [ 1 ] in which a die-less reduction unit was used in conjunction with a viscous fluid. Reduction in the diameter of the wire is affected by the plasto-hydrodynamic pressure and shear stress generated by drawing the wire through a stepped bore reduction unit filled with a viscous fluid. The development of this new process towards a practical wire drawing process is given in Refs. [2,3 ]. A number of analytical models have been developed to optimise the geometrical 0924-0136/91/$03.50 © 1991--Elsevier Science Publishers B.V.
174
dimension of the reduction unit to produce maximum deformation of the wire. Closed form analytical models were presented in Refs. [3,4] and numerical solutions in Refs. [5,6]. The emphasis has been on using polymer melts as the pressure medium resulting in reductions of wire size using short units comparable with conventional methods. Another advantage of using polymer melts in the die-less wire drawing process is that the output wire is coated and the thickness of coat can be varied by changing the drawing speed. Previous work has concentrated on the process as a deformation system for the reduction in diameter of wire. In this paper an experimental programme has been carried out to investigate the quality of polymer coatings produced for different types of polymer using a fixed size stepped bore reduction unit. Coating thickness on the wire which is dependent upon deformation is measured in the experiments and comparisons made for change in melt temperature and polymer.
2. Experimental procedure and equipment A purpose built wire drawing machine was used to carry out the experimental programme. Figure 1 (a) shows a schematic diagram of the drawing machine which incorporated a coil holder, the die-less reduction unit and a bullblock. The drawing speed range was 0.05 to 0.8 m s - 1. The same reduction unit was used for all polymer tests consisting of a stepped bore cylinder and a melt chamber rigidly fastened to a drawing bench as shown in Fig. 1 (b). The length of the cylinder was 10 mm with a gap ratio of 2.6 and land ratio of 3.0. The polymer was fed into the melt chamber in granular form and heated by a jacket type electrical heater band. Temperature of the polymer melt were varied by thermostat control ranging from 120-270 ° C. Copper wire 0.45 mm diameter was used for the test. Five types of polymer were tested each over the speed range, with various melt temperatures to suit the polymer. To start a test for a selected polymer, the wire was fed through the melt OZELESS ~ o u c n o .
,J~
~ESSOeE :¥~NOE~
F'OLYME R
/
/
i
~
~E~TE Ft
~ 5 i ~ 1 0 N OF r ~ E ~aessueE
(a)
TeANSOUtEeS
(b)
Fig. 1. Schematic diagram showing: (a) the drawing machine; and (b) the reduction unit and polymer melt chamber.
175
chamber and through the reduction unit of a fixed geometry. The wire was then attached to the motorised bull-block. When the process is started, the wire is pulled through the melt chamber and reduction unit and drags the molten polymer into the unit causing hydrodynamic action generating pressure and shear stresses in the polymer. If the magnitude of these pressures and shear stresses are equal to the yield stress of the wire materials then reduction in diameter takes place and an increase in polymer coating thickness is produced on the output wire. For a set stable melt temperature outputs of coated wire were measured for percentage reduction in area, coating thickness and surface quality for a change in drawing speed. The experiments were repeated for a series of melt temperatures. On completion of the tests, the melt chamber was purged and cleaned before a new polymer was used for the same experimental procedure. 3. E x p e r i m e n t a l results
Five polymers were tested in the die-less drawing machine: Alkathene WVG 23 BP D2145 SW 6034 BP D2133 SR7329 Elvax 650 Nylon 6
-
low density polyethylene low density polyethylene high density polyethylene EVA Nylon
All the polymers except the high density polyethylene produced reduction in area and coatings of the wire. The melt temperatures were varied through a wide range for BP D2133 but flow through the reduction unit proved unsuccessful hence no results are available for this polymer. Alkathene WVG 23 has been tested previously as shown in Ref. [3] with success in producing deformation and coating of the wire. Figure 2 shows the repeated test results on deformation on the selected size of reduction unit used for all the tests reported in this paper. The results for three polymer melt temperatures are shown with a maximum reduction in area of 11 percent. The other low density polyethylene BP D2145 produced higher reductions in area up to 15 percent per pass with the melt temperatures at higher values as shown in Fig. 3. Similarly Elvax 650 produced reduction in area of the wire up to 14 percent as shown in Fig. 4, but was sensitive to melt temperature. The reductions in area produced by Nylon 6 shown in Fig. 5 were of the same order of magnitude to the other polymers. Due to the wire breaking at reductions larger than 15 percent per pass indications were that this polymer would otherwise produce maximum reductions and coating thickness. Polymer coatings of the wire were produced for both the low density polyethylenes, EVA and Nylon. Experimental results are shown in Fig. 6 of the size of coatings for WVG 23 and the effects
176 polymer
material:
wv923
12-11
Cl 180
lo
+ 130
i¢
9
b 140
/
8
°
7
f
/
5~
4//
3
~; x
+
2 1 0
I
I
0
I
I
i
0.2
I
0.6
0.4
0.8
drow;ng speed rn/s
Fig. 2. Experimental results of percentage reduction in area of wire against drawing speed for WVG 23 polymer at different melt temperatures ( ° C ). polymer material: BPD2145/SW6054
16 15
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14
+210
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~~=~::~
°
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~
= 0.4
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] 0.6
l 0.8
drawing speed m/s Fig. 3. Experimental results of percentage reduction in area of wire against drawing speed for B P D2145/SW6034 polymer at different melt temperatures ( ° C ).
177 polymer moteriol: elvax650
u
14
1+o
~-"
+ 150
13-
/
/ +/~
+
/
i 12
o 16G
11
A 180
/ /
10 o
/
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9
9
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I
0.4 drawing speed
I
--
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0.8
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Fig. 4. Experimental results of percentage reduction in area of wire against drawing speed for Elvax 650 at different melt temperatures ( oC ). polymer material: nylon 6 +
17
o~.
16
~ 230
15
+ 24o
14
<> 250
13
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Fig. 5. Experimental results of percentage reduction in area of wire against drawing speed for Nylon 6 at different melt temperatures ( ° C ).
178 polymer moteHol: wvg23 0.045
- -[] 180
+ 130
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+
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Fig. 6. Experimental results of coating thickness against drawing speed for WVG23 polymer at different melt temperatures ( ° C ). polymer material: nylon 6 0.06
[]
/~"v f
0.05 "
E E
,'
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t
///
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.
~
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O 250 n 260
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Fig. 7. Experimental results of coating thickness against drawing speed for Nylon 6 at different melt temperatures ( ° C ).
179
of drawing speed and melt temperature. The coating results using Nylon 6 are shown in Fig. 7. The nylon coatings strongly adhered to wire in which thickness of coat was sensitive to change in drawing speed. 4. D i s c u s s i o n
The results show that polymer coatings on copper wire for four types of polymer using the die-less wire drawing process produce coat thicknesses which can be varied by drawing speed and melt temperature. The minimum coat thickness was set by the choice of outlet size of the stepped bore in the reduction unit and increases in coatings were produced by deforming the wire. Maximum change in coat thickness with speed was obtained from Nylon 6. This polymer was only limited in further reductions of the wire with increase in speed by the strength of the wire itself rather than the rheological behaviour of the polymer melt. All the polymer results indicate a maximum condition of reduction and hence coating thickness when the polymer is used just above its melt temperature. For this condition Nylon 6 trebled its coating thickness when increasing the drawing speed from 0.05 m / s to 0.3 m / s producing an even adhered coat. A similar performance was found from WVG23 over a wider speed range but with no adherence of the polymer coat to the wire. At the higher drawing speeds both EVA and BPD2145 produced a roughness in the coat surface with sharkskin appearing at the maximum speed whereas the nylon and WVG23 gave smooth surface finishes. No evidence of die swell was noticed. Although there was little difference in the maximum reductions in wire diameter for the four successful polymers over the full drawing speed range and coating thickness, there were significant differences in the rates of change with speed and the adherence of the coating to the wire. 5. C o n c l u s i o n s
Copper wire has been successfully coated using a stepped bore die-less drawing process in conjunction with a variety of polymer melts. Reductions in area of the wire have simultaneously been achieved providing an ability to produce polymer coatings in which their thickness depends upon the speed of drawing. Low density polyethylenes produced consistent coatings with little adhesion to the copper wire. Less success in producing coatings was found from a high density polyethylene. Coatings with good adherence to the wire were produced from Elvax and Nylon 6.
References 1 M.S.J. Hashmi, G.R. Symmons and H. Parvinmehr, A novel technique for wire drawing, J. Mech. Eng. Sci., 24 ( 1 ) ( 1982 ) 1.
180 2 M.S.J. Hashmi and G.R. Symmons, UK Patent No. 8311301, 1983. 3 G.R. Symmons, M.S.J. Hashmi and H. Parvinmehr, Plasto-hydrodynamic lubrication, dieless wire drawing, Proc. Int. Conf. on Developments in Drawings of Metals, Metals Society, London, P. 54, 1983. 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, Proc. 4th Int. Conf. on Mathematical Modelling, Zurich, August 1983. 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, Proc. 2nd Int. Conf. on Numerical Methods for Non Linear Problems, Barcelona, April 1984. 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.