Abrasion Automotive Cables

8/16/2019 Abrasion Automotive Cables

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Evaluation on the Abrasion Resistance of Automotive Wires

Lin Fu, Thomas S. Lin, Caroline H. N. LauferDow Wire & Cable, The Dow Chemical Company

Piscataway, NJ 08854

+1-732-563-5713 · [email protected]

Abstract One of the automotive wire market trends is downgauging of wire

size and insulation thickness so that OEMs can install more wires

in the harness assembly to meet increasing demand for power and

infotainment system in the car. As the insulation wall thickness is

reduced, the abrasion resistance of the automotive wire needs to

be robust to be handled during the harness assembling as well as

wire installation in the car. In this paper, the abrasion resistance of

ultrathin wall automotive wires (0.2 mm insulation thickness) was

studied. Five automotive wire compounds were evaluated for

Taber abrasion, scrape abrasion, and sandpaper abrasion

resistances. These five compounds consist of peroxide

crosslinkable, e-beam irradiation crosslinkable, and thermoplastic

types of formulations. The details of three abrasion testingmethods were compared. Correlations between Taber abrasion

resistance and material properties including flexural modulus,

Shore D hardness and tear strength were investigated. Different

abrading mechanisms of scrape abrasion and Taber abrasion on

the insulation materials were also discussed.

Keywords: Automotive wires; ultrathin wall; sandpaperabrasion; scrape abrasion; Taber abrasion.

1. IntroductionAutomotive wires require well balanced material properties of the

insulation materials, including pinch resistance, scrape abrasion

resistance, sandpaper abrasion resistance, flame resistance,

chemical resistance, heat aging resistance, etc. One of theautomotive wire market trends is downgauging of wire size and

insulation thickness so that OEMs can install more wires in the

harness assembly to meet increasing demand for power and

infotainment system in the car. For some cases, OEMs require the

wire with reduced insulation thickness has the performance

comparable to that of the wire insulation with regular insulation

thickness. Therefore, it becomes very challenging for the wire

with reduced insulation thickness to meet the wire performance

requirements such as sandpaper abrasion resistance, scrape

abrasion resistance, and pinch resistance.

There are three common standards that specify the automotive

wire performance requirements: SAE J-1128[1], SAE J-1678[2],

ISO-6722[3]. In these standards, the automotive wire insulationsare classified into different temperature classes (from 85 ºC to 250

ºC) as well as different insulation thickness. The insulation

thickness is categorized into ultra-thin wall (0.2-0.25 mm), thin

wall (0.25-0.65 mm), and thick wall (0.6-1.6 mm) for different

conductor diameters. Automotive wire compounds can be further

divided into three material categories: peroxide crosslinkable, e-

beam irradiation crosslinkable, and thermoplastic compounds. The

requirements on abrasion resistance depend on the insulation

thickness, conductor size and polymer type (thermoplastic vs.

crosslinked).

Abrasion resistance of polymers and polymer composites can

involve many complex phenomena. There are a lot of literature

reviews on abrasion of polymers and how to improve the abrasion

resistance of polymers and polymer composites [4-7]. When

mechanical, impact, and other kinds of forces are repeatedly

applied, the polymer surface loses mechanical cohesion and debris

is formed on the surface. Depending on the types of polymeric

materials, abrasion mechanisms can be abrasive, adhesive, fatigue,

corrosive, erosive, and delamination, etc. The abrasion resistance

of polymers or polymer composites is generally improved with the

addition of reinforcing fillers. Reinforcing fillers generally

increase the strength of the materials and thus abrasion resistance.

Abrasion resistance of filled polymer composites will depend on

filler hardness, stiffness of polymer matrix, and interfacial

adhesion between fillers and polymers.

In this study, we aim to understand how the wire abrasion

resistance is affected by insulation thickness, crosslinking method,

and material properties. We also investigate the correlations

between wire abrasion resistance (sandpaper abrasion and scrape

abrasion) and plaque abrasion testing (Taber abrasion).

Five representative automotive compounds including two

peroxide crosslinkable (Compounds 1 and 2), two irradiation

crosslinkable compounds (Compounds 3 and 4), and one

thermoplastic compound (Compound 5) were studied, as shown in

Table 1. Compound 1 is a polyethylene copolymer based material

with metal hydrate flame retardant. Compound 2 is another

polyethylene copolymer based material with metal hydrate flame

retardant. Compound 3 and 4 are polyethylene based materials

with metal hydrate flame retardants. Compound 5 is engineering

polymer based compound with non-metal hydrate flame retardant.

Compounds 1 and 2 are designed for 0.4 mm thin wall J-1128

applications. Compounds 3 and 4 are designed for 0.25-0.3 mm

thin wall ISO-6722 applications, and Compound 5 is designed for

0.2 mm ultrathin wall ISO-6722 applications.

Table 1. Comparison of five automotive wire compounds

1 2 3 4 5

Polymer PO1 PO2 PO3 PO4 Engineering polymer

Flame

retardants

Metal

hydrate

Metal

hydrate

Metal

hydrate

Metal

hydrate

Non metal

hydrate

Crosslink Peroxide Peroxide Irradiation Irradiation Thermoplastic

Standards J1128 J1128 ISO 6722 ISO 6722 J1678/ISO 6722

Insulation

thickness

0.4mm 0.4mm 0.25-

0.3mm

0.25-

0.3mm

0.2mm

International Wire & Cable Symposium 230 Proceedings of the 58th IWCS/IICIT


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Plaques and wires were first made with the five automotive wire

compounds listed in Table 1. Thermoplastic and crosslinked wire

and plaques were studied. Material properties including flexural

modulus, Shore D hardness, tensile properties, and tear strength

were measured on plaques.

2. Experiments

2.1 Sample preparation

For the five automotive compounds, plaques with 1.9 mm, 3.2 mmand 6.4 mm thicknesses were made by compression molding. The

five compounds were also extruded in a ¾” single-screw

Brabender extruder to make wires with 0.2 mm insulation layer.

The wire construction used in this study is 18 AWG/19 strand bare

copper. Wires made from Compounds 3 and 4 were e-beam

irradiation crosslinked at 18 Mrad. For peroxide crosslinked

Compounds 1 and 2, the insulations were extruded on 20 AWG/7

strand bare copper wires using a 2.5” single-screw extruder with

steam curing..

2.2 Material property testingThe five compounds were evaluated for the tensile properties

(ASTM 683, 500 mm/min pulling speed), Shore D hardness(ASTM D2240, 15 second delay), and tear strength (ASTM

D1004, Die “C”). The above properties were measured on the test

specimens with nominal 1.9 mm thickness. Flexural modulus

(ASTM D790) was measured on the test specimen with nominal

6.4 mm thickness.

2.3 Abrasion resistance testingSchematics for three abrasion testing methods are shown in Figure

1. Taber abrasion was conducted on plaques with two rotating

abrading wheels weighing 1.25 kg each. Taber abrasion resistance

was tested on disks with nominal 3.2 mm thickness using

Teledyne Taber Dual Abrader. Two round disks with 10 cm

diameter were used for each sample. The disks were cleaned with

isopropanol and the initial weight of each disk was recorded. Bothdisks were secured to the Teledyne turntables. Each turntable has

two wheels (13 mm thickness) that are lined with a 180 grit

sandpaper. Each wheel was weighted with 1250 grams. The

wheel rotated tangentially to the turntable to impart the abrasion.

Each disk was subjected to 600 revolutions of abrasion cycle.

After each 100 revolution, each disk was cleaned with isopropanol

and the new weight was recorded. The weigh losses of the last

300 revolutions for each disk were used for the data analysis.

This procedure was performed on both sides of each disk. A total

of 6 measurements of the weight loss for each disk were collected

(12 measurements for each sample).

The scrape abrasion resistance was tested using the scrape tester

according to ISO 6722[3]

. It was conducted with a needlescratching wire surface under 7N load. The number of cycles that

the needle takes to abrade through the insulation was recorded.

Sandpaper abrasion resistance was tested according to SAE

J1678[2]. It was conducted with a sandpaper sanding wire surface

under 163 g load. The total length of sandpaper that is used to

abrade through wire insulation was recorded.

(1) Wire scrape abrasion tests

(2) Wire sandpaper abrasion tests

(3) Taber abrasion tests on plaques

Figure 1. Comparison of three abrasion testingmethods. (1) Wire scrape abrasion

[3], (2) Wire sandpaper

abrasion[2]

and (3) Taber abrasion.

3. Results and Discussion

3.1 Taber abrasion resistance3.1.1 Comparison of Taber abrasion resistances

Plaques of five automotive compounds were tested on Taber

abrasion resistance. For each compound, both thermoplastic and

crosslinked version of plaques were tested, except that Compound 5

is not crosslinkable and only thermoplastic data is shown. Figure 2

shows the Turkey-Kramer statistical comparison of Taber abrasionmass losses for the above compounds. By comparing thermoplastic

and crosslinked versions of Compound 1 (1TH vs. 1XL), it can be

seen that crosslinking reduced the weight loss per 100 cycles and

improved the Taber abrasion resistance over thermoplastic version.

However, crosslinking of polymers doesn’t always help improve

Taber abrasion resistance. Crosslinked Compounds 3 and 4 had

comparable abrasion resistance (mass loss) as the thermoplastic

versions. Compounds 3 and 4 consist of a high crystallinity

polyethylene and Compound 1 consists of low crystallinity



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polyethylene copolymer. It is thus inferred that crosslinking

improves the Taber abrasion resistance for low crystallinity

materials but not for high crystallinity materials.

High crystallnity materials show higher Taber abrasion resistance

than low crystallinity materials (e.g. 1TH vs. 3TH, 1XL vs. 3XL).

Thermoplastic Compound 5 doesn’t contain any metal hydrate flame

retardant but it shows very low mass loss compared to other

compounds. The engineering polymer based Compound 5 has high

abrasion resistance due to its intrinsic high hardness and toughness.

Figure 2. Taber abrasion resistance on five automotivewire compounds.

3.1.2 Correlation between Taber abrasion and material

properties

In Figure 3, the Taber abrasion weight loss is plotted against the

flexural modulus for these five compounds. A relatively moderate

correlation is seen between Taber abrasion weight loss and flexural

modulus. Taber abrasion weight loss decreases with increasing

flexural modulus. The correlation in Figure 3 suggests that the

stiffness of materials plays an important role in preventing materials

from being removed by sandpaper on the abrading wheels.

Generally more energy is required to cut and remove a stiffer

material from the bulk materials. The abrasion depth after 600 Taberabrasion cycles is about 0.38mm. This suggests that the abrasion

resistance is a surface phenomenon which occurs within a very thin

layer on the plaque. Although the general trend between Taber

abrasion weight loss and flexural modulus is seen in Figure 3, Taber

abrasion weight loss can be different for materials with comparable

flexural modulus if these materials show different surface

morphology, smoothness, or coefficient of friction.

R2 = 0.66

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 200 400 600 800 1000 1200

Flexural modulus (MPa)

W e i g h t l o s

s ( g / 1 0 0 c y c l e s )

Figure 3 Correlation between Taber abrasion resistance

and flex modulus.

Figure 4 shows that weight loss in Taber abrasion decreases with

increasing tear strength of materials. The mechanism of Taber

abrasion is to remove materials off the surface, which involves the

detachment of fillers from polymer matrix and the tearing of

polymer chains. Tear strength reflects a response to the tearing

force induced during the abrasive action. Therefore, it is

reasonable to see the trend of decreasing Taber abrasion weight

loss with increasing tear strength.

R2 = 0.72

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.0E+00 5.0E+04 1.0E+05 1.5E+05 2.0E+05

Tear strength (N/m)

W e i g h t l o s s ( g / 1 0 0 c y c l e s )

Figure 4 Correlation between Taber abrasion resistanceand tear strength.

3.2 Scrape abrasion resistance3.2.1 Comparison of scrape abrasion resistances

The scrape abrasion resistances for five automotive wires are

shown in Figure 5. The study includes both crosslinked and non-

crosslinked versions of wire insulations. The requirement in ISO

6722 for scrape abrasion resistance is 350 cycles. Compound 5,

which is designed for ultrathin auto wire application, is the only

sample meeting this requirement. All other compounds for thin-

wall automotive wire application have significantly lower scrape

abrasion resistances. It was found that crosslinking the

compounds could slightly improve the scrape abrasion resistance,

e.g., 1TH vs. 1XL and 4TH vs. 4XL. The reverse trend seen in

Compound 3 is very likely due to unexpected diameter change

after irradiation curing. It was found that high crystallinitycompounds (Compounds 3 and 4) show higher abrasion resistance

than low crystallinity Compounds 1. Compound 5 contains high

hardness engineering polymer and it has the highest scrape

abrasion resistance.

1

10

100

1000

1TH 1XL 3TH 3XL 4TH 4XL 5TH

4

8

12

4

9

27

739

N u m b e r o f c y c l e s

Figure 5 Scrape abrasion resistance.

3.2.2 Correlation between Scrape abrasion and flexural

modulus

Figure 6 shows relatively strong correlation between scrape

abrasion resistance and flexural modulus. The scrape abrasion

M a s s l o s s ( g / 1 0 0 c y c l e s )

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

1 TH 1XL 2XL 3TH 3XL 4TH 4XL 5TH



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resistance (number of cycles to fail) increases with flexural

modulus. This correlation is consistent with what we observed in

Figure 5. The high crysallinity and crosslinked materials, which

generally have high flexural modulus, show high scrape abrasion

resistance. The strong correlation indicates that scrape abrasion

resistance highly depends on the ability for a material to deform

under an applied load. This also suggests that the mechanisms for

scrape abrasion and Taber abrasion are different. More on the

difference between scrape abrasion and Taber abrasion will be

discussed in 3.2.3.

R2 = 0.91

1

10

100

1000

0 200 400 600 800 1000 1200

Flexural Modulus (MPa)

S c r a p e r e s i s t a n c e ( c y c l e s )

Figure 6 Correlation between scrape abrasionresistance and flexural modulus.

3.2.3 Correlation between Scrape abrasion and Taber

abrasion resistance

Figure 7 shows poor correlation between scrape abrasion

resistance and Taber abrasion resistance. The poor correlation

results from different mechanisms of abrasion in these two tests.

In the scrape abrasion resistance test, a needle (polished spring

wire) with a 0.45 mm diameter abrades the wire surface along the

longitudinal direction. The main abrasion mechanism is the initial

surface deformation by the needle pressing into the insulation

surface and a subsequent removal of the insulation material by the

friction force between the needle and polymer surface. In the

Taber abrasion test, the sample surface is abraded repeatedly bythe rough sandpaper. The main abrasion mechanism is the

removal of the insulation material by the rough particles imbedded

in the sandpaper. Further discussion on the differences can be

found in a separate IWCS paper [7].

y = 275.11e-29.042x

R2 = 0.3414

1

10

100

1000

0 0.05 0.1 0.15 0.2

Figure 7 Correlation between scrape abrasion and Taber

abrasion resistance.

3.3 Sandpaper abrasion resistance

3.3.1 Comparison of sandpaper abrasion resistances

The sandpaper abrasion resistances are shown in Figure 8. The

requirement in J1678 is a minimum 200 mm sandpaper length to

abrade the whole insulation. Most of wires marginally passed the

requirement. Compound 5 with the highest flexural modulus did

not show a high sandpaper abrasion resistance. The high abrasion

resistance of crosslinked Compound 1 may have resulted from the

relatively high gel content (80 wt%) of the compound. The large

standard deviation was due to the non-centering of wire insulation.

The above results indicate that high crystallinity, crosslinking, and

engineering polymer did not improve significantly sandpaper

abrasion resistance as they did in scrape abrasion resistance.

0

200

400

600

800

1000

1200

1400

1TH 1XL 3TH 3XL 4TH 4XL 5TH

Figure 8 Sandpaper abrasion resistance.

3.3.2 Correlation between Sandpaper abrasion resistance

and Taber abrasion resistance

Figure 9 shows the correlations between sandpaper abrasion

resistance of wires (thin wall and ultra thin wall) and Taber

abrasion weight loss. Thin wall wires have higher sandpaper

abrasion resistances than ultrathin wall wires due to the thicker

insulation layer and lower abrasion stress experienced.

The results show a good correlation between sandpaper abrasion

and Taber abrasion weight loss for thin wall wires, but not for

ultrathin wall wires. The typical thickness change was ca. 0.38

mm after 600 cycle Taber abrasion. Therefore, Taber abrasion

test is similar to sandpaper abrasion test on 0.4 mm thin wall

automotive wire. The good correlation between sandpaper

abrasion resistance and Taber abrasion resistance suggests that

these two tests share a similar abrasion mechanism. Both tests usesandpaper to abrasively remove materials off surface. On the

other hand, the thickness of ultrathin wire insulation is 0.2 mm, in

which surface finish, surface smoothness, and skin layer near the

outer surface of the insulation all become dominant factors in

determining the sandpaper abrasion resistance. This could be the

reason that Taber abrasion test does not correlate well with the

sandpaper abrasion test for the ultrathin wire.

y = -688.65x + 280.27

R2 = 0.2941

y = -12375x + 2546.4

R2 = 0.9884

0

200

400

600

800

1000

1200

1400

0 0.05 0.1 0.15 0.2

Figure 9 Correlation between sandpaper abrasion and

Taber abrasion resistance.

R2=0.34

Thin wall

R2=0.98

Ultrathin wall

R2=0.26

Taber abrasion (g/100 cycles)

Taber abrasion (g/100 cycles)

S c r a p e r e s i s t a n c e

( c y c l e s )

S a n d p a p

e r r e s i s t a n c e

(

m m )



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4. ConclusionsFive automotive wire compounds were evaluated for Taber

abrasion resistance, scrape abrasion resistance, and sandpaper

abrasion resistance. These five compounds consist of peroxide

crosslinkable, e-beam irradiation crosslinkable, and thermoplastic

types of formulations. Effects of crosslinking, crystallinity and

insulation thickness, and material properties on abrasion resistance

were discussed for each abrasion test.

The abrasion resistances of ultrathin wall and thin wall automotivewires, both crosslinked and thermoplastic, were investigated.

Generally speaking, thin wall wires have higher abrasion

resistance than ultrathin wall wires due to the thicker insulation

layer and lower abrasion stress experienced. It was found that

crosslinking improved the Taber abrasion resistance for low

crystallinity materials but not for high crystallinity materials.

Crosslinking improves scrape abrasion resistance for both low

crystallnity and high crystallinity materials. Generally, low

crystallinity materials show lower Taber abrasion resistance and

scrape abrasion resistance than high crystallinity materials.

However, high crystallinity materials did not improve sandpaper

abrasion resistance compared to low crystallinity materials.

The correlations between Taber abrasion resistance, scrape

abrasion resistance, and material properties were examined.Strong correlations were found between scrape abrasion resistance

and flexural modulus. Moderate correlations between Taber

abrasion and flexural modulus/tear strength were observed.

Different abrading mechanisms of Taber abrasion, sandpaper

abrasion, and scrape abrasion were discussed. Taber abrasion and

sandpaper abrasion show strong correlation for thin wall wires,

which suggests a similar mechanism of abrasion in these two tests.

No correlation is seen between scrape abrasion resistance and

Taber abrasion resistance. This indicates different mechanisms

between Taber abrasion and scrape abrasion. The main abrasion

mechanism in scrape abrasion is the initial surface deformation by

the needle, followed by the removal of the insulation material by

the friction force between the needle and polymer surface. In the

Taber and sandpaper abrasion tests, the main abrasion mechanismis the removal of the insulation material by the rough particles

imbedded in the sandpaper.

5. AcknowledgementsThe authors would like to acknowledge Dr. Scott Wasserman for

his support in this project and Dr. Jeffrey Cogen and Kurt Bolz for

their helpful discussion. A special thank is extended to Erik

Groot-Enzerink for his help and discussion on the scrape abrasion

test.

6. References[1] SAE J1128, “Low Voltage Primary Cable”, (2005).[2] SAE J1678, “Low Voltage Ultra-Thin Wall Primary Cable”,

(2004).

[3] ISO 6722, “Road Vehicles -60 V and 600 V Single-coreCables – Dimensions, Test Methods and Requirements,”

(2006).

[4] A. Dasari, Z.Z. Yu and Y.W. Mai, “Fundamental aspectsand recent progress on wear/scratch damage in polymer

nanocomposites”, Mater. Sci. Eng. R (2008).

[5] J.Song and G.W. Ehresntein, in: K.Friedrich Eds. Advances inComposite Tribology, Elsevier Science Publishers B.V.,

Amsterdam, (1993).

[6] S.J. Kim, M.H. Cho, R.H. Basch, J.W. Fash, and H. Jang,“Tribological Properties of Polymer Composites Containing

Barite (BaSO4) or Potassium Titanate (K 2O · 6(TiO2))”,

Tribology Letters 17, 655-661 (2004).

[7] C. Laufer, T.S. Lin and L. Fu, “Fundamentals of abrasionmechanisms in automotive wires”, 58th IWCS Conference,

(November, 2009).

7. Authors

Dr. Lin Fu is a senior engineer in the Wire and Cable R&D group

of The Dow Chemical Company. She has her Ph.D. in chemical

engineering from Princeton University and B.S. degree from

Tsinghua University in Beijing, China. Her expertise includesmaterial science, polymer rheology, self-assembly of

macromolecules and colloid science. She is a member of American

Institute of Chemical Engineers and American Chemical Society.

Dr. Thomas S. Lin is a senior research specialist in the Wire and

Cable R&D group of The Dow Chemical Company. He has a

B.S. in Chemical Engineering from University of Washington and

a Ph.D in Chemical Engineering from Cornell University. His

present research areas include polymer flame retardancy, polymer

stabilization, and nanocomposites for wire and cable applications.

He is presently an active member of SAE Cable Task Force. He is

a member of American Institute of Chemical Engineers, Society

of Plastics Engineers, and Society of Automotive Engineers.

Dr. Caroline H. N. Laufer is a senior engineer in the Wire and Cable

R&D group of The Dow Chemical Company. She earned her B.E.

in chemical engineering from The Cooper Union, and a Ph.D in

chemical engineering from the New Jersey Institute of Technology.

Following her postdoctorate fellowship in chemical engineering at

the University of Delaware, she joined The Dow Chemical

Company in Bound Brook, NJ, where her research areas include

polymer compatibilization and nanocomposities.


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