Research Papers: Internal Combustion Engines

Improved Embeddability for Polymeric Bearing Overlays

[+] Author and Article Information
David Latham

MAHLE Engine Systems,
Rugby CV23 0WE, UK
e-mail: david.latham@gb.mahle.com

Ian Laing

MAHLE Engine Systems,
Rugby CV23 0WE, UK
e-mail: ian.laing@gb.mahle.com

Ronald Brock

MAHLE Engine Components, Inc.,
Farmington Hills, MI 48335
e-mail: ronald.brock@us.mahle.com

Contributed to the Internal Combustion Engine Committee for publication in the ASME Journal of Engineering for Gas Turbines and Power. Manuscript received January 27, 2016; final manuscript received February 1, 2016; published online March 22, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(9), 092805 (Mar 22, 2016) (8 pages) Paper No: GTP-16-1039; doi: 10.1115/1.4032714 History: Received January 27, 2016; Revised February 01, 2016

Recent engine developments toward higher loads (down-sizing) and thinner oil films have increased the severity of plain bearing operating conditions [1]. These factors, combined with lower viscosity oils, have resulted in a greater sensitivity of bearings to damage by foreign debris particles. Traditional highly embeddable materials, such as lead, are being progressively phased out. This lead-free trend observed in the passenger car market is likely to spread to the truck market in the future. As a result, it is becoming increasingly challenging to balance the conflicting hard and soft requirements of bearing materials. Although new generations of bearing materials, particularly polymeric overlays, have shown excellent fatigue and wear capabilities [2], they would benefit from enhanced embeddability properties. This demand has led MAHLE to take a new approach with the development of a polymeric overlay material that has both hard and soft characteristics. This newly developed soft-phase copolymer resin has been synthesized from monomers selected to give the desired properties. Conventional polyamide-imide (PAI) monomers have been combined with polydimethylsiloxane (PDMS) macromonomers. PDMS was selected to improve embeddability as it is softer and offers more flexibility than PAI. Via a polymerization reaction, chains of hard, fatigue resistant PAI are alternately combined with short chains of PDMS. This produces a polymer matrix which has a very fine distribution of soft phase due to the microphase segregation created as the soft and hard segments of neighboring polymer chains preferentially align with each other [3,4]. The relative lengths of the hard and soft sections can be “tuned” to produce domains of differing size and therefore adjust the balance of properties. Experiments have been carried out varying the overall percentage of PDMS and also with the molecular weight of the PDMS segments. Initial embeddability testing has shown an improvement in embedment over current polymer products and further work is ongoing to optimize this new resin system.

Copyright © 2016 by ASME
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Fig. 1

Schematic of a synthesized block copolymer chain showing the alternating blocks of PAI and PDMS

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Fig. 2

Generic structural representation of the PAI/PDMS block copolymer. The PAI block is shown to the left of the diagram and the PDMS is shown on the right.

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Fig. 3

Embeddability test rig

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Fig. 4

Boundary lubricated Viper wear test rig

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Fig. 5

Sapphire fatigue rig test setup

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Fig. 6

TGA graph showing comparison between copolymer and PAI resins

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Fig. 7

Graph showing the DSC traces of standard PAI resin and the 3000 g/mol soft-phase copolymer resin

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Fig. 8

Tapping mode AFM images of copolymer resins revealing the expected surface texturing and microphase segregation. Lighter contrast shows raised PDMS regions.

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Fig. 9

Tapping mode AFM image of the copolymer resin revealing phase separation and the height of surface peaks. Light contrast denotes raised regions.

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Fig. 10

FTIR comparison between PAI and the 80/20 3000 g/mol soft-phase copolymer. The additional and shifted peaks due to the PDMS incorporation in the copolymer are highlighted on the copolymer trace. The amide I band is also shown for reference.

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Fig. 11

Graph comparing the embeddability of soft-phase copolymer resin variants and the final formulated copolymer coating on the same MSB21 substrate

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Fig. 12

Graph comparing embeddability of the copolymer coating against different bearing overlay materials

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Fig. 13

Embedment iron prints of selected bearing overlays. (a) PAI polymer, (b) copolymer, (c) leaded electroplate, and (d) lead-free electroplate.

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Fig. 14

Graph comparing the accelerated wear results for a current PAI polymer coating, the new copolymer coating, and a current lead-free electroplated solution

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Fig. 15

Sapphire fatigue test results for the copolymer overlay tested at 110 MPa. Samples 1, 2, 4. and 5 passed while the remaining six samples showed signs of fatigue cracking in the overlay, suggesting the material was tested at its limit. No samples seized during testing.

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Fig. 16

Radar diagram of HDD bearing demands with comparison of copolymer and electroplated solutions (note: seizure testing has not yet been conducted on the copolymer)




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