Society of Plastics Engineers Europe - VeMet · Society of Plastics Engineers Europe Tribologie/polymeren. Friction and wear of plastic products Spoormaker Consultancy in Reliability

Wrijving en slijtage van kunststofproducten

Jan Spoormaker

Spoormaker-Consultancy in

Reliability and Liability of

Plastic Products

Society of Plastics Engineers Europe

Tribologie/polymeren

Friction and wear of plastic products

Spoormaker Consultancy in Reliability & Liability of Plastic Products

Dictaat Hfdst. 3 tekst

Friction

Friction is a force that resist relative movements between two surfaces in contact.

Wear

Wear is a process in which interaction of surface(s) or bounding face(s) of a solid with

the working environment results in the dimensional loss of the solid, with loss of

material.

Friction and wear are system properties

Tribology

Science about friction, lubrication and wear

Tribotechnology

Engineering application of tribology

Tribological System according to Czichos


Relative movement

Gliding, rolling

Load Fn

Velocity v

Ambient temperature

Friction force Fw

Friction coefficient f, μ

Wear h

Friction temperature

Noise

Loads &

environment

Loads &

environment

Tribological

quantities

Surface parameters

Roughness

Macro geometry

1. Body

2. Body

3. Substance

4. Environment

Dictaat Hfdst. 3 Fig. 3.1

- polymerisatie

- ketenopbouw en ketenlengte

- fysische eigenschappen

- kristallisatie


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Polymeren

Plastics are fantastic, they can fail in many

unexpected ways

Polymeriseren en ketenlengte

additiepolymerisatie


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Polymeriseren van etheen C2H4 PE


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Polymeriseren van etheen C2H4 PE


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onvertakt

vertakt

Ketenlengte



Ketenlengte



Ketenlengte van PE

Paraffine (500 g/mol ) lijmtube (105 g/mol) UHMW-PE (5.106 g/mol)


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Molecuulmassa - sterkte en viscositeit


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Amorf en semi-kristallijn


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tie-molecule

Kristallisatiesnelheid


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wrijving

slijtage

contactoppervlak

vervorming

cohesie en adhesie


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Pwrijving en slijtage bij kunststoffen

Normal force, drag force and friction force


Material combination μ, f

PA6 - PA6 (no lubrication)

1.20

PA6 – POM (no lubrication)

0.60

PA6 – PTFE (no lubrication)

0.10

POM – POM (no lubrication)

0.55Dictaat Hfdst. 3 Fig. 3.3

Wear


Material combination wear factor k

POM – steel (Ra = 0.1 μm) 2 10-15 m2/N

POM – steel (Ra = 0.6 μm) 80 10-15 m2/N

h k p v t


Micro contact surface



Deformation



Physical processes cohesion and adhesion


Bonding forces

Cohesion

Adhesion ----------


ruwheid

snelheid

stick-slip effect


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Wrijving bij kunststoffen

Friction coeeficient as a function of roughness


High yield strength Low yield strength

Surface roughness Surface roughness


Friction coefficient as a function of roughness for

POM and HDPE


Roughness Ra (μm) Roughness Ra (μm)


Friction coefficient as a function of speed


Speed


Mass-spring model



Stick-slip effect


time


deformatie

adhesieve slijtage

abrasieve slijtage

pitting


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slijtage bij kunststoffen

Boundary and deformation zone


• Boundary zone

• Deformation zone

Hard roughness

asperity top


Adhesive wear



Abrasive wear



Shear stress for rolling contact



Pitching as a result of fatigue


Fatigue cracks Pitting


Knieprothese


Knieprothese


Putvorming in UHMPE


slijtage – ruwheid

meten van slijtage

vlaktedruk – pv waarde

warmte-ontwikkeling

PTFE

Hardheid


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Lagers

Wear as a function of roughness for POM and HDPE



Wear as a function of roughness and pressure for PA6.6



Wear as a function of pressure



Different wear tests



Pin on disk



Calculation of average bearing pressure and wear


p 43MPa

h k p v t

FT D

p

Extra

Heat flux and Average Bearing Pressure


2(W/m )h f p v

- heat flux

f – friction coeficient

p – average bearing presure

v - velocity


Critical pv-values



Prediction of wear


h k p v t

k – wear factor

p – average bearing presure

v – velocity

t - time


Coefficients of friction and wear rates


1 1h k p v t 2 2h k p v t

Extra

Effect of PTFE content on wear


Extra

PTFE & silicone to reduce friction and wear


Extra LNP Lubricomp

Effect of hardness on wear


Extra LNP Lubricomp

Effect of shaft finish on wear (micro-inches!)


Extra LNP Lubricomp

warmte-ontwikkeling

vermoeiing


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Tandwielen

Failure analysis


Extra

Failure analysis


Extra

Guidelines for plastic bearings


• Metal bearing surfaces must be smooth (< 1 μm), hard and corrosion

resistant.

• Wear particles must be collected in grooves.

• Bearing clearance must account for high thermal expansion and absorption

of water (PA)

• The average bearing pressure should preferably be not higher than 1 N/mm2

and at most 5 N/mm2.

• The out-of-roundness of bearings should be as small as possible and film

gates are preferred.

• Bearing plastics with PTFE are preferred especially for applications without

lubrication.

• Boundary lubrication is must better than running dry.

• Grease or oil can affect plastic bearings (swelling & ESC)


Documents

Society of Plastics Engineers Europe - VeMet · Society of Plastics Engineers Europe Tribologie/polymeren. Friction and wear of plastic products Spoormaker Consultancy in Reliability