why (and how) you should implement plastic bearings
TRANSCRIPT
Why (and how) You Should Implement Plastic Bearings
This webinar will be available afterwards at
designworldonline.com & via email
Q&A at the end of the presentation
Hashtag for this webinar: #DWwebinar
Before We Start
Moderator
Leslie Langnau Design World
Presenters
Matt Mowry igus
Nicole Lang igus
Donna Meyer University of Rhode
Island
Why (and how) to
implement plastic
bearings into your
application.
• Development
• Advantages
• Simple polymers vs. composite
polymers
• Selection criteria
Polymers in general
• Natural polymer lubricants
• Oils and greases
• Incorporated into solids
• Plastics and rubbers
Why use polymer bearings?
• Fluid lubricants not effective
• Fluid lubricants not safe
• Maintenance issues
• Insufficient boundary lubrication
Possible environments
MARINE: seawater and fresh water
Possible environments
AGRICULTURE: moisture, chemicals, dirt
Possible environments
MEDICAL: equipment, implantable devices
Possible environments
PACKAGING: food and pharmaceuticals
Simple polymers
Stachowiak & Batchelor,, Engineering Tribology, 2005, 3rd Ed., Elsevier Inc., Chp. 16, Fig.16.1, pp. 653.
Bunn & Howells, (1954), “Structures of Molecules and Crystals of Fluorocarbons”, Nature, 174, pp. 549-551.
Makinson & Tabor, (1964), “The Friction and Transfer of Polytetrafluoroethylene”, Proc. Roy. Soc. (A), 281, pp. 49-61.
Simple polymers
Ludema, Friction, Wear, Lubrication: A Textbook in Tribology, 1996, CRC Press, Chp. 8, Fig. 8.15, pp.143.
Stachowiak & Batchelor,, Engineering Tribology, 2005, 3rd Ed, Elsevier Inc., Chp. 16, Fig. 16.3, pp. 655.
Makinson & Tabor, (1964), “The Friction and Transfer of Polytetrafluoroethylene”, Proc. Roy. Soc. (A), 281, pp. 49-61.
Limitations of simple polymers
• High wear rates
• Frictional heating
• Solvent damage
• Soft – easily deforms
• Mostly low loads
Stachowiak & Batchelor,, Engineering Tribology, 2005, 3rd Ed, Elsevier Inc., Chp. 16, Figs. 16.7, 16.9, and 16.26, pp. 657-672.
Arnell, Tribology: principles and design applications, 1991, Macmillan, pp. 110.
Khonsari,& Booser, Applied Tribology: Bearing Design and Lubrication, 2008, Wiley & Sons, pp.97.
Composite polymers
• Improved mechanical strength
• Improved wear resistance
• Reduce coefficients of friction
Stachowiak & Batchelor,, Engineering Tribology, 2005, 3rd Ed., Elsevier Inc., Chp. 16, Fig.16.29, pp. 677.
Tsukizoe & Ohmae, Friction and Wear of Polymer Composites,1986, K. Friedrich, Ed, pp.205-231.
Composite polymer bearing
Solid lubricants lubricate the
system independently,
mitigating friction and
reducing wear rates
Base polymers are
responsible for low
coefficients of
friction.
Fibers and filler materials
reinforce the bearing and
allow for high forces or edge
loads on the bearing.
Advantages of composite polymers
• Improve mechanical and thermal properties
• Addition of reinforcing fibers and fillers
• Reduce wear rates
• Effective under high and low loads
More advantages . . .
• Low friction coefficients with mating materials
• Inert
• Biocompatible
• Self-lubricating
• Serve as reservoir for boundary lubricants
• Tune material properties
• Make into any shape: molding or machining
Selection criteria
• Maximum load
• Sliding speed
• Environmental conditions
• Counterface roughness
• PV limit
• Wear factor k
Stachowiak & Batchelor,, Engineering Tribology, 2005, 3rd Ed, Elsevier Inc., pp. 658-659.
Arnell, Tribology: principles and design applications, 1991, Macmillan, pp. 1111-112.
Khonsari,& Booser, Applied Tribology: Bearing Design and Lubrication, 2008, Wiley & Sons, pp. 356-358.
Blanchet, (1997), ‘‘The Interaction of Wear and Dynamics of a Simple Mechanism,’’ ASME J. Tribol., 119, pp. 597–599.
Composite plastic bearings vs.
- simple plastic bearings
- bronze bearings
- PTFE-lined, metal-backed bearings
- ball bearings
Composite plastic bearings vs.
simple plastic bearings
• Composites enhance the benefits of plastics
• Base materials
• Fillers - increase load capacity
• Solid lubricants - reduce friction
Composite plastic bearings vs.
simple plastic bearings
0
10
20
30
40
50
60
70
80
90
100
material
Polyamide 6.6
Polyacetal (POM)
igus H370
igus L280
igus J
Parameters: P = 0.7 N/mm2, v = 0.15 m/s, case-hardened steel shaft
0
10
20
30
40
50
60
70
80
90
100
material
Polyamide 6.6
Polyacetal (POM)
igus L280
igus J
igus H370
Friction Wear
Composite plastic bearings vs.
bronze bearings
• 1930’s technology
• High speed and rotational movement necessary to
draw oil out and create a lubricant film
• Shaft oscillation, slow speed, linear and
intermittent use can all inhibit this process
“Shaft oscillation or slow speed, intermittent use, pulsating or
uneven loads are conditions that inhibit full-film lubrication
from developing or being maintained” – from oilite
manufacturer’s product information
Composite plastic bearings vs.
bronze bearings
Bronze bearings:
+ low coefficient of friction (if maintained)
+ slightly more precise (low thermal expansion)
+ high speeds are possible
+ high p x v value
- limited application temperatures
- poor chemical/corrosion resistance
- not ideal in dirty environments
- must be reamed at install
- unsuitable for linear motions
- low impact load capability
Composite plastic bearings vs.
bronze bearings
Composite plastic bearings:
+ higher load possible
iglide® composite bearing: <21,500 psi
bronze bearing: <8000 psi
+ no external lube or maintenance required
+ better in aggressive environments
+ ideal for rotating, pivoting and linear use
+ great for impact loads and high-vibrations
+ can use non-hardened shaft materials
+ lightweight
• better lifetime than bronze
• grease and oil-free
• dirt and dust resistant
• ideal in pivoting/intermittent
applications
• increased lifetime
• easy to assemble (no reaming)
• better suited for impact loads
Composite plastic bearings vs.
bronze bearings
Composite plastic bearings vs.
PTFE, metal-backed bearings
• 1950’s technology
• steel/bronze outer layer is rolled
• ID contains thin layer of bronze
• Impregnated with PTFE and lead
Composite plastic bearings vs.
PTFE, metal-backed bearings
PTFE, metal-backed bearings:
+ good thermal conductivity/heat dissipation
+ ability to withstand high operating temperatures
+ max speed 1,000 fpm
+ PV 50,000 psi/fpm continuous
+ PV 100,000 psi/fpm short term
- thin wear surface
- corrosive
- contain lead
- heavier than plastic bearings
- difficult installation procedures
Composite plastic bearings vs.
PTFE, metal-backed bearings
Composite plastic bearings:
+ Suitable for a wide range of applications
+ Dimensionally Interchangeable
+ More wear surface
+ Lightweight
+ Corrosion-Resistant
+ Better for dirty environments
+ Predictable lifetime
PTFE-lined vs. iglide® bearing - wear
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
HC AL Case-HardSteel Machine Grade 304SS
igus J
igus L280
igus Z
PTFE-Lined
Parameters: Pressure = 1 MPa, Velocity = 0,01 m/s
Oscillating movement
PTFE-lined replaced with composite plastic
“iglide® bearings cost slightly less, but the most
important advantage is that they don’t need to be
replaced by riders. They last for the entire life of our
pedals.”
• dirt and dust resistance
• lightweight
• corrosion resistance
• proven to require less maintenance than the alternative
in this application, plus a longer life
with plastic
spacers
standard version: one
ball pushes the next
Recirculating ball bearings
• Balls run through a linear raceway
• Contain a lubrication-bath
• May require constant maintenance
• Additional components are often
required: Zerks, lube lines, seals, etc.
Recirculating linear ball bearings
+ higher combination of dynamic load vs. speed
+ high precision possible (micron level)
+ low friction (if properly maintained)
+ suitable for highly cantilevered loads
- expensive
- must be lubricated/maintained
- require hardened steel shafting
- poor in dirty environments
- not ideal for clean applications
- limited accelerations possible
Plastic linear bearings
+ lower cost of ownership
+ suitable for harsh environments (dirt, chemicals, water)
ideal for high-impact loads (shocks/vibrations)
+ higher static loads than ball bearings
+ suitable for soft shafting (aluminum/300-SS)
+ suitable for short strokes
+ quiet/lightweight
Recirculating ball bearings replaced
Vertical-Form-Fill-Seal
packaging machine:
Welding jaws
+ Increased machine’s
cycles-per-minute by 20%
+ Ball bearings limited by
accelerations and bad
environments
+ Lower cost than ball
bearings
Implementing
iglide® plastic
bearings in your
application
iglide® plastic bearings
• Check temperature, static-surface pressure, speed.
• Max. P x V value is 28 571 Psi * fpm in a permanently dry-running application.
• Typical application involves low speeds < 60 fpm or high loads up to 14,500 psi (rotating oscillating.)
• Use hardened shaft in applications > 700 psi
• When the total sliding distance is less than 6,000 miles
• Use a clearance of 0.002” – 0.004” (0.05 - 0.10 mm)
PV Value • In a plain bearing, friction heat is created when the shaft moves inside the
bearing.
• We determine p*v by the values present in the application for pressure and
speed.
• By multiplying these two factors we find the p*v (measure for the amount of
heat created):
o Pressure in psi
o Velocity in fpm
PV Value
Via the bearing into the housing
Via the shaft outside the bearing
2 ways to dissipate the heat from the bearing:
Factors influencing PV
• Thermal conductivity of shaft, housing and bearing material.
• Coefficient of friction.
• Maximum temperature limit of the bearing material.
• Ambient temperature in the application.
• Wall thickness of the bearing and length.
The 2:1 Rule
Other considerations
• Shaft material
• Shaft roughness
• Shaft hardness
• Housing material
• Environment
• Chemicals
• Certifications (ex. FDA compliance, UL94 horizontal burn test etc.)
iglide® bearings are engineered plastics
More than 30 iglide® materials:
iglide® bearings are available in more than 30 tribopolymers to meet your specific needs.
More than 150 additional materials for special custom requests or needs.
All tested and predictable.
dry-tech
more than 30 dry-tech
tribopolymer materials
What is iglide®?
The igus® test facility
Over 10,000 plastic
bearing tests annually
Focus on coefficients of friction and wear under all possible conditions and
at a wide range of speeds. Factors such as dirt and climate also tested.
Founded: October 1964, Cologne Germany
Approx. 1,600 employees in inland and overseas
28 igus® subsidiaries worldwide and distributors in more
than 42 countries.
Product groups:
- Energy Chain® cable carriers
- Chainflex® continuous-flex cables
- ReadyChain® pre-harnessed systems
- iglide® polymer plain bearings
- igubal® self-aligning plastic bearings
- DryLin® linear bearings
igus®, Inc.
•US, Canada, Mexico
•More than 50 Sales Engineers Throughout North America and in
our Rhode Island office available for support
•Available for visits within 24-48 hours
•Stock held in East Providence, RI
•No Minimum Orders
•Over 10,000 sizes available in stock ready to ship within 24 hours
Contact Us
Tel. (800) 521-2747 or (401) 438-2200
Twitter: http://www.twitter.com/igus_Inc
http://www.igus.com
Questions?
Design World Leslie Langnau [email protected] Phone: 440-234-4531 Twitter: @DW_RapidMFG
igus Matt Mowry [email protected] Phone: 888-803-1895 ext. 140 Twitter: @igus_inc
igus Nicole Lang [email protected] Phone: 888-803-1895 ext. 111 Twitter: @igus_inc
University of Rhode Island Donna Meyer [email protected]
Thank You
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