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Commercial Tire Retreading

Robert C. McElroy, Ph.D.

www.ForensicAccident.Com

Canadian Association of Technical Accident Investigators and Reconstructionists - 1999 1

Tire Definition

Bubba
Academic big & dirty
flexible pressure vessel flat-on-bottom


Retread Training Program

Dr. McElroy Attended ITRA Training
Institute 40 Hour Commercial Tire
Retreading Class


Retreading Is:

•
Bonding a new
tread to a worn
tire casing


What is a Worn Casing

•is a properly
It
maintained tire that
has worn out its useful
tread life and been
removed from service
for retreading.


Vulcanizing or Curing

•
Process of chaining
macromolecules
together.


Vulcanizing Involves

•
Time
•
Temperature
•
Pressure


Tire Classification
•
Passenger
• Truck
Light
•
Medium Truck
•
Heavy Truck
•
Off-Road
•
Aircraft
•
Agricultural
•
Industrial / Mining
•
Racing

Tire Retreading Involves
•
Inspection
•
Repairing
•
Buffing / Skiving
•
Cementing / Filling
•
Tread Application
•
Wicking / Enveloping
•
Vulcanization
• Inspection
Final

Mold Cure Retreading


Pre Cure Retreading


Today’Professional Retreader
s
Must Know & Understand
• construction
Tire
• sizes & what they
Tire
mean
• usage & application
Tire
• maintenance
Tire
•
Tread design &
functions
•
Retread processing
technology

Maintenance &
Wheel Position


Tread Compounds
Should Have:

• heat generation
Low
• traction
Good
• tear resistance
High
• rolling resistance
Low


Rolling Resistance
Is Affected By:
• load
Tire
•
Inflation
•
Tread compound
• construction
Tire
•
Tread depth
•
Tread design


Road Factors

•
Surface Characteristics
•
Water depth
•
Temperature


Vehicle Factors
•
Speed
•
Mode of operation
•
Suspension
•
Braking system
•
Types of load
–
liquid
– CG
high


Heat History

• quantity of heat accumulated
The
over a period of time.


Tire Heat Exposure

•
Original manufacturing
temperatures.
•
Original tread life
operating temperatures.
•
Retread process
temperatures.


Typical Radial Truck Tire
Operating on the Road

200o F 93o C


Typical Radial Truck Tire
Original Tread Life

200,000 to 250,000 Miles
320,000 to 400,000 KM


Loads

Heat buildup area


Tire Inflation Pressure
• / under inflation.
Over
•
Buffed too round / too
flat.
• retread / narrow
Wide
retread.
• / narrow
Wide
processing rims or
narrow road rims.


Low Air Pressure

•
Increases running
temperature.
•
Reduces fuel economy.
•20% reduction in
A
inflation pressure
causes a 16% reduction
in tread life.


Effects On Tread Wear
• inflation by 10%
Over
reduces tread life 5-
8%.
• inflation by 20%
Over
reduces tread life 16%.
•
Matching duals
•
Torque, braking,
stopping & cornering.


To Select Tires for Retreading

•
Manufacturing defects
•
Non-repairable
damage
•
Excessive age
• tire be retreaded
Can
again?


Inspect Tires
•
Physical inspection
–
hands
–
grazing light
•
Electronic inspection
•
Ultrasonic inspection
• destructive
Non
testing
•ray
X


Electronic Inspection


Physical Inspection


Non Retreadable Tires
•
Damaged cord • blister
Liner
•
Improper repair • heat stress
Liner
•
Chipped bead •
Mount/demount damage
•
Broken body plies •
Improper repair
•
Zipper rupture • splice separation
Liner
•
Sidewall separation • damage
Liner
• stress
Flex •
Regroving damage
• turnup separation
Ply • deterioration
Age

New Tire DOT Codes

DOT MC 31 2XOW 086
• - Meets or exceeds DOT safety standards
DOT
• - Manufacturer & plant code
MC
•
2XOW - optional identification symbols
• - date of manufacture (08 week, 1996)
086


Retread Plant DOT Codes
R - ARA CI XXX 086 FI
• identifies as retread
R-
• - shop identification code
ARA
• - identifies matrix that the tire was
C1
cured in or is a tire size code
• - optional grouping
XXX
• - date code
086
• - steer axle option
F1

Buffing Template Shape


Buffed Radius Check Gauge


Buffing Machine

Buffing Head

Template

Apply Cement To:

•
Protect buffed surface & exposed cords
from oxidation.
•
Improves adhesion by providing for more
“intimate contact” to buffed casing.


Cement Tire Casing


Cement = Rubber Solids
Dissolved in Solvents

•
Allow 15 minutes to dry after application.
•
Install tread within 12 hours.
•
Chemical
• vulcanizing
Black
•
Concentrated or brush
•
Spray
•
Extruder or hot tack

Cement Application


Gum Cushion Application

•
Apply gum cushion
base material,
• a prepared casing.
To


Gum Cushion to Tire Contact


Trim Gum Cushion


Gum Cushion Base Material

•
Pressure roller ensures
attachment of gum
base material to
prepared casing.


Precure Tread Installation
•
Texturize tread end & cement.
• tread straight holding tightly.
Feed
• cut point even or slightly longer.
Mark
• straight & match tread design if possible.
Cut
• cushion between tread ends.
Place
• splice with least amount of hump.
Butt
• rubber toward splice & from center out.
Work
•
Install DOT identification code.
•
Apply poly.

Precure Tread
Installation & Cutting


Gum Cushion Base Material
Connects Tread Ends


Poly Installation


DOT Identification Code
Installation


Select Tire Envelope


Envelope on Expander


Envelope Expanded


Tire Insertion


Envelope Adjustment


Rim & Flange Installation


Prepared Tires For Chamber


Curing in
Autoclave or Chamber


Track Installation


Envelope & Rim
Pneumatic Connections

Envelope
Rim Connection
Connection
Vacuum
Pressure


Seal & Lock Chamber


Set Time & Temperature


Post Vulcanization


Final Inspection


References


Dr. McElroy Examining Retreaded Tire The End


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