Presentation by Kevin Spoo, Owens Corning Senior Research Associate, at CAMX 2015. This research highlights bow in pultruded parts, which is different from the dimensional changes caused by resin. The choice of glass fiber reinforcement can cause a stress differential, which can cause issues of bow through the cross-section of a pultruded part. In the experiment that was discussed, two types of glass reinforcements were fed into a pultrusion die with all other parameters of the system being equal.

2. HOW GLAS S R E INFOR CE ME NT
CHOICE CAN AFFE CT B OW IN
PULTR UDE D PAR TS
Kevin Spoo
Sr. Research Associate
Owens Corning
Dallas Convention Center | Dallas, Texas, USA

3. The B ack S tory
• Shear strength
• Flexural strength
• Tensile strength
• Compression str.
• Bearing strength
• Fiber packing
• Wet out
• Fuzz
• Drag/tension
• Package transfer
• Guiding
• Humidity resistance
• Knots

4. Introduction
Pultruders are aware of a number of items
that affect part dimens ions .
• Resin related
– Resins shrink 4-8%
– Exotherm
temperature
– Speed of gelation
– Viscosity
– Mold release
– additives
• Design related
• Part symmetry
• Sharp radii
• Heat transfer
• Unbalanced layup
• Glass content
• Process related
• Line speed
• Fiber guiding
• # of contacts
• sizing type
• pathway
• Preformer design
• Alignment

5. S tres s /s train Induced B ow
Some of these dimensional changes are due to stress applied in
the die inducing strain in the longitudinal reinforcement which
relieve itself when exiting the puller.

6. R einforcement B enchmarking
lower is better
Materials
Fuzz
number
Drag
(Tension)
(g/lb) (g)
Product OC-1 113 yield 0.0020 1360
Product OC-1 56 yield 0.0075 3275
Product OC-2 113 yield 0.0007 985
Product OC-2 56 yield 0.0088 3365
Product J2 113 yield 0.0260 2660
Product J2 56 yield 0.0229 5435
Product P 113 yield 0.0021 1560
Product P 56 yield 0.0112 3110

7. E xperimental

8. Unexpected R es ult
OC1 J2

9. R es ults & Dis cus s ion
Part Identification Bow in inches at midsection of 208cm part
600mm/minute (24”/minute) 10.3mm (13/32”)
900mm/minute (36”/minute) 12.7mm (16/32”)
900mm/minute (36”/minute) tension added 19mm (24/32”)
OC2
J2
OC1
J2
OC1
J2

10. R es ults & Dis cus s ion
Glass weight percent comparison Scanning Electron Microscopy comparison
EDS confirms glass location

11. Conclus ions
• The amount of drag or tension associated with the selection
of glass fiber reinforcement can negatively affect bow in a
pultruded part.
• Selection of a glass fiber reinforcement which minimizes this
drag can have a positive effect in maintaining the
straightness of pultruded shapes and allows a wider process
control window to address bow issues.
• Tension added to the reinforcement regardless of whether it
is added at the creel rack, guide boards, resin bath, or pre-
former can result in additional strain in the pultruded part.
Whether this strain results in bow will depend on numerous
factors such as the amount of strain, part symmetry, part wall
thickness, and section thickness.