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Nyb engineering letter 2
ENGINEERING LETTER 21
The New York Blower Company ●7660 Quincy Street, Willowbrook, Illinois 60521 -5530
S U R F A C E V E I L F O R F R P F A N S
ASTM STANDARD D4167
This Engineering Letter has several functions: to describe nyb
The American Society for Testing and Materials (ASTM) D41
surface veil characteristics, define the purposes of surface veil,
67, Standard Specification for Fiber-Reinforced Plastic Fans
explain the relationship between surface veil and ASTM
and Blowers defines the basic guidelines for the construction
D4167, detail the specific corrosive agents that require a
double layer of veil, and describe the special construction
specifications within D4167 is that the laminate construction be
requirements involving hypochlorite applications.
in accordance with another ASTM standard, C582. Thatstandard specifies that the working surface (the surface to be in
SURFACE VEIL CHARACTERISTICS
contact with corrosives) of the laminate consist of one layer ofsurface veil backed by two layers of chopped-strand mat or
The synthetic surface veil used exclusively by nyb
is Nexus®. It
equivalent from a chopper gun, followed by the structural
is a non-woven formed fabric produced from Dacron® 106
layers. Therefore, in order to comply with ASTM D4167, all
homopolymer. This binder-free polyester fiber has an apertured
FRP fans must be furnished with at least one layer of surface
(perforated) design that provides the necessary flexibility for
the fabrication of fans. Each layer of surface veil contains about90% resin and 10% veil material and is applied at a minimum of
CORROSIVES REQUIRING A DOUBLE LAYER OF
There are some chemical agents that are aggressive toward
glass. For these specific corrosives, nyb
’s resin suppliers
recommend the addition of a layer of surface veil for increased
corrosion resistance. Additionally, in those applications where
the corrosive agent is extremely aggressive, a second layer of
veil is required. The corrosion-resistance guide found in
Engineering Letter 18, Corrosion Resistance of FRP Fans,
indicates where one or two layers of veil are required. The
corrosives listed as requiring a double layer of surface veil
include fluorine gas, hydrochloric acid, hydrofluoric acid,
hydrogen fluoride, potassium hydroxide,
Nexus Synthetic Surface Veil
ADDITIONAL REQUIREMENTS FOR HYPOCHLORITE
PURPOSES OF SURFACE VEIL
One purpose of surface veil, also referred to as surfacing mat
hypochlorite, lithium hypochlorite,
or sodium hypochlorite
or tissue, is to prevent protrusion of the chopped-strand mat
require special FRP construction considerations. In addition to
glass fibers to the surface which could allow chemical wicking
the aforementioned double layer of surface veil, resin suppliers
recommend a substitution for nyb
’s standard catalyst and
A second, but equally important, purpose is to providereinforcement to the surface layer of resin to prevent crackingand crazing.
’s standard polyester and vinyl ester resins both use cobalt
napthanate (CoNap) as a promoter and Lupersol®, a methyl
Finally, the addition of surface veil allows nyb
fans to meet
ethyl ketone peroxide (MEKP), as a catalyst. Gas streams
the requirements of ASTM Standard D4167.
containing hypochlorites attack CoNap whenever MEKP isused as a catalyst. Therefore, a benzoyl peroxide (BPO)catalyst is recommended for these applications because it
Dacron® is a registered trademark of E.I. DuPont de Nemours & Company, Inc.
Nexus ® is a registered trademark of Precision Fabrics Group, Inc.
Lupersol ® is a registered trademark of Elf Atochem North America, Inc.
does not use CoNap as its promoter. The BPO catalyst requires
grounding by graphite impregnation is not an available option
dimethyl aniline (DMA), which is unaffected by hypochlorites,
when used in conjunction with a BPO catalyzed resin.
as its accelerator in lieu of the CoNap.
Special BPO/DMA construction is limited in that it cannot beused for FRP wheel construction. It can only be used to apply
This Engineering Letter and any discussions between nyb
surface veil to the wheel. All other FRP components can be
representatives and the customer should not be construed as a
constructed using this special catalyst/accelerator system.
warranty of material suitability for a particular application. Thesystem designer should have sufficient knowledge of, or
In addition, note that due to reactivity between BPO catalysts
experience with, the application to select the appropriate resin or
and graphite, which reduces the graphite’s conductivity, static
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