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
INTRODUCTION
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
SURFACE VEIL
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, and various
hypochlorite compounds.
Nexus Synthetic Surface Veil
ADDITIONAL REQUIREMENTS FOR HYPOCHLORITE
APPLICATIONS
PURPOSES OF SURFACE VEIL
hypochlorite,
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
promoter.
A second, but equally important, purpose is to providereinforcement to the surface layer of resin to prevent crackingand crazing.
nyb’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.
CUSTOMER RESPONSIBILITY
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

Source: http://www.newyorkblower.cn/Catalog/Letters/EL-21.pdf