SAMPE Journal - September/October 2020 - 18

FEATURE / OPTIMUM NUTPL ATE PERFORMANCE
Similar results have been observed on other substrate materials including bare metal, anodized
and primed aluminum 70758.
Through this work, it has been observed that
proper preparation of the nutplate surface is essential for achieving strong, reliable bonded nutplates.
Analysis of the specimens after mechanical testing
indicated that the nutplate interface is often the
weak link of the bonded assembly. Consequently,
there has been a need to develop an alternative
nutplate surface preparation technique. Preparation of the nutplate via solvent wiping consistently resulted in interfacial bond failures when using
CB301 adhesive6,7. While grit blasting was capable
of producing strong bonded nutplates, this method is time consuming and impractical in most nutplate installation settings. Meanwhile, plasma was
shown to rapidly produce strong bonded nutplates
and to eliminate the occurrence of interfacial failures at the nutplate surface.
In order to improve on the drawbacks that are
inherent in manual abrasive preparation methods,
Surfx Technologies has produced two purpose-built
plasma devices for optimal surface preparation of
the nutplate and structure. In order to establish a
dependable, high quality bond, a portable plasma
device has been developed that cleans a nutplate
seconds. Used in concert with a handheld plasma
source for the substrate, a fast and reliable surface
preparation technique is realized for installing
bonded fasteners on aerospace structures.
Additional work was needed to expand the
scope of these previous studies by exploring additional substrates and adhesives as well as optimizing the plasma process conditions. This work
continues the examination of atmospheric plasma
cleaning and activation for bonded nutplate installation. The novel plasma devices have been used
to demonstrate this plasma technique as a replacement for abrasion processes. The plasma process

can also be tailored to any specific combination
of adhesive, fastener type and substrate material.
Below, results are presented for the surface preparation of unprimed, stainless steel nutplates and
aluminum substrate coupons using atmospheric
pressure plasma.
EXPERIMENTAL METHODS
Materials
Dome-style (CB6010 CR3) and open-end style
(CB6003 CR4) nutplates were used along with
CB301 epoxy adhesive from Click Bond, Inc. and
Epibond 1544-1 epoxy adhesive from Huntsman.
Aluminum sheets made from alloys 7075, 6061
and 2024 were used for substrate materials. The
substrate materials were machined into 2" x 8"
coupons. A schematic of the test coupon with the
locations of the five holes is shown in Figure 1. Five
equidistant holes were drilled into the center of the
rectangular coupon.
Solvent Wiping
Substrate surfaces were cleaned with Dysol DS-108
solvent or isopropyl alcohol (IPA) using DuPont
Sontara lint-free cloth wipes. This process consisted of three steps: a one directional dry wipe, a one
directional wipe with the cloth saturated with the
solvent, and a final one directional dry wipe.
Grit Blasting
Prior to bonding, one subset of the nutplates and
substrate coupons were grit blasted using a King
#4004-0 grit blasting cabinet. Grit blasting was performed using fresh Elfusa ALR 240 grit aluminum
oxide media with an air compressor regulated to 80
lbs. of pressure. Each item was grit blasted with the
gun nozzle kept between 45 and 90 degrees to the
bonding surface. An approximate distance of 10 cm
was maintained between the nozzle and the surface. Samples were abraded until a matte finish was

Figure 1. Schematic of nutplate test coupon with dimensions.

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SAMPE Journal - September/October 2020

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