DeFelsko PosiTest AT-A, PosiTest AT-M Quick Manual

Quick Guide v. 5.0

PosiTest AT-A

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automatic

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PosiTest AT-M

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manual

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1

Introduction

The PosiTest AT Pull-Off Adhesion Tester measures the force
required to pull a specified test diameter of coating away from its
substrate using hydraulic pressure. The pressure is displayed on
a digital LCD and represents the coating's strength of adhesion to
the substrate.

In accordance with ASTM D4541, D7234, ISO 4624 and
others, the PosiTest AT evaluates the adhesion (pull-off strength)
of a coating by determining the greatest tensile pull-off force that
it can bear before detaching. Breaking points, demonstrated by
fractured surfaces, occur along the weakest plane within the
system consisting of the dolly (loading fixture, stub), glue, coating
layers and substrate.

This quick guide summarizes the basic functions of the instrument.
Download a full instruction manual at:

www.defelsko.com/manuals

Basic Steps to Perform a Pull-Off Test

1. Dolly & Coating Preparation

The dolly and the coating are cleaned and abraded (see pg.2).

2. Glue & Dolly Application

The glue is prepared and applied to the dolly. The dolly is
is then adhered to the coated surface and the glue is allow­ed to cure (see pg. 2).

3. Test Area Separation - optional

The test area of the coating is isolated from the area
surrounding the dolly by cutting or drilling (see pg. 3).

4. Pull-Off Test

a) PosiTest AT-M (manual) (see pg. 5)
b) PosiTest AT-A (automatic) (see pg. 7)

5. Analysis of Test Results

The dolly and the coating are examined and evaluated to
determine the nature of the coating failure (see pg. 4).

2

Dolly & Coating Preparation

Dolly Preparation

1. To remove oxidation and contaminants, place the included

abrasive pad on a flat surface and rub the base of the dolly
across the pad 4-5 times.

2. As required, remove residue left from the abrading process

using a dry cloth or paper towel.

Coating Preparation

1. Lightly roughen the coating using the included abrasive pad.

As coating abrasion may introduce flaws, it should
only be used when necessary to remove surface contaminants,
or when the bond strength between the glue and the coating
is insufficient for pull testing.

2. To promote the bond between the dolly and the coating,

degrease the area of the coating to be tested using alcohol or
acetone to remove any oil, moisture or dust.

Ensure that any alternative abrasion techniques,
degreasers or adhesives do not alter the properties of the coating.
Test by applying a small amount of degreaser or glue to a sample
area and observing effects.

NOTE:

NOTE:

Glue & Dolly Application

Glue Selection

The glue included in the PosiTest Adhesion Tester kit has been
selected due to its versatility. This glue has minimal impact on a
variety of coatings and has a tensile strength exceeding the
maximum performance capabilities of the pressure system under
ideal conditions. Other glues may be preferred based on
requirements such as cure time, coating type, working temperature
and pull-off strength. Quick curing one-part cyanoacrylates (super
glues) may be sufficient for painted surfaces, but two-part epoxies
are preferred for porous or rough coatings.

3

Dolly Application

1. Mix the glue per manufacturer’s instructions and apply a

uniform film of glue on the base of the dolly

2. Attach the dolly to the prepared coating test area.

If the coated surface to be tested is overhead or vertical,
a means to hold the dolly in place during the cure time may be
required, i.e. removable tape.

3. Gently push down on the dolly to squeeze out excess

adhesive. Do not twist or slide the dolly back and forth on
the coating as air bubbles may be generated.

4. Carefully remove excess adhesive from around the edges

of the dolly with included cotton swabs.

5. Allow to cure per the adhesive manufacturer's instructions.

NOTE:

Test Area Separation

The decision of when to cut around a dolly is dependent on the
standard, specification or contractual agreement to which the test
is to comply. The primary purpose for cutting through the coating
is to isolate a specific diameter test area. When the decision to cut
into the coating has been made, it is recommended to cut all the
way through to the substrate. As a minimum, it is suggested to
carefully cut away excess glue from the dolly application process.
This typically prevents a larger area of coating from being pulled
away from the substrate, resulting in a higher pull-off pressure.

Cutting Instructions

1. Cut through the coating around the edges of the dolly with

the included cutting tool, removing any excess glue.

2. Clear away any debris from the cutting process.

NOTE:

- Cutting may induce coating surface flaws such as

microcracking that may alter test results.

- For coatings with strong lateral bonding, it is recommended to
cut completely through the coating down to the substrate.

Drilling Template

When testing very thick coatings, an optional drilling template
may be preferred.

4

Analysis of Test Results

Glue failures typically occur when the glue is improperly mixed or
the coated surface has not been adequately prepared (see pg.2).

Upon completion of the pull-off test, the dolly and coated surface
should be examined. In addition to pull-off force, many National
and International standards such as ASTM D4541 and ISO 4624
require the nature of the fracture to be recorded.

The PosiTest AT-A model provides an interface to document the
nature of the fracture for each pull-off test (see pg. 10). Fracture
results are included in test reports.

Glue failure: visible separation of the glue from itself,
the coating or dolly (no coating visible on the dolly face).

Dolly Face

Coated Surface

Dolly

Glue

Cohesive fracture

(intercoat)

Adhesive fracture

(between layers)

Glue failure

(coating/glue)

Substrate

Adhesive fracture:
fracture occurs at the interface
between layers (coating on
dolly face differs from surface).

Cohesive fracture:
fracture occurs within a coating
layer (same coating on dolly
face and coated surface).

5

Pump Handle

Display

USB Data Transfer /Power Port

Actuator Handle

Quick Coupling

Actuator
Assembly

Hose

Pump

Quick Guide

(1) Open pressure relief valve completely (turn counter clockwise)
(2) Connect the actuator to the dolly
(3) Close the pressure relief valve completely (turn clockwise)
(4) Zero - Press the button
(5) Pump pressure into the system until the dolly pulls

The PosiTest AT-M powers-up and displays dashes when the

button is pressed. To preserve battery life, the instrument

powers-down after 5 minutes of no activity.

1. Ensure the pressure relief
valve is completely open.
(turn counter clockwise)

OPEN

2. Push the actuator handle completely down into the actuator

assembly. Place the actuator over the dolly head and attach the
quick coupling to the dolly by reaching through the holes in the
actuator and lifting the coupling. Release the quick coupling when
the dolly head is completely engaged.

PosiTest AT-M Manual