24-07-2012, 09:46 AM
COEFFICIENT OF FRICTION, THE DEVELOPMENT OF A STANDARD PORTABLE DEVICE FOR THE US NAVAL FLEET
COEFFICIENT OF FRICTION, THE DEVELOPMENT OF A STANDARD PORTABLE.pdf (Size: 344.18 KB / Downloads: 55)
ABSTRACT
Operational and maintenance requirements have required improved decking systems, particularly
non-skid, to be incorporated within the US Navy. For those who have experienced rough seas and foul
weather, the importance of good non-skid (or slip resistant) deck coverings on weather decks becomes
very apparent. But what defines “good” may be easier to qualify rather than quantify. This is directly
related to the methodologies employed to evaluate slip resistance of these surfaces and other deck
systems.
INTRODUCTION
Numerous devices exist to measure the coefficient of friction (COF) for flooring, roads, runways,
and deck surfaces. As non-skid systems have evolved, the device to evaluate the frictional
characteristics within the technical specifications changed to meet testing requirements within the Navy.
The proceeding addresses the problems encountered leading to the development of a compact, portable
fieldable COF testing system. The parameters/procedures, used to evaluate non-skid deck coatings to
verify their suitability for service or their need for replacement, are also reviewed; this review is not
limited to the safety impacts of COF but also the operational readiness impacts on the Fleet.
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HISTORY OF NON-SKID DECK COVERINGS
In order to appreciate the development of COF machines for non-skid, it is valuable to
understand the evolution of the non-skid. From available documentation, current and past, the
chronological path of non-skid implementation and development within the Navy can be mapped from
the first use of non-skid materials to the current technologies used today.
The earliest coatings were first called non-slip, and they were simply cast aggregate (sand) into wet
paint. The aggregate that did not adhere after the paint dried was simply swept away. Durability of this
type of system was questionable, especially under aircraft and heavy equipment traffic which prompted
the Navy to develop a technical standard.1
The first military specification for non-slip deck coverings was MIL-D-23003, Type I & II (12
September 1961). Type I coatings were single component paints with aggregate mixed in. Developed by
industry, they were mostly applied by trowel, or notched trowel. However, they could also be brushed,
rolled or sprayed, and had a manageable pot-life of 6-8 hours.2 Since they did not have a curing agent
component, they could be sealed for additional applications if used within 4-6 hours of opening.
Type I was not as wear resistant as Type II. Type II was a two component non-slip, aggregate deck
covering. It had a significantly shorter pot-life than the single component predecessors. While a 1-2 hour
pot-life required some technical changes to the way it was applied, it was not a real problem for
experienced applicators.3
In 1964, BUSHIPS Notice 9190 (25 February 1964) directed that MIL-D-23003, Type I deck coverings
be discontinued on Aircraft Carriers, Submarines and other service areas. In carrier landing areas, Type
I was to be replaced by either a non-abrasive MLC-1157A (two part epoxy resin) or non-abrasive MLC-
1169A (two part moisture cure polyurethane resin) to reduce wear of arresting cables. In all non-landing
areas, Type I was replaced with MIL-D-23003, Type II deck coatings due to coating wear/durability
issues.4
Both the MLC-1157A and MLC-1169A were developed to reduce the abrasiveness of non-slip deck
coverings in the arresting cable areas of carriers. Many materials were evaluated. Eventually, mineral
grit was replaced by both beads and angular glass in these two non-abrasive formulations.5
In 1968, a repair material, designated NASL-C-1350, was used to repair damaged or worn areas on
MLC-1169A. It was a quick curing, non-cable wearing (angular glass), single-component moisture-cure
polyurethane that was trowel applied. One characteristic of this material was that it was ready for traffic
after 5 hours of cure (~60oF); this was an important feature of a repair compound for in-service flight
decks. Its properties were compared with other Type II, MIL-D-23003 materials. It was found to be
suitable for use over worn epoxy-based, non-slip coatings and worn MLC-1169A deck coverings.6
In 1969, due to increased air operations, the durability of the MLC-1169A and other commercially
available glass bearing coatings became an issue as they needed more frequent repair. The Navy
evaluated a new commercially available non-abrasive, non-slip. This commercially available non-slip
contained aluminum particles instead of glass.
This aluminum filled particle material was tested and evaluated to have similar COF values to MLC-
1169A in both new and worn states. But it was slightly less abrasive on the arresting gear cables, and it
was significantly more wear resistant than the MLC-1169A formulation. As a result, this commercially
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available aluminum filled particle non-slip soon replaced MLC-1169A on metal decks in landing areas.
However, MLC-1169A with its glass grit was still used on landing areas of wooden deck carriers. The
success of aluminum particles in landing areas is still seen in today’s non-skid.7
A move in the coating industry, from towel applied methods to spray, were incorporated within a new
specification standard. MIL-D-24483 was released on 8 May 1973 and updated on 19 August 1974 as
MIL-A-24483A. MIL-D-24483A had a dramatic life; it was canceled by official notice on 11
September 1986, reinstated on 17 April 1989 only to be cancelled again on 31 March 1997. During its
tenure, this specification addressed spray-applied, non-slip deck coverings. It consisted of two types:
Type I General Purpose
Type II Aircraft carrier landing areas
These non-slip deck coverings were designated a two coat system with the primer conforming to MIL-P-
24441/1 (F-150) and the topcoat, a two part synthetic resin compound consisting of a base resin with
aggregate and a hardener. Type II was required to have cable abrasion resistant properties.
Requirements for dry, wet and oily values for coefficient of friction were designated (Table 1).
On 25 February 1980, MIL-D-23003 was superseded by MIL-D-23003A (Revision A). In this revision
there were three classification types:
Type III General Purpose
Type IV Aircraft carrier landing and run-out area (non-abrasive to
steel arresting cable)
Type V General Purpose interior or exterior
Revision A specifically addressed application by roller only (smooth, hard core), as well as a description
of the peak texture of the rolled non-slip.
The Revision A non-slip was described as a system designating conformance to MIL-P-24441/1 (F-150)
for the primer and topcoat consisting of a two part synthetic resin compound (base resin with aggregate
and hardener). Requirements for dry, wet and oily values for coefficient of friction were also designated
(Table 1). MIL-D-23003A was amended on 10 January 1983, inactivated on 22 April 1998, and finally
cancelled on 13 April 1999 ending nearly a forty-year life of this military specification.
Finally, the Navy issued DOD-C-24667 on 11 September 1986; it superseded both MIL-D-23003A and
MIL-D-24483A. DOD-C-24667 initially combined the spayed and rolled non-skid into one
specification. It is also important to note that this was the first document referencing these deck
coverings as non-skid instead of non-slip. Amendments soon followed the initial release of DOD-C-
24667.
DOD-C-24667 Amendment I was issued on 30 October 1986, and Amendment II was issued on 9
February 1987. In the first set of iterations, there were three basic types:
Type I (A/B) General Purpose deck coating
Type II (A/B) General Purpose interior or exterior deck coating
Type III
(A/B)
General Purpose resilient deck coating (for use on wooden decks or where
more flexibility is required and where increased weight is not a factor)
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Each type had a further designator for High (A) or Low (B) volatile organic content. Also each type had
a choice of either:
Composition G- General use abrasive deck coating
Composition L- Limited use aircraft carrier landing and run-out deck coating, except for Type III
The final designator for these three types were:
Grade A High durability
Grade B Standard durability
Class 1 – Application by roller trowel
Class 2 – Application by spray, except for Type III
DOD-C-24667 specification also references the non-skid system as a multi-coat deck covering. Both the
primer and the non-skid were to have organic binders and pigments. The non-skid was to also have
aggregate incorporated. Coatings in this system could be either one or two part materials. Requirements
for dry, wet and oily values for coefficient of friction were also designated for Grades A and B for initial
and worn states.
Eventually the Military Specification for non-skid was replaced by a Performance Specification MILPRF-
24667A, issued on 14 August 1992. While the COF value requirements and criteria for the coating
system stayed the same, the most notable change was the simplification of the classification of non-skid
types:
Type I High durability, rollable deck coating
Type II Standard durability, rollable or trowel deck coating
Type III Standard durability, rollable resilient deck coating (for use on exterior wooden
decks or where flexibility is required and where increased weight is not a factor)
Type IV Standard durability, sprayable deck coating
Most types had a choice of either:
Composition G General use abrasive deck coating (Types I, II, III, and IV)
Composition L Limited use aircraft carrier landing and run-out area deck coating which is
not abrasive to the steel arresting cable (Types I & II only)
At this present time, the most current Naval non-skid reference is MIL-PRF-24667B, issued on 3 June
2005. The major difference between the current version and its predecessor is the increased variety of
non-skid Types:
Type I High durability, rollable deck coating
Type II Standard durability, rollable or trowel deck coating
Type III Standard durability, rollable resilient deck coating (for use where flexibility is
required and where increased weight is not a factor)
Type IV Standard durability, sprayable deck coating
Type V Extended durability, rollable deck coating
Type VI High durability, fast cure, rollable deck coating
Type VII Fast cure, temporary repair, rollable deck coating
Type VIII Low temperature cure, rollable deck coating
4
Type IX High temperature resistance deck coating
Type X Submerged applications
Most types have a choice of either:
Composition G General use abrasive deck coating (all Types)
Composition L Limited use aircraft carrier landing and run-out area deck coating that is
not abrasive to the steel arresting cable (Types I, V, VI, VII, VIII & IX
only)
HISTORY OF COF NON-SKID TESTING
Each non-skid specification had its own variation for determining the minimum acceptable
values for COF. Before we discuss these various methods used throughout non-skid history, let’s first
firmly grasp the concept of what the coefficient of friction really is. Consider a block on a flat table
(Figure 1). If a force (F) is applied to the block, a frictional force (f) acts in the opposing direction. If F
is not larger than f, the block remains stationary. This force acting in the opposite direction is called the
force of static friction (fs). However, if the applied force F is large enough to overcome the force of
static friction, the block will start to move. At this point, the static frictional force is at its maximum
(fs,max). When the block slips, it will accelerate in the direction of the applied force F. Once the block it
is in motion, the retarding fictional force is less than fs,max and is called the force of kinetic friction, fk.
Figure 1 graphically depicts the change in frictional state.