Jim Neel Discusses Coefficients of Friction

Jim Neel discusses coefficients of friction: Tile Files

By Jim Neel

 

Friction is a materials property. Basically, it is the force that resists the sliding motion of one surface against another. Contaminants, such as liquids, can change this value.

The coefficient of friction (COF) is the ratio of the pull force it takes to slide the surfaces divided by the weight pushing down on the surfaces. It may sound a bit complex, but the math is simple. For example, if it takes 30 pounds to push a 60-pound crate across a factory floor, then the COF would be 30/60 or 0.50.

There are two types of friction, static (SCOF) and dynamic (DCOF). SCOF is the ratio of forces necessary to start two surfaces sliding. This is what ASTM C1028 measured. DCOF is the ratio of forces necessary to keep two surfaces sliding. This is what the BOT 3000 is evaluating. There is generally a spike in the force necessary for movement to occur; in other words, you have to push harder to get something moving than you do to keep something moving, so typically SCOF is greater than DCOF.

Slip resistance is the ability of a surface to inhibit the movement of another surface. Although there are many components, the coefficient of friction is thought by many to be an important one. Other factors may include, but are not be limited to, grout joint spacing, tile texture, slope of the floor, and contaminants.

Since the COF can be readily measured, safety professionals often use it to gauge the slip resistance of a floor. A numerical value also makes it a very useful tool for quality assurance at the manufacturing level.

FROM EVOLUTION TO REVOLUTION: HOW DID WE GET HERE?
Historically, tile manufacturers want something relatively simple, statistically repeatable and reproducible, and reliable for processes control. ASTM C1028 filled this role for several decades. During this time, a tremendous amount of historical data was gathered about product performance.

The industry pseudo-standard for SCOF was considered to be 0.60. This value originates from an obsolete ADA bulletin that was published a decade ago (this document was later withdrawn). However, it recommended a minimum SCOF of 0.60 for flat surfaces and a value of 0.80 for ramps. Even though this recommendation was only official for a few years, these values stuck with the tile industry. These numbers were never reflected in ANSI; they were simply what our customers started asking for.

Many consider a COF measurement to be integral to safety, and, therefore, the most important test for floor tile. There is also the potential for increased legal exposure. These factors, coupled with the fact that C1028 has been around for a long time, meant that there were significant political challenges in attempting to improve on the status quo.

In 2001, a device called the Sellmaier FSC 2000 was brought into the main testing lab of Daltile. It seemed to be a promising alternate way of getting SCOF data that correlated quite well with ASTM C1028. The device underwent a series of changes and was later named the Universal Walkway Tester (UWT). At about this time, Daltile took its findings to the Tile Council of North America (TCNA) and the rest of the tile industry. A few years later, the instrument was re-badged as the BOT 3000.

The BOT turned out to be so promising that other (non-tile) groups also started to work with it. On the tile side, the effort took several years. The TCNA Tile Technical Committee further worked on developing a test method around this device.

In slip resistance circles, there is some debate about SCOF versus DCOF techniques and which one best reflects the safety of a floor. While exploring the capabilities of the BOT, the tile industry discovered that there was a very strong correlation between SCOF and DCOF, which essentially made this argument moot.
The BOT 3000 test uses slightly soapy water. This lowers the value from the old 0.60. To assist with educating the marketplace, DCOF was chosen as the technique to use. Basically, we are now measuring something slightly different.

After ten years or so of method development, ANSI A137.1 approved the BOT 3000 as the standard test method for COF. ASTM C1028 was removed as a requirement at the same time. The industry standard is now DCOF as measured per ANSI A137.1-2012 Section 9.6. Also adopted at the same time was a minimum value of 0.42 for areas likely to be walked upon when wet.

The end result is a test method that is not just a modern replacement for C1028; the new method achieves stricter statistical criteria and surpasses alternate methods in just about every category. The ANSI A137.1 test method for DCOF established a new benchmark for COF (and slip resistance) measurement systems. 

WHAT IS THE BOT 3000?
The BOT 3000 is a robot that is capable of taking friction measurements of a flooring surface. It is programmable and has the ability to print out and electronically store the data.

This instrument is capable of both laboratory and field measurements. Although the BOT can measure friction in different ways, dynamic COF was chosen as the unit for ceramic tile values. Unlike ASTM C1028, the BOT gives realistic values on high gloss or polished surfaces.

It is important to note that the BOT 3000 instrument is a tool. Tools can be used in different ways. As such, there are other test methods that use this device. Variations in a test method can result in variations of test results. These alternate test methods may yield different results, even if they use the BOT 3000.

A decade of work and research went into the current ceramic tile BOT 3000 (AcuTest) method. There was widespread industry cooperation and participation.

We feel that the method specified in ANSI A137.1-2012 (also called the AcuTest) is the most robust and statistically valid method for COF testing. It should set the benchmark for COF/slip resistance testing in the standards community for years to come.



TRANSLATING THE NUMBERS
Many ceramic tile folks are used to 0.60, so they ask, “What do you mean the number is 0.42? Isn’t that less?” It is important that customers understand that most ceramic tile products (including Daltile’s) have not changed. Most products that met a C1028 value of 0.60 will meet the BOT 3000 AcuTest DCOF value of 0.42.

The BOT is simply measuring something different. ASTM C1028 measures the static coefficient of friction (SCOF). The BOT is measuring the dynamic coefficient of friction (DCOF). And the BOT’s use of slightly soapy water to make the measurement differs from the clean water used in the ASTM test.

Separate research has been done by The University of Wuppertal (Germany), the TCNA, and Daltile over the past ten years. A value of 0.42 DCOF was found to be representative of a slip-resistant surface.

What does the specification of 0.42 DCOF mean? This is the minimum value required by ANSI A137.1-2012 for interior spaces that are expected to be walked on when wet.

Is a product having a DCOF value of 0.42 appropriate for any application? Absolutely not. The specification is intended to be a starting point. DCOF values are only one component of slip resistance. Factors such as, but not limited to, tile texture, number of grout joints, end use conditions, footwear type (or lack thereof), expected maintenance, expected wear, and manufacturers’ guidelines should also be considered.

In general, most tile producers can provide suitable recommendations for using their products in specific usage areas.

Copyright 2013 Floor Focus



Other Archived Articles

Home Builder Sentiment Ticks Down in January   Full Article
Washington, DC, Jan. 20, 2015 -- U.S. homebuilder sentiment edged lower in January but remained well in positive territory, according to the National Association of Home Builders.

Remodeling Market Index Hits Record Level   Full Article
Washington, DC, Jan. 20, 2015 -- The National Association of Home Builders’ Remodeling Market Index posted a record-high result of 60 in the final quarter of 2014.

Fuse Alliance Names Gordon Executive Director   Full Article
Laguna Niguel, CA, Jan. 20, 2015 -- Fuse Alliance, a member-owned organization of professional, commercial flooring contractors, said it has named Geoff Gordon as executive director.

RAK Ceramics Selling Stake in RAK Laticrete   Full Article
United Arab Emirates, Jan. 20, 2015 -- RAK Ceramics plans to sell its stake in RAK Laticrete as part of the company’s strategy to focus on core assets, the firm said.

Julius 'Bud' Shaw, Founder of Shaw Industries, Dies   Full Article
Cartersville, GA, Jan. 20, 2015 -- Julius Clarence "Bud" Shaw, age 85, founder of Shaw Industries, died Jan. 16.

TISE East Changes Location, Dates   Full Article
Dallas, TX, Jan. 20, 2015 -- Informa Exhibitions said that the second annual International Surface Event East 2015 dates have shifted to Nov. 2-5 and the location is moving to Orlando, Florida at the Orange County Convention Center.

Shaw Introduces New Carpet Backing, Protection System   Full Article
Dalton, GA, Jan. 19, 2015 -- Shaw Floors said it is introducing LifeGuard, a new carpet protection system that covers the entire product, from face fiber to backing.

Valinge, System SpA Form Printer Partnership   Full Article
Viken, Sweden, Jan. 19, 2015 -- Välinge Innovation and System SpA have entered into a strategic partnership to supply the flooring and building panel industry with industrial single-pass printers .

Surfaces Show Featuring Booth Crawl Challenge   Full Article
Dallas, TX, Jan. 19, 2015 -- This week's Surfaces show will feature a Booth Crawl Challenge, a new show promotion.

Ceramics of Italy Contest Deadline Extended   Full Article
Bologna, Italy, Jan. 19, 2015 -- The submission deadline for the 2015 Ceramics of Italy Tile Competition has been extended to Jan. 23.

Polley To Be Inducted into WFCA Hall of Fame   Full Article
Anaheim, CA, Jan. 19, 2015 -- David Polley is the newest inductee to the World Floor Covering Association Hall of Fame.

HPS Schönox To Name Contest Winners on Thursday   Full Article
Las Vegas, NV, Jan. 16, 2015 -- HPS Schönox will present the winner of its Schönox Worst Subfloor in North America Contest at Surfaces next Thursday at 11 a.m..

Shnier To Distribute Metroflor's Aspecta in Canada   Full Article
Norwalk, CT, Jan. 16, 2015 -- Metroflor Corp. said it has formed a partnership with Shnier, a leading Canadian floor covering company, to distribute its commercial Aspecta LVT.

Dealer Discovers Rug Owned by FDR   Full Article
New York, NY, Jan. 16, 2015 -- John Ahdoot of Ahdoot Oriental Rugs recently discovered a rug in a New Jersey couple’s home that once belonged to Franklin Delano Roosevelt.

Consumer Sentiment at 11-Year High   Full Article
Ann Arbor, MI, Jan. 16-2015 -- Consumer sentiment in January surged to the highest level in 11 years, according to the preliminary reading of the University of Michigan/Thomson Reuters consumer sentiment index.

Consumer Prices Fall Most in Six Years   Full Article
Washington, DC, Jan. 16, 2015 -- U.S. consumer prices fell 0.4% in December, the largest drop since the end of 2008, according to the Labor Department.

Pharr Yarns Invests in New Space Dye Technology   Full Article
McAdenville, NC, Janu. 15, 2015 -- Pharr Yarns said it has invested in space dye technology for its McAdenville facility to handle the growing demand for sophisticated design.

Engineered Floors Using Dye, Stain Technologies in Soft Nylon   Full Article
Dalton, Ga., Jan. 16, 2015 – Dream Weaver Carpet and Engineered Floors say they are using technology they developed for coloring polyester fiber and applying it to soft nylon.

IVC Deal a Good Sales Opportunity for Mohawk   Full Article
New York, NY, Jan. 15, 2015 -- Stifel Nicolaus still has a "buy" rating on shares of Mohawk Industries following Mohawk's announced acquisition of vinyl firm IVC for $1.2 billion.

Producer Prices Decline in December   Full Article
Washington, DC, Jan. 15, 2015 –- Producer prices fell by 0.3% in December, according to the Commerce Department.