Predicting Sports Equipment Performance Through Surface Cleanliness Testing

Written by Pierce Geary

Products used in athletics need to conform to some pretty stringent standards. Manufacturers of these products are well aware of this and work hard to make sure every unit they build meets the performance standards of professional, collegiate and other athletic organizations.

Nearly all of this takes place long before a football, golf club or tennis racket reaches the hands of an athlete. But, regardless of the public’s awareness of it, manufacturers of athletic equipment need to make sure their products are reliable and durable enough to not fail when the heat is on.

To increase certain characteristics of the equipment, manufacturers will replace legacy materials with advanced materials for lighter weight, increased flexibility, decreased flexibility, aerodynamics and so on. But introducing these materials without understanding the effect on adhesion and assembly processes can lead to failures that disqualify the equipment from use in regulated sports.

So, what are the questions these manufacturers need to be asking themselves? How can they predict the highest quality outcomes when introducing new materials and processes? What matters most to determine if sporting goods will cross the finish line?

Enhanced Needs of Advanced Materials in Manufacturing

Using composite materials in manufacturing has led to extraordinary improvements in fuel economy in aerospace and automotive, strong and resilient devices in the medical industry and more powerful equipment used in the most demanding sports.

One of the biggest benefits of using composites in manufacturing is the ability to decrease the overall footprint of the product. Composites are able to be adhesively bonded to other materials which means mechanical fasteners and bulky materials are no longer necessary. Steps such as hole drilling and riveting are unnecessary but are replaced with other extremely important procedures.


To learn more about how BTG Labs uses simple, fast and accurate surface quality measurements to conduct root cause analysis, download our free eBook: Checklist: Adhesion Failure Root-Cause Analysis for Manufacturers


In order for an adhesive to create a strong bond with any material, the surface of the material must be chemically attractive to the adhesive. Epoxies are common adhesives used when bonding composites, and these require the composite surface to have a certain level of surface energy in order to create reliable adhesion. Surface energy can be boiled down to how chemically reactive a surface is.

When a material that has high surface energy, molecules in the air or in an adhesive want very badly to bond with the molecules on the material surface. A major manufacturing goal is to create a high energy surface, verify it and repeat the process for every product. When that is achieved, well, you got yourself a predictable process that will result in reduced costs, scrap, time-waste, warranty claims, recalls and a host of other ways that manufacturers realize loss.

Creating a high energy surface is done through cleaning and then maintaining the surface of the composite. Manufacturers are no stranger to cleaning processes but they may not be certain about what method is best for their process and their materials. Those are the right questions to ask. It is imperative that the cleaning process is appropriate for the materials and that the desired results are actually achieved.

For composite cleaning, grit or media blasting is a go-to surface preparation method. This method grinds away particulate and contaminants by “blasting” the surface with abrasive materials through a type of spray gun. This can be effective if monitored and maintained, however, in BTG Labs’ experience, this step can be the root cause of unintentional contamination of the surface.

If media is reused as a cost-saving measure it can inadvertently transfer what the procedure was able to remove from one part directly onto the surface of the next part. We’ve even found that there have been times when, after some surface analysis, a part was actually sufficiently cleaned by a preceding surface cleaning and the poorly maintained grit blasting only served to destroy a perfectly acceptable surface.

For this reason, it is crucial that manufacturers look at their cleaning and adhesion processes holistically so they can measure the impact of each step on the cleanliness of their surfaces.

Another manufacturer BTG Labs partnered with was experiencing failures due to contamination on their surfaces. Their part supplier told them it was likely residual mold release applied to the composite so it would slip out of the mold it was formed in easily. These release agents are often washed off by the part forming company but they do not always meet the quality standards OEM’s are looking for. After testing by BTG Labs, however, we discovered that the raw material and the material supposedly contaminated with mold release were testing the same levels of surface energy so it was likely a downstream step that was contaminating the surface. Another good reason why comprehensive testing is vital to assessing root causes of adhesion issues.

So, some of the major questions manufacturers need to be asking themselves are:

  • Are my materials affecting my adhesion outcomes, if so, in what ways?
  • Are my cleaning and surface preparation methods appropriate for my materials?
  • Are my cleaning and surface preparation methods being conducted and maintained properly?
  • How clean do my surfaces need to be in order to achieve perfect adhesion?
  • Am I adequately measuring surface cleanliness to understand how well the bonded materials will perform?
  • How clean are the material surfaces when I receive them from a supplier?
  • Where is contamination being introduced to the material surfaces?

Surface Energy’s Impact on Athletic Regulations

Let’s use golfing as an example. In professional golf, the United States Golf Association (USGA) and the R&A (which used to stand for The Royal and Ancient Golf Club of St. Andrews but is now unaffiliated with the club and is focused on adjudicating regulations for the British Open Championship) have created standards for what is deemed legal and illegal for golfers’ equipment performance.

A somewhat esoteric measurement of a golf club’s legality on the course is what is called characteristic time (CT). CT essentially refers to how long a golf ball remains in contact with the club face upon impact. If there is a high CT then this probably means there is too much elasticity or flexibility in the golf club materials. This was determined by the agencies as a corollary to the more commonly known coefficient of restitution (COR). COR refers to the transfer of power from club to ball and since this is difficult to measure in the field, the USGA and R&A rely on golf club manufacturers to test their clubs’ CT instead.

According to the USGA and R&A, the current CT tolerances are stated like this: “If the CT value at the centre of the face is greater than 239 µs plus an 18 µs tolerance then the club does not conform to the Equipment Rules…” That essentially means that the maximum amount of time a golf ball is allowed to stay in contact with the club face is 257 microseconds.

Golf club manufacturers test this by using a pendulum to conduct a series of thousands of impacts and measuring how many microseconds the golf face is keeping contact. If after a certain amount of trials the CT remains below the tolerance then the manufacturer knows it is within the specification.

This minute characteristic is very meaningful to the regulatory bodies. They disqualified the use of a driver ahead of the 2019 British Open Championship because it was just 1µs over the 257 maximum.

CT is affected by the assembly integrity of the golf clubs. Manufacturers need to be able to build sturdy clubs that are guaranteed to have a low CT. This means controlling their surfaces so none of the bonded interfaces become weakness vulnerabilities that cause CT creep during performance testing.

How to Predict Performance Outcomes by Measuring Surface Quality

The best way to predict performance outcomes of adhesively bonded materials is to quantitatively measure the surface quality at every Critical Control Point, or every single place in the production process where the surface has an opportunity to change in positive or negative ways.

The testing that BTG Labs conducted with the manufacturers mentioned earlier were quantifiable measurements of surface cleanliness. We were able to assess the cleanliness and quality of surfaces based on these quick and accurate measurements letting us know when surfaces were clean and exactly how clean they were. It’s important to know that a clean surface on a Friday may no longer be clean on Monday if the production lines have been shut down over the weekend and prepared surfaces are left to collect molecules from the environment that whole time.

With predictive data from smart sensors installed throughout the adhesion process, manufacturers can know precisely when abrasive material in a media blaster is no longer cleaning properly. They can also know before an epoxy is even applied to a surface that it won’t create a strong enough bond to meet the CT requirements. If the surface quality measures below the threshold for cleanliness then the adhesion strength won’t be there when it counts.

To learn more about how BTG Labs uses simple, fast and accurate surface quality measurements to conduct root cause analysis, download our free eBook. This book, “Checklist: Adhesion Failure Root-Cause Analysis for Manufacturers”, is a step-by-step guide to conducting your own analysis to know precisely where your process vulnerabilities are. Download your copy today.

Adhesion Failure Root-Cause Analysis for Manufacturers