Beyond Omniseal® Blog

Steering You to Ball Joint Bearings: The Polymer Solution to Driving Comfort & Safety

Nov 21, 2018 / by Erich Weissflog

Since the invention of the first automobile “powered by a gas engine” in 1886 by Karl Benz, traveling by car has become a central part of our lives. According to a Harvard Health Watch study, an average person will spend about 38,000 hours driving a car in their lifetime. When we get into our vehicle, we automatically adjust the seat position, head restraint and steering wheel ... all done to make our ride as comfortable and safe as possible. It’s no wonder that automobile manufacturers are taking note to improve driver comfort and safety as important selling points since consumers are spending more time not only driving but also sitting and waiting in traffic. 

As with all good things, driver comfort packages come in different sizes and shapes that can be seen, felt and touched, such as seat warmers and ambient lighting. They also come in engineered parts that are not in plain view such as ball joint bearings (also referred to as ball sockets, ball bearing liners or ball casings), which do play a critical role in smooth, stable steering for safety and suspension for a more enjoyable ride. 

The Importance of Ball Joints 

Much like rectangular seals are critical in transmissions to save space and money, ball joints are critical to maintain the parts’ stable properties over lifetime. Named after the ball-and-socket design of the human hip, they are comprised of a tapered and threaded bearing stud that fits in the hole of the steering knuckle, a socket (or ball) that provides the motion and a casing that encloses the ball or ball joint bearing. These important parts serve as a pivot between the wheels and front (and often the rear) suspension in connecting the control arm to steering systems on automobiles. Most automobiles have upper and lower ball joints on each side to offset suspension to ensure a smooth ride, even with contraction and shock. They are installed in moving parts to avoid wear from metal-on-metal contact and enable even and stable coefficient of friction. 

Other key benefits of the ball joint bearing include:

  • Smooth steering and suspension
  • A quieter, more comfortable ride, with suspension introduced in controlled increments
  • Longer tire life with less wear on treads 
Not All Ball Joint Bearings Are Created Equal 

Ball joint bearings that are not adequately pre-sized, i.e., with bearing slots that are too big or dimensions that are not designed to specifications, can pose physical issues. Parts can become twisted in production causing tangling, crimping of metal and even stopping the assembly line. An inadequately sized ball joint bearing that may cost less than one Euro (or dollar) can require an entire suspension arm (worth €100 in parts) to be scrapped, creating an expensive amount of waste. A ball joint failure will be dangerous and costly as there may be a loss of control and debris may damage other parts of the automobile. 

Important considerations to look for in ball joint bearings include:

  • Low creep tendency under mechanical stresses for high stability of the material throughout the lifetime
  • Flexible design options with low-friction polymer seals able to be modified and customized with special tooling properties to suit the OEM’s requirements
  • Heat resistance for better performance in smaller operating areas
  • Chemical resistance to grease that is used in lubrication and salt water from driving
  • Low coefficient of friction against solid surfaces
  • Low wear to ensure extended life
  • High tensile and fatigue strength for greater endurance against stress (increasing surface loads)
  • Good safety reserves to address extreme situations, such as high load conditions, like carrying the weight of the vehicle over a curb. This is an important aspect for OEMs to calculate in design.

Additionally, to be effective, ball joint bearings must provide a tight, stable fit over the lifetime of the parts. Process requirements such as the following are essential:

  • Small tolerances to help ensure higher quality parts that achieve their function.(and to ensure a stable assembly process; to avoid the need of adapting the dimensions of the metal counter parts due to fluctuating quality/dimensions of the ball joint bearing)
  • Prediction of shrinkage in manufacturing, with the fit between the ball studs and ball joint bearing needing to be as precise as possible. When materials cool down from hot injection molding, they can shrink. This should be accounted for in advance, with the cavity of the manufacturing tool needing to be bigger than the part’s geometry.(which requires a profound knowledge on the material behavior in the injection molding process)
  • Special material and tooling experience with demolding of the parts after cooling having the potential to cause deformations. Inner geometry of parts can stick, causing them to rip or become deformed if not skillfully removed.(by specially adapted/developed handling process)
The Material Formula for Success: POM or PEEK 

Often manufacturers look to POM, also known as polyoxymethylene or polyformaldehyde, as a very reliable material for ball joint bearings. This thermoplastic material is readily available with better: sufficient mechanical properties, low stiffness and very good tribological properties;. It is also easy to assemble (because of its low stiffness) given its forgiveness in dimensioning. POM is known for good performance in cold temperature; however, it can be limited in temperatures and load variables. With the growing trend of ball joint bearings needing to address higher heat levels, given the decreasing space of brake discs and electrification in many automobiles and assembly lines (that result in surface load getting higher), it may not be the best material for these types of applications. 

PEEK, or polyether ether ketone, is an opaque thermoplastic polymer that can address high temperatures and chemicals and offer a greater lifetime. Additionally, PEEK materials are able to support higher loads and are also more rigid (especially the carbon-fiber reinforced grades that we  specialize in processing these very tricky materials for ball joint bearings), which can be beneficial in ball joint bearing design, but can make their production more difficult without the right expertise and tools. 

Ball Joint Bearing Design Experts 

With more than 40 years of experience with OEMs, Tier 1, and Tier 2 companies, Saint-Gobain Seals has been commended for manufacturing difficult-to-process ball joint bearings with the highest precision and competency in high volumes. In fact, a key automotive OEM named Saint-Gobain Seals as their exclusive supplier, awarding us a quality award. 

With the acquisition of LS Kunststofftechnologie GmbH in 2014, Saint-Gobain Seals further strengthened its position in the automotive sector, specifically for the powertrain and transmission segments and injection-molded seals. By working closely with customers, we are able to custom-tailor compounds to best address their direct needs. We draw on extensive molding, quality, analysis, tool design, and tool shop (built in house) expertise to ensure high-quality parts to address their current applications as well as investing in the future with new resources at our Wertheim headquarters. 

We understand that Tier 1 and 2 companies and OEMs have many challenges on the road, striving to reduce friction, wear, and noise as well as increase safety for their end customers. Using our design engineering and R&D resources, we are committed to giving both our customer and the consumer the most comfortable ride as possible wherever they go. 

To learn more about our ball joint bearings and other precision parts, please contact us.

Topics: Education

Erich Weissflog

Written by Erich Weissflog