Assembly in Action: Dispensing System Ensures Mixing Ratios for Foam Padding
Brock USA (Boulder, CO) has developed a foam bead technology using closed-cell polymer spheres that range in size from 2 to 6 millimeters in diameter. They are encapsulated by an elastomeric coating during the manufacturing process. It produces a protective foam with mechanical and physical properties that lessen impacts.
The foam was developed for padded liners used in single-impact helmets, such as motorcycle helmets, as well as multiple-impact helmets, such as those for hockey and football. Brock’s foam incorporates polyethylene or poly-propylene spheres of different densities, which can be formed into discreet layers or a homogeneous mix. This construction enables a helmet liner or other protective pad to dissipate both high- and low-energy impacts more effectively than foam consisting of a single density.
In Brock’s design, the thousands of tiny spheres making up a helmet liner or other protective pad appear to be in direct contact with one another. However, the elastomeric coating bonds them, with air pockets in between. This permits the foam to absorb energy by using both plastic and elastic deformation.
“When a pad made with Brock foam is subjected to an impact, the initial deformation occurs at the elastic interface,” says Dave Bainbridge, vice president of product development at Brock. “As the elastomeric binder begins to compress between the spheres and adhesion points elongate, the air channels collaspe. The spheres deform and further absorb the blow. This gives the entire construction the benefits of both a high-volume, low-density foam and a low-volume, high-density pad in the same material.”
The greater the impact force, the harder the liner becomes. A soft liner is desirable for preventing multiple-impact injuries caused by low energy forces, and a firmer liner is preferred for high-energy impact. So a padding material that exhibits this ability is ideal for sports padding.
Additionally, unlike conventional foam padding, Brock’s padding cools the body instead of increasing unwanted thermal insulation that contributes to overheating. It promotes convective and evaporative cooling by virtue of the abundant air channels. Pads made with this technology not only keep the wearer more comfortable during strenuous exercise, but they also help prevent heat-related injuries, such as exhaustion and heat stroke.
“To meet rigorous standards for the foam, we needed very precise control over our mix ratios and dispensing rates,” says Bainbridge. “It was critical that we be able to deliver both components of the two-part formulation in exact quantities, even in small volumes dispensed at just a few grams per second.”
Brock contacted Fluid Research Corp. (Tustin, CA) for dispensing equipment. The new equipment is based on progressive cavity pump technology that eliminates phasing errors and is highly accurate. Programmable controls have also simplified changeovers from one production run to the next.
“We manufacture different types of foam, and each one can be made in different densities,” says Bainbridge. “This system offers a short turnaround time for material supply changes, and it can purge lines and recall a different program in seconds. Because the material chemistries in this application are similar enough to prevent contamination, it’s typically ready to resume production in a few minutes.”
The base material in the foam is a two-part urethane, with one component of the formulation having a filler. A material management unit heats and recirculates the formulation to maintain stability, and constant dispersion provides control. Even when the machine has been idle for some time, it recirculates all the material back into the feed tank to be reagitated at startup. Therefore, each component is thoroughly mixed, and the fillers are correctly suspended. The material supply containers can also be exchanged without introducing air into the system. Supply containers can be disconnected and replaced without stopping production or the need to “de-air” the entire dispensing station.
For more information on dispensing, call 714-258-2350 or visit www.fluid research.com.