“Composite Flow Technology (CFT) Core”:
Optimum Chemical Engineering Fluid Mechanics Yield Increased Quality & Maximum Mass Property Stabilization
Senior Design Engineer
Bowling ball core designs often include a specific purpose for which they were designed. Different densities, shapes, and sizes all come together to yield a targeted Radius of Gyration (Rg), Differential Radius of Gyration, and Rg contour plots that influence the bowling ball motion. 900 Global has released many innovative core designs over the past years with different intended purposes to help generate the optimum ball reaction. Recent designs such as the Double Cross Core, Combustion Core, and SRC have all had unique applications related to design principles and performance. 900 Global is now excited to introduce another break through in core design. The innovative “Composite Flow Technology (CFT)” core uses intricate chemical engineering fluid flow design tactics to both increase quality and maximize mass property stabilization after drilling.
Figure 1: “Composite Flow Technology (CFT)” Core Design
A composite material is made from two or more materials with individually different physical and/or chemical properties that when combined produce a different trait than either of the individual materials. A finished core is comprised of a variety of dry substrates mixed with a specific ratio of polyester resin. This liquid/paste mixture that hardens into the shape in which it is poured into is called a composite material blend because of its multiple material make-up. During the second stage of core production a round, lighter density composite material core is poured around the inner core shape. This process allows for different weight bowling balls to be made as well as a range of mass properties. The lighter density composite material must flow around the already positioned inner core within the mold. This process can be seen in Figure 2. The complexity of different shapes can hinder a portion of the material flow.
Figure 2: Outer Core Pouring Process w/ Inner Core Positioned Inside
To analyze the affect of different inner core shapes on efficiency and the quality of outer core material consistency flow, fundamental principles that apply to the analysis of fluid flow must be incorporated. The flow of outer core composite material around the inner core while filling the mold is mathematical governed by the equations of continuity conservation of mass (Mass Balance) and conservation of momentum (Momentum Balance). These equations are summarized below in Figure 3 and Figure 4.
(Rate of Material Mass Flow in) – (Rate of Material Mass Flow out) = (Rate of Material Mass Accumulation)
Figure 3: Material Flow Mass Balance Continuity Equation
(Rate of Momentum in) – (Rate of Momentum out) + (Sum of force acting on system) = (Rate of Momentum Accumulation)
Figure 4: Material Flow Momentum and Force Balance Equation
These equations when applied to a flowing fluid material allow for a comprehensive and in depth analysis of how the material is behaving during the flow process and allow for optimization calculations to maximize production productivity and quality. The equations help to analyze the material behavior with respect to flow rates, density, momentum, forces (gravity), and accumulation in all three directional aspects (x, y, z) during the mold filling process. Figure 5 displays the equation that allows for determining the overall average velocity (V) of the composite material flowing into the outer core mold per unit area (A). Integrating the results from the mass and momentum balances with the average material velocity then help determine the overall flow characteristics for the composite material.
Figure 5: Average Material Velocity
Finally, to complete an understanding of the flowing composite material in the outer core mold as it flows around the inner core while filling the mold, a concept of boundary layer phenomenon must be analyzed. A boundary layer is created when the direction of a moving fluid is influenced by the presence of a solid boundary. In this case, the fluid flow is the outer core material and the solid boundary is the inner core within the mold. An example of two types of boundary layers is shown in Figure 6 (a, b).
Figure 6: Boundary Layer Material Flow
The new CFT core allows for composite outer core material to flow with similar flow characteristics as shown in Figure 6a due to the cut out slits and voids. As you can see the composite material flow is minimally impacted by the design and maintains its flow properties and consistency from the top to bottom side of the mold. However, Figure 6b represents other core designs that have a large solid mass interrupting the flow of composite material filling the mold. The material must slow down, change direction around the obstruction, and attempt to re-organize itself into its original flow pattern. This transition is known as boundary layer separation where large eddies (vortices) are formed on the other side of the solid object. Additional, more complex equations are needed to evaluate the flow parameters in this region. However, the swirling effect consumes considerable amounts of energy and leads to a large pressure loss in the material. These eddies (vortices) cause the composite material consistency and density not to be 100% uniform across the entire mix within the mold. It is important to have uniformity across the mix to improve not only the durability of the bowling ball but also to maintain designed mass properties of the bowling ball. The CFT core aids in ensuring the proper amount of uniformity.
This unique CFT design also yields maximum mass property stabilization that is derived from the slits and voids within the core structure. Typically when holes are drilled into a ball the Rg values on one or more of the primary axis are changed due to the removal of mass from the holes and usually affect the total differential. The changes in mass properties can lead to increased or decreased altered ball motion that a bowler might not expect. Modeled and measured values of the primary Rg values on bowling balls drilled with the CFT core inside maintain and hold the undrilled Rg values through the drilling process. Figure 7 below shows the designed undrilled Rg and Differential Rg of previous 900 Global high performance cores. This chart then displays the resulting Rg and Differential Rg values on three common drill patterns (~ 5x5 pin up, 3-3/8th x 4- ½ pin next to fingers; ~ 5x5 pin down). Notice the large percentage changes of total differential on recent core designs once holes are drilled. Figure 8 shows the average change in Diff Rg across the three drillings for recent cores.
Figure 7: Rg Pro-Engineer Model Calculations
Figure 8: Average % Change in Differential Rg of Recent Cores After Drilling
These recent cores designs, although help provide unique ball motion, range from 7% to 22% in total differential change from the undrilled ball to the drilled ball. The CFT core minimizes these changes in total differential and thus maximizes the stability of the mass properties after drilling. Figure 9 shows the equivalent mass property analysis on the CFT core. As noted, the first two drill patterns have ZERO % change from before drilling to after drilling. When placing the pin below the fingers a 7% decrease in total differential is measured. Although not zero, the 7% is the lowest change in total differential for that drill pattern.
Figure 9: RG Pro-Engineer Model Calculation for the CFT Core
Figure 9: RG Pro-Engineer Model Calculation for the CFT Core
The stability in maintaining the total differential values is a direct correlation from the minimization of the drilled holes impacting the large cylinder interior of the core. As an example below, Figure 10 shows an image of the drilled holes using the “pin up – Above Finger” pattern. The finger holes subtly graze the top portion of the core while the thumb hole penetrates through the outer ring and removes a portion of the outer core composite material versus impacting the inner core cylinder. By designing the CFT to ensure minimal mass is removed when drilling the overall measurable affect is maximum mass property stabilization.
Figure 10: Pin-Up Drilling on the CFT Core Design
In conclusion, the CFT core design incorporates fundamental design principles derived from chemical engineering theory to help ensure quality and durability of the final product. The design also yields maximum mass property stabilization due to the unique ring shape that surrounds the inner cylinder of the core. These design applications help to ensure that the CFT core links a high complex engineered design with enhanced performance on the lanes.