Carbide-tipped bit wear patterns and productivity with concrete drilling

Drilling into concrete with carbide-tipped bits using a hammer drill is a physically demanding task performed in commercial construction for setting anchors and rebar. Bit wear will not only decrease productivity (rate of penetration) but can also increase drill handle vibration, noise and dust exposure to workers. The purpose of this study was to evaluate the relationships between geometric patterns of bit wear and rate of penetration. Image analysis methods were used to quantify 13 geometric parameters of the carbide tip at various levels of wear, and the changes in the geometric parameters were then compared to changes in penetration rate. Two different bit designs were studied. New bits were worn by repeatedly drilling into aged concrete. Penetration rate was determined on a test bench system programmed to drill into aged concrete to a specific depth under force control while the time to complete the hole was measured. Increasing fluke slope, increasing shoulder rounding, and decreasing bit width were highly correlated to reduced productivity. The findings have practical value for contractors and bit manufacturers in providing a method to identify concrete bits that should be replaced due to reduced cutting ability.