Three-edged replaceable head drill bit
Machining heat exchangers with a three-edged drill bit
Heat exchangers can be used in many variants and in a wide range of industries. The heat generated can be used for other processes. In the case of recuperators, two liquid or gaseous media of different temperatures are pumped into separate circuits. Heat is exchanged without the media mixing. Recuperators include shell and tube heat exchangers, which are usually made of metal and consist of a tube bundle through which one medium is passed and a shell space with a tube plate at the front through which a second medium flows. Depending on the size of the heat exchanger, the tube plate at the front has a large number of holes, which are subject to high requirements in terms of positioning accuracy and dimensional stability. This ensures that the medium does not escape at this component transition.
The three-edged TTD-Tritan replaceable head drill from Mapal impressed during the test in the petrochemical industry when machining a pipe plate. The tool head and tool holder of the TTD-Tritan are connected via a Hirth coupling. This interface is easy to use and particularly stable, so that the drill achieves the performance level of its solid carbide counterpart. It guarantees the best torque transmission with high changeover and concentricity accuracy. The drill bit centers itself via its pronounced drill point and ensures very good roundness. With the replaceable head system, the cost-intensive carbide is limited to the tool head, resulting in low tool costs even with large diameters. The replaceable head system also has a positive effect on stock-keeping, as the wear parts are mainly limited to the drill heads: As a consequence, the capital tied up in storage is also reduced.
In one specific case, the customer requires each diameter variant in several lengths for processing the different variants of tube plates. The company's comprehensive range makes it possible to provide all the desired variants. Smaller diameters are also served with the solid carbide version.
The customer's carbon steel tube plates are drilled into the solid with the replaceable head drill. The bore diameter is 25.6 mm and the bore length is 63.5 mm. The TTD-Tritan works at a 59 percent higher feed rate than the double-edged replaceable head drill previously used by a competitor. In the full drilling operation described above, it achieves a tool life of a good 53 meters, whereas the previously used drill was only just under 28 meters. In addition to this significant increase of 90 percent, the tool performs the full drilling operation in a single work step and only needs 29 minutes to drill the complete tube plate with 550 holes. In contrast, the previous machining process required piloting. In addition, the pipe plate had to be manually cleaned of the sometimes very long chips after piloting. Overall, the replaceable head drill reduces the machining time by 57 percent.
In addition to the two frontal tube plates, slightly thinner intermediate plates with the same drilling pattern are installed in the tube bundle heat exchangers. These intermediate plates are stacked on top of each other for processing, spot-welded, drilled and then separated again. With the QTD cutting insert drill with innovative, patented pyramid tip, the company also has a solution for this type of machining in its range. The newly developed cutting insert with pyramid tip has a very small transverse cutting edge and a tip angle of 120°. As a result, the cutting insert centers itself and ensures reliable bore entry. The intermediate plates can be drilled reliably in a single operation.
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