Page 280 - ISCAR(HOLE_MAKING_CATALOG_65)
P. 280

USER GUIDE
      DEEP DRILLING - BTA SYSTEM



          Coolant

              Successful deep hole drilling is achieved by an               STS - Double tube system
              optimal combination of the tool, the machine and                    Outer     Double tube
              the coolant. Coolant plays an essential role in    Workpiece        tube      connector
                                                                 material
              achieving secure and cost-efficient deep hole drilling    Drill   Guide
              operations. Therefore, it is very important to choose     head  bush   Inner           Chip
              the correct type of coolant and use it appropriately.                  tube            box
              Coolant
              Coolant plays an essential role in lubricating tools,
              cooling cutting edges, chips and guide pads, as well
              as evacuating chips when drilling. It also improves                 No need for sealing
              tool life, surface finish and cutting accuracy when
              continuously supplied during the machining process.   Coolant unit
                                                                A coolant unit is also important to obtain
            1  Lubrication                                      the best effect from the coolant.
              Lubrication of cutting edges and guide pads is
              necessary in deep hole drilling. For efficient lubrication,   1  Coolant pressure and volume should
              it is recommended to use EP (Extreme Pressure)    be fixed and continuous.
              additives which contain sulfur or chlorine.
                                                                An ideal coolant unit should be able to set any valve of
                                                                coolant pressure and volume and monitor the condition
            2  Temperature reduction                            with gauges. A system that can detect trapped chips
              The ability to cool down the cutting edge and     by a pressure gauge and the screw pumps with
              chips depends on such characteristics as          an inverter controller are  both recommended.
              thermal conductivity and relative heat. Coolant
              with good cooling ability increases tool life, but   2  Coolant temperature should be maintained.
              water-soluble coolant is not preferred in deep    Coolant is heated by factors, such as:
              hole drilling because it reduces effectiveness. If
              water-soluble coolant is used, the recommended   •  Cutting edge
              concentration is 10% (dilution rate 1/10) or more.   •  Friction on guide pad
                                                              •  Contact time of heated chips and coolant
            3  Chip evacuation                                •  Pump
                                                                Maintaining coolant temperature is important to
              Coolant helps push chips through the back end of the   keeping stable cutting conditions, chip formation
              boring bar (for STS) or inner tube (for DTS) until the chips   and cutting accuracy. The temperature should
              are separated from the workpiece in general cutting   be lower than 40°C (100°F) for EP additives to
              conditions. The flow and the pressure of coolant are   provide sufficient lubrication. Therefore, the coolant
              also important in order to control chip evacuation.  temperature should be kept between 30 - 40°C
                           STS - Single tube system             (90 - 100°F) throughout the cutting operation.
               Workpiece
               material               Oil                     3  Filtering
                               Guide   pressure
                    Drill   Drill   bush  head  Bar   Chip      Unwanted particles are contained in coolant after the
                                                                cutting operations, thus filtration is necessary to remove
                    head  tube Sealing         rest  box
                                                                them. The filter size should be selected carefully to catch
                                                                particles but not EP additives. Filter size depends on the
                                                                coolant, but around 10 - 20 μm is generally suggested.
                                                                For iron-based workpieces, a magnetic separator is helpful
                                                                as it decreases the frequency of filter maintenance.


              Flow chart of coolant in deep hole drilling
                                                                Pressure
                                                                gauge     Flow
                                                                          gauge
                                                                                                 Motor
                                                                            M         Pump    P     M
                                             Chipbreaker
                                                                            P
                        Drill
                        head   Drill tube                          Filter
                 Workpiece                                                     Chiller
                                     Oil
                                     pressure   Chip     Dirty tank                      Clean tank
                                     head       box





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