Cutting by use of rotating axially moving tool – Processes – Bit detachable
Patent
1997-05-27
1999-06-29
Howell, Daniel W.
Cutting by use of rotating axially moving tool
Processes
Bit detachable
408 56, 408 83, 408147, B23B 3500, B23B 2502
Patent
active
059158905
DESCRIPTION:
BRIEF SUMMARY
Machining straight deep hole drilled passages oriented as precisely as possible in metal objects is sufficiently commanded by the so-called gun-barrel drilling method for a ratio of roughly 1:100 of diameter to drilling depth. However, improving the directional stability and straightness of the drilled passage even in this range still leaves something to be desired.
Where very long and narrow drilled passages are concerned, as well as in the case of materials lacking homogenity, deflection of the drilled passages, i.e. the deviation from the ideal run, is particularly a problem. This is explained in the following by way of the example of so-called peripherally drilled heated rolls as employed in papermaking and paper finishing techniques.
In rolls of this type it is desirable for axially parallel drilled passages located just beneath the roll surface to handle the passage of a fluid heat transfer medium and to thereby bring the roll surface to an elevated operating temperature, as a result of which improvements in quality and economy of production in making and finishing paper and other web materials are achieved. Relative to the cross-section of the roll these peripheral drilled passages represent singular sources of heat. To achieve a roll surface temperature as homogenous as possible, as many peripheral drilled passages as possible having a diameter as small as possible are of advantage. This applies also to the thermal deformation of the cross-section of the roll in operation.
A typical calender roll of this type has, for instance, a roll diameter of 1,350 mm for a length of the roll body of 8,000 mm. Roughly 45 peripheral drilled passages having a diameter of 32 mm are arranged on a pitch circle of 1,220 mm diameter. In such a roll the peripheral drilled passages need to be drilled in two steps from both ends of the roll respectively up to roughly the middle of the roll. However, it is often not possible to dimension them so that the cited diameter/drilling depth ratio of 1:100 can be maintained, which is why the drilled passages "wander", i.e. depart from the straight line connecting input and output to a degree which is intolerable, and in differing directions--to the side (in the direction of the most adjacent drilled passage) to the roll surface or to the roll center in a combination of the cited deviations also spirally or totally undefined.
It goes without saying that a satisfactory flow of the heat transfer medium requires the corresponding drilled passages to meet as best possible in the middle of the roll, there being in addition a variety of reasons to be cited why the peripheral drilled passages need to be as straight as possible.
Especially in the case of calender rolls of chilled cast iron, a material which is used with preference, a tendency of the drill to "dive" into the roll is observed, i.e. the drilled passages are spaced further away from the surface at the middle of the roll than at the ends of the roll. As a result, in heated operation of the roll lower surface temperatures occur in the middle of the roll due to the heat flow being confronted by a greater resistance in the form of a greater wall thickness.
Another effect viewed as being undesirable is that runs of drilled passages dispersing individually introduce imbalance in the rolls, especially at the position where they have the worst effect on the balance of the rolls, namely in the middle of the roll. This, together with the deterioration in true rotation, may cause the roll to vibrate at high operating speeds and be a serious detriment to proper operation of the machine.
The main cause of the drill "diving" is the structure of the chilled cast iron roll which exhibits an extremely hard "white" shell and a softer "gray" core. Although care is taken to ensure quenching being restricted as best possible so that the peripheral drilled passages can be arranged in the "gray" zone of the cross-section of the roll, the quenching effect of the molds extend beyond the "white" shell. The strength of the structure of the "gray" zone
REFERENCES:
patent: 3635108 (1972-01-01), Prince
patent: 5451126 (1995-09-01), Brun
patent: 5544985 (1996-08-01), Lane
patent: 5788433 (1998-08-01), Grund et al.
Rittweger Wolfram
Zaoralek Heinz-Michael
Howell Daniel W.
Schwabische Huttenwerke GmbH
Tabaddor Rouzbeh
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