MILLING CUTTER FOR CUTTING THE RADIOACTIVELY CONTAMINATED SURFACE OF CONCRETE

Abstract: A milling cutter for cutting the radioactively contamin­ ated surface of concrete and used at the time of repairing and dismantling nuclear facilities. The milling cutter is characte­ rised in that guide grooves (4) are provided on the outer surface of a body (1), with their edges slanted from both sides of the body (1) toward the centre thereof, and that cutter inserts (2) are located along the stepped edge of each of the guide grooves (4) in such a manner that the cutter inserts (2) can be easily detached and that those located along the stepped edges of the adjacent grooves (4) are symmetrical in relation to the centre line of the body (1).

Description: The present invention relates according to the precharacterising part of claim 1 to an improved milling cutter as used to cut the radioactively contaminated surface of concrete at the time of repairing and dismantling nuclear facilities. As the number of nuclear facilities increases, it is necessary previously to study those techniques which will be needed at the sites of large-scaled repairing and dismantling works in the future. The inventors of the present invention have disclosed from this viewpoint a technique for cutting the radioactively contaminated surface of concrete in Japanese Patent Application 58-153740 and 58-157406. We have also disclosed an improved milling cutter in Japanese Utility Model Application 59-10292. As milling cutters for use with contaminated concrete surface cutting apparatus, there have been well known those which have carbide chips or diamond chips embedded on the outer circumferential surface of the rotating drum, but the cutting depth to which the contaminated surface of concrete is cut by these cutting apparatus ranges from 1mm to 3mm and their maximum cutting capacities per hour reach only 5m² or less. These values were not satisfactory and it was also impossible to cut aggregates in concrete. Further, when the inserts were used up, it took a long time to exchange them with new ones and embed them on the outer circumferential surface of the drum. Moreover, drums and inserts must be cleaned up to avoid radioactive contamination before they are removed for exchange work. DE-A-2 549 757 as description of the closest prior art discloses a milling cutter comprising a cylindrical cutter body having arranged on its surface groups of inserts each including a cutter blade, each group of inserts being angularly pitched from a preceding group of inserts in the direction of rotation of the cutter body, each group of inserts comprising a first sub-group of at least one insert at or towards a first end of the cutter body with the blade or blades thereof slanted towards the second end of the cutter body, and a second sub-group of all the remaining plurality of inserts of the group at or towards the second end of the cutter body with the blades thereof slanted towards said first end of the cutter body, each insert of the first and second sub-groups respectively, being further in front, relative to the cutting direction, than an adjacent insert if any further from said first or respectively in the same sub-group, the cutter body providing a groove in front of each blade. However, in DE-A-2 549 757 each blade in the second sub-group is slanted at the same angle as the line from that blade to an adjacent blade, which is not ideal for the purpose of cutting concrete and also cutting aggregates in concrete. Also, in DE-A-2 549 757 there is no "mirror symmetry" relative to a centre plane between successive groups of blades, for avoiding any tendency of the cutter to move to one side or the other when rotated in use. FR-A-397 058 discloses a milling cutter having a series of blades in shallow Vee-angled rows, each blade being aligned with its side of the row. Although less relevant to the present invention than the above-mentioned DE-A-2 549 757, FR-A-397 058 could be said to disclose a milling cutter comprising a cylindrical cutter body having arranged on its surface groups of inserts each including a cutter blade, each group of inserts being angularly pitched from a preceding group of inserts in the direction of rotation of the cutter body, each group of inserts comprising a first sub-group of a sub-row of inserts at or towards a first end of the cutter body with the blades thereof slanted towards the second end of the cutter body, and a second sub-group of all the remaining plurality of inserts of the group at or towards the second end of the cutter body with the blades thereof slanted towards said first end of the cutter body, each insert of the first and second sub-groups of each group being further in front, relative to the cutting direction, than an adjacent insert if any further from said first or second end respectively in the same sub-group. The present invention provides a milling cutter having the features of claim 1 to which reference is directed. A preferred use of such a milling cutter is for cutting radioactively-contaminated concrete at the time of repairing and dismantling nuclear facilities. The intention of the present invention is therefore to provide an above-mentioned milling cutter which is capable of cutting the surface of concrete to 5mm or more, and also of cutting aggregates in the concrete. Other intentions are to facilitate rapid exchange of used inserts with new ones on site so as to avoid the necessity for moving the whole apparatus to somewhere else. These and other features and merits of the present invention should become more clearly apparent from the following detailed description with reference to the accompanying drawings. In these drawings: Fig. 1 is a front view showing an embodiment of the present invention; Fig. 2 is a sectional view showing the mechanism for attaching cutter inserts; and Fig. 3 is a development showing an arrangement of the cutter inserts. Referring now to the drawings, there is shown a cylindrical cutter body 1 having a diameter of about 120 mm and a length of about 110mm. The cutter body 1 has arranged on its surface twenty-four inserts 2 in six groups of four inserts 2 per group. For example, as shown in Fig. 3, there are inserts A₁, A₂, B₁, B₂ in a first such group, and inserts A₃, A₄, B₃, B₄ in the next following group. Each group of inserts is angularly pitched, at 60 degrees, from the preceding group of inserts 2 in the direction of rotation of the cutter body 1. Each insert 2 has a blade 3 slanted at about 5 degrees to the direction of cutting, to reduce cutting resistance and to enable the cutter body 1 to be smoothly rotated. Each group of inserts 2 is arranged in a formation which will now be described in detail. More particularly, each group of inserts 2 is divided into two sub-groups, that is, a first sub-group A₁, A₂ and a second sub-group B₁, B₂ for the first group of inserts 2 and a first sub-group A₃, A₄ and a second sub-group B₃, B₄ for the second group of inserts 2. The blades 3 of the sub-groups A₁, A₂ and B₃, B₄ on the left of Fig. 3 (and hence at, or towards the left-hand end of the cutter body 1) are slanted 5 degrees towards the right (that is, the right-hand end) of the cutter body 1, whilst the blades 3 of the sub-groups B₁, B₂ and A₃, A₄ on the right of Fig. 3 (and hence at, or towards the right-hand end of the cutter body 1) are slanted 5 degrees towards the left (that is, the left-hand end) of the cutter body 1. Each of the inserts A₁, B₁, A₃, B₃ of the first and second sub-groups of each group respectively is further in front, as shown, relative to the cutting direction, and is nearer to the corresponding end of the cutter body 1, than the adjacent insert A₂, B₂, A₄, B₄ of the same sub-group. Whereas each of the blades 3 is only slanted at 5 degrees (see above), the angle is quite steep, about 60 degrees, of each of the imaginary lines, not shown, from insert A₁ to insert A₂, from insert B₁ to insert B₂, from insert A₃ to insert A₄, and from insert B₃ to insert B₄ of each respective sub-group. The inserts A₁, A₂ of the first sub-group of the first group are in mirror-symmetrical relationship to the inserts A₃, A₄ of the first sub-group of the second group, whilst the inserts B₁, B₂ of the second sub-group of the first group are in mirror-symmetrical relationship to the inserts B₃, B₄ of the second sub-group of the second group, relative to the middle of the cutter body 1, except for the angular pitch between the groups of inserts. The cutter body 1 provides twenty-four grooves 4, each in front of the blades 3 of a respective group of the inserts 2, to collect dust. Because of the slanting at only 5 degrees of the blades 3, and the steeper slant at 60 degrees of the imaginary lines between inserts 2 of each of the sub-groups described above, each of the grooves is stepform in shape. The dust tends to collect near the middle of each groove 4, more particularly, just in front of the rearmost insert 2 of the group, such as A₂ and A₄ in Fig. 3. The inserts 2 can be detached from the surface of the body 1 by turning a screw 5 one revolution and removing a wedge 6. Each insert 2 can therefore be easily exchanged for a new one. According to the above mentioned embodiment, it can be made to cut the surface of the concrete plane, and easily determine radioactive contamination of the cut surface. It should be understood that the present invention as claimed is not limited to the embodiment shown in the Figures but also includes the following embodiments: 1) The arrangement, location and number of the inserts 2 and the shape of the guide grooves are not limited to those shown in the Figures, various design modifications can be made to them. For example, the number of the inserts A in a group is not limited to two but may be three or more. 2) The blade 3 may be formed integral with the wedge 6, or a means for combining both the blade 3 and the wedge 6 may be prepared. According to the milling cutter of the present invention as described above, the above-mentioned objects can be achieved. Namely, 1) since the inserts 2 are slanted towards the centre of the body and their cutting operation advances from the outer sides to the centre of the body, the thrust of the body can be prevented and the cutting rotation of the body can be smoothly performed; 2) as the result, the cutting capacity can be enhanced sufficiently to cut all of the contaminated surface of concrete, as compared with conventional milling cutters, and aggregates in concrete can be cut, thereby enabling the cutting capacity per hour to be drastically enhanced; and 3) since the blades 3 are slanted toward the centre of the body and the guide groove 4 is provided in front of them, their cutting operation advances from the outer sides to the centre portion of the body, so that dust produced can be collected to the centre portion of the body, without scattering around, thereby making it easier to collect the dust.

Claims: A milling cutter comprising a cylindrical cutter body (1) having arranged on its surface groups (A₁,A₂,B₁,B₂;B₃,B₄,A₃,A₄) of inserts (2) each including a cutter blade (3), each group of inserts (2) being angularly pitched from a preceding group of inserts (2) in the direction of rotation of the cutter body (1), each group of inserts (2) comprising a first sub-group (A₁,A₂;A₃,A₄) of at least one insert (2) at or towards a first end of the cutter body (1) with the blade or blades (3) thereof slanted towards the second end of the cutter body (1), and a second sub-group (B₁,B₂;B₃,B₄) of all the remaining plurality of inserts (2) of the group at or towards the second end of the cutter body (1) with the blades (3) thereof slanted towards said first end of the cutter body (1), each insert (2) of the first and second sub-groups respectively being further in front, relative to the cutting direction, than an adjacent insert (2) if any further from said first or second end respectively in the same sub-group, the cutter body (1) providing a groove (4) in front of each blade (3), characterised in that each blade (3) is substantially less steeply slanted than the line from that blade (3) to the or each adjacent insert (2) if any, in the respective sub-group, and in that each groove (4) extends across the cutter body (1) in front of all the insert blades (3) of a respective said group of inserts (2), being stepform in shape, and in that each group of inserts is in mirror-symmetrical relationship to said preceding group of inserts (2) relative to the middle of the cutter body (1), except for the angular pitch between said groups of inserts (2) A milling cutter as claimed in claim 1, wherein at least the blade (3) of each insert (2) is removable. A milling cutter as claimed in claim 2, wherein the blade (3) of each insert (2) is fixed by means of a removable wedge (6).

Inventors: DEMURA, HAJIME, FUNAKAWA, NAOYOSHI, NAGAMORI, NOBUYUKI
Applicants: HITACHI CARBIDE TOOLS LTD., SATO KOGYO CO. LTD.
Application year: 1986
Main classification: B23C5
IPC codes: B23C5, G21F9, B28D1