WO1984000987A1

WO1984000987A1 - Cutting tool for use in the milling of, for example, asphalt roads

Info

Publication number: WO1984000987A1
Application number: PCT/DK1983/000078
Authority: WO
Inventors: Keld Lundqvist
Original assignee: Keld Lundqvist
Priority date: 1982-08-26
Filing date: 1983-08-24
Publication date: 1984-03-15
Also published as: DE3390200T1; AU1890083A; GB2136730A; GB8408942D0; DK381382A; EP0119213A1

Abstract

When asphalt is desired to be reused, the used asphalt is milled up with cutting tools which must be very resistant against wear. The actual milling tool consists of a cutting tool (3) of hard and brittle material which is supported in a holder (1) of less brittle and wear-resistant material. Many such tools are disposed along the circumference of a rotor. The tools are mounted in an inclined manner and are free to rotate around their longitudinal axes. With this known technique, the cutting tool falls out when it has been half worn away. According to the present invention, a technique is presented by which the tool can be held until it is almost completely worn away.

Description

CUTTING TOOL FOR USE IN THE MILLING OF, FOR EXAMPLE, ASPHALT ROADS.

The invention relates to a tool for the working of hard materials, for example subsurfaces, rocky ground, asphalt, oil gravel or concrete, and which consists of a holder, preferably in the form of a substantially round shank designed to be mounted in larger numbers on a rotating element, in that the round shanks are secured freely rotatable around their longitudinal axes in bores in the rotating el¬ ement, preferably with the axes at an angle to both the tangential and the radial direction, and where in each of the round shanks there is fitted a cutting element of hard metal in a central blind hole in the end of the shank.

Because they can rotate freely around their longit¬ udinal axes, such tools normally wear evenly around the circumference. In order to ensure rotation, the axes are often allowed to form a slight angle to the plane of rotation. The free rotation thus results in the cutting element and the surrounding part of the holder being worn to a conical form. Thus, when the surrounding part of the holder has worn down, the support for the cutting element disappears, with the end result that it falls out. However, because of the conical form, this occurs at a relatively early time, and if one makes the top angle of the cone greater by reducing that angle which the axis of the holder forms with a radius on the rotating element, the res¬ ult is that the force applied to the cutting element is, rather than an axial force, a moment which seeks to break it loose from the holder. It is therefore realized that the angle which the axis of the holder forms with the radial or tangential direction has an optimum size in relation to the wish to secure the cutting element for as long as possible during its process of wearing out. In the best cases a half of the cutting element is worn, and the last half falls out.

The object of the present invention is thus to prov- ide other means of extending the lifetime of the cut¬ ting element, in that the overall costs of operating with such tools are, on the whole, proportional to the lifetime.

The tool according to the invention is characteristic in that contact surfaces of the cutting element are formed in such a manner that the lowest part of the blind hole's side surfaces is free, i.e. they do not engage with the cutting element during mounting or when the first period of use has taken place, and that the cutting element is hereby pressed into the shank. In other words, the holder and the cutting el¬ ement are dimensioned in such a way that there is air under the cutting element after the pressing in. The pressing in takes place upon mounting and during use, which involves the influence of an axially-directed force component which results in a further pressing in. It is important, however, to emphasize that the dimensioning is effected in such a manner that the cutting element is not pressed in to the bottom after its first period of use, and neither after the wear¬ ing down of the first part.

One embodiment is characteristic in that the cutting

'BUREA _. OMPI element is conical. A further pressing down during the work will thus result in the cutting element com¬ ing to sit even more firmly. This, of course, is of immediate importance when the work and the consequent wearing away of the extreme ends of the shank has -^■ brought about the opposite effect. It is obvious that the same effect can be achieved if the blind hole is conical or both parts are conical, and one embodiment is thus characteristic in this respect. According to the invention, the half cone angle can be approx. 3 .

A further development is characteristic in that the blind hole is less conical than the cutting element, the result being that the frictional forces which secure the cutting element will, to a higher degree, be concentrated at the extreme end of the shank, whereby the resistance moment which opposes the for¬ ces which seek to break the cutting element out of its seating will be greater. Conversely, if the' two parts have the same conicity, the distribution of force will be reversed because of the elasticity in the holder, in that there will be more holding mater¬ ial surrounding the lower part of the cutting elem¬ ent.

A further development of this construction is char¬ acteristic in that the blind hole is cylindrical with a bevelled edge, or that only the upper part of the blind hole is conical. There is hereby presented a preferred embodiment which gives rise to the same ideal distribution of stresses as described above with reference to the embodiment wherein the conic¬ ity of the blind hole is less than the conicity of the cutting element.

^'BURHΛT

OMPI Moreover, the costs of manufacture are much less, the reason being that it is far cheaper to drill a cylin¬ drical hole than a tapered hole. The cutting element can be made conical as a matter of course, the reason being that it is pressed by powder pressing. Further¬ more, it is cheaper and easier to produce a conical cutting element than a cylindrical cutting element.

Another embodiment is characteristic in that the bot- torn of the blind hole is provided with a second cen¬ tral blind hole (of smaller diameter) , and that the bottom end of the cutting element is formed with a guide stud, or that to its bottom end there is se¬ cured a guide stud which fits down into the second bottom hole, hereby enabling the lifetime of the cut¬ ting element to be further extended.

Another embodiment of this further development is characteristic in that the cross-section of the guide stud is an equilateral polygon, for example an equi¬ lateral hexagon, and that it is soldered firmly to the cutting element, in that it projects into the central bottom hole in the cutting element. It is hereby possible to achieve a good soldered connection between the guide stud and the cutting element, while at the same time the guide stud retains its charact¬ eristics as such in a cylindrical hole.

Finally, the tool according to the invention can be characteristic in that the fit between the guide stud and the second blind hole is a press fit. Thus in a simple manner there is presented a guide stud which does riot give any play, but which still allows itself to be pressed deeper down into the hole. This applies particularly if the cross-section is an equilateral polygon.

The invention will now be described in closer detail with reference to the drawing, where

fig. 1 shows one embodiment of a tool accord¬ ing to the invention, seen from the side and with the shank in longitudinal section,

fig. 2 is a longitudinal section of the outer end of a holder according to a second preferred embodiment, and with a cut- ting element shown with stippled lines during its insertion into the holder,

fig. 3 is the same, but with the cutting ele¬ ment fully inserted, and

fig. 4 shows the holder from fig. 1 after the wearing down of the cutting element.

The drawings are dimensionally correct on the scale of 2:1.

In fig. 1 there is shown a holder or shank 1 of known type for securing to the circumference of a rotating element together with a number of similar holders in a manner known within the art, so that the longitud¬ inal axis of the holders forms an angle to both the tangential and the radial direction, also an angle which deviates slightly from 90 with the axial dir¬ ection----. During the work, the latter gives a rotation of the holders around their longitudinal axes. In the outer end of the holder 1 there is provided a conical bottom hole 2 with a half cone angle of 3°. Into the bottom hole 2 there is pressed a similarly conical cutting element 3 of hard, wear-resistant pressed -. metal, in that the selection of the diameters is such that the cutting element lies in the position shown after having been pressed in. The top end of the cut¬ ting element is provided with a conical surface 4, so that a generatrix in the cone surface is directed in the tangential direction. The cone surface thus already has the shape that it will assume on being worn down. The lower part of the cutting element 3 is provided with a bottom hole 5 with a semi-spherical bottom, and having sides formed with slip. The cut¬ ting element is produced by powder pressing, and the semi-spherical surface is necessary for generating sufficient pressure in the mould. If this pressure was not achieved, the outer conical surface would be given a slight indentation, i.e. it would be slightly concave or hourglass-shaped. The bottom hole 5 serves to secure a piece of hexagon bar steel 6 which, by soldering, brazing or welding, is fastened centrally in the hole 5 to form a guide stud 6 which, with its largest cross dimension, forms a press fit in a sec¬ ond central bottom hole 8, the bottom end of said guide stud 6 being provided with a bevel 9.

Fig. 2 shows a holder 11 according to a preferred em- bodiment. A blind hole 12 is cylindrical at its low¬ est part, but has a conical part or bevelling 13 above, so that a conical cutting element 14 indicated by the stippled lines and, for that matter, identical to that shown in fig. 1, can be inserted in precisely this part of the hole. When the cutting element 14 is inserted in the position shown in fig. 2, the holder 11 and the cutting element 14 are placed in a press capable of exerting a pressure of 5 - 10 tons. The cutting element is then pressed in to the position shown in fig. 3, whereby the holder 11 is deformed, in that annular stresses arise which by friction se¬ cure the cutting element. If the blind hole and the cutting element have the same conicity, as is the case with the construction according to fig. 1, the annular stresses will be greatest at the bottom be¬ cause of the shape of the holder, the reason being that the thickness of the material around the blind hole 2 increases downwards, and the deformations as a result hereof become smaller downwards. If, on the other hand, the conicity of the blind hole is less than the conicity of the cutting element, which in principle can also be said to be the case for the construction with regard to figs. 2 and 3, with a suitable choice of conicities one can ensure that the annular stresses are greatest at the top. This natur¬ ally gives a greater power of resistance against non -central outer forces on the cutting element.

During the wearing down, however, it is the most de¬ formed areas which are worn away, i.e. those areas in which the greatest stresses exist, and which contri¬ bute the most towards the securing of the cutting el¬ ement, and it is precisely here that a surprising factor is to be found in the invention. Fig. 3 with the shown position of the cutting element 14 is that position which the parts have when the holder is mounted and ready for use. The cutting element will remain in this position for a very long time. Approximately the upper third part of the cutting el¬ ement will first be worn away, though the cone shape at the top will be retained for reasons of the above- mentioned angles chosen in the mounting. The angle in fig. 3 is the angle which the axis of the holder forms with the tangential direction. The wearing down of the outermost parts of the holder will then begin, and consequently the securing forces will get smal¬ ler. The angle, however, is of such a size that the outer forces which influence the cutting element will have a component in the holder's longitudinal direc¬ tion, and this will result in the cutting element be¬ ing pressed deeper down into _.the blind hole, whereby there naturally arises a new clamping zone with an- nular stresses. The clamping zone with these annular stresses thus moves downwards concurrently with the wearing down which takes place. It may be assumed that the conditions are determined by a certain maxi¬ mum thrust force which arises at regular intervals. When the contact surface has worn down to half the size, the maximum thrust force will naturally still arise. Everything else being equal, the same force will be distributed over an area which is half as great. This is possible if the-holder material around the place of friction is of suitably great thickness at the bottom, without the cutting element being im¬ mediately pushed down into the bottom of the hole. Finally, the cutting element will be pushed complete¬ ly down into the bottom of the blind hole, as shown in Fig. 4. The holder 21 is the same as shown in the foregoing drawings, and this could also apply with regard to both the cutting element 22 and the guide stud 23. The bottom of the blind hole, which from the beginning has been conical as shown in the foregoing drawings, because it is drilled, will be deformed at the largest diameter as shown by the cutting element 22 which, with its lower edge, has pressed a flat an¬ nular surface 24. Last of all, the remains, of the cutting element will fall out. Fig. 4 does not repre¬ sent assumptions with regard to a desirable course of events. Practical experiments have shown that with the dimensions illustrated, one achieves the result as shown, while the explanations concerning the ef- feet provided above rest partly on hypotheses with regard to the course taken by the stress.

The cutting element is made of hard metal, the holder or shank of hardened chrome-nickel steel of the type 34 Ch Ni Mo 6 , and the guide stud of so-called mach¬ ine steel, for example steel 37.

According to the known technique, the cutting element will fall out as soon as it is worn down to approx. half its size. With the present preferred embodiment, there will be only very little of it remaining when it falls out, see fig. 4. It must be emphasized, how¬ ever, that a construction without the guide stud al¬ ready represents a technique which is quite superior to the known technique. Thus the guide stud does not constitute a necessary prerequisite in achieving the new technical effect.

OMPI fry-,, ^Wιp0 _*

Claims

C I M S

1. Tool for working hard materials, for example sub¬ surfaces, rocky ground, asphalt, oil gravel or con- crete, said tool consisting of a holder, preferably in the form of a substantially round shank which is designed for mounting in larger numbers on a cylind¬ rical rotating element, in that the round shanks are secured freely rotatable around their longitudinal axes in bores in the rotating element, and preferably with the axes at an angle to both the tangential and the radial direction in relation to the axis of the rotating element, and where in each of the round shanks there is inserted a cutting element of hard metal in a central blind hole in the end of the shank, and where there occurs a wearing away of mat¬ erial around the cutting element in such a manner that it continues to be a rotating element, c h r ¬ a c t e r i z e d in that the cutting element*s con- tact surfaces with the blind hole and the blind hole's contact surfaces are formed in such a way that the lowest part of the side surfaces of the blind hole are free, i.e. are not in engagement with the cutting element when the mounting or the first period of use has taken place, and that the cutting element has -thereby been pressed into the shank.

2. Tool according to claim 1, c h a r a c t e r ¬ z e d in that the cutting element is conical, i.e. it has the shape of a round chisel.

3. Tool according to claim 2, c h a r a c t e r ¬ i z e d in that the half cone angle is approx. 3 .

4. Tool according to claims 2 or 3, c h a r a c t ¬ r i z e d in that the blind hole has the same con¬ icity as the cutting element.

5. Tool according to claims 2 or 3, c h a r a c t ¬ r i z e d in that the blind hole has a smaller conicity than the cutting element.

6. Tool according to claims 2 or 3, c h a r a c t - e r i z e d in that the blind hole is cylindrical with bevelled edge, or in that only the upper part of the blind hole is conical.

7. Tool according to one or more of the foregoing claims, c h a r a c t e r i z e d in that in the bottom of the blind hole there is provided a second central blind hole (of smaller diameter) , and in that the bottom end of the cutting element is shaped in the manner of a guide stud, or that a guide stud is secured to the bottom end, said guide stud fitting down into the second blind hole.

8. ^• Tool according to claim 1 , c h a r a c t e r ¬ i z e d in that the depth of the second blind hole is the same as or greater than the free length of the guide stud, and that the clearance under the guide stud is greater than or the same as the clearance un¬ der the cutting element.

9. Tool according to claims 7 or 8, c h a r a c t ¬ e r i z e d in that the cross-section of the guide stud is an equilateral polygon, for example an equilateral hexagon, and that it is soldered firmly to the cutting element, in that it extends into a

-BUREA OMPI central blind hole in the cutting element.

10. Tool according to claims 7, 8 or 9, c h a r a c¬ t e r i z e d in that the fit between the guide stud and the second blind hole is a press fit.