Toolholder for milling drums of scarifying machine

Abstract: The invention concerns a toolholder (1) for milling drums of scarifying machines. The body (2) of the toolholder (1) defines a longitudinal axis (3) and is provided with: an annular groove (6) to reduce the resisting section of said toolholder (1) defining a pre-set breaking area; a through going axial hole (4) defining the housing (4) suitable to house a milling tool at one end (2a); a truncated cone shaped base (5); a collar (7) to prevent intrusion of dirt; projection (8) and collar (7) defining the annular groove (6) are provided with rounded edges (6b,7c,8a,8b,9a); a truncated cone shaped nose at milling tool end (2a) with a concave surface; a longitudinal plane surface (10) to inhibit rotation of the toolholder (1).

Description: The invention relates to a toolholder suitable to be applied to milling drums of scarifying machines. It is known that scarifying machines are used for the removal of the bituminous carpet covering roads. Such machines are provided with a milling drum having a plurality of projecting active elements that, during the rotation of the milling drum to which they are applied, crumble the surface to be removed with which they come into contact. Each active element comprises a milling tool which is inserted by applying pressure in a toolholder in which it is free to rotate around its own axis, but from which it can not be separated because of the stopping action of an interposed elastic element. The toolholder consists preferably in a steel body extending mainly longitudinally, in which there is formed a housing for receiving the milling tool. The toolholder is removably inserted in a hole made in a prismatic base, which is removably fixed in a base block welded to the drum. Toolholders of the above mentioned type are those which are described also in the Italian patent applications registered in the name of the same applicant of the present patent and having the filing numbers VI95A000170 and VI96A000071. VI95A000170 is the priority document to EP-A-0 771 911, published 7/5/1997. In the mentioned patents each one of the active elements applied to the milling drum is provided with a toolholder having a cylindrical central area. On one side of the said cylindrical central area there is a first truncated-cone shaped surface coupled in the respective hole of the prismatic base. On the opposite side of the cylindrical ares is a second truncated-cone shaped surface with an inclination converging toward the tool. These toolholders constructed in the above described way have some drawbacks. A first drawback is that, because of the particular shape according to which the toolholder is built, it is not the less strong or weakest part of the active element to which it belongs. This implies that, if during the manufacturing or operation of the machine the active element is exposed to a greater stress than the greatest allowed stress, it will break preferably in correspondence with the areas in which the prismatic base is connected to the base block or in correspondence with the weldings fixing the base block to the drum. It can be understood that the second or latter possibility can damage even seriously the milling drum as a whole, creating expensive maintenance costs. A further drawback is that the coupling between the first truncated-cone shaped surface and the respective hole made in the removable prismatic base or bar which houses it, is not enough protected against the accidental intrusion of dirt and generally of foreign bodies. The present invention overcomes such drawbacks by providing a toolholder which is the most structural yielding part among all the parts forming the active element applied to the milling drum of a scarifying machine. Further, the toolholder has, with respect to toolholders of the known type, a better resistance to abrasion. In accordance with the invention there is provided a toolholder as set forth in claim 1. Preferred embodiments are disclosed in the dependent claims. The toolholder for milling drums of scarifying machines includes a body defining a longitudinal axis, at one end provided with a housing suitable to house a milling tool and having a truncated-cone shaped piece of the external surface with an inclination converging toward the end opposite to the end housing said tool, said lateral external surface having the shape of a truncated cone being suitable to house removably in a respective truncated-cone shaped hole present in a support unit belonging to the external lateral surface of said milling drum, and is characterized in that the body of said toolholder has outside an annular groove projecting from said support unit and reducing the resisting section of said toolholder in order to define wherein a pre-set breaking area. According to a preferred embodiment said groove is included between an annular collar and an annular projection, spaced and both projecting radially from the toolholder body, with the annular collar placed just close to the hole housing the toolholder. The toolholder end housing the milling tool has the shape of a truncated-cone with the conicity turned toward the tool. The surface of the said toolholder end has a truncated-cone shape and has in a longitudinal section, a curved outline with the concavity turned towards the outside. Advantageously the presence of the annular groove assures, in the case of exceeding the greatest admitted stress, that the toolholder breaks in correspondence with the section where the groove is made, which avoids breaking of the removable base and/or of the base block welded to the drum. Still advantageously the annular collar defining the groove, works as a protection against the intrusion of foreign bodies in the coupling between the truncated-cone shaped part and the respective housing. This is described in more detail in the description of a preferred embodiment of the invention referring to the enclosed drawings in which: Fig. 1 shows a view of the toolholder of the invention, sectioned according to the longitudinal direction; Fig. 2 shows the front side view of the toolholder of fig. 1; Fig. 3 shows an enlarged detail of the toolholder of fig. 1; Fig. 4 shows another enlarged detail of the toolholder of fig. 1; Fig. 5 shows the toolholder of the invention with the removable base and with the block which is welded to the milling drum in order to build the active element; Fig. 6 shows the active element of fig. 1 once it has been assembled; Fig. 7 shows the active element of fig. 1 applied to the milling drum. As it can be seen in the Figs. 1, 2, 3, 6 and 7, the toolholder of the invention, marked with 1 as a whole, is of the type which can be applied to a support unit marked with G as a whole. The latter is fixed to the external lateral surface S of the milling drum T of a scarifying machine, not shown. The support unit G, as it can be seen in particular in Fig. 5, includes a removable base Ba provided with a hole Bf housing the toolholder 1 with the tool U applied thereto. Said removable base Ba is supported by a base block Bb welded to the external lateral surface S of the milling drum T. The toolholder 1 and the respective tool U, with the removable base Ba and the base block Bb supporting it, form the active element of the milling drum T visible in Figs. 5, 6 and 7 where it is marked with A as a whole. The toolholder 1, as it can be seen, has a body 2 defining a longitudinal axis 3 and is provided with a longitudinal through hole 4. In correspondence with the first end 2a the through hole 4 houses removably the tang Uc of the tool U. The lateral external surface of the body 2 of the toolholder has a truncated-cone shaped surface 5 having an inclination converging toward the end 2b of the body 2 and placed on the part opposite to the end 2a housing the tool U. The truncated-cone shaped surface 5 is coupled to the corresponding truncated-cone shaped surface through a hole Bf made in the removable base Ba. Preferably, the truncated-cone shaped surface 5 has an inclination to help the toolholder to be extracted from the removable base in which is housed. An inclination of about three degrees has been found useful for this purpose. According to the invention the body 2 of said toolholder 1 has an externally formed annular groove 6 on a portion projecting from said supporting unit G, said groove reducing the resisting section of said toolholder 1 in order to define in it a pre-set breaking area. Therefore, if the active element as seen in the Figs. 4 to 7 and marked with A as a whole is exposed to greater stresses than the greatest admitted stress, the toolholder 2 will yield in correspondence with the groove 6 avoiding the breaking both of the removable base and of the base block Bb. It can be observed that the groove 6 is included between an annular collar 7 and an annular projection 8, both projecting radially from the body 2 of said toolholder and both realized above the larger base 9 of said truncated-cone shaped base C. As can be seein in particular in the enlarged drawings of Figs. 3 and 4, the annular collar 7 is defined between a first annular wall 7a connected to the larger base 9 of said truncated-cone shaped surface 5 through a first connection 9a circularly outlined, and a second annular wall 7b connected to the groove 6 through a second connection 6b circularly outlined too. In particular the groove 6 has a bottom surface 6a developing or exdending circumferentially to the body 2 of the toolholder and therefore has a substantially circular configuration. The external perimetric surface 7c of the annular collar 7 has a curved outline that is convex relative to the outside of the toolholder 1 and that is connected to both the annular walls 7a and 7b. The presence of the annular collar 7 protects the truncated-cone shaped surface 5 and in particular it prevents foreign bodies from penetrating between the truncated-cone shaped surface 5 and the hole Bf housing it during manufacture. With regard to the annular projection 8, it has a curved surface 8a that is convex relative to the outside and which is connected on one side to the bottom 6a of the groove 6 through an inclined wall 8b and on the opposite side to the end 2 housing the tool U through a curved surface 8c that is concave relative to the outside of the toolholder 1. Said concave outline 8c that is concave relative to the outside helps the sliding of the material during the excavation, reducing the abrasive effects on the toolholder. It can be observed in Fig. 2 that in order to prevent the toolholder 1 from rotating around its own longitudinal axis when it is inserted in the respective hole Bf, a plane surface 10 extending along all the longitudinal length of the toolholder is made on the outside of the toolholder 1. It can be understood that on the basis of what has been said, the toolholder of the invention solves the problems identified above. In practice, it is possible to modify the toolholder outlines. Therefore the said outlines can have different shapes and dimensions than what has been described and shown in the enclosed drawings. Thus, it is intended that possible different embodiments are also considered as protected as long they fall within the scope of the invention as set out in the appended claims.

Claims: Toolholder (1) for a milling drum (T) of a scarifying machine, said toolholder includes a body (2) defining a longitudinal axis (3) and comprising: a first end (2a) provided with a housing (4) which is adapted to house a milling tool (U); a second end (2b) opposite to the first end (2a) provided with a portion having an external surface (5) having the shape of a truncated cone with an inclination converging toward the second end (2b) and which is adapted to be removably housed in a respective truncated-cone shaped hole (Bf) in a support unit (G) provided on an external lateral surface (S) of said milling drum (T), characterized in that said toolholder further comprises an annular groove (6) on a portion of the body (2) of said toolholder (1) projecting in use from said support unit (G), said annular groove (6) defining a pre-set breaking area. Toolholder (1) according to claim 1, wherein said annular groove (6) is located adjacent an annular collar (7) projecting radially from the body (2) of said toolholder (1) and being formed above a larger base (9) of said portion with said external surface (5) adapted to be housed in said hole (Bf) of said support unit. Toolholder (1) according to claim 1 or 2, wherein said annular collar (7) has a first annular wall (7a) connected to said larger base (9) of said portion with said truncated-cone shaped external surface (5), and a second annular wall (7b) connected to a bottom surface (6a) of said groove (6), said annular walls (7a, 7b) being placed spaced to each other and orthogonal to the longitudinal axis (3) of said body (2). Toolholder (1) according to claim 3, wherein said annular walls (7a, 7b) are connected to said larger base (9) of said portion with said truncated-cone shaped external surface (5) and to the bottom surface (6a) of said groove (6) through connections (9a, 6b) having a circular outline. Toolholder (1) according to one of the preceding claims, wherein the body (2) of said toolholder (1) includes a plane surface (10) formed parallel to the longitudinal axis (3) of the toolholder (1) and along the length of the body (2). Toolholder (1) according to one of the preceding claims, further comprising an annular projection (8) having a curved surface (8a) being convex relative to the outside of said toolholder and being connected at one side to a bottom surface (6a) of said groove (6), and on the opposite side to the first end (2a) of the body (2) of the toolholder (1) which houses said milling tool (U). Toolholder (1) according to claim 6, wherein an external surface of said first end (2a) housing said milling tool (U) has, as viewed in a longitudinal cross section, a curved outline (8c) being concave relative to the outside of the toolholder and being connected to said annular projection (8). Toolholder (1) according to one of the preceding claims, wherein said first end (2a) which houses said milling tool (U) has an external surface of a truncated-cone shape converging towards the tool (U). Toolholder (1) according to one of the preceding claims, wherein said housing receiving said tool (U) is a through hole (4) provided in the body (2) of said toolholder (1) coaxially to the longitudinal axis (3) thereof. Toolholder (1) according to one of the preceding claims, further comprising a transverse throughole in an area of said annular groove (6), a longitudinal axis of said transverse throughole being perpendicular to said longitudinal axis (3) of said toolholder (1).

Inventors: BITELLI ROMOLO, BITELLI, ROMOLO
Applicants: BITELLI SPA, BITELLI S.P.A.
Application year: 1999
Main classification: B28D1
IPC codes: E21C35, B28D1