Durable chisel

Abstract

The invention relates to a chisel (10) comprising a working section (12), a shank section (14), a striking surface (16), and a longitudinal axis (L) extending through the working section (12), the shank section (14), and the striking surface (16). It is characterized in that, in a cross-section of the working section (12) extending transversely to the longitudinal axis (L), a first structural core area (KB1) has a first core hardness (HK1) that is significantly lower than a first outer hardness (HA1) in a first outer area (AB1) outside the first structural core area (KB1) of the same cross-section. Furthermore, a method (1000) for manufacturing such a chisel (10) is presented. The chisel (10) is characterized by a particularly long service life.

Description

[0001] The invention is based on a chisel comprising a working section, a shaft section and a striking surface, and a longitudinal axis running through the working section, the shaft section and the striking surface.

[0002] These chisels are used on construction sites for chiseling mineral rock, such as concrete. During use, the cutting section wears down, so the cumulative use from the first use to the last possible use after the cutting section is maximally worn results in a theoretically maximum possible service life, i.e., the maximum theoretical service life. Particularly with intensive use of such chisels in heavily reinforced concrete, the chisels can break, significantly reducing their maximum actual service life in these cases.

[0003] For example, US20190111488A1 discloses a chisel with different hardnesses according to the preamble of claim 1.

[0004] The object of the present invention is therefore to offer chisels of this type with a low risk of breakage. Furthermore, a method for manufacturing such chisels is desirable.

[0005] The problem is solved by a chisel according to claim 1, which has a working section, a shank section, a striking surface, and a longitudinal axis extending through the working section, the shank section, and the striking surface. In a cross-section of the working section extending transversely to the longitudinal axis, a first structural core region has a first core hardness that is significantly lower than a first outer hardness in a first outer area outside the first structural core region of the same cross-section.

[0006] Therefore, the chisel can have material of varying hardness in the working area. In particular, the chisel can be softer inside the working area than on its surface.

[0007] Conversely, the interior, especially the first structural core area, may exhibit higher toughness than the surface and / or the first outer area.

[0008] Investigations by the applicant have shown that the risk of breakage is extremely low with such chisels.

[0009] A "significant" difference between two values ​​of a measured quantity can be understood as a difference of at least 10%, in particular of at least 20%.

[0010] Accordingly, an insignificant difference between the two values ​​can be understood as a deviation of, for example, less than 10 percent, and in particular less than 5%.

[0011] The longitudinal axis can also be considered to be a longitudinal plane of the chisel, for example in the case of a non-rotationally symmetric chisel such as a channel chisel.

[0012] The work area may have ledges, projections, and / or similar features. These may be designed to reduce the risk of the workpiece becoming stuck in the substrate being worked.

[0013] Hardness values ​​can be determined using the Vickers method. Alternatively or additionally, hardness values ​​can also be determined according to Rockwell, for example, scale C.

[0014] In a cross-section of the shaft section, a second structural core area may exhibit a second core hardness.

[0015] The second core hardness is significantly lower than a second outer hardness in a second outer area outside the second core area of ​​the same cross-section.

[0016] In particular, the shaft section can therefore have a core that is soft in relation to its surface area.

[0017] The first core hardness is significantly greater than the second core hardness, so the working section is harder overall than the shank section. The working section, and therefore the chisel, can thus maintain a high theoretically maximum possible service life.

[0018] The first core hardness can be significantly lower than the second outer hardness.

[0019] The first structural core region may contain tempering martensite, and in particular may consist of tempering martensite. The tempering martensite-containing microstructure may be produced by at least two heat treatments, in particular including at least one shock induction heat treatment.

[0020] The first outer surface may contain martensite, in particular may consist of martensite. The microstructure may be produced by at least one induction heat treatment.

[0021] The cross-section of the chisel, encompassing the first outer area and the first structural core area, can have a geometric core area defined by the ellipse inscribed in the cross-section with the largest area.

[0022] Particularly fracture-resistant chisels can then have an area ratio of the first structural core area to the geometric core area in the range of 40 to 80%.

[0023] At a Verfahren To manufacture a chisel with the features described above and / or below, a chisel blank having a working section, a shank section and a striking surface and a longitudinal axis running through the working section, the shank section and the striking surface can be machined.

[0024] The chisel blank may not yet have been heat-treated.

[0025] The method preferably comprises an induction heat treatment of the working section, wherein both the first outer area and the first core area are hardened, and an induction heat shock treatment of the working section, such that the first outer area has a significantly greater hardness than the first core area.

[0026] Preferably, the induction heat treatment is performed first, followed by the induction heat shock treatment.

[0027] The induction heat shock treatment can extend over the entire chisel, especially over the working section and the shank section.

[0028] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, with reference to the figures in the drawing, which show essential details of the invention, as well as from the claims. The features shown therein are not necessarily to scale and are depicted in such a way that the inventive features can be clearly seen.

[0029] The schematic drawing shows exemplary embodiments of the invention, which are explained in more detail in the following description. Es zeigen:

[0030] Fig. 1 a chisel, Fig. 2 a hardness diagram of a chisel, Fig. 3 a schematic longitudinal section through a chisel, Fig. 4a and 4b schematic cross-sections of various chisels with markings of geometric and structural core areas, Fig. 5 a flow diagram of a process, and Fig. 6a and 6b diagrams of experimentally determined tool lives of chisels.

[0031] In the following description of the figures, the same reference numerals are used for identical or functionally corresponding elements to facilitate understanding of the invention.

[0032] Fig. 1 shows a chisel 10. Chisel 10 is designed as a pointed chisel. It has a working section. 12, a shaft section 14 and a striking surface 16 The chisel 10 has a point at the free end of its working section 12. 18 on.

[0033] A longitudinal axis runs through the working section 12, the shaft section 14 and the striking surface 16. L.

[0034] The chisel 10 can be moved by striking its striking surface 16, for example by means of a machine tool mounted in the area of ​​the striking surface 16 (in Fig. 1 (not shown), into an underground 20 to be driven. The subsurface 20 is in the example according to Fig. 1 a mineral substrate, for example reinforced concrete.

[0035] In the Fig. 1 In the illustrated embodiment of the chisel 10, the working section 12 has several ribs. 22 to simplify the presentation. Fig. 1 Only one of the ribs 22 is marked with a reference symbol. The ribs 22 may be designed to prevent the chisel from becoming stuck in the substrate 20 or at least to reduce the risk of such sticking.

[0036] Over the service life of the chisel 10, the working section 12 typically wears down, but the shank section 14 does not, or at most only to an insignificant extent. The chisel 10 reaches its maximum service life when the working section 12 is completely or at least shortened to a certain minimum, unless the chisel 10 breaks or is similarly severely damaged beforehand.

[0037] There is a plug-in end at shaft section 14. 24 trained. At the in Fig. 1 In the illustrated embodiment, the insertion end 24 can be designed as a hexagon and / or include one. Alternatively, it is also conceivable that the insertion end 24 conforms to another standard, for example, a standard commonly referred to as "SDS-Plus" or "SDS-Max".

[0038] Fig. 2 The diagram shows a hardness diagram of the local hardness of the chisel 10 along its longitudinal axis L. In the diagram, the abscissa corresponds to the respective position along the longitudinal axis L.

[0039] In Fig. 2 The graph shows a progression of hardness in outer areas as well as in core areas according to the respective position x or the respective cross-section at position x along the longitudinal axis L.

[0040] Fig. 3 shows a schematic longitudinal section view of the chisel 10 along the longitudinal axis L, so that it can be seen on which sections the hardnesses apply according to Fig. 2 each refer to.

[0041] In Fig. 3 are a first structural core area KB1, a first outer area, radially surrounding the first structural core area KB1 AB1 as well as a second structural core area KB2 with a second outer area radially surrounding this AB2 shown.

[0042] The chisel 10 exhibits a first core hardness in the area of ​​its working section 12 in the first structural core area KB1. HK1 The first core hardness HK1 is significantly lower than the hardness in the first outer area AB1, hereinafter referred to as the first outer hardness. HA1 Designated outside the first structural core area KB1 within the same cross-section of working section 12, the first core hardness HK1 is between 50 and 80 percent, for example, between 60 and 70 percent, of the first outer hardness HA1. For example, the first core hardness HK1 can be in the range of 400 to 450 HV. The first outer hardness HA1 can be in the range of 600 to 650 HV.

[0043] A second structural core area KB2, which is formed along the shaft section 14, exhibits a hardness in at least one cross-section, hereinafter referred to as the second core hardness HK2 This is referred to as, on. This is significantly less than a second external hardness. HA2 in a second outer area AB2 outside the second structural core area KB2 of the same cross-section of the shaft section 14.

[0044] As in Fig. 2 It can be seen that the core hardness HK1 is significantly greater than the second core hardness HK2.

[0045] In the outer regions AB1 and AB2, the hardness values ​​along the longitudinal axis L can be constant or at least substantially constant. In particular, the first outer hardness HA1 and the second outer hardness HA2 can be the same or at least substantially the same.

[0046] Fig. 2 This further shows that the first core hardness HK1 is significantly lower than the first outer hardness HA1. Moreover, it is significantly lower than the second outer hardness HA2, particularly when the first and second outer hardnesses HA1 and HA2 are equal or at least substantially equal.

[0047] Out of Fig. 3 It can also be seen that the microstructure of the first outer area AB1 differs from that of the first structural core area KB1.

[0048] The first outer layer AB1 is formed from martensite. It can be fully hardened. In contrast, the first structural core area KB1 is formed from tempered martensite.

[0049] The tip 18 may also be composed of martensite. However, it is also conceivable, particularly after a certain amount of wear on the chisel 10 and especially the tip 18, if the first structural core area KB1 extends to the tip 18, that the tip 18 alternatively or additionally exhibits temper martensite.

[0050] Inside the shaft section 14, particularly in the second structural core area KB2, other microstructures, especially pearlite and / or ferrite, may be present.

[0051] Fig. 4a und Fig. 4b The cross-sections of various chisels are shown as examples. 10. The cross-sections each come from the respective work sections. 12 (see Fig. 1 ). Fig. 4a shows cross-sections of pointed chisels, whereas Fig. 4b Shows cross-sections of flat chisels.

[0052] In each example cross-section, the respective first core areas KB1 are marked, as well as the associated geometric core areas. KG. The geometric core areas KG are defined as the ellipses with the largest area inscribed in the respective cross-section of work section 12.

[0053] The area ratios of the first structural core areas KB1 to their respective geometric core areas KG range from 30 to 90 percent, particularly from 40 to 80 percent. For example, the ratio of the diameter dKB1 of the first structural core area KB1, which is circular in cross-section, to the diameter dAB1 of the associated outdoor area AB1 at the first pointed chisel from the left in Fig. 4a approximately 63%, resulting in an area ratio of 0.4, corresponding to 4 * 10 1< percent.

[0054] Fig. 5 shows a flowchart of a process 1000 for the manufacture of a chisel 10.

[0055] In a preparation phase 1010 First, a chisel blank is produced, which has a working section 12, a shaft section 14 and a striking surface 16.

[0056] The chisel blank to be produced has an elongated shape, so that a longitudinal axis L runs through its working section 12, the shaft section 14 and the striking surface 16.

[0057] During a warming phase 1020The working section 12 is heat-treated using induction heating. During this initial heating, both the first outer surface AB1 and the first structural core area KB1 reach a homogeneous austenitizing temperature. Due to sufficiently rapid cooling, the entire cross-section of the working section 12 is hardened. In this process, both the first outer surface AB1 and the first structural core area KB1 are transformed into martensite and hardened accordingly.

[0058] In a subsequent shock-heat phase 1030The working section 12 is now subjected to shock heat treatment using an induction heat shock treatment. This further hardens the first outer area AB1. As a result, the first outer area AB1 acquires a significantly greater hardness than the first structural core area KB1. In contrast, the shock heat treatment in the first structural core area KB1 results in a lower temperature increase than in the first outer area AB1. In particular, reaching an austenitizing temperature can be avoided, so that at least essentially no further allotropic transformation takes place. A phase comprising α + Fe 3 C can form in the first structural core area KB1.

[0059] The shaft section 14 can be heat-treated before the shock heat treatment.

[0060] The applicant has conducted comparative studies on the service life of chisels 10, in particular manufactured according to method 1000, in comparison to previously known comparative chisels.

[0061] In a first series of tests, chisels to be tested were subjected to a standard chisel hammer with an impact energy in the range of 25 to 30 J per blow for up to six hours in heavily reinforced concrete, in particular with three-layer steel reinforcements with a diameter of 16 mm and spacing of 150 x 150 mm, and concrete of class C25 / 30 GK32.

[0062] A total of 10 comparison chisels showed a failure rate of approximately 50% within the test duration of a maximum of six hours. In contrast, among 40 chisels, not a single one failed over the respective maximum test duration of six hours.

[0063] In a second series of tests, rotational bending tests were carried out and the number of cycles that each tested chisel could withstand was recorded. One cycle corresponds to a complete rotation.

[0064] As shown in the diagram Fig. 6a As can be seen, the comparison chisels achieved BM1, BM2, BM3, BM4 and BM5 Only two chisels had a lifespan of at least 100,000 cycles. None of the comparison chisels survived more than 150,000 cycles. Two of the five comparison chisels didn't even reach 100,000 cycles.

[0065] However, all tested chisels survived 10 as shown in the diagram. Fig. 6b As shown, 150,000 cycles. Individual chisels 10 even achieved lifetimes of just under 500,000 cycles.

[0066] Thus, the risk of breakage of the tested chisels 10 is significantly reduced compared to the tested comparison chisels. Bezugszeichenliste

[0067] 10 Chisel 12 Working section 14 Shank section 16 Striking face 18 Tip 20 Base 22 Rib 24 Insertion end 1000 Process 1010 Preparation phase 1020 Heat phase 1030 Shock heat phase AB1 Outer area AB2 Outer area HA1 Outer hardness HA2 Outer hardness HK1 Core hardness HK2 Core hardness KB1 Structural core area KB2 Structural core area KB2 Structural core area KG Geometric core area L Longitudinal axis dAB1 Diameter dKB1 Diameter x Position

Claims

1. Chisel (10) which has a working section (12), a shaft section (14), a striking surface (16) and a longitudinal axis (L) running through the working section (12), the shaft section (14) and the striking surface (16), wherein, in a cross section of the working section (12) running transversely to the longitudinal axis (L), a first structural core region (KB1) has a first core hardness (HK1), which is substantially less than a first external hardness (HA1) in a first external region (AB1) outside the first structural core region (KB1) of the same cross section, wherein, in a cross section of the shaft section (14), a second structural core region (KB2) has a second core hardness (HK2), which is substantially less than a second external hardness (HA2) in a second external region (AB2) outside the second structural core region (KB2) of the same cross section, characterized in that the first core hardness (HK1) is substantially greater than the second core hardness (HK2).

2. Chisel according to the preceding claim, characterized in that the first structural core region (KB1) comprises tempered martensite, in particular consists of tempered martensite.

3. Chisel according to one of the preceding claims, characterized in that the first external region (AB1) comprises martensite, in particular consists of martensite.

4. Chisel according to one of the preceding claims, wherein the cross section of the chisel (10) comprising the first external region (AB1) and the first structural core region (KB1) has a geometric core region (KG) which is defined by the largest-area ellipse inscribed in the cross section, wherein the area ratio of the first structural core region (KB1) to the geometric core region (KG) is in the range from 40 to 80%.

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