EP0855950B1 - Process for improving the durability of hydraulic chisels - Google Patents

Description

When the chisel is used, the impact is transmitted over the striking head (2), the core (4) onto the working tip (1). For this requirement there are high hardness values of 50-53 HRc necessary. A deformation (compression with burr formation) on the impact head is avoided. The working tip (1) receives a high one Wear resistance, which over the entire period of wear Work area is preserved.

Damage to the surface (3) of the chisel and the milling (6) for holding the chisel in the hammer. If the chisel is very hard and has a lateral force, this damage will cause it to crack and then cause the chisel to fail due to permanent fatigue. With the hardness of 46-48 HRc used to date, attempts are being made to reduce the influence of damage with high nickel contents of up to 4.5%.
By tempering the shaded area (5) to hardness values of 40-43 HRc on the surface (3 + 6) the influence of the damage is practically eliminated even without adding nickel to the steel.
With the continuous tempering treatment, the negative influences of partial surface treatments (Japanese Patent JP-A-6 031 653; file number: Appl. No. 4-195386; publication: M-1602 May 10, 1994 Vol. 18 / No 243; Int B25D17 / 02; applicant: Nippon Pneumatic MFG CO LTD) avoided especially in critical areas.

In the milling (6) there are high surface pressures with little relative movement between the chisel surface and the holding wedge. Uniform lubrication is very prolematic and therefore only low surface hardness values of 40-43 HRc guarantee the avoidance of pitting, corrosion and cracking with chisel failure. A chisel break in this area can also lead to severe destruction in the hammer.
The end of the annealing treatment at the japan. Patent, in the area of the milling (6) has a negative influence at high hardness values due to the notch effect of hard / soft surface. The aforementioned problems in the area of milling (6) are in japan. Patent not dealt with at all.

In the chisel guide (7), careless lubrication leads to problems similar to those in milling. Annealing treatment to hardness values of 20 HRc (Japanese patent) may not be the ideal solution. Due to the very low strength, material compressions and displacements are possible due to lateral force when working. However, this leads to a further deterioration in the lubrication and thus ultimately to the failure of the chisel. To solve the above-mentioned problems, a method according to claim 1 is proposed.
The 40-43 HRc of the present application are clearly the better solution. You avoid pitting and - the lubrication is not hindered.

Another method is proposed in claim 2.

On the surface (3) of the chisel, in the work area, damage during work cannot be avoided. In the case of high hardness (50-53 HRc), this damage caused by lateral force (practically unavoidable) on the chisel leads to cracks, which ultimately lead to fatigue in a short time. The same applies to the transition from hard to soft on the surface when the annealing treatment of the japan patent ends.
Hardness values of 40-43 HRc prevent this crack formation and thus the premature failure of the chisel.
If the depth of the tempered layer (5) is set accordingly, even slight bending of the chisel does not lead to the formation of cracks.
Theoretically, with a corresponding setting of hard core and falling hardness to the surface, there is a certain self-sharpening of the working tip.

Summary, one can say:

• Longer tool life due to the high working hardness of 50-53 HRc over the entire working length of the chisel.
• Due to the low surface hardness of 40-43 HRc premature chisel failures due to damage avoided.
• Use of inexpensive steels due to elimination or reduction of nickel.

Claims (2)

1. A process is disclosed for improving the durability of hydraulic chisels, characterised by the fact that, after hardening and tempering the chisel to up to 50-53 HRc, the outer diameter (3), including the cut-out (6), is once again tempered at high temperatures to achieve a surface hardness of 40-43 HRc.
2. Process after claim 1, characterised by the fact that the hydraulic chisel, before hardening and tempering, is subjected to a specific surface decarbonization on the outer diameter including the cut-out (3+6). During the following hardening and tempering, the decreased carbon content on the surface (3+6) will cause a hardness of 40-43 HRc on the surface, and a hardness of 50-53 HRc on the shock head (2), the working end (1) and the centre in hardness.

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