Metal deforming – With cutting – Machining after final metal-deforming
Patent
1997-08-27
1999-11-30
Crane, Daniel C.
Metal deforming
With cutting
Machining after final metal-deforming
72 53, 761041, 76115, 144176, B21D 5364, B27G 1300
Patent
active
059922044
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FI95/00139, filed Mar. 15, 1995.
This invention relates to a method of increasing the strength of the cutting point part of a blade. The invention also relates to a cutting blade.
The invention is primarily applicable to a sharp blade used for chipping wood and usually made of steel for cutting wood or other material so that the cutting force is applied to the point of the blade and forms a force wearing and breaking the point. For example, patent specification FI 79799 describes a disc chipper provided with blades and used for chipping wood.
A problem with present blades is that blade durability requires a relatively big sharpening angle, and with an impact-like cutting process the hardness of the blade must be limited so that the blade point will not scale.
Today the durability of the blade point very often limits the sharpening angle of the blade so that it is 34-35.degree., for example, in cellulose wood chipping. Blade hardnesses in a range of 56-60 HRC can hereby be used. A too sharp or too hard blade point will scale during use. The blade point is nowadays made more durable by providing it with a counter-chamfer resulting in a point angle of 38-40.degree. along a distance of about 2 mm from the point.
Blade point wear is a main problem with hard wood as blades must be replaced when the chipper will not receive any more wood.
According to the theory of the strength of materials it is common knowledge that breakage will result when tensile stress exceeds a certain limit or repeated tensile stress peaks break the material by fatiguing, whereby an initial crack leading to breakage will occur at a considerably lower level of tension.
A publication (Andreas Uhmeier) by Kungl. Tekniska Hogskolan Stockholm 1993 deals with forces affecting the blade point in wood chipping.
Shot-peening is a known method of cold working metal. Utilization of shot-peening is taught in the Peening Reference Manual (January 1991). Shot-peening is also the subject matter of Konepajamies (November/1992), a publication of the VTT.
The method according to the invention is characterized in that by cold working the blade, compression stress is formed in at least one blade surface forming the point. The blade according to the invention is characterized in that considerable compression stress exists on at least one blade surface forming the point.
An advantageous application of the method according to the invention is based on the fact that on that side of the blade point which detaches chips, compression stress is formed when manufacturing the blade, whereby the blade point bends towards the sharpening surface so that compression stress also results on the clearance side of the blade, which stress reduces quickly as the bent area ends. In connection with the manufacturing method according to the invention a very short shape also results which corresponds to the present counter-chamfer and which strengthens the blade point and on the other side of the point a "beak"-like blade point is formed, protruding from the sharpening surface and adding to the chipper's suction.
In the method according to the invention, compression stress is formed on the surfaces starting from the blade point on the part actively working the wood. At the same time a blade point results which increases chipper suction and after-sharpening may be performed on the point.
The invention and its details are described more closely in the following referring to the appended drawings, wherein the blade is shown in cross-section.
FIG. 1 shows the way in which a chipper works when used for chipping pulp wood.
FIG. 2 shows how a blade point penetrates into the wood.
FIG. 3 shows the forces occurring in the blade point.
FIGS. 4 and 5 show the method of making a blade in accordance with the invention.
FIGS. 6, 7, 8 and 9 show states of stress in the blade point.
FIGS. 10 and 11 show shapes of a finished blade in accordance with the invention.
FIGS. 12 and 13 show an after-grinding method.
FIG. 1 shows how a blade functions when used for chippin
REFERENCES:
patent: 849329 (1907-04-01), Colthar
patent: 3714850 (1973-02-01), Peters
patent: 4628976 (1986-12-01), Loring
patent: 4669516 (1987-06-01), Carpenter et al.
patent: 4674356 (1987-06-01), Kilgore
patent: 5077961 (1992-01-01), Schumacher
patent: 5249485 (1993-10-01), Hayden
patent: 5351595 (1994-10-01), Johnston
patent: 5765452 (1998-06-01), Roux
Peening Reference Manual, Jan. 1991 (1 page).
Kungl. Tekniska Hogskolan Stockholm, 1993, pp. 15 to 17.
Kuulapommituksella lisaa lujuutta Konepajamies, Nov. 1992, VTT, pp. 54 to 57.
Jonkka Arvo
Tohkala Antti
Crane Daniel C.
Sunds Defibrator Woodhandling Oy
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