BLADE OF A TOOL FOR CUTTING A DUCT, MORE PARTICULARLY A VENTILATION DUCT

The object of this invention is a blade of a tool for cutting, e.g. for truncating, a duct, more particularly a ventilation duct, which blade is fixed to the tool in a detachable manner.

Many different tools and methods for truncating, or cutting in some other way (making a service aperture, etc.), ventilation ducts.

Different electrically-operated and pneumatically operated tools are most commonly used. Conventionally, e.g. an angle grinder is used, which however comprises the drawback of, among other things, sparking, in which case the use of it requires a hot work permit. In addition it produces a lot of impurities on the inner surface of the pipe.

Many tools are suited for truncating only smaller duct sizes. These types are e.g. manually-operated metal shears, a piercing saw and certain nibblers.

Nowadays an electrically-powered metal shear is generally used, especially a metal shear manufactured by Draco, which is fast and produces very few impurities in the duct to be truncated. The cut edge it produces is also so neat that it does not require after- treatment. Furthermore it is noiseless and safe in operation, and also it is suited in practice to pipes of all sizes.

Before this metal shear can be used, a starting hole must be made in the duct, e.g. by punching with a sheath knife or by drilling. This is of course an extra work phase and nowadays requires a separate tool. Additionally, the use of a sheath knife is often an occupational safety risk.

The purpose of the invention is to achieve a new type of blade of a tool, more particularly a metal shear, with which the aforementioned drawback is avoided. The blade of the tool according to the invention

is characterized in that the tip part of the blade is shaped to be sharp such that by means of it a starting hole can be punched in the duct.

One preferred embodiment of the blade according to the invention is characterized in that the tip part of the blade is shaped to curve downwards, in which case it does not impair the actual cutting of the duct.

One advantage of the invention that can be mentioned is that a starting hole can be made in the duct with the same tool with which the actual cutting, e.g. truncation, is performed. This speeds up the procedure, requires fewer tools and also increases occupational safety.

In the following, the invention will be described in more detail by the aid of a preferred embodiment with reference to the attached drawings, wherein

Fig. 1 presents a tool, which is provided with a blade according to the invention.

Fig. 2 presents the blade detached from the tool.

Figs. 3A-3D present the different phases of the use of the tool and its blade.

Fig. 1 thus presents a prior-art metal shear 1 (e.g. a metal shear manufactured by Draco), into which the new type of blade 2 according to the invention is installed in a detachable manner. This type of metal shear can preferably be electrically-operated, containing possibly also a provision for battery powering. The invention is not limited to exactly this shear and to electrical powering, however, but instead other types of cutters are viable, e.g. pneumatically-operated or even manually-operated shears.

The prior art cutting blade in this type of tool is shorter and it comprises an obtuse tip, because the actual cutting is performed with

a vertical to-and-fro movement of the blade, in which the grooved upper surface 3 (Fig. 2) together with the adjacent countersurfaces of the tool perform the actual cutting in a manner that is in itself prior art.

In the blade 2 according to the invention this cutting procedure occurs with a fully known method (as described above). The difference to a prior-art blade, however, is the shaping of the tip of the blade. The tip of the blade 2 is elongated and sharp. In addition, it curves preferably downwards, in which case it does not impair the actual cutting. If the blade were straight, the tip would engage the inner surface of the duct when truncating a duct of round cross- sectional shape.

Figs. 3A-3D present the use of the blade according to the invention in a prior-art tool in connection with the cutting of a duct 4. The duct can be a conventional sheet metal ventilation duct. In the first phase (Figs. 3A and 3B) the blade 2 of the tool 1 is punched through the flank of the duct at the desired point for in order to make the starting hole. After this the truncating (cutting) of the duct is performed with the tool, in a manner that is in itself prior-art, by turning the tool to- and-fro as indicated by the arrows (Figs. 3C and 3D) and by pushing the tool forwards as the truncating progresses.

It is obvious to the person skilled in the art that the invention is not limited to the embodiments presented above, but that it can be varied within the scope of the claims presented below. By means of the blade according to the invention it is possible, not only to truncate a ventilation duct at the desired point, but also to cut an inspection hatch or corresponding in it.