Composite smooting tool and its manufacturing

The present invention relates to a composite smoothing tool and a process for manufacturing it.

A related two-part scraping and smoothing tool is known from the Swiss patent application CH 699 114 A2. In the tool described in this document, a steel blade having a holding rib is form fitted in an L-shaped recess in an aluminum hollow profile having support brackets. The blade is slid sideways into the recess and then fixed against displacement by covers attached to the side surfaces of the scraping and smoothing tool.

The known tool has been found occasionally not to be able to withstand the stresses and strains of everyday use. It is therefore desirable to have at hand a sturdier tool.

The invention provides a composite tool in which two brackets of a light metal hollow profile grip part hold a steel blade form fittingly and in frictional connection, and one or two clamping ribs clasp the corresponding bracket(s), so as to increase the frictional force. Thereby further fixing means are not necessary, but the tool is still able to withstand extraordinary stresses and strains.

In embodiments, the blade has an arrow shaped cross section and one or two support ribs accommodated in support grooves of the grip part. In further embodiments, the grip part has an inside rib, preferably arranged between two opposing grip recesses formed in parallel faces of a trapezoidal hollow profile. In some embodiments, the rearward face of the grip part is perpendicular to the faces adjacent to it.

In some embodiments, the steel for the blade is cold drawn, thereby increasing its hardness and wear resistance. In still further embodiments, the blade is at least partially coated to increase corrosion resistance where the brackets of the aluminum grip part clasp the steel blade.

Under another aspect, the invention provides a process of gradually cold drawing the blade steel into a shape having a cutting edge, a rearward extension with at least one support rib and one or two clamping ribs extending obliquely from the cutting edge towards the rearward extension, cutting it to a desired length and introducing the tailored blade part into a respective collet in an aluminum grip part. Similarly as in the above, in this manner the steel blade is securely held by the frictional forces eliminating the need for separate fixing steps. In embodiments, the steel blade may be coated with an insulating film before introducing it into the collet, at least at parts where direct contact to aluminum is to be avoided in order to increase corrosion resistance.

Further aspects and advantages will become apparent from the detailed description below, and by reference to the appended drawings. These show:

Figure 1

a conventional smoothing tool in cross section;

Figure 2

an embodiment of the invention in cross section;

Figure 3

another embodiment of the invention in a close-up view; and

Figures 4A-D

several views of another embodiment.

In the drawing of Figure 1, a conventional tool is shown in cross section: A steel blade 3 having a holding rib 1 is slid sideways into an L-shaped recess formed between two brackets 4 of an aluminum hollow profile 2 constituting the grip part.

In contrast to the tool of Figure 1, the tool 10 according to the invention (Figures 2 + 3) has a blade part 12 which has two clamping ribs 14 together with a rearward extension 16 providing an arrow shape. At the rearward extension, there are two oppositely projecting support ribs 18 engaging into corresponding recesses 20 of the grip part 22. Between the clamping ribs 14 and the support ribs 18, the grip part has clasping brackets 24 forming a collet for the blade part 12.

In cross sections parallel to the length direction of the blade part and orthogonally to the rearward extension 16, the clamping ribs 14 are spaced from the rearward extension 16. In other words, in length direction of the blade part 12 a recess for receiving the clasping brackets 24 of the grip part 22 is formed between the clamping ribs 14 and the rearward extension 16 of the blade part 12.

According to embodiments, the blade part has a curvature encircling an angle of between 100° and 160° at a tip portion opposing the rearward extension 16. Furthermore, the blade part may have a curvature encircling an angle of more than 100° at a protruding portion of the at least one clamping rib 14, the protruding portion being the part of the at least one clamping rib that is located most distant from the tip portion of the blade part. Alternatively or additionally, the blade part may have a curvature encircling an angle of more than 100° at a connection portion between the at least one clamping rib 14 and the rearward extension 16.

The grip part 22 is of generally prismatic or trapezoidal shape, the latter having two parallel faces in each of which a grip recess 28 is formed for ease of holding the tool. On the inside of the tool's hollow profile, made of aluminum or an aluminum-base alloy, a reinforcement rib 26 is formed between the grip recesses 28. The rearward face of the trapezoid is in this embodiment perpendicular to the adjacent faces. Of course, the general shape of the tool is ergonomic, therefore the rearward edges are appropriately rounded so as not to cause pain when held in use. For the same reason, suitable thicknesses l₁ will be within 25 ± 10 mm between the parallel faces, a width l₂ will be within 35 ± 10 mm between the rearward face and the deepest point of the grip recess 28, and an angle α of the blade holding part is ca. 15-30°, in embodiments preferably 20-25°.

The steel blade has an additional function of clasping the brackets 24 of the grip part, requiring particular attention to its manufacturing. It has been found that particularly suitable blades can be made by cold drawing, adding to the hardness and wear resistance and also providing elasticity to the clamping ribs 14. The process for manufacturing accordingly includes gradually cold drawing the blade steel into a shape having a cutting edge, a rearward extension with at least one support rib and two clamping ribs extending obliquely from the cutting edge towards the rearward extension and subsequent cutting of the blade steel, in embodiments followed by film coating and then introducing it into the collet provided by the grip part brackets 24. The frictional forces resulting in this manner are sufficient to securely support the blade without any danger of it ever inadvertently coming loose.

In another embodiment shown in Figures 4a to 4d, the tool 10a has a very similar shape, as has a blade part 12a inserted. Figure 4A shows a cross section, Figure 4B an overall view, and Figure 4C shows but the blade part 12a in close-up. Figure 4D shows both the tool 10a and the blade part 12a, indicating where the latter is inserted (actually along a line perpendicular to the paper plane). The difference in this embodiment is that when the blade part 12a is inserted into the grip part 10a, a hole 30 remains. The angle α in this embodiment is identical to the one of the previously described embodiment of Fig. 2.

The skilled person will be aware of modifications to the above embodiments feasible without departing from the scope of the invention as defined by the appended claims.