DURABLE SMOOTHING TROUGH

Description

Field of the invention

[0001] The present invention relates to a tool that can be used for spreading and smoothing building materials, particularly plaster and mortar. It is typically used for plastering. The tool is generally referred to here as a smoothing trowel. However, the invention equally applies to spatulas, in particular, surface spatulas, painter's spatulas, and plaster filler knives, as well as, in individual cases, squeegees. The invention also relates to corner trowels, inside and outside corner trowels, mortar trowels, and point trowels, each in toothed and untoothed versions. Background of the invention

[0002] Utility model DE 1 754 183 discloses a smoothing trowel whose main elements are the blade, a handle support, and the handle. The handle support is attached to a bar that stabilizes the blade. As the utility model discloses, it can be advantageous to manufacture all three parts in one piece from plastic. This also avoids the difficulty of achieving a reliable connection, as the mechanical stress on the trowels and contact with mortar can weaken connections over time.

[0003] German Patent Application DE 1 684 410 discloses a bricklayer's trowel with a soldered joint between the blade and the handle support. The soldered joint is intended to improve the strength of the connection between the handle and the blade. The solder is introduced into holes in the soleplate of the handle, which are additionally provided with extensions at the end facing the blade. This solution may have proven successful for various trowels. However, it seems desirable to be able to offer alternatives to the soldered joint, at least to allow for more freedom in the design and material selection for the handle support and the blade.

[0004] German patent application DE 25 40 885 discloses a smoothing trowel or "smoothing chip" for plastering with a movable and replaceable handle. For this purpose, a guide rail is provided on the smoothing blade, to which the handle is attached. The guide rail is welded to the steel smoothing blade.

[0005] Patent document DE 3639978 discloses a trowel in which the handle is positioned behind the blade and connected to the blade by a curved piece of tubing, the so-called tang. The attachment between the tang and the blade is to be achieved by welding. This design may produce a very durable connection, but it is not very suitable for other trowel shapes, for example, those in which the handle is located above the center of the blade.

[0006] US Patent 9,784,000 discloses that bolts can be welded onto the top of the trowel blade and a handle can be attached via these bolts.

[0007] US2005034262A1 discloses a smoothing trowel according to the preamble of claim 1 and a method according to steps a. to e. of claim 8.

[0008] The invention aims to overcome the disadvantages of the prior art. It aims to provide a durable and robust smoothing trowel that can also be produced efficiently.

[0009] This object is achieved by a smoothing trowel according to claim 1.

[0010] Advantageous developments are specified in the subclaims. These and further advantages can also be achieved with a method according to claims 8 to 14.

[0011] In the context of this invention, "smoothing trowel" is also to be understood as a term used to describe related tools used for spreading building materials, especially those exemplified above with typical names. A smoothing trowel comprises at least a smoothing blade and a handle. The smoothing blade is usually a completely or predominantly flat surface, allowing it to be used for smoothing on a single level across the entire surface. Exceptions are corner trowels for internal or external corners / edges, where the smoothing blade is curved so that the two main working surfaces are at a 90° angle to each other.

[0012] A handle holder connects the handle to the smoothing blade. The handle holder can be a separate component, or alternatively, it could be made integrally with the handle or the smoothing blade. The handle holder can be conveniently made of a metal, such as steel, stainless steel, or aluminum. It is particularly suitable to manufacture the handle holder as a cast component, preferably as a die-cast aluminum component. The handle holder could also be made of plastic, even using an injection molding process.

[0013] The handle holder is to be connected to the screed blade with a plurality of bolts. "Plenty" here means at least two bolts, but between four and ten bolts are often used. The bolts are preferably made of metal, such as steel, stainless steel, or aluminum. A metal that is easy to weld is advantageous. It is also possible to weld the bolts to the handle holder. It may also be advantageous to screw the bolts. It may be advisable to select the bolt material so that a press fit can be achieved.

[0014] It is advantageous if the majority of the bolts, or even all of them, have the same diameter. This ensures an attractive appearance of the trowel and simplifies manufacturing. Trowels are available in which the first and last bolts in a connecting row of bolts are thicker than the remaining bolts. Since the first and last bolts are subjected to greater loads than the remaining bolts, this can offer advantages. However, the present invention allows for a secure and permanent connection without requiring the first and last bolts to be thicker.

[0015] According to the invention, recesses are to be provided in the smoothing blade.

[0016] These recesses can be round holes, for example. The bolts are inserted into these recesses. This means that the bolts are not supposed to rest on the screed, but rather are at least partially passed through it. This type of connection geometry, unlike conventional bolted connections, results in a stronger and more durable joint. A smoothing trowel is often used for several years, sometimes even for more than a decade. It is exposed to high mechanical stress, particularly because at least the screed typically has a certain degree of elasticity. It is also exposed to chemical stress, especially when in contact with alkaline mortar or plaster.

[0017] According to the invention, the bolts are welded to the screed blade. Of the multitude of bolts used, at least some should be welded, preferably all of them. It has proven particularly advantageous to provide these welds on the working side of the screed blade and / or in the region of the recesses (i.e., between the working side and the opposite upper side of the trowel). It may be appropriate to provide welds on the working side of the screed blade, or to provide welds in the region of the recesses, or to provide welds on the working side of the screed blade and in the region of the recesses. Individual or all welds may be positioned in this way.

[0018] This approach presents certain challenges, as the smoothness of the sheet must then be restored. However, this type of bond has been shown to be particularly strong and durable, as well as cost-effective in manufacturing.

[0019] Laser welding, also known as laser beam welding, is particularly suitable for connecting the bolts to the smoothing plate. It can be used as heat conduction welding or deep penetration welding. In individual cases, it can be combined with other welding, joining, or connection techniques. Preferably, the connection is made solely by laser welding. Preferably, no filler metal is used.

[0020] It has proven expedient to manufacture the smoothing plate from chromium-molybdenum steel. Generally, it is advantageous to manufacture the smoothing blade from steel. Torsion-resistant steels are particularly suitable for this. However, these steels also mean that high forces act on the handle and thus the handle holder. It should also be considered that chromium-molybdenum steel, in particular, is brittle. Therefore, high thermal or mechanical stress during the connection between the smoothing blade and handle holder must be avoided. This is precisely what the present invention achieves. Chromium-molybdenum steel is also used here as a generic term for alloys that contain other (smaller) components; it is particularly advantageous if the alloy contains nickel.

[0021] It is advantageous if the handle holder comprises a grip shoe, a handle shaft, and a handle core. These can each be designed as separate components or the handle holder can be a single piece. The connection to the smoothing blade is established via the grip shoe. For this purpose, the grip shoe can be cuboid-shaped, for example, and have a flat surface on its underside facing away from the handle shaft for contact and connection with the smoothing blade.

[0022] The handle shaft serves as the connection between the grip shoe and the handle core. It runs essentially perpendicular to the contact surface of the grip shoe, meaning, when mounted, it is essentially perpendicular to the smoothing blade.

[0023] The handle core typically runs essentially parallel to the smoothing blade.

[0024] Typically, the handle core is surrounded by a grip. The grip can be designed for ergonomic convenience. It is often made of plastic, but can also be made of cork, for example. The grip can be made in one piece with the handle core, but a removable and, if necessary, replaceable grip is advantageous. The grip can then be attached to the handle core and connected to it, for example, by wedges, glue, or even screws.

[0025] It is advantageous if the bolts are connected to the handle holder by pressing. To do this, the bolts are inserted into recesses in the handle holder (provided the handle holder has a grip shoe). The bolts are then compressed under high pressure so that they completely fill the recesses, usually round holes, in the handle shoe. During the pressing process, a bolt cap can also be created that protrudes beyond the holes in the handle shoe and has a thickened portion at the top, creating an additional (positive-locking) connection with the handle shoe.

[0026] The invention also relates to a method for producing a smoothing trowel according to the appended claim 8.

[0027] It's usually very helpful to load the handle holder with the numerous bolts before welding, ideally all of the bolts to be welded. It may be useful to secure the bolts with a holder after inserting them into the respective recesses.

[0028] The holder can stabilize the bolts in the correct position for welding. After welding, the holder can be removed. A variety of devices can be used as a holder. A mechanical holder can also be used to temporarily support the bolts in an appropriate manner, for example, by supporting them from the top side of the screed blade. (The top side is the side opposite the working side.) The handle holder itself can serve as a holder during this process step.

[0029] It may generally be expedient to weld the studs from any direction. However, according to the invention, the studs are welded from the direction of the working side of the smoothing blade. It is fundamentally advantageous for processes for producing smoothing blades if the feed direction of the studs and the direction from which welding is performed are opposite one another. For example, the first direction (feed direction) can lie in a first hemisphere and the second direction (direction of approach of the welding device) can lie in a second hemisphere, with both hemispheres arranged opposite one another around a central axis.For example, the first direction (feed direction) can lie within a first right circular cone, and the second direction (welding device approach direction) can lie within a second right circular cone. Both circular cones are arranged opposite each other around a central axis, forming a double cone. Both circular cones can have a central angle of 90° or less.

[0030] It's certainly possible for the studs to protrude a certain distance above the screed blade. However, this distance is usually much shorter than the stud length. Therefore, if a large number of studs are used, especially more than four, and the studs are spaced closer than 5 cm apart, and especially closer than 3 cm or 2 cm apart, welding studs from the work side is easier. On the upper side of the screed blade, the protruding studs would obstruct the free approach and movement of a welding machine or welding torch.

[0031] According to the invention, the handle holder is first equipped with bolts and the bolts are then provided together with the handle holder.

[0032] In a subsequent process step, the handle holder, along with the studs, would then have to be transported to the welding station. However, by appropriately preparing the handle holder, the welding process itself can be completed more quickly. This is particularly advantageous when the welding equipment used is expensive and a high throughput at the welding station is advantageous.

[0033] In particular, it is useful if the bolts are welded by laser welding.

[0034] It is advantageous if the studs used protrude beyond the working side of the screed blade and stud material is removed there during the welding process. This is particularly advantageous if stud material is moved into the gap between the stud and the hole. For this purpose, material can be melted. In this process, all or just part of the material protruding beyond the working side can be moved. In this way, the hole, which must be at least slightly larger than the stud circumference, is completely or partially closed. The movement of material can be made easier by the effect of gravity if the studs are oriented accordingly. It is therefore advisable for the stud ends to point upwards.

[0035] The sealing could be achieved using a welding filler, such as a welding wire, but in the context of the present invention, welding without a welding filler is preferred. The welding process without a welding filler is even more economical and faster.

[0036] A bolt protrusion is not advantageous in itself, and this process concept is therefore not intuitive. Nevertheless, it has proven advantageous within the scope of the present invention to accept the occurrence of a bolt protrusion in the corresponding process step.

[0037] A method in which at least two or all of the recesses to be provided in the smoothing blade are produced in one work step is also advantageous. Fig. 1 shows a perspective view of a ready-to-use smoothing trowel according to the invention. Fig. 2 shows the same perspective view of a smoothing trowel according to the invention with the handle removed. Fig. 3 shows a cross-sectional view of the receiving of a bolt by the smoothing blade. Fig. 4 shows an enlarged perspective view of a section of the smoothing trowel according to the invention.

[0038] Figure 1 shows a smoothing trowel according to the invention in perspective view.

[0039] The smoothing trowel 10 has a smoothing blade 20, which is guided by the handle 30. The handle holder 40 connects the handle 30 and the smoothing blade 20. The handle holder 40 is connected to the smoothing blade 20 by a plurality of bolts 50.

[0040] Figure 2shows, in the same perspective view, a smoothing trowel 10 according to the invention, but with the handle 30 removed. This allows the design of the handle holder 40 to be more clearly seen. The handle holder 40 comprises the grip shoe 42. The grip shoe rests directly on the upper side of the smoothing blade 20. (Indirect resting via an intermediate layer is also conceivable.) It extends over a substantial part of the length of the smoothing blade, expediently generally over more than 50% of the length, typically between 50 and 80% of the length of the smoothing blade. The grip shoe 42 is connected to a handle shaft 44 projecting from the handle shoe 42. The handle shaft 44 establishes the connection to the handle core 46. The handle core 46 is expediently a rod or tube section. It has essentially the length of the handle 30.The handle core 46 can have a profile, for example, a square or rectangular profile, that prevents the handle from twisting around the longitudinal axis of the handle core 46. A square profile is shown here. A thread can also be provided at the end of the handle core, for example, through which the handle 30 can be secured with a nut to prevent it from slipping off the handle core 46.

[0041] Figure 3 shows a schematic representation of the connection of a bolt 50 to the smoothing blade 20. The bolt has a lower end 52, a bolt shaft 54, and a bolt head 56. A recess 60 is provided in the smoothing blade 20 for the bolt. For a round bolt, this recess is preferably provided as a round hole. The recess can be created by drilling or punching.

[0042] The lower bolt end 52 is pushed from the top of the smoothing blade 20 completely through the recess 60. Therefore, the lower bolt end 52 of the bolt 50 protrudes and projects beyond the working surface 70 of the smoothing blade 20.

[0043] This positioning of the bolt deviates significantly from known connection types. Typically, for welding, the bolt is placed on top of the screed blade 20. In this variant, no recess is required at all. In principle, a form-fitting connection would also be conceivable. The lower bolt end 52 could have a thickened portion for this purpose, and an area of ​​the recess could have a corresponding widening. However, this approach has been examined more closely and has proven to be disadvantageous, particularly with regard to its longevity. In particular, when a thin screed blade is used, a stable connection may be established initially; however, this connection does not remain stable over its service life. Since the screed blade is exposed to pressure during use and regularly bends as a result, such a mechanical connection is subjected to considerable stress.The connection may then quickly come loose. Furthermore, it usually happens that the connection is no longer completely flat. In some cases, the bolt end either protrudes beyond the working side 70 of the smoothing blade 20 or it retracts behind it. In one case, a protrusion occurs, in the other, a hollow is formed. Both adversely affect the smoothing result that the smoothing trowel usually has to be taken out of service.

[0044] Within the scope of the present invention, however, the bolt 50 is guided through the recess 60 in the smoothing blade to create a weld. Such a weld can be provided in the first welding area 62. This welding area lies in the gap between the walls of the recess 60 and the outer circumference of the bolt 50, entirely or substantially between the top side and the working side of the smoothing blade 20. Welding can also be carried out there using a filler metal, if necessary. Alternatively or additionally, welding can be carried out in the second welding area 64. This welding area lies in the exit area of ​​the bolt. Welding therefore takes place directly on the working side 70 of the smoothing trowel 20. Typically, a weld seam runs in a ring shape along the edge of the recess and thus also in a ring shape around the bolt. With a round hole, this results in a round ring. Welding can be carried out with the aid of a filler metal.Alternatively, welding can also be performed without filler metal. It may be advisable to melt off part of the bolt material, especially parts of the protruding bolt material, and use it to form a weld seam.

[0045] In this way, a very strong and permanent connection of the bolt 50 with the smoothing trowel 20 can be made.

[0046] The portion of the bolt projecting beyond the top side of the trowel 20, essentially the bolt shank 54, creates a connection to the handle holder 40. For this purpose, the bolt shank 54 is inserted into corresponding holes or recesses in the handle holder, typically the handle shoe 42. The connection can be made by screwing. A thread would then be provided on the bolt shank 54. The connection can also be made by pressing. In this case, sufficient pressure is exerted on the bolt from the direction of the bolt head 56 that it fills a correspondingly sized recess in the handle holder. For the purpose of pressing, a softer bolt material, such as aluminum, should be used.

[0047] Figure 4shows, with an enlarged section, how the connection between the smoothing blade 20 and the handle holder 40 can be established. As shown, a plurality of bolts 60 are connected to the smoothing blade 20. A number of two to twelve bolts is generally expedient within the scope of the present invention. The bolts are connected to the smoothing blade 20 at regular or variable intervals. The bolts are then inserted into matching recesses in the handle holder 40, preferably in the handle shoe 42. Bolts which have been pressed in are shown. Accordingly, it is not necessary to provide nuts on the top side of the bolts 60. It is expedient if the top side 48 of the handle shoe 42 is ground down after pressing. This results in a flush end of the bolts 60 with the top side 48 of the handle shoe 42, as shown.

[0048] Overall, it is clear how a practical device suitable for mass production and universally applicable can be produced in a cost-effective manner. List of reference symbols

[0049] 10Smoothing trowel 20Smoothing blade 30Handle 40Handle holder 42Handle shoe 44Handle shaft 46Handle core 48Top of handle shoe 50Bolt 52Lower bolt end 54Bolt shaft 56Bolt head 60Recess 62First welding area 64Second welding area 70Working surface

Claims

1. Smoothing trowel (10), which comprises a smoothing blade (20) and a handle (30) and in which a handle holder (40) connects the handle (30) to the smoothing blade (20), the handle holder (40) being connected to the smoothing blade (20) by a plurality of bolts (50), wherein openings (60) are provided in the smoothing blade (20) and the bolts (50) are guided into these openings (60), characterised in that the handle holder (40) is connected to the smoothing blade (20) with a plurality of bolts (50) by welded joints.

2. Smoothing trowel (10) according to the preceding claim, in which welded joints are provided on the working side of the smoothing blade.

3. Smoothing trowel (10) according to one of the preceding claims, wherein welded joints are provided in the region of the recesses.

4. Smoothing trowel (10) according to one of the preceding claims, wherein the welded joints are realised by laser welding.

5. Smoothing trowel (10) according to one of the preceding claims, wherein the smoothing blade (20) is made of chromium-molybdenum steel6. Smoothing trowel (10) according to one of the preceding claims, in which the pins (50) are guided into bushings of the handle holder (40) and pressed there.

7. Smoothing trowel (10) according to one of the preceding claims, wherein all pins (50) have the same diameter8. A method of manufacturing a trowel (10) comprising the following steps: a. Providing a smoothing sheet with a top side and a working side b. Providing a handle holder with a variety of bolts c. Creating openings in the smoothing blade d. Inserting the large number of bolts into the openings e. Welding the large number of studs from the side9. Method for manufacturing a trowel (10) according to claim 6 or 7, in which the welding of the bolt is carried out by laser welding.

10. A method of manufacturing a trowel (10) according to any one of claims 8 to 9, wherein the stud protrudes beyond the working side of the trowel blade and stud material is displaced into a gap between the stud and the hole in the welding process.

11. A method of manufacturing a smoothing trowel (10) according to the preceding claim, in which a pin projection is removed over the working side of the smoothing blade.

12. A method of manufacturing a trowel (10) according to any one of claims 8 to 11, wherein the direction from which welding is performed is opposite to the direction from which studs are fed.