The invention concerns the connection of sheets and consists of a clamping piece that includes slits with protrusions, which bind sheets of wood or other material with grooving along their edges. In this way, it is ensured that the piece is securely joined to the sheets. These pieces can be used for the production of crates used for packing fruit or other products.

Crates used for packing fruit are made of either wood, cardboard or plastic. Wooden fruit crates consist of wooden corners joined to sheets of wood, plywood, MDF and hardboard. Wooden corners make the crates very resilient, because when they contain packaged products and are stacked, the corners bear the vertical gravitational loads safely. However, wooden corners are joined to the rest of the sheets with wire stitches. In the case of cardboard crates, single sheets of compact or corrugated cardboard are used. The sheets of cardboard are shaped into crates and then their edges are glued together in a suitable way. The use of glue does not always ensure that the edges of the crates will remain joined. Moreover, the resistance of cardboard crates during packing and stacking is significantly limited, due to the absence of robust elements such as corners at the edges that can bear vertical gravitational loads.

The aim of this invention is to solve the problem created by the presence of metal stitches on wooden crates, and also significantly to improve the resistance of cardboard crates, without requiring glue. In this invention, the clamping piece (1) in figure 1a consists of slits (2) that contain protrusions (3). Equally, the sheets (4) joined to piece (1) have grooving (5) along their edges. When connecting piece (1) to sheets (4), the protrusions (3) of piece (1) fit into the grooves (5) of the sheets (4). The protrusions (3) of piece (1) are of various shapes such as (7), (8), (9), (10), shown in figure 2, or any other shape. The type of protrusion is determined by the material used to make the sheets (4). The grooving (5) of the sheets (4) is of a corresponding shape. Moreover, there can be 1 , 2, 3 or more protrusions (3) in each slit. Equally, there can be 1 , 2, 3 or more grooves (5) along the edges of the sheets (4). The clearance (18) of the slits (2) depends on the thickness of sheets (4).

The shape of piece (1) depends on the number of sheets that it joins together and also the required mechanical resistance. The piece (1) can have 1 , 2, 3 or more slits with protrusions, connecting 1 , 2, 3 or more sheets. Piece (1) can have shape (11), figure 3, so that it can be joined to one sheet, shapes (12) and (35) to be joined to two sheets, shape (13) to be joined to three, and shape (14) to be joined to 4 sheets, as well as any other shape with the slits (2) and protrusions (3) of figure 1a, for even more than 4 sheets. The reinforcement section (6) of figure 1a significantly improves the resistance of piece (1).

Piece (1) can be made of any synthetic material such as HDPE, LDPE, ABS, PLA, PP, PE, PVC, WPC (synthetic material consisting of wood fibre and polymers), aluminium and also any other material that can be suitably shaped so as to have slits (2) and protrusions (3), as shown in figure 1a. Sheets (4) can be made of wood, plywood, hardboard, MDF, cardboard, synthetic material, iron and also any other material on which the grooves (5) of figure 1a can be created. Grooves (5) are created either by pressure or by removal of material.

Sheets (4) are mounted on piece (1) by moving sheets (4) along the grooves (5) and protrusions (3), as shown in figure 4a. Moreover, sheets (4) can be mounted on piece (1) by moving them vertically to the direction of the grooves (5) and protrusions (3), figure 4b, provided pressure is applied on piece (1) by parts (15) and (16), resulting in the widening of opening (18) to the extent that the clearance is larger than the thickness of sheet (4), as shown in figure 4c. When sheet (4) has been inserted in the slit (3) of piece (1), the loads applied by pieces (15) and (16) are removed; as a result, opening (18) returns to its initial position and clamps sheet (4).

Slipping between sheets (4) and piece (1) is avoided by deforming piece (1) at positions (19), (20), (21) and (22) of figure 5a, which are right next to the edges of the sheets. Deformation is achieved by cold or hot compression using a punch. Due to compression, slits (2) of figure 1a become narrower in the areas adjacent to sheets (4) and do not allow slipping in relation to piece (1). In order to save space, part (23) of the corner of sheet (4) in figure 5b is cut off so that the points of deformation (21) and (22) approach points (19) and (20), thus reducing the necessary length of piece (1). The shape of part (23), which is cut off, can be rectangular, round or anything else and it can be located at other points as well, such as position (24). When a part is cut off, like at position (24), which is outside the corners of sheet (4), then deformation of piece (1) is only required at positions (19) and (20) to secure the sheet, and not at the edges of the sheet.

In the present invention, it is also suggested that sheets (4) are secured to piece (1) using the auxiliary piece (25) of figure 5d. Piece (25) has protrusions (38) and (37), as well as grooves (27) and (28). The grooves (5) of sheets (4) extend to area (26) of figure 5c. When sheets (4) are mounted on piece (1), areas (26) protrude. Protrusion (38) of piece (25) is introduced by clamping in recess (39) of piece (1). The grooves (27) are larger than area (26) of sheet (4), which protrudes from piece (1). Thus, piece (25) is fitted to piece (1), figure 5e, and does not allow slipping between sheets (4) and piece (1). Recess (28) allows disassembly of piece (25) from piece (1) using an ordinary screwdriver.

The present invention can be applied to the production of packing crates and crates used for packing agricultural products, in particular. A crate consisting of a folded sheet (29) and four clamping pieces (1) in its corners is shown in figures 6a and 6b. According to this invention, corners (1) include slits (2) and protrusions (3), as in figure 1a. Sheet (29) originates from the flat sheet (29) of figure 6c, whose contour has been cut, engraved along lines (30), and grooves (5) have been created, as defined by this invention. Sheet (29) is folded along the engraving (30) forming a box with parts (34) as its sides, as shown in figure 6b. The clamping pieces (1) fit into the grooves (5) and connect the edges of parts (34). Then points (19), (20), (21) and (22) of each piece (1) are compressed, as shown in figure 6a, so as to secure the positions of pieces (1) with the edges of sides (34) of sheet (29). The material of sheet (29) can be similar to that defined by patent FR 2 810 962 - A1. The formation (40) on sheet (29) of figure 6c allow safe stacking and transportation of crates because when the crates are placed one on top of the other and surfaces (41) and (36) of figure 6d touch, surfaces (40) prevent pieces (1) from moving. The openings (31) of figure 6c help to ventilate the products, and openings (32) assist the handling of the crate by consumers. For better securing of the above crates during stacking, recesses (28) and (33) of figure 7a can be created on the clamping piece (1). Recesses (28) and (33) secure the crates and prevent them moving around during stacking and transportation, as shown in figure 7c.

The use of the auxiliary component (25) of figure 5d improves the stability of the crates during stacking, because protrusion (37) is freely introduced into slit (39) of piece (1), and does not allow a crate to move in relation to another one.