TECHNICAL FIELD

The present invention relates to a method and a device for fastening an object in a fiber-reinforced composite material. One example of such fiber- reinforced composite material is glass fiber-reinforced plastic, also called fiberglass. Fiberglass is a material with many uses, including boats, automo- biles and similar. Fiberglass comprises a plastic matrix, which plastic matrix may be epoxy, a thermoplastic or a thermosetting plastic, such as polyester or vinylester. When used for the body or hull or other parts of boats the fiberglass can be coated with a conventional gelcoat. PRIOR ART

According to the prior art screws are commonly used for fastening an object in a fiber-reinforced composite material, such as for fastening objects to fiberglass parts on a boat. Such screws can be arranged in stainless steel and can comprise a substantially cylindrical body provided with a thread and a head to be engaged by a tool. Usually a hole is drilled in the material, wherein the screw is screwed into the hole and brought into contact with the object to be fastened in a conventional manner.

One problem of such prior art devices and methods for fastening an object in a fiber-reinforced composite material is that the screw tends to wear on the material around the screw and turn loose. Hence, the material around the screw can get damaged, wherein it is difficult to use the same hole again for fastening an object.

Another problem of such prior art devices and methods is that it is diffi- cult to repeatedly use the same hole for the same or different objects to be fastened. For example, some objects are fastened during use and are removed for storage or similar when not in use for a longer time period. Such an object cannot easily be fastened at the same place as before as the holes previously used are damaged or do not engage the screws properly. To be able to use the same hole again the material must be repaired, which is time consuming, expensive and can result in a less durable and strong material for the object to be fastened in. Alternatively, a hole having a substantially larger diameter can be drilled, wherein a considerably larger screw must be used. Drilling a larger hole and using a larger screw may not always be an option and is not a suitable solution for repeated fastening and removal.

SUMMARY

One object of the present invention is to eliminate the above mentioned problems and provide a method and a device for secure and reliable fastening an object in a fiber-reinforced composite material, also when subject to repeated fastening and removal of the object at the same position. One further object of the present invention is to make it possible to provide a secure and reliable fastening in a position in which there is an existing hole for a conventional fastening screw, wherein the material around said existing hole may be damaged.

The invention relates to a method for fastening an object in a fiber- reinforced composite material, comprising the steps of

arranging a hole in the material for receiving the device, the device having a body, en external thread extending from said body and an axial bore with an internal thread, wherein the diameter of the hole is arranged larger than the diameter of the body to form a gap between the material in the hole and the body when the device is inserted in the hole,

applying an adhesive on the external thread of the device and/or on the material in the hole,

screwing the device into the hole, so that the external thread of the device engages the material and the adhesive is provided in the gap between the material in the hole and the body,

screwing a screw having an external thread into the bore, so that the external thread of the screw engages the internal thread of the device to fasten the screw, and engaging the screw with the object to be fastened to fasten the object to the material.

The thread of the device can primarily be for fixing the device while the adhesive is setting. For example, the thread of the device is only partially en- gaged with the material, wherein the thread is a minor part of the final fastening of the device and the adhesive forms the major fastening of the device after setting. Further, the thread can form an enlarged contact surface between the device and the adhesive. The adhesive can at least partially or entirely fill the gap between the material in the hole and the body. The adhe- sive can be provided in the gap, so that the adhesive extends between the material in the hole and the body. The adhesive can fill the gap in a radial direction and at least partially in an axial direction. The screw can be screwed into the device after setting of the adhesive.

The material can be fiberglass, such as a fiberglass material coated with a gelcoat, such as used for boats and boat parts. The method can comprise the step of arranging the hole through said gelcoat. The hole can be provided with a countersink and the device can be inserted so as to form a gap between a head of the device and the countersink. Further, the gap between the head of the device and the composite material in the countersink can be filled with adhesive. For example, the external thread and/or an axially extending outer surface of the head can be provided with adhesive. Hence, a considerable surface for the adhesive is provided so as to obtain a further reinforced fastening of the device.

The method can further comprise the step of cutting the composite ma- terial in the hole by means of the external thread of the device. For example, the material in the hole can be cut by means of the external thread of the device having a sharp or pointed thread profile. Hence, the risk of damage to the material in the hole is reduced. Further, the external thread can have a relatively low pitch of thread to reduce the risk of damage to the material in the hole while obtaining a relatively large engagement surface between the device and the material. The method can further comprise the step of bringing less than half the depth of the external thread of the device to engage the composite material in the hole. Hence, a considerable gap is provided, which results in a substantial amount of adhesive. This has proven to provide a strong and durable fastening between the device and the material.

The present invention also relates to a device for fastening an object in a fiber-reinforced composite material, comprising a body having an external thread for engaging the composite material in a hole therein, characterised in that the body is provided with an axial bore having an internal thread for a screw, so that an external thread of the screw can engage the internal thread of the device for fastening of the screw to the device, the body is arranged to form a gap for an adhesive between the body and the composite material in the hole, and the external thread of the device is arranged with a depth of thread so as to only partially engage the composite material in the hole.

Further characteristics and advantages of the present invention will become apparent from the description of the embodiments below, the appended drawings and the dependent claims.

SHORT DESCRIPTION OF THE DRAWINGS

Non-limiting examples of the container according to this disclosure will now be described in more detail with reference to the appended drawings, in which: Fig. 1 is a schematic view of a device for fastening an object in a fiber- reinforced composite material according to one embodiment,

Fig. 2 is a schematic section view along line ll-ll in Fig. 1 ,

Fig. 3 is a schematic view of a portion of the device according to Fig. 2, showing the thread profile, and

Fig. 4 is a schematic section view of the device according to Fig. 2, wherein the device is fastened to a material. DESCRIPTION OF EXAMPLES

With reference to Fig. 1 and Fig. 2 a device 10 for fastening an object in a fiber-reinforced composite material according to one embodiment of the present invention is illustrated. For example, the material is a fiberglass material, such as an epoxy based fiberglass provided with a gelcoat or similar as used for construction of boats and boat parts.

The device 10 comprises a body 1 1 provided with an external thread 12, so that the device 10 can be screwed into the material or a hole in the material while the external thread 12 engages the material for fastening the device 10 therein. Optionally, the device 10 comprises a head 13. The device 10 comprises an axial bore 14 having an internal thread 15, wherein the device 10 is formed as a screw insert for receiving a screw in the axial bore 14, so that an external thread of the screw can engage the internal thread 15 of the device 10 for fastening of the screw to the device 10. The screw is not illustrated in the drawings. The device 10 is, for example, made of metal, such as stainless steel, or any other suitable metal.

The axial bore 14 extends in a direction perpendicular to or substantially perpendicular to the depth of the external thread 12. The axial bore 14 is formed with a tool engaging portion 16 for engagement with a tool for screwing the device 10 into a hole in the material. The tool engaging portion 16 is arranged at one end of the device 10. For example, the tool engaging portion 16 is arranged through the head 13 of the device 10. According to the embodiment illustrated in Fig. 1 the tool engaging portion 16 is arranged as a hexagon for receiving a hexagonal wrench. Alternatively, the tool engaging portion 16 is formed as a rectangle or any suitable shape for cooperation with a corresponding tool.

The axial bore 14 continues beyond the tool engaging portion 16 further into the device 10 in the axial direction to form a screw receiving portion 17. The screw receiving portion 17 comprises the internal thread 15. For example, the screw receiving portion 17 is arranged with smaller diameter than the tool receiving portion 16. According to one embodiment example, the diameter A of the tool receiving portion 16 is 2-20 mm, 3-15 mm, 4-10 mm or about 5-6 mm. The axial bore 14 ends with the screw receiving portion 17, wherein the axial bore 14 is formed with a bottom 18. For example, the device 10 is water-proof, so that water cannot enter the axial bore 14 through the bottom 18 or through the body 1 1 . Hence, according to one embodiment the axial bore 14 is not a through bore, wherein the device 10 is provided with a single opening in one end of the axial bore 14 and the bottom 18 in the opposite second end of the axial bore 14. Alternatively, the axial bore 14 is a through bore, wherein the device 19 is provided with two openings to the axial bore 14.

With reference to Fig. 2, the head 13 is provided with a larger diameter

B than the body 1 1 . For example, the diameter B of a radially extending top surface 19 of the head 13 is 5-25 mm, 10-15 mm or about 12 mm. For example, the head 13 is conical, wherein an external and axially extending surface 20 of the head 13 is bevelled an angle a. For example, the angle a of the bevelled surface 20 is about 20-70°, 30-60°, 40-50° or 45°.

The body 1 1 is substantially cylindrical or conical cylindrical, wherein the body 1 1 is arranged with a larger diameter at the head 13 and the opening into the axial bore 14 than at the bottom 18. For example, the body 1 1 is tapered an angle β about 2-20°, 3-10°, 4-8° or about 5-7°.

According to one embodiment the total length C of the device 10 is 5-

50 mm, 10-30 mm or about 15-20 mm. The radius D of the device 10 at the bottom 18 is, for example, about 2-15 mm, 3-5 mm or 3.45 mm. The tool engaging portion 16 is, for example, arranged with a depth E in the axial direction of about 2-10 mm, 3-6 mm or 4-5 mm. The screw receiving portion 17 of the axial bore 14 is, for example, arranged with a depth F, i.e. substantially the distance between the tool receiving portion 16 and the bottom 18 or the axial length of the internal thread 15, in the axial direction of about 5-40 mm or about 10-20 mm. According to one embodiment example, the depth F of the screw receiving portion 17, or the length of the internal thread 15, is 9.5 mm.

With reference to Fig. 3 the external thread 12 of the device 10 is illustrated more in detail. For example, the external thread 12 is a cutting thread for engaging the material around a hole therein, so that the external thread 14 cuts into the material. Hence, the external thread 12 is not a forming thread. For example, the external thread 14 is arranged with a thread profile Y of 10-30°, 15-20°, 17-18° or about 17.5°. The external thread 14 is, for ex- ample, arranged with a thread pitch G of about 0.5-3 mm or 1 -2 mm. For example, the external thread 14 is arranged with a depth of thread H of about 0.5-5 mm, 1 -3 mm, 1 .5-2 mm or about 1 .6 mm.

With reference to Fig. 4 the device 10 is fastened to the material 21 , wherein a screw can be screwed into the device 10 to fasten an object to the material 21 . According to the embodiment illustrated in Fig. 4 the material 21 comprises a fiber-reinforced composite material 21 a, such as fiberglass, coated with a conventional gelcoat 21 b. According to one embodiment a hole 22 is drilled in the material 21 . For example, the hole 22 is drilled in previously untouched material. Alternatively, the hole 22 is drilled in the position of a previously damaged or not damaged screw hole for a conventional screw. The hole 22 is arranged larger than the diameter of the body 1 1 of the device 10, so that a gap 23 is formed between the body 1 1 and the material 21 in the hole 22 when the device 10 is arranged therein. According to the illustrated embodiment the hole 22 is countersunk forming a countersink 24 having a bevelled surface around the hole 22. An adhesive is applied to the external surface of the device 10 and/or to the material surface in the hole 22. For example, the adhesive is applied to the external thread 12 of the device 10 and optionally also to the bevelled surface 20 of the head 13. For example, the adhesive is a two-component adhesive, such as a two-component epoxy adhesive. Then, the device 10 is positioned in the hole 22 and a tool for screwing the device 10 into the hole 22 is engaged with the tool engaging portion 16 of the axial bore 14, wherein the device 10 is screwed into the hole 22. For example, the device 10 is screwed into the hole 22 leaving a gap 25 also between the bevelled surface 20 of the head 13 and the countersink 24. The gap 23 between the body 1 1 and the material around the hole 22 and the gap 25 between the countersink 24 and the bevelled surface 20 of the head 13 is filled with adhesive 26. Hence, the body 1 1 is arranged to form the gap 23 for the adhesive 26 between the body 1 1 and the composite material 1 1 in the hole 22 and the head 13 is arranged to form the gap 25 for the adhesive 26 between countersink 24 and the bevelled surface 20 of the head 13.

The external thread 14 of the device 10 is arranged with a depth of thread H so as to only partially engage the material 21 in the hole 22. For example, the body 1 1 , the hole 22 and the external thread 14 is arranged so that less than half the depth of thread H is engaged with the material 21 when the device 10 is mounted and wherein more than half the depth of thread H form the gap 23 for the adhesive 26. For example, about one third or less of the depth of thread H is engaged to and enclosed by the material 21 in the hole 22. For example, the gap 23 is about 0.5-3 mm or about 1 -2 mm, which distance is illustrated in Fig. 4 by means of the letter I.

Then, preferably after setting of the adhesive 26, a screw having an external thread corresponding to the internal thread 15 of the device 10 is inserted into the axial bore 14 to fasten an object to the material 21 , which is not illustrated in the drawings.