METHOD AND ARRANGEMENT FOR FORMING A LOAD-BEARING JOINT BY MEANS OF COMPRESSED CELLULAR PLASTIC MATERIAL THAT HAS BEEN MADE TO EXPAND BY HEATING

Abstract: The present invention is a method for forming load-bearing joint s through the use of a compressed cellular plastic material (3) having a stable form at room temperature, and which, after insertion into the joint area (1), is made to expand through heating so that the whole of the joint area is filled. Bonding between the filler material and the base material can be secured by means of a hot melt adhesive or a hot melt adhesive with setting agent (4) which, during the expansion phase of the filler material, melts under elevated temperature, and thereby a bond is formed between the filler material and the base material (5). Through this method, when the filler material heats up, the joint area is filled, pressure is exerted on the adhesive, and bonding to the base material is secured at one and the same time. With the present method, the components comprising the joint are dry when being handled. The method is applicable for the load-bearing joining of core material in sandwich constructions. It can also be used for joining concrete panels, wall panels, window panels, etc. in building construction.

Description: METHOD AND ARRANGEMENT FOR FORMING A LOAD-BEARING JOINT BY MEANS OF COMPRESSED CELLULAR PLASTIC MATERIAL THAT HAS BEEN MADE TO EXPAND BY HEATING The present invention is a method for forming load-bearing joints through the use of compresse cellular plastic material having a stable form at room temperature, and which, after insertion int the joint area, is made to expand through heating so that the whole of the joint area is fille Bonding between the filler material and the base material can be secured by applying a one o two-component adhesive. Alternatively, bonding can be secured by means of a hot melt adhesiv or a hot melt adhesive with setting agent which, during the expansion phase of the plastic fillin material, melts under elevated temperature, and thereby a bond is formed between the fille material and the base material. Through this method, when the filler material heats up, the joint area is filled, pressur is exerted on the adhesive, and bonding to the base material is secured at one and the same tim Furthermore, with the present method, the components making up the joint are dry when bein handled. The method is applicable for the load-bearing joining of core material in sandwic constructions, but it is also applicable for joining concrete panels, wall panels, window panel etc. in building constructions. STATE OF THE ART There are a number of methods for filling joints areas. The following are examples of method that have already been patented: U.S. 3,806,566; U.S. 4,898,630; U.S. 4,647,716; DE 1,963,267; and DE A 1,784,467. Common to most of the above methods, however, is that their purpose is primarily to fil or seal a cavity, gap or enclosed space, and not to form a load-bearing joint. Furthermore, mos of the methods are based on a chemical process, e.g. foaming or vulcanization. The presen method is based instead on storing energy in the form of compressed gas at room temperature which energy is then released at elevated temperature (the heat distortion temperature of th plastic filler material). In patent No. DE A 1,784,467, a non-chemical sealing method is described. The metho is based on the compression of an elastic cellular plastic material having open cells. The metho is not applicable for forming a rigid, load-bearing joint. Furthermore, the plastic material use in the method, when compressed, does not have dimension stability at room temperature. U.S. Patent 4,647,716 describes a method that is similar to the present method. However even in this case the purpose is to seal. In order to obtain a sealed electrical connection, compressed cellular plastic material i placed between the wires and the shrink tube which completely encloses the connector Thereafter, the connector is heated in a conventional manner. It is reasonable to suppose tha heating is by means of a hot air gun, by which means the tubing shrinks and the piece of cellula plastic material expands, thus sealing the connector. The patent also refers to the possibility o applying hot melt adhesive to the cellular plastic material (called sealing member in the patent) thereby further ensuring that adequate sealing will be obtained. Thus, the above-cited paten describes a method for sealing electrical connectors and is not a method for forming a load bearing joint. EXAMPLES OF APPLICATIONS Present method: Cellular plastic material is used as core material in sandwich constructions. Ships and boats, fo example, are often constructed in accordance with this principle. The core material is fixed t a wooden construction formed in the shape of the boat. Fiber-reinforced plastic is then applied to both the inside and the outside of the core material. The core material used in this type o sandwich construction is in the form of boards of various sizes. When the boards are fitted together, gaps are left between them. In order to obtain a continuous interaction of forces in the sandwich construction, these gaps are filled with a material that joins the edges of the boards together. Up to now, this has been done using a putty compound with a density of ca. 0.6-1.5 kg dm 3 . Cellular plastic material usually has a density of between 0.045 to 0.25 kg dm* ** . Using a putty compound increases the weight of the construction, which is not desirable, and results in discontinuities in the core material which may have a negative affect on the strength of the sandwich construction in cases e.g. of impact or when the structure is overloaded. Other negative affects are the occurrence of thermal bridges and acoustic transmission. Normally, the joints, the dimensions of which are shown in fig. 1, are filled by injecting the putty compound. This method has been shown to result in incompletely filled joints, which also weakens the sandwich construction. Example of an alternative method in accordance with the present invention The filler material is first prepared by pressing together strips (2) of cellular plastic material under elevated temperature, see fig. 2, so that their thickness is reduced to the thickness required by the method, e.g. 30% of their original thickness, see fig. 3. By allowing the compressed strips to cool before the pressure is removed, the strips will retain their reduced thickness even after the pressure has been removed. A film of moisture-cured hot melt adhesive (4) is applied to the filler material, either during compression or afterwards. The filler material with adhesive coating is inserted into the joint area (1), see fig. 4. By heating the strips of filler material to approx. 7fC, the filler material softens and expands because of internal excess pressure, until the joint area is filled. When heating the filler material and the adhesive, the adhesive melts, and because the filler material expands, it presses the adhesive against the base material so that a bond is formed between the filler material and the base material (5), see fig. 5. After cooling, the filler material hardens and regains its original properties. With the hardening of the filler material, further expansion is prevented, which ensures that the joint remains stable. The adhesive is cured through the humidity of the air. In order to obtain a joint with load-bearing properties such as good tensile and compression strength as well as shear strength, the method, must satisfy the following requirements: 1. The filler material must meet set strength requirements. 2. The adhesive must meet set strength requirements. 3. The bond between the filler material and the base material must meet the same requirements as are set on the components which make up the joint, i.e. the filler material, the hot melt adhesive, and the base material. In order for the last requirement to be met, the filler material must fill the joint ar completely, i.e. the filler material must expand evenly and completely along the whole of t joint. Also, the hot melt adhesive must melt completely during the time that the filler mater is exerting the necessary pressure on the adhesive. This means that the heat must be applied such way that the above requirements can be met. The present invention offers a solution to t problem of forming an essentially load-bearing joint in e.g. sandwich constructions. The present invention offers a method which allows bonding at relatively l temperatures, e.g. at 60°C, and where the filler material, when expanded, regains its origi form. Thus the size of the filler strips can be predetermined. Expansion through chemi foaming, on the other hand, is always uncontrolled. In the present invention, rigid cellular plastic material with closed cells is used. This a prerequisite for expansion to occur as well as for ensuring sufficient rigidity and strength the finished joint. EXAMPLE OF PROCEDURE Preparing the filler material Strips of filler material, in the dimensions desired, are sawn, or by some other means cut o from the base material, e.g. PVC cellular plastic. In order to achieve sufficient pressure on t adhesive, the strips of filler material, before compression, should be somewhat thicker than t joint area they are to be inserted into. The thicker are the strips of filler material, the greater w be the pressure on the adhesive when the filler material expands during the heating stage. B if the filler material is to regain maximum strength, the filler material must expand as complete as possible, so that the cells in the material will have maximum spherical form and thus give t desired strength. The filler material is then placed in a heating unit that has been heated to approx. 8CP After heating, the filler material is then placed in a press where it is compressed to approx. 20 50% of its original thickness. During this operation, the filler material can be coated with a fil of hot melt adhesive which, because of the pressure and the heat from the filler material, wi adhere to the filler material in the designed manner. If the film of hot melt adhesive is prepare a few minutes before it is applied (just before the press stage), some hot melt adhesives will sti adhere to the filler material even after they have stiffened. The hot melt adhesive can also be applied to the filler material at a later stage. T simplest way is to fold the adhesive film around the strip of filler material before it is inserte into the joint area. The adhesive film may even consist of two separate layers applied one to eac side of the' filler material. Heating by means of microwaves The compressed strips of filler material are inserted into the joint area and are heated by mean of electromagnetic radiation, e.g. microwaves. The hot melt adhesive, consisting e.g. polyurethane, is affected by the elecromagnetic field and thus becomes heated. The filler materi is indirectly heated when the adhesive is heated. Since the electromagnetic field is formed in suc a way that it is homogeneous in the area of the joint, an immediate and uniform heating of th hot melt adhesive takes place. The indirect heating of the filler material is, thereby, also unifor Expansion is uniform and an evenly distributed pressure on the adhesive is obtained. In most cases where sandwich constructions are used in ships and boats, PVC is used a core material. PVC is affected hardly at all by the electromagnetic field and thus will not becom heated. The same app es to t e er mate a w c , w t a vantage, can e made o t e sam material as the core material. The only heating that takes place comes from the hot melt adhesiv which comprises a very small volume of the whole assembly. This heat is enough, however, t cause the filler material to expand to the desired extent. The filler material in compressed stat is so thin, and contains so little mass in relation to the width of the joint area, that it become heated without difficulty. The finishing stage of the process is limited to removing excess hot melt adhesive whic has been pressed out during the expansion stage. What remains, after the hardening process i complete, is a well-filled, load-bearing joint. Other cellular plastics than PVC can be used as filler material, or as core material, e.g cellular plastic of PUR, PS, etc. Most cellular plastics are little affected by electromagneti radiation, and thus the advantages of the heating procedure are retained, i.e. unnecessary heatin of the base material is avoided. Note also that although polyurethane in the form of hot mel adhesive becomes heated very quickly, a cellular plastic of the same material becomes hardly heated at all by electromagnetic radiation during the same period of time. After a sufficiently long period of time, however, most cellular plastic materials will eventually become heated through e.g. microwave radiation. For e.g. PVC, however, this occurs in an unstable manner, which causes an uncontrolled temperature rise locally in the material. This is not desirable, and thus indirect healing is more advantageous. It is also possible, during the chemical process used in the production of cellular plastic materials, to use additives which are affected by electromagnetic radiation. Examples of such additives are powdered coal and powdered steel. This makes the material more expensive, however, and also creates problems during foaming. Thus, it is difficult to obtain cellular plastic material with sufficiently good properties. Heating with hot air When building ships or boats with sandwich construction, heat can be applied by means of a hot air device, electric blankets, etc. When heating by means of hot air, care must be taken to regulate the temperature so that the material of which the construction is comprised will not be damaged. This is particularly important in large constructions where the heat is to be applied for relatively long periods of time, e.g. for a few hours at a time.

Claims: PATENT CLAIMS 1. A method for forming a load-bearing joint, characterized by the use of a cellular plasti material as filler material (2); by the compression of the cellular plastic to a form that is stabl at room temperature(3); by applying adhesive (4) to the bonding surfaces of at least the fill material, fig. 4; by inserting the filler material, (3) and (4), into the joint area (1), fig. 4; and b causing the filler material to expand by means of heating so that the fusion surfaces of the fill material are pressed against the restricting surfaces of the joint area, fig. 5, after which the fill material is allowed to cool. 2. A method as claimed in claim 1, characterized by the use of an adhesive (4) which is hot melt adhesive or a hot melt adhesive with setting agent, said adhesive being made to me during the heating phase of the filler material. 3. A method as claimed in claim 1, characterized by the use of a one or two-componen adhesive (4) in liquid form. 4. A method as claimed in claim 1, characterized by the use of a one or two-componen adhesive (4) in liquid form, or the use of a hot melt adhesive or a hot melt adhesive with settin agent, said adhesive being heated by means of electromagnetic radiation. 5. A filler material used to form a load-bearing joint, characterized by a strip of compressed cellular plastic (3) which expands under heat, and which has been coated on opposite sides with an adhesive film (4), fig. 4.

Inventors: DOLK AAKE, GRIP SVEN, LOENNOE ANDERS, DOLK, AAKE, GRIP, SVEN, LOENNOE, ANDERS
Applicants: DOLK AAKE, GRIP SVEN, LOENNOE ANDERS, DOLK, AAKE, GRIP, SVEN, LOENNOE, ANDERS
Application year: 1992
Main classification: B29C65
IPC codes: B29C65, B29K105, B29L31, C09J5, E04B1