Technical Field The present invention relates to the art of joining construction materials by plugs.

Background Art 5. Plastic plugs of different types are nowadays used for joining of chipboard and the like at e.g. furniture joine¬ ries. By different methods these plugs are fitted into pre- -bored holes through and in the boards. These plugs have in common that they are of certain dimensions and that they in

10. some cases can expand at the fitting into the hole. This means that holes of certain dimensions must be bored in or¬ der to fit the plug. Other disadvantages of these systems are among other things that for the solid plugs the diame¬ ter of the holes must be adjusted quite precisely. The holes

15. must be precisely bored so that the plug will not make the board crack at the fitting. This is to a even higher degree essential for the plugs which expand when they are driven in. When the plugs are pressed into the holes in order to give a satisfactory grip they subject the material to stres-

20. ses which can give rise to cracks etc.

Disclosure of Invention The present invention eliminates these problems and does also give other advantages. This is attained by the steps and means stated in the claims.

25. The invention relates to a method and a device for in¬ jecting plastic material according to an extrusion-process directly into the holes made in the chipboards or other pla¬ tes, as well as to the replacement of conventional plugs with this plastic material with the advantages which are

30. obtained herebv.

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It is not necessary to select different dimensions for different holes.

The plastic material can be injected under pressure 5. whereby it penetrates ^' into pores in the material and gives a better hold than plugs which are driven in mechanically. As the plastic material is injected in a liquid state it does not give rise to the stresses and risk of cracks which are caused by driving a plug in mechanically.

10. The plastic material injected in liquid form is net subjected to stresses or cold creep wherefore the obtained plug retains its dimensions better than plugs which have been driven in.

One is not reduced to using the plugs and the colours

15. which are offered for sale. It is possible to buy optional plastic materials and colour them as desired.

The plug can be made to have an elevation above the edge of the hole. Hereby the plug can be filed to the leve of the chipboard whereby post-puttying is not necessary as

20. is in certain cases with conventional plastic plugs when th aι*§ driven in beneath the surface of the board.

As plastic material all types can be used which can b transformed from fluid to solid form at ambient temperatur and which have sufficient strength and capacity of adheren

25• to the joined material in order to give a joint of satisfa tory strength. Curable resin systems can be used, such as epoxy adhesives or formaldehyde based pre-condensates with phenol, resorcinol, melamin or urea. Curable adhesives do however cause problems as there is a risk of pre-curing in

30. the apparatus and a relatively long delay before the curi is complete. The curable adhesives are further generally expensive and tend to contract and to crackle during the curing thus making fillers or reinforcing material require for a reliable joint. Thermoplastics do not have these dra

35• backs and are consequently preferred in connection with th invention. They are warmed to a fluid state before they ar filled into the joining cavity or bored hole and are then very rapidly solidified so that long delays during which t parts must be kept together by mechanical means are avoide

They can be stored for unlimited time without problems of clogging, they do not contract severely in connection with the solidification and they are comparatively cheap. Poly¬ ethylene is the preferred thermoplastic. Other suitable. 5. thermoplastics are polystyrene and polyvinyl chloride.

The plastic material is first of all, and preferably, intended to alone form the joint between the parts without the assistance of screws, nails or suchlike which have sub¬ sequently been driven in. The greatest simplification by

10. means of the invention is gained this way. For certain pur¬ poses it might however be suitable to add to the plastic material in the cavity a reinforcement of metal, wooden plug or the like, which reinforcement then preferably is of con¬ siderably smaller volume than the cavity and is introduced

15. into the joining cavity before the solidification of the plastic material, before or after the moulding thereof in the cavity. Depending on the additional working moment this - means and the problems of certain size adjustment of the re¬ inforcement, a plastic joint without reinforcement is pre-

20. ferred. It can however be advantageous to add a filler in powder form to the plastic material in order to extend it, increase the strength and counteract contraction. The filler is then suitatly present as an additive to the starting ma¬ terial to avoid additional working moment for the addition

25. of the filler at the fitting. Wood flour, plastic powder or inorganic powders are suitable fillers. A certain simplifi¬ cation of conventional screw joints with plugs can be obtai¬ ned according to the invention as size adjustment of the plug and risks of mistakes connected therewith are elimina-

30. ted. In these cases the screw is easily pressed or screwed in when the plastic has been moulded in the cavity and pre¬ ferably before it is completely solidified. The screw can be smaller than the actual cavity or somewhat larger, in the later case stresses in the material will however arise. A

35- screw joint of this type is however more complicated than a pure plastic plug joint, with our without reinforcement according to what has been said above.

The method according to the invention is preferred for wood materials such as pure wood, or composite materiaj_&

such as chipboard, fibre-board, paper board and the l ke. Materials which are not based on cellulose can also be joined according to the invention, e.g. plaster board. The condition for this is then generally that the materials are, 5. or can be made, porous at the joining cavity so that the plastic material will get a grip. Materials which do not satisfy these conditions may be included but only if the plastic material has a good adherence to the material or if the material is present between materials having better ad-

10. herence to the plastic material. In some cases such mate¬ rials can be joined by a cavity ^" of conical or other shape which does not allow the plug to move out of the cavity. Although porous or rough materials can be effectively . held together by. a simple conical connecting bore-hole it is

15. all the same preferred also in these cases to use a cavity with conical or otherwise enlarged shape of the central parts relative to the opening to these parts in order to provide an additional fastening mechanism. A simple and preferred way of obtaining such a back-release security is to assemble

20. the parts to be joined and to drill the connecting hole through all the parts at the same time and then tilt or ro¬ tate the drill when in the hole. The largest movements of the drill will then be performed by its tip and its base around a more static node-point therebetween. The bore-hole

25. will hence have a shape like a double-cone with its largest circumference at the top and bottom and a waist portion therebetween with less circumference and this form of the hole will give satisfactory back-release security rather independently of the exact position of the joint surface in

30. relation to the waist portion. Of course a similar shaping can be obtained by other means, for example a cone-shaped drill by which the hole is drilled from two different direc¬ tions, but in general such other alternative methods are more complicated and require more elaborate equipment than

35. the method outlined above. By use of two or more joining cavities in co-operation with each other it is possible to obtain another type of back-release security, for example by drilling two holes with different angles relative the joint

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It is evident that the exact shape of the connecting hole is not critical since the injected fluid material can fill up most cavity forms unless the cavity includes very

^• 5 - long or thin parts in which case the solidification of first injected material can prevent penetration of further material to the innermost parts of the cavity. It is for example not necessary that the material is injected in the same direction as the hole is drilled but it is also possible to provide a

10. separate hole or channel into the cavity for the injection of material. A separate injection hole can be used to inject the material into an otherwise closed cavity, whereby the injection hole can be drilled rather freely, for example in a hidden place. A closed cavity can for example be formed

15. by drilling a hole from the joint surface of both parts to be joined a bit into the material but not through it and then placing the parts together with their hole openings opposite each other so as to form the closed cavity. An injec¬ tion hole can then be drilled from any desired place into the

20. cavity.

It is not necessary that the cavity to be filled with plastic material is closed except for the opening necessary to introduce the material. It is for example possible to have a connecting hole which extends fully through the materials

25. to be joined thereby forming at least two openings to the cavity. In such a situation the cavity can be filled with the plastic material by use of a form, a plug or an additio¬ nal filling machine pressed to the second opening. In order to avoid additional means for the filling it is, however, pre-

30. ferred that the connecting cavity is closed except for the injection opening which can be the bore-hole opening or a specially formed opening as above discussed. By a closed cavi¬ ty shall also be understood a cavity in which one or more openings has first been closed by the introduction of a small

35- amount of plastic material which has been allowed to solidify to close the opening before introduction of the rest of the material to fill up the complete cavity volume.

Besides giving great variability in the possible layout of the connecting cavities, the present invention also gives

certa n var a t es n e poss e unc ons o e n¬ jected materials. In addition to forming the bond between the parts, the plastic material can also act as a sealant between the parts when it is injected in such a way as also

'5. to form a layer in the gaps between the parts over the hole or a part of the joined surfaces. In the same way elastic properties can be given to the joint if an elastic plastic material is selected.

The plastic material can be moulded into the cavity

10. without pressure but injection under pressure is preferred as it improves the filling degree in the hole, the wetting to the material and causes a limited penetration into the pores of the material. Suitably a supply pressure between

0.5 and 10 kp/cm 2 and preferably between 1 and 5 kp/cm2 is

15- used. The best way of obtaining a pressure in the hole is t in some way seal the mouthpiece of the injection device to the hole opening and then apply the necessary force to the device, during the filling procedure or at least the last part of it. To avoid the disadvantages with shrinking of th

20. plastic material pressure can be applied also during solidi fication.

The plugging process according to the invention can ma up the only joint of the treated parts or it can be supplem ted with gluing in other surfaces or other joining methods.

25. A preferred embodiment of a device for carrying out th method is shown in the accompanying drawing. The device con sists of an apparatus 1 which can be fitted to a convention hobby machine, drilling machine or other actuating means 2. Preferably the activating means 2 are selected to make the

30. entire unit portable and easy to work by hand. It is prefer that the actuating means or the other parts of the device i provided with a handle, grip area or similar means placed t facilitate a manually applied pressure force to the unit in the extrusion direction. The injection part consists of a

35. holder device 3 which in a suitable manner is connected di¬ rectly to the boring machine or fixed to this. Further it comprises a helicoidal axis or spindle 4 designed to work t designed to work the plastic and press it forward by extru sion. The screw H is fitted to the chuck or actuating axis

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runs in a cylinder 6 adjusted for extrusion and pressing forward of the plastic. Electrical heating elements 7 are inserted in the cylinder β or mounted on the outside. These

^' 5 - can be connected to ordinary wall sockets and the heat is controlled by conventional thermostat or thermoelement sys¬ tems. The cylinder ends in a nozzle 8 which can be replace¬ able and adjusted to different holes in the chipboards and slabs. Preferably the size of the nozzle is such as to allow 10. insertion of at least a part of it into the injection hole allowing sealing of the nozzle against the hole opening. The nozzle preferably has a circular cross-section and most pre¬ ferably has a conical configuration. Due to the generally slippery properties of the fluid plastic material it has

15. been found difficult to center the nozzle over the injection hole unless the nozzle penetrates a bit into it. The sealing possibility is preferred for making injection under pressure possible. The conical shape makes it possible to use the same nozzle for different hole diameters, improves the sealing at

20. a given applied force, enhances the pressure in the hole for a given applie'd force by minimizing the area over which the force is applied and improves distribution and filling degree in the hole by allowing small movements of the nozzle tip in the hole. In order to obtain these advantages the closing

25. angle of the tip should suitably not exceed 90° and preferab¬ ly not 60°. In order to avoid a too deep penetration in holes with large openings and to avoid breakage due to wedge effects the angle should suitably exceed 10° and preferably exceed 20°. In one part of the cylinder and the screw a receptacle

30. for the plastic material 9 is attached via an opening. This receptacle can have a lid 10, optionally supplemented with a pressure plate with a spring 11 which presses the plastic ma¬ terial down into the cylinder if this is necessary. Preferab¬ ly the plastic material is automatically fed to the extruder

35- screw from the hopper in a conventional manner. Preferably the hopper is designed in such a manner as to allow free flow of plastic material into the screw independent of the working position of the device. To make this possible the receptacle must be closed, the feeding area 9 to the screw must not be

too small, the spring 11, or other transporting mecha¬ nism, pressure must not be too small and the plastic materi must be in a suitable form, e.g. fluid or pelletized. The r ceptacle can either be permanently fixed to the device or 5. can be equipped with fastening means allowing replacement of cassette-like receptacles, e.g. for different colours or qualities of plastic materials.

In case the number of revolutions of the boring machin is not sufficiently low the device can e.g. be supplemented

10. with a gear change device between the boring machine and th screw which makes a lower number of revolutions possible. This gear change device can be of conventional type. The device works in the following manner. Thermoplastic material of suitable quality, and desire

15. colour, in granular form is filled in the hopper. The cylin is warmed to a suitable temperature. The nozzle 9 of the ap ratus is connected to holes 13 bored in the chipboards 12, which are assembled against each other in a conventional ma ner. When the boring machine is operated in ordinary manner

20. the extruder screw rotates and the melted plastic material is with pressure pressed into the cavity in the boards. Whe the apparatus is removed the cavities are filled with plast material which has been injected under pressure and which solidifies forming a plastic plug.