Thermally modified repair insert for sealing defects in thermally modified wood products

Abstract

This utility model relates to the woodworking industry and can be used to repair decking, planks, and facade elements made of thermally modified wood. The technical problem is that currently, holes caused by fallen or broken knots in thermally modified wood are filled with putty, which leaves visible stains, and branches and knots, which are production waste, are not used for repairs. A thermally modified knot is proposed, consisting of a cylindrical pin made from a branch of the same species as the item being repaired. The repair pin is thermally modified along with the lumber being repaired, and its side surface is roughened. The technical result is an increased fixation strength of the repair pin in the hole and a longer-lasting repair due to the equal expansion of the repair pin and the base due to temperature and humidity, combined with the developed roughness, which increases mechanical adhesion.Additionally, the repair is visually unnoticeable due to the preservation of the annual ring pattern and the identical color of the thermally modified wood. 6 z.p. f-ly.

Description

[0001] FIELD OF TECHNOLOGY

[0002] The utility model relates to the woodworking industry, in particular to devices for the restoration and repair of products made from thermally modified wood, namely to repair pins designed to fill holes from fallen or burst knots in calibrated boards, terrace and deck boards, planks, facade elements and other moldings used in conditions of variable humidity, ultraviolet radiation and temperature.

[0003] STATE OF THE ART

[0004] Currently, the production technology for thermally modified wood products lacks an effective method for mechanically sealing holes caused by fallen or cracked knots. Common practice is to fill such defects with fillers, mastics, or adhesives. These compounds, after drying and finishing, remain visually visible, forming noticeable stains that disrupt the uniformity of the texture and color of the thermally modified wood. At the same time, branches, an inevitable waste product of sawmills and woodworking industries, are not properly utilized and are typically disposed of or incinerated. In fact, their natural structure, shape, and annual rings are most similar to fallen knots and could serve as ideal blanks for repair pins if they are given the properties of thermally modified wood.

[0005] A wooden plug for patching knots in boards is known from the prior art, according to Author's Certificate SU 38775 A1, published on September 30, 1934. This plug is made from scrap lumber of the same species as the item being repaired and has a conical side surface. A hole for this plug is made with a step or conical drill bit, after which the plug is glued in.

[0006] A drawback of the known device is that it is not intended for use with thermally modified wood. The physical and mechanical properties of ordinary dried cork differ significantly from those of thermally modified wood treated in a superheated steam environment at temperatures ranging from 180 to 230 degrees Celsius. Due to the difference in temperature and humidity expansion between the cork and the substrate, cracking of the glue joint and cork loss occur over time. Furthermore, the smooth conical surface does not provide reliable mechanical adhesion under the reduced adhesive properties of thermally modified wood.

[0007] The closest analog, adopted as a prototype, is a repair plug used in the method for sealing knotholes according to Russian Patent No. 2157753 C2, published on October 20, 2000. The plug in the prototype is a cylindrical piece made from a branch of the same tree species as the item being repaired, with a chamfer on one end. Using a branch as a blank allows for the preservation of the natural pattern of annual rings, similar to the texture of a fallen knot, thereby enhancing the aesthetics of the repair.

[0008] However, the cork in the prototype is not thermally modified and has a smooth side surface. Since the repaired part is made of thermally modified wood, which has reduced wettability and poor adhesion to adhesives, the smooth surface of the cork is unable to compensate for the lack of chemical adhesion with mechanical adhesion. Furthermore, the coefficient of temperature-humidity expansion of the cork material does not match that of thermally modified wood, leading to internal stress in the glue joint due to seasonal fluctuations in humidity and temperature, and, consequently, failure of the repaired part.

[0009] DISCLOSURE OF THE ESSENCE OF THE UTILITY MODEL

[0010] The problem that the claimed utility model is aimed at solving is the creation of a repair pin for thermally modified wood that provides increased strength of fixation in the hole and durability of the repair.

[0011] The technical result achieved by using the utility model consists in increasing the force of holding the repair pin in the hole due to the combination of temperature-humidity expansion identical to the base and a developed rough surface that increases mechanical adhesion.

[0012] The essence of the utility model is that a thermally modified repair insert for patching defects in thermally modified wood products is a repair pin made from a wood branch with the same chemical composition, the same degree of thermal modification, and the same grain direction as the lumber being repaired, with a final moisture content in the range of 3-7%, corresponding to the moisture content of the board being repaired. The difference is that the side surface of the repair pin is made with a microrelief. The microrelief can be created mechanically, for example, by sandblasting, abrasive machining, or knurling, or obtained directly by turning the workpiece without subsequent finish grinding. It can be made in the form of a spiral thread or annular grooves of a triangular profile with a depth of 0.1-0.5 mm and a pitch of 1-3 mm, forming cavities for placing and holding the adhesive composition.It is the microrelief, combined with the thermally modified state of the pin material, that ensures the technical result. The developed microrelief increases the contact area between the pin and the hole walls and creates multiple zones of mechanical engagement between the pin's microroughness and the thermally modified wood fibers after the adhesive polymerizes. Furthermore, the identical physical and mechanical properties of the pin and the base, due to the same thermal modification regime, guarantees equal response of both elements to changes in temperature and humidity, preventing the occurrence of destructive stresses at the interface.

[0013] In specific embodiments of the utility model, a small-diameter blind hole may be made in the body of the repair pin at one end to compensate for excess adhesive and air pressure during installation. The product may also have a swirl texture with a radial grain orientation identical to the texture of the knot being replaced, as well as an eccentric core offset from the geometric center. The diameter of the repair pin ranges from 10 to 100 mm and is determined by the size of the fallen knot.

[0014] IMPLEMENTATION OF A UTILITY MODEL

[0015] The claimed thermally modified repair insert is manufactured as follows. During the pre-production stage, branches of the same wood species as the lumber being repaired are selected. The blanks are loaded into the thermal modification chamber along with the base material—boards or planks. Thermal modification is carried out in a superheated steam environment at a temperature of 180 to 230°C, maintaining the conditions established to achieve the desired degree of thermal modification and color tone. After the chamber has cooled, the thermally modified branches are cut into sections whose thickness exceeds that of the item being repaired, allowing for an allowance. The resulting blanks are turned on a lathe to the desired diameter, corresponding to the diameter of the calibrated hole prepared in the board. During turning, final grinding is intentionally avoided; instead, a cutting mode is selected that creates the desired roughness on the side surface.Alternatively, roughness can be achieved by a separate sandblasting or abrasive processing operation.

[0016] The hole in the thermally modified board being repaired is prepared by drilling or milling the fallen knot area to a calibrated diameter, ensuring a clearance of 0.1-0.3 mm between the hole wall and the repair pin. During installation, a weather-resistant adhesive is applied to the side surface of the repair pin or to the hole walls. The repair pin is then oriented, aligning the direction of the annual rings with the grain of the board. The repair pin is pressed into the hole with a hammer until excess adhesive is released. It is then trimmed flush with the board surface, and the repair area is sanded.

[0017] Tests confirmed that a thermally modified knot with a microrelief on its side surface can withstand at least twenty cycles of alternating soaking and drying without developing defects along the cork's contour, while smooth corks exhibit delamination under similar conditions. The pull-out strength of roughened pins is 18-25% higher than that of smooth-surfaced plugs of the same diameter. The repair remains visually invisible due to the matching color of the thermally modified wood and the texture of the annual rings.

Claims

1. A thermally modified repair insert for sealing defects in thermally modified wood products, made in the form of a cylindrical wooden rod - a pin made from a branch, wherein the side surface of the repair pin is made with a microrelief.

2. An insert according to paragraph 1, characterized in that the microrelief is made in the form of a spiral thread or annular grooves of a triangular profile with a depth of 0.1-0.5 mm and a pitch of 1-3 mm, forming cavities for placing and holding the adhesive composition.

3. An insert according to paragraph 1, characterized in that the side surface is additionally provided with a relief in the form of a helical groove, annular notches or longitudinal grooves.

4. An insert according to paragraph 1, characterized in that a central blind hole is made on the side of one of the ends to compensate for excess pressure of glue and air during pressing.

5. The insert according to paragraph 1, characterized in that the diameter is in the range from 10 to 100 mm.

6. An insert according to paragraph 1, characterized in that it has a final moisture content in the range of 3-7%.

7. An insert according to paragraph 1, characterized in that it has a wavy texture with radial fiber orientation, as well as a core offset from the geometric center - eccentricity.