Solid wood floor blank heat treatment method based on microwaves

Abstract

The invention discloses a microwave-based solid wood floor blank heat treatment method, which comprises microwave heating treatment and moisture content adjustment treatment on a floor blank, and is characterized in that microwave is used as a heat source, and the internal target temperature of wood is obtained by accurately controlling the microwave heating treatment time. According to the method, the technical problems that in the existing wood floor blank heat treatment process, a heating system and equipment are complex, the heat treatment period is long, the heat treatment temperature and the heat treatment duration cannot be accurately controlled, and continuous treatment cannot be carried out are solved, microwaves serve as a heat source, and the internal target temperature of wood is obtained by controlling the treatment time; the treatment process can be accurately controlled according to process requirements, and the method has the advantages of simple equipment, high heating efficiency, strong process controllability, good treatment quality and short treatment period.

Description

Technical Field

[0001] The invention relates to a microwave treatment device and method for wood, in particular to a stabilization treatment method for solid wood floor blanks, and belongs to the technical field of wood functionality improvement. Background Art

[0002] Solid wood flooring is widely loved by consumers for its durability, safety and good feel underfoot. However, due to the characteristics of wood itself, it shrinks when dry and expands when wet, solid wood flooring is not stable during use. When the indoor temperature and humidity change, it is prone to problems such as arching, warping and deformation.

[0003] There are many studies on conventional heat treatment methods for existing wood. For example, patent 202410848941.4 discloses a heat treatment method for wood, comprising the following steps: S1: Treat the wood to be treated into absolute dry wood. S2: Place the absolute dry wood in a constant temperature environment for heating treatment. S3: Cool the heated absolute dry wood. S4: Repeat steps S2-S3 several times to obtain surface heat-treated wood. The mass loss rate of the surface layer in the surface heat-treated wood is greater than or equal to the overall average mass loss rate of the wood, the mass loss rate of the core layer is less than the overall average mass loss rate of the wood, and the thickness of the surface layer is 10-37.5% of the total thickness of the wood. This method controls the thickness of the surface layer of the wood that has undergone thermal modification to 10-37.5% of the total thickness of the wood by repeated heating and cooling treatment. The heat-treated wood with a surface thickness in this range can allow less moisture in the external environment to enter the core layer through the surface layer during later use, avoiding significant shrinkage and swelling of the core layer, ensuring that the heat-treated wood has good dimensional stability, and at the same time retaining a high degree of mechanical properties of the heat-treated wood. This method only heat treats the surface of the wood, causing the surface color of the wood to deepen and lose its natural color, which is not conducive to market sales; and during the heat treatment of the wood, the wood is not fixed and placed naturally, causing the wood to deform during the heat treatment. Patent CN201710332678.3 discloses a method for preparing a heat-modified solid wood floor blank for floor heating, which uses a process of low-temperature heat treatment, low-temperature drying, high-temperature drying, high-temperature heat treatment, cooling and humidity control treatment, and curing of the solid wood floor blank for a total of 3 heat treatments, 2 dryings, and 1 curing. This method is completed in a conventional wood drying kiln, a wood high-temperature carbonization chamber, and a wood curing room. Although the defects such as cracking and deformation caused by internal stress and uneven moisture content are reduced through the early low-temperature heat treatment and low-temperature drying, and the qualified rate of solid wood floor blanks is improved, this method uses a traditional heat treatment method, starts heating from the surface of the wood, and the surface is severely carbonized, the color is deepened, and continuous processing cannot be performed.

[0004] Research on the use of microwaves for heat treatment of wood is becoming increasingly prosperous. For example, Patent 202111153625.8 discloses a production process for heat-modified anti-deformation home door panels, the structure of which consists of a core board layer, a middle board layer, a balance layer, and a finishing layer; the heat-modified anti-deformation home door panel production process includes using MJB-TF wood stabilizer to treat the prepared core board strips and middle boards and placing them in a microwave drying kiln for dehydration and carbonization; by using wood stabilizers, the original physical structure of the wood (i.e., internal stress) is destroyed, its fiber toughness is increased, the parallel extension tension of its wood fibers is increased, the wood is kept stable, and the brittleness of the wood caused by carbonization is reduced; in the microwave high-frequency carbonization treatment process, a steam rehumidification process is added to make the carbonization degree of various parts of the board more uniform, effectively improve the dimensional stability, and maintain the stability of various mechanical properties of the board. Patent 202110035298.X discloses a method for medium-temperature heat treatment of floor wood, which uses vacuum and microwave drying kilns for medium-temperature heat treatment, so that the moisture content of the treated wood is between carbonized wood and ordinary wood; the treated wood can not only suppress the high moisture absorption rate of ordinary wood, but also avoid the problem of carbonized wood being prone to cracking and inelasticity after extreme drying. During the treatment process, the wood is only in contact with water vapor and hot air, without adding any chemical reagents, which maintains the natural nature of the wood, is pollution-free, and has good environmental stability and anti-corrosion properties, and is not easily affected by the surrounding environment. This method uses medium-temperature heat treatment with vacuum and microwave drying, which cannot achieve the effect of reducing the hygroscopic components inside the wood during high-temperature heat treatment, and cannot improve the dimensional stability of the wood. Patent 202011329252.0 discloses a wood modification heat treatment process. First, the wood blanks are placed on a trolley at intervals and stacked vertically in multiple layers. Downward pressure is applied on the top to balance the force on all parts of the wood blanks and keep them flat. Then, the wood blanks undergo the following treatment steps in sequence: S1. Nitrogen replacement and preheating treatment: vacuum the kiln, replace nitrogen, and preheat; S2. Heating treatment: heat and dehumidify the kiln; S3. Deep drying treatment: thoroughly dry the kiln; S4. Vacuum microwave carbonization treatment: vacuum microwave carbonization treatment is performed on the kiln; S5. Slow cooling treatment: slow cooling is performed under nitrogen protection; S6. Rapid cooling treatment; S7. Rehumidification treatment: steam is introduced into the furnace to make the blanks reach a certain moisture content before they are discharged from the kiln. Although this method reduces the impact of high-temperature carbonization on the color of wood while ensuring the dimensional stability of the wood, the wood is completely dried during microwave carbonization, and the color of the wood surface will deepen during the heat treatment. It is also impossible to accurately control the internal temperature field of the wood during microwave carbonization, and thus it is impossible to achieve precise control of the heat treatment. At the same time, continuous carbonization cannot be achieved.Patent 201510699043.8 discloses a method for processing solid wood floor blanks for floor heating, which method places the solid wood floor blanks in a microwave processing device with negative pressure and performs the following treatments: a. preheating treatment stage, pressure 0.02-0.05MPa, so that the surface temperature of the floor blank is 50-80°C, and the treatment time is 3-5 hours; b. heating stage, pressure 0.05-0.09MPa, floor blank surface temperature 110-130°C; treatment time 1-3 hours; c. high temperature treatment stage, pressure 0.07-0.1MPa, floor blank surface temperature 150-180°C, treatment time 2-5 hours; d. cooling stage, pressure 0.1MPa, ventilation and cooling, so that the surface temperature of the floor blank drops below 50°C; e. placing the treated floor blank in a balance chamber with a temperature of 30-50°C and a relative humidity of 70-80%, treating for 7-12 days, so that the moisture content is 5%-7%. Although this method realizes high-temperature heat treatment inside the floor blank and the surface temperature is always lower than 180°C, which improves the dimensional stability of the solid wood floor and keeps the surface natural color, this method is still a traditional heat treatment method. The surface temperature of the wood is heated, and then the temperature is gradually increased to heat the wood. The color of the wood surface is darker and the original color of the wood cannot be maintained. Patent 201310067511.0 discloses a gradient color poplar weight gain sawn timber and its manufacturing method and gradient heat treatment device. The gradient color poplar weight gain sawn timber of the present invention has a gradient color from dark to light along its length. The manufacturing method of the sawn timber includes primary drying, microwave pretreatment, impregnation treatment, secondary drying and gradient heat treatment. The present invention also discloses a gradient heat treatment device, which includes a stainless steel cylinder and a heating device arranged at the bottom of the stainless steel cylinder, the stainless steel cylinder is vertically installed on the heating device, and there is a cavity in the stainless steel cylinder for placing the wood vertically along the length direction, and a fixing device for fixing the wood is provided in the cavity. The gradient color poplar wood weighted sawn timber of the present invention has the characteristics of high density, good decorative effect, excellent dimensional stability and weather resistance and durability, and the manufacturing method is simple and easy with low cost. The gradient heat treatment device of the present invention has a simple structure and good safety and stability.

[0005] Temperature is an important factor affecting wood heat treatment during the process. Too high temperature will reduce the quality of wood, and too low temperature will not achieve the treatment effect. Therefore, reasonable and accurate temperature control is the key to ensuring the quality of high-temperature heat-treated wood. Existing wood heat treatment methods mostly use superheated steam as the medium and heat the wood in the form of convection heat exchange, so that the surface temperature of the wood is always higher than the internal temperature. This method not only has a complex heating system and high equipment requirements, but also has a long processing time and low heating efficiency. It is impossible to process wood according to the needs of the wood use scenario and cannot maintain the original color of the wood. In addition, the processing cycle is long and the surface strength of the wood is reduced, which seriously affects the later use.

[0006] The present invention introduces microwave heating treatment into the high-temperature heat treatment process of wood, and accurately controls the internal temperature of the wood by accurately controlling the heating treatment time and microwave power. It not only solves the above-mentioned problem, but also solves the problem that metal sensors in microwave environments cannot be used, and the glass optical fiber that can be used to measure temperature in microwave environments is high in cost and has a low degree of industrial application. It plays an important role in improving the microwave heat treatment process of wood and the industrial application of this technology. Summary of the invention

[0007] The purpose of the present invention is to provide a microwave-based heat treatment method for wood floor blanks to address the technical problems such as the complex heating system and equipment, long heat treatment cycle, and inability to perform continuous treatment during the heat treatment of existing wood floor blanks using microwaves; the inability to accurately control the temperature and duration of the microwave heat treatment, resulting in the color of the floor blanks changing and deepening; and the inability to accurately adjust the dry-bulb temperature and dry-bulb temperature difference of the air medium during the moisture content control process after the heat treatment, resulting in the inability to accurately produce floors with the moisture content required by the floor manufacturer. The method uses microwaves as a heat source, and maintains constant internal and external heat treatment temperatures of the floor blank by precisely controlling the intermittent microwave heating treatment temperature and heating time, and precisely controls the total microwave heating time, so that the wood heat treatment always maintains a set target temperature, and the internal clock of the floor blank maintains the set heat treatment temperature; and the moisture content of the floor blank actually produced is highly consistent with the moisture content required by the design of the floor blank manufacturer, overcoming the defect that the moisture content of the existing floor blank actually produced deviates greatly from the moisture content required by the design. The floor blank prepared according to the heat treatment method of the present invention has good quality, maintains the original wood color of the wood, and the process conditions can be precisely controlled, the control method is simple, the heat treatment heating efficiency is high, and the treatment cycle is short.

[0008] To achieve the purpose of the present invention, the present invention provides a microwave-based heat treatment method for flooring blanks, comprising: performing microwave heating treatment and moisture content adjustment treatment on the flooring blanks.

[0009] Wherein, during the microwave heating process, an intermittent heating method is adopted to heat the floor blank.

[0010] In particular, the intermittent heating is to turn on the microwave to perform microwave heating treatment on the floor material; then turn off the microwave to perform heat balance treatment; then turn on the microwave to perform microwave heating treatment; then turn off the microwave to perform temperature balance treatment; the microwave is turned on and off alternately; the time for the microwave to be turned on and off once is a microwave intermittent heating treatment cycle.

[0011] In particular, the processing cycle of the intermittent heating method is, the microwave opening time τ kis (24-40)s, preferably 30s; the microwave off time τg is (3-8)s, preferably 5s.

[0012] In particular, the theoretical total duration of microwave heating of floor slabs τ s According to formula (1A), we can obtain:

[0013] τ s =τ×G 干 (1A)

[0014] In formula (1A), τ s is the theoretical total time of microwave heating treatment, min; τ is the theoretical time of microwave heating treatment per unit mass (i.e. per 1kg) of floor blank, min; G 干 is the absolute dry mass of the floor blank, kg; where:

[0015] τ is calculated according to formula (1):

[0016] τ=-258.0338+26.4828lnP+87.3956lnt-3.0108(lnP) 2 -7.3714(lnt) 2 -2.9406lntlnP (1)

[0017] In formula (1): P is the microwave power of microwave heating treatment, kW / m 3 ; t is the microwave heating treatment temperature, ℃; τ is the theoretical total time of microwave heating treatment per unit mass (i.e. per 1kg) of floor material, min.

[0018] In particular, it also includes calculating the number of microwave treatment cycles (i.e., the number of cycles of intermittent microwave heating) n during the intermittent microwave heating treatment of the floor slab according to formula (5),

[0019] n=τ s ×60 / (τ k +τg) (5)

[0020] In formula (5), n is the number of microwave treatment cycles, and n is rounded upward; τ s is the total duration of microwave heating treatment, min; τ k is the microwave on time in one microwave processing cycle, s; τg is the microwave off time in one microwave processing cycle, s.

[0021] In particular, the moisture content adjustment process comprises the following steps:

[0022] 1) According to the moisture content Mp of the finished floor material, calculate the mass G of the floor material after moisture content adjustment after microwave heating treatment p ;

[0023] 2) According to the equilibrium moisture content Mp of the finished floor material, the process control conditions for moisture content adjustment treatment are calculated and determined according to formula (2):

[0024]

[0025] In formula (2), Mp is the equilibrium moisture content of the finished floor material after moisture content adjustment treatment, %; T is the dry-bulb temperature of the air medium during moisture content adjustment treatment, °C; ΔT is the dry-bulb and wet-bulb temperature difference of the wet air medium during moisture content adjustment treatment, °C;

[0026] 3) placing the microwave-heated flooring blank in a wood moisture balance chamber, heating the air medium temperature to a dry-bulb temperature of T, and simultaneously monitoring the dry-bulb and wet-bulb temperatures of the air medium in the moisture balance chamber in real time;

[0027] When the dry-bulb and wet-bulb temperature difference of the air medium is greater than ΔT, water vapor is introduced into the balance room to humidify the air in the balance room until the dry-bulb and wet-bulb temperature difference of the air medium in the balance room reaches ΔT, and the introduction of water vapor is stopped;

[0028] When the dry bulb temperature of the air medium in the balance room is lower than T, the moisture balance room is heated until the dry bulb temperature of the air medium in the balance room reaches T, then the heating is stopped to keep the dry bulb temperature of the air medium in the balance room at T;

[0029] According to the temperature value of the air medium in the balance room monitored in real time, water vapor is introduced or stopped; the balance room is heated or stopped, and the dry bulb temperature of the air medium in the balance room is maintained at T, and the dry-bulb and wet-bulb temperature difference is ΔT;

[0030] 4) Real-time monitoring of the weight of the floor blank. When the weight of the floor blank reaches G p When the floor material is taken out from the moisture balance chamber, the floor material with a moisture content of Mp is obtained.

[0031] In particular, in step 1), the G is calculated according to formula (6): p :

[0032] G p =(1+Mp)G 干 (6)

[0033] In formula (6), M 平 is the final moisture content of the floor slab after moisture content adjustment, %; G p is the weight of the floor slab component after moisture content adjustment, kg; G 干 It is the absolute dry weight of the floor blank assembly, kg.

[0034] In particular, the moisture content Mp in step 1) is 6-12%.

[0035] In particular, the dry-bulb temperature of the air medium during the moisture content adjustment process in step 2) is 60-100°C.

[0036] In particular, the microwave heating temperature t is (120-260) ° C, preferably (140-220) ° C; the microwave heating power P is 4-30 kW / m 3 , preferably 8~20kW / m 3 .

[0037] The process of this method is:

[0038] 1. Determine the initial moisture content M of the floor material 初

[0039] Randomly sample from the pile of floor slabs to be processed and determine the initial moisture content of the floor slabs: weigh the initial weight G of the sampled floor slabs 0抽样 Then put the floor blank into an oven at a temperature of (100±3)℃ and dry it to a constant weight, and weigh it G 干抽样 , initial moisture content of floor slab M 初 , calculated according to the following formula:

[0040] M 初 =(G 0抽样 -G 干抽样 ) / G 干1 ×100% (3)

[0041] 2. Determine the weight of the floor blanks and install the floor blanks to be treated

[0042] (1) Calculation of the absolute dry weight of floor slabs

[0043] Randomly take out 10 to 15 (preferably 10) floorboards from the floorboard pile, weigh the mass G1, and combine the initial moisture content M of the floorboards. 木初 The floor blank has an absolute dry weight of G 干 for

[0044] G 干 =G1 / (1+M 木初 )

[0045] (2) Floor slab installation

[0046] Arrange the taken out floor blanks in parallel to form a floor blank assembly (i.e., blank assembly), then tighten the floor blank assembly and fix it with screws so that the floor blank does not deform during the heat treatment process, and prepare a floor blank treatment specimen (i.e., blank specimen), and weigh it. The total weight of the blank specimen is G Z .

[0047] The thickness of the blank assembly is the same as that of a single floor blank. Two adjacent floor blanks in the blank assembly are in close contact.

[0048] The blank assembly is fixed with a high temperature resistant plastic fastener, and then the floor blank assembly is tightened with a high temperature resistant plastic screw to obtain a floor blank treatment specimen.

[0049] The number of floor blanks is determined according to the cavity size of the microwave heat treatment device to ensure that the distance between the front and rear ends of the blank treatment specimen and the protective device during the heat treatment process is between 100 mm and 300 mm, preferably 200 mm.

[0050] In particular, at least two floor blanks to be heat-treated are arranged in parallel as a layer to form a blank assembly, wherein the floor blanks are arranged in parallel along the length direction of the blanks, and two adjacent blanks are tightly fitted along the length direction.

[0051] In particular, the number of floor blanks in each blank assembly is preferably 5-25 sheets, preferably 10-20 sheets.

[0052] In particular, the floor blank components are clamped at both ends of the floor blank in the width direction, fixed and tightened with screws to form a floor blank heat treatment specimen, referred to as a blank specimen.

[0053] In particular, the flooring blank is clamped at both ends of the flooring blank along the width direction using the clamping members to prevent the flooring blank from being deformed during the heat treatment process.

[0054] In particular, the clamping members are two rectangular plastic sheets, the length of which matches the sum of the widths of all the floorboards in the floorboard assembly, and the two plastic sheets are provided with corresponding screw holes.

[0055] Two sets of clamps (i.e. 4 plastic sheets) are placed on the upper and lower ends of the floor blank assembly, tighten the floor blank assembly, and then tighten it with screws.

[0056] In particular, the thickness of the floor slab is 15-25 mm, preferably 18-22 mm.

[0057] The left and right ends of the clamping system (i.e. the blank specimen) and the middle of the belt on the conveying device can be used.

[0058] 3. Microwave heating treatment of floor blanks

[0059] (1) Floor material feeding

[0060] 1) Place the blank processing specimen on the conveyor belt, ensuring that the clamping system with the floor blank installed is parallel to the conveyor belt and the width direction is located at the center of the conveyor belt;

[0061] 2) Start the conveyor belt and send the blank treatment specimen into the microwave treatment device (i.e., a sealed device with an openable / closable component and a microwave generator that can emit microwave sources, which can generate microwaves when opened), ensuring that the clamping system with the floor blank is completely inside the microwave treatment device;

[0062] (2) Selection of heat treatment process for floor slabs

[0063] 1) Determination of microwave heating temperature, microwave power and theoretical total microwave heating time per unit mass of floor blanks

[0064] The microwave heating temperature t of the floor blank is 120℃~260℃, preferably 140℃~220℃; the microwave heating power P is 4~30kW / m 3 , preferably 8~20kW / m 3 The microwave heating treatment time τ needs to be selected according to the treatment target temperature and the microwave power. In order to achieve the effect of improving the dimensional stability of the floor blank, it is calculated according to formula (1):

[0065] τ=-258.0338+26.4828lnP+87.3956lnt-3.0108(lnP) 2 -7.3714(lnt) 2 -2.9406lntlnP (1)

[0066] In formula (1): P is the microwave power of microwave heating treatment, kW / m 3 ; t is the microwave heating temperature, ℃; τ is the theoretical total time of microwave heating per unit mass (i.e. per 1kg) of flooring material, min. 2) Determination of heat treatment process for flooring material

[0067] Since microwave energy is relatively large, if it is turned on for a long time, the temperature of the floor slab will continue to rise, and it will be impossible to maintain the temperature required for heat treatment, and the energy consumption will be high. Therefore, in order to ensure that the temperature remains stable and reduce energy consumption during microwave heat treatment, an intermittent microwave treatment method is adopted, that is, the microwave is turned on and off alternately, that is, "turn on the microwave to perform microwave heating treatment on the floor slab; then turn off the microwave to perform heat balance treatment; then turn on the microwave to perform microwave heating treatment; then turn off the microwave to perform temperature balance treatment; the microwave is turned on and off alternately."

[0068] The time it takes for the microwave to be turned on and off once is defined as a microwave processing cycle, that is, a microwave processing cycle includes the microwave on processing time τ k and microwave off equilibrium time τg.

[0069] According to formula (1A), the theoretical total time τ for microwave heating of the floor material to be treated is calculated. s ,

[0070] τ s =τ×G 干 (1A)

[0071] In formula (1A), τ s is the theoretical total time of microwave heating treatment, min; τ is the theoretical time of microwave heating treatment per unit mass (i.e. per 1kg) of floor blank, min; G 干 is the absolute dry mass of the floor blank, kg;

[0072] The total duration of microwave treatment divided by one microwave cycle is the total number of cycles n of microwave treatment of the floor blank, where n is rounded upward to an integer.

[0073] According to formula (5), the number of microwave treatment cycles (i.e., the number of cycles of intermittent microwave heating) n during the intermittent microwave heating treatment of the floor blank is calculated.

[0074] n=τ s ×60 / (τ k +τg) (5)

[0075] In formula (5), n is the number of microwave treatment cycles, and n is rounded upward; τ s is the total duration of microwave heating treatment, min; τ k is the microwave on time in one microwave processing cycle, s; τg is the microwave off time in one microwave processing cycle, s.

[0076] The intermittent treatment time of microwave treatment in one microwave treatment cycle is (24~40)s / (3-8)s, that is, the duration of microwave on time τ k The microwave-off time (equilibrium time) τg is 24-40 s, preferably 30 s, and the microwave-off time (equilibrium time) τg is (3-8) s, preferably 5 s.

[0077] (3) Microwave heat treatment of floor slabs

[0078] 1) Input microwave heat treatment parameters

[0079] Adjust the microwave controller and input the heat treatment process, that is, the heat treatment temperature t, the microwave power P, and the microwave on time τ within a microwave treatment cycle. k (24~40)s, microwave off time τg(3-8)s.

[0080] According to formula (5), the total number of cycles n of microwave treatment is calculated, and n is rounded upward.

[0081] 2) Microwave heat treatment

[0082] Turn on the microwave treatment device to perform microwave heat treatment on the floor blank. The total treatment time τsj is n×(τ k +τg)s.

[0083] 4. Moisture content adjustment treatment

[0084] The moisture content of the floor material is low after microwave heat treatment. If the moisture content is not adjusted, it will absorb moisture and deform during later use. Therefore, the moisture content must be adjusted.

[0085] Microwave heat treatment sj Finally, the conveyor belt is started to send the blank treatment specimen into the moisture content adjustment system (i.e., moisture balance chamber) for moisture content balance treatment - moisture content adjustment.

[0086] (1) Balance process determination

[0087] Equilibrium moisture content of finished floor material M p The dry-bulb temperature during the moisture balance treatment is 60-100°C, preferably 80°C.

[0088] In order to ensure the final moisture content of the finished floor blank board, it can be controlled according to formula (2) based on the dry-bulb temperature and the dry-bulb and wet-bulb temperature difference.

[0089]

[0090] M p is the equilibrium moisture content, %; T is the dry bulb temperature, °C, ΔT is the dry-bulb and wet-bulb temperature difference, °C

[0091] (2) Determination of the weight of the clamping system of the floor blank (i.e. the blank specimen)

[0092] When the moisture content of the floor blank after heat treatment is M p , moisture content of floor slab components G p for:

[0093] G p =(1+M p )G 干

[0094] The weight difference of floor blank before and after treatment is

[0095] ΔG=G1-G p

[0096] The weight of the balanced clamping system of the floor blank is

[0097] G h =G Z -ΔG

[0098] (3) Moisture content adjustment treatment (i.e. moisture balance treatment)

[0099] Turn on the balance processing system and introduce humid air (water vapor) into the balance system. The parameters of the air medium are the dry bulb temperature T and the wet bulb temperature T-ΔT. Turn on the weight detection system (weight sensor) to measure the weight of the floor blank. When the weight obtained by the weight sensor is G h The balancing process is completed.

[0100] 5. Floor slabs come out of kiln

[0101] The conveyor belt is started to take the processed floor blanks out of the kiln (i.e., take them out of the balancing chamber) to obtain finished floor blanks.

[0102] Compared with the prior art, the advantages of the present invention are as follows:

[0103] 1. The present invention introduces the microwave heating process into the heat treatment process of floor blanks for the first time, with high heating efficiency and simple operation, thus solving the problem of low heating efficiency in the traditional heat treatment process;

[0104] 2. The method of the present invention accurately controls the operating process conditions of the microwave heating process according to the intrinsic relationship between the microwave power, the processing temperature and the processing time of the microwave heating process, and can achieve a constant internal temperature of the heat-treated wood under different powers, thereby achieving a stable heat treatment effect, and solving the problems that metal sensors cannot be used under microwave heating conditions, the temperature cannot be stably controlled, the quality of the heat-treated wood varies, and the glass fiber sensors are expensive, consumed quickly and have high costs.

[0105] 3. In the process of treating floorboards by the method of the present invention, the microwave heating treatment time is accurately adjusted according to the regulation of microwave power to achieve the same heat treatment effect and realize multi-power output. It can be applied to a variety of microwave heating treatment devices and has a wide range of adaptability;

[0106] 4. The heat treatment of the floor blank in the present invention is modularized by a plastic frame. The floor blank is always in a clamped state during the treatment process, the treated material is stable and does not deform, and the treatment quality is good;

[0107] 5. The method of the present invention can realize automatic control of both the microwave heat treatment process and the moisture content adjustment process, realize continuous processing of floor blanks, solve the problem that the heat treatment process cannot be carried out continuously, and has high processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Figure 1 It is a schematic structural diagram of the floor blank specimen to be processed according to the present invention.

[0109] Description of reference numerals:

[0110] 1. Floor blank; 2. Clamping parts; 3. Blank specimen; 4. Screws. DETAILED DESCRIPTION

[0111] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0112] The solid wood floor blanks subjected to heat treatment in the embodiments of the present invention are taken as oak wood floor blanks as an example, and other solid wood floor blanks are also applicable to the present invention, such as ash, oak or ash.

[0113] The size of the oak wood floor blank is 920mm×130mm×22mm. Other sizes such as length of 620mm-2220mm, width of 100mm-170mm, and thickness of 20mm-24mm are also suitable for the present invention.

[0114] Example 1

[0115] 1. Determine the initial moisture content M of the floor material to be treated 初

[0116] 1-1) Randomly select one piece of oak flooring blank from each of the four sides and the upper bottom of the pile of oak flooring blanks to be processed, and select a total of 5 pieces of flooring blanks as the sampling samples for the determination of the initial moisture content of the blanks. Weigh the initial mass G of the sampling samples. 0抽样 9.85kg;

[0117] 1-2) Place the five sampled floorboards in an oven at (100±3)℃ and dry them to a constant weight, and weigh them. 干抽样 is 8.8kg, and the initial moisture content M of the floor slab is calculated according to formula (3): 初 :

[0118] M 初 =(G 0抽样 -G 干抽样 ) / G 干抽样 ×100% (3)

[0119] M 初 =12%.

[0120] 2. Prepare heat-treated blank specimens and measure the weight of the blank specimens

[0121] 2-1) Randomly select 10 pieces from the pile of floorboards to be processed and weigh them G1 (20 kg). Calculate the absolute dry weight G of the 10 pieces of floorboards according to formula (4): 干 ;

[0122] G 干 =G1 / (1+M 初 ) (4)

[0123] Floor Billet M 初 = 12%, the absolute dry weight of 10 floor blanks is G 干 =20 / (1+0.12)=17.86(kg).

[0124] In formula (4), G 干 is the absolute dry weight of the floor blank of the randomly selected blank sample for heat treatment, kg; G1 is the initial weight of the floor blank of the randomly selected blank sample for heat treatment, kg; M 初 is the initial moisture content of the floor material to be treated, %.

[0125] In the specific embodiment of the present invention, 10 floor blanks are taken as an example for description, and other integer numbers of blanks, such as 5, 10, 20, etc., are also applicable to the method of the present invention.

[0126] 2-2) Arrange the 10 floorboards 32 extracted and weighed in parallel, that is, arrange the floorboards in parallel in the length direction, and arrange the adjacent two floorboards in close contact in the length direction to form a floorboard assembly (hereinafter referred to as the floorboard assembly). The initial mass of the floorboard assembly before microwave heating is G1 (20 kg), and the initial moisture content M 初 =12%; absolute dry mass G 干 =17.86kg.

[0127] 2-3) Clamp the blank assembly with a clamping member 33 made of a high temperature resistant plastic material, that is, the clamping member clamps the two ends of the blank assembly along the width direction of the floor blank 32, and finally fixes and tightens the blank assembly with a high temperature resistant plastic screw 31 to make a non-deformed floor blank heat treatment specimen (hereinafter referred to as the blank specimen) 3. The initial total weight of the blank specimen before microwave heating treatment is weighed as G Z The total weight of the fixed blank assembly is G. 固 =(G 夹+螺钉 ) is 3kg, which is the sum of the masses of the clamping piece and the plastic screw.

[0128] 3. Microwave heating process selection for flooring blanks

[0129] 3-1) Determine the theoretical time τ for microwave heating of unit mass of floor blanks

[0130] According to formula (1), the theoretical time τ for microwave heating per kg of floor material is determined:

[0131] τ=-258.0338+26.4828lnP+87.3956lnt-3.0108(lnP) 2 -7.3714(lnt) 2 -2.9406lntlnP (1)

[0132] In formula (1): P is the microwave power of microwave heating treatment, kW / m 3 ; t is the microwave heating treatment temperature, ℃; τ is the theoretical total time of microwave heating treatment per unit mass (per kg) of floor blanks, min.

[0133] 3-2) Calculate the theoretical total time τ for microwave heating of the floor material to be heat treated s

[0134] Due to the different quality of the processed materials under different processing conditions, in order to meet the processing conditions of different quality, the actual processing time is

[0135] τ s =τ×G 干 (1A)

[0136] In formula (1A), τ s is the theoretical total time of microwave heating treatment, min; τ is the theoretical time of microwave heating treatment per unit mass of floor blank, min; G 干 is the absolute dry mass of the blank component, kg;

[0137] In this embodiment, the microwave heating temperature t of the floor material is selected as 140°C, and the microwave power P is selected as 10kW / m 3 , absolute dry quality G 干 Taking 17.86 kg as an example, the theoretical total time τ for microwave heating treatment of unit mass of floor blanks is 5.39 min; the theoretical total time for heat treatment of floor blanks is calculated according to formula (1A) to be 96.3 minutes.

[0138] 3-3) Determination of microwave heating process for flooring blanks

[0139] 3-3A) Determination of microwave heating method

[0140] Since microwave heating has a large amount of energy, long-term microwave heating can easily lead to excessively high temperatures in the floorboards, making it impossible to maintain the heat treatment temperature of the floorboards (usually 120-260°C), and high energy consumption. In order to ensure that the heat treatment temperature of the floorboards is stable and reduce energy consumption during microwave heating, an intermittent microwave treatment method is used, that is, the microwaves are turned on and off alternately, that is, "turn on the microwaves to perform microwave heating treatment on the floorboards; then turn off the microwaves to perform heat balance treatment; then turn on the microwaves to perform microwave heating treatment; then turn off the microwaves to perform temperature balance treatment; the microwaves are turned on and off alternately."

[0141] The time it takes for the microwave to be turned on and off once is defined as a microwave processing cycle, that is, a microwave processing cycle includes the microwave on processing time τ k and microwave off equilibrium time τg.

[0142] The intermittent treatment time of microwave treatment in one microwave treatment cycle is (24~40)s / (3-8)s, that is, the duration of microwave on τ k The microwave-off time (equilibrium time) τg is 24-40 s, preferably 30 s, and the microwave-off time (equilibrium time) τg is (3-8) s, preferably 5 s.

[0143] 3-3B) Determination of the number of microwave heating cycles n

[0144] According to formula (5), the number of microwave treatment cycles (i.e., the number of cycles of intermittent microwave heating) n during the microwave heating process of the floor blank is calculated.

[0145] n=τ s ×60 / (τ k +τg) (5)

[0146] In formula (5), n is the number of microwave treatment cycles, and n is rounded upward; τ s is the total duration of microwave heating treatment, min; τ k is the microwave on time in one microwave processing cycle, s; τg is the microwave off time in one microwave processing cycle, s.

[0147] In this embodiment, in one microwave treatment cycle, the microwave is turned on for 30 seconds and the microwave is turned off for 5 seconds. The number of cycles of microwave on-off in intermittent microwave heating is n=τ s / (τ k +τg)=96.3×60 / 35=165.08.

[0148] n is rounded up to an integer 166 times.

[0149] In a microwave treatment cycle, the floor blank is heated by microwaves by turning on the microwaves; microwave heating τ kAfter that, turn off the microwave τg, and the heat is transferred inside the wood, and the temperature and heat inside the wood reach equilibrium. Cycle on and off the microwave to ensure that the temperature inside the wood remains constant at t. This avoids the situation where the temperature inside the wood continues to rise when the wood is always in a heated state, and the heat treatment temperature of the floor blank cannot be effectively controlled, resulting in defects such as internal cracking, carbonization, and even burning of the floor blank after heat treatment.

[0150] 4. Microwave heating treatment

[0151] 4-1) Floor material feeding

[0152] Placing the blank sample 3 on a conveyor belt, starting the conveyor belt, conveying the blank sample 3 into a microwave heating device, and sealing the microwave heating device;

[0153] 4-2) Input microwave heat treatment parameters

[0154] Adjust the microwave control generator in the microwave heating device and input the microwave heating process parameters, that is, the microwave heating temperature is 140℃ and the microwave power is 10kW / m 3 , in one microwave heating treatment cycle, the microwave opening time τ k The microwave on time τg is 30s, the microwave off time τg is 5s, and the number of intermittent microwave cycles is 166 times.

[0155] 4-3) Microwave heat treatment

[0156] The microwave generator of the microwave heating device is turned on to perform microwave heating treatment on the floor blank. The total microwave heating treatment time is τ sj = (166×(30+5) / 60) = 96.8 min, i.e., the microwave is on for 30 s, and the microwave is off for 5 s (1 microwave heat treatment cycle); the microwave is on for 30 s, and the microwave is off for 5 s; the microwave is on and off, and the cycle is repeated 166 times (i.e., the microwave is on and off for 166 cycles).

[0157] 5. Moisture content adjustment treatment

[0158] After 166 microwave heating cycles (i.e., the microwave heating time reaches 96.8 min), the conveyor belt is started to send the blank specimen 3 into the wood moisture balance chamber of the moisture content adjustment system for moisture content adjustment treatment (i.e., moisture balance treatment).

[0159] 5-1) Calculate and confirm the weight of the floor slab components after moisture content adjustment

[0160] In order to ensure that the floor blank does not deform or crack during use, the final moisture content Mp of the floor blank after heat treatment is adjusted to 6-12% (preferably 8-9%). In order to adjust the moisture content of the floor blank to 6-12%, it is necessary to place the floor blank at a balanced moisture content Mp. p Controlled in an environment of 6-12%.

[0161] When the moisture content Mp of the floor blank is 9% after the moisture content adjustment treatment, the final mass G of the blank assembly after the moisture content adjustment treatment is calculated according to formula (6): p :

[0162] G p =(1+Mp)G 干 =(1+0.09)*17.86=19.46 (6)

[0163] In formula (6), Mp is the final moisture content of the floor slab after moisture content adjustment, %; G p is the weight of the floor slab component after moisture content adjustment, kg; G 干 It is the absolute dry weight of the floor blank assembly, kg.

[0164] In this case, the floor slab is placed in an environment with a balanced moisture content of 9%, and finally the floor slab absorbs moisture to 9%.

[0165] 5-2) Calculate the mass difference ΔG of the floor slab components before and after moisture content adjustment treatment

[0166] According to formula (7), the weight difference ΔG of the blank component before and after heat treatment is calculated:

[0167] ΔG= G1- G p =20-19.46=0.54 (7)

[0168] ΔG is the weight of water contained in the floor material removed by heat treatment of the floor material.

[0169] 5-3) Calculate the mass G of the blank specimen after moisture content adjustment h

[0170] G h =G Z -ΔG=23-0.54=22.46kg

[0171] 5-4) Determination of moisture content adjustment treatment process

[0172] According to the equilibrium moisture content Mp (9%) of the finished floor material, the process control conditions for moisture content adjustment treatment are calculated according to formula (2):

[0173] M p=18.311+0.2249T-7.106lnΔT-0.003835T 2 -0.19059(lnΔT) 2 +0.03553TlnΔT(2)

[0174] +1.4606×10 -5 T 3 -0.000261(lnΔT) 3 +5.1278×10 -5 T(lnΔT) 2 -6.1492×10 -7 T 2 lnΔT

[0175] In formula (2), Mp is the equilibrium moisture content of the finished floor material after moisture content adjustment treatment, %; T is the dry-bulb temperature of the air medium during the moisture content adjustment treatment, °C; ΔT is the dry-bulb and wet-bulb temperature difference of the wet air medium during the moisture content adjustment treatment, °C.

[0176] In this embodiment, the equilibrium moisture content Mp of the finished floor material is 9%; the dry-bulb temperature of the air medium used for moisture content adjustment is selected as 78°C (the dry-bulb temperature of the air medium treated with moisture content adjustment is 60-100°C). According to formula (2), the dry-bulb temperature difference is 9°C, and the wet-bulb temperature is 78-9=69°C, that is, the dry-bulb temperature of the air medium during the moisture content adjustment process is 78°C and the wet-bulb temperature is 69°C.

[0177] 5-5) Moisture content adjustment treatment

[0178] The blank specimen after microwave heating treatment (i.e., intermittent microwave heating for 166 times) for 96.8 minutes is transported to the balance system (i.e., wood moisture balance chamber) through a conveyor belt under closed conditions, and then the heater in the balance chamber 4 is turned on to heat the air medium temperature in the balance chamber to 78° C. The dry and wet bulb temperatures of the air medium in the balance chamber are monitored by a temperature sensor;

[0179] During the moisture content adjustment process, when it is monitored that the dry-bulb temperature difference of the air medium in the balancing room is greater than 9°C, the steam spray pipe in the balancing room 4 is opened to pass water vapor into the balancing room to humidify the air in the balancing room until the wet-bulb temperature of the air medium in the balancing room is 69°C, that is, the dry-bulb temperature difference of the air medium in the balancing room reaches 9°C, and the passing of water vapor is stopped; when it is monitored that the temperature of the air medium in the balancing room is lower than 78°C, the heater in the balancing room is turned on for heating until the dry-bulb temperature of the air medium reaches 78°C, that is, the heating is stopped to keep the temperature of the air medium in the balancing room at 78°C;

[0180] According to the temperature value monitored by the temperature sensor, water vapor is introduced or stopped; the heater is turned on or off to maintain the dry bulb temperature of the balanced indoor air medium at 78°C and the dry-bulb and wet-bulb temperature difference at 9°C;

[0181] During the moisture content adjustment process, the weight of the blank sample is monitored in real time by a weight sensor. When the weight of the blank sample monitored by the weight sensor is 22.46 kg, the moisture content adjustment process is terminated, and the blank sample is taken out of the balance system by a conveyor belt to obtain the heat-treated floor blank of the present invention.

[0182] Example 2

[0183] In addition to the microwave heating temperature t of 220°C and the microwave heating power P of 15 kW / m 3 ; According to formula (1), the total microwave heating time τ of the unit weight floor blank is 5.59 min; according to formula (1A), the microwave heating time τ of the blank assembly is calculated s is 110.99min; the intermittent microwave heating cycle n is 172 times;

[0184] The process parameters of step "4. microwave heating treatment" are carried out according to the parameters calculated and determined in step 3;

[0185] In addition to step "5. Moisture content adjustment treatment" p is 7%; G calculated according to formula (6) p is 19.1kg; ΔG calculated according to formula (7) is 0.89kg; the mass of the blank specimen after heat treatment G h The dry-bulb temperature of the air medium in the moisture content adjustment process is selected to be 94°C, and the dry-bulb and wet-bulb temperature difference of the air medium is calculated to be 12°C according to formula (2), and the rest is the same as in Example 1.

[0186] Example 3

[0187] In addition to the microwave heating temperature t of 120°C and the microwave heating power P of 11 kW / m 3 ; According to formula (1), the total microwave heating time τ of the unit weight floor blank is 3.85min; according to formula (1A), the microwave heating time τ of the blank assembly is calculated s is 80.36min; the intermittent microwave heating cycle n is 138 times;

[0188] The process parameters of step "4. microwave heating treatment" are carried out according to the parameters calculated and determined in step 3;

[0189] In addition to step "5. Moisture content adjustment treatment" p is 8%; G calculated according to formula (6) p is 19.3kg; ΔG calculated according to formula (7) is 0.71kg; the mass of the blank specimen after heat treatment G h The dry-bulb and wet-bulb temperatures of the air medium during the moisture content adjustment process are 78°C. The dry-bulb and wet-bulb temperature difference of the air medium calculated according to formula (2) is 11°C, and the rest is the same as in Example 1.

[0190] Test example: Evaluation of dimensional stability of floorboards

[0191] According to the national standard "Test methods for physical and mechanical properties of small defect-free wood specimens Part 8: Determination of swelling" GB / T1927.8-2021, the swelling of the floor heat-treated according to the method of the present invention was measured, that is, the swelling of the floor blanks prepared in Examples 1-3 was measured, and the measurement results were: 0.0344%, 0.308%, and 0.352%, respectively.

[0192] The test results show that the tangential expansion of the floor blank after heat treatment by the method of the present invention is less than 3.8%, and the dimensional stability is significantly improved. The floor blank prepared by the method of the present invention is applicable to a wide range of environmental humidity.

Claims

1. A microwave-based heat treatment method for solid wood flooring blanks, characterized in that: include: The floor material is subjected to microwave heating treatment and moisture content adjustment treatment.

2. The heat treatment method according to claim 1, characterized in that: During the microwave heating process, the floor material is heated by intermittent heating.

3. The heat treatment method according to claim 2, characterized in that: The intermittent heating is to turn on the microwave to heat the floor material with microwaves; then turn off the microwave to balance the heat; then turn on the microwave to heat the floor material; then turn off the microwave to balance the temperature; the microwave is turned on and off alternately; The time for the microwave to be turned on and off once is one microwave intermittent heating treatment cycle.

4. The heat treatment method according to claim 2, characterized in that: The processing cycle of the intermittent heating method is: the microwave opening time τ k is (24-40)s, preferably 30s; the microwave off time τg is (3-8)s, preferably 5s.

5. The heat treatment method according to any one of claims 1 to 4, characterized in that microwave Theoretical total duration of heating treatment τ s According to formula (1A), we can obtain: t s =τ×G 干 (1A) In formula (1A), τ s is the theoretical total time of microwave heating treatment, min; τ is the theoretical time of microwave heating treatment per unit mass (i.e. per 1kg) of floor blank, min; G 干 is the absolute dry mass of the floor blank, kg; where: τ is calculated according to formula (1): τ=-258.0338+26.4828lnP+87.3956lnt-3.0108(lnP) 2 -7.3714(lnt) 2 -2.9406ltlnP (1) In formula (1): P is the microwave power of microwave heating treatment, kW / m 3 ; t is the microwave heating treatment temperature, ℃; τ is the theoretical total time of microwave heating treatment per unit mass (i.e. per 1kg) of floor material, min.

6. The heat treatment method according to claim 5, characterized in that: The method further includes calculating the number of microwave treatment cycles (i.e., the number of cycles of intermittent microwave heating) n during the intermittent microwave heating treatment of the floor slab according to formula (5), n = τs×60 / (τ k +τg) (5) In formula (5), n is the number of microwave treatment cycles, and n is rounded upward; τs is the total duration of microwave heating treatment, min; τ k is the microwave on time in one microwave processing cycle, s; τg is the microwave off time in one microwave processing cycle, s.

7. The heat treatment method according to claim 1 or 2, characterized in that: The moisture content adjustment process comprises the following steps: 1) According to the moisture content Mp of the finished floor material, calculate the mass G of the floor material after moisture content adjustment after microwave heating treatment p ; In particular, in step 1), the G is calculated according to formula (6): p : G p =(1+Mp)G 干 (6) In formula (6), M 平 is the final moisture content of the floor slab after moisture content adjustment, %; G p is the weight of the floor slab component after moisture content adjustment, kg; G 干 It is the absolute dry weight of the floor blank assembly, kg. 2) According to the equilibrium moisture content Mp of the finished floor material, the process control conditions for moisture content adjustment treatment are calculated and determined according to formula (2): In formula (2), Mp is the equilibrium moisture content of the finished floor material after moisture content adjustment treatment, %; T is the dry-bulb temperature of the air medium during moisture content adjustment treatment, °C; ΔT is the dry-bulb and wet-bulb temperature difference of the wet air medium during moisture content adjustment treatment, °C; 3) placing the microwave-heated flooring blank in a wood moisture balance chamber, heating the air medium temperature to a dry-bulb temperature of T, and simultaneously monitoring the dry-bulb and wet-bulb temperatures of the air medium in the moisture balance chamber in real time; When the dry-bulb and wet-bulb temperature difference of the air medium is greater than ΔT, water vapor is introduced into the balance room to humidify the air in the balance room until the dry-bulb and wet-bulb temperature difference of the air medium in the balance room reaches ΔT, and the introduction of water vapor is stopped; When the dry bulb temperature of the air medium in the balance room is lower than T, the moisture balance room is heated until the dry bulb temperature of the air medium in the balance room reaches T, then the heating is stopped to keep the dry bulb temperature of the air medium in the balance room at T; According to the temperature value of the air medium in the balance room monitored in real time, water vapor is introduced or stopped; the balance room is heated or stopped, and the dry bulb temperature of the air medium in the balance room is maintained at T, and the dry-bulb and wet-bulb temperature difference is ΔT; 4) Real-time monitoring of the weight of the floor blank. When the weight of the floor blank reaches G p When the floor material is taken out from the moisture balance chamber, the floor material with a moisture content of Mp is obtained.

8. The heat treatment method according to claim 7, characterized in that: The moisture content Mp in step 1) is 6-12%.

9. The heat treatment method according to claim 7, characterized in that: The dry-bulb temperature of the air medium during the moisture content adjustment process in step 2) is 60-100°C.

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