CN111941702A - Microwave curing device for composite material and curing method thereof - Google Patents
Microwave curing device for composite material and curing method thereof Download PDFInfo
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- CN111941702A CN111941702A CN202010816405.8A CN202010816405A CN111941702A CN 111941702 A CN111941702 A CN 111941702A CN 202010816405 A CN202010816405 A CN 202010816405A CN 111941702 A CN111941702 A CN 111941702A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
- B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
- B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
- B29C2035/0855—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using microwave
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Abstract
The invention relates to a microwave curing device for composite materials and a curing method thereof, wherein the microwave curing device comprises a microwave magnetron, a microwave cavity, a shelf table, a magnetron controller, an infrared thermal imager, a vacuum positive and negative pressure bag and an indirect detection device, wherein the microwave cavity is a positive n-edge microwave cavity, n is 6 or 8, and the shelf table is placed at the center of the microwave cavity; the microwave cavity adopts a double-layer structure and specifically comprises an inner shell and an outer shell. During curing, putting the composite material sample on the surface of the object placing table, closing the bin door, and then starting the microwave magnetrons to heat in sequence or symmetrically in groups; heating to the temperature of the sample, raising the temperature to the glass transition temperature at a constant speed, continuing heating until the temperature of the sample reaches Tg +5 ℃, fixing the temperature of Tg +5 ℃ and continuing heating until the temperature of the sample begins to drop, finishing the curing reaction, and stopping heating by the microwave magnetron. The invention can obtain uniform microwave electromagnetic field easily, replaces instantaneous uniformity with uniformity in period, and is superior to the condition of unbalanced curing speed in the traditional microwave heating mode.
Description
The technical field is as follows:
the invention is used in the field of composite material curing and forming, and particularly relates to a microwave curing device for a composite material and a curing method thereof.
Background art:
at present, with the increasing demand of the aerospace industry for light high-performance materials and the demand of civil use for improving the production efficiency of products, a new production process of composite materials capable of meeting the requirements of efficiency, cost and performance has a firmer demand foundation.
In the traditional process, the autoclave technology is mainly adopted to carry out curing treatment on the thermosetting resin-based composite material, which requires a long-time thermosetting process at a high temperature and has the problems of high energy consumption, low production efficiency, high autoclave cost and the like. Meanwhile, when the resin-based material is heated by the autoclave technology in a heating mode, the cold center phenomenon exists due to low thermal conductivity, so that the autoclave technology is not suitable for curing large and thick components, is easy to cure incompletely, causes residual internal stress due to uneven curing, and reduces the performance of the components.
The microwave curing mode has the advantages of high efficiency, low energy consumption, avoidance of cold center, avoidance of incomplete curing, no inertia in heating, easiness in continuous production and the like. However, the microwave heating method has disadvantages that the non-uniformity of the microwave electromagnetic field easily causes the non-uniformity of the heating of the component, the heating efficiency is too high and the local ablation phenomenon is easily generated, and the microwave heating method cannot linearly and directly control the heating speed and temperature because the polar molecules in the heating object are easily changed due to the heating process, and needs to rely on the temperature sensor to perform real-time monitoring and control on the heating process. Therefore, in order to solve the problems of local uneven curing, local overburning and the like during microwave curing, realize uniform, quick and high-toughness curing and better meet the high-efficiency curing requirement of thermosetting resin-based composite materials, the invention provides a universal microwave curing device for composite materials, which comprises a microwave magnetron, a regular polygon microwave cavity, a placing table, a magnetron controller, an infrared thermal imager, a vacuum positive and negative pressure bag, an indirect detection device and the like.
The invention content is as follows:
the invention aims to overcome the defects in the prior art and provides a microwave curing device for composite materials and a curing method thereof. The microwave curing device is provided with a regular polygon column structure cavity on the outer surface, the whole shell inner shell is assembled by welding, and the metal inner cavity forms an electrostatic shielding effect. The outer shell is convenient for later maintenance by adopting an assembling mode, a filtering and wave-absorbing plate is embedded in the middle for protection, the microwave magnetron is uniformly arranged at the central position of each surface of the inner shell of the device, the power transformer and the controller are arranged at the rear end of the device, and a PLC (programmable logic controller) supporting a high-speed pulse switch is adopted for carrying out programmable control switching. The microwave heating power is not controlled by regulating the actual power of the magnetron but by regulating the switching frequency period of the magnetron, so that the microwave electromagnetic field power of the device can be regulated. The infrared thermal imager is arranged in front of a hole in the upper part of the cavity of the device and is shielded and protected by a wave-absorbing filtering composite material plate, when the infrared thermal imager is subjected to independent control operation, the magnetron is powered off and stops operating, the shielding protection is opened, and after the operation is finished, the baffle is reset firstly and then the magnetron is restored to supply power. All control components of the device can be directly controlled by a computer, and the obtained experimental data and experimental scheme are directly recorded by the computer. All control and monitoring components of the device are positioned in a single-chip microcomputer control panel on the device, the thermal imager, the pause, the power supply and the like are provided with independent control switches, and part of experimental parameters can be directly input by the controller. The device can not work when the door is opened due to safety consideration, and the device automatically stops working when the door is opened during working.
In order to achieve the purpose, the invention adopts the following technical scheme:
the utility model provides a microwave solidification equipment for combined material, includes parts such as microwave magnetron, microwave cavity, puts the thing platform, magnetron controller, infrared thermal imaging appearance, positive negative pressure bag in vacuum and indirect detection device, the microwave cavity be positive n polygon microwave cavity, n be 6 or 8, wherein:
the object placing table is placed in the center of the microwave cavity;
the microwave cavity adopts a double-layer structure and specifically comprises an inner shell and an outer shell so as to restrain a microwave electromagnetic field to prevent microwave radiation from leaking, the microwave magnetron is convenient to mount and protect, and meanwhile, the regular n-edge structure of the microwave cavity also reduces the difficulty of obtaining a uniform microwave electromagnetic field through subsequent adjustment. And an electrostatic shielding effect is formed in the microwave cavity of the regular n-polygon.
A filtering/wave absorbing plate is filled between the inner shell and the outer shell of the microwave cavity;
the microwave cavity comprises a microwave cavity inner shell, a microwave magnetron, a positive n-edge microwave cavity outer shell and a positive n-edge microwave cavity inner shell, wherein the microwave magnetron is arranged between the microwave cavity inner shell and the microwave cavity outer shell, and is uniformly arranged in the center of each cavity surface of the positive n-edge microwave cavity, and the arrangement direction is horizontal.
The infrared thermal imager is arranged in the microwave cavity interlayer, the regular n-edge-shaped microwave cavity inner shell is provided with an opening for the position of the infrared thermal imager, and the opening is provided with a movable metal plate for protection.
The object placing table is made of a wave-transparent material so as to prevent interference with a microwave electromagnetic field in the cavity, and the edge of the object placing table is provided with a waterproof edge so as to prevent liquid leakage from damaging microwave equipment.
The object placing table is adjustable in horizontal and vertical distance, and the sample is positioned in the center of the microwave cavity by adjusting the vertical height and the horizontal distance.
The microwave magnetron is provided with a mica sheet in a matching way for protection.
The microwave cavity inner shell and the outer shell are made of metal, the inner shell is in welded connection, and the outer shell is in spliced connection, so that the microwave cavity is convenient to maintain.
A layer of wave absorbing material is compounded between the inner shell and the outer shell of the microwave cavity, so that the risk of microwave leakage is further reduced.
The microwave cavity comprises a bin door, and a glass window is embedded in the middle of the bin door and is used for observing the curing process of a sample in the bin body at any time; the glass window has a filtering effect.
The infrared thermal imager is used for ensuring that the temperature of the sample is quickly obtained when the microwave curing device stops so as to judge whether microwave curing heating is uniform or not and indirectly obtain a magnetron control scheme required by more uniform microwave electromagnetic field generation.
The microwave curing device for the composite material is connected with a power transformer and a controller, and programmable control switching is performed by adopting a PLC supporting high-speed pulse switching. The microwave heating power is not controlled by regulating the actual power of the magnetron but by regulating the switching frequency period of the magnetron, so that the microwave electromagnetic field power of the device can be regulated.
The microwave magnetron is connected with a microwave magnetron controller, the microwave magnetron controller is used for controlling the on-off of each magnetron, and the microwave magnetron controller is specifically arranged through a single chip microcomputer or a computer and can be used for independently setting the working power, the working cycle, the frequency and the like of each magnetron.
All control components of the microwave curing device for the composite material can be directly controlled by a computer, and the obtained experimental data and experimental scheme are directly recorded by the computer.
The vacuum bag is used for carrying out vacuum and pressurization treatment on the sample so as to obtain a vacuum and gas medium environment required by sample curing; wherein:
when conductive fibers such as carbon fibers exist in the composite material sample, the vacuum bag is used for defoaming the sample in a vacuum environment, so that the void ratio of the sample is reduced; and pressurizing by filling a gas medium, wherein the inert gas is injected, so that the generation of sparks of materials containing carbon fibers and the like in the composite material in the microwave curing process is avoided, the local ablation phenomenon of the sample is avoided, the effect of pressurizing to reduce the porosity is also achieved, and the vacuum defoaming time is adjusted according to different normal-temperature curing speeds, viscosities, room temperatures and vacuum degrees of the sample precursor.
Put thing platform axial and evenly be equipped with a plurality of indirect detection device, indirect detection device include the positive cubic ripples glass container that passes through of thin wall, the glass container be furnished with and take the aperture bottle lid, the glass container built-in capacity two thirds about decide the even granular material of ripples of inhaling of quality, inhale even granular material of ripples and include ferrite, zirconium nitride or silicon nitride etc. to the stable and do not take place the reaction with alcohol or pure water of property as the requirement, the glass container in inject the alcohol or the pure water of looks quality to the filler that is used for supplementary even evaporation is filled, including glass fiber cloth etc..
The microwave curing device for the composite material has the function of automatically cutting off power when the bin gate is opened, and the device automatically suspends work when the bin gate is opened.
The method for curing the composite material by adopting the microwave curing device for the composite material comprises the following steps:
put the combined material sample into on thing platform surface, close the door after, open the microwave magnetron and heat, wherein:
n magnetrons corresponding to the regular n-polygon microwave cavity are arranged clockwise by taking any magnetron as a starting point, the number of the magnetrons is 1234 … … n correspondingly, the total opening time of the magnetron in one period is T (S), the number of the periods is S (S), the total opening time is T S, the opening power of each magnetron is P (w), and the heating mode is sequential heating or symmetrical grouped heating, wherein:
when the microwave oven is sequentially heated, the sequential heating mode is that 1234 … … n microwave magnetrons are sequentially and continuously started, and the starting time in each magnetron period is T/n;
when heating sequentially for symmetrical groupings, wherein:
when n is 8, the symmetrical grouping form is four groups of 15, 37, 26 and 48, two microwave magnetrons in the same group are simultaneously started, the symmetrical grouping heating mode is that the four groups of 15, 37, 26 and 48 are continuously started in sequence, and the starting time in each group of magnetrons in a period is T/4;
when n is 6, the symmetrical grouping form is three groups of 14, 25 and 36, two microwave magnetrons in the same group are simultaneously started, the symmetrical grouping heating mode is that three groups of 14, 25 and 36 microwave magnetrons are sequentially and continuously started, and the starting time in the period of each group of the magnetrons is T/3.
And controlling the heating process:
according to the starting mode of the magnetron, after the sample is heated to the temperature of the sample and the temperature is raised to the glass transition temperature at a constant speed, the sample is continuously heated until the temperature of the sample reaches Tg +5 ℃, the corresponding temperature is fixed and the heating is continuously carried out until the temperature of the sample begins to drop, the curing reaction is finished, and the microwave magnetron heating is stopped.
In the curing process of the composite material, for most of heat curing reactions, the reaction process releases heat, and when the sample stops further temperature rise and starts to descend, the curing process tends to be finished, so that the method can be used for preliminarily judging whether the curing is finished. In the whole curing process, the temperature of the sample rises uniformly by adjusting the power, and finally the temperature is kept to be higher than the glass-transition temperature, and in the whole curing process, the curing speed is stable, so that the space network structure is more uniform after the composite material is cured, the ablation phenomenon caused by overlarge local power is avoided, the quality of the product is ensured, and the production efficiency can be improved to the maximum extent.
The composite material curing process, through infrared thermal imager real-time supervision temperature, infrared thermal imager temperature measurement process does: and (4) disconnecting the magnetron, opening the protection plate, measuring the temperature by adopting an infrared thermal imager, closing the protection plate after the temperature is measured, and restarting the microwave magnetron for heating.
The integral microwave heating scheme is divided into sub-schemes (M1, M2) according to different heating powers so as to deal with the phenomenon that the microwave catalytic curing reaction has the defects that the dielectric loss factor is higher in the initial stage, the violent reaction power is too high, the ablation damage is easy to cause, and the dielectric loss factor is reduced in the later stage of the reaction, the power is relatively too low, the incomplete curing reaction is caused, the catalysis can be carried out at the lower power in the initial stage of the reaction, and the power is increased along with the reaction process so as to ensure the continuous catalysis of the curing reaction. According to experience, when the temperature of the sample is lower than the glass transition temperature, the power, the cycle length and the times are adjusted to enable the temperature of the sample to be raised at a uniform speed, when the temperature of the sample exceeds the glass transition temperature, the sample is kept at a fixed temperature slightly higher than the glass transition temperature through adjustment, and the reaction is finished until the temperature of the sample begins to drop.
The invention has the beneficial effects that:
1. the uniform microwave electromagnetic field is easier to obtain, the heating mode is more free, the research is convenient, and the application in the actual production is facilitated. The alternate heating mode is specially used for microwave heating, and uniform in period replaces instantaneous uniform, so that the advantage that microwave heating is different from the traditional autoclave process is embodied, and the curing speed is unbalanced in the traditional microwave heating mode.
2. The use of the vacuum bag simulates two steps of defoaming and pressurizing in the traditional hot-pressing process, and has positive effect on the reference of hot-pressing process experience. In practical experiments, the situation that point discharge fires occurs when the conductive fibers are used as reinforcements by microwave heating is found, and the situation can be improved by using inert gas.
3. The indirect detection device is started from the reality, the microwave heating research has some defects, theoretically uniform fields have the situation of harsh implementation conditions in the reality, and the microwave heating is self-heating, so that the detection device adopting the indirect detection device as the principle can timely adjust errors generated in the reality and plays the role of negative feedback in cooperation with an infrared thermal imager.
Description of the drawings:
FIG. 1 is a schematic view of the overall structure of a microwave curing apparatus according to embodiment 1 of the present invention;
fig. 2 is a schematic view of an internal structure of a microwave curing apparatus according to embodiment 1 of the present invention, in which:
1-object placing table, 2-infrared thermal imager, 3-single chip microcomputer, 4-microwave cavity, 5-shell, 6-filtering wave-absorbing composite board, 7-bin gate, 8-observation window and 9-microwave magnetron.
The specific embodiment mode is as follows:
example 1
In the following examples, the curing material is epoxy resin, and the curing process is described.
The utility model provides a microwave curing device for combined material, its overall structure sketch map is shown as figure 1, and the internal structure sketch map is shown as figure 2, including parts such as microwave magnetron 9, microwave cavity 4, put thing platform 1, magnetron controller, infrared thermal imaging system 2, vacuum positive negative pressure bag and indirect detection device, microwave cavity 4 be positive 6 polygon microwave cavities, wherein:
the object placing table is placed in the center of the microwave cavity 4;
the microwave cavity 4 adopts a double-layer structure, and specifically comprises an inner shell and an outer shell 5, so that a microwave electromagnetic field is bound to prevent microwave radiation from leaking, the microwave magnetron 9 is convenient to mount and protect, and meanwhile, the regular 6-edge structure of the microwave cavity 4 also reduces the difficulty of obtaining a uniform microwave electromagnetic field through subsequent adjustment. And an electrostatic shielding effect is formed in the microwave cavity with the positive 6-edge shape.
A filtering and wave-absorbing composite plate 6 is filled between the inner shell and the outer shell of the microwave cavity 4;
the microwave cavity 4 is characterized in that a microwave magnetron 9 is arranged between the inner shell and the outer shell, the microwave magnetrons 9 are uniformly arranged at the center of each cavity surface of the microwave cavity, and the arrangement direction is horizontal.
The infrared thermal imager is arranged in the interlayer of the microwave cavity 4, the inner shell of the microwave cavity 4 is provided with an opening for the position of the infrared thermal imager, and the opening is provided with a movable metal plate for protection.
The object placing table is made of a wave-transparent material so as to prevent interference with a microwave electromagnetic field in the cavity, and the edge of the object placing table is provided with a waterproof edge so as to prevent liquid leakage from damaging microwave equipment.
The object placing table is adjustable in horizontal and vertical distance, and the sample is positioned in the center of the microwave cavity 4 by adjusting the vertical height and the horizontal distance.
The microwave magnetron 9 is provided with mica sheets for protection.
The microwave cavity 4 inner shell and shell material be the metal, the inner shell be welded connection, the shell is for assembling the connection, the maintenance of being convenient for.
A layer of wave absorbing material is compounded between the inner shell and the outer shell of the microwave cavity 4, so that the risk of microwave leakage is further reduced.
The microwave cavity 4 comprises a bin door 7, and a glass observation window 8 is embedded in the middle of the bin door 7 and is used for observing the curing process of a sample in the bin body at any time; the glass window has a filtering effect.
The infrared thermal imager is used for ensuring that the temperature of the sample is quickly obtained when the microwave curing device stops so as to judge whether microwave curing heating is uniform or not and indirectly obtain a magnetron control scheme required by more uniform microwave electromagnetic field generation.
The microwave curing device for the composite material is connected with a power transformer and a controller, and programmable control switching is performed by adopting a PLC supporting high-speed pulse switching. The microwave heating power is not controlled by regulating the actual power of the magnetron but by regulating the switching frequency period of the magnetron, so that the microwave electromagnetic field power of the device can be regulated.
The microwave magnetron 9 is connected with a microwave magnetron controller, the microwave magnetron controller is used for controlling the on-off of each magnetron, and the microwave magnetron controller is specifically arranged through the singlechip 3 and can be used for independently setting the working power, the working cycle, the frequency and the like of each magnetron.
All control components of the microwave curing device for the composite material can be directly controlled by a computer, and the obtained experimental data and experimental scheme are directly recorded by the computer.
The vacuum bag is used for carrying out vacuum and pressurization treatment on the sample so as to obtain a vacuum and gas medium environment required by sample curing; wherein:
when conductive fibers such as carbon fibers exist in the composite material sample, the vacuum bag is used for defoaming the sample in a vacuum environment, so that the void ratio of the sample is reduced; and pressurizing by filling a gas medium, wherein the inert gas is injected, so that the generation of sparks of materials containing carbon fibers and the like in the composite material in the microwave curing process is avoided, the local ablation phenomenon of the sample is avoided, the effect of pressurizing to reduce the porosity is also achieved, and the vacuum defoaming time is adjusted according to different normal-temperature curing speeds, viscosities, room temperatures and vacuum degrees of the sample precursor.
Put thing platform axial and evenly be equipped with a plurality of indirect detection device, indirect detection device include the positive cubic ripples glass container that passes through of thin wall, the glass container be furnished with and take the aperture bottle lid, the glass container built-in capacity two thirds about decide the even granular material of ripples of inhaling of quality, inhale even granular material of ripples and include ferrite, zirconium nitride or silicon nitride etc. to the stable and do not take place the reaction with alcohol or pure water of property as the requirement, the glass container in inject the alcohol or the pure water of looks quality to the filler that is used for supplementary even evaporation is filled, including glass fiber cloth etc..
The microwave curing device for the composite material has the function of automatically cutting off power when the bin gate is opened, and the device automatically suspends work when the bin gate is opened.
The method for curing the composite material by adopting the microwave curing device for the composite material comprises the following steps:
put the combined material sample into on thing platform surface, close the door after, open microwave magnetron 9 and heat, wherein:
the 6 magnetrons corresponding to the microwave cavity 4 are arranged clockwise starting from any magnetron, and are numbered 123456 correspondingly, the total opening time of the magnetron in one period is T (S), the number of the periods is S (S), the total opening time is T × S, the opening power of each magnetron is p (w), and the heating mode is sequential heating or symmetric group heating, wherein:
when the microwave oven is sequentially heated, the 123456 microwave magnetrons are sequentially and continuously started in the sequential heating mode, and the starting time in each magnetron period is T/6;
when heating sequentially for symmetrical groupings, wherein:
the symmetrical grouping mode is 14, 25 and 36 groups, two microwave magnetrons in the same group are started simultaneously, the symmetrical grouping heating mode is that the 14, 25 and 36 groups of microwave magnetrons are started sequentially and continuously, and the starting time in the period of each group of the microwave magnetrons is T/3.
And controlling the heating process:
according to the starting mode of the magnetron, after the sample is heated to the temperature of the sample and the temperature is raised to the glass transition temperature at a constant speed, the sample is continuously heated until the temperature of the sample reaches Tg +5 ℃, the corresponding temperature is fixed and the heating is continuously carried out until the temperature of the sample begins to drop, the curing reaction is finished, and the microwave magnetron heating is stopped.
In the embodiment, the microwave heating mode considers the characteristic of microwave heating instantaneity, the uniformity of the microwave electromagnetic field is adjusted, and the microwave curing heating mode belongs to a penetrable uniform heating mode, so that the curing reaction uniformity of the sample depends on the uniformity of the microwave electromagnetic field. The magnetron tubes on all sides are heated by the same power and the same cycle length in turn, so that the uniformity in a certain heating cycle is achieved, and the instantaneous uniformity is replaced. The difficulty of adjusting a uniform microwave electromagnetic field is reduced by the alternate and symmetrical use of the magnetrons, and the influence of different heating modes on microwave curing can be further explored.
Six magnetrons on six surfaces of the microwave cavity can be independently controlled to open and close, and each magnetron can obtain different actual power through the control board. Since the microwave field is essentially a varying electromagnetic field, uniformity is difficult to control directly to ensure consistent uniformity. For an axisymmetric cylindrical space on the microwave cavity built-in object placing table, the cylindrical space is called cylindrical space for short, the middle point of the axis is superposed with the center of the microwave cavity, and the axis is vertical to the plane of the six magnetrons and is intersected with the center of the microwave cavity. For the cylindrical space, six magnetrons are in alternate symmetry, the magnetrons are sequentially and alternately started, the six magnetrons sequentially and respectively complete heating once to form a period, and the cylindrical space can be considered to be heated relatively uniformly in one period. In order to further ensure the uniformity of the generated microwave electromagnetic field, the six magnetrons are controlled at the same power, and the opening and closing of the magnetrons can be controlled to be accurate to millisecond level by a plc relay.
By changing the starting sequence, the period length and the magnetron power of the magnetron in one period, different heating modes can be obtained, and a foundation is laid for further research. The 6 magnetrons are numbered according to the clockwise arrangement 1-6, the period length is T (S), the magnetron power is P (w), and the heating mode is marked as M1 when the period repetition times is S: PTS-123456 represents the total cycle time T, the on-time within a single magnetron cycle is T/6, the power of each magnetron is P, the magnetron on-sequence is 1 to 6, and the total time is T × S. And M2: PTS-14-25-36 represents that three groups of 14, 25 and 36 of magnetrons are sequentially started in a period T, the starting time of each magnetron is T/3, and the starting power of each magnetron is P.
The integral microwave heating scheme is divided into sub-schemes (M1, M2) according to different heating powers so as to deal with the phenomenon that the microwave catalytic curing reaction has the defects that the dielectric loss factor is higher in the initial stage, the violent reaction power is too high, the ablation damage is easy to cause, and the dielectric loss factor is reduced in the later stage of the reaction, the power is relatively too low, the incomplete curing reaction is caused, the catalysis can be carried out at the lower power in the initial stage of the reaction, and the power is increased along with the reaction process so as to ensure the continuous catalysis of the curing reaction. According to experience, when the temperature of the sample is lower than the glass transition temperature, the power, the cycle length and the times are adjusted to enable the temperature of the sample to be raised at a uniform speed, when the temperature of the sample exceeds the glass transition temperature, the sample is kept at a fixed temperature slightly higher than the glass transition temperature through adjustment, and the reaction is finished until the temperature of the sample begins to drop.
Experiments show that the same microwave heating power and heating time are adopted, when the condition that the edge of a sample is not cured exists in the process of carrying out catalytic curing by using a common microwave oven, the curing speed of each part of the sample adopting the device is kept consistent, and the conditions of sample distortion, surface unevenness and the like caused by the internal stress generated by the uneven curing speed are avoided. And evaluating the uniformity of the heating effect by adopting a multi-cup test (GB/T18800 + 2008 microwave oven performance test method standard).
And in the overshoot of the heating curing of the sample, an infrared thermal imager is adopted to monitor the curing process of the sample.
In the sample temperature rise process, an indirect detection device is adopted, and the actual heating effect of the microwave is intuitively explored. The device is improved from the GB/T18800-2008 microwave oven performance test method standard;
the indirect detector is pre-treated before use as follows: each indirect detection device is internally provided with wave-absorbing materials with the same mass, such as ferrite and silicon nitride, and is preferably filled in a glass container. Numbering and placing the materials in a hot drying mode at 150 ℃, adding glass fiber evaporation cloth, injecting liquid for volatilization with the same mass, including but not limited to pure water, measuring the whole mass of the device, uniformly placing the detection device on a placing table, carrying out curing and heating operation, measuring the mass of each indirect detection device after heating and cooling, and indirectly judging the uniformity of the microwave electromagnetic field according to the mass difference between the front mass and the rear mass.
In the embodiment, the loss amount of the liquid in the device indirectly represents the external work done by the microwave at the point, and compared with a multi-cup test, the error is smaller, and the obtained data is more accurate.
Since the heating effect of the microwave electromagnetic field can be superimposed with the superposition of the fields, the heating effect of each point in the space under each fixed microwave electromagnetic field is fixed and non-uniform. As the volume of the device is small and the number of the monitoring points is assumed to be n, the mathematical derivation shows that theoretically, the heating effect at the n monitoring points can be consistent within a certain time by superposing at least n microwave electromagnetic fields and adjusting the action time of each microwave electromagnetic field, namely n linear equations with n elements must have unique solution. By uniformly arranging the devices, increasing the number of the devices and reducing the distance between the devices, a scheme of obtaining uniform heating devices can be used for obtaining practically approximate uniform microwave electromagnetic field in a certain time.
Before the epoxy resin is heated and cured, a vacuum positive-negative pressure bag is adopted to carry out vacuum defoaming on the sample, the defoaming time at the room temperature of 30 ℃ is controlled to be 10-15min, the defoaming time is short and insufficient, and the bubbles can not be removed due to the primary curing of the sample if the time is long. After defoaming, pressurizing by injecting inert gas, and taking the condition that the vacuum bag is not damaged as a standard.
The traditional autoclave process can know that pressurization has a remarkable effect on increasing the sample curing effect, compared with the traditional autoclave technology, the porosity of a microwave curing product is higher than that of a thermosetting product due to the lack of a pressurization process, and the vacuum bag is selected for vacuum pressurization treatment, so that the effect on improving the microwave curing porosity is remarkable.
Claims (7)
1. The microwave curing device for the composite material is characterized by comprising a microwave magnetron, a microwave cavity, a shelf, a magnetron controller, an infrared thermal imager, a vacuum positive and negative pressure bag and an indirect detection device, wherein the microwave cavity is a positive n-edge microwave cavity, and n is 6 or 8, wherein:
the object placing table is placed in the center of the microwave cavity;
the microwave cavity adopts a double-layer structure and specifically comprises an inner shell and an outer shell.
2. The microwave curing device for the composite material according to claim 1, wherein a filtering/absorbing plate is filled between the inner shell and the outer shell of the microwave cavity; the microwave cavity comprises a microwave cavity inner shell, a microwave magnetron, a positive n-edge microwave cavity outer shell and a positive n-edge microwave cavity inner shell, wherein the microwave magnetron is arranged between the microwave cavity inner shell and the microwave cavity outer shell, and is uniformly arranged in the center of each cavity surface of the positive n-edge microwave cavity, and the arrangement direction is horizontal.
3. The microwave curing device for the composite material according to claim 1, wherein the infrared thermal imager is disposed in the microwave cavity interlayer, the microwave cavity interlayer of the regular n-polygon shape is provided with an opening for the position of the infrared thermal imager, and the opening is provided with a movable metal plate for protection.
4. The microwave curing device for composite materials according to claim 1, wherein the material of the object placing table is a wave-transparent material, a waterproof edge is arranged on the edge of the object placing table, and the object placing table is adjustable in horizontal and vertical distances.
5. The microwave curing device for the composite material according to claim 1, wherein the microwave magnetron is connected to a microwave magnetron controller, and the microwave magnetron controller is used for controlling the on-off of the magnetron on each side.
6. The microwave curing device for the composite material according to claim 1, wherein the object placing table is axially and uniformly provided with a plurality of indirect detection devices, each indirect detection device comprises a thin-wall cube wave-transparent glass container, each glass container is provided with a bottle cap with a hole, two thirds of the glass container is internally provided with a wave-absorbing uniform particle material with a certain mass, each wave-absorbing uniform particle material comprises ferrite, zirconium nitride or silicon nitride, and the glass containers are filled with alcohol or pure water with the same mass and are filled with fillers for assisting uniform evaporation, and each filler comprises glass fiber cloth.
7. A method for curing a composite material using a microwave curing apparatus for a composite material according to claim 1, comprising the steps of:
(1) put the combined material sample into on thing platform surface, close the door after, open the microwave magnetron and heat, wherein:
n magnetrons corresponding to the regular n-polygon microwave cavity are arranged clockwise by taking any magnetron as a starting point, the number of the magnetrons is 1234 … … n correspondingly, the total opening time of the magnetron in one period is T (S), the number of the periods is S (S), the total opening time is T S, the opening power of each magnetron is P (w), and the heating mode is sequential heating or symmetrical grouped heating, wherein:
when the microwave oven is sequentially heated, the sequential heating mode is that 1234 … … n microwave magnetrons are sequentially and continuously started, and the starting time in each magnetron period is T/n;
when heating sequentially for symmetrical groupings, wherein:
when n is 8, the symmetrical grouping form is four groups of 15, 37, 26 and 48, two microwave magnetrons in the same group are simultaneously started, the symmetrical grouping heating mode is that the four groups of 15, 37, 26 and 48 are continuously started in sequence, and the starting time in each group of magnetrons in a period is T/4;
when n is 6, the symmetrical grouping form is three groups of 14, 25 and 36, two microwave magnetrons in the same group are simultaneously started, the symmetrical grouping heating mode is that three groups of 14, 25 and 36 microwave magnetrons are sequentially and continuously started, and the starting time in the period of each group of the microwave magnetrons is T/3;
(2) controlling the heating process: and according to the starting mode of the magnetron, after heating to the temperature of the sample and raising the temperature to the glass transition temperature at a constant speed, continuing heating until the temperature of the sample reaches Tg +5 ℃, fixing the temperature of Tg +5 ℃ and continuing heating until the temperature of the sample begins to drop, finishing the curing reaction, and stopping heating by the microwave magnetron.
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