A method for repairing surface defects of polyurethane-infused encapsulated transducer

Abstract

The present invention relates to the technical field of high-frequency underwater acoustic transducers, and in particular to a polyurethane perfusion encapsulated transducer surface defect repair processing method, comprising the following steps: step 1: dig out the place with bubbles to form a pit, clean the polyurethane surface in the pit, fill the perfusion type copolyether polyurethane to flat to slightly high after preheating at 70-90°C for 2-4h, and cure at 70-90°C for 6h; step 2: process a 1-2cm thick pad; step 3: after the transducer cools to room temperature, clean the entire filling cover, add a pad on the height positioning surface to raise the transducer and put it into a perfusion mold; step 4: put it into an oven and preheat at 70-90°C for 1-4h, and perfuse polyurethane; step 5: when the polyurethane is filled, take or do not take out the pad, cure at 70-80°C for 6-12h, and demould; step 6: after cooling to room temperature, demould and clean. The processing method of the present invention is simple to operate and is suitable for small, medium and large-scale plane or curved transducer sealing perfusion surface defect repair.

Description

Technical Field

[0001] The invention relates to the technical field of high-frequency underwater acoustic transducers, and in particular to a method for repairing surface defects of a polyurethane perfusion packaged transducer. Background Art

[0002] There are currently two ways to sound-transmitting encapsulation of underwater acoustic transducers: one is conventional vulcanization, which uses a solid mixed rubber at room temperature and pressure, and turns it into a viscous liquid by heating and pressurizing to fill the cavity. Under heating and pressurization, the mixed rubber gradually crosslinks from liquid to solid, and demolds after crosslinking and curing to complete the sound-transmitting encapsulation; the other is infusion vulcanization, which uses an infusion type copolyether polyurethane that is a relatively viscous liquid at room temperature and pressure, and reduces the viscosity of the prepolymer by heating, then adds a curing agent, mixes evenly, vacuum degassing and pouring to fill the cavity. Under heating and pressure, the polyurethane crosslinks from liquid to solid over time and then demolds to complete the sound-transmitting encapsulation. High-frequency underwater acoustic transducers have a precise structure and cannot withstand high temperature and high pressure during the preparation process. Therefore, infusion type copolyether polyurethane is widely used for infusion vulcanization encapsulation of high-frequency underwater acoustic transducers. During conventional vulcanization, since the vulcanization pressure is mostly between tens of megapascals and several megapascals, which is tens to hundreds of times of normal pressure, the bubbles in the vulcanized rubber are also compressed to a size of several tenths to several hundredths, which will not affect the performance and appearance of the transducer; and the injection-type copolyether polyurethane has the characteristics of normal pressure injection vulcanization molding, which makes it flow at normal pressure with low flow resistance in the cavity and fill the cavity without damaging the structure of the transducer. At the same time, it also makes it impossible to compress the bubbles generated during the injection process. Therefore, in the injection-type copolyether polyurethane During the preparation of ester, the bubbles in the glue are usually removed by heating to reduce the viscosity and then vacuuming. However, the spacing between the elements of the high-frequency underwater acoustic transducer is small, the decoupling materials are mostly porous, and the connecting wires are numerous and dense, which leads to bubbles when the fluid infiltrates it. Since the entire preparation process is at normal pressure, these bubbles are difficult to eliminate. After curing, they are often reflected on the surface of the package as bubbles. Therefore, the surface of the transducer perfusion package has more defects than the surface of the conventional vulcanized transducer, which not only affects the appearance of the transducer, but also affects the performance of the transducer. The structural diagram of a general high-frequency underwater acoustic transducer is shown in the figure below. Figure 1 If the bubbles are on the radiation surface, the acoustic performance of the high-frequency underwater acoustic transducer will be seriously affected due to its scattering and sound absorption effects, and its watertight performance will also be affected; if the bubbles are around the transducer, although it will not affect the acoustic performance of the transducer, it will affect its watertight performance due to shortening the water permeability path. Therefore, the defects on the polyurethane packaging surface of the high-frequency underwater acoustic transducer must be repaired.

[0003] There are three current repair methods: (1) Suitable for repairing defects on the plane, such as Figure 2. Dig out the places with bubbles to form pits, clean the polyurethane surface in the pits, preheat and fill with injection-type copolyether polyurethane until it is flat to slightly higher, and heat to cure. This method is easy to operate, but has two disadvantages: ① The original leakage path is from the joint surface of polyurethane and metal to the transducer module, and the current leakage path is from the joint surface of the newly filled polyurethane and the previously encapsulated polyurethane to the transducer module, which greatly shortens the transducer water permeability path and greatly increases the probability of water permeability, affecting its sealing reliability; ② Due to the volume shrinkage of the polyurethane adhesive during curing, obvious joint marks will be left at the junction of the original filling surface and the newly filled filling surface, which seriously affects the appearance and is difficult for customers to accept; (2) It is suitable for repairing defects on the plane, such as Figure 3 . Dig out the area with bubbles, clean the surface of the polyurethane in the pit, preheat and fill it with injection-type copolyether polyurethane to a level higher than the original filling cover. After the fluidity is slightly poor, press a flat plate with an area larger than the filled and repaired pit, flatten it on the original filling cover, and solidify it. Compared with method (1), this method is slightly more complicated to operate, but because the bonding surface between the newly filled polyurethane and the original filling cover is increased, the water permeability path of the transducer is extended, the probability of water permeability is reduced, and the sealing reliability is improved, but it is still lower than the sealing reliability of the original package; because the pressing block controls the flatness of the newly filled filling cover, the aesthetics is better than method (1), but there will still be obvious joint marks at the junction of the pressing block and the original filling cover, which affects the aesthetics and is difficult for customers with slightly higher requirements to accept; (3) It is suitable for repairing defects on both planes and curved surfaces. Remove the original encapsulated polyurethane as a whole to the transducer radiation surface, clean the surface, and then re-inject polyurethane and solidify. The advantage is that both the appearance and the sealing reliability are consistent with the original normal package. The disadvantage is that when removing the polyurethane on the radiating surface of the multi-element transducer, if all of it is removed to the radiating surface, the piezoelectric ceramic silver layer of the transducer will be damaged and the connecting wires on it will be pulled off, causing the entire transducer to be scrapped. If it is partially removed on the radiating surface, the adhesion force between the polyurethane and the piezoelectric ceramic silver layer is smaller than the cohesive force of the polyurethane, and due to the toughness of the polyurethane, partial removal of the polyurethane on the radiating surface is likely to cause damage to the adhesion between the polyurethane and the piezoelectric ceramic silver layer, resulting in decoupling, which seriously affects the acoustic performance of the high-frequency underwater acoustic transducer. Moreover, these damages cannot be discovered during processing and can only be discovered during testing after the packaging is completed. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention discloses a method for repairing surface defects of a polyurethane perfusion encapsulated transducer. The method of the present invention is simple to operate and is suitable for repairing surface defects of small, medium and large-sized flat or curved transducers.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for repairing surface defects of a polyurethane-infused encapsulated transducer comprises the following steps:

[0007] Step 1: Dig out the places with bubbles to form pits, clean the polyurethane surface in the pits, preheat at 70-90℃ for 2-4h, fill with perfusion copolyether polyurethane until it is flat to slightly higher, and cure at 70-90℃ for 6h;

[0008] Step 2: Process a 1-2cm thick pad;

[0009] Step 3: After the transducer cools down to room temperature, clean the entire casting surface, add a pad on the height positioning surface to raise the transducer and place it into the casting mold;

[0010] Step 4: Preheat in an oven at 70-90℃ for 1-4h and pour polyurethane;

[0011] Step 5: After the polyurethane is filled, take or do not remove the pad, cure at 70-80℃ for 6-12h, and demould;

[0012] Step 6: After cooling to room temperature, demould and clean.

[0013] Preferably, the polyurethane surface in step 1 and the filling surface in step 3 are both cleaned with acetone.

[0014] Preferably, the preheating in step 4 is performed for 3 hours.

[0015] Preferably, a layer of polyurethane with a thickness of 0.02-2 mm is poured on the original radiation surface.

[0016] Preferably, the pouring mold in step 3 comprises: a mold base, a metal stopper and a runner; the top of the mold base is sealed with the metal stops on all sides, so that a transducer placement cavity is formed between the metal stops on all sides, and the runner is opened on one of the metal stops.

[0017] Preferably, the runner is connected to the transducer placement cavity, and the inlet end of the runner is vertically opened upward near the opening of the placement cavity, and the outlet end is horizontally opened to the left at the bottom of the placement cavity for pouring polyurethane through the runner.

[0018] Preferably, the height positioning surface on the injection mold is used to place the cushion block, so that when the transducer is placed in the transducer placement cavity, the bottom of the metal cover plate of the transducer abuts against the top of the cushion block.

[0019] The present invention has the following beneficial effects:

[0020] The present invention first digs out the defective area, then fills it, and then pours polyurethane as a whole. Through the pads of different heights and whether to take away the pads, a layer of polyurethane with a thickness of 0.02-2 mm is poured on the original radiation surface, which will not damage the piezoelectric ceramic silver layer of the transducer and its connecting wires and the adhesion between the original packaging polyurethane and the piezoelectric ceramic silver layer, and will not change the acoustic performance, but also ensure the reliability of the sealing performance, and at the same time ensure the beauty of the poured surface, that is, the transducer without surface defects. The processing method of the present invention is simple to operate and is suitable for the sealing and pouring of small, medium and large flat or curved transducers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a schematic diagram of the structure of a high-frequency underwater acoustic transducer in the prior art of the present invention; Figure 1 Middle: 101-metal housing, 102-transducer, 103-injection copolyether polyurethane.

[0023] Figure 2 A schematic diagram of the repair process in method (1) of the prior art of the present invention; Figure 2 Middle: 201-original injection glue, 202-repair glue.

[0024] Figure 3 It is a repair schematic diagram of method (2) in the prior art of the present invention; Figure 3 Chinese: 301-original injection glue, 302-repair glue, 303-pressing block.

[0025] Figure 4 It is a schematic diagram of the structure of the pouring mold in the repair method of the present invention; Figure 4 Middle: 401-mold base, 402-metal stopper, 403-transducer, 404-metal cover plate, 405-injection copolyether polyurethane, 406-sprue, 407-pad. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 4 The embodiment of the present invention provides a technical solution for the surface defect repair treatment method of a polyurethane-infused encapsulated transducer, namely: first fill the defect, then clean the entire original infused encapsulated polyurethane surface, and then install the mold. When installing the mold, add a 1-2cm thick pad on the original height positioning surface to raise the transducer, and then perform preheating, infusion, and demolding and cleaning after curing according to the original encapsulation process. This treatment method is simple and easy to implement, which can restore the appearance and sealing reliability of the original encapsulated transducer without damaging the adhesion of the transducer piezoelectric ceramic silver layer and its connecting wires. It is suitable for all flat and arc-shaped transducer encapsulation surface defect treatment.

[0028] The above-mentioned injection mold has a structure including: a mold base 401, a metal stopper 402 and a runner 406; the top of the mold base 401 is sealed with metal stops 402 so that a transducer 403 placement cavity is formed between the metal stops 402, and a runner 406 is provided on one of the metal stops 402. The runner 406 is connected to the transducer 403 placement cavity, and the inlet end of the runner 406 is vertically opened upward near the opening of the placement cavity, and the outlet end is horizontally opened to the left at the bottom of the placement cavity, which is used for injecting the injection type copolyether polyurethane 405 through the runner 406. The height positioning surface on the injection mold is used for placing the cushion block 407, so that when the transducer 403 is placed in the transducer 403 placement cavity, the bottom of the metal cover plate 404 of the transducer 403 abuts against the top of the cushion block 407.

[0029] Example 1

[0030] A certain type of transducer, the structural diagram is as follows Figure 1 The appearance is a flat cylinder, one of the round surfaces is the radiation surface. After the packaging is completed, three bubbles with a diameter of about 3mm were found on the radiation surface. We repaired them according to the following steps:

[0031] (1) Turn off 1.5mm of polyurethane on the metal surface on the lathe (the thickness of polyurethane on the metal surface is 2mm);

[0032] (2) The areas with bubbles were dug out to form three pits with a diameter of about 8 mm and a depth to the bottom of the bubbles (higher than the piezoelectric ceramic silver layer and its connecting wires). The polyurethane surface in the pits was cleaned with acetone, preheated at 90°C for 2 hours, and then filled with injection-type copolyether polyurethane until it was flat to slightly higher, and cured at 90°C for 6 hours.

[0033] (3) Process a 2 cm thick pad.

[0034] (4) After the transducer cools to room temperature, clean the entire casting surface with acetone, add a pad to the original height positioning surface to raise the transducer and place it into the casting mold.

[0035] (5) Preheat in an oven at 80°C for 3 hours and pour polyurethane.

[0036] (6) After the polyurethane is filled, remove the spacer and allow the transducer to settle to the bottom due to its own gravity. Curing at 80°C for 8 hours, and demolding.

[0037] (7) After cooling to room temperature, demould and clean.

[0038] Results: The secondary potting glue layer is a thin layer on the radiation surface and a 1.5mm thick polyurethane outside the metal on the circumferential surface. The surface of the transducer after packaging is beautiful, no repair marks can be seen, the acoustic performance remains unchanged, and the height dimension meets the requirements of the drawing (the height of the original encapsulated transducer is -0.3mm of the height dimension of the drawing due to the shrinkage of polyurethane curing and thermal expansion and contraction. The secondary encapsulation is about 0.2mm higher than the original encapsulated transducer, so the total height is -0.1mm of the height dimension of the drawing. The height dimension of the drawing is qualified within ±0.5mm), the water pressure test is qualified, and all indicators meet the design requirements.

[0039] Example 2

[0040] A certain type of transducer is rectangular in top view, and has a long arc-shaped side and three straight lines in the main view. The arc surface is the radiation surface. After packaging, a bubble with a diameter of about 2mm was found on the arc radiation surface. We repaired it according to the following steps:

[0041] (1) Dig out the area with bubbles to form a pit with a diameter of about 5 mm and a depth to the bottom of the bubble (higher than the piezoelectric ceramic silver layer and its connecting wire). Clean the polyurethane surface in the pit with acetone and put it in a heating drying oven with the pit facing upwards.

[0042] (2) After preheating at 80°C for 2 hours, fill with injection-type copolyether polyurethane until it is flush with the periphery of the pit, and cure at 80°C for 6 hours.

[0043] (3) Process a 2 cm thick pad.

[0044] (4) After the transducer cools to room temperature, clean the entire arc surface, add a pad to the original height positioning surface to raise the transducer and place it into the casting mold. The stoppers on the two short sides of the casting mold are not installed.

[0045] (5) Preheat in an oven at 70°C for 3 hours and pour polyurethane.

[0046] (6) When the polyurethane adhesive comes out from the two short sides of the injection mold, it means that the entire curved surface is covered with polyurethane adhesive. Quickly remove the 2 cm thick pad and let the transducer settle to the bottom due to its own gravity. Curing at 70 ° C for 12 hours, demolding.

[0047] (7) After cooling to room temperature, demould and clean.

[0048] Results: The glue layer of the secondary potting is a thin layer of polyurethane on the curved radiation surface. The surface of the transducer after encapsulation is beautiful, no traces of repair can be seen, the acoustic performance remains unchanged, the height dimension meets the requirements of the drawing (free tolerance), the water pressure test is qualified, and all indicators meet the design requirements.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for repairing surface defects of a polyurethane-infused encapsulated transducer, characterized in that: The following steps are involved: Step 1: Dig out the places with bubbles to form pits, clean the polyurethane surface in the pits, preheat at 70-90℃ for 2-4h, fill with perfusion copolyether polyurethane until it is flat to slightly higher, and cure at 70-90℃ for 6h; Step 2: Process a 1-2cm thick pad; Step 3: After the transducer cools down to room temperature, clean the entire casting surface, add a pad on the height positioning surface to raise the transducer and place it into the casting mold; Step 4: Preheat in an oven at 70-90℃ for 1-4h and pour polyurethane; Step 5: After the polyurethane is filled, take or do not remove the pad, cure at 70-80℃ for 6-12h, and demould; Step 6: After cooling to room temperature, demould and clean; The pouring mold in step 3 comprises: a mold base, a metal stopper and a runner; the top of the mold base is sealed with the metal stopper on all sides, so that a transducer placement cavity is formed between the metal stoppers on all sides, and the runner is opened on one of the metal stoppers; The runner is connected to the transducer placement cavity, and the inlet end of the runner is vertically opened upward near the opening of the placement cavity, and the outlet end is horizontally opened to the left at the bottom of the placement cavity, for pouring polyurethane through the runner; The height positioning surface on the injection mold is used to place the cushion block, so that when the transducer is placed in the transducer placement cavity, the bottom of the metal cover plate of the transducer abuts against the top of the cushion block; Add a layer of 0.02-2mm polyurethane on the original radiation surface.

2. A polyurethane infusion encapsulated transducer surface defect repair processing method as claimed in claim 1, characterized in that: The polyurethane surface in step 1 and the filling surface in step 3 are both cleaned with acetone.

3. A polyurethane infusion encapsulated transducer surface defect repair processing method as claimed in claim 1, characterized in that: The preheating in step 4 is performed for 3 hours.

Images