A method for forming a mutual inductor epoxy resin vacuum casting mold

Abstract

The present invention discloses a method for forming a transformer epoxy resin vacuum casting mold, which relates to the technical field of electrical equipment manufacturing, and includes the following steps: step S1, pretreatment; step S2, preheating the casting system; step S3, mold loading and sealing; step S4, establishing a vacuum environment; step S5, resin mixing and anti-backflow control; step S6, vacuum casting; step S7, secondary defoaming treatment; step S8, pre-curing treatment; step S9, curing and molding. The present invention adopts the above-mentioned method for forming a transformer epoxy resin vacuum casting mold, and through the coordinated control of high-precision vacuum and intelligent defoaming, completely eliminates casting microbubbles, eliminates the hidden dangers of discharge during equipment operation, innovates cascade preheating and laminar casting technology, significantly shortens the manufacturing cycle, achieves double breakthroughs in high quality and high efficiency, greatly reduces rework and manufacturing costs due to the sharp reduction in defect rate and optimization of energy consumption, and improves the economic benefits of the industry.

Description

Technical Field

[0001] The invention relates to the technical field of electrical equipment manufacturing, in particular to a method for forming a transformer epoxy resin vacuum casting mold. Background Art

[0002] The epoxy resin vacuum casting process is a core step in the manufacturing of electrical equipment such as high-voltage transformers and dry-type transformers. Its insulation performance directly impacts the safety and lifespan of the equipment. However, the traditional casting process, which causes partial discharge due to residual bubbles, has become a key bottleneck restricting product reliability.

[0003] The technologies currently used in the industry have the following defects: most processes only preheat the resin or mold, and fail to achieve a three-stage temperature linkage between the coil, resin, and casting tank. As a result, when the temperature difference between the resin and the mold is greater than 15°C, curing shrinkage stress causes microcracks, and moisture inside the coil is not completely released (residual amount > 0.3%). During high-temperature casting, it vaporizes and forms subcutaneous bubbles. Conventional single-stage vacuum pump systems take more than 40 minutes to evacuate to 100Pa, which cannot meet the needs of efficient production. More seriously, vacuuming stops when the vacuum degree reaches 250Pa, but the microbubbles in the narrow gap (0.05-0.1mm) between the turns of the transformer coil require a vacuum environment below 100Pa to be removed.

[0004] The discharge valve is often used in the fully open mode, and turbulence is generated when the resin flow rate is greater than 5L / min, with the bubble entrainment rate as high as 12%; there is a lack of real-time monitoring means, and bubbles cannot be remedied after being injected into the mold. More than 98% of the processes rely solely on secondary vacuum pumping, which is ineffective for deep cavity and narrow gap structures (bubble residual rate >5%); although pressurized degassing technology exists, direct application to epoxy casting will lead to phase separation of resin components. Summary of the Invention

[0005] The purpose of the present invention is to provide a mutual inductor epoxy resin vacuum casting mold forming method, which completely eliminates casting microbubbles through the coordinated control of high-precision vacuum and intelligent degassing, puts an end to the hidden dangers of discharge during equipment operation, innovates cascade preheating and laminar casting technology, significantly shortens the manufacturing cycle, and achieves breakthroughs in both high quality and high efficiency. Due to the sharp reduction in defect rate and optimization of energy consumption, rework and manufacturing costs are greatly reduced, thereby improving the economic benefits of the industry.

[0006] The present invention provides a mutual inductor epoxy resin vacuum casting mold forming method, comprising the following steps: step S1, pretreatment;

[0007] Check and ensure that the pouring system is clean, there is no epoxy resin residue in the pouring tank, the observation window is clean, and the water level in the water tank meets the standard; check the vacuum pump oil level, the air and water pipelines for sealing, and verify that the power supply, voltage, temperature, and vacuum instruments are in normal condition; preheat the transformer coil mold to be poured; preheat the epoxy resin;

[0008] Step S2, preheating the pouring system;

[0009] Start the pouring tank heating system to preheat the empty tank;

[0010] Step S3: mold loading and sealing;

[0011] Open the pouring tank door and pull out the unloading platform car; place the preheated coil mold vertically on the platform car; insert the pouring pipe into the mold gate and fix it firmly; close and lock the tank door, and ensure that the safety valve is closed in place;

[0012] Step S4, establishing a vacuum environment;

[0013] Start the water pump, vacuum pump, evacuation valve and Roots vacuum pump in sequence to evacuate the pouring tank system and monitor the vacuum degree;

[0014] Step S5: resin mixing and anti-backflow control;

[0015] Close the discharge valve and vacuum valve; start the stirring motor and lifting motor to mix the epoxy resin;

[0016] Step S6, vacuum pouring;

[0017] Slowly open the pouring discharge valve and control the valve opening to avoid bubbles. After confirming that the resin flows without bubbles through the observation window, the mold is filled.

[0018] Step S7, secondary defoaming treatment;

[0019] After pouring, perform any of the following exhaust treatments: secondary vacuuming or applying pressure;

[0020] Step S8, pre-curing treatment;

[0021] Stop the vacuum pump and heating system; start the vacuum breaking device to inject air into the tank; open the safety valve and tank door; remove the pouring pipe and transfer the finished mold to the drying oven;

[0022] Step S9, curing and molding;

[0023] The epoxy resin in the mold is cured in a drying oven.

[0024] Preferably, in step S4, the vacuum pump is started in the order of water pump, vacuum pump, evacuation valve and Roots vacuum pump.

[0025] Preferably, in step S6, the opening speed of the discharge valve needs to ensure that the resin is injected into the mold in a laminar flow state.

[0026] Preferably, in step S1, the coil mold is preheated for 10-12 hours, and the epoxy resin is preheated at a temperature of 80°C.

[0027] Preferably, in step S2, the target preheating temperature of the final mixing tank is 65-70°C, and the target preheating temperature of the pouring tank is 75-80°C.

[0028] Preferably, in step S7, the second vacuuming time is 40-60 minutes.

[0029] Preferably, in step S7, the pressurization pressure is 2 kg / cm 2 , the pressure holding time is 30-40 minutes.

[0030] Therefore, the present invention adopts the above-mentioned mutual inductor epoxy resin vacuum casting mold forming method, which completely eliminates casting microbubbles through the coordinated control of high-precision vacuum and intelligent defoaming, puts an end to the hidden dangers of discharge during equipment operation, innovates cascade preheating and laminar casting technology, significantly shortens the manufacturing cycle, and achieves double breakthroughs in high quality and high efficiency. Due to the sharp reduction in defect rate and optimization of energy consumption, the rework and manufacturing costs are greatly reduced, and the economic benefits of the industry are improved.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a schematic diagram of the overall process of a mutual inductor epoxy resin vacuum casting mold forming method. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0034] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0035] The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative position relationships. When the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0036] Example 1

[0037] like Figure 1As shown, the present invention provides a mutual inductor epoxy resin vacuum casting mold forming method, comprising the following steps:

[0038] Step S1, preprocessing;

[0039] Check and ensure the pouring system is clean, including the presence of epoxy resin residue in the pouring tank to prevent contamination of the new resin and ensure pouring purity. Wipe the observation window with a dust-free cloth until it is transparent and free of marks. Ensure the observation window is clean to ensure clear visual monitoring of the pouring process. Confirm that the water level in the water tank is above the safety line and meets the standard. Maintain the normal operation of the vacuum pump cooling system to prevent equipment overheating and damage. Check the vacuum pump oil level and ensure that the oil level is at the center line of the sight glass to ensure that the vacuum pump is adequately lubricated and maintains efficient vacuuming capabilities.

[0040] Test the gas and water lines for leaks under pressure, improve their sealing, and verify their tightness to prevent gas infiltration during vacuuming, which can disrupt the negative pressure environment. Calibrate temperature sensors and vacuum gauges to verify the normal operation of power supply, voltage, and various temperature and vacuum instruments. Ensure the accuracy of process parameter (temperature, vacuum level) measurements, providing reliable data for subsequent control. Preheat the transformer coil mold to be cast in an oven for 10-12 hours to completely remove moisture from the coil and prevent bubbles from evaporating during casting. Preheat the epoxy resin in an oven at 80°C for 2 hours to optimize resin fluidity and ensure that there are no dead corners or gaps when filling the mold.

[0041] In step S1, the coil mold is preheated for 10-12 hours, and the epoxy resin is preheated at 80°C.

[0042] In step S2, the target preheating temperature of the final mixing tank is 65-70°C, and the target preheating temperature of the pouring tank is 75-80°C.

[0043] Through refined pretreatment, the causes of casting defects (contamination, moisture, high viscosity) are eliminated from the source, laying the foundation for subsequent high-precision casting.

[0044] Step S2, preheating the pouring system;

[0045] Start the pouring tank heating system and preheat the empty tank for 1-2 hours to prevent cold tanks from coming into contact with hot resin, which could cause localized curing and flow blockage. Continue until the temperature of the upper final mixing tank reaches 65-70°C to maintain the resin's low viscosity and flow, and the temperature of the lower pouring tank reaches 75-80°C. This compensates for mold heat absorption and ensures a constant temperature during the filling process. Stabilize heating elements (such as heating wires) in advance to avoid temperature fluctuations during pouring.

[0046] Step S3: mold loading and sealing;

[0047] Open the pneumatically sealed door of the casting tank and pull out the unloading platform cart. Place the preheated coil mold upright on the platform cart. This vertical placement prevents resin flow deviation, which can lead to localized material shortages, prevents the coil mold from tilting, and eliminates the risk of the casting tube dislocating due to mold tipping. Insert the casting tube into the mold gate and securely fasten it. Prevent gate leakage, close and lock the tank door, and ensure the safety valve is fully closed to ensure no gas leakage during vacuum or pressurization.

[0048] Step S4, establishing a vacuum environment;

[0049] Start the water pump, vacuum pump, evacuation valve, and Roots vacuum pump in sequence. Start the water pump first to cool the vacuum pump assembly and prevent overheating. Start the Roots vacuum pump last to enable high vacuum operation and avoid inefficient operation. Evacuate the casting tank system and monitor the vacuum level until the final mixing tank reaches 150-250Pa to ensure resin degassing without bumping. Achieve a casting tank vacuum of 100-150Pa to provide a deep degassing environment for the micron-level coil gap.

[0050] In step S4, the vacuum pump is started in the order of water pump, vacuum pump, evacuation valve and Roots vacuum pump.

[0051] The water pump starts first, providing thermal management protection and establishing a cooling water circulation system in advance to provide heat dissipation for the subsequent vacuum pump group. This prevents overheating (>80°C) during high-load operation, which can lead to seal failure or excessive oil temperature (reduced viscosity and reduced pumping efficiency). The vacuum pump generates significant frictional heat during operation, requiring continuous cooling water temperature control (maintaining the oil temperature between 40-60°C). If the vacuum pump is started before the water pump, the pump temperature will exceed the safety threshold within 3 minutes.

[0052] The vacuum pump is started next to establish a basic vacuum, pumping the system from atmospheric pressure to medium vacuum (approximately 100-1000Pa), creating the prerequisites for the efficient operation of the Roots pump (Roots pumps can only operate above medium vacuum). The primary pump has low efficiency when working alone (it takes ≥40 minutes to pump to 100Pa), but has low energy consumption (≤5kW), making it suitable for long-term operation in the initial stage.

[0053] The vacuum valve is then opened for safe isolation and flow control; physical isolation: prevents the air flow impact during initial vacuuming from damaging the Roots pump impeller; flow regulation: the valve is opened gradually to control the air flow speed to <15m / s to avoid turbulence causing resin splashing.

[0054] If the valve and pump are opened at the same time, the instantaneous pressure difference (normal pressure → 1000 Pa) will cause airflow burst (pressure fluctuation > 20%), destroying the resin flow state.

[0055] The Roots vacuum pump is started last, achieving high vacuum and efficient degassing. Based on the 1000Pa established by the primary pump, the vacuum degree is quickly increased to the target value (100-150 Pa), achieving micron-level bubble removal (bubbles within 0.05mm of the coil gap can be completely precipitated).

[0056] Roots pumps are most efficient in the 100-1000Pa range (pumping speed ≥ 300 m 3 / h), but if it is started directly from normal pressure, the power consumption will increase by 300% and it will be easy to overheat.

[0057] Step S5: resin mixing and anti-backflow control;

[0058] Close the discharge valve and vacuum valve; closing the discharge valve can physically block the resin from flowing into the mold, closing the vacuum valve cuts off the vacuum suction path to prevent the resin from being accidentally sucked into the pump, and start the stirring motor and lifting motor to mix the epoxy resin; ensure that the multi-component resin is evenly dispersed to prevent local polymerization.

[0059] Step S6, vacuum pouring;

[0060] Slowly open the pouring discharge valve to avoid vortexes caused by resin flow rates greater than 3m / s, and to prevent bubbles from being entrapped. Confirm that the resin is in a laminar state through the observation window, and monitor it in real time through the observation window to ensure that the resin front advances smoothly. Control the valve opening to avoid bubbles. After confirming that the resin is flowing without bubbles through the observation window, adjust the valve opening immediately if bubbles are found to achieve zero-defect injection and complete mold filling in 40-70 minutes. Adapt to different mold volumes (50-200L) to ensure filling density.

[0061] In step S6, the opening speed of the discharge valve must ensure that the resin is injected into the mold in a laminar flow state.

[0062] Step S7, secondary defoaming treatment;

[0063] After pouring, perform one of the following exhaust treatments: secondary vacuuming for 40-60 minutes or applying 2kg / cm 2 Maintain pressure for 30-40 minutes; the second vacuum can be applied to the surface and shallow bubbles, applying 2kg / cm 2 Pressure exerts osmotic pressure on deep-seated or narrow bubbles, driving them toward the surface. For open molds, vacuuming is preferred (to reduce energy consumption); for molds with complex cavities, pressurization is preferred (to address bubbles in blind areas).

[0064] Step S8, pre-curing treatment;

[0065] Stop the vacuum pump and heating system; activate the vacuum breaker to inject air into the tank; open the safety valve and tank door. Break the vacuum first before opening the door to prevent sudden pressure changes that could cause micro-cracks in the resin. Open the safety valve first to double-check the tank's explosion-proof performance. Remove the casting tube to avoid fractures in the mold gate caused by hard pulling. Transfer the completed mold to a drying oven to prevent vibration-induced displacement of uncured resin.

[0066] Step S9, curing and molding;

[0067] The epoxy resin in the mold is cured in a drying oven and cured in stages at 80°C, 110°C and 150°C to increase the cross-linking degree of the epoxy resin.

[0068] Therefore, the present invention adopts the above-mentioned mutual inductor epoxy resin vacuum casting mold forming method, which completely eliminates casting microbubbles through the coordinated control of high-precision vacuum and intelligent defoaming, puts an end to the hidden dangers of discharge during equipment operation, innovates cascade preheating and laminar casting technology, significantly shortens the manufacturing cycle, and achieves double breakthroughs in high quality and high efficiency. Due to the sharp reduction in defect rate and optimization of energy consumption, the rework and manufacturing costs are greatly reduced, and the economic benefits of the industry are improved.

[0069] 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 preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for forming a mutual inductor epoxy resin vacuum casting mold, characterized in that: The following steps are involved: Step S1, preprocessing; Check and ensure that the pouring system is clean, there is no epoxy resin residue in the pouring tank, the observation window is clean, and the water level in the water tank meets the standard; check the vacuum pump oil level, the air and water pipelines for sealing, and verify that the power supply, voltage, temperature, and vacuum instruments are in normal condition; preheat the transformer coil mold to be poured; preheat the epoxy resin; Step S2, preheating the pouring system; Start the pouring tank heating system to preheat the empty tank; Step S3: mold loading and sealing; Open the pouring tank door and pull out the unloading platform car; place the preheated coil mold vertically on the platform car, insert the pouring pipe into the mold gate and fix it firmly, close and lock the tank door, and ensure that the safety valve is closed in place; Step S4, establishing a vacuum environment; Start the water pump, vacuum pump, evacuation valve and Roots vacuum pump in sequence to evacuate the pouring tank system and monitor the vacuum degree; Step S5: resin mixing and anti-backflow control; Close the discharge valve and vacuum valve; close the discharge valve to physically block the resin from flowing into the mold, close the vacuum valve to cut off the vacuum suction path to prevent the resin from being accidentally sucked into the pump, start the stirring motor and lifting motor to mix the epoxy resin; ensure that the multi-component resin is evenly dispersed to prevent local polymerization; Step S6, vacuum pouring; Slowly open the pouring valve to avoid vortexes caused by resin flow rates exceeding 3m / s and to prevent air bubbles from being trapped. Confirm the resin is in a laminar state through the observation window, and monitor it in real time through the observation window to ensure that the resin front advances smoothly. Control the valve opening to avoid bubbles. After confirming that the resin is flowing without bubbles through the observation window, adjust the valve opening immediately if bubbles are found. This ensures zero-defect injection and completes mold filling in 40-70 minutes. Step S7, secondary defoaming treatment; After pouring, perform one of the following degassing treatments: secondary vacuuming for 40-60 minutes or applying a pressure of 2kg / cm² for 30-40 minutes; secondary vacuuming targets surface and shallow bubbles, while applying a pressure of 2kg / cm² applies osmotic pressure to deep / narrow bubbles, driving them to migrate to the surface; Step S8, pre-curing treatment; Stop the vacuum pump and heating system, start the vacuum breaking device to inject air into the tank, open the safety valve and tank door, remove the pouring pipe, and transfer the finished mold to the drying box; Step S9, curing and molding; The epoxy resin in the mold is cured in a drying oven.

2. A mutual inductor epoxy resin vacuum casting mold forming method according to claim 1, characterized in that: In step S1, the coil mold is preheated for 10-12 hours, and the epoxy resin is preheated at 80°C.

3. A mutual inductor epoxy resin vacuum casting mold forming method according to claim 1, characterized in that: In step S2, the target preheating temperature of the final mixing tank is 65-70°C, and the target preheating temperature of the pouring tank is 75-80°C.

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