Lightweight honeycomb sandwich structure well lid based on sheet molding compound and preparation method thereof

Abstract

The invention discloses a lightweight honeycomb sandwich structure well lid based on a sheet molding compound and a preparation method of the lightweight honeycomb sandwich structure well lid, and belongs to the field of municipal well lids. Comprising a protective outer surface layer, a honeycomb sandwich layer, a self-repairing coating and an embedded intelligent monitoring module. The periphery of the honeycomb sandwich layer is wrapped with the protective outer surface layer, the embedded intelligent monitoring module is embedded in the protective outer surface layer, the outer surface of the protective outer surface layer is coated with the self-repairing coating, and the honeycomb sandwich layer is made of a glass fiber reinforced sheet molding compound and hollow ceramic microbead composite material. Through integration of the honeycomb sandwich composite structure, the self-repairing coating and the intelligent monitoring module, high strength, light weight and multi-functionalization are achieved. The preparation method comprises the steps of segmented mold hot pressing, low-temperature coating curing and module packaging. The weight of the well lid is reduced by more than 40%, the bearing strength is larger than or equal to 50 tons, and the well lid is suitable for smart city construction.

Description

Technical Field

[0001] The present invention relates to the technical field of municipal manhole covers, and in particular to a manhole cover with a lightweight honeycomb sandwich structure based on sheet molding compound and a preparation method thereof. Background Art

[0002] SMC manhole covers are composite materials made from sheet molding compound (SMC). They offer high strength, corrosion resistance, and security, making them widely used in urban infrastructure construction. With their high performance, low cost, and environmental advantages, SMC manhole covers are gradually replacing traditional cast iron manhole covers and becoming the preferred choice for urban infrastructure upgrades. With technological advancements and market expansion, their application scenarios will become even more extensive, driving the industry towards intelligent and green development.

[0003] Existing SMC manhole covers are heavy due to their reliance on high-density fillers (such as glass fiber accounting for 35-40%). Although high-density fillers improve strength, the weight is still difficult to meet lightweight requirements; they lack additional functions such as intelligent monitoring and self-repair; and the homogeneous material distribution leads to low mechanical efficiency. Summary of the Invention

[0004] The present invention provides a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound and a preparation method thereof, which solves the problems of heavy weight, single function and structural redundancy of traditional SMC manhole covers, and integrates self-repairing, anti-corrosion and intelligent monitoring functions.

[0005] To achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0006] A lightweight honeycomb sandwich structure manhole cover based on sheet molding compound includes a protective outer layer, a honeycomb sandwich layer, a self-repairing coating and an embedded intelligent monitoring module. The protective outer layer is wrapped around the outer periphery of the honeycomb sandwich layer, the embedded intelligent monitoring module is embedded in the protective outer layer, and the self-repairing coating is coated on the outer surface of the protective outer layer. The honeycomb sandwich layer is made of a composite material of glass fiber reinforced sheet molding compound and hollow ceramic microspheres, and the density of the honeycomb sandwich layer is 0.3-0.5g / cm 3 The density of the protective outer layer is 1.6-2.0 g / cm 3 .

[0007] As a further solution of the present invention, the honeycomb unit of the honeycomb sandwich layer is an axisymmetric bevel structure with a bevel angle of 55-65°, a unit wall thickness of 0.5-1.2 mm, and a unit side length of 8-15 mm.

[0008] As a further solution of the present invention: the protective outer surface layer material comprises the following components in parts by weight:

[0009] 50-60 parts of unsaturated polyester resin;

[0010] 5-10 parts of carbon fiber;

[0011] 3-5 parts of nano silicon dioxide;

[0012] 30-35 parts of calcium carbonate;

[0013] 0.5-1 part of ultraviolet absorber;

[0014] 0.3-0.5 parts of antioxidant.

[0015] As a further solution of the present invention: the ultraviolet absorber is a benzotriazole, and the antioxidant is a phosphite.

[0016] As a further solution of the present invention: the honeycomb sandwich layer material comprises the following components in parts by weight:

[0017] 6-25 parts by mass of hollow ceramic microspheres;

[0018] 35-40 parts by mass of glass fiber;

[0019] 23-28 parts by mass of unsaturated polyester resin.

[0020] As a further solution of the present invention: the self-repairing coating is a photocatalytic TiO2 coating containing microcapsules, the microcapsule particle size is 5-20 μm, the core material is an epoxy resin repair agent, and the shell material is polyurethane.

[0021] As a further solution of the present invention: the embedded intelligent monitoring module includes a pressure sensor, a fair module and a piezoelectric power supply unit, the pressure sensor is embedded in the middle of the honeycomb sandwich layer, the fair module is fixed to the edge of the honeycomb sandwich layer, the piezoelectric power supply unit is installed in the vibrating area at the bottom of the manhole cover, and the piezoelectric sheet of the piezoelectric power supply unit is bonded to the honeycomb sandwich layer by epoxy resin.

[0022] The present invention also provides a method for preparing a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound, comprising the following steps:

[0023] Prepare honeycomb sandwich layer materials and extrude them into shape;

[0024] Prepare protective outer surface material and calendering;

[0025] Use segmented mold to hot press composite honeycomb sandwich layer and protective outer layer;

[0026] Spraying self-repairing coating and encapsulating intelligent monitoring module

[0027] As a further solution of the present invention: the preparation of the honeycomb sandwich layer material and extrusion molding includes:

[0028] Pre-dispersing glass fibers and hollow ceramic microspheres in unsaturated polyester resin and stirring to mix evenly;

[0029] The honeycomb unit is formed by multi-stage temperature control extrusion of a twin-screw extruder.

[0030] As a further solution of the present invention: the preparation of the protective outer surface layer material and calendering molding includes:

[0031] Mixing: First, mix the unsaturated polyester resin, calcium carbonate, UV absorber and antioxidant for 5 minutes, then add nano-silica and mix for 10 minutes until uniform, and finally add carbon fiber and mix for 15 minutes;

[0032] Calendering: Use three-roll calender to calender into sheet.

[0033] Beneficial effects of the present invention:

[0034] The present invention discloses a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound and its preparation method. Through the integration of honeycomb sandwich composite structure, self-repairing coating and intelligent monitoring module, it realizes high strength, lightweight and multifunctionality. The honeycomb core layer is made of glass fiber reinforced sheet molding compound and hollow ceramic microspheres, with a density of <0.5g / cm 3 Carbon fiber is added to the protective outer layer to enhance wear resistance. An intelligent monitoring module provides real-time monitoring of the manhole cover's status. The manufacturing method includes segmented mold hot pressing, low-temperature coating curing, and packaging. This manhole cover is over 40% lighter and boasts a load-bearing strength of ≥50 tons, making it suitable for smart city development. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] Figure 1 This is a schematic diagram of a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to the present invention;

[0037] Figure 2 This is a schematic cross-sectional view of a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of the tic-tac-toe support frame of the present invention;

[0039] Figure 4 This is a flow chart of a method for preparing a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to the present invention;

[0040] Figure 5This is a flow chart of the present invention using a segmented mold to hot-press a composite honeycomb sandwich layer and a protective outer surface layer.

[0041] In the figure: 1. Protective outer layer; 2. Honeycomb sandwich layer; 3. Self-healing coating; 4. Pressure sensor; 5. Fair module; 6. Piezoelectric power supply unit; 7. T-shaped support frame. DETAILED DESCRIPTION

[0042] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] Example 1

[0044] See also Figure 1-3 As shown, the first embodiment of the present invention provides a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound, including a protective outer surface layer 1, a honeycomb sandwich layer 2, a self-repairing coating 3 and an embedded intelligent monitoring module.

[0045] See also Figure 1 As shown, the protective outer layer 1 serves as the outermost functional barrier of the manhole cover, directly bearing environmental erosion and mechanical wear, and needs to have high strength, weather resistance and functional scalability: the thickness is 2-5mm, and it is coated on the outer surface of the honeycomb sandwich layer 2 to form a "sandwich" composite structure.

[0046] The protective outer layer 1 comprises the following components in parts by weight:

[0047] High-density SMC matrix: 50-60 parts of unsaturated polyester resin, viscosity 2000-2500cps, as the main bonding phase;

[0048] Reinforcement filler: Carbon fiber: 5-10 parts, length 3-5mm, surface oxidized with nitric acid for 30 minutes at a concentration of 65% to enhance interfacial bonding with unsaturated polyester resin; Nano-silica: 3-5 parts, particle size 20-50nm, surface grafted with γ-aminopropyltriethoxysilane (KH550), grafting rate ≥85%. After grafting with KH550, chemical bonds are formed with the unsaturated polyester resin to reduce interfacial defects, while improving surface hardness (Rockwell hardness ≥85HRM) and wear resistance through the nano effect;

[0049] Auxiliary filler: 30-35 parts of calcium carbonate, particle size 5μm, used to reduce costs and adjust rheological properties;

[0050] Functional additives: UV absorber (benzotriazole) 0.5-1 part, antioxidant (phosphite) 0.3-0.5 part.

[0051] By optimizing the material ratio and preparation process of the protective outer layer 1, this invention significantly improves the wear resistance, aging resistance, and interfacial bonding strength of the manhole cover. The directional distribution of carbon fibers and the synergistic effect of modified nano-silica impart high mechanical properties and durability to the surface layer, while also providing an ideal substrate for subsequent functional coatings. Combined with a honeycomb core design, the overall structure achieves multifunctional integration while maintaining a lightweight design, making it suitable for high-load municipal applications.

[0052] See also Figure 2 As shown, the honeycomb sandwich layer 2 is made of glass fiber reinforced sheet molding compound (SMC) and hollow ceramic microspheres, with a density controlled at <0.5g / cm 3 The honeycomb unit adopts an axisymmetric bevel design with a bevel angle of 45°-60°. The honeycomb unit is a regular hexagonal structure with a wall thickness of 0.5-1.2mm, a height of 10-30mm, and a density of 8-15 per 100cm. 2 The beveled edge design disperses load stress to improve compression and bending resistance; the honeycomb unit wall thickness to height ratio is 1:20-1:25, ensuring structural stability, a load-bearing strength of ≥50 tons, and a weight reduction of more than 40%.

[0053] The honeycomb sandwich layer 2 comprises the following components in parts by weight:

[0054] 6-25 parts by mass of hollow ceramic microspheres with a particle size of 10-50 μm, filled with an inert gas (such as argon) to reduce thermal conductivity;

[0055] 35-40 parts by mass of glass fiber, 3-5 mm in length, surface pretreated with silane coupling agent to provide high-strength support;

[0056] 23-28 parts by mass of unsaturated polyester resin, viscosity 2000-2500 cps, containing 0.5% benzoyl peroxide, benzoyl peroxide serves as an initiator.

[0057] Preferably, a cross-shaped support frame 7 is embedded in the lower section of the honeycomb sandwich layer 2 to further enhance the compression and bending resistance of the manhole cover.

[0058] See also Figure 1 and Figure 2 As shown, the embedded intelligent monitoring module includes a pressure sensor 4, a fair module 5, a piezoelectric power supply unit 6 and a data transmission module. The pressure sensor 4 uses a piezoresistive sensor with ZigBee wireless transmission protocol, embedded in the middle of the honeycomb sandwich layer 2, and evenly distributed through the honeycomb wall structure with a density of 3-5 / m 2, directly contact the protective outer layer 1, and monitor the local pressure concentration area. The fair module 5 is fixed to the reserved slot of the protective outer layer 1 at the edge of the manhole cover to avoid the honeycomb structure from shielding the signal. The exposed length of the antenna is ≤2mm. The piezoelectric power supply unit 6 is installed in the vibrating area at the bottom of the manhole cover (such as the vehicle rolling side). The piezoelectric sheet of the piezoelectric power supply unit 6 is bonded to the honeycomb sandwich layer 2 by epoxy resin. The piezoelectric power supply unit 6 is a vibration energy harvesting device based on piezoelectric ceramics with an output power of 0.5-1.2W. It is combined with thin-film solar cells (area 10-20cm 2 ) auxiliary charging, achieving long-term maintenance-free power supply. The data transmission module integrates an NB-IoT communication chip, uploading data to the cloud platform every 10-15 minutes and supporting real-time alarms for abnormal conditions (overload, displacement, illegal opening).

[0059] See also Figure 2 As shown, the self-repairing coating 3 is coated on the outer surface of the protective outer layer 1. The self-repairing coating 3 is a photocatalytic TiO2 coating containing microcapsules. The particle size of the microcapsules is 5-20 μm, the core material is an epoxy resin repair agent, and the shell material is polyurethane.

[0060] The honeycomb sandwich layer 2 of the present invention solves the core problem of "lightweight and high strength contradiction" of traditional manhole covers through material composite, structural optimization and process innovation. At the same time, it integrates self-repair and intelligent monitoring functions, providing an efficient and sustainable solution for municipal facilities.

[0061] Example 2

[0062] See also Figure 4 As shown, the second embodiment of the present invention provides a method for preparing a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound, comprising the following steps:

[0063] 1. Preparation of honeycomb sandwich layer 2

[0064] 1.1 Raw material ratio:

[0065] Hollow ceramic microspheres: 6-25 parts by mass (preferably 20 parts), particle size 10-50 μm (preferably 30 μm), filled with inert gas (such as argon) to reduce thermal conductivity;

[0066] Glass fiber: 35-40 parts by mass (preferably 38 parts), 3-5 mm in length, surface pretreated with silane coupling agent;

[0067] Unsaturated polyester resin: 23-28 parts by mass (preferably 25 parts), viscosity 2000-2500 cps, containing 0.5% benzoyl peroxide (initiator).

[0068] 1.2 Mixing process:

[0069] Pre-disperse the glass fiber and hollow ceramic microspheres in unsaturated polyester resin and mix them at 300 rpm for 15 min using a double planetary mixer. The temperature is controlled at ≤40°C to ensure mixing uniformity.

[0070] And add 0.2% defoaming agent (silicone) to reduce the generation of bubbles during the extrusion process.

[0071] 1.3 Extrusion molding:

[0072] After the materials are mixed, they are extruded through a multi-stage temperature-controlled twin-screw extruder to form honeycomb units;

[0073] Twin-screw extruder: L / D = 40, screw speed 50 rpm, torque ≤ 80%, extrusion pressure 8-10 MPa;

[0074] Segmented temperature control: Zone 1 80°C (unsaturated polyester resin plasticization), Zone 2 100°C (glass fiber dispersion), Zone 3 120°C (hollow ceramic microsphere stabilization); temperature difference ≤ 10°C to avoid local overheating that may cause breakage of hollow ceramic microspheres or degradation of unsaturated polyester resin.

[0075] 2. Preparation of protective outer layer 1

[0076] 2.1 Raw material pretreatment:

[0077] The carbon fibers were soaked in 65% nitric acid for 30 min, washed with water until neutral, and then dried;

[0078] Nano-silica and KH550 were ultrasonically dispersed in ethanol at a mass ratio of 1:10 for 2 h and dried at 80 °C to obtain modified particles.

[0079] 2.2 Internal mixer mixing:

[0080] Equipment: X(S)M-50 internal mixer, mixing temperature 80±5℃, rotor speed 40rpm;

[0081] Feeding order:

[0082] a. First, mix the unsaturated polyester resin, calcium carbonate and functional additives (UV absorber and antioxidant) for 5 minutes;

[0083] b. Add modified nano-silica and mix for 10 minutes until uniform;

[0084] c. Finally, add carbon fiber and mix for 15 minutes to avoid excessive fiber breakage.

[0085] 2.3 Calendering into sheets:

[0086] The mixed material was rolled into sheets using a three-roll calender, with a roller temperature of 70±5°C, a roller distance of 2.0±0.1mm, and a roller surface roughness of Ra≤1.6μm.

[0087] 3. Use segmented mold to hot press composite honeycomb sandwich layer 2 and protective outer layer 1, please refer to Figure 5 As shown, the specific steps include:

[0088] 3.1 Mold pretreatment

[0089] Mold cleaning: Use acetone to clean the segmented mold (6-8 modules) to remove oil and residue;

[0090] Anti-stick treatment: Apply polytetrafluoroethylene release agent (thickness 10-15μm), preheat at 80℃ for 20 minutes to cure;

[0091] Sensor slot activation:

[0092] Magnetic positioning pins (tolerance ±0.02mm) are embedded in the inner wall of the mold to fix the sensor module carrier.

[0093] 3.2 Material layering

[0094]

[0095] 3.3 Segmented mold assembly

[0096] Mortise and tenon joints: 6 mold modules are joined sequentially through dovetail joints (slope 1:50), with a hydraulic locking force of 8-10 MPa;

[0097] Precision control: Laser positioning device calibrates the joint seam (gap ≤ 0.05mm), and the overall flatness error is <0.1mm / m;

[0098] 3.4 Pre-embedded intelligent modules:

[0099] The pressure sensor 4 is embedded in the middle slot of the honeycomb sandwich core, the fair module 5 is fixed to the edge slot, and silicone sealant is injected into the slot.

[0100] 3.5 Hot pressing curing

[0101] Upper mold contact surface: 138±2℃;

[0102] Lower mold contact bottom layer: 133±2℃;

[0103] 0-60s: step-by-step pressure increase to 5MPa (exhaust stage) → 60-240s: steady pressure at 15MPa (main curing stage) → 240-300s: pressure reduction to 2MPa (anti-deformation relaxation).

[0104] 3.6 Cooling and demoulding

[0105] The pressure drops to 0 MPa and the mold temperature changes from 135°C to 100°C;

[0106] The mold opening gap was 0.5 mm, and the temperature was cooled by jet cooling (nitrogen flow rate 10 L / min) to 80 °C;

[0107] Completely open the mold and demould (temperature ≤ 60℃) to prevent thermal deformation of SMC.

[0108] 4. Spray self-repairing coating 3 and encapsulate intelligent monitoring module

[0109] Self-repairing coating 3 spraying:

[0110] Coating formula: TiO2 microcapsules (core material is epoxy resin, shell material is polyurethane, particle size 15μm) and water-based acrylic resin are mixed in a ratio of 1:3;

[0111] Spraying process: high-pressure airless spraying, spraying thickness 200μm, spraying twice (10min interval);

[0112] Curing conditions: Curing in a 75℃ oven for 30 minutes to avoid thermal deformation of the SMC matrix (traditional processes require above 120℃).

[0113] Smart module packaging: Two-component epoxy resin, vacuum potting and room temperature curing for 24 hours; passed the IP68 test: no water leakage after immersion in water at a depth of 1m for 30 minutes.

[0114] The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound of the present invention has the following advantages:

[0115] Lightweight: Honeycomb core density is only 0.3-0.5g / cm 3 , the total weight is reduced by more than 40% compared with traditional SMC manhole covers;

[0116] High strength: Passed the GB / T23858-2009 standard test, bearing strength ≥50 tons, bending strength ≥18MPa;

[0117] Functional integration: The self-healing coating3 repairs 90% of surface damage within 24 hours; the intelligent monitoring module works continuously for 12 months without failure, with a positioning accuracy of ≤1 meter.

[0118] It is suitable for scenarios such as urban roads, parking lots, and airports that have high requirements for load-bearing strength and lightweight; and for scenarios in smart cities that require real-time monitoring of manhole cover displacement, illegal opening, and overload status.

[0119] The above detailed description of the preferred embodiments of the present invention should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A lightweight honeycomb sandwich structure manhole cover based on sheet molding compound, characterized by: It includes a protective outer layer, a honeycomb sandwich layer, a self-repairing coating and an embedded intelligent monitoring module. The protective outer layer is wrapped around the outer periphery of the honeycomb sandwich layer, the embedded intelligent monitoring module is embedded in the protective outer layer, and the self-repairing coating is applied to the outer surface of the protective outer layer. The honeycomb sandwich layer is made of a composite material of glass fiber reinforced sheet molding compound and hollow ceramic microspheres. The density of the honeycomb sandwich layer is 0.3-0.5g / cm 3 The density of the protective outer layer is 1.6-2.0 g / cm 3 .

2. The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 1, characterized in that: The honeycomb unit of the honeycomb sandwich layer presents an axisymmetric hypotenuse structure, with a hypotenuse angle of 55-65 degrees, a unit wall thickness of 0.5-1.2 mm, and a unit side length of 8-15 mm.

3. The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 1, characterized in that: The protective outer layer material comprises the following components in parts by weight: 50-60 parts of unsaturated polyester resin; 5-10 parts of carbon fiber; 3-5 parts of nano silicon dioxide; 30-35 parts of calcium carbonate; 0.5-1 part of ultraviolet absorber; 0.3-0.5 parts of antioxidant.

4. The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 3 is characterized in that: The ultraviolet absorber is a benzotriazole, and the antioxidant is a phosphite.

5. The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 1, characterized in that: The honeycomb sandwich layer material comprises the following components in parts by weight: 6-25 parts by mass of hollow ceramic microspheres; 35-40 parts by mass of glass fiber; 23-28 parts by mass of unsaturated polyester resin.

6. The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 5, characterized in that: The self-repairing coating is a photocatalytic TiO2 coating containing microcapsules, the particle size of the microcapsules is 5-20 μm, the core material is an epoxy resin repair agent, and the shell material is polyurethane.

7. The lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 1, characterized in that: The embedded intelligent monitoring module includes a pressure sensor, a fair module and a piezoelectric power supply unit. The pressure sensor is embedded in the middle of the honeycomb sandwich layer, the fair module is fixed to the edge of the honeycomb sandwich layer, and the piezoelectric power supply unit is installed in the vibrating area at the bottom of the manhole cover. The piezoelectric sheet of the piezoelectric power supply unit is bonded to the honeycomb sandwich layer by epoxy resin.

8. The method for preparing a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to any one of claims 1 to 7, characterized in that: The following steps are involved: Prepare honeycomb sandwich layer materials and extrude them into shape; Prepare protective outer surface material and calendering; Use segmented mold to hot press composite honeycomb sandwich layer and protective outer layer; Spray self-repairing coating and encapsulate intelligent monitoring module.

9. The method for preparing a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 8, characterized in that: The preparation of the honeycomb sandwich layer material and extrusion molding comprises: Pre-dispersing glass fibers and hollow ceramic microspheres in unsaturated polyester resin and stirring to mix evenly; The honeycomb unit is formed by multi-stage temperature control extrusion of a twin-screw extruder.

10. The method for preparing a lightweight honeycomb sandwich structure manhole cover based on sheet molding compound according to claim 8, characterized in that: The preparation of the protective outer surface layer material and calendering molding comprises: Mixing: First, mix the unsaturated polyester resin, calcium carbonate, UV absorber and antioxidant for 5 minutes, then add nano-silica and mix for 10 minutes until uniform, and finally add carbon fiber and mix for 15 minutes; Calendering: Use three-roll calender to calender into sheet.

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