GMT plate-based light and durable automobile hat rack and production process thereof

Abstract

The application discloses a light and durable automobile hat and coat rack based on GMT plate material, which comprises a hat and coat rack body, wherein the hat and coat rack body is a three-layer composite structure, and the three-layer structure is sequentially a heat insulation layer, a reinforcing layer prepared based on GMT plate material and a toughness layer; a buckle is arranged at the top of the hat and coat rack body, a hinged rod for rotating opening and closing is arranged at the bottom of the hat and coat rack body, foldable compression plates are arranged at the two sides of the hat and coat rack body, and accessory mounting holes, ventilation holes and sound mounting holes are arranged on the inner side surface of the hat and coat rack body; the production process of the automobile hat and coat rack comprises the following steps: S1, melt blending; S2, net preparation; S3, vacuum introduction; S4, compression molding and hot rolling compounding; and S5, heating; the automobile hat and coat rack prepared based on the GMT plate material further strengthens the heat insulation effect, and the toughness of the hat and coat rack is improved through the toughness layer, so that the compression resistance and tensile strength of the automobile hat and coat rack are further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile hat racks, in particular to a light and durable automobile hat rack based on GMT plate material and a production process thereof. BACKGROUND

[0002] At present, the commonly used base materials for automobile hat racks mainly include the following: PP-based composite materials, PU-based foaming materials and other fiber composite materials. For automobile hat racks, the rigidity of the automobile hat rack is very important for the realization of its function. The rigidity of the automobile hat rack is not only related to the design structure, but also the rigidity of the base material of the automobile hat rack itself. The rigidity of the material is an important reference factor for the selection of the base material. In addition, the tensile properties, dimensional stability performance at high temperature, organic volatile content, mass and cost of the base material are also important reference factors. The selection of the base material is very critical. In addition to the structure design, the performance of the base material determines whether the hat rack can meet the above performance requirements of the hat rack.

[0003] GMT is a kind of glass fiber thermoplastic prepreg, which is a semi-finished sheet made of glass fiber and thermoplastic plastic, and is often used as the base material of automobile hat racks. However, while improving the lightness, the heat insulation effect of GMT material is not outstanding, and the flowability of the fiber is weak during the molding process, thereby affecting the overall strength uniformity of the material.

[0004] Therefore, the present application designs a light and durable automobile hat rack and a production process thereof to optimize the above problems. SUMMARY

[0005] To solve the above technical problems, the present application provides a light and durable automobile hat rack based on GMT plate material and a production process thereof.

[0006] The technical scheme of the present application is: a light and durable automobile hat rack based on GMT plate material, comprising a hat rack body, the hat rack body is a three-layer composite structure, the three-layer structure is a heat insulation layer, a reinforcing layer prepared based on GMT plate material and a toughness layer in sequence;

[0007] The top of the hat rack body is provided with a buckle, the bottom of the hat rack body is provided with a hinge rod for rotating opening and closing, the two sides of the hat rack body are provided with foldable compression plates, and the inner side surface of the hat rack body is provided with an accessory mounting hole, a ventilation hole and a sound mounting hole.

[0008] According to the production process of the light and durable automobile hat rack based on GMT plate material, the following steps are included:

[0009] S1, melt blending:

[0010] PP powder, microsphere foaming agent and dispersant are melt blended in a weight ratio of 1:0.6:0.03 to obtain a mixed glue A, and then silicon carbide, a surfactant and 60-70 wt.% of the mixed glue A are melt blended in a weight ratio of 1:1:15-20 to obtain a mixed glue B;

[0011] Then, the remaining 30-40 wt.% of the mixed glue A is immersed in the catalytic solution for 40-50 min to obtain a mixed glue C;

[0012] S2, net making:

[0013] The hemp fiber composite material and the glass fiber are mixed to obtain mixed fibers, wherein the glass fiber accounts for 50-60% of the mass of the mixed fibers, and then the mixed fibers are opened, mixed, carded and cut to form a fiber web, and the area density of the fiber web is 15-20 g / m 2 ;

[0014] S3, vacuum introduction:

[0015] The mixed glue C is first laid on the fiber web, and then reinforced by needling to obtain a first layer of fiber felt; then, the initiator accounting for 0.6-1% of the mass of the mixed glue C is introduced into the first layer of fiber felt by vacuum introduction, the vacuum degree is-0.02 to-0.07 MPa, the pressure is maintained for 10-15 min after the introduction is completed, and then the solidification is carried out at 85-95℃ for 2-3 h;

[0016] After the solidification is completed, the mixed glue B is laid on the first layer of fiber felt, reinforced by needling, and then solidified at 70-80℃ for 1.5-2 h, and then foamed at 180-200℃ for 15-25 min; thus, a mixed fiber felt is obtained;

[0017] S4, press forming and hot rolling compounding:

[0018] The mixed fiber felt is preheated and then press formed to obtain a reinforcing layer, polyurethane rigid foam material is used as the material of the thermal insulation layer, and ultra-high molecular weight polyethylene fiber is used as the material of the toughness layer, and then the thermal insulation layer, the reinforcing layer and the toughness layer are compounded in sequence by hot rolling to obtain a composite board;

[0019] S5, heating:

[0020] The composite board obtained in step S4 is placed in an oven and heated to 160-190℃, and then cooled to room temperature after maintaining the temperature for 25-35 min, and then accessories, sound equipment, buckles, compression plates and hinged rods are installed on the composite board to obtain an automobile coat rack.

[0021] Further, in step S2, the hemp fiber composite material is a sisal fiber / phenolic resin composite material; wherein the mass ratio of sisal fiber and phenolic resin is 1:0.9-1.

[0022] Note: Sisal fibers are long, corrosion-resistant, tough, low in density, and have high tensile strength and modulus; phenolic resin has good heat resistance, ablation resistance, flame retardancy, acid resistance, and electrical insulation. Combining them maximizes the advantages of both.

[0023] Furthermore, the catalytic solution is a concentrated phosphoric acid solution with a concentration of 5-6 wt.%.

[0024] Note: Concentrated phosphoric acid solution has high catalytic efficiency, and concentrated phosphoric acid has almost no oxidizing properties and is less corrosive.

[0025] Furthermore, in step S4, the preheating temperature is 200–240°C, and the preheating time is 1.5–2.5 min.

[0026] Note: Excessive preheating temperature or time will cause some fiber felt to solidify during the pressing process, affecting subsequent pressing; excessive preheating temperature or time will result in a large temperature difference between the preheating and pressing processes, thus affecting the bonding effect.

[0027] Furthermore, in step S4, the pressing pressure is 15-20 MPa, and the holding time is 85-90 s.

[0028] Note: If the pressing pressure is too low or the holding time is too short, the adhesion of the reinforcing layer will be poor and it will easily split; if the pressing pressure is too high or the holding time is too long, the expansion coefficient of the reinforcing layer will be reduced, thus reducing the internal bulkiness of the board.

[0029] Furthermore, in step S4, the hot rolling temperature is 180–230°C, the hot rolling speed is 5–7 r / min, and the hot rolling pressure is 8–10 MPa.

[0030] Note: Lower hot rolling parameters can lead to insufficient grain refinement, thus failing to achieve the desired performance; excessive hot rolling parameters, on the other hand, can cause the grains to coarsen, thereby reducing the material's resistance to deformation.

[0031] Further, in step S3, the initiator is composed of NaOH, sodium methoxide, and sodium isopropylbenzenesulfonate in a mass ratio of 1:0.6:0.05 to 0.09.

[0032] Note: The initiator composed of NaOH and sodium methoxide has a high monomer conversion rate in the polymerization reaction, which improves the polymerization rate to a certain extent and enhances the bonding between the fiber and the mixed glue interface. Furthermore, the addition of sodium isopropylbenzenesulfonate further improves the bonding efficiency between NaOH and sodium methoxide, thereby enhancing the effect of the initiator.

[0033] Furthermore, the thickness of the coat rack is 4 to 4.5 mm.

[0034] Note: If the coat rack is too thick, heat dissipation will be slow; if it is too thin, it is prone to breakage upon impact.

[0035] The beneficial effects of this invention are:

[0036] (1) The car coat rack of the present invention constructs a heat insulation layer, a reinforcing layer based on GMT board and a toughness layer. By sandwiching the reinforcing layer in the middle with the heat insulation layer and the toughness layer, the heat insulation effect of the outer surface layer in contact with solar heat is improved on the one hand, and the cracking of the inner surface layer of the coat rack in contact with the item is reduced due to the pressure of the item. The reinforcing layer in the middle can not only enhance the heat insulation of the surface heat insulation layer, but also has excellent tensile strength to provide a certain support for the toughness layer, thereby improving the service life of the coat rack.

[0037] (2) The production process of the car coat rack of the present invention involves melting and blending a portion of the main material PP for preparing GMT sheet with other auxiliary materials to obtain a mixed adhesive B with strong activity. When combined with fiber web, it can promote the flow and dispersion of fibers in the mixed adhesive, thereby obtaining a fiber felt with more stable and uniform strength. A portion of PP is impregnated in a catalytic solution to further improve the activity of mixed adhesive A, thereby improving the reaction efficiency with the initiator during subsequent vacuum introduction, thereby reducing the reaction time and improving the preparation efficiency.

[0038] (3) The production process of the car hat rack of the present invention strengthens the interfacial bonding between the mixed fibers and the mixed adhesive by vacuum introducing the initiator into the fiber felt, thereby further improving the adhesion between the mixed fibers and the mixed adhesive, increasing the density of the mixed fiber felt, reducing the fabric curling caused by subsequent composite, and thus obtaining a composite GMT board with high tear resistance. Attached Figure Description

[0039] Figure 1 This is an internal structural diagram of the car coat rack of the present invention;

[0040] Figure 2 This is a structural diagram of the car coat rack of the present invention;

[0041] Among them, 1-clothes rack body, 11-heat insulation layer, 12-reinforcement layer, 13-toughness layer, 14-buckle, 15-ventilation hole, 16-accessory mounting hole, 17-speaker mounting hole, 18-compression plate, 19-hinged rod. Detailed Implementation

[0042] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0043] Example 1

[0044] A lightweight and durable car coat rack based on GMT sheet material includes a coat rack body 1, which is a three-layer composite structure, wherein the three layers are, in order, a heat insulation layer 11, a reinforcing layer 12 made of GMT sheet material, and a toughness layer 13.

[0045] The top of the coat rack body 1 is provided with a buckle 14, the bottom of the coat rack body 1 is provided with a hinge rod 19 for rotating opening and closing, the two sides of the coat rack body 1 are provided with foldable compression plates 18, and the inner side of the coat rack body 1 is provided with accessory mounting holes 16, ventilation holes 15, and speaker mounting holes 17.

[0046] The manufacturing process of the aforementioned car coat rack includes the following steps:

[0047] S1, melt blending:

[0048] PP powder, microsphere foaming agent and dispersant were melt-blended in a weight ratio of 1:0.6:0.04 to obtain mixed adhesive A. Then, silicon carbide and surfactant in a weight ratio of 1:1:18 were melt-blended with 65 wt.% of mixed adhesive A to obtain mixed adhesive B.

[0049] The remaining 35 wt.% of mixed gel A was then immersed in a catalytic solution for 45 min to obtain mixed gel C; the catalytic solution was a concentrated phosphoric acid solution with a concentration of 5.5 wt.%.

[0050] S2, Netting:

[0051] A mixed fiber is obtained by mixing sisal fiber / phenolic resin composite material and glass fiber, wherein the glass fiber accounts for 55% of the mass of the mixed fiber. The mixed fiber is then opened, mixed, carded, and cut to form a fiber web with an areal density of 18 g / m². 2 ;

[0052] In the sisal fiber / phenolic resin composite material, the mass ratio of sisal fiber to phenolic resin is 1:0.95;

[0053] S3, Vacuum Induction:

[0054] First, the mixed adhesive C is laid flat on the fiber mesh and reinforced by needle punching to obtain the first layer of fiber felt; then, an initiator accounting for 0.8% of the mass of mixed adhesive C is introduced into the first layer of fiber felt by vacuum introduction, with a vacuum degree of -0.04MPa. After the introduction is completed, the pressure is maintained for 13 minutes, and then cured at 90°C for 2.5 hours.

[0055] The initiator is composed of NaOH, sodium methoxide, and sodium isopropylbenzenesulfonate in a mass ratio of 1:0.6:0.07;

[0056] After curing, mixed adhesive B is laid flat on the first layer of fiber felt, reinforced by needle punching, and cured for 1.8 hours at 75°C, followed by foaming at 190°C for 20 minutes to obtain mixed fiber felt;

[0057] S4, Compression forming and hot rolling composite:

[0058] The reinforcing layer 12 is obtained by preheating the mixed fiber felt and then pressing it. The preheating temperature is 220℃ and the preheating time is 2.0 min. The pressing pressure is 18 MPa and the holding time is 88 s.

[0059] Then, rigid polyurethane foam is used as the material for the insulation layer 11, and ultra-high molecular weight polyethylene fiber is used as the material for the toughness layer 13. The composite material is hot-rolled in the order of insulation layer 11, reinforcing layer 12 and toughness layer 13 to obtain the composite board.

[0060] The hot rolling temperature is 200℃, the hot rolling speed is 6r / min, and the hot rolling pressure is 9MPa;

[0061] S5, Heating:

[0062] The composite board obtained in step S4 is placed in an oven and heated to 175°C. After holding at this temperature for 30 minutes, it is cooled to room temperature. Then, the accessories, audio equipment, buckle 14, compression plate 18, and hinge rod 19 are installed onto the composite board to obtain a car coat rack with a thickness of 4.3 mm.

[0063] Example 2

[0064] The difference between this embodiment and Embodiment 1 is that in step S1, the weight ratio of PP powder, microsphere foaming agent and dispersant is 1:0.6:0.03, and the weight ratio of silicon carbide, surfactant and 60 wt.% of mixed adhesive A is 1:1:15.

[0065] Example 3

[0066] The difference between this embodiment and Embodiment 1 is that in step S1, the weight ratio of PP powder, microsphere foaming agent and dispersant is 1:0.6:0.05, and the weight ratio of silicon carbide, surfactant and 70 wt.% of mixed adhesive A is 1:1:20.

[0067] Example 4

[0068] The difference between this embodiment and Embodiment 1 is that, in step S1, the remaining 35 wt.% of the mixed adhesive A is immersed in a 5 wt.% concentrated phosphoric acid solution for 40 min.

[0069] Example 5

[0070] The difference between this embodiment and Embodiment 1 is that, in step S1, the remaining 35 wt.% of the mixed adhesive A is immersed in a 6 wt.% concentrated phosphoric acid solution for 50 min.

[0071] Example 6

[0072] The difference between this embodiment and embodiment 1 is that in step S2, the mass ratio of sisal fiber to phenolic resin in the sisal fiber / phenolic resin composite material is 1:0.9; and glass fiber accounts for 50% of the mass of the mixed fibers.

[0073] Example 7

[0074] The difference between this embodiment and embodiment 1 is that in step S2, the mass ratio of sisal fiber to phenolic resin in the sisal fiber / phenolic resin composite material is 1:1; and glass fiber accounts for 60% of the mass of the mixed fibers.

[0075] Example 8

[0076] The difference between this embodiment and Embodiment 1 is that the areal density of the fiber web is 15 g / m². 2 .

[0077] Example 9

[0078] The difference between this embodiment and Embodiment 1 is that the areal density of the fiber web is 20 g / m². 2 .

[0079] Example 10

[0080] The difference between this embodiment and embodiment 1 is that in step S3, an initiator accounting for 0.6% of the mass of the mixed adhesive C is introduced into the first layer of fiber felt by vacuum introduction, the vacuum degree is -0.07MPa, and the pressure is maintained for 10 minutes after the introduction is completed.

[0081] Example 11

[0082] The difference between this embodiment and embodiment 1 is that in step S3, an initiator accounting for 1% of the mass of the mixed adhesive C is introduced into the first layer of fiber felt by vacuum introduction, the vacuum degree is -0.02MPa, and the pressure is maintained for 15 minutes after the introduction is completed.

[0083] Example 12

[0084] The difference between this embodiment and Embodiment 1 is that in step S3, the material is cured at 85°C for 2 hours; then cured a second time at 70°C for 1.5 hours, and finally foamed at 180°C for 15 minutes.

[0085] Example 13

[0086] The difference between this embodiment and Embodiment 1 is that in step S3, the material is cured at 95°C for 3 hours; then cured a second time at 80°C for 2 hours, and finally foamed at 200°C for 25 minutes.

[0087] Example 14

[0088] The difference between this embodiment and Embodiment 1 is that the initiator is composed of NaOH, sodium methoxide, and sodium isopropylbenzenesulfonate in a mass ratio of 1:0.6:0.05.

[0089] Example 15

[0090] The difference between this embodiment and Embodiment 1 is that the initiator is composed of NaOH, sodium methoxide, and sodium isopropylbenzenesulfonate in a mass ratio of 1:0.6:0.09.

[0091] Example 16

[0092] The difference between this embodiment and embodiment 1 is that in step S4, the preheating temperature is 200-240℃, the preheating time is 1.5-2.5 min, the pressing pressure is 15-20 MPa, and the holding time is 85-90 s.

[0093] Example 17

[0094] The difference between this embodiment and embodiment 1 is that in step S4, the preheating temperature is 200-240℃, the preheating time is 1.5-2.5 min, the pressing pressure is 15-20 MPa, and the holding time is 85-90 s.

[0095] Example 18

[0096] The difference between this embodiment and embodiment 1 is that in step S4, the hot rolling temperature is 180°C, the hot rolling speed is 5 r / min, and the hot rolling pressure is 8 MPa.

[0097] Example 19

[0098] The difference between this embodiment and embodiment 1 is that in step S4, the hot rolling temperature is 230°C, the hot rolling speed is 7 r / min, and the hot rolling pressure is 10 MPa.

[0099] Example 20

[0100] The difference between this embodiment and Embodiment 1 is that the thickness of the car coat rack is 4mm.

[0101] Example 21

[0102] The difference between this embodiment and Embodiment 1 is that the thickness of the car coat rack is 4.5mm.

[0103] Experimental Example

[0104] For each embodiment of the car coat rack produced, five samples from each embodiment were taken to test the performance of the car coat rack. The average performance measurement results of the five samples in each embodiment were taken as the performance measurement result of that embodiment. The specific investigation is as follows:

[0105] 1. Investigate the impact of various parameters in the production process on the performance of car coat racks.

[0106] The difference between Comparative Example 1 and Example 1 is that the mixed adhesive A is completely melt-blended with silicon carbide and surfactant;

[0107] The difference between Comparative Example 2 and Example 1 is that no initiator was introduced during the preparation of the mixed fiber felt; the difference between Comparative Example 3 and Example 1 is that the initiator component did not include sodium isopropylbenzenesulfonate; Table 1 shows the effect of Examples 1-21 and Comparative Examples 1-2 on the tensile strength (MPa) and thermal insulation rate (%) of automotive clothing frames.

[0108]

[0109] As shown in Table 1, the lack of impregnation in the mixed adhesive A of Control Example 1, the lack of the initiator in Control Example 2, and the lack of the promoting effect of sodium isopropylbenzenesulfonate in the initiator of Control Example 3 all significantly reduced the tensile strength and heat insulation rate of the car coat rack. Therefore, it can be seen that these two steps and parameters are indispensable for maintaining excellent performance.

[0110] Furthermore, a comparison of Examples 1-21 reveals that excessive or insufficient PP powder content, excessive or insufficient content of mixed adhesive A2 used for impregnation, excessive or insufficient content of mixed adhesive A1 in mixed adhesive B, excessive or insufficient impregnation time of mixed adhesive A2, excessive or insufficient concentration of catalytic solution, excessive or insufficient mass ratio of each fiber in mixed fibers, excessive or insufficient mass of vacuum initiator, excessive or insufficient vacuum degree and other parameters, excessive or insufficient temperature for two curing cycles, excessive or insufficient foaming parameters, excessive or insufficient proportion of sodium isopropylbenzenesulfonate in the initiator, and excessive or insufficient thickness of the coat rack will all reduce the tensile strength and heat insulation rate of the automotive coat rack. Among them, the tensile strength of Example 9 is higher than that of Example 1, but the required areal density in Example 9 is higher, meaning the process is more complex, and the improvement is smaller. The tensile strength of Example 17 is the same as that of Example 1, but the required temperature, pressure, and time are all greater and longer, and the heat insulation rate is lower than that of Example 1.

[0111] Therefore, from an economic point of view, Example 1 is relatively the most effective.

Claims

1. A manufacturing process for a lightweight and durable car coat rack based on GMT sheet material, characterized in that, The coat rack includes a coat rack body (1), which is a three-layer composite structure, consisting of a heat insulation layer (11), a reinforcing layer (12) made of GMT board, and a toughness layer (13). The top of the coat rack body (1) is provided with a buckle (14), the bottom of the coat rack body (1) is provided with a hinge rod (19) for rotating opening and closing, the sides of the coat rack body (1) are provided with foldable compression plates (18), and the middle part of the coat rack body (1) is provided with an accessory mounting hole (16), a ventilation hole (15), and a speaker mounting hole (17). The manufacturing process of the coat rack includes the following steps: S1, melt blending: PP powder, microsphere foaming agent and dispersant are melt-blended at a weight ratio of 1:0.6:0.03~0.05 to obtain mixed adhesive A. Then, silicon carbide and surfactant at a weight ratio of 1:1:15~20 are melt-blended with 60~70wt.% of mixed adhesive A to obtain mixed adhesive B. The remaining 30-40 wt.% of mixed gel A is then immersed in the catalytic solution for 40-50 minutes to obtain mixed gel C; S2, Netting: Hemp fiber composite material and glass fiber are mixed to obtain a mixed fiber, wherein the glass fiber accounts for 50-60% of the mass of the mixed fiber. The mixed fiber is then opened, mixed, carded, and cut to form a fiber web with an areal density of 15-20 g / m². 2 ; S3, Vacuum Induction: First, the mixed adhesive C is laid flat on the fiber mesh and reinforced by needle punching to obtain the first layer of fiber felt; then, an initiator accounting for 0.6~1% of the mass of mixed adhesive C is introduced into the first layer of fiber felt by vacuum introduction, with a vacuum degree of -0.02~-0.07MPa. After the introduction is completed, the pressure is maintained for 10~15 minutes, and then cured at 85~95℃ for 2~3 hours. After curing, mixable adhesive B is laid flat on the first layer of fiber felt, reinforced by needle punching, and cured a second time at 70~80℃ for 1.5~2h, followed by foaming at 180~200℃ for 15~25min; thus obtaining the mixable fiber felt. S4, Compression forming and hot rolling composite: After preheating the mixed fiber felt, a reinforcing layer (12) is obtained by pressing and molding. Then, rigid polyurethane foam is used as the material for the insulation layer (11), and ultra-high molecular weight polyethylene fiber is used as the material for the toughness layer (13). The composite board is obtained by hot rolling according to the composite order of insulation layer (11), reinforcing layer (12) and toughness layer (13). S5, Heating: The composite board obtained in step S4 is placed in an oven and heated to 160~190℃. After holding at the temperature for 25~35 minutes, it is cooled to room temperature. Then, the accessories, audio equipment, buckle (14), compression plate (18), and hinge rod (19) are installed on the composite board to obtain a car coat rack.

2. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, In step S2, the hemp fiber composite material is a sisal fiber / phenolic resin composite material; wherein the mass ratio of sisal fiber to phenolic resin is 1:0.9~1.

3. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, The catalytic solution is a concentrated phosphoric acid solution with a concentration of 5-6 wt.%.

4. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, In step S4, the preheating temperature is 200~240℃ and the preheating time is 1.5~2.5min.

5. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, In step S4, the pressure for pressing is 15~20MPa.

6. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, In step S4, the hot rolling temperature is 180~230℃, the hot rolling speed is 5~7r / min, and the hot rolling pressure is 8~10MPa.

7. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, In step S3, the initiator is composed of NaOH, sodium methoxide, and sodium isopropylbenzenesulfonate in a mass ratio of 1:0.6:0.05~0.

09.

8. The manufacturing process of a lightweight and durable car coat rack based on GMT sheet material according to claim 1, characterized in that, The thickness of the coat rack is 4~4.5mm.

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