At present, domestic thermal insulation refrigerator cars are mostly made of composite materials, and the car body structure is generally divided into two types. One is to use a composite material as a panel, cast a rigid polyurethane foam in the mold to form a single car panel, and then assembled. This method has the advantages of low investment, low cost, and ease of implementation, but the weakness is low strength, low bond strength, affecting the appearance of the vehicle and insulation performance. The other is the more popular dry-wet molding method. Put the prefabricated FRP panel into the mold, use the rigid polyurethane foam board as the insulation layer, and put the liquid resin and reinforcing material on the foam board under the two sides. The upper layer is then covered with a layer of FRP, which is then fed into a large press-molding machine where it is heated and pressurized. This method has good surface properties, can be continuous mechanical molding, low labor intensity, good product appearance quality, high strength of the car panel, panel does not peel off and other fine features, is a preferred composite car plate insulation and refrigerated truck. However, in the dry-wet molding process, since the panel (skin) is a pre-formed FRP plate, and then cut according to the process size requirements, then the row plate is pressed, and the phase change occurs when the adhesive resin is formed from the hydraulic pressure to the solid state solidification. If the carton skin is improperly treated, it will shrink and form wrinkles.
How can this problem be solved? Can be controlled according to the degree of wrinkles formed by various factors, the specific implementation methods are as follows:
1. Allow the composite board to fully cure
Composite panel molding process is at room temperature, in the role of curing agent and accelerator, the resin molecular functional group step by step cross-linking reaction molding, the reaction of raw materials before the resin molecules are linear macromolecules, molecules with more functional groups - not Saturation key. During the reaction process, under the action of styrene cross-linking agent, cross-linking forms bulky macromolecules, so that the entire structure becomes a bulk structure, that is, a thermosetting plastic is formed. The subsequent curing process takes longer at room temperature. If the curing period does not meet the requirements in the production process, ie, the degree of cure is not enough, the inside of the molecule is expressed as a part of the thermoplastic. Thermoplasticity is characterized by melting or softening by heat and plastic deformation. To make it larger than the original size, that is, the size of the panel is greater than the size of the mold. Due to the limitation of the mold, if it is larger than the panel of the mold and cannot be stretched, it is easy to wrinkle. As the temperature rises, the time lengthens, the degree of post-curing of the thermosetting resin molecules increases, and the molecule cross-links to form a bulk structure. The board is cured and the composite board is not easy to stretch, which is the root cause of the wrinkling of the refrigerated carriage panel. Based on this, in the quality control process, the composite board must undergo a one-week post-cure treatment after curing to ensure that its degree of cure meets the requirements of the state and reduces quality problems.
2. Reduce molding temperature and increase molding time     Â
Refrigerated truck compartment is a composite panels reinforced plastic resin by DSM company formula production, its properties and heat distortion temperature is preferred. If blindly increasing the heat distortion temperature increases the cost, it does not make much sense. Accordingly, when the carriage is formed, the original molding temperature is reduced by 5 to 6° C. In order to fully mold the car, the molding time can be extended by 10 minutes.
3. Avoid buried parts displacement
The embedded parts of the car panel are structural parts that are fastened by the car panel, and are indispensable. The requirement does not affect the structural strength, nor does it affect wrinkling. In this regard, improvements have been made in the size and structure of the embedded parts, that is, the size of the embedded parts is slightly smaller than the original design by 2 to 3 mm. In order to make up for the defects caused by this, reinforced materials can be used as cushions to enclose the embedded parts and to fill the space created by the small embedded parts. After curing, they are integrated with the car. This not only solves the problem of movement due to displacement of the embedded parts, but also enhances the structural strength.
4. Ensure the accuracy of blanking
Equipment maintenance personnel shall perform regular maintenance and overhaul of the composite board cutting equipment, and regular inspections shall be conducted on the measuring instruments. The precision of the cutting equipment must be high and must meet the accuracy requirements. Any key meter that does not meet the requirements must be repaired or replaced.
The artificial factors of the blanking error must be in accordance with the ISO9002 quality system operation requirements, strengthen employee training, and pass the training. Only after obtaining the employment license will the employee be allowed to work. Quality inspectors must strengthen inspections.
5. Laminate the composite board
First, the composite board is spread out, and the two ends of the composite board are clamped and pressed with a pre-prepared jig. After the refrigerated carriage panel is aligned, the fixture is removed before being pressed into the press. In this way, because the foam plate is pressed against the composite plate, the composite plate at the bottom no longer warps. The above composite panel, because its area is larger than the panel size, can be fixed on the mold with tape. After this treatment, the molded car panel was observed. The outer edge of the composite plate was flush with the outer edge of the car plate, and the dimensions of the surrounding edges were basically uniform.
6. How to eliminate foam plate thickness error
The reason for the thickness error of the foam board is mainly equipment and human factors. It is necessary to regularly maintain and maintain the equipment, and in particular, the knife edge should be regularly ground and maintained. Strengthening employee training is also an important part.
7. How to avoid inconsistent panel thickness
The thickness of the refrigerated truck composite board is inconsistent, and the local thinner is caused by the unevenness of the surface of the forming mold, the inconsistent thickness of the raw material reinforcement, and the inconsistency caused by inconsistency in the operation. Adjust the mold to reduce the error caused by the mold; Strengthen the inspection of raw materials, make the thickness error of reinforced materials controlled within ± 8%; Strengthen the training of operating skills, so that the product composite board error is controlled within ± 14%.
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