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What is fabrication of FRP model hull?

Mar 15, 2019

Fabrication of FPR model hull

There are many kinds of manufacturing methods for FRP hulls. Here, we mainly introduce two methods of hand-made male mold and negative mold.
1. Using the male mold method to make the model hull is simple, and it is more suitable for fans who make models for the first time. However, due to the characteristics of the process, the surface is rough, the error is relatively large, and the appearance needs to be trimmed. The production process is as follows:

(1) Wood, foamed plastic, paraffin and other materials can be used for making the male mold. The selected material is placed on a flat workbench, and a rectangular parallelepiped blank is made according to the drawing according to the length, width and depth of the model.

(2) Stake the blank on the blank according to the line drawing. Deck side lines, mid-longitudinal sections, and tailgate outlines are drawn on the top, side, and end faces, respectively.

(3) Remove excess parts other than the above three contour lines by means of sawing, planing, shovel, shovel, etc., to form a blank mold blank.

(4) According to the line type of each station number in the line drawing, the card board is made of hard cardboard or plastic board. The corresponding card is processed at the last position of the mold blank. During the processing, it is necessary to measure with the card of the corresponding position at any time, so that the line shape of the machining place must match the line shape of the card. The line types of each station are processed in turn and the excess between the two station numbers is trimmed in time. But pay special attention to the fact that the two station numbers are not straight lines, but arcs. If you have a longitudinal profile card, use it in the process. This is the key to ensuring that the model is consistent with the drawings. It must be strictly required and carefully processed.

(5) After each station is processed in place, the card is used for post-alignment, and after the anastomosis, the mold is completely polished with sandpaper.

(6) The surface painting process of the mold is the same as the process and method of other model surface treatment. Generally, the paint should be carried out 3-8 times until the wood grain of the surface is not visible and it is smooth. If you are not very satisfied with the surface, you can play the putty several times and spray several times until you are satisfied. At this point, an accurate M-class sailboat model has been completed.

(7) Before using the mold, be sure to let the mold lacquer thoroughly dry. Use 0.1-0.3 mm thick straight-spun glass fiber cloth, according to the size of the hull, cut into pieces that are enough to cover the positive male mold; put them into the oven one by one for 15 minutes, the temperature is controlled at 130-150 °C, to remove The wax remaining on the surface of the fiber facilitates the penetration of the resin glue into the glass fiber. If there is no oven, this work can be carried out on an electric furnace, and the glass cloth is heated and baked to remove the wax.

(8) Apply a release agent. Spray a layer of polyvinyl alcohol solution on the surface of the male mold (other types of release agents from chemical stores are also available). Spraying should be carried out 2-3 times; to be dried thoroughly, spray or brush the second and third times. If there is no release agent, apply a layer of car polish wax evenly on the surface of the male mold, and then apply a layer of butter or petrolatum. This process seems simple, but it is very important. The surface of the mold should be painted and should not be missed.

(9) Configure epoxy glue. The epoxy resin can only be configured after the preparation is completed. At present, there are many types of epoxy resin glues that can be used for smearing glass cloth. Each has its own characteristics. Fans should choose according to their own specific conditions. Because of the many grades of epoxy resin, the performance is different, even if the same grade, due to different manufacturers, quality and Performance also varies. Therefore, before a large number of epoxy resin adhesives are prepared, a small measurement test is first performed to determine a good formulation. In this way, we can do our best.The formulation of the epoxy resin is composed of an epoxy resin, a plasticizer (dibutyl acrylate), a curing agent (ethylenediamine, diethylenetriamine, etc.). The curing mechanism of the epoxy resin is a chemical reaction process, and the weight ratio of the constituent components is very strict. Any change in proportion will have an effect on curing and hull quality and must be strictly controlled. The specific ratio should be carried out according to the instruction manual. Now taking 618 epoxy resin as an example, it is for reference only. The operating site temperature is preferably 20-25 ° C, dry.
Use 618 epoxy resin 100 (configured by weight ratio), where:
Plasticizer Dibutyl 12-20
Curing agent diethylenetriamine 10-14
According to the actual needs and dosage, weigh accurately according to the proportion, mix together, and fully stir, then it can be used for the hull.

(10) When mixing the hull, two people should cooperate and wear medical gloves for personal protection. Cover the cut and waxed glass cloth on the male mold; apply the glue to the glass cloth evenly, and repeat the brush along the fiber direction of the glass cloth; make the glue to infiltrate the fiber as much as possible, but Do not overdo the glue between the fibers. After a layer of paste, and then a second layer of glass cloth, repeat the previous process. This layer is carried out. The bubbles on each layer must be squeezed out. Generally paste three or four layers. After finishing the last layer, the plastic film is then applied to the outside to be tensioned, and the bubbles and excess glue are squeezed out, and the outer surface is smooth.

(11) Curing conditions Generally, it can be cured at room temperature. It can be solidified at a temperature of 25 ° C or above and naturally allowed to stand for 12 hours; it can be cured in 24 hours. If there is no oven, after the epoxy resin is initially cured, put the mold together with the hull in a strong sunlight for 4-6 hours. In the case of an oven, the mold can be placed in an oven at 100 ° C together with the hull for 3 hours. This will not only shorten the curing time, but also greatly improve the strength of the hull. But be careful, you must slowly warm up gradually, reach the required temperature and keep it for a certain period of time, then slowly lower the temperature; you can not open the oven immediately and return to the natural temperature.

(12) Stripping After 24 hours of complete curing, the plastic film covering the outside of the ship is removed, and the burr outside the mold is removed to remove the hull from the yang film. Use steel rulers or long and thin plastic slats to insert into the gap between the hull and the mold along the two sides, so that the gap is gradually enlarged, and then the hull is slid outward along the ship's side. To gradually carry out, each time the amplitude can not be too large, and gradually take off. Then remove the excess burrs, wipe the inner surface, and remove the release material with an organic solvent (favorable model assembly) so that the hull is completed.

2. Use the negative mold to make the hull
It is more suitable to use a stencil process to produce a hull with a high surface finish. To make a good negative mold, we must first make a high-quality male mold. As mentioned above, after the male mold is finished, it is covered with a layer of FRP on the outside and carefully polished to make the surface. Very smooth and smooth, used to turn the negative mold. The manufacturing process is the same as that of the hull on the male mold. The method of making a mold is described below.

(1) High strength is required as a mold to ensure no deformation. Generally, the thickness is 0.5-0.8 mm, and the material is far more than the paste hull. In order to thicken quickly, a thick glass cloth can be used. The glue used can be selected from inexpensive unsaturated resins. The formulation is different from epoxy resin.

(2) Examples of unsaturated resin formulations:
Unsaturated resin 100
Ancient styrene 4-5
Cyclohexanone 4
Temperature conditions 20-30 ° C. Do a small sample test before pasting the negative mold to observe the curing process, and obtain a proper ratio to avoid unnecessary trouble and waste.

(3) The negative mold must first be coated with a layer of glue on the male mold coated with the release agent. The person in the industry calls it gel coat; after the initial curing of the gel coat for 3-4 hours, it can be on the gel coat layer. Glass cloth, coated with resin glue. It should be layer by layer to reach the required thickness; generally 6-8 hours of curing; after 12 hours, it can be demolded. In this process, the heating effect is better.

(4) Trimming the negative mold. After sufficient curing, the female mold is released from the male mold. The surface of the female mold should be very smooth and smooth. If there are occasional small bubble holes or unevenness, it needs to be carefully repaired and polished.

(5) When using the female mold to turn the hull, it is better to use epoxy resin. The specific process is the same as the previous positive mode. The surface finish of the hull that is turned out using a female mold is quite good.

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