Discussion on Vacuum Induction Technology for 12m Yacht

 

After decades of development, FRP materials have been widely used in the construction of small and medium-sized boats, and recently in fishing boats. The process has also evolved from the earlier hand-paste process to the vacuum infusion process (VIP), which is to lay “dry” reinforcement materials (glass fiber, carbon fiber, sandwich materials, etc.) on the mold, then lay vacuum bags, and extract the air in the system to form a negative pressure in the mold cavity.

 

The pressure generated by the vacuum is used to press the unsaturated resin into the fiber layer through the pre-laid pipeline, so that the resin infiltrates the reinforcement material and finally fills the entire mold. After the product is cured, the vacuum bag material is removed and the desired product is obtained from the mold.

 

VIP uses a single-sided mold (like the usual hand-paste and injection molds) to establish a closed system. The vacuum infusion process has been public for a long time, and the process was patented in 1950. However, it has only been developed in recent years. Since this process was introduced from abroad, it has many names, such as vacuum infusion, vacuum infusion, and vacuum injection.

 

 

Theory

The vacuum infusion process can be widely used, and it has its theoretical basis, which is Darcy’s Law t =ℓ 2η/(2 k ΔP ).

t is the infusion time, which is determined by four parameters. η-resin viscosity. From the formula, it can be seen that the lower the viscosity of the resin used, the shorter the infusion time required.

 

Therefore, the viscosity of the resin used for vacuum infusion is generally not too high. This allows the resin to quickly fill the entire mold. ℓ-injection length, which refers to the distance between the resin feed port and the outlet. The longer the distance, the longer the time required.

 

ΔP-pressure difference. The greater the pressure difference between the system and the outside of the system, the greater the driving force for the resin, the faster the resin flow rate, and of course the shorter the required infusion time.

 

k = permeability, which refers to the parameters of glass fiber, sandwich materials, etc. for resin infiltration.

 

A large k value indicates good infiltration, such as continuous felt and multi-directional felt are easier to be infiltrated by resin than gingham and chopped felt.

 

Therefore, in order to make the resin fill the system conveniently when the reinforcing material is compacted, some guide grooves are usually set up artificially, such as drilling holes on the upper and lower sides of the sandwich foam.

 

Step 1: Prepare the Mold

Like other lamination processes, high-quality molds are also necessary for VIP. The surface should have high hardness and high gloss, and the edge of the mold should be at least 15 cm to facilitate the laying of sealing strips and pipes. Clean the mold, and then apply release wax or mold water.

 

 

Step 2: Spraying Gel Coat

The gel coat surface can be applied according to the requirements of the product. It can be made of product gel coat and polished gel coat. The types of gel coat are orthophthalic, isophthalic and vinyl. Gel coat is applied by hand brush and spray.

 

Step 3: Laying Down Reinforcement Materials

The reinforcement materials – glass fiber, carbon fiber, sandwich material… should be selected according to the strength requirements of the product. For VIP, more considerations should be made. Although all fabrics can be used, different materials and weaving methods will affect the resin flow rate.

 

Step 4: Laying Down Vacuum Bag Materials

Lay down the demoulding cloth first, followed by the guide cloth, and finally the vacuum bag. Before closing the vacuum bag, carefully consider the direction of the resin and the vacuum pipeline, otherwise the resin will not be able to penetrate some places. Be very careful when laying down to prevent some sharp objects from piercing the vacuum bag.

 

 

Step 5: Vacuuming

After laying these materials, clamp the resin inlet pipes, vacuum the entire system, try to remove as much air as possible from the system, and check the air tightness. This step is critical. If there is a leak, when the resin is introduced, air will enter the system, and bubbles will penetrate from the leak to other places, and even the entire product may be scrapped.

 

 

The Advantages of Vacuum Resin Infusion Process are as Follows:

 

Excellent Product Performance and High Yield Rate.

Under the same raw material conditions, the strength, stiffness and other physical properties of vacuum resin infusion molded components can be improved by more than 30-50% compared with hand-layup components.

 

Stable Product Quality and Good Repeatability.

The components have a relatively constant resin ratio, generally 30-50%, so the uniformity and repeatability of product performance are better than those of hand-layup products, and there are fewer defects.

 

Improved Fatigue Resistance Can Reduce Structural Weight.

Due to the high fiber content and low porosity of the product, especially the improvement of interlayer strength, the fatigue resistance of the product is greatly improved. Under the same lightness or stiffness requirements, the products of vacuum infusion process reduce structural strength.

 

Environmentally Friendly.

The vacuum infusion process is a closed mold process. Volatile organic compounds and toxic air pollutants are confined to the vacuum bag. VOC emissions do not exceed the standard of 5ppm, which also greatly improves the working environment of operators.

 

Good Product Integrity.

The vacuum resin infusion process can simultaneously form reinforcing ribs, sandwich structures and other inserts, improving the integrity of the product.

 

Reduce the Use Of Raw Materials and Labor.

It can save more than 50% of labor compared to the hand lay-up process.

 

Good Product Precision.

The dimensional accuracy of the vacuum resin infusion process product is better than that of the hand lay-up product. Under the same lay-up, the thickness is 2/3 of the hand lay-up product.

 

 

Of course, the Current Vacuum Resin Introduction Process also has Certain Disadvantages:

(1) The preparation process takes a long time and is relatively complicated.

(2) The production cost is high and generates a lot of waste.

(3) The process manufacturing has certain risks.

 

The author of this article: Liu Hanyun, graduated from the School of Ocean and Ship Engineering of Dalian Fisheries College in July 2004 with a degree in marine fishery science and technology. In 2004, he worked in a yacht manufacturing company in Zhejiang Province on the application of FRP yacht manufacturing technology and vacuuming technology.

 

In October 2014, he worked in Zhejiang Yunyang Yacht Manufacturing Co., Ltd. on the process guidance and support of FRP ship vacuuming. He is currently working in Tongxiang Lanshi Composite Materials Company as a technical worker.