Common defects, causes and solutions of RTM products

2022-08-18 18:13:03

Common defects, causes and solutions of RTM products

01. The surface of the product is partially rough and dull

The main reason for this phenomenon in RTM products is the production of mild mucous membranes. When you touch the mold with your hand, when you touch these parts, it feels extremely rough. Usually, such a general problem occurs after the product is produced for a period of time, and the mold needs to be cleaned in time. First sand the rough parts of the mold with water, then scrub the entire mold with cotton silk dipped in acetone, and finally apply the mold release agent.

02. Wrinkling

This is one of the ills that often occur with gel coat products. The main reason for the wrinkling of the gel coat is that the gel coat resin is not fully cured before the resin is injected, and the monomer (styrene) in the injected resin partially melts the gel coat resin, causing swelling and wrinkles. So check the gel coat for cure before injecting resin.

03. Leakage of glue

The main reason for the leakage of glue is that the mold is not tightly closed or the gasket is not tight. Before closing the mold, check whether the gasket is in good condition and whether there are cracks. Discovery always has to be replaced in time. Check the sealing condition when closing the mold. When the mold is closed, the mold should be pressed against the gasket. Once the leakage of glue is found during pouring, the bolts around the leaking part should be tightened immediately.

04. Foaming

The main reasons for this phenomenon:

1) The heat release of the resin in the mold cavity is too high, and the curing time is too short, so that the gas in the mold cavity is not completely discharged.

2) When the resin enters the mold cavity, too much air is brought in, and the air bubbles cannot be completely discharged within the injection time.

3) If the resin viscosity is too large, the bubbles cannot all overflow from the product during injection.

4) The pressure of the resin injected into the mold cavity is too large, making it difficult to discharge the bubbles contained in the resin.

The corresponding solutions are:

1) Appropriately reduce the amount of resin curing agent used for perfusion;

2) Design the exhaust port on the mold;

3) Test the viscosity of the resin at 25°C, usually the viscosity of the resin for RTM is 0.5~1.5PaS. If the viscosity of the resin does not exceed the standard, it should be considered whether the ambient temperature is too low. If the temperature is too low, it can be properly preheated to a constant temperature before the resin is poured.

4) Reduce the resin injection pressure and increase the resin injection volume, thereby reducing the flow rate of the resin in the mold cavity and increasing the seepage flow.

05. Dry spots appear inside the product

The main reason for dry spots inside RTM products is insufficient glass fiber infiltration. If the dry spot in the same product is a certain part of a product, it should also be considered whether it is caused by the contamination of the glass fiber cloth quilt. Usually, the appearance of dry spots inside the product is also related to the viscosity of the resin, so the viscosity of the resin should be analyzed and adjusted first. Check whether the mold runner is too long or too narrow, and modify the mold in time. View the feed tube, improve the feed tube, improve the feed tube, increase the feed point.

06. Crack

Compared with foreign countries, there is still a certain gap between domestic RTM technology. The fiber content of domestic RTM process products is low (generally about 50%), and due to the immature technology of this process, the fiber content of some products is unevenly distributed, which leads to cracks in parts with too low fiber content. Theoretically, there are two reasons for cracks: 1. The cutting product is not completely cured in the mold cavity, and even after post-curing treatment, the interior of the product is still slowly curing, and the curing shrinkage of the resin is relatively large, so In the part with low fiber content in the product, the strength of the bearing carrier is not enough. Due to the effect of curing internal stress, cracks are formed on the surface of the product; 2. The product itself has been completely cured, but due to the large temperature difference during transportation, thermal expansion and contraction occur. The internal stress is large, and cracks are generated in the weak part of the product with the lowest fiber content.

Therefore, the process parameters should be adjusted according to the actual situation of the process to improve the uniformity of fiber content and fiber distribution. At the same time, attention should be paid to the curing shrinkage rate of the resin used in the RTM process. The resin curing shrinkage rate is large, which not only affects the surface effect of the product, but also increases the difficulty of demolding due to the internal stress generated by the curing shrinkage. At this time, low shrinkage additives should be used, or a mixed resin system should be used to reduce the curing shrinkage of the resin.

07. Core material movement

The main reason for this phenomenon in RTM products is the production of mild mucous membranes. When you touch the mold with your hand, when you touch these parts, it feels extremely rough. Usually, such a general problem occurs after the product is produced for a period of time, and the mold needs to be cleaned in time. First sand the rough parts of the mold with water, then scrub the entire mold with cotton silk dipped in acetone, and finally apply the mold release agent.