In the past more than 10 years, the RTM process has developed rapidly. Since 1995, foreign countries have grown at an annual rate of 20%.

Compared with several common processes, the RTM process can produce high-performance, large size, high degree of integration, batch medium products.

The number of products in 1500-40000 pieces, suitable for the RTM process. Therefore, RTM is a promising molding process.

At present, the RTM process has been widely used in construction, transportation, telecommunications, health, aerospace, and other fields.

The introduction of RTM process equipment in China began in the 80 ‘s, although the introduction of a lot of equipment, because the process is young, technical difficulties, products often appear some defects, this article on the common defects of RTM products for reference.

1、the product surface roughness matte.

The main cause of this phenomenon in RTM products is the mild viscosity of the product. Touch the mold with your hands, and when you touch these parts, feel extremely rough.

Usually, after the production of a period of time, there will be such problems, then need to clean the mold in time.

First of all, use sandpaper to polish the rough parts of the mold, and then wipe the whole mold with the cotton wire with acetone, finally to the mold coating release agent.

2、Plastic clothing wrinkling.

The main reason for the wrinkle is that before pouring resin, the resin is not cured completely, and the styrene monomer in the pouring resin expands the gel coat resin, resulting in wrinkles.

Therefore, the spraying of plastic clothing should pay attention to the following aspects:

1) coating thickness, usually 0.3-0.5mm or 400-500g/m², can increase its thickness when needed;

2) Check the Promoter, the addition of curing agent and mixing ratio, the promoter and the dosage of curing agent must be added sufficient;

3) After the gel coat is completely cured and then cast resin.

3、 leakage glue.

The main reason for the leakage of plastic die is not tight or tight sealing.

Close the mold should check whether the seal ring is intact, there is no cracks, etc., found that the problem to be replaced in a timely manner.

Die clamping, the mold should be pressed tight gasket, when the leak should be found when the leakage of glue should immediately tighten the surrounding bolts.

4、Air bubbles.

Theoretically, there are four causes of bubbles:

1) The mold cavity resin curing reaction heat is too high, curing time is too short, so the cavity in the gas is not completely discharged;

2) Resin injection mold cavity into the air too much, pouring time can not be all discharged, and even the bubble has been living in the top of the mold cavity, from the bottom of the resin can not be carried out;

3) resin bonding, bubble in the pouring time can not all overflow from the product. And because of the resin viscosity, slow flow, and may even just take the bubble to the middle of the product side (high product), so that after stripping the product containing bubbles (or pit-like gum) more;

4) Resin Injection mold cavity pressure is too large, resulting in the inclusion of bubbles in the resin, difficult to discharge.

The corresponding solution is:

1) Appropriate to reduce the dosage of resin curing agent;

2) Design the exhaust port on the mold;

3) Test the viscosity of the resin at 25°c, usually, the resin viscosity of RTM is 0.5-1.5pas.

If the resin viscosity does not exceed the standard, you should consider whether the ambient temperature is too low if the temperature is too low can be in the resin before the appropriate preheating to a thermostat, but the choice of temperature appropriate, resin viscosity too low will affect the mechanical properties of the product;

4) Reduce the resin injection pressure, increase the amount of resin injection, so as to reduce the resin in the mold cavity flow rate, increase the amount of seepage.

5、 the product appears dry spot.

The main dry spot in the RTM product is not enough glass fiber infiltration.

If the product in the same period of a certain part of the product appears dry spots, it may be the fiberglass cloth is caused by pollution.

Usually, the product inside the dry spot is also related to the resin viscosity, so we should first analyze and adjust the viscosity, to see if the mold flow is too long and too narrow, timely improvement of the mold, improve the feeding tube, increase the feeding point.

6、 Folds

Wrinkles are also a frequent problem with many RTM products. Wrinkles and wrinkling are different, wrinkles are due to the cloth layer wrinkling, after stripping the product appearance can be clearly seen cloth pleat, but the cloth folds between the resin filled.

The main causes of wrinkles are:

1) When the die, because the mold to the cloth layer squeeze and produce wrinkles;

2) resin in the mold flow when the cloth punching extrusion deformation and produce wrinkles.

Therefore, the production of RTM products should pay attention to the mode of operation and thickness of the cloth layer. Improper clamping operation or excessive thickness of cloth layer can cause wrinkle phenomenon easily;

Replace with good scouring resistance of glass fiber mat, preform or knitted combination mat, reduce injection pressure, thus reducing the impact of resin on the cloth layer.

7、 Crack

There are still some gaps in the RTM process in China.

The domestic RTM product’s fiber content is low (generally about 50%), and because the technology is immature, the fiber content distribution of some products is uneven, resulting in the low fiber content of the part being prone to crack.

Theoretically, there are two causes of crack:

1 products in the mold cavity curing is not complete, even after curing, the product is still slowly solidified inside, and the resin curing shrinkage is larger, so is the product of low fiber content, the strength of the carrier is not enough, due to the role of curing internal stress, product surface formation of cracks;

2 The product itself curing has been completed, but due to the transport process in the temperature difference, thermal expansion and contraction, resulting in greater internal stress in the product of the lowest fiber content of weak parts of the crack.

Therefore, the process parameters should be adjusted according to the actual conditions to improve the uniformity of fiber content and fiber distribution.

At the same time to pay attention to the RTM process resin curing shrinkage, resin curing shrinkage, not only affect the product surface effect but also due to the curing shrinkage caused by internal stress to increase demoulding difficulty. At this time should use a low shrinkage additive, or a mixed resin system to reduce the curing shrinkage of the resin.