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Causes And Prevention Methods Of Defects In FRP Molded Parts

Jun 09, 2020

1. Defects, causes and prevention methods in gel coat

1. Pinhole


cause:


When spraying, air is mixed, the vaporization of the solvent is enclosed, the amount of curing agent is too large, the atomization is poor during spraying, the surface of the spray gun and the mold is too close, and the thickness of the gel coat is uneven.


Solution:


Reduce the spraying pressure (2-5kg/cm2), slow down the curing, make the spraying thickness uniform, but thick, thin and uniform without bubbles, the curing dose should be controlled within 3%, reduce the viscosity appropriately, expand the spraying area, and control the distance during spraying Within 40-70 cm, the spray thickness is 0.3-0.5 mm.


2. Shrinkage


Cause: The gel coat is too thick (accumulation, too much gel coat).


Solution: formulate the correct material plan and spray evenly.


3. Row spacing (non-stick)


cause:


Insufficient erasing wax, the tendency of the silicone-based release agent to be displaced is obvious, and water or oil is mixed in the spraying.


Solution:


After the wax is fully wiped, immediately wipe it to light, use wax or release agent for the product and raw materials correctly, use dry air, and install an oil-water separator.


4. Foreign matter mixed in


cause:


Small clots and foreign objects in the gel coat, dirt on the mold surface, flying insects in spraying, and dust in the workshop.


Solution:


Use filtered gel coat. Before spraying the gel coat, the mold should be cleaned and cleaned. The static electricity on the surface of the mold should be removed under conditions to prevent the invasion of flying insects and keep the production workshop clean.


5. Wrinkling


cause:


The thickness of the gel coat layer is insufficient for the first time, and the time between brushing the gel coat (2 times) is too short. When the gel coat is applied, the mold or gel coat contains moisture, which causes poor curing of the gel coat, and the humidity of the work site is too high. Insufficient drying of PVA or too little amount of curing agent, slow curing of gel coat, and uneven curing of gel coat.


Solution:


Apply evenly so that the thickness of the first film is 0.2-0.25 mm. After the gel coat is fully cured, brush the gel coat or layer for the second time. After the mold is dried, coat the gel coat, dehumidify, or stop the operation in extreme cases. After the PVA is completely dried and then coated with gel coat, the amount of curing agent should be between 2.5% and 1%, increase the temperature of the working site, maintain ventilation, so that there is no styrene gas in the mold.


6. Release


cause:


After the gel coat is brushed, the mold is deformed during transportation and heated locally. The dosage of the gel coat curing agent is too high, the temperature difference is too large, the release coating is too much and the cleaning is not good, and the gel coat is placed for too long.


Solution:


Be careful not to deform the mold during transportation. The mold is not placed on the edge of the heat source during heating, so that the temperature difference does not change much. After the wax is applied, it is thrown to light. Use the mold release wax correctly. The placement time after applying the gel coat should be within 24 hours. .


7. Poor gloss


Causes: The surface of the mold is dark, the brightness of the mold surface is not strong, and the mold is poorly handled when it is made.


Solution:


After good mold maintenance, the mold should be re-polished and polished after a certain amount is produced. The wax should be polished to bright every time. The wax residue after waxing should be cleaned up. The mold should be used to make mold gelcoat, and carefully polished, polished, cleaned and sealed with 150#-2000# water sandpaper. Perform post-curing treatment of the mold.


8. Bubbles, empty bubbles between the gel coat layer and the layer


cause:


There is debris in the gel coat, but it is not defoamed seriously when applying the surface layer.


Solution:


Clean and paint tools, utensils and molds, and carefully defoam when laying.


9. Uneven color


cause:


Moisture is mixed into the gel coat, dripping occurs (pigment pigment separation), uneven coating (seeing the substrate through the gel coat), insufficient stirring (pigment precipitation in the container), undressing and stirring the pigment, the storage time is too long, add Pigments are mixed with noise.


Solution:


Improve the thixotropy of the gel coat, apply evenly (0.3-0. 5 mm), and fully stir. When using the added pigment (gel coat), the gel coat in the container should be fully stirred with the glue. The work site should be cleaned up when using the gel coat The warehouse where the gel coat is placed must be clean and tidy.


10. Poor curing


cause:


Forget to add accelerator or curing agent, the amount of accelerator is too small, poor stirring, styrene gas retention, temperature is too low.


Solution:


Confirm whether to add the accelerator before use. After adding the curing agent, it should be fully stirred and ventilated to evaporate the styrene gas remaining at the bottom and increase the temperature of the work site.


11. Scars


cause:


Scratches, wedges, demoulding blows (cobwebs), mold release agents, wax residue, PVA brush marks, mold scars.


Solution:


Operate carefully, protect the product with soft objects, use the cutting machine correctly, and use the demolding method correctly. When knocking the mold, it should be light, frequent mold maintenance and repair, and apply PVA thinly and evenly.


12. Crack


cause:


Barely demoulding, unreasonable shape, blow (spider web crack), barely assembled, stress concentration.


Solution:


Re-discuss the release treatment method and release agent brand, mold correction (release mold splitting mold), to avoid strong knocking, uniform coating of gel coat, not too thick, re-discuss the product single-piece size, and redesign the layering plan.


2. Defects, causes and solutions at the shop level

1 voids, bubbles


cause:


The method is incorrect when laying, the quality of the product is not enough, the corner parts are not handled properly, the felt is not moldable well, the mounting technology is poor, and the placement direction of the mold is not conducive to layering; insufficient light makes it difficult to find bubbles because the curing is too fast The shrinkage is large, forming a hollow; the work site is wet and the temperature is low.


Solution:


Re-recognize the basic essentials of layering operations, should not be sloppy, correct understanding of product quality, using the most reliable method. Correctly select surface felt and fiberglass cloth, and carefully study the essentials of layering. Re-examine the direction of mold placement, improve lighting, improve working environment, and increase temperature.


2 Too much resin


cause:


If you want to make it quickly soaked and use more resin, use excessive resin in the corner part due to the difficulty of handling glass fiber cloth. After the resin is saturated with glass fiber cloth, the resin is still painted.


Solution:


After the layer is leveled, apply the resin again. Use corners, brushes, and fingers to shape the glass fibers at the corners. Apply the resin as planned. The accumulated resin is scattered around with the brush.


3 Insufficient resin


cause:


Without correct product quality awareness, small thixotropy causes resin drip, incorrect curing dosage and accelerator dosage result in drip (vertical edge).


Solution:


Carefully study the layering technology, supplementing the lack of dolomite resin with brushes and resin, improve thixotropy, and speed up the gel; use the amount of curing agent and accelerator correctly.


4 color change


cause:


The resin scorches (partially) due to heat release during curing, because the work site is too humid or the glass fiber cloth is damp and the water content is too much.


Solution:


The thickness of the primary layer should be controlled below 5 mm, to reduce the amount of curing agent or the temperature of the work site, to avoid accumulation of local resin and change the environment of the work site.


5. Poor curing


cause:


Insufficient amount of curing agent, poor mixing of curing agent, mixed with water, styrene gas retention, low temperature.


Solution:


Carry out experiments so that the amount of curing agent can be increased or decreased according to the temperature and operating speed, fully stirred, use dry glass fiber cloth, and carefully study the principle that humidity, water, and oil are the main enemy of FRP. The core material should be dried to avoid Water enters the uncured product and maintains ventilation so that styrene does not remain on the bottom.


6. Foreign matter mixed in and noise


cause:


There is dirt on the fiberglass cloth or felt, the tools used for painting contain impurities, and the work site is not clean.


Solution:


Before use, remove the dirt on the fiberglass cloth or felt. The brush for gel coat and the brush for coating are separated to keep the work site clean.


7. Wrinkling, fluffing, layering


cause:


The creases folded by the glass fiber are cured too fast, the distribution of the shear openings is unreasonable, the resin dosage is insufficient and the layer is not pressed tightly, the glass fiber has poor wettability, and the first layer is cured before the second layer is laid.


Solution:


Lay the layer carefully, the second layer should cover the first layer of shearing, control enough glue when pasting, and brush with a knife to make the layer dense, catch up the air bubbles, release wax treatment before use, glass cloth To be fully dry, pay attention to the timing of laying.


8 Fiber revealed


Cause: The gel coat layer is too thin. Before the gel coat layer is fully cured, it should be spread and the mold release is too fast.


Solution:


Increase the thickness of the gel coat or put a layer of surface felt between the gel coat and the layer. After the gel coat is complete, the layer will be laid. After the product is fully cured and has a certain strength, it will be demolded.


3. Defects after demoulding

1. Deformation


Cause: The product is not completely cured when demoulding, the strength of the reinforcing rib is insufficient, and the product design is unreasonable.


Solution:


After the product is completely cured, it is demolded, the reinforcing ribs are correctly laid, and the resin with a low shrinkage rate is selected to reduce the curing shrinkage stress of the surface resin layer, maintain the shrinkage balance of the inner and outer sides of the product, improve the product design, and offset the bending stress.


2. Insufficient product hardness and rigidity


Cause: Incomplete curing.


Solution:


Check the amount of accelerators and catalysts, increase their proportions appropriately, avoid construction in cold and humid conditions, prevent the reinforcement materials from getting wet, and keep the storage environment dry; check whether the content of the reinforcement materials meets the design requirements, if the content meets the design requirements When the rigidity is still not enough, check the design itself, check the degree of curing of the resin, and perform post-curing treatment if necessary.


3. Crack or crack


cause:


The gel coat layer is too thick, the resin selection or the amount of curing agent is inappropriate, the styrene in the uncoating layer is excessive, the resin is not completely cured or the filler is added in an excessive amount, the product design is unreasonable, the abnormal stress layer is generated, and the crack occurs when it is impacted.


Solution:


Reduce the thickness of the gel coat layer, which should not exceed 0.5 mm. Use elastic gel coat resin. The filler should not be added in excess (25% of the product). The product should be designed reasonably. The proportion of curing agent and accelerator should be correct.


4. Dent


Cause: caused by resin shrinkage.


Solution: Partially solidify the product before adding ribs or iron parts.


Sourceļ¼šwww.up-resin.com

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