Skill Requirements
Can judge bubbles, pinholes, cracks, and incomplete curing caused by factors such as on-site conditions and process parameters detected and recorded, and can use tools and auxiliary tools to repair identified problems.
Product defect analysis and judgment
1. Pultruded product defects and correction knowledge
In pultrusion production, the operator should pay close attention to the online quality of the product, respond in time when the appearance and performance of the product are abnormal, observe whether the production site conditions have changed, whether the process parameters are stable, etc., and make an adjustment plan. During the production process, the types and causes of defects in pultruded products are analyzed as follows:
(1) Fiber and mat accumulation appear on the surface
Results: Reinforcement materials are entangled and squeezed at the entrance of the mold, resulting in increased resistance of the product in the mold, and in severe cases, product damage. Causes:
a. The accumulation occurs after the fiber is interrupted.
b. There are too many elastic strands in the yarn bundle.
c. Fiber viscosity is high, resulting in excessive cavity pressure.
d. The traction speed is too high.
e. The design of the mold entrance is unreasonable, and the reinforcement material is not smooth into the mold.
f. The design of the preforming system is unreasonable, resulting in the unsmooth movement of the reinforced material.
(2) The degree of product curing is not enough
Result: The appearance of the product is dull and the strength is not enough. Cause Analysis:
a. The traction speed is too fast.
b. The temperature setting is too low.
c. Insufficient amount of curing agent.
(3) The surface sticks to the mold, and local peeling occurs
Result: Part of the product adheres to the mold, resulting in increased resistance and a sharp increase in traction force, eventually blocking the mold.
Cause Analysis:
a. The fiber content is too low or the amount of filler added is too small.
b. The effect of the internal release agent is not good or the dosage is too small.
c. Too fast.
d. The temperature of the front zone is set too high.
(4) Flakes appear on the surface
Result: Poor surface finish.
Cause Analysis:
a. The stress at the breakaway point is too high, resulting in crawling and creeping.
b. The breakaway point is too far ahead of the solidification point.
(5) Cracks appear on the surface or inside of the product
The result: poor appearance and reduced performance. Cause Analysis:
a. The speed is too fast, and the internal and external curing of the product is inconsistent.
b. The temperature setting is unreasonable, and the product curing is too violent.
c. The mold is too short and the product is poorly cured.
d. Poor matching between reinforcing material and base material.
e. The base material has poor adhesion.
f. The product is thick and the curing heat release is too high.
(6) Powder attached to the surface of the product
Result: Increased internal resistance in the mold, leading to mold blocking. Cause Analysis:
a. The inner surface finish of the mold is poor, or the local coating falls off.
b. There is mold sticking in the mold, resulting in damage to the surface of the product.
(7) There is liquid viscous substance oozing from the surface of the product
Result: The appearance of the product is not good, and surface cracks appear. Cause Analysis:
a. The product is not fully cured, the temperature is low or the casting speed is too fast.
b. The fiber content is small, the shrinkage is large, and the uncured resin is ejected.
c. The temperature setting is unreasonable, and the internal and external curing is not synchronized.
(8) The surface is uneven and has dark groove marks
Phenomenon: The appearance of the product is poor. Cause Analysis:
a. Local fiber content is low.
b. There is mucous membrane phenomenon.
c. The surface felt layer is discounted.
(9) White gauze or whitishness appears on the surface
Result: The product has a poor surface.
Cause Analysis:
a. The impregnation of yarn and felt is not complete, the felt layer is too thick or the impregnation performance of the felt is not good.
b. There are impurities mixed in, forming air bubbles between the felt layers.
c. Fiber content is too high.
(10) Surface fluffing
Result: Fibers exposed on the surface.
Cause Analysis:
a: The fiber content is too high.
b: The resin and the fiber are not well matched, and the impregnation is poor.
(11) The product is bent, twisted and deformed
Cause Analysis:
a: The curing of the product is not synchronized, resulting in curing stress.
b: After the product is out of the mold, the pressure decreases and it deforms under the action of stress.
c: The material in each part of the product is not uniform, resulting in inconsistent curing shrinkage.
d: The product is not fully cured when it is released from the mold, and it is deformed under the action of external traction.
e: The relative position of the mold and the direction of the traction force needs to be adjusted.
f: Temperature and speed parameter settings do not match.
(12) Missing corners of products
Cause Analysis:
a: Local fiber content is not enough.
b: The matching accuracy between the upper and lower molds is poor or there are scratches, resulting in knots and accumulations on the load and mold lines, resulting in missing corners and less changes in the product.
Pultrusion product repair knowledge
For thermosetting pultruded products, under certain process parameter settings, after the product is pulled out of the mold, the appearance structure and internal performance of the product basically become an unchangeable state, and there is little room for repair. Of course, the defects of the appearance can be better treated by taking certain remedial measures such as spraying, but it will greatly increase the cost of the product. If there is no special requirement from the customer, this method is generally not recommended. For internal defects, it can only be improved by adjusting process parameters. Therefore, for normal pultruded products, all the operator can do is to perform appropriate post-processing to make the product more perfect.
1. The two sections of the product are headed
Some products need to be used in a harsh corrosive environment. In order to improve the service life of the product, the cross section of the product needs to be sealed to reduce the damage to the product performance caused by the cracks or defects of the corrosive medium passing through the cross section. The sealing material can be ordinary resin.
2. Cleaning method of burrs in pultruded products
There are generally few pultrusion burrs, and most of them appear on the cutting end of the product. In the post-processing process, it can be properly repaired with tools such as round files and flat files, and can also be polished with sandpaper.
Product inspection report
1. Skill requirements
Can carry out reasonable sampling and inspection of products, and can write product quality reports.
2. Relevant knowledge
(1) Inspection and sampling rules for pultruded products
The product inspection rule is a method and means adopted to assess and determine whether the product quality meets the standard requirements. It is the basic principle shared by the product manufacturing department and users to determine whether the product is qualified. In most product standards in our country, the inspection is unified into two types: type inspection (routine inspection) and factory inspection (delivery inspection). In all product standards, the rules and test items for ex-factory inspection should be stipulated, and for type inspection (routine inspection), the conditions, rules and test items should be specified in the specified product standards. Generally speaking, type inspection is a comprehensive inspection of various quality indicators of the product to evaluate whether the product quality fully meets the standards and meets all design quality requirements. The factory inspection is the final inspection that must be carried out on the formally produced products when they are delivered, to check whether the product quality at the time of delivery has the quality confirmed in the formal inspection. Only products that pass the factory inspection can be delivered as qualified products. The factory inspection project is part of the formal inspection project.
For pultruded products, the form test is carried out in one of the following situations:
a. When there are obvious changes in materials, structures and processes during the first production or after normal operation, which may affect product performance.
b. After being put into production, the product structure, materials, secondary technology and parameters have changed significantly, which may affect product performance.
c. After 12 months of normal production.
d. When the factory inspection result is quite different from the last type inspection.
e. When the national quality supervision agency proposes type inspection requirements.
Sampling of pultruded products can be done by random sampling from the inspection batch. The number of draws can be determined according to the specific situation of the product, or it can be agreed upon by both parties. If the samples taken are all qualified for the specified inspection items, it can be judged that all the products of the corresponding batch are qualified, otherwise they are unqualified.
(2) Writing method of pultruded product quality test report
Whether the pultrusion products meet the customer's requirements, in addition to the manufacturer's own inspection of its size and appearance, in most cases, the material performance test or the overall product performance test must be carried out according to the indicators provided by the customer. The results obtained through the test report can largely reflect the quality level of the product. It is also used as a basis for proving that the product is qualified. There are many institutions that conduct performance testing of FRP products. If it is a document provided to customers, a relatively large and authoritative testing department with certain qualifications should be selected. If it is only used by the manufacturer to compare the product performance of different formulations, as a technology accumulation or to explore material performance, a universal testing machine can be used for testing. For the preparation of product samples, if standards can be used, use standards as much as possible. If there is no standard, a test plan can be made according to the actual situation, but the conditions and environmental consistency of multiple tests must be ensured to reflect the performance to the greatest extent. The change.
3. Quality control and improvement
Whether the product can stably meet the required performance and quality level depends to a large extent on the manufacturer's efforts in quality control. There are many quality control points in pultrusion production, but due to the investment in test equipment and personnel, few manufacturers have achieved this to the greatest extent, and many manufacturers do not even have the most basic quality control capabilities. have. In fact, as long as we simply understand the key links in the quality chain, and rely on our own efforts and external support (such as strong raw material suppliers), manufacturers with limited conditions can still achieve good results. The quality control points and responsibilities in pultrusion are assigned as follows, and each link should be controlled if conditions permit.
(1) Acceptance of raw materials
The first level of control over raw materials lies with raw material suppliers. Raw material suppliers should provide stable raw materials. The most important focus of pultrusion manufacturers should be to grasp the characteristics of resin. Respond to the sampling inspection of each batch of resin entering the factory to verify whether it meets the specification requirements. The items checked include appearance, viscosity, acid value, solid content, and reactivity. The quality records of resin testing should be kept, so as to provide valuable raw materials for judging process problems.
Reinforced plastics are as functionally important as resins. Reinforcement materials mainly include roving, continuous felt and various forms of fabrics. For untwisted roving, the moisture content, combustible content and linear density should be tested. For felts, in addition to testing the mass per unit area and binder content, attention should also be paid to the uneven distribution of fibers. It is very useful to analyze the cause of some process quality problems through the determination of the moisture content of the reinforcing material. For fillers, the particle size that can meet the performance requirements of the product should be selected, and the particle size distribution should not be too wide; for pigments, special attention should be paid to the uniformity of its grinding and dispersion, otherwise it will bring serious color difference to the product. Attention should also be paid to its compatibility with the resin and its influence on the reactivity of the resin.
(2) Raw materials on the process line
The raw materials on the process line refer to the prepared resin mixture and the reinforcement materials that will be or are being converted into products. The main focus on this control point should still be resin performance. Mix various components in a mixer to make a uniformly dispersed resin mixture, and prevent the temperature from rising too much during the mixing process. Visually inspect for filler dispersion and contamination before removing resin from mixing equipment. It is extremely important for pultrusion whether the fibers are sufficiently infiltrated in the resin tank, and the viscosity of the resin is the most critical parameter to determine whether the fibers can be sufficiently infiltrated. For the continuous raw filament mat in the process, it should be checked whether its width is appropriate. When using a mat that is too narrow, exposed rovings will appear on the surface of the component, and other defects may appear, such as local surplus of resin and ugly appearance. Using a batt that is too wide may cause uncontrolled reinforcement positioning as it folds to fit the cavity. Also, since the felt must be pleated to enter the mold, this increases wear on the mold where the pleats are placed.
(3) Process parameter control
The main process parameters of pultrusion include cavity temperature, resin temperature, cavity pressure, curing speed, curing degree, traction force and traction speed, etc. Chief among these is cavity temperature. The resin system used for pultrusion is very sensitive to temperature, and the control of mold cavity temperature should be very strict. The temperature is low and the resin cannot be cured. When the temperature is too high, the glue will solidify as soon as it enters the mold, making molding and pulling difficult, and in severe cases, waste products will be produced or even equipment will be damaged. The mold cavity temperature distribution should be low at both ends and high in the middle. The second is cavity pressure. Cavity pressure is due to the viscosity of the resin, the friction between the product and the wall of the cavity, the volume expansion of the material when it is heated, and the gasification of part of the material when it is heated. Therefore, the mold cavity pressure is a comprehensive response parameter of the behavior of the product in the mold cavity, and the general mold cavity pressure is between 1. 7MPa--8. 6MPa. Another important parameter is the take-off speed, which is a parameter that balances the degree of curing and the speed of production. Under the condition of ensuring the degree of curing, the traction speed should be increased as much as possible.