Quality inspection and repair knowledge of glass fiber reinforced plastic pultrusion process products

Section One Product Appearance and Dimension Inspection

1.

(1) It can visually inspect whether the appearance of the product shape, color, etc.

(2) Can use measuring tools such as meter ruler and vernier caliper to measure the product size and confirm whether it is within the error range

(3) It can inspect the quality of FRP pultruded products, analyze the causes of defects such as burrs, bubbles, cracks, and complete uncuring, and propose solutions

2.

(1) Appearance characteristics of pultruded products

Qualified pultruded products should have a smooth and flat surface, free of pores, cracks, bubbles, delamination, whitening and other defects .

(2) Knowledge of surface defects of pultruded products

The main content of pultruded product inspection includes appearance inspection, integrity inspection and size inspection

(3) Use of the whole size measuring instrument

In pultruded products, the commonly used measuring instruments are as follows:

1.

2.

3.

4.

5.
The level is generally used when the mold is leveled to ensure the consistency of the mold and the traction table
.

(4) Quality inspection technology for pultruded products

The quality inspection content of pultruded products is more, including appearance, dimensional accuracy, performance indicators and other aspects
.

1.
Appearance products mainly refers color is uniform, and the end surface of the product for cracks, the surface is smooth and the like
.
Appearance is the most basic and most direct inspection item for pultruded products, and visual inspection is generally adopted
.

2.
Dimensional accuracy mainly refers to whether the thickness and angle of each part of the product section are within the tolerance range required by the customer.
Generally, vernier calipers and squares are used to measure
.
The products with higher requirements will also strictly control the flatness and straightness of the products, which need to be sent to a special testing organization for testing.
If it is a large batch production, it can also be specially made to measure the flatness and The straightness of the tooling is convenient for inspection at any time in daily production to ensure product quality
.

3.
Performance index There are many performance test items for pultruded products, generally by processing standard samples, testing in accordance with national standards, and there are special testing institutions
.

Section 2 Analysis, Judgment and Repair of Product Surface Defects

1.
Skill requirements

Can judge the bubbles, pinholes, cracks, and incomplete curing caused by factors such as on-site conditions and the process parameters of the inspection records, and can use tools and auxiliary tools to repair the identified problems
.
  

2.
Related knowledge

(1) Analysis and judgment of product defects

1.
Pultrusion product defects and correct knowledge

In pultrusion production, the operator should pay close attention to the online quality status 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 adjustment plans
.
In the production process, the types and causes of defects in pultruded products are analyzed as follows:

(1) Fiber and felt accumulation on the surface 

Result: 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, the product may be damaged
.
Causes:

a.
The accumulation of fibers occurs after interruption
.

b.
There are too many elastic strands in the yarn bundle
.

c.
The fiber viscosity is high, which leads to excessive pressure in the cavity
.

d.
Towing speed is too high
.

e.
The design of the mold entrance is unreasonable, and the reinforcement material does not enter the mold smoothly
.

f.
The unreasonable design of the pre-forming system causes the reinforcement material to travel unsmoothly
.

(2) The degree of product curing is not enough

Result: The product has a dull appearance and insufficient strength
.
Cause Analysis:

a.
Towing 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 there is partial peeling

Result: The product partially adhered to the mold, resulting in an increase in 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 small
.

b.
The effect of internal release agent is not good or the dosage is too small
.

c.
The speed is too fast
.

d.
The temperature in the front zone is set too high
.

(4) Scales appear on the surface

Result: Poor surface finish
.

Cause Analysis:

a.
The stress at the breakaway point is too high, causing creeping
.

b.
The breakaway point is too far ahead of the solidification point
.

(5) Cracks appear on the surface or inside of the product

Result: poor appearance and reduced performance
.
Cause Analysis:

a.
The speed is too fast, and the curing inside and outside 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 reinforcement material and base material
.

e.
The base material has poor adhesion
.

f.
The product is thick and the curing heat is too high
.

 (6) The powder is attached to the surface of the product

Result: The resistance in the mold increases, causing mold blockage
.
Cause Analysis:

a.
The inner surface of the mold is poorly polished, or the partial coating is peeled off
.

b.
There is a sticky mold in the mold, which causes damage to the surface of the product
.

(7) Liquid viscous substances ooze out on the product surface

Result: The appearance of the product is poor, and surface cracks appear
.
Cause Analysis:

a.
The product is incompletely cured, the temperature is low or the pulling 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.
The local fiber content is low
.

b.
There is mucosal phenomenon
.

c.
The surface felt is discounted
.

(9) White gauze or whitish on the surface

Result: The surface of the product is poor
.

Cause Analysis:

a.
Incomplete impregnation of yarn and felt, too thick felt layer or poor impregnation performance of felt material
.

b.
Impurities are mixed in and air bubbles are formed between the felt layers
.

c.
The fiber content is too high
.

(10) Surface fluffing

Result: Fibers are exposed on the surface
.

Cause Analysis:

a: The fiber content is too high
.

b: The resin is not well matched with the fiber, and the impregnation is poor
.

(11) Products are bent, twisted and deformed

Cause Analysis:

a: The curing of the product is not synchronized, resulting in curing stress
.

b: After the product is ejected from the mold, the pressure decreases and deforms under the action of stress
.

c: The materials in each part of the product are not uniform, resulting in inconsistent curing shrinkage
.

d: The product is not completely solidified when it is ejected from the mold, and it deforms under the action of external traction
.

e: The relative position of the mold and the traction direction needs to be adjusted
.

f: The temperature and speed parameter settings do not match
.

(12) Missing corners of products

Cause Analysis:

a: Insufficient local fiber content
.

b: The matching accuracy between the upper and lower molds is poor or scratched, resulting in knots and accumulation on the load and mold lines, resulting in missing corners and less changes in the product
.

(2) Knowledge of repairing pultruded products

For thermosetting pultruded products, under certain process parameter settings, after the product is drawn from 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 appearance of defects can be better by adopting certain remedial measures such as spraying, but it will greatly increase the cost of the product.
If it is not for the special requirements of the customer, this method is generally not recommended
.
The internal defects can only be improved by adjusting the process parameters
.
Therefore, for normal pultruded products, all the operator can do is to carry out appropriate post-processing to make the product more perfect
.

1.
The product is sealed in two sections 

Some products need to be used in a harsh corrosive environment.
In order to improve the service life of the product, the product section needs to be sealed to reduce the damage to the product performance caused by the cracks or defects of the corrosive medium through the section.
The sealing material can be ordinary resin
.

2.
How to clean up the burrs of pultruded products

Pultrusion burrs are generally relatively small, and most of them appear on the cut end surface of the product.
In the post-processing process, you can use round files, flat files and other tools for proper repair, or you can use sandpaper for sanding
.

(3) Product inspection report

1.
Skill requirements

Be able to take reasonable samples of products and submit them for inspection, and be able to compile product quality reports
.

2.
Related knowledge

(1) Inspection and sampling rules for pultruded products

Product inspection rules are a method and means used to assess and determine whether product quality meets standard requirements
.
It is the basic principle that the product manufacturing department and users must abide by to determine whether the product is qualified
.
In most product standards in China, inspections are unified into two types: type inspection (routine inspection) and factory inspection (delivery inspection)
.
In all product standards, the factory inspection rules and test items should be specified.
For type inspection (routine inspection), the conditions, rules and test items should be specified in the product standards
.
Generally speaking, the type inspection is a comprehensive inspection of the various quality indicators of the product to assess whether the product quality fully meets the standards and whether it meets all the design quality requirements
.
The factory inspection is the final inspection that must be carried out on the officially produced products at the time of delivery, to check whether the product quality at the time of delivery has the quality confirmed in the formal inspection
.
Products that pass the factory inspection can be delivered as qualified products
.
The factory inspection items are part of the formal inspection items
.

For pultruded products, form inspection in one of the following situations:

a.
When the material, structure and process have changed significantly after the first production or after normal production, which may affect the performance of the product
.

b.
After the production, the product structure, materials, second art and parameters have greatly changed, which may affect the product performance
.

c.
After 12 months of normal production
.

d.
When there is a big difference between the factory inspection result and the last type inspection
.

e.
When the national quality supervision agency proposes type inspection requirements
.
  

Sampling of pultruded products can be done by sampling randomly from the inspection batch of products
.
The quantity to be drawn can be determined according to the specific conditions of the product, or it can be negotiated by both the supplier and the buyer
.
If the samples are all qualified for the specified inspection items, it can be determined that the products of the corresponding batch are all qualified, otherwise it is unqualified
.

(2) Preparation method of pultruded product quality test report

Whether the pultruded product meets 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 conducted in accordance with the indicators provided by the customer
.
The results obtained through the test report can reflect the quality level of the product to a large extent
.
It is also used as a basis to prove that the product is qualified
.
There are many organizations that conduct performance testing of FRP products.
If it is a document provided to customers, a larger, 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 the material performance, you can use the universal testing machine to conduct the test
.
For the preparation of product samples, if standards can be used, standards should be used as much as possible.
If there are no standards, 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 Changes
.

3.
Quality control and improvement

Whether the product can stably achieve the required performance and quality level depends to a large extent on the manufacturer's effort in quality control
.
There are many quality control points in pultrusion production, but due to 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 you simply understand the key links in the quality chain, rely on your 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 the distribution of responsibilities in pultrusion are as follows, and each link should be controlled if conditions are available
.

(1) Acceptance of raw materials

The first hurdle in the control of raw materials is the raw material supplier
.
Raw material suppliers should provide stable raw materials
.
The most important focus of pultrusion manufacturers should be to grasp the characteristics of the resin
.
Each batch of resin entering the factory shall be sampled for inspection to identify whether it meets the requirements of the specification
.
The items to be inspected include appearance, viscosity, acid value, solid content, and reactivity
.
The quality records of resin testing should be kept, so as to provide valuable original data for judging process problems
.

Reinforced plastic is as important as resin in terms of function
.
Reinforcing materials mainly include untwisted roving, continuous felt and various forms of fabric
.
For untwisted roving, the moisture content, combustible content and linear density should be tested
.
For felts, in addition to testing the quality per unit area and the content of adhesives, attention should also be paid to the uneven distribution of fibers
.
It is very useful to analyze the cause of some process quality problems after measuring the moisture content of the reinforced material
.
For fillers, the particle size that can meet the product performance requirements should be selected, and the particle size distribution should not be too wide; for pigments, special attention should be paid to the uniformity of grinding and dispersion, otherwise it will cause 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 reinforcing materials that will or are being converted into products
.
At this control point, the main focus should still be on resin properties
.
The various components are mixed in a mixer to make a uniformly dispersed resin mixture
.
The temperature should be prevented from rising too much during the mixing process .
The dispersibility and contamination of the filler should be visually observed before removing the resin from the mixing equipment
.
Whether the fiber reaches sufficient infiltration in the resin tank is extremely important for pultrusion, and the viscosity of the resin is the most critical parameter that determines whether it can be sufficiently infiltrated
.
The continuous raw silk felt in the process should be checked frequently to see if its width is appropriate.
When using a felt that is too narrow, exposed rovings will appear on the surface of the part, and other defects such as partial excess of resin and unsightly appearance may appear
.
When using a felt that is too wide, it will fold to fit the mold cavity, which may cause the positioning of the reinforcement layer to be uncontrollable
.
In addition, since the felt must be pleated to enter the mold, it will increase the wear of the mold at the pleated area
.

(3) Process parameter control

The main process parameters of pultrusion are mold cavity temperature, resin temperature, cavity pressure, curing speed, curing degree, traction and traction speed
.
Foremost among them is the cavity temperature
.
The resin system used for pultrusion is very sensitive to temperature, and the control of the 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 it difficult to form and tow.
In severe cases, it will produce waste and even damage the equipment
.
The temperature distribution of the cavity should be low at both ends and high in the middle
.
The second is the cavity pressure
.
The cavity pressure is caused by the viscosity of the resin, the friction between the product and the cavity wall, the volume expansion of the material when it is heated, and the gasification of part of the material when it is heated
.
Therefore, the cavity pressure is a comprehensive reaction parameter of the behavior of the product in the cavity, and the cavity pressure is generally between 1.
7MPa--8.
6MPa
.
Another important parameter is traction speed, which is a parameter that balances curing degree and production speed
.
The traction speed should be increased as much as possible under the condition of ensuring the degree of curing
.