Particle Board QC Inspection Checklist : Part 1 Problems and product quality defects in hot pressing of particleboard or fiberboard

Particle Board QC Inspection Checklist : Part 1 Problems and product quality defects in hot pressing of particleboard or fiberboard

In the production process, due to various reasons such as raw material quality, operation level and equipment operation status, many potential adverse factors will be exposed in the hot pressing process, resulting in various defects of products. The more common ones are: bubbles,

In the production process, due to various reasons such as raw material quality, operation level and equipment operation status, many potential adverse factors will be exposed in the hot pressing process, resulting in various defects of products. The common ones are: bubbling, delamination, warpage, uneven thickness, local softness and surface indentation, etc.

1 bubbling

Bubble refers to the rapid vaporization of hot water in the Particle Board during the pressure reduction process of the hot press, and the sudden release of a large amount of steam, which destroys the bonding force between particles or fibers. Bubbles are loud, mostly in the middle of the Particle Board, and there is a protrusion on the Particle Board surface. Bubbles can occur in one place or in many places, and in severe cases can fill many parts of the board with bubbles.

The main reasons for bubble defects are: too high moisture content of slab, too fast pressure reduction speed, etc.

2 delamination

Particle Board delamination means that a large area of degumming occurs in the board, forming a certain separation boundary. Layering occurs mostly at the edges and corners of the board, and sometimes in the middle of the board.

The main reasons for delamination are: too high moisture content of particles or fibers, too low hot pressing temperature, too short pressing time, poor curing of core adhesive, insufficient unit pressure, poor quality of adhesives, too little sizing or uneven sizing. In addition, too low moisture content of particles or fibers and too fast pressure-reducing speed will also make the board stratified.

3 Warpage Deformation

Warpage deformation means that the edge and center of the Particle Board are not on the same horizontal plane. That is, the edge is warped and the middle is concave. Warpage deformation is expressed by warpage degree. The method to measure warpage is to place the concave Particle Board face up on the horizontal platform, and place the Particle Board ruler 1 m long in the diagonal direction of the Particle Board surface. The maximum chord height is measured with 150 mm steel ruler along the two diagonal directions, respectively.

The main reasons for warpage deformation are asymmetry of the paved slab, which makes the particle or fiber specifications of the symmetrical layer inside the slab inconsistent; or symmetrical of the paved slab, but too bumpy vibration in the transport process, which makes the fine particles or fibers deposited on the bottom of the slab and become asymmetrical structure, so that the slab will be warped when pressed into the slab. The pavement slab is not uniform, the density of the slab is different, the internal stress of the product is large, and the warping deformation is easy to occur. In addition, the asymmetry of hot pressing process can easily cause warpage deformation of products. For example, the temperature difference between upper and lower pressing Particle Boards is large, and the temperature distribution of the same pressing Particle Board is extremely uneven. It is easy to make the stress in the Particle Board uneven, thus making the product warpage deformation. The moisture content of the whole slab is not uniform, and even the storage of the flat slab is unreasonable, warpage deformation may occur to varying degrees.

  1. uneven thickness

The uneven thickness of the Particle Board can be expressed as a whole or a part. The main reasons are: uneven thickness of cushion, deflection of hot press, debris sticking on thickness gauge or wear of thickness gauge itself, insufficient stiffness of hot press Particle Board and deformation during pressure.

The products with uneven thickness bring more trouble to decoration and use, increase sanding allowance, waste of raw materials, and invisibly increase product cost.

  1. Local softness

Non-uniform slab pavement or local collapse during slab transportation results in local flake or insufficient fibre or weak bonding in slab. In severe cases, particles or fibers may fall off.

6 Surface indentation

Due to the improper control in the production process or the problems of the equipment itself, the surface of the processed Particle Board may be partly uneven, which is called surface indentation.

There are many reasons, such as falling large pieces of wood or other debris during paving, uneven or damaged cushion, hard debris sticking on cushion or hot pressing board, etc.

Keywords : China Particle Board inspection ,Chinese  Particle Board  QC, Particle Board  grading rules , Particle Board  manufacturing defects , Particle Board  quality control ,

Examples of particleboard surfaces: (top-left) quality surface, (top-right) hollow near the border, (bot- tom-left) pool of oil, (bottom-right) blot. 

Examples of particleboard surfaces: (top-left) quality surface, (top-right) hollow near the border, (bot- tom-left) pool of oil, (bottom-right) blot.

MDF and PB Grading System ,

The new  Grading System  is a powerful and effective system for  the inspection of all types of surface defects in particleboard and MDF surfaces. The system is designed to handle all panel sizes. The   system is designed to detect surface defects under the most challenging conditions. The system holds an unlimited number of grading
recipes, thus ensuring objective grading according to the customers’ defined surface quality. The strength of the system is its ability to detect, categorize and classify surface defects. For this purpose, multiple light sources are used to capture images with different properties to detect the defects. How visible each defect is depends on the viewing angle and light
distribution across the panel.The  system generates multiple images from the panel using different light sources in
different angels and direction, just like a human who changes the angle when holding the panel up against the light when looking for small defects. In one angle, the defect is not visible, while changing the angle, it is seen.
The increased use of thinner papers, high-gloss papers and high-quality lacquering no longer hides surface defects in the raw board. It is not uncommon that raw board defects count for up to 50% of the downgrades on laminations lines. The  system optimizes grading, depending on the end-use of the raw boards, and eliminates downgrades on the lamination
lines resulting from raw board defects. Existing customers have seen an increase of more than 2% on the lamination line after installing the system behind the sander.

INSPECTION ADVANTAGES
 100% inspection at full speed
 Every panel is graded
 Customized and consistent grading
 Objective grading, only relevant defects are downgraded
 Accurate reports and statistics, take control

Latest technology
The modular system can cover panel width up to  3  m  and generates multiple images for detection of   defects.
The images are transferred to a PC and analyzed for surface defects by the  image processing software. The built-in defect library contains separate detectors for each defect. It keeps track of defects by size and location and grading rules can be defined according to type of defect, location and amount. Digital signals controlling the sorter are activated based on the grading result. Customized grading depends on correct detection and categorization of all surface defects by downgrading only the defects that the customer cannot accept.

The next image processing technology
The latest   Image Processing software includes easy-to-use functionality for operation and adjustment of defects and recipes. It includes defect specific parameters and functionality for grouping defects. More efficient technology
Combining grading, chatter mark detection and thickness measurement systems in one, reduces the amount of hardware and simplifies the operators work environment. Integrate non-contact sensors, together with surface grading. Thickness measurement data is processed together with surface defects and panels are rejected due to wrong thickness or surface grading defects automatically.

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