Common quality defects and causes of MDF (MDF,HDF,HARDBOARD,CHIPBOARD,PARTICLE BOARD,OSB ,LDF)

Common quality defects and causes of MDF

I

Appearance defect

1. The three-layer structure is too obvious (1) the water content is too high;

(2) The setting of the first peak position is too low;

(3) The flow of small pump in drying plasticizing section is too large, and the second peak is not obvious or even no second peak; 2. The fiber is too thick

(1) Poor raw materials and too much hard miscellaneous wood( 2) The water content of raw materials is too low( 3) The shape of wood chips is too large( 4) The steam pressure is too low( 5) The cooking time is too short( 6) The selection of grinding plate tooth shape is unreasonable( 7) The precision and quality of the grinding disc itself are not good( 8) The parallelism deviation between moving disc and fixed disc is too large( 9) The clearance between moving disc and fixed disc is too large;

(10) The pressure of the pressurizing cylinder is set too low, and the grinding disc moves axially( 11) The feeding amount is too large or uneven( 12) The steam balance pipe of grinding chamber is not put into use( 13) Excessive opening or excessive wear of discharge valve; 3. Rough surface (1) too coarse fiber( 2) The moisture content of slab is too low;

(3) The pressing plate temperature is set too high and the closing speed of the press is too slow;

(4) The setting of hot pressing curve is unreasonable, the flow of small pump in drying plasticizing section is too small, and the position is too far from the plate thickness (171mm);

(5) The application amount of paraffin is too small( 6) The pre curing layer is not sanded off( 7) Sanding has sand marks and sand lines( 8) The sizing amount is too low;

(9) The rough board is controlled to be super thick, and the dense layer on the surface is sanded off during sanding; 4. Foreign matters on the surface

(1) The wood chip contains foreign matters (such as rubber and tied rope)( 2) The conveyor belt is degummed and falls into wood chips and slabs( 3) Carbon deposition in grinding chamber and drying pipeline;

(4) When overhauling the equipment, there are residues entering the fiber on the equipment and site;

(5) The materials recovered from site cleaning contain sundries;

(6) When the equipment and environment are cleaned irregularly, the long-term accumulated dust and fiber fall onto the slab to form local softness; 5. Sand mark sand line

(1) Unreasonable distribution of cutting amount of coarse sand and fine sand( 2) The model and collocation of coarse sand and fine sand are unreasonable( 3) The quality of sand belt is unqualified and sand particles are easy to fall off( 4) The cooling time of the rough board is not long enough and the sand belt is stuck( 5) The abrasive belt has been used for too long and has not been replaced in time;

(6) Poor quality of graphite belt and wool pad or not replaced in time after wear( 7) The contact roll and conveying roll are seriously worn, and the accuracy can not meet the requirements( 8) The horizontal deviation between the sand frame and the sand frame is too large( 9) Feeding speed of conveying roller is not synchronous( 10) The recovery of sanding powder containing sand particles is too large( 11) There are problems in the installation of sander, and the vibration is too large( 12) The precision of the sander itself can not meet the requirements; 6. Local sand leakage

(1) Uneven slab after paving;

(2) The slab is partially damaged during transportation and loading;

(3) The same arm of the press was not adjusted well, and some slabs were washed out during the rapid closing process of the press( 4) Deformation of pressing plate( 5) Insufficient thickness of rough board( 6) The density deviation of rough board is too large( 7) Rough plate deformation;

(8) The graphite belt and wool pad are of poor quality or not replaced in time after local wear( 9) Local wear of contact roll and conveying roll is serious; 7. Large thickness deviation of rough plate (1) excessive deviation of raw materials( 2) Inaccurate slab weighing( 3) Unstable slab weight control;

(4) There are sundries on the thickness gauge or the thickness gauge has been worn( 5) The position controller does not work normally( 6) Deformation of pressing plate; 8. Rough board delamination and bubbling

(1) The moisture content of slab is too high or uneven;

(2) The quality, viscosity and solid content of the adhesive do not meet the requirements;

(3) The position of the first peak of the hot pressing curve is too small, the pressure is too high, and the surface dense layer is too thick;

(4) The pressure relief of the press and the opening speed of the pressing plate are too fast( 5) The pressing plate temperature is too high or the hot pressing time is too long( 6) Excessive density; 9. Soft edges and corners

(1) Uneven pavement and low slab edge density;

(2) The equipment vibrates too much or the line pressure of the pre press is set too low, and the fibers at the edges and corners collapse and fall during slab conveying;

(3) The deformation of the push-pull plate is serious, and the fibers at the corners collapse and fall during the pushing process( 4) The hot pressing process conditions are not met, and the adhesive is not fully cured( 5) The service time of sanding edge cutting saw is too long; 10. Burr

(1) The length of the cross-section saw chain is wrong, which makes the slab itself shorter( 2) The line pressure of the pre press is too small, and the slab becomes shorter in the pushing process;

(3) The surface of the push-pull plate is not smooth, and the resistance of the slab is too large and becomes shorter in the pushing process( 4) There are water or oil substances on the surface of the push-pull plate;

(5) The travel of the loading trolley is not adjusted properly, and the slab is not delivered in place in the loading machine;

(6) The forward travel switch of the plate loading horizontal oil cylinder is not adjusted properly, and the slab is not sent in place in the press( 7) Improper adjustment of the fast closing stroke of the press, resulting in serious slab deformation( 8) Improper adjustment of the same arm of the press; II

Unqualified physical and chemical indexes

1. Low static bending strength (1) (2) (3)

Low product density;

The closing and pressurizing speed of the press is slow, and the product density gradient is small;

Insufficient amount and uneven distribution of adhesive, high or low moisture content of slab, resulting in incomplete curing of adhesive;

(4) (5)

Poor quality of fiber raw materials or low fiber separation; The hot pressing time is too long or insufficient;

2. Low internal bonding strength (1) (2) (3) (4) (5) (6)

Insufficient sizing;

The pressurization speed is too fast (the product density gradient is too large) and the hot pressing time is insufficient; The slab has high moisture content and low temperature, and the adhesive is not fully cured; Low density;

The proportion of recycled waste fiber or sanding powder is too large;

The cooling time of the board is not enough, the stacking temperature is too high, and the adhesive is over cured and degraded;

3. Poor dimensional stability and deformation (1)

During molding, the density and thickness of each layer are out of proportion, the difference is large, and the upper and lower layers are distributed asymmetrically and contain water

Uneven rate;

(2) (3) (4) (5) (6) (7)

The density gradient of surface and core layer is too large;

During hot pressing, the temperature difference between the upper and lower hot pressing plates or the same hot pressing plate is too large; If the plate is not cooled enough, it shall be stacked; The height of the stacking cushion is different; High air temperature in the storage place;

The amount of sanding on the upper and lower surfaces is different, or the pre curing of the lower surface is serious and the sand is not exhausted;

4. Low nail holding force (1) (2) (3)

The density is too low or too high; The density gradient of surface core layer is too large; Insufficient sizing;

5. High hygroscopic expansion rate (1) (2) (3) (4)

Insufficient sizing or insufficient curing of adhesive; Low wax application or uneven distribution; Low density, poor fiber shape and quality;

The pH value of fiber or adhesive is not properly controlled, which affects the curing of adhesive or the self condensation of fiber;

6. Low surface bonding strength (1) (2) (3) (4) (5) (6)

The moisture content of slab is too low; The hot pressing plate temperature of the press is too high; The closing speed of the press is too slow; The first peak pressure of hot pressing curve is too low; The rough board is super thick, and the dense layer is removed by sanding; The sizing amount is too small;

7. Large density deviation (1) (2) (3) (4) (5) (6)

Unreasonable collocation of raw materials; Uneven pavement;

The accuracy of thickness gauge changes;

The flatness and temperature of press plate and pressure distribution deviation are too large; Large deformation during slab conveying and loading; Improper adjustment of synchronous closing of press;

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