Knowledge points about wooden based board and plywood, series six.
51. The term “old third board” refers to plywood, particleboard, and hard fiberboard. The term “new third board” refers to waffle board, oriented particleboard, and medium density fiberboard.
- Development trend of wood-based panels
(1) Explore natural forests of new raw materials for wood-based panels: bamboo, wood from artificial forests, crop straws, and other wood resources (such as urban wood waste and shrubs)
(2) Take the road of clean production and circular economy, adhere to the 4R principle: Regrow — regeneration principle; Reduce — the principle of reducing entropy; Reuse — Reuse principle; Recyle — the principle of recycling
(3) Develop new products
(4) High and new technology applied to wood-based panels - Plywood unit: Veneer fiber Board Unit: Fiber particleboard Unit: particleboard
- The wood-based panel production process can be divided into two main parts: unit fabrication and board shaping and processing.
(1) Unit manufacturing such as plywood mainly includes: log or small path wood sawing, wood heat treatment, wood stripping, wood center and rotary cutting, edge sealing and drum, drying, veneer cutting, sorting, repair and processing, storage.
(2) board forming and processing such as urea-formaldehyde resin plywood mainly includes: preparation of dry panel, preparation of dry core board, preparation of adhesive, sizing, group blank, slab prepressing, hot pressing gluing, cutting, surface processing, grading and inspection, packaging storage. 55. Requirements for selection of plywood raw materials
(1) Log length,According to the national standard, plywood log length is 4m, 5m, 6m, according to the specification requirements of the production board, choose the reasonable length of wood section.
(2) log quality, there should be no defects that have a serious impact on plywood yield and veneer quality. Such as the log of the larger sharpening, bending, hollow, fracture, scar, decay, ring crack and other defects can reduce the utilization rate of wood; Log of twill grain manage, knot sub, change color to wait, make veneer surface quality and intensity reduce, affect the quality of products such as plywood thereby.
(3) Log diameter level, log diameter directly affects wood yield and labor productivity. The minimum diameter of plywood used by our country is 26cm. With the development and utilization of fast-growing plantation resources, it is a trend that the diameter class of veneer timber decreases.
(4) Wood properties, in addition to the requirements of the above aspects, special attention should also be paid to the wood properties. Trees with extremely high density, high hardness or severe warping deformation after drying should be avoided. Different species of wood is not the same, the process of raw materials can not be mixed at will. - Analysis of common defects in bonding.Request a Quote
I. does big glue
The reason:
(1)The deterioration of adhesive;
(2) insufficient curing of adhesive layer;
(3) glue moisture;
(4) Moisture content of veneer is unqualified;
Hot platen temperature is too low or part of the temperature is not uniform.
Solutions:
(1) replace the rubber material;
(2) improve the hot pressing temperature, prolong the hot pressing time;
(3) choose the formula with less water content or add flour, soybean powder and so on appropriately to absorb water;
(4) strictly control the moisture content of veneer and prolong the hot pressing time;
(5)Check the hot pressure plate steam access and air supply.
II. Reasons for bubbling and local glue opening:
The moisture content of veneer is too high;
(2) depressurization from the balance pressure to drop too fast;
(3) the use of rubber layer has been partially cured of the core board, or the slab mounting plate and pressing plate closed, the glue is partially cured;
(4)There are blank spots, grease or inclusions on the veneer surface;
The hot pressing time is not enough or the local temperature of the pressing plate is low.
Solutions:
① Reduce the moisture content of veneer or increase the concentration of glue liquid or reduce the amount of glue coating;
② Control the speed of the second stage of depressurization;
③ the core plate without curing glue is used to reduce the loading time or the device is closed at the same time;
④ remove grease or inclusions on the surface;
⑤ Extend the hot pressing time or check the hot pressing plate.
III. Low bonding strength
The reason:
①The deterioration of adhesive;
②The hot pressing pressure is low, the time is not enough, and the temperature is low;
③ The moisture content of veneer is too high;
④ too little glue, glue coated veneer aging time is too long, so that the glue too long into the back veneer;
⑤The viscosity of the glue is too low, too much glue into the veneer;
⑥The veneer cutting quality is poor, the surface roughness is large, the back crack is deep;
⑦ Some sizing core plate rubber layer has been partially cured, or blank plate and pressure plate closed, local curing.
Solutions: Request a Quote
(1) replace the rubber material;
(2) modification of hot pressing process parameters;
(3) Check the moisture content of veneer and control it within the specified range;
(4) increase the amount of glue coating and control the aging time;
(5) testing the quality of adhesive, improve the viscosity;
(6) Improve the quality of veneer cutting;
The use of glue is not cured core plate, reduce the loading time or the use of closed device.
IV. Reasons for glue penetration:
① The glue is too thin and too much water;
②large amount of glue;
③ The cracks on the back of the veneer are too deep;
④The moisture content of veneer is too high;
⑤ slab aging time is not enough;
⑥ The pressure is too high when hot pressing;
The veneer is thin and the tube hole of the ring hole is large.
Solutions:
① Detection of adhesive quality, viscosity of glue; Improve the resin content of the glue; Choose the formula with less water content;
② reduce the amount of coating, replace the wear of the coating roller;
③ Improve the quality of rotary cutting, adjust the position of the ruler to increase the compression rate of rotary cutting;
④ Reduce the moisture content of veneer;
⑤ Increase the aging time, so that the water in the glue part of volatilization;
⑥ Reduce the pressure, check the pressure gauge of the hot press;
⑦ Increase the viscosity of the glue.
V. Panel lamination seam
The reason:
① splicing veneer crack or degumming crack;
② Single board bubbling (tight side) or flounces (loose side).
Solutions:
Improve the quality of jointing and veneer edge sealing;
Check the installation of pressure ruler to improve the quality of veneer cutting.
VI. Core plate folding core seam
The reason:
(1) Manual core arrangement, the expansion gap between the zero pieces is not accurate;
(2) core plate dislocation when loading or moving;
(3) the preloading effect is not good, and the adhesion between veneers is not good;
The edge of the core plate is not straight;
The core plate edge has flounces or cracks.
Solutions: Request a Quote
(1) Realize the whole core plate, the aging time of the opening of the core plate is appropriate;
(2) the slab is installed after pre-pressing, and the slab should be moved smoothly;
(3) master the appropriate time and appropriate prepressing process;
(4) the core plate shall be leveled, and the core plate shall be leveled after drying after cutting first;
(5) Improve the quality of core plate cutting and drying.
VII Plywood warping.
The reason:
① The billet does not conform to the principle of symmetry;
② the positive and negative direction of the blank surface is not correct;
③Veneer from stress wood;
④ hot press plate deformation;
⑤ Plywood stacked uneven.
Solutions:
(1) The billet should conform to the principle of symmetry;
(2) the front side (close side) of the blank should be outward;
(3) Rotary cut veneer should be levelled (soft treatment);
(4)Repair or replace the pressure plate;
(5) Plywood should be neatly stacked. - At present, China’s wood-based panel output has ranked first in the world, and has become a major man-made production country in the world, but not a powerful country.
Main reasons:
① Wood resources are seriously insufficient, and the contradiction between supply and demand intensifies
② Most manufacturers have small production scale and low production efficiency
③ Product quality and environmental protection standards are backward
④ Fewer varieties, unreasonable structure
⑤ Low level of technical equipment - Polyvinyl chloride plastic (PVC) film
Process: PVC resin → film → printing pattern → molding on the board. Film adopts gravure printing technology to print wood grain or pattern. - Hot pressing process: prepressing slab → repair → sanding and thickness → hot pressing surface and back. Request a Quote
