Views: 5 Author: Site Editor Publish Time: 2020-06-28 Origin: Site
The slab obtained by paving different constituent units of the artificial board has a loose structure and a large thickness. In order to ensure the slab paving structure and a certain degree of compaction, prevent the slab from collapsing during transportation, reduce the opening between the press plates, and improve productivity, so a cold press needs to be pre-compressed before using the hot press .
Different artificial board, slab cold pressing process and cold press equipment are different.
1. Preloading of plywood
Before the hot press of plywood, the short-term pressure is often used in the cold press to make the veneer basically stick into a whole, so it can be loaded and unloaded without a pad, saving heat consumption and improving the capacity of the cold press.
In order to meet the requirements of the cold press process, the adhesive should have the performance of bonding in a short time. For the urea-formaldehyde resin glue, the current method is to add fillers such as stone powder, soy flour to improve the initial viscosity of the glue, or add a small amount of polyvinyl alcohol to modify the urea-formaldehyde resin glue synthesis. After phenolic resin sizing, it has a good initial viscosity during the aging period, and it is initially bonded by a cold press.
The process of the cold press using polyvinyl alcohol modified urea-formaldehyde resin glue is: slab closing and aging is not less than 40min, unit pressure is 1.0-1.2MPa, and cold pressing time is 10-20min. Using an ordinary cold press, the upper press type is the most convenient. The domestic design working interval height is 1.0~1.5m, the maximum unit pressure is 1.5MPa, and the total pressure is 450t.
2. Cold press of particle board
The purpose of using a cold press for particle board slabs is to make the slab structure compact, to eliminate the residual air in the slab, to prevent the air from rushing out and damaging the slab when the hot press is used, and to reduce the thickness of the slab. This can not only simplify the structure of the press, but also increase the output and ensure the quality of the product.
The process requirements for the use of cold presses for chipboard slabs are: the general slab compression is 1/3~1/2; the preload pressure is 1.5~1.6MPa, and the minimum is not less than 1.0MPa; the cold pressing time is 10~30 s . After cold pressing, the slab usually rebounds, and the rebound rate of the slab is generally 15% to 25%, which is the most suitable. There are two cold pressing methods for slabs: one is periodic flat cold pressing; the other is continuous cold pressing.
Periodic plane preload is divided into upper pressure type and lower pressure type. The upper pressure type is more recommended here. In this way, cold pressing requires several conveyor belts, which are used for slab weighing, flushing and cold pressing machine plate mounting device and maintaining a distance during flushing operation, so as to ensure the slab continuity when hot pressing the plate run.
Continuous cold press is in a continuous cold pressing machine, the slab is moved in a compressed state, and the slab is directly paved and cold pressed on the paving steel belt. Therefore, the speed of the steel belt is required to be fixed after being determined according to the needs of paving and cold pressing.
3. Cold pressing of fiberboard
The cold pressing of wet-process fiber slabs is mainly for dewatering of the slab, and the rolling dewatering method is commonly used. In order to prevent the sudden increase of applied pressure and cause the slab to rupture, four pairs of cold pressing rollers were gradually pressurized, and then two pairs of rolls reached the maximum pressure to reduce the moisture content of the slab to 65% -70%. A small number of flat cold presses of the upper pressure type are also used, and the dehydration efficiency is higher, and the water content of the slab can be reduced to 50%-55%.
The cold press of dry fiberboard is basically similar to the cold pressing of particleboard. The thickness of the slab after the formation of dry fiber fibers reaches 30-40 times the thickness of the product, so cold pressing must be performed. The degree of compression of the cold pressing of the fiber slab is related to multiple factors such as fiber separation quality, water content, raw material type, sizing amount, cold pressing pressure, molding method and process.
The above is the content of artificial board cold pressing. If you have any questions in the production of plywood, you can contact us at any time. We can provide you with plywood production solutions.