In the production process, the multilayer press frequently loads the slab and sends out the blank. Sometimes, hard objects (such as bolts, iron blocks, etc.) will be brought into the hot press with the slab, or the slab will be missing in the interval of a certain laminate. At this time, when the hot press is boosted, under the dual effects of temperature and pressure, the hot press plate will often appear pits, cracks, deformation and other phenomena, but also produce uneven temperature. After sanding, the surface of the pressed wool plate will appear white spots, local soft, tiger spots wrinkles, uneven thickness of the hard layer, which greatly affects the product quality. Especially after hot-pressing plate deformation, the thickness deviation of each layer of blank is larger, and some of them are thicker. When sanding, the hard layer of the plate surface is sanded out, and when sanding, the plate surface is not sanded. In order to reduce the quality problems such as sand failure and rough and soft surface, it is often necessary to increase the thickness of the board and the hard layer of the board in order to ensure the minimum sanding allowance, which not only increases the production cost of the product, but also causes the quality defects such as uneven density and warping deformation of the board, and at the same time brings difficulties to the adjustment of the sander.
Analysis of Deformation Cause of Hot Press Plate
Undoubtedly, the main reason for the large thickness deviation of wool sheet produced by multi-layer hot press production line is the deformation of hot press sheet. In recent years, we have studied and analyzed the deformation of hot-pressed plate, and found that most of the deformation of hot-pressed plate is regular transverse deformation and longitudinal deformation. The main reasons are as follows:
1) The heating is uneven, and the temperature rises too fast during preheating, especially when the cold start-up preheating is easier to deform.
2) When heated by steam, sometimes the steam pipe in the hot-pressing plate is blocked or scaled, and the heat conduction is not uniform, which makes the temperature rise of each part of the hot-pressing plate different, and has caused hot-pressing deformation. Sometimes the condensate water is not discharged smoothly and it is not easy to control the temperature, so it is easier to cause hot-pressing plate deformation.
3) In the production process, the density of missing slab, short slab or individual slab is too low, which makes the pressure concentrated on the thickness gauge and causes the deformation of hot-pressed plate.
4) If the hot press publishes poorly, unloads the plate rack chuck, the back slab collides with the front blank, which will cause the fibers in the front of the slab to pile up. If the operator fails to find out in time, the hot press boost will easily cause the bending deformation of the hot press plate.
Solution to Deformation of Hot Press Plate
In the production of medium density fiberboard, the deformation of hot-pressed plate not only affects the realization of production capacity, but also mainly affects the quality of products, which is related to the economic benefits of enterprises. Experience shows that the main way to solve the deformation of hot pressing plate is to prevent the deformation of the hot pressing plate, and to use the hot pressing machine correctly and strictly in accordance with the operating rules of the hot pressing machine, so as to prevent the hot pressing machine from air pressure and slab leakage; to inspect the production of formaldehyde, regularly remove the thickness gauge and the fibers on the hot pressing plate; to regularly detect and adjust the hot pressing machine, and to recognize the defects of the hot pressing plate. Really timely do a good job of hot press maintenance and maintenance. For the deformed hot-pressed plate, it should be repaired in time to avoid causing greater losses.
There are many ways to repair the deformation of hot-pressed plate, but in summary, there are mainly the following methods:
1) Planing hot-pressing board: This is the traditional solution. The deformed hot-pressing board is unloaded and planed on the gantry planer to achieve the required geometric accuracy. This method not only stops production for 2-3 days, but also reduces the strength and stiffness of the hot-pressed plate by cutting 4-8mm on both sides at a time in order to eliminate the deformation of the hot-pressed plate.
2) Mechanical correction: With the help of some mechanical methods to eliminate deformation and restore the original geometric accuracy of the hot-pressed plate. The principle is that the deformed part of hot-pressing plate can eliminate the deformed part under the action of correcting the external force. 3) Flame correction: refers to heating the deformed part of the hot-pressing plate with a B flame or other gas flame, and correcting the deformed part by using the new deformation caused by local heating of steel.
Which method to repair the deformed hot-pressed plate can be adapted to local conditions according to the existing conditions of the enterprise.