Harnstoff-Formmasse

How to use Urea-formaldehyde moulding compound? pretreatment a, electric material In the progress of the compression of the electric material, the common method of pretreatment is of putting the material into heat moulding chamber, under the average pressure of 100kg/cm2 or 120 kg/cm2. The time can be set according to the condition: when we continue to press the material, it can still flow and be filled with the moulding chamber. Normally, 10s 15s can be the optimum time. b, toilet seat cover material There are three existing methods of pretreatment for the toilet seat cover material. a) high frequency preheating High frequency preheating is the most popular one in the China mainland. The advantage is that time is very short. The disadvantage is that the time can’t be controlled and the material can easily be destroyed because of the high temperature of microwave drying. It will lead to the emerging of the stains of the products and influencing the flow ability of the material. The time of ordinary suggestion is less than or equal to 60s. b) oven preheating In the method of oven preheating, the preheating temperature and time can be operated according to the heat resistance of the material. However, the disadvantage is that the heating uniformity of material depends on the thickness of the bed of material, because the wind pressure of oven is lower. The suggestive temperature is less than or equal to80°C, and the time can be available as long as the material can be useable. c) drum-type preheating The method of drum-type preheating is very ideal. The material is rolling in the roller and the heating temperature of jacket can be controlled. Normally, the temperature is 70 80°C. Because the heating way is stable and round-the-clock and the material should be used and filled continuously, the progress can be easily operated, the fluctuation is low and the continuity is good. d) screw preheating The method of screw preheating has been widely used in the injection molding products, with the characteristic of high efficiency. Normally, the preheating temperature is divided into three periods: the temperature of the first period (adding the material) is 70°C, the second one is 80°C and the third one is 80 85°C. Also, the preheating temperature can be divided into two periods: the temperature of the first period is equal or greater than 70°C, and the second one is 90°C. the method of material mouldinga) the temperature of mould cavity <a> toilet seat cover material: the temperature of upper mold is equal or greater than145°C and the temperature of the lower one is less than or equal to140°C. <b> electric material: the temperature of upper mold is equal or greater than150 155°C and the temperature of the lower one is 150°C. <c> injection molding material: the temperature of fixed mold is 150°C and the temperature of movable one is equal or greater than150°C. b) When the material is moulded by the way of compression, firstly, the material which has been preheated should be put into the moulding chamber, and the material should be compressed into incipient melting stably under the average pressure of 100kg/cm2 120 kg/cm2. Then the material should be pressured until reaching the condition of maintaining pressure which is 180 200kg/cm2. After 5 10s, the pressure should be released to the zero position and be kept for 8 10s. Afterwards, the material should be pressured to the given pressure and then the pressure should be maintained until the material reaches the condition of the total solidification. c) The injection material is added from the hopper at a certain amount. After preheating by the method of screw preheating, it can be filled with the cavity through extrusion in 10 15s, under the pressure of 100 kg/cm2. And then the pressure should be maintained according to the given time until the last step which is demoulding. the selection of the liquidity of the material The selection of the liquidity of the material for the moulded products is very important. Normally, the liquidity is divided into three levels by the material manufacturer, which is high liquidity, normal liquidity and special liquidity (lower liquidity). Because the shape, structure, thickness and size of the products are very different, and different products need different suitable liquid material, it comes to be very vital to choose the suitable liquid material according to the acquirement of the products under the standard pressure. a, the way of selection a) The high liquid material should be chosen by the thick and large product as well as the products from one mould. b) The normal liquid material should be chosen by the normal products. c) The special liquid material should be chosen by the small-size products. b, the influence of the liquidity towards the products a) For the products, the over-good liquid material at least can decrease the compactness of the product, extend the processing period and affect the quality and labor efficiency. b) For the products, worse liquid material will affect the cost rate of the product because of the incomplete filling. And it will lead to the rising cost. c) For the products, the suitable liquid material will be favorable not only to the quality, but also to the cost.