How to repair plastic stool cracks?
Plastic parts appear (cracks) cracks, mainly due to the stress caused by plastic parts too large or stress concentration, the main factors are injection mold, injection molding, plastic parts and raw materials. Mold is generally open, and this does not say, and if the following methods can not be resolved, then we must consider whether it is necessary to change the mold
1, if the holding time is too long, plastic parts are subjected to excessive pressure, there will be a greater residual stress, easy to cause plastic parts and cracks, which can properly shorten the holding time.2, if the injection pressure is too large, the residual stress will also increase, this stress easily causes cracks in the plastic parts, which should be appropriate to reduce injection pressure.3, if the injection molding must use higher injection pressure, in order to reduce the residual stress in the plastic parts, can reduce the melt and mold temperature, mold temperature and improve the barrel, extend the cooling time of plastic parts, the molecular chain orientation can have time to recover.
Plastic parts1, if the contour sharp changes of the place of plastic parts, but also the stress concentration, the most easy to crack, in this regard, in plastic design, the shape of the exterior angle and the interior should as far as possible with a large circular arc.2, the plastic parts with embedded metal and plastic, due to thermal expansion coefficient differences, such as thermoplastic thermal expansion coefficient is 6-11 times that of steel, aluminum 3-6 times, therefore, the overall contraction in the plastic block will hinder the plastic, the resulting stress will lead to plastic parts in order to reduce or avoid cracks due to crack insert appears, from the following aspects:First of all, in the selection of materials, as far as possible the use of thermal expansion coefficient close to the resin metal, such as zinc, aluminum, copper and other non-ferrous metals.Next, insert the piece as far as possible in the high molecular weight resin manufacture piece of plastic, this kind of resin crack resistance is stronger.Furthermore, the thickness of the plastic around the insert should be thicker, and the minimum wall thickness will vary with the variety of the plastic.Three, raw materials1, release agent and melt difficult to dissolve, such as too much dosage, easy to crack, this should be as little as possible or no release agent.2, too many recycled materials, do not add too much water intake3, do not use low viscosity raw materials, low molecular weight4, resin moisture content can not be too much, drying of the resin5, multi use crystallization resin6, if the material is more pressing, the injection machine must adhere to the raw material parts thoroughly clean, so as not to the performance of different raw materials after mixing, cause plastic parts cracks.
