Analysis and Control to Prevent Weld Coating Defects

Weld geometry mutations on stress corrosion cracking of the main floor has two. First, because the high weld stay more than the same width, same height when molten plastic extruded film on steel cladding, coating the inevitable formation of the weld zone and thin compared to steel area, if the weld reinforcement than the standard provides more severe than this thickness. As we all know, when the plastic wall thickness is uneven, not only led to the plastic layer to form a ring body strength is poor, resulting in stress cracking caused by the weak link, the more serious is forming in its cooling process, will lead to shrinkage of residual stresses in thin cooling zone accumulation, in other words, the residual stress concentration in the weld zone coating body. Second, due to the geometry of the weld bead formed mutation weld reinforcement, under the same heating conditions, different thickness of the steel substrate different heat storage capacity, resulting in the formation of the weld zone area and the pipe heat tolerance, heat tolerance, if not in such effectively eliminated under cooling conditions, weld bead zone stress cracking corrosion layer also has a serious impact. 
As mentioned before, in the same frequency heating conditions, due to the presence of weld reinforcement, heat storage capacity greater than steel weld zone, if the weld reinforcement exceed standards, this is more serious heat tolerance. The effect of water cooling process mainly in the steel pipe weld zone and the formation of different residual heat pipe area. Because of the large heat storage capacity weld area, under the same cooling conditions, if the molding production line water cooling parameters insufficient cooling of residual heat after forming the weld zone is greater than the accumulated steel area, the residual heat by heat conduction with the weld area the second plastic layer is heat capacity, resulting in a temperature region higher than the plastic layer plastic pipe layer region, in other words, causes the strength of the plastic layer is less than the area of Plastic pipe layer. Impact of room cooling process mainly in the steel pipe weld zone formed different cooling systolic velocity and steel area. After forming pipe assembly line, with the contraction of the coating further cooling at room temperature, due to the residual heat of the weld zone, so that the plastic is heated again in the region, so the cooling contraction velocity is always slower than the steel area, combined with steel area Partial total coating thickness of the weld zone cooling contraction and thin area much larger than the total area of the coating cools and contracts, the impact is self-evident. 
Steel welding wire wound coating Layer PE molding process, because there is actually a mutation weld geometry, with the width of the extruded film, with the molten plastic with a high degree of thinning in the weld zone is normal and can be compensated by the technical parameters set technical standards so as to meet the requirements. Side seam coating thinning is discussed herein refers glue transfer roll or roller rolling part in unpredictable and non-normal cooling and shrinking polymer quality defects caused by the plastic material. Steel body and a smooth transition on both sides of the weld, epoxy powder electrostatic spraying hot melt technology, it will not form a coating on both sides of the weld defects, unless there is a big transition pit, very evenly coated with epoxy powder . An intermediate adhesive layer and an outer layer winding method using a polyethylene extrusion coated onto the tube film must have a certain tension, the film thus formed will Bohou uniform, smooth appearance, this time in the transition of the weld will form a cavity layer, if smooth transitions, the cavity will be automatically eliminated, even for a cavity may be formed before forming the roll by rolling the high elastic deformation under the action can be eliminated. Therefore, the side seam coating delamination only have three conditions: First, the effects of compaction roller defects; Second, the impact of the stress; Third, the effect of temperature.