Spider lines

Column pipe coupling Guide spider Line Shalt Line Shalt coupling Column pipe... 

The board shown in Figure 15.4 was produced without added antioxidants. It was exposed for 75°C (167°F) for 1 month, and then transferred to a weathering box (0.35 W/m, 1 42/0.18 cycle). After a month in the oven, at 167°F, the board s surface looked good. After just 1 day in the weathering box, at about the same maximum temperature (actually, about 10° lower) but with water spray for 18 min every 2 hours, its surface became slightly but noticeably soft. On the second day the deterioration increased, and after 5 days the boards cracked along spider lines and fell apart. 

The experiment was repeated with a similar board, but exposure in the oven at 75°C was for 3 months, and then the board was transferred to the weathering box as described above. After 72 h of exposure at 1 42/0.18 cycle, the board cracked along spider lines, and after 86 h the board broke itself in two parts. After 6 days the board was deeply crumbled. 

Spider lines are essential elements in extruded composite hollow deck boards. Spiders in an extrusion die interrupt the melt flow, causing it to separate and then rejoin (see Figs. 15.6 and 15.7). This welding of the profiles creates the so-called spider lines along hollow composite deck board profiles. 

Spider lines are usually visible to the naked eyes as linear surface depressions. They are stress concentrators. Figures 15.8-15.11 show the development of an oxidative crumbling of a composite deck board with clearly visible cracks along spider lines, and Figure 15.12 shows a catastrophic failure of WPC board due to oxidative decomposition. 

An inspection of the deck has shown that it began actively crumbling Some boards produced cracks along spider lines, and board fragments between these cracks started to fall out. Top surface of the deck became soft and easily scratchy. 

Die, weld, and spider lines Damaged die ring Repair or replace die tool-... 

Spider lines n. In blow molding or pipe extrusion, visible marks parallel to the par-ison or pipe axis and corresponding to the positions of the spider legs. They are due to incomplete welding of the divided stream downstream of those legs. These lines are the exterior traces of weld surfaces that go through the annular wall, surfaces that are sometimes weaker than the material between them. 

Section of poorly mixed extrudate with spider lines (two arrowed) from die head. 

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