Uneven Wall Thickness

A winchester of fuming nitric acid with a plastics cap burst, probably owing to internal pressure build-up and uneven wall thickness. The explosion fractured... 

A winchester of fuming nitric acid with a plastics cap burst, probably owing to internal pressure build-up and uneven wall thickness. The explosion fractured an adjacent bottle of acetone which ignited on contact with the oxidant [1]. Segregation of oxidants and fuels in storage is essential to prevent such incidents, which have occurred previously elsewhere. Another explosion resulted, when attempting to clear a jammed glass stopper by successive application of acetone and nitric acid [2],... 

Pack extension due to incorrect pressure balance during the autoclaving cycle— may be called dimpling if mild. Often associated with uneven wall thickness. The above cannot be predicted and are only discovered after storage. 

Thermoforming shows two important drawbacks. First, the pattern of deformation results in highly uneven wall thicknesses in the finished article. In a cup, for example, the lower brim may be half as thin as the middle or the upper rim. Second, the fact that deformation takes place in the rubbery condition. In this condition, straining is accompanied by chain orientation, which is frozen in upon rapid cooling. When the article is heated to above its Tg, it tends to recover its original shape and deforms, but at lower temperatures it shows a strong tendency to shrink. 

Uneven wall thickness circumferentially Pin not centered in die ring Adjust die pin position... 

Large flat surfaces are a major problem in rotationally molded parts as they tend to distort during cooling due to uneven wall thickness and uncontrolled release. The problem is most apparent in highly crystalline materials such as polyethylene. If... 

PLA has a low melt strength due to its low high shear viscosity and poor viscoelastic properties.[2] Poor polymer melt strength contributes to sag, uneven wall thickness and tearing in thermoforming [3], particularly in... 

In the wall thickness fluctuations up to 5 % may occur. As a result of the uneven temperature in the molten polymer during rotation, and also by the not always exactly reproducible rate of cooling, deviations in the dimensions of the finished product may amount to 5 %. Requirements are, that the materials can be molten completely, that the melt is sufficiently low-viscous, and that the molten polymer does not degrade too rapidly. Besides plasticised PVC, HDPE and LDPE are often used, as well as copolymers of PE such as EVA (ethylene - vinyl acetate copolymerj.Because the shear stresses in this process are extremely low, a narrow molar mass distribution is to be recommended, as discussed in 5.4. Cycle times vary between 3 and 40 minutes, dependent on the wall thickness. Cycle times can be reduced considerably by using machines with multiple moulds, since the cycle time... 

A typical H nmr sample is 0.3 to 0.5 mL of a 10-20% solution of a nonviscous liquid or a solid in a proton-free solvent contained in a 5-mm dia. glass tube. The sample tube must be of uniform outside and inside diameter with uniform wall thickness. Test a sample tube by rolling it down a very slightly inclined piece of plate glass. Reject all tubes that roll unevenly. 

Wall thickness uniformity Incorrect mold rotation because of equipment problems or the wrong rotation ratio Variation in the thickness of the mold wall resulting in uneven heat transfer, thus improper melting and fusion rate of the resin Variation in heat transfer to the mold... 

The blowing process, though simple, has a few disadvantages the wall thickness is uneven and the weld at the bottom is deformed. These drawbacks are partly taken care of by a variant of the process, that is, the injection-molding blowing process. Here, a preform is made by injection molding, comparable to the extruded portion, but now more adjusted to the ultimate shape of the bottle. This preform is transported to a second part of the mold, in which it is blown up under pressure. 

A European chemical factory had corrosion/erosion problems in an inlet pipe, particularly weld corrosion. Traditional UT was seen to be unreliable because the uneven surfaces and varying wall thickness (not to mention the cramped space) made it a very challenging task for even the most experienced UT operator. Equipping the inlet with a sensing matrix allows the factory to regularly inspect for the onset of corrosion, with more intensive inspection if corrosion occurs. UT is also difficult to apply in high temperature. 

If the manufacturing practices show that the walls of the part are uneven, a remedy can be found through the installation of auxiliary panels made from sheet metal, through painting with aluminum colors, or through wall thickness modifications of rotational mold. Inserts made from plastic material or steel can be fixed into the walls of the molded parts, but must be preheated to initial temperature of the mold. It is important that the pins, which are necessary for the acceptance, are properly installed so that no plastic can leak at these points during the rotation. 

---