Pipe Extrusion Research Articles

Quantitation of Employee Exposure to Emission Products Generated by Commercial-Scale Processing of Polyethylene

Although considerable research has been performed on the thermal degradation products of polyethylene, no data that can be compared to occupational exposure limits have been reported on the exposure of workers in commercial polyethylene extrusion operations. In this study, the actual airborne concentrations of previously identified analytes were measured during the commercial-scale processing of polyethylene resins. Nine polyethylene resins, spanning LDPE, LLDPE, and HDPE product slates were processed under commercial-scale conditions appropriate to their application: blown film, extrusion coating, blow molding, pipe extrusion, and rotational molding. Air samples were taken from operator breathing zones and of representative workplace air and contained air (inside film bubbles and molded parts) using recognized occupational health and safety protocols. The compounds selected for monitoring consisted of aldehydes (formaldehyde, acetaldehyde, acrolein, butyraldehyde, crotonaldehyde, and benzaldehyde), aromatics (benzene, toluene, xylenes, and styrene), formic and acetic acids, furan and tetrahydrofuran, and acetone. Airborne particulates also were measured. Of the 450 concentrations measured from workplace air and operator breathing zones, 440 were below detection limits. Nine of the remaining ten concentrations were <10% of the established exposure limits, while one particulate measurement was <50% of the established exposure limit. As well, 180 contained-air samples were taken. Off-gases trapped inside film bubbles and molded parts accumulated to concentrations above those measured in the ambient air. It was concluded that polyethylene extrusion presents minimal inhalation hazards in a moderately ventilated environment.

Quantitation of employee exposure to emission products generated by commercial-scale processing of polyethylene.

Although considerable research has been performed on the thermal degradation products of polyethylene, no data that can be compared to occupational exposure limits have been reported on the exposure of workers in commercial polyethylene extrusion operations. In this study, the actual airborne concentrations of previously identified analytes were measured during the commercial-scale processing of polyethylene resins. Nine polyethylene resins, spanning LDPE, LLDPE, and HDPE product slates were processed under commercial-scale conditions appropriate to their application: blown film, extrusion coating, blow molding, pipe extrusion, and rotational molding. Air samples were taken from operator breathing zones and of representative workplace air and contained air (inside film bubbles and molded parts) using recognized occupational health and safety protocols. The compounds selected for monitoring consisted of aldehydes (formaldehyde, acetaldehyde, acrolein, butyraldehyde, crotonaldehyde, and benzaldehyde), aromatics (benzene, toluene, xylenes, and styrene), formic and acetic acids, furan and tetrahydrofuran, and acetone. Airborne particulates also were measured. Of the 450 concentration measured from workplace air and operator breathing zones, 440 were below detection limits. Nine of the remaining ten concentrations were < 10% of the established exposure limits, while one particulate measurement was < 50% of the established exposure limit. As well, 180 contained-air samples were taken. Off-gases trapped inside film bubbles and molded parts accumulated to concentrations above those measured in the ambient air. It was concluded that polyethylene extrusion presents minimal inhalation hazards in a moderately ventilated environment.

Experimental simulation of metal flow in porthole-die extrusion

The metal flow in the extrusion of a pipe through a porthole-die has been analyzed experimentally, regarding the process as a combination of multi-hole die and multi-billet extrusions. The distorted grid patterns on some symmetrical planes of metal flow were observed continuously using a split-tool assembly and split specimens having square grids inscribed on their surfaces, the distribution of particle velocity being determined from the grid distortion observed. In the so-called welding plane, a symmetrical plane of metal flow, the region where welding occurs is actually located near to the die exit and occupies only a small area. To inspect the reliability of simulation results, the extrusion of A1050 pipe through a porthole-die was carried out, metal flow in the container and in the welding chamber being investigated by macro etching.

UBA analysis of the process of pipe extrusion through a porthole die

The deformation behavior in the extrusion of pipes through a porthole die has been analyzed by means of the upper-bound approach (UBA) and the results compared with experimental ones. The proposed model has a smooth boundary to the plastic region and a continuous velocity field. The predicted extrusion loads were found to be less than 10% greater than the experimentally recorded loads. The results of the analysis show that there exists an optimum depth of the welding chamber with regard to the extrusion pressure. The analysis suggests also that the pressure is greater with a larger ratio of the diameter of the welding chamber to that of the container, and that the variation tendency of the pressure with the number of portholes is effected by whether the circumcircle of portholes is fixed or not. When the length of the billet remaining in the container is smaller than the radius of the container, the plastic region extends over the whole of the billet. For the distribution of the flow velocity and the shape and volume of the dead-metal zone, there exist some differences between the predicted and the experimental results.

A Spectral Element Simulation of Gravitational Flow During Plastic Pipe Extrusion

When plastic pipe is extruded, it emerges from an annular die and passes through a sizing sleeve to set its outer diameter. The pipe is then solidified in a cooling tank by spraying the outer surface with cold water. For thick walled pipe, material on the inside stays molten for a long time, and flows under its own weight. This gravitational flow (or sag) therefore governs the final pipe wall thickness distribution. Thus the solidification of extruded plastic pipe involves heat transfer with phase-change coupled with gravitational flow. The inside thermal boundary condition is arguably adiabatic. For the outside boundary, one can use either Newton’s law of cooling or an isothermal condition. In this paper, a commercially available spectral element code for simulating unsteady incompressible fluid flow with heat transfer, has been used to simulate sag flow. The model predictions of the solid pipe thickness distribution compared well with process data. Also, the effects of different heat transfer parameters on the thickness profile are evaluated. The extrusion temperature is found to have the greatest effect on the pipe wall profile.

Characterisation of polymer masterbatches by modern thermal methods of analysis

Thermoplastic masterbatches are a complex blend of the base thermoplastic resin, a pigment and a range of additive materials. End use applications of masterbatches include agricultural film, packaging film, injection moulding of small and large bottles, boxes and crates and extrusion of pipe and sheet.

Elimination of Sag in Plastic Pipe Extrusion

Abstract Plastic pipe is produced by extruding molten polymer through an annular die. As the pipe leaves the die, it passes through a sizing sleeve and then a cooling tank where it solidifies slowly. For thick walled pipe, the inside of the pipe remains molten for as long as ten hours causing downward melt flow called sag. Sag can cause serious non-uniformity in pipe wall thickness. The conventional way to reduce sag is by manually adjusting the die eccentricity, until an acceptable wall thickness profile is achieved. This tedious trial and error procedure can take up to four attempts to get the right profile. In this paper a new way has been proposed to reduce sag, by rotating the pipe during cooling. A numerical simulation of sag flow while pipe is rotating, predicts that for rotational speeds between 0.1 to 10 rad/s, sag is virtually eliminated for thick walled, large diameter HDPE pipe extrusion.

Simulation of Slump in Plastic Pipe Extrusion

Extruded plastic pipe leaving an annular die is solidified in a long cooling tank by spraying the outer surface with cold water. The inside surface can take a long time to solidify as the solidification progresses radially inward. This results in flow of molten polymer down the inside of the pipe. This gravity flow of molten extrudate is called slumping, and it can cause serious nonuniformity in pipe wall thickness particularly in large diameter, thick walled pipes. It can also lead to another phenomenon known as “knuckle” formation where melt accumulates at specific locations. A simple numerical scheme to model this flow has been developed. Three-dimensional graphical illustrations of the slumping phenomenon based on this simulation are presented in this paper. The model predictions have been compared with commerical pipe data and they are in qualitative agreement.

Prediction of residual stress distribution in plastic pipe extrusion

AbstractIn thermoplastic pipe extrusion, the extrudate emerging from the die is typically sized and cooled from outside in a quench tank. This process causes quick solidification of the external layer, while the inner mass of molten material cools only gradually. The slow cooling and crystallization, and the associated shrinkage of this material, can lead to build‐up of severe stresses in the final part that can affect the long term service performance. In this paper, a simple theoretical analysis of this process of residual stress build‐up is presented. The pipe undergoing quenching is modeled as an annular cylinder of molten polymer being cooled at a controlled rate from outside. The overall stresses are derived numerically by adding up the stress contributions due to incremental advance of the solidification boundary. The results of the analysis are found to be in qualitative accord with the experimentally measured stress profiles in thermoplastic pipe.

Physical and chemical changes during the extrusion process

AbstractChemical and physical processes are attracting increasing attention from plastics processors. The reasons for this are basically twofold. On the one hand, more and more processors are recognizing that the quality of their products is highly dependent upon physical processes (cooling, temperature control, blending, etc.) and, on the other hand, new methods of physical and chemical treatment are being developed which are bringing improvements in quality and hence, virtually inevitably, greater profitability in production. This technology has made its impact both on discontinuous processing (reaction injection molding), on cable and pipe extrusion, and on the direct polymerization of tapes and films. The formulations that can be applied here are monomer casting systems. A prerequisite for the industrial utilization of this system is a process analysis of the reaction molding compound processing in a parallel‐running twin screw extruder to allow the influence of the process parameters on product quality (e.g., molecular weight) to be clarified and the polymerization to be integrated into other processing sequences, such as panel extrusion. The modification of tried and tested plastics through blending with other polymers, however, can also change the properties of the material in such a way that cost‐intensive plastics can be replaced or even new fields of application can be opened up. The attainable properties are just as much a function of the individual components and their percentage content as they are of the blending technique, as investigalions on a corotating twin‐screw extruder have shown. The melting zone takes on primary significance, since it is here that both the homogenization and desired or undesired high shearing takes place. The crystallization of semicrystalline plastics also has a considerable influence on product quality. To date this has been influenced by the selective addition of nucleiproducing foreign substances. A new process substitutes electron‐irradiated granules for these nucleating agents, such that the drawbacks of the foreign particles (toxicity, notch effect, and optical impairment) are eliminated. The effectiveness of this measure is reflected in better mechanical characteristic values. These both allow a higher product quality and a shortening of cooling time and hence higher productivity. Modijication of material properties through subsequent crosslinking represents the state of the art in rubber and polyethylene extrusion for cables and pipes. Special peroxides and the application of microwave energy make it possible to crosslink extrudates (pipes, profiles) made of HDPE and EPDM. The kinetics of crosslinking are explained, taking the example of crosslinking with peroxides. It is seen that the process technologv has to be adapted to the compound in terms of residence time and temperature. Under these conditions the microwave energy crosslinking plant operates with considerably shorter plant lengths and hence with lower energy losses.

Flow induced fiber orientation in an expanding channel tubing dies

AbstractIn the application of plastic pipes for fluid transport and for the protection of underground electrical cables, it is desirable to improve mechanical properties, particularly in the hoop direction. The use of orientable reinforcing particles such as chopped glass fibers could make possible such an improvement if the orientation of the fibers could be controlled. While conventional pipe extrusion dies tend to promote axial fiber orientation, the use of an expanding channel die has been proposed to produce a preferential hoop orientation of fibers. In this paper, a theoretical model of the flow of a fiber suspension through an expanding channel die that predicts the fiber orientation distribution at the die exit is described. The effects of Theological properties and die geometry on the final fiber orientation distribution are predicted. The results of an experimental study of fiber orientation in pipe extruded using an expanding channel die are shown to be in agreement with the theoretical predictions.

A finite element computer simulation of a pvc pipe extrusion process

AbstractThis paper discusses the development and verification of a finite element heat transfer computer program which can simulate a PVC pipe extrusion process. The simulation is broken down into seven phases which represent various thermal conditions throughout the process.

Single-screw extrusion of polypropylene pipes

Single-screw extrusion of polypropylene pipes

小径ビレットよりの大径管製造法の研究

小径ビレットよりの大径管製造法の研究

Effect of PVC resins on multi‐screw pipe extrusion

AbstractThe increased use of multi‐screw (twin) extruders by pipe producers brought on this study of available PVC homopolymer “pipe grade” resins. Basic tests on resin were examined via a “Correlation Matrix” computer program. Highly significant test data were determined to be internal pore volume and centrifuge plasticizer adsorption. Additional compound evaluation proceeded via torque rheometer followed by twin‐screw extrusion. Significant resin test values affecting extrusion properties are inherent viscosity, apparent bulk density, porosity uniformity and melt viscosity. The work shows that the compounder should know resin properties in order to benefit from processing equipment developments.

Poly (alpha‐methylstyrene) as a processing aid for rigid poly (vinyl chloride)

AbstractPoly (alpha‐methylstyrene) (PAMS) is a new approach to process improvement in rigid poly (vinyl chloride) (PVC)—the use of a low molecular weight polymer as a process aid. PAMS can reduce fusion time, melt viscosity and improve heat stability of rigid PVC compounds. The reduced melt viscosity allows the addition of fillers to PVC without adverse effect on extrusion rates. This polymer also improves the resistance to melt fracture and shear “burning” at high shear rates. When used within the optimum concentration range, physical properties such as tensile strength, Izod impact and heat distortion are maintained. In addition, PAMS gives, improved production rates in both pipe extrusion and injection molding processes without sacrifice in properties.

The Properties of Pipes Produced under the Conditions of Spiral Flow

Abstract The present communication is concerned with the relation between the strength properties and the morphology of low-and high-density polyethylenes in the extrusion of pipes under the conditions of spiral flow. It has been found that the optimal strength properties of pipes result when lamellar crystals are oriented in the middle portion of the pipe wall about 45° relative to its axis. Model experiments have been carried out on polystyrene melts through the use of optical-polarization technique and, as a result, the data obtained for polycrystalline polymers have been verified from the qualitative point of view.

STUDIES ON THE EXTRUSION (5TH REPORT)

In this report, it is described the effect of mandrel size on extrusion pressure for pipe making of Pb and Sn, various properties of pure Al pipe, and the doudle pipe making by direct extrusion.By studing these problems mentioned above, the results obtained are as follows:(1) When the pipe is extruded by the same form die and the different mandrel in dia., max. or min. extrusion pressure is proportional to A1/A2.If by the same mandrel in dia. and the different die in form, it is proportional to the logarithmic A1/A2.(2) Hardness of pure Al pipe is higher in outerside and is mild at inerside. And it is ununi form at the head of pipe.(3) Double pipe extrusion pressure vs. stroke curves resemble to one of pure metal bar extrusion.And it is uniform in thickness ratio of double pipe at high temperature extrusion.

A Lead Extrusion Phenomenon

IT has been known for the past two decades that in the extrusion of lead cable sheaths and pipe on the hydraulic press, the presence of oxides may result in the existence of irregularities in the structure which are brought to light by suitably etching a polished section. In this case, the feature originates in the oxidation of a surface of the metal exposed at an earlier stage in the process, and the layer of oxide, formed at right angles to the direction of flow, may be folded over, and appear afterwards as a radial line of weakness in the finished pipe. An important distinguishing feature in this type of irregularity is the fact that the crystal structures on the two sides of the feature are quite separate and distinct; there is no growing of the crystals across the line of oxide (see Fig. 1).