Extrusion Tests Research Articles

Second Paper: Extrusion of Steel and Titanium

This paper describes the results of forward and backward extrusion tests on steel and titanium specimens at very high impact speeds, using reductions in area of 44 to 86 per cent. The specimens were in all cases of 1-in diameter, 1.5 in long. For the cold forward extrusion of steel, impact speeds over the range 68-310 ft/s were used. Comparison of mean extrusion and work of deformation at these high speeds was made with the values arising at very low speed. Extrusion pressures were minimal in the impact velocity range 40-80 ft/s. Tests using steel billets preheated to temperatures between 300 and 600°C showed no great advantage in preheating above 400°C. This degree of preheating showed considerable advantages over the cold process, in that extrusion pressures were much reduced, product quality was improved, and higher extrusion ratios could be obtained. Limited backward extrusion tests at 66 ft/s proved the feasibility of the process. Gold forward extrusion of titanium at 65 and 167 ft/s was successful only at the relatively low reductions in area of 44 and 61 per cent. At higher degrees of deformation, the extruded product broke into small pieces.

The Flowability and its Temperature Susceptibility of Carbon Paste

Favorable flow properties of carbon paste are required for Soderberg anodes of aluminium reduction cells and for the extrusion of carbon products, however, the carbon industry still lacks in the adquate knowledge of the rheological properties of paste. The flowability test and the extrusion test were carried out in order to study correlation between the flow properties of paste and the qualities of the binder.The flowability of the paste increases with the increase of temperature, but becomes nearly constant at temperatures over 70-80°C above the softening point in the flowability test and over 40-50°C above, in the extrusion test. The maximum flowability at temperature-insensitive range decreases with the increase of the percent of quinoline insoluble, acting as a coke flour, of the binder. When the flow behaviour of paste is measured at high shear stress by the extrusion test, the quinoline insoluble matter has a little effect on the extrusion pressure. The correlation between the temperature susceptibility of flowability and the properties of the binder is not detected for pitches used in this experiment.

Some analytical and experimental studies of axi-symmetric cold forging and extrusion—II

The results obtained from several forging and extrusion tests at room temperature and low speed are compared with theoretical results, and the following conclusions emerge. 1. (1) The working pressures for the compression of soft aluminium cylinders between rough flat dies, for the compression of soft aluminium annuli in a container between lubricated or rough dies and for the steady-state lubricated extrusion and piercing of hard aluminium and copper cylindrical billets, are 10–20 per cent below the calculated upper bound. 2. (2) Calculated upper bounds agree qualitatively with the working pressures obtained during some non-steady extrusions and piercings of soft aluminium, hard aluminium, copper and soft brass. 3. (3) The steady pressures divided by the mean yield stress in combined bar and tube extrusions from cylindrical billets and in tube extrusions from hollow billets, together with those in ordinary extrusion and piercing, were found to be almost entirely a function of the total reduction in area, when the tools are lubricated. 4. (4) The working pressure in opposed extrusion-piercing-forging is considerably lower than that for a one-way extrusion-forging. The working pressures in opposed extrusion-forging with two dies and in opposed piercing-forging with two punches were lower than that in corresponding one-way working, using a die or punch of the larger orifice when the length of billet is moderate. In symmetrically opposed working, the pressure exceeds that in one-way working when the billet length becomes very small. When the material flow through one orifice is interrupted midway in an opposed forging, the working pressure thence follows that of the corresponding one-way working. 5. (5) The deformation of hard aluminium and copper annuli compressed between lubricated flat dies was as predicted from the most suitable velocity field. The speed of efflux of material through two separate orifices was affected by the frictional resistances acting on the material rather than by the difference in the areas of the orifices when the billet length was moderate. But, as the length was reduced, the speed from the wider orifice tended to increase. These results were in qualitative accordance with those derived from plane-strain analysis. 6. (6) The internal flow pattern observed on the meridian section of a lead billet as photographed through a glass plate was in qualitative agreement with the corresponding most suitable velocity field and was very similar to that of the comparable plane-strain working. 7. (7) The main types of defect found in the various extruded and extrusion-forged products were skin inclusion, cavity formation and internal cracking. They were predicted quantitatively and qualitatively from the velocity field of the least upper bound. The inclusion was prevented by using a rough die in contact with the material surface from which the skin was unfolded. Cavity formation and internal cracking was thought to be prevented by restraining the material flow through the orifices. The onset of the latter defects was retarded by intermediate annealing. 8. (8) The internal pressure acting on the container during extrusion-forging and coining was found to be lower than the mean working pressure within the range of conditions tested. The pressure acting on the projection of the coining die was in excess of the mean working pressure, the difference being larger for higher projections and for thinner slug thicknesses. The residual pressure between the material and the container after extrusion or closed-die coining was found to be nearly equal to the uniaxial yield stress of the material.

Influence of Moisture Content of Carbon Black on Rubber Properties

Abstract The moisture content of carbon black should be kept approximately constant if maximum accuracy in rubber testing is to be attained. In this laboratory we have found it convenient to equilibrate blacks at about 30 per cent humidity, under which condition most rubber channel blacks adsorb 1.5 to 2.0 per cent water. In the case of most of the properties of tread stocks, this precaution decreases the average deviation from the mean value in any series of experiments. In the case of extrusion tests, the effect of adsorbed moisture is so great that the use of a standard moisture content, or at least the determination of moisture content at the same time as the black is milled for extrusion, is necessary if reproducible results are to be expected.

A Simplified Extrusion Plastometer for Unvulcanized Rubber

Abstract An extrusion plastometer operating at rates of shear comparable with those existing in rubber tubing machines has been described previously. This plastometer was not designed to be a routine testing instrument, but rather was intended for use in the determination of the value of a high speed extrusion test for the factory control of rubber stocks. The plastometer served satisfactorily in the capacity of a research instrument, and has for some time been in constant use as a physical testing instrument where great rapidity of operation is not essential. The results obtained with this plastometer were found to correlate with tubing machine behavior. It was also found that the extrusion plastometer results agreed better with factory experience with various types of masticated rubber than did the Williams plastometer results. It was learned by experience with the extrusion plastometer, when used as a physical testing instrument, that its results agreed closely with calender behavior. In many cases, it was found that the extrusion plastometer results did not correlate with the Williams plastometer results and that, in general, the extrusion plastometer appeared to be much more sensitive than the Williams plastometer. The next step after establishing the value of the high speed extrusion test was to design an extrusion plastometer suitable for routine control testing. Such an instrument must be rugged in construction, rapid and simple in operation, and must yield precise results. The extrusion plastometer, which is described in this paper, was designed to fulfill these requirements and at the same time to give the same type of test results as those given by the original experimental plastometer.

Some Low-Temperature Characteristics of Bituminous Paving Compositions

Stability at temperatures approximating hot-weather temperatures in the pavement has become thoroughly established as a basic requirement of bituminous compositions. Means of measuring and rating this important property have been perfected as a result of laboratory experiments and have been proved sound through several years of practical application. Two contemporary tests have evolved with resistance to shear the basic principle of both: In one (the extrusion test) the shear is measured indirectly and in the other (the direct test), simple shear is measured directly, and values are expressed in pounds per square inch. The latter method is distinctly convenient in comparing a variety of compositions which may have been tested in cylinders of from 1 in to 6 in., or more, in diameter, since values by the extrusion test are not reducible to unit loads.