Stiff extrusion

Designation used in structural ceramic industry Soft extrusion Semi-stiff extrusion Stiff extrusion ... 

Extruder and de-airing single shaft mixer. This machine combination is the superior choice for stiff extrusion purposes in the heavy clay industry. One of the reasons for this is the fact that a stiff body could cause warping of the mixer shaft, which could prove to be problematic with a double shaft mixer. 

In the 1960s Messrs. Uniceram SA of Marseille, France, built a hydraulically-driven piston extruder for the stiff extrusion of structural clay products, combined with a de-airing double-shaft mixer, was operated as a combined de-airing extrusion unit (Fig. 5). On the whole however the piston extruder has been of relatively little importance in comparison to the auger extruder within the field of structural ceramics. 

The rudiments of stiff extrusion were already known in the United States by the end of the 19 century but were only employed in Europe for... 

Similar difficulties were encountered in the United States, when the column extrusion method was introduced there in 1870, which continued until the patented Niedergesaess Patent Lubrication Brick Die was brought onto the market. This made it possible to lubricate the column either by water, oil or steam. It was discovered that dry steam was more effective than water or oil for certain clays (Fig. 21). Development of oil-lubricated and steam-heated dies also marked the beginning of stiff extrusion in the United States with material moisture contents as low as approx. 12%. 

The arrival of stiff extrusion in the Eirrope in the 1960s - in the USA since 1920 or earlier - also brought the pressure head/die combination with oiling ring. With this system, oil is injected with a pump to improve the sliding behaviour of the clay (Fig. 24). Circa 1970 regulating pressure heads came into use, featuring slides or brakes, which could be externally adjusted and which had an effect on the material flow (Fig. 25). 

Steam-heated pressure heads and extruder barrels had been known in the United States since the 1890s in context with stiff extrusion. After 1950, with the increasing importance of advanced ceramics and the use of nonplastic materials or bodies which were difficult to extrude and which had to be plastified with the aid of suitable bonding agents, there was also a... 

Hydraulically-operated de-airing piston extruder for stiff extrusion by Uniceram, Marseille, France... 

Stiff extrusion is the shaping of a clayey body with as low a water content as possible while applying as little pressure as possible. Normally, body intended for stiff extrusion contains between 12 % and not more than 20 % by weight water in the extruded body. The extrusion pressure, as measured in the pressure head, amounts to roughly 25 to 35 bar, and the penetromet-ric value stays somewhere between 2.8 and 4.5 kg/cm. ... 

Experience shows that the impact deformation heights according to Pfefferkorn for bodies to be extruded lie within a span of approx. 25 mm for soft extrusion and approx. 37 mm for stiff extrusion. 

Steele AP (unknown) Some advantages of stiff extrusion. 

The plasticity of the samples was measured fi om the Atterberg Limits (Plastic Limit, LP, and Liquid Limit, LL) and Plasticity Index (TP). The amount of added water in the mixer depends on the clay plasticity an on the consistency at which the extrusion is performed. The moisture content for stiff extrusion is 15-20 %, and 21-26 % for soft extrusions [36]. In the present work, FW, OW or OOW was added to 22 wt %, the results indicated that the plastic limit or amoimt of minimal water to mold the mixture decreased when using OW (19.7 %) or OWW (20,1 %) as mixing water. These results demonstrated that the volume of OW or OWW amount needed to produce the optimum extrusion performance is smaller than that the fresh water was used (21,9 %). This would be attributed to an additional lubricating effect performed by the addition of the wastes. Similar results were previously found in the extrusion effect when adding olive oil mill wastewater (OMW) [31, 32]. However, the plasticity index that establishes a range of moisture content in which the clay is moldable, decreased when FW is replaced by OW or OOW from 9.6 % to 6.1 % and 5.9% respectively. 

Thermal dilatometric curves obtained for six bricks extruded from different raw materials are shown in Fig. Curves for those manufactured from similar raw materials, but made by different forming methods, i.e., soft mud, dry press, and stiff extrusion, are shown in Fig. 23. From room temperature up to 500°C, the dimensional change is approximately linear and is due to thermal expansion. The abrupt increase in expansion (500-800°C) is due to phenomena such as quartz inversion, exfoliation of the illitic, and chloritic minerals due to dehydroxylation, and, possibly, the escape of CO2 under pressure. 

In many cases supports are shaped into simple cylinders (1-5 mm in diameter and 10-20 mm in length) in an extrusion process. The support powder is mixed with binders and water to form a paste that is forced through small holes of the desired size and shape. The paste should be sufficiently stiff such that the ribbon of extmded material maintains its shape during drying and shrinking. When dried, the material is cut or broken into pieces of the desired length. Extrusion is also applied to make ceramic monoliths such as those used in automotive exhaust catalysts and in DeNOx reactors. 

Flexible film applications are much more demanding regarding the stiffness/ toughness ratio of the Ecoflex /PLA compound. Usually, polypropylene with a stiffness of 1,600 MPa is the stiffest product to be used in blown film extrusion. But,... 

POLYETHYLENE, A thermoplastic molding and extrusion material available in a wide range of flow rates (commonly referred to as melt index) and densities. Polyethylene offers useful properties, such as toughness at temperatures ranging from —76 to +93°C. stiffness, ranging from flexible to rigid, and excellent chemical resistance. The plastic can be fabricated by all thermoplastic processes. 

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