Fixture expansion

Another error associated with temperature programming is sample and fixture expansion. As mentioned above, a typical change in the gap is 1 /um/°C due to fixture expansion. This can cause significant errors for thin cone and plate or parallel disk samples. With solids it can lead to high normal forces at low temperatures and sample buckling at high temperatures. Some instruments automatically adjust the gap based on the normal force (Rheomet-rics, 1990). 

The reactor assembly was heated by electric heaters. The maximum operating temperature Is determined by the window construction. Sapphire windows (from EIMAC), brazed into Kovar sleeves, were used the sleeves were then welded directly into the stainless steel reactor housing. We found that the cell so constructed was capable of trouble-free, continuous operation at 450°C operations at somewhat higher temperatures are probably still possible but were not explored. Sapphire was chosen as a window material because it is insensitive to water vapor and is transparent in tljie wave number range of our interest (about 2400 cm to 2000 cm in these experiments). Moreover, the thermal expansion characteristics of the reactor were found to match well with those of the window fixture. 

Experimentally, TMA consists of an analytical train that allows precise measurement of position and can be calibrated against known standards. A temperature control system of a furnace, heat sink, and temperature-measuring device (most commonly a thermocouple) surrounds the samples. Fixtures to hold the sample during the run are normally made out of quartz because of its low CTE, although ceramics and invar steels may also be used. Fixtures are commercially available for expansion, three-point bending or flexure, parallel plate, and penetration tests (Fig. 4). 

Expansion studies can also be run on samples immersed in solvents to measure the swelling of a polymer. This test is commonly used with rubbers to measure the cross-link density of the rubber. As cross-linking increases, the amount of swelling will decrease. Special fixtures are commercially available... 

Wheel-speed sensors are available with or without (direct connected sensors) cable. Cable routing in the car is important and many types of sensor configuration (cable layout) are possible. Grommets and clips can fix the cable to the car body. Expansion bellows of plastic protect the cable from damage. Fig. 7.9.12 shows a complete WSS consisting of sensor head, connector, grommets, clips, and expansion bellows. The fixture to the car body with clips and grommets is shown in Fig. 7.9.13. 

Thermal Expansion - Thermal expansion was measured using a horizontal pushrod dilatometer with alumina fixtures under flowing nitrogen. Specimens of approximately 10 mm in length were used. The temperature was measured with a platinum thermocouple located approximately 8 mm from the sample. Heating rates of 5°C/min were used to heat the sample from room temperature to 600 C. The sample was cooled at 10°C/min. 

Difference in linear expansions coefficients of guiding channels of the assembly and reactor core barrel is compensated by increase of the working stroke of spring block of FA cap. For connection/disconnection of AFA stainless cap and GC a simple device is used not requiring replaceable fasteners or complicated fixtures with power nut drivers. As the inspection stand is available the procedure on dismounting or mounting the AFA cap takes a minimum time. 

Pressure devices should be designed to maintain constant pressure on the bond during the entire cure cycle. They must compensate for thickness reduction from adhesive flow-out or thermal expansion of assembly parts. Thus, screw-actuated devices like C-clamps and bolted fixtures are not acceptable when constant pressure is important. Spring pressure can often be used to supplement clamps and compensate for thickness variations. Deadweight loading may be applied in many instances however, this method is sometimes impractical, especially when heat cure is necessary. 

Fixtures. In fixturing titanium components or assemblies to prevent distortion, the thermal-expansion charac-... 

When setting the bonded anchor, no expansion forces are produced. These forces are produced due to all types of fastening on the prestress and due to the loading of the anchor. However, they are much lower than for metal expansion hence, anchors are bonded especially at small component thicknesses and fixtures with a low edge distance to the mechanical expansion anchors (Geiss 2006b). 

The measurement of normal stress differences in transient deformations is extremely sensitive to small variations in gap spacing, which can arise from instrument compliance or minute temperature variations. Venerus and Kahvand [43] have shown how to evaluate the effect of instrument compliance by measuring the response using several sets of cone-plate fixtures. If a Force Rebalance Transducer is used for a transient normal stress measurement to compensate continuously for compliance in order to keep the gap constant, the response time of the transducer may affect the data. Also, the thermal expansion that results from the power dissipated in the transducer can affect the gap spacing and is of particular concern when normal stresses are being measured [104]. 

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