THE CLAMPING FIXTURE

Solvent should be applied to only one of the bonding surfaces while the other half remains dry and ready in the clamping fixture. As soon as the two parts have been put together, pressure should be applied immediately. Pressure between 200 and 600 psi is suggested for best results. Holding time in the pressure fixture is approximately 1-5 min, depending on the size of the bonding area. 

Gauge length n. On a dog bone-shaped, tensile-test specimen before stress is applied, the distance between two marks on the narrow part ( waist ) of the specimen, perpendicular to the direction of pull that will be used to measure elongation. If the specimen is of uniform thickness and width, gauge length may be taken as the nip-to-nip distance between the clamping fixtures. 

The clamp fixture will only take a few minutes to make. It consists of two end plates, two 6 lengths of 3/8-16 threaded rod and four 3/8-16 nuts with flat washers. Make each end plate from 1/4 X 2-1/2" X 3-1/2" C.R.S. fiat bar. See figure 84. Locate and drill the 3/8" holes located 1/2 back from each end of each plate. Cut out the 3/8" slots in each end with a bandsaw or hacksaw. 

Fig. 85 Using the clamp fixture to clamp the knob mold.

With the clamp fixture holding the mold halves together, set the knob mold on the adjustable table. Align the sprue opening in the mold with the injector nozzle on the heater block. Raise the table to force the mold tight against the injector nozzle. Pull the injector lever to force plastic into the mold. Maintain pressure on the lever for a couple of minutes to allow the plastic to harden in the mold. Remove the mold from the machine and separate the mold halves. Unscrew the socket head screw from the top mold half and remove the finished knob. 

While detail may be found in the ASTM D-3330 or PSTC-1 and PSTC-2 standards, the peel test is typically carried out as follows The tape is conditioned at 23°C and 50% relative humidity for 1 day. Next, the tape is rolled down with a weighted standard roller onto a clean test substrate (usually polished 302 stainless steel), allowed to dwell for a specified time (usually 1 min), and then clamped with the testing fixture in the test machine and peeled at a specified rate. 

In such a measurement, the sample is clamped as lightly as possible, and the displacement of the surface in monitored. The amount of sample clamping is important, because the mechanical constraints can impact the ferroelastic response of the sample. That is, in samples where the mechanical coercive stress is low, it is possible to change the domain state of the material by improperly clamping it in the sample fixture. This is especially important in elastically soft piezoelectrics, such as many of the relaxor ferroelectric PbTiC>3 single crystals. 

Dynamic Z,S—End-loaded split specimens were also tested in the drop tower, but were mounted horizontally in a custom clamping fixture as shown in Fig. 2. This fixture consists of a side grooved Palmgren vise (Chicago, IL) mounted to a custom pedestal. The pedestal is constructed of 50 x 50 mm steel box tubing welded to 6.4 mm steel plates and is clamped to the drop tower base using 100 mm C-clamps. In this case, a hemispherically-tipped steel tup is attached to the drop tower sled and travels downward, striking the end of the specimen as shown in the schematic in Fig. 2. 

Results for the various combinations of reverse current, field dropping to zero, and fixed field are shown in Fig. 2, and should be contrasted with the results of curves 1 and 2 of Fig. 2, where the holder was clamped securely. All the scatter in the data (Fig. 2) has been eliminated (curves 1 and 2) and, consequently, slight movements of the wire or of the holder must have been responsible for the scatter. The measurements recorded in curves 1 and 2 of Fig. 2 were repeated with the whole fixture immersed in frozen glycerin, and the results obtained were unchanged. 

Load/Unload Stations Load/unload stations are employed to clamp/fixture parts on pallets before entering the system, and remove finished parts after their process cycle has been completed. These stations can employ human operators or robots to accomplish the task. 

Cut two, 6" lengths of 3/8-16 threaded rod, gather up four, 3/8-16 nuts and four, 3/8" flat washers and you have a clamping fixture. The drawing in figure 85 shows how it works. 

Tension. In the tension fixture a sample is strained in tension between a fixed clamp and a moving clamp. In tensile oscillation a static load (pretension) must be applied to prevent buckling and creep. This is discussed in Section 5.8.5.I. 

Shielding of the underside of a weld is provided by slotted backing bars, usually copper, through which a diffuse flow of argon or helium is maintained. Gas channels in the clamping fixtiires also provide diffuse flow of inert gas to the weld area. These fixtures are placed close to the weld to avoid the danger of air contamination. 

Compression molding (continuous fibers) The same principle as for short fiber materials. Continuous fibers require special clamping fixtures for the sheets and can primarily be used for simple geometries. 

---