Gracin, Renato (Poljanice Pete 24, Zagreb, 10000, HR)
| 1. | Rotating probe flexible shaft assembly providing good flexibility, while maintaining feature to be pushedpulled and rotated in the same time. Rotating probe flexible shaft assembly is determined by flexible shaft with diameter 03.2 mm (tolerance ±0.1 mm), made of tensile wires (4 or 5 layers, shaft designed to have low torsional deflection). |
| 2. | Rotating probe flexible shaft assembly, determined by two coaxial cables 00.5 mm (AWG40, stranded, 40 or 50 ohm) wounded around flexible shaft. |
| 3. | Rotating probe flexible shaft assembly, determined by fixing coaxial cables to the shaft every 50 mm by heat shrink tubes (06x4 mm, heat shrink ratio 3:1 , glue on inner radius). |
| 4. | Rotating probe flexible shaft assembly, determined by flexible nylon hose (material nylon 66nylaflow, 07.9305.9 mm) mounted over shaft and cables. |
| 5. | Rotating probe flexible shaft assembly, determined by bearing assemblies made as shown in Figure 2. |
DESCRIPTION OF INVENTION
Field of Invention
This invention relates to rotating probe flexible shaft assembly used as carrier of eddy current rotating probe made for examination of curved tubing. Basically this invention was developed to be used in the assembly of rotating probe for examination of steam generator tubing in WWER type of nuclear power plants (inside diameter of tubing is 13 mm).
Technical Problem
Since eddy current probe (sensor and shaft) needs to be pushed and then pulled through curved and wet tubing by friction system with 2 pairs of driving wheels, it often becomes difficult problem.
Prior Art
Usually, shaft used on rotating eddy current probes for 013 mm inside diameter of tubing is flexible shaft with diameter of 03.2 mm (flexible shaft with four layers). Regardless if rotating probe has cross wounded or pancake coil mounted, two coaxial cables are wounded around the shaft, connecting sensor of the probe with probe's connector. By connector, probe is attached to motor unit having duty to rotate flexible shaft and probe's sensor around its axis. Thin coaxial cables are wounded around flexible shaft and protected by nylon pearls fixed to the shaft at spacing of approximately 6 mm. The rotating probe is rotated by speed of 300 rpm, while pulled with 5 mm/s.
This system is successfully applied on straight tubing or less curved tubing than it is case on tubing in steam generators of WWER type of nuclear power plants. In that particular case, the most of tubes start with bend right after the tube
entrance. This bend does not allow motor unit to enter inside the tube. Due to fact that requirement for inspection is up to 9 m inside tube, it follows that length of flexible shat assembly shall be at least 9 m.
Today, fixtures designed for eddy current inspection of tubing in steam generators of WWER type of plant, mostly have probe pusher-puller installed inside generator's collector in order to be close to the tube entrance (for "bobbin" type of eddy current probes). Therefore, mentioned type of the rotating probe can not be used, because request is that shaft shall be rotated and in the same time axially moved by friction system of probe pusher-puller acting on the same shaft.
Summary of Invention
Based on mentioned limitations, the new flexible shaft assembly was developed with intention to pass easily through the tube's bends, while being rotated and axially moved in the same time.
Basic element of assembly is flexible shaft with diameter 03.2 mm, length up to 10 m.
Around the shaft are wounded two coaxial cables with diameter 00.5 mm. On every 50 mm is mounted heat shrink tube with inserted glue on inner radius (length of shrink is 4 mm). Every heat shrink tube is heated by fan, and by this way fixing cables to shaft on every 50 mm distance. Flexible nylon hose is mounted over such prepared shaft. On the both ends of the shaft bearing assembly is mounted. This way allows probe pusher's driving wheels to push-pull nylon hose, while flexible shaft is rotating inside the hose.
Brief Description of Drawings
Figure 1. shows the rotating probe's assembly drawing including assembly of sensor attached to the flexible shaft assembly. The flexible shaft assembly is ended with connector used to attach the probe to the motor unit assembly. Figure 2. gives cross section detail of the rotating probe flexible shaft assembly and it is suitable to be published with summary of invention.
Figure 3. shows "Stud", Figure 4. shows "Bearing", Figure 5. shows "Nut", items mounted in bearing subassembly.
Description of preferred Embodiment
Basis element of the assembly is flexible shaft with diameter of 03.2 mm (designed for low torsional deflection). On both ends of the shaft are mounted studs, showed in Figure 3. made of stainless steel. Studs are soldered to the shaft. After that, cables (already attached to the probe's sensor) are mounted on the shaft by wounding around shaft. Further, heat shrink tubes (06x4 mm, glue on inner radius, shrink ratio 3:1) are placed over shaft and cables, spaced 50 mm from each other. By using heating gun, shrinks are heated and fixed together with cables to the shaft. Next step is preparation of nylon hose (material nylon 66- nylaflow, dimension 5/16 T - 07.93/05.9 mm). Nylon hose is cut on desired length and on each end is made thread 1/4-28, length 6 mm. Prepared hose is placed over shaft to the front stud. During this process, every heated shrink tube is greased (lithium grease). Now, item from Figure 4. bearing (material, bronze) is wounded inside hose with added Loctite 262 as threadlocker. Also, grease is placed over stud (contact with bearing). Finally, item shown in Figure 5., nut, is mounted on stud, holding the whole bearing assembly. Nut (made from stainless steel) is soldered to nut in order to prevent nut to be moved (180 ° opposite from wire track). The same procedure is repeated on the connector end of shaft.
Application of Invention
As mentioned before, this rotating probe flexible shaft assembly is developed to be used in eddy current rotating probe for examination of tubing in steam generators installed in VWVER nuclear power plants. However, assembly can be used also for the other similar applications.