CAD assembly of a fixture to achieve concentricity in an axial housing of primary air or forced draught fan
Axial housings for primary air or forced draught fans used in boilers in power plants have a cylindrical core and a cylindrical outer shell. Core and outer shell are fabricated with vanes in between them to guide airflow with minimum energy loss. The challenge in the fabrication is concentricity of core and outer shell. In fabrication industries, the concentricity is generally achieved manually that takes substantial amount of time. To reduce the time required to achieve concentricity, a modular design of fixture is presented here, in other words, a single fixture can be used to fabricate all designs of axial housing. The fixture assembly consists of circular plates (lower and upper), fixture plate, fixture rod, fixture pin, fixture plate inner tube, fixture plate outer tube (Refer to the attached figure). Upper circular plate has four circular grooves to accommodate four designs, if there are more designs then more circular grooves can be created in the CAD with respective diameters and thicknesses. Upper circular plate can be moved up and down with the help of screw and nut mechanism between upper circular plate and fixture rod, therefore an axial distance can be maintained between core and outer shell depending on the design requirement. To maintain radial clearance between core and outer shell of an axial housing, a translational joint is given between fixture plate inner tube and fixture plate outer tube enabling to achieve exact radial clearance. The length of these tubes can also be changed depending upon design requirements of different manufacturers of primary air and forced draught fans. Fixture plate must be welded with fixture plate outer tube. Following are the steps to achieve concentricity in an axial housing using the fixture- 1- Fix the fixture in bed. To maintain an axial distance between core and the outer shell, move upper circular plate up and down by rotating it. Use fixture pin to arrest the rotation and fix the upper circular plate. 2- Use fixture plate inner tube to maintain a radial clearance between core and outer shell by moving it radially. 3- Place the outer shell using the fixture plate inner tubes’ radial location; the inner surface of the outer shell must touch fixture plate inner tube. 4- Remove fixture plate along with fixture plate outer tube and fixture plate inner tube. 5- Place the core using one of the circular grooves whose diameter must be equal to the diameter of the core and thickness equal to the thickness of the core. After this, the usual fabrication of the axial housing can be executed. The CAD assembly (fixture_assem.SLDASM, fixture_assem.IGS) was executed in Solidworks that can be used to manufacture a fixture that will drastically reduce the cycle time of axial housings thereby increasing the productivity and effectiveness in the production shop. The CAD can also be modified to manufacture a fixture for achieving concentricity in any product having a cylindrical core and shell.