Both ends construction of the second
raschig ring 3 is such that as shown in FIGS. 1 to 3, an upper surface of one end is formed with a notch 9 which opens to an outer peripheral surface of the raschig ring and an end surface 8, and the other end is also formed with a notch so that a projecting portion 11 to be arranged at a portion of the notch 9 is provided in the other end. The notch 9 and the projecting portion 11 have the same triangular shapes in longitudinal-section taken in a radial direction. An inclined surface 13 of the projecting portion 11 in the other end is overlapped on an inclined surface 12 of the notched portion in one end. The
raschig ring 3 is fitted in the raschig ring groove 3A, leaving a predetermined clearance between both end surfaces 8 and 10. While in the above illustration, the sectional shapes of the notch 9 and the projecting portion 11 are triangular shapes, it is to be noted that the shape is not limited thereto but other shapes such as a rectangular shape may also be employed.
One example of a method for manufacturing
raschig ring the second raschig ring 3 will be described below. A coiled material is prepared from a (martensitic) stainless steel wire. This coiled material is cut into a plurality of raschig rings, and then both ends of each
raschig ring are machined to have notches. Then, these raschig rings are inserted around the outer peripheral surface of a cylindrical member of a jig to have a stacked configuration. Clamp disks of the jig are disposed on opposite ends of the stacked raschig rings. A nut is threadedly engaged with a tapped portion of a shaft portion which extends from one clamp disk and extends through a center hole of the other clamp disk, and the nut is axially tightened and fixed. Then, the nitriding is applied to the outer peripheral surface in a plasma nitriding oven. The conditions of the plasma nitriding are, for example, as follows:
By the selection of the plasma nitriding as a nitriding having a directivity of treatment without the application of a particular anti-nitriding treatment or of the work removing a nitrided layer, nitriding can be easily applied to only the outer peripheral surface without the upper and lower surfaces and an inner peripheral surface of the compression
raschig ring being nitrided. Since the nitriding can be applied to only the outer peripheral surface, in the case that a thick nitriding is applied to a raschig ring which is thin in width and provided with both ends having notches, the raschig ring can retain strength against breakage of a notched portion having a small sectional area in each end. Accordingly, there can be obtained a raschig ring which is thin in width, which has a strength of breakage and which is excellent in wear resistance. Great effect can be obtained particularly in the
raschig ring which has a raschig ring width of less than 1.2 mm and a thickness of a nitrided layer of 70 m or more.
