The present invention relates to an umbrella frame.  More particularly, the present invention relates to an umbrella frame which has an upper runner and a lower runner to be assembled easily. 
A conventional umbrella frame has an upper runner and a lower runner as shown in U.S. Pat.  Nos.  4,567,907, 4,993,445, 5,601,103, 5,617,888, 5,020,557, 4,622,987, and 4,319,660.  When a stretcher is broken, all the stretchers should be detached in order to replace the broken stretcher. 
An object of the present invention is to provide an umbrella frame which has an upper runner and a lower runner to be assembled easily. 
Another object of the present invention is to provide an umbrella frame which has an upper runner and a lower runner to be detached easily. 
Accordingly, an umbrella frame comprises a hollow shaft, an upper runner disposed on the hollow shaft, a lower runner receiving the hollow shaft, the upper runner having a first upper casing and a first lower casing, the lower runner having a second upper casing and a second lower casing, a key-shaped hole formed on the second upper casing, a thread inserted through the key-shaped hole, the thread having a blocking end, a plug inserted in the key-shaped hole, a winding device inserted through the hollow shaft, and the thread connected to the winding device.  A plurality of ribs are connected to the first upper casing.  Each of the ribs has a pivot end having a through aperture.  A plurality of stretchers are connected to the lower runner and the ribs.  The first upper casing has a plurality of spaced hollow seats, a plurality of threaded holes, and a plurality of spaced blocking plates.  Each of the spaced hollow seats has an opening and two lower notches.  Each of the spaced hollow seats receives the respective rib.  The first lower casing has a plurality of spaced upper bars and a plurality of spaced blocking posts.  Each of the spaced upper bars has a threaded aperture matching the respective threaded hole of the first upper casing.  A plurality of pivot pins are disposed in the first upper casing.  Each of the pivot pins passes through the lower notches of the respective spaced hollow seat and the through aperture of the pivot end of the respective rib.  Each of the pivot pins is blocked by two of the spaced blocking plates.  The first lower casing engages with the first upper casing.  A bolt passes through one of the threaded holes of the first upper casing and the threaded aperture of the respective spaced upper bar to fasten the first upper casing and the first lower casing together.