This invention relates generally to machines for centering and rotating workpieces such as pipe to be threaded, cut or otherwise subjected to a forming on e particularly the invention concerns improvements having to do with gripping, centering, and rotating of plastic sheath covered pipe.
It is a major object of the invention to overcome certain disadvantages associated with the operation and performance of prior machines for rotating workpieces, such as pipe, upon which threads are to be formed. If the pipe to be rotated is covered by a synthetic plastic layer, such as a plastic sheath, gripping problems arise. These involve possible damage to the plastic sheath, as during gripping and rotating. There is need for improvements in pipe gripping and rotating apparatus, which will overcome such problems and difficulties.
It is a major object of the invention to provide improved apparatus for gripping and rotating pipe, especially plastic covered pipe, as referred to, to avoid damage to the plastic material. Basically, apparatus incorporating the invention includes:
a) a drive rotor rotatable about a central axis,
b) a set of jaws spaced about the central axis, and operatively connected to the rotor to rotate about parallel jaw axes in response to rotation of the drive rotor,
c) the jaws having work engaging surfaces extending eccentrically relative to their respective jaw axes,
d) each of such surfaces extending generally circularly about a locus offset from a jaw axis associated with the surfaces.
For best results, the described offset is less than the radius of a circle defined by the work engaging surface.
Another object of the invention includes provision of a series of work engaging projections at the work engaging surface, the projections staggered in widthwise and lengthwise directions along said surface. The pipe plastic surface becomes compressed by the projections which indent the plastic material, the projections having heights less than the thickness of the plastic layer defining said surface. Further, the projections are preferably tilted relative to radii extending to said projections from the jaw axes.
Yet another object is the provision of links interconnecting the drive rotor with the jaws. As will be seen, only a single link is needed to connect the drive rotor with each jaw, as referred to.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: