Chain introduction means for a crystal growth pulling head

In an apparatus for drawing a crystal from a melt, said apparatus comprising:

• (a) crucible means for holding said melt;
• (b) pulling-head means for drawing a seeded crystal from said melt;
• (c) means providing relative rotation between said melt and a crystal drawn therefrom along a vertical axis of rotation of said crystal;
• and
• (d) housing means to provide a sealed, contamination-free environment for the apparatus, including the pulling head, said pulling head comprising
• (i) seed-holder means for grasping a seeded crystal drawn from said melt,
• (ii) chain means, having a one end for pulling said seed-holder means along a vertical axis and another free end, said chain means comprising a plurality of flexibly coupled chain links,
• (iii) take-up means cooperating with said chain means, to move said seeded crystal along the vertical axis, said take-up means comprising sprocket means, including teeth spaced along the periphery thereof to engage said chain links, said sprocket means disposed to align a vertically oriented tangent from said sprocket means congruent with said vertical axis,
• (iv) means for rotating said sprocket means to move said chain along the vertical axis,
• (v) containment means to store the free end of untensioned chain taken up by said sprocket and chain discharged therefrom,
• (vi) the housing means enclosing said pulling head and comprising a cover plate disposed above said sprocket and characterized by an aperture in said cover plate vertically aligned with the plane of said sprocket, and
• (vii) sealing means to seal hermetically the aperture, whereby the chain means may be replaced without removing of the cover plate and breaking into the sealed environment of the pulling head, by directing new chain through the aperture and into engagement with the sprocket means.