Process and apparatus for precasting prestressed-concrete workpieces

Abstract

Workpieces of prestressed concrete, specifically railroad ties, are molded in a form having its bottom covered with several transversely separated templates whose outline corresponds to that of respective ties to be produced; the form is longitudinally traversed by reinforcing rods or cables attached to its ends under tension. Each template is provided with several countersunk nuts to be engaged by retaining bolts which pass through upright screw anchors with downwardly opening throats loosely occupied by internally threaded centering sleeves that come to rest on the associated template. With the form compartmented by removable spacers separating the templates, concrete is poured into each compartment and allowed to harden about the screw anchors rising therein; the retaining bolts are then withdrawn along with the spacers to provide the resulting concrete blocks with a certain mobility whereupon the tensioned reinforcing armatures are released to prestress these blocks and are subsequently cut between them. The blocks can now be individually extracted from the form, with the aid of lifting hooks or draw bars threaded from above into the centering sleeves; after removal of these sleeves from the inverted blocks, mounting bolts are threaded into the screw anchors by way of cleats serving to hold two rails in position on each tie-forming block.