A method of roll forming hollow parts comprises introducing a workpiece into the space between a plurality of rolls rotatably arranged in spaced and parallel relationship, in parallel with the axes of the rolls, imparting rotation to the workpiece from drives through either the rolls or flanges disposed at both ends of the workpiece, at the same time forcing mandrels, slidably fitted at ends in the central openings of the flanges, through the openings into the workpiece, longitudinally from the both ends thereof, toward each other, and removing the excess metal left in the midportion of the workpiece between the mandrels by slightly moving the rolls toward each other for added compression, thereby producing spaces between the mandrels and the workpiece, and by moving the mandrels axially together with the excess metal to separate the latter from the rest of the workpiece.

Apparatus and a method for burnishing gears incorporating a pair of gear racks having opposed forming faces with teeth spaced therealong for meshing with a toothed gear received therebetween to provide the sole support for the gear as it is rotated by rack movement while the rack teeth burnish the gear teeth. A loader is positioned on one lateral side of the gear racks and includes a movable gripper mechanism that positions the gears to be burnished between the racks for meshing engagement therewith as the racks are driven by a reciprocal drive mechanism of the apparatus. Grippers of the gripper mechanism grip the gears during loading and have pushers that push the burnished gears to a delivery guide on the opposite lateral side of the gear racks from the loader. A movable guide member of the guide is fixed to one of the gear racks and receives the burnished gears to feed the gears to a stationary guide member as a pusher fixed to the other gear rack moves the burnished gears during reciprocal driving of the gear racks. A conveyor for feeding the loader includes gear carriers supported by a continuous chain trained over a pair of spaced sprockets. One of the sprockets is adjustably supported by a chain tensioner while the other sprocket is driven by a cylinder and indexing arm through a one-way clutch in order to move the chain and the gears carried by the carriers on the chain.

A hollow rack shaft is produced by forming a plate work piece and has continuous metal flow along the contour of rack teeth surface without being cut. A series of wave-like concave-convex sections is formed on the inner surface of the shaft. Thickness of tooth body and tooth bottom of the rack teeth is adjusted by dimensions of the unevenness. Thereby, stress concentration at each point of the rack shaft is prevented and the shaft is strengthened and its weight reduced.

A machine and process for forming a high strength precision bar joint and more particularly for forming rolled tapered threads on a bar end such as the tapered end of a reinforcing bar used in concrete construction. Such machine and process employs opposed oppositely rotating die disks which have conical opposed die surfaces. A thread form die is provided on the conical die surfaces in the form of thread form spirals which bear against the opposite sides of the tapered bar surface as the die disks rotate. The die surfaces include opposed recesses into which the bar end is inserted. The bar may be held for rotation aginst a stop as the die disks oppositely rotate. Alternatively the bar end may be held against rotation and the die disks orbited around the bar end as the die disks oppositely rotate. A tapered surface is formed on the bar end prior to roll forming of such threads as by hot or cold forging or by cutting. The bar is held by a transfer vice for transfer from the tapered surface forming operation to the thread rolling operation to ensure that the tapered surface is properly centered while the threads are formed.

A machine and process for forming a high strength precision bar joint and more particularly for forming rolled tapered threads on a bar end such as the tapered end of a reinforcing bar used in concrete construction. Such machine and process employs opposed oppositely rotating die disks which have conical opposed die surfaces. A thread form die is provided on the conical die surfaces in the form of thread form spirals which bear against the opposite sides of the tapered bar surface as the die disks rotate. The die surfaces include opposed recesses into which the bar end is inserted. The bar may be held for rotation against a stop as the die disks oppositely rotate. Alternatively the bar end may be held against rotation and the die disks orbited around the bar end as the die disks oppositely rotate. A tapered surface is formed on the bar end prior to roll forming of such threads as by hot or cold forging or by cutting. The bar is held by a transfer vice for transfer from the tapered surface forming operation to the thread rolling operation to ensure that the tapered surface is properly centered while the threads are formed.