![]() The splines are class B, which are nonsliding under a load. Full fillet 30-deg pressure angle splines are preferable because they are the strongest kind. Involute splines are the most efficient way to transmit torque. ( Advancing both gears one spline tooth in the same direction only changes the position of the outer gear one-thousandth of an inch at the pitch diameter.) This set of timing gears has 5445 possible timing positions, of which 907 are accurate timing positions (see the next section for the timing process). 001-in at the pitch diameter of the gear, which is 4 times closer than limits preset at the beginning. It works out to be a difference of about. When you slide the outer portion of the timing gear off the splines, roll it one tooth and slide it back, one gear advances at a rate of 1/83 and the other gear advances at a ratio of 1/82. One of the timing gears will have 83 splined internal teeth, and the mating timing gear will have 82 splined internal teeth. Both timing gears have 33 external teeth. 004-in control how many splines are used in a set of timing gears.įor example, for the size NF pump with a center distance of 3.375-in, each of the outer gears will have 33 gear teeth with an outside diameter of 3.500, which is standard with twin screw pump manufacturers. 004-in distance in circumference at the pitch diameter of the timing gears. In the average twin screw pump, the change in clearance between the meshing screws is about. The number of splines are determined by the pump size and the clearance required by the individual pump. This component is bored and internally splined to properly slip onto the spline hub. Each gear-one for each rotating shaft-has two components: a splined hub that is bored and keywayed to fit the existing rotating shaft of the pump, and a gear of the same style, tooth type and outside diameter of the original timing gear. In two-piece timing gears, the hardened keyway and bore eliminate these problems. Even with a re-keywayed gear, a large gaping slot takes away from the alignment area of the bore. If the gear stripped the keyway, it quite often gaulded on the shaft and made the gears unusable for a second run. The bore also became oversized, and the gears became unusable for any further service. Possible problems included a wallowed out and oversized keyway, which caused the gear to move around, wear the shaft and require repairs. The bore was left soft so that the keyway could be cut to time the pumps. In the past, timing gears were made with hardened gear teeth only. Self-timing, two-piece timing gears have changed the timing procedure and increased the life cycle of twin screw pumps.
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