Inner gear, cylindrical product with inner gear, mold for inner gear, mold for cylindrical product with inner gear, method of manufacturing inner gear, and method of manufacturing cylindrical product with inner gear

Abstract

A cylindrical product with an inner gear formed by injection molding, a mold for the cylindrical product, and a method of manufacturing the same are disclosed. The molded product may include a cylindrical base member, a spiral inner gear formed on an inner peripheral surface of the cylindrical base member so as to be inclined to a circumferential direction of the cylindrical base member, and a spiral relief groove formed on the inner peripheral surface of the cylindrical base member adjacent to the inner gear. The relief groove may be wider than a tooth width of the inner gear. The method of manufacturing the cylindrical product includes the steps of inserting a first cylindrical mold into a hole at the center of a second cylindrical mold, engaging a toothed portion on the first cylindrical mold with a spiral groove on the second cylindrical mold to provide a lower mold, mounting an upper mold thereon to form a space for forming the cylindrical product, injecting molten resin material into the space to harden it therein, withdrawing the second cylindrical mold in a direction to allow the mold to be opened, axially moving the first cylindrical mold to insert the toothed portion into a relief groove on a flat portion of the second cylindrical mold, rotating the first cylindrical mold in a direction to withdraw it along the flat portion, and removing the upper mold to extract the cylindrical product.

Dependencies are inferred from the claim text.