| 摘要 |
PURPOSE:To improve mechanical strength against a load in a radial direction by controlling generation of a weld line in a thrustward direction, by performing injection through a plurality of a top and bottom gates provided on positions inthe different radial directions on both end faces. CONSTITUTION:Molten resin is injected through a plurality of a top and bottom gates provided on position in the different radial directions on both end faces, in a manufacturing method of a hollow cylindrical molding frame body 1 to be used for a bell frame for a lens of an optical instrument. As a weld line consists or thrust weld lines 14, 15 extending short in a thrustward direction from the end faces and an endless weld line 16 extending in the circumferential direction and the weld line extending from one end face to the other face is not generated like a case wherein injection is performed from the one end face, mechanical strength against a laod from the radial direction is high and it does not happen that the weld line cracks in the thrustward direction. |
