How we make ball cage and guide bush

Published: 21st October 2011
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The ball cage and guide bush play important part in the guiding and positioning of fixed mould and moving mould in addition to relevant mould plate (such as runner plate and ejection plate), and also protect cores during the assembly of moulds.

(1) The ball cage is usually set on the moving mould, whereas the guide bush is set on corresponding part of the fixed mould; sometimes the two pieces are assembled vice versa based on the structure of the mould (such as the runner plate in the fixed mould).

(2) The injection mould is usually provided with four ball cages and guide bushes, scattering in the margin of four corners of the mould plate, wherein distance between center of the ball cage and margin from the plate is usually 1~1. 5 times of the diameter of the pillarís retaining end.

(3) Heated ball cage
are usually applied to small moulds or moulds with scarce productivity, while large and medium-sized injection moulds of moulds with rich productivity are mostly provided with shouldered ball cages. To reduce friction and oil storage tank can be cut on your ball cage according to the actual use; spiral oil storage tanks can be found in some large moulds.

(4) Straight guide bushes are usually applied to simple moulds or moulds with thin plate; Ⅰ-type heated guide bush is mainly applied to complicated moulds or the guide of fixed as well as moving moulds of large and medium-sized moulds; Ⅱ-type heated guide bush is principally used in the guide of ejection mechanism. To reduce friction, an oil storage tank can also be cut in the guide bush or use a self-lubricating guide bush (Use Mos2 in the annular groove of steel guide bush and use solid graphite within the side wall hole of high-intensity brass guide bush).

(5) To ensure sound fitting of parting line after mould closing, a cuttings shoot of the ball cage and guide bush should be made on the parting line: generally one of the sides is cut or chamfered on the orifice from the bush, as indicated in Fig. 2-28.

(6) Length of the ball cage on the working part should be 6~8mm higher than the end plane of the core as indicated in Fig. 2-29.

(7) The surface roughness for the working part of the ball cage takes Ra0. 4um (micron purchase Ra0. 2um), and take Ra0. 8um or Ra1. 6um (micron order of the inner cylinder can take Ra0. 2um).

(8) Clearance fit is adopted between the ball cage and guide bush, with the quality of fit usually as H7/f7 (G6/h5 for high quality of fit and H8/f8 or H9/f9 for poor of fit) and the slip length usually takes 1. 5~2 times of the mating diameter, whereas the remaining parts are countersunk to reduce friction. Transitional fit is usually adopted between the mould plate and the ball cage and guide bush, with the quality of fit as H7/k6 orH7/m6. Additionally, to prevent the straight guide bush from falling off, a retaining groove can be applied to the flank of the straight guide bush, screwed with hexagonal socket head plug.

(9) For moulds with small batch of production and of low precision, the ball cage can be directly fitted pilot hole about the plate. The hole should be generally made into through hole; when the cavity plate is rather thick, if the pilot hole is a blind hole, a blowhole should be made on the side wall of the blind hole, or a vent groove can be abraded ion the main body from the ball cage and at the open end of the pilot hole; length and surface roughness of the slide guiding plane on the pilot can be adopted in accordance with the size of guide bush of equal specifications, and the diameter with exceeding length should be expanded so as to reduce the slip surface.

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