GB869126A - Improvements in or relating to can testing machines - Google Patents

Abstract

869,126. Testing cans for leaks electrically. METAL BOX CO. Ltd. April 9, 1959 [May 8, 1958], No. 14820/58. Class 40 (1). [Also in Group XIX] A machine for testing cans for leaks comprises a circular support to which a succession of cans can be clamped and sequentially supplied with compressed air, leaks being detected by movement of the diaphragm of a differential pressure gauge, producing a capacity variation which is detected in a frequency-sensitive circuit to operate a reject mechanism. As shown (Figs. 1, 2), the rim 3 of a wheel carries an apertured support 1 of e.g. rubber, against which is pressed a cam 12 by a plate 13 operated via shaft 18 by a cam follower 21 and cam surface 22. The inside of the can 12 communicates via a pipe 25 with one side 27 of a differential pressure gauge, separated by a steel diaphragm 29 from the other side 28, both sides being communicable with a gas line 33 through a valve 32 operated by a cam follower 41, 42 co-operating with cam surfaces 42, 43 on the machine frame. A gas line 33 and pressure gauge is supplied for each aperture 2 on the wheel, the lines being individually connected to gas inlet and outlet pipes via ports in a fixed member 55 as the wheel rotates. The diaphragm 29 forms a test capacitor with an electrode 45 in side 28 of the pressure gauge. A coarse leak detector 58 is located in pipe line 33, and comprises two chambers 61, 64 (Fig. 4), separated by an insulating diaphragm 65 carrying a bolt 66 attached via spring 69 to a lead wire. During test, a coarse leak in the can allows the bolt 66 to contact a boss 63 on the earthed casing 59. Leads from each bolt 66 and each electrode 45 are taken to contacts 74, 75 respectively of a synchronous switch 72, where co-operating brushes on a fixed bracket 78 sequentially connect the contacts to the measuring circuit (Fig. 7). The capacity between the diaphragm 29 and electrode 45 is connected across the grid circuit of a tuned-grid, tuned-anode oscillator valve V1, followed by a phase-change frequency detector valve V2, to produce a drop in anode voltage with change in frequency, as produced by a faulty can. This causes the normally conducting section of a doubletriode valve V4 to be blocked, and the other section conducts to energize a relay 92 operating can re-ject mechanism. A short-circuit at the coarse leak detector 58 produces a similar result. The cams are fed from a shoot 89 and automatically clamped to the rim 3 by operation of lever 20. As the wheel rotates, compressed gas is fed through line 33 to the cans and to both sides 26, 28 of the pressure gauges, further rotation sealing the system. If a can has a bad leak an indication is quickly obtained from the coarse leak detector 58. After a further rotation the appropriate contacts reach the brushes at switch 72, and the capacity between diaphragm 29 and electrode 45 indicates the loss in pressure inside the can 12.