PRODUCTION

SLIDE VIEWERS WELDED ULTRASONICALLY

Faced with the problem of stepping up the output of their range of plastic injection moulded slide viewers, Photax Ltd investigated the use of ultrasonic welding and Dawe Instru- ments Ltd were requested to supply one of their commercial welders for testing. Subsequently, although not designed for ultrasonic welding, the existing range of Photax viewers was found to be very suitable for assembly by ultrasound after a suitable horn had been designed by Dawe for their ultrasonic welding machine.

So impressed were Photax by the economies effected by the new assembly method that the latest additions to their range of viewers, the 401 and 402 models, were specifically designed for ultrasonic welding. Fig 1 shows the 402 model in a dis- sected form and indicates where the welding horn is applied.

Previous assembly methods were based on trichloroethane solvent. Drying times for solvent assembly were of the order of 8h. Using ultrasonic welding, however, there is of course no drying time problem and as the components are rigidly joined immediately after bonding, subsequent assembly can proceed at once. Another problem with solvent assembly is that excess solvent wells up out of the joints and can cause the operator to deposit fingermarks on the polished surface of the components. Not only did Photax find that ultrasonic bonding removed this problem, but as the handling of each component was cut to a minimum, the need for final buffing and polishing was greatly reduced.

Pulsed operation of the Dawe Welding Head, model 113/220, at 2OKHz produces welding times of about 0.5s per weld. Welding forces have been found to be optimum at 35osi and Photax now show a throughput of 1,800 completed viewers per day with a labour force reduced to 50%.

At present, Photax use ultrasonic welding to bond Pocket Colourflash flash guns, their complete range of slide viewers and tine/tape spools. For future product design, assembly will will be based firmly on ultrasonic techniques.

Photax (London) Ltd, 70 Charlotte Street, London Wl

Dawe Instruments Ltd, Concord Road, Western Avenue, London W3

Fig 2 The assembled viewer indicating the layout of the welded components

ULTRASONIC PROBES CLEAN FOSSILS

One of the main problems encountered in the Fossil Fish Section of the British Museum (Natural History) when freeing embedded fossil fish from the surrounding calcerous rock was the final removal of clinging sludge and acetate film from crevices and natural indentations in the bone.

Removal of embedded fossil bone from the surrounding rock is usually accomplished by immersing the rock in a bath of dilute acetic acid and allowing the limestone to dissolve away. A decision must be made, however, as to how far to allow the acid process to proceed. If allowed to continue for too long, fine detail on the fossil bone may be lost but, in contrast, by halting the acid process too early, there will re- main much excess limestone to be removed.

From an idea of Mr C. I. Macadie of the Fossil Fish depart- ment, Simms Group Research and Development Ltd develop- ed their existing ultrasonic fuel atomizer into an Ultrasonic

Fig 1 A dissected view of a Photax 402 viewer indicating the ultrasonic welding procedure and welding horn application sites

ULTRASONICS April 1969 87