Salter 59 kitchen scales

Once again flicking through the trade journals in our collection and recognising an object that we own has enriched our record with a wealth of information.  This time I was looking through an edition of British Plastics from February 1955 and I stumbled across a fabulous article about the manufacture of the Salter 59 kitchen scale.  This article has offered up a firm date and title of the object and some fabulous detail about how exactly the case was made and who did the moulding.

Salter 59 kitchen scales, AIBDC : 0_2337

Here is the article:

Three polystyrene mouldings for domestic scale

A great deal of progress has been made lately in the application of plastics to household appliances, especially where streamlined shape, appearance and ease of cleaning are essential properties. This recent trend is exemplified in the modern domestic scale where a number of new or redesigned models have plastics components; in particular polystyrene finding favour on account of the excellent finish obtainable with this material.

The Salter 59 scale uses high impact polystyrene for its scoop, general purpose for the housing, and general purpose for the dial cover, where the glass-like transparency of the material is of special advantage. The moulding is carried out by E. Elliott, Ltd. Birmingham, and the technique used to mass-produce three items mentioned is of additional interest in that all of the finishing, apart from a cementing operation, is carried out at the press.

The pictures on these pages (come and see the article if you would like to see them all) show the stages in moulding the Salter 59 case. Production is carried out on an 8-oz injection machine, using general-purpose polystyrene in a cream (yellow in our case) shade. Injection is at the centre top of the case where a square aperture is later punched out to accommodate a plunger when the scale is assembled.

Punching the square aperture from the housing after moulding, and, right, a housing placed in the jig for drilling in four positions

The circular aperture in the housing is produced by having a blank face on the mould (which closes on a bevel positioned half-way across this blank face); another interesting feature is the method of producing a slot at the rear of the housing by moulding a projection running on a taper.  Purpose of this slot is to accommodate a knurled wheel which allows the scale to be set (and reset) to zero.  About 55 lifts an hour are achieved, the cycle time being closely integrated with the finishing time. Weight of the shot as it comes of the machine is about 5 ¾ oz.

At the completion of each cycle the operator clips off the sprue and stamps out the square aperture on an electrically heated punch, the temperature of which accurately maintained by a Sunvic control system.  After this the housing is placed in a jig, which is designed both to hold the shape of the moulding as it finally cools and to allow the simultaneous drilling of four 1/16 in holes, two on each side; the purpose of these holes is to accommodate attachment of the inner mechanism of the scale. Drilling is carried out by four drills each operated by an air valve supplied from the normal press air line; a master valve enables the complete system to be switched in and out, and thus cutting out noise when the drills are not actually operating, and thus making the operator's job less fatiguing. The housing then wrapped in tissue and at once packed in a cardboard box for transfer to the Walsall works where the moulding dial cover cemented in.

Production of the dial cover is carried out on a 4-oz machine, using single-impression three-plate tool working with clear transparent material. Gating is at the centre of the cover, and to disguise the tiny scar at this point the mould is blasted over a small circular area, thus producing circle of matt finish in the centre of the cover when moulded. Weight of shot is 1 ½ oz. Removal of the sprue is interesting in that a tapered dowel provides a positive movement of the sprue in the tool, so that  after the stripping plate has cleared the moulding , the sprue can be removed backwards from the gate.

The dial covers are wrapped tissue and packed straight from the press and, as previously stated, sent away for cementing into the housing. Thus the handling of both is reduced to the barest minimum, thereby cutting down the possibility of rejects through accidental damage in the factory.

The scoop of the scale is run alternately with the housing.  A single-impression tool is used and the scoop is gated on the centre under-surface. The colour used is cream, and the weight of the shot is just over 3 ½ oz. The sprue is removed from the operator, who then packs the scoop in similar fashion to the housing. The scoop is embossed to provide graduations in fluid ounces and pints on the inside.

It is so interesting to see the number of different steps needed and the care given to the end product to ensure it arrived at its destination in good order.  I do love finding these fascinating articles.

Louise Dennis, Curator of MoDiP