GB412641A - Improvements in the chromium-plating of needles - Google Patents

Abstract

412,641. Electroplating. HORST, H. VAN DER, 22, Alexanderlaan, Hilversum, Holland. Jan. 6, 1933, Nos. 565 and 9039. [Class 41.] The pointed ends of metal articles such as gramophone needles are prepared for chromium-plating by anodic etching in an acid bath. During the subsequent plating the average current density over the whole surface to be plated is maintained at a constant value lying between 16 and 25 amps. per sq. dcm. ; the bath temperature is maintained at 53‹ C. for the lower current density value and at 65‹ C. for the higher value, and correspondingly for intermediate values. The anodes are arranged in such a way that the current density at the tips of the articles lies between 30 and 60 amps. per sq. dcm. ; the current density at the tips is estimated by the thickness of the deposit there in relation to the average thickness. The preliminary etching may be continued until the depth of metal removed from the points is substantially the same as that to be deposited. By etching for a suitable time all the needles of a batch mounted in the same holder may be etched to the same degree of sharpness. A holder for gramophone needles comprises a pair of plates 10, 11, Fig. 3, hinged at 12. The needles 13 are held between a rubber strip 17 and a copper strip 18 which are forced into engagement by a cam 15 operated by a handle 16. The engaging faces may be grooved. The anodes consist of lead or mild steel wires 24 disposed some distance above the points of the needles. The wires are anchored at one end and at the other end are slidably mounted in a grooved plate 32 secured to the underside of a block 25, provided with a curved surface 33 round which the wires are bent upwardly. The upward limbs are passed through an abutment bar 29 and maintained taut by a spring 30. The blocks 25 are mounted on guide bars 26 by clamps 28. The plates 11 of the holders are provided with lugs 19 engaging slots in conducting supporting bars 21.