IE950275A1 - A jewellery production process. - Google Patents

Abstract

In production of enamelled jewellery there is a comprehensive metal preparation operation stage. This involves a dilute acid dip (25), a three-stage rinse (26), a concentrated acid dip (27), a hot rinse (28) and a drying stage (29). The concentrations and durations of these dips provide an extremely clean metal blank which is very suitable for reception and adherence of enamel. Enamel is wet-filled and there is direct flame heating for firing of the enamel. Both the enamel firing stage (32) and an annealing stage (24) are carried out by direct application of heat which has been found to be extremely effective and with a low defect rate. For plating, there is a sequence of steps involving a detergent dip (40), a rinse (41), an acid de-grease (42), and a rinse step (43) which further prepares the jewellery item for plating (44). <Fig. 1(a).

Description

The invention relates to the production of jewellery, and more particularly jewellery items which have enamel coatings .

For many centuries now, various decorative items have been coated with enamel to provide a hard, durable and coloured decorative finish. It has been used in particular for pottery. The principle of enamel coating is based upon preparation of an enamel powder which may, as described in Soviet Union Patent Specification No. SU 1,493,629 comprise materials such as oxides of antinomy, lead, sodium, potassium, boron, arsenic, tin, lithium, zinc, zirconium, molybdenum, and silicon. As described in Soviet Union Patent Specification No. SU 1,775,494, the enamel raw material may be placed on a metal structure and then fired. In this specification, a silver platelet is used to support the component structure during a first firing process, and is removed before a second firing process. Soviet Union Patent Specification No. SU 1,257,116 describes a process in which the brass surface is dipped in a solution of sodium hexametaphosphate at 600-800°C for three to ten minutes before heat treatment. It would appear that the processes involved in the Soviet Union Patent Specifications are relatively complex as they involve a large number of steps. For example, in SU 1,257,116, it would appear that there is surface treatment before heat treatment and as the heat treatment would result in additional surface treatment being necessary, it appears that this method is relatively complex.

In GB 2,120,956A, a method is described whereby a frosted appearance is achieved by use of electroforming, cleaning, chemical erosion, application of a coating and of an enamel with a binder, curing, application of more enamel layers, curing, and application of adhesive. It would appear that this method is also quite complex.

The invention is directed towards providing a jewellery production process which provides for production of enamelled jewellery items which have intricate designs and are of a very high quality.

Another object is that the process be versatile to facilitate a large number of different jewellery items with small production lead times being involved.

A still further object is that the quality of the jewellery items be repeatable by the process to provide a consistently high-quality final product. This latter object is particularly important where intricate designs are involved in which case it is quite difficult to avoid problems arising whereby enamel thickness is insufficient for good durability and it is quite easy for enamel crossover to occur on the metal surface.

According to the invention, there is provided a jewellery production method comprising the steps of :pressing out a blank from a sheet of copper alloy raw material; stamping a pattern in the blank leaving a margin surrounding the patterned area, the pattern including even-surface protrusions and mottledsurface indentations; clipping the blank in a press to remove the margin excess; annealing the blank in a flame and simultaneously making any required solder joints; preparing the blank for enamel application in a batch by dipping the blanks in a dilute nitric acid solution for oxidation removal, rinsing in water, dipping in concentrated nitric acid solution, and drying; mounting the cleaned blank in a jig and placing wet enamel in the indentations; hardening the enamel by heating with a direct flame, thus providing an enamelled jewellery item; preparing a batch of items for coating by dipping in a dilute nitric acid solution for oxidation removal, rinsing in water, dipping in a concentrated nitric acid solution, and drying; and plating the item in a batch by :mounting the items on a frame having electrically conductive supports; dipping the frame in a detergent; rinsing by dipping the frame in water; plating the items with nickel in a nickel electroplating solution at a temperature elevated from room temperature; removing excess electroplating solution by dipping in water; 0 Ζ 7 5 plating the items in an electroplating solution which is agitated; removing excess electroplating solution by dipping in water; and drying the items on the frame.

In one embodiment, the nitric acid solution has a volume ratio composition of approximately 6:1 water to nitric acid.

Preferably, the dilute nitric acid dip has a duration of 100 to 140 seconds.

In another embodiment, the rinsing steps carried out after dipping in dilute nitric acid are each carried out as a sequence of three water dips in water flowing continuously between baths .

In a further embodiment, the concentrated nitric acid dip has a duration of two to five seconds.

Ideally, the blanks are dried after the concentrated nitric acid dip by being placed in warm particles.

In another embodiment, the blank is prepared for enamel hardening by soaking of excess wet enamel by absorption into a woven cloth.

Preferably, the detergent cleaning step has a duration of 12 to 18 seconds.

In one embodiment, the detergent cleaning step is followed by de-greasing in a nitric acid bath.

In another embodiment, the duration of nickel plating is six to eight minutes with a temperature of approximately 45°C and anode current of 14-16A at approximately 3V.

In a further embodiment, the frame for plating is of rectangular configuration in which three sides are surrounded by a coating of electrically insulating material, and the frame supports comprises a length of conducting wire connected to the conducting side and trained around opposed sides.

Ideally, the excess nickel electroplating solution is removed by dipping for three to six seconds in still water and subsequent dipping for three to six seconds in agitated water.

Preferably, the electroplating step has a duration of 45 to 55 seconds with an electroplating current of approximately 15A and 3V DC.

In another embodiment, electroplating solution excess is removed by dipping for three to six seconds in still water followed by dipping for three to six seconds in agitated water.

In a further embodiment, the plated item is dried under a hot air stream.

In one embodiment, the raw material has a composition of approximately 85% copper to 15% zinc.

Preferably, the pattern is stamped in the blank by use of a hardened steel die under a pressure in the range 180 to 220 bar.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which :Figs. 1(a), 1(b) and 1(c) are together a flow chart illustrating a jewellery production process of the invention; Fig. 2 is a perspective view of a press machine for operation on a blank; Fig. 3 is a perspective view of a blank; Fig. 4 is a diagrammatic view showing a stamping machine and various dies which are used with the machine; Fig. 5 is a perspective view of a stamped blank; Fig. 6 is a perspective view of a stamped and clipped blank; Fig. 7 is a perspective view showing an enamel preparation station for use in the process; and Fig. 8 is a perspective view of a plating station for use in the process.

Fig. 1 generally illustrates the various steps of a production process 1 of the invention. The process is in three stages, namely a metal preparation stage 2 having steps 20 to 29, an enamel stage 3 having steps 31 to 38, and a plating stage 40 having steps 40 to 51.

V Γ <; , The metal preparation stage 1 is possibly the most important part of the process as it ensures that the remaining steps are relatively simple to carry out to achieve a high quality product. In particular, it helps to ensure that enamel adheres to the surfaces at the correct positions, has the correct thickness and that the overall appearance of the jewellery item is satisfactory. Some of the items of equipment which are used in the process 1 are illustrated in Figs. 2 to 8 inclusive.

The process starts by taking a sheet of raw material which in this embodiment is a brass which has an 85% copper composition and approximately 15% zinc. In step 20, the sheet is pressed to provide a cut-out blank which in this embodiment is disc-shaped as shown in Fig. 3. A press 60 is used to cut the blank. As shown in Fig. 2, the press comprises a support frame which supports a press head and a rotatable actuator 62. A material support 63 is mounted on a base 64 for the press 60. Rotation of the actuator 62 causes the head 61 to move downwards in a stroke which cuts the sheet to create a blank 70 shown in Fig. 3. Of course, any suitable press such as an hydraulically or electrically-operated press may be used, particularly for high-volume production. In step 21, a pattern is stamped in the blank by use of a press 75 having a press head 76 and a workpiece support 77. The head 76 supports a stamping die such as a die 78 or 79, also illustrated in Fig. 4. The die 78 has a projecting pattern whereas the die 79 has a recessed pattern. An important aspect of the patterns on the dies 78,79 is that the indentations which are created on the blank for reception of enamel at a later stage in the process have a rough or mottled surface. In the process, the blank 70 which is cut is of a significantly larger size than the jewellery item which is eventually required and $95 0 2 75 accordingly, the pattern which is stamped takes up only a portion of the surface of the blank 70. A stamped blank is shown in Fig. 5 in which there is a central pattern and a margin 73 of excess brass.

In step 22 of the method, the excess is removed by use of the press 60 and in step 23 the blank is pierced, also by use of the press 60 or an equivalent machine. Of course, not all jewellery items will require piercing in the centre, as this may not be incorporated in their design. An important part of the process is the fact that the press which is used for stamping the pattern in the blank operates at approximately 200 bar pressure for a blank thickness of 2 to 3 mm for sufficient penetration.

In the process 1, the blank is annealed and various fixtures, eyelets etc. are soldered in the one operation. This is very simply carried out by direct heating to a temperature of 1100°C to 1200°C with a flame torch and carrying out the necessary operations so that there is simultaneous annealing and soldering. Of course, the step 24 helps to ensure that the correct temperature is reached for annealing for each individual item and the problems of blind spots which can arise with heating furnaces and kilns are avoided. It is also of course an extremely quick annealing step as it takes only a matter of 20 to 30 seconds for both operations.

At this stage in the process, the blank is completely discoloured by oxidation during annealing in step 24 and steps 25 to 29 are then carried out for preparation of the blank for enamelling. Step 25 involves dipping the blank among a batch of approximately 300 to 400 blanks placed in a stainless steel basket in various baths. These operations are carried out at an enamel preparation station 80 which has a dilute acid bath 81, a sequence of three rinse baths 82, 83 and 84, a concentrated acid bath 85, and finally a hot water rinse bath 86. The station 80 also comprises a container 87 for warm sawdust 88 which may be used in drying of the item. The stainless steel basket which is used for dipping of the blanks is indicated by the numeral 89.

In more detail, step 25 involves a dip in acid in the bath 81 for a time period in the range of 100 - 140 seconds. The bath 81 has a dilute nitric acid solution in which the ratio of water to nitric acid is 6:1. The rinse baths 82, 83 and 84 have a continuous flow water system which is interconnected with the water running from bath 82 to 83 and from bath 83 to 84. There is a relatively short dip for approximately two to five seconds in each of these baths in turn for step 26 before a dip in the concentrated acid bath 85 which contains a solution of almost pure nitric acid with salt additives. This dip (step 27) has a duration of only two to five seconds and is required for providing an extremely bright surface on the metal blank as the first acid dip bath 81 serving to remove the surface oxidation. In step 28, there is a rinse in hot water at a temperature of approximately 80°C in the bath 86 to remove any traces of the acid and this is followed by drying (step 29) in warm sawdust 88 in a container 87. The sawdust is of uniform composition and does not include very fine dust which can become entrapped in indentations in the blank.

Once the blanks have been prepared for enamelling, the enamelling stage 3 is then undertaken. In step 31, there is wet filling of enamel into the various indentations on each blank in turn. This is performed manually using a nib instrument with the blank mounted in a jig at the correct angle to ensure that there is no cross-over of enamel between different indented parts of the blank. The S95 0 2 75 fact that the surface of the indented parts of the blank have a roughened or mottled surface helps to ensure good adhesion.

In step 32 there is direct flame heating of the blank for firing of the enamel. During this step the blank is mounted on a mesh and heated to a temperature in the range of 1100 to 1150°C, causing the sand in the enamel to crystallise to form glass and causing evaporation of the moisture.

The enamel which is used may be of the transparent or of the opaque type. If of the transparent type, a glistening light effect is provided by access of light to the mottled surface which has been very thoroughly cleaned during the enamel preparation step.

The enamelled blank (hereinafter referred to as a jewellery item) is then filed on an emery belt to smoothen the enamel in step 33. At this time, any repairs which may be required are carried out and the item is heated a second time to remove file marks and restore a high gloss finish to the enamel.

The enamel stage 3 is completed by steps 34 to 38 inclusive which are carried out at the station 80. The steps 34 to 38 are similar to the steps 25 to 29 of the enamel preparation stage 2. This is very important as it helps to ensure that there is consistency in the manner in which these steps are carried out as similar personnel may be used to carry them out and parameter settings are seldom changed.

After this sequence of steps the blank is now a jewellery item which has a highly-polished metal surface and an extremely clean enamelled surface which would be quite acceptable as a jewellery item in its own right. However, the method also involves plating of the metal part of the jewellery item to provide an improved finish. In this embodiment, the plating is an 18 carat gold plating. Although the jewellery item is at this stage extremely clean and free of foreign matter, the plating stage 40 involves a number of steps 40 to 43 which essentially prepare the jewellery item for an initial plating step 44. The jewellery items are mounted on a frame 100 which has a support 101 and a rectangular frame portion with a top bar 102 which is conductive. The frame portion also has three other sides 103 which have a plastics sleeve so that no metal surface is presented for any of the electroplating steps. A conducting wire, in this case copper is trained between the conductor 102 and the bottom non-conductive bar 103 in a continuous manner so that current flows from an external source through the support 101, through the conductor 102, and to the copper wire 104 which supports the jewellery items 105. It has been found that this arrangement of support frame is particularly useful as it minimises unwanted plating and allows for support of a large number of jewellery items without loss of plating quality.

The initial dip 40 is in a bath 110 in which there is a detergent in a water solution which helps to prevent breaking of enamel. This dip is for a period of approximately 15 seconds and is followed by a dip in the bath 111 containing water for rinsing of the items. There is then a dip in a bath 112 which has electrical terminal supports 113 for reception of the support 101. The bath 112 contains a de-greasing acid such as a dilute nitric acid solution. This dip is for a period of five to ten seconds and helps to ensure that there are no remaining grease or dirt deposits on the jewellery items. There is then a series of rinsing steps in three water baths 114, followed by a nickel plating step 44 in a nickel plating bath 115. This step has a duration of seven minutes and the nickel plating solution is maintained at a temperature of 45°C. Again, current is transmitted through the support 101 to the jewellery items 105 mounted on the frame 100. Because only a small part of the frame 100 has exposed metal, namely the upper bar 102, little of the nickel is lost through deposition on the frame 100.

A still water bath 116 is used for removal of excess plating which drips from the frame 100 in step 45 and following this in step 46 the frame is dipped in a pair of sequential water baths 117. These baths are agitated to ensure that all excess nickel plating solution is separated from the jewellery items and the frame 100.

In step 47, the jewellery items are plated with gold in a bath 118 with an anode current of 15 Amps DC and three Volts. The time duration for the bath 118 is 50 seconds. In step 48, the excess gold plating solution is removed by dipping in a still water bath 119 and there are then rinsing steps 49 and 50 in agitated water in baths 120 and 121. It has been found that by mounting the jewellery items in the particular manner illustrated and by carrying out the initial cleaning and de-greasing steps in the manner illustrated, there is a very low defect rate. In particular, the problems of plating of areas of the jewellery item which should be covered with enamel are minimised.

Following plating, the jewellery items are left on the frame 100 in a drying chamber where they are dried by a hot air blower. By doing this, staining by rinsing water is avoided. The end product therefore has an extremely clean and glistening appearance in which not only the S950275 - 13 exposed metal surfaces but also the enamel surfaces are very clean. For example, where the enamel is of the transparent type, passage of light through the enamel and into the background mottled surface which had been prepolished during enamel preparation provides a very attractive glistening effect.

It will also be appreciated that the method in general provides for a production of a wide variety of different jewellery items with different designs in an effective manner. There is no need for large batch runs through kilns where only items of a particular type may be fired. The method of application of the wet enamel and of firing the jewellery item allows use of intricate patterns having a mixture of exposed metal and enamel to provide a detailed design which can be very meaningful. It could be said that the invention provides the technical steps which minimise the limitations on the artist when designing a jewellery pattern.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (18)

1. A jewellery production method comprising the steps of :pressing out a blank from a sheet of copper alloy 5 raw material; stamping a pattern in the blank leaving a margin surrounding the patterned area, the pattern including even-surface protrusions and mottledsurface indentations;

2. A method as claimed in claim 1, wherein the nitric acid solution has a volume ratio composition of approximately 6:1 water to nitric acid.

3. A method as claimed in any preceding claim, 20 wherein the dilute nitric acid dip has a duration of 100 to 140 seconds.

4. A method as claimed in any preceding claim, wherein the rinsing steps carried out after dipping in dilute nitric acid are each carried out Se5 ο 275

5. A method as claimed in any preceding claim, wherein the concentrated nitric acid dip has a duration of two to five seconds. 5 rinsing by dipping the frame in water; plating the items with nickel in a nickel electroplating solution at a temperature elevated from room temperature; removing excess electroplating solution by 10 dipping in water; plating the items in an electroplating solution which is agitated; removing excess electroplating solution by dipping in water; and

6. A method as claimed in any preceding claim, wherein the blanks are dried after the concentrated nitric acid dip by being placed in warm particles.

7. A method as claimed in any preceding claim, wherein the blank is prepared for enamel hardening by soaking of excess wet enamel by absorption into a woven cloth.

8. A method as claimed in any preceding claim, wherein the detergent cleaning step has a duration of 12 to 18 seconds.

9. A method as claimed in any preceding claim, wherein the detergent cleaning step is followed by de-greasing in a nitric acid bath.

10. A method as claimed in any preceding claim, wherein the duration of nickel plating is six to eight minutes with a temperature of approximately 45°C and anode current of 14-16A at approximately 3V. 10 clipping the blank in a press to remove the margin excess; annealing the blank in a flame and simultaneously making any required solder joints; preparing the blank for enamel application in a 15 batch by dipping the blanks in a dilute nitric acid solution for oxidation removal, rinsing in water, dipping in concentrated nitric acid solution, and drying; mounting the cleaned blank in a jig and placing 20 wet enamel in the indentations; hardening the enamel by heating with a direct flame, thus providing an enamelled jewellery item; preparing a batch of items for coating by dipping in a dilute nitric acid solution for oxidation 25 removal, rinsing in water, dipping in a concentrated nitric acid solution, and drying; and Su .5 s Γ 7 ·<> Λ .J · plating the item in a batch by :mounting the items on a frame having electrically conductive supports; dipping the frame in a detergent;

11. A method as claimed in any preceding claim wherein the frame for plating is of rectangular configuration in which three sides are surrounded by a coating of electrically insulating material, and the frame supports comprises a length of ^ γ Ο0275

12. A method as claimed in any preceding claim wherein the excess nickel electroplating solution is removed by dipping for three to six seconds in still water and subsequent dipping for three to six seconds in agitated water.

13. A method as claimed in any preceding claim wherein the electroplating step has a duration of 45 to 55 seconds with an electroplating current of approximately 15A and 3V DC.

14. A method as claimed in any preceding claim, wherein electroplating solution excess is removed by dipping for three to six seconds in still water followed by dipping for three to six seconds in agitated water.

15. A method as claimed in any preceding claim, wherein the plated item is dried under a hot air stream. 15 drying the items on the frame.

16. A method as claimed in any preceding claim, wherein the raw material has a composition of approximately 85% copper to 15% zinc. - 16 as a sequence of three water dips in water flowing continuously between baths.

17. A method as claimed in any preceding claim, wherein the pattern is stamped in the blank by use of a hardened steel die under a pressure in the range 180 to 220 bar. 18. A method substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings . - 17 conducting wire connected to the conducting side and trained around opposed sides.

18. - 18 19. A jewellery item whenever produced by a method as claimed in any preceding claim.