EP0415130A1

EP0415130A1 - Method to eliminate the filling in wrought hollow gold and wrought hollow gold thus processed

Info

Publication number: EP0415130A1
Application number: EP90115041A
Authority: EP
Inventors: Vincenzo Longo; Ferdinando Foschini
Original assignee: LED ITALIA Srl
Current assignee: LED ITALIA Srl
Priority date: 1989-08-31
Filing date: 1990-08-04
Publication date: 1991-03-06
Also published as: IT1235130B; IT8983469A0; JPH0397900A

Abstract

Method to eliminate the filling in wrought hollow gold which is in the form of a wrought article consisting of a gold leaf wrapped about a core of copper or of an alloy of copper or of another metal and/or alloy of another metal, the gold leaf having its edges mating with each other and at least partly not welded together, the gold also being of any desired title or carat weight, the gold article undergoing an operation of electrolysis which eliminates the core.

Article made of hollow gold which is processed in the form of a wrought article, the article consisting of a gold leaf wrapped about a core of copper or of another metal or of an alloy, the gold leaf having its edges mating with each other and at least partly not welded together, the gold also being of any desired title or carat weight and undergoing a process of electrolysis to remove the core according to the above method.

Description

This invention concerns a method to eliminate the filling in wrought hollow gold. The invention concerns also the wrought hollow gold thus processed.
The wrought hollow gold with which this invention is concerned is the type of gold which may have any title or carat weigth and is produced in the form of wrought articles such as chains (necklaces, bracelets, brooches, etc.) or other articles and which has a hollow interior at the time it is sold.
Such hollow gold is produced by wrappping on a core of copper or copper alloy such as, for instance, tombac or prince's metal, or of other metals or alloys a gold leaf and by making the edges of the leaf mate together.
The edges are caused to mate together but are normally not welded together or are not welded along their whole mated length.
When the gold article has been wrought, the gold is emptied of its core and is marketed after further possible finishing and completing operations.
At the present time the removal of the core takes place by immersing the wrought hollow gold article in a hot bath of nitric acid HNO₃ or hydrochloric acid HCL or another mineral acid and keeping it there for a required time of about 8 to 24 hours.
The nitric or hydrochloric or other acid flows through the interspaces between the edges of the gold leaf, attacks the copper and/or any other metals or alloys forming the core and converts the components of the core into nitrates, chlorides or other salts according to the acid employed.
This operation entails a plurality of limits and shortcomings. A first limit consists in the environmental problem linked to the disposal of the fumes of the oxides of nitrogen; such disposal now takes place into the atmosphere and is forbidden or alternatively requires chemical absorption of the fumes and thereafter the disposal of the chemical solutions employed for such absorption.
Another limit is the cost and difficulty of removal and disposal of the spent solution and sediments forming wastes designated as being toxic and harmful.
One shortcoming is the fact that the method is not automated since completion of the operation is evaluated by an empirical check using a sample of the article and checking it with sonorous and visual means.
Another shortcoming, which is particularly noticeable in low carat weights or titles of gold, is the attack which takes place on the component admixed with the gold, for this attack becomes apparent with a reduced sheen and less rich finish of the surface of the gold article.
A method which provides for the use of a cupro-ammoniac solution has been disclosed for the emptying of a wrought hollow gold article on a copper core; this method provides for a first bath in the cupro-ammoniac solution, a rinse with a solution of diluted acid and a final cleansing rinse.
This method, however, raises a plurality of problems such as a plurality of apparatus, a high cost of investment and high working and maintenance costs.
Moreover, the control of the operations is complex and delicate and the process causes the release of gases which have to be purified.
These shortcomings and limits have been considered by the present applicant, who has evolved the present invention to overcome them and to provide further advantages which will become clear in the following description.
The method to eliminate the filling in wrought hollow gold according to this invention is set forth in the first independent claim, whereas the dependent claims describe variants of the idea of the solution.
The wrought hollow gold according to this method is set forth in the relative general claim.
According to the invention the wrought hollow gold article still containing the core undergoes an action of electrolysis in a solution of 10 grs/lt. of sulphuric acid H₂S0₄ and 50 grs/lt. of copper sulphate CUS0₄ 5H₂O, namely in an electrolytically active acid solution.
Where the core consists of a copper alloy, the above solution may also contain products which attack the metal admixed with the copper and/or products to flocculate and/or make complex the resulting compound or the admixed metal.
According to the invention the solution in one of its basic formulations may consist as follows:
H₂SO₄ from 7 to 18 grs/lt., normally 10 grs/lt.
CUSO₄ 5H₂O from 35 to 75 grs/lt., normally 50 grs/lt.
Zn (zinc) from 1 to 20 grs/lt., normally 10 grs/lt.
The temperature may vary between 35 and 85°C but will normally be between 50 and 70°C.
The electrolytic action is obtained by using the wrought hollow gold article as the anode, while the cathode will advantageously, but not only, consist of copper, and a voltage of between 200 and 900 millivolts will be applied to the cathode; the size of the cathode will be such as to have a density of current between 2 and 3.5 amperes/dm², normally 2.5 amperes/dm².
A constant voltage will be applied advantageously.
According to a variant the voltage will be variable over a period of time and the variation may be correlated with the concentration of the active elements existing in the bath.
The current applied is a consequence of the electrochemical potential of the bath.
According to the invention the control of the electrical parameters enables the cycle to be automated and also makes possible the programming of the renewal of the active elements by means of topping up.
The topping up may be performed gradually or may take place upon arriving at a pre-set threshold of the active elements.
The topping up will take place advantageously by means of a concentrated solution suitable to bring the active elements up to optimum values.
The invention enables the copper deposited as electrolytic copper on the cathode, and therefore re-usable, to be recovered.
As regards the other components of the core in the event of a copper alloy, such components may remain in solution in the form of salts or be flocculated and perhaps discharged periodically.
The topping up liquor may also contain chemical elements suitable to treat such other components of the core in one way or another.
Moreover, the topping up liquor may also contain elements to modify the crystallization of the cathodic deposit, such as ammonium sulphate, sodium sulphate, dextrins, polyglycols or thiourea.
Besides removing the limits and shortcomings of the state of the art, the invention provides an absence of toxicity concerning the atmosphere and also concerning the working environment.
Moreover, the invention enables the copper to be recovered as electrolytic copper, the level of the solution to be pre-established and the parameters of attack on the copper to be pre-determined, ensuring that the auxiliary components included in the alloy together with the gold are not attacked.
This entails a better surface finish on the finished gold and a better sheen of the same.
By the parameters themselves of the electrolytic process the invention makes it possible to obtain a sure indication of the end of the cycle and therefore the result can be pre-established by adjusting the electrical parameters and checking the values of the bath.

Claims

1 - Method to eliminate the filling in wrought hollow gold which is in the form of a wrought article consisting of a gold leaf wrapped about a core of copper or of an alloy of copper or of another metal and/or alloy of another metal, the gold leaf having its edges mating with each other and at least partly not welded together, the gold also being of any desired title or carat weight, the method being characterized in that the gold article undergoes an operation of electrolysis which eliminates the core.

2 - Method as claimed in Claim 1, in which the process of electrolysis is carried out in a solution containing sulphuric acid and copper sulphate or, in any event, in an acid environment.

3 - Method as claimed in Claim 1 or 2, in which the solution contains at least 7 to 18 grs/lt. and advantageously 10 grs/lt. of sulphuric acid H₂SO₄, and 35 to 75 grs/lt. and advantageously 50 grs/lt. of copper sulphate CUSO₄ 5H₂O and is kept at a temperature between 35 and 85°C and advantageously between 50 and 70°C.

4 - Method as claimed in any claim hereinbefore, in which the solution contains also up to 20 grs/lt. of Zn (zinc).

5 - Method as claimed in any claim hereinbefore, in which the solution contains substances which attack the auxiliary components of the alloy of which the core consists.

6 - Method as claimed in any claim hereinbefore, in which the solution contains substances to flocculate the auxiliary components of the alloy of which the core consists.

7 - Method as claimed in any claim hereinbefore, in which the solution is topped up during the process so as to restore the values of the active elements.

8 - Method as claimed in any claim hereinbefore, in which the topping up is carried out with a concentrated solution containing also elements to modify the crystallization of the cathodic deposit, such as ammonium sulphate, sodium sulphate, dextrins, polyglycols or thiourea.

9 - Method as claimed in any claim hereinbefore, in which the topping up is automatic, being correlated with the physical-chemical parameters of the bath.

10 - Method as claimed in any of Claims 1 to 8 inclusive, in which the topping up is carried out automatically upon reaching pre-set physical-chemical parameters of the bath.

11 - Method as claimed in any claim hereinbefore, in which the gold article is used as the anode, while the cathode consists of copper or an analogous material, a voltage between 200 and 900 millivolts being applied.

12 - Method as claimed in any claim hereinbefore, in which the dimensions of the cathode are correlated with a current density between 2 and 3.5 amperes/dm² and advantageously 2.5 amperes/dm².

13 - Method as claimed in any claim hereinbefore, in which a constant value of voltage is applied.

14 - Method as claimed in any of Claims 1 to 11 inclusive, in which in at least a part of the method a variable value of voltage is applied and is correlated with the concentration of the active elements.

15 - Method as claimed in any claim hereinbefore, in which the end of the cycle is monitored by controlling the electrical parameters.

16 - Method as claimed in any claim hereinbefore, in which the copper of the core is recovered in the form of electrolytic copper.

17 - Article made of hollow gold which is processed in the form of a wrought article, the article consisting of a gold leaf wrapped about a core of copper or of another metal or of an alloy, the gold leaf having its edges mating with each other and at least partly not welded together, the gold also being of any desired title or carat weight, the article being characterized in that it undergoes a process of electrolysis to remove the core according to the method of any of the claims hereinbefore.