It may be prudent that some information is provided for a typical plating bath setup as used in the record industry
The nickel electroplating solutions commonly used for electroforming are the Watts, and conventional nickel sulfamate solutions with and without addition agents.
It should be noted that additions to the baths have detrimental effects on the final product They are only used in very small quantities much lower than recommended by the suppliers
As a rule only a wetter as well as some anti pitting additive is used and very sparingly at that
From the record industry perspective, the most important baths are those based on nickel sulfamate.
The advantages of nickel electroforming from sulfamate solutions are the low internal stress of the deposits and the high rates of deposition that are possible,
A typical formulation of the electroforming solution used in the record industry is as follows
Electrolyte Composition,
Conventional Sulfamate Ni(S03NH2)2 usually at 315-450 grams per liter
Nickel chloride NiCl2.6H20 usually at 3-15 grams per liter This is used by some plants so as to ensure anode corrosion in the process As a rule about 3 grams per liter and no more is used as chloride has a tendency to increase stress on the deposit
Nickel metal content: Optimal at 75 grams per liter although it must be noted that higher levels improve the speed of metal deposition with some added steps
Temperature is variable according to the step involved in so far as making matrices is concerned more information on my previous post
Operating Conditions
Temperature, C 35 to 60
Lacquers at low temperature around the 35-38 degrees C
First negative at a higher temperature at around the 48-52 C
Metal to metal at around 60 degrees C
Higher temperatures than 60 are generally avoided as the Sulfamate solution hydrolyzes at a temperatures around and above 70 C and as the temperature at the interface between anodes and cathode will certainly reach that if the solution is higher than 60 degrees C it is a good idea to keep it at around 60 C although with cooling down of the solution via a heat exchanger higher temperatures can be used
Agitation mechanical is generally used however since there is a rotating movement applied to the lacquer via the spindle there is ample extra mechanical agitation of the solution
Cathode Current Density, A/f from 3 to 250 according to the step required
Anodes De-polarised Nickel crowns
PH 3.5 to 4.2
Mechanical Properties resulting from a typical nickel sulfamate bath as used for the production of stampers
Tensile Strength, 415 to 620 MPA
Elongation, % 10 to 25
Vickers Hardness, 100 gram load 170 to 230
Internal Stress, MPa 0 to 55 (tensile)
It is possible to achieve zero stress deposits but extremely difficult to maintain on a day to day basis
The purpose of having zero or low stress deposit is very important
As mentioned beforehand the stamper undergoes continuous expansion and contraction during the pressing process
Besides the electroform has to be shaped as well as having the center formed so as to be mounted on the press tensile deposits would certainly hinder this process
It is necessary that a ductile rather than a tensile deposit results from the process so the stamper is able to with stand the conditions it is placed under
A tensile plate would split when it is formed or when it is on the press something that is not desirable but not uncommon in our industry
The baths are normally kept quite pure as any tramp metals will effect the deposit in a variety of ways normally making them brittle or with very high tensile stress
As an example 4 ppm of copper and or about the same amount of iron will make the bath unsuitable for stamper production although they would be suitable for other purposes as in decorative finish in any plating application
In the end making stampers for the record industry is a case of about 60-70% experience 10-20% knowledge and the balance is black craft
Since the good old days where there was quite a few people with the know how around have gone there very few people around who have that magic touch so as to run a successful operation constantly producing stress free stampers which are able to do the job consistently
The point being that it is not an easy task and when there are issues there not that many people one can turn to for help
It is not a task for the beginner or the light hearted as for every 1000 electroplaters there would be 1 electroformer and that is from the mouth of a Mr Spiro a famous man in the game who if he is around today he would be a very old man indeed
Cheers