Saturday, September 23, 2017

Baths for Bright Dipping of Metals

Chemicals Composition For Bath of Certain Metal For Bright Dipping


1. General Steel

  • 25 to 30 g/l oxalic acid plus 10 to 15 g/l 100-volume hydrogen peroxide and 0.08 g/l of sulfuric acid.


2. Copper and Copper Base Alloys

  • 40 to 45% (vol) sulfuric plus 20 to 25 %(vol) of nitric acid and 0.1% (vol) of hydrochloric acid at room temperature.
  • 270 g/l chromic acid at room temperature.
  • 55% phosphoric acid, 20% nitric acid, and 25% acetic acid, all by volume, at 55 to 80oC.

3. Stainless Steel

  • 25% sulfuric acid, 4% hydrochloric acid, and 3% nitric acid, all by volume.


4. Lead

  • 3.5% glacial acetic acid and 3.5% 30-volume hydrogen peroxide by volume.

5. Nickel, Nickel Alloys or Alloy Steel

  • Various combinations of sulfuric acid, phosphoric acid, and nitric acid are used. A typical bath contains 60% phosphoric acid, 20% sulfuric acid, and 20% nitric acid, all by volume. Operates at room temperature.
Last Blog: Chemical and Electrolytic Brightening

Thursday, September 14, 2017

Bath Function on Chromium Plating

Bath Function for Chromium Plating


There only two essential constituents in conventional chromium plating bath; chromic acid and one or more catalyst acid radicals or anions. Chromium metal will not serve satisfactory as anode, owing two high solubility, insoluble anodes are used, generally lead.

Chromium metal is also appreciably more expensive. The chromium to be deposited is introduced into the bath as chromium trioxide, CrO3 (Chromic anhydride), commonly called chromic acid. It is reddish brown, hygroscopic material, easily soluble in water to give solution containing mainly H2Cr2O7. Many manufacturers, now aware of the effect of even small amount of catalyst acid radicals, furnish a pure grade of chromic axid especially suited for chromium plating. The chromic acid is made to meet sprcification which require that it contain not more than a small of percent of sulfate and be free from other catalyst such as chloride.

To convert a pure chromic acid solution to a chromic plating bath a catalyst is necessary. With given set of conditions of bath temperature, current density, and chromic acid concentration, too small amount of catalyst will result in either no plate or in brown anode stains. Too high catalyst contain will result in either partial plating with poor throwing power or no plate at all, owing to depolarizing action or easy formation of chromium (III) at the cathode. The essential criterion of bath composition in chromium plating from the conventional chromic acid-sulfate solution is the ratio, by weigth, of chromic acid to sulfate. The ratio should be kept within the limit of 50:1 and 250:1; and preferebly at about 100:1. A ratio of 90:1 is common; ratio of 70:1 to 80:1 are common in hard chromium baths especially at higher temperatures.

A typical formula for a chromium plating bath using sulfate as the catalyst acid radical is
  • chromic acid (CrO3), 250 gr/lt.
  • sulfate (SO4=), 2.5 gr/lt.

Saturday, September 2, 2017

Basic Process of Electroplating

There is an automatic bath function of electroplating process, so the agitate can control the condition of bath
Automatic Bath

BASIC PROCESS ELECTROPLATING


Electroplating is the deposition of a metal onto a metallic surface from a solution by Electrolysis process. It is used for purpose of decoration and protection of the metal. Metals commonly use to plate surface are silver, chromium, cadmium, zinc, gold and copper. Each metal as coating have specific solution that can work effectively. In the below example copper have chemical symbol of Cu, and after dilute in the solution can become ion and give the symbol Cu++. Because Cu have ion in the solution. In the case of copper platting for example electroplating takes place by means of the reaction of

     Cu++ + 2e ====> Cu. Cu++

in this equation represent an ion that is carried to the metal surface to be plated, known as the CATHODE, from the source of the metal being plated, known as ANODE. The ion forced to the cathode by an external source such as a battery. The electrolytic solution is a salt of the metal being plated; in the case of copper plating. It is copper sulfate, CuSO4.5 H2O.

The appearance, adhesion, porosity, and protection value of electroplated coatings depends on several things, including the type of base metal be plated, the preparation of the metal to be plating, and the electrodepositing process itself.

Base Metal Use for Electroplating


It is not possible to apply high quality coatings to metals of poor quality. The composition of the base metal is usually known and controlled. The condition of the surface, including the degree and nature of the polishing processes, may also have a direct bearing on the characteristic and porosity of the coating.

Preparation for Metal Plating


It is necessary to have the base metal surface chemically clean in order to secure good adhesion of deposits. The preparation usually involve cleaning that is, removal of grease and foreign particles and picking in the case of steel, or remove oxides or other compounds, and is some instances, to etch the surface. Because of a thin, natural oxide film, aluminum alloys do not usually respond to the cleaning and surface preparation treatments employed for other metals; special techniques must be used for such alloys.

Electrodeposition of Electroplating

Metal ion will transfer from Catode to Anode
Electrode-position of Metal

In the plating process many variables are involved that are subject to control. The composition and temperature of the electrolytic bath itself must be closely maintained. Agitation of the bath often permits an increase in current density. Filtration, either continuous of intermittent, is often used to keep the solution free of suspended matter. The average current density should be kept within desired limits for the sake of uniformity in thickness and quality of coating.

Finally, the anodes should ordinarily be of such composition and structure as to maintain the metal concentration and the pH. Where insoluble anodes are used, the metal content is maintained by replenishment.

Most commercial plating with potentials of conducted with motor generator sets, usually with potentials of from 6 to 12 volts, and with current outputs, depending on the area of work to plated and the current density.

Friday, September 1, 2017

ANODE

How the process of Electroplating can work for Chrom Plating, Nickel Plating, Gold Plating, Copper Plating, etc.
Electroplating

Anode For Electroplating Process


If you do an electroplating process, there are two electrode that immerse to the solution, and each of electrode is connect to electric current. For electroplating process use direct current. Beside chromium plating there are many other kind of electroplating like nickel plating etc. Anode is function as positive electrode on electroplating process, and the plate or other thing to plating will function as negative electrode and at the end of the process negative electrode will receive metal electron from the solution, if want to plating with chrome, then this negative electrode will cover with chromium layer. If you try plating metal for small piece, you can use car battery with about 100 A.

These are made of lead strips. Various sources can be found, but the material I use is about 1/8" (3.175 mm) thick cut or formed into the required shapes from a 4" (101.6 mm) waste pipe section available from plumbing/hardware stores. Joiner sections can be bought about 8" (203.2 mm) long.

Lead is attacked by chromic acid and an insulating layer of lead chromate (yellow in colour) will be formed if the anodes are not first treated. This lead chromate interferes with the plating current flow, but is easily avoided by transforming the working surface of our anodes into lead peroxide. The oxide prevents the formation of lead chromate, whilst allowing the passage of our plating current.

5.1 PEROXIDING THE ANODES


NOTE: For current density required for this treatment, the current is 5A/sq ft. (0. 035A/sq. in., or 0.55A/DM2) of total wetted anode areas.
  • Make up a 5% solution of sulphuric acid in water
  • Clean by scraping the lead anodes
  • Connect two of these lead anodes to the DC power supply, one positive, one negative
  • Adjust the current density to 5 A and maintain this for 15 minutes
  • Reverse the polarity of the DC supply and maintain 5 A for 15 minutes
  • Finally, reverse the polarity of the DC supply one more time and maintain 5 A for another 20 minutes
A dark brown coating on the anodes will indicate the presence of our protective layer of lead peroxide. Dry the prepared anodes and put them aside, ready for use. This process will be repeated on any anodes which tend to develop yellow spots during use (because of the lack of the lead peroxide coating).

5.2 SHAPE AND SIZE OF THE ANODES


How many size of Anode should be applied it normally 100 times to the piece you plate
Shape and Size of Anode
A good rule to follow is to allow for at least 50% more area of anodes in the bath than the surface area being chromed This will avoid problems due to the hexavalent balance of the solution from developing, and we'll not go into that here. Just use generously sized anodes.

The anodes must also be spaced equidistantly from the cathode (the part) being plated and following the shape of the part. They may be interconnected in the bath by soldered lead strips of narrow section (also for lead-outs) or above the solution level by soldered copper flex Due to the importance of an even deposit on pistons, or cylinders, for these I use a cylindrical-shaped anode. Spacing of cathode to anode is not critical, as long as it is even and wide enough to allow free flow of the solution by the action of agitation.

6. AGITATION


This is necessary in order to continually refresh the chrome solution plating the cathode-connected workpiece. Shaking the jar around will only succeed in disrupting contacts to electrodes; upsetting anode spacing -or worse still -spilling the chromic acid.
Agitation can be accomplished by mechanical means such as a propeller in the bath or a motorised crank made to move the cathode up and clown at about one motion per second, or slower. I prefer air agitation because it is so simple:

An inexpensive fish tank air pump connected to 1/4" (6.35 mm) plastic tubing, terminated in the bottom of the plating solution container and the end blocked but a series of pin holes placed in the tube at the bottom. These holes emit a stream of air bubbles under the cathode workpiece and serve to constantly pump fresh solution from the bottom of the tank upwards. This pumping motion also maintains an even temperature in the bath by helping circulate the plating solution around the tank heater business end.

A simple control valve in series with the air supply pipe is adjusted to limit the stream of bubbles to below the splash level on the surface of the bath. This method is just great in our small tanks.

7. DC CURRENT SUPPLY AND CONTROL


For chrome plating direct current is required, strictly. The reason is that chromic acid has a strong etching action on most metals when no current is flowing and chrome is deposited on the work-piece only when current is flowing. We cannot use a battery charger; or unfiltered power supplies. Full wave rectification of AC remains at 60 cycles/sec. resulting in a pulsing DC current, which reduces to zero volts, or no current flow. 120 times a second. The chrome would be dissolved away as quickly as it was being plated if this type current were to be used.

Power Source of Electroplating Process better using DC electric current like Battery
Battery For Electroplating
Smooth DC is required, such as that obtained from batteries or well filtered AC power supplies - and it must be controlled at the high-current levels required for chrome plating. I happen to have, and therefore use, a filtered AC current regulated bench power supply capable of delivering five amps DC at various voltages. The readers who have such a supply will find it ideal for chroming small parts up to 6.5 sq. in. For larger parts, and for readers who do not possess such a power supply, we'll examine a practical alternative at the 10-amp level.

7.1 BATTERIES


Because of the current requirements, about the only choice left here is the common lead/acid car type battery - the problem is that we do not always need 12 volts, but rather need to be able to select the voltage required to drive the desired current through the resistance of the plating bath. Of course, if the reader has access to individual six-volt batteries, which were common at one time, these can be used hooked up in series and a simple tap taken oft between the two. In order to use a regular 12-volt car battery we can tap into the lead-interconnecting strip between cells with a brass screw. Battery terminal grease applied at the threads will help to prevent sulphate build-up problems.

You can, of course, use a 12-volt supply with an adjustable series controller, but because you most often will not require more than six volts to obtain the required current density, it is not sensible to be dissipating the other six volts as heat in the controller. A simple switch will add the other six-volt cells only when required.

A variable resistance (rheostat) in series with the battery and an ammeter to tell you what is flowing is all that is required. The problem is that a rheostat of the power dissipation required would be a very large heat-dissipating component. Let us assume that you have a work piece to chrome plate and you have calculated the surface area to be 2.5 sq. in. The current density you need is going to be 0.75 x 2.5= 1.875A, or ll.25W @ 6 V.

If you only had 12V available, the same current requirement would result in 22.5 W and half of this would be dissipated as heat in the rheostat. Of course, if, as is usually the case, you only need a lower voltage to drive the plating current through the low resistance of the bath, the difference would be dissipated as additional heat in the rheostat at six or 1 2 V, but the controller would run a lot cooler at six volts.

7.2 CONTROL OF THE PLATING CURRENT


An electronic controller makes a lot more sense than the unobtainable power rheostat. I have made up one and tested it for this article and propose the simple schematic here. It requires the minimum of electronic knowledge and can be made up essentially of Radio Shack components. Peak current is limited to a maximum of ten amps, which is sufficient for chroming up to 13 sq. in. The ammeter can be any zero to one amp DC ammeter - with internal shunt and of the common moving coil type. Moving iron ammeters (el cheapos) are too inaccurate for our use.

We are going to make it read 0-10 amp by using an external shunt made up of resistance wire.
The shunt resistance in ohms = meter resistance in ohms over (multiplication factor - 1).
So, if we take the suggested 0-1 amp meter, which has a resistance of .05 ohm, the additional shunt required for the 10 amp range is: 0.05 / 9 = .0055 ohm.

This is a very small resistance which can conveniently be made of common 14GA (0.064") iron wire and safely carry our ten amp max current. From the wire tables, bare iron (baling) wire measures 0.015 ohms/ft. If it is galvanised, rub this down to bare iron or the resistance will be different.

We will need exactly: (12 / 0.015) x .0055 = 4.4 inches. Due to unseen variations, the exact and final shunt length should be finely adjusted and solidly soldered to binding posts, close to the ammeter and range switch. A Multimeter with a suitable range (10 or 20 amps) will serve for this calibration.

Every component, including this shunt and the meter, is hooked up using the recommended 12 GA copper wire. You can, of course, apply this shunt calculation to the ammeter you may happen to have access to, as long as the full-scale deflection current and the internal meter resistance are known parameters.

7.3 PANEL POLARITY REVERSING SWITCH


I have found it handy to provide a polarity reversing switch in the DC controller by now you know that to deposit metal on the workpiece, it must always be connected to the negative (cathode) terminal. The polarity of this set-up is only reversed and the workpiece made positive (anode) for treating steel prior to plating. This polarity-reversing switch is more convenient than changing leads around but must be correctly marked and not left in the wrong position. I recommend using even the cheapest portable voltmeter to make sure of this polarity and avoid frustrations.

7.4 PANEL VOLTMETER


A panel-mounted voltmeter is optional. It is not needed for the plating process because we only need to know about and control the current. A voltmeter will indicate what voltage (pressure) is required to drive the desired current (flow) through the plating solution, and that the battery charge is not dropping off. The reason I use one is that it also indicates the plating solution normal resistance, in series with all our hook-up wires to the cathode and anodes: If the voltage is high and we can't drive enough current through the bath, it indicates bad contacts or something wrong with the solution or anodes (high resistance).

7.5 DC CONTROLLER CONSTRUCTION NOTES


First, you couldn't get all the parts you needed at Radio Shack. They used to carry good-size utility chassis and business-like heat sinks, but no more; and they don't have a 1-amp meter, which we do need. We'll also need a 2.5 K 114 in. shaft potentiometer and a common garden PNP driver transistor such as a 2N1 131 or 2N2905. These, for mysterious reasons, are not stocked by Radio Shack either. So, get them from your electronics’ components stockist. You can bend up your own chassis or buy the one suggested.

The layout is not critical, but here are a few pointers to bear in mind:
  1. The chassis cover must be well ventilated/perforated;
  2. Do not skimp on the size of the heat sink for the power transistors or they will overheat and burn out. If you use the RS insulating mounting hardware, make sure the transistor case is insulated from the heat sink by doing a continuity check. If you use insulating Teflon mounts, the heat sinks must be insulated from the chassis. Ensure this by doing a continuity check before wiring. The transistor cases are the collectors;
  3. Use short lengths of 2OGA wire where indicated on the schematic and solid soldered joints;
  4. The RS#274-661 5-lug tie down strips are used to mount resistors/capacitors as required. The centre lug is bolted to chassis ground, so don't use it. One of these insulated tie-down strips will also support the 10A shunt and another the 2N5783 driver transistor (or 2N1 131 or 2N2905);
  5. The .001 de-coupling disc ceramic capacitors are best soldered directly across each transistor base and emitter leads after installing the transistor; and,
  6. The current control potentiometer from Electro Sonic (2.5K ohm) is a sealed quality component and linear. For good control reliability, do not substitute this for an open frame 'cheapo' from the junk box, unless you happen to have a similar good quality one. The 2.5K value is worked into the bias requirements for the driver transistor; so don't substitute the value either, unless you want to re-bias the transistor differently.

7.6 LEAD-ACID BATTERY CARE


A few recommendations may be appropriate here because we don't want the battery going flat during the plating operation.

Neglected lead-acid batteries develop a layer of insulating lead sulphate on the battery's plates. This is only removed by deep charging (time) and monitored by the use of a battery hydrometer. As the offending lead sulphate is transformed back into sulphuric acid by the charging process, the hydrometer reading will increase to the fully charged reading of
SG 1275/1280 slowly.
  • A low hydrometer reading will indicate a weak cell.
  • A long, slow charge is much better for continued battery life than a fast charge - and uses a hydrometer.
  • Battery voltage is a good indication but does not tell you much about remaining capacity; the hydrometer reading does.
  • A fully charged cell will measure a nominal 2.2V. We have six in series for a 12V battery
  • A fully discharged cell will drop to 1.8V and if left there will build up sulphate.
Following the above instructions and charging correctly will give us 13.2V for a fully charged battery (any over-voltage present immediately after a charge will soon level off) and at 10.8V the battery is fully discharged.

CAUTION: Remember the hydrogen and oxygen gasses produced by these batteries IS VERY EXPLOSIVE! (Ed note: This is not the time to say to yourself 'Ah, it won't happen to me. You could have your battery explode in your face. I don't believe I need tell you the consequences to life and limb in such an event).

Protect yourself and others by simply making sure the charger Is OFF before connecting /discharging clip. At the battery terminals - then switch ON and adjust the charge. The same simple rule applies to the feeder lines from the battery: Make sure the controller switch S2 is OFF before connecting/disconnecting at the battery.

DO NOT DO ANYTHING THAT COULD CAUSE A SPARK AT THE BATTERY TERMINALS!

Observation of these simple requirements should lead to a happy relationship between you, your chrome plating current requirements, and your lead-acid battery cells.