physics

Mechanical plating

Mechanical plating is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mechanical plating rather than just read about it. In short: Mechanical plating, also known as peen plating, mechanical deposition, or impact plating, is a plating process that imparts the coating by cold welding fine metal particles to a workpiece. Mechanical galvanization is the same process, but applies to coatings that are thicker than 0.001 in (0.025 mm).

Key takeaways

Mechanical plating belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mechanical plating to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mechanical plating from memory before moving on to harder problems.

Reference excerpt

Mechanical plating, also known as peen plating, mechanical deposition, or impact plating, is a plating process that imparts the coating by cold welding fine metal particles to a workpiece. Mechanical galvanization is the same process, but applies to coatings that are thicker than 0.001 in (0.025 mm). It is commonly used to overcome hydrogen embrittlement problems. Commonly plated workpieces include nails, screws, nuts, washers, stampings, springs, clips, and sintered iron components. The process involves tumbling the workpieces with a mixture of water, metal powder, media, and additives. Common coating materials are zinc, cadmium, tin, copper, and aluminium. Invented by the Tainton Company in the 1950s, it was further developed by the 3M company.

Process The process begins with a descaling and removing soil from the workpiece. This can be done in the tumbler or in a separate cleaning system. After cleaning, the parts are prepared by combining them with water, medium, and a surface conditioner. The surface conditioner lightly coats the workpiece in copper, while the medium removes any residual mill scale or oxides. Finally, accelerators, promoters and metal powder are added to the mix. The accelerators and promoters provide the proper chemical environment for the plating to occur, such as the maintenance of a pH level of 1 to 2 to prevent oxidation and promote adhesion. The medium that is already in the mixture cold welds the metal powder to the workpiece through impacts that are induced by the tumbling action of the tumbler. At this point the surface finish is typically matte to a semi-bright finish, however the finish can be improved with a water polish. The time required for the above process is approximately 50 minutes. For some thinly coated workpieces a chromate passivation is necessary. Finally, the workpiece, whether passivated or not, is dried. The medium material is usually soda lime glass or a ceramic. It is usually spherical in form, but angular shapes are also used. For plating, medium usage is usually 1 part medium for every workpiece, but for galvanization the ratio is 2:1. However, various sized media are used in each batch with a typical batch consisting of 50% 4–5 in (100–130 mm) sized beads, 25% 2–2.5 in (51–64 mm) sized beads, and 25% 1–1.25 in (25–32 mm) sized beads. The smaller media are omitted when the workpiece has a cavity that the medium can get caught in, such as a fastener's recessed head. Note that the medium is reused many times. This process works better if the workpieces' surface finish is slightly rough.

Equipment The most important piece of equipment in the process is the tumbler. It is constructed of steel or stainless steel and lined with an acid and abrasion resistant material, such as neoprene, polypropylene, and polybutylene. The barrel sizes range from 0.04–1.13 m3 (1.4–39.9 cu ft), however the working volume is only 25 to 35% of the total volume. For most plating applications the tumbler is rotated at 60 RPM, however it can vary. If the speed is too fast then lumpy deposits will form on the workpieces, but if the speed is too slow then the metal powder will not deposit onto the workpiece. The separator separates the coated workpieces from the medium after coating. It can be as simple as a screen with water nozzles or as complicated as a vibratory system with magnetic separators. A medium handling machine then takes the separated medium and transports it to a storage tank for reuse. The separated workpieces are then taken to a dryer to remove any moisture. Usually centrifugal dryers are used, however oven are used for larger parts or loads.

Advantages and disadvantages

The greatest advantage of the process is its ability to overcome hydrogen embrittlement problems, which is important for workpieces that have a hardness greater than HRC 40. Note that there still is some embrittlement of the workpiece. While this process does not cause problems with hydrogen embrittlement, and electroplating does, it still offers equivalent corrosion protection. There is a great cost savings in using mechanical plating over electroplating on hardened workpieces, because the electroplating processes requires a pre- and post-plating operation to overcome hydrogen embrittlement problems. Moreover, because mechanical plating occurs at room temperature there is no tempering of hardened workpieces. Another advantage is that mechanical plating evenly coats all surfaces and features, unlike electroplating which has issues plating recesses. Mechanical plating can evenly coat up to 75 μm thick. For thicker plating mechanical plating is especially cost advantageous versus electroplating, because the cycle time does not increase much for the thicker plating, unlike electroplating. One of the disadvantages is the processes size limitations. Workpieces heavier than 1 lb (0.45 kg) can be damaged by the process, while flat lightweight workpieces tend to stick together so they are not properly plated.

References

Bibliography Dini, J. W. (1993), Electrodeposition: the materials science of coatings and substrates, William Andrew, ISBN 978-0-8155-1320-9. Gale, William Francis; Totemeier, Terry C.; Smithells, Colin James; ASM International (2004), Smithells metals reference book (8th ed.), Butterworth-Heinemann, ISBN 978-0-7506-7509-3. Gillespie, Laroux K.; Society of Manufacturing Engineers (1988), Troubleshooting Manufacturing Processes: A Reference Book for Manufacturing Engineers, Managers, and Technicians (4th ed.), Society of Manufacturing Engineers, ISBN 978-0-87263-326-1.

Worked examples

Example 1 — a first encounter with Mechanical plating

Start with the simplest possible case. Write down what Mechanical plating claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mechanical plating before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mechanical plating ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mechanical plating

In research: Mechanical plating appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mechanical plating in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mechanical plating is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coatings, Metal plating, so understanding it makes those chapters shorter.
In everyday life: Look for Mechanical plating outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mechanical plating in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mechanical plating means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mechanical plating out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mechanical plating in simple terms?

Why does Mechanical plating matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mechanical plating?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mechanical plating.