Bolt and Nut Selection

For example use stainless steel 316 for the bolts and stainless steel 304 for the nuts. The two different grades of stainless steel help to prevent the nuts seizing if they have to be removed for maintenance, etc.

I had an application on a wind farm where we had to hack year old SS bolts off because they had seized, and anti-seize compound was used as were dissimilar SS grades. It was quite a shock.

:(

Sometimes nothing seems to work, but at least with dissimilar grades of SS you don't have to worry about the anti-seize compound being washed off or forgotten or misused in the first place, that and there is less chance of it polluting sensitive production lines.

;)

Thank you. But it's very costly. If to save cost, what type of coating/plating will you recommend? We used to bolt painted panel to painted panel together.

You don't have anyone on staff who knows these things?

Have you searched for answers on the net?

We just started to find solution to this problem. Previously, we used stainless steel or steel applied anti rust or zinc-coated steel. S/S can be costly. Grade 8.8 Steel bolt have high tensile strength but costly to maintain coz of anti rust application and removal & cleaning of excessive anti rust at site. Zinc-coated one will have lower strength and resulted in mechanical failure. So, we are looking for better solution.

I have searched through the net, but there's no webpage telling me the best solution. I would need advise from those who have experience or in the same industry.

<...costly to maintain coz of anti rust application...>

What's the cost of not doing it, i.e. the Customer rejecting the equipment and the despatch being delayed because of not following a specification? Which is cheaper? (Rhetorical questions - NNTR)

John 11, 35.

What materials are you bolting together?

Use fasteners that are the same.

Some useful details would give us a chance to really advise you properly.

Otherwise, use stainless steel. But, if you have Aluminum parts, stainless steel is a very bad choice. Galvanic corrosion will kill you.

That's why, "Some useful details would give us a chance to really advise you properly."

Thank you. We used to bolt painted steel panel to each other. Or sometimes zinc-coated steel to painted steel panel.

And, what was the result?

You haven't even told us what hardware you are using now.

I know cost reduction at any cost is the goal. Sometimes the loss of customers could be avoided by proper materials engineering and selection.

The choice is up to you. Satisfied customers or cheap manufacturing costs.

Lyn, thanks for continuous feedback. We used sus304 bolt and nut which is good but expensive. We also used steel bolt and nut grade 8.8 applied with anti rust but still rusty sometimes. We also used zinc-coated steel bolt and nut grade 8.8. It turns into white rust.

The above resulted regardless of the type of material that we bolted together. Rust appear most probably due to the moist during shipment. Vacuum pack can be very expensive.

Have you not answered your own question.

The only material that gives satisfactory results is more expensive.

The only material that gives satisfactory results is more expensive.

That's customer satisfaction. It will pay off later.

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I would use grade 8.8 bolts, coat the theads with grease before assembly and put more on the outside after. Inspect after shipping and if the grease has washed off apply some more. Repeat at regular intervals during operation.

I would echo Lyn's sentiment a thousand times over. The few dollars you save by cheaping out on the fasteners pales in comparison to the customer's impression of your product. I can't tell how many times I have been FURIOUS with a product that totally FRUSTRATED me because some cheap ass bean counter saved a few cents that cost me HOURS of work and MANY DOLLARS later on. And these products would have been stunningly good if it were not for some very short-sighted decisions. I REMEMBER those and avoid them at all costs in the future.

In fact, for many of my purchasing decisions at home and where I work, I go for the more expensive product because it is cheaper.

Your solution to save money may not be limited to material selection, which seems limited to SS, but in a business solution....Your company invests in part ownership of a steel supplier, a first step towards vertical integration....

If you are only interested in preventing corrosion during shipping ONLY and don't care once the equipment arrives then consider sealing the equipment along with packs of desiccant (or similar) to control moisture and hence corrosion inside the packed equipment being shipped.

That's about the simplest and cheapest thing I can think of.

It needs to be compatible with the materials being conveyed, Murphy.

For load bearing bolts you should use high tensile steel bolts. These bolts should be elctro galvanised so as to avoid rusting due salty sea weather. Better to apply light film of light viscosity oil to prevent jamming.

You asked about common fasteners for the type of equipment you build and ship: Zinc plated fasteners are common for above equipment, if your fasteners break because they are not strong enough then perhaps they are not large enough for the application.

For conveyors, the nuts used are usually serrated, flanged whiz nuts, this eliminates the need for lock washers.

If you are joining zinc plated steel together, do not use SS fasteners.

Offer your customer zinc plated fasteners as a standard offering and certainly offer them SS fasteners for an upcharge if they are really worried about corrosion. Let them pay for the added cost, this will increase their perception of value and you get to mark up the added cost and increase your margin so you are still in business the next time they need equipment from you.

Zinc plating is subject to abrasive wear and tear. Rather go for a "DISTek sheradising zinc diffusion coating" for both bolts and nuts. You can find applicators by doing a Google or similar search for "distek".

If the nuts & bolts are only used during shipment and will be discarded by the customer, maybe plastic fasteners would work. They wouldn't rust and they are cheap. Their tensile strength may not be adequate.

When I was manufacturing light truck accessories for outside application had rust issues so I switched to stainless but they turned black in time then we had steel hardware plated with cadmium but I think due to environmental issues this is not available. Final solution was to zinc plate and install with a good fitting plastic cover over the head of the bolt. This was most acceptable. In marine applications the bolt are selected for length so that when the nut is tightened there is no thread showing and this allows for disassembly. Another favorite of mine is integral flange bolts and nuts, they clamp better with little deflection and seem to be vibration resistant. I understand rail way equipment uses this fastener a lot.

The best place to look for information is the marine industry; but even there, regular maintenance is still required. One of the best is K-monel, but it is expensive. If possible, go with passivated SS 304 condition A with an anti-seize agent. If you can up the bolt size to compensate for less strength, that would help.