Dacromet Coatings for fasteners?

[WCL]

Metal Coatings International has a zinc and aluminum flaked coating (called Dacromet) they can apply to capscrews for corrosion protection and very consistent "K" factor (torque tension relationship). I believe the automotive industry uses this coating.
I've seen some remarkable data on corrosion protection compared to zinc plating. Zinc plating has awful torque tension consistency so Dacromet would seem to be ideal for this, too.
Anyone have experience with Dacromet or products like it? What were the positives and negatives?
Thanks!

 

[unclesyd]

We tried Dacromet, Magni(?), and several other coatings on 1/4-20 Grade 5 SHCS and HHCS of various lengths in an effort to replace SS in one are of our plant.
All the coatings performed adequately and substantially better the yellow zinc. The Dacromet coating was the best taking 4 times as long to rust spots as the yellow zinc. All the others were in between.
The atmosphere was 70°F with very high humidity and the presence of numerous fatty acids and oils, yarn finishes.
We decided to stay with SS.

We used the Dacromet and Magni Coated fasteners to mount KTA panels on 4 racks scattered around the plant on building tops, five to 7 stories up. They were in good shape after 2 years when this area of testing/oversight was taken from our group. Atmosphere was heavy industrial on tidal river within 1 mile of a saltwater bay. The plant atmosphere would at times be on the acid side.

We never tried the coated fasteners on highly stressed bolts, B7, B16, and H11. The coated bolts (coating) did not survive a trip through our cleaning process.

 

[CoryPad]

The auto industry does use zinc-rich multi-layer coatings. Good suppliers include Doerken (Delta Protekt), Magni (565), and Metal Coatings (Dacromet). These coatings are much better than electroplated zinc. I recommend their use.

Positives: low friction (high preload for a given input torque, minimizing tool/human size requirements), high corrosion resistance, improved resistance to hydrogen embrittlement, value (performance vs. cost).

Negatives: until recently, only available in silver color; cost (can be higher than electroplated zinc); doesn't eliminate hydrogen embrittlement/stress corrosion cracking

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[nashjp]

Cory summed it up, but here are some other consderations. I recommend looking at Dacromet's environmentally friendly version called Geomet if you need to avoid hexavalent chrome. Geomet is usually applied thicker than Dactromet, but performance is the same.

Advantages
- 5x corrosion protection of the best electroplated zinc
- Torque coefficient range can be chosen by selecting which topcoat to use. Torque coefficient is more consistent with less standard deviation. (Torque scatter lower)
- Color stability - the silver/grey color will have minimal change/fade/bleed unlike you can expect with the chromate coatings on electrolplated zinc.
- Paintable - paint sticks, (comparable teflon coatings are not)
- Coaters available worldwide.

Disadvantages
- Cost is slightly higher than electroplated zinc
- Conductivity - If you need electical grounding through your bolt, you may need something else.
- As I said above, Dacromet has some hexavalent chrome which is banned in vehicles in EU after 2007, but Geomet appears to be an excellent substitute.

Regards,

Jeff