Molycote

Molycote is a grease with MoS2 content. Even dry MoS2 has a low friction coefficient as for instance graphite. MoS2 can also be sprayed on surface to form a dry film. Avoids corrosion in high temp. applications and allows the unscrewing after long periods. The low friction which is quite constant gives a guaranty for an uniform and repetitive pre-loading. The low friction coefficient (0.07...0.08) must be taken into consideration when the torque is specified. In tabels the usual coefficients are used and they are around 0.12...0.14 If same toeque is used an overloading is very probable and a loss of preload due to relaxation of screw loaded in the transelastic range.

Follow the link to various alternatives

http://www.neverseezproducts.com/?gclid=CMLF44zR_JECFRQViQod5ktE4w

There are restrictions based on heat range & the potential for contamination of the fluid or product being used in the heat exchanger, mostly a concern for food processing, or if the anti seize ingredients might affect adversly affect your process

You can't properly measure torque on a dry thread. They should always have "some" sort of oil or grease on them. Your engineer specified a moly grease because it likely has a lot of other great properties besides lubrication.

I work for Hydratight (www.hydratight.com) and we speciify Molykoyte 1000 for many of our bolting applications.

The reason you need to use some type of lubricant is so that you can accurately determine the amount of torque you need to place on the bolt/nut combination to achieve the correct load in the joint to seal. The way to determine the load is taken from a large mathematical formula found in ASME VIII Division 2 appendix 3. There are lots of variables other then the lubricant which affect the amount of torque you put into the joint but the lubricant does play a major role.

Without lubricant, you would be tightening metal on metal which is not as accurate for the calculations. There is a specified CoF for bare metal but I am not going to say what it is here as history has told us that bare metal tightening is very unreliable.

Lubricant also protects the joint to a certain degree and also aids the operator when coming to break out the joint.

You need to also look at the reactions in the joint. A lot of lubricant manufacturers state a CoF but this is questionable as to how it is calculated. In a bolted joint you usually apply lubricant to the thread and the spot face of the nut. With the spot face you 'simply' have two surfaces sliding against each other as the nut turns, whereas the lubricant on the threads is being subjected to a 'wedging' action. This is why if you do a web search on Molykote 1000 or other lubricants, the spec sheets sometimes give you different CoF for the thread and spot face. A lot of the time though it is taken as an average value.

Check out our Bolt Up software on our website at:

http://www.boltup.com/

It is free to sign up to and look through. With this I believe you can look at the different values that a range of differing CoF can give you.

If you need any further information regarding our products or services you would need to speak to one of our sales people. You can find links on our website.

I hope that is all of help to you.

Kind Regards

Kev Brown

What is the C of Friction then for that Molycote product? Meassured in a reliable way, i.e.Optimol SRV test, 2 hours, 50 C, according ASTM standard?

I heard that the lower the coefficiento of friction, the more you tight the bolt, and so you overstretch the material leading to brittle corrosion and breakages. We use normally a metallic paste with a SRV friction coefficient of 1.1 as standard for large equipment asembly in the cement industry.

Otto34,

The co-eficient of Friction for Molykote 1000 is 0.11 according to the literature available.

Our products and services are based around international standards such as ASME and EN ISO.

As the co-efficient of friction changes, the torque on the tool and pressure in the pump change to achieve the required bolt load. We always work to within a certain safety limit of the yield strength of the bolt/flange assembly.

I think you may be getting mixed up between torque and bolt load. There is a correlation between torque and CoF of the lubricant but the actual bolt load should never change (provided you dont change the parameters of the bolt/flange/gasket).

For example, I have just done a quick series of calculations using our software. Using a 2" flange, class 600 (PN100), spiral wound gasket, carbon steel flange, Residual bolt stress of 345N/mm^2 (50000 psi) and ASTM A193 B7 bolts I get the following for different CoF values:

1) u=0.11 (molykote 1000)

Torque = 117Nm / Bolt load = 46039N

2) u=0.13 (Molykote 7443)

Torque = 135Nm / Bolt load = 46039N

3) u=0.09 (Copperslip)

Torque = 99Nm / Bolt load = 46039N

If you were to change the residual bolt stress then the bolt load would change too.

The standards take into account the bolt material and size so you would never be able to overstretch the bolt without being warned prior to doing so by the calculation process.

Where do you get a CoF of 1.1 from? Is this just a typing error?

I hope this is of help to anyone. Any questions feel free to ask.

Kind Regards

Kev Brown

Sorry, it is a typo, it was meassured in an Optimol SRV tribometer as 0.11 accoding DIN 51834/2 / ASTM 6425 see www.optimol-instruments.de

Hi Kev

I was looking at the bolt up calc, and have a few questions

my example is a 2"150 swg flange

if I go through the program following the ANSI flange route and use 0.1u then the torque comes out as 87 NM

If I use the torque only program (which could be usefull as it gives the pressure for the hydraulic's) it comes out at 114NM

In our tables onboard it says 110NM

When I fill out the forms for tightening the flange I require to fill in the bolt stress, the ANSI flange route gives this but the torque is a lot lower.

Why is this? and is there any way to change this

Cheers

Molykote will provide thread lubrication which helps setting proper torque, but in some applications it provides vital lubrication to prevent galling of the nut and bolt - especially large fasteners in high-temperature applications.

In addition to application of Molykote (or equal) to the threads, it is important to apply it to the joining surfaces of nuts, bolts and washers, facilitating movement of all assembly faces when applying torque, and when attempting disassembly.

Most important is proper preparation and handling of all threads and mating surfaces prior to assembling threaded components. They must be thoroughly cleaned and remain absolutely clean during the assembly process. If grit or other contaminents get ino the thread joint, the assembly has every possibility to gall and lock tight - requiring drilling and machining to removed and repair the damaged threads.

Best if Luck!!!

Please, visit www.molyslip.co.uk.