Hi Noob and welcome to the forum. Not unusually, a little more information would help us.
I assume the platen faces are vertical? So the first consideration is shear load and bolt count for the 42k-lbs. Yes? No?
Is there ever likely to be much/any resistance to opening the mold? As in forcing slider blocks out for perpendicular cores? That will add tensile load to the bolts, nuts and thread engagement. That might push the thread engagement past the failure point when torqued to 400-ft/lb.
Does the 42K-lbs include coolant load? A mold that big probably has about 20 gallons of water/coolant when operational. Probably not a big deal in 42K-lbs, but stuff can add up.
Is there an anticipated stripper/ejector tensile load on the bolts at full open? Including the return spring load on the stripper/ejectors. Thread failure issue mentioned above?
Tensile load applied to the bolt by expansion as the mold comes up to working temperature may also have an affect on thread strength at torque figures. Thread failure issue mentioned above?
Lots to consider here.
At this point, I am not sure that tightening torque is all that important to require an exact ft/lb figure. I think that once you have the correct size and number bolts for the job, tightening torque should be just sufficient to prevent excessive stretch with opening-sliders and/or stripper loads all taken into consideration.
We had a recent thread on tightening torque, you may want to search back a week or two here as it is has some interesting issues covered. One of which is the failure point of the threads as a consideration factor in "guessing" a torque figure.
Generally, I will not give you the answer to your question, but I will guide you into discovering how to solve this yourself.
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