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Thread: Bolting an injection mold to platen

  1. #1
    Associate Engineer
    Join Date
    Jul 2011

    Bolting an injection mold to platen

    I am trying to create a torque value for bolting an injection mold to the press platens. The biggest mold we will hang weighs 42,000lbs. Using the axial load calculator with that weight, 1"-8 threads (4.5" length, 2.5" of thread, 1.5" of thread engagement minimum into press platen, grade 5 or 8 bolts), mold dimensions of 44.75" x 42" x 80".

    I calculated that we need 17000 in-lbs of torque to clamp and secure that load using the torque value calculator on this site.

    17000 in-lbs = 1416.667 ft-lbs (this would be the force needed to secure the entire mold)(I'm actually going to hang one half at a time, but wanted a very large safety factor)
    Using 8 bolts to distribute the load: 1415.667/8 = 177 ft-lbs per bolt. Using additional safety factor of 2.26, I was going to recommend that 400 ft-lbs be used to torque each bolt to safely secure the mold.

    Any insight on whether or not the way I approached the problem correctly and any additional guidance would be greatly appreciated!!

  2. #2
    Technical Fellow
    Join Date
    Feb 2011
    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.
    Insanity: "doing the same thing over and over again and expecting different results." Albert Einstein

  3. #3
    Associate Engineer
    Join Date
    Sep 2011
    it seems perfect. i like it very much.

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