Setting Correct Clamp Tonnage in Injection Molding

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Injection Molders need to check their clamp tonnage.

How much tonnage are you using?  How did you get there?  Are you setting clamp tonnage based on the mold or the machine?  Just because you are running in a 500-ton press doesn’t mean you should be clamping to 500 tons. 

To properly calculate necessary clamp tonnage, you must first know the projected area of the molded part/s plus any runners.  Area can be calculated by multiplying length times width,   A = L x W  or A=πr2.

 After calculating the projected area in square inches, you will need to know the material used to produce the molded part.  High flow materials like Polystyrene (PS), Polyethylene (PE) and Polypropylene (PP) require less tonnage to hold the mold closed than stiffer materials like filled Nylon (PA) and Polysulphone (PSU). 

Your material supplier can provide you with the required tonnage needed per square inch to mold their product.  For the higher flow materials like PS, PE and PP that generally falls into the 2-3 tons per square inch range.  The lower flow materials like PA, PC and PSU fall into the 3-5 square inch range.

Now you can calculate necessary tonnage based on the projected area times the clamp factor for the material used.  T = A x cf.  For example, the projected area of the molded part is 150 sq/in times a clamp factor of 3 (tonnage needed/square inch from material data sheet).  150 x 3 = 450 tons needed.

If you are running in a 500-ton press, try starting at 450 tons.  The lower tonnage will be easier on the whole mold, especially the parting line and vents.  The vents will last longer between PM’s, and you may just save a little money.   

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Topics: Troubleshooting, Injection Molding, Hot Runners, color contamination, carbon contamination, shutdowns, shutdown and sealing, preventative purging, value added, Preventative Maintenance, high cavitation injection molding

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