Mold Clamping Force
Compute the clamping force needed on a plastic injection machine, F = projected area · cavity pressure, to keep the mold closed against the molten plastic pressure. If the force is insufficient, the mold opens during injection and plastic leaks out at the parting lines (flash). It is the parameter that defines the machine tonnage required for a part. Enter the part's projected area (mm²) and the cavity pressure (MPa).
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Mold clamping force
During injection, molten plastic enters the mold cavity at very high pressure and pushes the two mold halves apart. The machine has to hold them shut with a clamping force greater than that pressure times the area: F = projected area · cavity pressure. The 'projected area' is the shadow of the part seen along the mold opening direction — the area over which the pressure acts. If the force falls short, the mold opens a small gap and plastic escapes through the parting line, leaving flash on the part. This very force is what gives an injection molding machine its rating: a '150 ton' press applies up to 150 tf of clamping. Oversizing the machine burns energy and money; undersizing it ruins the parts. Enter the projected area and the cavity pressure.
Related Tools
Mold Cavity Count
Compute the maximum number of mold cavities the machine can fill per cycle by dividing the machine's injection capacity by each part's mass (rounding down). More cavities increase productivity but require a larger machine and a more expensive, complex mold. It is a key calculation in production planning and mold selection. Enter the machine injection capacity and each part's mass.
Plastic Mold Shrinkage
Compute the final dimension of a plastic part after molding shrinkage, part_dim = mold_dim · (1 − shrinkage%/100). Every thermoplastic shrinks as it cools and solidifies in the mold — from ~0.5% (amorphous like ABS) to 2–3% (semicrystalline like PP and PA). That is why the mold cavity is machined larger than the final part, compensating exactly for this shrinkage. Getting it wrong ruins an expensive mold. Enter the mold dimension and the material's shrinkage rate.
Screw L/D Ratio (Injection)
Compute the L/D (length/diameter) ratio of an injection or extrusion screw by dividing the effective length by the diameter. It is a central parameter of the plasticizing design: long screws (L/D 20–24) give better melt mixing and homogenization; short ones (L/D < 18) plasticize less but are more robust. It defines melt quality and the ability to process different materials. Enter the screw length and diameter.
Mold Cavity Pressure
Estimate the pressure that actually reaches the mold cavity by multiplying the injection pressure (at the screw tip) by the pressure transmission factor, which accounts for pressure losses along the runners, nozzle and gates to the cavity. Typically only 40–60% of the machine pressure reaches the part. It is the cavity pressure that defines the clamping force and fill quality. Enter the injection pressure and the transmission factor.
Vessel Head Axial Force
Calculate the total axial force the internal pressure exerts on a pressure vessel's cover (or head), F = P · (π·D²/4), from the internal pressure P (MPa) and the internal diameter D (mm); the result is in N. A vessel's internal pressure acts on the ENTIRE internal surface, and on the cover (or closure flange) it generates an axial force tending to PUSH the cover outward — equal to pressure times the cross-sectional area. This force can be ENORMOUS: a modest 1 MPa (10 bar) pressure in a 1-metre-diameter vessel generates a force of nearly 800 kN (80 tonnes!) trying to blow off the cover. This force is what the closure-flange BOLTS (or the head weld) must resist — so flanged pressure vessels have many robust bolts, and computing this force is the starting point of sizing the flange, bolts and gasket. The force also explains why one must NEVER open a still-pressurized vessel: the cover can be hurled with lethal force (serious accidents happen this way, especially with autoclaves and filters). Knowing the cover force is essential for safe closure design and operating procedures. Enter the internal pressure and the diameter.
Plastic Injection Flow Rate
Compute the injection flow rate by dividing the injected volume by the fill time, in cm³/s. It is the speed at which the molten plastic enters the mold — a parameter that controls the shear rate, molecular orientation, surface finish and defects such as jetting or flow marks. High flow fills fast but may degrade; low flow may solidify before filling. Enter the injected volume and the fill time.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.