How
to Calculate Molding Machine Sizes
Producing quality
plastic products requires a molding machine that has been properly sized.
Molding machines come in a wide variety of
clamp tonnages. The clamp tonnage refers to the amount of force that the
machine can exert on a mold while the molten plastic is being injected. The
plastic is injected into the mold at high pressure in order to ensure that the
mold is completely filled before the plastic hardens. The pressure of the
injection when coupled with the surface area of the mold creates a force that
must be counteracted by the molding machine. The molding machine must be sized
to handle this force to produce acceptable products.
Instructions
1.
Sizing a Molding Machine
1
Determine the surface area of
the part that is being molded in square inches. If it is a multiple cavity
mold, the surface area associated with each cavity along with the runners that
feed each cavity should be included in the total surface area.
2
Determine the planned injection
pressure in pounds per square inch (psi). The injection pressure will be a
function of the material that you are using and the part wall thickness. A
material supplier can help determine the injection pressure.
3
Determine the pressintensification ratio for the molding machine. This is a function of the
machine's screw and the hydraulic piston that acts upon it. The machine
supplier can provide this information if it is not already known.
4
Multiply the injection pressure
by the intensification ratio. This provides the plastic packing pressure in
psi.
5
Multiply the plastic packing
pressure by the part surface area. This results in the total pounds of force
that will be exerted on the mold in pounds.
6
Divide the pounds of force by
2,000 (2,000 pounds = 1 ton). This provides the tons of force required to be
offset by the molding machine's clamp tonnage. This gives the minimum clamp
tonnage size needed for a molding machine for the specific product in question.
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