# Math Makes you a Better Molder

Many processors are guilty of “winging” it. Well don’t be one of them.

Math may not be your strong suit, but that’s ok because we’ve put together some of the core math equations you need to properly setup, process, and troubleshoot your injection molding machines.

Walk through the examples below and take note, it may save you a lot of money and downtime some day. Math for molders saves time and money.

## Examples of Math for Molders

**1. What is the area of a square part that is 4 inches by 5 inches?**

4″x5″ = 20 square inches

**2. What is the area of a 1.5 inch diameter screw?**

(Formula Diameter x Diameter x .7854= circular area)

1.5 x 1.5 x .7854 = 1.77 square inches

**3. This same 1.5 inch screw mnning a 2.5″ shot size on a machine is producing how many Cubic Inches of shot size?**

1.77 square inches x 2.5 inches = 4.43 Cubic Inches

**4. Later you move the same tool above (4.43 Cubic Inch shot) to a machine with a 2″ diameter screw. What would the shot sized be to maintain the 4.43 cubic inches?**

2″ x 2″ x .7854 = 3.14 square inches (screw area)

4.43 cubic inches / 3.14 square inches = 1.41 inches would be the equivalent shot size on the new machine.

**5. The diameter of the injection cylinder is 7 inches, the diameter of the screw is 2 inches, what is the Intensification Ratio?**

Ri=Ac/As where Ri: Intensification Ratio, Ac: Area of Cylinder, As: Area of Screw

7 x 7 x .7854 = 38.48 (Area of Cylinder)

2 x 2 x .7854 = 3.14 (Area of Screw)

38.14/3.14= 12.15:1 (Intensification Ratio)

Once you know the intensification ratio of a Hydraulic Machine, you can multiply it by any hydraulic pressure to calculate the plastic pressure (ppsi).

**6. If the peak pressure at transfer is 18,060ppsi and we had a twenty percent rise in viscosity^ what would potentially our new peak pressure at transfer be?**

18,000 xl.20= 21,600 ppsi

**7. Our new mold is two cavity hot runner, the part is round (8 in diameter) with a .750 hole in the center. At three tons per square inch, how many tons are needed to support this mold minimally and we will be using a 400 ton machine?**

8 x 8 x .7854 = 50.27 square inches minus .75 x .75 x .7854 (hole) = .44 square inches which equals 50.27-.44 = 49.83 sq inches x 2 cavities = a total area of 99.66 sq inches, x 3 tons per sq inch = 298.98 tons or 299 Tons

**8. The tool maker was asked to open the round gate from 0.025 in to 0.035 in. What was the effect on the area of the gate?**

% of difference is the ((AREA of .025 – the AREA of .035)/AREA of .025) x 100 = OR

0.00049 – 0.000962/0.00049 = OR

0.000472/0.00049= 0.9632653 x 100 = 96.32653% difference

**9. You are running a machine with a 1.25″ shot and the machines maximum injection stroke is 7.87″. What percentage of the shot are you using?**

1.25″/7.87″ = .158831 x 100 = 15.8831% or 16% of the shot

**10. You are running a 2.5″ shot at an injection speed of 3″/sec. How fast is it actually injecting if you f time is .93 seconds?**

2.5″ / .93 = 2.68″/sec

### Want to Know More?

Here is some more information on the Master Molder course from RJG.

## Return to the Support Center

If you are looking for some help with either getting equipment or setting it up, we have some articles that can help you.

Check out More Support ArticlesFeatured ArticlesSupport Process Cooling Smartflow

## Video: Tracer VM Flowmeter from Smartflow

The Tracer®VM Base Flowmeter is a non-display sensor that provides a 0.5 to 3.5 Volt [...]

Support Injection Molding TOYO

## Video: Why Top Medical Molders are Choosing TOYO Injection Molding Machines

Medical Molding around the country is choosing TOYO. Meet Brad, our Technical Support Manager, as [...]

Support Injection Molding Slide

## Slide Products Mold Metal Wipes

As a larger manufacturing company, if you are shutting down production for a temporary period [...]

Support Advantage Literature

## Sentra Series Water Temperature Control Units

Sentra Temperature Control Units with their advanced design & technology continue to prove why they [...]

Support Material Handling Rapid Recycling

## Video: Opening and cleaning of the Rapid RAPTOR DUO Shredder

Opening and cleaning of the Rapid RAPTOR DUO shredder. Rapid Raptor DUO, the combination of [...]

Support RJG Training

## Master Molder I – Make more parts and Money

2 weeks, 10 days, 64 hours of class, 17 hours of study, and 10 hours [...]

Support FCS Injection Molding

## Required Info for quoting a Hybrid Injection Molding Machine

The goal is to make sure that your mold will fit, the screw will work [...]

Support Automation Yushin

## Required Info for quoting an End of Arm Tooling

The goal is to make sure the robot fits your molding machine, then to make [...]