To start anything we need to make sure what equipment, resources we need, and the equipment we choose will define our success rate. Especially in the plastic molding industry, its the machines and processes that drive success, Hence while choosing such a plastic injection molding machine, one should take care of a few very important things.

Its as simple as that Quality machines produce quality Products, Quality Products place you at the top in the market-beating the competitive sellers. So the quality plastic molding machine will fetch more profits than the one you hardly pay attention to while purchasing.

Plastic injection molding machine.

Do you think the large scale companies will see the in-depth details when purchasing a plastic molding machine?

Yes the large companies will do deep analysis and take will not leave even minute defects while choosing the plastic molding machine

How does the Chapel Hill plant had lost money steadily ever since it was opened because of the faulty plastic molding machine?

The chapel Hill incurred most of the loss due to faulty plastic molding machine, It was using two new injection – molding machines which molded preformed soles to shoe uppers, However, the machine still had defects and resulted in substantial returns of defective shoes by customers.

There are many things to consider when considering purchasing plastic injection molding equipment but below are the must one should not miss:

  • Shot Size
  • Tie Bar Spacing
  • Ejector Stroke
  • Tonnage.
  • Platen Size

Let’s dig deep and understands how they play a vital role in defining your success in the plastic molding industry.

1. Shot size.:

The shot size is the maximum amount of plastic injection mold( (usually expressed in grams or ounces)) that can be injected in one molding cycle and is rated in ounces of general-purpose polystyrene (GPPS) for U.S. machines and cm3 for European and Asian machines.

For best quality, parts must use about 60 to 70% of machines rated shot size. Smaller shot sizes produce greater irregularities and loss of precision, whereas larger shot sizes do not allow sufficient melt cushion for packing and inefficiencies in plasticization.

The general Rule of Thumb is to use 50% of the shot capacity + 20%. Machines were originally quoted in Ounces or Grams. However, you had to understand this was in Ounces of General Purpose Styrene. So you had to go back and calculate the density to see if your material could be used in the machine.

A plastic injection molding machine of a specified shot weight can be used to mold articles including the runner weighing from 35% to 85 % of the shot weight. The lower limits come from bending on the platens, barrel resident time of the resign, and electric power consumption per kg of the processed material. •

BRT=wt of melt in barrel*ct/actual shot wt.


2.Tie Bar Spacing:

Tie Bar Spacing is defined as the space between the horizontal tie-bars on an injection molding machine. This measurement, along with the platen max spacing, determines the maximum size of molds that can be placed in the molding machine. This measurement limits the size of molds that can be placed between the tie-bars and into the molding machine.

plastic injection modling tie bar spacing


3.Ejector Stroke:

Ejector stroke is defined as the action of the machine pushing out (ejecting) the final workpiece from the platens using ejector pins.

To prevent the plastic product from deformation during ejection, the ejection force has to be distributed as evenly as possible, and as close as possible to the core wrapped by the shrinking plastic or to the part that is difficult to eject, e.g., the elongated pillar of a plastic product is ejected with an ejector sleeve.


The “tonnage” is an important factor while choosing the plastic injection molding in the machine, and it is defined as the measure of force that is required to keep the tool closed during the injection process. This force is the main factor in determining the injection molding machine size required for producing the other words it is about the clamping force of the machine. The amount of pressure the machine can exert on the mold, to keep it closed, while mold (tool) is being filled with molten plastic under enormous pressure.

5.Platen Size:

The platen is the “table” or tool that holds the mold cavity. Spaced apart, the mold is then inserted and clamped securely to the platens. Once the two platens come together, two plates will be kept closed and are held under the pressure of tonnage, the plastic will be heated, injected under pressure, and then allowed to cool through a molding cooling cycle, molding cooling cycle is key not when defining the strength of the finished product. Here, the plastic takes on its hardened, final shape while continuing to be kept in place with many tons of pressure to retain the desired shape.

Hope you got some idea on what are the key factors need to be considered in the checklist when purchasing the plastic injection molding machine


Leave a Reply

Your email address will not be published. Required fields are marked *


Enjoy this blog? Please spread the word :)