We have recently completed a unique injection molding project we would like to share with you.

A few months ago we were contacted by an award winning research scientist from the University of Illinois.  Our customer was developing a system for soil testing.  The soil sample needed to be incubated in a reusable plastic container resistant to mild acids and bases. It needed a lid that was easy to remove and provided an air-tight seal on the jar.

The customer brought in an initial prototype container that was not meeting his design criteria.  The container was a machined part that had a screw-on top.  This design was very expensive to make and the customer’s volume dictated that we redesign the container for injection molding.

Original Soil Container

Original design from machined material. Very expensive and time consuming to produce.

Our engineering department looked at the original design and determined that mold cost for the screw threads would not allow the project to continue to move forward.

The design challenge included the following four points:

  1. Design a lid that would replace the screw-on lid that will have a positive seal and maintain that seal up to 5 PSI pressure inside the container.
  2. Design the lid to be easily removable.
  3. Select a material that will be chemically resistant to the mild acid solution that the scientist uses.
  4. Design an internal structure that holds the test samples in the proper fashion.

New injection molded design

The design solutions were as follows:

  1. ShapeMaster engineering department decided that a glass filed polypropylene would give us the rigidity and chemical resistance that was needed.  Once the material was selected, the design team went to work on the lid design.
  2. The lid design had to be strong enough to handle the internal pressures but also be easy to mold.  The first design attempt was a simple 4 lug design in which the lid locked in place by engaging 4 pins on the container.  This design was very easy to mold but failed the pressure testing by the customer.  The lid seal was leaking where we did not have a locking lug on the container lid.  The ShapeMaster engineering team decided to design a multilug ¼ turn lock system that applied even pressure on the container.  With the right application of correct durometer (hardness) of an “O”-ring seal, we were able to meet the requirements.

Lid and base

Prototypes were then 3-D printed and actual physical testing was performed by the customer.

Test container using ABS plastic. Nice color, but not suitable for scientific research.

The next step was to design the tooling, have it built and run parts.

Watch for our next newsletter for information about the new and revolutionary soil testing device.