Acceptable Liners I – Liner Quality Testing

 Big Red here with a question for all you M-1 helmet lovers.

So, TAKE FIVE!

What made liners acceptable and what made them rejectable?

If you read through our review of the Quartermaster Corps' development of a new type plastic liner for the M-1 steel helmet, you encountered statements like “resulted in an acceptable liner” or “an acceptable liner must…” or similar. What made a liner acceptable or unacceptable? How were liners measured, and who did the measuring? These are all excellent questions that deserve top-notch responses, but unfortunately, the straight-up answers are rather technical, dry, and boring, so…

I have asked my good friend Staff Sgt. Quincannon to arrange some demonstrations outlining the tests developed to determine the suitability of liners for use by the Army. To spice things up a bit, the staff sergeant has personally volunteered our good friend Private Murphy, as he always manages to bring a certain flair to our presentations. 

The first big contract for M-1 helmet liners was issued on July 9, 1941, to McCord Radiator & Manufacturing Company, who in turn issued a purchase order to the Hawley Products Company for the first 950,000 fibre liner bodies. Before the ink was dry on these orders, the Standardization Branch of the Office of The Quartermaster General began research into the development of a plastic alternative.

In brief summary, the QMC provided a list of desirable qualities in a plastic liner but basically allowed the industrial firms they had picked as likely producers to use their expertise to define what a liner needed to be and how best to manufacture it. While these companies were in the process of making sample liners, the Standardization Branch met with members of the Bureau of Standards and together worked out testing procedures they felt would accurately discern the durability of a plastic liner. These tests were centered around the thermosetting of the impregnated cloth formed in molds under high heat and pressure, which results in a chemical change or curing of the plastic. If the cure was incomplete, the liner’s resistance to the conditions of these tests would prove to be low.

Although testing was devised for every aspect of the liner, from the shell to the suspension, including its inserts, we are only going to cover the seven main tests, which were Moisture Absorption, Ball Test, Delousing Treatment, Flammability, Flexibility, Weather Resistance, and Ballistics Impact Resistance.

The first two tests that we will cover are the Moisture Absorption Test and the Ball Test.

So, let’s get into it… 

Although the moisture absorption test uses weight gain as a tool to measure acceptability, it wasn’t concerned so much with the actual weight gain but rather the ability for moisture, represented by the additional weight, to penetrate the plastic shell.

An overcured shell would be highly resistant to water, but if water could get inside the structure of the lamination in high quantity, the resin was undercured and the liner body would deform, peel apart, or delaminate. Basically, this test verified that the plastic resin had a complete cure.

If you read through our discussion on “Are Plastic Liners Really Made from Plastic?” you will recall that duck cloth was impregnated with plastic resin to help keep the shape of the liner and add strength under tension. If a liner was overcured, it became brittle and would crack or splinter under impact, while a liner that was undercured or merely cemented together would delaminate under a 15 ft.-pound impact. In short, the ball test basically verified the cure was complete and that the liner’s construction would hold up as a good safety hat.

Hood Rubber liners developed a partial crack in the crown during the ball test. Even though no amount of hammering could force the crack all the way through the shell, the QMC considered this defect a failure to meet specifications and cited it as a primary consideration for not awarding additional contracts. 

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Well, I hope you’ve enjoyed today's demonstration. I know our participants have.

If your friends want to know how you gained your intel, tell em

Big Red Says!

FIVE'S OVER  -  MOVE OUT!

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