My first low pressure liner

[NickD]

hiya guys

this is my very first WW2 low pressure M-1 liner these are not easy or cheap to get hold of even in this condition but thanks to a friend from another forum i finally have one

[mauser98k]

Hi Nick
That,s a nice liner, just one question how can you tell the difference between a low pressure and a high pressure liner?

Martin

[NickD]

hiya Martin

the look of the low pressure liner & the high pressure liner is the main difference but also when you handle them the low pressure liner is a lot less rigged then the high pressure one.

[mauser98k]

Hi Nick
Thanks for that, at least that's one bit of confusion out of the way.

Martin

[emileverbunt]

There must be a specific difference in production method. But what is that difference?

Cheers,
Emile

[oradour]

the look of the low pressure liner & the high pressure liner is the main difference but also when you handle them the low pressure liner is a lot less rigged then the high pressure one.

NickD, its a bit more complicated than that.....from ''US Combat helmets of the 20th Century'' by M.A.Reynosa, published by Schiffer military history.........

''M-1 PLASTIC LINER PRODUCTION, COTTON 1942-1945

Contracts for the first plastic helmet liners were made by late February 1942. The initial production of the plastic helmet liners was contracted out to four companies and they were the Inland Manufacturing Division of General Motors, Dayton, Ohio; Micarta Division of the Westinghouse Electric and Manufacturing Corporation Company, Trafford, Pennsylvania; and the St. Clair Rubber Company, Marysville, Michigan. The St. Clair Company had joined the development program late, and had also submitted their low-pressure helmets to the test trials. While their helmet liners did not perform as well as the high-pressure liners, their method of low-pressure manufacture, instead of high-pressure, allowed for a greater number of plastic helmet liners to be more rapidly produced.

By April 1942 the second and last group of companies to receive plastic helmet liner contracts were chosen and they were the Capac Manufacturing Company, Capac, Michigan; Firestone Tire & Rubber Company, Akron, Ohio; Hood Rubber Company, Inc., Watertown, Massachusetts; International Molded Plastics, Inc,., Cleveland, Ohio; and the Seaman Paper Company, Chicago, Illinois. All of these new manufacturers adopted the high-pressure style of production with the exception of the Hood Rubber Company, which adopted its own manufacturing process, known as the ball-winding low-pressure method. [This] was allowed because it offered a less expensive form of production.

The plastic helmet liner was manufactured by the following method. Cotton ducking material was first impregnated with resin and then cut into various shaped segments. These shaped segments were then arranged and stapled or cemented together to create a pre-formed helmet liner. An extra piece of impregnated duck material was added to the interior crown for strength. [It] was then placed into a mold. For the high-pressure liners the male and female molds were made of steel [;] ... high-pressure force was applied and the helmet was then allowed to cure. The result was a hard, shaped helmet body [which] had a smooth finish both inside and out if made of high pressure, and only a smooth exterior if made of low pressure. The next operation called for the removal of excess flash from around the helmet edge, this was pre-formed by a punch press. Next the edges of the helmet were sealed by burnishing. This helmet was then finished by first being pierced by a hole punch, the holes being needed for the attachment by riveting of the suspension, neck strap, insignia eyelet, and the studs for the chinstrap, and then secondly by the riveting of those items. The final process called for the helmet to be painted and baked dry. The paint was only applied to the exterior of the liner and was olive drab in color. The exception was the St. Clair liners which had interior paint. In some plants, painting was accomplished using automatic spray machines, while other plants used hand paint spray. Baking of the paint was performed by either using an oven of infra-red lamps for two minutes, or using a horizontal drying oven for fifteen minutes.

The finished liner varied in thickness but averaged about 0.082" thick, and measured about 8.6" wide by about 10.6" long. The weight of the liner with all its components assembled was 0.75 pounds. The helmet liner shell, when finished, also contained a small molded marking on the interior of the crown to indicate the manufacturing company. The interior, which was not painted, presented a brown striped design which was attributed to the impregnated duck fabric segments used in the manufacture ...

PLASTIC HELMET LINER TOTALS, 1941-1945

Ten companies produced the helmet liner shell, while an additional 30 were responsible for the manufacture of the various components that went into the liner. The total number of plastic liners produced, were at least 39,723,000 during the years between 1941-1945. Helmet liner production was discontinued around 17 August 1945 ... Mine Safety Appliances, Capac, Seaman, and International Molded Plastics each produced between 2.000.000 and 4.000,000 plastic helmet liners''
hope that helps......

[davejb]

Thats a fascinating piece of information and clears up a number of questions that ive had buzzing around in my head for years, thanks, dave

[SteveR]

Low pressure liners have a slight bit of the side edge trimmed back to accomodate the bale for the chinstrap and the will be marked in the inside upper crown in white paint. SC and the other mark I cannot remember at they moment.

[NickD]

NickD, its a bit more complicated than that.....from ''US Combat helmets of the 20th Century'' by M.A.Reynosa, published by Schiffer military history.........

''M-1 PLASTIC LINER PRODUCTION, COTTON 1942-1945

Contracts for the first plastic helmet liners were made by late February 1942. The initial production of the plastic helmet liners was contracted out to four companies and they were the Inland Manufacturing Division of General Motors, Dayton, Ohio; Micarta Division of the Westinghouse Electric and Manufacturing Corporation Company, Trafford, Pennsylvania; and the St. Clair Rubber Company, Marysville, Michigan. The St. Clair Company had joined the development program late, and had also submitted their low-pressure helmets to the test trials. While their helmet liners did not perform as well as the high-pressure liners, their method of low-pressure manufacture, instead of high-pressure, allowed for a greater number of plastic helmet liners to be more rapidly produced.

By April 1942 the second and last group of companies to receive plastic helmet liner contracts were chosen and they were the Capac Manufacturing Company, Capac, Michigan; Firestone Tire & Rubber Company, Akron, Ohio; Hood Rubber Company, Inc., Watertown, Massachusetts; International Molded Plastics, Inc,., Cleveland, Ohio; and the Seaman Paper Company, Chicago, Illinois. All of these new manufacturers adopted the high-pressure style of production with the exception of the Hood Rubber Company, which adopted its own manufacturing process, known as the ball-winding low-pressure method. [This] was allowed because it offered a less expensive form of production.

The plastic helmet liner was manufactured by the following method. Cotton ducking material was first impregnated with resin and then cut into various shaped segments. These shaped segments were then arranged and stapled or cemented together to create a pre-formed helmet liner. An extra piece of impregnated duck material was added to the interior crown for strength. [It] was then placed into a mold. For the high-pressure liners the male and female molds were made of steel [;] ... high-pressure force was applied and the helmet was then allowed to cure. The result was a hard, shaped helmet body [which] had a smooth finish both inside and out if made of high pressure, and only a smooth exterior if made of low pressure. The next operation called for the removal of excess flash from around the helmet edge, this was pre-formed by a punch press. Next the edges of the helmet were sealed by burnishing. This helmet was then finished by first being pierced by a hole punch, the holes being needed for the attachment by riveting of the suspension, neck strap, insignia eyelet, and the studs for the chinstrap, and then secondly by the riveting of those items. The final process called for the helmet to be painted and baked dry. The paint was only applied to the exterior of the liner and was olive drab in color. The exception was the St. Clair liners which had interior paint. In some plants, painting was accomplished using automatic spray machines, while other plants used hand paint spray. Baking of the paint was performed by either using an oven of infra-red lamps for two minutes, or using a horizontal drying oven for fifteen minutes.

The finished liner varied in thickness but averaged about 0.082" thick, and measured about 8.6" wide by about 10.6" long. The weight of the liner with all its components assembled was 0.75 pounds. The helmet liner shell, when finished, also contained a small molded marking on the interior of the crown to indicate the manufacturing company. The interior, which was not painted, presented a brown striped design which was attributed to the impregnated duck fabric segments used in the manufacture ...

PLASTIC HELMET LINER TOTALS, 1941-1945

Ten companies produced the helmet liner shell, while an additional 30 were responsible for the manufacture of the various components that went into the liner. The total number of plastic liners produced, were at least 39,723,000 during the years between 1941-1945. Helmet liner production was discontinued around 17 August 1945 ... Mine Safety Appliances, Capac, Seaman, and International Molded Plastics each produced between 2.000.000 and 4.000,000 plastic helmet liners''
hope that helps......

thanks for the info

i was going for the basics as i dident have all the technical info

[emileverbunt]

thanks Oradour!
Emile