Sometimes when I look at something, I ask myself “How did they do that?” When I looked at a pair of safety glasses, it was no different. So, I set out to get an overview of how they are made. This I did and now I am going to share that overview with you.
The primary material used to make a pair of safety glasses is a polycarbonate plastic resin. This material has properties that are ideal for the manufacture of safety glasses. Polycarbonate plastic resin is used as a shatter resistant substitute for glass, has a high-impact strength, is flexible and lightweight.
The material is delivered to the manufacturer as clear plastic granules. These granules are loaded into the appropriate part of the molding machine before being heated to a temperature of around four hundred and eighty degrees Fahrenheit or about two hundred and fifty degrees Celsius in order to liquefy the polycarbonate plastic resin.
Once heated to the correct temperature the liquefied resin is now ready for use. The material is then pressure injected into the part of the molding machine containing the molds, over a period of up to a minute. The molds for the machine are made of steel, having been carefully designed and manufactured for this very purpose.
The area that will be the mold for the lenses is mirrored in order to give the plastic lenses the required transparency.
As this is part of a mass production cycle, more than one pair of safety glasses is molded at the same time. After injection into the mold, the polycarbonate plastic quickly hardens and is then mechanically removed from the mold.
Once they are removed from the mold, they are delivered for a quick visual inspection. The inspector looks for any imperfections in the resultant molding from flaws to scratches in the molded parts. Those safety glasses that pass this inspection are moved along to the next process.
Those safety glasses passing the initial inspection are then placed onto a rack before being washed to remove dust, dirt and deposits from them. Once washed they are rinsed in clear water.
The safety glasses are now submerged in a chemical solution that helps prevent misting and scratching of the lens.
The final part of this process sees the safety glasses being cooked at about two hundred and forty-eight degrees Fahrenheit or one hundred and ten degrees Celsius.
The soaking and cooking processes can take up to two hours per batch of safety glasses.
Putting It All Together.
After the safety glasses are cooked, they are once again inspected for imperfections or distortions to the lenses. Those that make it past the last inspection are mounted onto a support that passes the safety glasses to a milling machine that automatically removes the last piece of polycarbonate, the still attached sprue.
The glasses have up to this point always been handled, whether manually of mechanically, by the sprue. Essentially, the sprue is a piece of waste material formed in the injection channel as the safety glasses cooled and sticks out from the glasses themselves.
With the sprue removed. Final assembly of the pair of safety glasses can begin. It is at this point the nose piece is added to the glasses before being moved along for further assembly.
We now arrive at the final phase of assembly where the ear stems or arms are added to the glasses before being packaged for sale.
During all of this manufacturing and assembly, random parts are removed from the line and tested for impact strength. This ensures the batch of safety glasses meets or exceeds safety requirements.
Once I learned the overview of how polycarbonate resin is transformed from granules to safety glasses, I cannot help but have a better appreciation for them. Everytime I see a pair of these glasses now I have to give a little smile to myself.
One way in which safety glasses are tested is by having a racket ball launched at them at eighty-seven miles per hour or one hundred and forty kilometers per hour. Only a batch that survives this and other tests will make it through the entire process.
The knowledge that my safety glasses came from a batch that survived severe impact testing together with other tests gives me a secure feeling about my eyes and vision being as safe as they can be in the world around me. Hopefully this overview has helped do the same for you.
Aim for zero accidents and be safe!