Thread: commercial razor blades

The question has come up several times about why straights don't keep their edge the way cheap cartridge razors do. Because cartridge and DE blades will never be sharpened again they receive extensive post-sharpening treatment that substantially increases their short-term durability at the expense of reusability.

Schick history article
(if this link takes you to the schick top page, select your country, then "shaving history", then "Making of the Modern Blade: miles of steel behind the modern razor")

Excerpt:

A soft, stainless steel strip, containing at least 12% chromium, goes through a series of steps before being made into razor blades. Large coils, weighing up to 110 pounds (50 kg) each and containing over two miles (3.2 km) of this steel, are used at the start of the process and must meet strict tolerances for metallurgical composition, width and thickness. Most of the razor blades first travel through a press to precisely perforate the blade with a series of notches and holes. These are used for locating the position of the blade in subsequent operations and for placement in the cartridge during the final assembly process. After the strip is notched and perforated, it proceeds to the next step in the process.

PERFECT TEMPERATURES CREATE THE PERFECT BLADE
The blade strip, as it arrives from the steel manufacturer, is too soft to grind into a shaving edge and must first be hardened. Furnaces with temperatures of more than 2,000°F (1,110°C) heat the blade strip in a controlled atmosphere to prevent oxidation. Both the time and temperature under which the strip is heated are critical to the final product. If the time is too short or the temperature is too low, a soft strip will be produced. If the time is too lengthy or the temperatures too high, the strip will be undesirable for grinding. The strip is then subjected to temperatures below –100°F (–70°C) in a deep-freeze chamber to complete the hardening process. It is then heated again to only a few hundred degrees in order to temper it. Tempering gives some ductility or flexibility back to the hard but brittle strip of steel. A great deal of control is required at each step of heat treatment. And, if any one of the steps is compromised, the resultant steel will not be suitable for a high-quality blade edge. Only highly skilled manufacturers are capable of producing hardened steel that meets the physical characteristics needed for grinding a superior razor blade edge.

Next, the hardened and tempered coil of steel is sent to the grinding area to have a sharp edge formed on the strip. Unlike the commonly held belief that a razor blade is simply a sharpened piece of steel, the blade edge is actually composed of three distinct facets, each working together to form a strong edge that is both sharp and durable. The blade strip is fed through a series of progressively finer grinding wheels. Coarse grinding wheels remove material to approximate the desired profile. Finer grit wheels shape the edge more precisely, and extremely fine grit wheels finish forming the blade tip profile. High-speed leather-like strops provide the shape and smoothness to the ultimate tip of the blade.

The thickness of the blade profile must be tightly controlled. If a blade is too blunt, it will give an uncomfortable shave. If it is too sharp, the edge will break down more quickly. The grinding equipment used to form the edge is developed by highly skilled, in-house designers and engineers. This is necessary to protect the proprietary nature of the equipment. High precision is required in equipment design to obtain the proper edge profile and to ensure the consistency of the millions of blades processed each day. After grinding, the strip is cut into individual blades and stacked on long pins, called bayonets, so they can be finished and assembled into shaving products


COATED BLADES FOR A SAFER SHAVE

Although a properly formed blade is quite sturdy, additional durability is generally obtained by depositing a layer of hard metal directly onto the edge in a sputtering process. After all impurities are removed from the blade edges, bayonets of blades are placed inside high-vacuum chambers in which an inert ionized gas is present. High-energy ions bombard a chromium target and eject chromium atoms, depositing them on the razor blade edges.

In spite of the finely shaped blade apex, if an uncoated stainless steel blade is used to cut the hair, the friction between the cut surfaces of the hair and the steel would cause pulling and discomfort. In order to reduce this friction, the blade edges are sprayed with a coating of Vydax, a low molecular weight polymer of polytetrafluoroethylene (PTFE) with low-friction qualities similar to Teflon. The film is then melted on the blade edges and cured at temperatures over 500°F (276°C). After the first few strokes with a Vydax coated blade, the excess Vydax is peeled back from the apex of the blade and a thin layer is left on the surface to reduce friction and improve comfort. All Shaving Products Group razor blades meet high specifications for quality. Some systems may have slightly different coating characteristics or steel composition, but all are designed to enhance the shaving performance of the systems.

For a number of reasons, the two coatings are the probably the key difference between straights and disposable blades. The pure chromium coating is very hard and prevents the fin from deforming. It also resists corrosion which must be removed from the straight every shave with the strop. Also, the polymer coating helps keep the blade feeling sharp even after the fin degrades, because part of the pulling feeling is due to friction. The disposable blades tend to have a primary bevel at a shallow angle, then a smaller cutting bevel at a steeper angle where the fine polishing is done. This reduces cost because the slower fine-grit wheels have less work to do and endure less wear and tear, and it also strengthens the blade because the more obtuse bevel angle is stronger. The penalty for a steeper cutting bevel is increased cutting friction, which is countered by the friction-reducing properties of the polymer coating.

Interesting article/observations. Thanks for sharing MP.

So why can I get more shaves out of a straight before honing compared to a disposable before throwing away?

(not to taunt simple an observation and an honest question.)

Originally Posted by LX_Emergency

So why can I get more shaves out of a straight before honing compared to a disposable before throwing away?

(not to taunt simple an observation and an honest question.)

Stropping and edge density are two reasons I can think of.

X

Probably stropping. If you're sufficiently interested there are DE blade stroppers on ebay, these were very popular in the 20's - 40's.