How Magnetic Tape is Made
February1955 Popular Electronics
Magnetic tape was the
recording medium de rigueur for more than half a century, after the era of wax and wire and before the era of
magnetic and optical disks. In fact, magnetic tape is still the storage medium of choice when analog signals must
be stored without first being digitized.
February 1955 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Magnetic data storage media each has its own characteristic
lifetime because of factors like the initial quality of the magnetic domains, the dimensional stability of the
substrate, and susceptibility to outside influences. Although opinions vary, here are some typical lifetimes of
the different storage media:
* Floppy disk: 3-5 years
* Flash media: 1-10 years
* Hard drive: 2-8
* CD/DVD/Blu-ray optical disk: 2-10 years
* Magnetic tape: 10-30 years
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How Magnetic Tape is Made
public's enthusiastic and ready acceptance of tape recording has rather overshadowed the "miraculous" quality of
this new medium. We all, more or less, take our tape machines and recording tape for granted.
A lot of
time, money, research, and engineering ingenuity goes into each reel of tape you so casually purchase over the
counter. As an example of the painstaking care lavished on this product, the manufacturing operation of OR Radio
Industries Inc. is pictured on these pages. This firm, which makes the "Irish" brand magnetic tape line, is
primarily a tape maker so its operation will be described.
Research and development play an important part
in the operations of most electronic firms and the tape industry is no exception. Continuing efforts are made to
improve the product and one such operation is the experimental formulation for dispersion in a laboratory scale
When the laboratory has OKed a new formula or procedure, the technique is incorporated in
the manufacturing process. Mass production of the magnetic coating lacquer is accomplished by huge grinding mills
which are capable of delivering 500 gallons of coating. A slow and continuous grinding results in a uniform
dispersion of the iron oxide particles in the lacquer type base. Special wetting agents and highly effective
lubricants are incorporated during the grinding process.
The precision coating of the magnetic lacquer on the plastic film is the most delicate operation in the
manufacture of magnetic tape. The coating machinery required for this operation is manufactured to watchmaker
tolerances. The company's tape is coated to a tolerance of a half of 1/10,000 of an inch since a variation of less
than 1/10,000 of an inch in thickness may vary the amplitude of the audio output as much as one decibel.
Huge batches of the magnetic coating lacquer are mixed in 500 gallon mills like this one.
A laboratory technician prepares an experimental formulation in a laboratory grinding mill.
The next step in the operation is the production of 1/4" tapes from coated rolls. This is done by the slitter
operator who cuts the 12" coated rolls into 1/4" tapes and winds it on 1200 foot reels, the standard 7" reel of
After the tape is wound on the reels, it is subjected to a thorough audio analysis. Professional recording and
test equipment is used for this operation. The tape is tested for frequency response, amplitude variation, signal
output, and noise level.
The final step in the manufacturing process before shipment to distributors is
the careful visual inspection of the tape. This inspection is made under fluorescent lighting with the operator
checking for inconsistencies in the winding and slitting of the tape and for fractures and molding imperfections
in the reel.
The next time you casually pop a reel of tape on your recorder, stop just a second and
consider the "little miracle" you hold in your hand.
The tape coating operation is extremely critical.
It is performed on precision machines.
Producing 1/4" tapes from the large coated rolls is a responsibility of slitter operator.
A thorough audio analysis is made on each production run of the tape made by factory.
The final visual inspection of the tape is made by
skilled operators who use fluorescent lighting boxes.