Types and types of magnetic tapes.
Tape, magnetic tape, ferromagnetic tape, is a magnetic recording medium used in tape recorders and. Belongs to the group.
Tape
Magnetic tapes were divided into single-layer - solid, in which particles of magnetic material are distributed in a film-forming material over the entire thickness of the tape, and two-layer, non-magnetic base - cellulose ester or plastic film, paper, etc. - and a ferrolayer of magnetic powder applied to it, sprayed in film-forming material.
In 1958, the industry produced two-layer tapes according to GOST 8303-57: type I, type IB and type II, intended for household and special (professional) tape recorders.
Type I tape was intended for use in professional-type magnetic sound recording devices (in radio broadcasting, cinematography, etc.) at a pulling speed of 76.2 cm/sec. The tape consists of a non-flammable cellulose acetate base and a ferromagnetic layer applied to one of its sides. Tape dimensions: width 6.35 mm, total thickness 50-60 µ, magnetic layer thickness 10-20 µ. Type I tape was produced wound on cores (bosses), the length per roll was 1000+50 m. Each roll was packed in a cardboard box that had a special holder for the core.
Type IB tape was intended for use in household magnetic sound recording devices (tape recorders and tape recorders) at speeds of 76.2 and 38.1 cm/sec. In all respects, except for electroacoustic ones, type IB fully corresponded to tape type I. The total thickness of type IB tape is 50-60 µ. It was produced in rolls of 1000±50 m, wound on a core, or on cassettes of 100, 180, 350 and 500+20 m.
Type II tape intended for use in professional and household sound recording devices (MEZ-15, Dnepr, Yauza tape recorders, MP-2 set-top boxes, etc.) at a transfer speed of 38.1; 19.05 and 9.5 cm/sec. The tape had a cellulose acetate base and a ferrocobalt magnetic layer (a mixture of ferrite and cobalt). The thickness of the tape base is 40–45 µ, the thickness of the magnetic layer is 15–20 µ. To improve the frequency response, Type II tape was ground on the magnetic layer side. This layer had a shiny surface, in contrast to the matte magnetic layer of Type I and Type IB tapes. Compared to Type I and Type IB tape, Type II tape was more sensitive; the magnitude of its return is approximately twice as high. Type II tape was produced in rolls of 1000 m on cores and on standard cassettes corresponding to GOST 7704-55.
Schematic section of a two-layer tape
Replacing a type II tape at low pulling speeds with a type 1 tape narrowed the frequency range and greatly reduced the playback volume, for example, at a tape pulling speed of 19.05 cm/sec, such a replacement led to a narrowing of the frequency range to 6000-7000 Hz and a decrease in volume by almost half (with the same nonlinear distortions), replacing type II tape with type IB, the frequency range narrowed to 4000-4500 Hz.
The use of Type II tape at higher speeds, for example, 76.2 cm/sec, is impractical, since this increases the noise level and worsens the erasure of old recordings.
Characteristics of tapes
Type I and type IB tapes were produced in rolls of 1000+50 m on standard 100 mm metal cores and on cassettes.
Standard tape core
Type II tapes were produced in rolls of 1000+50 m and 500+20 m on cores, as well as on standard cassettes.
The cassettes were made of polystyrene, duralumin, or a combination (plastic sleeve, duralumin cheeks). The cassette was supposed to secure the inner end of the tape roll. The nominal capacity of cassettes and the approximate duration of their playback at a tape speed of 19.05 cm/sec are shown in the table below.
Characteristics of tape cassettes (according to GOST 7704-55)
If broken, the tape could be glued together. To do this, the ends of the torn tape were cut off, a drop of glue was applied to one of them from the side of the magnetic layer, after which the ends were overlapped with an overlap equal to the width of the tape (0.5-1.0 cm). When gluing, the ends of the torn tape should not have lateral displacement or skew. The manufacturers recommended the following glue recipe for gluing tape: acetic acid 23.5 cm³, acetone 63.5 cm³, butyl acetate 13.0 cm³. The tape could also be glued with acetone, vinegar essence or universal glue BF-2.
The marking is applied on the smooth (back) side of the manitophone tape (from the base side) along its entire length and included: the name or trademark of the manufacturer, type of tape, year of manufacture and irrigation number.
Standard tape cassette
Signs of defective and poor quality of a tape were cracked or broken cassettes and bushings, bent metal cassettes and cores, breaks in the tape. The end of the tape, after winding it onto the cassette, was glued and sealed with a factory mark; The watering number was indicated next to it. Each roll of tape or cassette, along with instructions for use, was placed in a cardboard folder; the folder was placed in a cardboard box on which the relevant data was indicated.
Tapes should be stored in boxes, in dry, ventilated areas at a temperature of 10-20°C and relative humidity air 50-60%, protecting from overheating, dampness and exposure sun rays. Recording tapes should be stored away from large iron masses or strong electromagnetic fields (electromagnets, electric motors, transformers, etc.). When storing records, boxes with tapes were numbered, on the back of them were indicated the names of the recorded works, performers, recording dates, etc. If necessary, information about the recordings in the music library could be compiled into a general catalogue.
Is it true that magnetic tape with a working layer of chromium dioxide wears out magnetic heads with a permalloy core faster?
Indeed, the chrome dioxide working layer has a higher hardness than gamma iron oxide and has an increased abrasive effect on the head. On the one hand, its greater hardness makes it possible to achieve ideal polishing with higher smoothness than that of gamma iron oxide. In addition, it is necessary to take the so-called running-in period, during which the abrasiveness of the belt is most pronounced, after which the abrasiveness decreases sharply (the working surface of the belt is, as it were, polished) and further wear of the head core occurs very slowly.
Tests of various tapes have shown that if for tapes with a working layer of gamma-iron oxide, the running-in period lasts 5-7 passes of a 525 m long tape, then for chrome dioxide tape it usually stops after the second pass. Therefore, a magnetic tape with a working layer of chromium dioxide, which has a high degree of initial polishing, wears out the head core at a speed of 4.76 cm/s no less than a tape with a working layer of gamma iron oxide.
To reduce the abrasiveness of the tape, you can artificially break it in. To do this, you need to take a strip of steel grade 20 - 40 with a width of 3.5 mm, anneal it well, bend it to the body of the universal head, stick a piece of yarn inside and, putting the strip on the head, pass several passes of the tape in both directions. After this, the abrasiveness of the tape is noticeably reduced.
Can a tape with a working layer of chromium dioxide be used in tape recorders designed to work with a tape whose working layer is made of gamma iron oxide?
Chrome dioxide tape requires higher bias and erase currents, as well as an increased recording current and modified frequency response correction in the high-frequency part of the operating range compared to a tape with a working layer of gamma iron oxide. In order for the tape recorder to work with tapes whose working layers are made of different magnetic powders, a switch is introduced into the circuit that changes the recording, bias and erase currents when moving from one tape to another, and also changes the frequency response correction. In some simple tape recorders, such a switch only changes the bias and erase current, which does not allow using all the positive properties of chrome dioxide tape. In tape recorders that do not have such a switch, it is not advisable to use chrome dioxide tape.
Are there any other higher quality magnetic tapes available?
The trend towards improving the quality indicators of cassette tape recorders required the creation of tapes capable of providing high parameters of the devices at low speeds. One of the first such tapes was a tape with a working layer of gamma iron oxide powder of a finer-grained structure, which had an improved polishing of the working surface. 3a due to the better fit of the tape to the head and the finer structure of the working layer powder, the dynamic range of the phonogram on such a tape is 2 - 4 dB better than on a regular one. Higher sound frequencies are recorded and reproduced better on it, which further improves the quality of the phonogram. (Foreign cassettes with such a tape were equipped with the inscription “Low noise” - small). Let us also add that its use is advisable only in cassette tape recorders at low speeds, and the hardness of the surface of the working layer makes it possible to achieve almost perfect polishing and, therefore, a better fit to the head and greater output at high frequencies.
Relatively recently, a tape with a working layer of gamma-iron oxide with a cobalt additive, which is called cobaltized, has become widespread. The main advantage of such a tape is a higher level of recording. When using it, it becomes possible to increase the magnetization of the tape from 250 to 320 nWb/m reel-to-reel tape recorders and from 160 to 250 nWb/m - in cassette ones. Such tapes also include domestic tapes of types A4309-6B, A4409-6B and A4205-ZB.
One of the varieties of tapes with a working layer of gamma iron oxide is a tape that can provide an increased dynamic range of the phonogram and a slightly higher level of high-frequency recording. Improvement in the parameters of the tape was achieved by reducing the size of the ferroparticles of the working layer (0.4 microns instead of 1 microns in a conventional tape), high density and their uniform distribution in the working layer. Abroad, such a tape was called “Super Dynamic” (SD).
The latest innovation is the so-called “metal” tape, the working layer of one of the variants of which is made on the basis of powdered pure iron. “Metal” tape has a higher coercive force than chrome dioxide and requires even higher bias and erase currents. So, for example, for such a tape, the bias should be approximately 6 dB more than for chrome dioxide, and 9 dB more than for a tape with a working layer of gamma iron oxide. For a “metal” tape at a speed of 4.76 cm/s, the magnetization level at a frequency of 12 kHz is almost 12 dB higher than for a conventional tape. The domestic industry does not yet produce such a tape.
Does the speed of magnetic tape affect the quality of recording (playback)?
Affects. To explain this, we must remember that the records TO is directly proportional to the forward speed V of the tape recording medium and inversely proportional to the recording frequency f (see p. 4). It should also be recalled that e. d.s. playback head depends on the length of the recorded oscillations and decreases as the recording wavelength approaches the effective width of the working gap of the head, and when the recording wavelength becomes equal to the width of the working gap - e. d.s. playhead will be zero. This is called "gap loss" and is described by the so-called "gap function".
It has been practically established that the minimum wavelength of effectively reproduced oscillations should be twice the effective width of the working gap of the GV. Let's illustrate this with an example. Let's say we have a magneto with a belt speed of 9.53 cm/s, in which a GW is installed with a geometric working gap width of 3 microns. Since the effective width of the working gap l is usually 20 - 25% greater than the geometric width, then l = 3-1.25 = 3.75 microns. Replacing the recording wavelength with twice the effective width of the working gap, we determine the upper frequency of the operating range f= =V/2l=95,300/7.5=12,707 Hz. This approximately upper operating frequency range (12500 Hz) is established by regulatory documents. Under the same conditions, at a speed of 19.05 cm/s, recording and playback of frequencies up to 25400 Hz is possible, and at a speed of 4.76 cm/s - up to 6347 Hz. It is also necessary to take into account the fact that as the quality indicators of tapes and magnetic heads improve, the working range of recorded and reproduced frequencies continuously expands.
It is known that the working gap of a magnetic head is characterized by its width, depth and length. What is the effect of the depth and length of the working gap on sound recording and playback?
The influence of the depth and length of the working gap (the influence of the width is described in the previous answer) of the magnetic head (Fig. 3) is not so obvious and is often not taken into account, since radio amateurs use ready-made heads with known parameters.
The length of the working gap, which is the same as the width of the head core, is determined by the width of the recording track. The use of four-track recording in modern tape recorders has led to a reduction in the core width to 1 and 0.66 mm with a magnetic tape width of 6.25 and 3.81 mm, respectively, and this, in turn, affected the residual magnetic flux of the phonogram, lowering it compared to two-track recording. Under these conditions: reducing the width of the working gap leads to a deterioration in the signal-to-noise ratio and a decrease in dynamic range phonograms. One of the ways to combat this is to increase the efficiency of the main zone and the return of the hot water by reducing the depth of the working gap.
Rice. 3. Working gap of the magnetic head and its parameters
The effectiveness of the GB is determined by the cross-section of the core in the zone of the working gap of the firebrand. The smaller the core cross-section, the higher the GB efficiency, which determines the write current required to create the required GB working gap magnetic field records. With an increase in the efficiency of the GB, the recording current can be reduced, which is important for tape recorders powered by autonomous current sources and especially cassette tape recorders.
GW recoil is e.g. . s., induced in the winding when playing a phonogram. The electromotive GW is proportional to the rate of change of the magnetic flux in the GW core and depends on the residual magnetic field of the phonogram and the parameters of the GW magnetic circuit. For effective closure of the magnetic flux of the phonogram through the GV core, and not through the working gap, it is necessary that the magnetic resistance of the GV working gap be significantly greater than the resistance of the core. For a given width of the working gap, this is achieved by reducing its depth. In modern HV and GU reel-to-reel tape recorders, the depth reaches 0.15 - 0.25 mm, and in cassette recorders - about 0.1 mm.
Reducing the gap depth entails a decrease in the durability of the head due to the abrasion of the working surface of the head by the working layer of the magnetic tape. However, modern tapes with a base made of polyethylene terephthalate and a high degree of polishing of the working surface make it possible to build tape drive mechanisms with a pressing force of the tape to the head of about 4 - 6 N (400 - 600 g) in reel-to-reel tape recorders and about 2 N (200 g) - in cassette and receiving heads up to 1000 hours or more.
What caused the increase in the nominal value of the short-circuit magnetic flux to 320 nWb/m in reel-to-reel tape recorders and to 250 nWb/m in cassette tape recorders?
The short-circuit flux of the phonogram characterizes the quantitatively but useful effect of recording and is represented through a GW core with zero magnetic resistance. The normalized value of the recording level is called nominal. It is easy to show that the recording level under these conditions largely depends on the quality of the magnetic tape. With the advent of magnetic tapes with improved properties and especially high-coercivity tapes, recording capacity can be increased. The introduction of new magnetic tapes of types A4409-6B and A4205-ZB made it possible to increase the nominal value of the short-circuit flux to 320 nWb/m for a speed of 19.05 cm/s in reel-to-reel tape recorders and to 250 nWb/m for speed 4. 76 cm/s in cassette. This allows tape recorder developers to expand the -mic recording range, reduce nonlinear distortion and improve a number of other parameters of the tape recorder.
What other requirements apply to magnetic tapes?
In modern tape recorders, when the width of the recording track has become less than 1 mm, and the geometric width of the working gap of the head is approaching 1 micron, to achieve high-quality performance, a magnetic one must be used, which allows to ensure the best between the working layer of the tape and the head.
To ensure this, high elasticity of the base material of the tape is required. All newly developed tapes, especially for cassette tape recorders, are therefore made with a base of polyethylene terephthalate (trade name ""). New tapes of types A4309-6B, A4409-6B, A4205-ZB, etc. have this basis.
Another feature of the tapes is high degree polishing the working layer. With a well-polished surface of the working layer, the contact between the tape and the head is noticeably improved, the wear of the heads is reduced, the recording and playback of high frequencies is improved due to the reduction of contact losses, and the signal-to-noise ratio also increases.
Another specific quality is the absence of defects in the working layer. It is known that the tape’s own noise is determined by the composition, uniformity and homogeneity of the magnetic material of the working layer. The entry of foreign inclusions into the working layer or the appearance of microbubbles in it leads to signal loss and, likewise, to loss of information. This is especially noticeable in music recordings.
What should the signal level indicator show?
In household magnetic sound recording equipment, a built-in indicator is used to constantly monitor the level of the signal sent for recording. Since most tape recorders have a universal amplifier, the signal level indicator is turned on at its output. With separate recording and playback amplifiers and separate heads, built-in indicators allow you to monitor both the signal supplied for recording and the already recorded signal, thereby monitoring the end-to-end signal. Under these conditions, the indicator must show the values of the monitored signals, and the maximum permissible signal must correspond to the nominal recording level.
The tapes are characterized by three groups of indicators: physical and mechanical, magnetic and working.
Main physical and mechanical properties tapes are: load corresponding to the fluidity of the base material; residual relative elongation after removing the load, relative elongation when exposed to impact load; adhesive strength; sabreability and warping (saberability is determined by the degree of deviation of a piece of tape 1 m long, loosely laid on a flat surface, from a straight line, and warpage is determined by the degree of deformation of the surface of the tape); heat and moisture resistance.
The strength characteristics of magnetic tape are almost entirely determined by its base. The lavsan base, as a rule, provides the strength characteristics required for the tape.
Saber and warping are types of deformation of magnetic tapes that occur due to improper cutting, drying or winding them during the production process, as well as violations of storage conditions. The consequence of these deformations is a poor fit of the tape to the magnetic head, which leads to defects during recording and playback of the phonogram.
Below are the main physical and mechanical characteristics for a magnetic tape with a width of 3.81 mm on a lavsan base with a thickness of 12 microns:
Magnetic properties of tapes characterized by coercive force (ranges from 20 to 80 kA/m for various types of tapes); residual saturation magnetic flux (5-10 nWb); saturation magnetization (90 - 120 kA/m); residual saturation magnetization (70 - 100 kA/m); relative initial magnetic permeability (1.7 -2.2).
The basic magnetic properties of the tape can be determined from the magnetization curves of the working layer of the tape, which have the form of hysteresis loops. Figure 4.2 shows magnetization curves related to three different compositions of the working layer of the tape based on Fe 2 O 3, CrO 3 and metal powder. Residual induction is the most important characteristic of the magnetic tape material. The higher this indicator, the greater will be the maximum residual magnetic flux of the tape and, therefore, the greater, all other things being equal, the maximum achievable signal-to-noise ratio.
The magnetization characteristic shows that “metal” tape is capable of providing approximately a twofold gain in the level of the recorded signal compared to chromium dioxide and ferrooxide. “Metal” tapes have minimal distortion and a wide frequency range, but to realize these characteristics, special heads are required that ensure the creation of a significantly higher field strength both when recording a signal and when erasing it.
To the main performance characteristics include: relative sensitivity of the tape and its maximum level; signal-to-noise ratio; signal/echo ratio; frequency range; erasability.
Rice. 4.2. Magnetization curves of tapes with different compositions of the working layer: 1 - Fe 2 O 3 ; 2 - СrO 2; 3 - Me
Relative tape sensitivity - the ratio of the sensitivity of the test tape to the sensitivity of the primary standard tape. The sensitivity of a tape is characterized by the degree of its magnetization, which is defined as the ratio of the residual magnetic flux to the low-frequency field of the head created by the recording field. The higher the sensitivity, the lower the gain the recording amplifier can have.
Primary standard tapes are batches of magnetic tapes with the most optimal properties, produced by leading manufacturers. They are like a standard with which the parameters of the tested tapes are compared when evaluating them. Typical tapes and their characteristics are established by the IEC - the International Electrotechnical Commission.
Uneven sensitivity is characterized by fluctuations in sensitivity along the length of the tape and depends mainly on the uneven thickness of the working layer and the concentration of magnetic powder in it, the deposition of wear products of the tape and dust on the working layer. Within one roll of magnetic tape, sensitivity unevenness should not exceed ± 0.6 dB.
Signal-to-noise ratio is determined by the ratio of the voltage of the maximum reproduced signal to the noise voltage of a tape magnetized by a constant field. Modern tapes have a signal-to-noise ratio of 57 - 62 dB.
Third harmonic coefficient - the ratio of the third harmonic voltage of the reproduced signal with a frequency of 400 Hz to the signal voltage at the output of the reproduction amplifier. The value of this parameter is usually 0.5 -3%.
It was widespread. This was one of the forms of storing acoustic information. And today, despite the fact that more perfect forms records of information, such storage media are still in demand. However, they are already used in a slightly different quality, and they contain audio signals quite rarely. In addition, it should be borne in mind that this recording principle has become the basis for a huge number of developments. Video cassettes, streamers, hard disks computers - all of them appeared as a result of the development of this technology, the foundations of which were laid at the beginning of the last century.
Design Features
Long time audio information was recorded by changing the magnetized state of certain devices. During the recording process, the power of the created field was distributed in accordance with the recorded signal. They called such a device magnetic tape. Such storage media consist of two main layers:- . flexible working basis. It is made from a variety of materials. Initially, even paper and polyethylene were used, but due to their fragility they were not widely used. As the requirements for the quality and service life of the carrier increased, other types of materials, mainly of synthetic origin, began to be used: polyamide, lavsan, etc.;
- . working layer with longitudinal particle orientation.
As for the working layer, it is a one-sided spraying of ferrite particles into special varnish. Both pure metals and various oxides are used. It is on the parameters of this layer, on its varieties and the sprayed substance that the performance characteristics carrier.
Several layers of powder can be applied. Despite this, the thickness of the media does not exceed several micrometers, and the width of the magnetic tape varies depending on the purpose of the product and can range from a few millimeters to 10 cm or more. To improve the adhesion of the main layers, reduce friction and improve sliding, some manufacturers added intermediate layers.
Main varieties
Despite the same purpose, such storage media may differ somewhat from each other, including by type of device. In addition to the design option described above with the spraying of metal powder onto the working base, there are other types of tapes:- . single-layer. Ferrite powder is evenly distributed in the base layer;
- . all-metal. They are a strip of carbon steel.
Such products differ in purpose. They can be reel-to-reel or cassette. In the first case, they are supplied wound on reels of various sizes. However, loading such media into a playback device can be somewhat difficult. This is why compact cassettes were developed. In them, the body and the carrier itself are a single functional element. This design simplified operation.
The most widespread are compact cassettes with multilayer media. Depending on the composition of the working layer, there are several varieties:
- . with ferroxide coating (regular or “normal” carrier);
- . chromium-based layer;
- . two-component working layer. Internal - ferroxide coating, external - chromium oxide;
- . a working layer of the finest metal iron powder.
Nowadays, reel-to-reel tape recorders are valued by enthusiasts for their “warm tube” sound.
Magnetic tape quality indicators
The durability of the recording is determined sufficiently a large number parameters. Among the main electroacoustic factors are:- . sensitivity to exposure;
- . presence of nonlinear distortions;
- . level of echo, noise, recording and erasing.
Conventional solid magnets are used to solve a huge number of applied problems, but in some cases the possibilities of their use are limited. In particular, in the production souvenir products or outdoor advertising, there is a need for flexible and flat materials. In search of the best option for such situations, users will learn what magnetic tape is. This material is one of the varieties of magnetic plastics - magnetic vinyl, cut into strips of a certain width. The tape is characterized by the following features:
Application of magnetic tape
So, we figured out what magnetic tape is. Now let's find out how it can benefit you. This flexible material is used in the following areas:
