At the request of netizen curelfox, this post talks about honeycomb coils.
Honeycomb coils are rarely seen nowadays. Their appearance is roughly as shown in Figure (01).
Figure (01)
The insulated wire used to wind the honeycomb coil is usually a multi-strand enameled wire (7-strand, 13-strand, 19-strand, etc.) twisted together and then covered with yarn or silk, which is called yarn-covered wire or silk-covered wire.
Netizens are mainly concerned about two issues about honeycomb coils: one is how this type of coil is wound, and the other is what advantages this type of coil has compared to other types.
Let's first talk about how the honeycomb coil is wound.
To illustrate how the honeycomb coil is wound, the coil tube must first be cut open and then flattened, as shown in Figure (02).
In Figure (02), we cut the coil tube open along the axial direction of the cylindrical coil tube, and then roll the upper part of the cut line to the bottom, as shown in red in the figure. This unfolds the outer surface of the coil tube into a rectangular plane. Note: Although the upper part is rolled to the bottom, this is only for the convenience of viewing. It is not physically cut open, and the upper and lower edges of the shape are still connected together.
Figure (02)
The honeycomb coil is wound using a special honeycomb winding machine and must be wound on a round tube or a round shaft, not a square tube. The honeycomb winding machine has a winding head, and the insulated wire must pass through the winding head and then be wound on the coil tube. The winding head can swing along the axis of the coil tube. The winding head swings back and forth once for every rotation of the coil tube (strictly speaking, a little more than one rotation, which will be explained in detail later). The swing is a uniform swing as the coil tube rotates.
Figure (03) is the middle part of the coil tube after it is unfolded.
In Figure (03), the blue vertical lines are the two extreme positions of the winding head swinging along the axis of the coil tube.
Figure (03)
When winding begins, first stick the end O of the wire to the coil tube, as indicated by the red arrow at O in Figure (03).
Then the coil tube begins to rotate, and the point where the wire contacts the coil tube is marked as 0° of rotation, as indicated by the black arrow in the figure. As the coil tube rotates, the wire moves to the right in the figure with the winding head. After rotating a little more than half a circle (for example, 185°), the right limit position of the winding head is reached, and the wire begins to move to the left in the figure with the winding head. Move downward to the lower edge (note that this is an expanded view, and it actually turns to the dividing line, that is, reaches the upper edge in the figure). The coil tube continues to rotate, and after passing 0°, it reaches the left limit position of the axial movement of the winding head at 370°, that is, 10°, and then moves to the right with the winding head. After passing 0°, the wire presses the beginning of the wire, as indicated by the red arrow at A in the figure.
The coil tube continues to rotate, and at 195°, the winding head reaches the right limit position and begins to move to the left. The wire also folds back to the left with the winding head. After crossing 185°, the wire presses down the first turn again, as shown by the red arrow at B in the figure.
Continue winding in this way, with each turn passing over the previous turn a little and pressing down the previous turn. Continue winding in this way until the required number of turns is reached. This method of folding back and pressing down the previous turn can be seen clearly in Figure (01). Rolling the upper and lower edges of Figure (03) back together will form the winding method of Figure (01).
Now, it is very clear why the winding head does not move back and forth once for every rotation of the coil tube. The winding head must move back and forth once a little more than one rotation of the coil tube, in order to allow the wire to pass over the previous turn and press down the previous turn.
So, how much more is this "a little more"?
In Figure (03), we draw the angle between the wire and the axis of the coil tube. The axial direction of the coil tube is represented by a red line, and the angle between the wire and the axial direction is θ. Then the distance between two adjacent turns of wire on the coil tube along the circumferential direction is the "slightly" angle of the extra turn multiplied by the radius of the coil tube. This "distance of the wire along the circumferential direction" must be greater than or equal to the wire diameter divided by cosθ, so that the wires will not overlap. It is allowed to have a slightly larger "slightly" angle of the extra turn. At this time, the two adjacent turns of wire are not close together, but slightly separated. In fact, as the wires are continuously stacked, the winding radius gradually increases, and the "distance of the wire along the circumferential direction" also increases. The distance between two adjacent turns of wire is also gradually increasing.
The reason why the honeycomb winding machine can have a "little bit" more angle per turn is achieved by a complex gear system. Changing different gears is like changing gears in a car, which can change the speed of the reciprocating movement of the winding head and wind a honeycomb coil with different turns per layer. The distance of the reciprocating movement of the winding head can also be adjusted, which is convenient for winding honeycomb coils of different widths.
Honeycomb coils can be stacked in multiple layers, and will not slip even if they are wound in 10 or even 20 layers. This is because: 1. The conductor is yarn-wrapped or silk-wrapped, and the friction on the surface of yarn-wrapped wire or silk-wrapped wire is much greater than that of enameled wire. 2. Each turn of the conductor presses down on the previous turn of the conductor when it turns. Therefore, the honeycomb winding method can produce coils that are stacked very high without using a frame. Of course, the honeycomb coils that have been wound usually need to be impregnated to stick the turns of the coils together to prevent them from loosening. Figure (01) uses a thin varnish for impregnation.
In fact, a coil wound by the honeycomb winding method is the same as a coil in Figure (04). It's just that Figure (04) uses enameled wire for overlapping winding without crossing, and each turn of the conductor cannot press down on the previous turn of the conductor. If there is no retaining wall, the coils cannot be stacked that high.
If each grid of the skeleton shown in Figure (04)
and Figure (05) is fully wound with insulated wire, it is equivalent to a honeycomb coil.
As shown in Figure (05),
you can also wind one honeycomb coil and then move a certain distance along the axial direction and wind another one, or even wind three or four coils in succession. As shown in Figure (01), you wind one honeycomb coil and then move a certain distance and wind another one. This is exactly the same as using the bobbin in Figure (05) to wind multiple grids in succession. The only difference is that the honeycomb winding method does not require a bobbin.
The history of honeycomb coils is quite long. It was mentioned in the magazine "China Radio" founded in 1933. At that time, the coils and even all the components were imported. It is estimated that honeycomb coils appeared in Western countries even earlier, perhaps in the 1920s.
Why did the coils have to be wound in a honeycomb pattern at that time?
The reason is very simple: at that time, there was no ferrite or other types of magnetic materials that could be used for high frequencies (tens of kHz to several MHz), so only hollow coils could be wound. In this way, the number of turns of the coil must be relatively large. If it is wound flat in a single layer, the volume of the coil must be very large. To reduce the volume, it can only be wound in multiple layers. It is also important to know that in that era, there were no thermoplastics such as nylon, polystyrene, polyester, etc., only phenolic thermosetting plastic. Phenolic plastic parts are difficult to process and the processing speed is very slow. The mold processing technology at that time was also quite underdeveloped, so it was difficult to make a skeleton like Figure (05), and it was also difficult to wind a coil like Figure (04). In order to have a large number of turns and a small volume, there was no skeleton, so the honeycomb winding method had to be used. Although the wire of the honeycomb coil must be multi-strand enameled yarn or silk, the wire production is difficult and the cost is high. The honeycomb winding machine has a complex structure, the gear processing is complex, and the cost is quite high. The use of the honeycomb winding method is a last resort, a solution among other solutions.
Now there are ferrite materials with very high magnetic permeability and good high-frequency performance, so the number of coil turns does not need to be so large, and the volume of the coil is relatively small. If a large number of turns is required, a multi-grid skeleton can also be made and wound in sections to reduce the distributed capacitance. In modern times, it is no longer necessary to use yarn or silk to wind the coil using the honeycomb winding method.
Some websites have posts about hand-wound honeycomb coils, and some even use enameled wire to wind honeycomb coils. I want to tell netizens: it is very difficult to wind a honeycomb coil by hand, although it is not absolutely impossible. It is even more difficult to wind a honeycomb coil with enameled wire. Moreover, even if a honeycomb coil is wound by hand, the various properties of this honeycomb coil will not be better than a single-layer coil or a multi-cell coil with a ferrite core.
This content is originally created by EEWORLD forum user maychang . If you want to reprint or use it for commercial purposes, you must obtain the author's consent and indicate the source
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
