Why hollow matrices?
Hollow matrix - a matrix for molding hollow, as well as the semi-profiles - have their own characteristics adjustment. Sometimes hollow matrix is a matrix for double-press. This makes them more difficult to adjust.
They are called matrices because double-press, they are first separated stream into two metal blanks, three or more portions at a time, when a workpiece for the first time faced with the "front" part of the matrix - divider. After the preform was divided into several metal flows, Each of these flows extends along the mandrel until, All these streams will not work out of the matrix, where they are connected again and form a given final shape of the extruded aluminum profile (Figure 1).
Adjustment of hollow matrices – simpler and more complex
Hollow extrusion dies They are more complex in structure, than the solid matrix, and so their adjustment must take into account a lot more different parameters. Moreover, hollow structural matrix include several types - are selected for different types of hollow profiles.
The advantage of adjusting the hollow matrices is, they have a few places, where you can make adjustments before you adjust the belts directly matrices. A well-designed hollow matrix may require only a small grinding in ports and often before adjustment belts deal does not reach.
principle corrections – balancing ports
Before adjusting the hollow mold first inspect ports. This is to ensure, To make sure, that the amount of aluminum, which goes through each port, It is balanced with the volume of metal in other ports. The volume of metal through the port depends on the area of that part of the cross-sectional profile, which he feeds (drawing 2).
The principle of correcting hollow matrices is based on this consideration: by expanding or hindering the flow of metal through the port, achieve acceleration or deceleration for the metal in any part of the hollow profile, which is pressed.
The difficulty of flow of aluminum on one of the walls of the hollow profile may be due to thinning of the wall thickness. In this case, you must look for other reasons for this, before milling ports hollow matrix. The reasons for this thinning of the wall may be the following:
1) the mandrel of the splitter has shifted in relation to the die outlet;
2) insufficient supply of metal along the mandrel;
3) the final slot for the wall at the die outlet is too narrow.
The figure 3 shows an example of the shift of the mandrel relative to the output matrix. You can not make any adjustments to the matrix while the matrix assembly defect is eliminated.
Another feature is that the hollow matrices, that ports around the mandrel acting as a kind of long belts. Aluminum, which passes through these ports may be excessively heated. In such cases, the removed portion of the metal on the mandrel, to facilitate the flow of metal, which runs along the mandrel (Figures 4a and 4b).
As shown in Figure 4A, large angle at the inlet of the mandrel creates obstacles for the flow of metal - metal flow decelerates. Below 4B repair otfrezerovali and otšlifovali, to remove these obstacles to the flow of metal. a mandrel entry angle is smaller and therefore it may pass through more metal. Therefore, the increase rate of the metal.
Manufacturers often deliberately matrices operate on the mandrels such barriers to metal flow. This is done to slow the flow of metal there, where it is needed. In many cases it is simply a reserve for adjusting the flow of metal in the matrix, I would not touch it for this purpose, working wraps matrices.
Source: Luis Bello, Die Corrections for Changing Flow Characteristics, Aluminum Extrusion Technology Seminar, Chicago, 1977