DE9216390U1 - Screening device for an injection molding or extrusion unit - Google Patents

Description

Screening device for an injection molding or extrusion unit

The invention relates to a screening device according to the preamble of claim 1.

Such screening devices are used in injection molding or extrusion machines to remove foreign bodies from the melted plastic mass to be processed, which must be injected into a mold under pressure via channels and nozzles. Such foreign bodies are, for example, metal, paper, glass, wood or similar particles that are in the plastic melt. They must be removed from the melt stream before entering the mold. Such particles are particularly found in the melt when recycled material is used as granulate, which usually cannot be completely cleaned of foreign additives.

From DE-AS 27 45 871 such a screening device is

en 'Bank code 694 70Q39 ¹ , ' 46332

for filtering heated, sprayable plastic masses. It consists of a sieve sleeve that is fitted inside a central bore of a nozzle body. The sieve sleeve has a central axial inflow bore that extends like a blind hole over most of the axial extent of the sieve sleeve. Starting from the inflow bore, a large number of radially running bores of small diameter are fitted and represent the sieve openings or sieve bores. They open into grooves that are arranged axially in the outer surface of the sieve sleeve. This creates channels in the outer surface of the sieve sleeve in which the melt can combine after passing through the sieve bores. The grooves each extend from the topmost continuous bore to the bottommost sieve bore, but do not reach the respective end faces of the sieve sleeve. In order to allow the filtered melt flow to flow into the outlet bore of the nozzle body, radial and diagonal through-bores are provided at the downstream end section of the groove below the last screen bore.

Although such a screening device has proven itself in practice in principle, it does have a number of disadvantages. The main problem is that the introduction of the through holes provided at the downstream end section of the grooves is complex in terms of production technology, since the angular position must be maintained exactly in both the radial and axial directions. In addition, it has been found that in many cases the cross section of the through holes is too small to allow the melt flow in the desired amount or at the desired speed.

to be able to discharge the burden.

The invention was therefore based on the problem of providing a screening device of the type mentioned at the beginning which no longer has these disadvantages.

This problem is solved by a screening device having the features of claim 1. Advantageous further developments of the invention are specified by the features of the subclaims.

The invention is based on the idea of creating the through-openings to be attached to the downstream end section of the grooves by making a central cylindrical recess in the sieve sleeve from below, i.e. on the downstream side. The depth of the recess is dimensioned in such a way that it axially covers the downstream end section of the grooves. The radius is selected at least so that the recess reaches the bottom of the groove and radial openings are created in this way. These represent the through-openings through which the melt flow is guided from the grooves, running radially inwards, to the recess and thus to the outlet bore of the nozzle body.

This makes it possible to set the height of the opening and thus the flow cross-section of the through-hole to a desired, optimal value by selecting the appropriate degree of overlap between the recess and the groove. In terms of manufacturing technology, there are further advantages, as the through-holes can be produced by a single drilling or milling process, so the creation of individual through-holes is no longer necessary.

Savings are all the more important as the sieve sleeve is a mass-produced item that must be manufactured as cost-effectively as possible.

According to an advantageous embodiment of the invention, the radius of the recess is in exact agreement with the vertical distance between the axis of rotation and the inner edge of the groove. This ensures that a through opening is created which extends over the entire width of the groove.

If desired, the width of the through openings can be reduced by slightly reducing the diameter compared to the above case when the groove base is flat, i.e. when the profile cross-section of the groove is rectangular, so that the openings only cover a smaller area of the groove base.

To further reduce manufacturing costs, it is possible to install the grooves along the entire length of the sieve sleeve. It is therefore no longer necessary to position the grooves in such a way that only the area between the top and bottom sieve holes is covered.

Such a configuration also provides flow-related advantages for the melt flow in that there are no longer any so-called dead corners in which material can collect and settle without being caught by the melt flow.

Material deposits can also be avoided by moving away from the previous attempt to

to fit the nozzle body using precisely dimensioned flanges, deliberately allowing a certain amount of play in both the radial and axial directions. It has proven particularly advantageous to select both the length and the external diameter of the sieve sleeve to be approximately 0.2 to 0.3 mm smaller than the corresponding dimensions of the mounting hole in the nozzle body.

A further advantage of the screening device according to the invention is that, for a given size of the receiving bore in the nozzle body, the effective screening surface is larger than with conventional screening sleeves. The central feed bore can be brought axially close to the downstream recess, so that only the thickness of the partition wall required for strength remains. This is possible because no more diagonal bores are required.

In the configuration with continuous grooves, the effective screen area can be further increased, since the screen holes in the inflow area can be installed upwards up to the vicinity of the front surface.

The invention is explained in more detail below using the illustrated embodiment. Shown are:

Figure 1 Top view of the sieve device with half-broken sieve sleeve and

Figure 2 Sieve device in longitudinal section, sieve sleeve in half section.

The screening device 1 consists of a nozzle body 2 into which a screening sleeve 3 is inserted.

For this purpose, the nozzle body 2 has a central receiving bore 21, which on the downstream side merges into an outlet bore 22. The transition area has a countersink 23.

The sieve sleeve 3 has the shape of a circular cylinder. Twelve continuous, axially running grooves 32 are provided in the outer surface, which have a rectangular cross-sectional shape. A web 36 remains between each two adjacent grooves 32. At the intersection point between a flank 38 of the web 36 and a groove base 37 of the groove 32, an axially continuous inner edge 33 runs.

On the inflow side from above, a central axial inflow bore 39 is provided, which starts from the inflow side end face 34 and extends to the vicinity of a recess 31 provided on the outflow side end face.

Starting from the inflow bore 39, a large number of fine sieve bores 40 are arranged in a radial direction. These open into the grooves 32. In order to achieve the largest possible effective sieve surface, the sieve bores 40 are arranged with a small distance between them. In the illustrated embodiment, there are 26 sieve bores 40 per groove.

The recess 31 is made in the form of a circular cylinder from the downstream end face 35. Its axial extension D determines the height of the through openings 30 as openings at the downstream end of the grooves

32. The radius R corresponds exactly to the distance from the rotation axis 100 to the inner edge 33 of the groove 32. This results in an opening or through-opening 30, which extends over the entire width of the groove base 37. Thus, only the webs 36 remain in the area of the recess 31.

The sieve sleeve 3 is guided with a small radial and axial clearance in the receiving bore 21 of the nozzle body 2. The clearance is approximately 0.2 to 0.3 mm in both the axial and radial directions. This clearance is sufficient on the one hand to reliably prevent undesirable material deposits, but on the other hand to reliably prevent the unintentional passage of contaminants through the gaps created by this.

Optimum flow conditions in the area of the recess 31 can be achieved if the axial extension of the recess 31 and thus the axial overlap D is between two and five percent of the total length L of the sieve sleeve 3. Thus, at least 90 percent of the sieve sleeve 3 can be used to create the sieve holes 40.

Dipl.-Ing. KLAUS WESTPHAL Dr, rer. nat. BERND MUSSGNUG

Walas Street 33
D-7730 VS-ViLLINGEN

Telephone (07721) 56007 Telex 7 921 573 wemu d Fax (07721)55164

Dr. rer. nat. OTTO BÜCHNER

PATENT ATTORNEYS European Patent Attorneys

Flossmannstrasse 30 a
D-8000 MUNICH 60

Telephone (0 89) 832446 Fax (0 89)8340966

hub008

FIGURE LEGEND

Sieving device

2 Nozzle body 21 Mounting hole 22 Exit hole 23 Countersinking 3 Sieve sleeve 30 Passage opening 31 Recess 32 Groove 33 Inner edge 34 Front face, inflow side 35 Front face, downstream 36 web 37 Groove base 38 flank 39 Inflow bore 40 Screen bore

Rotation axis

radius

axial overlap

Length of the sieve sleeve

Post office: Karlsruhe 76979-754 Bank account: Deutsche Sank Afc Vilingen (bank code 69470039) 146332

Claims (8)

1. Screening device for filtering heated, sprayable plastic masses, consisting essentially of a screen sleeve inserted in a nozzle body, the nozzle body having a central receiving bore which merges into an outlet bore for the plastic mass, and the screen sleeve having a plurality of radially extending screen bores which start from a central axial inflow bore and open into axially extending grooves in the outer surface of the screen sleeve, which in turn are each provided with a through-opening running radially towards the outlet bore at the downstream end section, characterized in that the through-openings (30) are formed by a central cylindrical recess in the sieve sleeve (3) on the downstream side (31) is attached, the axial extent of which is dimensioned such that it axially covers the downstream end section of the grooves (32) and the radius (R) of which is selected to be at least large enough to create openings at the base of the grooves (32). 2. Sieve device according to claim 1, characterized in that the radius (R) of the recess (31) corresponds to the vertical distance between the axis of rotation (100) of the sieve body (3) and the inner edge (33) of the groove (32). Postgiroamt: Karlsruhe 76979-754 Bank account-Deutsche 3a=ik AG Viilingen (bank code 69470039) 146332 3. Sieve device according to claim 1 or 2, characterized in that the axial overlap (D) is between two and five percent of the axial extension (L) of the sieve sleeve (3). 4. Screening device according to one of the preceding claims, characterized in that the grooves (32) at the inflow and/or outflow end are guided continuously up to the end face/end faces (34, 35) of the screen sleeve (3). 5. Sieve device according to one of the preceding claims, characterized in that the diameter of the sieve sleeve (3) is slightly smaller than the diameter of the receiving bore (21) of the nozzle body (2). 6. Sieve device according to claim 5, characterized in that the diameters differ by approximately 0.2 to 0.3 mm. 7. Sieve device according to one of the preceding claims, characterized in that the axial extension (L) of the sieve sleeve (3) is slightly smaller than the axial extension of the receiving bore (21) of the nozzle body (2). 8. Sieve device according to claim 7, characterized in that the sieve sleeve (3) is approximately 0.2 to 0.3 mm shorter than the receiving bore (21).