WO2006024607A1

WO2006024607A1 - Backflow stop for injection molding machines

Info

Publication number: WO2006024607A1
Application number: PCT/EP2005/054067
Authority: WO
Inventors: Martin Würtele
Original assignee: Krauss-Maffei Kunststofftechnik Gmbh
Priority date: 2004-09-01
Filing date: 2005-08-18
Publication date: 2006-03-09
Also published as: DE102004042615A1; DE102004042615B4; CN101022934A; KR20070048198A

Abstract

The invention relates to a backflow stop for an injection molding machine comprising a screw head (10), which has an end piece (12), a middle piece (14), a pressure ring (16), and a mounting end (20), and comprising a stop ring (18), which is arranged coaxial to the longitudinal axis of the middle piece (14) while forming an annular gap (22) therewith. The stop ring (18) can, with a stroke A, be axially displaced with regard to the screw head (10) between an open position and a stop position and comprises openings (32) for permitting the flow of plastic melt. The end piece (12) has a recess (40) whereby enabling the formation of a slider (42) with a length L ≥ A, against which the stop ring (18) rests via its inner side (34) in a manner that enables it to move axially and in the peripheral direction. During injection, plastic melt can flow back only via openings (32). The cross-sectional area that is flowed against can be enlarged by forming an edge (54), against which melt flows, and/or by providing one or more channels (50) in the end piece (12).

Description

Backflow barrier for injection molding machines

The invention relates to a non-return valve for injection molding machines according to the preamble of patent claim 1.

Such backflow stops are mounted on an ejection-side end of a plasticizing screw in an injection cylinder and serve as a "valve" to prevent plasticized plastic material from being forced back into the flight during an injection process.

A non-return valve according to the preamble of claim 1 is known from DE 198 36 871. In this known Rückströmsperre a locking ring is concentric with the center piece of a worm head between an open position in which he tangs with his front page to a stop surface on the back of the tail of the Seh ncke Nes, and a blocking position in which it rests against a thrust ring of the worm head , axially and circumferentially displaceable, ie during rotation of the screw, the locking ring is not necessarily carried by the screw head. The distance that the locking ring is displaceable relative to the screw head is to be referred to below as stroke A. The locking ring forms an annular gap together with the center piece and has holes for the material passage in the vicinity of the end face. In the open position of the locking ring is located with its front side on the stop surface on the back of the tail and plastic melt can flow through the holes and then past the tail of the screw head in the Schneckenvorraum.

At the beginning of injection, the locking ring is in the aforementioned open position. Due to the forward movement of the screw, the plastic melt flows in the direction of the locking ring and moves it backwards to the worm. As a result, the locking ring is lifted from the stop surface on the tail. The stroke A is reduced to a smaller degree A '. As a result, the plastic melt can increasingly flow through the annular gap between the inner diameter of the locking ring and the outer diameter of the middle piece. Thus, shortly after the start of injection, an approximate pressure equalization occurs over the backflow barrier. Due to the pressure build-up in the antechamber as a result of the injection process, the plastic melt is pressed through the not yet closed backflow and the stroke of the locking ring is further reduced. This is done by the pressure loss along the locking ring in the direction of the pressure ring and the shear stresses occurring on the locking ring due to the movement of the screw head. The Hubreduzierung has the consequence that the durchströmbare cross-sectional area between Sperring and pressure ring is getting smaller, whereby the pressure in this area increases. Thus, the pressure difference along the blocking ring can be reversed. This has the consequence that the further movement of the locking ring in the direction of the pressure ring is delayed or prevented, which adversely affects the closing behavior of the backflow.

Furthermore, from DE 100 59 615 A1 a backflow lock is known in which the locking ring has a plurality of melt lines in the form of holes that are not in communication with each other. The locking ring is guided on a shoulder of the screw head, which is smaller than the screw head outer diameter, and taken in the tip, i. the locking ring rotates forcibly with a screw rotation with the main body of the backflow lock. A disadvantage of this embodiment are the measures that must be taken to minimize the wear effect of the co-rotating Sperringes on the corresponding inner wall of the plasticizing, because this, the gap between these parts must be large enough. This is particularly important for large screw diameters. However, this measure has the consequence that occur after closing the locking ring leakage flows from the Schneckenvorraum through the gap to the rear and required during injection molding emphasis can not be applied to the desired extent. When dimensioning the gap width, the shear sensitivity of the plastics must also be taken into account. Since there is a melt film in the gap, too narrow a gap would exert large shear forces on the plastic, which leads to decomposition, color changes or changes in additives, such as the oxidation of flame retardant additives. The melt components thus changed enter the cavity together with the clean melt and lead to losses in quality in the finished molded part. However, a too large gap leads to the already mentioned leakage flows. As a result, a compromise must always be made in this embodiment between a low leakage flow on the one hand (smallest possible gap width) and a low wear of the backflow lock and the cylinder and low shear forces in the plastic on the other hand (as large a gap width)

Accordingly, the invention has the object, so to develop a return flow lock of ein¬ initially mentioned type that it has an improved closing behavior and low wear on the cylinder inner surface and a low material damage. The solution of this object is achieved by a non-return valve with the features of claim 1; the following claims relate to advantageous developments of the invention.

According to the invention it is proposed that the end piece has a recess in the region between the center piece and its stop surface, such that the end piece in this area has a slider with a diameter D _GL on which the locking ring with its inside axially and circumferentially relative to the tail and slidably rests on the middle piece, wherein the slider has a length L which is greater than the stroke A of the locking ring and the locking ring is not necessarily carried by the main body of the backflow preventer (Seh tease head) in the circumferential direction. This solution prevents plastic melt from flowing between the locking ring and the end piece into the annular gap. During the injection process, the pressure in front of the locking ring is thus kept constant or increased. Due to the significantly lower pressure loss between locking ring and pressure ring compared to the prior art, the pressure difference along the backflow in the direction of the pressure ring - which is responsible for the closing behavior of a non-return valve, kept constant or increased. With the lifting of the locking ring of the tail created an additional surface for inflating the locking ring, namely its head-bearing surface. The erfin¬ dungsgemäße Rückströmsperre has over the prior art on a much better closing behavior. By not necessarily carried by the screw head during its rotation locking ring is no wear on the inner surface of the cylinder before.

Below, the invention will be explained with reference to the accompanying drawings, in which Figures 1 to 3 show a first variant respectively in different working positions and Figures 4 to 6 further variants of the Rückströmsperre invention.

1 is a longitudinal sectional view of the first variant in the open position,

Fig. 2 is a longitudinal sectional view of the first variant in an intermediate position shortly after

Beginning of the injection process,

3 shows a longitudinal section of the first variant in the blocking position,

4 is a longitudinal sectional view of a second variant in the open position,

5 longitudinal sectional view of a third variant in the blocking position.

6 shows a longitudinal section of a fourth variant in the blocking position

FIG. 7 Top view of the non-return valve of FIG. 5 from the direction of the arrow in FIG. 5. The Rückströmsperre shown in Figures 1 to 3 comprises a screw head 10 with an ejection-side end piece 12, a cylindrical centerpiece 14 and a Montage¬ end 20 for mounting at one end of an injection screw, wherein the screw head 10 between its mounting end 20 and the center piece 14 a Pressure ring 16 carries. Concentric to the center piece 14, a locking ring 18 is arranged and forms together with the center piece 14 an annular gap 22. The outer diameter of the locking ring 18 is dimensioned so that the locking ring is just axially displaceable in a plasticizing cylinder, not shown here, on the one hand an open position (Figure 1) and a locking position (Figure 3) to take, but on the other hand to allow almost no relative movement in the circumferential direction.

The locking ring 18 is axially displaceable with respect to the Seh tease head, in an open position (Fig. 1), in which a stop surface 30 of the end piece 12 with a head-bearing surface 28 of the locking ring 18 comes into contact, and in a locking position (Fig 3), in which a stop surface 24 of the pressure ring 16 comes into contact with a locking bearing surface 26 of the locking ring 18. In the open position, a flow of material passes the gap between the surfaces 24 and 26, the annular gap 22 and the bores 32. In the blocking position, the locking ring is in its right end position, and the gap between the surfaces 24, 26 is closed, so that no Material can be pressed in the direction of the screw. Shortly after the start of the injection of the locking ring 18 assumes an intermediate position (Figure 2), in which both the head-bearing surface 28 of the locking ring of the stop surface 30 and the locking-bearing surface 26 are spaced from the pressure ring 16. For the passage of plastic melt into the Scheckenvorraum the locking ring 18 distributed over the circumference a plurality of holes 32.

The end piece 12 has on its back - so the locking ring side facing - a recess 40, such that a slider 42 is formed with a diameter D _GL . This slider 42 forms an over the entire circumference extending and continuous support surface on which the locking ring 18 is displaceable with its front end 46 both in the axial direction and in the circumferential direction. The locking ring 18 is not taken by the worm head during its rotation. The length L of the slider 42 is greater than or equal to the stroke A of the locking ring 18 between the open and the locked position. This ensures that plastic melt can only penetrate through the openings 32 into the annular gap 22 during injection (see FIGS. 2 and 3). As a result, an increased volume flow through the annular gap (as in the prior art) and thus also an increased pressure between locking ring 18 and pressure ring 16 is avoided, which would delay the closing of the backflow. By compared to the stand the technique lower pressure between locking ring and pressure ring thus the pressure difference along the backflow in the direction of the pressure ring - which is responsible for the closing behavior of a backflow preventer - held constant or increased. Since with the start of the injection of the locking ring 18 is lifted from the stop surface 30 of the end piece 12, the head abutment surface 28 is provided as an additional anströmbare cross-sectional area and thus increases the force on the locking ring 18 in the direction of the pressure ring 16. This further improves the closing behavior of the non-return valve.

To improve the closing behavior, a part of the stop surface 28 can already be made available in the open position as an inflatable cross-sectional area. Various embodiments of this are shown in Figures 4 to 6. It remains up to the expert to design further embodiments with an inflatable cross-sectional area.

According to Figure 4, for example, the outer diameter D _{AE of} the end piece 12 may be smaller than the outer diameter D _{AS of} the locking ring 18 at its front end 46, so that a leading edge 54 is formed.

According to FIGS. 5 and 6, the end piece 12 may, for example, have at least one axial or angled channel 50, wherein the diameter D _{K of} the end piece 12 in the region of the channel 50 at the channel bottom is the same (as shown in FIG. not shown here), or smaller (as shown in Figure 6) than the diameter D _{GL of} the slider 42 may be. If the diameter D _κ at the channel bottom smaller than the diameter D _{GL of} the slider 42, the length U of the channel 50 is to be designed so that it ends in the region of the length L of the slider 42, so that a shoulder 52 remains, in which the locking ring 18 still rests tightly on the slider 42 and no plastic melt from the annular gap 22 in the channel 50 and vice versa can pass, but the plastic melt continues to flow exclusively through the openings 32.

FIG. 7 shows the top view of the embodiment according to FIG. 5 from the direction of the arrow in FIG. 5. In the present case, four channels 50 distributed over the circumference are provided in the end piece 12 and four openings 32 are distributed over the circumference in the locking ring 18.

Finally, it should be noted that, unlike the figures shown in a screw head, the mounting end may also be integrally formed together with the pressure ring and the middle piece, in which case the tail is attached to the center piece, for example by screwing. LIST OF REFERENCE NUMBERS

10 snail head

12 tail

14 center piece

16 pressure ring

18 Sperring

20 end of assembly

22 annular gap

24 stop surface of the pressure ring

26 locking bearing surface

28 head contact surface

30 stop surface of the tail

32 openings for plastic melt

34 inside of the locking ring

36 recess at the front end of the locking ring

38 edge piece of the locking ring

40 recess in the tail

42 slider

44 outside of the tail

46 Front end of the locking ring

50 channel

52 paragraph

DQ _L Outer diameter of the slider 42

D _K diameter at the bottom of the channel 50

D _AS outer diameter of the locking ring 18 at its front end 46th

D _ES Outer diameter of end piece 12

D _S p Outer diameter of the locking ring 18 in the middle and rear area

D _M Outer diameter of centerpiece 14

Claims

claims

A backflow barrier for an injection molding machine with a screw head (10) having an end piece (12), a center piece (14), a pressure ring (16) and a mounting end (20), and with a locking ring (18) coaxial with Is arranged longitudinal axis of the central piece (14) and between an open position in which it abuts with a head-abutment surface (28) on a stop surface (30) of the end piece (12), and a blocking position in which it with a locking-bearing surface ( 26) bears against a stop surface (24) of the pressure ring (16) relative to the screw head (10) both in the circumferential direction and a stroke A is axially displaceable, wherein the locking ring (18) and the central piece (14) has an annular gap (22 ), and wherein in the locking ring (18) openings (32) are provided for the passage of plastic melt, characterized in that the end piece (12) in the region between the central piece (14) and its stop surface (30) has a recess (40 ), dergest Old, that a slider (42) is formed with a diameter D _GL , on which the locking ring (18) with its inner side (34) axially and circumferentially slidably rests, and that the slider (42) has a length L, the larger as the stroke A of the locking ring (18).

Second backflow barrier according to claim 1, characterized in that the outer diameter D _A s of the locking ring (18) at its front end (46) is greater than the outer diameter D _{AE of} the end piece (12), so that a leading edge (54) is formed ,

3. backflow barrier according to claim 1 or 2, characterized in that in the end piece (12) at least one axially or at an angle extending and extending into the region of the slider (42) extending channel (50) are provided.

4. Rückströmsperre according to claim 3, characterized in that the diameter D _{κ of} the end piece (12) in the region of the channel (50) at the channel bottom is smaller than the diameter D _{GL of} the slider (42) and that of Channel (50) in the region of the length L of the slider (42) terminates, so that the slider (42) in this area has a shoulder (52) on which the locking ring (18) rests.

5. backflow barrier according to claim 3 or 4, characterized in that the diameter D _{κ of} the end piece (12) in the region of the channel (50) at the channel bottom is equal to or greater than the diameter D _G ι_ of the slider (42).

6. non-return valve according to one of claims 1 to 5, characterized in that the front end (46) of the locking ring (18) tapers conically.

7. non-return valve according to one of claims 1 to 6, characterized in that the outer diameter D _A s of the locking ring (18) at the front end (46) is smaller than the outer diameter D _{SP of} the locking ring (18) in the middle and rear of the locking ring (18), and that the locking ring (18) in the transition region to this front end (46) is conical.

8. non-return valve according to claim 6 or 7, characterized in that the openings (32) in the conical region of the locking ring (18) are arranged.