DE20221731U1 - Reverse flow barrier for an injection moulding machine, comprises a base member with a conical head, a smaller diameter section, non-return valves, and a pressure ring - Google Patents

Abstract

A reverse flow barrier for an axially movable plastifying and injection worm in the plastifying cylinder of an injection moulding machine, comprises a base member (1) with a conical head (2) and a smaller diameter section behind it. The base member has one or more channels (6) for molten plastic, which contain non-return valves. An axially movable ring (10) is located on the inner wall of the cylinder, behind the head section and forms a gap with the base member. The front ring surface is in contact with the base, and the rear surface seals against a pressure ring. The channel inlet openings are arranged so they are not blocked by the front surface when in the ring open position. The outer diameter is 70-90, especially 75-85% of the cylinder inner diameter. The surfaces have hard metal and/or ceramic inserts.

Description

The The invention relates to a non-return valve according to the preamble of claim 1.

At the injection molding of thermoplastics, snails are used the axially displaceable in plasticizing and in defined Direction are rotatable. Due to the friction occurring here and by additionally outside on the plasticizing cabled heating tapes is the Kuntstoffgranulat melted. For injecting the plastic compound into the cavity a mold, the screw is used as a piston and this moved axially in the plasticizing. To prevent that in this injection process, ie in forward movement of the non-rotating Snail, melted plastic flows back, become backflow stops used.

Out the prior art are backflow stops known (WO 00/23248), about a locking sleeve or a locking ring on the front end of the screw. At the Injecting this locking ring against a pressure ring surface of a Pressed at the head of the screw body. When dosing, i.e. when returning rotating worm, the locking ring is lifted from the pressure and stop surface and against the stop surfaces from the head of the main body arranged wings pressed. The Sperring is opposite The worm freely movable and rotates when dosing due the friction on the wall of the plasticizing cylinder or not only with low speed. This causes a friction between the locking ring and the contact surfaces the wing.

Furthermore Ringrückströmsperren are known ( DE 32 47 272 C2 ), in which distributed over the circumference of balls between the locking sleeve and the stop surface of the arranged on the worm head body of the Rückströmsperre are provided, which serve as a spacer between the locking sleeve and the body and at the same time act as a ball bearing, so better friction conditions between the Create body of the backflow and the locking sleeve.

One significant disadvantage of Ringrückströmsperren is that the closing process usually subjected to stochastic influences is and thus scatters are caused during the injection process. In addition, Ringrückströmsperren have usually a comparatively bad response or closing behavior during the injection process.

Another type of Rückströmsperren are so-called Kugelrückströmsperren in which in a cylindrical portion of the screw head a ( DE 198 19 808 A1 ) or more ( DE 1 266 486 ) Balls are arranged in the manner of a ball check valve in corresponding holes. These holes each have two areas of different diameters and a transition area that acts as a sealing surface. The diameter of the region of the bores lying upstream of the transition region in the direction of the flow of the melt is greater than that of the region located behind it and serves to receive the ball serving as a blocking element. During the metering operation, the plastic melt flowing through the narrow bore lifts the ball from the sealing surface and releases the passage of the melt into the area of larger diameter. The melt can then flow through the bore and past the ball (s) into the screw antechamber. So that the balls can not leave the wider area of the holes, the holes extend obliquely toward the inner wall of the plasticizing cylinder, as is the case in the cited prior art. However, there are also embodiments in which the holes open into the screw antechamber; In this case, webs or the like are provided in the bores, which prevent the ball from emerging from the bore.

Ball return valves have the great advantage over ring backflow barriers that they have a better response and closing behavior. Disadvantageous, however, are the measures that have to be taken in order to minimize the wear effect of the cylindrical region of the screw head on the corresponding inner wall of the plasticizing cylinder, since for this purpose the gap width between these parts must be selected large enough. This plays an important role, especially with large screw diameters. However, this measure has the consequence that occur after closing the ball leakage flows from the Schneckenvorraum through the gap to the rear and required for 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 thus changed melt constituents enter the cavity together with the clean melt and lead to losses of quality in the finished molded part. However, a too large gap leads to the already mentioned leakage flows. As a result, a ball-lock must always compromise between a low leakage flow on the one hand (smallest possible gap width) and a low wear of the screw and low shear forces in the plastic on the other hand (the largest possible gap width).

Of the Invention is therefore based on the object, a Rückströmsperre on the one hand a good response and closing behavior on the other hand, both leakage flows from the screw antechamber as well as unwanted shear to be avoided on the plastic.

The solution This object is achieved by a Rückströmsperre with the features of Claim 1. Advantageous embodiments and developments can be found in the subclaims 2 to 5.

Of the The main advantage of the present invention is that the ball first for a quick closing the melt channel leads (fast response) and that as a result of now under the locking ring interrupted reflux a pressure gradient arises, which pushes the locking ring against the pressure ring and the Worm vestibule seals. By dividing the functions "closing" on the one hand and "sealing" on the other hand, the Base of the head part a clear gap with the inner wall of the Forming plasticizing. This way occurs in this area no friction and no wear on. Furthermore, undesirable shearing forces can occur the plastic in this area can be avoided. In addition, the flow conditions in the gap by suitable dimensioning of the base of the head part be targeted.

following the invention is based on an embodiment and with reference closer to the figures explained become. In these figures, the backflow preventer is in the closed position shown.

It demonstrate:

1 : Front view of the backflow barrier;

2 : Longitudinal section of the non - return valve (section AA in 1 );

3 : 90 ° longitudinal section of the non-return valve (section BB off 2 )

4 : Cross section of the backflow barrier along the line CC of 3 ,

The non-return valve according to the invention has a base body 1 , which consists of a forward tapered headboard 2 , a cylindrical shaft part 3 and a tail 4 consists. The diameter D _{K of} the base of the head part is smaller than the inside diameter of the plasticizing cylinder, not shown here, so that a clear gap is formed between the outside of the base and the inside wall of the plasticizing cylinder. The diameter D _{S of} the shaft part is opposite D _K and the diameter D _{E of} the tail 4 is reduced compared to D _S. At the front end of the tail 4 is a pressure ring 5 provided while the rear end of the tail 4 has a thread to attach the backflow in the plasticizing screw can.

In the main body extends from the shaft part 3 starting a channel 6 with a first region having a first diameter D1 and a second region having a second diameter D2, wherein D1 is smaller than D2, and a transition region 7 , Between one in the front area of the canal 6 arranged bridge 8th and the transition area 7 is a ball 9 versatile. In the closed position of the Rückströmsperre shown here is the ball 9 firmly at the transition area 7 and seals the channel 6 against refluxing plastic melt.

On the shaft part 3 is a locking ring 10 between the pressure ring 5 and the headboard 2 axially movable. The outer diameter of the locking ring is chosen so that the locking ring is tight against the inner wall of the plasticizing cylinder and thus no melt between the outer wall 11 and the inner wall of the plasticizing cylinder can flow out of the screw antechamber. Between the inner wall 12 of the locking ring 10 and the shaft part 3 becomes an annular gap 13 formed in which the inlet opening of the channel 6 empties. In the closed position of the Rückströmsperre shown here is the locking ring 10 with its rear stop surface 14 close to the pressure ring 5 while in the open position the locking ring 10 with its front stop surface 15 at the headboard 2 is applied. It is important to note that the entrance opening of the channel 6 such in the shaft part 3 is arranged to be in the open position of the locking ring 10 not from its front stop surface 15 is covered.

In the open position, so when dosing, the locking ring is located 10 at the headboard 2 on and the rear stop surface 14 forms with the pressure ring 5 a gap through the plastic melt in the annular gap 13 can flow in. From there, the plastic melt enters the inlet opening of the channel 6 , lifts the ball 9 from the transition area 7 and pushes her against the jetty 8th , The channel 6 is free and the plastic melt can be attached to the ball 9 flow past into the worm anteroom.

When the dosing is complete and the plasticizing screw for injecting the art molten material is moved forward into the mold, the ball is 9 quickly back to the transition area 7 pressed and the channel 6 closed. Here, the fast response of Kugelrückströmsperren or generally used by ball check valves. After the ball has closed, the reflux of plastic melt between the locking ring 10 and the pressure ring 5 interrupted. The resulting pressure gradient between this area and the antechamber leads to the fact that the locking ring 10 back against the pressure ring 5 is moved and the Schneckenvorraum is completely sealed to the rear. Upon further forward movement of the plasticizing screw now the desired emphasis during injection can now be applied easily.

1

body

2

headboard

3

shank part

4

tail

5

pressure ring

6

channel

7

Transition area

8th

web

9

Bullet

10

lock ring

11

outer wall of the locking ring

12

inner wall of the locking ring

13

annular gap

14

Rear stop surface of the locking ring

15

Front stop surface of the locking ring

Claims (5)

Backflow barrier for a plasticizing cylinder in an axially movable plasticizing and injection screw of an injection molding machine, with a base body ( 1 ), which is a preferably forward tapered headboard ( 2 ) and a to the headboard ( 2 ) to the rear adjacent area ( 3 ) with a smaller diameter than the base of the head part ( 2 ), wherein in the base body ( 1 ) one or more channels ( 6 ) for the flow of plastic melt from the screw in the screw antechamber, and wherein in the channels check valves ( 9 ) are provided, characterized in that a resting against the inner wall of the plasticizing and axially movable locking ring ( 10 ) is provided behind the headboard ( 2 ) of the basic body ( 1 ) in that area ( 3 ) is arranged with the smaller diameter and in this area with the main body ( 1 ) a gap ( 13 ), wherein the front stop surface ( 15 ) of the locking ring ( 10 ) in the open position with the base of the head part ( 2 ) and the rear stop surface ( 14 ) in the closed position with a on the base body ( 1 ) located pressure ring ( 5 ), and that the inlets ( 16 ) of the channels ( 6 ) in the main body ( 1 ) are arranged so that they in the open position of the locking ring ( 10 ) not from its front stop surface ( 15 ) are covered. Non-return valve according to claim 1, characterized in that the outer diameter of the base of the head part ( 2 ) is between 70% and 90%, preferably between 75% and 85%, of the inner diameter of the plasticizing cylinder. Backflow barrier according to claim 1 or 2, characterized in that in the channels ( 6 ) Ball check valves ( 9 ) are provided. Non-return valve according to one of claims 1 to 3, characterized in that the stop surfaces ( 14 . 15 ) of the locking ring ( 10 ) and / or the parts of the basic body cooperating with these surfaces ( 1 ) Have ceramic and / or carbide inserts. Non-return valve according to one of claims 1 to 4, characterized in that the stop surfaces ( 14 . 15 ) of the locking ring ( 10 ) and / or the parts of the basic body cooperating with these surfaces ( 1 ) are provided with wear protection layers.