JPH0735018U - Backflow prevention device for injection molding machine - Google Patents

Abstract

(57) [Abstract] [Purpose] Backflow prevention device that does not cause variations in sealing time during resin injection [Configuration] The contact area of the front end surface 28a of the ring valve 28 with the rear wall surface 22a of the head portion 22 is equal to the pressure receiving area A1. Two
It is less than 0%. That is, the effective pressure receiving area A2 of the ring valve 28 is 80% or more of the pressure receiving area A1. As a result, the pair of pressing forces acting on the ring valve 28 at the time of injection are F2> F1, and the ring valve 28 is reliably sealed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a backflow prevention device installed in a heating cylinder of an injection device for injecting a molten molding material into an injection molding machine. More specifically, it is an injection device that reduces variations in the seal valve seal time during injection. The present invention relates to a backflow prevention device for a molding machine (hereinafter, also simply referred to as a backflow prevention device).

[0002]

[Prior art]

 Conventionally, in an injection molding machine that injects a molten molding material into a mold and solidifies and molds it, an injection device for injecting and filling the molten molding material has a backflow prevention device in the heating cylinder. Various injection devices are known.

As shown in FIG. 1, a backflow prevention device 10 mounted on this type of injection device is rotatable about an axis (direction of arrow C) and axially (direction of arrow L) in a heating cylinder 12 serving as an outer shell. , R), and a screw 14 inserted so as to be able to move forward and backward. The screw 14 has a flight 16 that slides and rotates in the internal hole 12a of the heating cylinder 12, and a screw head 20 is fixed to the tip of the screw 14 via an annular wear plate 18. The screw head 20 is composed of a bullet-shaped head portion 22 arranged on the tip side and a shaft portion 24 provided with a taper 24a on the wear plate 18 side, and a rear wall surface 22a of the head portion 22 and a shaft portion 24. The annular groove 26 is formed by the front wall surface 18a of the wear plate 18. A resin groove 22b is bored in the head portion 22, and the annular groove portion 26 and the front side (arrow L) of the screw head 20 communicate with each other through the resin groove 22b. Further, the shaft portion 24 is provided with a cylindrical ring valve 28 having a through hole 30 in which a main hole portion 30a is formed in the front from the center and a taper 30b is formed in the rear portion so as to maintain a predetermined gap with the shaft portion 24. It is fitted out. The ring valve 28 is provided between an open position (a state shown in the drawing) where the front end surface 28a is brought into close contact with the rear wall surface 22a of the head portion and a shut-off position where the rear end surface 28b is brought into close contact with the front wall surface 18a of the wear plate 18. It is possible to reciprocate in the annular groove portion 26 by sliding along the inner hole 12a of the heating cylinder 12 along the directions of arrows L and R.

With such a configuration, the molding material, such as pellets, supplied to the rear end side of the heating cylinder 12 (not shown) is transferred to the injection nozzle (not shown) side by the rotation of the screw 14. While melting, it can be stored in the resin reservoir 32 in front of the screw head 20. At this time, the ring valve 28 is brought to the illustrated position (open position) by the pressure of the resin to be transferred (acting in the direction of the arrow L), and inside the heating cylinder 12, the internal hole 12a of the heating cylinder 12 and the internal hole 12a are formed. A space between the screw 14 → a gap between the through hole 30 of the ring valve 28 and the shaft portion 24 of the screw head 20 → a resin groove 22b → a space in front of the screw head 20 (direction of arrow L) and a series of resin passages 40. Reserved.

Further, when the screw 14 is advanced in the direction of arrow L while the resin is stored in the resin reservoir 32, the ring valve 28 is relatively moved in the direction of arrow R by the pressure of the resin on the resin reservoir 32 side. The rear end surface 28b of the ring valve 28 is brought into close contact with the front wall surface 18a of the wear plate 18. As a result, the resin passage 40 is blocked and the movement of the resin to the screw 14 side is restricted, so that the resin backflow is prevented. When the screw 14 is further advanced, the resin in the resin reservoir 32 is pressurized and injected from the injection nozzle.

At the start of the forward movement of the screw 14, a pressing force F1 in the arrow L direction is applied from the screw 14 side to the ring valve 28 and a pressing force F2 in the arrow R direction is applied from the screw head 22 side to the ring valve 28. To move in the direction of arrow R,

[0007]

[Equation 1]

Is essential. Also,

[0009]

[Equation 2]

It is However, P1 is the resin pressure on the screw 14 side, P2 is the resin pressure on the screw head 20 side, A1 is the pressure receiving area of the ring valve 28, A2 is the effective pressure receiving area of the front end surface 28a of the ring valve 28, and FIG. As indicated by hatching in c), A1 corresponds to the cross-sectional area of the ring valve 28, and A2 is (area of the front end face 28a of the ring valve 28)-(rear part of the head portion 22 in contact with the ring valve 28). The area of the wall surface 22a).

[0011]

[Problems to be solved by the device]

 However, depending on the pressure loss ΔP2 due to the reverse flow of resin from the screw head 20 side to the screw 14 side, the effective pressure receiving area A2 of the ring valve 28, etc.

[0012]

[Equation 3]

In some cases, the above may not be realized, and the time from the start of the forward movement of the screw 14 to the displacement of the ring valve 28 to the blocking position (sealing time) may vary. As a result of intensive research aimed at preventing such variations in the backflow prevention device, the inventors have determined that the ratio of the effective pressure receiving area A2 of the ring valve 28 to the front end surface 28a of the ring valve 28 is a specific ratio. It was discovered that the above variation in the sealing time can be prevented, and the present invention has been completed.

[0014]

[Means for Solving the Problems]

 As a means for solving the above problems, a backflow prevention device for an injection molding machine according to the present invention is a backflow prevention device for an injection molding machine which is installed in a heating cylinder of an injection molding machine for melting and injecting a molding material, A screw head fixed to the tip of the screw to form an annular groove with the inner wall of the heating cylinder, a blocking position for bringing the rear end face into close contact with the screw-side wall surface of the annular groove, and the screw head of the annular groove. A backflow prevention device for an injection molding machine, comprising: a ring valve that is reciprocally displaced in the annular groove between a communication position where the front end surface closely contacts the side wall surface; and a screw on the front end surface of the ring valve at the communication position. The contact area with the wall surface on the head side is less than 20% of the pressure receiving area of the front end surface of the ring valve.

[0015]

[Action]

 In the backflow prevention device of the injection molding machine configured as described above, the contact area of the front end surface of the ring valve with the wall surface on the screw head side at the communicating position is less than 20% of the pressure receiving area of the front end surface of the ring valve. That is, the effective pressure receiving area of the front end face of the ring valve is 80% or more of the pressure receiving area of the front end face.

Therefore, when the screw starts to advance when the resin is injected,

[0017]

[Equation 4]

Therefore, the sealing time does not vary.

[0019]

【Example】

 Next, an embodiment of the present invention will be described. Since the structure of the backflow prevention device of the injection molding machine of this embodiment is the same as that of the backflow prevention device 10 of FIG. The same reference numerals as in FIG. 1 are used for the names of the respective parts of the backflow prevention device, and the description of the configuration is omitted.

Although FIG. 1 shows the case where the number of the resin grooves 22b is four, the present invention is not limited to the backflow prevention device having the four resin grooves 22b, and the number is three or less. May be 5 or more. For example, assuming that the total contact area of the rear wall surface 22a with the ring valve 28 is the same, the area of one portion of the rear wall surface 22a (the portion sandwiched by a pair of resin grooves 22b) is three resin grooves 22b. It is possible to make it larger than four resin grooves 22b. Therefore, when the number of the resin grooves 22b is three, the contact surface pressure per location of the rear wall surface 22a can be reduced more than when the number of the resin grooves 22b is four, and the contact between the rear wall surface 22a and the ring valve 28 is reduced. Friction on the sliding surface can be reduced. (Seal time measurement experiment) The following Table 1 shows that the contact area between the front end surface 28a of the ring valve 28 and the rear wall surface 22a of the head portion 22 in the backflow prevention device 10 was changed (= the effective pressure receiving area A2 was changed. The results of the sealing time measurement experiment in which the presence or absence of variations in the sealing time were measured are shown.

In this experiment, in addition to the backflow prevention device (see FIG. 1) in which the ring valve 28 has a free type ring valve 28 that is rotatable relative to the screw head 20 about its axis, a claw is used. The backflow prevention device has a hooking type ring valve that engages with the screw head and rotates together with the screw head (screw) (however, axial displacement is possible).

[0022]

[Table 1]

As is clear from Table 1, the ratio of the contact area between the front end face 28a and the rear wall surface 22a to the pressure receiving area A1 of the ring valve 28 is less than 20% (= the effective pressure receiving area A2 with respect to the pressure receiving area A1). If the ratio is 80% or more), the variation of the sealing time is prevented.

As described above, the backflow prevention devices of Examples 1 to 3 do not cause variations in sealing time. For reference, the theoretical values of P1 = ΔP1 and P2 = P1 + ΔP2 can be calculated by the following formulas.

The resin pressure P1 on the screw 14 side when the screw 14 moves forward is equal to the pressure loss ΔP1 due to the backward flow of the resin to the rear side of the screw 14 at this time. The pressure loss ΔP1 = P1 when the resin flows backward one pitch of the flight 16 of the screw 14 is

[0026]

[Equation 5]

Here, η; viscosity of resin [kgf · sec / cm ² ] L; flow length [cm] Q; flow rate [cm ³ / sec] l; screw groove width [cm] h; screw groove depth [Cm].

On the other hand, the resin pressure P2 on the screw head 22 side of the ring valve 28 is a value obtained by adding the pressure loss ΔP2 due to the resin flowing back in the ring valve 28 to the resin pressure P1.

[0029]

[Equation 6]

It is Here, L1; flow length [cm] of main hole 30a L1 '; flow length of taper 30b [cm] b; gap [cm] b'between shaft 24 and main hole 30a; shaft 24 [Cm] d between the taper 30b and the taper 30b; inner diameter [cm] d ′ of the main hole 30a; opening diameter [cm] of the taper 30b.

Therefore, if one of the pressure receiving area A1 or the effective pressure receiving area A2 of the ring valve 28 is determined, the other can be determined based on the calculated theoretical values of P1 and P2 and the equation (1). However, since such a theoretical value and the actual behavior of the resin do not completely match, an appropriate ratio of the effective pressure receiving area A2 should be determined by taking into account experiments and the like based on such theoretical calculation. It is desirable to determine it within the range of 80% or more of the pressure receiving area A1.

[0032]

[Effect of device]

 As described above, the backflow prevention device of the present invention does not cause variations in sealing time during injection of resin.

[Brief description of drawings]

1A and 1B are explanatory views of a backflow prevention device of a conventional technique and an embodiment, FIG. 1A is a partial cross-sectional view near a screw head, and FIG. 1B is a line XX of FIG. 1A. End view, Figure 1
(C) is a right side view of the ring valve.

[Explanation of symbols]

10 ... Backflow prevention device, 12 ... Heating cylinder, 14 ...
・ Screw, 18 ・ ・ ・ Wear plate, 18a ・ ・ ・
Front wall surface (wall surface on screw side), 20 ... screw head, 22a ... rear wall surface (wall surface on screw head side), 26 ... annular groove portion, 28 ... ring valve,
28a ... front end face, 28b ... rear end face, A1 ...
Pressure receiving area, A2 ... Effective pressure receiving area.

Claims (1)

[Scope of utility model registration request] 1. A backflow prevention device for an injection molding machine, which is installed in a heating cylinder of an injection molding machine for melting and injecting a molding material, the annular groove being fixed to the tip of a screw and the inner wall of the heating cylinder. Between the screw head that forms a groove, a blocking position where the rear end surface is in close contact with the screw-side wall surface of the annular groove portion, and a communication position where the front end surface is in close contact with the screw head-side wall surface of the annular groove portion. In a backflow prevention device for an injection molding machine, which comprises a ring valve that reciprocates inside, a contact area between a front end surface of the ring valve and a wall surface on the screw head side at the communication position is a pressure receiving area of the front end surface of the ring valve. Is less than 20% of the backflow prevention device of the injection molding machine.