JPS6024570Y2 - Screw - Screw for inline injection molding machine - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a screw for a screw in-line injection molding machine, and is particularly suitable for molding urea resin.

Usually, the screw of an injection molding machine is the most important part of the injection molding machine, as it kneads the resin, turns it into a gel under pressure, and injects it.

In other words, there are many types of thermoplastic resins, each with different physical and thermal properties, so the design of the screw must also meet these special characteristics.

A common single screw can be roughly divided into a material feeding section, a compression section and a metering section.

The material supply section is a section of 2 to 3 pitches per hopper that feeds the material from the hopper and sends it to the next compression section.

In addition, in the compression section, the supplied solid material is compressed, heated and kneaded, and most of it becomes a semi-molten state and is sent to the next metering section.

An important thing in this compression part is the compression ratio.

There are two ways to obtain this compression ratio: one is to compress gradually from the supply part to the metering part, and the other is to compress rapidly.
There are two methods: one method is to change the groove depth, and the other method is to keep the groove depth constant and change the groove width.

The shape of the screw thread also has a large effect on kneading and metering.

Generally speaking, a screw having a compression ratio of -2 to 4 is used for vinyl chloride injection molding, and a compression ratio of about 3 to 5 for polyethylene.

The screw thread shape also has a propulsion angle of 3 to 5R to advance the material.
7rrIrL (radius of curvature in millimeters) and a back pressure angle of 3 to 5Rvrrn to improve the kneading effect.

Next, the metering section is located at the tip of the screw, and is a section that feeds the semi-molten material in the compression section into the cylinder tip in fixed amounts under constant pressure.

In particular, the object of the present invention is to provide the best screw for an in-line injection molding machine for mass-producing products of a fixed shape using urea mixed powder.

Conventionally, when molding this kind of mixed powder, there are two methods: first, molding using a plunger-type injection molding machine;
Another method involves molding at high pressure using a screw in-line injection molding machine.

However, these first and second methods have the following drawbacks.

In other words, the first method requires a preheating melting chamber, etc., and the machine is quite complicated, resulting in poor workability.In addition, in order to completely melt the material, it takes a long time to cool down after injection into the cavity, making production difficult. In addition, since the urea mixed powder is heated above its melting point for a long period of time, it not only has a negative effect on the various properties of the urea mixed powder, but also produces ammonia gas and cyan gas when heated above its melting point for a long period of time. etc., resulting in a poor working environment.

In addition, the second method requires a large machine to inject at high pressure, and a rigid mold, making it difficult to create a cored shape with low strength such as ceramic. becomes.

As a method to eliminate the above-mentioned drawbacks, it is optimal to perform injection molding using a screw in-line method instead of using a single plunger method, and at low pressure instead of using high pressure.

However, as a powder, it is usually subject to large injection resistance, making it difficult to inject at extremely low pressure.

Therefore, it is necessary to completely melt the urea mixed powder and to reduce the injection resistance as much as possible.

On the other hand, if it is completely melted, there will be problems with the material feedability of the screw, and therefore a new screw for fused urea mixed powder, such as the one of the present invention, is required.

An embodiment of the present invention will be described below with reference to the drawings.

In the drawing, 1 is a hopper, 2 is a material supply port, 3 is a screw, 4 is a heater that heats the cylinder, 5 is a propulsion angle of the screw 3, 6 is a back pressure angle of the screw 3,
7 is the groove wall of the screw 3, 8 is the mold cavity, 9
and 10 is a cross section of the screw groove, and 11 is the screw 3
12 is the screw groove depth, 13 is the backflow prevention ring, 14 is the backflow prevention ring clearance, 15
is the tip of the cylinder.

First, when several tens of meshes of urea mixed powder are put into the hopper 1, the powder passes through the supply port 2 and is fed into a cylinder heated by the heater 4.

Here, the material is fed into the cylinder tip 15 and simultaneously compressed and kneaded by the interaction between the propulsion angle 5 and the back pressure angle 6 of the screw 3 rotating at a constant speed, and the gas generated from the material is transferred to the rear. It functions to send the water back to the supply port.

In the present invention, the propulsion angle 5 and the back pressure angle 6 herein are set to 2.5R771771 or less and 5 to 7R7rr/n, respectively.

If the propulsion angle 5 exceeds 2.5 Rwn and the back pressure angle 6 falls below 5 Rmm, it will take time to feed the molten urea mixed powder to the cylinder tip 15 because it has a high viscosity like a plastic material. The molten urea mixed powder that has once melted on the screw wall surface 7 solidifies again, and eventually no material is fed at all.

Furthermore, when the back pressure angle 6 exceeds 7 Rmm, the molten urea mixed powder can be sent to the cylinder tip 15 at a sufficient speed, but the gas generated from the fused urea mixed powder cannot be sent back to the rear. The gas is also sent to the cylinder tip 15 at the same time as the molten urea mixed powder, enters the cavity 8, and entrains gas into the molded product after injection, resulting in very poor surface roughness and weakening of its strength.

In addition, the compression ratio of the screw 3, that is, the ratio of the groove cross-sectional area 10 at the root of the screw 3, the groove cross-sectional area 10 at the tip of the screw 3, and the groove cross-sectional area 9 at the tip of the screw 3, is , the viscosity range is small, especially when it is molten, the viscosity becomes extremely small, which has a big impact on the metering time and gas entrainment.

Therefore, in the present invention, the compression ratio is set to 0.8 to 1.0.

When the lower limit value of 0.8 is below, that is, when the pitch 11 of the screw thread is constant and the groove depth 12 is increased toward the tip of the cylinder, the speed at which the molten urea mixed powder is advanced is sufficient. However, gas generated from the molten urea mixed powder is entrained.

Moreover, if the upper limit value exceeds 1.0, that is, if the screw thread pitch 11 is constant and the groove depth 12 decreases toward the screw tip, it will take a long time to feed the cylinder to the cylinder tip 15, and the screw wall surface The molten urea mixed powder that has melted once in step 7 solidifies again, and in the end, no material is sent at all.

Next, regarding the backflow prevention ring 13, the present invention has the backflow prevention ring 13 and its clearance 14.
The cross-sectional area of the gap shall be at least 1 times the cross-sectional area of the groove at the leading edge of the screw.

First, if there is no backflow prevention ring 13, when injecting the molten urea mixed powder sent to the tip of the cylinder,
Because its viscosity is so low, it flows backwards through the screw groove to the rear of the cylinder.

In addition, if the ratio of the cross-sectional area of the gap created by the clearance 14 to the cross-sectional area of the screw groove 9 is less than 1, the molten urea mixed powder that has passed through the screw groove and is sent in a fixed amount from the rear will not pass through because the backflow prevention ring clearance is small. The molten urea mixed powder is gradually sent back to the rear, and finally solidifies on the screw wall surface, preventing the molten urea mixed powder from moving forward.

Regarding the upper limit of the clearance 14, the only way to increase the clearance 14 is to make the tip of the screw thinner or reduce the thickness of the backflow prevention ring 13, so if the clearance 14 is made larger than necessary, , strength problems arose, and the backflow prevention ring 13 was removed during injection.
may break.

Therefore, it seems that the limit is up to twice as much.

Next, using a 140-ton vertical tightening horizontal side screw inline injection molding machine, we manufactured screws with various shapes, and determined the compression ratio of the screw, the thread shape, the presence or absence of a backflow prevention ring, its clearance, etc., and the material supply. Table 1 shows the results of examining the effects.

However, in Table 1, O: When the supply speed is fast and stable.

△: Supply speed is too fast, gas is involved molding, defective molded products, or slow feeding speed. cycle time can have a negative impact. If.

×: When not supplied at all.

The material used in this experiment was a urea mixed powder of several tens of meshes, the temperature inside the injection cylinder was set near the melting point of the urea mixed powder, the screw rotation speed was lxorpm, the screw diameter was 50 mm, and the groove depth was limited to a screw with a compression ratio of 1. was 5wn, the screw pitch was 50mm, and the screw length was constant.

In Table 1 above, looking at test numbers 1 and 2.3, the compression ratio of 1.0 is the best, and test number 2
, 4 and 5.6, it is clear that a backflow ring is necessary and the clearance is greater than the groove depth, and when we look at test number 7.8.9,
It is clear that the following conditions are required: the propulsion angle is 2.5R or less, and the back pressure angle is 5 to 7Rnvn.

Therefore, the screw for the screw in-line injection molding machine of the present invention has a compression ratio of 0.8 to 1.0, a screw thread propulsion angle of 2.5 Rrtrrt+ or less, and a back pressure angle of 5 to 1.0.
7 Rmm, and has a backflow prevention ring near the tip, making the clearance cross-sectional area between this ring and the screw more than 1 times the screw groove depth cross-sectional area, as described in the above embodiments and experimental examples. In addition, it is suitable for molding urea mixed powder, which is difficult to mold, and is particularly suitable for injection molding to mass produce products of a fixed shape using urea mixed powder.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; Fig. 1 is a partially cutaway side sectional view including the forming plate and cavity, Fig. 2 is a partially cutaway sectional side view of the screw, and Fig. 3 is a reverse flow diagram. FIG. 4 is an enlarged partially sectional side view of the prevention ring, and FIG. 4 is a rear view of FIG. 3. 1...Hopper, 2...Material supply port,
3...Screw 4...Heater
5... Propulsion angle, 6... Back pressure angle, 7...
...Screw groove wall, 8...Mold cavity, 9, 10...Screw groove cross section, 11.
...Thread pitch, 12...Screw groove depth, 13...Backflow prevention ring, 14...
...Backflow prevention ring clearance, 15...
Cylinder tip.

Claims (1)

[Scope of utility model registration request] Compression ratio 0.8-1.0, radius of curvature of screw thread propulsion angle 2.5M or less, radius of curvature of back pressure angle 5-7rrvn
A screw in-line injection molding machine characterized in that it has a backflow prevention ring near the tip, and the clearance cross-sectional area between the backflow prevention ring and the screw is 1 to 2 times the depth cross-sectional area of the screw groove. Screw for use.