JPH10315270A - Stress calculating method of nozzle for injection molder, and nozzle based thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate the stress at the corner part of the edge face of an opening part by a method wherein the stress is obtained by multiplying the value of the circumferential stress of a cylinder, which is obtained through the formula on a thick cylinder under the supposition that the cylinder has a crosssection having the same as that of the edge face of the opening part, with a function, which is obtained through a structural analysis, as a factor. SOLUTION: Under the supposition that a cylinder has a crosssection having the same as that of the edge face 6 of an opening part, the circumferential stress δ of the cylinder is calculated from a formula: δ=P(D<2> +d<2> )/(D<2> -d<2> )×P, in which P is the resin pressure (kgf/ cm<2> ) of a molten resin, D (cm) is the outer diameter of the edge face 6 of the opening part, (d) (cm) is its inner diameter, t(cm)=(D-d)/2 is the wall thickness of an imaginary cylinder. A function (f) for mating the value obtained from the formula with the group of the stress values of the corner part of the edge face of the opening part, which are obtained through a large number of structural analyses carried out under the condition that the value of (d) or D are varied, is found out. By multiplying the formula with the (f) value as a factor, the stresses of the corner of theedge face of the opening part in the range of the ratio t/d or the ratio of the thickness of the edge face of the opening part to its inner diameter of 0.1-0.3 are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nozzle for an injection molding machine having a structure that is easily damaged due to concentration of stress, and proposes a method of calculating the stress of the nozzle and a structure of a nozzle that is not damaged based on the method.

[0002]

2. Description of the Related Art A conical passage of a nozzle for an injection molding machine having a conical molten resin passage therein has a complicated shape, and the stress at the opening end face corner can be obtained by calculation based on general material mechanics. Have difficulty. However, the stress in this portion is higher than in other portions, and it is extremely important to determine the stress in designing the nozzle. Therefore, conventionally, the stress in a thick-walled cylinder having a cross section of the opening end face has been calculated by a formula, and the stress has been obtained by multiplying by a reduction coefficient such as an empirical value based on the conical shape.

[0003]

However, there is an individual difference between designers in setting the coefficient, and when the reduction rate is set to an excessively large value, the stress is designed to be small so that the corresponding portion of the nozzle may be damaged. Become. Conversely, when the reduction rate is set to be too small, the stress is designed to be large, and the dimensions of the nozzle and, consequently, the heating cylinder, etc., become large, leading to an increase in cost.

[0004]

Accordingly, in the present invention, a cylinder having a cross section at the end face of the opening is imagined, the circumferential stress in the cylinder is determined by the formula of a thick cylinder, and the value is determined by structural analysis. The function f is multiplied as a coefficient to obtain the stress at the corner of the opening end face. Here, when the angle of the conical passage is 45 °, the function f is f = 1.6 × t / d + 0.4 (where 0.1 ≦ t / d
≦ 0.3). When the value of t / d is 0.
If it is 175 or more, a change in stress with respect to a change in t / d is small, and a nozzle which is not damaged even with a general material such as nitrided steel can be obtained.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. FIG. 1 shows a nozzle 1 according to the present invention, which is screwed to a tip of a heating tube (not shown). Reference numeral 2 denotes a contact portion having a spherical surface, which is pressed against a mold (not shown) by an injection device including the heating cylinder to inject and fill a molten resin in the heating cylinder into a cavity of the mold. Reference numeral 3 denotes a distal end hole formed in the center of the contact portion 2, which communicates with the conical passage 4 having an angle α and serves as a passage for the molten resin. Reference numeral 5 denotes a mounting screw for screwing the nozzle 1 to the heating cylinder. Reference numeral 6 denotes an end face of the opening of the conical passage 4 on the opening side, which is in close contact with the end face of the heating cylinder when the nozzle 1 is screwed onto the heating cylinder. 7 is a corner of the opening end face;
When injection pressure is applied to the molten resin in the conical passage during injection, this is a portion where the largest stress is generated as compared with other portions. The outer diameter and inner diameter of the opening end face 6 are represented by D (cm) and d (cm), respectively, and the thickness of (D−d) / 2 is represented by t (cm).

In the nozzle 1, the opening end face corner 7
Is difficult to calculate by calculation using general material mechanics because the nozzle 1 has a complicated shape. Therefore, in the present invention, first, a cylinder having a cross section of the opening end face 6 is imagined, and the circumferential stress σ in the cylinder is obtained by the thick cylinder formula. Here, P is the resin pressure (kgf / cm ² ) of the molten resin. σ = (D ² + d ² ) / (D ² −d ² ) × P Next, the value obtained by the equation was obtained by a number of structural analyzes performed by changing the value of d or D variously. Function f for matching the stress value group at the opening end face corners
And multiplying the equation by using the f-value as a coefficient, so that the stress at the corner of the opening end face can be obtained when the ratio t / d between the thickness of the opening end face and its inner diameter is in the range of 0.1 to 0.3. It was.

Accordingly, the stress calculation formula of the present invention for determining the stress σt at the corner of the opening end face is as follows: σt = (D ² + d ² ) / (D ² −d ² ) × P × f. When the angle α of the passage is 45 °, f is expressed by the following equation. f = 1.6 × t / d + 0.4 where 0.1 ≦ t / d ≦ 0.3. Although the equation changes when the angle α of the conical passage is other than 45 °, a similar function f can be obtained.

FIG. 2 is a graph in which the stress when the t / d value is changed in the above range is calculated by an equation and graphed.
According to FIG. 2, the t / d value is 0.16 at the maximum injection pressure of 2000 kgf / cm ² in a normal injection molding machine.
When smaller, the allowable stress of nitrided steel (SACM645), which is a general material of the nozzle, is 4800 kgf / cm ^2.
It can be seen that the stress increases beyond. Therefore, t
It is necessary that the / d value be greater than 0.16, preferably 0.17 or more, in designing a nozzle that does not break. The stress at t / d = 0.175 is P = 20
It is 4666 kgf / cm ^{2 at} 00 kgf / cm ² .

[0009]

EXAMPLES Examples of the present invention will be described specifically. In the nozzle of Example 1, D = 3.7 cm, d = 3.0c
m, t = 0.35 cm, t / d = 0.117, P = 17
50 kgf / cm ² , material: nitrided steel (SACM645)
In the case of, the stress obtained by the equation is 4970 kgf / cm
² At this time, the nozzle of Example 1 was broken. In the nozzle of Example 2, D = 4.2 cm, d = 3.0c
m, t = 0.6 cm, t / d = 0.2, P = 1750k
gf / cm ² , Material: The stress determined by the equation when using nitrided steel (SACM645) is 3885 kgf / cm ² . At this time, the nozzle of Example 2 was not broken.

[0010]

As described above, the stress of the nozzle, which was conventionally difficult to calculate, can be easily obtained, the nozzle can be designed quickly without any individual difference, and the nozzle having the minimum size can be obtained within the range that does not damage the nozzle. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a nozzle according to the present invention.

FIG. 2 is a graph showing a relationship between stress and t / d according to a calculation formula of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle 2 Contact part 3 Tip hole 4 Conical passage 5 Mounting screw 6 Opening end face 7 Opening end face corner D Outside diameter of opening end face d Inner diameter of opening end face t Thickness of opening end face α Conical passage Angle of

Claims (3)

[Claims] 1. A method for calculating a stress at a corner of an end face of an opening of a conical passage of a nozzle for an injection molding machine having a conical molten resin passage therein, the cylinder having a cross section of the end surface of the opening. The circumferential stress in the cylinder is determined by the formula for a thick cylinder, and the stress at the opening end face corner is obtained by multiplying the value by a function f determined by structural analysis as a coefficient. To calculate the stress of a nozzle for an injection molding machine. 2. When the angle of the conical passage is 45 °, the function f is f = 1.6 × t / d + 0.4, where 0.1 ≦ t / d (the thickness of the opening end face and its thickness). The method for calculating stress of a nozzle for an injection molding machine according to claim 1, wherein the ratio is expressed by the following equation. 3. A nozzle for an injection molding machine having a conical molten resin passage therein, wherein the ratio of the thickness of the end face of the opening to the inner diameter thereof, t / d, is 0.175 or more. Nozzle for injection molding machine.