CN112140490A

CN112140490A - Evaluation method and evaluation kit for plastic weld line

Info

Publication number: CN112140490A
Application number: CN202011073824.3A
Authority: CN
Inventors: 欧相麟; 严卫卫; 俞飞; 张云青; 杨良波; 黄佳佳; 周琴平; 杨明; 孙长周; 丁正亚
Original assignee: Kingfa Science and Technology Co Ltd
Current assignee: Kingfa Science and Technology Co Ltd
Priority date: 2020-10-09
Filing date: 2020-10-09
Publication date: 2020-12-29
Also published as: WO2022073326A1

Abstract

The invention provides a plastic weld line evaluation method and a corresponding evaluation kit. The inserts with different shapes are replaced in the injection mold, the fusion angle of the molten resin is changed, the evaluation structure with different fusion lines is obtained, the appearance and the mechanical property of the fusion line are tested based on the evaluation structure, and the quality of the fusion line generated by the different fusion angles of the molten resin during injection molding can be effectively and accurately evaluated. In addition, the inserts can be fixed in the injection mold through modes such as bonding, magnetism or inlaying, conveniently replace the inserts of different shapes and need not to change injection mold's original structure, and convenient to use is swift.

Description

Evaluation method and evaluation kit for plastic weld line

Technical Field

The invention belongs to the technical field of injection molding, and particularly relates to an evaluation kit and an evaluation method for a plastic weld line.

Background

In the injection molding production process of plastic products, the molten resin can flow in at least two directions in the mold, when two or more molten resins meet, because the molten resin close to the mold cavity can be cooled rapidly, the joint of the two or more molten resins can not be completely combined, a weld line can be formed in the plastic products, and the weld line can influence the appearance and the mechanical property of the plastic products, such as: stripes and nicks may appear in the weld line region; trapped air exists in the weld line region, and the trapped air can interfere with the winding effect between polymer molecules, so that molecular chains are separated from each other, and the mechanical strength of the weld line region can be lower than that of the non-weld line region. Most injection molding products have weld lines which are difficult to completely eliminate, the influence on the products caused by the weld lines can only be weakened as far as possible, and different mold structures and different materials can influence the generation and the performance of the weld lines, so that higher requirements are provided for the evaluation method of the weld lines.

At present, technicians in an injection molding factory usually design a mold by experience or debug an injection molding process, so that a weld line on a product obtained by injection molding meets the requirements on appearance and mechanical properties, but a set of system and an effective evaluation system are not formed, and the energy and the mold testing cost are wasted.

In summary, the prior art cannot accurately, effectively and objectively evaluate the appearance and mechanical properties of the weld line, so that improvement on the prior art is needed.

Disclosure of Invention

The invention provides an evaluation method of a plastic weld line and a corresponding evaluation kit, which are used for solving the problem that the appearance and the mechanical property of the weld line cannot be evaluated accurately, effectively and objectively in the prior art. The evaluation method comprises the following steps:

the method comprises the following steps: preparing an insert, wherein the insert comprises a shunting part and a converging part, the shunting part is used for shunting the injected molten resin, and the converging part is used for guiding the molten resin in different directions to converge at one position;

step two: preparing an injection mold having a gate and capable of accommodating the insert;

step three: fixing the insert in the injection mold, wherein the flow dividing part is close to the sprue, and the converging part is far away from the sprue;

step four: injecting molten resin into the injection mold fixed with the insert from the gate, cooling and molding, and opening the injection mold to obtain an evaluation structure, wherein a welding line is formed on the evaluation structure;

step five: and evaluating the quality of the welding line.

Further, the number of the inserts prepared in the first step is more than one;

step six, judging whether all the inserts are used in steps three to five, and if so, finishing; if not, the insert having a different junction is replaced to change the angle of fusion of the molten resins, and then the steps three to six are repeated.

Further, the evaluation in the fifth step includes evaluating the appearance and/or mechanical properties of the weld line.

Further, in the fifth step, the appearance of the weld line is evaluated by providing the depth, length, morphology or structure of the weld line; and/or evaluating the mechanical properties of the weld line by testing the tensile strength, bending strength and impact strength of the weld line.

Further, the insert is fixed in the injection mold in the third step, and the fixing is specifically completed in a bonding, magnetic attraction or embedding manner.

The invention also provides a plastic welding line evaluation insert which comprises a flow dividing part and a converging part, wherein the converging part is triangular, and the vertex angle of one end of the converging part, which is far away from the flow dividing part, is set as the supplementary angle of the converging angle of the molten resin; setting the extending direction of the opposite sides of the vertex angle to be transverse, and setting the direction vertical to the opposite sides in the plane of the junction part to be longitudinal; the lateral length of the flow dividing portion increases in the longitudinal direction from a direction away from the opposite edge to a direction close to the opposite edge.

Further, the shape of the flow dividing portion is any one of a triangle, a semicircle or a polygon.

Further, the inserts are of a bilateral symmetry structure.

Furthermore, the insert is made of a material which can resist the temperature higher than the melting temperature of the resin.

Further, the length of the bottom side of the flow dividing portion is L1, the width of the gate is L2, and t is the wall thickness of the evaluation structure, and the above parameters satisfy the following formula:

L2≥L1，L1≥10t。

correspondingly, the invention also provides a plastic weld line evaluation kit, which comprises an insert and an injection mold, wherein the injection mold is provided with a pouring gate and can accommodate the insert; the insert is as described above.

Furthermore, an adhesive structure, a magnetic attraction structure or an embedding structure is arranged between the insert and the injection mold.

The invention at least comprises the following beneficial effects: through the inserts of different shapes of installation in injection mold, can conveniently change the angle that converges of molten resin to conveniently obtain the evaluation structure that has the weld line that corresponds different angles that converges, can be accurate, high-efficient, objectively evaluate the outward appearance and the mechanical properties of weld line. The insert can be made of metal materials and is fixed in the injection mold through a magnetic attraction structure or an embedding structure, so that inserts in different shapes can be replaced conveniently; the inserts can also be bonded and fixed in the injection mold, the inserts and the injection mold do not need to be additionally processed, the inserts with different shapes can be conveniently replaced, the inserts cannot shake or shift, the inserts are accurately positioned, and the evaluation accuracy is improved; meanwhile, the insert can be made of a plastic material or a material with higher temperature resistance than molten resin, so that the cost is reduced, and the mold is not easy to scratch.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a flow chart of a method for evaluating a plastic weld line according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of inserts of different shapes of an evaluation kit of a plastic weld line according to an embodiment of the invention.

Fig. 3 is a schematic view of an evaluation structure of an evaluation kit for a plastic weld line according to an embodiment of the present invention.

Fig. 4 is a schematic view of an evaluation structure of an evaluation kit for a plastic weld line and a corresponding insert according to an embodiment of the invention.

Fig. 5 is a schematic diagram of the evaluation structure design dimensions of an evaluation kit for a plastic weld line according to an embodiment of the present invention.

1-evaluation structure, 11-hole site structure, 111-upper part, 112-lower part, 12-weld line, 2-insert, 21-shunt part and 22-confluence part.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The following detailed description of specific implementations of the present invention is provided in conjunction with specific embodiments:

the invention provides an evaluation method of a plastic welding line shown in figure 1, which comprises the following steps:

the method comprises the following steps: preparing an insert 2, wherein the insert 2 comprises a shunting part 21 and a converging part 22, the shunting part 21 is used for shunting the injected molten resin, and the converging part 22 is used for guiding the molten resin in different directions to converge at one position;

step two: preparing an injection mold which has a gate and can accommodate the insert 2;

step three: fixing the insert 2 in an injection mold, wherein the branch part 21 is close to a sprue, and the confluence part 22 is far away from the sprue;

step four: injecting molten resin into an injection mold fixed with the insert 2 from a pouring gate, cooling and molding, and opening the injection mold to obtain an evaluation structure 1, wherein a welding line 12 is formed on the evaluation structure 1;

step five: the weld line 12 quality was evaluated.

Further, the number of the inserts 2 prepared in the first step is more than one; step six, judging whether all the inserts 2 are used in the steps three to five, and if so, finishing; if not, the insert 2 having a different junction 22 is replaced to change the angle of fusion of the molten resins, and then the steps three to six are repeated.

Fig. 2 is a schematic view of the insert 2 of the present embodiment. The insert 2 of the present embodiment is an integrally formed bilaterally symmetric structure including the merging portion 22 and the diverging portion 21. The shape of the flow dividing portion 21 may be any one of a triangle, a semicircle, or a polygon; the junction 22 is triangular in shape. The vertex angle of the end of the merging portion 22 away from the diverging portion 21 is set to be a complementary angle to the merging angle of the molten resin; the extending direction of the opposite sides of the vertex angle is set to be transverse, and the direction vertical to the opposite sides in the plane of the junction part 22 is longitudinal; the lateral length of the flow dividing portion 21 increases in the longitudinal direction from the opposite side to the direction close to the opposite side. When the insert 2 is placed in the injection mold, the diverging portion 21 needs to be close to the gate of the injection mold, and the converging portion 22 needs to be far from the gate of the injection mold.

In the present embodiment, the insert 2 is installed in the injection mold, and illustratively, an adhesion structure is provided between the injection mold and the insert 2, so that the insert 2 can be adhered in the injection mold by the adhesion structure without changing the mold structure. For example, epoxy resin is used as an adhesive between the insert 2 and the injection mold to fix the insert 2 in the injection mold, so that it is not necessary to change the original structure of the injection mold, the installation is easy, the surface of the injection mold can be protected from being damaged, and the cost can be reduced. Alternatively, an inlay that is adapted to the insert 2 can also be provided in the injection mold, so that the insert 2 can be fixed in the injection mold by the inlay.

In some embodiments, the material of the insert 2 may be plastic, metal, or other material that is more resistant to heat than the molten resin. When the insert 2 is made of metal, a magnetic attraction structure, such as a strong magnetic block, can be arranged inside the injection mold, so that the insert 2 is fixed in the injection mold under a magnetic field formed by the strong magnetic block, and the effect of easy placement and taking can be achieved. The insert 2 can also be made of plastic, and exemplarily, the insert 2 is bonded in the injection mold through epoxy resin, so that the original structure of the injection mold is not required to be changed, the installation is easy, the surface of the injection mold can be protected from being damaged, and the cost can be reduced. Both metal materials and plastic materials need to be resistant to heat higher than molten resin so as to prevent the insert 2 from being bonded with the molten resin due to high-temperature melting in the injection molding process, thereby preventing the evaluation structure 1 from being smoothly demoulded.

After the mold is closed, the molten resin is injected into the injection mold and is branched by the branching portion 21 of the insert 2, and the branched molten resin then flows along the merging portion 22 to merge at a certain merging angle at a vertex angle of one end of the merging portion 22 away from the branching portion 21. The vertex angle of the end of the merging portion 22 remote from the diverging portion 21 is set to α, which is in a complementary relationship with the merging angle.

Thereafter, the molten resin was cooled and molded in an injection mold, and the injection mold was opened to obtain an evaluation structure 1. As shown in fig. 3, the evaluation structure 1 includes a hole site structure 11 and a weld line 12, wherein the hole site structure 11 is formed in the form of an insert 2, and the shape of the hole site structure 11 is identical to that of the insert 2 and is symmetrical left and right. The weld line 12 is a thin line generated by incomplete fusion of the molten resins from different directions at the fusion portion 22 at a certain fusion angle.

By changing the fusion angle of the molten resin by replacing the insert 2 having a different α fusion portion 22 in the injection mold, a different fusion-bonding line 12 is obtained. Wherein α ranges from 0 ° to 180 °. Further, the appearance and mechanical properties of the weld line 12 are tested, and the appearance and mechanical properties of the weld line 12 caused by different fusion angles of the molten resin during injection molding can be effectively evaluated.

Fig. 4 is a schematic view of an evaluation structure 1 and a corresponding insert 2 according to an embodiment of the present invention. The evaluation structure 1 shown in fig. 4(b) was obtained by replacing the insert 2 having a different α junction portion as shown in fig. 4(a) in the injection mold so that the fusion angles of the molten resins were 90 °, 135 °, and 150 °, respectively. As shown in fig. 4(b), when the fusion angle is 90 °, the weld line 12 is long, has a more pronounced V-shaped notch and is deeper; the weld line 12 having a convergence angle of 135 ° is shallower than the weld line 12 having a convergence angle of 90 °, the length is shorter, and no significant V-shaped notch is observed; the weld line 12 having a fusion angle of 150 ° was least noticeable in the three sets of weld lines 12 and was hardly observed. The quality of the weld line can be qualitatively evaluated from the depth and length of the weld line, and from the above appearance results, the quality of the weld line is relatively good when the depth and length of the weld line having a convergence angle of 150 ° are shallow and short.

Further, the weld line 12 was quantitatively evaluated for mechanical properties by testing the tensile strength of the weld line 12 using a plastic tensile property test method (ISO527/2), the bending strength using a plastic-bending property measurement method (ISO178), and the impact strength using a plastic-cantilever beam impact test method (ISO 180). The evaluation results were as follows:

TABLE 1 weld line tensile, flexural and impact Strength test results

Convergence angle (°)	Tensile Strength (MPa)	Flexural Strength (MPa)	Impact Strength (kJ/m)²)
				90	15.46	1638	25.71
120	16.56	1755	27.54
				150	17.48	1852	29.07

As is apparent from Table 1, when the fusion angle of the weld lines was 90 °, the tensile strength was 15.46MPa, the bending strength was 1638MPa, and the impact strength was 25.71kJ/m²(ii) a When the fusion angle of the weld line is 120 degrees, the tensile strength is 16.56MPa, the bending strength is 1755MPa, and the impact strength is 27.54kJ/m²(ii) a When the fusion angle of the weld line was 150 degrees, the tensile strength was 17.48MPa, the flexural strength was 1852MPa, and the impact strength was 29.07kJ/m². From the above evaluation results, it is understood that the larger the fusion angle of the weld line 12, the larger the tensile strength, bending strength and impact strength at the weld line position, and the less likely the weld line position is to be deformed or broken.

As shown in fig. 5, in the present embodiment, the length of the bottom side of the flow dividing portion 21 is L1, the width of the gate is L2, the height of the flow dividing portion 21 is h1, the distance from the flow dividing portion 21 to the gate when the insert 2 is fixed in the injection mold is h2, and t is the wall thickness of the evaluation structure 1. The size of h1, i.e., the height of the flow dividing portion 21 affects the flow dividing of the molten resin; the size of h2, i.e., the distance from the flow dividing portion 21 to the gate, affects the flow direction of the molten resin. Wherein h2 is less than h1, and h1 is less than L1. Preferably, the above parameters satisfy the following formula:

L2≥L1，L1≥10t。

the appearance and the mechanical property of the welding line 12 with different fusion angles of the plastic to be evaluated can be obtained by the evaluation kit and the evaluation method. In a specific embodiment, an ABS material is used for injection molding to produce an induction cooker base, and the injection molding simulation analysis finds that the position of the induction cooker base radiating grid is provided with a weld line 12 with a 70-degree convergence angle, and the induction cooker base radiating grid is large in size and irregular in shape, so that the weld line 12 at the position cannot be conveniently evaluated by using a test instrument. The invention uses ABS material which is the same as the part to obtain the evaluation structure 1 with the 70-degree fusion angle welding line 12 through injection molding of the evaluation kit, and can conveniently evaluate the appearance and the mechanical property of the evaluation structure 1, thereby judging whether the appearance and the mechanical property of the base of the induction cooker meet the requirements or not.

Therefore, the invention provides an evaluation kit and an evaluation method of a plastic welding line. By replacing inserts of different shapes in the injection mold, the fusion angle of the molten resin is changed, and the evaluation structure with fusion lines of different fusion angles is obtained. And then the appearance and the mechanical property of the welding line are tested, so that the appearance and the mechanical property of the welding line generated by different fusion angles of the molten resin during injection molding can be effectively and accurately evaluated.

The above description is only exemplary of the present invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating a plastic weld line is characterized by comprising the following steps:

step five: and evaluating the quality of the welding line.

2. A method for evaluating a weld line of plastics according to claim 1, wherein said insert is prepared in said first step in more than one number;

3. The method of claim 1, wherein the evaluating in step five comprises evaluating the appearance and/or mechanical properties of the weld line.

4. The method for evaluating a plastic weld line according to claim 3, wherein in the fifth step, the appearance of the weld line is evaluated by providing the depth, length, morphology or structure of the weld line; and/or evaluating the mechanical properties of the weld line by testing the tensile strength, bending strength and impact strength of the weld line.

5. The method for evaluating the plastic weld line according to claim 1, wherein the step three is to fix the insert in the injection mold, specifically by means of adhesion, magnetic attraction or embedding.

6. The insert for evaluating the plastic welding line is characterized by comprising a flow dividing part and a converging part, wherein the shape of the converging part is triangular, and the vertex angle of one end of the converging part, which is far away from the flow dividing part, is set as the complement angle of the converging angle of the molten resin; setting the extending direction of the opposite sides of the vertex angle to be transverse, and setting the direction vertical to the opposite sides in the plane of the junction part to be longitudinal; the lateral length of the flow dividing portion increases in the longitudinal direction from a direction away from the opposite edge to a direction close to the opposite edge.

7. The plastic weld line evaluation insert of claim 6, wherein the shunt portion is in the shape of any one of a triangle, a semicircle or a polygon.

8. The plastic weld line evaluation insert of claim 6, wherein the insert is of a left-right symmetrical configuration.

9. The plastic weld line evaluation insert of claim 6, wherein the insert is made of a material resistant to temperatures higher than the melting temperature of the resin.

10. The plastic weld line evaluation insert of claim 6, wherein the bottom side of the flow dividing portion is L1, the width of the gate is L2, and t is the wall thickness of the evaluation structure, and the above parameters satisfy the following formula:

L2≥L1，L1≥10t。

11. a plastic weld line evaluation kit comprising an insert and an injection mold having a gate and capable of receiving the insert; the insert is according to any one of claims 10-14.

12. The insert for evaluating the plastic welding line according to claim 11, wherein an adhesive structure, a magnetic attraction structure or an embedding structure is arranged between the insert and the injection mold.