Determining the influence of the roughness at the contact surface for the injection mould bi-component parts.

Mihaila, Stefan ; Ilie, Sorin ; Porumb, Camelia 等

1. INTRODUCTION

One of the most important characteristic of an injection bicomponents plasticity part is the adhesion between the two components. Why is this characteristic the most important? Because, all the injection mould, bi-component parts needs to be absolute inseparable all of his life time. This made the difference between an assembly part from two different plastics parts components and an injection molding bi-components plastic part. (Fig. 1)

[FIGURE 1 OMITTED]

The adhesion or the bonding between the two components are influence of a few factories like the chemical affinity between the different plastics materials, the injection mould parameters of the bi-component molding injection machine and also the roughness of the contact surface between the two components. The last one I thing was not enough study he has a big influence for the adhesion between the two components. This influence has also theoretical fundamental explications but, also was demonstrated with several experimental researches using an experimental mould for bi-components laboratory samples for tensile test.

2. CASE OF STUDY

I have used same metallic inserts which I have positioned in the cavity of the mould with five different roughness (Fig.2.) at the contact surface between the two components .These roughness have been made using classical cutting methods, like: milling, polishing and sand blasting. The values of the roughness chosen for study are presented in the table. (Tab.1.), these values are very different with big variations to see their influence into the bonding between the two components of an injection bi-components plastic part.

[FIGURE 2 OMITTED]

I have injected several laboratory bi-component samples using a soft polyurethane material for the first component and a hard and rigid polyurethane thermoplastic material for the second component. I have use firstly component the soft polyurethane named LRP5260 and for the second component the hard polyurethane LRP 5260.

To define the best injection mould parameters to inject the laboratories samples using a bi-component injection mould machines, I have used CAE programs which simulate the bi-component injection process. For this reason I have design with a big accuracy the 3D model of the laboratory samples which are injected at one shot of a bi-component injection mould machine, (Fig.3).

Using the characteristics of the two polyurethanes from the data base and the 3 D model of the laboratory samples, the CAE programs simulate the injections mould bi-component process. After several iterations the computers simulate the program which calculates the best injection condition recommended for inject the laboratory samples on an injection mould machine. (Ilie, 2008)

[FIGURE 3 OMITTED]

These best injection conditions are: injection time, mould temperature, melt temperature of the two components and most important the melt temperature at the contact surface between the two components.(FigA).

[FIGURE 4 OMITTED]

Using the results of CAE simulation program I have adjust all the parameters of the bi- component injection machine to obtain same values of the computer simulation. The principal injection parameters which I have set for the first thermo plasticity material and also for the second are: mould temperature, melt temperature, injection speed, holding pressure, holding time and cooling time. I have injected 15 laboratory samples (fig.5.) with each special metallic inserts (notated A, B, C, D and E) using exactly the same parameters for the bi-component injection machine presented in table. (Tab. 2.).

3. CONCLUSIONS

I can say that, these results show the influence of the roughness of the contact surface for the injection mould bi-components parts. Because all the other parameters of the bi-component injection mould machine was constant only one variable can be the cause of different values of the tensile force at bonding break. The results show us such as, increase the roughness of the contact surface between two polyurethanes thermoplastic for an injection mould bi-components part the adhesion between the two components also increase. But this value of the bonding between the two components has a limit value and she is depending of the roughness of the contact surface and also the local injection condition. The local mould condition are very important because depend of this values we can influence the thickness of the interfusion layer.

These conclusions are very important for the plasticity literature because I like to clarify the very different and opposite opinions about adhesion of multi components injected parts.

Research for the future:

In this area you can make more research on the influence of pigments on the adhesion of the injected bi component parts.

4. REFERENCES:

Ilie, S., (2008). Study to determinate the influence of the roughness at the contact surface for the injection molding of the bi-components parts, Annals of the Oradea University pp 1499-1502. ISSN 1583-0691, Vol.7. May 2008

Mihaila, s.., Chira, D., Ungur, P.. (2007) Stady regarding the analysis of the injection process of the two-components products. The 1st International Conference on Polymers Processing in Engineering, PPE. pp 60-66, ISBN 978-973-30-1970-1,. Gala|i, Romania October 2007

Seres, I. (1999). Moulds for injection. ISBN 973-8195-42. West Publishing printing Oradea.

*** (2004) Combimelt: Composite injection-molding technique for hard-soft material combinations, Technical Information by Engel

*** (2005)Examples of multi-component mould designs, ARBURG processing technology

Tab. 1. Roughness value for different metallic insets

Designation [R.sub.a] [R.sub.z]
of insert [[micro]m] [[micro]m]

Insert A 3,2 12,5
Insert B 0,1 0,5
Insert C 1,6 8
Insert D 25 50
Insert E 50 200

Tab. 2. The value sets for the bi-component injection machine
used for the experimental trials

Name of the injection Values for the Values for the
parameters first component second component

Melt temperature [[degrees]C] 220 240
Mould temperature 45 45
Injection time [s] 2,50 0,58
Switch over pressure [bars] 150 100
Holding pressure [bars] 200 200
Holding time [s] 20 16
Cooling time [s] 18 12