Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
1999-01-20
2001-05-01
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S328160
Reexamination Certificate
active
06224813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling the temperature of a mold for an injection molding and more particularly, to a method for controlling the temperature of a mold for an injection molding for restraining the generation of a weld line and a chromatic aberration at the position where two melted and separated resins flow together, by separately controlling the temperature of each region of the mold.
2. Description of the Related Art
Generally, among the molding conditions of the injection molding, injecting pressure, injecting velocity, weighing and the temperature of the injector can be controlled using a controller mounted on the injector. However, the temperature of the mold should be separately and externally controlled. Otherwise, the control of the temperature of the mold is difficult.
At this time, when the temperature of the mold is controlled simply by cold water, the temperature of the mold becomes different on each region of the mold because of the change of the external environment and the flow of the melted resin in the cavity. Therefore, a continuous working for manufacturing a good product could not be accomplished. Further, even though the continuous working is not required, the molding condition should be frequently changed for the stability of the products. If the temperature of the mold is not constantly controlled, the standardization of the molding condition could not be accomplished due to the change of the injecting pressure, injecting velocity, etc.
Even though the size of the mold is dependent on the size of the mould product, initial defect may be generated during increasing the temperature of the mold from the low temperature state of the mold to the temperature of the mold where the good product can be obtained. As a result, the establishment of the standard molding condition is difficult.
For solving the above-mentioned problem, generally the injecting pressure is increased. In this case, the temperature of the mold increases to some degree according to the increase of the injecting pressure, however, burr of the mould product at the parting line may be generated.
FIG. 1
illustrates the relation of the temperature of the mold with respect to the distribution of the number of defects. Region A corresponds to the portion at which the molding is not completed and so a compression defect is generated. Region B corresponds to the medium portion of the good product and the defect. At region B, a crack may be generated owing to the defect of the weld line and this portion affects the reliability of the product. For minimizing this region, the mold is heated in advance through implementing a preheating process for stabilizing the temperature of the mold.
It is important to keep the temperature of the mold at a constant degree through heating as described above, however, it also is important to cool the mold for the cycle time of the mold.
The controlling of the temperature of the mold plays an important role for improving the productivity of the product and also plays an important role for generating the defect of the product.
That is, when the temperature of the mold is not homogeneous, a compression defect is generated at a boss portion and/or a rib portion where compression degrees are great. And when the temperature of the mold is too low, the molding is not completed or a silver streak defect is generated. Further, a defect of deflection deformation also is generated owing to the regional difference of the mold temperature.
Among the defects, the weld line generated on the surface of the product, is formed as a thin solid line at the portion where two melted and separated resins flow together in the mold. The main reason of the generation of the weld line is the incomplete mixing of the two separated and melted resins at the meeting portion because of the low temperature of the front end portions of two resins. The weld line also can be generated by moisture or a volatile matter contained in the resin, or by a mold release used during the injection molding.
Particularly, the generation of the weld line is caused when a hole is present in a mould product or two gates are present in the mold. For carrying out the injection molding, the gate for passing the resin is needed. And when the mould product is large or complicated, two or more gates are needed. Accordingly, the weld line is liable to be formed. Even though the melted resin is supplied through one gate, when an inserting component or a hole is present in the mould product or when the building thickness of the mould product is different, the weld line may be generated.
FIGS. 2A and 2B
are typical views for explaining the generating process of the weld line. The melted resin is supplied into the cavity through two gates
12
and
14
and a weld line
16
is generated where the two separated portions of the resin flow together as shown in FIG.
2
A.
At this time, the weld line is not formed even though the separated and melted resins flow together near the gates
12
and
14
but the weld line is formed far from the gates
12
and
14
. The melted resin gets cool through the mold and the two portions far from the gates
12
and
14
could not mix together completely because of the low temperature of the resins, thereby generating the weld line
16
.
Meanwhile, even though the melted resin is supplied through one gate
12
, the weld line
16
is generated when a hole
18
is provided in the mould product because the melted resin is separated around the hole
18
and then flow together, as shown in FIG.
2
B.
Thus formed weld line deteriorates the exterior view of the mould product and therefore, a painting process for eliminating the weld line is additionally implemented after the injection molding. This makes the working process complicated and increases the manufacturing cost.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention considering the above-mentioned problem, to provide a method for controlling the temperature of the mold for an injection molding for restraining the generation of a weld line at the position where two melted and separated resins flow together or restraining a chromatic aberration at the surface of a product, by separately controlling the temperature of each region of the mold.
To accomplish the object, there is provided in the present invention a method for controlling the temperature of a mold for the injection molding comprising an upper mold having a recess and a lower mold having a core portion protruded in the recess of the upper mold to form a mold cavity therebetween, said method comprising the steps of: controlling a temperature of a front surface portion of the upper mold neighboring a gate which is connected to a spool to which the melted resin is injected through a runner, as 65-75° C.; controlling a temperature of a side surface portion of the upper mold between the front surface portion and a parting line, as 45-55° C.; and controlling temperature of the core portion, as 35-45° C.
REFERENCES:
patent: 4338068 (1982-07-01), Suh et al.
patent: 5656228 (1997-08-01), Fujii et al.
patent: 5762972 (1998-06-01), Byon
patent: 5772933 (1998-06-01), Kotzab
patent: 5830515 (1998-11-01), Pleasant et al.
patent: 59-140040 (1984-08-01), None
patent: 62-176815 (1987-08-01), None
patent: 88/00116 (1988-01-01), None
Daewoo Electronics Co. Ltd.
Heitbrink Jill L.
Pillsbury Madison & Sutro LLP
LandOfFree
Method for controlling temperature of mold for injection... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for controlling temperature of mold for injection..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for controlling temperature of mold for injection... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2508225