Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With product ejector
Reexamination Certificate
2002-01-07
2003-11-25
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With product ejector
C425S577000, C264S334000
Reexamination Certificate
active
06652263
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an injection moulding assembly and a mould therefor and, more specifically, such a mould comprising two mutually joinable mould halves which in their joined state define at least one cavity, and a sprue formed in the mould for passing a melt to each cavity.
BACKGROUND ART
In injection moulding of a plastic component, a plastic melt is introduced into a cavity defined by two mould halves of a mould. More specifically, the plastic melt is passed through a channel system extended in the mould, such as a hot runner system, up to an ingate through which the melt enters the cavity.
It will be appreciated that the ingate causes a surface defect in the component. The location and design of the ingate is thus dependent on the surface requirements that are placed on the completed component.
In some cases it is desirable for the surface defect caused by the ingate to be as small as possible and located on an inside or rear side of the component. The ingate is placed on a side of the cavity that corresponds to the inside or rear side of the component. Examples of components where it is most important for such minor surface defects to appear on a side that is not exposed to the surroundings are high status products, such as casings for mobile phones.
This can be achieved, for example, by placing a suitably designed ingate directly at the end of the hot runner system and simultaneously forming the cavity in such manner that the inside of the component faces the hot runner system.
This solution, however, suffers from a number of drawbacks. For removing the completed component from the mould, ejectors are normally used, which when operated are caused to engage the component. Ejectors are normally arranged in such manner as to engage the inside of the component so as to guarantee an outside without surface defects caused by the ejectors. To render this possible in the solution described above, the ejectors must thus be arranged in the same mould half as the hot runner system. The hot runner system, which is usually arranged in a fixed first mould half, is however in most cases fairly bulky, and therefore it may be difficult to find space for the ejectors in the same mould half as said hot runner system. Moreover, it may be difficult to arrange the mechanism that drives the ejectors in the fixed mould half.
It is thus common to arrange the ejectors in a movable second mould half and, if the ejectors are to engage an inside of the component, consequently it is necessary to conduct the melt from the hot runner system, on to the second mould half and then on to the ingate which leads to the cavity on a side corresponding to the inside of the component.
A prior art method of accomplishing this is illustrated in
FIGS. 1-4
. According to this solution, an insert
101
is arranged in the second mould half
102
. The insert
101
defines two interconnected channels
103
,
104
. A first
103
of the channels forms an extension of an ejector channel
105
formed in the second mould half
102
. A second
104
of the channels forms a trunk-like intake and extends arcuately in and under the cavity
106
and leads to an ingate positioned on a side of the cavity
106
corresponding to the inside of the component.
In said ejector channel
105
, a first ejector
110
is arranged, which thus forms a demarcation of the first channel
103
.
When producing a component
107
, a melt
108
is introduced through a hot runner system
109
into the two channels
103
,
104
, which is clearly to be seen in FIG.
2
.
That part of the melt
108
which is introduced into the second channel
104
fills the cavity
106
through the ingate
111
.
The injection moulded component
107
is then cooled, after which the mould halves
102
,
112
are divided and the ejectors
110
,
113
operated, as shown in FIG.
3
.
By operation of the ejectors
110
,
113
they are caused to engage the component
107
for ejection.
That part of the melt
107
which fills the two channels
103
,
104
forms a sprue slug
114
. When operating the ejectors
110
,
113
, the first ejector
110
will engage the cylindrical part
115
of the sprue slug
114
which fills the first channel
103
. By ensuring that the length of the first channel
103
is greater than the length of the arcuate portion
116
of the second channel
104
it is ensured that the trunk-like part
117
of the sprue slug
114
which fills said arcuate portion
116
is released from the component
107
and extracted from the arcuate portion
116
.
FIG. 4
illustrates both the component
107
and the sprue slug
114
in the ejected state.
This prior art method, however, suffers from a number of drawbacks. First, it causes a considerable amount of waste material in the form of sprue slugs
114
. The insert
101
must be made of two pieces which in their joined state define said channels
103
,
104
. The reason for this is that it would otherwise not be possible to provide said arcuate portion
104
of the second channel
104
. Finally, there is a risk of the trunk-like part
117
of the sprue slug
114
being broken off from the cylindrical part
115
. In particular it will be impossible to use non-elastic plastics in injection moulding, such as thermosetting plastics or reinforced plastics.
There is thus a need for an improved method of producing components which have a minor surface defect caused by an ingate on their insides or rear sides.
SUMMARY OF THE INVENTION
In view of that stated above, an object of the present invention is to provide an improved mould for producing plastic components.
Another object is to provide such a mould for producing components which have a minor surface defect caused by an ingate on a side that is not exposed to the surroundings.
It is also an object of the invention to provide an injection moulding assembly having such a mould.
According to the present invention, the above objects and also other objects that will appear from the following description are achieved by a mould having the features stated in claim
1
and an injection moulding assembly having the features stated in claim
10
. Preferred embodiments of the mould are evident from claims
2
-
9
.
More specifically, according to the present invention a mould is provided, comprising two mutually joinable mould halves which in their joined state define at least one cavity and a sprue formed in the mould for passing a melt to each cavity, said mould being characterised in that the sprue comprises an ingate portion connecting to each cavity and formed in a first ejector of an ejector means.
This results in an improved mould which allows production of components having a minor surface defect caused by an ingate and located on an inside or rear side of each component. This is achieved thanks to the fact that the sprue that passes the melt to the cavity comprises an ingate portion contained in one of the ejectors. As a result, the need for complicated inserts in the mould is eliminated while at the same time it will be possible to injection mould components of reinforced plastics or thermosetting plastics.
According to a preferred embodiment of the inventive mould, the ejector means comprises additional ejectors, each ejector being arranged in an ejector channel formed in said second mould half. Said first ejector is advantageously adapted to perform its ejecting motion with a time delay in relation to the other ejectors. This makes it possible to accomplish release of a sprue slug from the completed component during the initial ejecting process. For instance, this can be achieved by the mould comprising press pins which are insertable into said ejector channels for engaging the ejectors. The press pin which engages said first ejector is arranged in such manner that its engagement is delayed in terms of time compared with the engagement of the other press pins with associated ejectors.
According to another preferred embodiment, the ingate portion contained in said first ejector comprises an inlet in the circumferential surface of the eje
Burns Doane Swecker & Mathis L.L.P.
Heitbrink Tim
Nolato AB
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