The present invention refers to a particular kind of pick-up
plugs, ie. those devices which are adapted to engage respective plastic preforms
in view of supporting, orienting and carrying them throughout the various steps
which the preforms themselves go through for further processing, in particular during
the phases of temperature conditioning and blow moulding.
The term "pick-up plug" is a term taken from the technical
parlance that is commonly used in the particular branch, where such other terms
as "tournette", "mandrel", "preform holder", "carrier" are anyway also used to identify
the same device.
Therefore, the use of the term "pick-up plug" in this context
should not create any difficulty or confusion to those skilled in the art.
The task that a pick-up plug is required to perform lies
in engaging a respective preform by getting inserted in it, and then support it,
carry it through the various processing steps, and finally release it, at the end
of a processing cycle, by slipping off from it.
When chains of pick-up plugs are used in blow-moulding
installations, the number of such pick-up plugs is generally very large and this
imposes, for obvious reasons of costs and reliability, an as simple construction
Pick-up plugs can be subdivided into two main categories,
ie. inner-engagement devices and outer-engagement devices.
Pick-up plugs for inner engagement work by getting inserted
in the neck portion of the preform, whereas pick-up plugs for outer engagement work
by letting the neck portion of the preform into a portion thereof.
Generally speaking, the use of such pick-up plugs is connected
with following problems and drawbacks:
- the neck portions of the individual portions are actually variable in their
size and quite often exceed the specified dimensional tolerance limits;
- an insertion of pick-up plugs in preforms that are too small, out of tolerance
or at the limit thereof, proves quite difficult, if not almost impossible to be
carried out, since this would require a lot of strain with the risk of the preform
- too large preforms, out of tolerance or at the limit thereof, fall off during
All this involves real risks of shutdowns, and related
downtimes, of the entire production plant, with serious and easily imaginable economic
Pick-up plugs are known in the art which are provided with
an annular spring that is intended to ensure a firm grip of the preforms by slipping
thereinto; such springs may be in a toroidal or a cylindrical shape.
These pick-up plugs, however, have following drawbacks:
- the gripping force, ie. effect exerted by the spring depends to a considerable
extent on the actual diameter of the preform; in fact, it may quite easily occur
that such effect changes all too quickly from a condition of an inadequate or even
non-existing grip in the case of a too large perform, to a condition of an excessively
strong grip, and resulting stoppage due to jamming, in the case of too small a preform;
- in the case of such a jamming or stoppage situation, the considerable axial
insertion or disengagement thrust pushes the annular spring against the edges of
the related housing, thereby increasing the force of friction opposing the contraction
thereof (which would in fact enable the preform to move).
A penalty could furthermore be imposed by an effect deriving
from the arc of the annular spring being squeezed , as this is illustrated schematically
in Figure 1.
Devices based on the use of such annular springs, owing
to the inherent nature thereof, do not allow for their axis to be maintained in
position in an adequately accurate manner (the ring tends to move and get displaced
in its housing) and, during the passage through the conditioning ovens, the preforms
come in this way to rotate about an off-centre axis; this of course causes the preforms
to undergo a non-symmetric heating effect.
All above cited drawbacks are referred to pick-up plugs
for inner engagement of the preforms. In the case of pick-up plugs intended for
outer engagement of the preforms, similar drawbacks are experienced, which should
however be described in a reversed manner, owing to the different and symmetrical
coupling intervening between an outer-engagement pick-up plug and the preform. However,
since such a description is perfectly and readily imaginable by all those skilled
in the art, it is intentionally omitted here for reasons of greater brevity.
Largely known in the art there are also inner-engagement
pick-up plugs that make use of rings made of elastic polymeric material; although
these pick-up plugs actually seem effective in reducing or doing away with some
of the above cited drawbacks, they anyway still have a number of other drawbacks
left that may be summarized as follows:
- difficulty in obtaining a stable, constant quality, as well as adjustment and
- sensitiveness of the polymeric material to the heat developed in conditioning
ovens, under a resulting quick deterioration of the quality and the performance
- need for an additional mechanical function to be provided to ensure compression
and decompression of the annular elastomeric joint.
Also known in the art, eg. from the disclosure in US 4,678,425
in the name of Cincinnati Milacron Inc., there are pick-up plugs in which the function
of engaging the respective preform is assigned to a cylindrical elastic portion
of the pick-up plug to be inserted in the preform, as well as to an appropriate
annular protuberance (bulge 70) provided on said elastic portion. However, this
solution has some serious drawbacks, such as in the first place the utmost rigidity
(in the sense of aptitude to comply) with respect to even very small variations
in the inside diameter of the neck portion of the preform.
From US 4,483,436 a pick-up plug (so-called collet) is
known, which is rotatably journalled within the bar so that it may be rotated to
facilitate the even heating preforms; the lower end of each collet is provided with
ball detents devices which are so associated with a retaining surface on each preform
so as to effect a tight, but releasable holding of the preform able to perform a
snap engagement with the relevant preform.
This is a type of pick-up plug whose drawbacks have already
been described in the above comments relevant to the annular spring plugs, and therefore
will not be repeated.
From US 4,487,568 a type of pick-up (carrier) is known,
in which the preforms are clamped by a type of gripper assemblies 206, which are
basically realised by opposing levers 232, 236 pivoted on relevant pivot pins; however
this type of preform engagement results in a quite wearing and complicate assembly
From US 4,199,183 an internal gripper is known, provided
with gripper fingers 58 extending outwardly and inclined so as to engage with the
containers 24 and more particularly with the inner region of the slight step or
ridge 92 adjacent to the top of the container.
This kind of gripper too requires a very complicate way
of use as said fingers have to be independently controlled in each time of operation
by proper corresponding mechanism.
In conclusion, currently employed pick-up plugs prove quite
difficult to adjust and scarcely adaptable to the dimensional variations of the
preforms; as a result, they give rise to reductions in the industrial efficiencies
of the production plants using them, owing to frequent accidents occurring in the
insertion or release of the preforms, or even during the transport thereof.
Moreover, the need arises for all pick-up plugs in a plant
to be duly replaced whenever the type of preforms being processed is going to be
changed, regardless of such preforms being more or less similar dimensionally to
the previously processed ones.
Based on the above considerations, it is therefore desirable,
and it is actually a main purpose of the present invention, to provide pick-up plugs,
both of the inner-engagement and outer-engagement type, of a kind that is capable
of automatically minimizing or doing away with the above mentioned drawbacks.
Furthermore, such pick-up plugs shall be capable of being
easily implemented using readily available and, therefore, cost-effective materials
Such an aim of the present invention, along with further
features thereof, is reached in pick-up plugs of a kind that is made and operates
as recited in the appended claims.
The present invention may take the form of a preferred,
although not sole embodiment such as the one that is described in detail and illustrated
below by way of non-limiting example with reference to the accompanying drawings,
- Figure 1 is a conventional pick-up plug;
- Figure 2 is an inclined outer perspective view of a pick-up plug generally according
to the present invention;
- Figure 2a is a median-section view of a portion of the pick-up plug illustrated
in Figure 1;
- Figure 2b is a view of the portion of pick-up plug illustrated in Figure 2a,
in a particular condition and position thereof;
- Figure 3 is a median-section view of a pick-up plug according to an improvement
of the present invention;
- Figure 4 is a perspective view of a component part of the pick-up plug illustrated
in Figure 3;
- Figure 4a is a cross-section view, orthogonally to the axis thereof, of the
component part illustrated in Figure 4;
- Figure 5 is a perspective view of a different component part of the pick-up
plug illustrated in Figure 3;
- Figure 6 is a plan side view of the component part illustrated in Figure 5;
- Figure 7 is a schematised vectorial view of the forces acting on a preform that
is firmly applied to a pick-up plug according to the present invention;
- Figure 8 is a schematised vectorial view of the forces acting on a preform during
the phases in which a preform is inserted in and released from a pick-up plug according
to the present invention;
- Figure 9 is a diagrammatical view of two curves representing the characteristic
evolution of the values of elastic strength of two elastic members included in the
pick-up plug according to the prior art (A) and the present invention (B), respectively;
- Figure 10 is a median vertical section view of an outer-engagement type of pick-up
plug according to the present invention;
- Figure 11 is an enlarged view of a portion of the pick-up plug illustrated in
- Figure 12 is a plan section view of the pick-up plug illustrated in Figure 10,
as taken from the section plane B - B that is orthogonal to the axis of the pick-up
With reference to the above listed Figures, an inner-engagement
type of pick-up plug according to the present invention comprises a central body
1, on the outer cylindrical surface of which there are provided a plurality of groove-like
recesses 2 that open radially outwards.
In each one of these groove-like recesses there is arranged
a respective individual and independent gripping member 3 adapted to protrude outwards
from the cylindrical surface of said central body.
In order to ensure that said gripping members are all able
to at the same time expand radially outwards, thereby engaging the inner surface
of the preform, each one of such gripping members is forced and pressed outwardly
by a respective spring 4 that is provided in the gap existing between the inner
wall 5 of each such gripping member and the face 6 looking towards the outside of
the respective groove-like recess. As a result, each such groove-like recess holds
both a respective gripping member and the related spring.
As illustrated in Figures 2 and 2a, the simplest possible
embodiment involves a pick-up plug, in which on the edges of said groove-like recesses
there are provided appropriate prominences 7, and the related gripping member is
provided with corresponding appendices 8 in such a manner as to make it possible
for said prominences 7 and said appendices 8 to engage each other under the action
of the spring 4, wherein said gripping members are at the same time retained and
prevented from disengaging by the respective groove-like recess.
Through an appropriate sizing of the various parts involved
in relation to each other, the possibility is given for a pick-up plug to be provided,
in which the engagement means enable the pick-up plug to be inserted under the action
of just a small insertion force, even if the preforms to be so inserted may actually
have some slight variations, ie. tolerances in the inside diameter thereof.
However, this solution still retains two of the afore described
- a) the strain involved in the insertion of the preform may still prove quite
considerable in the case of preforms with a reduced diameter, whereas when the same
preforms must then be released, ie. removed therefrom, it is highly desirable that
the ejection strain is as low as possible, anyway compatibly with the need for the
preforms to be prevented from releasing and falling off accidentally, as this might
for instance occur owing to vibrations or abrupt changes in the orientation thereof:
these quite obviously are mutually contrasting requirements and the proposed solution
does not solve such a contradiction;
- b) when preforms having different inside diameters are processed, in order to
allow for and take the largest inside diameter into due account, the need arises
for the gripping member 3 to protrude by a distance h (see Figure 2b), which may
actually prove excessive when preforms with a minimum diameter (as referred of course
to the diameter of the body of the pick-up plug) are on the contrary handled, owing
to the considerable interference that would derive therefrom; under such circumstances,
the need would therefore still arise for the pick-up plugs to be each time replaced
with conespondingly sized ones and this would in turn force the entire plant to
be shut down and, as a result, put quite heavy a penalty on the overall productivity
and efficiency thereof.
To the purpose of doing away with such drawbacks, the following
described improvement is therefore adopted: with reference to Figures 3, 4 and 4a,
the groove-like recess 2 is provided with a niche 22 at an extremity thereof, which
preferably is the extremity oriented towards the edge 13 of the pick-up plug to
be inserted in the preform, as this shall be explained in greater detail further
In correspondence thereto, also the gripping member 3 is
so shaped as to provide an appendix 33 having following characteristics:
- a) said appendix 33 is capable of being accommodated into a corresponding niche
- b) the sizing and the geometry selected for the appendix and the respective
niche in relation to each other are such as to allow for a partial rotation of the
gripping member 3 about an axis Y that is centred on said niche 22 and substantially
orthogonal to both the axis X of the pick-up plug and the radial straight line R
joining the centre of said niche with said axis X.
In substance, the gripping member is as if it were "hinged
on" and constrained to rotate with its own appendix within the respective niche,
so that no real physical pivot member actually exists, but the instant axis of rotation
is determined by the constraint for the appendix to constantly remain inside the
As far as the spring 4 is concerned, it is quite logically
arranged so as to be able to act on to the free side of said gripping member; such
a contrivance, along with other construction-related solutions, can be easily inferred,
without any need for particular explanations, from the illustration in Figure 3.
The preferred geometry of the gripping member 3 is on the
contrary illustrated in Figures 5 and 6.
Furthermore, in view of attaining the best possible stability
of and centering effect in relation to the preform, said groove-like recesses and
the respective gripping members shall be at least in the number of three and shall
further be preferably distributed in a uniform manner along the outer surface of
the pick-up plug.
Figures 4 and 4a illustrate the toroidal portion 12 of
the pick-up plug, which comprises three groove-like recesses 2 as shown without
the related gripping members.
As brought about in this manner, the positioning of the
axis of rotation of the gripping members with respect to the friction zones of the
preforms enables the so-called "harpoon effect" to be appropriately dosed, in the
sense of facilitating the insertion of the preform and, on the other hand, hindering
it from disengaging and falling off.
In a simplified manner, the above cited "harpoon effect"
may be explained as follows: with reference to Figure 7, the gripping member 3 is
represented by the segment OA, the preform is shown by the body 15, and the force
acting on said gripping member 3 is the sole torque of rotation F (in fact, no other
forces act on the gripping member 3 than those that are totally counterbalanced).
When the preform 15 is standing still, said rotating torque
F acts on to the contact point A with a force G, which may be broken down into a
force component G1, which is orthogonal to the contact wall 16 of the preform 15,
and a tangential force G2, which has of course the same direction as the wall 16
that is so rectilinear.
Said force G2 would bring about a vertical displacement
of the preform, which would be in turn opposed by a respective friction; however,
since the preform is constrained to remain still, such a friction does not come
about and said force is necessarily compensated.
When the preform is displaced vertically in the direction
of insertion, as this is shown in Figure 8, on to the point A there is also applied
the force T that opposes friction, and, if such a force is brought back to the extreme
B of the force vector of the force G, an overall force vector of the forces G and
T represented by S, ie. by the vector of the segment AD, will be obtained.
It can therefore be clearly appreciated that, during the
insertion of the preform, the tangential force acting on the preform is given by
the segment CD, which is obviously lower than the segment CB.
If the preform is at this point displaced vertically in
the direction of disengagement, ie. release, as this is shown again in Figure 8,
on to the point A there is also applied the force U, that adds up to friction, and
if such a force is brought back again to the extreme B of the force vector of the
force G, an overall force vector of the two forces G and U represented by Z, ie.
by the vector of the segment AN, will be obtained.
It can therefore be clearly appreciated that, during the
release of the preform, the tangential force acting on the preform is given by the
segment CN, which is obviously higher than the segment CD.
Anyway, such a "harpoon effect", apart from the explanations
of a technical nature that may be given in view of describing the working mechanism
thereof, is a universally known fact as continuously verified by common experience.
A further advantageous improvement derives from the fact
that the springs 4 are appropriately preloaded in such a manner as to obtain that
said gripping members 3 are permanently forced, ie. biased into the outermost position,
so that all preforms, which can be inserted in the central body of the pick-up plug,
are at the same time capable of being engaged by said gripping members with a sensibly
constant pressure and, within certain limits, regardless of their inside diameter.
With reference to the diagram illustrated in Figure 9,
this can be noticed to include two curves showing the evolution of the pressure
of the gripping member as a function of the inside diameter of a general preform,
in which A is used to indicate the curve relating to the case of a non-preloaded
spring 4, while B indicates a similar curve referred to the case of a pre-loaded
spring: given the minimum and maximum deviations that are actually attainable by
said diameter, it can be readily observed that, if the spring is selected in a correct
manner with respect to said deviations, the minimum and maximum values, min and
max respectively, (curve B) reached by the pressure of the spring are almost constant,
and anyway significantly closer to each other, than the minimum and maximum values,
MIN and MAX respectively, taken by the pressure of the non-preloaded spring (curve
The above described embodiment of the present invention
allows for a number of further improvements: it has in fact been observed that the
afore mentioned "harpoon effect" can be enhanced if the outer surface 9 of the gripping
member 3 is so shaped as to feature a convex curvature towards the outside, as this
is best shown in Figure 6; furthermore, with reference to Figure 3, it has similarly
been found that, to the purpose of facilitating the insertion of preforms with a
minimum inside diameter, it proves suitable for the outer surface 10 of the cylindrical
portion of pick-up plug that is adjacent to said groove-like recesses and opposed
to the insertion edge thereof, with respect to said groove-like recesses, to be
in the shape of a frustum of cone or a flared shape.
A further advantageous embodiment of the present invention
consists in providing said individual and independent gripping members 3, 103, at
their extremity that is opposed to said respective terminal appendix 33 thereof,
with a stop surface 14, 1014 that is adapted to move into abutting, as pushed by
the spring, against a portion of the surface 10, 1010 of the central body 1, 101;
said surface is of course located on the opposite side with respect to said terminal
By suitably sizing and shaping the parts involved in the
process, this enables the travel and, therefore, the excursion of said gripping
member 3 towards the interior or, anyway, towards the neck of the preform to be
limited; such a value may therefore be freely selected so as to ensure that the
gripping member 3 protrudes to an adequate extent so as to be able to engage preforms
whose neck is small down to a pre-established value, but not so small as to hinder
the movement of or damage those preforms whose neck is larger or quite close to
maximum value that still enables the preform to be applied to the pick-up plug.
It will be appreciated that all the related manners of
construction and the various improvements are capable of being most readily figured
out, adapted and implemented by those skilled in the art, who will not find any
difficulty in interpreting the related numbering, which is similar to the numbering
adopted for the equivalent parts of the preform for inner engagement; with reference
to Figures 10, 11 and 12, which illustrate a pick-up plug for outer engagement,
all considerations set forth above apply in general in an analogous manner, while
the fact shall of course be taken into due account that the pick-up plug for outer
engagement of the preform is substantially constituted by a central body 101 formed
in the shape of an external crown that is provided internally with a cylindrical
cavity in which the related preform is inserted and then firmly held.
On the inner cylindrical side of such a crown there are
arranged both the groove-like recesses 102 and the gripping members 103, along with
the elastic devices 104, in a manner that is substantially symmetrical with respect
to what has been described above in connection with the afore considered cases.
In fact, in this case both the groove-like recesses and the gripping members are
directed inwardly, ie. towards the interior cavity in which the preform is inserted.
From the illustration in Figure 11 it can be readily inferred
that, in the case of a pick-up plug for outer engagement of the preform, such a
pick-up plug obviously engages, with its gripping members 103, corresponding portions
of the outer surface of the preform and, as a result, also the related threads 30.
Those skilled in the art will therefore readily understand
that the pick-up plug for outer engagement of the preform illustrated in Figures
10, 11 and 12 is substantially specular, as far as such functional members and parts
as the recesses 102, the gripping members 103, the springs 104, the niches 122 and
the related appendices 133, as well as the stop surfaces 1014 are concerned, to
a pick-up plug for inner engagement of the preform, eg. of the type that has been
illustrated and described earlier in this specification. As a matter of fact, the
pick-up plug is a device comprising surfaces that are provided with appropriate
means adapted to exert a controlled pressure against the walls of the neck portion
of the preform, wherein such a controlled pressure is produced by the reaction of
appropriate springs which, when they act from outside, press against the outer surface
of the walls of said neck portion, whereas, when they act from inside, they press
against the respective inner surface. If such gripping means are applied from outside,
they are supported in a corresponding carrier member that is generally defined as
pick-up plug for outer engagement, or the like. If on the contrary such means are
applied from inside, the respective carrier member is called by the name of pick-up
plug for inner engagement, or the like. Anyway, all such means and members may be
designed, made and described in an absolutely similar or equivalent manner.