Mold apparatus for molding containers and forming hole therein

A male and female mold parts combination for forming a latch opening in a container molded from a softened sheet of plastic having a female mold key member arranged on the female mold part; a male mold key member arranged on the male mold part; a cutting edge adjacent to a planar face of one key and a vertical surface having a bevelled edge surface on the other key. The keys being normally registered so that on closure of the mold parts, initial contact will involve the cutting edge, the bevelled edge surface and the plastic therebetween. One of the keys is fixed in one of the mold parts and the other of the keys being located in the other of the mold parts and free to move independently of its mold part so that on closure of the mold parts the cutting edge will ride off the bevelled edge surface and slide across the vertical surface piercing and enlarging a latch opening in the plastic. The free to move key is carried so that on separation of the mold parts it is returnable to its original position and attitude occupied just prior to said initial contact.

The present invention relates to a method for forming an orifice in a 
plastic part during the shape molding thereof and an apparatus for 
accomplishing the same. 
Beginning in the 1960's, thermoplastic containers began to compete with 
containers traditionally made of paper pulp or comparatively dense organic 
plastic materials. U.S. Pat. Nos. 3,845,187 and 3,862,817 (the disclosures 
of which are incorporated in their entirety herein) are concerned with the 
thermoplastic molding of containers such as egg cartons and the like. 
These patents teach that latch hole openings can be formed in the top 
front cover of egg cartons during the process of molding the container. 
The patents teach that moldable plastic is shape-molded by forming and 
compression between a pair of cooperating mold members; and, during this 
molding, key members cooperate with a combination of a bevel and oblique 
surfaces to first pierce said plastic, and, second, continuation of 
relative motion between the key members, enlarges the regions pierced to 
create the needed orifices by scraping and tearing the side edges. These 
orifices then serve as latch hole openings. They cooperate with a lower 
flap member and together form a secure latching arrangement which can keep 
the container structure closed. 
Automatic thermoformation equipment designed to form a plurality of 
structures simultaneously are normally massive pieces of equipment which 
are expected to continuously operate up to 3 work shifts per day, seven 
days a week. This equipment utilizes male and female mold members which 
define the thermoformed structures. Each half of the mold is a dense 
machined tool member which must stand up to repetitive thermoformation 
operations which not only involve physical force but rapid wide changes in 
temperature. Failure of even the smallest component of the mold structures 
will cause a shutdown of the thermoformation apparatus. If, for example, a 
thermoformation apparatus includes 8 egg carton molds, i.e., 16 half 
molds, a failure in any component part of any of the 16 half molds will 
cause a shutdown of the system until the cause is corrected. 
A common cause of shutdown in the system involves the key members utilized 
in the half molds for forming the orifices in the containers. In order to 
extend the life of the key members, at least one of them may be made to 
yield in a direction transverse to the closure of the molds in order to 
avoid destruction or early wear failure. These key members are usually 
spring biased so that this transverse motion can be permitted with return 
of the key member to its proper location after the transverse motion is 
completed. It has been suggested to either place a resilient member or a 
spring member behind one or the other of the key members so that during 
mold closures any misalignment of the key member will not lead to early 
self-destruction. These spring or elastic means have not always served the 
purpose for a reasonable period of time. Failure of the resilient or 
spring member leads to failure of the key members soon thereafter, or 
inadequate formation of latch holes. 
It is an object of the present invention to improve the reliability of the 
members employed to form the desired orifices in plastic parts. 
SUMMARY OF THE INVENTION 
The present invention is concerned with male and female mold parts 
combination for forming a latch opening in a container molded from a 
softened sheet of plastic. The combination includes: 
(a) a female mold key member arranged on said female mold part; 
(b) a male mold key member arranged on said male mold part; 
(c) a cutting edge on one key adjacent to a planar surface thereof and, a 
vertical surface having a bevelled edge surface on the other key, said 
keys being normally registered so that on closure of said mold parts, 
initial contact will involve said cutting edge, said bevelled edge surface 
and said plastic therebetween; 
(d) one of said keys being fixed in one of said mold parts and the other of 
said keys being located in the other of said mold parts and free to move 
independently of its mold part so that on closure of said mold parts said 
cutting edge will ride off said bevelled edge surface, said planar and 
vertical surfaces will assume a contacting parallel relationship and slide 
across one another, this action resulting in piercing and enlarging a 
latch opening in said plastic; and 
(e) said free to move key being carried so that, on separation of said mold 
parts, it is returnable by force of gravity to its original position 
occupied just prior to said initial contact. 
The present invention is also concerned with a process of creating an 
orifice in a plastic part during the shape molding thereof. In a prior art 
technique, moldable plastic is placed between a pair of conformable mold 
members and compression is applied thereto and, during said molding, 
opposed key members in each mold member pierce and form an orifice in the 
plastic. The process of the present invention utilizes an improvement in 
this process comprising: providing a cutting edge on one key member 
adjacent to a planar surface thereof and a vertical surface having a 
bevelled edge on the other key member, one of said keys being fixed in its 
mold part and the other key being located in its mold part and supported 
so as to be free to move independently thereof; registering said keys and 
closing said mold parts so that initial contact will involve said cutting 
edge, said bevelled edge and said plastic therebetween, on further closure 
riding said cutting edge off said bevelled edge surface, causing said 
planar and vertical surfaces to assume a contacting parallel relationship 
and to slide across one another thereby piercing and enlarging a latch 
opening in said plastic; and separating said mold parts, removing the 
shaped plastic and positioning the mold member carrying said free to move 
key so that it will return by force of gravity to its original position 
occupied just prior to said initial contact. 
It is important that the key that is free to move in relation to the mold 
half in which it is mounted, be returnable to its original position 
occupied just prior to said initial contact so that it will always be 
properly positioned and ready to form the next orifice during the next 
molding cycle. As alternatives to it being returnable by force of gravity, 
there are several other techniques which can be employed to return this 
key to its appropriate position. One alternative technique involves the 
use of magnetic forces in order to draw the movable key back to its 
original position. Further details of this technique will be discussed 
below. Yet another alternative technique for returning this key to its 
original position is to employ hydraulically transmitted forces which act 
on the movable key to return it to its original position. Yet another 
technique is to return the key in response to the force of propelled gas, 
e.g., a short blast of air. This technique is particularly attractive 
because it can be employed in combination with the force of gravity and at 
the same time act as a cleaning means to expel any debris from the key 
area. Therefore, it is to be understood that the above-described mold 
combination and method of molding and hole formation can be appropriately 
modified to employ these other techniques alone or in combination to 
return the movable key to its appropriate position.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, there is seen in an enlarged fragmentary side 
elevational cross section, a portion of two mold halves of the type which 
would form, for example, a 12-cell egg carton as illustrated in 
above-referenced U.S. Pat. Nos. 3,845,187 and 3,862,817. FIG. 1 
illustrates the component parts of the mold half combinations which, 
during molding of a heat softened plastic sheet, would simultaneously, 
with shape molding the plastic, form latch hole or latch holes therein. 
While reference will be given to top and bottom herein in relation to the 
mold halves, it is to be understood that the bottom and the top can be 
reversed and therefore it is only relative position which is important. 
Moreover, the location of the specific keys of the drawings as being in 
the male and female mold half is for illustration only. They can be 
reversed and function essentially in the same fashion. 
FIG. 1 shows the front part of top female mold 10 normally spaced from part 
of the front of bottom male mold 12. These members are shown in their 
normally spaced apart relationship, early in a molding operation where a 
heat softened sheet of thermoplastic material 22 is beginning to be shape 
formed. Carried by top female mold 10 is a female key 14 and carried by 
bottom male mold 12 is a male key 16. Female key 14 is held in position in 
a chamber 15 machined out of top mold 10. It is held in position, for 
example, by means of a shoulder bolt 18. The female key 14 is held so as 
to be freely moveable within a particular range to be described 
hereinafter. Male key member 16 is fixed in position in bottom male mold 
12 by means of, for example, shoulder bolt 20. Female key 14 has a cutting 
edge 24 located thereon. This cutting edge is shown as having an acute 
angle in cross section, but it is to be understood that the cutting edge 
can range from a 90 degree corner edge to any angle less than this 
consistent with durability and long term use. The length of the cutting 
edge, of course, will be consistent with the size of the orifice desired. 
Female key 14 has a planar face 28 in association with cutting edge 24. 
Male key 16 has a bevelled or chamfered edge 26 located in association 
with a vertical face 30. 
FIG. 2 shows the female and male mold halves in motion towards each other 
as indicated by direction arrows 34 and 36. The male and female mold 
halves, and therefore the female key 14 and the male key 16, are normally 
registered in relation to each other so that on closure of the mold halves 
initial contact between the male and female keys will be the cutting edge 
24 and bevelled edge 26. This is the relationship shown in FIG. 2 wherein 
the initial contact involves cutting edge 24, bevelled edge 26 and 
softened plastic 22 therebetween. Male key 16 is fixed in place and female 
key 14 is free to move, to a certain extent consistent with its loose 
support by shoulder bolt 18 and appropriate clearances between the 
shoulder bolt, female key 14 and the top female mold. As the mold halves 
continue to approach one another, cutting edge 24 rides off bevelled edge 
or surface 26 and in so doing pierces through softened thermoplastic film 
22. Since female key 14 is free to move, planar surface 28 is turned or 
tilted so as to be in contact with and parallel to vertical face 30. As 
the mold halves move still closer together, planar face 28 slidingly 
engages vertical face 30 so as to push apart the edges of the slit orifice 
formed after initial contact of cutting surface 24 and bevelled surface 
26. FIG. 4 shows the mold halves in their final molding relationship and 
male and female keys 14 and 16 effecting full expansion of the latch hole 
orifice in the molded plastic 22. Using this technique the two latch hole 
orifices for a 12 cell egg carton could measure 2 cm by 1 cm. Separation 
of the mold halves 10 and 12 to the position they occupy in FIG. 1, 
permits removal of the molded member 22 now containing an orifice therein. 
Located in top female mold 10 adjacent to the chamber occupied by female 
key 14 are a pair of gas tubes 32 communicating with said chamber. After 
separation of the mold halves a force of compressed gas, for example, air, 
is directed through gas tubes 32 so as to impinge upon female key 14. This 
will cause female key 14, which is free to move, to return to its original 
position and attitude occupied at the beginning of the molding cycle. The 
gas force accomplishing this movement comes from some appropriate gas 
source not shown. Planar face 28 and vertical face 30 of the male and 
female keys are machined or otherwise prepared so that when in parallel 
contacting relationship they can slide across one another. One skilled in 
the art can easily determine the tolerances necessary to permit the 
necessary degree of freedom of female key 14 as it is held in position in 
top female mold half 10. 
It is within the skill of the art to determine the optimum angle for the 
bevelled or chamfered edge. Knowing that the object of the operation is to 
permit cutting edge 24 to glance off of bevelled surface 26, it can be 
readily appreciated that this can be best accomplished when the bevel is 
less than some critical angle, e.g. 45.degree. or less. Angles greater 
than this will induce unwanted interference and wear. 
Once the molding operation has been completed and simultaneously therewith 
the desired orifice has been created in the molded member and the mold 
halves separated for removal of the molded part, there are alternative 
techniques for returning the female key member to its original position or 
attitude that it occupied at the beginning of the molding cycle. For 
example, referring to FIG. 5, instead of returning female key member 14 to 
its original position by way of the force of a gas stream, the force of 
gravity is permitted to accomplish this return. In FIG. 5, female key 
member 14 is held in its chamber in mold half 10 by shoulder bolt 38. 
Shoulder bolt 38 threads into top female mold half 10 at an angle to the 
horizontal and female key member 14 has a shaft to receive shoulder bolt 
38. This shaft is at an angle corresponding to angle shoulder bolt 38 
makes to the horizontal. Thus if this angle is, for example, 30 or 45 
degrees to the horizontal and the degree of freedom between the shoulder 
bolt and the female key will permit planar face 28 to be brought parallel 
to vertical face 30, then on completion of the operation and separation of 
the mold halves, the force of gravity will return female key member to its 
original position. 
It is to be understood that the gravity technique of returning the female 
key to its original position can be combined with the utilization of the 
force of compressed gas to return the female key to its original position. 
An important advantage of employing the compressed gas is that in addition 
to returning it to its original location, the force of the gas can always 
keep the chamber housing and female key 14 free of debris, thereby 
avoiding the possibility of jamming the female key in a fixed position. 
FIG. 6 illustrates another technique of returning female key member 14 to 
its original position. This technique involves associating a permanent 
magnet 40 in a position of attraction so as to exert a slight counter 
clockwise turning moment on the female key member to return it to its 
original position or attitude after separation of the mold halves. 
Obviously the attractive force of the magnet on the female key member 14 
is easily overcome as the female key cutting edge rides off the chamfer of 
the male key member. Space 41 between shoulder bolt 18 and female key 14 
gives the degree of freedom to permit planar face 28 to be turned parallel 
to vertical face 30. Other appropriate magnetic systems including 
electromagnetic systems can be employed to reposition the free-to-move key 
member. 
FIG. 7 illustrates still another technique for returning key member 14 to 
its original position. Shown therein is hydraulic line 42 operatively 
associated with push rod 43. Push rod 43 is located so that, in response 
to a force transmitted through hydraulic line 42, it reacts to push on key 
14 thereby returning it to its original location upon completion of the 
orifice forming function. During the next cycle the hydraulic force is 
relaxed and female key 14 is free to ride off chamfer 26. 
As indicated above, the key members described can be reversed in position. 
In other words, the key member carrying the chamfer 26 can be fixed in the 
top or female mold and the key 14 carrying the cutting edge can be located 
in the bottom mold and positioned so as to be free to move as described 
above. The described mold arrangement can be employed to form one or any 
number of orifices during a molding system. Specific utility can be its 
employment in the formation of egg cartons, sandwich containers, etc. The 
thermoplastic material employed to form such molded structures can be any 
thermoplastic film, both of the foamed or unfoamed variety. 
It is to be understood that the foregoing description is merely 
illustrative of preferred embodiments of the invention, of which many 
variations may be made by those skilled in the art within the scope of the 
following claims without departing from the spirit thereof.