Patent Application
20070079634
In the production of glass containers on the well known I.S. type machine, glass is formed into a parison in a blank mold and then blown into a bottle in a blow mold, each of the blank mold and the blow mold comprising two mold members movable between a closed position, in which they define a mold cavity, and an open position. Both the blank mold and the blow mold are cooled in the operation of the machine and such cooling is often carried out by providing the mold members with cooling passages extending axially therethrough from a lower end face to an upper end face of each mold member, and providing cooling air to these passages.
When the cooling passages in the mold members are provided with cooling air from a plenum chamber, it is possible to calculate the cooling effect of a cooling passage, and thus to determine a pattern of cooling passages which will give the required cooling. However, it is sometimes desirable to modify the cooling of a mold member, but this usually requires a modification of the cooling passages by way of addition or removal of cooling passages which modification is not readily reversible.
It is one of the objects of the present invention to provide an improved method of cooling a mold member.
It is another of the objects of the present invention to provide an improved mold for use in a glassware-manufacturing machine.
Other objects and advantages of the present invention will become apparent from the following portion of this specification and from the accompanying drawings, which illustrate a presently preferred embodiment incorporating the principles of the invention.
When the mold member 2 is in use in an I.S. machine, compressed air from a plenum chamber is provided at the lower ends of the cooling passages 10 to cool the mold member. In general, the passages 10 are provided in the mold member 2 in a pattern and of a size calculated to provide the desired cooling. However, on occasion it is found that in the production of a particular container, the calculated cooling is inadequate. Such inadequacy [both in the horizontal and the vertical temperature profile in the mold member] can be remedied by modifying the pattern of cooling passages, but such modification is usually irreversible and the mold member 2 cannot readily be returned to its original configuration. When air passes through a cooling passage in a mold, the flow of air is generally turbulent, but a laminar boundary layer is formed which is in contact with the material of the mold and which gets very hot. We have found that by providing an appropriate insert in the cooling passage, this boundary layer can be disrupted and the hot air from the boundary layer, mixed with the cooler air of the center of the air stream, thus to give a more effective extraction of heat from the mold. According to the invention, the mold member 2 is modified from its original configuration by the positioning (friction fit) in one or more of the cooling passages of a twisted metal strip 14. Such a strip with one 360° twist is shown in
The twisted metal strip may have one or more, preferably two 360° twists.
The length of the strip is related to the amount of twist. The strip may extend for substantially the length of the cooling passage, but we prefer to use a strip with two 360° twists extending for about half the length of the cooling passage in which it is inserted. If the amount of twist is too great, the resistance to the air flow is such that the cooling effect is reduced rather than increased. Preferably, the strip has at least one full 360° twist.
The strip is preferably a close fit in the cooling passage, and of a material, which has the same or slightly greater coefficient of expansion as the material of the mold member.
When air passes through an unobstructed passage 10, it shows turbulent flow, but with a laminar boundary layer in contact with the wall of the cooling passage. This results in the outer portion of the airflow, which is in contact with the hot metal of the mold member, getting hotter than the central portion of the airflow. In a cooling passage 10, with a twisted metal strip 14 positioned in it [as shown in
The strip 14 is of mild steel and about 0.2 mm in thickness. Strips of up to 0.5 mm in thickness can be used. Such material can readily be twisted. Copper could also be used. The strip 14 extends for just over half the length of the passage 10, is formed with two 360° twists, and is a close fit in the passage 10.
We have found that air passing through a passage 10 with the strip 14 in position extracts approximately 15% more heat from the mold than similar air passing through an unmodified passage 10. We prefer to use a strip 14 having two 360° twists. If the amount of twist is too great, the resistance to the air flow is such that the cooling effect is reduced rather than enhanced. In the case of a strip having one full 360° twist, approximately 6% more heat is extracted than by similar air passing through an unmodified passage. By selection of strips of appropriate lengths, it is possible to modify the vertical temperature profile in the mold member.
It will be understood that while we have described the invention in relation to a blow mold, corresponding use of inserted strips may be used with a blank mold having axial cooling passages.
