Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
1998-10-23
2001-03-27
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S297200, C264S328800, C264S334000, C425S073000, C425S152000, C425S135000
Reexamination Certificate
active
06207087
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally pertains to injection molding and is particularly directed to improved insulated runner injection molding methods and systems.
An insulated runner system includes mold-cavity-encasing mold parts and channel-encasing mold parts. The mold-cavity-encasing mold parts encase the mold cavities; and the channel-encasing mold parts encase a channel, in which injected plastic material forms an insulated runner with a solidified insulating plastic shell and a molten plastic core for conducting injected molten plastic material toward the mold cavities. A preferred method of operating and controlling an insulated runner injection molding system includes the step of:
(a) injecting molten plastic material into the channel to form an insulated runner in the channel and into the at least one mold cavity in accordance with parameters of a molding sequence including a plurality of injection molding cycles.
The core eventually solidifies to form a sprue when the molding sequence is interrupted or after a run of normal production cycles. Upon occurrence of full solidification of the insulated runner to form the sprue molten plastic can no longer be injected through the insulated runner channel, whereby the injection molding system automatically ceases operation, an alarm is provided to alert a system operator to such occurrence, and an end-of-sequence signal is provided. The system operator responds to the alarm and/or a status indication provided pursuant to the end-of-sequence signal by performing a series of steps required for removing the sprue from the channel-encasing mold parts and enabling the molding system for another molding sequence including a plurality of injection molding cycles.
Initially, the operator causes the mold-cavity-encasing mold parts to be disengaged. Then the operator causes the opening of a machine gate that controls access to a space between the disengaged mold-cavity-encasing mold parts, whereupon the operator inspects the disengaged mold-cavity-encasing mold parts and causes any debris to be removed from the disengaged mold-cavity-encasing mold parts.
Subsequent to inspection of the disengaged mold-cavity-encasing mold parts, the operator causes the closing of the machine gate, and then causes re-engagement of the mold-cavity-encasing mold parts. Then, after causing the machine gate to be opened, the operator causes the molding system to be adjusted to enable disengagement of the channel-encasing mold parts. Then, after causing the machine gate to be closed, the operator causes the channel-encasing mold parts to be disengaged. The operator then causes the opening of the machine gate, whereupon the operator causes the sprue to be removed from the channel-encasing mold parts. The operator then inspects the disengaged channel-encasing mold parts and causes any debris to be removed from the disengaged channel-encasing mold parts.
Subsequent to removal of the sprue and inspection of the disengaged channel-encasing mold parts, the operator causes the closing of the machine gate, and then causes re-engagement of the channel-encasing mold parts. Then, after causing the machine gate to be opened, the operator causes the molding system to be adjusted to prevent disengagement of the channel-encasing mold parts. Then, after causing the machine gate to be closed, the operator causes plastic material to be injected into the insulated runner channel and into the mold cavities in accordance with the molding sequence having the predetermined plurality of injection molding cycles.
The operator causes the above-described steps other than the inspection steps to be performed by selectively operating a myriad of control buttons that actuate various mechanisms.
For many years hot runner injection molding methods and systems have been favored over insulated runner injection molding methods and systems for most injection molding applications. In a hot runner injection molding system, the mold parts that encase a runner-system channel, in which injected molten plastic material flows from an injection unit to product-forming mold cavities, are heated in order to maintain the plastic material within the runner-system channel in a molten state.
There is an inherent inefficiency in hot runner injection molding. A substantial amount of electrical energy is required to heat the runner-system channel, and heat leaks from the channel-encasing mold parts to the mold parts that encase the mold cavities to thereby heat the mold cavities and retard the cooling required to solidify products formed in the mold cavities. Consequently, another substantial amount of electrical energy is required to cool a coolant that is circulated in the mold-cavity-encasing mold parts to counteract the heat that is leaked from the heated channel-encasing mold parts. Even with such counteractive cooling, the heat leaked from the channel-encasing mold parts still retards cooling of the products formed in the mold cavities to such an extent as to substantially increase the duration of each molding cycle.
There has been a long felt need to overcome the above-described energy-loss and cooling inefficiency problems incident to hot runner injection molding. Even though these inefficiency problems can be overcome by utilizing an insulated runner injection molding system, since operation of an insulated runner injection molding system does not require that the channel-encasing mold parts be heated, the state of the art of insulated runner injection molding has had various perceived problems associated therewith, as will be discussed below, such that insulated runner injection molding is not currently in common use and is largely thought of by those of ordinary skill in the art as a thing of the past.
The literature available to persons wishing to learn about the art of insulated runner injection molding is contradictory and sometimes misleading, such as in the following examples.
Temesvary “Mold Design for High Speed Production of Disposables”, SPE Journal, February 1968—Vol. 24, page 25, states at page 27, “The advantage of the insulated runner system lies mainly in its simplicity and strength. Its disadvantage is that with every shut down, the solidified runner must be removed and, of course, startup is more critical and difficult than start up of the hot runner mold.” However, Filbert, Jr. and Williams, “Runnerless Mold Design”, Technical Report 196, E. I du Pont De Nemours & Co., Inc., Wilmington, Del., 1977, under the heading, “Insulated Runner Molds” at page 3 state, “(S)hould the internal runner freeze solid, the runner can be removed quickly (at the parting line), and molding resumed with little lost time.”; and Dym, “Injection Molds and Molding”, Second Edition, Van Norstrand Reinhold, New York, 1987, states at page 230, “Quick-acting latches and movement of the press are employed to accomplish the removal of (insulated) runners with little delay.” (parenthetical text added).
Pye, “Injection Mold Design”, Fourth Edition, Longman Scientific & Technical, Harlow, 1989, states at page 502, “This technique (insulated runner molding) is only practicable because thermoplastics have good insulating properties.” (parenthetical text added). However, Dym, , supra, states at page 230, “It (resin for an insulated runner) should have a low specific heat and a high thermal conductivity so that it can be melted quickly and attain temperature uniformity.” (parenthetical text added).
Csaszar, “Runnerless Molding Without Hangups”, SPE Journal, February 1972—Vol. 28, page 20, states at page 21, “Except for the relatively large runner diameter, the insulated runner in no way differs from runners in other systems.” However, U.S. Pat. No. 5,069,615 to Schad et al. states at column 8, lines 4-12, “By having the (insulated) runner systems cut in the face of the plates (
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,
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), the ability to machine smoothly curved runner passages is greatly facilitated. As a result, sharp corners and other undesired runner features founded in hot runner channels which cause the resin to hang up
Brown Paul Philip
Sorensen Jens Ole
Callan Edward W.
Heitbrink Jill L.
Universal Ventures
LandOfFree
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