Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Patent
1985-07-08
1988-02-02
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
264511, 264522, 264551, 264555, 2642105, 2642893, 264294, 425325, 425388, B29C 4790
Patent
active
047228202
DESCRIPTION:
BRIEF SUMMARY
A number of thin wall packaging thermoforming plants now use direct in-line extrusion to feed hot webs of thermoplastic to traditional intermittent pressure forming presses.
The main advantages of in-line feeding are:
(a) Energy savings: re-heat of cold pre-extruded sheet is partially or wholly avoided;
(b) Material savings: in-line scrap regranulation reduces material losses and labour costs when recirculating the trim scrap;
(c) Labour savings: handling and clean storage of separately extruded roll-stock sheet is avoided.
Other advantages include easier web temperature control of the feed to the press, more uniform and controllable process conditions, work-in-progress inventory reductions and quality control savings.
The currently known methods of in-line feeding of webs, are derived from conventional extrusion sheet line technology. In these conventional type processes, the web is "s-rolled" around two or three temperature controlled rolls. The material thus makes intimate contact with the circumferential surface of the wide, cylindrical rolls, usually for a circumferential distance exceeding 100 mm.
In all cases, the material or at least the surface of the material, is chilled below its melting point, before it leaves the roll-stack. The warm but solid sheet is then usually fed to an accumulator section of one or more moveable rollers, which maintain tension in the web, as the intermittent feed of the sheet into the cycling forming press, takes place.
From the accumulator rolls, the web usually has to be reheated by radiant heaters. This is required to bring the actual sheet to be fed back to a uniform temperature in the longitudinal direction. Even a web which is fed directly from an extruder will have a uniform temperature drop in the longitudinal direction which must be corrected by partial reheat, unless the web speed is high or the distance between extruder and forming press is small.
Bellaplast Maschinenbau GmbH, West Germany have developed and patented (see U.S. Pat. No. 4,039,609) a modified version of the standard method of in-line extrusion feed for thermoplastic materials such as polypropylene. The Bellaplast method and machines for its operation rely on the cooling of the web surfaces to form supportive layers for the molten core of the web and for reheating of these layers by heat transfer from the core. Polypropylene, unlike other common thermoformable polymers, has a sharp melting point and a soft, fluid melt, which makes it very difficult to feed, in sheet form, into conventional thermoforming equipment of the Bellaplast type.
In the Bellaplast method, the sheet extruder feeds a thermoplastics material of regular structure into a series of two or more temperature-controlled rolls, partially "s" rolling the web on these rolls, to bring the web surface skin temperature to just below its crystalline melting point, so enabling sufficient strength to develop in the now solid-phase skins, to support the sagging molten core layer inside the web.
This enables the web to be fed to the intermittently fed press, via a single "dancing" roller, which helps to keep the web from becoming slack, whilst it is transported to the press.
Australian Patent Specification No. 460,849 details a continuously in-line with an extruder without the need for cool supporting skins in the web, or "dancing roller" web control arrangements of the Bellaplast type. However, the method disclosed therein suffers from the limitation of having no intermediate means of cooling the web to its best thermoforming temperature and no means of ensuring proper control of the web thickness across its width. The web issuing from an extruder slot die is usually not-uniform in thickness, either across its width or long its length, without further mechanical gauging.
It is an object of the present invention to provide a method and apparatus which will enable the continuous feeding in a sheet web form of thermoplastic material of regular structure, in a manner avoiding or minimizing the above noted disadvantages of the prior art.
According
REFERENCES:
patent: 3429854 (1969-02-01), Siggel et al.
patent: 3886250 (1975-05-01), Danko
patent: 3931383 (1976-01-01), Erlewine et al.
patent: 3963813 (1976-06-01), Keith
patent: 4025599 (1977-05-01), Keith
patent: 4304539 (1981-12-01), Hagiwana et al.
Search Report
A.A.R.C. (Management) Pty. Limited
Thurlow Jeffery
LandOfFree
Molten theromplastic web feeding process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Molten theromplastic web feeding process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Molten theromplastic web feeding process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1635066