Plastik malzemelerin ekstrüzyon kalıpları ve ekstrüderin teknolojik incelenmesi
Extrustion dies of the plastic materials and technological investigation of extruder
- Tez No: 21985
- Danışmanlar: DOÇ. DR. SELMA AKKURT
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 60
Özet
ÖZET Bu çalışmada plastik malzemelerin üretim yöntemlerinin basında gelen ekstrüzyon ele alınmıştır. Ekstrüzyon makinasını oluşturan en önemli kısımlar olan kalıp, silindir ve vida çalışmasının esas konusunu oluşturmuştur. Kalıp, plastik malzemeye esas şeklini veren kısımdır, bu yüzden çok hassas işlenmiş ve yüksek parlaklık verilmiş olmalıdır. Yüksek mukavemetli paslanmaz çelikten yapılır, ayrıca krom kaplama işlemi uygulanır. Çeşitli kalıp türleri vardır: Tektel kalıpları, Profil kalıpları, Çubuk kalıpları, Levha kalıpları, Tel kaplama kalıpları ve Boru kalıpları gibi. Silindir ise içinde ekstrüzyon vidasının dönerek malzemeyi kalıba ittiği kısımdır. Silindirin ısıtılması çok önemlidir. Başlıca ısıtma yöntemleri: Elektrikle ısıtma, Akışkan ile ısıtma ve Buhar ile ısıtmadır. Silindir 3 ana bölümü ayrılır: Besleme bölümü, Ana bölüm ve kalıp adaptör dizaynı bölümü. Vida ise erimiş plastiği kalıba iten parçadır. Genel olarak kanatlı ve torpido tipi olmak üzere 2 tiptir. Üretilecek malzemeye göre vida seçimi yapılmalıdır. Ayrıca vida çapı ve uzunluğunun belirlenmesi çok önemlidir.
Özet (Çeviri)
SUMMARY EXTRUSTION DIES OF THE PLASTIC MATERIALS AND TECHNOLOGICAL INVESTIGATION OF EXTRUDER EXTRUSION DIES: Tha forming die is the term applied to the device which determines the sizes and cross-section of extruded part. It is usually inserted in adie holder. Which is either bolted. Clamped or threaded to the head of the extrusion machine. The metal used in fabricating the die should be nickel- chrome steel, stainless steel or Hastelloy or any good grade of tool steel which will take a high polish. It is not necessary in all cases to harden the die, but if this is done, the proper size and shape should be determined first, and tha hardening, polishing and plating should follow. The various general types of dies are monof lament, rod, sheet (flat and circular), tube and wire. A- MONOFLAMENT DIE; For the extrusion of monoflaments the head and die are in a vartical position. The direction of extrusion is usually downword, to prevent the hot, solf f laments from sticking together. B- ROD DIE: The section of the extrussion machine leading to the die should be streamlined in the case of a single cavity it should be funneled to direct the plastic flow into the die For a multiple-opening die a built in spreader serves the same purpose. The take off equipment should be flexible to care for a variety of sizes. viA variety of methods are employed for heating the die. Usually the die derives its heat from the die holder, which may be heated directly with a band heater or by a transfer liquid circulating through the die holder or the cylinder heater. C-WIRE-COATING DIES: It is customary to bring the wire across the face of the extrusion machine in wire or cable coating. There has been limited use in Europe of the straightthrough wire-coa ting machine, in which the wire is fed through the screw and thence into the die. The operation is somewhat similar to that of making tubes. The wire enters one side of the cross head, recei ves its coating at the die and passes out thee opposite side as a coated product. The assembly include a die from the out side of the sheating, a core or mandrel through which the wire passes, often referred to as the guider. The guider tips are replaceable to accommodate various sizes of wires. The die bushing is ordinarly fitted into the die holder, which is adjustable during operaiton by means of set screws to insure a concentric sheathing around the wire. Some designs are so accurately fitted and so well streamlined that they are self centered. Cross-heads in wire extrusion are commonly fitted with an adjustable outlet, permitting the compound to overflow from the cross-head. This prevents the development of excessive pressure in the extrusion machine in case of wire stoppage, when it is imposible to shut down the machine for fear of decomposition of the plastic inthe equipment. D-SHEET DIE; These may be rectangular for the direct extrusion of a sheet, or they may be circular to extrude a tube which is later slit to give a flat sheet. Sheet dies are made in split from, and the resistance to flow at the edges by varying the size of the opening and by diferences in the length of the lands at the center and edges of tha die.Chrome-plating and burnishing are often required to give the proper surface finish to the extruded material. Circular dies usually permit the production of wider sheed than rectanfular dies. E-PROFIL DIES: The production of profiles is usually carried out horrizontally, the extruded product being handled on a belt conveyor, which must be selected with due regard to the properties of the extruded mixture and its shape. For example, a ethylcellulose, because the etxtuded shape picks up makings from weave in the canvas. F-TUBE DIES: The tube die is the most complicated but requires the same careful observance of channeling and streamlining. It consists of two parts: an adjusstable, repleceable pin or mandrel. The mandrel controls the inside diameter of the tube and is held in the die by a spider arrangement. It must be arranged to introduce clean, dry air into the interior of the tubing at pressures of 2 to 6 psi to prevent the tubing from collapsing after it leaves the die. The necessity of using air to preserve the shape of the tube becomes less important as the thickness of the tube wall increases. Alternativelly, the tube can be expanded after it leaves the die by means of the interior pressure. By careful control of revolutions of the screw, the speed of take off, and the internal air pressure, it is possible to manifacture several different size of tubing with the same die assembly. Special take off equipment retains concentricity of the tubing and provides a means of decreasing or increasing the size of the extruded material. Increased take off speed decreases the diameter of the tubing, whereas higher air pressures and slower speeds increase the diameter of the tubing.BARREL Tpe barrel of an extruder is the parallel cylindrical chamber on which the screw rotates and forwards the thermo plastics material. Early machines were constructed with barrels in sections to facilitate raanifacture but modern machines are equipped with one piece barrels which avoid leakage of material and overcome the problem of misalign ment between sections. 1- FEED SECTIONS, This section as its name implies, is that part of the extuder barrel m which the material is fed to the screw, or screws, of machine. There are two basic reguirements for this section; firstly, the feed opening should be desig ned to permit the feed material to flow freely from the hopper, or feed device, into the screws without the posıbı- lity of bridging, and secondmy, facilities should be available for watercooling the sectionb. 2- MAIN SECTION. The main barrel section of the extruder is both a pressure vessl and a heating chamber, since the material is sub jectedto a gradually increasing pressure and suffers a considerable temperature rise during its passage through part of the machine. The barrel therefor, must be able to withstand pressure of up to 140 MN/m2 in some cases and be capable of tranferrmg heat both to and from the material passing throgh. 3- DIE ADAPTOR DESIGN The die adaptor of an extruder is that part of the machine which lies between the barrel and the die profile, and some parts of this assembly are sometimes referred to as the head or die body. Because of the relatively complex nature of many dies, the die body (head) are often to all intents and purposes the samething, and the whole assambly attached to the and of the barrel is frequently referred to marely as the die. IX
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