Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
  • B29C48/50—Details of extruders
  • B29C48/505—Screws
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
  • B29C48/50—Details of extruders
  • B29C48/505—Screws
  • B29C48/507—Screws characterised by the material or their manufacturing process
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion

Definitions

• the invention relates to a screw set element for screw machines, in particular for twin-screw machines for plasticizing thermoplastic plastics, which is designed in combination with other screw set elements on a screw shaft as a screw shaft, which has a screw core and z.
• B. has helical screw webs and in which the screw core consists at least in regions of a core material which is formed from a softer material than a jacket material of the worm webs and which is produced at least in regions by hot isostatic pressing from a powder-like starting material.
• Such a screw set element is described for example in DE 43 28 160 C2.
• the core material of this screw set element consists of Steel, on the hülsenför ⁇ ig d urch h ei ß isostatisc h presses it is applied, the coat layer to form the screw flights.
• Another material is arranged between the steel core and the sleeve, which is also solidified by hot isostatic pressing and is connected to both the steel core and the outer sleeve. This produces a multi-layer shaft blank. After subsequent processing of the blank, the screw webs are provided with a wear layer in the region of their outer boundaries facing away from the steel core, which is formed from the material of the sleeve.
• wear-resistant materials for the screw set elements is particularly important when filled or reinforced plastics are processed.
• the wear resistance is usually achieved by using alloys with a high carbide content and a relatively large layer thickness.
• Damage to the screw set element which leads to cracks, can occur under different influences. For example, it is possible for contact to be made with a housing bore when the screws start up. In addition, foreign bodies can get into the area of the screw or Uneven forces can attack due to dosage fluctuations. These forces lead to compensating movements of the screws, which can cause metallic contact with the housing bore. This metallic contact leads to braking effects that cause the worm to overheat for a short time. The short-term local overheating can cause cracks.
• the course of the crack is interrupted in the transition area from the hard to the soft material.
• a similar interruption of the crack propagation can be observed when the hard wear layer has been attached to a ductile base material by means of weld-overlay welding.
• This base material is usually tempered and can consist of nitriding steels.
• the welded-on, highly wear-resistant alloy can be applied with a layer thickness of 2 mm to 5 mm. Additional nitriding is carried out to improve wear protection in the area of the flanks of the screw flights.
• the nitride layer thickness is usually only 0.5 mm and a high hardness can only be found in the outer area of this layer.
• hard screw set elements which consist of forged materials or materials produced by powder metallurgy. These materials have a fine-grained isotropic structure and are therefore relatively tough. Due to the high notch sensitivity, however, both torque-related breaks from the inside and start-up breaks from the outside can occur. In order to provide a compromise between sufficient hardness and sufficient breaking strength, the fully hardened screw set elements are therefore tempered with lower hardness in the tougher areas. However, this results in a loss in wear resistance, which is usually more than 30% of the wear resistance that can be achieved with greater hardening.
• the composite materials already mentioned in the introduction have the disadvantage that the combination of hard shell materials and soft core materials provides both a high wear resistance and a limitation of the crack expansion, but on the other hand, after the hard shell material has completely torn, the torque introduced is reduced only by the Cross section of the snail core is transmitted, which due to its soft consistency is not able to transmit such torques in the long run.
• the core material therefore usually breaks near the cracks in the jacket material.
• the object of the present invention is therefore to construct a screw set element of the type mentioned in the introduction in such a way that the operating properties are improved without a substantial increase in the production costs.
• the core material has an outer diameter which is at least as large as an inner diameter of the screw webs.
• This dimensioning of the core material limits the crack expansion to a smaller part of the diameter of the screw set element.
• the knowledge is taken into account that the wear in the area of the external expansion of the screw webs is significantly greater than in the area of the expansion of the screw webs facing the core material. It is therefore sufficient to provide a lower hardness in the inner region of the screw walls.
• the stresses causing the wear on the outer area of the screw flights are typically four times as great as in the area located further inside.
• the larger dimensioning of the core material also makes it possible to transmit an increased torque while the outer diameter of the screw set element remains the same. Typically, the overall performance of the machine can thus be increased by at least 20%.
• a suitable choice of material consists in that both the core material and the jacket material are formed from hot isostatically pressed metal powders.
• the core material is made of a solid material and the jacket material is made of a hot isostatically pressed metal powder.
• Another variant consists in that the core material is formed from a hot isostatically pressed metal powder and the sheath material is formed from a solid material.
• the core material be made hardenable.
• a high-strength material resistance on the outer circumference of the screw is provided in that the casing material is designed to be hardenable.
• the core material is formed from a highly ductile material.
• the core material have a lower carbide content than the jacket material.
• a greater hardness in the area of the jacket material relative to the core material is achieved in that the jacket material has a greater tempering resistance than the core material.
• a further possibility for receiving a drive shaft is obtained if, as further proposed, the core material is tubular.
• FIG. 1 shows a cross section through a screw set element with screw core and screw webs
• FIG. 2 shows a cross section to illustrate the production of composite rods for screw set elements, in which both the core material and the casing material are formed from hot isostatically pressed metal powders,
• 3 shows an embodiment for producing composite rods, in which the core material is made of a solid metal and the jacket material is made of a pressed metal powder
• 4 shows a further variant for the production of composite rods, in which the core material is made of pressed metal powder and the sheath material is made of a solid material
• 5 shows a wear-time diagram to illustrate different material properties.
• Fig. 1 shows in cross section a screw set element, which consists of a screw core 1 and z. B. helical circumferential screw webs 2 is formed.
• the screw core 1 consists of a core material 3 and the screw web 2 is made of a jacket material 4 at least in the region of its extension facing away from the screw core 1.
• the screw set element is provided with an outer web diameter 5, an inner web diameter 6, an outer core diameter 7 and, in the case of a tubular design of the screw core 1, with an inner core diameter 8.
• the outer core diameter 7 is dimensioned such that it is at least as large as the inner web diameter 6.
• a drive shaft 9 can be introduced into the interior space thereby clamped, which is connected to the core material 3 in a rotationally secured manner via profiles 10.
• FIG. 1 an area of lower wear resistance 11 is entered in FIG. 1, in which the core material 3 down to the area of the exposed surface of the
• FIG. 2 explains one possibility of producing a composite rod, from which the screw set element can be produced by machining the outer area.
• a capsule 14 the interior of which is divided into two concentric areas by a separating plate 15, suitable metal powder is introduced into both the inner and the outer area.
• the material for the core material 3 is filled into the inner region and the material for the sheath material 4 into the outer region.
• the partition plate 15 is removed and the blank production is completed by hot isostatic pressing. After removal from the mold, further processing can be carried out.
• a solid material with a lower wear resistance relative to the jacket material 4 is used as the core material 3.
• Metallic powder, which is hot isostatically pressed, is again filled between the capsule 14 and the core material 3.
• a nozzle 16 is provided for filling and venting the space between the core material and the capsule 14.
• the jacket material 4 consists of a solid and wear-resistant material and the core material 3 is filled in as a powder and then hot isostatically pressed.
• 5 illustrates in a wear-time diagram 17 the different wear resistances of two exemplary selected materials.
• a time axis 18 is scaled in minutes and a wear axis 19 in mm.
• a nitriding steel 1.8519 which is plasma nitrided 0.5 mm deep, there is a layer wear of 2 mm after 13 min after course 20, and a chromium steel 1.4122, which is hardened with HRC45 + and has an impact resistance of 80 Joules , after course 21, the same layer wear only occurs after 24 min.
• the above-described material combination of core material 3 and sheath material 4 according to FIGS. 2 to 4 reduces crack initiations, which are caused by voltage peaks during torque transmission, in such a way that no breakage can occur from the inside.
• the crack propagation is interrupted when the core material 3 is reached, and a sufficient material cross section remains to transmit the torque present.
• the core material 3 and the shell material 4 can be hardened and tempered together.
• the core material 3 and the jacket material 4 have the same thermal expansion coefficients as possible.
• One possibility for providing these material properties is that the core material 3 is provided with a lower carbide content than the jacket material 4. This provides higher toughness in the area of the core material 3.
• a wear-resistant combination of materials can be achieved by using 4 2.5% by weight carbon (C), 5% by weight chromium (Cr), 1% by weight molybdenum (Mo) and 10 for the jacket material %
• vanadium (V) By weight of vanadium (V) can be used.
• An iron material is used as the material for the remaining weight percentages.
• the core material 3 has a composition of 1.7% by weight of carbon (C), 5% by weight of chromium (Cr), 1% by weight of molybdenum (Mo) and 9% by weight of vanadium (V).
• iron is used as the material for the remaining weight percentages.
• a joint hardening and tempering process results in a hardness of 60 HRC, a toughness of 60 joules, a wear-related weight loss ⁇ G of 40 mg with a coefficient of thermal expansion OC of 11.9 [m / m ° ⁇ ' ] for the jacket material 4.
• an alloy of 0.90% by weight carbon (C), 18.5% by weight chromium (Cr) is used for the jacket material 4. and 1.2 wt% molybdenum (Mo) is used.
• 0.35% by weight of carbon (C), 16.5% by weight of chromium (Cr) and 1.2% by weight of molybdenum (Mo) are used for the core material 3.
• a filling to 100 wt .-% takes place here with an iron material.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Powder Metallurgy (AREA)
• Gears, Cams (AREA)
• Gear Transmission (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=7769550

Family Applications (1)

Country Status (8)

Families Citing this family (2)

Family Cites Families (7)

• 1995
  • 1995-08-16 DE DE19530026A patent/DE19530026A1/de not_active Withdrawn
• 1996
  • 1996-07-26 EP EP96927613A patent/EP0844925A1/de not_active Withdrawn
  • 1996-07-26 CA CA002229566A patent/CA2229566A1/en not_active Abandoned
  • 1996-07-26 AU AU67378/96A patent/AU6737896A/en not_active Abandoned
  • 1996-07-26 JP JP9508866A patent/JPH11510749A/ja active Pending
  • 1996-07-26 WO PCT/EP1996/003307 patent/WO1997006937A1/de not_active Application Discontinuation
  • 1996-07-26 KR KR1019980701057A patent/KR19990036388A/ko not_active Application Discontinuation
  • 1996-07-26 BR BR9610230A patent/BR9610230A/pt not_active Application Discontinuation

Non-Patent Citations (1)

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