Sectional variable pitch screw

Abstract

The invention discloses a sectional variable pitch screw, which is an outer screw thread straight rod member with a pitch of 100-140 mm and a tooth height of 14-23 mm, and is sequentially divided into a conveying section A, a feeding section B, a compression section C and an extrusion section D from the root to the end of the screw. The conveying section A is provided with 5-7 teeth, and the feeding section B is provided with 2-3 teeth, wherein an axial section area of each tooth of the feeding section B is 20-30% larger than an axial section area of each tooth of the conveying section A. The compression section C is provided with 2-3 teeth, wherein an axial section area of each tooth of the compression section C is 20-30% smaller than an axial section area of each tooth of the feeding section B. The extrusion section D is provided with 3-5 teeth, wherein parameters of various teeth are different, pitches are sequentially increased, tooth heights are sequentially decreased, axial section areas of various teeth of the extrusion section D are maintained to the same, and the section area is equal to an axial section area of each tooth of the extrusion section D. With the screw having a differentiation structure design, pasty BMC produces a kneading effect during extrusion, such that BMC homogenization is promoted, the material can not overflow in a reverse direction, and glass fibers in the pasty BMC can not be broken without reason.

Description

technical field [0001] The invention relates to a screw of a screw extruder, in particular, the invention relates to a segmented variable-pitch screw of a screw extruder. Background technique [0002] In the production of plastic molded products, the raw materials are usually smelted first, and then the paste-like raw materials are injected into the mold through the screw extruder. BMC is a glass fiber-reinforced unsaturated polyester bulk molding compound. This type of plastic is a new type of contemporary engineering plastic. Compared with ordinary plastics, its physical properties are quite different. Product structural strength. The heat resistance of glass fiber is between 450°C and 500°C, and the melting temperature of BMC is only about 230°C, so the contained glass fiber will not be melted. When extruding BMC with a commercially available screw extruder, due to the fixed-pitch structure of the screw, it is easy to reverse the overflow during extrusion. The reverse o...

AI Technical Summary

Problems solved by technology

When extruding BMC with a commercially available screw extruder, due to the fixed-pitch structure of the screw, it is easy to reverse the overflow during extrusion. The reverse overflow causes the glass fiber contained in it to be torn off, and the damaged glass fiber reduces the original reinforcement. function, so that the strength index of subsequent molded products will decrease

If the incremental glass fiber is reserved in the combination, the torn glass fiber can be compensated, but the production cost is increased, so this method is rarely used

In addition, there is still a big disadvantage when commercially available screw extruders extrude BMC, that is, the fixed-pitch screw has a zero compression ratio during extrusion, and the density of the extruded BMC paste material is not enough, which makes the subsequent molded products The quality index does not meet the design requirements

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