RU2238800C2 - Cast double-layer flour milling roll - Google Patents

Abstract

FIELD: milling equipment.

SUBSTANCE: flour milling roll has double-layer hollow barrel with working and inner layers, two supporting journals and lead inserts at its end surfaces. Thickness ratio of working and inner layers is set within the range of 1/1.45-1/1.95 and 1/3.1-1/4.1.

EFFECT: increased strength mechanical and antifriction characteristics of rolls, enhanced reliability in operation and prolonged service life of roll.

2 cl, 1 dwg

Description

The invention relates to the field of metallurgy, foundry, in particular centrifugal casting of two-layer rollers.

A known method of centrifugal casting of rolling rolls (Ukrainian patent No. 1737, IPC B 22 D 13/00), which includes sequential pouring of the melt of the outer and inner layers into a rotating metal mold and supplying the estimated amount of alloying metal to the melt.

In order to improve the quality of the rolls and simplify the casting process, three-calcium borate is fed with a fraction of 0.2-0.5 mm, with 70-75% of it being introduced before the start of casting, and the remainder is introduced into the stream of metal, which is filled in 25-30 s from the start of casting and 30-60 s before the end of the pouring of the metal of the outer layer. The rotation speed of the metal mold is increased 1.8-2.0 times.

The disadvantage of this method is that it does not have the proper alloying effect on the formation of a high-quality microstructure of castings. Parts made from such castings lacked a uniform structure, corrosion phenomena developed along the grain distribution boundaries, which significantly reduced their service life.

There is also a method of centrifugal casting of rolls (Ukrainian patent No. 1640, IPC B 22 D 13/02), which includes pouring liquid metal into a mold whose rotation speed corresponds to the values of the gravitational coefficient 60-150, in order to improve the quality of cast rolls by reducing destruction of the mold by a jet of liquid metal. The metal was poured in two stages. At the first stage, the liquid metal is poured during rotation of the mold at a speed of 0.14 from the value of the gravitational coefficient during shaping of the working layer of the roll to completely fill the lower neck of the roll with liquid metal, and then at the second stage, the remaining metal is poured into a fixed mold.

The disadvantage of this method is the uneven structure and the presence of residual stresses in the working layer of the casting, which lead to cracks, chips during machining and further operation of the rollers.

The closest in technical essence to the proposed invention is the patent of Ukraine No. 1697, IPC B 22 D 19/00, B 22 D 13/00, B 22 D 25/00. A two-layer flour mill containing a two-layer empty barrel with a working and inner layers and a ratio of the thickness of the working layer to the outer diameter of the barrel equal to 1 / 8-1 / 10, and pins, characterized in that in order to improve its quality and operational properties, the ratio of the working thickness layer to the inner is 1/2 -1/3.

The disadvantage of this invention is that the rolls with the proposed ratio of the thicknesses of the working and inner layers have the following defects in the structure of the alloy of the working layer:

- uneven structure of the working layer with the presence of spotty hardness over the entire surface of the drum barrel;

- chips and cracks of the outer layer when cutting corrugations and during operation of the drum;

- the presence of vibrational loads due to the imbalance of the rotating roller during operation, which reduce the durability of the bearing assemblies and other important working parts of the roller machine.

The basis of the invention is the task to obtain a cast two-layer flour mill, in which by optimizing the ratio of the thicknesses of the working and inner layers of the roll casting, depending on the size of the grooves and the functional purpose of the roller in operation, achieving a controlled casting speed of the working and inner layers of the casting, significantly reducing vibration loads by eliminating the imbalance of the rotating roller provides a uniform, spotless structure of the working layer over the entire surface o roll casting, obtaining a clear uniform columnar structure across the entire thickness of the working layer of the roll casting without the presence of non-metallic and gas inclusions, reducing the level of residual stresses in the working layer of the casting and the occurrence of chips and cracks when cutting corrugations and further operation of the roll, improving machinability, obtaining the necessary strength and mechanical characteristics of the casting, increasing the durability of the bearing assemblies and other important working parts of the roller machine.

The problem is solved in that in a cast two-layer milling mill, containing a two-layer empty barrel with a working and inner layers, two support pins and lead inserts on its end surfaces, in accordance with the invention, the ratio of the thicknesses of the working and inner layers is set within 1/1, 45-1 / 1.95 and 1 / 3.1-4.1.

In addition, holes with lead inserts are located on its end surfaces, and with the proposed and established ratio of the thicknesses of the working and inner layers, the holes are made only in the inner layer at a constant distance from the transition zone of the distribution of layers.

The cast two-layer flour mill proposed to the invention, hereinafter referred to as the “drum", is shown schematically in the drawing (section along the main central axis).

The drum is a two-layer empty cylindrical barrel with support pins pressed on both sides and consists of a working layer (1), an inner layer (2), an axial cavity (3), two pins (4), lead inserts (5), which dynamic drum balancing.

The working layer is obtained from synthetic, hard, wear-resistant, low-alloy cast iron. After rough machining of the working layer and fine grinding on the cylindrical surface of the drum barrel along the axis along the helix, working teeth (corrugations) with a height of 0.15 mm to 0.85 mm are cut, depending on the functional purpose of the drum. To obtain premium flour, the polished surface of the drum barrel is treated with a special mixture of abrasive material using compressed air. The obtained cylindrical rigid working surface of the roller has the technical term “matted surface”.

During the operation of the drum, the work surface under the action of a product that is milled, withstands cyclic, alternating, shock loads, gradually due to electrochemical corrosion and abrasion, it becomes unsuitable for use in its functional purpose. The worn-out work surface of the drum can be machined, ground and cut into new grooves or to obtain a new “matted surface”. This process is repeated several times depending on the hardness, thickness and uniformity of the spotless columnar structure of the working surface of the roller.

After machining, dynamic balancing of the assembled roller is carried out on a special balancing stand. In pre-prepared holes, which are always located on the end surfaces of the “soft” inner layer, lead inserts are “choked” with the mass necessary to eliminate the roller imbalance.

Thus, the inventive cast two-layer milling mill, unlike the prototype, has the following main characteristic essential features:

- in the barrel of the drum intended for cutting corrugations, the ratios of the thickness of the working layer to the thickness of the inner layer are provided within 1 / 1.45-1 / 1.95, and in the barrel of the drum, which is designed to obtain a “frosted surface”, the ratio of the thickness of the working layer to the thickness of the inner layer are provided within 1 / 3,1-1 / 4,1. As an exception, in case of production necessity, when performing machining, it is possible to cut corrugations at a thickness ratio of 1 / 3.1-1-1 / 4.1, and obtain a “frosted surface” at a ratio of 1 / 1.45-1 / 1.95;

- holes with lead inserts are made on the end surfaces of the drum barrel to eliminate the imbalance of the drum, and with the established ratio of the thicknesses of the working and inner layers, the holes are made only in the inner layer, because with other ratios of the thicknesses of the layers, for example, with an increased thickness of the working layer, the holes or part holes fall into the area of the solid bleached working layer and obtaining holes is almost impossible.

The cast bilayer flour mill proposed for the invention has advantages over the prototype:

- reduction of marriage in 1.8-2.4 times in connection with obtaining uniform spotless hardness over the entire working surface of the roller;

- increase in strength mechanical and antifriction characteristics of the rollers by 12-15% in connection with obtaining a uniform columnar structure throughout the entire thickness of the working layer of the casting of the roller without the presence of non-metallic and gas inclusions, improving their machinability;

- a reduction of 20-25% in the cost of expensive alloying materials and a reduction in the unit cost of electricity per cast by 10-15%;

- increase the reliability and durability of roller machines by 1.7-1.9 times due to a decrease in the level of residual stresses in the working layer of the casting and the occurrence of chips and cracks when cutting corrugations and further operation of the roller.

Claims (2)

1. Cast two-layer flour mill containing a two-layer empty barrel with a working and inner layers, two support trunnions and lead inserts on its end surfaces, characterized in that the ratio of the thicknesses of the working and inner layers is set at 1 / 1.45-1 / 1 95 and 1 / 3.1-1-1 / 4.1. 2. The cast bilayer flour mill according to claim 1, characterized in that holes with lead inserts are located on its end surfaces, and with the established ratio of the thicknesses of the working and inner layers, the holes are made only in the inner layer at a constant distance from the transition zone of the distribution of layers.