GB2023464A - Bar-stock feeding - Google Patents

Abstract

A low-noise stock tube consists of an outer tube 1 in which are mounted rotary bushes 2 which may be of polyurethane and separated by rotary polyurethane or nylon spacers 3. <IMAGE>

Description

SPECIFICATION Stock tube This invention relates to stock tubes. A stock tube is employed to enclose rotating metal stock in rod form fed to a machine tool for the repetitive production of machined parts.

Stock tubes originally consisted of plain steel tubes and gave rise to high noise levels, the noise being generated by the frictional engagement of the metal stock, and particularly its extremity, with the bore of the tube. Various expedients have been proposed to reduce the noise generated and transmitted by stock tubes. Those expedients have taken two forms: attempts to reduce the noise generated by lining the interior of the steel tube or by a convolute spring inserted within the tube, and attempts to reduce the noise transmitted from the stock tube to the air by applying vibrationabsorbing lagging to the stock tube exterior.None of those expedients has to our knowledge been entirely successful in reducing the transmitted noise to a comfortable ievel, and indeed many stock tubes placed on the market with claims to low noise level have displayed little reduction in noise compared with a standard stock tube.

A stock tube according to the present invention comprises an outer tube and a plurality of bushes which are mounted in the outer tube for free rotation therein about an axis substantially parallel with the axis of the outer tube and which have bores enabling stock rod to pass therethrough.

As to the material of the bushes, it is preferred to employ a material giving the bushes at least some of the following properties: (a) low coefficient of friction between each bush and the outer tube, so that the bush may rotate readily in the outer tube when engaged by the stock; (b) relative softness to absorb vibrational energy transmitted to the bushes by the stock and to minimise noise generation when the bushes are rotated relative to the outer tube; (c) high wear resistance to enable the stock tube to operate without maintenance over significant periods; and (d) resilient deformability, enabling the bushes to accept impact with the stock without damage and with minimum of noise generation.

While it is possible to utilise for the bushes metals, wood and other synthetic resins, both thermoplastic and thermosetting, such as nylon, it is preferred to emply a suitable polyurethane having the properties listed above. The hardness of the polyurethane may vary according to requirement, but should be in the range from 40 to 100 Shore A; thus a relatively hard polyurethane may be advantageously employed where the section size of the stock is large and a relatively soft polyurethane employed with stock of small cross-section.

During operation of the stock tube, contact between the stock and the outer tube is prevented by the bushes; when the stock contacts a bush, the latter is rotated with the stock so that there is little relative frictional movement between the stock and the bushes, giving rise to frictional vibration.

The bushes are preferably spaced apart by tubular spacers, which may be made of nylon and are advantageously made of the same material as the bushes, e.g. polyurethane. Normally the internal bore of the bushes is smaller than that of the spacers, so that the stock engages the rotary bushes in preference to the spacers. For a stock tube for rod finishing, e.g. on a Schumag straightener and polisher where the rod is not fed positively but is push-fed by the preceding section, the internal bores of the bushes and the spacers are preferably substantially the same.

However, the spacers may be omitted, the interior of the outer tube then containing a series of loosely contiguous bushes.

The invention will be more readily understood by way of example from the following description of stock tubes in accordance therewith, reference being made to the accompanying drawings, each of Figures 1 and 2 thereof showing a part of the length of a stock tube in radial section.

The stock tube shown in Figure 1 consists of a steel outer tube 1 in which are number of rotary bushes 2 spaced at intervals along the length of the outer tube 1 by tubular spacers 3. The spacers 3 are not secured to the interior of the outer tube 1 and can also turn within that tube; the assembly of bushes 2 and spacers are restrained axially by removable end caps on the tube 1, the cap at the end adjacent to the machine being of annular form and that at the other end closing entirely the open end of the tube 1.

The outer diameter of each bush 2 is slightly less than the inner diameter of the outer tube 1 so that each bush can rotate freely within that tube.

While other suitable materials can be used, the preferred material of the bushes is polyurethane, the rotation of the bushes being then not unduly resisted by friction and the wear-resistance of the bushes being high. The inner bore 4 of each bush has convergent portions 4A at each end to facilitate feeding of the feed stock through the bushes.

The spacers 3 are made of polyurethane, nylon or other material having like properties. Although not found to be necessary, a vibration-attentuating layer (not shown) may be interposed between outer tube 1, and the spacers 3. The cap closing the end of tube 1 distant from the machine also is made of or contains vibration-attentuating material.

While the bore 4 of the bushes 2 must have a diameter greater than the diameter of the largest stock to be accommodated and a diamter less than the internal diameter of the spacer tubes 3, it is not essential that the bore diameter should be closely related to the stock size and in fact a given size of bush can be used with stock within a relatively wide range of diameters, the precise bore diameter being found empirically.

In operation, the stock having a circular or noncircular (e.g. hexagonal) cross-section is fed through the stock tube and passes through the bores of the bushes. The forward end is secured in the spindle of the machine as usual. The bushes hold the stock away from the spacers 3 as the former rotates in the stock tube sot that in particular the tail of the stock cannot scrape along the interior of those tubes and generate vibratory noise. In most instances, the stock is not a close fit within the bushes and contact between the stock and any bush is intermittent; each time contact is made beteen the bush and the stock, the former is caused to rotate with the stock, the relative movement between the two whilst in contact being minimal with the result that again generation of vibratory noise is small. The bushes have been found to suffer minimal wear after prolonged use.

The noise transmitted to the air by the stock tube described and illustrated in Figure 1 has been found to be at a low ievel compared with that from stock tubes at present on the market. The stock tube can be made even quieter if the bore diameter of the bushes 2 can be chosen to be only slightly larger in size than the stock to be used.

Figure 2 illustrates a stock tube for rod finishing, e.g. for use with a Schumag straightener and polisher, where the rod is push-fed through the stock tube by the preceding section. In Figure 2, 11 is the outer tube and 12 are rotary bushes separated by spacers 13. In this instance, each bush 12 has a uniform internal bore 14, while each spacer 13 has an internal bore 1 5 of the same diameter as bore 14, with the result that the series of bushes and spacers present a constant diameter bore to the stock.

The spacers 13 are mounted for rotation within the outer tube 11 and, in order that the spacers and the bushes should be subject to minimum frictional restraint to rotation, the areas of contact with the outer tube is reduced to a minimum consistent with strength by recessing the outer faces of the bushes and spacers as shown at 16 in the case of the bushes 12 and 17 in the case of the spacers 1 3.

If desired the spacers 13 may be omitted, the outer tube 11 then being lined by a series of contiguous but relatively rotatable bushes 12.

Where the term "stock diameter" or the equivalent is used in this specification it is to be understood in relation to stock of non-circular section to mean the maximum diameter of the section.

Claims (8)

1. A stock tube comprising an outer tube and a plurality of bushes which are mounted in the outer tube for free rotation therein about and axis substantially parallel with the axis of the outer tube and which have bores enabling stock rod to pass therethrough.

2. A stock tube according claim 1, in which the bushes are spaced apart axially by tubular spacers.

3. A stock tube according to claim 2, in which each spacer is rotatable in the outer tube.

4. A stock tube according to claim 2 or claim 3, in which the bore diameter of the spacers in greater than that of the bushes.

5. A stock tube according to any one of claims 2 and 4 in which the spacers are made of nylon.

6. A stock tube according to any one of the preceding claims, in which each bush is made of a synthetic resin having the properties of high wear resistance, vibrational absorbance and low friction when in rotating contact with the outer tube.

7. A stock tube according to claim 6, in which the synthetic resin is polyurethane.

8. A stock tube substantially as herein described with reference to the accompanying drawings.