CA2061290C

CA2061290C - Sifting drum

Info

Publication number: CA2061290C
Application number: CA002061290A
Authority: CA
Inventors: Werner Lange
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1991-02-15
Filing date: 1992-02-17
Publication date: 1998-05-05
Anticipated expiration: 2012-02-17
Also published as: EP0499154A1; FI920653A0; KR960006218B1; JPH05117989A; NO920563D0; EP0499154B1; ES2077260T3; FI97105C; NO179401B; NO920563L; NO179401C; FI97105B; ATE127181T1; DE59203410D1; DE4104615A1; FI920653A; BR9200538A; KR920016153A; CA2061290A1

Abstract

A sifting drum which features sifting bars mounted along a cylindrical surface in parallel to the central cylinder axis, with the spaces between sifting bars forming the sifting gaps. The sifting bars are held by supporting rings in an axially equidistant configuration circumferentially to the cylinder circumference in peripherally open recesses in the supporting rings. The invention is characterized by the sifting bars relative to the sight line having lateral surfaces in a direction radial (V) to the sifting drum. At least one of these lateral surfaces in inclined by an angle away from the radius (V), resulting in a conicity between the two lateral surfaces of between 14 and 35° which corresponds at least to a major extent to the corresponding lateral surfaces of the supporting ring recesses. Consequently, when supporting bars of the appropriate length are transformed into supporting rings, the sifting bars are clamped into the supporting rings at these points, with at least one of the lateral surfaces of the sifting bars having at least one projection or one cutout corresponding to an opposing cutout or projection, as the case may be, in the recesses of the supporting ring.

Description

2 0 6 1 2 9 0 The present invention relates to a sifting drum and to a process for the m~n-lfaçhlre thereof.

Sifting drums are known in the art. For example, German Patent DE-OS
37 38 746 (published May 24, 1989) discloses a sifting drum wherein the strainer bars are principally attached in the recesses of supporting bars by conventional welding.
However, the use of conventional welding techniques in this lll~e. results in a number of disadvantages. First, there is the disadvantage that the res ~lt~nt weld cannot always 0 be produced in a reliable fashion. Second, the welds obtailled are prone to eventual failure due to fatigue of the weld. Third, some welding techniques (e.g. pressure welding) result in the likelihood that globules or sharp edges are formed in the weld and this can lead to adhesion of particles of the fibre suspension being sifted in the sifting drum. Such adhesion can result in the onset of a severe blockage of the affected sifting gaps.
It is an object of the present invention to provide a novel sifting drum which obviates or mitiE~tes at least one of the above-m~ntinned disadvantages of the prior art.

It is a further object of the present invention to provide a novel process for the manufacture of a sifting drum.

Accordingly, in one of its ~cpect~, the present invention provides a sieve, such ac a curved or ho.;7Ont~l sieve or sifting drum, comprising: a plurality of sifting bars arranged subst~nti~lly parallel to one anotl,cr to define sifting gaps in a sifting surface includinp- entry and e~cit sides, each said sifting bar inl~lv~ing lateral surfaces, at least one said lateral surface being intlined from a d,reclion norrnal to said sifting surface by an angle which pr~luces a conicity ~t~n the two lateral s~ e~s of between 14 and 35~, each said sifting bar further inrlutli~ at least one of a pl~;~tinn and a ret~ining recess; and a plurality of spaced support bars a~ranged substarlLially parallel to one another and each support bar inclu~ing a plurality of recesses to receive said sifting bars transverse the longihl-lin~l axis of said support bars, said recesses including lateral surfaces and further including at least one of a rel~ining cutout and a projection ~imil~rly shaped to said projection and ret~ining recess of said sifting bars to m~int~in said sifting 5 bars in said recess, wherein the width of the sifting gap defined by adjacent pairs of sifting bars at said entry side is the ~m~llest ~i~t~nce be~ween the lateral smf~c~s of adjoining sifting bars.

In another aspect, the present invention provides a process for the 10 manufacture of a sifting drum made up of sifting bars fitted in an essentially axially parallel configuration into peripherally open recesses in coaxial supporting rings that are arranged axially equidistant from each other, char~cteri7~d by the following features: a) arranging a plurality of support bars, each said support bar insl~ldin~ a plurality of lateral reces~s, longihl~in~lly parallel to one another with said recesses facing a common 15 direction and the recesses of each support bar being aligned with those of the other support bars; b) inserting sifting bars into aligned support bar lecesses to form a mat, the sifting bars eng~ging the recesses to form 'snap-in' connections therebetween; c) forming the support bars into circles with said sifting bars on the inner surface of said circles and welding the ends of the support bars together to form support rings.
It is very advantageous to design the connection between individual strainer bars and the supporting bars as a "snap-in" connection, allowing the strainer bars to be pressed into place transversely to the supi)olling bars. This avoids difficulties in inserting the strainer bars lengthwise into the sup~lling bars and avoids the problems 25 with the prior art welded strainer drums.

P~felled embcAim~ont~ of the present invention will now be described, by way of example only, with reference to the ~tt~hed figures wherein:

Figure 1 is a perspective view of part of a sifting drum;

20~1Z90 Figure 2 is a cross-section view of strainer bar sections in a portion of a ~upl)olling ring;
Figure 3 is a cross-section view of a support bar prior to its being formed into a supporting ring;
Figures 4 to 8 are cross-section views of additional strainer bar and support bar design~; and Figure 9 shows a curved horizontal screen.

A portion of a sifting drum, in a~cor~lce with the present invention, is shown in Figure 1. The drum is subst~nti~lly cylindri~l with strainer bars 3 arranged about its circumference in parallel to its longitudin~l axis.

As shown in Figure 2, strainer bars 3 are held in recesses 2' in support rings 1'.
The support rings 1' are formed from support bars 1 by first inserting the strainer bars

3 into the recesses 2 of the initially straight ~uppolling bars 1, as shown in Figure 3, and then bending the support bar 1 to form a ring. The ends of the support bar 1 are welded together to form the support ring 1', as shown in Figure 1.

To fa~ilit~te the insertion of the strainer bars 3 into the recesses 2, projections and ret~ining recesses are provided on the strainer bar profile sections which engage into corresponding cutouts and projections in the suppolling bars; i.e., the strainer bars 3 are pressed into the recesses of the supporting bars transversely to the latter.

In principle, the strainer bar profile is essenti~lly a blunted conical shape with the base of the cone located radially inside the sifting drum and the suppolling ring 1', as shown in Figure 2. The cross section of the recess 2 can also be regarded as a narrow, acute triangle in which the apex is blunted and the basal plane is the shortest side of the triangle, as shown in Figure 3. The two lateral, longer sides diverge by a given angle a or J~ from a radius of the sifting drum drawn through the im~gined apex of the cone or triangle relative to the recesses in the support rings, and, by the angles ~ and ~ 20~ 129 Q

relative to the cross section of the strainer bar profile.

In practice, this means that angles ~ and ~ of the strainer bar profile are onlyslightly smaller than the collt;sponding angles a and B of the recesses in the ~u~ol~ing S bars l; i.e. the strainer bar profile sections are somewhat narrower than the l~cesses in the supporting bars 1. Figures 2, 4, 5, 6, 7 and 8 show the s~lp~l~ g bars 1 transformed to ~iUppGlling rings 1' which means that angles a and B and angles ~ and ~
are essPn~;~lly equal. In this contlition~ the ~ldiner bar profile sections are firmly clamped into the recesses of the s.lp~l ~ing rings 1 ' . When the strainer bars are snapped 10 into place in the recesses 2 of the support bars 1, the lugs of the supporting bars projecting bet-ween the recesses are naturally deformed. Neither the projections nor the ret~ining recesses in the strainer bars 3, nor the cutouts in the supporting bars 1 may be too large, since the strainer bars are arranged in close proximity to each other, because between them, at their radially inner area, the very narrow sifting gap, often be~ween 0.15 to 0.3 mm, exists. Consequently, the depth of the projections or recesses must not exceed a range of approx. 0.2 to 0.5 mm. Depending on the diameter of the entiresifting drum, it should be noted that some 400 to 1300 strainer bars with a maximum profile thicknes~ of about 4.0 mm in the lon~it~l-lin~l direction of the supporting bars are located around the circumference of the sifting drum cylinder. Transversely to the 20 circumference, i.e. in the normal direction V, the thicl~n~ss is approx. 5.0 to 7.0 mm.

Preferably, the strainer bar profiles are drawn sections and the recesses in thes~p~ol~ g bars are produced autom~tic~lly by laser cutting. Suppolting bars are arranged and secured in parallel at an int~ l distance colles~nding to the distance 25 between supporting rings, whereafter the strainer bars are sequentially pressed into the recesses of all supporting bars ~imulhneously. It is, of course, also possible to slide the strainer bars into the recesses of the suppoltillg bars lengthwise, provided the strainer bar profile and the recesses have been produced to very exact measurements. This strainer mat, which has been so practically produced from the parallel suppol~ g bars and the 30 strainer bar profiles, is then shaped into a cylindri~l sifting drum by bending the 20~1290 suppolling bars into annular shapes, whereafter the two ends of each sup~lling bar are welded together. The sifting drum produced in this manner has the advantage thatconnections b~lween strainer bars and ~uL~polling rings are entirely free of welds.

The ~uppollillg rings can be connected by welding to leillfol~lllent rings, preferably along the external radius, and these in turn welded to axially parallel pins 38 in Figure 1.

Shown in Figure 2 is a strainer bar profile f~ in its outer radial sepmP,nt a unilateral projection 36 which engages into a colles~onding cutout in the recess on the sup~olling bar. ~ltern~tively, as in~ ted by the ghosted line at 36, the strainer bar can be provided with two projections. The angles ~ and ~ of triangle sides 7 and 8 are shown. The collesponding recesses 2 in the sup~olling bars 1 are shown in Figure 3.

The projections on the strainer bar profile shown in Figure 4 are also bilateral;
their lateral surface angles ~ and ~ being equal to the corresponding angles of the triangle sides relative to the normal V. In this case, projections 27 and 28 in practice form a thickening, i.e. a type of base section to the strainer bar profiles which holds them in place in the suppolling rings 1' and the supporting bars 1. These projections hold the strainer bar profiles throughout the entire manufacturing process, from insertion of the strainer bar 3 into the sul.polling bars 1 to completion of the circular sifting drum.

A somewhat simpler strainer bar profile is shown as a ghosted line in Figure 4.
The profile sections of strainer bars 22 shown in Figure 5 likewise encompass the lateral surfaces 39 and 40 of the triangle, on each side re~t~,;ng a recess, 41 and 42 respectively; i.e. the lateral s~ c~s 27' and 28' in the outer radial area are ess~-nti~lly in ~lignmPnt with the lateral smf~ces 39 and 40 in the inner radial segment. In practice, recesses 41 and 42 are shaped in the basic triangular form of the profile section.

Shown in Figure 6 is a bar profile with a unilateral recess 41" which is engaged _5 by a projection 41' in the recess of the ~uppolling ring. This design would appear relatively advantageous from the manufacturing standpoint. The illustration also suggests that while projections 41' do not ~lfespond exactly to the recesses 41n, they mesh exactly in the outer radial area which allows the strainer bars to be very precisely 5 positioned in the radial direction also during the process of bending the supporting bars.
Essentially, the rccesses in the ~uppolling rings and ~uppo~ling bars are only required to agree by about 70% to the collcsL~nding profile sections, since the snap-in connection does not have to cover the entire potential contact area.

In particular, lccesses on the ~uppOl ling rings can be larger than the corresponding supporting bar profile, especially in the outer radial area where a gap of e.g. 0.2 to 0.4 mm is acceptable. This gap should nevertheless be minimi7~d to prevent the risk of stress. Any gap between strainer bar and supl~olling bar can be sealed with a suitable liquid plastic, for example Loctite0, after bending. This is also suggested in 15 Figure 6. As a general rule, the sum of angles ~ + ~ of the basic form of the bar profile section should be between 14 and 34~.

Figure 7 shows an additional design which may be especially suited to the snap-in process due to the shape of the lugs 32 between recesses 5" and 6" on the ~uppollillg 20 bars. The reason is that a relatively flexible point is formed at the base of the lug in the area of the single projection 29 on the strainer bar profile, which limits deforrnation of the lug to tempol~uy distortion during snap-in with no significant plastic deformation.
It is, on the other hand, also possible to leave a broader "tooth" of e.g. 10 mm at the end of the supporting bars in order that all strainer bars and intermeAi~t~ lugs can be pressed 25 back in the correct position without residual defollllalion after the last ~l,ainer bar has been snapped in. Once the ~ul,po, ling bars have been bent, or the screen mat shaped into a cylinder with adjoining ends of individual suppol~ g rings welded together, the strainer bars will in practice keep each other in the correct position. As stated, the rigidity of the entire sifting drum can be increased by widened ~u~polling rings.

- 2Q~129~

All designs shown in Figures 4 to 7 are also a~plopliate for the production of aso-called horizontal screen 123 (see Figure 9) which can be design~d with flat or curved supporting bars; the strainer bars being snapped into the lccesses in the suppo,ling bars.
In this case, the cross section of the strainer bars must not be narrower than the cross S section of the recesses in the ~ul)polling bars. With this type of screen, recesses in the ~up~lLing bars must be dim~n~ioned approxim~tPly 0.02 to 0.2 mm smaller than thecross section of the sl,diner bar profile in the snap-in area. As described above, larger gaps are acceptable between the strainer bars and the recesses in the suppol~ing bars outside the snap-in areas. It should be noted that the cross section of s~l;~ er bars in the 10 case of horizontal screens can be ~ignifi~ntly larger than the dimçncions described for (cylindrical) sifting drums.

Hence, it is feasible first to bend (back) the ~uppolling bars 145 in order to expand their reces~s, thus making it easier to snap the strainer bars 144 into place.
Depending on requirements, this backward bending can utilize both the purely elastic and the plastic char~tçristics of the supporting bar m~t~ri~l. The suppolling bars are then returned to their straight shape (circllm~t~nces permitting, simply by means of the elastic rebound). Ren~ing back the supporting bars can also be achieved by means of external pressure (on a rounding device), which allows the strainer bars to be even more firmly wedged into the recesses on the ~upl)olling bars.

Naturally, this effect also occurs when straight supporting bars are bent into the curved shape of an arched horizontal screen as shown in Figure 9, which also provides for transverse supporting bars 146.
Figure 8 shows another favourable snap-in connection design for strainer bars 51with ~c;cesses (cutouts) 52 inten~ed for a horizontal screen fitted with suppolling bars 145 that feature pouch-shaped recesses with a narrowed area 52 at a point c~llcs~nding to the outer segm~nt of the pcllail ing strainer bar profile. When this design is used, the 30 strainer bar profile can be very small, as indicated mlmeri~lly above, which f~cilit~tçs the production of a curved sieve for straining of fibre ~uspen~ions. To facilit~te insertion of the strainer bars 51, the recess 145 is made somewhat larger in the area of deepest penetration into the supporting bar profile, than would be required to accommodate the width (breadth) of the sll~iner bar, thus producing a void 53. Within this area, the width 5 of the strainer bar profile is gr~-lu~lly reduced towards the base of the ~up~~ g bar recess. However, it is not e~ ti~l that the void 53 be provided.

Claims

WE CLAIM:

1. A sieve, such as a curved or horizontal sieve or sifting drum, comprising:
a plurality of sifting bars arranged substantially parallel to one another to define sifting gaps in a sifting surface including entry and exit sides, each said sifting bar including lateral surfaces, at least one said lateral surface being inclined from a direction normal to said sifting surface by an angle which produces a conicity between the two lateral surfaces of between 14 and 35°, each said sifting bar further including at least one of a projection and a retaining recess; and a plurality of spaced support bars arranged substantially parallel to one another and each support bar including a plurality of recesses to receive said sifting bars transverse the longitudinal axis of said support bars, said recesses including lateral surfaces and further including at least one of a retaining cutout and a projection similarly shaped to said projection and retaining recess of said sifting bars to maintain said sifting bars in said recess, wherein the width of the sifting gap defined by adjacent pairs of sifting bars at said entry side is the smallest distance between the lateral surfaces of adjoining sifting bars.

2. A sieve, such as a curved or horizontal sieve or sifting drum, comprising:
a plurality of substantially parallel sifting bars, each including at least one of a projection and retaining recess;
a plurality of support bars each including recesses, each said recess further including at least one of a cutout and a projection similarly shaped to said projection and retaining recess of said sifting bars, said support bars extending in parallel transversely to the longitudinal axis of said sifting bars, said sifting bars being received in said recesses of support bars in a snap-in connection when the sifting bars are inserted into the recesses of said support bars transversely to the longitudinal direction of said support bars.

3. A sieve in accordance with claim 1 or 2, wherein at least one of the projections and cutouts have a depth of at least 0.20 mm.

4. A sieve in accordance with claim 1, wherein at least one of the projections and cutouts have a depth of between 0.2 and 0.5 mm.

5. A sieve in accordance with claim 2, wherein at least one of the projections and cutouts have a depth of between 0.2 and 0.5 mm.

6. A sieve in accordance with claim 1, wherein the angle between the lateral surfaces of said sifting bars and the angle between the lateral surfaces of recesses in said support bars is substantially equal.

7. A sieve in accordance with claim 1, 4, 5 or 6, wherein each said lateral surface of said sifting bars includes said projection, said projections producing a terminal area which serves as a mounting support in said support bars and forms a thickened base section.

8. A sieve in accordance with claim 1, 2, 4, 5 or 6, wherein at least 50% of said lateral surfaces of said sifting bar are complementary to the recess in the support bar when the sifting bars are snapped into position in the support bars of the completed sieve.

9. A sieve in accordance with claim 1, 4, 5 or 6, wherein each said lateral surface of said sifting bars includes said projection, said projections producing a terminal area which serves as a mounting support in said support bars and forms a thickened base section and at least 50% of said lateral surfaces of said sifting bar recesses are complementary to said recesses in said support bar when the sifting bars are snapped into position in the support bars of the completed sieve.

10. A sieve in accordance with claim 1, wherein said sifting bars include said projections with a maximum depth adjacent the point of said conicity and retaining recesses adjacent the base of said conicity, said projections and retaining recesses being dimensioned so as to achieve exact radial positioning of the sifting bars when they are snapped into the support bars.

11. A sieve in accordance with claim 4, 5 or 6, wherein said sifting bars include said projections with a maximum depth adjacent the point of said conicity and retaining recesses adjacent the base of said conicity, said projections and retaining recesses being dimensioned so as to achieve exact radial positioning of the sifting bars when they are snapped into the support bars.

12. A sieve in accordance with claim 10, wherein said projections and retaining recesses on the sifting bar act with the corresponding cutouts and projections in the support bars to form snap-in connections when the sifting bars are inserted into the support bars transversely to the longitudinal direction of the latter.

13. A sieve in accordance with claim 1 or 2, wherein said support bars include a pouch-shaped retaining recess and said sifting bars include a substantially complementary narrowing.

14. A process for the manufacture of a sifting drum made up of sifting bars fitted in an essentially axially parallel configuration into peripherally open recesses in coaxial supporting rings that are arranged axially equidistant from each other, characterized by the following features:

(a) arranging a plurality of support bars, each said support bar including a plurality of lateral recesses, longitudinally parallel to one another with said plurality of lateral recesses facing a common direction and the recesses of each support bar being aligned with those of the other support bars;

(b) inserting sifting bars into aligned support bar recesses to form a mat, the sifting bars engaging the aligned support bar recesses to form 'snap-in' connections therebetween;

(c) forming the support bars into circles with said sifting bars on the inner surface of said circles and welding the ends of the support bars together to form support rings.

15. The process in accordance with claim 14, wherein the recesses taper conically from the interior to the exterior of the support rings.

16. The process in accordance with claim 15, wherein the recesses on the support bars further include projections or cutouts which engage complementary formations on the sifting bars when said snap-in connections are formed.

17. The process in accordance with claim 14, wherein the recesses in said support bars are produced by laser cutting.

18. The process in accordance with claim 14, wherein the support bars are bent to expand said recesses prior to the insertion of the sifting bars to facilitate the insertion thereof.