Bulk Material Belt Conveyor CEMA 502-2004.pdf

CEMA
STANDARD
NO. 502-2004
Revision of
CEMA Standard 502-2001
Bulk Material Belt Conveyor
Troughing and Return Idlers
Selection and Dimensions
®
CONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATION
ISBN 1-891171-52-6

Conference
CEMA ORGANIZATIONAL CHART
COMMITTEES BOARD OF DIRECTORS
Meet in March and/or September
OFFICERS
Finance and Budget
General Bulk Handling Section Unit Handling Conveying Section
Strategic Planning
Insurance
Meetings
Membership
Past Presidents
Public Relations
Bulk Handling
Components
and Systems
Screw
Conveyors
Bulk
Accessories
Meets Each June
Engineering Conference
Committees
Controls
Conveyor
Chain
Accessories
Idlers
Pulleys
Palletizers
Statistics
Safety Steering
Conveyor Chain
Performance Terminology
Unit Handling Standards
Safety
Unit Handling
Section
Terms and
Controls
Definitions
Bulk Handling
Section
International
Standards
Screw
Conveyors
Belt
Systems
Belt
Manual
For Information on Company Membership
visit the CEMA Web Site at
http://www.cemanet.org
SAFETY NOTICE
The Conveyor Equipment Manufacturers Association has developed Industry Standard Safety Labels
for use on the conveying equipment of its member companies.
The purpose of the labels is to identify common and uncommon hazards, conditions, and unsafe
practices which can injure, or cause the death of, the unwary or inattentive person who is working
at or around conveying equipment.
The labels are available for sale to member companies and non-member companies.
A full description of the labels, their purpose, and guidelines on where to place the labels on typical
equipment, has been published in CEMA’s Safety Label Brochure No. 201. The Brochure is available
for purchase by members and non-members of the Association. Safety Labels and Safety Label
Placement Guidelines, originally published in the Brochure, are also available free on the CEMA
Web Site at http://www.cemanet.org/Safety/
PLEASE NOTE: Should any of the safety labels supplied by the equipment manufacturer become
unreadable for any reason, the equipment USER is then responsible for replacement and location
of these safety labels.
Replacement labels and placement guidelines can be obtained by contacting your equipment supplier
or CEMA.

DISCLAIMER
The information provided in this document is advisory only. These recommendations
are provided by CEMA in the interest of promoting safety in the work place. These
recommendations are general in nature and are not intended as a substitute for a thorough
safety program. Users should seek the advise, supervision or consultation of qualified
engineers or other safety professionals. Any use of this document, the information contained
herein, or any other CEMA publication may only be made with the agreement and
understanding that the user and the user’s company assume full responsibility for the design,
safety, specifications, suitability and adequacy of the system component, or mechanical or
electrical device designed or manufactured using this information. The user and the user’s
company understand and agree that CEMA, its member companies, its officers, agents and
employees shall not be liable in any manner under any theory of liability for the user or user’s
reliance on these recommendations. The users and the user’s company agree to release, hold
harmless and indemnify CEMA, its member companies, successors, assigns, officers, agents and
employees from any and all claims of liability, costs, fees (including attorney’s fees), or damages
arising in any way out of the use of this information. CEMA and its member companies,
successors, assigns, officers, agents and employees make no representations or warranties
whatsoever, either express or implied, about the information contained in this document,
including, but not limited to, representations or warranties that the information and
recommendations contained herein conform to any federal, state or local laws, regulations,
guidelines or ordinances.

CEMA STANDARD 502-2004
Bulk Material Belt Conveyor Troughing and Return Idlers Selection and Dimensions
FOREWORD
This standard has been established to provide uniformity of clearance and mounting dimensions among the various
manufacturers of conveyor belt troughing idler and return rolls.
This standard assures the users of conveyor idlers interchangeability of complete idler assemblies but does not restrict
the manufacturer, who has complete freedom to design all parts of the idler according to its best engineering judgment.
The various idlers are separated into nine different classes according to load ratings and roll diameters. There are some
overlaps because of wide variation in idler construction. All manufacturers must specify into which class their particular
designs fall.
It is hoped this standardization will eliminate requests for special idler designs. Conformance with this standard will
provide better designs at lower cost.
The 1998 edition added technical data for expanded belt widths on CEMA C, D, and E Rollers and Returns and the
tables have all been reformatted to make the material easier to access.
This 2001 edition has added technical data for CEMA C, D, and E Picking Idlers, Live Shaft Idler Dimensions and Load
Capacities for Rubber Disc and Steel Tube Designs, and has modified the Idler Selection Procedures to include Impact
Idler Selection.
This 2004 edition has:
1. Reformatted the tables for CEMA Class B,C,D, and E Troughing Idlers, Picking Idlers, and Return Idlers
for easier reference.
2. Redrawn the Idler Diagrams to conform with the revised tables.
3. Added CEMA Class F Idlers
4. Reformatted and Consolidated CEMA Load Ratings and Capacities Tables
Prepared by
The Idler Committee
of the
CEMA Engineering Conference
CONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATION
6724 Lone Oak Blvd.
Naples, Florida 34109
(239) 514-3441
Fax: (239) 514-3470
E-Mail: cema@cemanet.org
Web Site: http://www.cemanet.org
Standard No. 502 - Copyright 2004
Conveyor Equipment Manufacturers Association
ISBN 1-89117-52-6
Publication Date: June 30, 2004

IDLER NOMENCLATURE
This standard provides uniform dimensional and load capacity information for several idler types, as follows.
-Troughing Idlers, with equal length rolls.
-Picking Idlers, with unequal length rolls.
-Return Idlers, with a single steel roll but typically available with rubber discs.
-V Return Idlers, with a pair of steel rolls but typically available with rubber discs.
-Live Shaft Idlers with steel or rubber surfaces.
Nomenclature and selection methods have been developed to provide a realistic and versatile means of classifying idlers. The
idler classifications and historic series are tabulated below.
CEMA Class Former Series Roll Diameter Belt Width Description
A4
A5
STANDARD WITHDRAWN - October 1, 1996
STANDARD WITHDRAWN - October 1, 1996
Light Duty
B4
B5
C4
C5
C6
D5
D6
E6
E7
F6
F7
F8
II
II
III
III
IV
None
None
V
VI
New
New
New
4"
5"
4"
5"
6"
5"
6"
6"
7"
6"
7"
8"
18" through 48"
18" through 48"
18" through 60"
18" through 60"
24" through 60"
24" through 72"
24" through 72"
36" through 96"
36" through 96"
60" through 96"
60" through 96"
60" through 96"
Light Duty
Medium Duty
Heavy Duty
Heavy Duty
Idler Designation
TABLE OF CONTENTS
Type and Angle Page
CEMA
CEMA
CEMA
CEMA
CEMA
CEMA
B4, B5
C4, C5, C6
D5, D6
E6, E7
F6 F7 F8
B4 and B5
Troughing
Troughing
Troughing
Troughing
Troughing
Flat Return
20º 35º 45º
20º 35º 45º
20º 35º 45º
20º 35º 45º
20º 35º 45º
2
3
4
5
6
7
CEMA
CEMA
CEMA
CEMA
CEMA
CEMA
CEMA
C4, C5, C6
D5,D6
E6, E7
F6 and F7
C4, C5, C6
D5 and D6
E6 and E7
Flat and V Returns 10º & 15º
Flat Return
Picking 20º
Picking 20º
Picking 20º
8
9
10
11
12
12
12
CEMA Live Shaft Idler Dimensions and Load Capacities
Rubber Disc and Steel Tube Designs
CEMA Belt Scale Idler Standard
Selection of Idlers
Idler Selection Procedure
Load Ratings and Capacities Tables
Example: Idler Selection
Conversion Factors to SI-Metric Units
1
13
13
14
15
17
24
25
29
For final design, request certified prints

CEMA CLASS B TROUGHING IDLERS
CEMA CLASS B TROUGHING IDLERS
BELT WIDTH
18
24
30
36
42
48
Trough Angle
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
∅ 4
10
11 1/2
12 1/2
10 3/4
12 3/4
14
11 1/2
13 3/4
15 3/4
12 1/4
15
18
13 1/2
16 3/4
19 3/4
13 3/4
18
20 3/4
A
E Max
∅ 5
10 1/4
12
12 3/4
11 1/4
13 1/4
14 1/4
12
14 1/4
15 3/4
12 3/4
15 1/2
17 1/4
14
17 1/4
19 1/4
15
18 1/2
20 3/4
∅ 4
22
20 1/4
18 1/2
28
25 3/4
23 3/4
34
31 1/4
28 3/4
40
37
35
46
42 1/2
39 1/4
52
48
44 1/2
C MAX
H Max
∅ 5
21 3/4
19 3/4
18
27 3/4
25 1/4
23
33 3/4
30 3/4
28
39 3/4
36 1/2
33 1/4
45 3/4
42
38 1/4
51 3/4
47 1/2
43 1/4
∅ 4
7
7
7
7
7 1/2
7 1/2
K ± 1/4
∅ 5
7 1/2
7 1/2
7 1/2
7 1/2
8
8
BELT WIDTH STD. BASE WIDE BASE STD. BASE WIDE BASE B D MAX
18
24
30
36
42
48
27
33
39
45
51
57
29 1/2
35 1/2
41 1/2
47 1/2
53 1/2
59 1/2
6
6
6
6
7 1/2
7 1/2
8 1/2
8 1/2
8 1/2
8 1/2
10
10
2.

BELT Trough
CEMA CLASS C TROUGHING IDLERS
CEMA CLASS C TROUGHING IDLERS
E Max H Max
K ± 1/4
WIDTH
18
24
30
36
42
48
54
60
Angle
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
∅ 4
10 3/4
12 1/2
14
11 1/2
13 3/4
15 1/2
12 1/2
15
17
13 1/4
16 1/4
18 3/4
14
17 3/4
20 1/4
15
19
21 3/4
16 3/4
20 1/4
23 1/4
17 3/4
21 1/2
25
∅ 5
11 1/4
13
14
12
14 1/4
15 1/2
12 3/4
15 1/2
17 1/4
13 1/2
16 3/4
19
14 1/2
18 1/4
20 1/2
15 1/2
19 3/4
22
16 1/2
21
23 1/2
18 1/2
22 1/4
25
∅ 6
12 3/4
14 3/4
15 3/4
13 1/2
16
17 1/2
14 1/4
17 1/4
19 1/4
15 1/4
18 3/4
20 3/4
16 1/4
20
22 1/4
17 1/4
21 1/4
23 3/4
19 1/4
22 1/2
25 1/4
∅ 4
22 1/2
21
19
28 1/2
26 1/2
24
34 1/2
32
29
40 1/2
37 1/2
34
46 1/2
43
39
52 1/2
48 1/2
44
58 1/2
54
49
64 1/2
59 1/2
54
∅ 5
22 1/2
21
19
28 1/2
26 1/2
24
34 1/2
32
29
40 1/2
37 1/2
34
46 1/2
43
39
52 1/2
48 1/2
44
58 1/2
54
49
64 1/2
59 1/2
54
∅ 6
27 1/2
25
22 1/2
33 1/2
30 1/2
27 1/2
39 1/2
36
32 1/2
45 1/2
41 1/2
37 1/2
51 1/2
47
42 1/2
57 1/2
52 1/2
47 1/2
63 1/2
58
52 1/2
∅ 4
8
8
8
8
8 1/2
8 1/2
8 3/4
8 3/4
∅ 5
8 1/2
8 1/2
8 1/2
8 1/2
9
9
9 1/4
9 1/4
∅ 6
9
9
9
9 1/2
9 1/2
9 3/4
9 3/4
BELT
WIDTH
18
24
30
36
42
48
54
60
STD. BASE
27
33
39
45
51
57
63
69
A
WIDE BASE
33
39
45
51
57
63
69
75
STD. BASE
29 1/2
35 1/2
41 1/2
47 1/2
53 1/2
59 1/2
66
72
C MAX
WIDE BASE
35 1/2
41 1/2
47 1/2
53 1/2
59 1/2
65 1/2
72
78
B
6
6
6
6
7 1/2
7 1/2
9
9
D MAX
10
10
10
10
10
10
11 1/2
11 1/2
3.

CEMA CLASS D TROUGHING IDLERS
CEMA CLASS D TROUGHING IDLERS
BELT WIDTH Trough Angle
20°
24 35°
45°
20°
30 35°
45°
20°
36 35°
45°
20°
42 35°
45°
20°
48 35°
45°
20°
54 35°
45°
20°
60 35°
45°
20°
72 35°
45°
BELT WIDTH
∅ 5
12
14 1/4
15 1/2
12 3/4
15 1/2
17 1/4
13 1/2
16 3/4
19
14 1/2
18 1/4
20 1/2
15 1/2
19 3/4
22
16 1/2
21
23 1/2
18 1/2
22 1/4
25
20
25
28
A
E Max
∅ 6
12 3/4
14 3/4
15 3/4
13 1/2
16
17 1/2
14 1/4
17 1/4
19 1/4
15 1/4
18 3/4
20 3/4
16 1/4
20
22 1/2
17 1/4
21 1/4
23 3/4
19 1/4
22 1/2
25 1/4
20 1/2
25
28 1/4
∅ 5
28 1/2
26 1/2
24
34 1/2
32
29
40 1/2
37 1/2
34
46 1/2
43
39
52 1/2
48 1/2
44
58 1/2
54
49
64 1/2
59 1/2
54
76 1/2
68 1/2
64
C MAX
H Max
∅ 6
27 1/2
25
22 1/2
33 1/2
30 1/2
27 1/2
39 1/2
36
32 1/2
45 1/2
41 1/2
37 1/2
51 1/2
47
42 1/2
57 1/2
52 1/2
47 1/2
63 1/2
58
52 1/2
75 1/2
69
62 1/2
B
∅ 5
8 1/2
8 1/2
8 1/2
9
9
9 1/4
9 1/4
9 1/2
K ± 1/4
D MAX
∅ 6
9
9
9
9 1/2
9 1/2
9 3/4
9 3/4
10
24
STD. BASE WIDE BASE STD. BASE WIDE BASE
33 39 35 1/2 41 1/2 6 10
30
36
42
48
54
60
72
39
45
51
57
63
69
81
45
51
57
63
69
75
87
41 1/2
47 1/2
53 1/2
59 1/2
66
72
84
47 1/2
53 1/2
59 1/2
65 1/2
72
78
90
6
6
7 1/2
7 1/2
9
9
9
10
10
10
10
11 1/2
11 1/2
12
4.

CEMA CLASS E TROUGHING IDLERS
CEMA CLASS E TROUGHING IDLERS
Dimension K for 84" and 96" belt w idths may differ w ith some manufacturers.
E Max H Max K ± 1/4
20°
∅ 6
16 1/2
∅ 7
17
∅ 6
42
∅ 7
42
∅ 6 ∅ 7
36
42
48
54
60
72
84
96
BELT WIDTH
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
21
21 1/2
17 1/2
22 1/2
23
18 1/2
24
24 1/2
19 1/2
25 1/2
26
20 1/2
27
27 1/2
22
29
31
24
31
34
26
33
37
A
21 1/2
22
18
23
23 1/2
19
24 1/2
25
20
26
26 1/2
21
27 1/2
28
22 1/2
29 1/2
31 1/2
24 1/2
31 1/2
34 1/2
26 1/2
33 1/2
37 1/2
38
35
48
43 1/2
40
54
49
45
60
54 1/2
50
66
60
55
78
71
65
90
82
75
102
93
85
C MAX
38
35
48
43 1/2
40
54
49
45
60
54 1/2
50
66
60
55
78
71
65
90
82
75
102
93
85
B
10 3/4
10 3/4
10 3/4
10 3/4
10 3/4
11 1/2
11 3/4
11 3/4
D MAX
11 1/4
11 1/4
11 1/4
11 1/4
11 1/4
12
12 1/4
12 1/4
36
45 51 53 54 9 1/2 14
42
48
54
60
72
84
96
51
57
63
69
81
93
105
57
63
69
75
87
99
111
59
65
71
77
89
101
113
60
66
72
78
91
103
115
9 1/2
9 1/2
9 1/2
9 1/2
9 1/2
12
12
14
14
14
14
14
16 1/2
16 1/2
5.

CEMA CLASS F TROUGHING IDLERS
CEMA CLASS F TROUGHING IDLERS
Dimension K for 84" and 96" belt w idths may differ w ith some manufacturers.
20°
∅ 6
21 1/2
E Max
∅ 7
22
∅ 8
22 1/2
H Max
∅ 6 ∅ 7 ∅ 8
66
∅ 6
K ± 1/4
∅ 7 ∅ 8
60
72
84
96
35°
45°
20°
35°
45°
20°
35°
45°
20°
35°
45°
BELT WIDTH
28
28 1/2
22 1/2
29 1/2
31 1/2
24 1/2
31 1/2
34 1/2
26 1/2
33 1/2
37 1/2
A
28 1/2
29
23
30
32
25
32
35
27
34
38
29
29 1/2
23 1/2
30 1/2
32 1/2
25 1/2
32 1/2
35 1/2
27 1/2
34 1/2
38 1/2
C MAX
60
55
78
71
65
90
82
75
102
93
85
11 3/4
12
12 1/4
12 1/4
B
12 1/4
12 1/2
12 3/4
12 3/4
D MAX
12 3/4
13
13 1/4
13 1/4
60
69 75 77 78 12 15
72
84
96
81
93
105
87
99
111
89
101
113
91
103
115
12
12
12
15
15
15
6.

CEMA CLASS B RETURN IDLERS
FLAT RETURNS ( 4" AND 5" DIAMETERS )
For wide base returns, use next higher belt width.
*Some differences may exist in dimensions with some manufacturers.
**Also available with 1 1/2" drop.
BELT WIDTH
18
24
30
36
42
48
A
STD BASE
27
33
39
45
51
57
7
C
MAX
29 1/2
35 1/2
41 1/2
47 1/2
53 1/2
59 1/8
F
MIN
22
28
34
40
46
52

CEMA CLASS C RETURN IDLERS
FLAT RETURNS ( 4", 5", AND 6" DIAMETERS )
BELT
WIDTH
18
24
30
36
42
48
54
60
66
A
STD BASE
27
33
39
45
51
57
C
MAX
29 1/2
35 1/2
41 1/2
47 1/2
53 1/2
59 1/8
USE CEMA "D" RETURN ROLLER
V-RETURNS
F
MIN
23
29
35
41
47
53
**Also available with 4 1/2" drop which decreases all vertical dimensions by 2 1/2".
For wide base returns use next larger belt width.
BELT WIDTH
24
30
36
42
48
54
60
66
A
33
39
45
51
57
63
69
75
10°
37 1/2
43 1/2
49 1/2
55 1/2
61 1/2
67 1/2
73 1/2
79 1/2
C Max
15°
38 1/4
44 1/4
50 1/4
56 1/4
62 1/4
68 1/4
74 1/4
80 1/4
• 5
6 3/4
7 1/2
7 7/8
8 1/2
9
9 5/8
10 1/8
10 3/4
10°
•6
6 1/4
7
7 3/8
8
8 1/2
9 1/8
9 5/8
10 1/4
E ± 1/4
•5
8
9
9 5/8
10 1/2
11 1/4
12 1/8
12 7/8
13 5/8
15°
•6
7 1/2
8 1/2
9 1/8
10
10 3/4
11 5/8
12 3/8
13 1/8
10°
15 7/8
16 3/8
16 3/4
17 3/8
17 7/8
18 7/8
19 1/2
20 3/8
G Max
15°
16 3/4
17 3/4
18 1/2
19 1/4
20
21 5/8
22 3/8
23 5/8
8 For final design, request certified prints

CEMA D RETURN IDLERS
BELT WIDTH
24
30
36
42
48
54
60
66
72
78
A
STD BASE
33
39
45
51
57
63
69
75
81
87
V-RETURNS
C
MAX
35 1/2
41 1/2
47 1/2
53 1/2
59 1/8
65 1/2
71 1/2
77 1/2
83 1/2
89 1/2
F
MIN
29
35
41
47
53
59
65
71
77
83
E ± 1/4
BELT
WIDTH
36
42
48
54
60
66
72
78
A
45
51
57
63
69
75
81
87
10°
49 1/2
55 1/2
61 1/2
67 1/2
73 1/2
79 1/2
85 1/2
91 1/2
C Max
15°
50 1/4
56 1/4
62 1/4
68 1/4
74 1/4
80 1/4
86 1/4
92 1/4
• 5
7 7/8
8 1/2
9
9 5/8
10 1/8
10 3/4
11 1/4
11 3/4
10°
•6
7 3/8
8
8 1/2
9 1/8
9 5/8
10 1/4
10 3/4
11 1/4
•5
9 5/8
10 1/2
11 1/4
12 1/8
12 7/8
13 5/8
14 5/8
15 1/2
15°
•6
9 1/8
10
10 3/4
11 5/8
12 3/8
13 1/8
14 1/8
15
10°
16 7/8
17 1/2
18
18 7/8
19 1/2
20
20 1/2
21
G Max
15°
18 1/2
19 1/4
20
21 5/8
22 3/8
23 5/8
24 1/4
25 1/8

CEMA E RETURN IDLERS
*Some differences may exist in dimensions with some manufacturers. **Also available with 1 1/2" drop.
BELT WIDTH
36
42
48
54
60
66
72
78
84
90
96
102
A
STD BASE
45
51
57
63
69
75
81
87
93
99
105
111
C
MAX
48 1/2
54 1/2
60 1/2
66 1/2
72 1/2
78 1/2
84 1/2
90 1/2
96 1/2
102 1/2
108 1/2
114 1/2
V-RETURNS
D
MAX
12 1/2
12 1/2
12 1/2
12 1/2
12 1/2
12 1/2
12 1/2
12 1/2
14 1/2
14 1/2
14 1/2
14 1/2
F
MIN
41
47
53
59
65
71
77
83
89
95
101
107
E ± 1/4
BELT WIDTH A C ± 1/4 10°
•6 •7 •6
15°
•7 10°
G Max
15°
36
42
48
54
60
66
72
78
84
90
96
102
45
51
57
63
69
75
81
87
93
99
105
111
49
55
61
67
73
79
85
91
97
103
109
115
7 5/8
8 1/8
8 5/8
9 1/8
9 5/8
10
10 5/8
11 1/8
11 5/8
12 1/8
12 5/8
13 1/8
7 1/8
7 5/8
8 1/8
8 5/8
9 1/8
9 1/2
10 1/8
10 5/8
11 1/8
11 5/8
12 1/8
12 5/8
9 1/8
9 7/8
10 5/8
11 3/8
12 1/8
13
13 5/8
14 1/2
15 1/4
16 1/8
16 7/8
17 3/4
8 5/8
9 3/8
10 1/8
10 7/8
11 5/8
12 1/2
13 1/8
14
14 3/4
15 5/8
16 3/8
17 1/4
18 1/4
18 3/4
19 1/4
19 3/4
20 1/4
21 1/2
22
22 1/2
23 1/8
23 5/8
24 1/4
24 3/4
20 1/4
21
21 7/8
22 3/4
23 1/2
25
25 3/4
26 1/2
27 1/4
28 1/8
28 7/8
29 3/4

CEMA F RETURN IDLERS
FLAT RETURNS ( 6", 7" and 8" DIAMETERS )
A
BELT WIDTH STD BASE
C
MAX
F
MIN
60
72
84
96
69
81
93
105
73 1/2
85 1/2
97 1/2
109 1/2
65
77
89
101
V-RETURNS
For Vee Returns consider using CEMA E.

BELT E Max
CEMA PICKING IDLERS
H Max K ± 1/4
L
CEMA
CLASS
C
PICKING
IDLERS
24
30
36
42
48
54
60
∅ 4
10 7/8
10 7/8
10 7/8
11
11
11 1/4
11 1/4
∅ 5
11 3/8
11 3/8
11 3/8
11 1/2
11 1/2
11 3/4
11 3/4
∅ 6
11 7/8
11 7/8
11 7/8
12
12
12 1/4
12 1/4
∅ 4
33
35
41
47
53
59
65
∅ 5
32 3/4
34 3/4
40 3/4
46 3/4
52 3/4
58 3/4
64 3/4
∅ 6
32 3/8
34 3/8
40 3/8
46 3/8
52 3/8
58 3/8
64 3/8
∅ 4
8
8
8
8 1/2
8 1/2
8 3/4
8 3/4
∅ 5
8 1/2
8 1/2
8 1/2
9
9
9 1/4
9 1/4
∅ 6
9
9
9
9 1/2
9 1/2
9 3/4
9 3/4
Bolt Dia.
1/2
1/2
1/2
5/8
5/8
5/8
5/8
BELT E Max H Max K ± 1/4 L
CEMA
CLASS
D
PICKING
IDLERS
WIDTH
24
30
36
42
48
54
60
72
∅ 5
11 5/8
12 1/4
12 1/4
12 1/4
12 1/4
12 1/4
12 1/4
12 1/4
∅ 6
12 1/8
12 3/4
12 3/4
12 3/4
12 3/4
12 3/4
12 3/4
12 3/4
∅ 5
32 3/4
34 3/4
40 3/4
46 3/4
52 3/4
58 3/4
64 3/4
76 3/4
∅ 6
32 3/8
34 3/8
40 3/8
46 3/8
52 3/8
58 3/8
64 3/8
76 3/8
∅ 5
8 1/2
8 1/2
8 1/2
9
9
9 1/4
9 1/4
9 1/2
∅ 6
9
9
9
9 1/2
9 1/2
9 3/4
9 3/4
10
Bolt Dia.
1/2
1/2
1/2
5/8
5/8
5/8
5/8
5/8
NOTE: ROLL LENGTHS VARY
WIDELY BETWEEN
MANUFACTURERS. CONSULT
BELT
WIDTH ∅ 6
E Max
∅ 7 ∅ 6
H Max
∅ 7 ∅ 6
K ± 1/4
∅ 7
L
Bolt Dia.
SPECIFIC MANUFACTURERS FOR
ACTUAL DIMENSIONS.
CEMA
CLASS
E
PICKING
IDLERS
36
42
48
54
60
72
84
14
14
14
14
14
14 3/8
14 5/8
14 1/2
14 1/2
14 1/2
14 1/2
14 1/2
14 7/8
15 1/8
43 1/8
49 1/8
55 1/8
61 1/8
67 1/8
79 1/8
91 1/8
42 7/8
48 7/8
54 7/8
60 7/8
66 7/8
78 7/8
90 7/8
10 3/4
10 3/4
10 3/4
10 3/4
10 3/4
11 1/2
11 3/4
11 1/4
11 1/4
11 1/4
11 1/4
11 1/4
12
12 1/4
3/4
3/4
3/4
3/4
3/4
3/4
3/4
BELT
96
A
14 5/8 15 1/8 103 1/8 102 7/8 11 3/4
C MAX
12 1/4
B
3/4 CEMA
CLASS
D MAX
WIDTH
24
30
STD.
BASE WIDE BASE
33 39
39 45
STD. BASE
C/D E
35 1/2
41 1/2
WIDE BASE
C/D E
41 1/2
47 1/2
C/D
6
6
E C/D
10
10
E
36
42
48
54
60
72
84
96
45
51
57
63
69
81
93
105
51
57
63
69
75
87
99
111
47 1/2
53 1/2
59 1/2
66
72
84
53
59
65
71
77
89
101
113
53 1/2
59 1/2
65 1/2
72
78
90
54
60
66
72
78
91
103
115
6
7 1/2
7 1/2
9
9
9
9 1/2
9 1/2
9 1/2
9 1/2
9 1/2
9 1/2
12
12
10
10
10
11 1/2
11 1/2
12
14
14
14
14
14
14
16 1/2
16 1/2
12.

CEMA LIVE SHAFT IDLER DIMENSIONS (Inches)
CEMA Live Shaft Load Capacity (lbs)
Live Shaft Idlers are developed to be compatible with commonly available bearing assem-
blies which may not be part of the idler assembly. Load ratings are developed for uniformly
distributed steady running loads. Consult the manufacturer for non uniform loading and
for application information important for long bearing life.
For Live Shaft Load Capacities, Refer to Chart on Page 35
Rubber Disc and Steel Tube Designs
Dim A Dim B Dim C Dim D Dim E
BW+9
CEMA Class C: J = 1.4375" Live Shafts; O.D. = 5" & 6"
BW+2.875 to 3.75 BW+12 to 13.125 4.13 m inim um
CEMA Class D: J = 1.9375" Live Shafts; O.D. = 5" & 6"
1.50 m inim um
BW+9 BW =2.875 to 3.875 BW+ 12.3125 to 14 3.88 m inim um 1.75 m inim um
BW+9
BW = Belt Width (in)
CEMA Class E: J = 2.4375" Live Shafts; O.D. = 6" & 7"
BW+1.75 to 4.625 BW+ 13.25 to 14 4.50 m inim um 2.25 m inim um
13.

CEMA BELT SCALE IDLER STANDARD
Idlers and rolls produced to the basic CEMA Standard No. 502 have dimensional tolerances which, under
certain conditions, may be insufficient to meet the requirement of a specific accuracy of an in-motion
weighing system. The table below specifies dimensional tolerances for idlers and rolls to be classified for
use with non-certified scales for belt conveyor systems. These will be referred to as “Scale Quality”
idlers.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Roll run-out, mounted .015 T.I.R. max. (all rolls)
Axis of roll ± 0.031" from perpendicular through center of base
End brackets perpendicular to base angle 90O ± 1O
Bottom of base to top of center roll + 0", - 1/8"
Troughing angle by template ± 1O
Foot plates to be flat within 0.030"
Idler base deflection not to exceed 1/1000 of the span at published CEMA idler load
rating. Deflection measured at support for center roll.
"Scale Quality" Idlers
When considering the installation and or maintenance of a belt scale system, the use of like idlers and
rolls within the scale area is important. Proper alignment of all components and the control of contami-
nants are essential.
Belt conveyor scales from different manufacturers vary in characteristics, accuracy, and dimensions.
Therefore, the basic installation requirements relative to idler spacing and position must be obtained
from the respective scale manufacturer.
14.

THE SELECTION OF IDLERS
Foreword
Previous to 10/1/96 CEMA ratings were based on 90,000 hours Bu (useful bearing life) at 500 RPM. Bu values
were approximately 3 times L10. The Bu (useful bearing life) theory was technically correct. However, L10 bearing
life is more commonly used and accepted for bearing life calculations and rating. Previous CEMA idler selection
procedure used idler life (K) factors to calculate an adjusted idler load. Some of these (K) factors were entirely
independent of idler load and bearing L10 life. This procedure provided a conservative selection based on load but
did not necessarily provide clear data relative to expected idler life.
Rating and Idler Life
Idler life is determined by a combination of many factors, such as seals, bearings, shell thickness, belt speed, lump
size / material density, maintenance, environment, temperature and the proper CEMA series of idler to handle the
maximum calculated idler load. While bearing life is often used as an indicator of idler life it must be recognized
that the effect of other variables (e.g., seal effectiveness) may be more important in determining idler life than the
bearings. Nevertheless, since bearing rating is the only variable for which laboratory tests have provided standard
values, CEMA uses bearing L10 life as a guide for establishing idler ratings.
The definition of L10 for belt conveyor idlers: The basic rated life (number of operating hours at 500 RPM) based on
a 90 percent statistical model which is expressed as the total number of revolutions 90 percent of the bearings in an
apparently identical group of bearings subjected to identical operating conditions will attain or exceed before a
defined area of material fatigue (flaking, spalling) occurs on one of its rings or rolling elements. The L10 life is also
associated with 90 percent reliability for a single bearing under a certain load.
Tables 2-11 through 2-14 show load ratings for CEMA B, C, D, and E idlers. These load ratings are based on
the following:
CEMA B load rating based on minimum L10 of 30,000 hours at 500 RPM
CEMA C load rating based on minimum L10 of 30,000 hours at 500 RPM
CEMA D load rating based on minimum L10 of 60,000 hours at 500 RPM
CEMA E load rating based on minimum L10 of 60,000 hours at 500 RPM
CEMA F load rating based on minimum L10 of 60,000 hours at 500 RPM
These loads and L10 life ratings are minimum ratings for CEMA rated idlers. Actual values for load ratings and L10
life for specific series and belt sizes supplied by CEMA manufacturers may be higher. In some cases the idler
frame design could be the limiting factor for load with L10 life being a higher value.
Idler Selection
There are many conditions that affect idler life. Those considered in this selection procedure are:
1. Type of material handled
2. Idler load
3. Impact forces
4. Effect of load on predicted bearing L10 life
5. Belt speed
6. Roll diameter
7. Environmental, maintenance and other special conditions
In addition to information provided in the Idler Selection Procedure the above items are summarized as follows:
15.

Type of Material Handled
The characteristics of the material handled have a direct bearing on the idler selection. The weight of the material
governs the idler load and spacing, and lump size modifies the effect of weight by introducing an impact factor.
Table 2-2 combines the unit weight and the lump size into a group of empirical factors referred to as K1. Note that
in the table “lump size” means the largest lump which may occasionally be carried rather than the average lump.
Lump Size Considerations
The lump size influences the belt specifications and the choice of carrying idlers. There is also an empirical
relationship between lump size and belt width. The recommended maximum lump size for various belt widths is as
follows:
For a 20º surcharge, with 10% lumps and 90% fines, the recommended maximum lump is 1/3 the belt
width (bw/3). With all lumps the recommended maximum lump is 1/5 belt width (bw/5).
For a 30º surcharge, with 10% lumps and 90% fines, the recommended maximum lump is 1/6 the belt
width (bw/6). With all lumps maximum lump is 1/10 the belt width (bw/10).
Idler Load
To select the proper CEMA class (series) of idler, it is necessary to calculate the idler load. This procedure is
shown in IDLER SELECTION PROCEDURE (Step No. 1) for troughing idlers and (Step No. 2) for return idlers.
The idler load should be calculated for peak or maximum conditions. The belt conveyor designer should thoroughly
investigate all conditions relative to calculating idler misalignment load (IML), in addition to structure misalignment.
The idler height deviation between standard fixed idlers and training idlers (or other special types of idlers) must be
accounted for either by idler series selection or by conveyor design and installation control.
Impact Forces
Impact forces at conveyor loading points are yet another consideration for idler selection. Whether the conveyed
material contains large lumps or is a continuous flow of homogeneous material with no lumps, the impact force
should be studied. This process is demonstrated in Step No. 3.
When large lumps (greater than 2 inches) are present, the impact idler energy rating, WH, may become a factor.
Table 2-4 shows the minimum energy rating and the maximum lump size for each CEMA series impact idler. The
impact force, F, is then given by the following equation:
F = W + 2kWH
If the conveyed material does not contain lumps, but instead is a homogeneous stream of material, the impact
force is simply a function of the rate of flow and the height of fall. This impact force is given by the following
equation:
F = (0.1389) Q H
Effect of Load on Predicted Bearing L10 Life
When calculated idler load (CIL) is less than CEMA load rating of series idler selected, the bearing L10 life will
increase. Figure 2.5 (Step No. 4) shows this relationship for either a tapered roller bearing or a ball bearing idler
design. This chart can be used in conjunction with the type of service or life expectancy of the conveyor system. If
the specified design life of the conveyor system exceeds the CEMA L10 life rating at rated load it may still meet
specification based on percent of rated idler load vs calculated idler load (CIL).
16.

Belt Speed
Bearing life (L10) is based on the number of revolutions of the bearing race. The faster the belt speed, the more
revolutions per minute and consequently, a shorter life for a given number of revolutions. All CEMA L10 life ratings
are based on 500 RPM. The following table lists belt speed at 500 RPM for standard roll diameters.
Roll Diameter (in.)
4"
5"
6"
7"
8"
Belt Speed (FPM)
524
654
785
916
1048
Figure 2.6 (Step No. 5) shows the effect of belt speed on predicted bearing L10 life. However, suitable belt conveyor
speeds also depend upon the characteristics of the material to be conveyed, the capacity desired and the belt
tensions employed. This subject is covered in more detail in CEMA "Belt Conveyors for Bulk Material," Fifth Edition
(or later), Chapter 4.
Roll Diameter
For a given belt speed, using larger diameter rolls will increase idler bearing L10 life. Figure 2.7 (Step No. 6) shows
this relationship. In addition, since larger diameter rolls will be contacting the belt less due to a slower RPM the
wear life of the shell will be increased.
Environmental, Maintenance and Other Special Conditions
Step No. 7 in the idler selection procedure identifies conditions that will affect potential idler life. All of these
conditions do not have an exact mathematical basis and therefore can be very subjective. The most important
phase of this step is in identifying the idler life condition for the application and then arrive at solutions to obtain
maximum idler life for that application. Since idler roll configuration, type of bearing and seal design can vary with
each idler manufacturer it is logical to state that idler life can also vary for a given environmental and maintenance
condition.
Figures 2.8, 2.9 and 2.10 show general conditions which will affect idler life. Those conditions are independent of
idler load but can cause idler failure before obtaining predicted L10 life rating. CEMA recommends contacting your
CEMA idler manufacturer for assistance in establishing guidelines for "POTENTIAL IDLER LIFE" for the various
conditions shown or any unusual conditions not listed.
Special Conditions
Idler roll shell material usually used throughout the industry is electric resistance welded steel mechanical tubing.
For most belt conveyor applications this material provides sufficient idler life, most economically. For severe
abrasive or corrosive conditions, covered idler rolls are available in a variety of materials. CEMA has not compiled
a relative wear index or corrosion compatibility index for these various materials. This information can be supplied
by your CEMA idler manufacturer. However the economic issue vs increased life should be investigated thoroughly.
Some of the generic available materials are listed below. There are numerous grades available in each of these
materials which will affect performance.
1. Steel sleeves
2. Rubber lagging
3. Neoprene lagging
4. Polyethylene sleeves / rolls
5. Carboxylated nitrile
6. Urethane
7. Ceramic
17.

Another consideration for increasing shell wear life is to use thicker metal shells. Some idler manufacturers
customarily supply larger diameter rolls with thicker metal shells and usually offer optional shell thickness for all roll
diameters.
Idler shell wear life is more of a factor for the return idlers since it normally contacts the "dirty" side of the belt
resulting in abrasive wear of the shell. The exception to this would be a conveyor system with a belt turnover
system.
With normal conveyor systems, materials build up on the roll and increase its effective diameter. Because the
buildup is never uniform and usually is less at the belt edges, the clean sections of the return roll travel at a slower
surface speed than that of the belt. This results in relative slippage, thereby accelerating wear of both the belt
cover and the surface of the roll. Thus the life of the roll shell is usually shorter on return belt idlers than on carrying
idlers. The material buildup can also aggravate belt training.
18.

IDLER SELECTION PROCEDURE
Preface to Selection Procedure Figures and Tables.
Initial Selection; Steps 1, 2 and 3:
Select idler class by comparing calculated idler load with idler load ratings (CIL and CILR) from Tables 2-11
through 2-14. Select impact idler class, if necessary, as shown in Step 3. CEMA idler manufacturers have standard
designs meeting these load ratings and dimensional standards shown in tables listed in this publication.
Bearing L10 Life Correction; Steps 4, 5, and 6:
Factors K2 (Fig. 2.5) and K3A (Fig. 2.6) are multiplying factors used to adjust basic L10 life rating of idler class
selected. Factor K2 is based on percent of idler load and K3A is factor for actual roll speed (RPM). Factor K3B
(Fig. 2.7), step 6 is an optional step showing advantage of using larger diameter rolls. It can be used as a
multiplier to save repeating step 5 if a larger diameter roll is used.
Determine Potential Idler Life; Step 7:
Factors K4A (Fig. 2.8), K4B (Fig. 2.9) and K4C (Fig. 2.10) show conditions which will affect idler life and are
independent of bearing L10 life, idler load and idler class. Use these figures to evaluate the potential expected
idler life. Contact your CEMA idler manufacturer for recommendations.
Step No. 1 - Troughing Idler Series Selection
Calculated Idler Load (lbs.) = CIL = ((WB + (WM x K1)) x SI) + IML
Where:
WB = Belt weight (lbs./ft.) use actual or estimate from Table 2-1
WM = Material weight (lbs./ft.) = (Q x 2000) / (60 x V)
Q = Quantity of material conveyed (Tons per hour)
V = Design belt speed (FPM)
SI = Spacing of idlers (ft.)
K1 = Lump adjustment factor (see Table 2-2)
Note: Actual weight of lump should be compared with WM value.
In situations it may be necessary to use actual lump weight
as WM. Contact your CEMA idler manufacturer if you have
doubts as to which value to use.
IML = Idler misalignment load (lbs.) due to idler height deviation and
belt tension = (D x T) / (6 x SI) where:
D = Misalignment (inches)
T = Belt tension (lbs.)
SI = Idler spacing (feet)
When an idler is higher than adjacent idler, a
component of belt tension will add load to that idler.
The amount of height deviation can vary with the
installation and type of idler. CEMA publication on "Conveyor Installation Standards" ( also found in Appendix D,
"Belt Conveyors for Bulk Material," Fifth Edition or later) lists recommendations on structure misalignment).
Use CIL and select proper series of idler from Tables 2-11 through 2-15.
CIL value should be equal to or less than idler rating.
19.

This troughing idler selection procedure for calculated idler load does not include impact force on idler at loading
points or the effect of belt transitions (head and tail pulley) on idler load. See Step No. 3 for impact idler series
selection. Contact your CEMA idler manufacturer for idler series selection for other loading conditions.
Table 2-1 WB-Estimated average belt weight
multiple and reduced ply belts. lbs./ft.
Material Carried, lbs./cu. ft.
Belt Width (inches (b))
30-74 75-129 130-200
18
24
30
36
42
48
54
60
72
84
96
3.5
4.5
6
9
11
14
16
18
21
25
30
4
5.5
7
10
12
15
17
20
24
30
35
4.5
6
8
12
14
17
19
22
26
33
38
1. Steel cable belts - increase above value by 50%.
2. Actual belt weights vary with different constructions, manufacturers, cover gauges,
etc. Use the above values for estimating. Obtain actual values from the belt manufacturer
whenever possible.
Table 2-2 K1-Lump adjustment factor
Material Weight, lbs./cu. ft.
Maximum Lump Size (inches)
4
6
8
10
12
14
16
18
50
1.0
1.0
1.0
1.0
1.0
1.1
1.1
1.1
75
1.0
1.0
1.0
1.1
1.1
1.1
1.1
1.1
100
1.0
1.0
1.1
1.1
1.1
1.1
1.2
1.2
125
1.0
1.1
1.1
1.1
1.2
1.2
1.2
1.2
150
1.1
1.1
1.2
1.2
1.2
1.2
1.3
1.3
175
1.1
1.1
1.2
1.2
1.2
1.3
1.3
1.3
200
1.1
1.1
1.2
1.2
1.3
1.3
1.3
1.4
Step No. 2 - Return idler series selection
Calculated Idler Load (lbs.) = CILR = (WB x SI) + IML
Use CILR and select proper series of idler from Tables 2-11 through 2-14. CILR should be equal to or less
than return idler rating.
20.

Step No. 3 - Impact Idler Series Selection
For homogeneous material without lumps:
Impact Force (lbs) = F = (0.1389) Q H
Where:
Q = Rate of flow (ST / hr)
H = Height of fall (ft)
The calculated impact force is then multiplied by an impact idler
spacing factor, f (Table 2-3), to determine the impact force on one idler.
Unit Impact Force (lbs) = Fu = F (f)
Use this unit impact force, Fu, and select proper series of impact idler from Tables 2-11 through 2-14.
Fu should be equal to or less than idler rating.
For material containing large lumps:
Impact Force (lbs) = F = W + 2kWH
Where:
W = Weight of lump (lbs)
H = Height of fall (ft)
k = Spring constant for specific idler type (lbs / ft)
(CONSULT IDLER MANUFACTURER)
Use calculated energy rating, WH, and maximum lump size to select
proper series of impact idler from Table 2-4. Both WH and lump size
should be equal to or less than energy rating and maximum lump
size.
Note: Both cases (material without lumps and material containing large lumps) should always be considered
and the heavier duty idler selected to insure adequate impact resistance capabilities.
Table 2-3 Impact Idler Spacing Factor
Impact Idler Spacing, SI
1' - 0"
1' - 6"
2' - 0"
> 2' - 0"
Impact Idler Spacing Factor, f
0.5
0.7
0.9
1
Table 2-4 Minimum Energy Ratings for Impact Idlers
3-Roll Rubber Impact Idlers (Equal Length Rolls)
CEMA Series
B
C
D
E
F
WH (lbs-ft)
40
160
240
460
870
21.
Maximum Lump Size (in.)
4
6
8
12
18

Step No. 4 - K2 = Effect of load on predicted bearing L10 life
When Calculated Idler Load (CIL) is less than CEMA load rating of series idler selected, the bearing L10 life will
increase.
Figure 2.5 K2 = Effect of Load on Predicted Bearing L10 Life
10.0
8.0
6.0
4.0
2.0
○
○
○
○
○
○
○
○
○
○
○
○
○
○
○
○ ○
○ ○
○
○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○
○ ○
Ball Bearing
Roller Bearing
0.0
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ 1.0
0.5 0.6 0.7 0.8 0.9 1.0
CIL (Calculated Idler Load)
Idler Load Rating
Step No. 5 - K3A = Effect of belt speed on predicted bearing L10 life
CEMA L10 life ratings are based on 500 rpm. Slower speeds increase life and faster
speeds decrease life. Figure 2.4 shows this relationship.
Figure 2.6 K3A = Effect of Belt Speed on Predicted Bearing L10 Life
10.0
9.0
8.0
Belt Speed (fpm) x 12
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
50 100 200 300
RPM =
Roll Dia. (in.) x p
400 500 850
Roll Speed (rpm)
Step No. 6 - K3B = Effect of roll diameter on predicted bearing L10 life.
For a given belt speed, using larger diameter rolls will increase idler L10 life. Figure 2.5 depicts L10 life adjustments
for various roll diameters using 4” diameter as a value of 1.0. Percent life increase can be calculated for each roll
diameter increase.
1.5 for 6" dia
Example: = 1.20 or 20% increase in L10 life.
1.25 for 5" dia
Figure 2.7 K3B = Effect of Roll Diameter on Predicted Bearing L10 Life
(Based on same belt speed)
1.75
1.50
1.25
1.00
Note: In addition to increased predicted bearing L10 life, larger diameter rolls can increase idler wear life.
22.
K3A
Factor
K3B
Factor
K2Factor

Step No. 7 - K4 = Environmental, maintenance and other special conditions
Figure 2.8: K4A = Effect of maintenance on potential idler life
Figure 2.9: K4B = Effect of environment on potential idler life
Figure 2.10: K4C = Effect of operating temperature on potential idler life
Based on collective application experience by CEMA idler manufacturers these conditions are very important in
determining potential idler life. However, exact mathematical basis is very subjective so contact your CEMA idler
manufacturer for assistance or for any unusual conditions not listed.
Figure 2.8: K4A = Effect of maintenance on potential idler life
GOOD FAIR POOR
Figure 2.9: K4B = Effect of environment on potential idler life
Figure 2.10: K4C = Effect of operating temperature on potential idler life
1.0
0.0
0 130 150 170 190 210 300
Temperature (degrees F)
23.
K4C
Factor
K4B
Factor
K4A
Factor
Clean,
Dry
Dusty
,
Dry
Dirty
,
Dry
Clean,
We
t
Dusty
,
W
et
Dirty
,
We
t
W
et
w/pH
Press
W
ash
Down

Idler Class Belt Width
CEMA LOAD RATINGS AND CAPACITIES TABLES
Load Ratings for CEMA Idlers - Rigid Frame (Lbs)
Trough Angle Single Roll
CEMA B
Idlers
(Inches)
18
24
30
36
42
48
20°
410
410
410
410
390
380
35°
410
410
410
410
363
353
45°
410
410
410
396
351
342
Return Two Roll Vee
220
190
165
155
140
125
NOTES FOR TABLES
1. TROUGHING IDLER LOAD RATINGS ARE FOR
THREE EQUAL LENGTH ROLLS.
2. LOAD RATINGS ALSO APPLY FOR IMPACT ROLLS.
Ratings Based on Min L10 of 30,000 Hours at 500 RPM
18 900 900 900
24 900 900 900
30 900 900 900
36 900 837 810
475
325
250
200
500
500
3. TROUGHING IDLER LOAD RATINGS ARE BASED
ON A LOAD DISTRIBUTION OF 70% ON CENTER
ROLL AND 15% ON EACH END ROLL FOR ALL
TROUGH ANGLES.
CEMA C
Idlers
42
48
54
60
66
850
800
750
700
791
744
698
650
765
720
675
630
150
125
*
*
*
500
500
500
500
500
* Use CEMA "D" Return Idler
24 1,200 1,200 1,200 600
CEMA D
Idlers
30
36
42
48
54
60
66
72
78
1,200
1,200
1,200
1,200
1,200
1,150
1,050
1,200
1,200
1,200
1,200
1,116
1,070
977
1,200
1,200
1,200
1,200
1,080
1,035
945
600
600
500
425
375
280
215
155
125
850
850
850
850
850
850
850
850
36 1,800 1,800 1,800 1,000 1,300
CEMA E
Idlers
42
48
54
60
66
72
78
84
90
96
102
1,800
1,800
1,800
1,800
1,800
1,674
1,750
1,800
1,800
1,800
1,800
1,800
1,674
1,628
1,800
1,800
1,800
1,800
1,800
1,620
1,575
1,000
1,000
925
850
775
700
625
550
475
400
250
1,300
1,300
1,300
1,300
1,300
1,300
1,300
1,300
1,300
1,300
1,300
Rigid Frame and Catenary Where Applicable
60 3,000 3,000 3,000 1,500 **
CEMA F
72
84
96
3,000 3,000 3,000
3,000 3,000 3,000
2,800 2,800 2,800
1,200
900
600
**
**
**
Idlers Ratings Based on Min L10 of 60,000 Hours at 500 RPM
Rigid Frame and Catenary Where Applicable
** For Vee Returns Consider Using CEMA "E" Series
Picking Idler Load Ratings (Lbs.)
Belt Width CEMA C CEMA D CEMA E
Liver Shaft Idler Load Capacities (Lbs.)
Belt Width CEMA C CEMA D CEMA E
24
30
475
475
600
600
18
24
1,200
1,200 1,400 2,100
36
42
48
54
60
72
84
96
325
250
200
150
125
600
600
530
440
400
280
1,260
1,200
1,000
1,000
1,000
925
775
625
30
36
42
48
54
60
72
84
24.
1,200
1,200
1,100
1,000
875
780
1,400
1,400
1,400
1,275
1,150
1,000
850
2,100
2,100
2,100
2,100
2,100
2,100
2,100
1,825
TABLE
2-15
TABLE
2-13
TABLE
2-14
TABLE
2-11
TABLE
2-12

Customer Furnished Data:
EXAMPLE: IDLER SELECTION
Peak Load: 3,000TPH Coal at 55/60 PCF minus 8" size (Maximum lump weight = 18 lbs.)
60" BW @ 650 FPM
T1 (Belt tension carrying side)__________________ 37,000 lbs.
T2 (Belt tension return side) ___________________ 12,000 lbs.
Belt weight _______________________________ 19 lbs./ft.
D (Misalignment due to installation tolerances) ______ ¼&"
H (Drop height at transfer point) ________________ 10 ft.
Conveyor system component design life 50,000 hours
Requested Information:
Recommended Idler Series and Spacing:
3000 x 2000
WM = = 154 lbs./ft.
60 x 650
Optional verification of customer data
Reference: CEMA "Belt Conveyors for Bulk Materials", Fifth Edition (or later)
A. Page 53 table 4-3: 35º Troughed belt cross section of load
60" BW @ 20º Surcharge = 2.876 ft
2
Full belt load: 2.876 ft
2
x 55 PCF = 158 lbs/ft.
154
Percent full load (<100) = 100 x = 97.47%
158
Since this has been identified as Peak Load the belt width, belt
speed and trough angle shown, are good selections.
B. Page 64 table 5-2: Suggested normal spacing of belt
conveyor idlers (SI).
60" BW @ 50 PCF = 4.0 ft.
60" BW @ 75 PCF = 3.5 ft.
Note: Factors to be considered when selecting idler spacing are belt weight, material weight, idler rating, idler life,
belt rating and belt tension. For general conveyor design and selection, limit belt sag to 2% of idler spacing at
minimum tension conditions. Sag limits during conveyor starting and stopping should also be considered in overall
selection. For more details on this use CEMA "Belt Conveyors for Bulk Materials".
Idler selection:
Step No. 1: Carrying / Troughing idler series selection based on Item B above. Use preliminary selection of 4 ft.
37,000 x .25
CIL = ((19+(154 x 1.0)) x 4) + = 1077 lbs.
K1 = 1.0 for 8” lump 6 x 4
Per table 2-13: D x 35º = 1070 lbs. rating
Per table 2-14: E x 35º = 1800 lbs. rating
25.

Note: Although it is recommended that CIL be equal to or less than CEMA Idler Load Rating, there is a certain
amount of judgment involved in final selection. In this example an experienced belt designer would know that max.
IML load based on belt tension occurs at head or discharge for a level or incline conveyor. Since belt tension would
be decreasing from this point towards tail or loading end, the number of idlers that slightly exceeded CEMA Idler
Load Rating could be determined and D series x 35º could be used and request verification from CEMA idler
manufacturer.
Other choices are:
A. D series at less than 4 ft. spacing
B. E series at greater than 4 ft. spacing
C. Increase belt speed which will decrease WM. This option would also decrease T1 belt tension which
would decrease IML.
D. Customer to maintain less than ¼&" height deviation due to installation tolerances.
Some of these choices would require recalculating belt tensions, etc., and then weigh the economics with ex-
pected performance of each selection. For this example we will select D series x 35º troughing idlers at 4 ft.
spacing, although optional choices C & D have great merit. Rated bearing L10life is 60,000 hours.
Step No. 2: Return Idler Series Selection
Option: From "CEMA Belt Conveyor Manual" (5
th
edition or later)
page 64 table 5-2: suggested normal spacing of belt
conveyor idler (SI)
Return idlers 60" BW = 10 ft.
12,000 x .25
CILR = (19 x 10) + = 240 lbs.
6 x 10
Based on above option, use preliminary selection of 10 ft. spacing.
Note: Quite often it is desirable to have return idler spacing at a
multiple of troughing idler spacing to simplify stringer or truss design.
However, this should not be the control for selection.
Per table 2-13: D series single roll return = 280 lbs. rating
Per table 2-12: C series two roll V-return = 500 lbs. rating
If this conveyor has long centers, consideration should be given to using two roll V-returns and increasing spacing.
With this choice it would not be necessary to use training idlers. For this example select D series single roll return
at 12' - 0". Rated bearing L10 life is 60,000 hours.
12,000 x .25
CILR = (19 x 12) + = 270 lbs.
6 x 12
26.

Step No. 3: Impact Idler Series Selection
Case of material without lumps: F = (0.1389) Q H = (0.1389) (3000) 10 = 1318 lbs.
Assuming the impact idler spacing is 1.5 ft, from Table 2-3, f = 0.7
Fu = F (f) = (1318) (0.7) = 922.6 lbs.
Per Table 2-13: D x 35° = 1070 lbs. rating
This case requires a D series impact idler.
Case of material with large lumps: WH = (18) (10) = 180 lbs-ft
Per Table 2-4: D = 240 lbs-ft minimum energy rating
Per Table 2-4: D = 8 in. maximum lump size
This case requires a D series impact idler.
Note: The impact idler series chosen here must satisfy both the minimum energy rating and the maximum
lump size criteria from Table 2-4.
Comparing the two cases, a D series impact idler should be selected to handle the heavier impact load. This step
completes the impact idler selection process.
Steps 1, 2 and 3 have selected idlers based on load. Steps 4, 5 and 6 deal with predicted bearing L10 life and
Step 7 covers conditions affecting potential idler life.
Step No. 4: K2 Effect of Load on Predicted Bearing L10 Life
CIL 1077
Troughing Idler = = = 1.007
Idler Load Rating 1070
K2 (from Figure 2.3 Tapered Roller Bearing) = 1.0
Bearing L10 = (60,000 x 1.0) = 60,000 hours
Return Idler =
CIL
=
270
= .96
Idler Load Rating 280
K2 (from Figure 2.3 Tapered Roller Bearing) = 1.15
Bearing L10 = (60,000 x 1.15) = 69,000 hours
Step No. 5: K3A Effect of Belt Speed on Predicted Bearing L10 Life
650 FPM Belt speed specified.
Select minimum roll dia. For < 500 RPM at 650 FPM From chart pg. 23, 5" dia. = 654 FPM
K3A (from Figure 2.6) = 1.0
Bearing L10 life for D5 series idlers at 650 FPM
Troughing idler = (60,000 x 1.0) = 60,000 hours
Return idler = (69,000 x 1.0) = 69,000 hours
27.

Step No. 6: K3B Effect of Roll Diameter on Predicted Bearing L10 Life
Compare bearing L10 life increase for 6” diameter roll.
6" Dia. Roll = 1.50
K3B (Figure 2.7) = = 1.20 or 20% increase in bearing L10 life.
5" Dia. Roll = 1.25
Troughing Idler = (60,000 x 1.2) = 72,000 hours
Return Idler = (69,000 x 1.2) = 82,800 hours
Note: In addition the 6" roll would have longer wear life and roll resistance would be less which would decrease
belt tension and reduce IML.
D6 idlers are recommended. Idler selection based on customer furnished data.
Troughing idlers D6 x 35° at 4 ft spacing with 72,000 hours predicted bearing L10 life.
Return idlers D6 at 12 ft spacing with 82,800 hours predicted bearing L10 life.
Step No. 7: K4 Effect of Environmental, Maintenance and Temperature on Potential Idler Life
For purpose of example we will assume the following conditions.
K4A (Figure 2.8) Maintenance:
K4B (Figure 2.9) Environmental:
K4C (Figure 2.10) Temperature:
Good to Fair
Dirty
< 120 F
Hostile environmental conditions and the level of commitment to the belt conveyor installation and
maintenance will affect idler life. With above assumed conditions it is apparent that potential idler life will
be less than predicted bearing L10 life. These conditions should be discussed with your CEMA idler
manufacturer.
Expected or potential idler life may also be limited by shell wear. Shell wear can vary considerably with
each installation. In addition to conveyed material characteristics, environmental, and maintenance factors,
idler alignment and belt cleaning can have a significant effect on shell wear and idler life.
Note: Calculated idler loads should be repeated for training idlers (if used). Height deviation of training idlers must
be included for IML calculation or controlled by shimming and maintaining closer installation tolerances at these
areas of conveyor.
Conclusion: There are numerous options available to the belt conveyor designer in regard to idler selection.
Through involving your CEMA idler manufacturer in this selection process these options can be explored, resulting
in a reliable cost effective installation.
28.

APPENDIX
CONVERSION FACTORS TO SI-METRIC
UNITS
This Appendix is not part of the standard, but it is included for the information of those who wish to become
acquainted with the international system of measurement called SI-Metric. The conversion factors shown below
are only for those measured quantities appearing in this standard and are based on the American National Standard
Metric Practice Guide.
To convert from:
inches (in)
feet (ft)
mass (lbs)
pound-force (lbf)
velocity (fpm)
mass per length (lbs/ft)
pounds per cubic foot (lbs/ft3)
To:
millimeters (mm)
meters (m)
kilograms (kg)
newton (N)
meters per sec (m/s)
kilograms per meter (kg/m)
kilograms per cubic meter (kg/m3)
29.
Multiply by:
25.40
00.3048
00.4536
04.4482
00.0051
01.4882
16.0185

®
Conveyor Equipment Manufacturers Association
6724 Lone Oak Blvd.
Naples, Florida 34109
Web Site: http://www.cemanet.org

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