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BUCKET ELEVATOR - WORKING GROUPChapter 9-D- 6NOTE: This DRAFT is for CEMA BE Committee USE ONLY. No further distribution without permission from CEMA.

CEMA Bucket Elevator Book, Best Practices in Design1st Edition-SECTION 9, Chain Selection

Bucket Elevator CommitteeChair: Warren Knapp, SCC

Vice-Chair: Kris Gililland, KWS

ATTENTION: EDITORS / REVIEWERS, you must add your name and Draft number below is you are providing suggested edits and or reviewing.

Contacts and ReferencesName Company Email AddressKurt Robinson, Chapter Lead Webster [email protected] Cline Webster [email protected] Matheson Webster [email protected]

DRAFT HISTORY

DRAFT's # (i.e. D-1, D-2, etc.) Submittal Name DateD-1 11/13/2013D-2 4/29/2014D-3 8/18/2014D-4 Kurt Robinson 3/04/2015D-5 Kurt Robinson (E.Matheson) 4/17/2015D-6 Kurt R. & Erik M. 8/18/2015-em & 10/1/15-kr

REVIEWER's # (i.e. R-1, R-2, etc.) Name DateR-1 , sent 10/6/15 Erik Matheson

FINAL

Draft Section 9 – Chain SelectionOct 1 2015- D-6 -PLEASE NOTE, NO FURTHER DISTRIBUTION WITHOUT PERMISSION FROM CEMA.

Chapter 9

CHAINS


CHAIN SELECTION

Bucket elevators equipped with Engineered Steel Chain are designed to lift enormous quantities of heavy materials to considerable heights, thus chain selection is key to the proper functioning of bucket elevators. Chain type is broadly based on the type of bucket elevator. In most applications, straight sidebar, hardened bushed rollerless chains are applied; however, most continuous high capacity elevators use straight sidebar, hardened bushed roller chain whose rollers ride on guides which are integral with the elevator casing. Offset style sidebar chains have been used for years but with chain manufacturing technology improving, offset chains are far less common for new equipment. Chain selection is mostly dependant on the type of bucket elevator.

Centrifugal Discharge ElevatorsCentrifugal discharge elevators are designed so that the buckets are fed material from the inlet feed chute at the boot section and discharge material down the discharge chute via centrifugal force at the head section discharge chute. This style of elevator typically operates at a higher chain speed, when compared to the other elevator styles, which usually fall in the 220-330 fpm (feet per minute) range. Since the chain will usually run through the material in the boot section, steel bushed rollerless chain is recommended. The use of a single strand rollerless chain with a K-style attachment (every 12-18”) is very common in such elevators, with attachments ranging from every 2nd pitch to every 4th pitch. Chains which have a roller in this application will often become loaded with the conveyed material between the rollers and bushings, and are typically not recommended. The presence of the conveyed material along with any moisture will cause the rollers to cease onto the bushings preventing them from turning.

Continuous Bucket ElevatorsContinuous bucket elevators are designed for capacity requirements of nearly twice that of a positive discharge elevators, but not quite that of high speed centrifugal discharge elevators. The buckets are spaced continuously (thus the name) and discharge is by virtue of gravity. Chain speeds in continuous style bucket elevators are typically in the 100-150 fpm range. The use of steel bushed rollerless chain with a K-style attachments are very common in this application. Elevators which use a double strand of chain will typically use an A-style (back hung) or G-style (side hung) attachment to the bucket, and are usually spaced every 2nd pitch on 4”- 6” pitch chains depending on bucket size.

Super Capacity ElevatorsSuper capacity elevators are a special kind of continuous bucket elevator designed for higher capacity requirements. Extra long buckets spaced continuously on the chain are end-hung between 2 stands of chain. Typical chain speeds are in the range of 120 fpm or less and discharge of the buckets is by virtue of gravity. The use of a steel bushed roller chain with a G-Style attachment every pitch is very common in this elevator. Buckets are typically spaced every 2nd pitch on 6”, 9” and 12” pitch chains.

Positive Discharge ElevatorsChains used in a positive discharge, or perfect discharge elevators usually run at a slower chain speed when compared to a Centrifugal style elevator. Typical chain speeds in a positive/perfect discharge elevator are 120 fpm (feet per minute) or less. Buckets used in these elevators are end-hung between two strands of Engineered Steel Chains with bucket wing attachments (common bucket spacing is 20-24”).


Elevator Chain Types

Hardened Steel Bushed elevator chains typically feature straight sidebars with heat treated pins and bushings. These types of chains are used for centrifugal discharge and continuous discharge chain bucket elevators.

Steel Bushed Roller elevator chains feature straight sidebars with a heat treated roller, pins and bushings. These chains are typically applied in super capacity, dual strand, gravity chain bucket elevators.

Chain Attachment Types

K Style attachments - Double sided attachment used on single strand and double strands of chain attached to the back of the bucket. This is the most common type of attachment primarily used for centrifugal discharge and continuous discharge bucket elevators.

A Style attachments - Single sided attachment typically used on double strand of chain back hung on the buckets. Centrifugal discharge and continuous discharge elevators will use A attachments.

G Style attachments – Are used on dual strand/double strand super capacity gravity discharge chain bucket elevators. The attachments are mounted to the side of the bucket.

Floating attachments - This type of attachment is used primarily by European original equipment manufacturers. The attachments are bolted to the back of the bucket and then slide on to a holding pin with a retaining ring or pin. This type of attachment is primarily used for centrifugal discharge and continuous discharge bucket elevators.

Figure 9.01 - K Style attachments

Figure 9.02 - A Style attachments

Figure 9.03 - G Style attachments

Figure 9.04 - Floating attachments


General Rules of Thumb for Selecting the Type of Chain

1. Use straight sidebar engineered steel bushed rollerless chain for elevators in which the

chain hangs free and/or is exposed to the conveyed material as the material is typically

scooped up in the boot section during loading.

2. Use straight sidebar engineered steel bushed roller chain for elevators in which the

chain will ride on a track/support during operation, generally super capacity elevators.

3. In elevators which utilize a single strand of chain, the bucket length should not exceed

5 times the bushing/bearing length of the chain (inside width + 2 inside sidebar

thicknesses).

4. For materials that are non corrosive, many chain manufacturers will utilize medium to

low carbon steel sidebars alloy steel pins and bushings. The pins and bushings will

either have a carburized, induction hardened heat treat process or a mixture of both.

The heat treatment prescribed by each chain manufacturer will vary slightly. This is due

to experience and the overall cost associated with the heat treat process.

5. When handling corrosive materials (coal, grain, ethanol, fly ash, gypsum, and other

caustic materials) a stainless steel bushing and pin may be prescribed to fight the

corrosiveness of the handled material. Different stainless steels will provide different

types of protection to the bushings and pins. Stainless steels all react differently to the

heat treat process and the stainless steel selected will be up to the chain manufacturer

based on experience and the specific material handled. Martensitic stainless steels are

typically used due to their ability to react to the heat treat process. Martensitic steels

with the proper heat treat will increase in hardness to help prevent wear along with

increasing the life of the components compared to other base alloy steels.

6. When handling materials that are very abrasive in nature (finished cement, clinker, sand,

and other materials high on Moh’s scale of hardness) a sealed joint chain can be used.

The sealing mechanism is designed to keep the fine particles from working in between

the chain joints. The abrasive material will wear away the outside diameter of the pin as

well as take material away from the inside diameter of the pin. Dry abrasion wear is

typically experienced in these types of applications, also known as dry pin cavitation.


Type Capacity in (tons/hr) * Speed (fpm) **Distance between shaft

centers (ft)

Common Materials

Handled

Centrifugal Discharge 400 330 200 Cement, Ash, Coal,

Wheat, Grains

Super Capacity 750 100-150 120

Cement, Gravel,

Potash, Phosphate,

Gypsum

Continuous Bucket 120 140-150 150 Cement, Coal

* Based on approximately 60-90 pounds per cubic foot** The figures included in this table are normal and based on optimum standards relating to chain speeds, head sprocket diameter, and other criteria which reflect good general practices. Do not exceed these figures without contacting the chain manufacturer.*** Typical capabilities are listed in the chart above. Maximum capacities and maximum distance between shaft centers will be determined by the maximum chain tension/pull at the head shaft as calculated by the formulas on the following pages.

Selection of Chain and Design Pull Calculations

The following information should be known or determined prior to the selection of chain:

Required capacity in tons per hour (TPH)

Type of material being handled

o Abrasiveness of the material

o Corrosiveness of the material

Density of the material (lbs/ft3)

Distance between sprocket centers, usually the elevating height (ft) – “C”

Operating/Service conditions

o Cleanliness of material

o Operating Temperature

o Degree and frequency of shock

o Operating hours per day

Elevator chain and bucket speed in feet per minute (fpm) – “S”

Weight of chain and buckets per foot (lbs) – “W”

o W may not be known at this point, but an approximation can be used at this point. Once

the calculations are completed and “W” is determined the calculations will need updated

to ensure proper chain selection.

Table 9.05 - Typical Capabilities of Chain Bucket Elevators***


General Symbols and Definitions

C Elevator distance from centerline of head shaft to centerline of tail/boot shaft (ft)

CFM Elevator capacity or conveyed material flow rate (ft3/min)

Dt Pitch Diameter of tail or boot sprocket (in)

fd Digging factor

fd = 0.50 for continuous discharge elevators

fd = 0.67 for centrifugal discharge elevators (fine material)

fd = 1.00 for centrifugal discharge elevators (coarse material)

Fn Multiple strand factor

Fp Composite service factor equal to the product of all fp’s. (see Table 9.07)

fp Service factors

Fs Speed factor (see Table 9.08)

M Weight per foot of conveyed material (lbs/ft)

Nt Number of teeth on tail/boot sprocket (not the driving sprocket)

n Number of chain strands

Pd Design chain pull (lbs)

Pmax Total chain or elevator pull at the head shaft (lbs)

Ptu Elevator take-up tension (200-300 lbs is a good estimate if not known, 500 lbs max) (lbs)

p Chain pitch (in)

Q Elevator or chain pull from digging the material out of the boot section (lbs)

q Density of conveyed material (lbs/ft3)

S Chain speed (ft/min)

TPH Elevator Capacity or conveyed material flow rate (tons/hr)


v Bucket weight (lbs)

W Weight per foot of moving conveyor components including buckets (lbs/ft)

w Weight per foot of chain (estimated chain weight) (lbs/ft)

X Bucket spacing (ft)

FORMULAS

Pmax = [(M + W) * C] + (0.5 * Ptu) + Q

M = (33.3 * TPH) / S or (CFM * q) / S

W = (n * w) + (v / x)

w = [(# of standard pitches * weight per ft) + (attachment

weight per ft)] / (# of total pitches)

x = (Attachment spacing * chain pitch) / 12

Q = M * Dt * fd

Dt = p / sin(180/Nt)

For multiple chain strands:

Fn = 1.2 / n (when n = 2 or more)

= 1 (when n = 1)

Pd = Pmax * Fn * Fp * Fs

Once Pd has been determined for the application, compare the answer against the Rated/Allowable Working Load of the chain. Pd must be less than the rated/allowable working load of the selected chain; Increase or decrease the chain size to select a suitable chain. Once a chain has been selected update the value of “W” and recalculate Pd.


Example Information

Centrifugal Discharge Elevator

Required Capacity – 45 tons/hr

Type of material – Bituminous Coal

Density of material – 50 lbs/ft3

Shaft centers – 55 ft

Service and Conditions:

- Moderately dirty

- Moderate to normal operating temperatures

- Infrequent shock loads

- Operates 8 hrs per day

Speed – 300 fpm

Use of a single strand rollerless chain with a K-style attachment every 4th pitch:

- Weight of chain with no attachment = 6.9 lbs/ft

- pitch = 4 inches

- K2M attachment every 4th pitch = 9.1 lbs/ft

- 12 x 7 inch Style AA bucket = 12.0 lbs each

Head Sprocket / Traction wheel pitch diameter ~ 30”

Tail Sprocket = 19 tooth sprocket


Example Equations

M = (33.3 * TPH) / S = (33.3 * 45) / 300 = 5.0 lbs/ft

w = {[(# of standard pitches * weight per ft) + (attachment weight per ft)] / (# of total pitches)} * # of strands of chain = {[(3 * 6.9) + 9.1] / 4} * 1 = 7.45 lbs/ft

x = (Attachment spacing * chain pitch) / 12 = (4 * 4) / 12 = 1.333 ft

W = (n * w) + (v / x) = (1 * 7.45) + (12.00 / 1.333) = 7.45 + 16.0 = 23.45 lbs/ft

Dt = p / sin(180 / Nt) = 4 / sin (9.4737) = 24.302 inches

Q = M * Dt * fd = 5.0 * 24.302 * 1 = 121.51 lbs

Pmax = [(M + W) * C] + (0.5 * Ptu) + Q = [(5.0 + 23.45) * 55] + (0.5 * 300) + 121.51 = 1715 lbs

Fp = product of service factors, fp’s (see Table 9.07) = 1 * 1 * 1.2 * 1 = 1.2

Pd = Pmax * Fn * Fp * Fs = 1715 * 1 * 1.2 * 1.04 = 2140 lbs

Now compare the Pd to the Rated/Allowable Working Load of the chain.

The Pd must be less than the RWL/AWL

If not select a suitable chain, update your calculations with the new weights and get your new Pd.

Check to be sure the bucket length is less than 5 times the length of the chains bushing. - For larger buckets, 2 strands of chain may be required.

Table 9.07 – Service Factors

Conditions Affecting Chain Life ExpectancyService

Factors (fp)

Frequency of

Shock

Infrequent Shock 1

Frequent Shock 1.2

Character of

Chain Loading

Uniform or Steady Load 1

Moderate Shock Load 1.2

Heavy Shock Load 1.5

Atmospheric

Conditions

Relatively Clean and Moderate Temperature (less than 350°F) 1

Moderately Dirty and Moderate Temperature (less than 350°F) 1.2

Exposed to Weather, Very Dirty, Abrasive, Mildly Corrosive and Reasonably High

Temperatures (350°F - 700°F)1.4

Daily

Operating

Range

8-10 hours

10 - 24 hours

1

1.2


Frequent and infrequent shock in high speed centrifugal elevators Infrequent shock would be considered if a shock load is not expected to occur at any

given frequency but might happen occasionally, once a month, due to accidental happenings.

Frequent shock is considered if a shock load occurs a few times a day or more.

Frequent and infrequent in low speed elevators (less than 150 fpm) Infrequent shock is considered if the shock load on the elevator happens 50 or less

cycles per day. Frequent shock would be considered to have more than 50 cycles per day.

Uniform or steady loading has only minor load fluctuations.

Moderate shock load has relatively smooth load fluctuations of a large magnitude.

Heavy shock load has rapid load fluctuations of a large magnitude.

Table 9.08 - Speed Factors For Steel Chain


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Home - Conveyor Equipment Manufacturers Association · Web view2015/10/01 · Martensitic steels with the proper heat treat will increase in hardness to help prevent wear along with