1、CEMA STANDARD NO. 575-2000Bulk Material Belt ConveyorImpact Bed/CradleSelection and DimensionsPDF VersionCONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATIONFor Information on Company Membershipvisit the CEMA Web Site athttp:/www.cemanet.orgOFFICERSCOMMITTEESGeneral Bulk Conveyor SectionUnit Handling Convey
2、or SectionBulk HandlingSectionCommitteesUnit HandlingSectionEngineering ConferenceConveyorChainScrewConveyorsAdministration and OperationsManagers ConferenceConferenceStrategic PlanningInsuranceMeetingsMembershipPublic RelationsStatisticsSafety SteeringFinance and BudgetPolicy and NominatingIdlersPu
3、lleysBeltSystemsScrewConveyorsBeltManualSafety ControlsTerms andDefinitionsCEMA ORGANIZATIONAL CHARTInternationalStandardsJoint Management ConferenceBulk HandlingComponentsand SystemsControls PalletizersMeet Each MayMeet in March and/or SeptemberBOARD OF DIRECTORSAccessoriesConveyor ChainPerformance
4、 Terminology400 Series StandardsDISCLAIMER 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 saf
5、ety 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 users com
6、pany 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 users company understand and agree that CEMA, its member companies, its offic
7、ers, agents and employees shall not be liable in any manner under any theory of liability for the user or users reliance on these recommendations. The users and the users company agree to release, hold harmless and indemnify CEMA, its member companies, successors, assigns, officers, agents and emplo
8、yees from any and all claims of liability, costs, fees (including attorneys 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
9、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 NO. 575-2000Bulk Materia
10、l Belt ConveyorImpact Bed/CradleSelection and DimensionsPrepared byThe Bulk Belt Conveyor Accessories CommitteeOfThe CEMA General Bulk Handling SectionPublished byCONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATION6724 Lone Oak Blvd.Naples, Florida 34109(239) 514-3441Fax: (239) 514-3470E-Mail: cemacemanet.
11、orgWeb Site: http:/www.cemanet.orgStandard No. 575 - 2000Copyright 2000Approved October, 2000Conveyor Equipment Manufacturers AssociationISBN 1-891171-43-7PDF Version ofISBN 1-891171-31-3Printed in USAiForewordImpact Beds/Cradles are used to reduce premature idler failure and reduce belt damage in t
12、he load zoneof bulk material handling conveyor systems. This standard has been established to provide a uniformmethod of rating and dimensioning among the various manufacturers of conveyor belt Impact Beds/Cradles.This standard assures the users of conveyor Impact Beds/Cradles that an Impact Bed/Cra
13、dle is dimen-sionally compatible with conveyor idlers manufactured to the CEMA Standard No. 502, most current revision.The 575 standard establishes impact energy ratings to assure the end user the Impact Bed/Cradle isstructurally suitable for the application. This standard does not restrict the manu
14、facturer, who has com-plete freedom to design all parts of the Impact Bed/Cradle according to its best engineering judgementbased upon the information supplied by the end-user.There are three classes of Impact Beds/Cradles rated according to the weight and height of fall of the bulkmaterial and conv
15、eyor idler class. Manufacturers voluntarily specify into which class their particular de-signs fall.It is hoped this standard will assist the end user in receiving an Impact Bed/Cradle, which is structurallysuitable for the specified conditions and reduce the misapplication of Impact Beds / Cradles.
16、The capacity of the conveyor belt to withstand impact varies according to belt construction. Contact thebelt supplier for information regarding the ability of a specific conveyor belt to withstand impact.Contents PageForeword iiDefinitions 1Rating system 1-2Impact bed/cradle dimensions .2Location of
17、 impact bed/cradle 2Impact bed/cradle selection . 2Example: impact bed/cradle selection .3Power requirements . 4-5Typical specification . 6Units . 6iiCEMA STANDARD NO. 575-2000Bulk Material Belt ConveyorImpact Bed/Cradle -Selection and DimensionsDefinitionsA: Base width mounting holes center to cent
18、erdistance in inches.a: Distance from the center of an idler to the lead-ing edge of the Impact Bed/Cradle.B: Mounting foot mounting holes center to centerdistance in inches.C: Overall width of the Bed/Cradle in inches.D: Overall length of the mounting foot in inches.E: Maximum height of the outer e
19、dge of the Bed/Cradle in inches.F: Force resulting from a falling lump of bulk solidor a homogeneous stream of bulk material inpounds.f: Coefficient of friction, dimensionless.H: Maximum distance from outer edge to outeredge of the Bed/Cradle sliding surface, in inches.h: Vertical fall distance of a
20、 lump from the centerof gravity of the homogeneous load or lump to thebelt in feet.K: Maximum height of the center roller of theinbound/outbound idler, or distance to the bottomof the belt in inches.Kx: Factor used to calculate the frictional resistanceof the idlers and the sliding resistance betwee
21、n thebelt and idler rolls, lbs per foot.Ky: Carrying run factor used to calculate the com-bination of the resistance of the belt and theresistance of the load to flexure as the belt andload move over the idlers, lbs per foot.k: The spring constant of the entire Impact Bed/Cradle including the slidin
22、g surface and supportstructure in lbs per foot.L: Mounting bolt diameter in inches.M: Clearance between the belt and the centersliding surface in inches.N: Length of the impact zone in feet.Te (IB): Effective belt tension at Impact Bed, lbs.Te (TI): Tension from frictional resistance of theloading z
23、one idlers and the tension from the resis-tance of the material to flexure as it rides the belt inthe loading zone, lbs.V: Belt speed in feet per minute.Q: Flow rate of the bulk solid in short tons per hour.W: Weight of single lump in pounds.Wb: Weight of belt in lbs per foot of belt length.Wm: Weig
24、ht of material in lbs per foot of belt length.Impact Bed: A conveyor component that is locatedunderneath the belt in the impact or loading zoneof a bulk material handling conveyor belt transferpoint designed to support the belt and help absorbthe impact of falling material.Impact Cradle: See Impact
25、Bed.Outbound Idler: The idler immediately after theImpact Bed/Cradle in the direction of belt travel.Inbound Idler: The idler immediately preceding theImpact Bed/Cradle in the direction of belt travel.Transition Distance: The distance between wherethe belt leaves a terminal pulley of a belt conveyor
26、and the point where the belt is fully troughed.Transition Idler: An idler with metal rollers andadjustable wing angles to help support the belt inthe transition from a terminal pulley to a troughedconfiguration.Slider Bed: A support under the carrying side of aconveyor belt that is designed to handl
27、e the slidingload of the belt and the bulk solid.Loading Zone: The area where material is receivedon the conveyor belt.Rating and class systemImpact Beds/Cradles are rated according to theirstructural capacity to absorb the force of impactfrom a falling lump or stream of bulk solid. Thereare three s
28、implified ratings based upon the weightof the bulk solid multiplied by the height of the fall(W h) or rate of flow, Q, and the height of fall h.Various combinations of W h and Q h canproduce the same result but varying the values ofW and h or Q in the design formulas will have aneffect upon the impa
29、ct force calculations. The de-sign of the impact bed/cradle determines the springconstant, k. For these reasons there may be anoverlap of designs for the same ratings amongmanufacturers.The impact force from a falling single lump is sig-nificantly more than that from a homogeneousstream of bulk mate
30、rial so in most applications theweight of the largest lump that can be expected isthe critical variable. Table 1 gives the force ratingranges for Impact Beds/Cradles. Since most userswill not have the value k readily available, valuesof W h are given in Table 1 for reference only.1Contact a CEMA mem
31、ber for impact forces over17,000 lbf or impact energies over 2000 ft-lb, asthe impact may exceed the impact ratings of mostfabric ply belts.Table 1 - Impact Bed/Cradle ratingImpact EnergyImpact Force W h (Reference)L Light Duty 17,000 lbf or 2,000 ft-lbThe designation for an Impact Bed/Cradle shall
32、bethe duty rating followed by the Idler class. Forexample a Heavy Duty Impact Bed/Cradle whichis dimensionally compatible with CEMA D6 idlersin the load zone shall be designated as H-D6.HD6Heavy duty impact rating CEMA idler class D6for dimensionsImpact Bed/Cradle dimensional standardThe CEMA Idler
33、Class for the idlers used in theload zone shall determine the dimensional class ofthe Impact Bed/Cradle. The dimensions A throughKcorrespond to the dimensions in the CEMA Stan-dard for Bulk Material Belt Conveyor Troughing andReturn Idlers No. 502, most current revision (seefigure 1).Location of Imp
34、act Beds/CradlesImpact Beds/Cradles are placed in load zone inthe area of direct impact from the falling lumps orstream of material. The Impact Bed/Cradle shouldbepositioned so the impact is striking the impact barsor pads at the center. The belt must be fullytransitioned with properly fitted metal
35、transitionidlers before the entry into the Impact Bed/Cradle.A suitable idler which is dimensionally compatiblemay be used as the inbound idler just precedingthe first Impact Bed/Cradle. When the impact areais long or there are multiple load points intermedi-ate idlers which are dimensionally compat
36、ible maybe used to separate Impact Bed/Cradle sections(see figure 2).The belt must be fully troughed according to CEMA“Belt Conveyors for Bulk Materials” and the transi-tion idlers must be constructed with metal rollers.Impact Bed/Cradle selection1) Determine the dimensional classThe dimensional cla
37、ss of the Impact Bed/Cradle isthe same as the CEMA class of the idlers in theload zone. All of the idlers in the load zone mustbe from the same manufacturer, have the sametrough angle, be of the same CEMA class and bein good working condition or the Impact Bed/Cradlewill not fit or function properly
38、. Contact a CEMAmember if your load zone is not fitted with idlers allfrom the same manufacturer, of the same troughangle or all of the same CEMA class. Example:The idlers in the impact zone are CEMA D6. Thedimensional class of the Impact Bed/Cradle istherefore D6.2Figure 2 - Transition distance, in
39、bound and outbound idler positionsOutbound idlerImpact areaIntermediate idlerInbound idlerImpact areaTransition idlerwith steel rollsTransition idlerwith steel rollsTransitiondistanceImpactBed/Cradle“a”“a”“a”“a”3Figure 1 - Typical Impact Bed/Cradle*Note: Some manufacturers designs do not use standar
40、d CEMA Dimensions for L, B or D.“N”Length of impact zone (contact manufacturerfor length & no. of supports)“L” Bolt diameter* “B” Mounting holescenter to center*“D” Overall width*Center idlerheight“H”Max. idler width“A”Base width mounting holes“E”Max. idlerheight“K”“C”Overall width“M” Belt clearance
41、(5/8”+3/8”)2) Determine the duty ratingThe duty rating of a CEMA Impact Bed/Cradle isdetermined by the maximum impact force that willbe created by the falling lump or stream of mate-rial. A simplified formula of the weight of the largestlump, W, or the rate of flow, Q, of the material andthe vertica
42、l height of fall, h, is used to determinethe rating. Calculate both quantities and select thelarger of the two values for determining theappropriate duty rating.Material containing large lumpsDetermine the maximum lump size that will be con-veyed. Calculate the weight, W (lbs.), of the lump.If slabs
43、 of material are likely to pass through thesystem use the maximum size slab to determinethe maximum lump weight. Determine the maxi-mum vertical fall distance, h (ft). The impact force,F, is given by equation #1. Equation #1 F(lbs) =W + square root (2 k W h) (see figure 3).Consult Table 1 to determi
44、ne the appropriate dutyrating.Homogeneous stream of material withoutlarge lumpsDetermine the maximum vertical fall distance h (ft).Determine the design rate of flow, Q (short tonsper hr.), of conveyed material. The impact force, F,is given by equation #2. Equation #2 F (lbf) = .1389 Q square root(h)
45、 (see figure 4).Consult Table 1 to determine the required dutyrating.Power requirementsImpact Beds/Cradles can have a significant effecton the power requirements of a conveyor particu-larly for short conveyors. It is advisable to calculatethe theoretical horsepower requirements for an Im-pact Bed/Cr
46、adle and check the availablehorsepower of the drive.The horsepower requirement is determined by theformulas:Te(IB) = L (Wm + Wb) fTe(TI) = L Kx + (Ky Wb) + (L Ky Wm)HP Increase = (Te (IB) - Te (TI) x V 33,000Typical materials used for the surface in contactwith the belt on Impact Beds/Cradles are UH
47、MWPE and Polyurethane. For estimating purposesthe following values of coefficient of friction, f, havebeen found to be conservative. For critical appli-cations contact a CEMA member company.Table 2 - Coefficient of frictionf Static f DynamicUHMW PE .50 .33Polyurethane 1.00 .66ExampleA 60-inch convey
48、or traveling at 750 fpm is convey-ing 8 inch minus ore, which weighs 120 lb/ft3at therate of 2500 tph. The conveyor is equipped withCEMA D6 impact rollers in the load zone. The ver-tical drop at the transfer point is 12 ft and the impactis confined to an area approximately 4 feet long.4Figure 4 - De
49、termine impact force from astream of materialFigure 3 - Determine impact force from asingle lumpF = W+ 2 x k x W x hF = .1389 x Q x hDetermine the rating and class for an Impact Bed/Cradle for this application. Determine the horse-power requirements for the Impact Cradle.RatingSince the lump size is large in this application it isprobably material from a primary crusher that haspassed through a grizzly with 8-inch square open-ings. It is accepted practice to assume the largestslab that could pass through the grizzly would be8 inch thick by
