Data Sheet. Linear bearings

Transcription

1 Data Pack G Issued Septembe Data Sheet Linea beaings Instument ball beaings and shafts The RS ange of instument quality ball bushing beaings ae fo 1 8in, 3 16in and 1 4in shafts. Each beaing contains thee complete ball cicuits. They ae extemely ugged in constuction and withstand high vibational and shock loads. Pecision manufactuing combined with the anti-fiction olling design assue minimum static and olling fiction, high eliability and epeatability. Fiction test These beaings ae 100% factoy inspected fo fiction and dimensional accuacy. The citeion fo fiction is the angle of a shaft down which they will continuously oll. The beaings ae oiented with one ball tack at the top of the shaft. Unde clean conditions with one woking tack positioned diectly unde the load the instument ball bushing beaing will oll down a shaft angle of 14 minutes ( 1 4 degee) with only a thee-ounce load. The coefficient of fiction unde this vey light load is Unde heavie loads the coefficient of fiction is even less, as illustated in Figue 1. Figue 1 μ Static coefficient of fiction Tack oientation W (oz.) Shaft/Bushing cleaance.0001in Load in ounces Fo optimum sensitivity the RS ange of shafts ae hadened to Rockwell 55 to 60c with a suface finish of 2-4ms. Boe measuement Rotate with light finge pessue on a seies of plug gauges anging in diamete fom the nominal woking boe diamete to the toleance limit of minus in. These plugs should take the toleance ange in in steps; in othe wods, a total of fou plug gauges fo each bushing. When a slight dag o feel is expeienced a slight intefeence fit has developed and the beaing should be coded fo use on a shaft having a diamete at least in smalle than the plug gauge. An intefeence fit must be avoided o oughness and possible damage will esult. Cleaning Absolute cleanliness is of utmost impotance. These beaings have been assembled, cleaned, tested and packed in clean cabinets in filteed ai. Installation should be conducted unde simila clean conditions. Note that thee ae though passages between the etaine and the oute sleeve. These pemit cleaning solvent to be blown though and the escape of dust paticles fom the outside of the etaine as well as fom the inside. Only cleaning solvent leaving no film o deposit should be used. Special machining These shafts can be specially machined to suit individual equiements fo mounting o use. The shafts ae most eadily modified by simple seconday ginding. Reduced diametes, flats and special chamfes can be done this way. It is to the custome s advantage to limit special machining to these opeations if possible. Recommendations Fo optimum pefomance the cleaance between shaft and ball bushing beaing should be at least in. An intefeence fit must be avoided o oughness and possible damage will esult. In applications whee intechangeability is desied, the selection of the pope shaft size will esult in a cleaance of in to in.

2 Metic ball bushings The RS ange of linea ball bushings is designed to offe a life expectancy of 100,000 metes of linea movement. This is based on the dynamic load ating tables shown in the RS Catalogue assuming nomal opeating conditions. The capacity figues listed assume the wost possible oientation of the bushing tacks; some incease can be achieved by optimum mounting. Life expectancy will also be affected by a vaiety of factos such as shaft hadness, opeating tempeatues and loading conditions. Unde nomal opeating conditions the following ae assumed: Shaft hadness 60HRC Tempeatue <100 C In most applications unde nomal conditions tavel life expectancy can be calculated using the following equation: Whee L = ( C ) P L = Life expectancy in metes of tavel C = Dynamic capacity in Newtons P = Beaing load in Newtons Co-efficient of fiction The co-efficient of fiction of eciculating ball bushings, to 0.004, is extemely low and can usually be disegaded in most applications. It is fa less, but moe constant, than the co-efficient of fiction of plain beaings, which is of consideable advantage in applications whee stick-slip action affects pefomance. Dy ball bushings have the lowest co-efficient wheeas oil gives fiction values slightly highe than those fo gease. The co-efficient of static, o beakaway fiction is highe, and in some cases can be as much as twice the dynamic figue. Whee wiping contact seals, o flexible bellows coves, ae used fo potection, fictional esistance fom those souces must be taken into account when assessing total fiction losses, since it may be consideable. Lubication A linea ball bushing equies fa less lubication than a plain sliding beaing. Fo most applications a lubicant seves mainly to potect the vital beaing pats against atmospheic coosion. A beaing gease (of lithium base and numbe 2/3 consistency) has the advantage of good suface adhesion, and etention, and minimises sealing poblems. A geneous gease pack befoe mounting is ecommended, woking the gease well into each individual ball cicuit. Pecision linea shafting Diamete toleance Shaft dia mm Weight mm ISO toleance band kg/m h6 5 0 to to to to to to Ball bushing pillow blocks The ball bushing is secued in the housing by two extenal ciclips (supplied) fitted to the gooves fomed in the outside diamete of the bushing. The pillow blocks ae fomed fom aluminium alloy (BS1474 HE30) extusions and have a matt natual anodised finish. Refe to page 4 of this data sheet fo a typical application. Supe Plus open ball bushings Supe Plus ball bushing beaings ae self-aligning, and povide smoothe opeation and a constant low coefficient of fiction. They have thee times moe load capacity o 27 times moe tavel life than conventional linea beaings, (Figue 2). Figue 2 Load The beaing plates ae hadened steel, pecision gound with ball-confoming gooves (Figue 3). The goove is slightly lage than the ball diamete, poviding an optimal aea fo ball contact. The geate ball-to-beaing plate contact is what povides the inceased load capacity o tavel life of Supe Plus ball bushing beaings. Figue 3 Beaing Plate Inne Race 2

3 Zeo cleaance fit The beaing plates ae also designed to float adially. When the beaing is mounted in an adjustable housing, selected fit-ups can be achieved on the shaft. (Figue 4). Figue 4 Coss section of Supe Plus ball bushing beaing Self-Aligning The pecision gound beaing plates ae designed to pivot about thei centes (Figue 5) to assue smooth enty and exit of the balls. Each plate aligns automatically to compensate fo inaccuate housing boe alignment, base flatness o caiage machining. This povides unifom ball loading, smooth ball eciculation and lowe fiction opeation. Figue 5 Beaing Plate Balls Inne Race Smooth quiet opeation The beaing s oute sleeve and etaine ae made of wea-esistant, low-fiction engineeing polyme. It educes inetia and opeating noise levels significantly. Load atings The dynamic load atings listed in the RS Catalogue ae fo ated tavel life of 100km. Fo longe tavel lives, educe load to W.(100L) 0.33 whee L(km) is the equied tavel life. Do not exceed the Dynamic Load Rating fo tavel life of less than 100km. The Dynamic Load Ratings ae valid fo a esultant load applied at 90 with the ball tacks oientated as shown in the pola gaphs (See figue 6). If the esultant acts along anothe diection, the appopiate multiplicative coection facto, Kθ o Kθ 0,should be applied espectively. K 0 elating to Dynamic load ating and Kθ 0 elating to static load ating. Figue RS stock nos RS stock nos K U O K U K U O K U Standad diametal cleaances The intenal beaing diamete is affected by the housing boe, see Table 1 below. Diametal cleaance Nominal Housing Housing size d boe H7 boe H6 (mm) (μm) (μm)

4 Typical application X-Y positioning system Objective to build a X-Y system that tansfes the wok piece between two sepaate machine stations. Poducts specified: Quantity RS stock no. Poduct Shaft suppot blocks to suit 8mm shafting type ASBM mm diamete 600mm long pecision linea shafting Ball bushing pillow blocks type HSGSPB8M Metic ball bushings fo 8mm shaft type MC8-2LS Shaft suppot blocks to suit 25mm shafting type ASBM mm diamete 900mm long pecision linea shafting Ball bushing pillow blocks type HSGSPB25M Metic ball bushings fo 25mm shaft type MC25-2LS 8mm dia 600mm long pecision linea shafting RS stock no Shaft suppot blocks to suit 8mm shafting type ASBM 08 RS stock no Ball bushing pillow blocks type HSGSPB8M RS stock no housing metic ball bushings fo 8mm shaft type MC8-2LS RS stock no Shaft suppot blocks to suit 25mm shafting type ASBM25 RS stock no mm dia 900mm long pecision linea shafting RS stock no Ball bushing pillow blocks type HSGSPB25M RS stock no housing metic ball bushings fo 25mm shaft type MC25-2LS RS stock no

5 Linea guides Metic hi-load seies The nominal life of a linea ball guide system is calculated as follows: L = ( C ) metes fw.f Whee L = Nominal life (metes) C = Basic dynamic load ating (N) f = Applied load on beaing block (N) fw = Load facto fo smooth opeation 1.2- fo nomal opeation -3.0 fo shock and vibation. Intenal cleaance This efes to the amount by which the beaing will move vetically afte fitting to the ail. The RS standad is mm maximum. Accuacy standad The high standad of manufactuing contol of the RS guide ails and beaing blocks pemits intechangeability of components without loss of pefomance. The accuacy standads shown oveleaf will be maintained in all cicumstances of basic component eplacement. Figue 8 Paallelism Paallelism (0.001mm) Abutment shoulde heights and cone adii In ode to ensue the minimum cleaance between the beaing block and a mounting shoulde, the shoulde height, H must not be exceeded Figue 9. The maximum cone adii fo the ail and the block must be obseved to ensue coect seating. Table 3 Abutment dimensions Guide ail length (mm) Unit mm Guide ail Beaing block Size Cone adius shoulde height, shoulde height, (max.) H H b Table 2 Unit 0.001mm Toleances Size See Figue 2 fo symbols Oveall height, H ±30 ±35 Dimension A 1 ±40 ±40 Figue 9 H Running paallelism of face C to face A Running paallelism of face D to face B See Figue 3 Figue 7 D Figue 10 C A H b H Datum gooves to be on the same side A A1 B Dimensions Type A A 1 H HL20NTZ HL25NTZ

6 Lead scew assemblies Specifications Lead eo ±.015in/ft (±0.12mm/100mm) Repeatability.003in (0.08mm) Staightness 0.15in/ft (0.12mm/100mm) Backlash.003in(0.08mm) (zeo when using anti-backlash nut) Tempeatue ange -50 F to +200 F ( 45 C to +93 C) Design consideations Citical speed The citical speed of a lead scew shaft is the maximum speed (pm) befoe the scew will become dynamically unstable. This esults when the foced fequency of the otating scew coesponds to its natual fequency. Its value is dependent on the length of the scew, the diamete of the thead, and the suppot configuation. The citical speed value is govened by the following equation: d Citical scew speed (N) = K C D Whee: K = End suppot facto 0.36 one end fixed, othe fee (Figue 11) 1.00 simple suppots both ends (Figue 12) 1.47 one end fixed, one simple (Figue 13) 2.23 both ends fixed (Figue 14) C =Mateial facto 4.5 fo stainless steel scews d = Root diamete of the scew D = Length between beaing suppots Figue 11 Figue 13 Load In ode to popely incopoate a lead scew into a design, load equiements must be taken into account. Maximum load values fo the nuts ae listed in the tables below. These numbes ae based on the shea of the nuts and do not take shaft buckling into account (see Maximum column load fomula below). Wheeve possible, nuts should be positioned so as to be put in tension, pulling the load. This eliminates the need fo buckling consideations. Listed below ae some helpful fomulas to assist in pope lead scew selection. Maximum column load (F) = K C 10 6 d 4 /D 2 Whee: K = End suppot facto 0.25 one end fixed, othe fee (Figue 11) 1.00 simple suppots both ends (Figue 12) 2.00 one end fixed, one simple (Figue 13) 4.00 both ends fixed (Figue 14) C =Mateial facto 13.4 fo stainless steel scews d = Root diamete of the scew D = Length between the nut and the suppot beaing Toque to move a load (T) = F L/2 Pi E Whee: F = Load L = Lead E = Efficiency Maximum load values fo nuts RS stock no. Load ating (N) Efficiency % % % % % % % % Figue 12 Figue 14 The infomation povided in RS technical liteatue is believed to be accuate and eliable; howeve, RS Components assumes no esponsibility fo inaccuacies o omissions, o fo the use of this infomation, and all use of such infomation shall be entiely at the use s own isk. No esponsibility is assumed by RS Components fo any infingements of patents o othe ights of thid paties which may esult fom its use. Specifications shown in RS Components technical liteatue ae subject to change without notice. RS Components, PO Box 99, Coby, Nothants, NN17 9RS Telephone: An Electocomponents Company RS Components 1997