savremeni razvoj konstrukcije i proizvodnje vij^anih kompresora ...

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
SAVREMENI RAZVOJ KONSTRUKCIJE I PROIZVODNJE
VIJ^ANIH KOMPRESORA
Prof. dr Nikola Sto{i} i mr Ahmed Kova~evi}, Centre for Positive Displacement
Compressor Technology, City University, London EC1V OHB, U.K.
REZIME
PREGLEDNI RAD
Vij~ani kompresori dominiraju u oblasti kompresije zraka, procesnih plinova i u rashladnoj tehnici.
Razvoj matematskih modela i unapre|enja u oblasti ra~unarske simulacije kombinovani sa rezulatima
eksperimentalnih istra`ivanja ~ine sna`an sistem za analizu procesa i optimizaciju konstrukcije vij~anog
kompresora. Kao rezultat, u nekoliko zadnjih godina profil zuba rotora vij~anog kompresora zna~ajno
je evoluirao i na taj na~in su pobolj{ane performanse ma{ine. Iako efikasnost rada vij~anog kompresora
najvi{e zavisi od profila zuba rotora kao i distribucije zazora izme|u rotora i izme|u rotora i
ku}i{ta kompresora, ostale komponente, kao {to su otvori na ku}i{tu, le`ajevi, zaptivke i sistem za
podmazivanje, moraju biti tako projektovani da se u potpunosti iskoristi potencijal ostvaren razvojem
profila rotora.
Klju~ne rije~i: vij~ani kompresori, konstrukcija, proizvodnja
RECENT DEVELOPMENTS IN SCREW COMPRESSORS
Nikola Sto{i}, Ph.D. and Ahmed Kova~evi}, Ms.C., Centre for Positive
Displacement Compressor Technology, City University, London EC1V OHB, U.K.
SUMMARY
SUBJECT REVIEW
Screw compressor dominate today compression of air, process gas and refrigerants. The recent
advances in mathematical modelling and computer simulation combined with experimental test data
form a powerful tool for process analysis and design optimisation. As a result, the screw rotors lobe
profiles have evolved over the past few years enhancing machine performance. Although an efficient
operation of screw compressors is mainly dependent on a rotor profile and clearance distribution,
other components, like housing, ports, bearings, seals and lubrication system sholud be designed to
take advantage of their potential if the full performance gains are to be achieved.
Key words: screw compressors, construction, manufacturing
1 UVOD
Vij~ani kompresori su rotacione volumetrijske ma{ine
jednostavne konstrukcije koje mogu raditi na vrlo
visokim brojevima obrtaja u {irokom dijapazonu radnih
pritisaka i protoka ostvaruju}i visok stepen iskori{tenja.
Oni su kompaktni i pouzdani tako da su danas na
trzi{tu zastupljeni u vi{e od 80% slu~ajeva dok se u
pogonu ve} nalazi oko 50% vij~anih kompresora u
odnosu na ukupan broj industrijskih kompresora.
Osnovni razlog za ovako zna~ajan uspjeh vij~anih
kompresora na tr`i{tu valja tra`iti u savremenom razvoju
proizvodne tehnike koja je omogu}ila da se linearne
tolerancije pri proizvodnji rotora preciznim profilnim
glodanjem ili bru{enjem svedu na vrijednost ni`u
1 INTRODUCTION
Screw compressors are rotary positive displacement
machines of simple design with the moving
parts comprising only two rotors rotating in four
to six bearings. They are capable of efficient
operation at high speeds over a wide range of
operating pressures and flow rates. They are
therefore both reliable and compact and consequently
they comprise 80% of all positive displacement
compressors now sold and 50% of
those currently in operation. Their remarkable success
is mainly due to improvements in high accuracy
profile milling and grinding which now make
it possible to reduce linear tolerances to below
- 63 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
od 10 µm. Na taj na~in se ostvaruje ekonomi~na
proizvodnja rotora sa me|usobnim zazorima u granicama
od 35-50 µm. Unutra{nje curenje se time svodi
na mali dio vrijednosti ostvarenih u prija{njim konstrukcijama
vij~anih kompresora. Kao rezultat se dobiva
manji vij~ani kompresor sa ve}im stepenom iskori{tenja
u pore|enju sa ostalim tipovima kompresora.
Vij~ane ma{ine se danas upotrebljavaju kao kompresori
ili kao ekspanderi i imaju najraznovrsnije namjene.
Oni rade sa razli~itim vrstama radnih fluida koji mogu
biti gasovi, pare ili vi{efazne mje{avine sa promjenom
faze unutar ma{ine. Mogu raditi bez unutra{njeg podmazivanja,
ili kao uljno podmazivani, ili sa drugim fluidom
koji se ubrizgava u radni prostor za vrijeme
procesa kompresije ili ekspanzije ili prije ili poslije njih.
Da bi se postigle optimalne karakteristike kompresora,
razli~ite aplikacije vij~anog kompresora zahtijevaju
razli~itu konstrukciju i druk~iji na~in rada. Zbog toga
nije mogu}e upotrebljavati univerzalne rotore ili izabrati
univerzalne radne parametre koji }e dati optimalnu
efikasnost ~ak unutar vrlo uskog dijapazona rada
ma{ine. Detaljna termodinamska analiza i poznavanje
uticaja razli~itih konstruktivnih parametara na karakteristike
vij~ane ma{ine su, zbog raznolikosti primjene i
geometrijske kompleksnosti ma{ine, sigurno mnogo
zna~ajniji i slo`eniji nego u slu~aju drugih sli~nih
ma{ina. Odavde slijedi da je za optimalne performanse
ma{ine za odre|enu primjenu neophodno dobro
postaviti optimizacione kriterije. Ovakav pristup je, isto
tako, od velikog zna~aja za eventualna unapre|enja
postoje}ih konstrukcija vij~anih ma{ina i za pro{irenje
domena njihove primjene.
10 µm. This permits rotors to be manufactured
with interlobe clearances of 30-50 µm at an economic
cost. Internal leakages are thus far less
than in earlier machines of this type and as a
result, twin screw compressors are more efficient
than other types.
Screw machines are used today for different applications
both as compressors and expanders. They
operate on a variety of working fluids which may
be gases, dry vapours or multi-phase mixtures
with phase changes taking place within the
machine. They may operate with oil flooding, with
other fluids injected during the compression or
expansion process, or without any form of internal
lubrication. Their geometry may vary depending
on the number of lobes in each rotor, the
basic rotor profile and the relative proportions of
each rotor lobe segment. It follows that there is
no universal configuration which would be the
best for all applications. Hence, detailed thermodynamic
analysis of the compression process
and evaluation of the influence of the various
design parameters on performance is more important
to obtain the best results from these
machines than from other types which could be
used for the same application. It follows that a
set of well defined criteria governed by an optimisation
procedure is a prerequisite for achieving
the best design for each application. Such guidelines
are also essential for the further improvement
of existing screw machine designs and
broadening their range of uses.
Industrijski kompresori komprimiraju zrak, rashladne
fluide ili procesne plinove. Za svaku od ovih namjena
konstrukcija ma{ine se mora razlikovati kako
bi se postigli o~ekivani rezultati. U rashladnim
ma{inama i kod kompresije procesnih plinova, gdje
je vrijeme rada kompresora zna~ajno du`e od vremena
stajanja, obi~no se kao osnovni preduslov
postavlja visok stepen iskori{tenja kompresora. Za
zra~ne kompresore, posebno u mobilnim agregatima,
efikasnost mo`e biti ni`a i obi~no je manje zna`ajna
od veli~ine kompresora i njegove cijene.
Oblast kompresije zraka je, kako u slu`aju suhoradnih
tako i u slu~aju uljno podmazivanih kompresora, gotovo
isklju~ivo pokrivena vij~anim kompresorima. Situacija
je vrlo sli~na i u procesnoj industriji, dok se u rashladnoj
tehnici klipni i lamelni kompresori sve vi{e
zamjenjuju vij~anim kompresorima, tako da se u narednim
godinama mo`e o~ekivati dramati~no pove}anje
zahtjeva za vij~anim rashladnim kompresorima.
Veli~ina vij~anih kompresora koji se danas koriste u
komercijalne svrhe je izmedju 75 i 620 mm u
Typically, refrigeration and process gas compressors,
which operate for long periods, must be
designed to have a high efficiency. In the case of
air compressors, especially for mobile applications,
efficiency may be less important than size and
cost.
For both dry and oil free air compression, screw
compressors are used almost exclusively. This is
also gradually becoming the case for process gas
compression. In the field of refrigeration, the use
of reciprocating and vane compressors is
decreasing and a dramatic increase in favour of
screw machines is expected in the next few
years.
Screw compressors in normal commercial usage
today have main rotors whose outer diameters vary
between 75 mm and 620 mm. These deliver
between 0.6 m3/min and 600 m 3 /min of compressed
gas. The normal pressure ratios attained in a single
- 64 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
pre~niku vode}eg rotora. Dobava tih kompresora je
izmedju 0,6 i 600 m 3 /min gasa na uslovima usisa.
Odnos pritisaka je oko 3.5 za suhoradne kompresore
dok se za uljnopodmazivane kre}e do 15.
Uobi~ajena razlika pritisaka je do 15 bara ali se u
nekim slu~ajevima de{ava da ona prelazi 40 bara.
Volumetrijsko iskori{tenje uljno podmazivanih vij~anih
kompresora obi~no je preko 90%, tako da je danas
specifi~na snaga vij~anih kompresora svedena na
vrijednosti koje su se prije samo nekoliko godina
smatrale nemogu}ima.
stage are 3.5:1 for dry compressors and up to 15:1
for oil flooded machines. Normal stage pressure
differences are up to 15 bars, but maximum values
sometimes exceed 40 bars. Typically, for oil flooded
air compression applications, the volumetric efficiency
of these machines now exceeds 90 % while
specific power inputs, which are both size and performance
dependent, have been reduced to values
which were regarded as unattainable only a few
years ago.
2 SKRIVENI DETALJI
2 SCREW COMPRESSOR PRACTICE
[vedska kompanija SRM je pionir u razvoju i primjeni
vij~anih kompresora. I drugi proizvo|a}i, kao
{to su Compair u Velikoj Britaniji, Atlas-Copco u
Belgiji, Ingersol-Rand i Denver Gardner u Americi,
GHH u Njema~koj, nalaze se neposredno do njih.
York, Trane, Carrier i Bitzer su vode}e kompanije
koje vij~ane kompresore koriste u rashladnoj tehnici
i klimatizaciji. Japanski proizvo|a}i vij~anih kompresora,
kao {to su Hitachi, Mycom i Kobe-Steel su
tako|er vrlo dobro poznati. U zadnje vrijeme se na
Srednjem i Dalekom Istoku pojavljuje veliki broj kompanija
koje se se bave vij~anim kompresorima.
Otvaranjem novih tr`i{ta, u Kini i Indiji, a i u drugim
zemljama u razvoju dolazi do otvaranja fabrika
vij~anih kompresora. Iako se ne bavi proizvodnjom
vij~anih kompresora, Britanska kompanija Holroyd je
najve}i proizvo|a} rotora za vij~ane kompresore i
vode}i konstruktor i proizvo|a} alata i ma{ina za
proizvodnju rotora vij~anih kompresora.
Iako popularnost vij~anog kompresora raste iz dana
u dan, otvorena literatura je u toj oblasti jo{ uvijek
ograni~ena. Tri klasi~ne knjige o vij~anim kompresorima
su publikovane na ruskom jeziku u ranim
{ezdesetim godinama. [40] 1960, daje potpuni pregled
na~ina generisanja kru`nog, elipti~nog i cikloidnog
profila i u detalje izvodi ruski asimetri~ni
profil kasnije nazvan SKBK. Na~in generisanja profila
opisan u toj knjizi bazira se na takozvanom metodu
obvojnice. [2] 1961. ponavlja teoriju generacije
profila time daju}i svoj doprinos oblasti profilisanja
alata za proizvodnju rotora. [15] je knjiga sa generalnom
kompresorskom tematikom, ali je dio o
vij~anim kompresorima vrlo interesantan i informativan.
Priru~nik [1] na ruskom jeziku iz 1977 godine
daje potpuno reproducibilan prikaz asimetri~nog
SRM profila 5 godina nakon {to je ovaj patentiran
skupa sa Lysholmovim profilom. Dvije knjige su publikovane
na njema~kom jeziku [35] 1979, prezentira
metod generacije profila baziran na teoriji zup~anika
Svenska Rotor Maskiner (SRM), a Swedish company,
was the pioneer and are still leaders in the field
of screw compressor design and development practice.
Other companies, such as Compair in the U.K,
Atlas-Copco in Belgium, Ingersoll-Rand and Denver
Gardner in the USA and GHH in Germany are the
main air compressor manufacturers. York, Trane and
Carrier in the USA lead in refrigeration and air conditioning
applications. Japanese screw compressor
manufacturers, such as Hitachi, Mycom and Kobe-
Steel are also well known. In recent years there
have been a number of mergers and buy outs of
smaller companies by these larger ones. New markets
in China, India and other developing countries
in the Middle and Far East have led to new screw
compressor companies being founded there as well
as factories being built there by the major manufacturers.
Although they do not manufacture compressors,
Holroyd, a British company is the world's
largest screw rotor manufacturer. They are also
world leaders in tool design and machine tool production
for the manufacture of screw compressor
rotors.
Despite the rapid growth in screw compressor
usage, public knowledge of the scientific basis of
their design is still limited. Three classical screw
compressor textbooks were published in Russia in
the early nineteen sixties. [40] 1960 gives a full
analysis on how to generate circular, elliptic and
cycloidal rotor profiles as well as a russian asymmetric
profile later named SKBK. The method of profile
generation in this book was based on an envelope
approach. [2], 1961 demonstrates this theory
and, in addition, makes a contribution to the field
of rotor tool profile generation. [15], 1964, is a more
general textbook but its section on screw compressors
is very interesting and informative. A Russian
handbook, [1], published in 1977, gives a reproducible
presentation of how to generate the SRM
- 65 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
kako bi rekonstruisao SRM asimetri~ni profil 7 godina
nakon {to je patentiran, a [23] 1988, publikuje
neke in`enjerske aspekte vij~anih kompresora.
Mali je broj knjiga koje se bave vij~anim kompresorima
objavljen na engleskom jeziku: [32] 1993, o
industrijskim kompresorima i [3] 1994 o rotacionim
kompresorima sa dva vratila. Me|utim, sve one su
suvi{e generalne da bi bile razmatrane kao referentna
literatura o vij~anim kompresorima.
Nekoliko priru~nika o vij~anim kompresorima su
objavili proizvo|a}i vij~anih kompresora, isto kao i
odre|eni broj bro{ura koje daju korisne informacije,
ali su one ili povjerljive ili su nedostupne i daleko
od javnosti. Neke od njih, kao {to je, na primjer,
SRM Data Book, ina~e dobro ~uvane i dostupne
samo licensorima, ~esto su citirane kao literatura iz
oblasti vij~anih kompresora.
Me|utim, broj patenata koji su se pojavili u zadnjih
trideset godina je neproporcionalno velik, mo`e se
re~i da je patenata objavljeno na hiljade. Samo je
SRM objavio 750 patenata. Svi se patenti bave
razli~itim aspektima vij~anih kompresora a njihov
najve}i broj profilima rotora. SRM je objavio patente
[33] 1946 simetri~nog, [41] 1973 za asimetri~ni i [4]
1982 za "D" profil. Oni su klasi~na referentna literatura
koja prikazuje vje{tinu profilisanja rotora
vij~anog kompresora. Jo{ neki patenti mogu se
spomenuti kao primjer uspje{nog na~ina generacije
profila: Atlas-Copco, Compair [19], Denver Gardner
[9], Hitachi [20], Ingersol-Rand. U posljednjih je
nekoliko godina jedan broj relativno malih kompanija
objavio vi{e izuzetno uspje{nih patenata, kao {to
su, na primjer, [24] i [8]. Potpuno novi pristup generaciji
profila po kojem se polazne krive zadaju na
zup~astom stapu objavljen je u [37] i u [50].
Svi patentirani profili su generisani na osnovu neke
valjane metode, ali su korisne informacije o
kori{tenim metodama pa`ljivo uklonjene iz patenta ili
iz prate}ih publikovanih radova. Informacije u patentima
su ili sakrivene ili je iz njih gotovo nemogu}e
direktno dobiti profil. Ova se ~injenica mo`e ilustrovati
kroz tri primjera. U radu [29] 1978 objavljuje
se izvodjenje simetri~nog kru`nog profila koji je
patentiran 32 godine prije toga. U [35] se koristi
klasi~nim uslovima sprezanja konjugovanih zup~anika
da bi reprodukovao asimetri~ni SRM profil 9 godina
nakon {to se patent pojavio. Kao kuriozitet mo`e se
pomenuti da je jedan SRM-ov licencor, nakon 13
godina proizvodnje kompresora, iskoristio sav
akademski potencijal kako bi analiti~ki reprodukovao
SRM "D" profil.
asymmetric profile only 5 years after it was patented
as well as the classical Lysholm profile. There
are two German textbooks. [35], 1979, used a profile
generation method based on gear theory to
reconstruct the SRM asymmetric profile 7 years after
it was patented. [23], 1988, published some engineering
aspects of screw compressors.
Only recently have any textbooks on screw compressors
been published in English. [32], 1993, was
on industrial compressors and [3], 1994, was on
rotary twin shaft compressors. However, these are
too general to be useful as detailed reference literature.
A few compressor manufacturers' handbooks on
screw compressors and a number of brochures give
useful information, but they are either classified or
of very limited accessibility. Some, like the SRM
Data Book, although cited in screw compressor literature,
are available only to SRM licencees.
Literally thousands of patents have been awarded
on screw compressors in the past thirty years and
SRM alone has 750. They cover various aspects of
screw compressor design but are mainly for rotor
profiles. SRM patents [33], 1946, for symmetric,
[41], 1973, for asymmetric and [4], 1982, for the
"D" profiles are classical examples of state of the
art screw compressor profile generation. Other
succesful profiling patents are those of Atlas-Copco,
Compair [19], Denver Gardner [9], Hitachi [20] and
Ingersoll-Rand [6]. In recent years, several highly
successful patents such as [24] and [8] have been
granted to relatively small companies. A fresh
approach to profile generation based on the use of
a rack for the primary curves was published in [37]
and [50].
Although all patented profiles were generated by
well defined procedures, so little of the methods on
which they were based was published that it was
very difficult to reproduce them. Thus details of how
to derive the circular symmetric profile, [29], were
not published until 1978, 32 years after it was
patented. Similarly, a derivation of the SRM asymmetric
profile based on classical gear conjugacy criteria,
[35], was not published until 9 years after the
patent appeared. It is even more interesting to note
that one SRM licencee funded a university research
programme to obtain an analytical derivation of the
SRM "D" profile in 1995, after 13 years of manufacturing
it.
- 66 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
Me|u patentima iz podru~ja vij~anih kompresora mogu
se na}i i oni koji se bave drugim aspektima ove
oblasti. Uglavnom su patentirane sve dobro poznate
karakteristike vij~anih kompresora, kao {to je ubrizgavanje
ulja, usisni i tla~ni otvori koji prate helikoidu
rotora, kompenzacija aksijalnih sila, rastere~enje kompresora,
usisni klip, ekonomajzerski otvor, uglavnom od
strane SRM-a, ali i neke druge kompanije tako|er vrlo
revnosno objavljuju patente. Izgleda da patentni
stru~njaci za vij~ane kompresore imaju isti ili sli~an
zna~aj kao i in`enjeri koji se bave njihovim razvojem.
Iako su ~lanci o vij~anim kompresorima rijetkost u
~asopisima, oni su izuzetno korisna literatura o kompresorima
mada ne odaju mogo detalja o profilisanju
vij~anih kompresora. Tako Lysholmovi klasi~ni ~lanci
[26] iz 1942 i [27] iz 1966 ne spomenju ni jedan detalj
o profilisanju koje je autor koristio u svojoj uspje{noj
praksi da bi pobolj{ao zaptivenost kompresora. ^lanci
[45] i [46] se mogu vi{e smatrati izuzetkom nego praksom.
U posljednje vrijeme je objavljivano ne{to vi{e
materijala o vij~anim komopresorima u ~asopisima, {to
je podstaknuto od strane nekoliko institucija, kao {to
su International Institution of Refrigeration [15] i [48],
IMechEng [44], [12], [13], [55] i [57] i ASME [16] i [51].
Ovakvom aktivno{}u je u nekoliko zadnjih godina u
~asopisima distribuirano vi{e informacija o vij~anim
kompresorima nego {to je objavljeno tokom svih
prethodnih godina zajedno. [52] je primjer ~lanka koji
je objavljen u skladu sa najmodernijim trendovima vremenski
dobro izabranog trenutka za publikovanje.
Tri kompresorske konferencije su u potpunosti ili djelomi~no
orjentisane na vij~ane kompresore: Purdue
Compressor Technology Conference u Lafayette, SAD,
IMechEng konferencija o industrijskim kompresorima u
Londonu, Engleska i "VDI Schraubenkompressoren
Tagung" u Dortmundu, Njema~ka. Usprkos obilju
~lanaka o vij~anim kompresorima, samo mali broj
~lanaka sa konferencija daje korisne informacije o profilisanju
rotora vij~anog kompresora i o konstrukcijama
kompresora. Svi ~lanci sa konferencija daju valjan
prikaz obavljenih istra`ivanja ali skoro ni jedan od njih
ne daje reproducibilne informacije koje se odnose na
kori{tene metode profilisanja. ^lanci kakakteristi~ni za
Purdue konferenciju su oni koji se vrlo ~esto citiraju,
ali iz kojih ~italac mo`e saznati vrlo malo o generaciji
profila, kao {to su: [11], [47] i [49], a tako|er i [42],
[43], [53] i [56]. ^lanci [34], [58], [59] i [60] ukazuju na to
da je teorija obvojnice naj~e{}e kori{tena metoda za
izra~unavanje geometrijskih karakteristika rotora. U
zbornik radova sa Dortmundske konferencije nalazi se
odre|eni broj vrlo interesantnih ~lanaka o vij~anim
kompresorima. [36] iz 1984 prezentira na~in generisanja
profila na bazi zup~astog {tapa pri ~emu daje
potpuno reproducibilan patent [37] baziran na klasi~noj
Most of the well known characteristics of screw
compressors, such as oil flooding, making the suction
and discharge ports follow the rotor tip helices,
axial force compensation, unloading, the slide valve
and the economizer port, were also patented, mainly
by SRM. However other companies were equally
keen to file patents. It appears that, in the field
of screw compressors, patent experts are as important
as engineers.
There are surprisingly few journal publications on
screw compressors in the technical literature.
Notable exceptions are Lysholm's [26-27] classical
papers of 1942 and 1966. However neither of
these described any of the profiling details which
he developed successfully in order to reduce the
blow-hole area. Other exceptions are [45] and
[46]. In recent years, journal publication of screw
compressor material has been encouraged by the
International Institution of Refrigeration [15] and
[48], the IMechE [44], [12], [13], [55] and [57] and
ASME [16] and [51]. This led to more information
on screw compressors in journals during
recent years than in all previous years together.
[52] is an example of the modern practice of more
timely publishing.
There are three compressor conferences which deal
exclusively or partly with screw compressors. These
are: the Purdue University compressor technology
conferences in the U.S.A, the ImechE conferences
on industrial compressors in England and the "VDI
Schraubenkompressoren Tagung" in Germany.
Despite the wealth of screw compressor papers
which these contain, very few give useful information
on rotor profiling procedures and compressor
design.
Typical Purdue papers, frequently cited, from which
a reader will gain a little on profile generation are:
[11], [47] and [49] , also [42], [43], [53], [56]. Refs
[34], [58], [59], and [60] indicate that envelope theory
was used to calculate some geometric features
of their rotors.
The "VDI Schraubenkompressoren Tagung" proceedings
contain some interesting screw compressor
papers. [36] 1984 presents a rack method
of rotor profile generation, based on classical
gearing theory, which is fully reproducible.
Unfortunately, although soundly conceived, profiles
produced by this method were not commercially
successfull because of their poor tightness. [16]
and [18] give some more details on profiling and
manufacturing control. [21], [22] and [54] are typi-
- 67 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
teoriji zup~anika. Me|utim, na`alost, na prikazani na~in
dobiveni profil, iako baziran na odli~nim osnovama
nema velik komercijalni zna~aj zbog vrlo slabog zaptivanja.
[16] i [18] daju ne{to vi{e detalja o profilisanju
i kontroli proizvodnje. [21], [22] i [54] su tipi~ni primjeri
uspje{nog akademskog istra`ivanja primjenjenog na
stvarno in`enjerstvo. [38] i [39] se mogu nazvati primjerom
prakti~ne primjene preciznog in`enjerskog
rada. Londonska kompresorska konferencija, iako ne
tako u~estala, dala je nekoliko vrlo interesantnih ~lanaka
kao {to je, na primjer [10].
Mnoge referentne knjige o zup~anicima su korisna
polazna osnova za profilisanje rotora vij~anog kompresora,
ali je ve~ina od njih ograni~ena na klasi~e
uslove sprezanja zup~anika. Kao primjer se mo`e
ista}i klasi~na knjiga [7]. Knjiga [25] se mo`e smatrati
izuzetkom od ovog pravila jer daje teoriju
sprezanja zup~anika koja se direktno mo`e primijeniti
i na profilisanje rotora vij~anog kompresora.
3 SAVREMENI RAZVOJ VIJ^ANOG
KOMPRESORA
Efikasan rad vij~anog kompresora uglavnom zavisi
od pravilne konstrukcije njegovih rotora. Dodatno se
kao uslov za uspje{nu konstrukciju razli~itih vrsta
kompresora postavlja i sposobnost da se radne
karakteristike mogu precizno predvidjeti u slu~aju da
se promijeni bilo koji parametar kao {to je na primjer
zazor, oblik profila rotora, pozicija i koli~ina
ubrizganog ulja ili nekog drugog fluida u radni prostor,
pre~nik i proporcija rotora i brzina obrtanja.
Danas, kad su zazori u kompresoru mali, unutra{nje
curenje koje ima veliki uticaj na efikasnost sve vi{e
zavisi od du`ine linije dodira rotora, tako da kao
mogu}nost za pobolj{anje kompresora ostaje jo{
samo bolje profilisanje rotora. Tako se posebna
pa`nja posve}uje unapredjenju karakteristika rotora
da se, {to je god vi{e mogu}e, pove}a unutra{nji
protok kompresora a da se linija dodira izmedju
rotora smanji, te da se istovremeno unutra{nje trenje
usljed relativnog klizanja dodirnih povr{ina rotora
u~ini {to je mogu}e manjim.
Mada na prvi pogled izgleda da je u profilisanju rotora
dosad u~injeno sve {to je bilo mogu}e, to je
daleko od istine. U stvari, ima jo{ mnogo prostora za
zna~ajna pobolj{anja. ^ini se da na~in profilisanja koji
kao polaznu osnovu uzima zup~asti {tap, ima najvi{e
izgleda da postigne najbolje rezultate jer se njime
mogu dobiti ja~i i lak{i rotori sa ve}om dobavom i
manjim kontaktnim naponima. Ovo posljednje
omogu}ava da se u radni prostor kompreora ubrizgava
fluid ni`e viskoznosti.
Kori{tenjem metoda vi{eparametarske optimizacije
dobivaju se sve bolje oblikovani otvori na ku~i{tu
vij~anog kompresora. Time se smanjuju gubici na
cal examples of successful university research
applied to solve real engineering problems. [38]
and [39] may be regarded as examples of fine
engineering work.
Although relatively infrequent, the London compressor
conferences included some interesting papers,
such as [10].
Many reference textbooks on gears give a useful
background to screw rotor profiling. However all of
them are limited to the classical gear conjugate
action condition. One example of this is [7]. [25] is
an exception to this practice which contains gear
theory directly applicable to screw compressor profiling.
3 RECENT DEVELOPMENTS
The efficient operation of screw compressors is
mainly dependent on proper rotor design. An additional
and important requirement for the successful
design of all types of compressor is the ability to
predict accurately the effects on performance of
the change in any design parameter such as clearance,
rotor profile shape, oil or fluid injection position
and rate, rotor diameter and proportions and
speed.
Now that tight clearances are achievable, internal
compressor leakage rates become small. Hence, further
improvements are only possible by the introduction
of more refined design principles. The main
requirement is to improve the rotor profiles so that
the internal flow area through the compressor is maximised
while the leakage path is minimised and internal
friction due to relative motion between the contacting
rotor surfaces is made as small as possible.
Although rotor profiling procedures may appear to be
fully defined, substantial improvements are still possible.
The most promising approach for this seems
to be through rack profile generation which gives
stronger but lighter rotors with higher throughput and
lower contact stress. The latter enables fluids with
lower viscosity than oil to be used for lubrication.
Rotor housings with better shaped ports can be
designed using multivariable optimization techniques.
Flow losses may thereby be reduced permitting
higher rotor speeds and hence more effective compressors.
- 68 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
usisu i na izlazu {to omogu}ava pove}anje broja
obrtaja kompresora, a time se direktno pove~ava i
njegova efektivnost.
Zna~ajni uspjesi su u nekoliko zadnjih godina postignuti
i u razvoju le`ajeva za kompresore, ~ime je omogu}eno
podmazivanje kompresora fluidom viskoznosti
manje nego kod obi~no kori{tenih ulja. Zaptiva~i su,
takodjer, mnogo efikasniji nego ranije. Sve ovo je dalo
dobru osnovu za efikasniji rad kompresora.
3.1 Profili rotora
Naj~e{}e kori{ten metod generacije profila rotora
vij~anog kompresora je da se defini{e primarni profil
na jednom od rotora a da se nakon toga tra`e
odgovaraju}e krive na drugom rotoru primjenom
razli~itih uslova sprezanja. Na osnovnom rotoru je
mogu}e definisati bilo koju krivu liniju ali je tradicionalno
naj~e{}e kori{tena kriva upravo kru`nica.
Bilo koja kru`nica sa centrom na podionom krugu
generisa}e sli~nu kru`nicu na drugom rotoru. Ista
situacija se dobije ako je centar kru`nice u osi rotora.
Kru`nice sa centrom van podionog kruga na isti
na~in kao i ostale krive: elipsa, parabola ili hiperbola
proizve{}e na drugom rotoru neku generisanu
krivu, koja se naziva trohoida. Sli~no tome, ta~ka
koja je fiksirana na jednom rotoru generisa}e epi- ili
hipocikloidu na drugom rotoru. Sva vje{tina profilisanja
rotora se decenijama svodila na pravilan izbor
primarnih krivih na jednom rotoru koje }e omogu}iti
izvo|enje odgovaraju}eg profila na drugom rotoru.
Kru`ni simetri~ni profil se sastoji samo od kru`nica,
dok se Lysholmov profil, osim od kru`nica postavljenih
u centar podionog kruga, sastoji od sistema
cikloida na strani visokog pritiska ~ime je dobiven
prvi asimetri~ni profil rotora vij~anog kompresora. Za
asimetri~ni SRM profil je prvi put iskori{tena ekscentri~na
kru`nica na strani niskog pritiska na
vo|enom rotoru dok je na SKBK profilu isto ura|eno
na vode}em rotoru. U oba slu~aja su izvedene krive
analiti~ki definisane kao epi- ili hipocikloide. SRM
"D" profil se sastoji samo od kru`nica od kojih su
neke sasvim male, ali su sve ekscentri~no postavljene
na vode}em ili vo|enom rotoru. Svi patenti koji
slijede nakon toga baziraju se na definisanju jednog
od rotora i izvo|enju drugog, i svi su, vjerovatno,
bazirani na klasi~nom sprezanju zup~anika ili na
nekim sli~nim uslovima. Tek u posljednje vrijeme
kru`nice su postepeno zamjenjuju nekim drugim
krivuljama kao {to su: elipsa kod FuSheng profila
[24], parabola na Compair [19] i Hitachi profilima i
hiperbola na "hyper" profilu [8]. ^ini se da je hiperbola
na posljednjem profilu odgovaraju}a zamjena za
ostale krive, jer daje najbolji odnos dobave rotora i
du`ine linije zaptivanja.
3.1 Rotor Profiles
The normal procedure used to generate rotor profiles
is to create primary profile curves on one rotor
and, by use of an appropriate conjugate criterion,
a corresponding secondary profile curve on the
other. Any curve can be used as the primary one,
but traditionally a circle is the most comon. All circles
with their centres on the pitch circle generate
a similar circle on the other rotor. This is also true
if the circle centres are at the rotor axes. Circles
with centres not on the pitch circle and other
curves, like ellipses, parabolae and hyperbolae
require more elaborate curves to be generated, on
the other rotor which are described as trochoids.
Similarly, points located on one rotor will cut epior
hypocycloids on the other rotor. For decades,
the skill required to produce rotors was limited to
the ability to choose a primary arc which would
permit the derivation of an appropriate secondary
profile.
The symmetric circular profile consist of circles only.
Apart from the use of pitch circle centred circles,
Lysholm introduced a set of cycloids on the high
pressure side to form the first asymmetric screw
rotor profile. Later the SKBK profile used the same
curves. The SRM asymmetric profile employs an
eccentric circle on the low pressure side of the
gate rotor. In all these cases the curves evolved
analytically from them were epi- or hypocycloids.
The SRM "D" profile consists exclusively of circles,
almost all of them eccentrically positioned on the
main or gate rotor. All patents which followed, specify
primary curves on one rotor and secondary generated
curves on the other rotor. All are probably
derived from classical gear contact theory or a similar
alternative criterion. More recently, circles have
gradually been replaced by other curves such as
ellipsae in the FuSheng profiles [24], parabolae in
the Compair [19] and Hitachi [20] profiles and hyperbolae
in the 'Hyper' [8] profile. Replacing the circle
by a hyperbola in the latest profile, seems to give
the best ratio of rotor displacement to sealing line
length.
Another method of rotor profile generation is to
consider imaginary, or 'nonphysical' rotors. Since
all gearing equations are independent of the coordinate
system in which they are expressed, it is
possible to define primary arcs as given curves
using a coordinate system which is independent of
both rotors. By this means, in many cases the
defining equations may be simplified. Also, the
- 69 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
Drugi na~in na koji je mogu}e definisati profil rotora
je da se osnovne krive izaberu na nekom
zami{ljenom, "nefizikalnom" rotoru. Po{to su sve
jedna~ine zup~anika neovisne od koordinatnog sistema
u kojem su izra`ene, primarni luk je mogu}e
definisati i u nekom koordinatnom sistemu koji je ne
ovisi ni o jednom rotoru. U ve~ini slu~ajeva se na
taj na~in jedna~ine mogu pojednostaviti. Upotreba
jednog koordinatnog sistema za definisanje svih krivih
na rotoru tako|er mo`e pojednostaviti proces
profilisanja. Tako se polazni profil u cijelosti mo`e
definisati u koordinatnom sistemu koji ne zavisi od
rotora, {to vrijedi i za rotor sa beskona~nim
pre~nikom koji se naziva zup~asti {tap. Prvi ikada
publikovani patent koji prikazuje ovakvu generaciji
profila rotora [30] objavljen 1977, iako nije prakti~no
primjenljiv, vje{to koristi pomenutu teoriju. [37] i kasnije
[50] prvi daju dobru osnovu za generaciju profila
vij~anog kompresora.
Efikasan vij~ani kompresor mora imati rotore ~iji profil
osigurava veliki proto~ni presjek, kratku liniju zaptivanja
i mali nezaptiveni prostor na vrhu rotora. To
zna~i, da je za ve}i proto~ni presjek i broj obrtaja
kompresora, i dobava kompresora ve}a. Kra}e linije
dodira i manji nezaptiveni prostor smanji}e unutra{nje
curenje. Ve}a dobava i manje curenje }e pove}ati
volumetrijski stepen iskori{tenja kompresora, koji je
defini{an kao dobava podijeljena zbirom ukupnog
protoka i curenja. Time se dalje pove}ava adijabatski
stepen iskori{tenja, jer se za kompresiju gasa koji
recirkuli{e unutar kompresora tro{i manje snage.
Izbor odnosa veli~ine nezaptivenog prostora i broja
radnih zapremina zavisi}e od namjene kompresora.
Kako je za manje razlike pritisaka curenje proporcionalno
manje, dobici postignuti velikim proto~nim
presjekom mogu poni{titi ili smanjiti gubitke nastale
usljed velikog nezaptivenog prostora. Na sli~an na~in
se mo`e dobiti optimalni broj zuba vij~anog kompresora,
po{to manji broj zuba daje ve}i proto~ni
presjek ali i rezultira u ve}oj razlici pritiska izme|u
radnih prostora.
Sa smanjenjem zazora izmedju rotora, bez obzira na
podmazivanje kompresora uljem, vjerovatno}a direktnog
dodira me|u rotorima sa pove}ava. Dodir
me|u rotorima dovodi do pove}anja kontaktnih sila i
optere}enja rotora {to dalje uzrokuje deformaciju
vo|enog rotora. Zbog toga, njegov profil mora biti
konstruisan tako da se rizik od pucanja ili plasti~ne
deformacije rotora smanji na najmanju mogu}u mjeru.
Brzi razvoj metoda matematskog modeliranja i
ra~unarske simulacije je, u posljednje vrijeme, podstakao
i olak{ao istra`ivanje novih profila rotora.
use of one coordinate system to define all the
curves, simplifies the design process. Typically, the
template is specified in a rotor independent coordinate
system. This is valid for a rotor of infinite
radius, which is a rack. From this, a secondary arc
on some of the rotors is obtained by a procedure,
which is called 'rack generation'. The first patent
on rack generation published, [30], is based on
this theory but lacks practicality. [37] and, more
recently, [50] give a good basis for rotor profile
generation.
For a screw compressor to be efficient, the rotor
profile must form a large flow cross section area, a
short sealing line and a small blow-hole area. The
larger the cross section area, the higher the flow
rate for the same rotor sizes and speeds. Shorter
sealing lines and a smaller blow-hole reduce leakages.
Higher flow and smaller leakage rates both
increase the compressor volumetric efficiency, which
is the rate of flow delivered as a fraction of the
sum of the flow plus leakages. This in turn increases
the adiabatic efficiency because less power is
wasted in the compression of gas which is recirculated
internally.
The optimum choice between blow hole and flow
areas depends on the compressor duty since, for
low pressure differences, the leakage rate will be
relatively small and hence the gains achieved by
a large cross section area may outweigh the losses
associated with a larger blow-hole. Similar considerations
determine the best choice for the number
of lobes since fewer lobes imply greater flow
area but increased pressure difference between
them.
As precise manufacture permits rotor clearances to
be reduced, despite oil flooding, the likeliehood of
direct rotor contact is increased. Hard rotor contact
leads to deformation of the gate rotor, increased
contact forces and ultimately rotor seizure. Hence
the profile should be designed so that the risk of
seizure is minimised.
The search for new profiles has been both stimulated
and facilitated by recent advances in mathematical
modelling and computer simulation. These
analytical methods may be combined to form a
powerful tool for process analysis and optimisation
and thereby eliminate the earlier approach of intuitive
changes, verified by tedious trial and error testing.
As a result, this approach to the optimum
design of screw rotor lobe profiles has substantial-
- 70 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
Analiti~ke metode je mogu}e kombinovati na taj
na~in da se dobije mo}no sredstvo za analizu i optimizaciju
procesa vij~anog kompresora, ~ime se u
potpunosti mo`e zaobi}i ranije kori{tena metoda intuitivne
konstrukcije zasnovana na mukotrpnom metodu
poku{aja i pogre{ke. Kao rezultat, ovaj pristup optimalnom
konstruisanju rotora vij~anog kompresora
zna~ajno je evoluirao u nekoliko zadnjih godina sa
velikim {ansama da se u narednim godinama
postignu dalja pobolj{anja karakteristika ma{ine.
Me|utim, i geometrija rotora, isto kao i radni proces
u vij~anom kompresoru su toliko kompleksni da je
potrebno uvesti niz aproksimacija kako bi modeliranje
bilo ostvarivo. Kao posljedica, u otvorenoj literaturi
se mogu na}i matematski modeli i numeri~ki
kodovi sa vrlo {arolikim pristupom problemu i sa
razli~itim matematskim nivoima modeliranja fenomena
u vij~anom kompresoru. Nedostatak uporedivih
eksperimentalnih rezultata jo{ uvijek onemogu}ava
verifikaciju i svestranu ocjenu razli~itih koncepcija
modeliranja. Uprkos tome, matematsko modeliranje i
simulacija ra~unarom sve vi{e dobivaju na popularnosti
i sve se vi{e koriste za unapre|enje konstruktivnih
karakteristika vij~anog kompresora.
Na slici 1. prikazan je niz rotora vij~anog kompresora
tako da se oni mogu me|usobno usporediti.
Profili su ozna~eni brojevima u zagradama, koji u
popisu literature ukazuju na patente za te rotore.
U prvu prikazanu grupu spadaju rotori sa 4 zuba na
vode}em i 6 zubi na vo|enom rotoru. Ovakva konfiguracija
rotora je kori{tena skoro za svaku aplikaciju.
Asimetri~ni SRM profil [41], koji se mo`e smatrati
do sada najuspje{nijim profilom rotora vij~anog
kompresora, nalazi se na po~etku. Slijede}i je SRM
"D" profil [4]. Na kraju je prikazan profil generisan
na osnovu zup~astog {tapa - rack generisan profil
[50]. Izbor i raspored osnovnih krivih na zup~astom
{tapu pomo}u kojih su generisani ovi rotori daje
ve}i popre~ni presjek me|uzublja i ja~i zub vo|enog
rotora u odnosu bilo koji drugi poznati profil rotora
vij~anog kompresora ove konfiguracije.
Konfiguracija vij~anog kompresora sa 5 zubi vode}eg
i 6 zubi vo|enog rotora postaje sve popularnija, jer
se njome postize kompromis izmedju velike dobave i
velikog tla~nog otvora sa skoro nenadma{nim strujnim
karakteristikama za manji pre~nik rotora.
Kompresori sa ovakvom konfiguracijom rotora su jednako
pogodni za kompresiju zraka kao i za rashladnu
tehniku ili za klimatizaciju. U nastavku je, radi
upore|enja, data ve}a skupina ovih rotora koja
po~inje sa SRM "D" profilom [4], nakon toga slijede
"Sigma" profil [5], FuSheng [24] i "Hyper" profil [8].
Svi ovi profili su 'rotor generisani' profili a osnovna
ly evolved over the past few years and is likely to
lead to further improvements in machine performance
in the near future.
A comparison of several pairs of screw compressor
rotors is shown in Fig. 1. Each pair is labeled by
a number in brackets which denotes its patent.
The first group gives rotors with 4 lobes on the
main and 6 lobes on the gate rotor. This rotor configuration
is the most universally accepted for almost
any application. The SRM asymmetric profile [41],
which historically was the most successful, is on the
top. The next one is the SRM "D" profile [4]. The
Ingersol-Rand profile, [6], shows how attempts were
made to produce more displacement from the same
compresor size. Finally, rack generated rotors [50]
are presented.
The second group shown are 4/5 rotors which is
becoming a very popular combination for oil-flooded
air compressors. The first pair, SRM "D" [4]
rotors are applied in "Tamrotor" compressors which
are regarded as best compressors in their class.
They are followed by "Cyclon" [19] rotors. The last
in this group are 'rack-generated' rotors [50]. The
selection and distribution of primary curves on the
rack which was used to create these rotors, gives
a larger cross section area with stronger gate rotor
lobes than any other known screw compressor
rotor pair.
The largest group of rotors presented has a 5/6
configuration. This is becoming the most popular
rotor combination because it permits a good compromise
between large displacement and large discharge
ports with favourable load characteristics in
small rotor sizes. These rotors are equally successful
for air compression and refrigeration and air-conditioning
applications. The group starts with the SRM
"D" profile, [4], followed by the "Sigma", [5],
FuSheng, [24] and "Hyper" [8] profiles. All are 'rotorgenerated'
profiles and the main diference between
them is in the leading lobe which is mainly an
eccentric circle followed by a line, ellipse and
hyperbola respectively. The hyperbola appeared to
be the best possible geometrical solution for that
purpose. However at the end of the group are two
rack-generated profiles, [37] and [50]. The last of
these shows the best delivery for its size. it also
has two additional features. Firstly, the rotors retain
a seal over the entire contact length while maintaining
a small blow-hole, which was not the case
in [37]. Secondly, two contact bands in the prox-
- 71 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
Slika 1. Upore|enje nekih rotora vij~anih kompresora
Figure 1. A comparison of several pairs of screw compresor rotors
- 72 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
razlika izme|u njih se uo~ava na vode}em rotoru koji
po~inje sa ekscentri~nom kru`nicom a nastavlja se
linijom, elipsom ili hiperbolom respektivno. Pokazuje
se da je hiperbola najbolje mogu}e primjenjivo
geometrijsko rje{enje. Na kraju grupe se nalaze dva
'rack generisana' profila [37] i [50]. Mo`e se vidjeti da
posljednji profil ima najve}u dobavu. Tako|er, mogu
se uo~iti jo{ dvije osobine koje karakteri{u te rotore
i favorizuju ih u odnosu na ostale. Postignuto je zaptivanje
du` cijele linije dodira i time manji nezaptiveni
prostor, {to nije slu~aj kod profila [37]. Dodatno, kontaktne
povr{ine sa jedne i druge strane profila u blizini
podionog kruga su ravne linije na zup~astom {tapu
tako da formiraju evolventu na rotorima. Zbog toga
{to je relativno kretanje jednog rotora u odnosu na
drugi gotovo ~isto kotrljanje, to je najbolji dodir {to
ga je mogu}e posti}i izme|u rotora. Rack generisani
rotori konfiguracije 5/6 su prikazani na slici 2.
Posljednja grupa rotora sa 4 i 5 rotora u vode}em
i vo|enom vijku respektivno, postaje sve vi{e popularna
za uljnopodmazivane zra~ne kompresore. Prvi
par rotora su "Cyclon" rotori [19]. Iza njih su SRM
"D" rotori [4] i na kraju grupe rotori generisani
pomo}u zup~astog {tapa [50].
3.2 Konstrukcija kompresora
Iako je moderan profil rotora neophodan uslov da
bi vij~ani kompresor bio efikasan, sve ostale komponente
tako|er moraju biti konstruisane tako da se
na najbolji na~in iskoristi potencijal rotora i ostvare
najbolje mogu}e performanse kompresora. Zbog
toga je vrlo va`no pravilno odabrati zazor izme|u
ku}i{ta i rotora, posebno na strani visokog pritiska.
To, povratno, zahtijeva ili skuplje le`ajeve sa manjim
zazorima ili jeftinije le`ajeve kod kojih su prednaprezanjem
zazori svedeni na prihvatljivu veli~inu.
Vij~ani kompresor je op}enito, a slu~aju uljnopodmazivanog
kompresora, kada radi sa velikom razlikom
pritisaka, posebno optere}en aksijalnim i radijalnim
silama koje se na ku}i{te prenose preko
le`ajeva. Za vij~ane kompresore malog i srednjeg
kapaciteta obi~no se koriste kotrljaju}i le`ajevi, koji
u tom slu~aju moraju biti tako dobro odabrani da
zadovolje sve zadane uslove rada. Obi~no se koriste
dva le`aja na tla~noj strani vratila rotora kako bi se
aksijalne i radijalne sile na ku}i{te prenijele odvojeno.
Tako|er je bitno je da je me|uosno rastojanje
djelimi~no odre|eno i veli~inom le`ajeva i njihovim
unutra{njim zazorima.
Kontaktne sile, koje su definisane obrtnim momentom
koji se prenosi izme|u rotora, igraju klju~nu ulogu
kod kompresora sa direktnim dodirom rotora. Ove su
sile relativno male u slu~aju pogona preko vode}eg
imity of the pitch circles are straight lines on the
rack which form involutes on the rotors. Hence the
relative motion between the rotors is close to pure
rolling which is the best possible.
3.2 Compressor Design
Screw compressor design has gradually evolved and
the trend is to get as small as possible a machine
to meet the required performance. This means that
rotor tip speeds are as high as possible within the
limits imposed by efficiency requirements. Normal
practice is to use rolling element bearings wherever
possible because these permit smaller clearances
than journal bearings. Similarly, the ports are made
as large as possible to minimize suction and discharge
gas speeds. These features lead to great
similarity in all designs for any specified application.
Although advanced rotor profiles are a necessary
condition for a screw compressor to be efficient, all
other components must be designed to minimise
losses if maximum improvements are to be
achieved. Thus the rotor to housing clearances must
be properly selected, especially at the high pressure
end. This in turn requires either expensive
bearings with small clearances or cheaper bearings
with their clearances reduced to an acceptable
value by preloading.
A screw compressor, especially of the oil flooded
type, operates with high pressure differences.
These create large axial and radial bearing forces.
Rolling element bearings are normally chosen for
small and medium screw compressors and these
must be carefully selected to obtain a satisfactory
design since, inter alia, the distance between the
rotor centre lines is in part determined by them. It
must be added that recent advances in the development
of advanced low friction rolling element
bearings greatly contributes to this choice [31].
Usually two bearings are fitted at the high pressure
end of the rotor shafts in order to absorb the radial
and axial loads separately.
The contact force between the rotors is determined
by the torque transferred between them and is very
significant when they make direct contact. It is relatively
small when the compressor drive is through
the main rotor. However, when the drive is through
the gate rotor, the contact force is substantially larger
and, as far as possible, this arrangement should
be avoided.
- 73 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
Slika 2. Rack generisani rotori vij~anog kompresora konfiguracije 5/6
Figure 2. A pair of 5/6 rack generated screw compressor rotors
rotora. Pogon preko vo|enog rotora uzrokuje
zna~ajno pove}anje kontaktnih sila tako da se ovaj
slu~aj mora isklju~iti iz bilo kakvog ozbiljnijeg razmatranja.
Ulje koje se u vij~anom kompresoru ubrizgava izme|u
rotora za podmazivanje, hladjenje i zaptivanje, koristi
se i za podmazivanje le`ajeva. Pri tom je vrlo va`no
uspostaviti odvojen sistem snabdijevanja le`ajeva
uljem i sistem za evakuaciju ulja iz le`ajeva da bi se
gubici usljed trenja smanjili. Ulje se u radni prostor
kompresora ubrizgava na onom mjestu na kojem se,
prema termodinamskim prora~unima, temperature
radnog fluida i ulja podudaraju. Polo`aj otvora za
ubrizgavanje ulja je definisan uglom na helikoidi rotora
ali se obi~no postavlja tako da ulje tangencijalno
ulazi u radni prostor kako bi se iskoristilo {to je god
mogu}e vi{e njegove kineti~ke energije.
Kompresor moderne konstrukcije treba imati male
gubitke na usisu i potisu. Zato se usisni otvor unutar
ku}i{ta kompresora postavlja tako da usisani gas na
svom putu {to manje mijenja smijer kretanja te da
bi imao malu brzinu strujanja. To se posti`e
pove}anjem zapremine usisnog otvora. Veli~ina i
oblik tla~nog otvora definisani su ugra|enim odnosom
pritiska koji }e dati optimalne termodinamske
performanse kompresora. Nakon toga se popre~ni
presjek izlaznog toka dodatno pove}ava da bi se
smanjila brzina toka na izlazu i time postigla minimizacija
gubitaka u unutra{njem i izlaznom toku.
Ku}i{te treba da bude pa`ljivo dimenzionisano kako
bi se smanjila te`ina kompresora a jedan od na~ina
da se to postigne je ugradnja pre~ke u usisnom
otvoru u cilju pove}anja ~vrsto}a kompresora na
vi{im pritiscima.
Vij~ani kompresor je vrlo jednostavna toplotna ma{ina
The oil which is injected into the compressor for
flooding is also used for bearing lubrication but, to
minimise friction losses, the bearing feed and return
system is separate. The position in the compressor
chamber where the oil is injected is set at the
point where thermodynamic calculations show the
gas and oil inlet temperatures to coincide. It is
defined on the rotor helix with the injection hole
located so that the oil enters tangentially in line with
the gate rotor tip in order to recover as much as
possible of the oil kinetic energy.
To minimise flow losses in the suction and discharge
ports, the following features must be included.
The suction port should be positioned in the
housing to let the gas enter with the fewest possible
bends and the gas approach velocity kept low
by making the flow area as large as possible. The
discharge port size is first determined by estimating
the built-in-volume ratio required for optimum thermodynamic
performance. It is then increased in
order to reduce the exit gas velocity and hence
obtain the minimum combination of internal and discharge
flow losses.
The casing should be carefully dimensioned to minimize
its weight and contain reinforcing bars across
the suction port to improve its rigidity at higher
pressures.
- 74 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
sa samo nekoliko pokretnih dijelova: dva rotora i
obi~no ~etiri ili {est le`ajeva. Tokom njegovog razvoja
do{lo se do vrlo tipi~nog oblika po ~emu postaje
vrlo prepoznatljiv. Tendencija je da se dobije {to
je god mogu}e manja ma{ina koja }e jo{ uvijek dati
zadovoljavaju}e performanse. To zna~i da se brzina
vrha zuba mora {to je mogu}e vi{e pove}ati, ali je
treba jo{ uvijek dr`ati u granicama koje daju prihvatljive
mehani~ke gubitke. Upotreba kotrljaju~ih
umjesto kliznih le`ajeva skoro da se mo`e postaviti
kao pravilo koje treba uvijek po{tovati, jer su zazori
na kotrljaju~im le`ajevima, a i gubici zna~ajno manji.
Otvori za komunikaciju radnog fluida moraju biti {to
je god mogu}e otvoreniji da bi se smanjile brzine
gasa na usisu i izlazu. Sve ovo dovodi do vrlo sli~nih
konstrukcija kompresora tako da su izuzetci vrlo rijetki
i skoro zanemarivi. Primjer savremene konstrukcije
uljnopodmazivanog vij~anog kompresora sa reduktorom
dat je na slici 3.
Valja tako|er napomenuti da je u zadnje vrijeme
dosta uradjeno na razvoju kotrljaju~ih le`ajeva sa
vrlo niskim trenjem [31], {to }e zna~ajno doprinijeti
pobolj{anju performansi kompresora.
Na slici 4. prikazuju se svi vitalni dijelovi modernog
uljnopodmazivanog vij~anog kompresora.
4. CONCLUSIONS
At the onset of the millenium, the twin screw compressor
has become a mature product. As a result
of orchestrated efforts by a large number of companies,
driven by market forces, it has become a
compact, efficient and reliable machine. Every detail
counts today. Even small advances in any feature
will give distinctive improvements which may be
used to gain commercial advantage. Hence,
despite its now established role in industry, efforts
continue to make advances in every aspect of its
design, manufacture and mode of operation.
Although improvements so gained are most likely to
be evolutionary, there is still scope for revolutionary
methods or procedures to achieve a better product.
The most promising development appears to be
rack profile generation to produce stronger but
lighter rotors with higher displacement
and lower contact stress.
4 ZAKLJU^AK
Vij~ani kompresor je proizvod koji je dorastao
trenutku smjene vijekova. Pa`ljivo usmjereni napori
velikog broja kompanija dirigovani zahtjevima tr`i{ta
rezultirali su kompaktnom i efikasnom vij~anom
ma{inom. U razvoju vij~anih kompresora do{lo se u
fazu kad se unapre|enja razmatraju do najsitnijih
detalja. Male razlike dovode do malih ali zna~ajnih
pomaka koji ~ine individualne prednosti svakog od
kompresora.
Iako se ~ini da se samo kontinualnim razvojem
vij~ani kompresori mogu promijeniti na bolje, jo{ uvijek
ima dosta mjesta za primjenu manje ili vi{e revolucionarnih
metoda ili procedura koje }e rezultirati
boljim proizvodom. ^ini se da je najperspektivniji
metod generacije profila pomo}u zup~astog {tapa
koji daje ja~e, ali i lak{e rotore sa ve}om dobavom
i manjim kontaktnim naponima me|u rotorima.
- 75 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
Slika 3. Konstrukcija vij~anog kompresora sa reduktorom
Figure 3. A screw compressor with a gearbox design
Slika 4. Sastavni dijelovi modernog uljnopodmazivanog vij~anog kompresora
Figure 4. A modern oil floded screw compressor parts
LITERATURA - REFERENCES
[1] Amosov P.E et al, 1977: Vintovie kompresornie
mashinii - Spravochnik (Screw Compression
Machines - Handbook), Mashinstroienie, Leningrad
[2] Andreev P.A, 1961: Vintovie kompressornie
mashinii (Screw Compression Machines), SUDPROM
Leninngrad
[3] Arbon I.M, 1994: The Design and Application of
Rotary Twin-shaft Compressors in the Oil and Gas
Process Industry, MEP London
[4] Astberg A, 1982: Patent GB 2092676B
[5] Bammert K, 1979: Patent Application FRG
2911415
[6] Bowman J.L, 1983: US Patent 4,412,796
[7] Buckingham E, 1963: Analytical Mechanics of
Gears, Dover Publ, N.York
[8] Chia-Hsing C, 1995: US Patent 5,454,701
- 76 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},..: SAVREMENI RAZVOJ KONSTRUKCIJE...
[9] Edstrom S.E, 1974: US Patent 3,787,154
[10] Edstrom S.E, 1989: Quality Classes for screw
Compressor Rotors, Proc IMechE Conference
Development in Industrial Compressors, 83
[11] Edstrom S.E, 1992: A Modern Way to Good
Screw Compressors, International Compressor
Engineering Conference At Purdue, 18
[12] Fleming J.S, Tang Y, 1994: The Analysis of
Leakage in a Twin Screw Compressor and its
Application to Performance Improvement, Proc
IMechE, Journal of Process Mechanical Engineering,
Vol 209, 125
[13] Fleming J.S, Tang Y, Cook G, 1998: The Twin
Helical Screw Compressor, Part 1: Development,
Applications and Competetive Position, P. 2:A
Mathematical Model of the Working process, Proc
IMechE, Journal of Mechanical Engineering Science,
Vol 212, p369
[14] Fujiwara M, Osada Y, 1995: Performance
Analysis of Oil Injected Screw Compressors and their
Application, Int J Refrig Vol 18, 4
[15] Golovintsov A. G et al, 1964: Rotatsionii kompresorii
(Rotary Compressors), Mashinostroenie,
Moscow
[16] Hanjali} K, Sto{i} N, 1994: Application of mathematical
modeling of screw engines to the optimization
of lobe profiles, Proc. VDI Tagung
"Schraubenmaschinen 94" Dortmund VDI Berichte
1135
[17] Hanjali} K, Sto{i} N, 1997: Development and
Optimization of Screw Machines with a Simulation
Model, Part II: Thermodynamic Performance
Simulation and Design, ASME Transactions, Journal
of Fluids Engineering, Vol 119, p 664
[18] Holmes C.S, 1994: Towards a Core program for
the Measurement of Screw Rotor Bodies by Co-ordinate
Measuring Machine, Proc. VDI Tagung
"Schraubenmaschinen 94", Dortmund VDI Berichte
1135
[19] Hough D, Morris S.J, 1984: Patent Application
GB 8413619
[20] Kasuya K. et al, 1983: US Patent 4,406,602
[21] Kauder K, Harling H.B, 1994: Visualisierung der
Olverteilung in Schraubenkompressoren (Visualisation
of Oil Effects in Screw Compressors), Proc. VDI
Tagung "Schraubenmaschinen 94", Dortmund VDI
Berichte 1135
[22] Kauder K, Helpertz M, 1998: Einlauf- und
Hybridschichten für Schraubenkompressoren (Run-in
and Hybrid Coatings for Twin-Screw Compressors),
Proc. VDI Tagung "Schraubenmaschinen 98",
Dortmund VDI Berichte 1391
[23] Konka K-H, 1988: Schraubenkompressoren
(Screw Compressors) VDI-Verlag, Duesseldorf
[24] Lee H-T, 1988: US Patent 4,890,992
[25] Litvin F.L, 1956: Teoria zubchatiih zaceplenii
(Theory of Gearing), Nauka Moscow, second edition
1968, also Gear Geometry and Applied Theory
Prentice-Hill, Englewood Cliffs, NJ 1994
[26] Lysholm A, 1942: A New Rotary Compressor,
Proc. I.Mech.E. 150,11
[27] Lysholm A, 1966: The Fundamentals of a New
Screw Engine, ASME Paper No 66-GT-86
[28] Lysholm A, 1967: US Patent 3,314,598
[29] Margolis D.L, 1978: Analytical Modelling of
Helical Screw Turbines for Performance Prediction,
J.Engr.for Power 100(3)482
[30] Menssen E, 1977: US Patent 4,028,026
[31] Meyers K, 1997: Creating the Right Environment
for Compressor Bearings, Evolution, SKF Ind.Journal,
Vol 4, 21
[32] O'Neill P.A, 1993: Industrial Compressors,
Theory and Equipment, Butterworth-Heinemann,
Oxford
[33] Nilson, 1952: US Patent 2,622,787
[34]Peng N, Xing Z, 1990: New Rotor Profile and its
Performance Prediction of Screw Compressor,
International Compressor Engineering Conference At
Purdue, 18
[35] Rinder L, 1979: Schraubenverdichter (Screw
Compressors), Springer Verlag, New York
[36] Rinder L, 1984: Schraubenverdichterl?ufer mit
Evolventenflanken (Screw Compressor Rotor with
Involute Lobes), Proc. VDI Tagung
"Schraubenmaschinen 84" VDI Berichte Nr. 521
- 77 -

Ma{instvo 2(3), 63 - 78, (1999)
N.Sto{i},...: SAVREMENI RAZVOJ KONSTRUKCIJE...
[37] Rinder L, 1987: US Patent 4,643,654
[38] Sauls J, 1994: The Influence of Leakage on the
Performance of Refrigerant Screw Compressors,
Proc. VDI Tagung "Schraubenmaschinen 94",
Dortmund VDI Berichte 1135
[39] Sauls J, 1998: An Analytical Study of the Effects
of Manufacturing on Screw Rotor Profiles and Rotor
Pair Clearances, Proc. VDI Tagung
"Schraubenmaschinen 98", Dortmund VDI Berichte
1391
[40] Sakun I.A, 1960: Vintovie kompresorii (Screw
Compressors), Mashinostroenie Leningrad
[41] Shibbie, 1979: US Patent 4,140,445
[42] Singh P.J, Onuschak A.D, 1984: A
Comprehensive Computerized Method For Twin
Screw Rotor Profile Generation and Analysis, Purdue
Compressor Technology Conference 544
[43] Singh P.J, Schwartz J.R, 1990: Exact Analytical
Representation of Screw Compressor Rotor
Geometry, International Compressor Engineering
Conference At Purdue, 925
[44] Smith I. K, Sto{i} N, Aldis C. A, 1996:
Development of the trilateral flash cycle system, Part
3: The design of high efficiency two-phase screw
expanders, Proc IMechE, Journal of Power and
Energy, Vol 210, p 75
[45] Sto{i} N, Hanjali} K, 1977: Contribution towards
Modelling of Two-Stage Reciprocating Compressors,
Int.J.Mech.Sci. 19, 439
[46] Sto{i} N, Hanjali} K, Koprivica J, Lovren N,
Ivanovi} M, 1986: CAD of Screw Compressor
Elements, Strojarstvo Journal Zagreb 28, 181
[47] Sto{i} N, Kova~evi} A, Hanjali} K, Milutinovi}
Lj, 1988: Mathematical Modelling of the Oil
Influence upon the Working Cycle of Screw
Compressors, International Compressor Engineering
Conference at Purdue, 355
[48] Sto{i} N, Milutinovi} Lj., Hanjali} K, Kova~evi}
A, 1992: Investigation of the Influence of Oil
Injection upon the Screw Compressor Working
Process, Int.J.Refrig. 15,4,206
[49] Sto{i} N, Hanjali} K, 1994: Development and
optimization of screw engine rotor pairs on the basis
of computer modeling, Proc. XVII Conference on
Compressor Engineering at Purdue, 55
[50] Sto{i} N, 1996: Patent Application GB
9610289.2
[51] Sto{i} N, Hanjali} K, 1997: Development and
Optimization of Screw Machines with a Simulation
Model, Part I: Profile Generation, ASME Transactions,
Journal of Fluids Engineering, Vol 119, p 659
[52] Sto{i} N, Smith I K, Kova~evi} A, Aldis C A,
1997: The Design of a Twin-screw Compressor
Based on a New Profile, Journal of Engineering
Design, Vol 8, 389
[53] Sto{i} N, Kova~evi} A. and Smith I.K, 1998:
Modelling of Screw Compressor Capacity Control,
Proc. XIV Conference on Compressor Engineering at
Purdue, 607
[54] Sto{i} N, Smith I.K, Brasz J.J, Sishtla V, 1998:
The Performance of a Screw Compressor with
Involute Contact Rotors in a Low Viscosity Gas-
Liquid Mixture Environment, Proc. VDI Tagung
"Schraubenmaschinen 98", Dortmund VDI Berichte
1391
[55] Sto{i} N, 1998: On Gearing of Helical Screw
Compressor Rotors, Proc IMechE, Journal of
Mechanical Engineering Science, Vol 212, 587
[56] Tang Y, Fleming J.S, 1992: Obtaining the
Optimum Geometrical Parameters of a Refrigeration
Helical Screw Compressor, International Compressor
Engineering Conference at Purdue 213
[57] Tang Y, Fleming J.S, 1994: Clearances between
the Rotors of Helical Screw Compressors: Their
determination, Optimization and Thermodynamic
Consequences, Proc IMechE, J. of Process
Mechanical Engineering, Vol 208, 155
[58] Xion Z. Dagang X, 1986: Study on Actual Profile
Surface and Engaging Clearance of Screw
Compressor Rotors, Purdue Compressor Technology
Conference 239
[59] Zenan X, 1984: The Dynamic Measurement and
Mating Design of a Screw Compressor Rotor Pair,
Purdue Compressor Technology Conference 314
[60] Zhang L, Hamilton J.F, 1992: Main Geometric
Characteristics of the Twin Screw Compressor,
International Compressor Engineering Conference at
Purdue 2136
- 78 -