Task: Translation
Input (Czech): Popisuje se zp sob p° pravy rigidn  polyurethanov  p ny maj c  odrazovou pru nost pod 40 % p°i hustot  ve st°edu voln  vyp n n  p ny 3 a  27 kg/m.sup.3.n., p°i em  tato odrazov  pru nost je m °ena podle ISO 8307 s t m,  e vzorek se p°edb  n  nekondicionuje,  e pro ka d² vzorek je m °ena pouze jedna hodnota odrazov  pru nosti a  e testovan  vzorky jsou kondicionov ny p°i 23 .+-. 2 .degree.C p°i relativn  vlhkosti 50 .+-. 5 %, p°i kter m se spolu nechaj  reagovat polyizokyan t (1), slou enina (2) reaktivn  v  i izokyan t m o pr m rn  ekvivalentov  hmotnosti nejv² e 374 a o pr m rn m po tu 2 a  8 vod kov²ch atom  reaguj c ch s izokyan ty, slou enina (3) reaktivn  v  i izokyan t m o pr m rn  ekvivalentov  hmotnosti vy    ne  374 a o pr m rn m po tu 2 a  6 vod kov²ch atom  reaguj c ch s izokyan ty, a voda, p°i em  obsah slou eniny (2) je 2 a  20 hmotnostn ch d l , obsah slou eniny (3) je 5 a  35 hmotnostn ch d l  a obsah vody je 1 a  17 hmotnostn ch d l , vzta eno na 100 hmotnostn ch d l  polyizokyan tu (1), slou eniny (2), slou eniny (3) a vody, za podm nky,  e slou eninou (3) nen  polyoxyalkylenpolyol o funkcionalit  2 a  3,5, hydroxylov m   sle 28 a  90 mg KOH/g a o obsahu polyoxyethylenov²ch jednotek ne vy   m ne  5 % hmotnostn ch; zp sob p° pravy flexibiln  polyurethanov  p ny stla en m t to rigidn  p ny, a flexibiln  polyurethanov  p na takto z skan .\
Output (English): In the present invention there is described a process for preparing a rigid polyurethane foam exhibiting impact resilience below 40 percent at density in the center of a free foamed foam within the range of 3 to 27 kg per cubic meter, wherein said impact resilience is measured according to ISO 8307 with the proviso that a sample is not subjected to preliminary conditioning and that in  each sample only one values of the impact resilience is measured and that the tested samples are conditioned at 23 +/- 2 degC at relative humidity of 50 +/- 5 percent. The process is characterized by reacting a polyisocyanate (1), an isocyanate-reactive compound (2), having an average equivalent weight of at the most 374 and an average number of isocyanate-reactive hydrogen atoms of from 2 to 8, an isocyanate-reactive compound (3), having an average equivalent weight of more than 374 and an average number of isocyanate-reactive hydrogen atoms of from 2 to 6 and water, wherein the amount of the compound (2) ranges within 2 to 20 parts by weight, the amount of the compound (3) is within the range of 5 to 35 parts by weight and water amount is within 1 to 17 parts by weight, based on 100 parts by weight of polyisocyanate (1), compound (2), compound (3) and water, under condition that the compound (3) differs from polyoxyalkylene polyol exhibiting functionality within the range of 2 to 2.5, hydroxyl number ranging from 28 to 90 mg KOH per gram and content of polyoxyethylene units not exceeding 5 percent by weight. Disclosed is also a process for preparing a flexible polyurethane foam by compacting the above described rigid foam, and the flexible polyurethane foam obtained in such a manner.