HNBR roll covers for severe conditions.Rolls with a cover based on rubber are used in many industrial applications. The most important uses are in the following areas: printing industry; textile textile Any filament, fibre, or yarn that can be made into fabric or cloth, and the resulting material itself. The word originally referred only to woven fabrics but now includes knitted, bonded, felted, and tufted fabrics as well. industry; machines, e.g., copy and fax machines; steel industry; and paper industry The requirements for these very different applications vary over a broad range. In general, the subdivision shown in table 1 can be made based on the load (refs. 1 and 2). The construction of the roll must be designed in conformance con·for·mance n. Conformity. Noun 1. conformance - correspondence in form or appearance conformity agreement, correspondence - compatibility of observations; "there was no agreement between theory and to the requirements shown in table 2 (ref. 1)
Table 1
Load Hardness of rubber Thickness of
rubber
Low [is greater than or equal to] 40 Shore A 6 - 10 mm
[is less than or equal to] 200 P & J
Medium [is greater than or equal to] 70 Shore A 12 - 25 mm
[is less than or equal to] 75 P & J (may be more)
High [is greater than or equal to] 90 Shore A 12 - 25 mm
[is less than or equal to] 25 P & J
Table 2 - design requirements for roll covers
Load Maximum load Diameter Application
Low 10 N/mm [is greater than or Transportation and
equal to] 100 mm stator rolls
Medium 20 N/mm [is less than or Directing rolls
equal to] 400 mm
High 50 N/mm [is greater than or High pressure and
equal to] 200 mm high speed rolls
The required properties of the roll cover correlate with specific properties Specific properties of a substance are derived from other intrinsic and extrinsic properties (or intensive and extensive properties) of that substance. For example, the density of steel (a specific and intrinsic property) can be derived from measurements of the mass of a steel bar of rubber compounds. Examples are given in table 3.
Table 3 - roll covers - required general properties
Requirement of roll cover Property of vulcanizate
High restoring forces Low compression set
High wear resistance Low abrasion loss
Minimal change in dimen- Low swelling in ambient
sions media
Low hardening Good heat and chemical
resistance
Minimal change in linear Little dependence of physi-
pressure cal properties on tempera-
ture
Good dynamic behavior, Low heat build-up, low loss
minimal energy uptake factor tan [Delta], little
and dimensional stability flow, high fatigue resistance
under pressure
Good adhesion to metal or Excellent rubber metal
plastic at service tempera- adhesion (bonding system
ture must be selected accord-
ing to service temperature)
The choice of the rubber depends very much on the requirements of the roll, such as the service conditions, e.g., ambient temperature Outside temperature at any given altitude, preferably expressed in degrees centigrade. and required chemical resistance. Rolls for the paper industry Due to continuously increasing productivity, the peripheral speed of rolls in the paper industry has risen to 2,000 m/min and more. This service condition requires rolls with covers of high hardness and excellent pressure resistance. There are, however, further requirements of the roll cover. These requirements are summarized in table 4.
Table 4 - roll covers - paper industry requirements
Requirement Property of vulcanizate
Broad range of hardness 30 Shore A to 60 Shore D
(in general) (<3 P&J)
High wear (abrasion) < 50 [mm.sup.3] (DIN 53516)
resistance
Low compression set at < 20% (70 h./150 [degrees] C)
high temperatures
Good dynamic properties Tan [Delta] <0.1; Permanent set
<1% (Goodrich Flexo-
meter; 140 [degrees] C);
Very good aging resis- [Delta] EB <-20 [degrees] C
tance (7d/150 [degrees] C); [Delta] H
< +5 Shore A (7d/150 [degrees] C)
Good water and chemical Little change in physical
resistance properties; low volume swell
Good ozone resistance No cracks (200 pphm;
40 [degrees] C; 60% elongation)
Good mech. properties TS 15 > 30MPa
An excellent combination of all these requirements can be achieved by using hydrogenated acrylonitrile acrylonitrile /ac·ry·lo·ni·trile/ (ak?ri-lo-ni´tril) a colorless halogenated hydrocarbon used in the making of plastics and as a pesticide; its vapors are irritant to the respiratory tract and eyes, may cause systemic poisoning, and are butadiene butadiene (by  t'ədī`ēn), colorless, gaseous hydrocarbon. There are two structural isomers of butadiene; they differ in the location of the two carbon-carbon double bonds in the rubber (HNBR HNBR Hydrogenated Acrylonitrile-Butadiene Rubber ). In
particular, this means that the compound and the vulcanizate have to
show some specific characteristics:* Compound properties: - Mooney Mooney is family name, which is probably predominantly derived from the Irish Ó Maonaigh. It can also be spelled Moony, Meaney, Mauney, Moon, Money. The word can refer to: Companies
Meaney spelling - high tack for good construction of the roll cover; - long scorch time for sufficient flow time (scorch safety) and good adhesion adhesion /ad·he·sion/ (ad-he´zhun) 1. the property of remaining in close proximity. 2. the stable joining of parts to one another, which may occur abnormally. 3. of the parts; - light colored fillers without discoloring or staining staining /stain·ing/ (stan´ing) 1. artificial coloration of a substance to facilitate examination of tissues, microorganisms, or other cells under the microscope. For various techniques, see under stain. 2. components, e.g., antidegradants. * Vulcanizate properties: - high hardness (up to 60 Shore D; [is less than] 3 P&J); - sufficient elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. at break; - resistance to wear, high temperatures, water and process chemicals; - very good dynamical properties; - low compression compression, external stress applied to an object or substance, tending to cause a decrease in volume (see pressure). Gases can be compressed easily, solids and liquids to a very small degree if at all. set. These requirements can only be fullfilled by usage of the following components of a compound: * rubber: HNBR; * filler fill·er 1 n. One that fills, as: a. Something added to augment weight or size or fill space. b. A composition, especially a semisolid that hardens on drying, used to fill pores, cracks, or holes in wood, plaster, : silica silica or silicon dioxide, chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. (balanced ratio of compound viscosity and vulcanizate properties); * liquid (meth meth n. Methamphetamine hydrochloride. )acrylates: high hardness combined with low compound viscosity; * zinc zinc, metallic chemical element; symbol Zn; at. no. 30; at. wt. 65.38; m.p. 419.58°C;; b.p. 907°C;; sp. gr. 7.133 at 25°C;; valence +2. Zinc is a lustrous bluish-white metal. It is found in Group 12 of the periodic table. diacrylate batches: higher elongation at break, better flow properties, higher scorch safety and better abrasion abrasion /abra·sion/ (ah-bra´zhun) 1. a rubbing or scraping off through unusual or abnormal action; see also planing. 2. a rubbed or scraped area on skin or mucous membrane. resistance compared to liquid (meth)acrylates; * peroxide peroxide (pərŏk`sīd), chemical compound containing two oxygen atoms, each of which is bonded to the other and to a radical or some element other than oxygen; e.g. : determines crosslinking behavior and crosslinking network; * retarder retarder, n a chemical added to a substance to slow a chemical reaction, prolong the set of the material, and provide more working time. : extended scorch time provided that the crosslinking activity of the peroxide is not affected. The influence of the different ingredients will be discussed with some examples. Experimental To achieve the required hardness of the vulcanizate for roll covers, different additives can be used: Polybutadiene Polybutadiene is a synthetic rubber that has a high resistance to wear and is used especially in the manufacture of tires. It has also been used to coat or encapsulate electronic assemblies, offering extremely high electrical resistivity. with a high vinyl vinyl /vi·nyl/ (vi´nil) the univalent group CH2dbondCH—. vinyl chloride a vinyl group to which an atom of chlorine is attached; the monomer which polymerizes to polyvinyl chloride; it is toxic content (here: 1,2-vinyl polybutadiene); liquid methacrylate methacrylate /meth·ac·ry·late/ (meth-ak´ri-lat) an ester of methacrylic acid, or the resin derived from polymerization of the ester. See also acrylic resins, under resin. ; zinc diacrylate batches. These opportunities which are given by these additives will be discussed. 1,2-vinyl polybutadiene Compounds with a hardness beyond 90 Shore A are usually difficult to process if the hardness is only reached by increasing the amount of fillers. Therefore, components have to be used which lower the Mooney viscosity of the compound and simultaneously si·mul·ta·ne·ous adj. 1. Happening, existing, or done at the same time. See Synonyms at contemporary. 2. Mathematics increase the hardness of the vulcanizate. Reinforcing re·in·force also re-en·force or re·en·force tr.v. re·in·forced, re·in·forc·ing, re·in·forc·es 1. To give more force or effectiveness to; strengthen: The news reinforced her hopes. resins resins, n.pl complex, insoluble, sticky substances secreted by plants. Used as astringents, antimicrobials, and antiinflammatories, and are burned as incense. Can cause oral ulcers and epidermal irritations. cannot be used because they display thermoplastic A polymer material that turns to liquid when heated and becomes solid when cooled. There are more than 40 types of thermoplastics, including acrylic, polypropylene, polycarbonate and polyethylene. behavior. This leads to a negative influence on the compression set. Furthermore, the aging resistance is reduced. 1,2-vinyl polybutadiene is a liquid product used as a non-extractable plasticizer plas·ti·ciz·er n. Any of various substances added to plastics or other materials to make or keep them soft or pliable. plasticizer or -ciser Noun for the compounds to improve processability. As well as this effect, it is known to raise the crosslink density and the hardness of the vulcanizate. For improved handling, a dry liquid of this material can be used. Table 5 shows the general formulation formulation /for·mu·la·tion/ (for?mu-la´shun) the act or product of formulating. American Law Institute Formulation and the different combinations of the ingredients which have been varied in order to cover a broader range of hardness.
Table 5 - base HNBR formulation and combinations
Ingredients Phr
HNBR 1: 34% ACN 100.0
Plasticizer FH 5.0
Pigment 1 4.0
Silica 1 Variable
Vinyl silane Variable (relative
to silica)
Calcined clay Variable (relative
to silica)
1,2-vinyl polybutadiene Variable
Antidegradant 1 1.0
Antidegradant 2 0.4
Magnesium oxide 7.0
Active zinc oxide 4.0
Stearic acid 0.5
TAIC 1.8
Peroxide 1 9.0
Combinations
Silica 1 60 60 80 120 150
Vinyl silane 1.5 1.5 1.7 2.0 2.5
Calcined clay 40 40 60 90 120
1,2-vinyl polybutadiene 0 10 15 30 50
The compound viscosity ML 1+4/100 [degrees] C is shown in figure 1. As expected, the addition of 1,2-vinyl polybutadiene leads to a significant decrease of nearly 40 MU in the compound viscosity. On the other hand, this behavior opens up the opportunity to increase the filler content to a certain amount.
Figure 1 - influence of 1,2-vinyl polybutadiene
and filler content on the compound viscosity ML
1+4/100 [degrees] C
1 2 3 4 5
Silica 60 60 80 120 150
Vinyl silane 1.5 1.5 1.7 2.0 2.5
Calcined clay 40 40 60 90 120
1,2-vinyl polybutadiene 0 10 15 30 50
[GRAPH OMITTED]
In later developments, which are not described here, it could be shown that the dosage dosage /dos·age/ (do´saj) the determination and regulation of the size, frequency, and number of doses. dos·age n. 1. Administration of a therapeutic agent in prescribed amounts. of magnesium magnesium (măgnē`zēəm, –zhəm), metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.305; m.p. about 648.8°C;; b.p. about 1,090°C;; sp. gr. 1.738 at 20°C;; valence +2. and zinc oxide zinc oxide, chemical compound, ZnO, that is nearly insoluble in water but soluble in acids or alkalies. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. can be chosen at a lower level. How far the level can be reduced has to be decided from case to case depending on the application. Hardness is the other very important property of these compounds. The results of tests according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. Shore A and Shore D in relation to temperature are shown in figure 2. [GRAPHS This partial list of graphs contains definitions of graphs and graph families which are known by particular names, but do not have a Wikipedia article of their own. For collected definitions of graph theory terms that do not refer to individual graph types, such as OMITTED] It is obvious that the addition of 1,2-vinyl polybutadiene to the compound already yields an increase in the hardness of six points. If the amount of filler is increased, the hardness can be increased to 99 Shore A. The hardness, as measured by the Shore A method, shows little or no dependence on temperature. Using the Shore D test equipment, the temperature becomes more significant. This difference can be explained by the significantly smaller surface area of the test piston in the Shore D test. Further significant physical properties of the vulcanizate are summarized in table 6. Table 6 - influence of 1,2-vinyl polybutadiene and filler content on the physical properties Ingredients/properties Levels of material varied in formulation Silica 1 60 60 80 120 150 Vinyl silane 1.5 1.5 1.7 2.0 2.5 Calcined clay 40 40 60 90 120 Vinyl polybutadiene 0 10 15 30 50 Tensile strength (MPa) 24.0 22.3 22.3 19.8 19.2 Elongation at break (%) 185 150 100 50 40 Elasticity (%) 27 27 26 30 30 Abrasion loss ([mm.sup.3]) 55 77 125 216 246 The tensile strength tensile strength Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its of the compounds decreases a little with increasing amounts of 1,2-vinyl polybutadiene and filler, but the influence on the elongation at break is significantly stronger. The same is tree for the abrasion loss which becomes significantly higher with increasing hardness. Acrylates in HNBR Trimethylolpropane trimethacrylate (TRIM TRIM Tripartite Motif (protein) TRIM Truth in Millage (Florida) TRIM Total Risk Integrated Methodology TRIM Terrain Resource Information Management (Canada) ) - methacrylates can be used to significantly increase the hardness of roll covers and simultaneously decrease the compound viscosity. Triallyl isocyanurate (TAIC TAIC Transport Accident Investigation Commission TAIC Tokyo Atomic Industrial Consortium TAIC Tri Allyl Isocyanurate TAIC Tianjin Automotive Industry Corporation ) is usually used as an activator activator /ac·ti·va·tor/ (ak´ti-va?ter) 1. a substance that combines with an enzyme to increase its catalytic activity. 2. a substance that stimulates the development of a specific structure in the embryo. for the peroxidic crosslinking agent. The base formulation of the compounds is shown in table 7. Table 7 - base formulation of acrylate compounds Ingredients Phr HNBR 1: 34% 100.0 Stearic acid 0.5 Active zinc oxide 2.0 Magnesium oxide 2.0 Antidegradant 1 1.0 Antidegradant 2 0.4 Carbon black N 550 50.0 TOTM 5.0 TAIC varying TRIM varying Peroxide 1 7.5 TAIC is usually used in a dosage of 1.5 phr. This has been replaced by 5, 10 or 20 phr TRIM. The influence on the different properties of the compound is shown in figures 3 and 4. [GRAPHS OMITTED] From the graphs it can be clearly seen that the presence of TRIM has very different influences on several properties of the compound: * The Mooney viscosity of the compound is reduced significantly, which gives advantages in processing this compound; * the hardness is increased significantly; and * the tensile strength is not influenced very much and there is no trend to be seen. Zinc diacrylate (ZNDA) is often used to give vulcanizates very special properties, e.g., high hardness, but in most cases it is used in combination with TRIM. The experiments were performed again on a silica-filled compound with part of the TRIM replaced by ZNDA (table 8). Table 8 - silica filled formulation Ingredients Phr HNBR 1: 34% CAN 100.0 Active zinc oxide 2.0 Magnesium oxide 2.0 Silica 1 variable Vinyl silane 2.0 Antidegradant 1 1.0 Antidegradant 2 0.4 Pigment 2 5.0 TRIM variable Pigment 3 1.0 ZNDA variable Peroxide 1 7.5 or 0 Peroxide 2 0 or 7.5 Ingredients Combinations Silica 1 70 50 50 TRIM 30 20 20 ZNDA -- 20 20 Peroxide 1 7.5 7.5 -- Peroxide 2 -- -- 7.5 The compound viscosity ML 1+4/100 [degrees] C of these formulations is almost the same. The advantage of the ZNDA containing compounds is the significantly higher Mooney scorch MS - t5 at 120 [degrees] C and 140 [degrees] C. These results are shown in figure 5. [GRAPH graph, figure that shows relationships between quantities. The graph of a function y=f (x) is the set of points with coordinates [x, f (x)] in the xy-plane, when x and y are numbers. OMITTED] The introduction of ZNDA to the compound has some significant influences on the physical properties. Although the hardness remains the same (91 to 92 Shore A), the tensile strength and the elongation at break are improved (figure 6). [GRAPH OMITTED] These experimental results have shown that it is possible to produce vulcanizates with a very high hardness. Besides these positive effects, some other aspects also have to be mentioned. The use of zinc diacrylates may lead to a compression set which is not as good as described for other compounds and may also reduce the resistance against water and bases. HNBR masterbatch The disadvantage In policy debate, a disadvantage (abbreviated as DA, and sometimes referred to as a Disad) is an argument that a team brings up against a policy action that is being considered. Structure A DA usually has four key elements. of most of the ways described above for producing vulcanizates with a very high hardness is the very high Mooney viscosity of the raw compound. This means that these compounds are barely processable. On the other hand, it could be shown that acrylates and zinc diacrylates do yield very hard vulcanizates with very good physical properties. Therefore, the target of this development was to find a solution which offers good processability of the compound combined with high hardness of the vulcanizate. The formulation (table 9) which has been developed is based on experiences drawn from the above described experiments. Table 9 - HNBR masterbatch compound Ingredients Phr HNBR 2; 34% ACN 100.0 ZNDA 60.0 TRIM 2 (70% active 57.0 substance) Antidegradant 3 2.0 Antidegradant 4 1.0 Peroxide 3 3.0 This masterbatch has been compared to different other concepts which were developed for these applications: * HNBR 3 - HNBR with 34% ACN ACN Accenture (stock symbol) ACN Accenture ACN Australian Company Number ACN Automatic Collision Notification (US DOT) ACN Acetonitrile ACN Anglican Communion Network , partially hydrogenated; zinc diacrylate batch; * HNBR 4 - HNBR with 34% ACN, partially hydrogenated; zinc diacrylate batch; * HNBR 5 - HNBR with 36% ACN, partially hydrogenated; zinc dimethacrylate batch. The most important results are shown in figures 7-9. These are the Mooney scorch, the compound viscosity and the hardness. The data of the newly developed compound were compared to those of systems with similar targets. [GRAPHS OMITTED] Some important physical properties of this newly developed masterbatch are summarized in table 10. Table 10 - physical properties of HNBR/acrylate masterbatch Property Unit Measure Tensile strength MPa 21.2 Elongation at break % 110 Hardness at 23 [degrees] C Shore A 97 Hardness at 23 [degrees] C Shore D 52 Abrasion loss [mm.sup.3] 99 Compression set 70h./100 [degrees] C % 78 Compression set 70h./150 [degrees] C % 96 These data show that this formulation leads to a compound with excellent processability and a vulcanizate with outstanding physical properties. But besides all the advantages which can be achieved, the compression set shows a negative trend. Based on these results, it is possible to use the described masterbatch as blend component. This opens the opportunity to combine the positive effects of the described masterbatch, e.g., high tensile strength and high hardness, with the physical properties of a regular compound without sacrificing other properties as the compression set. Summary Rolls are used in many applications in different industrial sectors. The most severe service conditions have to be met by rolls in the paper industry where high production rates require roll covers of high hardness with low abrasion. Several potential solutions have been discussed: * Increasing the filler content usually leads to a significant increase in hardness, but the compound viscosity increases in a similar way so that the processability is limited. * The addition of 1,2-vinyl polybutadiene reduces the Mooney viscosity of the compound significantly. Simultaneously, the hardness becomes higher. This opens up the opportunity to use higher filler contents which leads to a further increase in hardness. However, this effect is limited due to the processability of the compound. * Trimethylolpropane trimethacrylate (TRIM) gives significant advantages in compound viscosity combined with an increase in hardness. * Zinc diacrylates as partial substitute for TRIM does not show a significant influence on the compound viscosity or the hardness of the vulcanizate, but the Mooney scorch MS-t5 at 120 [degrees] C and 140 [degrees] C is prolonged pro·long tr.v. pro·longed, pro·long·ing, pro·longs 1. To lengthen in duration; protract. 2. To lengthen in extent. in the presence of ZNDA. This can be improved further by using a different peroxide. Other advantages are the higher tensile strength and higher elongation at break. * Based on the above discussed results, an HNBR masterbatch has been developed which gives compounds with excellent processability (low compound viscosity, long scorch time) and vulcanizates with a higher hardness and very good physical properties. The results discussed in this report show a new route to produce roll covers for severe service conditions. References (1.) F. Zeppernick, Gummi Fasern Kunststoffe 45 (1992), 6, 305-308. (2.) F. Zeppernick, Gummi Fasern Kunststoffe 46 (1993), 8, 422-427. |
|
||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion