提高雙螺桿擠出機(jī)共混性能的十大絕招

1、提高雙螺桿擠出機(jī)共混性能的十大絕招上海北京順德(翻譯和整理)文章來(lái)自于塑料產(chǎn)業(yè)論壇（）英文原載plastics technology（上海北京順德email：jiazhiliao；手第一部分：翻譯There are many techniques known to operators and plant engineers for increasing the performance of a twin-screw compounding extruder. Because of their informal nature, however, most of thes

2、e methods do not appear in any equipment manuals. Nor are they generally mentioned in textbooks and technical papers. But sometimes attention to several small details can add up to make a big difference in extruder performance. The tips described in this paper fall into three broad categories: proce

3、ssing techniques,machine modifications, and maintenance procedures。 有很多提高雙螺桿共混擠出機(jī)性能的方法，為操作人員和工廠工程師所熟知。但是，由于這些信息的性質(zhì)，其中的許多方法沒(méi)有出現(xiàn)在設(shè)備手冊(cè)里。這些方法一般也不在教科書(shū)和科技論文中被提到。但是，關(guān)注一些小的細(xì)節(jié)會(huì)對(duì)增加擠出機(jī)性能大有裨益。本文描述的技巧分成三個(gè)大的類(lèi)別：加工工藝、設(shè)備改造和維護(hù)程序。1. THERMAL INSULATOR GASKETSThe feed barrel section is almost always water cooled. B

4、ut because this barrel is bolted flange to flange against barrel section #2, which is heated,heat is continuously transferred from the hotter to the cooler barrel section. As a result, barrel #2 is often not able to maintain a high enough temperature. In a typical case, the operator has a setpoint o

5、f 180 C for barrel #2 but can never get above 135 C because of heat loss to the feed barrel. The easiest solution is to install an insulator gasket between the flanges of the feed barrel and barrel #2. These gaskets are typically 1 mm thick, and we recommend stacking two together for better insulati

6、ng performance. There will still be some heat conduction through the bolts and the screw shafts, but not nearly as much as without the insulation. New extruders are often supplied with the insulator in place, but many operators don't realize its importance and throw it away when disassembling th

7、e barrels. After several years the insulator gasket should be replaced, as the material tends to degrade and crumble. 1。熱絕緣墊片機(jī)筒的喂料段幾乎總是水冷的。但是，由于這段筒體是用法蘭對(duì)法蘭緊挨第二段筒體(加熱的）鎖定的，熱量可以連續(xù)從溫度高的筒體傳導(dǎo)到冷的筒體。結(jié)果#2筒體不能維持足夠的溫度。通常，操作人員在2#筒體設(shè)定180的溫度，但是由于喂料段的熱量損失，2#段從來(lái)沒(méi)有達(dá)到超過(guò)135的溫度。最簡(jiǎn)單的方案就是喂料段與2#段筒體法蘭之間加一個(gè)隔熱墊片。這個(gè)墊片一般

8、是1mm厚。我們建議疊加兩個(gè)墊片，可以具有更好的絕熱效果。還有一些熱傳導(dǎo)通過(guò)螺栓和螺桿軸心損失掉，但是有沒(méi)有隔熱沒(méi)有打的影響。新的擠出機(jī)常常提供恰當(dāng)?shù)慕^熱措施。但是許多操作人員沒(méi)有意識(shí)到隔熱的重要性而在拆卸機(jī)筒時(shí)把它們?nèi)拥袅?。過(guò)了幾年后，隔熱墊片應(yīng)該更換，因?yàn)檫@些材料有老化降解和皺縮的傾向。2. SIDE STUFFING OF POWDERSSide stuffing is widely used for feeding fillers into twin-screw extruders. Many processors desire very high loadings of filler

9、s that are often low-bulk-density (fluffy) materials. The ultimateloading attainable is usually limited by two parameters:A) Volumetric capacities of the side-stuffer and main extruder screws. The volumetric capacity is based on the free volume of the side-stuffer's twin screws and of the main e

10、xtruder screws, as well as the rpm of both screw sets. If material is test run through the side stuffer unbolted from the extruder and discharging into a drum, it probably will easily feed a high rate of material. But when the stuffer is attached to the extruder, capacity is often limited by the amo

11、unt of material the main extruder screws can accept. Consequently, it is best to for the main extruder screws to have flighted elements with a long pitch (long flight advance) at the stuffer location, extending 2D to 4D downstream of the stuffer. This is to keep the melt in the extruder moving rapid

12、ly forward to allow the maximum free volume for the filler to enter. If the screw design causes any "dam-up" of material downstream of thestuffer, it will severely limit the amount of filler that can be fed.B) Venting capacity to allow air to escape the extruder. The object of venting is t

13、o allow air to escape easily, while preventing large amounts of filler from being lost out the vent. The best configuration is a top vent in the barrel immediately upstream of the side stuffer. Sometimes a small half-slot vent insert can also be used in the top of the side stuffer.Here are some othe

14、r factors to consider:feeder drop height: Ideally, the feeder should be positioned as close as possible above the side stuffer to minimize the drop height. If a fluffy material is allowed to drop through air, it becomes aerated to the point where its bulk density is significantly reduced. This can l

15、imit the throughput rate of the entire line.feeder agitation type: Make sure the agitator in the filler feeder isn't aerating the material and reducing the bulk density. Many feeder manufacturers have special agitator designs for powders.make sure stuffer hopper is vented: Along with the filler,

16、 thestuffer also introduces a lot of air into the extruder. An open top on the side-stuffer chute will take care of venting. If you have a solid cover on the chute with a round stubup and flex connector to tbe feeder, it's important to also have a vent opening.around all hoppers/chutes to drain

17、static electricity: Some materials generate static electricity from friction. Static charge can cause powder to cling to the inside surfaces of hoppers and chutes, leading to problems such as caking. An easy fix is to run a ground wire (10 gauge is recommended) from the chute to a known good ground

18、on the machine pressed-air blaster: If caking persists, sometimes a special solution is needed. Hopper vibrators can be used, but are tricky to size and mount. An alternative is a "blaster" witb air-jet nozzles strategically placed within the wall of the chute to break up any cake

19、s before they get too large. The air jets are connected to a solenoid valve, which is actuated by a repeat cycle timer. This lets you set both the blast period and dwell time between blasts. It's best to have a small air accumulator tank just upstream of the solenoid valve to provide a sharp pul

20、se of air.2。粉體側(cè)喂料側(cè)喂料通常用于把填料喂進(jìn)雙螺桿擠出機(jī)。許多加工者需要做很高填充量的填料，這些填料往往又具有很低的堆積密度。最終的填充量受兩個(gè)因素制約：A)側(cè)喂料的體積喂料能力和擠出機(jī)主螺桿的體積吃料能力。體積喂料能力取決于側(cè)喂料機(jī)和主螺桿螺桿的自由體積，以及這兩個(gè)螺桿的轉(zhuǎn)速。如果一種材料在測(cè)試中可以不受到主螺桿的阻力而流到儲(chǔ)料鼓中，那么這種材料喂料速度可以達(dá)到很好。如果側(cè)喂料機(jī)直接挨著主螺桿連接，那么助劑螺桿可以接受的材料量將受到限制。因此，主機(jī)螺桿最好有長(zhǎng)螺距的螺紋元件，在側(cè)喂料口下游延伸2D-4D長(zhǎng)度。這將允許熔體快速通過(guò)側(cè)喂料口，使填料最大限度地被主螺桿吃進(jìn)。如果主機(jī)螺

21、桿設(shè)計(jì)引起任何側(cè)喂料喂進(jìn)材料的堆積，那么將嚴(yán)重限制填料的喂料量。B)允許氣體從擠出機(jī)排出的排氣能力。排氣的目的就是使空氣容易逸出，同時(shí)還要保護(hù)填料不從排氣口大量逸失。最好的配置是在側(cè)喂料口的上游開(kāi)置向上排氣的排氣口。有時(shí)，在側(cè)喂料機(jī)的上部開(kāi)一個(gè)小的半狹縫排氣。還有一些其它因素要考慮：-喂料機(jī)的落料高度。理想情況下，喂料螺桿要盡可能近地安裝于側(cè)喂料口頂部，以減小落料高度。如果某種蓬松的材料從空氣中流過(guò)，那么它可能變得充滿(mǎn)空氣，從而使它在落下后假密度大大減小。-喂料機(jī)攪拌類(lèi)型。要確保填料喂料機(jī)中的攪拌器不使填料流態(tài)化。許多攪拌器制造商設(shè)計(jì)了特殊的攪拌器用于填料喂料。儲(chǔ)料器會(huì)連同填料一起引進(jìn)空氣進(jìn)入

22、擠出機(jī)。一個(gè)頂部敞開(kāi)的斜槽料斗有助于排氣。假如你的斜槽喂料料斗有一個(gè)實(shí)心蓋子并帶一個(gè)圓管，并且與喂料器是柔性連接，那么重要的要有一個(gè)排氣口。-料斗斜槽要接地防靜電。一些材料由于摩擦產(chǎn)生靜電。靜電引起粉體對(duì)料斗掛壁，從而導(dǎo)致粉體餅狀化。一個(gè)簡(jiǎn)易的方案就是接地。-壓縮空氣爆破器。如果料餅持續(xù)存在，常常需要一些特殊辦法?？梢允褂昧隙氛駝?dòng)器，但是它們占空間，還需要安裝。一個(gè)替代方案是安裝一個(gè)帶空氣噴嘴的爆破器，安裝在斜槽的恰當(dāng)位置上，在料餅長(zhǎng)大之前將其吹破。3. HIGH-PRESSURE WATER PUMPIt's well known that turbulent flow m a pi

23、pe will induce far greater heat transfer from the pipe wall than will laminar flow. Laminar flow occurs with low fluid velocities caused by lowpressure delivery. In a laminar-flow situation, a stable boundary layer develops, which acts just like an insulator between the main fluid flow and the pipe

24、wall. "Layers" of fluid slide over adjacent layers, without mixing and without removing much heat. With turbulent flow induced by high-pressure delivery, there is a high degree of transverse momentum exchange, which breaks up the boundary layer. As a result, the violent fluid motion causes

25、much greater heat transfer from the pipe wall to the fluid. The easiest way to induce turbulent flow in tbe barrel cooling bores is to increase tbe delivery pressure. Extruder cooling recirculation systems typically have supply pressures from 20 to 60 psi. To achieve turbulent flow, a pressure of ap

26、proximately 120 psi is desired. This can be attained relatively easily by changing the pump in the recirculation system to a high-pressure type. Almost all extruder cooling system components (hoses and valves) are rated for at least 150 psi, so 120 psi still allows some safety factor. The advantage

27、will be apparent immediately in a process that is highly exothermic. Temperature zone overrides can often be greatly reduced or even eliminated. A side benefit of turbulent flow is that it inhibits fouling of the cooling bores from scale buildup.3。高壓水泵大家知道，水泵中的紊流比層流可以導(dǎo)致更多的管壁熱交換。層流出現(xiàn)在低流速低壓輸送條件下。在層流情況

28、下，建立了一個(gè)穩(wěn)定的邊界層，就象在主料流和管壁之間建立了一個(gè)絕熱層。料流層沿著臨近的料流層滑過(guò)，沒(méi)有混合，沒(méi)有帶走更多的熱量。高壓傳輸中的紊流有高度的橫向動(dòng)量交換，它擊破了邊界層。結(jié)果劇烈的流體運(yùn)動(dòng)引起了管壁與流體之間大得多的熱交換。擠出機(jī)冷卻循環(huán)系統(tǒng)一般提供20-60psi的壓力。為了達(dá)到紊流，最好達(dá)到120PSI的壓力。把循環(huán)系統(tǒng)的水泵改成高壓泵就行了。擠出機(jī)幾乎所有的冷卻系統(tǒng)部件（軟管和閥）都要升級(jí)到150PSI,才能滿(mǎn)足120PSI的安全系數(shù)。優(yōu)點(diǎn)是在加工時(shí)馬上排出大量的熱。4. ACID-FLUSH COOLING BORESWater-cooled extruder barrels

29、 are heat exchangers, and like all other heat exchangers the coolant bores are subject to fouling from scale buildup. Most operators notice that the cooling performance of a new extruder is much better than an extruder after three or four years of running. This is because the new extruder barrel has

30、 smooth, shiny, fresh-drilled cooling bores. The older machine has a layer of crusty mineral deposits lining the bores, which act like an insulator. If left unchecked, scale buildup can lead to a much more serious problem. Eventually the cooling bores can become completely blocked so there is zero w

31、ater flow. If this happens, the only solution is to remove the barrels from the extruder and drill out all the cooling boresa time-consuming procedure.4.用酸沖洗冷卻水道水冷的擠出機(jī)機(jī)筒就是一個(gè)熱交換器，象所有的熱交換器一樣，水道易于結(jié)垢而變壞。許多操作人員注意到，一個(gè)新擠出機(jī)的冷卻性能要比使用三、四年的擠出機(jī)好很多。這是由于新擠出機(jī)機(jī)筒具有光滑的新鉆的冷卻水道。老機(jī)器有一層垢附著在水道內(nèi)表面，象一個(gè)隔熱層。如果年久失修，垢層會(huì)導(dǎo)致嚴(yán)重的問(wèn)題。

32、最終冷卻水道被完全堵死而滴水不流。到了這個(gè)時(shí)候，唯一的辦法就是從擠出機(jī)上摘掉機(jī)筒，拿出所有的冷卻水道-很費(fèi)時(shí)間的一個(gè)手續(xù)。5. SWITCH TO SYNTHETIC GEAR OILThe gearbox is the heart of a twin-screw extruder. If it fails, it's likely to be expensive to repair, and it may take quite awhile. There is one thing everyone can do, easily, to avoid gearboxproblems: s

33、witch to synthetic gear oil. Synthetic oil is a huge advance in lubrication technology:It's more "slippery," resulting in less frictionGears, bearings, and seals last longer.The gearbox runs cooler and quieter.Synthetic oil doesn't lose viscosity from mechanical shear.It maintains

34、higher viscosity at high temperatures.It improves the overall efficiency of the gearbox.5。切換到合成齒輪油齒輪箱式雙螺桿擠出機(jī)的心臟。如果它完蛋了，那要花很多錢(qián)維修，而且頗為費(fèi)時(shí)。這時(shí)，我們能做的一個(gè)事情就是避免齒輪箱問(wèn)題：切換到合成齒輪油。合成油在潤(rùn)滑上是一個(gè)巨大進(jìn)步：-更加滑膩，導(dǎo)致較小的摩擦；-齒輪、軸承和密封將更持久；-齒輪運(yùn)轉(zhuǎn)溫度更低，更安靜；-合成油不因?yàn)闄C(jī)器剪切而損失粘度；-它在高溫下維持較高的粘度；-改進(jìn)綜合齒輪效率6. USE ANTI-SEIZE LUBRICANTSMost peop

35、le in plastics are aware of the need for anti-seize lubricants. There are several different types: copper-based, molybdenum, lithium,  etc. For something like a bolt thread, probably any type will work. But for extruder spline shafts the choice of anti-seize is much more critical. Screw element

36、s fit onto the spline shafts with a very small gap tolerance, but low-viscosity polymers tend to creep down between adjacent elements and get into this gap. With time and heat, degraded polymer forms a high-strength adhesive just like an epoxy.If screws are left together in an extruder without being

37、 taken apart periodically, they can be extremely difficult to remove from the shafts. This is why the choice of anti-seize is so important. Many types of anti-seize lubricant are acceptable for a short period of time, but over long periods at high temperature, they degrade into a fine powder. This m

38、akes them a poor choice for spline shafts, where you need the anti-seize to perform when you're ready to disassemble the screws months or years later. After testing all the anti-seize brands on the market over a period of many years, Leistritz has found one that is ideal for this application: Fu

39、chs Gleitmo 820, manufactured by Fuchs Lubricants in Germany. Gleitmo 820 is a white grease containing high solids. It is very slippery and is rated for up to 1150 C. What makes it perfect for spline shafts is that it doesn't degrade into a powder. When the screw elements are removed aftermonths

40、 of use, the Gleitmo 820 is still a slippery grease. Fuchs Lubricants has U.S. distributors and a website () with technical information.6.（翻譯略）7. PURGE OFTENPurging is widely used as an easy way to clean out materials from the extruder and die and to avoid a time-consuming stripdown cleaning There a

41、re many types of materials used for purging, both commercial purge products and "home engineered" purges. These materials generally fall into two categories: chemical purges and mechanical abrasive purges. Many combine both chemical and abrasive actions.Chemical purges work by attacking th

42、e plastic residue like a solvent. Many of them also incorporate a foaming action and require a 5-min "soak" in tbe barrel to allow the chemical action to work. Mechanical abrasive purges work by scouring and scrubbing material off the metal surfaces, using friction and shear. Processors do

43、 a lot of trial-and-error experimentation to find the right purge material and technique. No "magic" purge material will work best for all materials. Commercial purge products are generally more expensive than "home engineered" purges. But if you can use less material with the co

44、mmercial purge, or get tbe job done quicker, the total cost may actually be less. Processors have run all sorts of materials through extruders, in the quest for a cheap and effective purge material. For instance,in the U.S. Midwest many operators use cattle-feed corn, because it's readily availa

45、ble and does a fairly good job of scouring out the machine. Here are two effective homemade purges:Mix #/; S0% HDPE (or another htgh-viscosity resin) +50% diatomaceous earth (DE): DE is finely milled fossil shells of tiny sea organisms. It is readily available in garden supply stores. DE looks like

46、a fine powder, but the particles have very sharp, angular edges, which produce a scouring action. Processors who run sheet and film use this purge, as it can sometimes get rid of die lines, saving a lengthy die teardown.*Mix #2; HDPE or other viscous resin with kitchen cleanser and water: Mix a slur

47、ry of water and three or four cans of Comet or Ajax kitchen cleanser in a bucket. Feed HDPE at a normal purging rate and temperature, and slowly pour the slurry into the main feed port. The water in the slurry will flash to steam, which gives a very good cleaning effect combined with the abrasive in

48、 the kitchen cleanser. (Safety note: Warn any operators nearby that steam may discharge from extruder openings. Do not look into the die or vents unless wearing a full polycarbonate face sbield andlong-sleeved shirt.) Probably the most important thing is to purge often. The object is to prevent old

49、materials from being "baked on" the metal surfaces.Once this happens, purging will generally not be able to remove thematerial, and a manual stripdown cleaning will be the only remedy. One mistake many processors make is to run the purge only at a fixed screw rpm. It's much more effect

50、ive to vary the speed, changing from low to medium to high rpm, running for perhaps30 sec at each speed. This induces different shear rates against the metal surfaces, helping to dislodge old material from the walls.7。常常清洗機(jī)器清機(jī)是把用于把擠出機(jī)和口模內(nèi)材料清除出來(lái)的簡(jiǎn)易而廣泛的方法，它避免了耗時(shí)的拆機(jī)清洗。有很多材料可用于清機(jī)。既有商用的清機(jī)產(chǎn)品，也有自個(gè)兒特制的清機(jī)產(chǎn)品。

51、這些材料常分成兩類(lèi)：化學(xué)清洗劑和機(jī)械摩擦清洗劑。許多清洗劑同時(shí)具有化學(xué)和摩擦功能。化學(xué)清洗劑象一種溶劑一樣進(jìn)攻塑料殘?jiān)ＴS多化學(xué)清洗劑還加入一種發(fā)泡功能，需要在機(jī)筒內(nèi)“浸泡”5分鐘，從而發(fā)揮化學(xué)作用。機(jī)械摩擦清洗的原理是從金屬表面摩擦和沖刷掉殘留材料，使用的是摩擦和剪切的方式。加工者做了很多試錯(cuò)試驗(yàn)來(lái)找到合適的清洗材料和方法。沒(méi)有什么“神奇”的材料對(duì)所有材料都管用的材料。商用清洗材料一般比自己制造的清洗材料貴。但是，假如你使用較少的商用清洗劑材料能更快把活干好，那么實(shí)際成本可能更小。加工者需要廉價(jià)而有效地清洗材料。比如，在美國(guó)中西部許多操作者使用喂牛的玉米，因?yàn)樗菀椎玫?，?duì)機(jī)器有好的清潔作用

52、。下面介紹兩種自己制造的有效地清洗劑：-1#混合物：50%HDPE50%硅藻土-2#混合物：HDPE水去污粉。將HDPE以通常速度在熔融溫度下加入螺桿。將去污粉用水在桶里攪拌成漿液，從主喂料口慢慢加入漿液。這些漿液因?yàn)榘l(fā)泡而沖擊、摩擦、清洗螺桿。8. EFFICIENT CHANGEOVERSColor or material changeovers tend to create problems. Extrusion people would like to always have nice long runs. But in the real world, demands from cus

53、tomers mean frequent changeovers to make 80 Ib of Product A, followed by 200 Ib of Product B, etc. So it is important to approach changeovers in a way tominimize operator effort and problems:Know how critical is cleanliness to the next product to be run. There are anecdotes around any extrusion shop

54、 of somebody purging for 16 hr to avoid pulling the screws to brush them off. The point is, if you know the next product requires a thorough manual brush cleaning,don't waste time and material trying to get by with purging.If possible, plan runs in order of decreasing cleanliness requirements. F

55、or example, this means going from light to dark colors. That way, you should face only one difficult changeover,when going from the dark color back to a light color.Have written purging or strip-down procedures to run each product. This helps operators plan their time, and eliminates discussions lat

56、er on about how many pounds of product have to bescrapped because the operator didn't clean the machine properly.Use the right size extruder for the lot size. This may seemobvious, but many processors don't plan runs for the right machine and end up running a 500-lh lot on a 75-mm extruder,

57、producing 300 Ib of scrap while getting it to run correctly.Help operators by organizing the necessary tools, cleaning supplies, screens, die plates, etc. near the extruder. If frequent changeovers are required, set up a workstation to have everything the operator needs right by his side.Study raw-m

58、aterial and end-product flow in and out of the process area. Try to arrange it for minimal operator effort. Theless operators have to move drums and gaylords around, the  more they can concentrate on maximizing running time.8. 有效切換顏色和材料切換常弄出問(wèn)題。搞擠出的人總是想把機(jī)器開(kāi)得長(zhǎng)一些時(shí)間。但是在現(xiàn)實(shí)中，由于客戶(hù)的需求，我們常常需要不斷切換，生產(chǎn)80磅產(chǎn)

59、品A，然后再生產(chǎn)200磅的產(chǎn)品B，等等。重要的是要找到一種方法，減少操作人員的工作量和出現(xiàn)的問(wèn)題:-知道下一個(gè)產(chǎn)品的清機(jī)是如何重要。假如你知道下一個(gè)產(chǎn)品要求徹底的手工清機(jī)，那你就不要浪費(fèi)時(shí)間和材料來(lái)糊弄清機(jī)。-假如可能，要按照減少清機(jī)的順序排產(chǎn)。這就意味著要從淺色做到深色。反之，你只有拆機(jī)。-寫(xiě)出生產(chǎn)每個(gè)產(chǎn)品的清機(jī)或拆機(jī)的程序，這有助于操作人員計(jì)劃時(shí)間，消除他們關(guān)于會(huì)產(chǎn)生多少機(jī)頭料的爭(zhēng)論。-產(chǎn)品的批量要與機(jī)器大小相對(duì)應(yīng)。這似乎是不言而喻的。但是許多加工者排產(chǎn)無(wú)計(jì)劃，用75機(jī)生產(chǎn)500磅的單子，結(jié)果產(chǎn)生了300磅的廢料。-幫助操作人員，把清潔的操作工具擺放在擠出機(jī)周?chē)?，如果頻繁換料，那就在擠出機(jī)周?chē)阋粋€(gè)工作臺(tái)，把需要的東西都準(zhǔn)備好。-研究原材料和成品流進(jìn)流出操作現(xiàn)場(chǎng)的順序。安排好以使操作人員花費(fèi)較少的精力在移動(dòng)運(yùn)輸工具上。9. WARM-UP/COOL DOWNExtrusion people tend to keep the machinery hot all the time. Operators typically turn the heat z