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MIXING ROLLS

MIXING ROLLS

DEFINITION:

                         Mixing roll mixer is a type of mixer in which deformable  material and pastes are dmixed by intense shear by passing them b/w two smooth rolls turning at different speeds

Diagram

                                 

                                                    mixing rolls

  

Mixing and blending units

For equal homogenizing of rubber batches.

The stockblender consist of a pair of rolls. It is mounted above the roll nip and each roll is separately driven. Between the rolls of the mill and those of the stockblender a guide fork is situated, which is moved from side to side by a threaded spindle over the entire width of the mill.

Functioning: as soon as a cohesive slab has formed on the working roll of the mill, it is cut by the operator and fed through the guide forks to the stockblender. The stockblender transports the irregular slab and feeds it vertically downwards again into the mill roll nip. As these processes are effected alternately from the left and from the right side, an extremely good mixing effect is achieved due to the reciprocating motion of the fork.

Further advantages:

• Considerable ease of operation as the usually repeated cutting and rolling operation of the compound does not have to be carried out any longer.
• Favourable cooling conditions due to the increased travel of the compound.
• Increased capacity of the mill.

working

A mill is typically assembled on a steel foundation plate, which is again set on rubber-pads or sound-metals adjustable, to isolate noise-levels to the building also to avoid tensions on the mill structure, precisely levelling out of the mill is very important for smooth operationTwo rigid pillars with removable tops carry the rolls, which are placed either in friction/bush bearings or high quality anti-friction roller bearings. Roller bearings are pretty much standard nowadays, as they allow for 20 – 30 % in power-savings. A lubrication system is no longer requiredAdjustment of the front roll used to be made by hand (manual by ratchet) or later motorized by worm gear.Nowadays hydraulic pistons adjust the rolls and also protect rolls from high forces that can build up in between the rolls (roll safety). They also open roll gap immediately when pushing the safety bar in front or back in case of emergency (required by European Safety standards CE).A mixing mill has 2 horizontal rolls set up back to back. They are made of ground chilled cast iron, with surface hardness ranging from 475 – 520 HV (Vickers hardness) up to 520 – 580 HV (or 68 - 72 HSD). The depth of hardened layer ranges from 10 to 16 mm.Rolls are made with a central bore for cooling through a spray-type lance (low cost type cooling) or peripheral drills, where bores are closer to the surface for better cooling and more equal distribution.The rotary joints connected to the spraying lance are supplied from tempering units to provide constant temperature during the mixing process.At the ends of the roll faces the roll nip is being limited by the compound guide cheeks. The compound guide cheeks of split design with “centre tongue” avoid lateral escape of compound from the working area in any case.

MULLER MIXER

DEFINITION:

                    The Muller Mixer consists of 2 to 4 heavy rollers that move under spring pressure within a pan. A scraping arrangement is also provided. The product dust formed during grinding is confined to within the equipment because of the provision of a hood type cover. The rollers rotate around their own axis and also about the axis of the pan. The number of rollers and their sizes can be customized to the specific applications. The equipment is most suitable for solid particle size reduction.A machine for the mechanical preparation of molding sands and core sands; it mixes silica sands and admixtures, such as molding clay, ground coal, water, and binders. Various types of mixers are used as mullers in the preparation of moldings and core-sand mixtures: standard batch-type mixers, double mixers, oscillating mixers, paddle mixers, and rollerless (vortex) mixers.

DIAGRAM:

                      Muller Mixer

WORKING:

                  Standard batch mixers have a fixed hopper, into which the material to be mixed is fed. Two smooth, vertical rollers move over the layer of material with a circular motion as plows guide the mixed material under the rollers. As the rollers move, the components of the mixture are mixed and become evenly distributed. After 3–12 min of mixing, the prepared mixture is removed through a discharge opening in the bottom of the hopper.

Double mixers have two pairs of vertical rollers and two hoppers interconnected in such a way that their sides form a figure eight. The molding materials are fed continuously into the first hopper, are mixed by the rollers and internal plows, and are then transferred by an external plow to the second hopper, where more mixing takes place. The prepared mixture is then removed from the second hopper by an external plow. Double mixers can produce up to 400 tons/hr, and the mixture can be removed either continuously or in batches.

An oscillating mixer has two or three horizontal rollers suspended on oscillators connected to a vertical shaft. As the shaft revolves, the rollers come close to the rubber-faced wall of the mixer’s hopper. The material to be mixed is fed by scrapers into the gap between the rotating rollers and the wall of the hopper. A batch is mixed in 1.5–3 min. The prepared mixture is removed through a small door in the wall of the hopper.

A paddle mixer may have one or two (parallel) shafts equipped with paddles mounted in a helical line and turning inside a trough. When the shaft turns, the mixture is mixed and simultaneously transported along the trough toward the outlet. Such machines can produce mixtures continuously or in batches.

A rollerless, or vortex, mixer has a vertical rotating shaft and a fixed hopper. The working elements are bent springs with heads at the end that press against the side of the hopper and mix the sand.

APPLICATIONS:

• Ayurvedic & Herbal Products
• Pharmaceutical
• Minerals (Mica Powder Mixing)
• Snuff
• Batteries
• Welding rod flux
• Abrasives
• Soaps
• Putty
• Paints

PUG MILLS

DEFINITION:

                         A pugmill or pug mill is a machine in which materials are simultaneously ground and mixed with a liquid. Industrial applications are found in pottery, bricks, cement and some parts of the concrete and asphalt mixing processes. A pugmill is a fast continuous mixer. A continuous pugmill can achieve a thoroughly mixed, homogeneous mixture in a few seconds. Mixing materials at optimum moisture content requires the forced mixing action of the pugmill paddles, while soupy materials might be mixed in a drum mixer

DIAGRAM:

                                                         PUG MILL

WORKING:

                        Pugmills provide excellent mixing for cement-treated materials because of the violent action of the mixing process. Typically a pugmill will have two horizontal shafts, each with dozens of paddles. The shafts turn in opposite directions, causing one set of paddles to turn clockwise, and the other set to turn counter-clockwise. This motion hurls the particles toward each other in a violent action that allows for uniform mixing.

The pugmill operates on a continuous basis, with an aggregate feed belt, water spray, and cement vane that are all computer controlled to provide accurate metering of the constituents. Pugmills can be set up with more than one silo, so cementitious products (such as portland cement and fly ash) can be blended at the plant.

The mixed material is taken by belt to a surge hopper (or gob hopper) where it will be dumped into a truck to be transported to the job site. The trucks will have tarps to cover the freshly mixed material so that moisture is not lost on the way to the site.

Pugmills on paving projects are typically portable, and can be set up and running in less that a day. Production for pugmills on these projects are normally in the range of 300 – 500 tons per hour.

APPLICATIONS:

• Roller Compacted Concrete (RCC)
• Cement Treated Base (CTB)
• Cold Mix Asphalt
• Hazardous Soil Remediation
• Oil Well Drill Cutting Stabilization
• Flowable Backfill
• Flyash Stabilization
• Lime Addition

China is not ready to take America's place

Beijing may complain about Washington, but its reliance on American debt stems from the China’s own economic policies

The Chinese sure are doing a lot of worrying these days about the stalemate in Washington. Li Keqiang, China’s Premier, told U.S. Secretary of State John Kerry that he was watching the tussle over raising the government’s debt ceiling with “great attention” in a meeting last week. He has good reason to be concerned. With a stash of nearly $1.3 trillion in Treasury securities, China is the world’s largest foreign owner of U.S. government debt. If U.S. Congress fails to lift the ceiling to allow the government to borrow more by Thursday, Washington may not have enough money to pay its bills, potentially leading to a default. That could sink the value of Treasuries — wiping out a big chunk of Chinese wealth in the process.

That possibility has caused much consternation in China. In a blistering (and highly hypocritical) editorial, state news agency Xinhua blasted what it sees as Washington’s irresponsibility in handling global affairs and called for greater say for developing nations in international institutions like the IMF and a new reserve currency to replace the dollar.

“As U.S. politicians of both political parties are still shuffling back and forth between the White House and the Capitol Hill without striking a viable deal to bring normality to the body politic they brag about, it is perhaps a good time for the befuddled world to start considering building a de-Americanized world,” the commentary recommended. “Such alarming days when the destinies of others are in the hands of a hypocritical nation have to be terminated, and a new world order should be put in place.”

Among the Chinese public, the stalemate in Washington has caused confusion and ire. Why, some Chinese are asking, have our leaders invested so much of the country’s money in a government that seems so dysfunctional? “Bought so much [American debt], now you are under the control of others,” went one typical comment posted on microblogging site Sina Weibo. “We should find out who made this decision and let him take the responsibility.”

The Chinese can blame themselves. Since the earliest days of Chinese economic reform, policies that the government has employed to create growth and exports have also made it dependent on debt issued by the U.S. Treasury. Those policies have generated huge current-account surpluses and gargantuan reserves of foreign currency that have left Beijing no other option but to invest in the U.S.

Chinese policy has generally pushed exports while discouraging imports. By controlling the value of its currency, the renminbi (RMB), to promote exports, China hasn’t allowed its exchange rate to adjust to shifts in trade in a way that would bring balance. Economist Huang Yiping once proffered that policies that reduce prices of land, energy and other costs of production also subsidize exports, and thus contribute to surpluses. Meanwhile, the government’s regulation of interest rates has favored investment and punished savers, suppressing domestic consumption.

The current-account surpluses China has notched over the years have resulted in a vault full of foreign-currency reserves — a staggering $3.66 trillion at last count. Though China’s surpluses have been declining (relative to GDP), the country is still adding to this mountain of foreign currency. In the third quarter, China’s foreign-exchange reserves jumped by the largest amount in more than two years.

To many, this ocean of foreign currency shows China’s economic strength, but at the same time, it is also a financial burden. Chinese policymakers simply don’t have many options when managing these giant reserves, and that has forced them to gorge on Treasuries. The U.S.-government-bond market is deep, liquid and reliable — the perfect (and, arguably, only) place to park all those greenbacks. Sure, the Chinese can switch some of their dollars into other currencies, but there is a limit to that strategy. Dumping the dollar would depress its value, eroding China’s own holdings. The only way for China to wean itself off its Treasury habit is to change its entire economic system.

That, though, is happening slowly. One strategy China is pursuing to lessen its dollar dependence is by promoting its own currency as an alternative to the greenback in global trade and finance. The government has had some success. The European Central Bank and China’s central bank recently agreed to a large swap of their currencies. And according to a recent survey from the Bank for International Settlements, the RMB entered the list of top 10 most traded currencies for the first time. Yet in order for the RMB to become a true rival to the dollar, China has to undertake far more reform.

The RMB isn’t fully convertible, nor does it trade freely around the world like the dollar, euro or yen. China is taking stabs at the sort of financial liberalization that would give the RMB an international boost — experimenting with freer capital flows in a new zone in Shanghai, for instance — but those steps are tentative at best. The Chinese government is still reluctant to throw open its financial sector and loosen capital flows and currency trading in a way that would turn the RMB into a solid reserve currency like the dollar.

“China’s policymakers remain deeply uncomfortable with allowing market forces a say in determining the exchange rate at times of uncertainty,” research firm Capital Economics said in a report on Monday. “Policymakers still see opening of capital controls as an important goal. But their actions underline that it remains a long way off.”

What this all means is that China and the U.S. Treasury remain locked in an embrace from which it is very hard for Beijing to escape. What it will take is extensive reform to China’s own economy that so far Beijing has been reluctant to undertake. So Beijing can call for a “de-Americanized world” all it wants. China is not ready to take America’s place.