For the manufacture of asbestos textiles, chrysotile asbestos is used almost exclusively. The longest fibres produced by the asbestos mines are used. Basically, the manufacturing process consists of:
€ Fiberizing asbestos and blending;
€ Carding to produce roving;
€ Spinning roving into yarn; and,
€ Weaving yarn into cloth.
Initially, different asbestos fibre grades must be fiberized individually prior to blending. Up to 25 % organic carrier fibres, such as rayon and cotton, may be mixed with the asbestos. Subsequent to blending, the normal asbestos textile process consists of carding, spinning and weaving, which is very similar to a conventional spinning process for cotton or wool.
The heart of the asbestos textile process is the carding operation. In this process, the fiberized and blended raw material is transformed into a blanket or lap by a series of needling operations which further open and intertwine the fibre. At the same time, impurities such as rock particles and short, cruddy fibre bundles, as well as dust, are removed from the fibre. It is obvious that this can be a very dusty process.
The lap produced by carding is then cut into strips or rovings which are wound onto spools. These spools are then submitted to spinning operations which twist and combine the roving to form yarn. The yarn is woven into cloth on various types of looms. Roving and yarn can also be used to produce twisted and braided rope, as well as a variety of yarns, threads and cords. Yarn can also be used to produce specialty items, such as tubing.
Receiving and Warehousing
The same problems as previously mentioned for other manufacturing processes exist for textile production. Consequently, the same dust control measures must be applied, and the same precautions exercised by workers active in this area.
Debagging, Fiberizing and Blending
The fibre preparation process begins with the debagging of asbestos fibre (using manual or automatic procedures with the same precautions as required for other processes), followed by fiberizing and finally, blending.
It is essential that asbestos be properly prepared prior to the carding step. It is recognized that fibre from different sources require different treatments. This is one of the reasons why different plants use different types of fiberizing equipment. The sequence of the opening operation in preparing a spinning mixture will depend on the type of fibre being processed and the type of yarn to be produced. The application of the finished product must also be considered.
As for other processes, the asbestos fibre is usually received in a semi-opened state. The purpose of the fiberizing stage is to soften the fibre, a process necessary for the subsequent carding operation. A kollergang, similar to the one used in the asbestos-cement industry, is suitable for this operation. Subsequently, the treated fibre is passed through another fiberizer, such as a creighton opener or willow, for further opening and fluffing.
Asbestos blending systems can be classified into the following methods: 1) floor blending, 2) rotary mixer, 3) hopper feed blending, and automatic blending.
Floor blending is a long-established method of producing blends of various types and grades of fibre by placing layers of the blend components one above the other. Each layer must be placed as uniformly as possible over the entire floor area. Material is withdrawn from the pile by taking vertical slices. Every slice removed contains the correct amount of each material.
A variation of this method is called belt blending, where, after opening, the fibre grades and types are placed on a conveyor belt. When the correct number of layers are deposited on the belt, the belt is started to feed the hopper for the card.
Both floor and belt blending are extremely dusty and workers must wear protective clothing (disposable or washable overalls) and personal HEPA respirators at all times. Also, prior to leaving the mixing room, vacuum equipment should be used to remove fibre adhering to clothing and shoes.
Dust control with the above methods or their modifications is extremely difficult. Hence, they are often replaced by automated mechanical devices, such as blending drums or single and multi-hopper blending units. This equipment is fitted with exhaust ventilation involving a bag house and a fan.
One such unit is the multi-hopper automatic blending unit that employs hopper type feeders that discharge into a weighing pan. Each single hopper weighs only one type of fibre which is dropped onto an apron to form a continuous blanket that is passed through a "picker" for further blending. The blended material is then conveyed to a collector cyclone which is used to drop the material directly into the feeding bin of the card. For small batches, single unit automatic blending machines have been designed. Fully integrated methods include a properly designed debagging station ahead of the fiberizer and blender. This equipment is capable of weighing and discharging fibre blends to the card without generating dust.
Carding Operation
After opening and blending, the fibre is fed to the card for further processing. The purpose of the card is to separate fibre bundles and to align fibre to produce a uniform sheet or lap. In the process, impurities and dust are removed.
Since asbestos yarn is spun directly from roving, uniform feed to the card is of great importance. This is accomplished by using a hopper feeder which is similar to the one used in the wool industry. The hopper may be mounted to the card or it may be mobile. In both cases, fibre is supplied to the card by batch weighing.
The card operates with three functions: working; stripping and brushing. The working action is the chief means by which the asbestos blend is opened and turned into a uniform web. The entire sequence of action is a complicated process involving many parts of the card.
Cards continuously clean the material whereby rocks and any heavy materials fall out. Dust is drawn into the exhaust system. Undoubtedly, carding of asbestos is one of the most dusty operations. Some steps towards reducing the magnitude of the problem have been made. For example, modern asbestos cards have a totally enclosed feeding and weighing system. Impurities are removed by mote knives and grid bars underneath the cards. However, for effective dust control, the card has to be totally enclosed. In extreme cases the condenser will have to be enclosed as well.
At the end of the carding process the web is transferred to the condenser. The function of the conveyor is to divide the uniform web into flat ribbons and to consolidate them into rovings.
Spinning Operation
The purpose of the spinning process is to impart a greater twist to the roving which is seldom used for itself. It is possible to insert wire or other yarn at this stage. Two types of equipment are normally used for this purpose, the ring frame and the flyer frame. In the doubler process, two or more yarns and possibly wire are combined and twisted into stronger yarn. The machines used for this process are similar to the ones used in the cotton and wool industry.
In preparation for weaving, the weft is prepared by re-spooling for the shuttle on the loom. The warp is prepared in a variety of ways. Equipment used in the wool industry is most suitable for this particular purpose.
The processes are basically dusty and hoods with exhaust ventilation must be used to maintain the dust at an acceptable level. In addition, workers must have access to clean-up equipment.
Weaving Operation
The equipment used for weaving asbestos yarn in the asbestos textile industry is similar to that used in the cotton and wool industry. Two types of weaving are used in the asbestos industry, creel weaving and beam weaving. The former obviates the re-spooling of the weft and warp because weaving can be done directly from the spinning bobbins. Weaving can be done on a variety of machines.
It is obvious that weaving is an extremely dusty process and total enclosure by appropriate hoods with exhaust ventilation must be used. The hood configuration has to be of a suitable design, otherwise it will interfere with the performance of the operator.
Miscellaneous Operations
Roving and yarn are used for the manufacture of twisted and braided rope, tubing, etc. These operations are performed by special machines. Although these are not as dusty as card, spinning frame or loom, general precautions and protection of the worker are still required.
Waste Disposal
The amount of waste material generated in an asbestos textile plant is relatively small. It consists mainly of dust and fibre collected by the various bag houses in the plant, and waste due to cutting of yarn or cloth. These materials should be collected in plastic bags and buried in an approved disposal site. The workers performing these tasks should wear personal HEPA respirators and protective clothing (disposable or washable overalls).
The following procedure* is recommended for removal of all types of fibre reinforced gasket materials. This process involves the use of a wet removal agent and a hand scraper.
1. Before breaking the flanges, position an open plastic bag underneath the flanges so the gasket and wetting agent will fall into it.
2. Wet the flanges and break the flanges apart.
3. If using a commercially available gasket removal spray solvent, follow the manufacturer's instructions. Spray the gasket and wait the recommended time, then scrape the gasket residue into the bag. Reapply the spray to keep the area wetted as necessary.
4. Although the wet solvent spray is preferable, if using water as a wetting agent, wet the gasket and begin scraping the gasket off the flanges and into the bag with a hand scraper. Reapply the wet spray as necessary.
5. After removal, wipe the flanges and tools with a rag. Dispose of rags into the bag and close.
6. After completion of flanging operations, move to the next flange, open and position bag and begin gasket removal as described above.
7. Dispose of nonfriable asbestos contained waste according to local regulations.
All dust producing processes (such as drilling, grinding, sanding and sawing) should not be used on any gasket materials. This is particularly applicable with compressed asbestos gasket materials as this will render the material friable.
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