Lựa chọn Coolant thế nào là hợp lí cho qui trình gia công ?

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Lựa chọn Coolant thế nào là hợp lí cho qui trình gia công ?

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Lựa chọn Coolant thế nào là hợp lí cho qui trình gia công? Các yếu tố cần xem xét:

 

– Qui trình gia công : Tiện (tốc độ cao hay thấp), phay, doa, mài,  v v…

 

– Nguyên liệu: Inox, thép, nhôm hay nhôm hợp kim, đồng, vv…

 

– Thời gian bảo quản sản phẩm sau khi gia công

 

– ……..

 

Coolant Selection

Coolants perform two important functions: lubrication and cooling.Lubrication is important because metal sliding on metal produces about 30% of the heat and the resistance of metal to being cut produces the rest.Good lubrication reduces friction and reduces heat.This increases tool life and helps keep the part temperature constant.Coolants reduce friction because chlorine, sulfur, and phosphorous atoms penetrate the metallic surfaces.This reduces friction and improves the shear angle.

Lubrication and cooling requirements vary according to the kind of operation, kind of part, type of metal, tool material and geometry as well as the machining parameters.Coolant effectiveness is tied in with a large number of factors including tool size shape and material as well as the properties of the material being worked and the machine doing the work.Coolant selection can affect cutting energy, which increases as you get deeper into a cut due to the increase in friction and reduce cutting noise.

Typically good lubricants are bad at cooling and vice versa. Water is the best coolant because it picks up the most heat, and transfers it fastest.Water is not a good lubricant. It rusts iron and steel and it doesn’t wet and penetrate well.Oil is an excellent lubricant, but it is a poor coolant and is flammable. A common and often good solution is to mix oils and similar with water to get both lubrication and cooling.

In general, tool wear is caused by the continuous abrasion of chips in front of the tool. The abrasion produced by coolant crushing is less.Washing clears the chips and dirt away from the working area.Mineral oils in some coolants will cause dirt to stick to the tool and part and will pollute the environment.

Don’t choose a fluid just on its initial cost but on the cost per gallon divided by its life expectancy.Although purchase of a premium product is initially more expensive, the long?term cost of the fluid will likely be lower than products of inferior quality because of its superior fluid life.

During fluid selection, the benefits of a fluid’s versatility should be weighed against its performance in each metalworking application. Because of significant improvements in fluid formulations, today’s fluids are capable of handling a wide variety of machining applications. Machine shops that once required several types of fluids may now find that one or two fluid types meet their needs. Consolidating the number of fluids used in the shop simplifies fluid management.

Easy removal of the slurry, chips, etc. from the coolant is also essential.

Try to avoid coolants containing chlorinated compounds, they may require hazardous waste disposal

Reduce the number of different coolants used in your shop, if possible. This can cut the cost of coolant maintenance and disposal, and permit your shop to buy in bulk.

Machining functions

  • Speed, feed and depth of the cutting operation
  • Type, hardness and microstructure of the metal being machined
  • Lubricity
  • Cooling
  • Coolant’s applicable temperature operating range
  • Optimal concentration and pH ranges
  • Dimensional control of parts
  • Surface finishes
  • Machine tool maintenance costs
  • Tool wear
  • Downtime for tool and wheel changes
  • Power draw
  • Noise
  • Range of compatible materials
  • Tramp oil rejection
  • Ability to settle out solids
  • Emulsification capability

Noncutting functions

  • Corrosion inhibition
  • Fluid residues
  • Flammability
  • Filtration
  • Toxicity
  • Recycling
  • Resistance to bacterial growth

Operator Acceptance

  • Operator safety
  • Dermatitis
  • Odor
  • Feel
  • Appearance

Financial return

  • Effect on production costs
  • Purchase price
  • Effective life
  • Usage over time
  • Disposal &/or recycling
  • Tool and wheel life

 

Coolant properties

  • Ease of fluid maintenance and quality control
  • Ability to separate fluid from the work and cuttings
  • Storage practices Surface tension
  • Hard water resistance
  • Densities
  • Biodegradability
  • Capacity of recycled coolant to prevent galvanic attack
  • Stability
  • Foaming nature and resistance
  • Precipitation properties
  • Ease of disposal